EP3417003A1

EP3417003A1 - Process for preparing polyamide powders by precipitation

Info

Publication number: EP3417003A1
Application number: EP17705862.5A
Authority: EP
Inventors: Angela Ulzhoefer; Simon Gramlich; Rainer Ostermann; Achim Stammer; Dirk Simon; Ning Zhu
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2016-02-19
Filing date: 2017-02-16
Publication date: 2018-12-26
Also published as: CN108602959A; JP2019507225A; IL261080A; US20210206919A1; TW201800450A; KR20180109942A; SG11201806152XA; CA3013565A1; WO2017140773A1; AU2017219199A1; MX2018010015A; IL261080B

Abstract

The invention relates to a method for producing polyamide powders and the polyamide powder obtained according to said method. The invention also relates to the use of polyamide powder in the form of a sintered powder during selective laser sintering.

Description

Process for the preparation of polyamide powders by precipitation The present invention relates to a process for the production of polyamide powders and the polyamide powder obtainable by this process.

Polyamides are characterized by high chemical resistance and very good mechanical properties. It is known to use powdered coating compositions based on polyamides for producing paint-like coatings of metals. The coating takes place here, for example, by vortex sintering process, flame spraying or by electrostatic coating process. In this case, preference is given to polyamide powders which have a narrow particle size distribution, a round shape and a smooth surface. Polyamide powders which fulfill the abovementioned properties are readily fluidisable and therefore particularly suitable for coating processes. The polyamide powders described above are usually prepared by precipitation processes.

DE 29 06 647 describes a process for the preparation of coating powders based on polyamides having at least 10 aliphatically bonded carbon atoms per Carboamidgruppe. To prepare the polyamide powder, the polyamides are dissolved under pressure at temperatures in the range of 130 to 150 ° C in ethanol. Subsequently, this solution is cooled to temperatures in the range of 100 to 125 ° C, wherein the polyamide precipitates in powder form. The polyamide powder is subsequently filtered off and dried. The polyamide powders obtainable by the process according to DE 29 06 647 have a relatively broad particle size distribution in the range from 40 to 250 μm.

DE 1 494 563 describes a process for the preparation of polyamide powders dyed with pigments. The polyamides described in DE 1 494 563 are polyamides of ε-caprolactam, of ω-aminoundecanoic acid and of polyamides of hexamethylenediamine and adipic acid. To prepare the colored polyamide powder, the polyamide is dissolved together with a pigment dispersion in an organic solvent. The mixture is heated to temperatures of> 100 ° C for this purpose. Subsequently, the solution thus obtained is cooled, wherein the polyamide precipitates together with the pigment as a powder. The dyed polyamide powder is subsequently filtered off and dried. The process described in DE 1 494 563 also gives polyamide powders which have a relatively broad particle size distribution. EP 0 863 174 likewise describes a process for the preparation of polyamide powders by precipitation processes. The polyamide component used are polyamides of lactams or ω-aminocarboxylic acids containing at least 10 carbon atoms. These polyamides are dissolved in an aliphatic alcohol having 1 to 3 carbon atoms under pressure. For this purpose, the solution is heated under pressure to 130 to 165 ° C. Subsequently, this solution is first cooled to a so-called nucleation temperature and held at this temperature for 10 minutes to 2 hours. Subsequently, the solution is further cooled, wherein the polyamide powder precipitates. The polyamide powder is subsequently filtered off and dried. According to the process according to EP 0 863 174, polyamide powders having a relatively narrow particle size distribution are obtained. One disadvantage of the process according to EP 0 863 174 is that very high pressures are necessary to achieve temperatures in the range from 130 to 165 ° C. when using alcohols as solvents. As a result, the process according to EP 0 863 174 is complicated and therefore expensive.

CH 549 622 describes a process for the preparation of polymer powders, in which a polymer, for example polyamide, is melted in a solid at 25 ° C organic solvent. The resulting melt is subsequently poured out, whereby the melt solidifies. The resulting solid is subsequently ground and the resulting powder is spotted. From this powder, the solid at 25 ° C organic solvent is extracted in a further process step, whereby the polymer powder is obtained. The process according to CH 549 622 is very complicated since a large number of process steps are required for the preparation of the polymer powders, including melting, solidification, production of a powder by a grinding process, screening of the powder, subsequent extraction of the solid at 25 ° C. organic solvent and drying. The method described in CH 549 622 is therefore technically extremely complex and expensive.

DE 1 089 929 describes a process for the preparation of polyamide powders for use in cosmetic and medical powders. Polyamides used are preferably polycaprolactams. The polyamides are subsequently heated in a carbamyl compound to give a clear solution of the polyamide in the carbamyl compound. Preferred carbamyl compounds are aliphatic compounds which are substituted on the nitrogen atom by alkyl groups. Particularly preferred are dimethylformamide, dimethylacetamide, diethylacetamide and acetamide. In addition, pyrrolidone is described as the cyclic carbamyl compound. For precipitation of the polyamide from the clear solution, DE 1 089 929 describes two alternatives. On the one hand it is possible to produce the polyamide powder by cooling the clear solution. As a second alternative describes the DE 1 089 929 the addition of water to the clear solution, whereby the polyamide powder precipitates. To separate the polyamide powder this is separated after precipitation from the solution and dried. The polyamide powders according to DE 1 089 929 are particularly suitable for use in cosmetic and medical powders. The polyamide powders obtained have a particle size distribution in the range from 1 to 25 μm.

The US 3,446,782 also describes a process for the preparation of polyamide powders. To prepare the polyamide powder, an aqueous solution of a lactam is initially charged and subsequently the polyamide is added. The resulting mixture is subsequently heated in an autoclave with stirring. The temperature is chosen to be above the softening point of the polyamide and below the melting point of the polyamide. The concentration of the lactam in the aqueous solution is in the range of 10 to 95 wt .-%, based on the total weight of the aqueous solution. After addition of the polyamide to the aqueous solution, a dispersion of the polyamide in the aqueous solution is obtained by stirring and heating. Subsequently, this dispersion is cooled, the resulting polyamide powder is filtered off and optionally washed with water. The high temperatures described in the process according to US Pat. No. 3,446,782 can lead to a reduction in the molecular weight of the polyamide used.

The present invention is therefore based on the object to provide a process for the preparation of polyamide powders, which does not have the disadvantages of the prior art described above or only to a reduced extent. The process should be simple and inexpensive to carry out and provide polyamide powder having a narrow particle size distribution and a spherical geometry. The process should also reduce the formation of fines or coarse fraction compared to the process described in the prior art. This object is achieved by a process for the preparation of polyamide powder comprising the process steps a) heating a mixture containing a polyamide and a lactam to a temperature greater than a turbidity temperature (T _T ) above which the polyamide is completely dissolved in the lactam, to obtain a melt , the the

Polyamide completely dissolved in the lactam contains,

b) cooling the melt obtained in process step a) to a temperature less than or equal to the clouding temperature (T _T ) and subsequently adding water to obtain a suspension containing the polyamide powder suspended in a solution containing water and the lactam, and

c) separating the polyamide powder from the suspension obtained in process step b). The process according to the invention gives polyamide powders which have a narrow particle size distribution. The particles of polyamide powder also have a round shape (sphericity). The inventive method significantly reduces the formation of fine and coarse particles in the polyamide powder in comparison with the process described in the prior art.

Polyamide As polyamide, exactly one polyamide can be used. It is also possible to use mixtures of two or more polyamides. Preferably, exactly one polyamide is used.

Suitable polyamides generally have a viscosity number of from 70 to 350, preferably from 70 to 240 ml / g. The determination of the viscosity number is carried out according to the invention from a 0.5 wt .-% solution of the polyamide in 96 wt .-% sulfuric acid at 25 ° C according to ISO 307th

As polyamides, semicrystalline or amorphous polyamides are preferred. Suitable polyamides have a weight-average molecular weight (M _w ) in the range from 500 to 2,000,000 g / mol, preferably in the range from 5,000 to 500,000 g / mol and particularly preferably in the range from 10,000 to 100,000 g / mol , The weight average molecular weight (M _w ) is determined according to ASTM D4001. As polyamides, for example, polyamides are suitable, which are derived from lactams with 7 to 13 ring members. Further suitable polyamides are polyamides which are obtained by reacting dicarboxylic acids with diamines.

Examples of polyamides derived from lactams include polyamides derived from polycaprolactam, polycapryl lactam and / or polylaurolactam.

Further suitable polyamides are obtainable from co-aminoalkyl nitriles. Preferred co-aminoalkylnitrile is aminocapronitrile, which leads to polyamide 6. Furthermore, dinitriles can be reacted with diamine. Adiponitrile and hexamethylenediamine are preferred, the polymerization of which leads to polyamide 66. The polymerization of nitriles takes place in the presence of water and is also referred to as direct polymerization.

In the case where polyamides are used which are obtainable from dicarboxylic acids and diamines, dicarboxylic acid alkanes (aliphatic dicarboxylic acids) having 6 to 36 carbon atoms, preferably 6 to 12 carbon atoms, and especially preferably 6 to 10 carbon atoms are used. In addition, aromatic dicarboxylic acids are suitable.

By way of example, adipic acid, azelaic acid, sebacic acid, dodecanedioic acid and also terephthalic acid and / or isophthalic acid may be mentioned here as dicarboxylic acids.

Suitable diamines are, for example, alkanediamines having 4 to 36 carbon atoms, preferably alkanediamines having 6 to 12 carbon atoms, in particular alkanediamines having 6 to 8 carbon atoms and aromatic diamines, for example m-xylylenediamine, di (4-aminophenyl) methane, di- (4 -aminocyclohexyl) methane, 2,2-di- (4-aminophenyl) -propane and 2,2-di- (4-aminocyclohexyl) -propane and 1, 5-diamino-2-methyl-pentane.

Preferred polyamides are polyhexamethylene adipamide, polyhexamethylene sebacamide and polycaprolactam and also copolyamide 6/66, in particular with a content of 5 to 95% by weight of caprolactam units.

Also suitable are polyamides which are obtainable by copolymerization of two or more of the monomers mentioned above and below, or mixtures of several polyamides, the mixing ratio being arbitrary. Mixtures of polyamide 66 with other polyamides, in particular copolyamide 6/66, are particularly preferred as mixtures.

Suitable polyamides are thus aliphatic, partially aromatic or aromatic polyamides. The term "aliphatic polyamides" means that the polyamides are exclusively composed of aliphatic monomers The term "partially aromatic polyamides" means that the polyamides are composed of both aliphatic and aromatic monomers. The term "aromatic polyamides" means that the polyamides are composed exclusively of aromatic monomers.

The following non-exhaustive list contains the above as well as other polyamides, which are suitable for use in the process according to the invention, as well as the monomers contained.

AB-polymers:

PA 4 pyrrolidone

PA 6 ε-caprolactam

PA 7 enantholactam

PA 8 capryllactam

PA 9 9-aminopelargonic acid PA 1 1 1 1 -aminoundecanoic acid

PA 12 laurolactam

AA / BB-polymers:

PA 46 tetramethylenediamine, adipic acid

PA 66 hexamethylenediamine, adipic acid

PA 69 hexamethylene diamine, azelaic acid

PA 610 hexamethylenediamine, sebacic acid

PA 612 hexamethylenediamine, decanedicarboxylic acid

PA 613 hexamethylenediamine, undecanedicarboxylic acid

PA 1212 1, 12-dodecanediamine, decanedicarboxylic acid

PA 1313 1, 13-diaminotridecane, undecanedicarboxylic acid

PA 6T hexamethylenediamine, terephthalic acid

PA 9T nonyldiamine, terephthalic acid

PA MXD6 m-xylyenediamine, adipic acid

PA 61 hexamethylenediamine, isophthalic acid

PA 6-3-T trimethylhexamethylenediamine, terephthalic acid

PA 6 / 6T (see PA 6 and PA 6T)

PA 6/66 (see PA 6 and PA 66)

PA 6/12 (see PA 6 and PA 12)

PA 66/6/610 (see PA 66, PA 6 and PA 610)

PA 6I / 6T (see PA 61 and PA 6T)

PA PACM 12 diaminodicyclohexylmethane, laurolactam

PA 6I / 6T / PACM such as PA 6I / 6T and diaminodicyclohexylmethane

PA 12 / MACMI laurolactam, dimethyldiaminodicyclohexylmethane, isophthalic acid

PA 12 / MACMT laurolactam, dimethyl-diaminodicyclohexylmethane, terephthalic acid PA PDA-T phenylenediamine, terephthalic acid

The present invention thus also provides a process in which the polyamide is at least one polyamide selected from the group consisting of PA 4, PA 6, PA 7, PA 8, PA 9, PA 1 1, PA 12, PA 46, PA 66, PA 69, PA 610, PA 612, PA 613, PA 1212, PA 1313, PA 6T, PA MXD6, PA 61, PA 6-3-T, PA 6 / 6T, PA 6/66, PA 6/12 , PA 66/6/610, PA 6I / 6T, PA PACM 12, PA 6I / 6T / PACM, PA 12 / MACMI, PA 12 / MACMT, PA PDA-T and copolyamides of two or more of the aforementioned polyamides.

Preferably, the polyamide is at least one polyamide selected from the group consisting of polyamide 6 (PA 6), polyamide 66 (PA 66), polyamide 610 (PA 610) and polyamide 6 / 6T (PA 6 / 6T). Particularly preferred polyamides are polyamide 6 (PA 6) and / or polyamide 66 (PA 66), with polyamide 6 (PA 6) being particularly preferred.

lactam

According to the invention, lactam is understood to mean cyclic amides which contain 3 to 12 carbon atoms, preferably 4 to 6 carbon atoms, in the ring. Suitable lactams are, for example, selected from the group consisting of 3-aminopropanoic acid lactam (β-lactam, β-propionlactam), 4-aminobutanoic acid lactam (γ-lactam, γ-butyrolactam), 5-aminopentanoic acid lactam (δ-lactam, δ-valerolactam), 6 Aminohexanoic acid lactam (ε-lactam; ε-caprolactam), 7-aminoheptanoic acid lactam (ζ-lactam; ζ-heptanolactam), 8-aminooctanoic acid lactam (η-lactam; η-octanolactam), 9-nonanoic acid lactam (Θ-lactam; Θ-nonanolactam) , 10-decanoic acid lactam (ω-decanolactam), 1-undecanoic acid lactam (ω-undecanolactam) and 12-dodecanoic acid lactam (ω-dodecanolactam).

The present invention thus also provides a process in which the lactam is selected from the group consisting of 3-aminopropanoic acid lactam, 4-aminobutanoic acid lactam, 5-aminopentanoic acid lactam, 6-aminohexanoic acid lactam, 7-aminoheptanoic acid lactam, 8-aminooctanoic acid lactam, 9-nonanoic acid lactam, 10 Decanoic acid lactam, 1-undecanoic acid lactam and 12-dodecanoic acid lactam.

The lactams may be unsubstituted or at least monosubstituted. In the event that at least monosubstituted lactams are used, these may carry on the nitrogen atom and / or on the carbon atoms of the ring one, two or more substituents which are independently selected from the group consisting of C to C ₁₀ alkyl, C ₅ - to C ₆ -cycloalkyl and C ₅ - to C ₁₀ -aryl.

Examples of suitable C 1 to C 10 -alkyl substituents are methane, ethane, propyl, isopropyl, n-butyl, sec-butyl and tert-butyl. Suitable C ₅ to C ₆ cycloalkyl substituents are cyclohexyl. Preferred C ₅ to Cio-aryl substituents are phenyl and antranyl.

Unsubstituted lactams are preferably used, preference being given to γ-lactam (γ-butyrolactam), δ-lactam (δ-valerolactam) and ε-lactam (ε-caprolactam). Particularly preferred are δ-lactam (δ-valerolactam) and ε-lactam (ε-caprolactam), with ε-caprolactam being particularly preferred.

Process step a)

In process step a) is a mixture containing a polyamide and a lactam, heated to temperatures above a cloud point temperature (T _T), above which the Polyamide completely dissolved in the lactam is present. For process step a), it is irrelevant whether the polyamide and the lactam are initially introduced together or are added in succession. It is possible to first heat the polyamide and then add the lactam. In addition, it is possible to co-heat the lactam and the polyamide. Preferably, however, the lactam is first heated and then add the polyamide.

Above the clouding temperature (T _T ), the polyamide is completely dissolved in the molten lactam. In other words, this means that an optically clear solution of the polyamide is obtained in the molten lactam. The melt of the lactam forms the solvency in this solution, the polyamide forms the solvate. The polyamide molecules are homogeneously and statistically distributed above the turbidity temperature (T _T ) in the molten lactam and can not be separated by filtration. Above the clouding temperature (T _T ), polyamide and lactam are thus present as an optically clear solution, the polyamide molecules being distributed homogeneously and statistically in the lactam.

The turbidity temperature (T _T ) in the process according to the invention depends on the type of lactam, the type of polyamide and the concentration of the polyamide in the melt produced in process step a).

In process step a), the mixture containing the polyamide and the lactam is generally at temperatures in the range of 170 ° C to 250 ° C, preferably at temperatures in the range of 170 ° C to 230 ° C, particularly preferably at temperatures of 170 ° C to 210 ° C and in particular heated to temperatures in the range of 180 ° C to 200 ° C.

In a further embodiment, the mixture is heated in process step a) to a temperature which is at least 10 ° C below the melting temperature of the polyamide used. The mixture is particularly preferably in process step a) to a temperature in the range of 10 to 50 ° C below the melting temperature of the polyamide used, more preferably to a temperature in the range of 10 to 35 ° C below the melting temperature of the polyamide used and in particular to a Temperature in the range of 10 to 20 ° C below the melting temperature of the polyamide used, heated.

The melting temperature of the polyamide used in process step a) is defined as the temperature at which the polyamide in the pure substance of the solid state of aggregation at least partially passes into the liquid state. The melting temperature of the polyamide is determined by differential scanning colorimetry. The present invention thus also provides a process in which the mixture is heated in step a) to obtain the melt to a temperature in the range of 170 ° C to 250 ° C. As a result, the lactam contained in the mixture melts and the polyamide completely dissolves in the molten lactam.

The melt produced in process step a), which contains the polyamide completely dissolved in the lactam, generally contains less than 5% by weight of water, preferably less than 4% by weight of water, more preferably less than 2% by weight of water and in particular preferably less than 1% by weight of water, in each case based on the total weight of the melt obtained in process step a), which contains the polyamide completely dissolved in the lactam. The lower limit of the water content of the melt obtained in process step a) is generally in the range from 0 to 0.5% by weight, preferably in the range from 0 to 0.3% by weight, particularly preferably in the range from 0 to 0, 1 wt .-%, each based on the total weight of the melt obtained in step a). The present invention thus also provides a process in which the water content of the melt obtained in process step a) is in the range from 0 to less than 5% by weight, based on the total weight of the melt obtained in process step a). The water content of the melt obtained in process step a) is decisively determined by the water content of the polyamide used and by the water content of the lactam used.

The water content of the polyamide used is generally in the range of 0 to <2.5 wt .-%, preferably in the range of 0 to 2 wt .-% and particularly preferably in the range of 0 to 1 wt .-%, each based on the total weight of the polyamide used in process step a). The lower limit of the water content of the polyamide used in process step a) is generally in the range from 0 to 0.5 wt .-%, preferably in the range of 0 to 0.2 wt .-%.

The water content of the lactam used in process step a) is generally in the range from 0 to <5 wt .-%, preferably in the range of 0 to <4 wt .-%, particularly preferably in the range of 0 to 2 wt .-%, and particularly preferably in the range from 0 to 1 wt .-%, each based on the total weight of the lactam used in step a). The lower limit of the water content of the lactam used in process step a) is generally in the range from 0 to 0.5 wt .-%, preferably in the range of 0 to 0.2 wt .-%, each based on the total weight of the process step a ) used lactams.

The water content of the polyamide used in process step a) and the water content of the lactam used in process step a) is generally selected so that the melt obtained in process step a) has the above-described water content, for which the above statements and preferences apply accordingly.

The mixture of lactam and polyamide used in process step a) and the melt obtained in process step a) are thus essentially anhydrous. This has the advantage that the melt formed in process step a) represents a true solution of the polyamide in the lactam. The formation of a dispersion or emulsion of the polyamide in the lactam is thereby prevented in process step a).

The polyamide is used in process step a) in amounts such that the melt obtained in process step a) contains the polyamide in amounts ranging from 5 to 60% by weight, preferably in the range from 8 to 50% by weight, and particularly preferably in the range of 10 to 30 wt .-%, in each case based on the total weight of the melt obtained in process step a), which contains the polyamide completely dissolved in the lactam.

The present invention thus also provides a process in which the melt obtained in process step a) contains the polyamide in amounts ranging from 5 to 60% by weight, based on the total weight of the melt obtained in process step a).

In process step a), it is possible, in addition to the polyamide and the lactam, if desired, to add further additives. The time of addition of additives is irrelevant here. The additives can be presented together with the polyamide and the lactam. In addition, it is possible to add the additives to the melt obtained in process step a). It is also possible to provide the additive or additives together with the polyamide or together with the lactam. Moreover, it is possible to use a polyamide which already contains additives. Preferred additives are antinucleating agents. Preferred antinucleating agents are selected from the group consisting of lithium chloride, nigrosine, methylene blue and neutral red. Preferred antinucleating agent is nigrosine. Nigrosine is one synthetic black dye, also known as "Solvent Black 5" (Color Index 50415) Nigrosine can be prepared, for example, by heating nitrobenzene and aniline and aniline hydrochloride in the presence of copper or iron.

Methylene blue is a dye which is also referred to as Λ /, Λ /, Λ / ', Λ /' - tetramethylenethionine chloride or Basic Blue 9 (Color Index 52015, CAS numbers 61-73-4 and 122965-43-9, respectively) becomes. Neutral red is a dye, also referred to as 3-amino-7-dimethylamino-2-methylphenazine hydrochloride or toluene red (Color Index 50040: CAS number 553-24-2).

The additives, preferably the antinucleating agents, are generally added in process step a) in amounts such that the polyamide powder obtained after process step c) has an additive content in the range from 0 to 3% by weight, preferably in the range from 0, 5 to 2.5 wt .-%, particularly preferably in the range of 0.5 to 2 wt .-%, in particular in the range of 1 to 2 wt .-%, each based on the total weight of the polyamide powder obtained according to process step c) ,

The present invention thus also provides a process in which the melt contained in process step a) contains at least one antinucleating agent selected from the group consisting of lithium chloride, nigrosine, methylene blue and neutral red.

The present invention furthermore relates to a process in which the antinucleating agent is added in process step a) in amounts such that the polyamide powder obtained after process step c) contains the antinucleating agent in amounts in the range from 0.1 to 3% by weight , based on the total weight of the polyamide obtained according to process step c).

Process step a) is carried out in a preferred embodiment under a protective gas atmosphere. As a protective gas, in this case, for example, nitrogen can be used. Process step a) can be carried out under atmospheric pressure, but process step a) is preferably carried out under pressure. The pressure during process step a) is generally in the range of 0.5 to 10 bar abs.

Process step a) is preferably carried out under agitation. Suitable devices for carrying out the process step a) to obtain the melt which contains the polyamide completely dissolved in the lactam are known to the person skilled in the art. Suitable devices are, for example, reactors, the Have stirring unit and can be pressurized. Suitable stirrers are, for example, anchor stirrers.

Process step b)

In process step b), the melt obtained in process step a) is cooled to a temperature <the turbidity temperature (T _T ). Preferably, the melt contained in process step a) is cooled to a temperature which is at least 0.5 ° C, preferably at least 1 ° C below the turbidity temperature (T _T ). Upon reaching or falling below the clouding temperature (T _T ) the melt melts, that is, it is no longer visually clear. The clouding can be perceived purely visually with the naked eye. In addition, it is possible to determine the reaching or falling below the turbidity temperature (T _T ) by a transmission measurement.

The reference value used here is the transmission of the melt produced in process step a), which contains the polyamide completely dissolved in the lactam. The transmission of the melt obtained in process step a) is hereby set to 100% and subsequently used as the reference value.

Upon reaching or falling below the turbidity temperature (T _T ) by the cooling in step b), the transmission decreases. In general, the transmittance of the melt during cooling in process step b) when reaching or falling below the turbidity temperature (T _T ) decreases by at least 5%, preferably by at least 20%, particularly preferably by at least 30%, based on the transmission in the process step a) obtained melt containing the polyamide completely dissolved in the lactam (transmission 100%).

In other words, this means that the melt in process step b), ie when reaching or falling below the turbidity temperature (T _T ) and before adding the water, when reaching or falling below the turbidity temperature (T _T ) has a maximum transmission of 95%, preferably of not more than 80% and more preferably of not more than 70%, based on the transmission of the melt obtained in process step a) (transmission 100%).

After reaching or falling below the clouding temperature (T _T ), water is added in process step b), whereby a suspension is obtained which contains the polyamide powder suspended in a solution containing water and lactam.

In process step b), in addition to water, further solvents such as, for example, alcohol may be added. Suitable further solvents are for example, methanol, ethanol, n-propanol or isopropanol. In the event that further solvents are added in process step b), these can be added before or after the addition of water. In addition, it is possible in process step b) to add a mixture which contains water and at least one further solvent. It is according to the invention only necessary that in step b) water is added. In a preferred embodiment, only water is added in process step b).

The addition of water can be added according to the invention before or after solidification of the melt 10. In the event that the water is added after solidification of the melt, the water dissolves the lactam, whereby the suspension of the polyamide powder is obtained. In a preferred embodiment, the addition of water in step b) before the solidification of the melt.

The clouding temperature (T _T ) thus forms the upper temperature limit at which water can be added in process step b). The lower temperature limit up to which water can be added in process step b) generally represents the melting temperature (T _s ) (melting point) of the lactam used in the process according to the invention. The melting point is at a pressure according to the invention

20 from 1, 01325 bar measured. According to the invention, the melting temperature (T _s ) is equal to the melting point of the lactam.

The present invention thus also provides a process in which the lactam has a melting temperature (T _s ) and the melt obtained in process step a) in process step b) to a temperature in the range of equal to the clouding temperature (T _T ) to greater than Melting temperature (T _s ) of the lactam is cooled and then water is added.

In the event that ε-caprolactam is used as the lactam, the lower limit, 30 must be added before the water, thus 68 ° C. In the case where δ-valerolactam is used as lactam, the lower limit above which water must be added in process step b) is thus 40 ° C.

The turbidity temperature (T _T ) depends, as stated above, on the properties of the polyamide and the lactam and on the concentration of the polyamide in the melt. Suitable temperature ranges within which the addition of water according to process step b) can be carried out are generally in the range of 80 to <170 ° C, preferably in the range of 90 to 160 ° C, more preferably in the range of 100 to 150 ° C and in particular Range of 120 to 40 145 ° C, wherein the addition of water takes place only after reaching or falling below the turbidity temperature (T _T ). In a particularly preferred embodiment, the addition of water in step b) in a temperature range whose upper limit is equal to the turbidity temperature (T _T ) and its lower limit by a temperature which is not more than 20 ° C below the crystallization temperature (T _K ) of the polyamide used lies, is defined.

The present invention thus also relates to a process in which the polyamide has a crystallization temperature (T _K ) and the melt obtained in process step a) in process step b) to a temperature in the range of equal to the turbidity temperature (T _T ) to a maximum of 20 ° C is cooled below the crystallization temperature (T _K ) of the polyamide and then water is added.

Polyamides are generally semicrystalline. The degree of crystallinity of polyamides is generally in the range of 20 to 50%. The degree of crystallinity is also referred to as crystallinity or degree of crystallinity. When heating the mixture according to process step a), a melt is formed which contains the polyamide completely dissolved in the lactam. In the formation of the melt in process step a), the crystalline regions of the polyamide dissolve. In addition, the polyamide goes from the form of a solid in the state of matter of a solution. Here, the polyamide absorbs heat (energy). This heat is also called latent heat. The latent heat is composed of the enthalpy that must be used to dissolve crystalline areas and the enthalpy required for the transition from the solid to the solution. The two enthalpies are also referred to as enthalpy of crystallization or enthalpy of solution.

During cooling of the melt obtained in process step a), the clouding temperature (T _T ) is first reached in process step b). The turbidity temperature (T _T ) is different from the crystallization temperature (T _K ). The crystallization temperature (T _K ) is generally below the turbidity temperature (T _T ). Upon reaching the crystallization temperature (T _K ), the polyamide is completely from the solution in the solid state, wherein the crystalline regions form again. The heat (latent heat) absorbed by the polyamide in process step a) is released here again in process step b). The onset of crystallization, that is, the achievement of the crystallization temperature (T _K ), can therefore be detected by a temperature rise.

The term "crystallization temperature (T _K )" is thus understood to mean the temperature at which the polyamide releases the latent heat received in process step a), that is to say the sum of solution enthalpy and crystallization enthalpy to the environment. The crystallization temperature (T _K ) can be determined, for example, by a resistance thermometer (PT100) or a thermocouple in combination with a torque measurement. The torque shows a marked change in slope at the crystallization temperature (T _K ), the torque increases significantly, while it increases only slightly in the cooling phase due to the viscosity increase of the continuous phase.

In a further embodiment, the crystallization temperature (T _K ) is determined by a temperature sensor, which is located in the reactor and measures the temperature of the melt in process step b). The crystallization temperature (T _K ) can therefore be detected by a temperature rise of the melt in process step b).

In a preferred embodiment of the process according to the invention, the addition of water in process step b) takes place above a temperature of not more than 20 ° C., preferably not more than 10 ° C., more preferably not more than 5 ° C. and more preferably not more than 2 ° C. below the crystallization temperature (T _K ). of the polyamide used. The crystallization temperature (T _K ) also depends on the properties of the polyamide and the lactam and on the concentration of the polyamide in the melt.

The amount of water added in process step b) can vary within wide limits. In general, at least one part by weight of water, preferably at least 2 parts by weight of water, more preferably at least 3 parts by weight of water and in particular at least 5 parts by weight of water are added in step b) based on one part by weight of the melt contained in the melt or at least partially solidified melt. In general, a maximum of 20 parts by weight of water, preferably not more than 15 parts by weight of water, more preferably not more than 10 parts by weight of water and in particular not more than 8 parts by weight of water are added, based in each case on one part by weight of the polyamide contained in the melt or the at least partially solidified melt. Of course, it is possible to add even larger amounts of water. However, this is not associated with an advantageous effect, since larger amounts of water have to be separated in the subsequent process steps, which makes the process according to the invention more expensive.

The present invention thus also provides a process in which the amount of water added in process step b) is from 1 to 100 parts by weight of water, based on one part by weight of the polyamide contained in the melt. The temperature of the water added in process step b) can vary within wide limits. In general, the temperature of the water added in process step b) is in the range from 20 to <170 ° C., preferably in the range from 20 to 160 ° C., more preferably in the range from 50 to 150 ° C. and especially preferably in the range from 60 to 145 ° C, wherein the addition of water takes place only after reaching or falling below the turbidity temperature (T _T ).

The present invention thus also provides a process in which the addition of water in process step b) takes place at a temperature in the range from 20 to <170 ° C. and after reaching or falling below the turbidity temperature (T _T ).

In order to prevent evaporation of the water added in process step b), process step b) is carried out under pressure in a preferred embodiment. For this purpose, for example, a closed reactor, such as an autoclave, can be used. Process step b) is also carried out under agitation in a preferred embodiment. Since process steps a) and b) are preferably carried out in the same reactor, the statements and preferences given for process step a) apply correspondingly to the reactors.

The present invention thus also relates to a process in which process steps a) and b) are carried out in the same reactor. After addition of water, a suspension is obtained in process step b) which contains the polyamide powder suspended in a solution of water and the lactam.

Process Step c) The polyamide powder obtained in process step b) in the form of a suspension can be separated off in process step c). The separation of the polyamide powder is carried out by the skilled person known methods such as filtration or centrifugation. In method step c), the polyamide powder is thus separated from the solution containing water and the lactam. The polyamide powder thus obtained may optionally be worked up further. In a preferred embodiment, the polyamide powder is washed with water in order to separate any residues of the lactam contained from the polyamide powder. In a further preferred embodiment, the polyamide powder is washed after the separation according to process step c) with water and subsequently dried.

The drying can take place thermally. Preferred thermal drying methods are, for example, drying in one with hot air pressurized fluidized bed or drying under a nitrogen atmosphere in vacuo at elevated temperatures, for example in the range of 50 to 100 ° C.

polyamide powder

The polyamide powders obtainable by the process according to the invention have a narrow particle size distribution (particle size distribution) and a substantially round shape. As a measure of this, the so-called Spärizitäts value (SPHT value) is used. The sphericity value of the polyamide particles indicates the ratio of the surface of the polyamide particles to the surface of ideal spheres of equal volume. The sphericity value can be determined by image analysis using, for example, a camsizer.

The polyamide powders obtainable by the process according to the invention generally have a sphericity value in the range from 0.4 to 1.0.

The polyamide powders obtainable by the process according to the invention have a narrow particle size distribution. In general, the polyamide powder

a D 10 value in the range of 5 to 50 μηη,

a D50 value in the range of 20 to 80 μηη and

a D90 value of 40 to 150 μηη

on.

In a preferred embodiment, the polyamide powder

a D 10 value in the range of 10 to 40 μηη,

a D50 value in the range of 30 to 70 μηη and

a D90 value of 45 to 130 μηι

on.

The present invention thus also provides a process in which the polyamide powder obtained after process step c)

a D 10 value in the range of 5 to 50 μηη,

a D50-Werrt in the range of 20 to 80 μηη and

a D90 value in the range of 40 to 150 μηη

having.

In the context of the present invention, "D10 value" in this context means the particle size at which 10% by volume of the particles, based on the total volume of the particles, is less than or equal to the D10 value and 90% by volume of the particles based on the total volume of the particles greater than the D10 value are. By analogy, the D50 value is understood to mean the particle size at which 50% by volume of the particles, based on the total volume of the particles, is less than or equal to the D50 value and 50% by volume of the particles, based on the total volume of the particles are greater than the D50 value. By analogy, the D90 value is understood to be the particle size at which 90% by volume of the particles, based on the total volume of the particles, is less than or equal to the D90 value and 10% by volume of the particles, based on the total volume of the particles greater than the D90 value.

To determine the sphericity value and the particle sizes, the polyamide powder obtained in process step b) is measured in the form of the suspension obtained in process step b). The D10, D50 and D90 values are determined by means of laser diffraction using a Mastersizer 3000 from Malvern. The evaluation is carried out by means of Frauenhofer diffraction. A measure of the width of the particle size distribution is the difference between the D90 and D10 values (D90 value minus D10 value). The closer these two values are together, that is, the smaller the difference, the narrower the particle size distribution. The polyamide powders obtainable by the process according to the invention generally have values in the range from 25 to 110 μm, preferably in the range from 10 to 50 μm, for the difference between the D90 and D10 values.

Another measure of the width of the particle size distribution is the so-called Span. The chip is defined as (D90-D10) / D50. The particle size of the polyamide powder obtainable by the process according to the invention is generally in the range from 0.5 to 2.5, preferably in the range from 0.6 to 1.2.

In addition, the polyamide powders obtainable by the process according to the invention have small amounts of fines and small amounts of coarse fraction. According to the invention, "fine fraction" is understood to mean polyamide particles which have a particle size of less than 10 μm. "Coarse fraction" is understood according to the invention to mean polyamide particles which have a particle size of greater than 130 μm.

In general, the polyamide powders obtainable by the process according to the invention contain less than 5% by weight, preferably less than 4% by weight and particularly preferably less than 2% by weight, based in each case on the total weight of the polyamide powder.

In general, the polyamide powders obtainable by the process according to the invention contain less than 5% by weight, preferably less than 4% by weight and more preferably less than 2 wt .-% coarse fraction, each based on the total weight of the polyamide powder.

Due to the narrow particle size distribution and the good sphericity values of the polyamide powder obtainable by the process according to the invention, it is readily fluidisable. In some cases, the polyamide powder obtained by the process according to the invention can be further processed without further classification. Separation of coarse or fines by sieving or screening is not required in some cases. As a result, consuming and costly classification steps can be saved in the inventive method.

The present invention thus also provides the polyamide powder obtainable by the process according to the invention. For the polyamide powder, the statements made above with regard to the process for the preparation of the polyamide powder and the preferences mentioned there apply accordingly.

Due to the above-described advantageous properties of the polyamide powder obtainable by the process according to the invention, these can be used advantageously in coating processes and in processes for sintering, preferably for laser sintering.

The present invention thus also relates to the use of the polyamide powder according to the invention in coating processes, preferably powder coating processes. The present invention furthermore relates to the use of the polyamide powders according to the invention in processes for sintering, preferably in processes for laser sintering.

The present invention thus also relates to the use of the polymamide powder obtainable by the process according to the invention as a sintering powder in a process for the production of moldings by selective laser sintering.

The present invention will be further illustrated by, but not limited to, the following examples.

example 1

40 g of polyamide 6 having a viscosity number of 144 ml / g and 160 g of ε-caprolactam were placed in a 1 L four-necked flask equipped with an internal thermometer. Subsequently, this mixture was rendered inert with nitrogen and heated with stirring to 190 ° C (internal temperature). After four hours, a melt was obtained which completely dissolved the polyamide 6 in the ε-caprolactam contained. Subsequently, the melt was cooled to a temperature less than the clouding temperature (T _T ). The contents of the flask solidified at an internal temperature of 125 ° C. Subsequently, 300 ml of deionized water (deionized water) was added to dissolve the ε-caprolactam. The flask contents were stirred at 5 100 revolutions per minute. A suspension was obtained containing the polyamide powder suspended in a solution containing water and ε-caprolactam. The polyamide powder was subsequently separated by means of a pressure filter (Seitz filter T 1500) and washed with water and subsequently dried for 16 hours at 80 ° C. under a nitrogen atmosphere in a vacuum drying oven.

0

The polyamide powder had a D 10 value of 24.0 μηη, a D50 value of 62.7 μηη and a D90 value of 129 μηη.

The particle size distribution was determined by means of laser diffraction with a Mastersizer 30005 from Malvern. The evaluation was carried out by means of Fraunhofer diffraction.

Example 2

18.5 g of polyamide 6 having a viscosity number of 144 ml / g and 166.5 g of ε-Caprolactam0 were placed in a pressure reactor and inertized with nitrogen. Subsequently, this mixture was heated with stirring to 190 ° C (internal temperature), whereby a melt was obtained, which contained the polyamide 6 completely dissolved in the ε-caprolactam. In a second pressure cylinder, 185 ml DI water were heated to 140 ° C. After 4.5 hours, the melt was slowly cooled to a temperature below the clouding temperature (T _T ). The outside temperature of the pressure reactor was 145 ° C. The internal temperature was determined by a temperature sensor and was 140.8 ° C. Thereafter, the internal temperature of the pressure reactor slightly increased. This is due to the onset of crystallization of the polyamide 6. Immediately after the detection of the temperature rise, the water preheated in the second pressure cylinder was supplied to the pressure reactor with stirring. The resulting suspension was stirred for 30 minutes. Subsequently, it was cooled to room temperature (20 ° C) and the resulting polyamide powder was separated as described above for Example 1, worked up and measured.

5

The polyamide powder thus obtained had a D10 value of 22 μηη, a D50 value of 38 μηη and a D90 value of 60 μηη.

The particle size distribution was determined by means of laser diffraction with a Mastersizer 30000 from Malvern. The evaluation was carried out by means of Fraunhofer diffraction. Example 3

166.5 g of ε-caprolactam was placed in a pressure reactor with internal thermometer and rendered inert with nitrogen. Subsequently, the ε-caprolactam was melted by heating to 5 120 ° C. 18.5 g of polyamide 6 having a viscosity number of 120 ml / g and 0.69 g Ultrabatch (40% nigrosine, 60% polyamide 6) were added with stirring to the ε-caprolactam melt and subsequently heated to 190 ° within 5 hours C (internal temperature) heated, whereby a melt was obtained which contained the polyamide 6 completely dissolved in the ε-caprolactam.

0

In a second pressure cylinder 185 ml of deionized water were heated to 170 ° C. The melt was slowly cooled to a temperature below the clouding temperature (T _T ). The outside temperature of the pressure reactor was 132 ° C. The internal temperature was 132.8 ° C. The mixture was held constant at 5 ° C for ten minutes. Thirty seconds after a rise in the internal temperature of the pressure reactor was detected, the water preheated in the second pressure cylinder was supplied to the pressure reactor with stirring. The suspension thus obtained was then heated again to 170 ° C. (internal temperature). After 10 minutes, the mixture was cooled to room temperature (20 ° C.) with stirring and the polyamide powder obtained was separated off, worked up and measured as described above for Example 1.

The polyamide powder thus obtained had a D10 value of 37.2 μηη, a D50 value of 63.2 μηη and a D90 value of 104.5 μηη.

5

The particle size distribution was determined by means of laser diffraction with a Mastersizer 3000 from Malvern. The evaluation was carried out by means of Fraunhofer diffraction.

Example 4

0

166.5 g of ε-caprolactam was placed in a pressure reactor with internal thermometer and rendered inert with nitrogen. Subsequently, the ε-caprolactam was melted by heating to 120 ° C. To the ε-caprolactam melt was added 18.5 g of polyamide 6 having a viscosity number of 120 ml / g and 0.69 g Ultrabatch (40% nigrosine, 60% polyamide 6) with stirring and then with stirring within 5 hours heated to 190 ° C (internal temperature), whereby a melt was obtained, which contained the polyamide 6 completely dissolved in the ε-caprolactam.

In a second pressure cylinder 185 ml of deionized water were heated to 20 ° C. The melt was slowly cooled to a temperature below the clouding temperature (T _T ). The outside temperature of the pressure reactor was 130 ° C. The internal temperature was 130.3 ° C. 2 minutes after a rise in the internal temperature of the pressure reactor, the water preheated in the second pressure cylinder was supplied to the pressure reactor with stirring. The resulting suspension was then cooled with stirring to room temperature (20 ° C) and the resulting polyamide powder as described above for Example 1 5 separated, worked up and measured.

The polyamide powder thus obtained had a D10 value of 19.4 μηη, a D50 value of 33.2 μηη and a D90 value of 49.2 μηη.

Example 5

15 166.5 g of ε-caprolactam was placed in a pressure reactor with internal thermometer and rendered inert with nitrogen. Subsequently, the ε-caprolactam was melted by heating to 120 ° C. 18.5 g of polyamide 6 having a viscosity number of 120 ml / g and 0.69 g of Ultrabatch (40% nigrosine, 60% polyamide 6) were added with stirring to the ε-caprolactam melt and subsequently dissolved in over 5 hours

20 190 ° C (internal temperature) heated, whereby a melt was obtained, which contained the polyamide 6 completely dissolved in the ε-caprolactam.

In a second pressure cylinder 185 ml of deionized water were heated to 150 ° C. The melt was slowly brought to a temperature below the turbidity temperature (T _T )

25 cooled. The internal temperature was 150 ° C. Before an increase in the internal temperature of the pressure reactor was detected, the water preheated in the second pressure cylinder was supplied to the pressure reactor with stirring. The resulting suspension was then cooled with stirring to room temperature (20 ° C) and the resulting polyamide powder as described above for Example 1

30 separated, worked up and measured.

The polyamide powder thus obtained had a D10 value of 30.2 μηη, a D50 value of 57.6 μηη and a D90 value of 100.4 μηη.

Claims

claims

Process for the preparation of polyamide powder comprising process steps

Heating a mixture containing a polyamide and a lactam to a temperature greater than a clouding temperature (T _T ) above which the polyamide is completely dissolved in the lactam, to obtain a melt containing the polyamide completely dissolved in the lactam, cooling the particles in step a ) to a temperature less than or equal to the clouding temperature (T _T ) and then adding water to obtain a suspension containing the polyamide powder suspended in a solution containing water and the lactam, and

Separating the polyamide powder from the suspension obtained in process step b).

Process according to Claim 1, characterized in that the lactam has a melting temperature (T _s ) and the melt obtained in process step a) in process step b) reaches a temperature in the range from equal to the clouding temperature (T _T ) to greater than the melting temperature (T _s ) of the lactam is cooled and subsequently water is added.

A method according to claim 1 or 2, characterized in that the mixture is heated in step a) to obtain the melt to a temperature in the range of 170 ° C to 250 ° C.

Method according to one of claims 1 to 3, characterized in that the addition of water in step b) at a temperature in the range of 20 to <170 ° C and after reaching or falling below the turbidity temperature (T _T ).

Method according to one of claims 1 to 4, characterized in that the polyamide has a crystallization temperature (T _K ) and the melt obtained in process step a) in process step b) to a temperature in the range of equal to the clouding temperature (T _T ) to a maximum of 20 ° C is cooled below the crystallization temperature (T _K ) of the polyamide and then water is added. Method according to one of claims 1 to 5, characterized in that the melt obtained in step a) contains the polyamide in amounts ranging from 5 to 60 wt .-%, based on the total weight of the melt obtained in step a).

Process according to one of Claims 1 to 6, characterized in that the water content of the melt obtained in process step a) is in the range from 0 to less than 5% by weight, based on the total weight of the melt obtained in process step a).

Method according to one of claims 1 to 7, characterized in that the amount of water added in step b) 1 to 100 parts by weight of water, based on one part by weight of the melt contained in the polyamide.

A process according to any one of claims 1 to 8, characterized in that the lactam is selected from the group consisting of 3-aminopropanoic acid lactam, 4-aminobutanoic acid lactam, 5-aminopentanoic acid lactam, 6-aminohexanoic acid lactam, 7-aminoheptanoic acid lactam, 8-aminooctanoic acid lactam, 9- Nonanoic acid lactam, 10-decanoic acid lactam, 1 l-undecanoic acid lactam and 12-dodecanoic acid lactam.

Method according to one of claims 1 to 9, characterized in that the polyamide is selected from the group consisting of PA 4, PA 6, PA 7, PA 8, PA 9, PA 1 1, PA 12, PA 46, PA 66, PA 69, PA 610, PA 612, PA 613, PA 1212, PA1313, PA 6T, PA MXD6, PA 61, PA 6-3-T, PA 6 / 6T, PA 6/66, PA 6/12, PA 66 / 6/610, PA 6I / 6T, PA PACM 12, PA 6I / 6T / PACM, PA 12 / MACMI, PA 12 / MACMT, PA PDA-T and copolyamides of two or more of the aforementioned polyamides.

A method according to any one of claims 1 to 10, characterized in that the melt contained in process step a) contains at least one antinucleating agent selected from the group consisting of lithium chloride, nigrosine, methylene blue and neutral red.

Process according to any one of Claims 1 to 11, characterized in that the antinucleating agent is added in process step a) in amounts such that the polyamide powder obtained after process step c) contains the antinucleating agent in amounts ranging from 0.1 to 3% by weight. contains, based on the total weight of the polyamide obtained according to process step c).

13. The method according to any one of claims 1 to 12, characterized in that the obtained after process step c) polyamide powder

a D10 value in the range of 5 to 50 μηη,

a D50-Werrt in the range of 20 to 80 μηη and

a D90 value in the range of 40 to 150 μηη

having.

14. Polyamide powder obtainable by a process according to one of claims 1 to 13.

15. Use of the obtainable by the process according to any one of claims 1 to 13 Polymamidpulvers as a sintering powder in a process for the production of moldings by selective laser sintering.