NL1039259C2

NL1039259C2 - Method for the preparation of polymer comprising particles.

Info

Publication number: NL1039259C2
Application number: NL1039259A
Authority: NL
Inventors: Rudolf Trion; Gerard Jager
Original assignee: Joa Technology Beheer B V
Priority date: 2011-12-22
Filing date: 2011-12-22
Publication date: 2013-07-01
Also published as: WO2013095149A1

Description

Method for the preparation of polymer comprising particles

The present invention relates to a method for the preparation of particles comprising at least a polymer, wherein a melt comprising the said polymer 5 is extruded by passing the melt through at least a die into a solidifying medium having a temperature of below the melting temperature of the melt, allowing the melt to solidify in the solidifying medium into the particles.

The invention further relates to particles obtainable by the said method, and to novel uses of such particles.

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Background of the Invention

The method for the preparation of particles as described above is also known in the art as underwater granulation. According to this technique a polymer melt is extruded and passed through a die, which die is submersed in water. 15 The water temperature may vary, usually between 20 and 100°C. As soon as the polymeric melt is passed through the die, the melt is cooled by the water and solidifies; the water has the function of solidifying medium.

A cutting device cuts the extruded material into pieces and the said pieces form particles during the solidification process. By cutting the melt, portions of 20 the melt are individually solidified. In the art methods are known for cutting the melt that exits a die. For example cutter blades circling around the die opening are known for this purpose. Straight and angled cutter blades can be used and spacing between the cutter blades is important to the process. Because of the surface tension of the melt, the melt rounds up upon solidification in the solidifying medium. The melt can 25 be passed through the die at a flow rate and wherein the cutting device is synchronized with the said flow rate such as to cut off equal portions of the passed melt. By synchronizing the cutting frequency with the flow rate of the melt through the die outlet opening it is possible to cut the melt at a predetermined length therewith controlling the shape of the particles to be formed upon solidification. By 30 underwater granulation particles of high sphericity and roundness can be obtained.

A common problem of underwater granulation is the fact that the polymeric melt tends to solidify rather quick in the water, as the temperature difference between the water and the melting point of the melt is rather high. This brings also the risk of clogging of the die outlet openings of the granulation 1039259 2 equipment, as the melt tends to solidify at the location of the die opening as the temperature at that location is too low to keep the melt in molten state. Further, optimal roundness and/or sphericity can not be obtained if the temperature difference between the solidifying medium and the melting point of the melt is too 5 high; the particles solidify before the optimal thermodynamic shape (a sphere) could form. Another problem is that polymers having a high melting point cannot be used in underwater granulation, in view of the above temperature difference between the melting temperature of the melt and the temperature of the water. Only rather large particles can be produced of polymers having a high melting temperature. For 10 example, particles of polyetherimid (PEI) and of polyetheretherketone (PEEK) could not be produced with a particle size of below 3.0 mm. Smaller particles could only be obtained by mechanical processing of larger particles, e.g. by cracking the obtained particulate to smaller sizes and sieving to an envisaged particle size. However, such processes have a deteriorating effect on the roundness and sphericity of the 15 particles.

In the art, the problem of clogging of the die outlet openings is known. There appeared to be some compensation possible by elevating the pressure or temperature of the melt. However it was found that using the conventional underwater granulation techniques at the required small diameters of the die outlet 20 opening resulted, in most cases, in clogging of the die opening by solidified polymer. Additional control appeared to be necessary, which is explained further below.

Because of this clogging, the process has to be stopped regularly, and losses of as high as 5 to 10% are no exception. The solution of the problem has been sought in technical adaptation of the equipment, such as described in US 25 5,143,673.

It is commonly known that polymers do not have a definite melting point but a melting range, starting at the onset temperature, here and in the ISO 11357-1 1997 standard indicated by Tim, and ending at the end temperature indicated in the ISO 11357-1 1997 standard indicated by Tfm. The melting point Tpm is 30 located between Tfm and Tpm, as indicated in the said standard. The term ‘melting point’ as used herein for polymers, refers to the peak melting temperature Tpm as determined according to the ISO standard 11357-1:1997. As a result the melt would solidify instantly upon contact with the water therewith clogging the die, as a result of which the extrusion apparatus becomes clogged.

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The present inventors have now surprisingly found that the granulation technique can be improved, avoiding clogging of the die outlet openings, and that polymeric particles can be obtained of polymers, that could not be produced by underwater granulation until the present invention was made. Also, polymers can 5 be used that have a melting point Tpm that is significantly higher than the temperature of the solidifying medium. Further, the particle size of polymeric particles can be much smaller by using the method according to the present invention, as compared to the particles, obtained by the common underwater granulation techniques. To this end, the invention is characterized in that the solidifying medium has a heat 10 conductivity of below 0.55 W/m/°C. The present invention breaks the paradigm that under water granulation needs to be done with water as solidifying medium. By the invention the term underwater granulation is actually outdated, as alternative solidifying media are used according to the invention that have a heat conductivity that is significantly lower than that of water. Nevertheless, the term ‘underwater 15 granulation’, or 'underwater pelletizing’ will be used herein as well, although the solidifying medium is different from water.

The heat conductivity of many liquids are known, and are published e g. on the website www.engineeringtoolbox.com. The heat conductivity is to be measured at atmospheric pressure and at room temperature, i.e 20°C and can be 20 measured according to the ASTM D2717 standard, e g. with the LabTemp30190 equipment of PSL Systemtechnik (Clausthal-Zellerfeld, Germany) according to the instructions of the manufacturer. The heat conductivity of water is e.g. 0.61W/m/°C.

The term ‘particle’ comprises particles of any shape, such as spherical, spheroidal, elliptical, and right cylindrical shapes. Spherical shapes are 25 preferred. The particle comprises at least one polymer, although polymer mixtures are also possible. It is however advantageous to use a single polymer as the polymer with the least qualities usually determines the properties of the particle.

Unless indicated otherwise, the term ‘particle size’ as used herein reflects the weight based particle size, which equals the diameter of the sphere that 30 has same weight as a given particle. The weight based particle size is defined by the following formula:2*(3*weight(particle)/4/pi/density(particle))A(1/3).

A lower heat conductivity ensures a slower solidification of the melt in the solidifying medium, avoiding clogging at the die outlet opening, and allowing the particles to obtain the envisaged thermodynamically optimal form, i.e. a spheroid.

4

Water has a high heat conductivity, and in addition thereto has a rather low atmospheric boiling point of 100°C. Therefore, by using water as solidifying medium a great amount of heat is absorbed by the solidifying medium from the melt as it passes the die outlet opening, therewith lowering the temperature of the melt within a 5 short time period, resulting in the risk that the melt solidifies as it is still at the die outlet opening, by direct cooling in contact with the solidifying medium or indirect cooling via the die-plate surface, resulting in clogging of the die outlet opening.

The present invention therefore allows currently known polymers to be shaped in particles of a smaller size and narrower size-distribution, having 10 improved roundness and sphericity. Further, as clogging of the die outlet openings is reduced or prevented, production losses can be minimized. Additionally, the production capacity can be increased significantly, as the die openings remain operable without clogging, resulting in in larger production volumes.

In a preferred embodiment, the heat conductivity of the solidifying 15 medium is below 0.50 W/m/°C, preferably below 0.40 W/m/°C, more preferably below 0.30 W/m/°C. The heat conductivity of ethylene glycol is 0.26 W/m/°C. It may even be preferred to have an even lower heat conductivity as low as below 0.20 W/m/°C. N-butylalcohol has a very low heat conductivity of 0.167W/m/°C, and a boiling point of 117.5°C. The skilled person will be aware of suitable liquids that can be used as 20 or in a solidifying medium to be used in the method of the invention.

Up to now the granulation technique has been performed with water, not only having a high heat conductivity, but also a low atmospheric boiling temperature of 100°C. The underwater granulation technique was simply limited to this temperature. The temperature could theoretically be elevated slightly by using 25 water under pressure, or by using an aqueous saturated salt solution. However, using pressure in the solidification process may lead to undesired risks, whereas the use of salt solutions implies a more intensive washing step when the particles are to be isolated. Furthermore, the elevation of the temperature is rather small (the atmospheric boiling point of a saturated NaCI solution is e.g. 108°C). Solutions in 30 the art have therefore been sought in technical changes in the equipment, without contemplating about the composition of the solidifying medium.

Preferably the temperature of the solidifying medium is above 90°C, preferably above 110°C, more preferably above 120°C, and even more preferably above 140°C.A relatively low temperature of e.g. 90°C can be chosen for polymeric 5 melts having a relatively low melting temperature. The low heat conductivity enables slow solidification, therewith allowing the particles to take their thermodynamically optimal form, i.e. a spheroid, and reduces clogging of the die outlet openings. A higher temperature is to be chosen when the melt has a higher melting temperature, 5 otherwise the risk of clogging may again occur, and the particles may solidify too quickly to arrive at their optimal shape. At higher temperatures, polymers having a higher melting point can be used for the ‘underwater’ granulation techniques of the present invention. A totally new range of polymeric particulate materials can therewith be provided, that are produced by under water granulation, without the 10 need for further processing such as cracking the obtained particles to smaller sizes and sieving to an envisaged particle size.

In another attractive embodiment, the temperature of the solidifying medium is below 250°C, preferably below 200°C. The temperature can be limited for reasons of safety, and by limitations of the equipment, or to fulfil local safety 15 regulations.

Preferably, the solidifying medium has an atmospheric boiling point of more than 100 °C, preferably more than 110°C, more preferably above 120°C, most preferably above 150°C. A high boiling point allows the solidifying medium to be used at higher temperatures which may be required for polymeric melts having a 20 relatively high melting temperature.

The solidifying medium preferably comprises an organic liquid. Preferably, said organic liquid has an atmospheric boiling point of above of 100 °C, preferably above 110°C, more preferably above 120°C, most preferably above 150°C. Suitable organic liquids are known to the skilled person.

25 In an attractive embodiment, the organic liquid is inert to the melt and the particles. With ‘inert’ is meant that the melt and the solidified particles do not dissolve substantially in the solidifying medium. A polar organic liquids may therefore be less suitable, as these liquids tend to dissolve the melt. However, it can be contemplated to use a solidifying medium, comprising a compound that reacts with 30 the particles, e g. to confer a specific coat to the particles during or after the solidification process.

In another attractive embodiment, the solidifying medium comprises a mixture of two or more organic liquids, or a mixture of one or more organic liquids with water.

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Preferably, the solidifying medium comprises a polar organic liquid. Polar organic liquids tend to be more inert for polymers as compared to a polar organic liquids.

The polar organic liquid preferably comprises an alcohol, ether, acid 5 or ester. Among suitable organic alcohols are aliphatic alcohols like octanol with a boiling point of 195°C and decanol with boiling point 220-235°C. Also glycols can be used e.g. propylene glycol with boiling point 188°C and ethylene glycol with boiling point 197°C. In general also ethers can be used, but these are less preferred because of the relatively low boiling point and tendency to react with oxygen to form 10 peroxides and explosive mixtures. Among the large group of organic acids and esters are e.g. propionic acid with a boiling point of 141 °C up to e.g. palmetic acid with boiling point 351 °C, which can also be used as attractive solidifying media in the method of the invention. Preferably the polar organic liquid preferably comprises an alcohol.

15 In a very attractive embodiment, the organic liquid comprises glycol, preferably ethylene glycol, propyleneglycol or a polyethylene glycol or mixtures thereof. Ethylene glycol has an atmospheric boiling point of 197°C, and can be used in any mixture with water. Ethylene glycol is therefore very versatile for use as solidifying medium, and polymers having a high boiling point, such as PEI or PEEK 20 can be subjected to underwater granulation resulting in small particles of high sphericity and roundness using ethylene glycol, optionally in admixture with water, as solidifying medium. Therefore, in a very attractive embodiment, ethylene glycol is used in or as solidifying medium.

In order to allow small particles to be formed, the outlet opening of 25 the die preferably has a diameter of 4.0 mm or less, preferably 2.0 or less, more preferably 1.2 mm or less, even more preferably 0.8 mm or less, most preferably 0.75 mm or less. Attractively, the outlet opening of the die has a diameter of 0.3 mm or more, preferably 0.4 mm or more, more preferably 0.5 mm or more, most preferably above 0.6 mm or more. Preferred ranges in this respect are 0.3 - 4.0 mm, 30 more preferably 1.0- 2.0 mm.

As indicated above, polymers can be used for the underwater granulation technique of the present invention having a high melting point. Therefore, in an attractive embodiment the melting temperature Tpm of the polymer is at least 120°C, preferably at least 150°C, more preferably at least 180°C.

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Preferably, the temperature of the melt is 180 - 400°C. The temperature of the melt also has an impact on the temperature of the die. A higher temperature of the melt assists in holding the temperature of the die at the required level. Further, the processability at higher temperatures is improved, as the viscosity 5 of the melt will be lower. A too high temperature will however result in degradation of the polymer in the melt. The temperature of the melt is preferably 220 - 400°C, more preferably 260-400°C.

As the present invention provides for the first time alternative solidifying media, the temperature difference between the melting temperature Tpm of 10 the melt and the temperature of the solidifying medium can be chosen to be rather small, enabling to form a polymeric particulate from polymers having a high melting temperature. To this end, the temperature difference between the solidifying medium and the melting point Tpm of the polymer is 150°C or less, preferably 100°C or less, more preferably 80°C or less. By choosing the temperature of the solidifying medium 15 accordingly, the temperature difference between the melt and the solidifying medium is large enough to allow a good solidification of the melt, without allowing the melt to cool off too much at the location of the die outlet opening, therewith avoiding clogging of the said outlet opening.

The particles that are formed by the method of the present invention 20 preferably have a particle size of at most 4.0 mm, preferably at most 3.0 mm, more preferably at most 2.5 mm, even more preferably at most 2.0 mm, most preferably at most 1.3 mm. Attractively the particles have a particle size of at least 0.3 mm, more preferably at least 0.5 mm, most preferably at least 0.6 mm. Preferred ranges are 0.3 - 3.0 mm, more preferably 0.5 - 2.5 mm, even more preferably 0.6 - 2.0 mm, most 25 preferably 0.6 - 1.3 mm.

Herein, the term ‘the polymer’ also encompasses an optionally cross linked polymer, an optionally cross linked copolymer, an optionally cross linked terpolymer, an optionally cross linked block(co) polymer or any mixtures thereof unless indicated otherwise. The particle can also advantageously comprise one or 30 more filler materials, e.g. to adjust the specific weight of the particle, to reinforce it, or to reduce costs of the particle material.

Many polymers are known that are suitable to be used as polymer for the polymer comprising particle of the present invention. The polymer in the melt preferably comprises an optionally crosslinked polymer, an optionally crosslinked » 1 8 copolymer, an optionally crosslinked terpolymer, an optionally crosslinked block(co) polymer or a mixture thereof.

The polymer is preferably thermoplastic in order to minimize abrasion in the fractures. The importance of the thermoplastic nature of proppants is 5 e.g. explained in US7,322,411, herein incorporated by reference.

The polymer is preferably chosen from the group consisting of polyolefines, polystyrenes, acrylonitrile-butadiene-styrene polymers, aromatic or aliphatic partially crystallized polyesters, polycarbonates, polyamides, polymethylmethacrylate, polyacetals, polyphenyleneoxides, polyphenylesulfides, 10 polyetheretherketons, polyetherketonketons, polysulphones, polyarylates or a mixture thereof.

As indicated above, the polymer preferablycomprises a thermoplastic polymer. Examples of suitable thermoplastic polymers include, but are not limited to, polyamides, polyacetals, polyesters (including aromatic polyesters and 15 aliphatic polyesters), liquid crystalline polyesters, polyolefins, polycarbonates, acrylonitrile-butadiene-styrene polymers (ABS), poly(phenylene-oxide)s, polyphenylenesulfide)s, polymethylmethacrylate, polysulphones, polyarylates, polyetheretherketones (PEEK), polyetherketoneketones (PEKK), polystyrenes, and syndiotactic polystyrenes. Preferred thermoplastic polymers include polyamides and 20 polyesters.

Polyamides may be homopolymers, copolymers, terpolymers, or higher order polymers. Blends of two or more polyamides may be used. Suitable polyamides can be condensation products of dicarboxylic acids or their derivatives and diamines and/or aminocarboxylic acids, and/or ring-opening polymerization 25 products of lactams. Suitable dicarboxylic acids include, adipic acid, azelaic acid, sebacic acid, dodecanedioic acid, isophthalic acid and terephthalic acid. Suitable diamines include tetramethylenediamine, hexamethylenediamine, octamethylenediamine, nonamethylenediamine, dodecamethylenediamine, 2-methylpentamethylenediamine, 2-methyloctamethylenediamine, trimethylhexa-30 methylenediamine, bis(p-aminocyclohexyl)methane, m-xylylenediamine and p-xylylenediamine. A suitable aminocarboxylic acid is 11-aminododecanoic acid. Suitable lactams include caprolactam and laurolactam.

Preferred aliphatic polyamides include polyamide 6, polyamide 6,6, polyamide 4,6, polyamide 6,9, polyamide 6,10, polyamide 6,12, polyamide 10,10, T * 9 polyamide 11 and polyamide 12. Preferred semi-aromatic polyamides include poly(m-xylylene-adipamide) (polyamide MXD.6), poly(dodecamethyleneterephthal-amide) (polyamide 12,T), poly(decamethyleneterephthalamide) (polyamide 10,T), poly(nonamethyleneterephthalamide) (polyamide 9,T), the polyamide of 5 hexamethyleneterephthalamide and hexamethylene-adipamide (polyamide 6,176,6); the polyamide of hexamethyleneterephthalamide and 2-methylpenta-methyleneterephthalarnide (polyamide 6,T/D,T); the polyamide of hexamethylene-isophthalamide and hexamethylene-adipamide (polyamide 6,1/6,6); the polyamide of hexamethyleneterephthalamide, hexamethyleneisophthalamide, and hexamethylene- 10 adipamide (polyamide 6.T/6, 1/6,6) and copolymers and mixtures of these polymers.

Examples of suitable aliphatic polyamides include polyamide 6/6 copolymer, polyamide 6,6/6,8 copolymer, polyamide 6,6/6,10 copolymer, polyamide 6,6/6,12 copolymer, polyamide 6,6/10 copolymer, polyamide 6,6/12 copolymer, polyamide 6/6,8 copolymer, polyamide 6/6,10 copolymer, polyamide 6/6,12 15 copolymer, polyamide 6/10 copolymer, polyamide 6/12 copolymer,polyamide 6/6,6/6,10 terpolymer, polyamide 6/6,6/6,9 terpolymer, polyamide 6/6,6/11 terpolymer, polyamide 6/6,6/12 terpolymer, polyamide 6/6,10/11 terpolymer, polyamide 6/6,10/12 terpolymer and polyamide 6/6,6/PACM (bis-p- {aminocyclohexyl)methane)terpolymer.

20 The polymer preferably comprises polyethylene terephtalate, preferably crosslinked, the polyethylene terephtalate preferably being recycled polyethylene terephtalate, most preferably crosslinked recycled polyethylene terephtalate. Polyetylene terephtalate, in particular crosslinked polyethylene terephtalate has appeared to be a very suitable polymer to be used as proppant, i.e.

25 having the desired properties as discussed above. In a very attractive embodiment the polyethylene terephtalate is recycled polyethylene terephtalate, preferably crosslinked.

In another attractive embodiment, the polymer comprises polycarbonate, PET, PEI or PEEK.

30 Preferably the polymer melt comprises a filler. The filler can be used to reinforce the particles, and also to modulate the specific weight of the particles and reduce cost. The filler should be capable of reinforcing the polymer, while also reducing the potential for crush as exemplified below.

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The filler is preferably chosen from the group of sand, carbon black, graphite, mica, silica, silicon carbide, alumina, quartz, nanotubes, coconut, walnut, natural fibre, glass fibre, glass beads, hollow glass spheres, glass powder, glass fibers, ceramics, grits, clays (e.g., kaolin), staurolite (including staurolite sand) and 5 wollastonite or a combination thereof. The fillers may be in a variety of forms such as ground particles, flakes, needle-like particles and the like. The size and form of the particles should be selected such that they may easily be incorporated into the polymeric carrier and allow for the formation of particles having the desired size.

The fillers preferably have a Mohs hardness of at least about 3, or more preferably of 10 at least about 5, or yet more preferably of at least about 6, or still more preferably of at least about 7.

The fillers may optionally be pre-treated with one or more compatibilising and/or coupling agents that facilitate adhesion to or other compatibility with the polymer. Compatibilising and/or coupling agents may also be 15 added to the filler and polymer mixture prior to or during melt blending to form the particles. The compatibilising and/or coupling agents may be used in about 0.01 to about 1 weight percent when they are added prior to or during melt blending. Examples of coupling agents suitable for use with sand or glass are silane coupling agents such as gamma-aminopropyltriethoxysilane (silane A-1100).

20 Preferably the particles according to the invention comprise about 20 to about 100 weight percent of polymer and about 80 to about 0 weight percent filler, wherein the weight percentages are based on the total weight of the particles. In a particular embodiment of the invention the polymer comprises 100% polymer. In another embodiment the particles according to the invention comprise about 20 to 25 about 80 weight percent of polymer and about 80 to about 20 weight percent filler.

The melts for the particles according to the invention that comprise one or more fillers can be formed by melt blending the fillers with the polymers. Any melt blending technique known in the art may be used. For example the component materials may be mixed using a melt-mixer such as a single- or twin-screw extruder, 30 blender, kneader, roller, Banbury mixer, etc.

Preferably the polymer has a VICAT softening point, expressed as the so-called VICAT softening point, according to ISO standard 306, of between 50 -200°C, more preferably between 70 - 160°C. A softening point in the said ranges is 11 \ advantageous, as the particles remain rigid at higher temperatures, although some deformation may take place.

Another embodiment of the invention comprises the use of flow-aids during extrusion and/or solidification of the particles in order to facilitate the 5 formation of small spherical and round particles. These flow-aids can be any known melt viscosity reducing agent such as wax, liquid or solid flame retardant, organic solvent, hydrocarbons in general etc. These flow-aids may optionally be removed from the particles once they are solidified in whole or in part in a subsequent process step by known extraction agents such as water, organic alcohols such as glycols or 10 any appropriate extraction medium. The extraction can also take place during solidification.

Preferably the portions of the melt after passing through the die and being cut by the cutting device have a length that corresponds with 0.7 to 5 times, in particular to 3 times, more in particular to 1.3 times the diameter of the outlet 15 opening of the die. More preferably, said length corresponds with the said diameter, in order to produce spherical particles.

In a very attractive embodiment the melt is passed through a die plate having a plurality of dies. In this way, many particles can be produced in parallel simultaneously. A suitable die plate is e.g. described in US7,776,244.

20 Therein the die plate is used for the preparation of expandable polystyrene. However particles according to the present invention are preferably not expandable.

Preferably the outlet openings of the dies of the plate are equal, enabling the preparation of particles of equal size.

The die preferably has an inlet having an inlet opening having a 25 diameter being larger than that of the outlet opening. The outlet comprises a number of individual outlet channels having a channel diameter. The outlet channel preferably has an inlet diameter that is at least equal to the outlet diameter. The die further preferably comprises a die area located upstream of the channels having a diameter of at least the diameter of the outlet opening. The channel has preferably a 30 total length of at least two times the diameter of the outlet diameter, preferably 6-4 times. These features are further in detail described in US7,776,224, herein incorporated by reference and it has been found that these features contribute to an equal flow distribution over the number of outlet channels and thereby to a uniform particle diameter. The pressure upstream of the die opening may be up to 250 bar,

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12 preferably between 60 and 200 bar, more preferably between 90 and 150 bar. As described above, the pressure may be of influence to the clogging of the outlet opening of the die. A higher pressure may give less clogging.

Attractively, the particles are recovered from the solidifying medium.

5 Many state of the art methods can be used to recover the particles, e.g. by filtration, centrifugation or by treatment in a cyclone. In another embodiment the particles can be dried and sieved.

Preferably, the particles are dried after recovery, i.e. by exposure to a stream of air or an inert gas. In case water was used as solidifying medium, the 10 particles are preferably dried by air. In case an organic liquid was used as solidifying medium it can be contemplated to wash the recovered particles with water or any other liquid first. However the recovered particles can also be dried without being washed. In that case, an air stream can be used to dry the particles. It can also be advantageous to use an inert gas such as nitrogen for drying. By washing with water, 15 the temperature of the particles may drop to an undesirably low temperature. The temperature is preferably kept as high as possible in order to provide for a cost effective drying process. Said drying can e.g. take place in a vertical falling bed, wherein the particles flow downward, and wherein the drying medium such as air or nitrogen is blown in counter current upward direction. The crystallisation and drying 20 step can preferably be efficiently combined into one unit operation.

If desired, e.g. when PET is used the particles can attractively be cured by incubation of the particles at or above the crystallisation temperature Tpc thereof. Such a curing step, or crystallisation step, provides additional hardness to the particles. This curing or crystallisation can e.g. take place in a residence time 25 crystalliser.

The crystallisation temperature is explained in figure 1 below. Although a separate curing step can be performed, the said curing can attractively take place during the solidifying process in the solidifying medium. In that case, the temperature of the solidifying medium must be chosen to be above the said Tpc of the 30 particles. The curing step can also attractively be combined with the drying step. In that case, the temperature of the drying medium should be above the said Tpc of the particles. Or the curing step can be performed by use of the latent heat of the particles or by external heating or by a combination thereof.

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The invention also relates to a particle, obtainable by the method according to the invention, having a diameter of 4.0 mm or less, preferably of 3.0 or less, more preferably of 2.0 or less. In another embodiment, the particles preferably have a particle size of at most 1.3 mm, preferably between 0.3 - 0.9 mm, most 5 preferably between 0.4 - 0.8 mm. Said particle sizes can be conveniently obtained by the choice of the diameter of the die outlet opening and of the length of the cut melt as indicated above.

Further, the invention relates to particles comprising at least a polymer, said particles having a density of 1.0 to 3.5 g/ml, and a particle size of at 10 most 3.0 mm. Such particles could not be made before the present invention was made.

Further, the invention relates to particles comprising at least a polymer, said particles having a density(i.e. specific weight) of 1.0 - 3.5 g/ml, preferably of 1.0 - 2.5 g/ml, more preferably of 1.0 - 1.5 g/ml. In case the particles 15 according to the invention should stay in aqueous suspension, the preferably have a density between 1.05 and 1.35 g/ml and most preferably between 1.05 and 1.10 g/ml. This is advantageous, as the particles have less tendency to settle, and can also be pumped by mechanical pumps without the risk of clogging the pump.

Preferably, the particles obtainable by the method according to the 20 invention have a particle size of at most 3.0 mm, preferably at most 2.5 mm, more preferably at most 2.0 mm, most preferably at most 1.3 mm. Said particles preferably have a particle size of at least 0.3 mm, preferably at least 0.5 mm and most preferably at least 0.6 mm. These sizes can be conveniently be obtained, e.g. by choosing a diameter of the die outlet opening to be equal to or somewhat smaller 25 than the envisaged particle size, and to synchronize the cutting device with the flow rate of the melt passing the die outlet opening accordingly, preferably to allow a length of the cut melt to be 0.7 to 1.3 times the said diameter. By solidification, the cut melt solidifies into a spherical particle of optimal roundness and sphericity.

In a further preferred embodiment the particles according to the 30 invention has a roundness and sphericity of 0.7-1, preferably of 0.8 - 1 according API19C. Such roundness can be obtained by underwater granulation techniques. Crushing elongated polymer bars into smaller particulate may also be an option, however this involves an additional processing step, and does not lead to optimal roundness and sphericity.

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The particle size can also be expressed as pellet weight, i.e. the weight of exactly 100 particles. The particles of the invention preferably have a pellet weight of 1.5 g or less.

The invention will now be further explained by the following figures 5 and examples, wherein:

Figure 1 is a graph, showing a dsc curve according to ISO 11357-1 1997,

Figures 2A-F show pellets of several samples as prepared according to the invention,

10 Figure 3 shows a reference table taken from the standard API19C

for the determination of particle roundness and sphericity,

Referring to figure 1, which is taken from ISO 11357-1 1997, to which is expressly referred to herein, polymers may display specific behaviours 15 called “glass transition”, “crystallisation" and “melting" as shown in the figure by ‘g’, ‘c’ and ‘m’, respectively. These transitions are characterised by the energy required for these transitions and thereby become measurable as described in IS011357. Of relevance is Tpm, the peak indicating the melting point of the polymer, although polymers have a melting range starting at Tim and ending at Ttm. Tpm, Tim, and Ttm, 20 can easily be determined following the instructions of the IS011357 protocol.

In figures 2A-F pellets of samples RPI061, RPI190, RPI081, RPI186, RPI111 and RPI196 are shown respectively. 10 Particles are encircled that we used to assess roundness and sphericity according to standardAPI19C, see also the below examples. Each figure 2A-I also shows a reference table that is magnified in 25 figure 3.

Figure 3 shows a reference table, used in standard API19C to determine the roundness and sphericity.

Examples 30 Example 1

Preparation of pellets Starting materials Polymers i 15

High impact polystyrene ( HIPS): polystyrene impact 6540 obtained from Total Petrochemicals64170 Lacq, France.

Polycarbonate : Xantar 18 UR , Mitsubishi Engineering- Plastics Corporation 40549 Düsseldorf, Germany.

5 Polycarbonate : Xantar 25 SR FD , Mitsubishi Engineering- Plastics Corporation 40549 Düsseldorf, Germany.

Recycled polyethylenetherephthalate (rPET): CorePET FR80 grün, Pet Recycling, Arnhem, Netherlands.

10 Table 1: Starting materials and production parameters

Sample RPI061* RPI190** RPI081* I RPI186** I RPI111* RPI196**

Formulation Weight % HIPS HIPS PËT PET PC18 PC25

Extruder X 2ÖÖ 210 265 28Ö 32Ö 31Ö temperature

Extruder RPM 15Ö Ï99 25Ö 35Ö 2ÖÖ 35Ö

Die plate type Number of 450 450 450 450 360 360 holes diameter of 0.5 0.5 0.5 0.5 0.75 0.75 holes in mm

Temperature X 226 238 3ÏÏ1 336 32Ö 385 of the melt

Feed rate RgTh 3ÖÖ 3ÖÖ 3ÖÖ 3ÖÖ 3ÖÖ 3ÖÖ

Die plate MPa 18 Ï1 Ï9 2Ö 25 22 pressure

Cutter hub Nr. Of knives 2Ö 18 12 18 18 18

Pelletizer RPM 3636 3695 3Ö25 364Ö 3630 3656 speed

Solidifying mVh 3Ö 13 3Ö 14 3Ï 2Ö medium flow

Solidifying X 48 77 95 Ï23 9Ï Ï21 medium temperature

Pellet Gram 0.0234 0.0194 0.0422 0.0187 0.0337 0.0230 weight/100

Sphericity 0.9 0.9 0.5 0.9 0.7 0.9

Roundness 0.9 0.9 0.9 0.9 0.8 0.9

Specific Kg/m3 1Ö6Ö 1Ö6Ö Ï34Ö Ï34Ö Ï2ÖÖ 12ÖÖ gravity

Nr. of open 294 388 326 1Ö8 227 33Ö die holes

Pellet size mm 0.75 0.71 0.84 0.64 0.81 0.72 » ♦ 16 * Comparative examples (solidified in water).

** Solidified in ethylene glycol.

One skilled in the art will notice that sample RPI111 was produced 5 using a polycarbonate with a low melt viscosity ( MVR 23) and that sample RPI196 was produced with a polycarbonate with a high melt viscosity (MVR 5). This further emphasizes the effectiveness of the present invention.

A polymer melt of starting materials according the formulations as given in table 1 was added via standard loss-in-weight feeders to the throat of a 6 10 barrel long extruder (Berstorff ZE60, Germany) a twin screw length of 2400 mm equipped with a standard vacuum set-up. At the outlet of the extruder, a screen pack changer with 630/315 sieve (K-SWE-121/RS, BKG, Germany) was installed to free the polymer melt from any solid particles followed by a 70/70 high pressure melt pump (BKG, Germany) to generate the required die plate pressure, as given in table 15 1. The polymer melt was passed through a multiple die-plate with a die-opening arrangement according to figure 1B of US7,776,244, the outlet opening having a diameter of 0.5 and 0.75 mm, respectively, as shown in the table above and cut to size by a cutter hub on a pelletizer (type AH2000, BKG, Germany). The solidifying medium was water or ethyleneglycol having a temperature as indicated in table 1. 20 The process parameters for each formulation can be found in table 1.

Samples of RPI186 and RPI196 we produced by using ethylene glycol as solidifying medium at a temperature of 123°C and 121°C respectively. This solidifying medium has a lower heat conductivity than water (water: 0.61 W/m/°C whereas most organic liquids have a substantially lower heat conductivity in the 25 range of 0.1-0.30 W/m/°C, the conductivity of ethylene glycol is 0.26 W/m/°C). Therefore the relatively cold solidifying medium flowing along the die-plate is causing a reduced temperature loss of the melt at the die outlet openings of the die plate. Organic fluids, in particular liquids, having a boiling temperature of more than 100°C, preferably between 100 - 200°C are suitable as solidifying medium, as long as said 30 fluids do not significantly react with the polymeric melt passing through the die outlet opening. Preferably, the solidifying medium is inert with respect of the said polymeric melt. The skilled person is capable to choose a suitable fluid, and to adapt the equipment if necessary, i.e. by adapting the chamber wherein the solidifying medium is accommodated. This enables the production of smaller pellets using common ♦ 17 pelletizing equipment. From the table, it can be seen that the pellet weight, being an indication for particle size, is 17% less for HIPS when produced with glycol as solidifying medium (RPI190) as compared to water (RPI061), For PC the said reduction is 32% (RPI196 andRPI111) and for PET the reduction is 56% (RPI186 5 and RPI081).

Determination of the theoretical particle size

From the extruder throughput, the density of the material, the number of die outlet openings, the cutting frequency of the cutter hub (to be 10 determined by the number of blades on the cutter hub and the speed of the cutter hub) one skilled in the art can easily calculate the expected particle size. In the comparative example of RPI061, the throughput was 300 kg/h, the number of die outlet openings was 450 and the melt passing each die outlet opening was cut by 20 knives, rotating at 3636 rpm (rotations per minute). The density of the material was 15 1060 kg/m3. The volume of the pellets can be calculated by the formula throughput per second per die opening divided by the density of the polymer melt, divided by the cutting frequency of the cutter hub per second. In this example, the particle volume is therefore 300/3600/450/1060/20/(3636/60)-109=0.144 mm3. This makes an expected particle size of about 0.65 mm diameter, as the shape is assumed to be 20 spherical (volume = TT/6*d3, i.e. 3.14/6*0.653=0.144 mm3).

Determination of the actual particle size.

The above expected particle size was compared with the actual particle size. The latter was obtained by weighing 100 particles (herein also ‘pellets’) 25 on a Sartorius A200S micro-scale from Sartorius GmbH, Gottingen Germany. From the said weight, one skilled in the art can now calculate the actual average pellet volume and size through the known density from the formulation. An actual pellet weight above the theoretical particle size is an indication of die-holes being clogged, as the same volume of material is passing through a lower number of open die 30 openings, resulting in a proportionally higher volume per open die opening. In this example the weight of 100 pellets is 0.0234 gram, or a volume per pellet of 0.0234*10/1.06=0.22 mm3 so the number of open holes is 450 -.144/.22=294. The acceptable limit for weight of 100 pellets can be calculated upfront from the 18 maximum allowable pellet size that is specified. Production was halted approaching this limit to free the frozen die-holes.

Separation of the pellets 5 The water/pellet slurry was separated in a standard centrifugal dryer. The remaining hot solidifying medium that passes through the centrifugal dryer 0.3 mm sieve was treated in a BKG Optigon filter drum (BKG, Germany) to remove the undersized pellets and to recuperate the solidifying medium that was recycled back to the pelletizer. The undersize pellets were either wasted, or recycled into the 10 extruder. The hot and dried pellets coming of the centrifugal dryer were subsequently sieved to remove oversized material before packaging. The oversized material was wasted, or recycled into the extruder.

Determination of pellet roundness and sphericity 15 10 individual pellets of different samples RPI061, RPI190, RPI081, RPI186, RPI111 and RPI196 as encircled in figures 2A-F, respectively, were visually examined for roundness and sphericity and valued in accordance with the standard API19C, shown in figures 2A-F. The average sphericity of comparative example RPI081 was e.g. determined to be 0.5, whereas that of example RPI186 was 20 determined to be 0.9 and the average roundness to be 0.9, based on the data as presented in figure 2.

25 1039259

Claims

Method for the preparation of particles comprising at least one polymer, wherein a melt comprising the polymer is extruded by flowing the melt through at least one die into a solidification medium having a temperature lower than the melting temperature of the melt through which the melt solidifies, characterized in that the solidifying medium has a thermal conductivity of less than 0.55 W / m / ° C.

2. Method according to claim 1, wherein the heat conductivity of the solidification medium is less than 0.4 W / m / ° C, preferably less than 0.3 W / m / ° C, more preferably less than 0.2 W / m / ° C.

A method according to claim 1, wherein the temperature of the solidifying medium is more than 90 ° C, preferably more than 110 ° C, more preferably more than 120 ° C, even more preferably more than 140 ° C.

Method according to claim 1 or 2, wherein the temperature of the coagulation medium is less than 250 ° C, preferably less than 200 ° C.

A method according to any of the preceding claims, wherein the solidifying medium has an atmospheric boiling point of above 110 ° C, preferably above 120 ° C, more preferably above 150 ° C.

A method according to any of the preceding claims, wherein the coagulation medium comprises an organic liquid.

7. Method according to claim 6, wherein the organic liquid has an atmospheric boiling point of higher than 100 ° C, preferably of higher than 110 ° C, more preferably of higher than 120 ° C, even more preferably of higher than 150 ° C.

The method of claim 5, wherein the organic liquid is inert to the melt and the particles.

The method of claim 5 or 6, wherein the coagulation medium comprises a mixture of two or more organic liquids.

The method of any one of claims 5-7, wherein the coagulation medium comprises a mixture of one or more organic liquids with water.

A method according to any of the preceding claims, wherein the coagulation medium comprises a polar organic liquid. 1039259 * •

A method according to any of the preceding claims, wherein the coagulating medium comprises an alcohol, ether, acid or ester, preferably an alcohol.

A method according to any of the preceding claims, wherein the coagulation medium comprises glycol, preferably ethylene glycol or propylene glycol or mixtures thereof.

A method according to any of the preceding claims, wherein the outflow opening of the mold has a diameter of 4.0 mm or less, preferably of 2.0 or less, more preferably of 1.2 mm or less, with More preferably of 0.8 mm or less, most preferably of 0.75 mm or less.

Method according to any of the preceding claims, wherein the outflow opening of the mold has a diameter of 0.3 mm or more, preferably 0.4 mm or more, even more preferably 0.5 mm or more, with the Most preferably above 0.6 mm or more.

A method according to any of the preceding claims, wherein the melting temperature Rpm of the polymer is at least 120 ° C, preferably at least 150 ° C, more preferably at least 180 ° C.

17. Method according to any of the preceding claims, wherein the temperature difference between the solidification medium and the melting point Rpm of the polymer is less than 150 ° C, preferably 100 ° C or less, more preferably 80 ° C or less.

18. Method according to any of the preceding claims, wherein the particles have a particle size of at most 4.0 mm, preferably at most 3.0 mm, more preferably at most 2.5 mm, even more preferably at most 2.0 mm, most preferably a maximum of 1.3 mm.

A method according to any of the preceding claims, wherein the particles have a particle size of at least 0.3 mm, more preferably at least 0.5 mm, most preferably at least 0.6 mm.

A method according to any of the preceding claims, wherein the melt polymer is a crosslinked polymer, crosslinked or unlinked, a crosslinked or unlinked terpolymer, a crosslinked (co) polymer or a crosslinked block mixture thereof.

The method of any one of the preceding claims, wherein the polymer is thermoplastic.

22. Method according to any of the preceding claims, wherein the polymer is selected from the group consisting of polyolefins, polyethylenes, polypropylenes, polystyrenes, acetronitrile-butadiene-styrene polymers, aromatic or aliphatic partially crystallized polyesters, polycarbonates, polyamides, polyacetals , polyphenylene oxides, polyphenyl sulfides, polyether ether ketones, polyether ketone ketones, polyether imide, polysulfons, polyarilates or a mixture thereof.

A method according to any of the preceding claims, wherein the polymer comprises polyethylene terephthalate, preferably cross-linked, wherein the polyethylene terephthalate is preferably recycled polyethylene terephthalate, most preferably cross-linked recycled polyethylene terephthalate.

24. Method according to any of the preceding claims, wherein the polymer comprises polycarbonate, PET, PEI or PEEK.

The method of any one of the preceding claims, wherein the polymer melt comprises a filler.

26. Method according to any of the preceding claims, wherein the filler is selected from the group consisting of sand, carbon black, graphite, mica, silica, silicon carbide, alumina, quartz, nanotubes, coconut, walnut, natural fibers, glass fiber , glass beads, hollow glass beads, glass powder, glass fibers, ceramics, grit, clay (for example kaolin), staurolite (including staurolite sand) and wollastonite or a combination thereof.

27. Method according to any of the preceding claims, wherein the particles are recovered from the coagulation medium.

The method of claim 26, wherein the recovered particles are dried.

29. A method according to any one of the preceding claims, wherein the particles are cured by incubating the particles at or above crystallization temperature Tpc thereof.

A method according to any of the preceding claims, wherein the particles are recovered from the solidification medium and dried.

The method of claim 30, wherein the particles are dried by exposing them to a stream of air or inert gas. i

A method according to any one of the preceding claims, wherein the particles are cured, preferably during the solidification process or, when carried out, during the drying step.

Particle obtainable by the method according to any of the preceding claims, with a diameter of 4.0 mm or less, preferably 3.0 or less, most preferably 2.0 or less.

34. Particles comprising at least one polymer, the particles having a density of 1.0 - 3.5 g / ml and a particle size of at most 3.0 mm.

Particles according to claim 33 or 34 with a density of 1.0 - 3.5 g / ml, preferably of 1.0 - 2.5 g / ml, more preferably of 1.0-1.5 g / ml ml.

Particles according to any of claims 33 to 35, wherein the particles have a particle size of at most 3.0 mm, preferably at most 2.5 mm, more preferably at most 2.0 mm, most preferably at most 15 1, 3 mm.

Particles according to any of claims 33 to 36, wherein the particles have a particle size of at least 0.3 mm, preferably at least 0.5 mm, most preferably at least 0.6 mm.

38. Particles according to any of claims 33 to 37, with a roundness and sphericity of 0.1 to 1, preferably from 0.8 to 1.

Particles according to any of claims 33 to 38, with a pellet weight of 1.5 g or less.

Particles according to any of claims 33 to 39, comprising PET, PEI or PEEK. 25 1039259