IE902507A1 - Amorphous blend comprising an amorphous semiaromatic¹polyamide and a semicrystalline polyamide of nylon type - Google Patents

Abstract

Single-phase and amorphous polymeric mixtures capable of being employed especially for producing shaped articles using moulding operations. According to the invention the said mixtures comprise: (i) an amorphous semiaromatic polyamide obtained from 2-methyl-1,5-pentamethylenediamine taken by itself or mixed with 2-ethyl-1,4-tetramethylenediamine and isophthalic acid taken by itself or mixed with terephthalic acid, and (ii) a semicrystalline polyamide of the nylon type chosen from the group made up of nylon 66, nylon 6, mixtures of these polymers and the copolymers obtained from monomers resulting in these nylons, the quantity of the semicrystalline polyamide of the nylon type (ii) representing not more than 40% of the weight of the combined semiaromatic polyamide (i) + semicrystalline polyamide (ii). The resilience properties of the semiaromatic polyamide at temperatures ranging from room temperature to -25 DEG C can be improved with such mixtures.

Description

The present invention relates to single-phase amorphous polyamide blends which can be employed especially for producing shaped articles by moulding, and to their preparation.

Wholly aliphatic linear polyamides of nylon type, of high molecular weight, have many physical and chemical properties which make them suitable for production of a wide variety of shaped articles such as fibres, films and other moulded objects. Polyhexamethylene adipamide or nylon 66 is an example of a polyamide which has been developed very extensively. However, these polymers show a number of defects whose importance depends on the intended use. In the majority of cases, these polyamides are semicrystalline and are therefore not transparent, and they cannot be employed in fields of application which require transparency; furthermore, these polyamides generally exhibit a shrinkage on moulding, which may not be insignificant, a water uptake which can be considerable and, as a corollary, a dimensional stability to moisture which may be insufficient and mechanical properties which are affected by the surrounding moisture and which drop, furthermore, at temperatures above 100°C, because of the insufficiently high value of their glass transition temperature Tg (which is generally below 80°C).

Very many patents describe polyamides which have different groups, such as particularly polyamides containing mixed aliphatic and aromatic units, which make it possible - 3 wholly or partially to remedy the defects just discussed.

The introduction of aromatic rings entails a rise in the melting or softening point and in the Tg, resulting particularly in a better retention of mechanical properties at high temperatures. Moreover, when their composition is adapted, these polyamides may be amorphous polymers. Typical amorphous semiaromatic polyamides are, for example: the copolymers obtained from hexamethylenediamine and isophthalic (60 to 90 mol% in the mixture of the diacids) and terephthalic acids (cf. US-A-3,382,216), which exhibit a Tg of the order of 100°C to 120°C, and the copolymers obtained from 2-methylpentamethylenediamine and isophthalic (15 to 30 mol% in the mixture of the diacids) and terephthalic acids (cf. FR-A-2,325,673), which exhibit a Tg 15 of the order of 137°C to 142°C. However, because of high melt viscosities, the conversion of these amorphous semiaromatic polyamides by a melt route, for example by injection, requires a high processing temperature which is liable to retard their development: this temperature is, for example, of the order of 280°C to 300°C in the case of the abovementioned copolymers obtained from hexamethylenediamine and aromatic acids, and from 290°C to 310°C in the case of the abovementioned copolymers obtained from 2-methylpentamethylenediamine and aromatic acids.

Furthermore, semiaromatic polyamides exhibit a very low shrinkage which frequently leads to difficulties in the operations of demoulding the shaped articles prepared with - 4 the aid of these materials.

There is therefore a need for polyamides exhibiting at least some of the following properties: - capable of use in fields of application which require 5 excellent transparency; - a Tg higher than 100°C so as to make it possible to produce, for example by injection, shaped articles capable of exhibiting a better polymer stability and a better retention of the mechanical properties at high temperatures, relative to what happens with a polyamide of nylon type, - easily converted by a melt route at a processing temperature which is not too high, eg. from 270°C to 290°C, because of a melt viscosity which is lower than that of a semiaromatic polyamide, and - having, where appropriate, a slight moulding shrinkage, the degree of which is greater than that obtained in the case of the semiaromatic polyamide but smaller than that obtained in the case of a polyamide of nylon type, so as to promote the demoulding of moulded shaped articles.

To satisfy at least some of these objectives the present invention provides single-phase, amorphous polyamide blends comprising an amorphous semiaromatic polyamide, which may be a homo- or a copolymer, comprising repeat units of formulae: CH3 -nh-ch2-ch-ch2-ch2-ch2-nh(I) H5 -hn-ch2-ch-ch2-ch2-nh(II) and (III) (IV) , the proportion of units of formula (II) being from to 15 mol% and that of units of formula (I) being from 100 to 85 mol% based on the total of units of formulae (I) and (II) ; the proportion of units of formula (IV) being from 10 0 to 90 mol%, and that of units of formula (III) being from 100 to 10 mol% based on the total of units of formulae (III) and (IV) ; and the molar ratio of units of formulae (I) and (II) to units of formulae (III) and (IV) being equal to 1; and (ii) a semicrystalline polyamide of nylon type, which may be a homo- or copolymer, chosen from: nylon 66 (polymer of hexamethylenediamine and of adipic acid), nylon 6 (polymer of e-caprolactam), mixtures of these polymers and the copolymers obtained from the abovementioned monomers for the preparation of nylons 66 and 6; the quantity of the - 6 semicrystalline polyamide (ii) being not more than 40 % of the combined weight of the semiaromatic polyamide (i) and the semicrystalline polyamide (ii).

The new blends make it possible to obtain: - in addition to the abovementioned objectives including especially the requirements for transparency, Tg values and conversion conditions discussed above, - the possibility of having resilience properties which, on the one hand, are superior to those obtained with the semiaromatic polyamide employed by itself at temperatures from room temperature (23°C) to temperatures as low as those, for example, from 0°C to -25°C and, on the other hand, remain substantially constant throughout this temperature interval from room temperature to, for example, -25°C.

The production of blends comprising an amorphous semiaromatic polyamide and a semicrystalline polyamide of nylon type has already been proposed in the prior art. In particular, EP-A-70,001 describes blends comprising 2 % to 95 % by weight of an amorphous semiaromatic polyamide obtained from hexamethylene-diamine, a cyclic diamine such as bis(p-amino-cyclohexyl)methane and isophthalic and terephthalic acids and 98 % to 5 % by weight of a semicrystalline polyamide of nylon type. This specification teaches particularly that the use of minor quantities of polyamide of nylon type (5 % to 40 % by weight in the blend of the two types of polyamides) is a way of improving the - 7 solvent resistance of amorphous semiaromatic polyamides, but there is nothing in this prior art to make it possible to foresee especially the particular behaviour concerning resilience which can be exhibited by blends of the present invention, in which the amorphous semiaromatic polyamide has a different chemical structure.

In the structure of the amorphous semiaromatic polyamide (i), the units of formula (I) are produced by 2methy1-1,5-pentamethylenediamine. The optional units of formula (II) derive from 2-ethyl-l,4-tetramethylenediamine. The synthesis of the 2-methylpentamethylenediamine employed can be carried out by hydrogenation of the dinitrile of 2methyl-glutaric acid using known processes. Similarly, the synthesis of 2-ethyltetramethylenediamine can be carried out by hydrogenation of the di-nitrile of 2-ethylsuccinic acid. The units of formula (III) and optionally (IV) originate respectively from isophthalic acid and optionally terephthalic acid or from a derivative of these acids, such as, for example, a dihalide or a diester.

According to a preferred embodiment, use is made in the present invention of an amorphous semiaromatic polyamide (i) which has: - on the one hand, a structure corresponding to that defined above, in which: the quantity of the units (II) in the mixture of (I) + (II) lies in the range from 0 to 5 mol%, and that of the units (I), relative to the same reference, lies in the - 8 range from 100 to 95 mol%, the quantity of the units (IV) in the mixture of (III) + (IV) lies in the range from 0 to 85 mol%, and that of the units (III), relative to the same reference, lies in the range from 100 to 15 mol%, - and, on the other hand, a viscosity index (VI), measured according to ISO standard R 307 (2nd edition of 1984) in meta-cresol at 25°C on a solution containing 0.5 g of polymer (dried for 2 hours at 60°C under argon purging) in 100 cm3 of meta-cresol, which is at least equal to 90 ml/g.

According to a still more preferred embodiment, use is made of an amorphous semiaromatic polyamide (i), which exhibits: - on the one hand, a structure corresponding to the preferred one just shown above, in which the quantity of the units (IV) in the mixture of (III) + (IV) lies in the range from 60 to 85 mol%, and that of the units (III), relative to the same reference, lies in the range from 40 to 15 mol%, - and, on the other hand, a VI between 100 ml/g and 150 ml/g.

The amorphous semiaromatic polyamides (i) are known (cf. in particular FR-A-2,325,673), and can be prepared by polycondensation processes which are well known to specialists in the polymer field: bulk polycondensation in the melt, starting from diamine(s) and diacid(s) or from diester(s) of diacid(s), or polycondensation in solution or interfacial polycondensation starting from diamine(s) and - 9 diahalide(s) of diacid(s).

To carry out this polycondensation it is preferred to operate in bulk in the melt, using the original process forming the subject of French Application No. 89/02,467, in the name of the Applicant Company, filed on 21 February 1989. In accordance with this process, a starting composition comprising either an amine reactant (2-methylpentamethylenediamine taken by itself or mixed with not more than 15 mol% of 2-ethyltetramethylenediamine) and an acidic reactant (isophthalic acid taken by itself or mixed with not more than 90 mol% of terephthalic acid), or their salt(s), is polycondensed, the operation being carried out in a closed system of the autoclave type and linking into a sequence the following stages: - stage 1: in which, the autoclave being closed, the temperature of the starting composition is progressively raised to a certain value Tl, above 110°C; then, at a constant pressure P equal to the autogenous pressure of water vapour obtained, which is above atmospheric pressure, the water present in the reaction mass is removed by steady distillation while simultaneously the temperature of the mass is raised progressively to a value T2, which is higher than the temperature Tl attained before distillation; - stage 2: in which the pressure is progressively lowered from the value of the autogenous pressure to the value of the atmospheric pressure and optionally the temperature of the mass is simultaneously raised to a value - 10 T3 which is some ten to several tens of degrees Celsius higher than the temperature T2 attained before decompression, while steady distillation of water continues to be ensured during this decompression period; - stage 3: in which the polycondensation is completed by stirring the reaction mass for some time, the operation being carried out at atmospheric pressure and optionally (or) at a lower pressure with a mass temperature equal to or above the temperature T2 or T3 obtained at the end of stage 2, for a sufficient period of time making it possible to obtain a polyamide which has the desired molecular and viscosity characteristics; the said process being characterized by the following points: the starting compositions, on the one hand, additionally necessarily contain water in sufficient quantity to permit the distillation of stage 1 to be conducted in the particular conditions of temperatures (TI and T2) and of pressure (P) which are shown in the subparagraph which follows, and, on the other hand, additionally but optionally contain a catalyst; in stage 1, after the autoclave has been closed, the temperature of the starting composition is progressively increased to a value TI lying in the range from 160°C to 190°C; then, at a constant pressure P equal to the autogenous pressure of water vapour obtained, which lies in the range from 0.5 to 1.2 MPa, the water present in the \£ 902507 - 11 reaction mass is removed by steady distillation while simultaneously the temperature of the mass is raised progressively to a value T2 lying in the range from 210°C to 235°C.

The process just described can be applied to compositions comprising either stoichiometric quantities of an acidic reactant and of an amine reactant contributing equivalent numbers of COOH and NH2 groups, or their stoichiometric salt(s).

The expression water present in the reaction mass which appears above in stage 1 concerning the distillation, is intended to define the water present in the starting compositions plus the water which may be formed by a polycondensation reaction of the acidic reactant and of the amine reactant. The quantity of water present in the starting compositions is not critical so long as it makes it possible to conduct the distillation of stage 1 in the particular conditions of temperatures (Tl and T2) and of autogenous pressure (P) which are indicated above; this quantity of water can be easily determined by the specialist using his or her common knowledge and simple tests.

To carry out stage l of the polycondensation process just described, it is possible to make use of starting compositions which are in the form of mixtures: either based on the acidic reactant, the amine reactant, water and optionally a catalyst, the acidic reactant being employed in the solid state and the amine reactant being - 12 employed, for example, in the state in which it is naturally to be found, or in the form of aqueous solution; or based on the salt(s) of diacid(s) and of diamine(s), water and optionally a catalyst, the salt(s) being employed, for example, in the solid state, in aqueous dispersion or in the form of aqueous solution.

With regard to the catalyst which can be employed, this generally consists either of a compound (a), or of a compound (B), (a) denoting an inorganic oxygen-containing mono- or polyacid or an organic oxygen-containing mono- or polyacid other than a carboxylic acid, in which at least one of the acidic functional groups has an ionization constant pka equal to or lower than 4 in water at 25°C, (B) denoting an alkali metal or alkaline-earth metal salt of this acid.

Concerning the conduct of stage 1 of the polycondensation process under discussion, it should be noted that the progressive heating of the starting composition to the temperature T1 can be done over a period lasting, for example, from 10 minutes to 2 hours. As for the distillation under constant autogenous pressure P, this is carried out over a period of time ranging, for example, from 30 minutes to 3 hours 30 minutes.

In the conduct of stage 1 it will be preferred to perform the distillation under a constant autogenous pressure P lying in the range from 0.6 to 1 MPa by choosing: a starting distillation temperature T1 lying in the range from 170°C to 185°C and a temperature T2 just before - 13 decompression, lying in the range from 215°C to 230°C.

In the conduct of stage 2, the decompression, which may take place in successive steps, is carried out over a period ranging, for example, from 20 minutes to 2 hours 30 minutes and the temperature of the reaction mass is simultaneously raised to a value T3 lying, for example, in the range from 250°C to 320°C.

In the conduct of stage 3, the polycondensation is finished by allowing the reaction mass to react at the temperature T3 or at a temperature which may be higher than T3 by a few degrees to about ten degrees, the operation being preferably carried out under a reduced pressure lying in the range from lxlO2 to lOOOxlO2 Pa for a period of time (including the period of applying reduced pressure) ranging, for example, from 10 minutes to 3 hours.

It would not constitute a departure from the scope of the present invention to use an amorphous semiaromatic polyamide (i) which additionally contains in its structure, besides units of formulae (I), (II) , (III) and (IV), repeat units generating amide functional groups, which have a structure other than those of units (I), (II), (III) and (IV) and chosen so as to increase the Tg of the semiaromatic polyamide.

The semicrystalline polyamide of nylon type used in the present invention is preferably a polymer, a mixture of polymers or a copolymer having a viscosity index (VI), measured according to ISO standard R 307 (2nd edition of - 14 1984) on the part which is soluble in formic acid of 90 % purity by weight, which is at least equal to 120 ml/g.

According to a still more preferred embodiment, the semicrystalline polyamide of nylon type used consists of a nylon 66 (polymer of hexamethylenediamine and adipic acid) exhibiting a VI between 130 ml/g and 180 ml/g.

The quantity of the semicrystalline polyamide (ii) in the combination of the polyamides (i) and (ii) does not exceed 40 % by weight. Above the maximum limit of 40 % the mixtures obtained no longer form part of the present invention, because they lose their character of a singlephase and amorphous blend: they then have a melting point. The minimum quantity of semicrystalline polyamide (ii) corresponds to the lower limit below which the blends obtained are difficult to convert by a melt route at a processing temperature which is not too high, of the type of those ranging from 270°C to 290°C; this minimum quantity usually represents approximately 10 % of the weight of the combination of semiaromatic polyamide (i) plus semicrystalline polyamide (ii). The quantity (iii) of the semicrystalline polyamide (ii) may thus lie between 10 % and 40 %. This quantity preferably lies between 20 % and 35 %, because it is with this range of quantities that the blends according to the invention exhibit the twin advantage of, on the one hand, being easily converted by a melt route at a processing temperature which is not too high, ranging from 270°C to 290°C, and, on the other hand, of giving a singleIE 902507 - 15 phase amorphous material offering resilience properties which are superior to those obtained with the semiaromatic polyamide employed by itself in the case of analysis temperatures ranging, for example, from room temperature to -25°C and, at the same time, also remain substantially constant throughout this temperature range.

The resilience behaviour of the blends of the present invention appears to be specific to the use of the specified semiaromatic polyamides, since the particular behaviour in question is not encountered when the said polyamide is replaced by an amorphous semiaromatic polyamide of another type, for example the copolymer obtained from hexamethylenediamine and isophthalic (70 mol% in the mixture of the diacids) and terephthalic acids (all the remaining operating conditions being otherwise the same). Another surprising factor lies in the fact that blends comprising an amorphous semiaromatic polyamide which is capable of crystallization, such as, for example, the semiaromatic polyamides obtained from a mixture of isophthalic and terephthalic acids which have a structure in which the quantity of the units (III) derived from isophthalic acid in the mixture of (III) + (IV) is small and lies in the range from 15 to 40 mol%, and a semicrystalline polyamide of nylon type, always yield a transparent amorphous material which, for example, does not crystallize on reheating during the conversion operations, in the case of quantities of semicrystalline polyamide as high as those ranging from 10 % - 16 to 40 %.

The blends according to the present invention can be prepared in various ways which are known per se.

According to a preferred embodiment, the blends are prepared in two stages: a first stage in which the constituents are stirred together at room temperature (23°C) in a conventional fast mixer for powder or granules, and a second stage in which this premix is homogenized by blending in the melt phase, at a temperature lying in the range from 270°C to 290°C, the operation being carried out in a device permitting blending of plastic materials in the molten state, preferably a single- or multiscrew extruder. At the end of this treatment the blends of the invention generally take the form of rods which are then chopped into granules; these granules will be subsequently employed for converting the blends of the invention with the aid of conventional machines, for example for injection moulding or extrusion, to give shaped objects such as particularly solid articles or hollow bodies. With regard to the conversion conditions, the blends according to the invention can, for example, be injection moulded easily by using a melt temperature which is not too high, of the type of those ranging from 270°C to 290°C.

The usual additives may be added to the blends of the invention, at any time during their preparation; these must, on the one hand, be advantageously soluble in the blend, since transparency plays an important part and, - 17 furthermore, they must not be crystallization nuclei. These additives are, for example, antioxidants, light stabilizers, heat stabilizers, plasticizers, optical whiteners, colorants, and the like.

The example which follows illustrates how the present invention can be put into practice.

EXAMPLE In this example, a blend in accordance with the present invention is illustrated, containing: (i) 75 % by weight of an amorphous semiaromatic polyamide obtained as shown below from 2-methyl-1,5-pentamethylenediamine, isophthalic acid (20 mol% in the mixture of the diacids) and terephthalic acid (80 mol% in the mixture of the diacids), exhibiting a viscosity index of 127 ml/g (determined as stated above in the description on a solution of the polymer in meta-cresol) and (ii) 25 % by weight of nylon 66 which is the product marketed by Rhdne-Poulenc Chimie under the registered trademark Technyl 50 AP, exhibiting a viscosity index of 140 ml/g (determined as stated above on the part which is soluble in formic acid). 1) Preparation of the amorphous semiaromatic polyamide: 1.1) Preparation of the methylpentamethylene-diamine salt of (isophthalic + terephthalic) acids in aqueous solution: The operation is carried out in a 100-litre reactor equipped: - 18 - with a heating system, - with a stirrer of the marine propeller type, - with a system permitting purging with nitrogen and maintaining an oxygen-free atmosphere, and - with a system enabling the volatile products to be condensed.

The following are introduced cold into the reactor which is kept under a gentle nitrogen purge: 5128.5 g of isophthalic acid (30.8944 moles), - 20513.9 g of terephthalic acid (123.5776 moles), 18635.5 g of 2-methyl-l,5-pentamethylenediamine (160.6509 moles), - 29518.6 g of distilled water.

The temperature of the mass is raised to 60°C and the 15 mixture is stirred for 2 hours while purging with nitrogen is maintained. An aqueous solution containing 60 % by weight of stoichiometric salt is thus obtained. The pH then reaches the value of 9.2; a molar excess of 4 % of amine reactant is used in this preparation. 2.1) Polycondensation in an autoclave: The apparatus employed consists of a 100-litre stainless steel autoclave which is stirred and equipped for working up to 300°C and 2.2 MPa pressure. It is fitted: with a jacketed heating system using a heat transfer 25 fluid, with a frame-type stirrer, with a system permitting pressurizing with nitrogen, - 19 with a circuit permitting volatile products to be condensed and collected, and with a system for applying a subatmospheric pressure.

The aqueous salt solution prepared above is introduced 5 into the autoclave. After 3 nitrogen purges by pressurizing to 4«105 Pa followed by decompression, the aqueous salt solution is concentrated from 60 % by weight to 70 % by weight over 30 minutes by evaporating off part of the water present in the mixture at atmospheric pressure; the temperature then reaches 110.5°C.

The following stages are then carried out in succession: Stage 1: The temperature of aqueous solution containing 70 % by weight of salt is raised to T1 = 179°C over 50 minutes while autogenous pressure is maintained. A pressure of 0.7 MPa (P) is then attained. The water present in the reaction mass is then distilled off at a constant pressure of 0.7 ± 0.02 MPa for 1 hour 55 minutes, so as to attain a mass temperature equal to T2 = 216°C; Stage 2: Decompression down to atmospheric pressure is carried out over 1 hour 45 minutes and the temperature of the mass is raised at the same time to the value T3 = 261°C while a steady distillation of water continues to be ensured; Stage 3: The temperature of the mass is then raised to 280°C and the polycondensation is finished while continuing to stir - 20 the mass at 280°C at atmospheric pressure for 30 minutes. Stirring is stopped and a nitrogen pressure is then established in the autoclave and the polymer is drawn off. The latter, extruded from the autoclave in the form of a rod is cooled by passing through a cold water bath and is then granulated and dried.

The polymer obtained is transparent and homogeneous. It has a viscosity index of 127 ml/g. 2) Preparation of the blend in accordance with the invention: The following constituents are brought into direct contact for 10 minutes at 23°C by operating in an Engelsmann model Roule Fut mixer rotating at 20-30 revolutions/minute: (i) 75 parts by weight of granules of amorphous semiaromatic polyamide prepared as shown in section 1), and (ii) 25 parts by weight of nylon 66 granules.

The premix obtained is then kneaded and homogenized in the molten state in a Leistritz trademark extruder with two screws rotating jointly, comprising screws of diameter D equal to 34 mm and with a length equal to 35 D and comprising a feed zone, a heated mixing zone and a 4-mm diameter die. The running parameters of the extruder are the following: - mixing zone temperature: 280°C, - die temperature : 280°C, - speed of rotation - 21 of the screws : 200 revolutions/minute, - material throughput : 10 kg/hour, - residence time : approximately 2 minutes.

At the exit of the extruder a rod is obtained, which is 5 cooled and cut into granules approximately 5 mm in length and 4 mm in diameter.

The blend of polyamides according to the invention which is thus obtained in the form of granules is amorphous: it exhibits a Tg of 106°C but no melting point, and it is transparent; the morphology of the blend and its Tg are established by differential calorimetric analysis (DSC) with the aid of a Mettler apparatus of the DSC 30 type (measurement on reheating with a temperature rise of 20°C/minute). The melt viscosity of the blend, determined with the aid of a capillary viscometer of registered trademark Instron 3211, equipped with a die which has a length/diameter ratio equal to 60, is 324 Pa s at 300°C and at a shear rate of 240 s”1.

Charpy impact tests are carried out in order to test the resilience properties of the articles obtained from granules of a blend according to the invention which have been obtained: the resiliences are measured (in kJ/m2) at various temperatures on notched bar-type test specimens according to the specifications of NF standard T 51035, the operation being carried out with test specimens conditioned at RH0 (0 % relative humidity). The test specimens employed were prepared by injection moulding with the aid of a Battenfeld - 22 trademark screw-plunger machine BSKM 100/70 DS 2000 under the following conversion conditions: material temperature (temperature of the coldest zone 5 and of the hottest zone) : 280 - 310°C, mould temperature : 80°C, injection material pressure : 6 MPa, holding pressure : 3 MPa.

Injection-moulded test specimens exhibit a perfect transparency state and the results of the Charpy impact tests are collated in the table which follows. It should be noted that moulded test specimens which have the same transparency and give the same impact strength values are obtained when the material temperature is lowered to lie in the range: 270-290°C when the blend according to the invention is converted with the aid of the Battenfeld screwplunger machine.

By way of comparison (test A), the same operations as those described above (passing through a twin-screw extruder followed by moulding test specimens) were reproduced, but this time operating with the amorphous semiaromatic polyamide by itself.

At the exit of the extruder the polymer obtained has a Tg of 142°C and its melt viscosity is 391 Pa s. The results of the Charpy impact tests are collated in the table which follows.

By way of further comparison (test B), the same - 23 operations as those described in the example were reproduced, but this time starting with the following constituents: (i) 50 parts by weight of semiaromatic polyamide and (ii) 50 parts by weight of nylon 66.

At the exit of the extruder the mixture obtained is no longer amorphous: it has a Tg of 82°C and a melting point of 248°C. The results of the impact tests are collated in the table which follows.

By way of further comparison (test C), the same 10 operations as those described in the example were reproduced, but replacing the semiaromatic polyamide used in this example with the same quantity (75 % by weight) of an amorphous semiaromatic polyamide obtained according to a conventional nylon 66 type process of bulk polycondensation in the melt, from hexamethylenediamine, isophthalic acid (70 mol% in the mixture of the diacids) and terephthalic acid (30 mol% in the mixture of the diacids), exhibiting a viscosity index of 112 ml/g (determined as shown in the description on a solution of the polymer in meta-cresol).

By way of further comparison (test D), test C above was reproduced, but this time using the amorphous semiaromatic polyamide by itself. Results of the impact strength measurements in tests C and D are collated in the table which follows. - 24 TABLE EXAMPLE/ CHARPY RESILIENCE (*) TEST in kJ/m2 23°C 10°C 0°C -10°C -25°C 1 11.1 10.9 11.1 10.9 10.9 A 9.8 9.6 8.9 8.6 7.4 B 5.9 5.4 6.4 8.3 6.8 C 6.4 7.6 a a 7.1 D 12.4 12.2 a a 10.9 (*) Each value shown is the average of 10 measurements which were carried out. a Value not measured.

Claims (11)

1. A single-phase, amorphous polyamide blend comprising: (i) an amorphous semiaromatic polyamide, which may be a homo- or a copolymer, comprising repeat units of formulae: -NH-CH2-CH-CH 2 -CH 2 -CH 2 -NH- (I) C 2 H 5 -hn-ch 2 -ch-ch 2 -ch 2 —nh— (II) co(III) and (IV) , the proportion of units of formula (II) being from 0 to 15 mol% and that of units of formula (I) being from 100 to 85 mol% based on the total of units of formulae (I) and (II) ; the proportion of units of formula (IV) being from 0 to 90 mol%, and that of units of formula (III) being from 100 to 10 mol% based on the total of units of formulae (III) and (IV); and the molar ratio of units of formulae (I) and (II) to units of formulae (III) and (IV) being equal to 1; and - 26 (ii) a semicrystalline polyamide of nylon type, which may be a homo- or copolymer, chosen from: nylon 66 (polymer of hexamethylenediamine and of adipic acid), nylon 6 (polymer of e-caprolactam), mixtures of these polymers and the copolymers obtained from the abovementioned monomers for the preparation of nylons 66 and 6; the quantity of the semicrystalline polyamide (ii) being not more than 40 % of the combined weight of the semiaromatic polyamide (i) and the semicrystalline polyamide (ii).

2. A blend according to claim 1, in which, in the amorphous semiaromatic polyamide (i), the proportion of units of formulae (II) in the mixture of units of formulae (I) + (II) lies in the range from 0 to 5 mol%, and that of the units of formulae (I) lies in the range from 100 to 95 mol% on the same basis; the proportion of units of formula (IV) in the mixture of units of formulae (III) + (IV) lies in the range from 0 to 85 mol%, and that of the units of formula (III) lies in the range from 100 to 15 mol% on the same basis; - and the viscosity index (VI) of the said polyamide (i), measured according to ISO standard R 307 (2nd edition of 1984) in meta-cresol at 25°C on a solution containing 0.5 g of polymer (dried for 2 hours at 60°C under argon purging) in 100 cm 3 of meta-cresol, is at least equal to 90 ml/g.

3. A blend according to claim 2, in which, in the amorphous semiaromatic polyamide (i) the proportion of units of formula (IV) in the mixture of units of formulae (III) + - 27 (IV) lies in the range from 60 to 85 mol% and that of the units of formula (III) lies in the range from 40 to 15 mol% on the same basis; - and the said VI is between 100 ml/g and 150 ml/g.

4. A blend according to any one of claims 1 to 3, in which the semicrystalline polyamide of nylon type has a viscosity index (VI), measured according to ISO standard R 307 (2nd edition of 1984) on the part which is soluble in formic acid of 90 % purity by weight, which is at least equal to 120 ml/g.

5. A blend according to claim 4, in which the semicrystalline polyamide of nylon type consists of a nylon 66 (polymer of hexamethylenediamine and adipic acid) having a VI of between 130 ml/g and 180 ml/g.

6. A blend according to any one of claims 1 to 5, in which the proportion of the semicrystalline polyamide (ii) represents 10 to 40 % of the combined weight of the semiaromatic polyamide (i) and the semicrystalline polyamide (ii) ·

7. A blend according to claim 6, in which the said proportion of the semicrystalline polyamide (ii) lies between 20 % and 35 % by weight.

8. Process for the preparation of a polyamide blend according to any one of claims 1 to 7, which comprises first stirring the constituents together at room temperature (23°C) in a conventional fast mixer for powder or granules, and then homogenizing this premix by blending in the melt ,ε 909507 - 28 phase, at a temperature in the range from 270°C to 290°C, in a device permitting the blending of plastics in the molten state.

9. Process according to claim 8 substantially as described in the foregoing Example.

10. A polyamide blend when produced by the process of claim 8 or 9.

11. A shaped article obtained from a blend according to any one of claims 1 to 7 or 10.