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`European Patent Office
`Office européen des brevets
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`EUROPEAN PATENT APPLICATION
`
`(43) Date 01 Publicationi
`02.07.2003 Bulletin 2003/27
`
`(21) Application number: 01130757.6
`
`(22) Date of filing: 21.12.2001
`
`(51) Int CI.7: C08L 23/10, CO8L 23/12,
`
`(84) Designated Contracting States:
`AT BE CH CY DE DK ES FI FR GB GR IE IT LI LU
`MC NL PT SE TR
`Designated Extension States:
`AL LT LV MK RO SI
`
`(72) Inventors:
`0 Rohne, Gunhild
`2819 Gjovik (NO)
`- Hesse, Achim Dr.
`01067 Dresden (DE)
`
`(71) Applicant: Borealis GmbH
`2323 Schwechat-Mannswiirth (AT)
`
`(74) Representative: VA TECH Patente GmbH & Co
`Stahlstrasse 21a
`4031 Linz (AT)
`
`(54)
`
`Foamed polyolefin sheets with improved property spectrum
`
`Foamed polyolefin sheets with an improved
`(57)
`property spectrum having a density of 50 to 750 kg/m3
`consist of amixture of modified propylene polymers hav-
`ing strain hardening behavior, silane crosslinked po|y—
`mers, unmodified olefin polymers and usual auxiliary
`
`materials.
`The foamed polyolefin sheets are suitable for the
`use inthe packaging sectorand in the motorvehicle sec-
`tor.
`
`1-
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`< 0
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`Page 1 of 16
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`Printed by Jouve, 75001 PARlS (FR)
`
`BOREALIS EXHIBIT 1047
`
`Page 1 of 16
`
`BOREALIS EXHIBIT 1047
`
`

`
`Description
`
`EP 1 323 779 A1
`
`[0001] The invention relates to the use of a polyolefin mixture for the production of foamed polyolefin sheets with
`improved property spectrum consisting of a mixture of propylene polymers and modified olefin polymers.
`[0002]
`Foamed polyolefin sheets from propylene polymers modified by high energy electron radiation are known (EP
`0 190 889 A2). These foams have only restricted impact properties.
`[0003]
`Silane crosslinkable propylene polymers (EP 0 821 018 A2, DE 196 37 602 A1) or heterophasic propylene
`polymers (DE 198 31 278 A1) and their application for foams are also known. The disadvantages of silane modified
`propylene polymers and the silane cross-linked polypropylene foam are the problematic processibility of propylene
`polymers into foams and the restricted impact properties of polypropylene foams.
`[0004]
`Further known are silane crosslinkable ethylene polymers (US 3,646,155; EP 0 821 018 A2) and their appli-
`cation forfoams. The disadvantages of silane crosslinked polyethylene foams are the low temperature resistance and
`stiffness of the foams.
`
`It is the object of the present invention to provide foamed polyolefin sheets with improved property spectrum,
`[0005]
`whereby impact properties and stiffness can be varied within a broad range and the starting products for the foams
`have a good processibility.
`[0006] According to the present invention, this object is achieved by using a polyolefin mixture comprising
`10 to 95 wt% of propylene polymers A and
`90 to 5 wt% of olefin polymers B where
`
`the propylene polymers A comprise modified propylene polymers with melt indices of 0.05 to 10 g/10 min at 230
`°C/2.16 kg, which modified propylene polymers have strain hardening behavior, whereby the modified propylene
`polymers are present in the propylene polymers A up to 1 00 wt%, preferably from 20 to 1 00 wt% and most preferably
`from 50 to 100 wt% in admixture with unmodified propylene polymers with melt indices of 0.1 to 20 g/10 min at
`230 °C/2.16 kg, and
`the olefin polymers B comprise silane precrosslinked and/or crosslinkable polymers which are selected from any
`one or mixtures of
`
`a) polymers which are grafted with ethylenically unsaturated hydrolyzable silane monomers, which polymers
`are selected from any one or mixtures of
`
`a1) ethylene homopolymers,
`copolymers of ethylene and oc—olefins with 3 to 18 carbon atoms,
`copolymers of ethylene and vinyl acetate, C1—C16 acrylic acid esters, C1—C15 methacrylic acid esters, acryl-
`ic acid and/or methacrylic acid,
`a2) propylene homopolymers,
`copolymers of propylene and ethylene or oc—olefins with 4 to 18 carbon atoms,
`heterophasic propylene polymers and
`elastomeric propylene polymers
`
`and
`
`b) polymers which are selected from any one or mixtures of — optionally elastomeric — copolymers of ethylen-
`ically unsaturated hydrolyzable silane monomers and
`
`b1) ethylene,
`ethylene and vinyl acetate, C1-C15 acrylic acid esters, C1-C16 methacrylic acid esters, acrylic acid or meth-
`acrylic acid,
`b2) propylene,
`propylene and vinyl acetate, C1—C16 acrylic acid esters, C1—C16 methacrylic acid esters, acrylic acid or
`methacrylic acid,
`
`where the olefin polymers B comprise 0.1 to 10 wt% of chemically bound silane monomers and where the olefin pol-
`ymers B have a gel content of 10 to 80 wt°/o, preferably of 35 to 70 wt°/o and where
`the silane precrosslinked and/or crosslinkable polymers are present in the olefin polymers B up to 100 wt°/o and pref-
`erably from 50 to 100 wt% in admixture with unmodified ethylene polymers and/or ethylene-C3-Ca-oc-olefin copolymers
`with melt indices of 0.1 to 20 g/10 min at 1 90 °C/2.16 kg, and/or unmodified propylene homopolymers and/orcopolymers
`of propylene and ethylene or oc—olefins with 4 to 1 8 carbon atoms, heterophasic propylene polymers and/or elastomeric
`propylene polymers with melt indices of 0.1 to 20 g/10 min at 230 °C/2.16 kg
`
`Page 2 of 16
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`Page 2 of 16
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`

`
`EP 1 323 779 A1
`
`forthe production of partly crosslinked foamed polyolefin sheets which have a combination of the following properties:
`
`a gel content from 5 to 60 wt%, preferably from 10 to 40 wt%
`a density from 50 to 750 kg/m3, preferably from 400 to 600 kg/m3
`a tensile modulus from 50 to 1100 MPa, preferably from 300 to 700 MPa
`and an Impact total penetration energy from 0.05 to 1.5 J/mm, preferably from 0.3 to 0.9 J/mm.
`
`[0007] Optionally, the foamed polyolefin sheets according to the invention may contain usual auxiliary materials, e.
`g. from 0.01 to 40 vvt% based on the polyolefin mixture A + B.
`The auxiliary materials may be selected from any one or mixtures of 0.01 to 1.5 wt% of stabilizers, 0.01 to 1 wt% of
`processing aids, 0.1 to 1 wt% of antistatic agents, 0.2 to 3 wt% of pigments, 0.01 to 1 wt% of oc—nuc|eating agents, 1
`to 30 wt% of inorganic and/or organic fillers and/or reinforcing materials, in each case based on the polyolefin mixture
`A + B.
`
`Stabilizers may be selected from any one or mixtures of e.g. 0.01 °/o to 0.6 wt% of phenolic antioxidants, 0.01
`[0008]
`% to 0.6 wt% of 3-arylbenzofuranones, 0.01 % to 0.6 wt% of processing stabilizers based on phosphites, 0.01 % to
`0.6 wt°/o of high temperature stabilizers based on disulfides and thioethers and 0.01 % to 0.8 wt% of sterically hindered
`amines (HALS).
`[0009]
`Suitable phenolic antioxidants are 2—t—butyl—4,6—dimethylphenol, 2,6—di—t—butyl—4—methylpheno|, 2,6—di—t—butyl—
`4—isoamy|phenol,
`2,6—di—t—butyl—4—ethylphenol,
`2—t—buty|—4,6—diisopropylphenol,
`2,6—dicyclopentyl—4—methylphenol,
`2,6—di—t—butyl—4—methoxymethylphenol,
`2—t—butyl—4,6—dioctadecylphenol,
`2,5—di—t—butylhydroquinone,
`2,6—di—t—butyl—
`4,4—hexadecyloxyphenol, 2,2'—methylene—bis(6—t—butyl—4—methylphenol), 4,4'—thio—bis—(6—t—butyl—2—methylpheno|), octa-
`decyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)-propionate,
`1,3,5-trimethyl-2,4,6-tris-(3',5‘-di-t-butyl-4-hydroxybenzy|)-ben-
`zene and/or pentaerythrito|—tetrakis—3—(3,5—di—t—buty|—4—hydroxypheny|)—propionate.
`[0010] As benzofuranone derivative, 5,7-di-t-butyl-3-(3,4-dimethylphenyl)-3H-benzofuran-2-one, in particular, is suit-
`able.
`
`[0011] As HALS compounds, bis—2,2,6,6—tetramethy|—4—piperidyl sebacate and/orpoly—1,1,3,3—tetra—methylbutyl)—im—
`ino)—1,3,5—triazine—2,4—diyl)(2,2,6,6—tetramethylpiperidyl)—amino)—hexamethy—|ene—4—(2,2,6,6—tetramethyl)piperidyl)—im—
`ino) are particularly suitable.
`[0012] The or—nucleating agents, optionally contained in the inventive foamed polyolefin sheets, preferably are talc,
`sorbitol and sorbitol derivatives, sodium benzoate orthe sodium salt of methylene-bis-(2,4-di-t-butylphenol) phosphoric
`acid.
`
`[0013] As processing aids, the inventivefoamed polyolefin sheets may contain calcium stearate, magnesium stearate
`and/or waxes.
`
`[0014] Examples of inorganic fillers and/or reinforcing materials, optionally contained in the inventive foamed poly-
`olefin sheets, are silica, particularly in the form of glass or quartz; silicates, particularly talc; titanates, titanium dioxide,
`aluminum oxide, kaolin, magnesium oxide, magnesite, iron oxides, silicon carbide, silicon nitride, barium sulfate, cal-
`cium carbonates and/or mica.
`
`[0015] Examples of organicfillers and/or reinforcing materials, optionally contained in the inventivefoamed polyolefin
`sheets, are mechanical wood pulp, fibers or particles of cellulose, starch, po|y(methy| methacrylate), polyvinyl alcohol,
`polytetrafluoroethylene, polyamide, poly-ethylene terephthalate or duroplastic synthetic materials.
`[0016] Modified propylene polymers can be produced by any number of processes, e.g. by treatment of the un-
`modified propylene polymer with thermally decomposing radical—forming agents and/or by treatment with ionizing ra-
`diation, where both treatments may optionally be accompanied or followed by a treatment with bi— or multifunctionally
`unsaturated monomers, e.g. butadiene, isoprene, dimethylbutadiene or divinylbenzene. Further processes may be
`suitable for the production of the modified propylene polymer, provided that the resulting modified propylene polymer
`meets the characteristics of strain hardening behavior, which is defined below.
`[0017] Examples of said modified propylene polymers A are, in particular:
`
`polypropylenes modified by the reaction of polypropylenes with bismaleimido compounds in the melt (EP 0 574
`801 A1; EP 0 574 804 A2),
`polypropylenes modified by the treatment of polypropylenes with ionizing radiation in the solid phase (EP 0 190
`889 A2; EP 0 634 454 A1),
`polypropylenes modified by the treatment of polypropylenes with peroxides in the solid phase (EP 0 384 431 A2)
`or in the melt (EP 0142 724 A2),
`polypropylenes modified by the treatment of polypropylenes with multifunctional, ethy-lenically unsaturated mon-
`omers under the action of ionizing radiation (EP 0 678 527 A2),
`polypropylenes modified by the treatment of polypropylenes with multifunctional, ethylenically unsaturated mono-
`mers in the presence of peroxides in the melt (EP 0 688 817 A1; EP 0 450 342 A2)
`
`Page 3 of 16
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`Page 3 of 16
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`

`
`EP 1 323 779 A1
`
`[0018] Strain hardening behavior as used herein is defined according to Fig. 1 and 2.
`Fig.
`1 shows a schematic representation of the experimental procedure which is used to determine strain hardening.
`The strain hardening behavior of polymers is analysed by Rheotens apparatus 1 (product of Gottfert, Siemensstr.2,
`74711 Buchen, Germany) in which a melt strand 2 is elongated by drawing down with a defined acceleration. The haul-
`ofi force F in dependence of draw—down velocity v is recorded.
`The test procedure is performed in a standard climatized room with controlled room temperature of T = 23 °C. The
`Rheotens apparatus 1
`is combined with an extruder/melt pump 3 for continuous feeding of the melt strand 2. The
`extrusion temperature is 200 °C, a capillary die with a diameter of 2 mm and a length of 6 mm is used and the accel-
`eration of the melt strand 2 drawn down is 120 mm/s2.
`
`The schematic diagram in Figure 1 shows in an exemplaryfashion the measured increase in haul—off force F (i.e. "melt
`strength") vs. the increase in draw—down velocity v (i.e. "drawability").
`[0019]
`Figure 2 shows the recorded curves of Rheotens measurements of polymer samples with and without strain
`hardening behavior. The maximum points (Fmax; vmax) at failure of the strand are characteristic for the strength and
`the drawability of the melt.
`The standard propylene polymers 4,5,6 with melt indices of 0.3, 2.0 and 3.0 g/10 min at 230 °C/2.16 kg show a very
`low melt strength and low drawability. They have no strain hardening and thus a poor processibility into extrusion foams.
`Modified propylene polymers 7 (melt index of sample in diagram is 2 to 3 g/10 min at 230 °C/2.16 kg) or LDPE 8 (melt
`index of sample in diagram is 0.7 g/10 min at 230 °C/2.16 kg) show a completely different melt strength vs. drawability
`behavior. With increasing the draw down velocity v the haul—off force F increases to a much higher level, compared to
`the standard propylene polymers 4,5,6. This curve shape is characteristic for strain hardening.
`"Modified propylen polymers which have strain hardening behavior" as used herein have enhanced strength with haul-
`off forces Fmax > 15 cN and enhanced drawability with draw—down velocities Vmax > 150 mm/s.
`[0020] Unmodified propylene polymer as used herein comprises propylene homopolymers, copolymers of propyl-
`ene and ethylene and/or or-olefins with 4 to 18 carbon atoms and mixtures of the aforementioned polymers.
`[0021] The term copolymer as used above particularly refers to random propylene copolymers, propylene block
`copolymers, random propylene block copolymers and elastomeric polypropylenes, but is not restricted to these types
`of copolymers.
`[0022] The modified propylene polymers are preferably prepared by
`
`a) mixing a particulate unmodified propylene polymer, which comprises
`
`a1) propylene homopolymers, especially propylene homopolymers with a weight average molecular weight
`MW of 500,000 to 1,500,000 g/mol, and/or
`
`a2) copolymers of propylene and ethylene and/or (x—o|efins with 4 to 18 carbon atoms, or of mixtures of such
`copolymers,
`with from 0.05 to 3 wt%, based on the polyolefin composition used, of acyl peroxides, alkyl peroxides, hy-
`droperoxides, peresters and/or peroxycarbonates as free-radical generators capable of thermal decomposi-
`tion, if desired diluted with inert solvents, with heating to 30-100 °C, preferably to 60-90 °C,
`
`b) sorption of bifunctional unsaturated monomers by the particulate propylene polymer at a temperature T(°C)
`of from 20 to 120 °C, preferably of from 60 to 100 °C, where the amount ofthe absorbed bifunctional unsatu-
`rated monomers is from 0.01 to 10 wt%, preferably from 0.05 to 2 wt%, based on the propylene polymer used,
`and then
`
`c) heating and melting the particulate polyolefin composition in an atmosphere comprising inert gas and/or
`the volatile bifunctional monomers, from sorption temperature to 210 °C, whereupon the free-radical genera-
`tors capable of thermal decomposition are decomposed and then
`
`d) heating the melt up to 280 °C in order to remove unreacted monomers and decomposition products,
`
`e) agglomerating the melt in a manner known per se.
`Usual amounts of auxiliary substances, which may range from 0.01 to 1.5 wt% of stabilizers, 0.01 to 1 wt% of
`processing aids, 0.1 to 1 wt% of antistatic agents, 0.2 to 3 wt% of pigments and up to 3 wt% of oc—nucleating
`agents, in each case based on the sum of the propylene polymers, may be added before step a) and/or e) of
`the method and/or before or during step c) and/or d) of the above described method.
`The particulate unmodified propylene polymer may have the shape of powders, granules or grit with grain
`sizes ranging from 0.001 mm up to 7 mm.
`
`Page 4 of 16
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`Page 4 of 16
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`

`
`EP 1 323 779 A1
`
`The process for producing the modified propylene polymer preferably is a continuous method, performed in
`continuous reactors, mixers, kneaders and extruders. Batchwise production of the modified propylene polymer.
`however is feasible as well.
`
`Preferably volatile bifunctional monomers are absorbed by the particulate propylene polymer from the gas
`phase.
`Practical sorption times 1: of the volatile bifunctional monomers range from 10 to 1000 s,
`
`where sorption times ‘E of 60 to 600 s are preferred.
`The bifunctional unsaturated monomers, which are used in the process for producing the modified propylene pol-
`ymers preferably are C4 to C10 dienes and/or C7 to C10 divinyl compounds. Especially preferred are butadiene,
`isoprene, dimethyl—butadiene or divinylbenzene.
`
`[0023] According to a further embodiment of the present invention and in addition to what is defined above, the
`unmodified propylene polymers are selected from any one or mixtures of
`
`a) conventional polypropylene polymers, preferably propylene homopolymers and/or copolymers of propylene,
`ethylene and/or or—olefins with 4 to 18 carbon atoms, obtainable by using Zieg|er—Natta catalysts or metallocene
`catalysts, having a propylene content of 80.0 to 99.9 wt%, in the form of random copolymers, block copolymers
`and/or random block copolymers with melt indices of 0.1 to 40 g/10 min at 230 °C/2.16 kg and preferably 1 to 8
`g/10 min at 230 °C/2.16 kg,
`b) a polyolefin mixture with an Mw/Mn ratio of 2 to 6 and a melt index of 1 to 40 g/10 min at 230 °C/2.16 kg, which
`comprises
`
`b1) 60 to 98 wt% of a crystalline copolymer of 85 to 99.5 wt% of propylene and 15 to 0.5 wt% of ethylene and/
`or an oc—olefin of the general formula CH2=CHR,
`in which R is a linear or branched alkyl group with 2 to 8
`carbon atoms, and
`b2) 2 to 40 wt% of an elastic copolymer of 20 to 70 wt% of ethylene and 80 to 30 wt% of propylene and/or an
`oc—o|efin of the general formula CH2=CHR, in which R is a linear or branched alkyl group with 2 to 8 carbon
`atoms, and
`
`c) essentially amorphous, non isotactic polymers of propylene with a melt index of 0.1 to 100 g/10 min at 230 °C/
`2.18 kg, the essentially amorphous polymers of propylene comprising homopolymers of propylene and/or copol-
`ymers of propylene comprising at least 85 wt% of propylene and not more than 15 wt% percent of one or more or-
`olefins of the general formula CH2=CHR, in which R is a linear or branched alkyl group with 2 to 8 carbon atoms.
`
`[0024] The polyolefin mixtures b) of crystalline copolymers and elastic copolymers, optionally as starting materials
`for the modified propylene polymers A as well as the unmodified propylene polymers of propylene polymers A, are
`polymer mixtures described, for example, in EP 0 400 333 A2 or EP 0 472 946 A2.
`[0025] The largely amorphous polypropylenes or propylene copolymers c), optionally as starting materials for the
`modified propylene polymers A as well as the unmodified propylene polymers of propylene polymers A are, in particular,
`stereo block polypropylenes, which are prepared, for example, by using highly active Ziegler—Natta catalysts fixed on
`a metal oxide (Collette, J., Macromolecules 22 (1989), 3851 — 3858; DE 28 30160 A1) or soluble Ziegler—Natta catalysts
`(de Candia, F., Makromol. Chem. 189 (1988), 815 — 821), optionally with subsequent reactive modification and/or deg-
`radation.
`
`Further examples of non isotactic propylene homopolymers c), optionally contained as starting materials for
`[0026]
`the modified propylene polymers A as well as the unmodified propylene polymers of propylene polymers A are products
`as described in EP 0 475 307 A1.
`
`[0027] Unmodified propylene polymers are preferably obtained by polymerization with a Ziegler—Natta catalyst sys-
`tem comprising titanium—containing solid components, an organo—aluminum compound as cocatalyst and an external
`donor having the general formula
`
`RxR'ySi(R"O)4_X_y
`
`wherein R, R‘ and R" are identical or different and are linear or branched or cyclic aliphatic or aromatic hydrocarbon
`residues, and y and x independently from each other are 0 or 1, provided that x + y are 1 or 2. R, R‘ and R" may range
`from 1 to 20 carbon atoms, where dicyclopentyldimethoxysilane is preferred as external donor.
`[0028] Examples of unmodified propylene polymers obtained by polymerization with a Ziegler—Natta catalyst system
`
`Page 5 of 16
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`Page 5 of 16
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`

`
`EP 1 323 779 A1
`
`as described above are propylene polymers as described in EP 0 790 262 A1; WO 99/24478 and WO 99/16797.
`Preferred are unmodified propylene polymers with a stereospecifity index ranging from 97 to 99 %, whereby the ster-
`eospecifity index is measured by lnfrared—spectroscopy and calculated as described in EP 0 277 514 A2 on page 3.
`[0029] According to a preferred embodiment the silane monomers ofthe olefin polymers B have the general formula
`XY3_nSiRn,
`in which X is an ethylenically unsaturated group which can be grafted or copolymerized, preferably vinyl,
`allyl, acryloxypropyl or methacryloxypropyl, Y is an alkyl or aryl group, preferably methyl or phenyl, and R is a C1-C8
`alkoxy, and/or carboxy group and/or halogen, preferably methoxy, ethoxy, acetoxy, chlorine, bromine or iodine, and n
`represents the numbers 1, 2 or 3.
`[0030] The silane monomers are selected from any one or mixtures of:
`
`acryloxyalkylsilanes, such as acryloxypropyltrimethoxysilane, acryloxypropyldimethyl—ethoxysilane, acryloxypro-
`pylmethyldiethoxysilane, acryloxypropyltriethoxysilane, acryloxypropyltrismethoxyethoxysilane, trimethylsi|oxye—
`thyl acrylate, acryloxypropyl—dimethylchlorosilane and acryloxypropyltrichlorosilane,
`alkenylalkoxysilanes, such as allyltriethoxysilane, allyltrimethoxysilane, octenyltrimethoxysilane, propenyltriethox—
`ysilane and/or propenyltrimethoxysilane,
`alkenylhalogensilanes such as allyldimethyldichlorosilane, allyldimethylchlorosilane, hexenyldimethylchlorosilane,
`methylcyclohexenylethyldichlorosilane, allyltrichlorosilane, hexenyltrichlorosilane, octenyltrichlorosilane, prope-
`nyltrichlorosilane and tetradecenyltrichlorosilane,
`aminoalkenylsilanes such as aminobutenyltriethoxysilane and aminoethylallyldimethoxysilane,
`aminovinylsilanes such as aminoethyldiethoxyvinylsilane, aminoethyldimethoxyvinylsilane and aminophenylvinylt—
`rimethoxysilane,
`cycloalkenylsilanes such as cyclohexenyltriethoxysilane, triethoxysilylbicycloheptene, cyclohexenylethy|trimeth-
`oxysilane, cyclohexenylethyldimethylchlorosilane, trichlorosilyl—ethy|cyc|ohexene and cyclohexenyltrichlorosilane,
`methacryloxyalkylsilanes such as methacryloxypropyltrimethoxysilane, methacryloxy-propyldimethylethoxysilane,
`methacryloxypropylmethyldiethoxysilane, methacryloxy—propyltriethoxysilane, methacryloxypropyltrismethox-
`yethoxysilane, trimethylsiloxyethyl—methacrylate, methacryloxypropyldimethylchlorosilane and methacryloxypro-
`pyltri—chlorosilane,
`vinylalkoxysilanes such as vinyltributoxysilane, vinyltriethoxysilane, vinyltriisopropoxy—si|ane, vinyltrimethoxysi-
`lane, vinyltrismethoxyethoxysilane, vinyltristrimethoxysilane, vi—ny|dimethylethoxysilane, vinyldimethylmethoxysi—
`lane, vinylethyldiethoxysilane, vinyl-methyldiethoxysilane, phenylvinyltrimethoxysilane, diphenylvinylethoxysilane,
`vinylphenyldiethoxysilane, vinylphenyldimethoxysilane and vinylphenylmethylmethoxysilane,
`vinylhalogensilanes such as vinylethyldichlorosilane, vinylmethyldichlorosilane, diphenylvinylchlorosilane, phenyl-
`vinyldichlorosilane, vinyldimethylchlorosilane and vinyltrichlorosilane,
`vinylcarboxysilanes such as vinylmethyldiacetoxysilane and/or vinyltriacetoxysilane.
`
`[0031] The silane precrosslinked and/or crosslinkable olefin polymer is preferably a crosslinked ethylene—methyl—
`methacrylate—vinyltrimethoxysilane terpolymer having a content of methylmethacrylate of from 25 to 35 wt% and a
`content of vinyltrimethoxysilane of from 0.1 to 2 vvt%.
`[0032] According to a further embodiment of the invention the foamed polyolefin sheets are obtained by adding 0.01
`to 1 vvt%, based on the polyolefin mixture, of silanole condensation catalysts and 0.5 to 12 wt%, based on the polyolefin
`mixture, of blowing agents to the polyolefin mixture,
`melting the polyolefin mixture,
`extruding the polyolefin mixture into a zone of reduced pressure and
`conditioning the polyolefin sheets in a moist atmosphere under crosslinking, whereby the olefin polymers B comprise
`silane crosslinkable polymers.
`[0033] The blowing agents, used in the process for producing extrusion foamed polyolefin sheets, are chemical
`blowing agents that split off gas, or hydrocarbons, halogenated hydrocarbons and/or gases. Examples of suitable
`chemical blowing agents, that emit a gas, are sodium hydrogencarbonate, azodicarbonamide and/or cyanuric trihy—
`drazide. Suitable hydrocarbons as blowing agents are readily volatile hydrocarbons, such as pentane, isopentane,
`propane and/or isobutane. Examples of suitable halogenated hydrocarbons are monofluorotrichlo—romethane and/or
`difluoromonochloromethane. Suitable gases as blowing agents are nitro—gen, argon and/or carbon dioxide.
`[0034] Examples of suitable silanole condensation catalysts are dibutyl tin dilaurate or dibutyl tin diacetate. Low
`molecular carbocylic acids or polymer bound carboxylic acids, e.g. stearic acid or ethylene acrylic acid copylemers,
`are also suitable.
`
`In the inventive process for producing extrusion foamed polyolefin sheets, the continuous kneaders for pro-
`[0035]
`ducing the foamed polyolefin sheets from the polyolefin mixture containing blowing agents and silanole condensation
`catalysts can be single screw extruders with an L/D of 20 to 40 or synchronous twin screw extruders or extruder
`cascades of homogenizing extruders (single screw or twin screw) and foaming extruders. Optionally, a melt pump and/
`
`Page 6 of 16
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`Page 6 of 16
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`

`
`EP 1 323 779 A1
`
`or a static mixer can be used additionally between the extruder and the die head. Advantageous die temperatures for
`discharging the melt, which contains the blowing agent and the silanole condensation catalyst, are 190 to 240 °C.
`[0036] According to a still further embodiment of the present invention the foamed polyolefin sheets are obtained by
`adding 0.01 to 1 vvt%, based on the polyolefin mixture, of silanole condensation catalysts and 0.5 to 12 wt%, based
`on the polyolefin mixture, of blowing agents to the polyolefin mixture,
`melting the polyolefin mixture,
`extruding the polyolefin mixture into a zone of reduced pressure and
`conditioning the polyolefin sheets in a moist atmosphere under crosslinking, wherebythe olefin polymers B com-
`prise silane precrosslinked polymers which have a gel content of 0.1 to 5 vvt%.
`[0037] The precrosslinked polymers are produced e.g. by melt extrusion of the polymers which are grafted/copoly—
`merized with silane monomers together with 0.005 to 0.05 wt%, based on the polyolefin mixture, of silanole conden-
`sation catalysts. The precrosslinked polymers may also be produced by storage of the catalyst—containing material in
`moist atmosphere.
`[0038] According to a feature of the present invention the foamed polyolefin sheets are used in the packaging sector,
`particularly of packaging, which can be used as reusable and transporting packagings, packaging corners and equip-
`ment hoods.
`
`[0039] Afurther object of the present invention is the use of the foamed polyolefin sheets in the motorvehicle sector,
`particularly for interior parts of motor vehicles, such as instrument panels, sunshades, arm rests, air ducts and door
`linings.
`
`Examples
`
`[0040] Characterisation of the foamed sheets
`
`1. Determination of the foam density
`The foam density is determined by a gravimetric method according to the formula:
`
`pf : pwater X mf,air/mf,water
`
`pf
`pwater
`mm,
`mf’water
`
`density of the foam
`density of water (= 1 g/cm3)
`weight of the test piece measured in air
`weight of water displaced by immersed test piece
`
`This method is suitable for samples with undefined geometry.
`The following tests of the foamed specimens were made after 7 days conditioning time:
`
`2. Tensile modulus was determined according to DIN 53504. The tensile test was carried out with the test spec-
`imen S2 at a temperature of 23 °C. The tensile testing rate was 1 mm/s during the modulus measurement and
`afterwards it was increased up to 50 mm/s.
`
`3. Impact total penetration energy was determined at 23 °C according to DIN 53443/ Part 2 with a drop height
`of 100 cm and the falling weight of 32 kg.
`
`4. Gel content was determined by extraction in boiling xylene of a foam sample during a period of 24 h. The
`insoluble content was dried in vacuum at 80 °C during a period of 16 h.
`
`gel content = weight of insoluble material x 100 /weight of foam sample
`
`Example 1
`
`1.1 Synthesis of the Modified Propylene Po|ymerA
`
`[0041] A powdery polypropylene homopolymer, with a melt index of 0.25 g/10 min at 230 °C/2.16 kg and an average
`particle size of 0.45 mm, is metered continuously into a continuous mixer. Furthermore, 0.45 wt% based on the pro-
`pylene homopolymer of tert butyl peroxybenzoate as thermally decomposing free radical forming agent is metered into
`
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`EP 1 323 779 A1
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`the mixer. While being mixed homogeneously at 50 °C, the propylene homopolymer containing the tert butyl peroxy-
`benzoate is charged absorptively during a residence time of 7 minutes at 50 °C by means of a mixture of butadiene
`and nitrogen with 0.135 wt% of butadiene, based on the polypropylene homopolymer. After transfer to a twin screw
`extruder, the powdery reaction mixture, in contact with the mixture of butadiene and nitrogen, with which it has been
`charged, is melted at a mass temperature of 230 °C and, after a coarse degassing, subjected to a fine degassing with
`addition of water as an entraining agent, an additive mixture of 0.1 wt% of tetrakis—(methylene—(3,5—di—t—butylhydroxy—
`cinnamate)-methane, 0.1 wt% of tris-(2,4-di-t-butylphenyl)-phosphite), 0.1 wt°/o of pentaerythritol tetrakis-3-(3,5-di-t-
`butyl-4-hydroxyphenyl)-propionate and 0.1 vvt% of calcium stearate is added to the melt. After distribution of additives
`the melt is discharged and granulated.
`[0042] The resulting, modified propylene polymerA shows strain hardening behaviorcharacterized by the Rheotens
`ITIBX _
`values of F
`— 30.5 cN and vmax = 210 mm/s measured at failure of the strand and a melt index of 2.3 g/10 min at
`230 °C/2.16 kg.
`
`1.2 Preparation of the Polyolefin Mixture
`
`[0043] A mixture of
`75 wt% of the modified propylene polymer A having strain hardening behavior characterized by the Rheotens values
`of Fmax = 30,5 cN and vmax = 210 mm/s measured at failure of the strand and a melt index of 2.3 g/10 min at 230 °C/
`2.16 kg,
`23 wt% of an ethylene—methy|methacrylate—vinyltrimethoxysilane terpolymer B having a content of methylmethacrylate
`of 31 wt%, a content of vinyltrimethoxysilane of 1.0 vvt% and contains 0.1 vvt% of calcium stearate, 0.1 by weight of
`tetrakis-(methylene-3,5-di-t-butyl-hydroxyhydrocinnamate)-methane and 0.1 wt% of tris-(2,4-di-t-buty|pheny|)-phos-
`phite as auxiliary materials and has a melt index of 10 g/10 min at 190 °C/2.16 kg, and
`2 wt% of a master batch containing 4 wt% of dibutyl tin dilaurate as silanole condensation catalyst,
`are melted
`in
`a
`PRISM TS E24HC twin
`screw extruder,
`L/D=30 with
`a
`temperature
`100/145/185/210/220/200/190/185 °C, homogenized, discharged and granulated.
`
`profile
`
`of
`
`1.3 Manufacture of the foamed polyolefin sheet
`
`[0044] A dry blend mixture of the stabilized polyolefin compound of the modified propylene polymer A, the ethylene-
`methy|methacry|ate—vinyltrimethoxysilane terpolymer B as described in 1.2 and 0.75 \Nt%, based on the polyolefin
`mixture, of a blowing agent based on bicarbonate and citric acid, is supplied by means of a metering system to the
`feeding funnel of a single screw extruder PM 30 L/D = 28 at 50 rpm having a screw with increasing diameter used for
`slow compression bui|d—up without mixing elements, a flat die (coathanger die), a chill roll (80°C) take off and a tem-
`perature profile of 200/220/240/240/220/170/170 °C. Initially, the mixture is melted and homogenized, subsequently
`the split off blowing gas is distributed homogeneously and the melt is foamed after leaving the flat die.
`[0045] After a conditioning time of 7 days the following properties of the foamed polyolefin sheet were measured:
`
`Density
`Tensile modulus
`Penetration energy at 23 °C
`Gel content
`
`0.51 g/cm3
`572 MPa
`0.49 J/mm
`18.2 \Nt%
`
`Example 2
`
`2.1 Synthesis of the Modified Propylene PolymerA
`
`[0046] A powdery random polypropylene copolymer, with an ethylene content of 4 vvt%, a melt index of 0.3 g/10 min
`at 230 °C/2.16 Kg and an average particle size of 0.85 mm, is continuously added into a heatable mixer of the exper-
`imental modification equipment. Furthermore, over a flanged-on auxiliary material metering device, 0.05 vvt% of hy-
`drotalcit, 0.05 wt% of calcium stearate and 0.075 wt% of di-tert-butyl peroxide, in each cased based on the propylene
`copolymer, are added continuously into the mixer. During the process of mixing homogeneously at 70 °C, the polypro-
`pylene copolymer, charged with the thermally decomposing free radical—forming agent and auxiliary material, is charged
`absorptively during a residence time of 10 minutes at 70 °C by a mixture of divinylbenzene and nitrogen, flowing in
`from the extruder overthe connecting piece, with 0.32 wt% of divinylbenzene, based on the polypropylene copolymer.
`[0047] After transfer to the twin—screw extruder, the powdery reaction mixture, in contact with the mixture of divinyl-
`benzene and nitrogen, is melted at a mass temperature of 225 °C and, after a coarse degassing, with the addition of
`
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