DE10320464A1 - Molding composition for producing sintered shaped articles, e.g. micro-electronic components, comprising sinterable powder, catalyst and polyamide binder - Google Patents

Abstract

In a molding composition (I) for producing sintered shaped articles, comprising of sinterable powder (a), a thermoplastic binder (b) and a catalyst (c). The binder (b) consists of a polyamide (PA). An independent claim is included for a method for production of components from (I), involving: (1) processing (I) in one or more stages to produce a green body; (2) converting the green body into brown body by catalytic removal of the binder (b) using the catalyst (c); and (3) sintering the brown body.

Description

The The invention relates to a molding composition for the production of sintered Molded parts containing a sinterable powdery material, a thermoplastic binder, and a catalyst according to the preamble of the first claim, a use of a molding composition according to claim 10 and a method for producing components from a Molding composition according to claim 12th

molding compounds for the production of sintered structures using powder metallurgical Manufacturing processes contain a sinterable material powder a binder component with which the required mechanical stability of a from the molding compound shaped green body in front a heat treatment is adjustable within the sintering process. During the binder before or at the actual sintering process various processes, for example thermal removal, the material powder sinters into a solid body.

The currently in industrial use or in research projects The binder systems used are mainly based on wax or polymer / wax mixtures, which can be easily heated Remove almost completely from the green body to let. A green body that has been released from the before the sintering process generally called brown body.

by virtue of the overall low degree of polymerization currently industrial Binder systems used is the strength of both the molding compounds and the green body made from it 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 the manufacture of printed circuit boards in microelectronics these molding compounds are unsuitable because they are already at too low temperatures melt and make exact structuring practically impossible.

to Avoiding the aforementioned disadvantages and expanding the The range of applications is aimed at, the degree of polymerization of binders increase significantly. One way to this goal is through one Use of thermoplastic polymers as binder systems, which however only about a catalytic reaction can be removed effectively and without residue from the green body are.

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

at the manufacture of metallic sintered structures are acidic atmospheres Often problematic during the delivery and therefore undesirable because the metallic material powder used in the molding compound size specific surface and therefore a distinctive one Has a tendency to oxidize. There are also processes with acid catalytic atmospheres not for health reasons unproblematic and require correspondingly complex safety precautions. In addition, the polyoxymethylenes (POM) used have a limited number Strength, which for example for the production of microtechnical Structures with high flow lengths too Wall thickness ratios with the usual ones Impression process reaches its limits.

From that starting from the object of the invention to propose a molding compound, which does not have the disadvantages described above or only in significantly smaller dimensions having. In particular, the molding compound should have a greater mechanical Have strength and residue-free in a less problematic atmosphere be releasable. It is also an object of the invention to use the molding compound and a production of components from the molding compound propose.

The The task is characterized by the features of the first, tenth and twelfth claims solved. 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, in addition to the binder, consists at least of a sinterable powdery material and a catalyst. Molding compositions with such a binder are not only easy to process, but also have a strength that is at least 20% higher than that of molding compositions with binders based on POM. Suitable polyamides are polycaprolactams, polyamide 6 (modulus of elasticity 3000 MPa, tensile strength 80 MPa), polyamide 6.6 (modulus of elasticity 3000 MPa, tensile strength 64 MPa) or polyamide 12. Since the binder is used during processing of the molding compound and then the Temperatures occurring green body safely survive on the one hand must and on the other hand must not cause undesirable changes in shape, the use of polyamides represents an advantageous extension of the processing possibilities of the molding compositions provided with such a binder. In order that this advantage for processing is not restricted again by disadvantages, the binder is exact with the aid of a suitable one assembled catalyst, ie removable without a thermally assisted debinding process.

This The process of debinding with the help is optional in two stages feasible. In a first stage, there is preferably an unpressurized one chemical degradation of the PA in places where it is in direct contact with the catalyst. This also creates a pore system in the PA fraction of the green body, which has a positive effect on the further delivery process. In an optional The second stage, however, is further debinding through a supports thermal process, whereby there is an accelerated decomposition of the PA. It is too note that the second stage of childbirth can only be planned is when the pore system in the green body has taken up a certain volume share, starting from the possible volume engaging decomposition products are absorbed by this and not to destruction of the green or brown body to lead. The for the temperatures required for the second stage reach at far from the temperatures, which are for an exclusively thermal Childbirth would be required.

The Invention, i.e. the molding compositions have a catalyst which on the one hand a local potential for electron density shift has at least one component of the binder, on the other hand to a part of the product or the material from which the Material exists, reacts. It therefore appears in the sintered component, d. H. after debinding and after sintering, in particular advantageously not as an additional component and leaves it nor the component. The catalyst ideally consists of an acidic or basic derivative of the material powder, which is introduced into the molding compound and during the sintering in the component built in or in the case of glassy or ceramic material powder to additional Quantities of this ceramic or glass react. The acidic or basic derivatives of the metal oxides generally include Hydroxyl groups, sulfate groups, nitrate groups, sulfates, phosphates or other salts.

The catalyst used is therefore only a basic or acidic modification of the material. The catalyst also acts advantageously 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 the very fine particle size enlarged specific surface the catalyst can still be improved. A particle size ratio of Catalyst to powder material from one in ten.

is the material which is present in the molding compound as material powder, essentially a metal oxide or an oxide of an alloy component the catalyst consists essentially of acidic or basic derivatives the metal oxide or the hydroxide of the metal or alloy component.

is the material which is present in the molding compound as material powder, essentially a non-oxide ceramic, the catalyst is made essentially from acidic or basic derivatives of this non-oxide ceramic.

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

is the material which is present in the molding compound as material powder, consisting essentially of a metal or a metal alloy Catalyst essentially from fine-grained additives of these metals or a metal suitable as an alloy component, possibly supplemented by small proportions of the metal oxide or the oxide of the alloy components.

Molding compounds, which contain glass powder as a material can already be added by adding a Mineral acid, e.g. silica, one for the debinding required to have an acidic pH and react catalytic for the dismantling of the PA. NaOH is also suitable in glasses with a high sodium content or KOH or a mixture of these hydroxides as a catalyst.

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

A thixotropic agent can also be added to the molding composition, for example very fine powders (nanopowder) or aerosils. Furthermore, the molding composition can be a processing aid such as at least one of the additives Lubricants, release agents or wetting agents can be added. In practical tests, such additives have only had a negative impact on the processability above 10% by volume of these additives, based on the proportion of binder. Too high proportions result in a reduced strength of the green bodies or lead to inadmissibly high deformations during the debinding and sintering process.

The The proportions by weight of the individual components in the molding composition are eliminated Ideally, 35 to 95 vol.% On the sinterable powdery material, 5 to 65 vol.% on the thermoplastic binder, as well as 0.01 to 20 vol.% On the catalyst. Green body, which is produced from such a shaped body are, on the one hand, have one for a subsequent one Sintering process required proportion of sinterable powdery material, on the other hand one for a subsequent machining process sufficient strength, d. H. a minimum required share on the thermoplastic binder. A machining process of those mentioned Art is any forming process for the molding compound. It includes at least one injection molding, an extrusion or other molding process step, a process step from thick-film technology to flat or selective coating of substrate surfaces with layers, preferably with a layer thickness between 0.1 to 1000 μm, on a substrate, a vacuum forming, a hot stamping or another forming process step or a cutting step or electroerodizing machining step, the requirements to the thermomechanical properties of the molding compound in a more advantageous Way individually the selection, morphology and quantitative composition of the molding compound is adjustable. The molding compound must not only meet the criteria with regard to the forming and possibly a demolding process, but also with regard to dimensional stability in the case of debinding, d. H. in the transfer of Green to Brown body, and with regard to reproducibility in a subsequent sintering process suffice.

The ideal composition depends especially on the powder type and the catalyst content. Determined the selection and morphology by the particle size of the catalyst and the dependent one specific surface and the resulting change the viscosity. at small particle size and if possible greater specific surface (BET) receives one a maximum activity of the catalyst. However, this must have a temperature threshold that is as sharp as possible have, so at the processing temperatures of the catalyst remains largely inactive and only at higher temperatures (debinding) becomes active.

Farther is for the solution the task of a method for producing components from a proposed molding compound proposed. It includes at least one Original or forming of the molding compound into a green body using a processing method with one or more processing steps. Following this there is a transfer of the Green body in a brown body by catalytic removal of the binder, preferably by a catalytic chemical breakdown of the binder in the green body volume an open pore system is created in the brown body. The follows Sintering of the brown body, this into the component, i.e. H. the actual molded body as the end product is transferred. While heating up to the actual sintering process is also carried out Degradation of the binder for the production of the brown or subsequently the Sintered body. This also has another positive effect on the environment not additionally through possible Breakdown products of the binder contaminated. When using polycaprolactam as a binder, degradation to its caprolactam starting material takes place, whereby in principle the recycling of the binder is made possible. A sintering process in a reactive atmosphere allows or accelerates a conversion of the catalyst by chemical conversion into a product. This integrates into the component or the component, which additionally which is an increase the density can be achieved.

A typical application includes the manufacture of precision components, micro-structured components or micro parts by powder injection molding from ceramic with complex Geometry. Molding compounds which are the binder systems currently available on the market based on waxes, polyolefin wax mixtures or polyacetals contain a reliable debinding alone moderate temperature treatments or with organic solvents, however significantly limit the reproducibility of the resulting manufactured green body and Brown Body. The use of PA creates a molding compound, which both the processing temperatures and processing times of the injection molding process persist, the green body is dimensionally stable during demolding holds and can also be properly debindered after demolding, d. H. Have all binder components removed catalytically from the green body. there with the use of a catalyst of the previously described Art temperature and time of debinding kept low, which in addition to advantageous energy saving effects, particularly in series production leads and saves time and money significantly.

Another typical application is generally offered by thick film technology for the production of protective coatings or microstructured layer structures, particularly in microelectronics nik or microsensor technology. The process steps of thick film technology are often combined with a large number of other process steps for the production of components or systems for microtechnology. The use of the molding compound expands the possibilities in a production process, particularly in processes with an elevated temperature.

The The invention is explained in more detail using the following exemplary embodiments:

Embodiment 1

On micro-structured molded body made of aluminum oxide, exemplary for an oxide ceramic, is said to be in the frame of the invention are manufactured using an injection molding process. The one for this The molding material used consists of 60 to 85% by weight of aluminum oxide powder, 15 to 40% by weight of a PA and between 6 and 9% by weight of a catalyst, for example acidic or basic aluminum oxide for chromatography. The production of the thermoplastic molding composition, d. H. mixing, was carried out in a twin-screw extruder, initially the Binder was melted at a temperature between 240 to 285 ° C. The Aluminum powder and the catalyst were in a ratio of 10: 1 premixed cold and hot Binder stream added, a powder filling degree of approx. 73% by weight being established. The mass was compounded in the subsequent kneading and mixing zones and subsequently tempered to a temperature between 150 and 250 ° C, preferably 180 ° C and for the injection molding process removed from the twin screw extruder.

The subsequent injection molding was carried out with a molding material temperature in the injection molding machine between 260 and 270 ° C and a tool temperature between 60 and 90 ° C for macroscopic Components. Molding material temperature and mold temperature had to Injection molding of Microstructures with increasing degree of miniaturization can be increased to 290 ° C or 100 ° C. The injection molding ended after a cool down with the removal of the green body the tool.

to Childbirth, i.e. the transfer of the green body into a brown body, goes through the green body depending on powdery Material in an 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 approx. 250 ° C, and a final temperature at approx. 310 ° C. The delivery lasted depending on the size of the components and their maximum cross sections between one and 24 hours.

The The first holding stage serves in particular to react the catalyst with the surrounding binder portion to form a preferably open pore system. The second level is an intermediate level, which moderately drives the debinding and thus contributes to the green body relieved the third stage. It is particularly in the case of thick-walled green bodies or with filigree green bodies with strong locality different cross sections or warping-prone geometry transitions are required. The the temporal extent of the holding stages generally increases with it the component thickness, are between 0.1 and 24 h and are ultimately to be determined experimentally and based on empirical values.

in the Debinding of a piece of a test specimen with an initial Mass of 41.65 mg and a proportion of aluminum oxide and catalyst (Inert fraction) of 73% by weight was started with a temperature program from a starting temperature of 25 ° C (Ambient temperature) at 5 ° C / min approached a first holding temperature of 214 ° C, already a debinding level of 4.9% when heated (reference in each case Total binder content in the green body) has been. After a holding time of 3 hours at 214 ° C, the degree of debinding was 17.4%, which increases with a subsequent temperature increase 1 ° C / min to 249 ° C and a holding time of 3 hours at this temperature increased to 29.8% and 46.8%. To a further temperature increase at 1 ° C / min to 304 ° C one observed a further increase the degree of debinding to 62.8%, which increases after a further 3 hours Set hold time at this temperature to 89.5%. The exact one Temperature and weight were recorded using a thermal scale in a helium flow of 100 ml / min. The remaining 10.5% of the binder can be at about 500 ° C in an oxidative atmosphere, for example Air, without any noticeable change in shape of the brown body across from remove the green body.

in the Connection to the full The alumina brown body was sintered under debinding known sintering conditions, with the catalyst in the sintered Component was integrated.

Embodiment 2

A microstructured molded body made of silicon nitride as a typical representative of the non-oxide ceramics is to be produced within the scope of the invention using an injection molding process. The molding composition used for this purpose consists of 60 to 85% by weight of silicon nitride powder, 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 silicon nitride. Grundsätz However, amino and amidosilanes (eg BSA, bistrimethylsilylacetamide), disilazanes (eg HMDS, hexamethyldisilazane) and their metal salts are also suitable as catalysts for silicon nitride. The thermoplastic molding composition, ie the mixing, was produced in a twin-screw extruder, the binder first being melted at a temperature between 180 and 280 ° C. The silicon nitride powder and the catalyst were cold premixed in a ratio of 10: 1 and added to the hot binder stream, a degree of powder filling of approx. 74% by weight being established. The mass was compounded in the subsequent kneading and mixing zones and then tempered to a temperature between 150 and 250 ° C. and removed from the twin-screw extruder for the injection molding process.

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 acidic or basic aluminum oxide are also suitable as catalysts, which creates a nitride-oxide composite ceramic. For example can be produced in this way Sialon moldings, one Such an aluminum oxide catalyst is added to silicon nitride powder , the proportion of catalyst depending on the desired sialon composition to over 40% by weight can be increased.

The injection molding was carried out with a molding material temperature between 140 and 170 ° C and one Tool temperature which is at least 10 ° C below the molding compound temperature was. It ended after a cool down with the removal of the green body the tool.

The Debinding was carried out using the same three-stage temperature program with the same parameters as specified specifically in embodiment 1. The degree of debinding after each temperature increase and each holding temperature corresponds essentially to the values according to the exemplary embodiment 1, which is also due to the fact that in both embodiments one during the Debinding inert material powder and a principle the same binder was present and the difference in debinding only was in the catalyst, but the same in both embodiments Had an effect on the binder. In contrast to the embodiment 1 the nitrides were debound in nitrogen instead of in Helium.

in the Connection to the full The silicon nitride brown body was sintered under debinding known sintering conditions, with the catalyst in the sintered Component was integrated.

Embodiment 3

On micro-structured molded body made of a metallic material, e.g. Fe, Cu, Ni, Ag, Ti, Cr, Mg or alloys, is intended in the context of the invention with a injection molding getting produced. The one for this The molding material used consists of 60 to 85% by weight of metal powder, 15 to 40% by weight of a PA and between 6 and 9% by weight of a catalyst.

in the In contrast to ceramics, the metal powders used are finely crystalline Form already catalytic properties that degrade the PA directly.

at Steel alloys offer the use of Ni, Cr or chromium dioxide as a catalyst. The material powder is in accordance with the alloying elements mentioned so to choose that only with the installation of the catalyst materials in the steel alloy the desired Composition is achieved.

Further So-called side effects of a catalyst are not only to be considered, but also specifically exploitable. For example, is alumina powder not only used as a catalyst, but also as a grain growth inhibitor for a sintered metal produced by powder metallurgy.

The Production of the thermoplastic molding composition, d. H. mixing, was done in a twin screw extruder using the procedure and the parameters as used in the two aforementioned exemplary embodiments are shown. This also applies to the injection molding process and debinding, with an oxidizing atmosphere definitely is to be prevented. The degree of debinding after each temperature rise and each holding temperature corresponds essentially to the values according to the exemplary embodiment 1 and 2, which is due to the largely identical process control. If the temperature is raised to approx. 500 ° C, however, it is necessary to remove it completely ensure an absolutely non-oxidizing atmosphere of the binder, the degradation products in the PA must also be taken into account.

in the Connection to the full The metal brown body was sintered under debinding known sintering conditions, with the catalyst in the sintered Component was integrated.

Claims (15)

Molding composition for the production of sintered moldings, containing a sinterable powder ges material, a thermoplastic binder, and a catalyst, characterized in that the binder consists essentially of a polyamide (PA). Molding composition according to claim 1, characterized in that the thermoplastic binder consists essentially of a polycaprolactam, Polyamide 6 or polyamide 6.6 is made. Molding composition according to claim 1 or 2, characterized in that that the catalyst has a local potential for electron density shift has at least one component of the binder. Molding composition according to one of claims 1 to 3, characterized in that that the material is essentially a metal oxide or an oxide of a Alloy component and the catalyst is essentially acidic or basic derivatives of metal oxide or hydroxides of Are metal oxide or an alloy component. Molding composition according to one of claims 1 to 3, characterized in that that the material is essentially a non-oxide ceramic and the catalyst is essentially acidic or basic derivatives of Contains non-oxide ceramics. Molding composition according to one of claims 1 to 3, characterized in that that the material is essentially a metal or a metal alloy and the catalyst is made of a finely crystalline metal or Metal oxide powder or an acidic or basic derivative of one Metal oxide exists. Molding composition according to one of claims 1 to 3, characterized in that that the sinterable powdery material is a powder mixture with at least two material fractions, where the material fractions are metals, metal alloys, non-oxide ceramics, Metal oxides, glasses or are metal glasses. Molding composition according to one of the preceding claims, characterized characterized in that a thixotropic agent is added to the molding composition is. Molding composition according to one of the preceding claims, characterized characterized in that the molding compound is a processing aid such as at least one of additives Mold release agent, lubricant, release agent is added. Use of a molding composition according to one of claims 1 to 9 for one Machining process, the proportions by weight of the molding compound 35 to 95 vol.% On the sinterable powdery Material, 5 to 65 vol.% On the thermoplastic binder, and 0.01 to 20% by volume on the catalyst. Use according to claim 10, characterized in that that the machining process has at least one injection molding, one Extrusion or other molding process step, a process step thick-film technology to flat or selective coating of substrate surfaces with layers with a Layer thickness between 0.1 to 1000 microns on a substrate, a Vacuum forming, hot stamping or another forming process step or a clasp or electro-eroding machining step. Process for the production of components from a Molding composition according to one of the claims 1 to 9, comprising the following process steps: a) Original or forming the molding compound into a green body using a processing method with one or more processing steps, b) transfer of the Green body in through a brown body catalytic removal of the binder using the catalyst, c) Sintering of the brown body, being the brown body is transferred to the component. A method according to claim 12, characterized in that the binder is removed in at least two stages, being in a first stage by a catalytic chemical Degradation of the binder in the green body volume an open pore system is created and in a further stage heating takes place, further degradation of the binder taking place. A method according to claim 13, characterized in that the further step in the process step of sintering with is included. Method according to one of claims 12 to 14, characterized in that that the sintering takes place in a reactive atmosphere, whereby during the Sintering a chemical conversion of the catalyst takes place.