Polyamid powder with stable, constant pourability

The present invention relates to a method for the coating of moldings and a process for production of test specimens by laser-sintering process. A further application is the use for the manufacture of cosmetics and paints.

Polyamide powder found in the technical fields, for example, for coating metal parts, as an additive in paints and cosmetics, as well as for the production of test specimens or small series after the rapid prototyping process by selective laser sintering. At the processability of the powder used high demands. A particularly critical parameter is the flowability of the polyamide powders used. Lumps in the powders used lead to inhomogeneities of the resulting coating or the specimen. The powder used must retain good flowability irrespective of the storage conditions in unopened or opened containers. Especially in open containers must independent of weather conditions of storage, such as temperature and humidity consistent processability be guaranteed.

Polyamide powder take over the hydrophilic carboxylic acid amide groups on water. There is a relationship between the chain length of the monomers used and the water absorption of the resulting polyamide. Thus, the powders based on polyamide 11 and polyamide 12 have a lower water absorption, as they related to the methyl groups in the polymer contain less carboxamide as polyamides prepared from shorter-chain monomers. The water absorption of the polyamide powders leads to clumping, which cause poor flowability of the powder. The lumps are manufactured in polyamide powders after milling process particularly pronounced. The poor flowability is accompanied by poor processability of the polyamide powder.

In the <patcit id="pcit0001" dnum="DE2906647"><text>DE 29 06 647</text></patcit> a process for the preparation of pulverulent coating compositions based on polyamides is described having at least 10 aliphatically bonded carbon atoms per carboxamide group. The coating compositions produced by this method can be used for producing paint similar coatings on metals. The coating can be effected by the fluidized bed coating process, the flame spraying method or the electrostatic coating method. The coating compositions produced by this process form upon heating to temperatures above the film formation temperature without generating disturbing smoke, coatings having a smooth surface, good edge coating, good elasticity and excellent resistance to alkaline aqueous solutions. In the<patcit id="pcit0002" dnum="DE2906647"><text>DE 29 06 647</text></patcit> Coating powders produced have a defined particle size distribution, which is determined by the manufacturing conditions. The flowability of the polyamides produced in this way is to be regarded immediately after the production as sufficient. occurs, as with all polyamide powders of the prior art even when prepared by this process powders after storage at varying temperature and humidity a deterioration in the flowability by a clumping.

In the <patcit id="pcit0003" dnum="DE3113392"><text>DE 31 13 392</text></patcit> is a method of reducing the electrostatic charge of thermoplastic powder polyamides disclosed. The coating powder produced by this process from thermoplastic materials contains thermoplastic powdered polyamides an addition of small amounts of a finely divided inorganic powder, wherein the finely divided inorganic powder is coated with an antistatic agent. The antistat agents are organic ammonium or amine compounds. From the thus coated powder 0.01 to 0.03 parts by weight based on 100 parts by weight polyamide be added. The resultant treated polyamide powder is compared with a non-finished powder improved Wirbelbarkeit the fluidized-bed process. However, in<patcit id="pcit0004" dnum="DE3113392"><text>DE 31 13 392</text></patcit> do not contain information about whether the described coating powders after storage at varying temperature and humidity maintains its flowability and hence its suitability as a powder coating. By the hydrophilic coating of the antistatic agent is to be assumed that the flowability of the coating composition decreases on storage at varying temperature or humidity.

<nplcit id="ncit0001" npl-type="s"><text>Petrovičová et al. [J. Appl. Polym. Sc. 77 (2000) 1684-1699</text></nplcit>; ibid.<nplcit id="ncit0002" npl-type="s"><text>78 (2000) 2272-2289</text></nplcit>] Describes the high velocity oxy-fuel process (HVOF) process. In the described HVOF process, a polymer powder is provided with pigments to improve the properties of the coating layer and used for the coating of metal parts. The polymer powder is melted by means of a combustion spray gun and applied to the material to be coated in the molten state. Petrovičová examined the influence of hydrophilic silicas, silicas, carbon black, or hydrophobic A 1100 γ-aminopropyltriethoxysilane-modified silica as the pigment in the mixture with nylon 11 on the properties of the resulting coating. To this end, 15 and 20 percent by volume of the pigments were respectively 5, 10, added to the nylon eleventh This corresponds to a proportion of 0.3 to 3 percent by weight of pigment in the coating composition. The respective pigment and nylon 11 are 48 mixed and ground in a mill containing zirconia balls as a grinding aid h. The long meal, the pigment is very homogeneously incorporated into the nylon 11 grains. Petrovičová found that the properties of the resultant coating on the proportion of pigment dependent. The highest strength properties of the resulting coating can be achieved with 20 percent by volume of pigment in the coating composition. In both documents is not described that the pigments used to improve the flowability of the coating composition. The expert also receives no indication of the influence of the pigments disclosed on the flowability of the coating composition.

The technical object of the present invention is to provide methods and uses comprising a composition containing a polyamide, derivatives of polyamides or mixtures provide the same, which ensures, regardless of the storage conditions of the composition consistent flowability and thus processability. The composition is independent of the storage conditions, especially in temperature or humidity, can be used with consistent quality for coating moldings, for the production of test specimens by the laser sintering process, the manufacture of cosmetics and for the manufacture of paints.

The technical problem is solved by the teaching of the independent claims, wherein a composition containing 88 - selected 99.99 weight percent of a polymer selected from the group polyamides, derivatives of polyamides or mixtures thereof, and 0.01 to 0.25 percent by weight of a flow aid from the group hydrophobicized silica, hydrophobic silica, or mixtures thereof, wherein the specific 787/2 ISO loss on drying of the flow aid after 5 days of conditioning at a relative humidity of 95% less than or equal to 1%, will be provided. In the composition optionally also from 0 to 11.99 weight percent of one or more conventional additives may be included.

Unexpectedly show as selected flow aids in combination with hydrophilic nature of polyamides is independent of the storage conditions good flowability. An anti-caking agent with a loss on drying is less than or equal to 1% after 5 days of conditioning at a relative humidity of 95% may even take no or very little water or water vapor from the environment. The anti-caking agent can not act as a drying agent and therefore does not decrease the water absorption of the polyamide in the composition therefore. The skilled person would assume that in the composition now receives the polyamide water or water vapor from the surrounding air and therefore clumped. This expected clumping of the polyamide is surprisingly not observed in the composition.

It is preferred that the polymer is selected from the group of the same polyamide 12, polyamide 11, polyamide 10/6, polyamide 6/12, polyamide 10/12, polyamide 6, polyamide 6,6 or mixtures thereof. Preferably from 95 to 99.99 wt .-%, in particular 97 to 99.99 wt .-%, more preferably 99.0 to 99.99 still more preferably 99.5 to 99.99, especially from 99.75 to 99, 99, and particularly preferably from 99.8 to 99.99 wt .-% of the polymer contained in the composition. In a further preferred embodiment, from 99.82 to 99.99 wt .-%, in particular 99.85 to 99.99 wt .-%, more preferably from 99.88 to 99.99 wt .-% and particularly preferably 99.9 to 99.99 wt .-% of the polymer contained in the composition.

The anti-caking agents used are in a preferred embodiment, selected from the group, hydrophobic silica, hydrophobic silica, or mixtures thereof. Preferably, 0.01 to 0.2, especially 0.01 to 0.18 wt .-%, more preferably 0.01 to 0.15, still more preferably 0.01 to 0.12 and particularly preferably 0.01 to 0.1 wt .-% of the anti-caking agent contained in the composition.

The hydrophobic or hydrophobized silica is preferably obtained by reacting silica with hydrophobing agents. The hydrophobization is preferably carried out by precipitation or pyrolysis of the silica and substantial reaction of free OH groups of the silica with, for example, silanes, silazanes or siloxanes. Preferred hydrophobicizing agents are hexadecylsilane, dimethyldichlorosilane, hexamethyldisilazane, octamethylcyclotetrasiloxane, polydimethylsiloxane or methacryloylsilanes

The polymer used has an average particle size d50 from 0.1 to 250 .mu.m, preferably 1-150 .mu.m, particularly preferably from 3 to 120 microns, and more preferably 5 to 80 microns.

Anti-caking agents are generally of nanoscale primary particles. Thus for example commercial Aerosils® a primary particle size of a few nanometers (z. B. 7 to 12 nm). The primary particles usually form from larger agglomerates or aggregates. When mixing the anti-caking agent in the polymer powder, the agglomerates or aggregates are broken only partially, so that in addition to individual nanoscale primary mainly agglomerates and aggregates perceive the function of the anti-caking agent. In determining the average particle size of the anti-caking agent usually both individual primary particles and aggregates and agglomerates are found.

The anti-caking agent according to the invention has an average particle size of 5 nm to 200 microns. It is preferred that the flow aid has a median particle size of 10 nm to 150 microns, more preferably 100 nm to 100 microns.

The anti-caking agent used has a specific surface area of ​​20 to 600 m²/G. It is preferred that the flow aid has a specific surface area of ​​40 up to 550 m²/ G, particularly preferably 60 to 500 m²/ G, and still more preferably 60-450 m²/ G has.

The additive optionally used, which is no anti-caking agent is an additive that is usually used. It can be selected from the group consisting of metal powder, ferrites, organic colored pigment, inorganic colored pigment, carbon black, uncolored organic filler, uncolored inorganic filler, amorphous or partially crystalline filler, supercooled melts, pH regulators or mixtures thereof. In a preferred embodiment, the additive is aluminum powder, barium sulfate, titanium dioxide, zirconium dioxide, glass fibers, glass beads or mineral fibers. The additives are used in a preferred Ausfuhrungsfbrm of another modification of the polyamide powders such as the stain or the optimization of the mechanical properties of the coating or the sample body produced with the polyamide powder. It may contain one or more additives in the composition, an additive, or a mixture. In the composition are in a preferred embodiment, 0 to 4.99 wt .-%, more preferably 0 to 2.99 wt .-%, in particular from 0 to 0.99 wt .-%, more preferably 0 to 0.49 weight. -%, especially from 0 to 0.249 wt .-% and particularly preferably from 0 to 0.19 wt .-% of the additive included. In a further preferred embodiment, 0 to 0.17 wt .-%, especially 0 to 0.14 wt .-%, more preferably 0 to 0.11 wt .-% and particularly preferably from 0 to 0.09 wt .-% the additive contained.

The change in Rieseldauer of polyamide powders after storage is an indication as to whether the flowability of the powder is changed by the storage. If the flowability of the polyamide powder has decreased by storage as a result of eg temperature and humidity fluctuations, the Rieseldauer will increase. The storage of polyamide powders under temperature and humidity changes can be simulated in the laboratory and the Rieseldauer can be determined according to DIN 53492nd

The polyamide powders exhibit after conditioning at 95% relative humidity (6 days, 40 ° C) followed by conditioning at 50% relative humidity (24 hours, 20 ° C) an increase in the Rieseldauer which is determined according to DIN 53492, of less than 20%. In a further preferred embodiment, the increase in the Rieseldauer less than 10%, more preferably less than 5%.

The drying loss of the anti-caking agent can be determined according to ISO 787/2. For this purpose, the anti-caking agent is conditioned for 5 days at a relative humidity of 95%. It is preferred that the conditioning is carried out at 20 ° C and under atmospheric pressure. After 5 days of conditioning the drying loss of the anti-caking agent according to ISO 787/2 is determined by heating for 2 hours at 105 ° C. The drying loss is given as change in the mass of the flow aid in percent. It is preferable that the loss on drying less than 0.8%, particularly preferably less than 0.6%, more preferably less than 0.5%, still more preferably less than 0.4% is.

In principle, all types of mixers are suitable to the polyamide powder manufacture. The mixing time is preferably less than 120 minutes, more preferably less than 90 minutes. In a preferred embodiment, the polyamide powder and flow aid are mixed in a high-speed mixer. It can be used any high-speed mixer, which enables a high shear during the mixing. The mixing time is in the range of less than 10 minutes. It is preferred that the mixing time is less than five minutes. The advantage of this preferred embodiment, in an intimate and homogeneous mixing of polyamide powder and flow aid without the anti-caking agent is forced into the polyamide particle.

The composition can be used in processes for the coating of moldings. The mold parts may consist of metal or a metal alloy. In the coating process the composition may be fluidized during the coating process by blowing a gas. Alternatively, the composition can be finely atomized through a spray gun. The methods used can be fluidized bed coating, rotational sintering process, electrostatic coating, the Tribobeschichten or minicoat process. Since the composition good trickling and has no lumps Homogeneous layers form on the moldings.

Surprisingly, it is found that when using the composition of the fluidized bed process, the so-called phenomenon of cratering is avoided on the resultant polyamide surface. An explanation of this phenomenon, to provide a theory for this purpose without however could be that the flow aids absorb only low or no water in comparison to the flow aids of the prior art,,. Thus evaporate from the resulting layer and therefore subject to a cratering during the coating process, no water.

In the construction of test specimens after the laser sintering process powders are applied in layers and merged respectively when exposed to laser light to form a homogeneous body. Agglomerates in the powder and / or an insufficient flowability of the powder may cause uneven powder layers in the respective building plane and cause the finished component cavities and interference at the edges and surfaces. Through an agglomerate powder with consistently good flowability form under the conditions of the laser sintering process are few and / or small cavities in the specimen, whereby in particular the mechanical properties of the component can be improved. At the same time minimizing the number of defects on the surface and the edges. The surface of the specimen is formed homogeneously. It was found that the composition due to an improved quality of the sample body in the production of test specimens by laser-sintering process. Because the composition is consistently flowing, no disturbing lumps and thus no major voids are present in it.

The composition may also be used for the preparation of cosmetics. It is shown that the consistently good flow moves in a very homogeneous mixing of the individual constituents of cosmetics. Lumps that are present in compositions of the prior art after storage at different temperature and humidity, lead to the use for the production of cosmetics into agglomerates in the cosmetics that affect it adversely in their quality.

The composition may also be used for preparing paints. Similar cosmetics, it is necessary with lacquers that the quality of the individual components is independent of the storage conditions. There occur no agglomerates in the paints, the mark in not desired extent the surface of the applied varnish, matt or thaw. The present Erfmdung is illustrated by the following examples.

Examples

example 1

The flow aid Aerosil® R 812 and Aerosil® R 972 and the comparative example Aerosil® 200 are conditioned for 5 days at a temperature of 20 ° C and a relative humidity of 95%. Subsequently, the loss on drying is determined according to ISO 787/2 after storage for 2 hours at 105 ° C. The drying loss is given as mass change of flow aids by drying in percent.<tables id="tabl0001" num="0001"><table frame="all"><title><b>Table 1:</b></title><tgroup cols="3"><colspec colnum="1" colname="col1" colwidth="40mm" /><colspec colnum="2" colname="col2" colwidth="37mm" /><colspec colnum="3" colname="col3" colwidth="35mm" /><thead valign="top"><row><entry>anti-caking agent</entry><entry>Loss on drying [%]</entry><entry>Remarks</entry></row></thead><tbody><row><entry>Aerosil® R 812 *</entry><entry>&lt;0.1</entry><entry>no clumping</entry></row><row><entry>Aerosil® R 972 *</entry><entry>&lt;0.1</entry><entry>no clumping</entry></row><row><entry>Aerosil® 200 * (Comparative Example)</entry><entry>18.8</entry><entry>caking powder</entry></row></tbody></tgroup><tgroup cols="3" colsep="0" rowsep="0"><colspec colnum="1" colname="col1" colwidth="40mm" /><colspec colnum="2" colname="col2" colwidth="37mm" /><colspec colnum="3" colname="col3" colwidth="35mm" /><tbody><row><entry namest="col1" nameend="col3" align="justify">* Aerosil® is a trademark of Degussa AG</entry></row></tbody></tgroup></table></tables>

The measured dry matter losses (Table 1) show that the flow aids Aerosil® R 812 and Aerosil® R 972 when stored in an environment with high relative humidity. absorb humidity no water (loss on drying &lt;0.1%) and do not clump. The comparative example Aerosil® 200 assumes when stored in an environment that has a very high humidity, the amount of water on that before flowing powder clumped.

example 2

To 2 kg (100 parts) Polyamide-12 powder, prepared according to <patcit id="pcit0005" dnum="DE2906647"><text>DE 29 06 647</text></patcit> having an average grain diameter d₅₀ of 98 microns (laser diffraction) and a bulk density to DIN 53466 of 480 g / l is, 5 g (0.25 parts) Aerosil®R 812 in dry-blend method using a Henschel mixer P10 at 400 rev / min 5 mixed minutes. The flowability of the resulting composition is determined according to DIN 53492 immediately after mixing. After a 6 days of conditioning at 40 ° C and 95% rel. Humidity and subsequent conditioning of the composition for 24 hours at 20 ° C and 50% rel. Humidity is the flowability redetermined. The flowability of the composition before and after conditioning is determined by determining the Rieseldauer in seconds for 150 grams of composition in accordance with DIN 53,492th The Rieseldauer is given in Table 2 below.

example 3

2 kg (100 parts) of nylon-12 powder from Example 2 and 5 g (0.25 part) Aerosil® R 972 are mixed in accordance with Example 2. FIG. The flowability of the composition is as described in Example 2 was determined and is placed moves in Table 2 below.

example 4

2 kg (100 parts) of nylon-12 powder from Example 2 and 0.5 g (0.025 parts) Aerosil® R 812 are mixed in accordance with Example 2. FIG. The flowability of the composition is as described in Example 2 was determined and is placed moves in Table 2 below.

example 5

2 kg (100 parts) of nylon-12 powder from Example 2 and 0.3 g (0.015 parts) Aerosil® R 812 are mixed in accordance with Example 2. FIG. The flowability of the composition is as described in Example 2 was determined and is placed moves in Table 2 below.

example 6

2 kg (100 parts) of nylon-12 powder from Example 2 and 5 g (0.25 part) Aerosil® 200 are as described in Example 2, mixed. The flowability of the resulting composition, as described in Example 2 was determined and is listed in Table 2 below.<tables id="tabl0002" num="0002"><table frame="all"><title>Table 2</title><tgroup cols="4"><colspec colnum="1" colname="col1" colwidth="39mm" /><colspec colnum="2" colname="col2" colwidth="23mm" /><colspec colnum="3" colname="col3" colwidth="46mm" /><colspec colnum="4" colname="col4" colwidth="59mm" /><thead valign="top"><row><entry>composition</entry><entry>Rieseldauer after mixing</entry><entry>Rieseldauer after conditioning at elevated humidity</entry><entry>Percent change Rieseldauer by conditioning at elevated humidity</entry></row></thead><tbody><row><entry>Composition of Example 2</entry><entry>12,8 s</entry><entry>13,2 s</entry><entry>+3%</entry></row><row><entry>Composition of Example 3</entry><entry>13,1 s</entry><entry>14,2 s</entry><entry>+8%</entry></row><row><entry>Composition of Example 4</entry><entry>13,4 s</entry><entry>13,9 s</entry><entry>+4%</entry></row><row><entry>Composition of Example 5</entry><entry>15,6 s</entry><entry>17,2 s</entry><entry>+10%</entry></row><row><entry>Composition of Example 6 (Comparative)</entry><entry>12,6 s</entry><entry>18,1 s</entry><entry>+44%</entry></row></tbody></tgroup><tgroup cols="4" rowsep="0"><colspec colnum="1" colname="col1" colwidth="39mm" /><colspec colnum="2" colname="col2" colwidth="23mm" /><colspec colnum="3" colname="col3" colwidth="46mm" /><colspec colnum="4" colname="col4" colwidth="59mm" /><tbody><row><entry namest="col1" nameend="col4" align="justify">The Rieseldauer the composition was determined for 150 g of the composition according to DIN 53492nd</entry></row></tbody></tgroup></table></tables>

The compositions of Example 2 to 5 after conditioning for 6 days in a climatic chamber at 40 ° C and a relative humidity of 95%, followed by conditioning for 24 hours at 20 ° C and 50% rel. Humidity no significant change in flowability. The increase in Rieseldauer is between 3% and 10%. Cond by the consistently good flowability irrespective of the storage conditions of the compositions of Examples 2 to 5, no deterioration in the processability of the compositions has occurred. Comparative Example 6 shows the freshly mixed state, a free-flowing, which is comparable with Examples 2 to. 5 Comparative Example 6 shows but after conditioning for 6 days in a climatic chamber at 40 ° C and 95% relative humidity and subsequent conditioning for 24 hours at 20 ° C and 50% rel. Humidity a significant increase in Rieseldauer by 44% and hence a significant deterioration in the flowability. This deterioration in the flow properties resulted in processing difficulties and quality problems produced by this composition products.