Title of Invention	USE OF POLYETHERESTERS FOR ROTOMOLDING.
Abstract	The present invention discloses the use in rotomolding or slush molding applications of a composition comprising a polyolefin, a processing aid and optionally a UV-stabilizer.

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WO 2005/118709 PCT/EP2005/052460 Use of Polvetheresters for Rotomoldinq Field of the invention The present invention relates to the use in rotomolding or in slush molding applications of a polyolefin composition comprising a processing aid and optionally a UV-stabilizer. The polyolefin composition can also be used for the production of articles by other processes such as injection molding, cast film, blown film, calendering, sheet.extrusion. Background of the invention The present invention primarily concerns the fabrication of articles by rotomolding, also called rotational molding. In rotomolding a premeasured amount of polymer is placed in one half of the mold, the mold is closed and then heated until the polymer is molten. The mold is rotated so as to get good distribution of the polymer in the mold. The mold can be rotated either uniaxially or biaxially, but biaxial rotation is widely preferred, i.e. simultaneous rotation around two perpendicular axes. In the following the mold is cooled, opened and the formed article Is removed from the mold. Rotomolding can also be used for multilayer molding, for example by using more than one polymer sequentially. Rotomolding allows the production of hollow articles with good wall thickness distribution and good mechanical properties. Slush molding is a process that is closely related to rotomolding. In the following the term rotomolding is therefore used to imply both, rotomolding and slush molding applications. WO 2005/118709 PCT/EP2005/052460 2 The most widely used polymer In rotamolding is polyethylene. Therefore a lot of offort has been invested to improve the processabillty of polyethylene in rotomolding. US 6,362,270 discloses polymer compositions particularly suited for rotomolding. These polymer compositions comprise of at least 94 % by weight of one or more thermoplastic polymers and a maximum of 6 % by weight of one or more processing additives. The thermoplastic polymer may be selected from copolymers of ethylene and styrene, etnylene and/or C3-C20 alpha-olefin homo- or copolymers, nylon, polyethylene terephthalate, polycarbonate, acrylic polymer, polystyrene, and blends of those polymers. Suitable processing additives include aromatic or aliphatic hydrocarbon oils. esters, amides, alcohols, acids, and their organic or inorganic salts as well as silicone oils, polyether polyole, grycerol monostearate (GMS), pentaerytntol monooleate, erucamide, stearamides, adipic acid, sebacic acid, styrene-alpha-methyl-styrene, calcium stearata, zinc stoarate, phthalates and blends thereof. The processing additive preferably decreases the composition's melt viscosity and/or elasticity at zero or low shear rates to allow for a reduction in sintering time, cycle time and/or maximum mold temperature. A recent report (LT. Pick, E. Harkin-Jones, Third Polymer Processing Symposium, 28-29.01.2004, Belfast, p. 259-268) shows a correlation between the number of bubbles in a rotomolded article and its impact performance, with a higher number of bubbles resulting in lower impact performance. In addition, a high number of bubbles has a negative influence on the optical properties of the finished articles. There Is thus a need to provide a rotomolded article with a reduced number of bubbles. There is also a need to provide a rotomoided article with improved optical properties. WO 2OO5/II8709 PCT/EP2005/052460 3 There is also a need to provide a rotomolded article with improved mechanical properties. It is an object of the present invention to provido a rotomolded article based on a polyolofin composition with improved processability In rotomolding applications. It is another object of the present invention to provide a rotomotded article based on a polyolefin composition that Improves the sintering and densification processes in rotomolding applications. It is another object of the present Invention to provide a rotomotded article based on a polyolefin composition that reduces bubble formation in the rotomolding process. it is another object of the present invention to provide a rotomotded article based on a polyolefin composition that improves optical properties of the articles produced by rotomolding applications. It is another object of the present invention to provide a rotomolded article based on a polyolefin composition that improves mechanical properties of the articles produced by rotomolding applications. it is another object of the present invention to provide a rotomolded article based on a potyolofin composition that allows reducing cycle time in a rotomolding process. it is another object of the present Invention to provide a process for producing by rotomolding an article with improved properties WO 2OO5/118709 PCT/EP2005/052460 4 it is yet anothor object of the present Invention to provide a rotomolding process with improved densification and/or sintering processes. Summary of the invention Accordingly, the present invention provides rotomolded or slush molded articles prepared from a polyolefin composition essentially consisting of (a) from 99 % by weight to 99.999 % by weight of (i) a polyolefin or (ii) a polyolefin composition comprising from 50 % by weight to 99 % by weight of a first polyolefin and from 1 % by weight to 50 % by weight of a different polymer, (b) from 0.001 % by weight to 1 % by weight of a densification aid; (c) optionaally from 0.025 % by weight to 0.500 % by weight of one or more UV-stabilizers. The present invention also discloses the use of that same composition in rotomolding and slush molding. Brief description of the drawings Figure 1 shows the temperature of air inside a mold expressed in degrees centigrade as a function of time expressed in minutes for a complete cycle in rotomolding applications Figure 2 shows a camera set-up used to study sintering and donsification behavior. Figure 3 represents a sequence of photographs showing the coalescence process. WO 2005/ 118709 PCT/EP2005/052460 5 Figure 4 represents a series of photographs showing the bubble removal process. Detailed description of the Invention The densification aid comprises a polyotherester, optionally consisting essentially of a mixture of a polyetherester as major component with a minor component selected from the group consisting of polyether-block co-polyamide. thermoplastic polyurethane. polyethylene glycol and fluoropolymer. By major component it is meant that such a component makes up more than 50 % by weight. By minor component it is meant that such a component makes up loss than 50 % by weight. Polyether-block co-polyamides are represented by the general formula HO-[C(O)-PA-C(O)-O-PEth-O)n-H (I) wherein PA represents the polyamide segment end PEth the polyether segment. For example the polyamide segment can be a PA 6, PA 66. PA 11 or a PA 12. Tho polyether segment can for example be a polyethylene glycol (PEG) of a polypropylene glycol (PPG) or a porytetrarnethylenglycol (PTMG). The molecular weight Mn of the polyamide sequence Is usually between 300 and 15,000. The molecular weight Mn of the polyether sequence is usually between 100 and 6000. Such materials are commercially available for example from Atofina under the Pebax® trade name. WO 2005/ 118709 PCT/EP2005/054260 6 The copolymers having polyammide blocks and polyether blocks are generally obtained from the polycondensation of polyamide blocks having reactive end groups with polyether blocks having reactive end groups, such as. inter alia: 1) polyamide blocks having diamine chain ends with polyoxyalkylene blocks having dicarboxylic chain ends, 2) potyamide blocks having dicarboxylic chain ends with polyoxyalkytene bkxks having diamine chain ends, obtained by cyanoethylation and hydrogenation of aliphatic dihydroxylated a1,?-polyoxyalkylene bloks called polyetherdiols; and 3) potyamid bloks having dicarboxylic chain ends with polyothordiols, the products obtained being, in this particular case, polyothoresteramides. The polyammide bloks having dicarboxylic chain ends dorive, for example, from tho condensation of polyamide precursors In the presence of a chain-stopping carboxylic diacid. The polyamide bloks having diamino chain ends derive, for example, from the condensation of potyamide precursors in the presence of a chain-stop ping diacid. The polymers having polyamido bloks and polyether bloks may also include randomly distributed units. These polymers may by prepared by the simultaneous reaction of tho polyether and of the precursors of the polyamide bkxks. For example, a polyetherdiol, polyamide precursors and a chain-stopping diacid may be made to react together. A polymer is obtained which essentially has polyether blocks and polyamide bloks of very variable length, but in addition the various reactants that have reacted randomly, which are distributed in a random fashion along tho polymer chain. WO 2005/118709 PCT/EP2005/05I46O 7 A poLyether diamine, polyamide precursors and a chain-stopping diacid may also be made to react together. A polymer is obtained which has essentially polyether blocks and polyamide blocks of very variable length, but also the various reactants that have reacted randomly, which are distributed in a random fashion along the polymer chain. The amount of polyether blocks in these copolymers having polyamide blocks and polyether blocks is advantageously from 10 to 70% and preferably from 35 to 60% by weight of the copolymer. The polyetherdiol blocks may either be used as such and copotycondensed with polyamide blocks having carboxylic end groups, or they may be aminated in order to be converted into polyetherdiamines and condensed with polyamide blocks having carboxylic end groups. They may also be blended with polyamide precursors and a diacid chain stopper in order to make the polymers having polyamide blocks and polyether blocks with randomly distributed units. The number-average molar mass Mn of the polyamide blocks is usually between 300 and 15,000, except in the case of the polyamide blocks of the second type. The mass Mn of the polyether blocks is usually between 100 and 6000. As regards tho polyetheresters, those are copolymers having polyester blocks and polyether blocks. They generally consist of soft polyether blocks, which are the residues of potyetherdiois, and of hard segments (polyester blocks), which usualy result from the reaction of at least one dicarboxyfic acid with at least one chain-extending short diol unit The polyester blocks and the polyether blocks are generally Iinked by ester linkages resulting from the reaction of the add functional groups of the acid with the OH functional groups of the polyetherdiol. The short chain-extending diol may be chosen from the group consisting of neopentyl glycol, cycloexanedimethanol and W O 2005/118709 PCT/EP2005/05246O 8 aliphatic glycols of formula HO(CH2)nOH In which n is an integer varying from 2 to 10. Advantageously, the diacids are aromatic dicarboxylic: acids having from 8 to 14 carbon atoms. Up to 50 mol% of the dlcarboxylic aromatic acid may be replaced with at least one other dicarboxylik; aromatic acid having from 8 to 14 carbon atoms, and/or up to 20 mol% may be replaced with a dicarboxylic aliphatic acid having from 2 to 12 carbon atoms. As examples of dicarboxylic aromatic acids, mention may be made of terephthalic. isophthalic. dibenzoic, naphthalenedicarboxylic acids, 4,4'-diphenylenedicarbaxylic acid, bts(p-carboxyphenyl)methane acid, ethylenebis(p-benzoic acid). 1,4-tetramethylenebis(p-oxybenzoic acid), ethylenebis(paraoxybenzoic acid) and 1,3-trimothylene bis(p-oxybenzoic acid). As examples of glycols, mention may be made of ethylene glycol, 1,3-trimethylene glycol, 1,4-tetramethylene glycol. 1,6-hexamethylene glycol. 1,3-propylene glycol, 1,8-octamethylene glycol, 1,10-decamethylene glycol and 1,4-cyclohexylenedimethanol. The copolymers having potyester blocks and polyether blocks are, for example, copolymers having polyether blocks derived from polyether diols, such as polyethylene glycol (PEG), polypropylene grycol (PPG) or polytetramethylene glycol (PTMG), dicarboxylic acid units, such as terephthalic acid, and glycol (ethanediol) or 1,4-butanediol units. The chain-linking of the poryethers and diacids forms soft segments while the chain-linking of the grycol or the butanediol with the diacids forms the hard segmonts of the copolyetherester. Such copolyetheresters are disclosed in patents EP 402 883 and EP 406 227. These polyetheresters are thermoplastic elastomers. They may contain plasticizors. Polyetherosters can for oxample bo obtained from Du Pont Company under tho HytreJ9 tradomark. As regards the potyurethanes, these in general consist of soft potyether blocks, which usualry aro residues of pofyet herd tots, and hard blocks WO 2005/118709 PCT/EP2005/052460 9 i (polyurethanes), which may result from the reaction of at least one diisocyanate with at least one short diol. The short chain-extending diol may i be chosen from the glycols mentioned above in the description of the polyether esters. The polyurethane blocks and polyether blocks are linked by i linkages resulting from the reaction of the isocyanate functional groups with the OH functional groups of the polyether diol. i Thermoplastic polyurethanes can for example be obtained from Elastogran GmbH under the Elastollan® trade name or from Dow Chemical Company under the Pellethane® trade name. i Polyethylene glycols have the general formula i H-(OCH2-CH2-)nOH (I) i Polyethylene glycols are commercially available in a wide range of molecular weights and viscosities. Depending upon their molecular weights polyethylene glycols can be liquid or solid. The polyethylene glycols used in the present invention usually have an average"-molecular weight from 100 to 2000 g/mol and more preferably from 150 to 700 g/mol. Suitable polyethylene glycols can for example be obtained from Dow Chemical Company or BASF under the Carbowax@and Pluriol E® trade names. The fluoropolymers suited as processing aid in the present invention are for example polymers of vinylidene fluoride (H2C=CF2) and/or copolymers of vinylidene fluoride and hexafluoropropyiene (F2OCF-CF3). Though the copolymers of vinylidene fluoride and hexafluoropropyiene do not have elastomeric properties they are commonly referred to as "fluoroelastomers". The content of the comonomer hexafluoropropyiene in a fluoroelastomer is usually in the range of 30 to 40 % by weight. Fluoropolymers suited as processing aids in the current invention are for example commercially WO 20OVII871H PC;T-'»:P2OOM*246O 10 available under the Dynamar*. Vton* and Kynar* trade namos from Dynoon, DuPorrt-Oow Elastomers or Atofina. Potyothytenos proparod with a 23ogler-Natta or with motallocene catalyst or with late transition metal catalyst systems am typically used in rotomoklog applications. Other materials can also bo used, such as for example polypropylene. Linear low density polyethylene Is preferably used as disclosed for exampto In "Somo new result* on rotational molding of metailocene polyethyienes" by D. Annechlni, E. Tafcacs and J vTachopoulos inANTEC.vol. 1.2001. The preferred potyotofin used in the compoatUon according to tho prosent invention is a homo- or co-polymer of ethytene produced with a catalyst comprising a metailocene on a sHtea/aluminoxane support. More preferably, the motaUocene component Is ethytene-bis-tetrahydroindonyl zirconium dlchkxWe or b^rvoutyi-cyclopentadienyl) zirconium dichlorfde or dJchtoro-(dlmethyte0ytene)bls In this description, the term copolymer refers to the polymerizatton product of one monomer and ono or more comonomers. Preferably the monomer and the one or more comonomers are alpha-otefins with two to ten carbon atoms, with monomer and comonomer(s) being different alpha-olefins. More preferably tho monomer Is either ethytene or propyiene and the ono or more comonomors are alpha-oioflns with two to eight carbon atoms. Most preferably the monomer is ethytene and the cornonomer is either 1-butane or 1-hexene. Tho melt index of the polyethylene or polypropylene resin preferably used in the present Invention typically falls in the following ranges: WO20UM1IP09 WT*P20O*05246O 11 - K Iho potyotofin of tbo prosont invention is a homo- or co-polymer of ethytono. its mott indox MI2 is typteaHy In the rango 0.1 to 25 dg/mki, preferably in tho range 0.5 to 15 dg/min and most preferably in the range 1.5 to 10 dg/min. The MI2 is measured according to ASTM D 1283 at a temperature of 190*C and a toad of 2.16 kg. - If the polyotefln of the present invention rs a homo- or copotymer of propyfene, its melt How Index (MFI) is typically in the range 0.1 to 40 dg/min, preferably in the rango 0 5 to 30 dg/min and most preferably in the range 1 to ?5 dg/min. The MFI is measured according to ASTM O 1263 at a temperature of 230*C and a load of 216 kg. For tho homo- and co-potymers of ethytone that can be used in the present invention, the density Is typically in the range 0.910 to 0975 g/ml and preferably in the range 0.915 to 0.955 g/ml, and most preferably in the range 0.925 to 0.945 g/ml. The donsity is measured according to ASTM D 1505 at 23*C. Tho potyoicfirts of the present invention may also have a W- or multimodal motoculaf weight distribution, I.e. they may be a blend of- two or more polyoieflns with different molecular weight distributions, which can be blended either physically or chemically, I.e. produced sequentially in two or more reactors. The potydispersity D of the pofyoJofms used in the present invention is defined as tho ratio Mw/Mn of the weight avorage molecular weight Mw over the number average motocutar weight Mn. H is In the range 2 to 20, preferably 2 to 8, more preforably loss than or equal to 5, and most preferably less than or equal to 4, the latter range being typtcalfy associated with tho preferred metaflooene-prepared polyethylene rosins. W O IOO5.! IJT09 PC"P"i:P2lK)V(>52460 12 The polyolofins erf tho present invention may also compete© other additfves such as for example antioxidants. acid scavongors, antistatic additives, fillers, slip additives or anti-oiocking additives. When a potyolefin composition is used as stalling material, the composition composes: • from 50 to 99 % by wotght of a first pofyotefin, preferably polyethylene; - from 1 to 50 % by weight of a second polymer, which is difforont from the processing aid, and which is preferably selected from the group consisting of polyamide, copolyamide, a second potyolefin different from the first one. copotymers of ethytene and vinyl acetate (EVA), copoJymers of ethytone and vinyl alcohol (EVOH), polystyrone, polycarbonate and potyvirtyl chloride (PVC). n is also possible to use a potyotefln comprising a densification aid as one or more layers of a muHJIayered rotomolded article with the other layers comprising a polymer preferably selected from the group consisting of polyamide, copofyamWe, a second potyolefln different from the first one, coporymors of ethytone and vinyf acetate (EVA), copotymers of ethytene and virryt alcohol (EVOH), polystyrene, polycarbonate and polyvfnyl chloride (PVC). The one or more UV-stabltoers can be selected from any known UV-stabillzer known in the art. The proforrod UV-stabilizers are hindered amine light stabHtzers (HALS). Commercially available examples of HALS include Chlmassorb* 944, Tlnuvin8 622 or TinuvJn* 783 from Ciba Specialty Chemicals. Sorprtsingly, it has been found that the addition of 0.001 % by weight to 1 % by weight of a processing aid Improves the processability of a potyolofln in rotonrtokJmg by modHytng the sintering and the densJftcatJon behavtor. WO 200 13 Tho uso of a processing ak) according to tho present invention results in cycle time reductions of at toast 10 %, preferably by at least 20 %. In order to obtain the samo numbor of bubbles in the rotomokied articles the peak internal air temperature (RAT) can be reduced by at (east 10 degrees centigrade Even more surprisingly, n has been found that tho further addition of from 0 025 % by wotght to 0.500 % by weight of one or more UV-stabJIizors to tho composition described hereabove comprising 0.001 % by weight to 1 % by weight of a processing aid even further improves the processabHity of the potyotefin in rotomolding. It is believed that there Is a synergy between the processing ak) and the UV-stabillser, and it is thus preferred to use both. In rotomolding a promeasured amount of polymer Is placed in one half of the moid, tho mold Is dosed and then heated until the potyrr.er is molten. The mold is rotatod so as to get an even distribution of the potymer in the mold. The mold can be rotated eithoruniaxtaUy or biaxially, but biaxial rotation Is wkJefy preferred, i.o. simultaneous rotation around two perpendicular axes. In the foflowirtg step tho mold is cooled, opened and the formed article is removed from the mold. The rotomolding cycto comprises three main steps, each of which has an impact on cycle time and tho properties of the so-produced article. The three steps comprise: • sintering or coalescence, • densiflcatJon or bubble removal, and - crystallization. This is Illustrated In Figure 1 gMng the air temperature In the mold, expressed in degrees centigrade, as a function of time, expressed in WO 20O5,11 »-W pc T.T P2OO5.05246O 14 minutos. during an oxompiary molding cycto. Tho first infloxion In tho curvo noted as point A mo its the beginning of tho sintering or coalescence of the pofymor particles. Sintering In the present application represents tho coalescence of tho potymor particles. The next inflexion in the curve notod as point B marks tho beginning of the densiffcatfon process of the motion polymer. Donstftcation In the present application means bubble removal. Throughout this application 3lntor1ng and densrftcatkxi are seon as two distinct processes; thoy vary independently with the rotomolding parameters and with the resin properties. Point C on the curve represents the Peak Internal Air Temperature (RAT), followed by point D that marks the beginning of the crystallization process. Point E is associated with the time at which the rotomolded article is completely solidified and starts receding from the walls of the mokJ. Point F marks the opening of tho mold, I.e. the end of the rotomolding cycle. The present invention Is mostty concerned with the modification of the potymer behavior In tho sintering (coalescence) and densiflcation (bubble removal) phases of the rotomolding cycle and slush molding cycle. Sintering Is measured according to a method described for example by Bellehumeur et al (C.T. Beltehumour, M.K. Blsarta, J. Vtachopoutos, Polymer Engineering and Science, 36, 2198, 1996). Dertsification and bubble formation has been discu&sod by Kontopouto ot a. (M. Kontopouk), E. Takacs, J. Vtachopoulos, Rotation, 28, January 2000). During metting air pockets or bubbles are trapped, thus delaying the formation of a homogeneous melt and also affecting tho aesthetJcaJ and/or mechanical properties of the finished product For the present Invention a charge-coupled device (CCD) camera was used to characterize the properties of potyoteftn powders during a rotomolding cyde or during sintering and/or denslfication simulations. WO 2005! 18-09 P€T/r.P20O5.-O5246O 15 Examples Characterization of the processing behavior was analyzed using a megapixel progrossivo scan Inteiiine CCO with on-chlp circuits commoroally available from Kodak. It has tho following characteristics: - architecture: interline CCO, progressive scan, non-Jnterteood - pbcel count :1000(H)xiOOO{V) - pixel st/a : 7.4 um(H) x 7.4 pm(V) - photosensitive area : 7.4 mm(H) x 7.4 mm(V) - output sensitivity : 12 pV/eJectron - saturation signal: 40,000 electrons - dark noise: 40 electrons rms - dark current (typical); - dynamic range : 60 dB - quantum efficiency at 500, 540,600 nm : 36%, 33%, 26% - blooming suspension : 100X • image tag : - smear; - maximum data rate: 40 MHz/channol (2 channels) - integrated vertical dock drivers - intograted correlated double sampling (COS) - integrated olectrontc shutter driver The high performance 15-oit The camera set-up used to study sintering and densifteatJon behavior Is illustrated In Figure 2 with the CCO camera (1), the IR probe (2), the computer (3), the heating system (4) and the annular lighting system (5). A UOKOMHPO* KT.'I:P20050«460 16 typical oxarnpfe foe sirrtorlng is shown In Figure 3 and a typical example for donslflcation or bobble removal in Figure 4. The progrossJvo disappearance of bubbles as a function of time and temperature Is ctoarty and Instantaneously followed. In addition to the visual aspect, the computer instantaneously produces a set of parameters resorting from picture analysis. Those parameters aro explained In Table I. TABLE I.Parameter Unit Description Ex - picture number t rrrin time of picture T *C IR temperature of sample N - number of bubbles on the picturo Na mm'7 number of bubbles per mm* A urn* total area covered by bubbles Aa • percentage of totaJ picture area covered by bubbles Do* urn average distance between 2 bubbles S pm* averago area of one bubble O pm perimeter of one bubble based on Crofton's integral DOQ pm equivalent diamotor of one bubble L pm largest sido of one bubbto W pm smallest side of one bubble { LO degree ohentation of the largest side [ WO degree orientation of the smartest side WO 2005/1 U*O9 KT/EP2OOMI5246W 17 The average distance between two bubbles D* is defined as D* «= 4 (1 -AaySv wherein Sv = 4n {Oc/lf . Aa / whonain the equivalent bubble diameter D«. Is defined ki torms of the avorage surface of one bubble S by the equation S = 4n (D*/2)*. The base potyethyienea were supplied as polets. The pellets were ground at 40 to 80*C on commercial grinding equipment e.g. a Wedco Series SE machino, to a powdor with grain sizes from 100 um to 800 pm. The processing aid or a blend of processing aids and a UV-stabiltzer or a blend of UV-stabillzers were added to the powder In commercial mixing equipment Irganox* B 215 to a blend of Irgafos* 168 and Irganox* 1010 and is commercialry available from Gba Specialty Chemicals. Tlnuvin* 783 b a UV-stabiltzer commercially available from Qba Specialty Chemicals. Cyasorb THT* 4611 and Cyasorb THT* 4802 are AJV-staWHzers commercialfy available from Cytec Industries. Hytrel* S556 can be obtained from Du Pont Company. Examples 1 to 4 and Comparative Example 1 The potyethyteoe used for examples 1 to 4 and comparative example 1 was a monomodal potyethytene with a MI2 of 8.0 dg/min and a density of 0.934 g/rrt; it was produced using a supported metallocene catalyst system. It is commercially available from Alofina under the name FTnaceoe* M3582. The processing aids, UV-stabilizers and other additives are given In Table II, together with thoir rospective amounts. WO 2005/118709 PCT/EP2005/052460 18 The samples were evaluated on a 10 L canister prepared by rotomolding usingj a commercial rotomolding equipment. Peak Internal Air Temperature (PIAT) was 210°C in all cases. Table II Comp. Ex. Ex.1 Ex.2i Ex.3 Ex.4 MI2 (dg/min) 8.0 8.0 8.0 8.0 8.0 Density (gSml) 0.934 0.934 ' 0.934 0.934 0.934 lrganox®B215 (ppm) 1500 1500 1500 1500 1500 Zinc stearate (ppm) 1500 Hytrel®5556 (ppm) I 500 1000 500 500 Tinuvin® 783 (ppm) i 1500 CyasorbTHt3>4611 (ppm) i 1000 Using the polygner compositions of examples 1 to 4 rotomolded articles withja low number of bubbles could be obtained. WO 2005/118709 PCT7EP2005/052460 19 Claims 1. Use of a polyetherester as component of a densification aid in a polyolefin composition in a process selected from rotomolding and slush molding, said polyolefin composition essentially consisting of (a) from 99 % by weight to 99.999 % by weight of (i) a polyolefin, or (ii) a polyolefin composition comprising from 50 % by weight to 99 % by weight of a first polyolefin and from 1 % by weight to 50 % by weight of a different polymer; (b) from 0.001 % by weight to 1 % by weight of a densification aid comprising a polyetherester, (c) optionally from 0.025 % by weight to 0.500 % by weight of one or more UV-stabilizers. 2. Use of a polyetherester according to claim 1, wherein the densification aid is a mixture of a polyetherester as major component with a minor component selected from the group consisting of fluoropolymer, polyether- 'block co-polyamide, thermoplastic polyurethane and polyethylene glycol. 3. Use of a polyetherester according to claim 2, wherein the polyolefin is a homo- or copolymer of ethylene or propylene. 4. Use of a polyetherester according to claim 3, wherein the polyolefin is a homo- or copolymer of ethylene prepared with a metallocene catalyst system. 5. Use of a polyetherester according to any of the preceding claims, wherein the peak internal air temperature is reduced by at least 10°C to obtain the same number of bubbles per mm2 with respect to the same process carried out on the same polyolefin under the same processing conditions without the addition of densification aid and optional UV-stabilizer. WO 2005/118709 PCTYEP2005/052460 20 6. Use of a polyetherester according to any of the preceding claims to reduce the cycle time by at least 10 % with respect to the same process carried out on the same potyolefin under the same processing conditions without the addition of densification aid and optional UV-stabilizer. 7. Article prepared by using a polyetherester as described in any of claims 1 to 6 in an application selected from rotomolding and slush molding applications.

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