DE10320464B4 - Use of a molding compound for the production of sintered molded parts - Google Patents

Abstract

Use of a molding composition for the production of sintered molded parts, comprising a sinterable powdery material and a thermoplastic binder based on polyamide (PA),
in which
the molding composition comprises a catalyst which promotes binder removal and reacts to a part of the sintered molding
characterized in that
a) the material consists of glass powder and the catalyst consists of NaOH and / or KOH or
b) the material consists of alumina powder and the catalyst of acidic or basic alumina or
c) the material consists of a nitride ceramic and the catalyst of amides or amines of the metals on which the nitrides are based exist.

Description

The The invention relates to a use of a molding composition for the production of sintered moldings containing a sinterable powdered material and a thermoplastic binder based on polyamide (PA) and a catalyst according to claim 1.

molding compounds for the production of sintered structures by means of powder metallurgy Manufacturing process included in addition to a sinterable material powder a binder content with which a required mechanical stability of a From the molding compound shaped green body before a heat treatment is adjustable in the context of the sintering process. While the binder before or at the actual sintering process over various methods, for example thermally removed, Sinters the material powder into a solid body.

The currently in industrial use or in research projects used binder systems are based predominantly on wax or polymer / wax mixtures which are easily heated remove almost completely from the green body to let. A debilitated green body becomes before the sintering process generally called brown body.

by virtue of the overall low degree of polymerization of currently industrial The binder systems used is the strength of both the molding compositions and the green body produced therefrom very limited, which in particular in the production of microforming bodies and microcomponents leads to unacceptable reject rates. Also for use in thick film technology, For example, in a printed circuit board manufacturing in microelectronics, are These molding compounds unsuitable, since they are already at low temperatures melt and make an exact structuring virtually impossible.

to Avoiding the aforementioned disadvantages and to extend the The application spectrum is aimed at the degree of polymerisation of binders significantly increase. One way to this goal is via one Use of thermoplastic polymers as binder systems, which but only about a catalytic reaction effectively and residue-free from the green body removable are.

In the DE 4021739 A1 a molding compound with a binder system based on polyoxymethylene (POM) is presented, which is successively degraded catalytically in a gaseous acid-containing atmosphere in a green body and eliminated as gaseous degradation products. Suitable acids which serve as the basis of the atmosphere, organic acids such as. A. HNO ₃ or hydrohalic acids, also called formic acids, acetic acid or trifluoroacetic acids above 130 ° C.

at However, the production of metallic sintered structures are acidic atmospheres in the debinding often problematic and therefore undesirable since the metallic material powder used in the molding compound size specific surface and thus a pronounced Has tendency to oxidation. Also, processes with acidic catalytic atmospheres not for health reasons unproblematic and require correspondingly elaborate safety precautions. In addition, the polyoxymethylenes (POM) used have a limited Strength, which, for example, for the production of microtechnical Structures with high flow-length to Wall thickness ratios with the usual for this Abformverfahren reaches its limits.

From that Based on the object of the invention, a use of a molding composition to propose, which does not have the disadvantages described above or only to a much lesser extent. In particular, should the molding compound a larger mechanical Have strength and residue in a less problematic atmosphere be debindable.

The Task is solved by the features of the first claim. advantageous Embodiments of the invention are specified in the subclaims.

The essential feature of the invention relates to the use of a thermoplastic binder based on polyamide (PA) (preferably polycaprolactam) in the molding composition, which consists of at least one sinterable powdery material and a catalyst in addition to the binder. Molding compounds with such a binder can not only be processed well, but also have a strength which is increased by at least 20% compared with molding compositions with binders based on POM. Polycaprolactams, polyamide 6 (modulus of elasticity 3000 MPa, yield stress 80 MPa), polyamide 6.6 (modulus of elasticity 3000 MPa, yield stress 64 MPa) or polyamide 12 serve as suitable polyamides. Since the binder forms the material used in the processing of the molding composition and then the Green body occurring temperatures must on the one hand safely survive and on the other hand must not cause undesirable changes in shape, the use of polyamides represents an advantageous extension of the processing capabilities of the molding compositions provided with such a binder. So that this advantage for processing is not limited by disadvantages, is the Binder with the help of a suitable exactly assembled catalyst, ie without a thermally supported Ent Binding process removable.

This Process of debinding with help is optional also in two stages feasible. In this case, in a first stage, a preferably depressurized chemical degradation of PA in the places where this in direct contact with the catalyst. This also creates a pore system in the PA fraction of the green body, which promotes the further debindering process. In an optional second stage, however, the further debindering by a supported by thermal process, there is an accelerated decomposition of the PA. It is too Note that the second stage of debindering is only then foreseeable is when the pore system in the green body one determined volume fraction, from the possible volume engaging decomposition products are absorbed by these and not to destruction of green or brown bodies to lead. The for but the second stage required temperatures reach far not the temperatures, which for a purely thermal Debinding would be required.

The Molding compounds have a catalyst, which on the one hand a Local potential for electron density shift at least one Part of the binder, on the other hand, part of the Product or to the material of which the material is made, responding. It thus appears in the sintered component, i. H. to debinding and after sintering, in particularly advantageous Way not as additional Component and leaves while the component is not.

Of the used catalyst provides a basic or acidic modification of the material. The catalyst also has an advantageous effect Way an increase the sintering activity of the material, resulting in a lower sintering temperature for sintering is to be provided. This causes a significant reduction in heating energy for the Sintering process. This effect is due to a very fine particle size with appropriate enlarged specific surface the catalyst can still be improved. Ideally, a particle size ratio of Catalyst to material powder from one to ten.

is the material which is present in the molding composition as material powder, essentially a metal based nitride ceramic, the catalyst consists essentially of amines or amides of these Metals or from acidic or basic derivatives of the corresponding Metal salts.

In strong sodium-containing glasses is suitable NaOH or KOH or a mixture of these hydroxides as Catalyst.

at A mechanical alloy in the molding material several different sinterable powdery Mixed materials. This results in a powder mixture as a material powder, which contains at least two material fractions, wherein the material fractions Metals, metal alloys, non-oxide ceramics or metal oxides are.

Of the In addition, a thixotropic agent can be added to the molding compound. For example, very fine powder (nanopowder) or aerosils. Furthermore, can the molding compound a processing aid such as at least one of the additives demolding aid, lubricant, Release agents or wetting agents are added. Negative influences such Additives to the processability were shown in practical experiments only above 10 vol.% Of these additives based on the binder content. Too high proportions cause in particular a reduced strength the green body or to lead too inadmissible high deformations during of the debinder and Sintering process.

The Parts by weight of the individual components in the molding compound account ideally to 35 to 95 vol.% on the sinterable powdery material, to 5 to 65 vol.% Of the thermoplastic binder, as well as 0.01 to 20 vol.% On the catalyst. Green body, which produced from such a shaped body are on the one hand have a for a subsequent Sintering process required proportion of sinterable powdery material, on the other hand but one for a subsequent processing procedure sufficient strength, d. H. a minimum required proportion on the thermoplastic binder. A machining process the mentioned Art is any forming process for the molding material. It includes at least one injection molding, an extrusion or other shaping process step, a process step from the thick-film technology for flat or selective coating of substrate surfaces with layers, preferably with a layer thickness between 0.1 to 1000 microns, on a substrate, a Vakuumumform-, a hot stamping or another forming process step or a chipping or electro-eroding machining step, the requirements to the thermo-mechanical properties of the molding composition in an advantageous Way individually about the selection, morphology and quantitative composition of the molding material is adjustable. Here, the molding material not only the criteria in terms of forming and possibly a demolding, but also in terms of a dimensional stability in a debindering, d. H. in the transfer of Green to Brown body, and in terms of reproducibility in a subsequent sintering process suffice.

The ideal composition depends on al Lem on the powder type and the catalyst content. The selection and the morphology are determined by the particle size of the catalyst and the specific surface area dependent thereon, as well as the resulting change in the viscosity. With a small particle size and the largest possible specific surface area (BET), maximum activity of the catalyst is obtained. However, this must have the sharpest possible temperature threshold so that the catalyst remains largely inactive at the processing temperatures and only becomes active at higher temperatures (debindering).

One Process for the preparation of components from one of the abovementioned Molding composition comprises at least one original or deformation of the molding composition to a green body with a processing method with one or more processing steps. This is followed by a transfer of the green body in a brownbody by catalytic removal of the binder, preferably by a catalytic chemical degradation of the binder in green body volume an open pore system in the brown body is created. It follows the sintering of the brown body, wherein this into the component, d. H. the actual shaped body as Final product is transferred. While the heating to the actual sintering process is also another Degradation of the binder for the preparation of the brown and then the Sintered body. As a result, the environment also becomes another positive effect not in addition through possible Degraded degradation products of the binder. When using polycaprolactam As a binder, degradation takes place to its educt caprolactam, which In principle, the recycling of the binder is made possible. A sintering process in a reactive atmosphere allows or thereby accelerates a conversion of the catalyst by chemical Transformation into a product. This integrates itself into the component or the component, which in addition the one increase the density is achievable.

A Typical application involves the manufacture of precision components, microstructured components or micro parts by powder injection molding of ceramics with complex Geometry. Molding compounds which are currently available on the market binder systems based on waxes, polyolefin-wax mixtures or polyacetals Although contain a reliable debindering alone with moderate temperature treatments or with organic solvents, however, significantly limit the reproducibility of this produced green body and Brown Body. The use of PA results in a molding compound which both the processing temperatures and the processing times of the injection molding process outlast at a demolding the green body dimensionally stable stops and can also be debindered clean after demolding, d. H. catalytically remove all binder components from the green body. there be with the use of a catalyst of the previously described Type temperature and time of debindering kept low, which in addition to especially in a mass production advantageous energy saving effects leads and saves time and costs significantly.

A another typical application is generally the thick film technique for the production of full-surface Protective layers or microstructured layer structures in particular in microelectronics or microsensors. Often the process steps become the thick film technology with a multitude of further process steps for the production of components or systems of microtechnology combined. Use of the molding compound expands the possibilities in a production process especially in processes at elevated temperature.

The Invention will be explained in more detail with reference to the following embodiments:

embodiment 1

One microstructured shaped body from alumina, by way of example for an oxide ceramic, is intended in the frame of the invention are produced by an injection molding process. The one for this used molding composition consists of 60 to 85 wt.% Alumina powder, from 15 to 40% by weight of a PA and from 6 to 9% by weight of a catalyst, for example, acidic or basic alumina for chromatography. The preparation of the thermoplastic molding composition, d. H. mixing, took place in a twin-screw extruder, wherein the first Binder was melted at a temperature between 240 to 285 ° C. The Aluminum powder and the catalyst was in the ratio 10: 1 cold premixed and hot Binder stream added, with a Pulverfüllgrad adjusted of about 73 wt.%. In the subsequent kneading and mixing zones, the mass was compounded and subsequently tempered to a temperature between 150 and 250 ° C, preferably 180 ° C. and for the injection molding process taken from the twin-screw extruder.

Of the subsequent injection molding was carried out with a molding compound temperature in the injection molding machine between 260 and 270 ° C and a tool temperature between 60 and 90 ° C for macroscopic Components. Molding compound temperature and mold temperature had to be at Injection molding of Microstructures are increased with increasing degree of miniaturization up to 290 ° C or 100 ° C. Of the injection molding ended after a cooling process with the removal of the green body the tool.

to Debindering, i. the transfer of the green body in a brownbody, goes through the green body depends on powdery Material in a inert or reactive atmosphere, a linearly increasing Temperature profile from 50 to 310 ° C or alternatively a three-stage temperature program with two holding temperatures, the first above 210 ° C and the second at about 250 ° C, as well as a final temperature at approx. 310 ° C. The debinding took depending on the size of the components and their maximum cross-sections between one and 24 hours.

The first holding stage is used in particular the reaction of catalyst with the binder portion surrounding it to form a preferably open pore system. The second stage is considered an intermediate, which the binder removal moderately pushes forward and so the green body relieved the third stage. It is especially in thick-walled green bodies or with filigree green bodies with locally strong different cross sections or distortion-prone geometry transitions required. The Time extension of the holding levels generally increase the component thickness, lie between 0.1 and 24 h and are ultimately determined experimentally and based on experience.

in the Deburring a piece of a specimen with an initial one Mass of 41.65 mg and a proportion of alumina and catalyst (Inertanteil) of 73 wt.% Was started with a temperature program from a starting temperature of 25 ° C (Ambient temperature) at 5 ° C / min a first holding temperature of 214 ° C started, where already when heating a debinding of 4.9% (reference each Total binder content in the green body) achieved has been. After a holding time of 3 hours at 214 ° C, the degree of binder removal was 17.4%, which in a subsequent increase in temperature with 1 ° C / min at 249 ° C and a holding time of 3h at this temperature to 29.8% or 46.8% increased. After a further increase in temperature at 1 ° C / min to 304 ° C observed one more raise the degree of debinding to 62.8%, which after another 3h Holding time at this temperature set to 89.5%. The exact one Temperature and weight measurement was carried out with a thermobalance in a helium stream of 100 ml / min. The remaining 10.5% The binder can be at about 500 ° C in an oxidative atmosphere, for example Air, with no apparent change in shape of the brown body across from remove the green body.

in the Following the full Debinding was carried out by sintering the alumina lignite under sintering conditions known, wherein the catalyst with sintered in the Component was involved.

embodiment 2

One microstructured shaped body made of silicon nitride as a typical representative of the non-oxide ceramics is to be made in the context of the invention with an injection molding. The one for this used molding material consists of 60 to 85 wt.% Silicon nitride powder, from 15 to 40% by weight of a PA and between 6 and 9% by weight of a catalyst in the form of a derivative of the silicon nitride. Basically for silicon nitride but also amino and amidosilanes (e.g., BSA, bistrimethylsilylacetamide), disilazanes (e.g., HMDS, hexamethyldisilazane) and their metal salts as catalysts into consideration. The preparation of the thermoplastic molding composition, d. H. mixing, carried out in a twin-screw extruder, wherein first the binder was melted at a temperature between 180 to 280 ° C. The silicon nitride powder and the catalyst were in the ratio 10: 1 cold premixed and hot Binder stream added, with a Pulverfüllgrad adjusted of about 74 wt.%. In the subsequent kneading and mixing zones, the mass was compounded and subsequently tempered to a temperature between 150 and 250 ° C and for the injection molding process taken from the twin-screw extruder.

suitable Catalysts for other nitride ceramics, e.g. Aluminum nitride or titanium nitride Amines or amides of the metals on which the nitrides are based. alternative Also suitable are acidic or basic alumina as catalyst, whereby a nitride-oxide composite ceramics is formed. For example can be prepared in this way sialon moldings, with a Silicon nitride powder added to such an alumina catalyst is, wherein the proportion of catalyst depending on the desired sialon composition to about 40 wt.% Is increasable.

Of the injection molding was carried out with a molding material temperature between 140 and 170 ° C and a Tool temperature, which is at least 10 ° C below the molding compound temperature was. He ended up after a cooling process with the removal of the green body the tool.

The binder removal was carried out with the same three-stage temperature program with the same parameters as specified concretely in Example 1. Also, the degree of debindering after each temperature increase and each holding temperature substantially corresponds to the values according to Embodiment 1, which is also due to the fact that in both embodiments, an inert during the binder removal behaved material powder and a principle the same binder was present and the difference in debinding only was in the catalyst, but which in both embodiments had the same effect on the binder. In contrast to the embodiment 1, the debinding of the nitrides was carried out in nitrogen instead of helium.

in the Following the full Debinding was carried out by sintering the silicon nitride lignite body sintering conditions known, wherein the catalyst with sintered in the Component was involved.

Claims (5)

Use of a molding composition for producing sintered molded parts, comprising a sinterable powdery material and a thermoplastic binder based on polyamide (PA), wherein the molding composition comprises a catalyst which promotes debindering and reacts to a part of the sintered molding, characterized in that a) the material consists of glass powder and the catalyst consists of NaOH and / or KOH or b) the material consists of alumina powder and the catalyst of acidic or basic alumina or c) the material of a nitride ceramic and the catalyst of amides or amines of the metals, on which the nitrides are based exist. Use according to claim 1, characterized in that a thixotropic agent is added to the molding compound. Use according to one of the preceding claims, characterized in that the molding compound has a processing aid such as at least one of additives Mold release, lubricant, release agent is added. Use according to one of claims 1 to 3, wherein the volume fractions the molding material to 35 to 95 vol.% Of the sinterable powdery material, to 5 to 65 vol.% Of the thermoplastic binder, as well as 0.01 to 20 vol.% Attributable to the catalyst. Use according to claim 4 for at least one Spritzgieß-, a Extrusion or other shaping process step, a Process step of thick-film technology for surface or selective coating of substrate surfaces with layers with a layer thickness between 0.1 to 1000 microns on one Substrate, a Vakuumumform-, a hot stamping or another forming process step or a cutting or electro-eroding machining step.