Polyamide-based thermoplastic compositions

Details Polyamide-based thermoplastic compositions Polyamide-based thermoplastic compositions

2000-03-27

2002-04-23

Woodward, Ana (Department: 1711)

Stock material or miscellaneous articles

Hollow or container type article

Polymer or resin containing

C428S035700, C428S036800

Reexamination Certificate

active

06376037

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to polyamide-based thermoplastic compositions and more particularly to thermoplastic compositions comprising by weight:
50 to 99% of a polyamide (A1),
1 to 50% of a catalysed polyamide (A2),
0 to 40% of a plasticizer,
0 to 60%, preferably 0 à 30%, of a flexible modifier, the total being 100%.
These compositions are of use for the manufacture, for example, of flexible pipes.
BACKGROUND OF THE INVENTION
Polyamides have to be modified by incorporation of rubbers or other polymers, for example, in order to modify the flexural modulus thereof or to improve the impact strength thereof.
U.S. Pat. No. 5,070,145 discloses compositions composed of 80 parts of polyamide-6 or polyamide-6,6 in which has been dispersed 20 parts of a mixture (i) of a copolymer of ethylene and of an ethyl or butyl acrylate and (ii) of a copolymer of ethylene, of ethyl acrylate and of maleic anhydride. These compositions exhibit good impact strength.
EP 284,379 discloses multiphase compositions comprising ethylene copolymer and polyamide which are provided in the form of a polyamide matrix in which are dispersed nodules (1) of a copolymer of ethylene, of ethyl acrylate and of maleic anhydride, nodules of polyamide being dispersed in these nodules (1). The starting point is the preparation of these nodules (1) by dispersing polyamide in the ethylene copolymer; crosslinking is then carried out and these nodules are subsequently dispersed in polyamide. These compositions are also presented as having good impact strength.
FR 2,719,849 discloses thermoplastic compositions comprising a matrix of a thermoplastic polymer in which are dispersed nodules of a second thermoplastic polymer which is partially or completely encapsulated by an ethylene copolymer. These compositions are prepared by first encapsulating the second polymer, and subsequently the other polymer is added, forming the matrix, under conditions such that the capsules are not destroyed. This preparation is carried out in two completely separate stages or one following the other in the same extruder. These compositions exhibit both good flexibility and good impact strength. The examples show polyamide-6, polyamide-12 or PBT (polybutylene terephthalate) matrices in which are dispersed nodules of polyamide-6,6 encapsulated by a copolymer of ethylene, of ethyl acrylate and of glycidyl methacrylate. A comparative example shows that, in a PA-6 matrix, the PA-6,6 nodules encapsulated by the ethylene copolymer are bigger than the nodules formed only of the ethylene copolymer.
Patent Application WO 97/46621 discloses polyamide mixtures which are provided in the form of a matrix in which are dispersed encapsulated nodules. It is explained that if, in a matrix (M) comprising nodules (S), a portion of (S) were replaced by a polymer (K), the tensile stress could be improved while retaining the flexural modulus. Furthermore, a reduction in size of the nodules of the phase dispersed in (M) also very often resulted therefrom.
The publication by M. Genas (“Rilsan PA11, synthesis and properties”, Angew. Chemie, 74(15), 535-540, 1962) describes the use of phosphoric acid catalyst for accelerating the polycondensation of PA.
Likewise, the publications by M. K. Dobrokhotova et al. (“Synthesis of PA12”, Plasticheskie Massy, 2, 23, 1979, and the subsequent publications by the same authors) describe the role of phosphoric acid: catalyst and chain-limiting agent.
SUMMARY OF THE INVENTION
It has now been found that polyamide compositions comprising catalysed polyamide exhibited the advantage of a notched Charpy impact strength at −40° C. (ISO 179/93) which increased with the intrinsic viscosity of the compositions, whereas polyamides comprising plasticizers and not comprising catalysed polyamide exhibited a low and constant impact strength (or an impact strength increasing in much lower proportions) as a function of the intrinsic viscosity (see table 1-2 and FIG.
1
).
The compositions of the invention are manufactured by mixing the various constituents in the molten state (twin-screw, Buss or single-screw extruders) according to the usual techniques for thermoplastics. The compositions can be granulated for the purpose of a subsequent use (it is sufficient to remelt them) or else can be immediately injected into a mould or an extrusion or coextrusion device, in order to manufacture pipes or sections. The intrinsic viscosity of the compositions thus obtained is higher than that of the starting polyamides (A1) and (A2).
The intrinsic viscosity (&eegr;) is measured with an Ubbelhode viscometer at 25° C. in meta-cresol for 0.5 g of polymer in 100 ml of meta-cresol. This principle is described in Ullmann's Encyclopedia of Industrial Chemistry, Vol. A 20, p. 527-528 (1995, 5
th
edition). In the continuation of the text, the intrinsic viscosity denotes the intrinsic viscosity normalized to the amount of polyamide, that is to say that it is the intrinsic viscosity of the composition *100/(%A1+%A2). It is therefore a matter of relating the measured value to the amount of PA present in the composition (it being possible for A1 and/or A2 themselves to be polyamide mixtures which are soluble in meta-cresol) by deducting the other constituents (flexible modifier, plasticizer, stabilizers, fillers, and the like). For example, the intrinsic viscosity of a composition comprising 70% of PA-12, 12% of catalysed PA-11, 10% of mEPR modifier and 8% of plasticizer is determined as being the ratio “measured viscosity”* 100%/(100%−10%−8%) or alternatively the ratio “measured viscosity”* 100%/(70%+12%).
Another advantage of the compositions of the present invention is the bursting stress of the manufactured pipes. This stress increases with the intrinsic viscosity of the compositions, whereas, for polyamides or polyamides comprising only plasticizer and not catalysed polyamide, the bursting pressure decreases when the intrinsic viscosity increases (see table 1-2 and FIG.
2
).
Another advantage of the compositions of the present invention is the accuracy of the sizing of the pipes extruded during their processing. For example, as regards pipes with an external diameter of 8 mm and a thickness of 1 mm, the accuracy is improved by approximately 3 hundredths of an mm in comparison with compositions comprising only plasticizer and not catalysed polyamide (see table 1-2 and FIG.
3
). This remarkable behaviour makes possible to increase the extrusion speed of the tubes, thus increasing productivity while keeping the same accuracy of the sizing of the pipes.
Another advantage of the compositions of the present invention is the excellent melt strength which is the holding of the melted compositions. They are particularly suited, not only for extrusion of pipes and profiles of standard sizes (example tube 8*1 mm or 12*1.5 mm), but for extrusion of large diameter pipes. They are particularly suited for blow extrusion of hollow bodies, even of large size. Thus the compositions exhibit a large spread of processing possibilities.
Another advantage of the compositions of the present invention is there is less trouble due to the exudation which is the plasticizer leaving the compositions with the temperature increase. In fact these compositions contain less plasticizer. Thus less problems of aspect (deposits) and dimensionnal variations (due to the release of plasticizer which could reach 10 to 30%) occur. The loss of plasticizer can create a decrease of the fittings' strength and variation of mechanical, physical and chemical properties. Under 7-8% of plasticizer the Tg of PA 11 and PA 12 is above ambient temperature. Due to the less molecular mobility, migration of plasticizer and polyamide oligomers (increased by presence of plasticizer) are reduced. It is very advantageous for pieces conveying fluids such as gasoline in which released oligomers can plug filtration systems.
Another advantage of the compositions of the present invention is the excellent resistance to abrasion.
Another advantage of the compositions of the pr

Affiliated with

Also associated with

Rating

Polyamide-based thermoplastic compositions does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Polyamide-based thermoplastic compositions, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Polyamide-based thermoplastic compositions will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2884154