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GB2123004A - Preparing crosslinked propylene polymer foams - Google Patents

Preparing crosslinked propylene polymer foams Download PDF

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Publication number
GB2123004A
GB2123004A GB08313991A GB8313991A GB2123004A GB 2123004 A GB2123004 A GB 2123004A GB 08313991 A GB08313991 A GB 08313991A GB 8313991 A GB8313991 A GB 8313991A GB 2123004 A GB2123004 A GB 2123004A
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United Kingdom
Prior art keywords
weight
parts
propylene polymer
mixture
crosslinked
Prior art date
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Application number
GB08313991A
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GB8313991D0 (en
Inventor
Ernst Lohmar
Jurgen Henke
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Carl Freudenberg KG
Original Assignee
Carl Freudenberg KG
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Filing date
Publication date
Application filed by Carl Freudenberg KG filed Critical Carl Freudenberg KG
Publication of GB8313991D0 publication Critical patent/GB8313991D0/en
Publication of GB2123004A publication Critical patent/GB2123004A/en
Withdrawn legal-status Critical Current

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    • CCHEMISTRY; METALLURGY
    • C08ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08JWORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J9/00Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
    • C08J9/0061Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof characterized by the use of several polymeric components
    • CCHEMISTRY; METALLURGY
    • C08ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08JWORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2201/00Foams characterised by the foaming process
    • C08J2201/02Foams characterised by the foaming process characterised by mechanical pre- or post-treatments
    • C08J2201/026Crosslinking before of after foaming
    • CCHEMISTRY; METALLURGY
    • C08ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08JWORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2323/00Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers
    • C08J2323/02Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers not modified by chemical after treatment
    • C08J2323/10Homopolymers or copolymers of propene
    • CCHEMISTRY; METALLURGY
    • C08ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08JWORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2409/00Characterised by the use of homopolymers or copolymers of conjugated diene hydrocarbons
    • CCHEMISTRY; METALLURGY
    • C08ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08JWORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2423/00Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers
    • C08J2423/02Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers not modified by chemical after treatment
    • C08J2423/16Ethene-propene or ethene-propene-diene copolymers

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Health & Medical Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Medicinal Chemistry (AREA)
  • Polymers & Plastics (AREA)
  • Organic Chemistry (AREA)
  • Manufacture Of Porous Articles, And Recovery And Treatment Of Waste Products (AREA)

Abstract

Low-density crosslinked propylene polymer foams are prepared by mixing a propylene polymer with up to 20% of its weight of low molecular weight liquid polybutadiene(s) containing at least 35% by weight of 1,2-vinyl- polybutadiene and from 10 to 100% of its weight of EPDM rubber, EPM rubber or chlorinated polyethylene, together with a crosslinking or foaming agent, irradiating the mixture for crosslinking and then foaming it.

Description

SPECIFICATION A process for preparing crosslinked propylene polymer foams The present invention relates to a process for preparing low-density crosslinked propylene polymer foams which have a fine regular cell structure. The foams combine a high dimensional stability under heat with a good low-temperature flexibility.
There are various known ways of foaming and crosslinking olefin polymers to give products having properties which differ depending on the choice of starting mixture and of the foaming and crosslinking conditions. Because propylene polymers require processing temperatures which are high compared with those of polyethylenes they are more difficult to process, for example because compounding with chemical blowing agents, for subsequent foaming, harbours the danger of the material reacting prematurely and thus not giving acceptable products.
For this reason German Offenlegungsschrift 1,769,492 describes a method whereby the polypropylene mixture is first crosslinked by means of high-energy radiation and is then foamed by means of a chemical blowing agent, for example azodicarboxamide. This method gives a foamed plastics material which has fine pores and is very useful when warm but which, when cold, is prone to fracture and very brittle. The material is therefore only of limited utility. This is particularly noticeable in insulating materials, which have to be not only dimensionally stable but also flexible over a wide temperature range.
German Patent 1,694,130 proposes to improve low-temperature flexibility by mixing polyolefins with rubber and to foam the resulting mixture. This method is essentially restricted to polyethylene. The foamed plastics have lowtemperature flexibility, but they have only poor dimensional stability under heat. This method cannot be used to process polypropylenes, since the processing temperatures for polypropylene are so high that it is impossible to prepare a mixture of polypropylene, rubber and blowing agent.
Because of the good thermal stability of propylene polymers and-the mechanical resistance of propylene polymers under heat, superior to that of polyethylenes, there is a need for an economical process for preparing not only free-rise but also moulded propylene polymer foams which should not only retain their good thermal stability but also have good lowtemperature flexibility. Prior art methods are unable to provide this desirable combination because these properties are opposites.
The present invention seeks to provide foamed plastics of the above-mentioned type, that is to say defect-free low-density propylene polymer foams, which have a fine regular cell structure and combine good dimensional stability under heat with good low-temperature flexibility.
According to the invention there is provided process for preparing a crosslinked propylene polymer foam comprising first preparing a homogeneous mixture of 100 parts by weight of propylene polymer with up to 20 parts by weight of liquid polybutadiene(s) containing at least 35% by weight of 1 ,2-vinyl-polybutadiene and having a molecular weight of 500 to 10,000 and a crosslinking agent and/or a foaming agent at below the decomposition temperature of the crosslinking and/or foaming agents, if desired shaping the mixture, then subjecting it to highenergy radiation for crosslinking and further treating it to cause foaming, in which process 10 to 100 parts by weight of EPDM rubber and/or EPM rubber and/or optionally chlorinated polyethylene are added to the mixture before the irradiation per 100 parts by weight of propylene polymer present in the mixture, and the material is homogeneously mixed, then irradiated, crosslinked and foamed.
The process according to the invention is based on the process described in German Patent 2,839,733. In that earlier process, crosslinked polypropylene foams are prepared by preparing a homogeneous mixture of the polypropylene which contains 2 to 20% by weight, relative to the weight of the polypropylene, of polybutadiene(s) having a molecular weight of 500 to 10,000 and optionally suitable crosslinkinag and/or foaming agents at below the decomposition temperature of the crosslinking and/or foaming agents then treating the mixture with a 2 to 20 Mrad dose of high-energy radiation, and then, if desired, crosslinking and foaming the mixture. This method gives optimum properties with liquid polybutadienes which contain 85 to 90% of 1,2vinylpolybutadiene, but at least 35% of that material should be present.The preferred highenergy radiation is provided by an electron beam in doses of 6 to 10 Mrad.
Polypropylene foams of the type produced according to that German patent have no significant low-temperature flexibility. They are very brittle at low temperatures. Another disadvantage is the relatively high dose of high energy radiation required for the crosslinking.
Surprisingly, we have found that the opposing properties of, on the one hand, a good thermal stability and, on the other hand, a good lowtemperature flexibility, may be obtained without difficulty in a fine-celled regular low-density foamed plastics material when a propylene polymer, especially a polypropylene homopolymer, is additionally blended in weight ratios of 10:1 to 1:1 with ethylene-propylene copolymer rubber (EPM) or ethylene-propylene terpolymer rubber (EPDM) or rubber based on chlorinated polyethylenes and optionally with polyethylene.
It is known in principle that polyolefins can be mixed with rubbers to give products which have low-temperature flexibility. However, this is not considered to make the process according to the invention obvious because, although rubbercontaining polyolefins generally have low temperature flexibility, they are not sufficiently dimensionally stable under heat, nor is it possible to prepare crosslinked low-density fine-celled foams in this way.
In contrast, the process according to the invention makes it possible to prepare a crosslinked chemically expanded light-weight foamed plastics material having a bulk density of about 20 to 200 kg/cm3. Such light-weight foams can only be obtained by crosslinking.
As rubber-containing propylene polymers could hitherto not be crosslinked in the present manner the process according to the invention makes it possible for the first time to crosslink even polypropylene- and polyethylene based blends in such a way that foamed plastics materials having a previously unobtainably broad range of uses, i.e. independent of temperature, are made possible. This cross-linking reaction can be controlled in such a way that a gel content of about 70% is obtained. The tackiness of the polymer fraction left uncrosslinked in this reaction, and amounting to about 30%. is sufficiently low to enable the foaming step to take place, for example, on a belt.
The process of the invention gives foamed plastics which are still flexible at temperatures of --500C.
The propylene polymer foam may be a homopolymer or a copolymer, more particularly a 'copolymer with an olefin, especially ethylene, e.g.
in an amount up to 50%, or more.
It is preferred to use liquid 1 ,2-polybutadienes having a high 1,2-content. Analogously to German Patent 2,839,733, preferred polybutadienes contain 85 to 90% of 1,2-vinyl polybutadiene but at least 35% of that material should be present.
It has been found to be very advantageous that, compared with German Patent 2,839,733, the process of the invention needs a significantly lower dose of high-energy radiation to give an optimum degree of crosslinking. Adequate crosslinking generally requires 1 to 2 Mrad. The radiation dose can be as high as 10 Mrad, but it is in any case lower than without the additives proposed by the invention. What is achieved with a 6 Mrad dose in the present invention would otherwise require about 1 5 Mrad.
The process is carried out by mixing the propylene polymer with the rubber(s), which may have been chosen on the basis of simple preliminary experiments, and the chemical blowing agent, for example azodicarboxamide.
The mixture can be prepared in an extruder or kneader. The mixture is then formed into a web, which is subjected to high-energy radiation, preferably using an electron beam, and thereby crosslinked. Foaming is then effected, for example in an oven.
The composition of the foamable mixture can be varied. It is proposed that 100 parts by weight of propylene polymer should be mixed with 10 to 100 parts by weight of polyethylene and 10 to 100 parts by weight of EPDM or EPM rubber and with 5 to 20 parts by weight of blowing agent, for example azodicarboxamide. These parts by weight are relative to the total weight of the polymer mixture. Particularly good results are obtained with 20 to 80 parts by weight of polyethylenes. To render the mixture more readily extrudable and to promote crosslinking, it is preferred to add 1 to 10% by weight, relative to the total mixture, of liquid 1 2-polybutadiene(s) containing at least 35%. by weight of 1,2-content and having a molecular weight of 500 to 10,000.
The ethylene-propylene terpolymer rubber can, for example, contain ethylene-narbonene, dicyclopentadiene or a 1,6-hexadiene as the third monomer.
The foamed plastics materials thus prepared not only have the good low-temperature flexibility already described but also very good elastic recovery. The method of preparation is economical and free of problems. The products always have properties in the same range.
The process according to the invention gives propylene polymer-based foamed plastics materials which have completely novel properties.
They are an inexpensive construction material which can be used not only for insulation purposes but also to cushion parts under severe thermal stress, for example instrument panels in automotive vehicles.
The examples which follow illustrate the process according to the invention. The 1,2polybutadiene used contains about 90% of 1,2vinylpolybutadiene.
Example 1 50 parts by weight of polypropylene (MFI 230/2.16=11.0) are homogenised in an extruder with 20 parts by weight of high pressure polyethylene (MFI 190/2.16=3.3-4.6), 20 parts by weight of ethylene-propylene terpolymer rubber (EPDM), 3 parts by weight of 1,2polybutadiene (molecular weight 3,000) and 1/ parts by weight of azodicarboxamide, and the mixture is extruded through a slot die to a web.
The web is then crosslinked with a 1.5 Mrad dose of electron beams. The web is then foamed at 2200C for 6 minutes in a circulating air oven. The foamed plastic has a bulk density of 50 kg/m3, and is flexible down to --500C.
The elastic recovery properties are tested as follows: A test specimen is compressed to 50% of its original thickness, is stored at 250C for 24 hours, and is then released from its load. The released sample is stored at room temperature for 100 hours before its recovery is measured. It is found to be 93%.
Example 2 50 parts by weight of propylene-ethylene copolymer (MFI 230/2.16=4.0) are homogenised in an extruder with 20 parts by weight of high pressure polyethylene (MFI 190/2.16=3.4 to 4.6), 20 parts by weight of ethylene-propylene terpolymer rubber, 3 parts by weight of 1 ,2- polybutadiene (molecular 3,000) and 10 parts by weight of azodicarboxamide. The mixture is extruded through a slot die to a web, which is then crosslinked with a 1.4 Mrad dose of electron beams. The web is then foamed at 2200C for 6 minutes in a circulating air oven.
The foamed plastic has a bulk density of 50 kg/cm3, and is flexible at -500C.
The recovery properties are measured as described in Example 1. The recovery is found to be 72%.
Example 3 50 parts by weight of propylene-ethylene copolymer (MFI 230/2.16=4.0) are homogenised in an extruder with 20 parts by weight of HDPE (MFI 190/2.16=3.4-4.6), 20 parts by weight of ethylene-propylene rubber, 6 parts by weight of 1,2-polybutadiene (molecular weight 3,000) and 10 parts by weight of azodicarboxamide, and the mixture is extruded through a slot die to a web.
The web is then crosslinked with a 6.5 Mrad dose of electron beams. It is then foamed at 2200C for 6 minutes in a circulating air oven. The resulting foamed plastic had a bulk density of 50 kg/m3, and was still flexible at -300C.
Example 4 50 parts by weight of propylene-ethylene copolymer (MFI 230/2.16=4.0) are homogenised in an extruder with 20 parts by weight of HDPE (MFI 1 90/2.16=3.4-4.6), 20 parts by weight of chlorinated polyethylene rubber, 6 parts by weight of 1,2-polybutadiene (molecular weight 3,000) and 10 parts by weight of azodicarboxamide, and the mixture is extruded through a slot die to a web. The web is then crosslinked with a 5.0 Mrad dose of electron beams. It is then foamed at 220or for 7 minutes in a circulating air oven. The resulting foamed plastic had a bulk density of 54 kg/m3, and fractured at OOC.
Example 5 70 parts by weight of propylene-ethylene copolymer (MFI 230/2.16=4.0) are homogenised in an extruder with 20 parts by weight of ethylene-propylene copolymer rubber, 6 parts by weight of 1,2-polybutadiene (molecular weight 3,000) and 10 parts by weight of azodicarboxamide, and the mixture is extruded through a slot die to a web. The web is then crosslinked with an 11 Mrad dose of electron beams. It is then foamed at 2200C for 6 minutes in a circulating air oven. The resulting foamed plastic had a bulk density of 50 kg/m3, and was still flexible at --200C.
Comparative Example 1 90 parts by weight of propylene-ethylene copolymer (MFI=4.0) are homogenised in an extruder with 10 parts by weight of azodicarboxamide and 6 parts by weight of 1,2-polybutadiene (molecular weight 3,000), and the mixture is extruded through a slot die to a web. The web is then crosslinked with a 10 Mrad dose of electron beams. It is then foamed at 2200C for 6 minutes in a circulating air oven. The resulting foamed plastic had a bulk density of 55 kg/m3, and was brittle at 250C.
Comparative Example 2 69 parts by weight of propylene-ethylene copolymer (MFI=4.0) are homogenised in an extruder with 21 parts by weight of polyethylene (MFI 3.4-4.6), 10 parts by weight of azodicarboxamide and 6 parts by weight of 1,2polybutadiene (molecular weight 3,000); and the mixture is,extruded through a slot die to a web.
The web is then crosslinked with a 7.5 Mrad dose of electron beams. It is then foamed at 2200C for 6 minutes in a circulating air oven. The resulting foamed plastic had a bulk density of 50 kg/m3. It was brittle at OOC.
Comparative Example 3 63 parts by weight of polypropylene (MFI 230/2.16=2.5-5.0) are homogenised in an extruder with 31 parts by weight of HDPE (MFI 190/2.16=3.4-4.6), 6 parts by weight of azodicarboxamide and 6 parts by weight of 1,2polybutadiene (molecular weight 3,000), and the mixture is extruded through a slot die to a web.
The web is then crosslinked with an 8.5 Mrad dose of electron beams. It is then foamed at 2200C for a 6 minutes in a circulating air oven.
The resulting foamed plastic had a bulk density of 72 kg/m3, and was brittle at as high a temperature as 230C.
The low-temperature flexibility was tested by bending over a 900 angle edge. The bending time was about 2 seconds.

Claims (7)

Claims
1. A process for preparing a crosslinked propylene polymer foam comprising first preparing a homogeneous mixture of 100 parts by weight of propylene polymer with up to 20 parts by weight of liquid polybutadiene(s) containing at least 35% by weight of 1,2vinylpolybutadiene and having a molecular weight of 500 to 10,000 and a crosslinking agent and/or a foaming agent at below the decomposition temperature of the crosslinking and/or foaming agents, if desired shaping the mixture, then subjecting it to high-energy radiation for crosslinking and further treating it to cause foaming, in which process 10 to 100 parts by weight of EPDM rubber and/or EPM rubber and/or optionally chlorinated polyethylene are added to the mixture before the irradiation per 100 parts by weight of propylene polymer present in the mixture, and the material is homogeneously mixed, then irradiated, crosslinked and foamed.
2. A process according to claim 1, in which the high-energy radiation used is provided by an electron beam and the irradiation dose is 1 to 10 Mrad.
3. A process according to claim 1 or 2, in which 20 to 80 parts by weight of optionally chlorinated polyethylenes are added to the mixture before the irradiation per 100 parts by weight of propylene polymer present in the mixture.
4. A process according to any of claims 1 to 3, in which 5 to 20 parts-by weight of azodicarboxamide or other chemical blowing agent are used.
5. A process according to any of claims 1 to 4, wherein the propylene polymer is polypropylene homopolymer or an ethylene-propylene copolymer.
6. A process for preparing a crosslinked propylene polymer foam carried out substantially as hereinbefore described and claimed or illustrated with reference to any of the foregoing Examples 1 to 5.
7. A crosslinked propylene polymer foam having a bulk density of 20 to 200 kg/m3 when prepared by a process according to any of claims 1 to 6.
GB08313991A 1982-05-22 1983-05-20 Preparing crosslinked propylene polymer foams Withdrawn GB2123004A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
DE19823219331 DE3219331C1 (en) 1982-05-22 1982-05-22 Process for the production of cross-linked polyolefin foams

Publications (2)

Publication Number Publication Date
GB8313991D0 GB8313991D0 (en) 1983-06-29
GB2123004A true GB2123004A (en) 1984-01-25

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GB08313991A Withdrawn GB2123004A (en) 1982-05-22 1983-05-20 Preparing crosslinked propylene polymer foams

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BE (1) BE896662A (en)
DE (1) DE3219331C1 (en)
FR (1) FR2527217A1 (en)
GB (1) GB2123004A (en)
SE (1) SE8300024L (en)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5541262A (en) * 1991-11-12 1996-07-30 Centro Sviluppo Settori Impiego S.R.L. Propylene polymer and copolymers grafted with vinylpolybutadiene and their preparation process
US20100105791A1 (en) * 2007-06-11 2010-04-29 Shunji Hyoudou Closed-cell foamed rubber sheet, and method for production thereof
EP2157124A4 (en) * 2007-06-04 2012-12-12 Nitto Denko Corp Thermoplastic resin foam and process for producing the same

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
IT1272915B (en) * 1995-01-20 1997-07-01 Commer Spa SCRAPED PROPYLENE POLYMERS AND COPOLYMERS

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5541262A (en) * 1991-11-12 1996-07-30 Centro Sviluppo Settori Impiego S.R.L. Propylene polymer and copolymers grafted with vinylpolybutadiene and their preparation process
EP2157124A4 (en) * 2007-06-04 2012-12-12 Nitto Denko Corp Thermoplastic resin foam and process for producing the same
US20100105791A1 (en) * 2007-06-11 2010-04-29 Shunji Hyoudou Closed-cell foamed rubber sheet, and method for production thereof
US8263673B2 (en) * 2007-06-11 2012-09-11 Sekisui Chemical Co., Ltd. Closed-cell foamed rubber sheet, and method for production thereof
CN101679660B (en) * 2007-06-11 2012-10-24 积水化学工业株式会社 Closed-cell foam rubber sheet and manufacturing method thereof
EP2159254B1 (en) * 2007-06-11 2016-03-30 Sekisui Chemical Co., Ltd. Closed-cell foam rubber sheet, and method for production thereof

Also Published As

Publication number Publication date
DE3219331C1 (en) 1983-12-29
SE8300024D0 (en) 1983-01-03
SE8300024L (en) 1983-11-23
BE896662A (en) 1983-09-01
FR2527217A1 (en) 1983-11-25
GB8313991D0 (en) 1983-06-29

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