AU2005200952A1

AU2005200952A1 - Process for the manufacture of polyamide-12 powder with a high melting point

Info

Publication number: AU2005200952A1
Application number: AU2005200952A
Authority: AU
Inventors: Karine Loyen; Francois-Xavier Pauly; Holger Senff
Original assignee: Arkema SA
Current assignee: Arkema SA
Priority date: 2004-03-02
Filing date: 2005-03-02
Publication date: 2005-09-22
Anticipated expiration: 2025-03-02
Also published as: ATE422512T1; DE602005012638D1; KR100638535B1; JP2005248180A; CA2498712C; CA2498712A1; AU2005200952B2; EP1571173B1; IL167198A; JP2012017476A; KR20060076759A; JP4886991B2; TWI293637B; CN1690103A; TW200600525A; FR2867190A1; DK1571173T3; PT1571173E; KR20060043341A; EP1571173A1

Abstract

Method for preparing polyamide-12 powder (A) by anionic polymerization of lauryl lactam (I) dissolved in a solvent in which (A) is insoluble. Method for preparing polyamide-12 powder (A) by anionic polymerization of lauryl lactam (I) dissolved in a solvent in which (A) is insoluble. Polymerization is done in presence of (a) a catalyst or activator (II); (b) a finely divided organic or inorganic filler (III), at not over 1.5 g per kg of (I), and (c) amide R1NHCOR2 (IV), at 0.001-0.03 mole per kg (I). R1 : aryl, alkyl, cycloalkyl, R3CONH or R3O; R2 and R3 : alkyl, aryl or cycloalkyl .

Description

P001 Section 29 Regulation 3.2(2)

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Application Number: Lodged: Invention Title: Process for the manufacture of polyamide-12 powder with a high melting point The following statement is a full description of this invention, including the best method of performing it known to us: The present invention relates to a process for the preparation of polyamide-12 powder with a high melting point. It is a synthesis of anionic type starting from lauryllactam. The powders obtained have a diameter of between 15 pm and 100 gm and a melting point of at least 180 0 C. These polyamide-12 powders are of use in numerous applications and in particular in the technology of polyamide powder sintering by melting caused by radiation, such as, for example, a laser beam (laser sintering), infrared radiation or UV radiation (UV curing).

The technology of the sintering of polyamide powders under a laser beam is used for the manufacture of objects in three dimensions, such as prototypes and models. A fine layer of polyamide powder is deposited on a horizontal plate held in a chamber heated to a temperature lying between the crystallization temperature Tc and the melting point Tm of the polyamide powder. The laser sinters powder particles at various points of the powder layer according to a geometry corresponding to the object, for example using a computer which has the shape of the object in its memory and which reconstructs this shape in the form of slices. The horizontal plate is subsequently lowered by a value corresponding to the thickness of a layer of powder (for example, between 0.05 and 2 mm and generally of the order of 0.1 mm) and then a new layer of powder is deposited and the laser sinters powder particles according to a geometry corresponding to this new slice of the object, and so on. The procedure is repeated until the complete object has been manufactured. A block of powder is obtained within which the object is present. The parts which have not been sintered have thus remained in the powder state.

Subsequently, the combination is gently cooled and the object solidifies as soon as its temperature falls below the crystallization temperature Tc. After cooling 2 is complete, the object is separated from the powder, which can be used in another operation.

It is recommended for the powder to have a difference Tm Tc which is as large as possible in order to avoid deformation (or curling) phenomena during manufacture.

This is because, at time to immediately after the action of the laser beam, the temperature of the sample is greater than the crystallization temperature (Tc) of the powder but the introduction of a new colder powder layer causes the temperature of the component to rapidly fall below Tc and results in deformations.

Furthermore, an enthalpy of fusion (AHf) which is as high as possible is required in order to obtain good geometrical definition of the components manufactured.

This is because, if the enthalpy of fusion is too low, the energy supplied by the laser is sufficient to cake, by thermal conduction, the powder particles close to the walls being constructed, and thus the geometrical precision of the component is no longer satisfactory.

It is clear that everything which has just been explained for the sintering of polyamide powders under a laser beam is valid whatever the radiation which brings about the melting.

Patent US 6 245 281 discloses the use of polyamide-12 (PA 12) powders in the technology of the sintering of powders under a laser beam. These powders are such that their Tm is between 185 and 189 0 C, their Tc is between 138 and 143 0 C and their AHf has a value of 112 17 J/g. These powders are manufactured according to the process disclosed in Patent DE 2906647 US 4 334 056). In the latter, PA-12 is first manufactured, is dissolved in ethanol between 130 and 150 0 C, and is then gently cooled below 125 0 C with stirring. The PA-12 precipitates in the powder form.

3 Patent EP 192 515 discloses the anionic polymerization of a lactam in a stirred reactor in a solvent in the presence of an N,N'-alkylenebisamide and of an organic or inorganic filler (for example, silica powder). The proportion of silica is from 1.7 to 17 g per 1000 g of lauryllactam. The reaction is carried out between 100 and 1200C. The polyamide-12 powder is collected by settling in the bottom of the reactor. A polyamide-12 powder with a melting point of 177 1°C is obtained.

This temperature is insufficient for the application in the manufacture of objects by the abovementioned sintering processes.

It has now been discovered that, by bringing the proportion of the organic or inorganic filler to less than or equal to 1.5 g per 1000 g of lauryllactam, the amount of amide of formula RI-NH-CO-R 2 in which RI can be replaced by an R 3 -CO-NH- or R 3 radical and in which RI, R 2 and R 3 denote an aryl, alkyl or cycloalkyl radical (preferably, the amide is the N,N'-alkylenebisamide) being less than 0.030 mol per 1000 g of lauryllactam, a polyamide-12 powder with a melting point of at least 1800C was obtained. Advantageously, the proportion of the organic or inorganic filler is between 0.05 and 1.5 g per 1000 g of lauryllactam.

Preferably, it is between 0.2 and 1.5 g per 1000 g of lauryllactam, indeed even more advantageously still between 0.35 and 1.3 g per 1000 g of lauryllactam, indeed even more preferably still between 0.35 and 0.9 g per 1000 g of lauryllactam.

It is also advantageous for the polymerization to be initiated at a temperature at which the solvent is in a state of supersaturation with lactam.

The present invention relates to a process for the preparation of polyamide-12 powder by anionic polymerization of lauryllactam in solution in a solvent of the said lactam, the polyamide-12 powder being 4 insoluble in this solvent, the said polymerization being carried out: in the presence of a catalyst and of an activator; in the presence of a finely divided organic or inorganic filler, the proportion of this filler being less than or equal to 1.5 g per 1000 g of lauryllactam; and in the presence of an amide of formula Ri-NH-CO-R 2 in which RI can be replaced by an R 3 -CO-NH- or

R

3 radical and in which RI, R 2 and R 3 denote an aryl, alkyl or cycloalkyl radical, the proportion of this compound being between 0.001 mol and 0.030 mol per 1000 g of lauryllactam.

According to one embodiment, the finely divided organic or inorganic filler is silica.

According to one embodiment, the proportion of the finely divided organic or inorganic filler is between 0.05 and 1.5 g per 1000 g of lauryllactam. It can also be between 0.2 and 1.5 g per 1000 g of lauryllactam, indeed even between 0.35 and 1.3 g per 1000 g of lauryllactam, indeed even also between 0.35 and 0.9 g per 1000 g of lauryllactam.

According to one embodiment, the amide is chosen from ethylenebisstearamide (EBS) and ethylenebisoleamide

(EBO).

According to one embodiment, the proportion of amide is between 0.002 mol and 0.022 mol per 1000 g of lauryllactam, indeed even between 0.005 mol and 0.020 mol per 1000 g of lauryllactam.

According to one embodiment, the polymerization is initiated at a temperature at which the solvent is in a state of supersaturation with lactam.

5 According to one embodiment, the polymerization is carried out in the presence of colouring pigments, of Ti02, of glass fibre, of carbon fibre, of nanofill, of nanoclay, of carbon nanotube, of pigments for infrared absorption, of carbon black, of inorganic filler or of flame-retardant additive.

The invention also relates to a process for the manufacture of objects made of polyamide-12 by sintering of powders by melting caused by radiation, the powders having been obtained according to the process described above.

Furthermore, it relates to the use of PA-12 powder obtained by the preparation process described above to manufacture objects.

The melting point of the polyamide-12 powder is at least 180 0 C and advantageously 183 1 0 C (temperature of first warming measured by DSC, abbreviation of Differential Scanning Calorimetry, according to Standard IS011357 at 20 0 C/min). The enthalpy of fusion (1st warming) is of the order of 114 4 J/g. The crystallization temperature is of the order of 135 1 0 C. The powder particles have a mean size of between and 100 gm and advantageously between 25 and 60 gm.

The process can be carried out in a stirred reactor equipped with a device for heating by a jacket or a coil, with an emptying system, such as a bottom valve, and with a device for introducing the reactants flushed with dry nitrogen. The process can be carried out continuously or batchwise.

There are numerous advantages to this process. The powder is obtained directly without an additional stage of retreatment or of dissolution/precipitation. The size of the powder particles can be adjusted by the parameters of the process and narrow particle size 6 distribution makes it possible to eliminate the phenomena of dust when the powder is used.

The flexibility of the Orgasol process disclosed in Patent EP 192 515 is retained, which is another advantage: on the one hand, the mean size of the powder can be adjusted by the conventional parameters of the process which are disclosed in Patent EP 192 515 (see Table on the other hand, the molecular masses can be adjusted while retaining the particle size distribution and the high melting point for the application (see Table 2).

Another advantage of this direct process is that it makes it possible to introduce, into the body of the material, additives which will contribute to improving the applicative properties of the powder. Mention may be made, for example, of pigments for colouring, TiO 2 fillers or pigments for infrared absorption, carbon black, inorganic fillers for reducing internal stresses and flame-retardant additives. It is also possible to add additives which make it possible to improve the mechanical properties (breaking stress and elongation at break) of the components obtained by melting. These fillers are, for example, glass fibres, carbon fibres, nanofillers, nanoclays and carbon nanotubes. The introduction of these fillers during the synthesis makes it possible to improve their dispersion and their effectiveness. The very narrow particle size distribution of these powders promotes their use in the manufacture of components by sintering under radiation (infrared, UV curing, and the like) because it results in very fine definition of the components and because it reduces the problems of formation of dust when the powder is used. Furthermore, the molecular mass of the polymer does not increase, not even after lengthy exposure to temperatures close to and below the melting point of the powder (see Table 3 below). This implies that the powder can be recycled a number of times 7 without modification to its behaviour during the manufacture of components by sintering under radiation, the properties of the said components not varying also during the process. In addition, this process makes possible the manufacture of objects by powder sintering having good mechanical properties (see Table 2 below).

The present invention also relates to a process for the manufacture of objects made of polyamide-12 by powder sintering by melting by using radiation, the PA-12 powder having been obtained beforehand according to the abovementioned process. Mention may be made, as example of radiation, of that supplied by a laser beam (the process is then known as laser sintering). Mention may also be made of the process in which a mask is positioned between the layer of powder and the source of the radiation; the powder particles protected from the radiation by the mask are not sintered.

As regards the solvent, this is a solvent of the lactam. In contrast, the polyamide-12 powder is insoluble in this solvent. Such solvents are mentioned in Patent EP 192 515. The solvent is advantageously a paraffinic hydrocarbon cut having a boiling range between 140 and 1700C.

As regards the catalyst, this is a base which is sufficiently strong to form a lactamate. Mention may be made, as examples of catalyst, of sodium, potassium, alkali metal hydrides and hydroxides, or alkali metal alkoxides, such as sodium methoxide or ethoxide.

As regards the activator, this term is used to denote any product capable of bringing about and/or accelerating polymerization. Mention may be made, as examples, of N-carboxyanilide lactams, isocyanates, carbodiimides, cyanimides, acyllactams, triazines, ureas, N-substituted imides or esters. The activator 8 can be formed in situ, for example an acyllactam is obtained by adding an alkyl isocyanate to the lactam.

The ratio of the catalyst to the activator, in moles, can be between 0.2 and 2 and preferably between 0.8 and 1.2. The proportion of catalyst in the lactam can be between 0.1 and 5 mol, preferably between 0.3 and per 100 mol of lactam.

As regards the finely divided organic or inorganic filler, its size can be between 0.01 gm and 30 pm and preferably between 0.01 and 10 gm. This filler can be added to the reactor after the introduction of the solvent. This filler can, for example, be silica. The proportion of this filler is advantageously between 0.35 and 0.9 g per 1000 g of lauryllactam. The lower the proportion of the organic or inorganic filler, the greater the size of the polyamide-12 powder.

As regards the amide, the copolymerization is carried out in the presence, generally, of amides of formula

R

1

-NH-CO-R

2 in which RI can be replaced by an R 3

-CO-NH-

or R 3 radical and in which RI, R 2 and R 3 denote an aryl, alkyl or cycloalkyl radical and in particular of an N,N'-alkylenebisamide, such as ethylenebisstearamide (EBS) or ethylenebisoleamide (EBO), which are disclosed in EP 192 515.

As regards more particularly the amides of formula

R

1

-NH-CO-R

2 and the R 1

R

2 and R 3 radicals, examples of aryl radicals can be phenyl, para-tolyl or a-naphthyl.

Examples of alkyls can be methyl, ethyl, n-propyl and n-butyl radicals and an example of a cycloalkyl radical is cyclohexyl. The preferred amides are those in which

R

1 and R 2 which are identical or different, are phenyl or an alkyl having at most 5 carbon atoms, it being possible for RI to be replaced by R 3 and R 3 being an alkyl having at most 5 carbon atoms. Mention may be made, for example, of acetanilide, benzanilide, 9 N-methylacetamide, N-ethylacetamide, N-methylformamide and (4-ethoxyphenyl)acetamide. Other preferred amides are alkylenebisamides, such as ethylenebisstearamide (EBS) and ethylenebisoleamide (EBO). It would not be departing from the scope of the invention to carry out a polymerization in the presence of two or more amides.

The lower the proportion of amide, the higher the molar mass of the powder. The higher the molar mass of the powder, the better the mechanical properties of the objects manufactured with these powders and in particular the better the elongation at break.

Advantageously, the process described above is carried out batchwise: the solvent and then, simultaneously or successively, the lactam, the amide, the divided filler, the catalyst and the activator are introduced.

It is recommended to introduce first the solvent and the lactam (or the lactam in solution in the solvent), then to remove any trace of water and, when the medium is perfectly dry, to introduce the catalyst. Traces of water may be removed by azeotropic distillation. The activator is subsequently added. The divided filler can be introduced, for example, after the introduction of the lactam. The amide can be introduced, for example, after the introduction of the lactam. The process is carried out at atmospheric pressure and at a temperature of between 200C and the boiling point of the solvent. It is recommended for the solvent to be in a state of supersaturation with lactam, that is to say that it is recommended to carry out the process at a temperature below the temperature for crystallization of the lactam in the solvent. Above this temperature, the lactam is soluble; below, lactam seeds appear: it is this which makes it possible to increase the melting point of the polyamide-12 powder. This supersaturation temperature is determined using the usual techniques.

The supersaturation of the solvent with lactam is also disclosed in Patent EP 303 530. The duration of the reaction depends on the temperature and decreases when 10 the temperature increases. It is usually between 1 h and 12 h. The reaction is total; all the lactam is consumed. On conclusion of the reaction, the solvent and the powder are separated by filtration or centrifuging and then the powder is dried.

According to an advantageous form of the invention, first the solvent and the lactam are introduced, separately or simultaneously, and then, after removing possible water, the catalyst is introduced.

Subsequently, the activator is introduced, either continuously or portionwise. Although stages of the process are continuous, it is described as "batchwise" because it is broken down into cycles beginning with the introduction of the solvent into the reactor and terminating with the separation of the PA powder and the solvent.

In Examples 1, 2, 4 and 5 below, the purpose of which is to illustrate the invention without, however, limiting it, the tests were carried out in a reactor with a capacity of 5 litres equipped with a paddle stirrer, with a jacket in which the heating oil circulates, with a system for emptying via the bottom and with a lock chamber for introducing the reactants which is flushed with dry nitrogen. A device for azeotropic distillation under vacuum makes it possible to remove any trace of water from the reaction medium.

Ex. 3 of EP-192 515 is a comparative example.

Example 1: 2800 ml of the solvent and then, successively, 899 g of dry lauryllactam, 14.4 g of EBS and 0.72 g of finely divided and dehydrated silica are introduced into the reactor maintained under nitrogen. After having begun stirring at 300 revolutions/min, the mixture is gradually heated up to 110 0 C and 290 ml of solvent are 11 distilled off under vacuum in order to azeotropically entrain any trace of water which might be present.

After returning to atmospheric pressure, the anionic catalyst, 1.44 g of sodium hydride with a purity of in oil, is then rapidly introduced under nitrogen and stirring is increased to 350 revolutions/min under nitrogen at 1100C for 30 minutes.

Subsequently, the temperature is brought back to 1000C and the chosen activator, namely stearyl isocyanate, is continuously injected into the reaction medium using a small metering pump according to the following programme: 10.7 g of isocyanate over 60 minutes; 17.7 g of isocyanate over 132 minutes; At the same time, the temperature is maintained at 1000C during the first 60 minutes, it is then raised to 1200C over 30 minutes and is maintained at 1200C for a further 2 hours after the end of introduction of the isocyanate.

The polymerization is then terminated. After cooling to 0 C, separation by settling and drying, the polyamide-12 powder obtained exhibits the following characteristics: intrinsic viscosity: 0.99; particle size of between 14 and 40 gm with the mean diameter of the particles being 24 gm, without agglomerates; and the reactor is virtually clean.

Example 2: 2800 ml of the solvent and then, successively, 899 g of dry lauryllactam, 7.2 g of EBS and 0.36 g of finely divided and dehydrated silica are introduced into the reactor maintained under nitrogen. After having begun stirring at 300 revolutions/min, the mixture is 12 gradually heated up to 1100C and 290 ml of solvent are distilled off under vacuum in order to azeotropically entrain any trace of water which might be present.

Subsequently, the temperature is brought back to 100.2 0 C and the chosen activator, namely stearyl isocyanate, is continuously injected into the reaction medium using a small metering pump according to the following programme: 10.7 g of isocyanate over 60 minutes; 17.7 g of isocyanate over 132 minutes; At the same time, the temperature is maintained at 100.2 0 C during the first 60 minutes, it is then raised to 120 0 C over 30 minutes and is maintained at 1200C for a further 2 hours after the end of introduction of the isocyanate.

The polymerization is then terminated. After cooling to 0 C, separation by settling and drying, the polyamide-12 powder obtained exhibits the following characteristics: intrinsic viscosity: 1.12; particle size of between 3.5 and 170 um with the mean diameter of the particles being 51 gm, without agglomerates; and the reactor is virtually clean.

Example 4: 2800 ml of the solvent and then, successively, 899 g of dry lauryllactam, 4.95 g of EBS and 0.36 g of finely divided and dehydrated silica are introduced into the reactor maintained under nitrogen. After having begun stirring at 300 revolutions/min, the mixture is 13 gradually heated up to 1100C and 290 ml of solvent are distilled off under vacuum in order to azeotropically entrain any trace of water which might be present.

After returning to atmospheric pressure, the anionic catalyst, 1.79 g of sodium hydride with a purity of in oil, is then rapidly introduced under nitrogen and stirring is increased to 400 revolutions/min under nitrogen at 110 0 C for 30 minutes. Subsequently, the temperature is brought back to 100.5 0 C and the chosen activator, namely stearyl isocyanate, is continuously injected into the reaction medium using a small metering pump according to the following programme: 3.6 g of isocyanate over 60 minutes; 5.9 g of isocyanate over 132 minutes; At the same time, the temperature is maintained at 100.5 0 C during the first 60 minutes, it is then raised to 120 0 C over 30 minutes and is maintained at 1200C for a further 2 hours after the end of introduction of the isocyanate.

The polymerization is then terminated. After cooling to 800C, separation by settling and drying, the polyamide-12 powder obtained exhibits the following characteristics: intrinsic viscosity: 1.48; particle size of between 15 and 120 m with the mean diameter of the particles being 30 gm, without agglomerates; and the reactor is virtually clean.

Example 2800 ml of the solvent and then, successively, 899 g of dry lauryllactam, 9.0 g of EBS and 0.36 g of finely divided and dehydrated silica are introduced into the reactor maintained under nitrogen. After having begun stirring at 300 revolutions/min, the mixture is 14 gradually heated up to 110 0 C and 290 ml of solvent are distilled off under a vacuum of 50 mbar in order to azeotropically entrain any trace of water which might be present.

After returning to atmospheric pressure, the anionic catalyst, 1.44 g of sodium hydride with a purity of in oil, is then rapidly introduced under nitrogen and stirring is increased to 400 revolutions/min under nitrogen at 110 0 C for 30 minutes. Subsequently, the temperature is brought back to 100.40C and the chosen activator, namely stearyl isocyanate, is continuously injected into the reaction medium using a small metering pump according to the following programme: 10.7 g of isocyanate over 60 minutes; 17.7 g of isocyanate over 132 minutes; At the same time, the temperature is maintained at 100.40C during the first 60 minutes, it is then raised to 120 0 C over 30 minutes and is maintained at 1200C for a further 2 hours after the end of introduction of the isocyanate.

The polymerization is then terminated. After cooling to 0 C, separation by settling and drying, the polyamide-12 powder obtained exhibits the following characteristics: intrinsic viscosity: 1.10; particle size of between 15 and 120 Am with the mean diameter of the particles being 40 Am, without agglomerates; and the reactor is virtually clean.

The results are collated in Tables 1 to 3 below.

15 Table 1 Powders Melting Enthalpy Crystal- Molecular Mean size point of lization mass of the TM, fusion, tempera- Mw powder 1st 1st ture Tc (g/mol) particles warming warming (OC) (AM) (OC) (J/g) Ex. 3 of 177 1 110 #26 000

EP

192 515 Example 184 1 117 135 1 25 500 Example 183 1 112 135 1 47 500 4 Example 183 1 109 135 1 23 000 24 1 Example 184 1 118 135 1 30 500 51 2 Table 2 Ex. 3 of Example 4 powder EP 192 515 Breaking stress or maximum stress 43-44 MPa 40 MPa on component Elongation at 8% break__ The mechanical properties were measured according to Standard ISO 527-2, at a pull rate of 50 mm/mmn.

16 Table 3 Powders Molecular Molecular mass mass Mw Mw (g/mol) after 8 h at 150 0

C

(g/mol) Polyamide-12 32 780 45 750 (obtained by polycondensation) Ex. 3 of 25 150 22 550 EP 192 515 Example 13 000 21 500 23 000 21 500 The average molecular masses Mw were measured by steric exclusion chromatography. The analysis was carried out in benzyl alcohol at 130 0 C. The average molecular masses Mw are expressed as polyamide-12 equivalent.

Claims

1. Process for the preparation of polyamide-12 powder by anionic polymerization of lauryllactam in solution in a solvent of the said lactam, the polyamide-12 powder being insoluble in this solvent, the said polymerization being carried out: in the presence of a catalyst and of an activator; in the presence of a finely divided organic or inorganic filler, the proportion of this filler being less than or equal to 1.5 g per 1000 g of lauryllactam; and in the presence of an amide of formula Ri-NH-CO-R 2 in which RI can be replaced by an R 3 -CO-NH- or R 3 radical and in which RI, R 2 and R 3 denote an aryl, alkyl or cycloalkyl radical, the proportion of this compound being between 0.001 mol and 0.030 mol per 1000 g of lauryllactam.

2. Process according to Claim 1, in which the finely divided organic or inorganic filler is silica.

3. Process according to either one of the preceding claims, in which the proportion of the finely divided organic or inorganic filler is between 0.05 and 1.5 g per 1000 g of lauryllactam.

4. Process according to either of Claims 1 and 2, in which the proportion of the finely divided organic or inorganic filler is between 0.2 and 1.5 g per 1000 g of lauryllactam.

Process according to any one of the preceding claims, in which the proportion of the finely divided organic or inorganic filler is between 0.35 and 1.3 g per 1000 g of lauryllactam.

6. Process according to any one of the preceding claims, in which the proportion of the finely divided 18 organic or inorganic filler is between 0.35 and 0.9 g per 1000 g of lauryllactam.

7. Process according to any one of the preceding claims, in which the amide is chosen from ethylenebisstearamide (EBS) and ethylenebisoleamide (EBO).

8. Process according to one of Claims 1 to 7, in which the proportion of amide is between 0.002 mol and 0.022 mol per 1000 g of lauryllactam.

9. Process according to one of Claims 1 to 7, in which the proportion of amide is between 0.005 mol and 0.020 mol per 1000 g of lauryllactam.

Process according to any one of the preceding claims, in which the polymerization is initiated at a temperature at which the solvent is in a state of supersaturation with lactam.

11. Process according to one of the preceding claims, characterized in that the said polymerization is carried out in the presence of colouring pigments, of Ti0 2 of glass fibre, of carbon fibre, of nanofiller, of nanoclay, of carbon nanotube, of pigments for infrared absorption, of carbon black, of inorganic filler or of flame-retardant additive.

12. Process for the manufacture of objects made of polyamide-12 by sintering of powders by melting caused by radiation, the powders having been obtained according to the process of any one of the preceding claims.

13. Use of PA-12 powder obtained by the preparation process according to one of Claims 1 to 11 to manufacture objects. Dated this 2 nd day of March, 2005 Arkema WATERMARK PATENT TRADEMARK ATTORNEYS 290 BURWOOD ROAD HAWTHORN VICTORIA 3122