(19)
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`J
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`Europaisches Patentamt
`European Patent Office
`Office europeen des brevets
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`(1 1 )
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`E P 0 5 8 8 3 2 1 B 1
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`EUROPEAN PATENT SPECIFICATION
`
`(45) Date of publication and mention
`of the grant of the patent:
`22.01.1997 Bulletin 1997/04
`
`(21) Application number: 93114846.4
`
`(22) Date of filing : 1 5.09.1 993
`
`(51) int. CI.6: B29C 44/02, C08J 9/22
`// B29K23/00
`
`(54) Process for the preparation of foamed propylene polymer articles
`Verfahren zur Herstellung von Gegenstanden aus geschaumtem Propylenpolymer
`Procede pour la fabrication d'objets en mousse de polypropylene
`
`(84) Designated Contracting States:
`AT BE CH DE DK ES FR GB IT LI NL SE
`
`(30) Priority: 15.09.1992 IT MI9221 23
`
`(43) Date of publication of application:
`23.03.1994 Bulletin 1994/12
`
`(73) Proprietor: MONTELL NORTH AMERICA INC.
`New Castle County Delaware (US)
`
`(72) Inventors:
`• Lesca, Guiseppe, Chem.-Eng.
`1-20121 Milano(IT)
`• Romanini, Daniele
`1-44100 Ferrara (IT)
`• Vezzoli, Annibale
`I-22060 Carugo, Como (IT)
`
`(74) Representative: Zumstein, Fritz, Dr. et al
`Patentanwalte,
`Dr. F. Zumstein,
`Dipl.-lng. F. Klingseisen,
`Brauhausstrasse 4
`80331 Munchen (DE)
`
`(56) References cited:
`EP-A- 0 224 265
`EP-A- 0 256 489
`US-A- 5 047 485
`
`EP-A- 0 248 305
`DE-A- 1 504 355
`
`• DATABASE WPI Week 8729, Derwent
`Publications Ltd., London, GB; AN 87-202611 &
`JP-A-62 130 831 (NIPPON STYRENE PAPE) 13
`June 1987
`• PLASTICS ENGINEERING, vol. 47, no. 3, March
`1991, pages 82 - 84 M. B. BRADLEY ET AL.
`'Novel polypropylenes for foaming on
`conventional equipment'
`• KUNSTSTOFFE vol. 82, no. 8, August 1992,
`pages 671 - 676 E. M. PHILLIPS ET AL.
`'Polypropylen mit hoher Schmelzestabilitat'
`• DATABASE WPI Week 845, Derwent Publications
`Ltd., London, GB; AN 84-026006 & JP-A-58 215
`326 (NIPPON STYRENE PAPE.) 14 December
`1983
`• DATABASE WPI Week 8408, Derwent
`Publications Ltd., London, GB; AN 84-046164 &
`JP-A-59 007 025 (SUMITTOMO CHEMICAL) 14
`January 1984
`
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`Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give
`notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in
`a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art.
`99(1) European Patent Convention).
`
`Printed by Rank Xerox (UK) Business Services
`2.13.13/3.4
`
`Page 1 of 6
`
`BOREALIS EXHIBIT 1046
`
`

`
`1
`
`EP 0 588 321 B1
`
`2
`
`Description
`
`s
`
`is
`
`The present invention relates to a process for pre-
`paring foamed beads of propylene polymers, as well as
`to the foamed beads thus obtainable and to a process
`for preparing foamed propylene polymer articles by
`using said beads.
`It is known that foamed polypropylene possesses
`chemical inertia, heat resistance, stiffness and impact
`resistance characteristics far superior to those of 10
`foamed polystyrene. Therefore, it is obvious that there is
`an interest in using foamed polypropylene in application
`fields where the foamed polystyrene cannot be used, or
`in fields where the foamed polystyrene is widely used,
`such as insulation and packaging for example, but it
`does not completely satisfy the demands of the users in
`terms of performance.
`One process which is used for the manufacturing of
`foamed polystyrene products, sometimes quite thick
`and with a complex shape, comprises the thermoform- 20
`ing of pre-foamed beads by sintering. However, this
`technique, although attractive because it can potentially
`be used for the preparation of articles with the most
`diverse shapes, is not easy to apply in the case of poly-
`propylene. In fact, the foamed polypropylene articles 25
`thus obtained tend to show poor cohesion between the
`single pre-foamed beads. Moreover, it is very difficult to
`eliminate the voids between said pre-foamed beads.
`Many approaches have been tried in order to prevent
`this drawback. For example, according to US patent 30
`4,840,973, one can obtain excellent foamed polypropyl-
`ene articles by pre-treating the pre-foamed beads made
`up of a particular random copolymer of propylene with
`ethylene. The pre-foamed beads, as shown in the
`examples, must be previously subjected to a long pres- 35
`surization treatment in compressed air. According to US
`patent 5,026,736, the foamed polyolefin articles (poly-
`propylene is cited as one of them), are obtained by sub-
`jecting pre-foamed beads
`to
`thermoforming by
`sintering, said beads preferably consisting of cross- 40
`linked polymer and being obtained in collapsed form.
`The above approaches, as explained in the above men-
`tioned US patent 5,026,736, avoid the use of compli-
`cated and costly pressure thermoforming techniques,
`which otherwise would be necessary in order to obtain 45
`a good cohesion among the pre-foamed beads and
`eliminate the voids among same. One example of pres-
`sure thermoforming pre-foamed polyolefin beads is
`based on the use of molds maintained under pressure
`with compressed gas, such as air, during the initial
`stage of thermoforming, followed by the sintering of the
`beads, which can be obtained by injecting steam under
`pressure. The cohesion among the pre-foamed beads
`is obtained by bringing the mold back to atmospheric
`pressure, so that the beads can reexpand and adhere to 55
`each other, thus eliminating voids. As an alternative, the
`compression of the pre-foamed beads can be obtained
`by reducing the volume of the mold by way of one or
`more movable walls.
`
`so
`
`2
`
`The Applicant has now perfected a process for the
`production of foamed articles by preparing pre-foamed
`propylene polymer beads by extrusion and then subject-
`ing said beads to thermoforming by way of sintering,
`which process not only does not require a thermoform-
`ing under pressure, but also allows to avoid the pretreat-
`ment described in US patent 4,840,973.
`Moreover the process of the present invention allows
`the use of uncollapsed beads.
`The Applicant has found that one can achieve the above
`advantages by using pre-foamed propylene polymer
`beads consisting essentially of a propylene polymer
`having a melt strenght from 5 to 40 cN, i.e. a propylene
`polymer having a high elongation viscosity in the molten
`state.
`The melt strength can be measured by the specific
`method described below.
`A propylene polymer having said melt strength values
`can be one wherein at least part of the macromolecular
`chains are branched, i.e. these are lateral chains where
`only one of their extremities is bonded to the macromo-
`lecular chain.
`It has also been found that the above high melt strength
`values render the propylene polymer more workable
`during the production of pre-foamed beads. Thus one
`obtains, without particular difficulty, pre-foamed polypro-
`pylene beads of good quality, i.e., having a regular cel-
`lular structure with cells having small dimensions.
`On the other hand, when using conventional propylene
`polymers, i.e. without having low melt strength values,
`the Applicant has found that the processing of the pre-
`foamed beads by extrusion experiences considerable
`problems, so that the quality of the resulting pre-foamed
`beads is unsatisfactory.
`A further advantage of the present invention is the fact
`that the processing waste produced in thermoforming
`by sintering process, as well as the articles which have
`been obtained with the same technique and have been
`already used, can be reconverted into pre-foamed
`beads by using the extrusion processes which will be
`described below, since the polymer is not cross-linked.
`Accordingly, the present invention provides a proc-
`ess for the preparation of foamed beads of propylene
`polymers, comprising extruding a propylene polymer
`having a melt strength from 5 to 40cN in the presence of
`a foaming agent.
`Moreover, the present invention provides foamed beads
`of propylene polymers, said beads being obtainable by
`extruding a propylene polymer having a melt strength
`from 5 to 40 cN in the presence of a foaming agent.
`According to another embodiment, the present
`invention provides a process for the preparation of
`foamed propylene polymer articles, comprising thermo-
`forming by sintering foamed beads of a propylene poly-
`mer having a melt strength from 5 to 40 cN.
`Preferably the foamed beads prepared and used
`according to the present invention have a poured bulk
`density from 10 to 500 kg/m3, more preferably from 15
`to 200 kg/m3, and an average cell diameter from 50 to
`
`Page 2 of 6
`
`

`
`3
`
`EP 0 588 321 B1
`
`4
`
`2000 urn, more preferably from 1 00 to 800 urn. It is also
`preferable that the average diameter of the foamed
`beads be from 1 to 1 0 mm.
`Moreover, in order to obtain particularly good processa-
`bility and finished articles having the best properties, it
`is preferable that the MIL (melt index, condition L) val-
`ues (ASTM D 1238) of the propylene polymers be com-
`prised between 0.5 and 10 g/10 min., more preferably
`between 1 and 6 g/10 min.
`Preferred values of melt strength for the propylene poly-
`mers are from 15 to 40 cN. The propylene polymers
`having, in whole or in part, a branched molecular struc-
`ture, and that can be used for the preparation of the pre-
`foamed beads and the articles of the present invention
`comprise the homopolymers of propylene and its copol-
`ymers thereof containing from 1 to 40% by weight, pref-
`erably from 3 to 30%, of ethylene and/or a-olefins, linear
`or branched, having 4-10 carbon atoms or mixtures of
`the above polymers. Among the copolymers are the
`crystalline propylene random copolymers containing
`from 1 to 25% by weight, preferably from 3 to 20% by
`weight, of ethylene and/or a-olefins having 4-10 carbon
`atoms, as well as the olefin polymer elastomers (EPR
`rubbers, for example), and the heterophasic blends
`comprising one or more crystalline polymers chosen
`from the above mentioned homopolymers of propylene
`and its random copolymers, and one or more of the
`above olefin elastomers. The heterophasic mixtures can
`also contain minor quantities of homo- and copolymers
`of ethylene (from 5 to 20%, for example). Examples of
`a-olefins having 4-10 carbon atoms that can be present
`in the above polymers are: 1-butene; isobutylene; 1-
`pentene; 3-methyl-1-butene; 1-hexene; 3,4-dimethyl-1-
`butene; 1-heptene; and 3-methyl- 1-hexene. As previ-
`ously stated propylene polymers characterized by high
`melt strength values, can be polymers consisting of or
`comprising polymers having, at least in part, a branched
`molecular structure. Said structure can be obtained with
`various techniques starting from conventional linear pol-
`ymers prepared with processes based on coordination
`catalysis, in particular using low- or high-yield Ziegler-
`Natta catalysts. In particular, it is possible to subject the
`linear polymers to controlled modification processes by
`way of free radical generators such as peroxides or radi-
`ation. A preferred technique comprises the treatment of
`linear polymers with high energy radiation (electrons
`and gamma radiations, for example), by the method
`described in US patent 4,916,198. For example, the
`amount of radiation is from 0.25 to 20 MRad, preferably
`3-12 MRad, with low amounts of radiations being pre-
`ferred when ethylene polymers are present. The radia-
`tion intensity, for example, ranges from 1 to 10,000,
`preferably from 18 to 2,000 MRad per minute.
`As previously stated, it is also possible to obtain the
`branched structure by treating the linear polymers with
`organic peroxides, by the method described in US pat-
`ent 5,047,485, for example. The linear polymers are
`blended with peroxides, and brought to a temperature
`which is sufficiently high to decompose the peroxides,
`
`5
`
`w
`
`thus obtaining the formation of free radicals which react
`with the polymer chain to form long chain radicals,
`which then recombine and form the branched structure.
`In particular, in order to obtain said branched structure
`one must select the proper peroxides with a half-life
`decomposition time less than or equal to 5 minutes at
`temperatures ranging from 90°C to 120°C, less than or
`equal to 40 minutes at temperatures ranging from 60°C
`to 90°C, less than or equal to 60 minutes at tempera-
`tures ranging from 25°C to 60°C.
`Examples of peroxides having the above properties
`are: di(sec.butyl)peroxydicarbonate; bis(2-ethoxy)per-
`oxydicarbonate; di-cyclohexyl peroxydicarbonate; di-n-
`propyl peroxydicarbonate; di-isopropyl peroxydicarbo-
`15 nate; di-n-butyl peroxydicarbonate; di-sec-butyl peroxy-
`dicarbonate; tert-butyl peroxydeneocanoate; tert-amyl
`tert-butyl peroxypivalate. The
`peroxyneodecanoate;
`quantities of peroxide used are generally comprised
`between 0.005 and 0.5 mmoles/g of linear polymer. The
`treatment temperature is generally lower than or equal
`to 120°C. In both the above types of treatment, after suf-
`ficient time to allow a substantial recombination of the
`long chain free radicals generated, the remaining free
`radicals are deactivated.
`The above treatments are preferably conducted on
`linear polymers having a crystallinity equal to at least 5-
`10%, measured by way of X-ray diffraction. However,
`polymers with a lower crystallinity (olefin polymer elas-
`tomers, for example) can be present, as long as the melt
`strength of the polymer mass of the pre-foamed beads
`is comprised within the above mentioned limits.
`Likewise, other thermoplastic or elastomeric poly-
`mers can also be present, as long as the above condi-
`tion is observed. Obviously, one does not exclude from
`the scope of the present invention other possible meth-
`ods of preparing propylene polymers having the above
`mentioned properties, such as direct synthesis in
`polymerization, for example.
`Generally, the branching index in the polymers that can
`40 be used according to the present invention ranges from
`0.1 to 0.9, preferably from 0.25 to 0.7.
`As cited in the above mentioned US patent 4,916,198,
`said branching index (g) is represented by the ratio
`
`20
`
`25
`
`30
`
`35
`
`45
`
`„ M i l
`9
`[Tl]Lin '
`
`where [r|]Br and ft] Lin are, respectively, the intrinsic vis-
`50 cosities (determined in decahydronaphthaline at 1 35°C)
`of the branched polymer and the corresponding non-
`branched one having the same weight average molecu-
`lar weight.
`By using the above polymers, the pre-foamed beads of
`the present invention are preferably prepared by extru-
`sion in the presence of foaming agents.
`In particular, by using, as foaming agents in extru-
`sion, hydrocarbons, optionally fluoridated and/or chlo-
`rinated, having a boiling point higher than 25°C, such as
`
`55
`
`3
`
`Page 3 of 6
`
`

`
`5
`
`EP 0 588 321 B1
`
`6
`
`w
`
`for example pentane, hexane, dichlorotrifluoroethanes,
`and methylene chloride, one can obtain foamed beads
`whose cellular structure is at least partly collapsed. By
`using gaseous or liquid foaming agents having boiling
`temperatures lower than 25°C, such as for example air, 5
`carbon dioxide,
`chloro-difluoromethane,
`nitrogen,
`dichlorodifluoromethane, butane, propane and isobu-
`tane, one can obtain foamed beads with a cellular struc-
`ture which does not collapse at ambient temperature
`and pressure even after prolonged storage.
`In order to prepare the foamed beads one can use
`extruders commonly known in the art, including single-
`screw extruders. The foaming agent is preferably
`injected into the melted polymer mass inside the
`extruder, from a part downstream from the point at 15
`which the solid polymer is feed into the extruders so that
`the distance between will allow the polymer to have
`reached the form of a melted, homogeneous mass. In
`the section of the extruder where the foaming agent is
`introduced, the temperature preferably ranges from 20
`125°C to 250°C. The temperature maintained at the
`extruder outlet, equipped with a die having round holes
`of the appropriate diameter, is the most adequate to
`obtain the foaming of the polymer, and it preferably
`ranges from 1 25°C and 1 80°C. The quantity of foaming 25
`agent that is added to the polymer ranges preferably
`from 1 to 30% by weight with respect to the polymer,
`more preferably from 2 to 1 5%.
`It may be also advisable to add to the polymer
`mass, before or during extrusion, one or more nucleat- 30
`ing agents (cell-forming nucleating agents), in quantities
`generally ranging from 0.5 to 3% by weight with respect
`to the polymer. Examples of the above mentioned
`nucleating agents are: talc, colloidal silica, sodium
`bicarbonate or its blends with citric acid, azo-derivatives 35
`such as azodicarbonamide.
`Other additives, dyes or fillers that may optionally
`be required, can be added before or during extrusion.
`The strands of foamed polymer exiting from the extruder
`dies are cut in segments, by way of rotating blades for 40
`example, thus obtaining foamed beads. The length of
`said segments is generally such that one obtains round
`or oval beads (due to the foaming), or cylinders having
`a height comparable to the base diameter (generally
`speaking the height is from 0.5 to 3 times the base 45
`diameter).
`Normally, the foamed beads obtained in this man-
`ner are kept at atmospheric temperature and pressure
`for a time sufficient to achieve the equilibrium between
`the pressure inside the cells and the one outside (cur-
`ing). Said period generally ranges from 10 to 30 hrs.
`As previously stated, the finished foamed polypropylene
`articles can be easily prepared by thermoforming the
`above mentioned pre-foamed beads by sintering. In
`particular, it is sufficient to fill a mold having the desired 55
`dimensions with pre-foamed beads and heat said beads
`to the proper temperature to obtain finished articles with
`a homogeneous structure, essentially without voids
`between the beads, and having excellent mechanical
`
`so
`
`properties. By using the pre-foamed beads of the
`present invention one does not need to maintain the
`molds under pressure during the sintering step, or use
`molds having movable walls. On the contrary, the entire
`step of thermoforming by sintering is preferably carried
`out at substantially atmospheric pressure. By "substan-
`tially atmospheric pressure" one means that no over-
`pressure is applied inside the molds where the sintering
`occurs, except for possible overpressures deriving from
`the passage of hot pressurized gases through the
`molds. As explained below, the above gases are used to
`heat the polymer mass uniformly and obtain the sinter-
`ing. The molds can also be filled at atmospheric pres-
`sure. Once the filling phase is completed, the sintering
`is done by heating the mass of pre-foamed beads con-
`tained in the mold. In order to obtain homogeneous
`heating, it is best to introduce into the mold a gas
`heated under pressure, such as super-heated steam for
`example (usually at 160-180°C). The sintering tempera-
`ture generally ranges from 120°C to 180°C, preferably
`from 130°C and 160°C.
`The following examples are given in order do illus-
`trate and not limit the present invention.
`The melt strength values reported in the examples
`are obtained by using the following method.
`The apparatus used is the Rheotens melt tension
`instrument model 2001 , manufactured by Gottfert (Ger-
`many); the method consists of measuring in cN (cen-
`tiNewtons) the tensile strength of a strand of molten
`polymer operating at a specific stretch velocity. In partic-
`ular, the polymer to be tested is extruded at 200°C
`through a die with a capillary hole 22 mm long and 1
`mm in diameter; the exiting strand is then stretched, by
`using a system of traction pulleys, at a constant acceler-
`ation of 0.012 cm/sec2, measuring the tension until the
`breaking point. The apparatus registers the tension val-
`ues of the strand (resistance in cN) as a function of the
`stretching. The maximum tension value corresponds to
`the melt strength.
`
`Example 1
`
`A blend consisting of 99 parts by weight of
`branched propylene homopolymer having a melt flow
`rate condition L (MFR/L) of 3 g/10 min., a 4% by weight
`fraction soluble in xylene at 25°C, a branching index
`0.56, and a melt strength of 23 cN, and 1 part by weight
`of Hydrocerol nucleating agent, marketed by Boe-
`hringer, is introduced at a flow rate of 75 kg/h in a Ber-
`storff single-screw extruder (screw diameter: 90 mm;
`L/D ratio = 40) maintained at a temperature of 230°C.
`The branched structure in the above polypropylene
`was obtained by subjecting a linear polypropylene hav-
`ing a MFR/L = 0.4 g/10 min , a 4% by weight of fraction
`soluble in xylene at 25°C, and a melt strength = 8 cN, to
`a 12 MRrad electron beam radiation (produced by a 2
`MeV Van De Graaf generator) for 3 seconds, and then
`to a heat treatment at 80-1 40°C in a nitrogen-flow fluid
`bed for 200 minutes.
`
`4
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`Page 4 of 6
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`

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`7
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`EP 0 588 321 B1
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`8
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`w
`
`At the same time, a mixture consisting of 70/30 by
`weight of n-butane/isobutane (foaming agent) in a quan-
`tity equal to 5% with respect to the polypropylene is
`introduced in the extruder. The part where the mixture is
`introduced in the extruder is located at a distance from 5
`the feed hopper equal to 16 D (D = screw diameter), i.e.,
`16x90 mm = 1440 mm. Prior to exiting the extruder the
`melted mass, made up by the polymer, the nucleating
`agent, and the foaming agent, has a temperature of
`160°C and a pressure of 100 atmospheres.
`The strands exiting the extruder die, which is posi-
`tioned at a 90° angle with respect to the extruder axle,
`are cut using a rotating-blades system. The resulting
`foamed beads have the form of a partially ovalized cyl-
`inder (due to the foaming action), and an average 15
`dimension of 3x4 mm.
`The cellular structure of the foamed product is
`medium-fine, with an average diameter of each cell
`ranging from 300 to 600 urn (optical microscopy). The
`poured bulk density of the pre-foamed beads is 30 20
`Kg/m3 (ASTM D 3575 method).
`After a 24 hour curing period at ambient tempera-
`ture the pre-foamed beads are subjected to thermofor-
`ming by sintering. The poured bulk density of the pre-
`foamed beads after curing has been reduced to 26 25
`Kg/m3.
`The internal form of the mold used for the sintering tests
`is that of a 70x70x70 mm cube, and the walls have a
`number of 1 mm-diameter holes for the steam to pass
`through.
`1 0 g of pre-foamed beads are introduced into the
`mold, and then one proceeds to the thermoforming step
`with steam at 5 atm. and 1 65°C for a period of 1 2 sec-
`onds.
`The foamed article thus obtained presents a perfect 35
`form, and the visual analysis of its cross-section shows
`a perfect union and fusion of the beads. The density of
`the foamed article is 29 Kg/m3 (ASTM D 3575 A).
`
`30
`
`Example 2
`
`40
`
`In the extruder described in Example 1 is intro-
`duced a mixture comprising 75 part by weight of the
`branched polypropylene used in Example 1,10 parts by
`weight of nonbranched linear propylene homopolymer 45
`having MFR/L = 4.0 g/10 min. , a 2% by weight of frac-
`tion soluble in xylene at 25°C, and a melt strength = 3
`cN, 15 parts by weight of nonbranched propylene/ethyl-
`ene copolymer containing 21% by weight of ethylene
`and having MFR/L = 0.45 g/10 min. and a 65% by
`weight of fraction soluble in xylene at 25°C, and 1 part
`by weight of the nucleating agent used in Example 1 .
`The foaming agent, its introduction, and the extrusion
`conditions are the same as for Example 1 . The pressure
`of the molten mass before the extruder output is 130 55
`atm. and the temperature 1 55°C.
`The pre-foamed beads thus obtained have a
`poured bulk density equal to 30 Kg/m3, which at the end
`of the curing period decreases to 27 Kg/m3.
`
`so
`
`5
`
`The thermoforming by sintering of the pre-foamed
`beads, carried our according to the process set forth in
`Example 1 , provides articles with beads perfectly fused
`together and having a density of 30 Kg/m3.
`
`Example 3
`
`The procedure and ingredients of Example 1 are
`repeated, but in this case isopentane is used as the
`foaming agent.
`The temperature of the melt before exiting the
`extruder is 140°C, and the pressure is 138 atm. The
`pre-foamed beads thus obtained have the form of par-
`tially collapsed cylinders. In particular, the cellular struc-
`ture of the foamed product is medium-fine, with an
`average cell diameter ranging from 200 and 500 urn.
`The poured bulk density of the beads is 44 Kg/m3,
`which decreases to 42 Kg/m3 after curing for 24 hours
`at ambient temperature.
`The thermoforming by sintering tests carried out in
`the cubic mold, according to the process described in
`Example 1 , supply articles with perfectly fused beads
`having a density of 40 Kg/m3.
`
`Example 4 (comparative)
`
`The procedure and ingredients of Example 1 are
`repeated, but in this case a nonbranched propylene
`homopolymer having a MFR/L = 1.8 g/10 min. , a 4%
`by weight of fraction soluble in xylene at 25°C, and a
`melt strength = 2.7 cN is used.
`The pressure measured prior to exiting the extruder
`is 125 atm., and the temperature 154°C; however, after
`the strands exiting the extruder die, when subjected to
`the rotating blades, they are not cut, but result in
`stretched and frayed strands. Even when increasing the
`amount of foaming agent (butane/isobutane) to 8% by
`weight with respect to the polypropylene, one does not
`obtain foamed beads.
`
`Claims
`
`1 . A process for the preparation of foamed beads of
`propylene polymers, comprising extruding a propyl-
`ene polymer having a melt strength from 5 to 40 cN
`in the presence of a foaming agent.
`
`2. The process of claim 1 , wherein the propylene pol-
`ymer is selected from the group consisting of pro-
`pylene homopolymers and propylene copolymers
`containing from 1 to 40% by weight of ethylene
`and/or a-olefins, linear or branched, having 4-10
`carbon atoms and mixtures thereof.
`
`3. Foamed beads obtainable by the process of claim 1
`or 2.
`
`4. Foamed beads of claim 3, having an average cell
`diameter from 50 to 2000 urn and a poured bulk
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`9
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`EP 0 588 321 B1
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`10
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`density from 10 to 500 kg/m3.
`
`les melanges en derivant.
`
`3. Billes expansees susceptibles d'etre obtenues par
`le procede selon la revendication 1 Ou 2.
`
`4. Billes expansees selon la revendication 3, presen-
`tant un diametre cellulaire moyen de 50 a 2000 urn
`et une masse volumique apparente a I'etat tel que
`verse de 10 a 500 kg/m3.
`
`5. Un procede de preparatin d'articles en polymere de
`propylene expanse comprenant le thermoformage
`par frittage des billes expansees, selon la revendi-
`cation 3 Ou 4.
`
`6. Le procede selon la revendication 5, dans lequel le
`thermoformage par frittage est mis en oeuvre a une
`pression sensiblement atmospherique, a une tem-
`perature de 120 a 180°C.
`
`5. A process for the preparation of foamed propylene
`polymer articles, comprising thermoforming by sin-
`tering the foamed beads of claim 3 or 4.
`
`5
`
`6. The process of claim 5, wherein the thermoforming
`by sintering is carried out at a substantially atmos-
`pheric pressure and a temperature from 120° to
`180°C.
`
`Patentanspruche
`
`1 . Verfahren zur Herstellung von geschaumten Kugeln
`aus Propylenpolymeren, umfassend Extrudieren
`eines Propylenpolymers mit einer Schmelzfestig-
`keit von 5 bis 40 cN in Gegenwart eines Treibmit-
`tels.
`
`2. Verfahren nach Anspruch 1 , wobei das Propylenpo-
`lymer ausgewahlt ist aus der Gruppe, bestehend
`aus Propylenhomopolymeren und Propylencopoly-
`meren, enthaltend 1 bis 40 Gew.-% Ethylen
`und/oder lineare Oder verzweigte, 4-10 Kohlenstoff-
`atome aufweisende a-Olefine, und Gemischen
`davon.
`
`3. Geschaumte Kugeln, erhaltlich durch das Verfah-
`ren von Anspruch 1 oder 2.
`
`4. Geschaumte Kugeln nach Anspruch 3, mit einem
`durchschnittlichen Zelldurchmesser von 50 bis
`2000 urn und einer gegossenen Schuttdichte von
`10 bis 500 kg/m3.
`
`5. Verfahren zur Herstellung von geschaumten Propy-
`lenpolymer-Gegenstanden, umfassend Warmfor-
`men der geschaumten Kugeln nach Anspruch 3
`oder 4 durch Sintern.
`
`6. Verfahren nach Anspruch 5, wobei das Warmfor-
`men durch Sintern bei im wesentlichen Atmospha-
`rendruck und einer Temperatur von 120° bis 180°C
`ausgefiihrt wird.
`
`Revendications
`
`1 . Un procede de preparation de billes expansees de
`polymere de propylene comprenant I'extrusion d'un
`polymere de propylene presentant une resistance a
`la fusion de 5 a 40 cN en presence d'un agent
`d'expansion.
`
`2. Le procede selon la revendication 1, dans lequel le
`polymere de propylene est selectionne dans le
`groupe consistant en homopolymeres de propylene
`