Stock material or miscellaneous articles – Composite – Of polyamide
Reexamination Certificate
1999-08-30
2001-03-20
Kiliman, Leszek (Department: 1773)
Stock material or miscellaneous articles
Composite
Of polyamide
C428S474700, C428S475500, C428S500000, C428S413000, C428S192000, C525S179000, C524S514000
Reexamination Certificate
active
06203920
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to compositions which are based on polyamide and are suitable for extrusion blow moulding. It relates more particularly to flexible compositions comprising a matrix of an alloy of polyamide and polymer having polyamide blocks and polyether blocks, dispersed in which matrix is a crosslinked phase, the said compositions having a melt strength of more than 1.5 and a flexural modulus (at 23° C. in accordance with ISO 178-93) of less than 700 MPa and preferably between 50 and 300 MPa.
BACKGROUND OF THE INVENTION
The melt strength is a measure of the suitability of a polymer or of a polymer mixture for extrusion blow moulding. A measurement is made of the time t2 required for the parison to drop by a height of 25 cm and the time tl required by the parison to drop by a height of 50 cm; the melt strength is the ratio t1/t2. If the polymer or polymer mixture is suitable for the blow moulding of large parts then a ratio close to 2 is found. If it is not close to 2, on the other hand, for example if it is 1.4, this value indicates flow of the parison under its own weight (quickening of the rate of descent) and hence poor suitability for extrusion blow moulding.
DESCRIPTION OF THE INVENTION
The compositions of the invention are useful for manufacturing flexible, extrusion blow-moulded automotive parts, especially the components situated beneath the bonnet which are required to be resistant to heat. Examples of such components are pipes for the cooling, air-conditioning and combustion air circuits, and various protective sheaths for electrical cables. Many of these parts are currently made of rubber, in other words of vulcanized synthetic or natural elastomers which have to be shaped and then vulcanized in their defined form. Vulcanization is carried out batchwise in ovens or furnaces, and the pipes, for example, are required to contain a mandrel of a substance which resists the vulcanization temperature. The advantage of the compositions of the invention is that, being thermoplastic, all that is required is to extrude them, to shape them by blow moulding and to allow them to cool. Certain ducts, for example the combustion air intake circuits in car engines, consist of rigid or thermoplastic parts and of flexible parts made of rubber, the parts all being joined by hose clamps. The advantage of the compositions of the invention is that it is possible by sequential extrusion blow moulding to extrude, for example, one part in polyamide and then one part in accordance with the compositions of the invention. The two parts become welded end to end under heat. The result is an extrusion blow-moulded part consisting of different materials, one at least of which is a composition according to the invention.
In the case of air intake ducts the result is a duct which can consist of rigid parts and of flexible parts, manufactured as a single part without joins. The present invention additionally relates to such parts.
Another advantage of the compositions of the invention is their resistance to thermal ageing, which is expressed by the half-life. Generally, the parameter used is the change in elongation at break in the course of ageing in a dry oven at 150° C.
The other advantage is the good thermo-mechanical strength: the part must be flexible from room temperature (for assembly of the installation) and yet must not flow under its own weight when the temperature reaches 120, 140 or even 150° C.
The prior art has already described polyamides which are flexible owing either to the incorporation of plasticizer in the polyamide or to mixing with polyolefins. However, in order to obtain low flexural moduli, it is necessary to incorporate large amounts of plasticizer or polyolefins, resulting alternatively in the exudation of plasticizer and thus a loss of flexibility, or in the loss of the polyamide matrix, or mixtures which no longer have mechanical properties or which are difficult to transform.
The prior art has also described mixtures based on polymers comprising polyamide blocks and polyether blocks; however, they are much too elastomeric and no longer have the properties of polyamide.
The water absorption is much lower than in the flexible polyamides of the prior art.
The impact resistance, like the heat resistance, is very good. The materials also feature elastic recovery and a low compression set (CS).
CH 655 941 describes the need to add copolyolefins grafted with maleic anhydride to block polyamide copolymers or to mixtures of these block polyamide copolymers with polyamides, in order to render them flexible. These prior art compositions do not have a polyamide matrix.
U.S. Pat. No. 5,070,145 describes mixtures of polyamide, ethylene-alkyl acrylate copolymers and ethylene-alkyl acrylate-maleic anhydride copolymer.
Although the impact resistance of the polyamides is improved, these compositions do not comprise block polyamide copolymers and do not have the flexibility of the compositions of the invention.
EP 564 338 describes mixtures of polyamide and ethylene-alkyl acrylate-glycidyl methacrylate copolymers and, optionally, ethylene-alkyl acrylate-maleic anhydride copolymer.
The non-polyamide part of these mixtures can therefore be crosslinked, which makes it possible to increase its quantity relative to the polyamide and to lower the flexural modulus. The addition of block polyamide copolymers is not described.
Thus the invention provides compositions comprising a matrix of an alloy of (a) polyamide and (b) polymer having polyamide blocks and polyether blocks, dispersed in which matrix is a crosslinked phase (c), the said compositions having a melt strength of more than 1.5 and a flexural modulus at 23° C. (in accordance with ISO 178-93) of less than 700 MPa and preferably between 50 and 300 MPa.
The term alloy is used to designate the matrix formed from (a) and (b) by virtue of the particularly high compatibility of these polymers.
By polyamide (a) is meant the condensation products:
of one or more amino acids, such as aminocaproic, 7-aminoheptanoic, 11-aminoundecanoic and 12-aminododecanoic acids or of one or more lactams, such as caprolactam, enantholactam and lauryllactam;
of one or more salts or mixtures of diamines such as hexamethylenediamine, dodecamethylenediamine, metaxylylenediamine, bis-p-aminocyclohexylmethane and trimethylhexamethylenediamine with diacids such as isophthalic, terephthalic, adipic, azelaic, suberic, sebacic and dodecanedicarboxylic acids;
or mixtures of some of these monomers, which results in copolyamides, for example PA 6/12 by condensation of caprolactam and lauryllactam.
Polyamide mixtures can be used. Use is made advantageously of PA 6.
The polymers having polyamide blocks and polyether blocks (b) result from the copolycondensation of polyamide sequences having reactive ends with polyether sequences having reactive ends, such as, inter alia:
1) Polyamide sequences having diamine chain ends with polyoxyalkyene sequences having dicarboxylic chain ends.
2) Polyamide sequences having dicarboxylic chain ends with polyoxyalkylene sequences having diamine chain ends obtained by cyanoethylation and hydrogenation of aliphatic alpha, omega-dihydroxylated poloxyalkylene sequences, referred to as polyetherdiols.
3) Polyamide sequences having dicarboxylic chain ends with polyetherdiols, the products obtained being, in this particular case, polyetheresteramides.
The polyamide sequences having dicarboxylic chain ends originate, for example, from the condensation of alpha,omega-aminocarboxylic acids and lactams or of carboxylic diacids and diamines in the presence of a carboxylic diacide chain-limiting agent. Advantageously, the polyamide blocks are of polyamide 12 or polyamide 6.
The number-average molar mass of the polyamide sequences is between 300 and 15,000 and preferably between 600 and 5000. The mass of the polyether sequences is between 100 and 6000 and preferably between 200 and 3000.
The polymers having polyamide blocks and polyether blocks may also include randomly distributed units. These polymers can be prepared
Bouilloux Alain
Teze Laurent
Elf Atochem S.A.
Kiliman Leszek
Smith , Gambrell & Russell, LLP
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