Title of Invention

PROCESS FOR THE CUTTING OF THERMOPLASTIC POLYMERS DOWNSTREAM OF A WATER-RING DIE

Abstract Process for the production of substantially cylindrical pellets of vinyl -aromatic (co) polymers, leaving a water- ring extrusion die, wherein the extrusion is effected so that the length/diameter ratio of the pellet ranges from l•3 to 2 and the diameter of the (base) ranges from 2 to 3.2 mm, with a flow-rate of the polymer, per hole of the die, ranging from 4 to 20 kg/h.
Full Text

Title: Process for the cutting of thermoplastic polymers downstream of a water-ring die
In the name of: Polimeri Europa S•p.A. having its head of¬fice in Brindisi, Via Enrico fermi 4
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The present invention relates to a process for the cutting of thermoplastic polymers downstream of a water-ring die.
More specifically, the present invention relates to a process for the production of substantially cylindrical pellets of thermoplastic polymers leaving a water-ring ex¬trusion die.
Even more specifically, the present invention relates to a process for the production of substantially cylindri¬cal pellets of vinyl-aromatic (co)polymers, for example, polystyrene, high impact polystyrene, SAN copolymers, ABS copolymers, leaving a water-ring extrusion die according to the "water-ring" technology.
Thermoplastic polymers in general are products in the form of pellets whose shape depends on the cutting technol¬ogy used. In the specific case of vinyl-aromatic polymers, such as styrene polymers, two methods are generally used,

known as *spaghetti cutting" and uwater-ring cutting", re¬spectively.
According to the spaghetti cutting method, the molten polymer is continuously discharged from a die, forms con¬tinuous filaments of polymer which, entrained by gears, are cooled in a water tank and are then cut at a low tempera¬ture by rotating knives.
According to the other water-ring cutting method, the granules are *fired" by high-speed rotating knives in a wa¬ter-ring circuit separated from the cutting head. Examples of scientific literature which describe the two methods are: "Palletizing; Choosing an Appropriate Method", Plastic Additives & Compounding, July/August 2005, page 22; and the
patents USA 3,207, 818; 4,245,972; a,SQgj B77.J 4,846,644; 4,978,288; 5,215,763; 6,551,087.
The preferred method, from the point of view of han¬dling and also with respect to the investment and mainte¬nance costs, is the so-called "water-ring" technology, With thie technique, in fact, the die is not in direct contact with the. water; the restarting of the production plant, in the case of short stops, is much simpler as it is much eas~ _i_er__,tq_keej> the polY¾©r ^ the molten state; furthermore during the .start-ups, the polymer is not handled directly by the operators and the fact of effecting the cutting on molten and not consolidated polymer, greatly reduces the

noise.
Finally, it should be pointed out that in the water-ring pelletizing system, the overall cutting device is much more compact and is also presented as a "closed" system so that the presence of vapours, residual monomers and possi¬ble additives in the environment can be more easily con¬trolled.
Due to their rounded geometry, basically spherical, or however free of sharp edges, the pellets produced with the water-ring system are subject to friction to a much lesser degree, with respect to the pellets having a cylindrical geometry obtained with spaghetti cutting, and also there¬fore their tendency to break in the pneumatic transporta¬tion phases present downstream of the production. An imme¬diate consequence of this phenomenon is the relatively low quantity of powder formed by disgregation of the pellet it¬self. It can be easily understood that the presence of pow¬der causes problems of production loss when separated, and inconveniences for the final client, when not separated.
The use of water-ring systems in the cutting of ther¬moplastic styrene polymers, which, as can be seen, has nu¬merous advantages, is limited however by the potentially negative impact of the rounded pellets on the most wide¬spread transformation processes, i.e. those using screws for the plasticization of the polymer, such as, for exam-

pie, extrusion and inj ection moulding. Due to their geome-try, in fact, this type of pellet reduces the generation of friction heat in the plasticization phase causing problems relating to production potentiality and stability.
With reference, for example, to injection moulding, this series of phenomena leads to an increase in the dosing time which is jeopardizing especially in fast injection molding. An indirect verification of this behaviour, but more generally of a correct feeding to the plasticization screw, is also provided by the determination of the xvrest angle", calculated according to the method ASTM C 1444-00, which is representative of the flow of a mass of pellets beneath their own weight. Rounded pellets normally have a value of 20-32.5°, whereas cylindrical pellets, for example those coming from spaghetti cutting, 35-45°.
The Applicant has now found that by suitably modifying the diameter of the die holes, the rate and number of knives and flow-rate per single hole, it is possible how¬ever to obtain a substantially cylindrically-shaped pellet also with a water-ring cutting system.
The pellet thus produced has, in the feeding area to the plasticization screws, a behaviour which is completely analogous to that obtained by the pellet obtained with spa¬ghetti cutting. The pellet thus obtained has a rest angle value ranging from 35° to 45°, and therefore within the

typical range of spaghetti cut cylindrical pellets* As en¬visaged therefore, the content of powder produced by fric¬tion in the pneumatic transportations is considerably re¬duced for the pellet thus obtained.
The object of the present invention therefore relates to a process for the cutting of thermoplastic polymers with substantially cylindrical-shaped pellets downstream of a water-ring die which comprises:
a. feeding a polymer in the molten state, for example pro¬
duced by a single- or twin-screw extruder or by a polym¬
erization plant, to a water-ring die;
b. extruding the polymer through the die to obtain a sub¬
stantially cylindrical pellet having a length/diameter
ratio ranging from 1.3 to 2 and a diameter (base) rang¬
ing from 2 to 3.2 mm;
characterized in that
c. the flow-rate of the molten polymer per hole of the die
is such as to give a (pellet number)/gram ratio ranging
from 25 to 70 gr"1; and
d. the time between two cuttings, referring to the same
hole, ranges from 5-10"3 to 2.10"2 seconds.
The pellet must be rapidly cooled as soon as it has been cut, by immersion in water at a temperature lower than 5O°C. For this reason, the temperature of the water at the inlet of the water-ring is below 5O°C,

According to the present invention, what is specified above in points (c) and (d), is obtained with flow-rates per hole ranging from 4 to 20 kg/h, with a diameter of the die holes ranging from 1.5 to 3 mm and a temperature of the polymer in correspondence with the die generally ranging from 200 to 26O°C. The result of this is that with respect to the conventional water-ring cutting, cuts are obtained with a more reduced diameter of the die holes and therefore a greater number of holes to contain the pressure drops through the die and a reduced number of knives.
Any thermoplastic polymer can be subjected to the cut¬ting process, object of the present invention, even if vi¬nyl-aromatic polymers and copolymers are preferred. Accord¬ing to the present invention, the vinyl-aromatic {co)polymer preferably has a weight average molecular weight ranging from 50,000 to 500,000 and can be obtained by polymerizing at least one vinyl-aromatic monomer which corresponds to the following general formula:

wherein n is zero or an integer ranging from 1 to 5, Y is a halogen, such as chlorine or bromine, or an alkyl or alkoxyl radical having from 1 to 4 carbon atoms and R rep-

resents a C1-C4 alkyl group.
Examples of vinyl-aromatic monomers having the general formula identified above are: styrene, methylstyrene,
ethylstyrene, butylstyrene, dimethylstyrene, a-
methylstyrene, a-ethylstyrene, mono-/ di-, tri-, tetra-, and penta-chlorostyrene, bromostyrene, methoxystyrene, ace-
toxystyrene , etc. The preferred vinyl-aromatic monomer is
styrene.
The term "vinyl-aromatic monomer", according to the present invention, implies that the vinyl-aromatic monomers having general formula " (I) can be used alone or in a mix¬ture of up to 50% by weight with other copolymerizable monomers. Examples of these monomers are (meth)acrylic acid, C1-C4 alkyl esters of (meth) acrylic acid, such as methyl acrylate, methylmethacrylate, ethyl acrylate, ethyl-methacrylate, isopropyl acrylate, butyl acrylate, amides and nit riles of (meth) acrylic acid such as acrylamide, methacrylamide, acrylonitrile, methacrylonitrile, butadi¬ene, ethylene, divinyl benzene, maleic anhydride, etc. Pre¬ferred copolymerizable monomers are acrylonitrile and me¬thylmethacrylate .
The definition of vinyl-aromatic (co)polymers includes polymers obtained by polymerizing the above monomers in the presence of unsaturated rubbers. Examples of unsaturated rubbers are polybutadiene, polyisoprene or monomodal or bi-

modal, linear or radial, block rubbers, containing, for ex¬ample, from 50 to 90% by weight of butadiene.
The pellets obtained with the conditions described above have rest angles comparable with those of the pellets obtained from spaghetti cutting (35º-45º). In the feeding to the plasticization screw, the cylinderized pellet, ob¬tained with the process, object of the present invention, does not have the complex feeding problems frequently ob¬served with spheroidal pellets obtained with the tradi¬tional water-ring system, where cutting parameters exceed¬ing those cited above, are used.
Another characteristic of the cylinderized pellets of the present invention is. that they produce very little pow¬der in the pneumatic transportation lines. As can be seen from the enclosed examples, the pellet does not have cracks or live edges.
A further characteristic is the appearance, at least for SAN pellets and polystyrene homopolymer pellets. The shape of the pellets obtained with the water-ring system is more regular and smoother. This characteristic enhances the visible appearance of the pellets which are considered pleasanter than those obtained with traditional cutting. The cylinderized pellets are in fact practically transpar¬ent also in the axial direction and this produces a greater number of luminous or black spots whereas the pellets ob-

tained with traditional cutting, as they have a much larger surface obtained from fragile breaking, disperse the light uniformly on the whole surface making them seem much greyer than they actually are.
The present invention is now better described with reference to the following examples which represent an il¬lustrative and non-limiting embodiment. EXAMPLE 1
A polystyrene homopolymer, EDISTIR N 2560 of the Ap¬plicant produced with the continuous mass polymerization technology, is fed directly to a Bandera twin-screw ex¬truder operating with a screw-bottom temperature of 225°C, eguipped with two cutting knives which rotate at 2200 rpm and a diameter of the die holes of 1.8 mm.
The extrusion and cutting of the polymer is carried out with a flow-rate per hole, Q, of 7 kg/h, a cutting wa¬ter temperature of 40°C, a polymer temperature of 225°C. At the end of the extrusion and cutting, cylindrical pellets are obtained, having the following characteristics:
Diameter of pellets (D) 2.8 mm
Length of pellets (L) 4.5 mm
Aspect ratio (L/D) 1.6
Pellets/gr 38 gr"1
Rest angle 36°
Apparent density 650 Kg/m3

EXAMPLE 2
A polystyrene homopolymer, EDISTIR N 1B40 of the Ap¬plicant produced with the continuous mass polymerization technology, is fed directly to a Bandera twin-screw ex¬truder operating with a screw-bottom temperature of 205°C, equipped with three cutting knives which rotate at 2250 rpm and a diameter of the die holes of 1.8 mm.
The extrusion and cutting of the polymer is carried out with a flow-rate per hole, Q, of 11.8 kg/h, a cutting water temperature of 4O°C, a polymer temperature of 2O5°C, At the end of the extrusion and cutting, pellets are ob¬tained, illustrated in Figure 1, having the following char¬acteristics:
D pellets 3 mm
L pellets 4.2 mm
Aspect ratio 1.4
Pel•lets/gr 34 gr"1
Rest angle 37.5°
Apparent density 640 Kg/irr
EXAMPLE 3
A high impact polystyrene, EDISTIR ICE PDR 835 D of the Applicant produced with the continuous mass polymeriza¬tion technology, is fed directly downstream of a polymeri¬zation line, operating with a temperature of the polymer in the feeding to the cutting group equal to about 240°C. The

cutting group is equipped with 4 knives which rotate at 1600 rpm and with a diameter of the die holes of 2.8 mm.
The extrusion and cutting of the polymer is carried out with a flow-rate per hole, Q, of 12.8 kg/h, a cutting water temperature of 45°C, a polymer temperature of 24O°C. At the end of the extrusion and cutting, cylindrical pel¬lets are obtained, illustrated in Figure 2, having the fol¬lowing characteristics:
D pellets 3.0 mm
L pellets 5*3 mm
Aspect ratio 1.7
Rest angle 42.5°
Pellets/gr 31 gr'1
EXAMPLE 4
An ABS, Sinkral B 432/E of the Applicant produced with the continuous mass polymerization technology, is fed di¬rectly downstream of a polymerization line, operating with a temperature of the polymer in the feeding to the cutting group equal to about 250°C. The cutting group is equipped with 4 knives which rotate at 1500 rpm and with a diameter of the die holes of 2.8 mm.
The extrusion and cutting of the polymer is carried out with a flow-rate per hole, Q, of 12 kg/h, a cutting wa¬ter temperature of 45°C, a polymer temperature of 250°C* At the end of the extrusion and cutting, cylindrical pellets

are obtained, having the D pellets L pellets Aspect ratio Pellets/gr

following characteristics: 3.1 mm 4. 6 mm 1.5 . 30 gr"1









CLAIMS
1. A process for the cutting of thermoplastic polymers
with substantially cylindrical-shaped pellets downstream of
a water-ring die which comprises:
a. feeding a polymer in the molten state, for example pro¬
duced by a single- or twin-screw extruder or by a polym¬
erization plant, to a water-ring die;
b. extruding the polymer through the die to obtain a sub¬
stantially cylindrical pellet having a length/diameter
ratio ranging from 1.3 to 2 and a diameter (base) rang¬
ing from 2 to 3.2 mm;
characterized in that
c. the flow-rate of the molten polymer per hole of the die
is such as to give a (pellet number) /gram ratio ranging
from 25 to 70 gr"1; and
d. the time between two cuttings referring to the same
hole, ranges from 5.10"3 to 2•l02 seconds.
2, The process according to claim 1, wherein the flow-rate of the polymer per hole ranges from 4 to 20 kg/h.
3, The process according to claim 1 or 2, wherein the pellet is rapidly cooled as soon as it has been cut, by im¬mersion in water at a temperature lower than 50°C,
4. The process according to any of the previous claims,
wherein the temperature of the molten polymer in correspon¬
dence with the die ranges from 200 to 26O°C.

5. The process according to any of the previous claims, wherein the diameter of the die holes ranges from 1.5 to 3 mm.


Documents:

2028-CHENP-2008 AMENDED PAGES OF SPECIFICATION 12-08-2013.pdf

2028-CHENP-2008 FORM-3 12-08-2013.pdf

2028-CHENP-2008 OTHERS 12-08-2013.pdf

2028-CHENP-2008 POWER OF ATTORNEY 12-08-2013.pdf

2028-CHENP-2008 AMENDED CLAIMS 12-08-2013.pdf

2028-CHENP-2008 EXAMINATION REPORT REPLY RECEIVED 12-08-2013.pdf

2028-CHENP-2008 CORRESPONDENCE OTHERS 17-01-2013.pdf

2028-CHENP-2008 CORRESPONDENCE OTHERS 23-08-2013.pdf

2028-CHENP-2008 FORM-3 23-08-2013.pdf

2028-CHENP-2008 OTHER PATENT DOCUMENT 12-08-2013.pdf

2028-chenp-2008-abstract.pdf

2028-chenp-2008-claims.pdf

2028-chenp-2008-correspondnece-others.pdf

2028-chenp-2008-description(complete).pdf

2028-chenp-2008-drawings.pdf

2028-chenp-2008-form 1.pdf

2028-chenp-2008-form 18.pdf

2028-chenp-2008-form 3.pdf

2028-chenp-2008-form 5.pdf

2028-chenp-2008-pct.pdf


Patent Number 257540
Indian Patent Application Number 2028/CHENP/2008
PG Journal Number 42/2013
Publication Date 18-Oct-2013
Grant Date 14-Oct-2013
Date of Filing 24-Apr-2008
Name of Patentee POLIMERI EUROPA S.P.A
Applicant Address PIAZZA BOLDRINI 1 I-20097 SAN DONATO MILANESE-MILANO
Inventors:
# Inventor's Name Inventor's Address
1 CASALINI, ALESSANDRO VIALE HERMADA 10 I-46100 MANTOVA
2 SAIU, MAURIZIO VIA A ANTOLDI 9 I-26100 MANTOVA
3 PASQUALI, FRANCESCO VIA ASPROMONTE 6 I-37100 VERONA
4 FERRI, DINO VIA CASTELLO 21 I-37067 VALEGGIO SUL MINCIO-VERONA
PCT International Classification Number B29B 9/06
PCT International Application Number PCT/EP06/10065
PCT International Filing date 2006-10-18
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 MI2005A002054 2005-10-27 Italy