IE69044B1

IE69044B1 - Thermoplastic molding compounds a process for their production and a process for the production of moldings of ceramic or metal by sintering

Info

Publication number: IE69044B1
Application number: IE922239A
Authority: IE
Inventors: John Huggins; Gebhard Wagner; Ottfried Schlak
Original assignee: Bayer Ag
Priority date: 1991-07-10
Filing date: 1992-07-09
Publication date: 1996-08-07
Also published as: IE922239A1; WO1993001146A1; JPH06509127A; ES2078748T3; EP0593548B1; EP0593548A1; DE59203599D1

Abstract

The invention concerns new thermoplastic moulding compounds for the manufacture of mouldings made of ceramic material or metal from the appropriate ceramic or metal powders. Thermoplastic moulding compounds can be used for instance in injection-moulding, extrusion or hot-pressing processes in which it is necessary for the moulding compound to have temperature-dependent flow characteristics.

Description

The present Invention relates to new thermoplastic moulding compositions for the production of moulded parts of ceramic or metal from the corresponding ceramic or metal powders.

Thermoplastic moulding compositions are used inter alia in processes such as injection moulding, extrusion or hot pressing, in which a temperature-dependent flow behaviour is necessary.

It is known that sinterable ceramic or metal powders can be processed together with thermoplastic binders and other auxiliary substances by injection moulding, extrusion or hot pressing to moulded parts (F. Aldinger and H.-J- Kalz, Anqew. Chem. 99 (1987) 381-391; P. Glutz, Feinwerktechnik & Messtechnik 97 (1989) (363-365); M.J. Edirisinghe, J.R.G. Evans, Inter. J. High Technology Ceramics 2 (1986) 1-31; W. Michaeli, R. Bieler, Ind.-Anz. 113 (1991) 12-14). After moulding, the binder is removed or burnt out from the moulded part (known as the green compact) at temperatures of between 200 and 1000 °C.

The green compact is usually then sintered at temperatures above 1000 °C, a process wherein a partial or complete phase transformation can occur and compacting of the body take place.

Purely organic binders are usually used in these processes. Examples are polystyrene, polyethylene, polypropylene, polybutyl acrylates and paraffin waxes. Organic binders have the disadvantage, however, that they must be burnt out slowly and with very careful temperature control, since otherwise green compacts with gross defects such as cracks or pores are obtained. In some cases also green compacts with inadequate strength are obtained after the burning out. A sufficient strength of the green compact is necessary for its subsequent processing and for flawless sintering.

Silicone resins have already been described many times as I have the advantage that the silicone resin binder is converted to ceramic during burning out, so that the moulded part can be fired more rapidly. The silicone resins described hitherto are not, however, suitable for processes entailing thermoplastic processing, such as, for example, injection moulding.

US 3,090,.691 describes a process for the production of moulded parts from ceramics that is characterized by firing a mixture of an organosiloxane and a ceramic powder. The organosiloxane has a total of 1 to 3 organic groups per silicon atom. The compositions are fired at 500 to 1550 °C and usually contain a curing catalyst such as, for example, lead oxide or lead stearate.

DE-A 2 142 581 describes compositions for the production of aluminium oxide ceramics that are characterized by low shrinkage on sintering owing to the selection of suitable inorganic additives. Several binders are described, but heat curable silicone resins are preferred. Polyethylene, polyvinyl chloride or a polyamide are preferred as binders for forming by injection moulding processes.

DE-A 2 106 128 and DE-A 2 211 723 describe heat curable moulding compositions from inorganic solids and solventfree liquid orqanosiloxanes, that contain organic peroxides as hardening catalysts. The moulding compositions are introduced into a mould by pressing and cured at elevated temperature during the moulding operation. The green compacts are subsequently after-hardened at 200 °C for 2 to 4 hours and then sintered for 32 hours at temperatures up to 1510 °C to solid ceramics.

US-A 4 888 376 and US-A 4 929 573 describe a process for the production of moulded silicon carbide parts using heat curable polyorganosiloxanes as binders. The polysiloxanes are highly viscous to solid at room temperature. In the I are highly viscous to solid at room temperature. In the pyrolysis of the polysiloxane, at least 0.2 wt% of free carbon, based on the weight of the silicon carbide powder, is said to be formed. The polysiloxanes according to these processes have ceramic yields from pyrolysis in an inert gas atmosphere of only 39 to 50.8 wt%.

The silicone resins described have one or more disadvantages which make them unsuitable for thermoplastic moulding processes. Many of the silicone resins are liquid and must be hardened in the mould in order to produce a sufficient strength of the moulded part. Hardening in the mould leads to long cycle times and therefore high piece costs. Solid silicone resins that do not soften at elevated temperatures, i.e. at processing temperatures, are likewise unsuitable for thermoplastic processing. Other silicone resins show only low yields of ceramic during the pyrolysis at 1000 °C. A high ceramic yield is, however, a precondition for a rapid, flawless firing. From this there is a technological demand for moulding compositions of ceramics or metallic powders as the case may be and binders which possess good thermoplastic processing properties and can be rapidly fired without additional hardening stages.

It has now been found that certain silicone resins possess excellent thermoplastic properties as well as high ceramic yields in the pyrolysis at up to 1000 C. Thermoplastic moulding compositions produced with these silicone resins possess excellent properties for thermoplastic methods of processing, especially injection moulding processes, and possible mechanical methods of aftertreatment and can be fired within a short period of time after moulding.

The present invention provides a thermoplastic moulding composition, containing at least one thermoplastic silicone resin, with a softening temperature of between 30 and 200 °C, of the average formula R1,Si(OH)b(OR2)eO(4.a.b.c)/2 (I) wherein a assumes values in the range of 0.95 to 1.5 and c values in the range of 0 to 0.2, the sum (a+b+c) is 1.05 to 1.7, the sum (b+c) is at most 0.3, R1 denotes one or more of the groups H, Cx- to CX8-alkyl, vinyl, allyl or phenyl, R2 denotes one or more of the organic groups Cx- to Cx8alkyl, at least 70 % of the groups R1 and R2 being methyl groups, and at least one sinterable powder.

In the thermoplastic moulding compositions according to the invention, in the case of the thermoplastic silicone resin, the average (arithmetic mean) molecular weight of the organic groups including the alkoxy groups is at most 50 divided by the sum (a+c).

The value of a should fall in particular in the range between 0.95 and 1.5, preferably between 1.0 and 1.5.

The value c can fall in the range from 0 to 0.2, preferably in the range from 0.05 to 0.15.

R1 is intended to denote in particular hydrogen, methyl, vinyl and phenyl, of which methyl and phenyl are preferred.

R2 denotes preferably a Cx- to C4-alkyl group.

According to the invention, the silicone resins are preferably used without catalysts, so that a further crosslinking and hardening does not occur during the moulding process.

To ensure good thermoplastic processing properties with a good strength of the moulding, a resin that has a very stiffly crosslinked SiOx/2 network, i.e. is characterized by a sum (a+b+c) in the neighbourhood of 1, can contain more higher-molecular organic groups than a softer SiOx/2 network, characterized by a sum (a+b+c) in the neighbourhood of 1.7, which on the other hand must contain a higher proportion of methyl groups.

For example, in the case that the sum (a+c) amounts to 1, the average molecular weight of all R1 and -OR2 can amount at the most to 50. In the case that the sum (a+c) amounts to 1.5, the average molecular weight will accordingly amount at the most to 50/1.5 = 33.

Resins are preferred in which the average molecular weight of the groups amounts to 40 divided by (a+c), particularly 30 divided by (a+c).

Resins are particularly preferred that have at least 70 %, preferably at least 80 %, of methyl groups in addition to phenyl, C2-C18-alkyl and vinyl groups.

Among the resins described by formula (I) the following resins II and III are particularly preferred: (II). ”QM” resin, composed of the following structural units: a) b) c) to 70 mol% SiO2 units, to 20 mol% R1SiO3/2 units 0 to 40 mol% R1(CH3)SiO or Ph2SiO units (IIA) d) 20 to 50 molt R^CH^SiO^ units with an alkoxy content according to Zeisel (A.L. Smith Analysis of Silicones, New York: Wiley, 1974, p. 155-156) of less than 20 % and on average between 1.0 and 1.5 organic substituents (via an Si-C bond) per silicon atom.

Among these, resins composed of a) 40 to 55 molt b) 10 to 35 molt c) 20 to 40 molt SiO2 units Ph2SiO, Ph(CH3)SiO, (CH2=CH) (CH3)SiO or (CH3)2Sio units, and R1(CH3)2SiO1y2 units (IIC) are preferred. particularly preferred a) 50 to 62.5 molt b) 0 to 10 mol% c) 35 to 45 molt SiO2 units Ph2SiO, Ph(CH3)SiO, (CH2=CH) (CH3)sio or (CH3)2SiO units, and R1(CH3)2SiO1y2 units; (IIB) (III). TM resins, composed of the following structural units: a) 50 to 98 molt al) 50 to 95 molt a2) 0 to 20 molt b) 0 to 30 molt bl) 5 to 30 molt b2) 0 to 20 molt R1SiO3^2 units, preferably CH3SiO3/2 and PhSiO3/2 units and/or VisiO3y2 units, Ph2SiO or R1(CH3)SiO units, preferably (CH3)2sio units and Ph2SiO units and/or CH3(R1)SiO units, (IIIA) c) 0 to 33 mol%, 0 to 5 mol%, and preferably SiO2 units Γ/ϊ d) to 10 mol% R^CH^jSiO^j units, preferably 0 to 5 mol% (Cf^^siO^ units, with an average of between 1.0 and 1.5, preferably 1.05 and 1.3, organic substituents per silicon atom. The sum of all trifunctional units a) and tetrafunctional units c) must amount to at least 70 mol% of the totality of all units. Especially preferred are thermoplastic silicone resins that consist substantially of al) 80 to 98 mol% CH3SiO3/2 units, a2) 0 to 5 mol% PhSiO3/2 units, b) 0 to 20 mol%, preferably up to 12 mol%, (CH3)2SiO units, (IIIB) and d) 0 to 10 mol%, preferably 2 to 8 mol%, (CH3)3SiO3/2 units.

Of these, the PhSiO3/2~free resins are particularly preferred.

The thermoplastic silicone resins according to the invention should preferably have softening temperatures of 40 to 200 ®C, in particular 40 to 150 °C and most preferably 50 to 120 °C, if only one silicone resin is used in the thermoplastic moulding composition.

Mixtures of silicone resins of different softening temperatures have particularly advantageous properties.

The resins used are a soft resin with a softening temperature of 30 to 120 °C, preferably 40 to 100 °C, mixed with a hard resin with a softening temperature of at least 60 °C, a difference in the softening temperatures of at least 20 ®C, in particular at least 30 “°C, being preferred.

The difference in the softening temperatures can amount to 100 °C or more. . However, the mixture as such should in addition have a softening temperature between 40 and 200 °C, preferably between 40 and 150 eC, even if the hard component contained therein itself has a higher softening temperature.

The softening temperature of the mixture is influenced by the softening temperatures of the components and by the proportions of the components in the mixture.

Proportions of hard to soft components of from 5 to 95 wt% to 95 to 5 wt% are used according to the invention.

A resin according to formulae (I) and (III-A) from the following structural units is suitable as a soft silicone resin: a) b) 75 to 95 mol% R1SiO3y2 units R1(CH3)SiO units 5 to 20 mol% c) 0 to 5 mol% SiO2 units (IIIC) d) 0 to 10 mol% R1(CH3)2SiO1y2 units Both TM and QM resins according to formulae (I) and (IIIA) or (HA), respectively are suitable as hard silicone resins: a) b) 85 to 98 mol% R1SiO3/2 units R1(CH3)SiO units (HID) 0 to 5 mol% c) 2 to 10 mol% R1 (CH3) 2SiO1/2 units and a) 55 to 62 .5 mol% SiO2 units, b) 0 to 5 mol% 1^(0¾) SiO units (IID) c) 33 to 45 mol% 1^(013) jSiOj^ units respectively.

Silicone resin mixtures with much hard TM or QM resin have high hardness and low tack in the cold state. Moulding compositions from such silicone resin mixtures are particularly preferred in the manufacture of complicated and thin-walled moulded parts, in which a high strength is required in order to ensure that the moulded part is released undamaged from the mould. The low tack of such silicone resin mixtures also facilitates the demoulding, so that the use of mould-release agents, such as silicone oil, is unnecessary.

Silicone resin mixtures with a small amount of hard TM or QM resin have relatively low hardness and relatively high elasticity in the cold state. Moulding compositions from such silicone resin mixtures are particularly preferred in the manufacture of thick-walled moulded parts, wherein large stresses can arise during the solidification of the moulded part in the mould. The elasticity of these silicone resin mixtures makes possible the reduction of the stresses on firing and as a result prevents cracks and other flaws in the fired part.

It has now been found that small proportions of hard TM or QM silicone resin according to the invention bring about a considerable improvement in the hardness and in particular the tack of the moulding compositions. For most forming functions, therefore, 10 to 50 wt% of the hard TM or QM silicone resin are sufficient to permit a simple removal of the moulded part from the mould.

The silicone resins according to the invention are prepared for example by cohydrolysis of an appropriate mixture of chlorosilanes or alkoxysilanes. Likewise, a mixture of one or more alkoxysiloxanes and one or more siloxanes can first be equilibrated and then hydrolyzed. The hydrolysis is carried out according to the customary methods, as is described in W. Noll Chemie und Technolooie der Silicone (Weinheim: Verlag Chemie, 1968, p. 162-169). For example, the mixture of chlorosilanes together with an organic solvent are added to an excess of water and optionally an aliphatic alcohol. The phases are separated and the organic phase washed until neutral. For the manufacture of the moulding compositions according to the invention, the silicone resin is used either as a solution or, after drawing off the solvent, as a solid.

It is known that the alkoxy and SiOH contents of silicone resins are reduced by condensation reactions and, as a result of this, the softening temperature of the resins can be raised. This process, often known as thickening of the silicone resin solution, is preferably carried out during the manufacture of the silicone resin by heating in the presence of catalysts. The manufacture of the silicone resins according to the invention must therefore be carried out in such a way that the desired softening temperature is obtained. The silicone resins must also be carefully neutralized in order to ensure a stable viscosity during the processing of the moulding composition.

In the solvent-free state at room temperature, the silicone resins or silicone resin mixtures according to the invention are solids having softening temperatures between 30 and 200 ”C. Above this temperature, the silicone resins or silicone resin mixtures are free-flowing to highly viscous. The silicone resin or silicone resin mixture preferably has a viscosity in the melt of less than 100,000 mPa.s, especially less than 10,000 mPa.s. In the solid state, the silicone resins are amorphous. Usually, therefore, the temperature at which plastic flow begins can be determined only approximately. The softening temperature is therefore quoted as a temperature range over 10 to 15 ®C.

The silicone resins or silicone resin mixtures according to the invention are characterized by high ceramic yields in the pyrolysis at up to 1000 °C of more than 60 wt%, preferably more than 70 wt%. The ceramic yield is defined as the residue in wt% after the pyrolysis. The ceramic yield is usually impaired by increasing proportions of PhSiO3/2 and Ph2SiO units as well as siloxy units with longchain alkyl groups; the sum of these units should therefore not exceed 40 mol%, preferably 20 mol%.

The thermoplastic moulding compositions according to the invention consist in the general formulation of a homogeneous mixture of at least one sinterable powder of ceramic or metal and at least one thermoplastic silicone resin or silicone resin mixture. In addition, the moulding compositions according to the invention may contain other auxiliary materials, such as sintering auxiliaries, flow aids and mould release agents.

In another embodiment of the present invention, the thermoplastic moulding compositions may contain in addition to the silicone resin other organic-based thermoplastic binders or copolymers of organic polymers with siloxanes.

In the case of the present invention, the advantage of rapid firing rests mainly on the silicone resin chosen. However, other thermoplastic polymers can improve properties of the moulding composition during the moulding without substantially prolonging the firing time.

All powders of metal or ceramic that can be sintered to a solid body, including mineral raw materials for the manufacture of ceramics, are suitable for the thermoplastic moulding compositions.

Sinterable powders usable according to the invention are 5 preferably of oxide ceramics or non-oxidic ceramics or their raw materials as well as hard metal, sintering metal, alloyed steel or pure metal.

Examples of preferred oxide ceramics are A12O3, MgO, ZrO2, Al2TiOs, BaTiO3 and silicate ceramics or their raw materials, such as porcelain as well as stoneware mixtures that can contain among other things clay, feldspar and quartz. Examples of non-oxidic ceramics are Sic, Si3N4, BN, B4C, AIN, TiN and Tic among others. Examples of sinterable hard metals are WC and TaC alloys. An example of a sinterable metal is silicon, which can be converted with nitrogen at high temperatures to silicon nitride. The powders can be used alone or also as a mixture of different powders.

In general, different sintering auxiliaries are added according to the ceramic or metal and, by forming lowmelting phases, accelerate the phase conversion or compaction during the sintering at relatively low temperatures. These sintering auxiliaries do not usually have a substantial effect on the thermoplastic properties of the moulding compositions.

The organic-based thermoplastic binders according to the invention are organic polymers and waxes that have a softening temperature between 40 and 200 °C, preferably between 40 and 160 °C, most preferably between 70 and 130 eC. Examples are polyethylene, polypropylene, polystyrene, polyacrylates, polyesters and ethylene-vinyl acetate copolymers. Polyethylene, polypropylene and their copolymers, as well as polymer-based waxes are preferred. Polar polyolefin waxes and their mixtures with non-polar thermoplastic polymers are preferred. Neutral and polar waxes of mineral occurrence or found in nature, such as paraffin wax, montan wax, beeswax or plant waxes and their subsequent products are also preferred. Thermoplastic copolymers of organic polymers with polydimethylsiloxanes or silicone resins are also preferably used. Polyestersiloxane copolymers, so-called combination resins, are examples. One or more binders can be used together with the silicone resin.

The polar polyolefin waxes to be used according to the invention are waxes that have acid numbers according to DIN 53 402 between 5 and 180 mg KOH/g. Examples are the commercial products Hostalub® H 22 and Hostaraont® TP EK 581 of Hoechst AG and the polymer additives A-C® 540 and A-C® 629 of Allied Corporation. The polar polyolefin waxes can be either of low or high viscosity in the melt. Waxes that have viscosities between 10 and 200,000 mPa.s at 140 °C are preferred.

The thermoplastic organic binders according to the invention and their copolymers with siloxanes are used in an amount which brings about an improvement of properties during the moulding or the properties of the moulded part but still permits a short firing time. As has been described previously, organic thermoplastics must be completely removed from the green compact during the firing. Excessive proportions of organic binders in the moulding composition therefore have a negative influence on the firing time. Moulding compositions wherein at least 10 wt% of the sum of all binders and auxiliary substances consist of the silicone resins according to the invention are preferred. Moulding compositions with relatively little silicone resin are particularly suitable for the manufacture of moulded parts wherein the ceramic residue of the silicone resin can have a negative influence on the properties of the moulded part, such as for example moulded parts of non-oxidic ceramics. Moulding compositions wherein at least 50 wt% of the sum of all binders and auxiliary substances consist of silicone resins are preferably used if the shortest possible firing time is desired.

The thermoplastic moulding compositions according to the invention usually contain in addition to the silicone resin or silicone resin mixture (and preferably the thermoplastic polymer) one or more flow aids or mould release agents, which ensure a reduction of the viscosity of the moulding composition during the moulding process as well as a clean and simple removal from the mould. Examples are aliphatic fatty acids and their salts and reaction products, such as stearic acid, calcium stearate, magnesium stearate, stearyl alcohol, stearamide, ethyl stearate or the like, oils, such as polydimethylsiloxanes, polyethylene oxides, polypropylene oxides and copolymers of polydimethylsiloxane and polyethylene oxide or polypropylene oxide and the like or low-molecular waxes such as paraffin wax, polyethylene oxide waxes or beeswax. Moulding compositions that contain 0.25 to 10 wt% (based on the sum of all binders and auxiliary materials) of stearic acid, its salts and reaction products or paraffin wax are preferred. In general only as much flow aid is added as is necessary to bring the viscosity during the moulding into the range required.

The thermoplastic moulding compositions according to the invention contain at least as much silicone resin, thermoplastic organic polymers and other auxiliary substances as are necessary to obtain a thermoplastically processible composition. Binders together with the other auxiliary substances must usually fill up at least the free volume between the powder particles in the moulded part. Different amounts are necessary for this, depending on the type of powder as well as its grain shape and grain size distribution. From experience, 25 to 60 vol% binders are necessary. Moulding compositions with 50 to 70 vol% powder and 30 to 50 vol% binders and auxiliary substances are preferred; powder contents of at least 60 vol% are particularly preferred.

The thermoplastic moulding compositions according to the invention are solid at room temperature but plastically deformable at temperatures above the softening temperature of the silicone resin used. In a preferred specific embodiment, the moulding compositions have viscosities of less than 10,000 Pa.s at the processing temperature. Viscosities between 100 and 5000 Pa.s are particularly preferred.

The thermoplastic moulding compositions according to the invention are manufactured by mixing the components named at a temperature above the softening temperature of the silicone resin, in the course of which possible residual solvent from the manufacture of the silicone resin is removed. It is advantageous to employ high shear forces during the mixing in order to reduce the size of powder aggregates and as a result to obtain a homogeneous mixture. Suitable mixing units are for example kneaders, doubleshaft extruders and roll mills. The moulding compositions can then either be used directly or first processed to powders or granulates.

The thermoplastic moulding compositions according to the invention possess excellent properties for thermoplastic moulding, as for example by injection moulding, extrusion or hot pressing. The moulding compositions can be processed plastically at temperatures above the softening temperature of the silicone resin and introduced under pressure into moulds whose temperature is below the softening temperature of the silicone resin. The moulding composition solidifies again as a result of cooling. The green compacts thereby obtained have good strengths and may be treated or finished by for example grinding, drilling or sawing. Residues from the moulding process can be reused.

The thermoplastic moulding compositions according to the v invention are particularly suitable for the production of complicated parts by moulding processes such as thermoplastic injection moulding. The moulding compositions possess good flow properties at temperatures of at least 20 °C above the softening temperature of the silicone resin used. The moulding compositions can contain high proportions of powder. The green compacts produced from the moulding compositions according to the invention suffer only a relatively small weight loss on firing at up to 1000 °C. The green compacts can therefore be fired in a short time. The fired green compacts possess high strengths and high densities.

The green compacts produced from the moulding compositions according to the invention can be fired in a short time either in air or in an inert gas atmosphere or in vacuum to produce flawless products.

The firing is preferably carried out with an ascending temperature programme of between 0.1 and 5 °C/min, preferably 0.5 to 5 ®C/min, up to 600-1000 °C. Moulding compositions based on silicone resin mixtures tolerate heating rates of up to 10 °c/min. Heating can also be carried out stepwise at o.l to 5 °C/min to a temperature between 200 and 800 *C, this temperature optionally being held until no further change of weight can be observed, and '' the temperature then increased at 5 to 50 °C/min to 1000 •C. The fired green compacts may generally then be sintered at temperatures between 1000 and 2000 °C, depending on the powder and sintering auxiliaries used.

The invention will now be further described with the aid of the following examples.

Examples General: The following substances were used in the examples: Al2O3 powder of Martinswerk GmbH, known as Martinoxid ZPS-402, having an average particle size of 2.0-3.0 microns, a density of ca. 3.95 g/cm3, an a-Al2O3 content of > 95 % and a loss on annealing of ca. 0.2 wt%. Porcelain a raw material mixture for the production of powder porcelain ceramics, consisting of about 50 % kaolin as well as about 50 % feldspar and quartz, having an average particle size of 4 to 5 microns and a loss on annealing of 6.1 %. Hard having a softening temperature of 52-54 °C, paraffin I Hard having a softening temperature of 90-94 °C, paraffin II Polystyrene of the type Hostyren N 2000 of Hoechst AG, Polyethylene oxide having a viscosity of 160 mPa.s at 25 °C, Polydimethyl- siloxane with a viscosity of 5000 mPa.s at 25 °C, Siloxane a 76 % solution in toluene of a block copolymer copolymer of (40:60) polydimethylsiloxane and polyethylene oxide, having an average molecular mass of 4230 g/mol.

Polar poly 5 olefin wax Montan wax of Hoechst AG, known as Hostalub H 22 and having a softening temperature of 103-108 °C, an acid number of 22-28 mg KOH/g, a saponification number of 45-65 mg KOH/g and a viscosity of about 300 mPa.s at 120 ec. of Hoechst AG, known as HoechstWachs-E and having a drop point of 79-85 °C, an acid number of 15-20 mg KOH/g, a saponification number of 130-160 mg KOH/g, a density of 1.01 g/cm3 and a viscosity at 100 °C of about 30 mPa.s.

Copolymer wax an ethylene-vinyl acetate copolymer of Allied Corporation, known as A-C Additive 400 and having a vinyl acetate content of 13 %, a drop point of 95 °C, a density of 0.92 g/cm3 and a viscosity at 140 °C of about 600 mPa.s.

Dynasil 40 a silicic acid ester of Hills Troisdorf AG of the formula (EtO)3SiO(Si(OEt)2o)nsi(OEt)3 (n = ca. 2.7 and Et = CH2CH3) with an SiO2 content of 40 wt%.

Example 1 (Silicone resin 1) Preparation of a silicone resin from CH3SiCl3, (CH3)2SiCl2 35 and (CH3)3SiCl.

A mixture of 880 g CH3SiCl3, 90 g (CH3)2SiCl2 and 12 g (CH3)3SiCl was slowly added dropwise to a stirred mixture of 3.8 1 water, 650 g xylene and 650 g n-butanol. The water phase was separated off and the solution washed three times with water. Xylene-n-butanol was then distilled off from the resin solution to obtain an 80 % solution, which was then diluted with toluene to obtain a resin solution with 64 wt% solids and a viscosity of 45 mPa.s at 25 °C.

In the solvent-free state, the silicone resin (1) is a solid with a softening temperature of 55 to 65 °C, a viscosity at 130 eC of 500 mPa.s and a density of 1.18 g/cm3. 2H NMR (300 MHz, CDC13, ppm): δ 0.15 (s, SiCH3, int: 150), 0.90 (mult, O(CH2)3CH3, int: 10), 1.35, 1.55 (mult, OCH2(CS2)2CH3, int: 14), 2.3 (br, SiOH, int: 0.9), 3.7 (mult, OCH2, int: 7). According to 29Si-NMR the silicone resin contains 1.15 methyl groups per silicon atom. From these values a molecular formula of (CH3)x>X5Si(O(CH2)3CH3)0>Og(OH)Oe007Ox,38 can be calculated.

The ceramic yield after pyrolysis at up to 1000 ®C (heating rate 1 °C/min) in air amounted to 76 wt%.

Example 2 (Silicone resin 2) Preparation of the silicone resin from CH3Sicl3 and (CH3)3SiCl. 420 g (2.81 moles) methyltrichlorosilane and 24 g (0.22 moles) trimethylchlorosilane were hydrolysed in 1.9 1 water, 335 g xylene and 335 g n-butanol as in Example 1.

The water phase was separated off and the still acidic solution stirred for 30 minutes at 80 ®C. The solution was washed three times with water. Xylene-butanol was then distilled off from the resin solution to obtain a 77 % resin solution.

In the solvent-free state, the silicone resin (2) is a solid with a softening temperature of 70 to 75 ®C and a density of 1.13 g/cm3. According to 29Si-NMR the silicone resin contains 1.17 methyl groups per silicon atom. The ceramic yield after pyrolysis at up to 1000 °C (heating rate 1 °C/min) in air was 74.2 wt%.

Example 3 (Silicone resin 3) Preparation of a silicone resin from (CH3)Sicl3 and (CH3)3SiCl. 420 g (2.81 moles) methyltrichlorosilane and g (0.11 moles) trimethylchlorosilane were hydrolysed in 1.9 1 water, 335 g xylene and 335 g n-butanol as in Example 1. The water phase was separated off and the still acidic solution stirred for 30 minutes at 80 °C. The solution was washed until neutral and xylene-butanol was then distilled off to obtain a 75 % solution of resin.

In the solvent-free state, the silicone resin (3) is a solid with a softening temperature of 80 to 100 °C and a density of 1.15 g/cm3. XH NMR (300 MHz, CDC13, ppm): S 0.15 (s, SiCH3, int: 149), 0.90 (mult, O(CH2)3CH3, int: 6), 1.35, 1.50 (mult, OCH2 (¾) 2CH3' int: 8) ' 2·2 (br, SiOH, int: 2.3), 3.7 (mult, OCHs(CH2)2CH3» int: 4). According to 29Si-NMR the silicone resin contains 1.08 methyl groups per silicon atom. From these values a molecular formula of (CH3)1<08Si(O(CH2)3CH3)gao43(OH)o.οΐ7θι.43 can be calculated. The ceramic yield after pyrolysis at up to 1000 °C (heating rate 1 *C/min) in air was 79.5 wt%.

Example 4 (Silicone resin 4) Preparation of the QM silicone resin A mixture of 1500 g (10.0 moles SiO2) Dynasil 40, 600 g (7.4 moles Me3SiO1^2) hexamethyldisiloxane, 2.4 g cone.

H2SiO4, 1.2 g C4FgSO3H and 1700 g xylene were charged to a 6 1 4-necked flask with stirrer, water condenser, thermometer and dropping funnel. The mixture was first boiled under reflux for 1 hour and then hydrolysed at a temperature of 90 to 100 °C with 263 g water (ca. 20 % excess). The mixture was then stirred for 2 hours at 100 °C and then neutralized for 1 hour at 100 °C with 21.7 g (0.265 moles) sodium acetate. 1600 ml xylene were then distilled off and the product filtered. 1580 g of a 75 % solution of the silicone resin were obtained.

In the solvent-free state, the silicone resin (4) is a solid with a softening temperature of 80 to 100 °C and a density of 1.20 g/cm3, an SiOH content (Karl Fischer) of less than 0.01 % and an ethoxy content (Zeisel) of 11.5 %. XH NMR (300 MHz, CDC13, ppm): δ 0.15 (s, SiCIJ3, int: 149.8), 1.20 (br, s, OCH2CQ3, int: 21.5), 3.80 (br, s, OCH2CH3, int: 14.5). IR (KBr, cm-1): 3450 (hr, m), 2970 (sh, m), 2910 (sh, w), 1260 (sh, s), 1050-1200 (br, vs), 870 (sh, s), 850 (sh, s), 760 (sh, m). From these values a molecular formula of (CH3) 1>46Si(OCH2CH3)021O116 can be calculated.

The ceramic yield after pyrolysis at up to 1000 °C (heating rate 2 °C/min) in air was 75.3 %.

Example 5 (Silicone resin 5) Preparation of a QM silicone resin As in Example 4, 1542 g (10.28 moles SiO2) Dynasil 40 and 583 g (7.2 moles Me^iO^) hexamethyldisiloxane were hydrolysed with 270 g water, neutralized with sodium acetate, concentrated and filtered. 1600 g of a 75 % solution of the silicone resin were obtained.

In the solvent-free state, the silicone resin (5) is a solid with a softening temperature of 100 to 110 °C, an SiOH content (Karl Fischer) of less than 0.01 % and an ethoxy content (Zeisel) of 11.8 %. XH NMR (300 MHz, CDC13, ppm): 6 0.15 (s, SiCH3, int: 149.2), 1.20 (br, s, OCH2CS3i int: 21), 3.80 (br, s, OCH2CH3, int: 14.5). IR (KBr, cm-1): 3450 (br, m), 2970 (sh, m), 2910 (sh, w), 1260 (sh, s), 1050-1200 (br, vs), .870 (sh, s) , 850 (sh, s), 760 (sh, m). From these values an empirical formula of CCH3)l.45Si(OEt)0.20Oi. 17 can be calculated.

The ceramic yield after pyrolysis at up to 1000 ®C (heating rate 2 ®C/min) in air was 76.7 %.

Example 6 (Silicone resin 6) Preparation of a QM silicone resin As in Example 4, 1154 g (7.69 moles SiO2) Dynasil 40, 311.5 g (3.85 moles Me3SiOX/2) hexamethyldisiloxane and 428 g (5.77 moles Me2SiO) octamethylcyclotetrasiloxane were hydrolysed with 202 g water, neutralized with sodium acetate, concentrated and filtered. 1300 g of a 54 % solution of the silicone resin were obtained.

In the solvent-free state, the silicone resin (6) is a solid with a softening temperature of 80 to 90 °C, an SiOH content (Karl Fischer) of less than 0.01 % and an ethoxy content (Zeisel) of 8.3 %. XH NMR (300 MHz, CDC13, ppm): δ 0.15 (s, SiCH3, int: 147.9), 1.20 (br, s, OCH2CH3, int: 15.3), 3.80 (br, s, OCH2CH3, int: 11). IR (film, cm-1): 2970 (br, m), 2905 (sh, w), 1400-1450 (br, W), 1265 (sh, s), 1050 to 1200 (br, vs), 850 (sh, s), 810 (sh, s), 760 (sh, m).

The ceramic yield after pyrolysis at up to 1000 ®C (heating rate 2 ®C/min) in air was 76.5 %.

Example 7 (Silicone resin 7) Preparation of a QM silicone resin As in Example 4, 1500 g (10.0 moles SiO2) Dynasil 40 and 516 g (6.4 moles Me3SiOX/2) hexamethyldisiloxane were hydrolysed with 290 g water, neutralized with sodium acetate, concentrated and filtered. 1600 g of a 75 % solution of the silicone resin were obtained.

In the solvent-free state, the silicone resin (7) is a solid with a softening temperature of 220 °C, an SiOH content (Karl Fischer) of less than 0.01 % and an ethoxy content (Zeisel) of 12.5 %. NMR (300 MHz, CDC13, ppm): S 0.15 (s, SiCH3, int: 149.2), 1.20 (br, s, OCH2CH3, int: 27), 3.80 (br, s, OCH2CH3, int: 18). IR (KBr, cm”1): 3450 .(br, m), 2970 (sh, m), 2910 (sh, w) , 1260 (sh, s), 10501200 (br, vs), 870 (sh, s), 850 (sh, s), 760 (sh, m).

From these values a molecular formula of (CH3) 1<16Si(OCH2CH3)0a21O1(31 can be calculated.

The ceramic yield after pyrolysis at up to 1000 °C (heating rate 2 °C/min) in air was 78.7 %.

Example 8 (Moulding composition from silicone resin 1) 395 g A12O3 powder, 100 g of the above 64 % resin solution from Example 1 (64 g resin), 4 g calcium stearate and 8 g polyethylene oxide were charged to a twin-screw continuous kneader and compounder. The mixture was kneaded at 110 °C and negative pressure for 15 minutes in order to remove the solvent. The composition was then kneaded for a further 15 minutes without vacuum. A plastic moulding composition with good flow properties was formed, which solidified on cooling. The volume fraction of A12O3 in the moulding composition amounted to about 61.5 %.

The moulding composition was pressed to pellets at about 120 °C and 500 bar. A 13 x 2.0 mm pellet was fired in air over 6.0 h to 1000 °C in a stepwise heating programme (25150 ®C/25 min; 150-400 *C/250 min; 400-600 °C/65 min; 6001000 °C/20 min). The fired pellet was of high strength and free from macroscopic defects. The weight loss on firing was 5.5 %.

Examples 9-13 Various moulding compositions were prepared in Example 8 from A12O3 powder and the silicone resin 1 in a kneader.

The compositions of these moulding compositions are listed in Table 1. The moulding compositions were pressed to pellets and fired in air: see Table 2.

Table 1: Composition of the moulding compositions NO. I Temp.* °C A1A 9 Resin solution 9 Calcium stearate 9 Others H IOS 415 « 94 5 8 g hard fl paraffin I fl 10 105 435 100 5 2 9 polyethylene H oxide I 11 105 415 100 5 8 g siloxane 1 copolymer I 12 130 415 86 5 9 g hard fl paraffin I I 8.5 g 0 polystyrene fl 13 120 375 100 9 g polar poly- fl olefin wax fl kneader temperature Table 2: Results of the firing a No. Size mm Temperature programme Firing time h Wt% loss Appear- fi ance fi 8 10 X 4.5 1 eC/min to 1000 °C 16.25 5.1 flawless 9 13 x 2.5 1 ®C/min to 1000 ®C 16.25 5.9 flawless 10 13 X 2.5 1 ®C/min to 1000 ®c 16.25 4.2 flawless 11 13 X 2.5 25-150 ®C/ 25 min, 150-400 ®C/ 250 min, 400-600 ®C/ 65 min, 600-1000 ®C/20 min 6.0 3.5 flawless 12 13 X 2.5 1 ®C/min to 1000 ®c 16.25 7.1 flawless 13 13 X 2 1 ®C/min to 1000 ®c 5.5 flawless Example 14 (Moulding composition from silicone resin 2) 32.5 g silicone resin solution 2 (25 g resin), 22.5 g montan wax and 2.5 g stearamide were charged to a kneader and heated to 120 °C. 222.5 g A12O3 powder were then incorporated and the solvent removed by N2 purging. A further 85 g A12O3 were then incorporated little by little. The composition was then kneaded for a further 60 min. A plastic moulding composition with good flow properties which solidifed on cooling was formed. The volume fraction of A12O3 in the moulding composition amounted to about 62.3 %.

The moulding composition was pressed to pellets at about 120 °C. A 13 x 2.0 mm pellet was fired in air with a heating programme of 1 ®c/min to 1000 °C. The fired pellet was of high strength and free from macroscopic defects.

The weight loss on firing was 8.4 %.

Example 15 (Moulding composition from silicone resin 4) 41.7 g of a 60 % silicone resin solution from Example 4 (25 g resin), 24.5 g montan wax and 0.5 g sodium stearate were charged to a kneader and mixed for 5 min at 120 °C. 220 g A12O3 powder were then added, and the composition kneaded for 30 minutes with continuous nitrogen purging in order to vaporize the xylene. A further 117 g A12O3 powder were added in portions to the composition and the mixture kneaded for a total of 1 hour. A plastic moulding composition with good flow properties which solidified on cooling was obtained. The volume fraction of Al2O3 in the moulding composition amounted to about 64.9 %.

The moulding composition was pressed to pellets at about 120 ®C and 100 bar. A 13 x 2.0 mm pellet was fired in air with a heating programme of 1 °C/min to 100 °C, 0.5 ®C/min to 400 ®C, 1 ®C/min to 600 ®C and 5 ®C/min to 1000 C. The fired pellet was of high strength and free from macroscopic defects. The weight loss during the firing was 9.0 %.

Examples 16 to 19 Various moulding compositions were prepared in a kneader as in Example 15 from A12O3 powder, silicone resin and auxiliary materials. The compositions of these moulding compositions are given in Table 3. The moulding compositions were pressed to pellets and fired in air: see Table 4.

Table 3: Composition of the moulding compositions No. A12O3 g Silicone resin Others No. g 16 328 4 35 10 g montan wax 5 g stearamide 17 246 4 35 5 g copolymer wax 5 g paraffin II 5 g stearamide 18 311 5 35 5 g paraffin II 9.5 g roontan wax 0.5 g sodium stearate 19 252 6 35 5 g copolymer wax 9.5 g montan wax 0.5 g sodium stearate H Table 4: Results of the firing | NO. Size mm Firing time* h:min Weight loss % Appearance 15 13 X 2 16:20 9.0 flawless 16 13 X 2 16:20 6.8 flawless 17 13 x 2 16:20 8.3 flawless 1 18 13 X 2 16:20 7.0 flawless19 13 X 2 16:20 8.3 flawless a Heating programme: 1 eC/min 25-100 °C, 0.5 °C/min 100400 °C, 1 °C/min 400-600 °C, 5 °C/min 600-1000 °C.

Example 20 In each case a soft and a hard resin were mixed according to Table 5 to show the properties of the mixture.

Example 21 Preparation of a moulding composition from the mixture of silicone resins (1) and (3) 39.1 g of a 64 % resin solution from Example 1 (25 g resin), 6.0 g of an 88 % resin solution from Example 2 (5.25 g resin), 12.5 g montan wax and 2.5 g stearamide were charged to a kneader and mixed for 5 min at 120 °C. 200 g A12O3 powder were then added and the composition kneaded for 30 minutes with continuous nitrogen purging to vaporize the solvent. A.further 76 g A12O3 powder were added in portions to the composition and the mixture kneaded for a total of 1 hour. A plastic moulding composition with good flow properties which solidified on cooling was obtained.

The moulding composition was pressed to pellets at about 120 °C and 100 bar. The pellets could easily be removed from the mould and were of high strength. A 13 x 2.0 mm pellet was fired in air with a heating programme of 1 °c/min to 100 °C, 0.5 °C/min to 400 °C, 1 ®C/min to 600 °C and 5 °C/min to 1000 °C. The fired pellet was of high strength and free from macroscopic defects. The weight loss on firing was 7.2 %.

Examples 22-26 Various moulding compositions were prepared as in Example 21 from A12O3 powder and various silicone resin mixtures in a kneader. The compositions of these moulding compositions are given in Table 6. The moulding compositions were pressed to pellets at about 120 °C. The moulding compositions could easily be removed from the mould and did not adhere to the mould walls. The pressed moulding compositions were of various hardnesses. With increasing proportion of the silicone resins (3), (4) and (7), the pressed moulding compositions became harder and more brittle. The pressed moulding compositions could be fired to flawless products in a short time: see Table 7.

Table 5: Properties of the silicone resin mixtures Resin 1 (Ex. 1) Hard resin Softening temperature, °C Viscosity mPa.s, 130 °C Hardness 1 a I Ex. No. Wt% 100 - 0 55-65 500 — 85 3 15 60-70 - 50 3 50 65-75 1080 + 25 3 75 80-90 ++85 4 15 60-70 — 50 4 50 75-80 +/- 75 7 25 80-90 +/- 50 7 50 125-135 ++ 3 100 80-100 6000 ++ - 4 100 80-100 ++ - 7 100 220 ++ a Hardness scale: ++ very hard, brittle; + hard, of low plasticity; +/- hard, plastic; - soft; — very soft.

Table 6: Composition of the moulding compositions 1 Example I No* ai2o3 g Silicone resin Other No. . g I 22 276 1 3 17.5 17.5 12.5 g montan wax 2.5 g stearamide 23 276 1 4 17.5 17.5 12.5 g montan wax 2.5 g stearamide 24 276 1 7 29.75 5.25 12.5 g montan wax 2.5 g stearamide 25 414 1 7 27.4 27.4 18.25 g montan wax 26 414 1 7 18.3 18.3 36.5 g montan wax Table 7: Results of the firing 1 Example I N°‘ Size mm Firing time® h:min Wt. loss % 1 Appear- I ance I 1 21 13 X 2 16:20a 7.2 flawless 1 22 13 x 2 16:20 7.2 flawless 23 13 x 2 16:20 7.3 flawless 1 24 13 X 2 16:20 7.3 flawless 1 25 13 X 2 ll:00b 5.8 flawless 1 26 13 X 2 11:00 9.4 flawless a Heating programme: 1 ®C/min 25-100 *C, 0.5 ®C/min 100400 ®C, 1 ®C/min 400-600 ®C, and 5 ®C/min 600-1000 ®C. b Heating programme: 1 ®C/min 25-600 °C, 4 ®C/min 60015 1000 ®c.

'A Example 27 Preparation of a moulding composition from porcelain powder As in Example 21, 39.1 g of a 64 % resin solution from Example 1 (25 g resin), 10 g montan wax, 10 g copolymer wax and 5 g stearamide were mixed with 253 g porcelain powder and kneaded for a total of 1 hour. A plastic moulding composition with good flow properties which solidified on cooling was obtained. The volume fraction of powder in the moulding composition amounted to about 62 %.

The moulding composition had a density of 1.97 g/cm3 and a viscosity of 700 Pa.s at a shear rate of 100 s-1 and 350 Pa.s at 700 s”1. The moulding composition was injected in an injection moulding machine at a composition temperature of 130-140 °C, a mould temperature of 35 °C and a pressure of 900 bar to rods of dimensions 80 x 20 x 5 mm. The moulded parts were free from macroscopic defects. The moulded parts could be fired flawlessly in less than 30 hours. The weight loss amounted to 17.7 %.

Claims

1. Patent Claims

1. Thermoplastic moulding composition, containing at least one thermoplastic silicone resin, with a 5 softening temperature of between 30 and 200 °C, of the average formula R\si (OH) b (OR 2 ) (I) 10 wherein a assumes values in the range of 0.95 to 1.5 It and

2. c values in the range of 0 to 0.2, the sum (a+b+c) is 1.05 to 1.7, the sum (b+c) is at most 0.3, R 1 denotes one or more of the groups H, C x to C 18 -alkyl, allyl, vinyl or phenyl, R 2 denotes one or more of the organic groups C x to C 18 -alkyl, at least 70 % of the groups R 1 and R 2 being methyl groups, and at least one sinterable powder. Thermoplastic moulding composition according to Claim 1, containing in addition another thermpplastic binder that is organic-based or based on a copolymer with siloxanes. (

3. Thermoplastic moulding composition according to Claim 2, characterized in that the organic-based binders are organic polymers or waxes that have a softening temperature of between 40 and 200 °C.

4. Thermoplastic moulding composition according to one of Claims 1 to 3, containing at least in addition a sintering auxiliary, flow aid and mould release agent. 10 5. Thermoplastic moulding composition according to one of

Claims 1 to 4, characterized in that the thermoplastic silicone resin is a mixture of at least 2 silicone resins, wherein the first silicone resin has a softening temperature of 30 to 120 °C and the other 15 silicone resin has a softening temperature of at least 60 °C and the difference between the softening temperatures is at least 20 °C.

6. Thermoplastic moulding composition according to one of 20 Claims 1 to 5, characterized in that it contains 50 to 70 vol% of a sinterable powder and 30 to 50 vol% of a thermoplastic silicone resin and auxiliary materials. i 1

7.

8. Process for the manufacture of thermoplastic moulding compositions according to one of Claims 1 to 6 by mixing sinterable powders with binders, sintering auxiliaries and other aids at temperatures above the softening temperature of the silicone resin or silicone resin mixture. Process for the manufacture of sintered compacts, characterized in that thermoplastic moulding compositions according to one of Claims 1 to 6, after shaping by means of injection moulding, extrusion or hot pressing, are initially fired at a temperature between 200 °C and 1000 °C and then sintered at temperatures between 1000 and 2000 °C. I

9. A thermoplastic moulding composition according to

Claim 1, substantially as hereinbefore described and exemplified. 5. 10. A process for the manufacture of a thermoplastic moulding composition according to Claim 1, substantially as hereinbefore described and exemplified.

11. A thermoplastic moulding composition according to 10 Claim 1, whenever manufactured by a process claimed in Claim 7 or 10.

12. A process according to Claim 8 for the manufacture of a sintered compact, substantially as herein15 before described.

13. A sintered compact whenever manufactured by a process claimed in Claim 8 or 12.