IE922239A1

IE922239A1 - 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: IE922239A1
Application number: IE223992A
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: 1993-01-13
Also published as: IE69044B1; JPH06509127A; EP0593548A1; WO1993001146A1; ES2078748T3; DE59203599D1; EP0593548B1

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

THERMOPLASTIC MOLDING COMPOUNDS, λ PROCESS FOR THEIR PRODUCTION AND A PROCESS FOR THE PRODUCTION OF MOLDINGS OF CERAMIC OR METAL BY SINTERING This invention relates to new thermoplastic molding compounds for the production of moldings of ceramic or metal from corresponding ceramic or metal powders. Thermoplastic molding compounds are used inter alia in such processes as injection molding, extrusion or hot press molding where temperature-resistant flow behavior is required.

It is known sinterable ceramic or metal powders can be processed together with thermoplastic binders and other auxiliaries by injection molding, extrusion or hot press molding (F. Aldinger and H.-J. Kalz Angew. 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 molding, the binder is removed, i.e. burnt out, from the molding (so-called green compact) at temperatures of 200 to l,000°C.

The green compact is then sintered, generally at temperatures above 1,000 °C, with partial or complete transfer conversion and consolidation of the compact.

Purely organic binders are generally used in these processes. Examples are polystyrene, polyethylene, polypropylene, polybutyl acrylates and paraffin waxes. However, organic binders have the disadvantage that their removal has to be carried out slowly and with considerable care in regard to temperature control because otherwise green compacts having serious defects, such as cracks or pores, are obtained. In some cases, green compacts having inadequate strength are also obtained after removal of the binder by burning out. Adequate strength of the green compact is necessary for further processing thereof and for β Le A 28 512-Foreign Countries 1 defect-free sintering.

Silicone resins have already been repeatedly described as binders for the production of ceramics. Silicone resins have the advantage that the silicone resin binder is converted into ceramic during burning out so that the molding can be fired more quickly. However, the silicone resins which have been described hitherto are unsuitable for processes involving thermoplastic processing, such as injection molding for example.

US 3,090,691 describes a process for the production of moldings of ceramic which is characterized by firing of a mixture of an organosiloxane and a ceramic powder. The organosiloxane contains a total of 1 to 3 organic groups per silicon atom. The mixtures are fired at 500 to 1,550°C and generaly 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 ceramic which are characterized by minimal shrinkage during sintering through the selection of suitable inorganic auxiliary components. Several binders are described, although heat-curing silicone resins are preferred. Polyethylene, polyvinyl chloride or a polyamide is preferred as binder for injection molding.

DE-A 2 106 128 and DE-A 2 211 723 describe heat-curing molding compounds of inorganic solids and solventless liquid organosiloxanes which contain organic peroxides as curing catalysts. The molding compounds are press-molded and are cured at elevated temperature during press molding. The green compacts are then post-cured for 2 to 4 hours at 200°C and then sintered for 32 hours at up to 1,510°C to form a solid ceramic.

US-A 4,888,376 and US-A 4,929,573 describe a process for the production of silicon carbide moldings with heatcuring polyorganosiloxanes as binder. The polysiloxanes are highly viscous to solid at room temperature. At least 0.2% by weight free carbon, based on the weight of the silicon carbide powder, should be formed during pyrolysis of the polysiloxane. The polysiloxanes used in these processes have ceramic yields of only 39 to 50.8% by weight where pyrrolysis is carried out in an inert gas atmosphere.

The described silicone resins have one or more disadvantages which make them unsuitable for thermoplastic molding processes. Many of the silicone resins are liquid and have to be cured in the mold to provide the molding with sufficient strength. Curing in the mold leads to long cycle times and hence to high unit costs. Solid silicone resins which do not soften at relatively high temperatures, i.e. processing temperatures, are also unsuitable for thermoplastic processing. Other silicone resins have only low ceramic yields where pyrrolysis is carried out at up to 1,000’C. However, a high ceramic yield is necessary for rapid defect-free firing. Accordingly, there is a need for molding compounds of ceramic or metal powders and binders which show favorable thermoplastic processing properties and which can be fired in short times without additional curing stages.

It has now been found that certain silicone resins have excellent thermoplastic properties and also high ceramic yields where pyrrolysis is carried out at up to 1,000’C. Thermoplastic molding compounds produced with these silicone resins have excellent properties in regard to thermoplastic processing, more particularly by injection molding, and possible mechanical aftertreatment and may be fired in a short time after molding.

The binders according to the invention consist of a thermoplastic silicone resin or a thermoplastic mixture of various silicone resins having a softening temperature between 3 0 and 200°C and corresponding to the following average formula R,Si (OH) b (OR2) eO(4.a.b.c)/2 (I) in which the sum (a+b+c) is 1.05 to 1.7, the sum (b+c) is at most 0.3, R1 represents one or more of the substituents H, C^18 alkyl, vinyl, allyl or phenyl, R2 represents one or more organic Cx_18 alkyl radicals, with the proviso that the average molecular weight (arith10 metic average) of the organic radicals, including the alkoxy radicals, should be at most 50 divided by the sum (a+c).

The value of a should be in particular in the range from 0.95 to 1.5 and is preferably between 1.0 and 1.5.

The value c may be in the range from 0 to 0.2 and is preferably between 0.05 and 0.15.

R1 is more particularly hydrogen, methyl, vinyl and phenyl, methyl and phenyl being preferred.

R2 is preferably a Cx.4 alkyl group.

According to the invention, the silicone resins are preferably used without catalysts so that there is no further crosslinking or curing during the molding process.

To guarantee favorable thermoplastic processing properties coupled with high strength of the molding, a resin having a very rigidly crosslinked SiOx/2 network, i.e. characterized by a sum (a+b+c) close to 1, may contain more organic radicals of relatively high molecular weight than a softer SiOx/2 network characterized by a sum (a+b+c) close to 1.7 which must contain a a correspondingly increased percentage of methyl groups.

For example, in cases where the sum (a+c) is 1, the average molecular weight of all the substituents R1 and -OR2 may be at most 50. In cases where the sum (a+c) is 1.5, therefore, the average molecular weight should be at most 50/1.5 = 33.

Preferred resins are those where the average molecular weight of the substituents is 40 divided by (a+c) and, more preferably, 30 divided by (a+c).

Particularly preferred resins are those containing at 5 least 70% and preferably at least 80% methyl groups in addition to phenyl, C2.18 alkyl and vinyl groups.

Of the resins corresponding to formula (I), the following resins II and III are particularly preferred: (II) · units: QM resin made up of the following structural a) 33 to 70 mol-% SiO2 units, b) 0 to 20 mol-% I^SiOj/z units t 15 c) 0 to 40 mol-% R1(CH3)SiO or Ph2SiO units (IIA) d) 20 to 50 mol-% R1 (CH3) 2SiO1/2 units with an alkoxy content according to Zeisel (A.L. Smith, Analysis of Silicones, New York: Wiley, 1974, pages 15520 156) of less than 20% and, on average, between 1.0 and 1.5 organic substituents (through Si-C bonding) per silicon atom.

OJ f these resins, resins made of 25 a) 40 to 55 mol-% SiO2 units, b) 10 to 25 mol-% Ph2SiO, Ph(CH3)Sio, (CH2=CH) (CH3)SiO or (CH3)2SiO units and (IIC) c) 20 to 40 mol-% R1 (CH3) 2SiO1/2 units 30 are preferred and resins made of a) 50 to 62.5 mol-% SiO2 units, b) 0 to 10 mol-% Ph2SiO, Ph(CH3)SiO, (IIB) 35 (CHZ=CH) (CH3)SiO or ΪΕ 922239 (CH3)2SiO units and c) 35 to 45 mol-% R1 (CH3)2SiO1/2 units are particularly preferred.

(III). TM resins made up of the following structural units: a) 50 to 98 mol-% R1SiO3/2 units, preferably 10 al) 50 to 95 mol-% CH3SiO3/2 units and a2) 0 to 20 mol-% PhSiO3/2 units and/or ViSiO3/2 units, b) 0 to 30 mol-% Ph2SiO or R1(CH3)SiO units, preferably bl) 5 to 30 mol-% (CH3)2SiO units and 15 b2) 0 to 20 mol-% Ph2SiO units and/or CH3(Rx)SiO units (IIIA) c) 0 to 33 mol-% and preferably 0 to 5 mol-% SiO2 units and 20 d) 0 to 10 mol-% R1 (CH3)2SiO1/2 units, preferably 0 to 5 mol-% (CH3)3SiO1/2 units, with on average between 1.0 and 1.5 and preferably between 1.05 and 1.3 organic substituents per silicon atom. The sum of all trifunctional units a) and tetrafunctional units c) should be at least 70 mol-%, based on the total content of all the units. Most particularly preferred thermoplas- tic silicone resins are those consisting essentially of 30 al) 80 to 98 mol-% CH3SiO3/2 units, a2) 0 to 5 mol-% PhSiO3/2 units, b) 0 to 20 mol-% and preferably up to 12 mol-% (CH3)2SiO units (IIIB) and 35 d) 0 to 10 mol-% and preferably 2 to 8 mol-% IE 922238 (CH3)3SiO1/2 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, preferably 40 to 150°C and, more preferably, 50 to 120 °C where only one silicone resin is used in the thermoplastic molding compound.

Mixtures of silicone resins differing in their softening temperatures have particularly advantageous properties. A ’'soft·' resin having a softening temperature of 30 to 120°C and preferably 40 to 100°C is used in admixture with a hard resin having a softening temperature of at least 60°C, a difference in the softening temperature of at least 20’C and, more particularly, at least 30°C being preferred.

The difference in the softening temperature may be 100°C or more. However, the mixture as such should still have a softening temperature of 40 to 200°C and preferably 40 to 150°C, even if the hard component present therein itself has a higher softening temperature.

The softening temperature of the mixture is influenced by the softening temperature of the components and the quantitative ratio between the components in the mixture.

Quantitative ratios of hard to soft component of 5:95% by weight to 95:5% by weight are used in accordance with the invention.

A resin corresponding to formula (I) and (III-A) of the following structural units: a) 75 to 95 mol-% b) 5 to 20 mol-% c) 0 to 5 mol-% d) 0 to 10 mol-% R1SiO3/2 units, R1(CH3)SiO units, SiO2 units, R1(CH3)2SiO1/2 units (IIIC) is suitable as the soft” silicone resin. and Both TM and QM (IIIA) or (IIA): resins corresponding to formulae 5 a) 85 to 98 mol-% R^iOj^ units, b) 0 to 5 mol-% Rx(CH3)SiO units, (HID) c) 2 to 10 mol-% R1 (CH3) 2SiO1/2 units or 10 a) 55 to 62. 5 mol-% SiO2 units, b) 0 to 5 mol-% R1(CH3)SiO units, (IID) c) 2 to 45 mol-% R1 (CH3) 2SiO1/2 units are suitable as the hard silicone resin.

Silicone resin mixtures containing a large quantity of TM or QM resin show extreme hardness and low tack in the cold state. Molding compounds of silicone resin mixtures such as these are particularly preferred for the production of complicated and thin-walled moldings, high strength being necessary to guarantee damage-free removal of the molding from the mold. The low tack of silicone resin mixtures of the type in question also facilitates demolding so that there is no need to use mold release agents, such as silicone oils.

Silicone resin mixtures containing only a small quantity of hard TM or QM resin show lower hardness and greater elasticity in the cold state. Molding compounds of silicone resin mixtures such as these are particularly preferred for the production of thick-walled moldings where serious stressing can occur during solidification of the molding in the mold. The elasticity of these silicone resin mixtures enables the stresses to be dissipated during firing and thus avoids cracks and other defects in the fired molding.

It has now been found that small quantities of hard TM or QM silicone resin according to the invention provide for a considerable improvement in the hardness and, more particularly, in the tack of the molding compounds. For most molding applications, therefore, 10 to 50% by weight of the hard TM or Qm silicone resin are sufficient to ensure simple demolding of the molding.

The silicone resins according to the invention are produced, for example, by co-hydrolysis of a corresponding mixture of chlorosilanes or alkoxysiloxanes. They may also be produced by first equilibrating and then hydrolyzing a mixture of one or more alkoxysilanes and one or more siloxanes. Hydrolysis is carried out by any of the standard methods described in W. Noll, Chemie und Technologie der Silicone (Weinheim: Verlag Chemie, 1968, pages 162169) . For example, the chlorosilane mixture is added together with an organic solvent to an excess of water and, optionally, an aliphatic alcohol. The phases are separated and the organic phase is washed until neutral. The sili20 cone resin is used either in the form of a solution or, after removal of the solvent, in the form of a solid for the production of the molding compounds according to the invention.

It is known that the alkoxy and SiOH content of silicone resins is reduced by condensation reactions so that their softening temperature can be increased. This operation, which is often referred to as thickening of the silicone resin solution, is preferably carried out during the production of the silicone resin by heating in the presence of catalysts. Accordingly, production of the silicone resins according to the invention has to be carried out in such a way that the desired softening temperature is obtained. The silicone resins also have to be carefully neutralized to guarantee a stable viscosity during processing of the molding compound.

In their solventless state, the silicone resins or silicone resin mixtures according to the invention are solids at room temperature which have softening temperatures of 30 to 200°C. Above this temperature, the silicone resins or silicone resin mixtures are liquid to highly viscous. The silicone resin or silicone resin mixture preferably has a viscosity in the melt of less than 100,000 mPa.s and preferably less than 10,000 mPa.s. The silicone resins are amorphous in the solid state. Accordingly, the temperature at which plastic flow begins generally cannot be accurately determined. Accordingly, the softening temperature is expressed as a temperature range over 10 to 15°C.

The silicone resins or silicone resin mixtures accord15 ing to the invention are characterized by high ceramic yields of more than 60% by weight and preferably more than 70% by weight where pyrolysis is carried out at up to 1,000°C. The ceramic yield is defined as the residue in % by weight after pyrolysis. The ceramic yield generally deteriorates with increasing numbers of PhSiO3/2 and Ph2SiO units and siloxy units with long-chain alkyl radicals, so that the sum of these units should not exceed 40 mol-% and preferably 20 mol-%.

The thermoplastic molding compounds according to the invention generally consist of a homogeneous mixture of at least one sinterable powder of ceramic or metal and at least thermoplastic silicone resin or silicone resin mixture. In addition, the molding compounds according to the invention may contain other auxiliaries, such as sintering aids, flow aids and demolding aids.

In another embodiment of the present invention, the thermoplastic compounds may contain other organic thermoplastic binders or copolymers of organic polymers with siloxanes in addition to the silicone resin. In the present invention, the advantage of rapid firing is mainly attributable to the silicone resin used. However, other thermoplastic polymers can improve properties of the molding compounds during molding without significantly lengthening the firing time.

Any powders of metal or ceramic, including mineral raw materials for the production of ceramic, which may be sintered to form a solid body are suitable for the thermoplastic molding compounds.

Sinterable powders suitable for use in accordance with 10 the invention preferably consist of oxide ceramic or nonoxidic ceramic or their raw materials and also hard metal, sintered metal, alloyed steel or pure metal.

Examples of preferred oxide ceramic are A12O3, MgO, ZrO2, Al2TiO5, BaTiO3 and silicate ceramic or their raw materials, such as porcelain, and stoneware mixtures which may contain inter alia clay, feldspar and quartz. Examples of non-oxidic ceramic are inter alia Sic, Si3NA, BN, B<,c, AIN, TiN and Tic. Examples of sinterable hard metals are WC and TaC alloys. One example of a sinterable metal is silicon which may be reacted with nitrogen at high temperatures to form silicon nitride. The powders may be used individually or even in the form of mixtures of various powders.

In general, various sintering aids may be added according to the ceramic or metal, accelerating phase transition or consolidation where sintering is carried out at relatively low temperatures through the formation of low-melting phases. These sintering aids generally have no significant effect on the thermoplastic properties of the molding compounds.

The organic thermoplastic binders according to the invention are organic polymers and waxes which have a softening temperature of 40 to 200°C, preferably 40 to 160°C and, more preferably, 70 to 130’C. Examples are polyethylene, polypropylene, polystyrene, polyacrylates, polyesters and ethylene/vinyl acetate copolymers. Poly11 ethylene, polypropylene and copolymers thereof and also polymer-based waxes are preferred. Polar polyolefin waxes and mixtures thereof with apolar thermoplastic polymers are preferred. Neutral and polar waxes of mineral or natural occurrence, such as paraffin wax, montan wax, beeswax or vegetable waxes, and derivatives thereof are also preferred. Thermoplastic copolymers of organic polymers with polydimethyl siloxanes or silicone resins are also preferably used. Examples are polyester/siloxane copolymers, so10 called combination resins. One or more binders may be used together with the silicone resin.

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

The thermoplastic organic binders according to the invention and copolymers thereof with siloxanes are used in quantities which, although still producing an improvement in the molding properties or rather in the properties of the molding, still provide for a short firing time. As already described, organic thermoplastics have to be completely removed from the green compact during firing. Accordingly, excessive amounts of organic binder in the molding compound have an adverse effect on the firing time.

Preferred molding compounds are those in which at least 10% by weight of the sum of all the binders and auxiliaries consists of the silicone resins according to the invention. Molding compounds containing relatively little silicone resin are particularly suitable for the production of moldings in which the ceramic residue of the silicon resin can have an adverse effect on the properties of the molding, such as for example moldings of non-oxidic ceramic. Molding compounds in which at least 50% by weight of the sum of all the binders and auxiliaries consists of silicone resins are preferably used where a very short firing time is required.

In addition to the silicone resin or silicone resin mixture (and preferably the thermoplastic polymer), the thermoplastic molding compounds according to the invention generally contain one or more flow aids or demolding aids which provide for a reduction in the viscosity of the molding compound during molding and for clean and simple demolding. Examples are aliphatic fatty acids and salts and derivatives thereof, such as stearic acid, calcium stearate, magnesium stearate, stearic alcohol, stearic acid amide, stearic acid ethyl ester or the like, oils, such as polydimethyl siloxanes, polyethylene oxides, polypropylene oxides, or copolymers of polydimethyl siloxane and polyethylene oxide or polypropylene oxide and the like, or low molecular weight waxes, such as paraffin wax, polyethylene oxide wax or beeswax. Preferred molding compounds contain 0.25 to 10% by weight (based on the sum of all the binders and auxiliaries) of stearic acid, salts and derivatives thereof or paraffin wax. In general, the flow aid will be only be added in the quantity necessary to bring the viscosity during molding into the required range.

The thermoplastic molding compounds according to the invention contain silicone resin, thermoplastic organic polymers and other auxiliaries in at least the quantity required to obtain a thermoplastically processable composition. In general, binders together with the other auxiliaries have to fill the empty spaces between the powder particles in the molding. Various quantities are required for this purpose, depending on the type of powder and its granulometry and particle size distribution. Experience has shown that 25 to 60% by volume binder is necessary. Molding compounds containing 50 to 70% by volume powder and 30 to 50% by volume binder and auxiliaries are preferred, powder contents of at least 60% by volume being particular5 ly preferred.

The thermoplastic molding compounds according to the invention are solid at room temperature, but plastic at temperatures above the softening temperature of the silicone resin used. In preferred embodiments, the molding compounds have viscosities of less than 10,000 Pa.s at the processing temperature. Viscosities of 100 to 5,000 Pa.s are particularly preferred.

The thermoplastic molding compounds according to the invention are produced by mixing the components mentioned at a temperature above the softening temperature of the silicone resin, any residual solvent from the production of the silicone being removed. It is of advantage to apply intense shear forces during mixing in order to break up powder aggregates and hence to obtain a homogeneous mix20 ture. Suitable mixing units are, for example, kneaders, twin-screw extruders or mixing rolls. The molding compounds may then either be directly used or may first be processed to powders or granules.

The thermoplastic molding compounds according to the invention have excellent properties for thermoplastic processing, for example by injection molding, extrusion or hot press molding. The molding compounds may be thermoplastical ly processed at temperatures above the softening temperature of the silicone resin and may be introduced under pressure into molds of which the temperature is below the softening temperature of the silicone resin. The molding compound becomes solid again by cooling. The green compacts formed have high strengths and may be machined, for example, by grinding, drilling or sawing. Processing residues can be reused.

The thermoplastic molding compounds according to the invention are particularly suitable for the production of complicated moldings by such processes as thermoplastic injection molding. The molding compounds show good flow properties at temperatures at least 20 °C above the softening temperature of the silicone resin used. The molding compounds can have high percentage powder contents. The green compacts produced from the molding compounds according to the invention undergo only a comparatively small weight loss during firing at up to 1,000°C. The green compacts may therefore be fired in a short time. The fired green compacts have high strengths and high densities.

The green compacts produced from the molding compounds according to the invention may be fired in a short time without any defects either in air or in an inert gas atmosphere or in vacuo.

Firing is preferably carried out in accordance with a temperature increase program of 0.1 to 5°C/min. and preferably 0.5 to 5°C/min. to 600-1,000°C. Molding compounds based on silicone resin mixtures withstand heating temperatures of up to 10°C/min. The compacts may also be heated in stages of 0.1 to 5°C/min. up to a temperature of 200 to 800°C, kept at that temperature optionally until there is no further change in weight and then heated at 5 to 50°C/ min. up to 1,000°C. Depending on the powder and sintering aids used, the fired green compacts may then be sintered, generally at temperatures of 1,000 to 2,000°C.

The invention is illustrated by the following Examples.

Examples General: The following A12O3 powder Porcelain powder Hard paraffin I Hard paraffin II Polystyrene Polyethylene oxide substances were used in the Examples: Martinoxid ZPS-402 (a product of Martinswerk GmbH), average particle size 2.0-3.0 microns; density approx. 2.95 g/cm3; a-Al2O3 content >95% by weight; ignition loss approx. 0.2% by weight a mixture of raw materials for the production of porcelain ceramic consisting of approx. 50% kaolin and approx. 50% feldspar, average particle size 4 to 5 microns; ignition loss 6.1%. softening temperature 52-54°C softening temperature 90-94 °C Hostyren N 2000 (a product of Hoechst AG) viscosity 160 mPa.s at 25’C Polydimethyl siloxane viscosity 5,000 mPa.s at 25’C 30 Siloxane copolymer a 76% solution in toluene of a block copolymer of (40:60) polydimethyl siloxane and polyethylene oxide, average molecular weight 4230 g/mol.

Polar polyolefin wax Hostalub H 22 (a product of Hoechst Montan wax Copolymer wax AG), softening temperature 103-108°C; acid value 22-28 mg KOH/g; saponification value 45-65 mg KOH/g; viscosity approx. 300 mPa.s at 120°C Hoechst-Wachs-E (a product of Hoechst AG), dropping point 79-85°C; acid value 15-20 mg KOH/g; saponification value 130-160 mg KOH/g; density 1.01 g/cm3; viscosity at 100°C approx. 30 mPa.s an ethylene/vinyl acetate copolymer (A-C Additive 400, a product of Allied Corporation), vinyl acetate content 13%; dropping point 95 °C; density 0.92 g/cm3; viscosity at 140°C approx. 600 mPa.s Dynasil 40 (a product of Hiils Troisdorf AG), a silicic acid ester with the formula (EtO3SiO (Si (OEt) 2O) nSi (OEt) 3 (n approx. 2.7 and Et = CH2CH3) , SiO2 content 40% by weight.

Example 1 (silicone resin 1) Production of a silicone resin from CH3SiCl3, (CH3)2SiCl2 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 was washed three times with water. Xylene and n-butanol were then distilled off from the resin solution to obtain an 80% solution which was then diluted with toluene to obtain a resin solution having a solids content of 64% by weight and a viscosity at 25°C of 45 mPa.s.

In its solventless state, the silicone resin (1) is a solid having a softening temperature of 55 to 65°C, a viscosity at 130°C of 500 mPa.s and a density of 1.18 g/cm3. XH NMR (300 MHz, CDC13, ppm): S 0.15 (s, SiCH3, int: 150), 0.90 (mult, O(CH2)3CH3, int: 10), 1.35, 1.55 (mult, OCH2(CH2)2CH3, int: 14), 2.3 (br, SiOH, int: 0.9), 3.7 (mult, OCHj, int: 7) . According to 28Si-NMR, the silicone resin contains 1.15 methyl groups per silicon atom. A molecular formula of (CH3)x.X5Si(O(CH2)3CH3)0.08(OH) 0 007Ox 38 can be calculated from these values. The ceramic yield after pyrolysis at up to 1,000°C (heating rate l°C/min.) in air was 76% by weight.

Example 2 (silicone resin 2) Production of the silicone resin from (CH3)SiCl3 and (CH3)3SiCl 420 g (2.81 mol) methyl trichlorosilane and 24 g (0.22 mol) trimethyl chlorosilane were hydrolyzed in 1.9 1 water, 3 35 g xylene and 335 g n-butanol in the same way as in Example 1. The aqueous phase was separated off and the still acidic solution was stirred for 3 0 minutes at 80°C. The solution was washed three times with water. Xylene/ butanol were then distilled off from the resin solution to obtain a 77% resin solution.

In its solventless state, the silicone resin (2) is a solid having 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 1,000°C (heating rate l’C/min.) in air was 74.2% by weight.

Example 3 (silicone resin 3) Production of the silicone resin from (CH3)SiCl3 and (CH3)3SiCl 420 g (2.81 mol) methyl trichlorosilane and 12 g (0.11 mol) trimethyl chlorosilane were hydrolyzed in 1.9 1 water, 335 g xylene and 335 g n-butanol in the same way as in Example 1. The aqueous phase was separated off, the still acidic solution was stirred for 30 minutes at 80’C and washed until neutral and xylene/butanol were distilled off to obtain a 75% resin solution.

In its solventless state, the silicone resin (3) is a 10 solid having a softening temperature of 80 to 100’C and a density of 1.15 g/cm3. NMR (300 MHz, CDC13 ppm): 6 0.15 (s, SiCH3, int: 149), 0.90 (mult, O(CH2)3CH3, int: 6), 1.35, 1.50 (mult, OCH2(CH2)2CH3, int: 8), 2.2 (br, SiOH, int: 2.3), 3.7 (mult, OCH2(CH2)2CH3, int: 4). According to 29Si-NMR, the silicone resin contains 1.08 methyl groups per silicon atom. A molecular formula of (CH3)108Si(O(CH2)3CH3)0.43(OH)0.017O143 can be calculated from these values. The ceramic yield after pyrolysis at to 1,000’C (heating rate l’C/min.) in air was 79.5% by weight.

Example 4 (silicone resin 4) Production of the QM silicone resin A mixture of 1,500 g (10.0 mol SiO2) Dynasil 40, 600 g (7.4 mol Me3SiO1/2) hexamethyl disiloxane, 2.4 g cone. H2SiO4, 1.2 g C<,F9SO3H and 1,700 g xylene were introduced into a 6 liter four-necked flask equipped with a stirrer, water cooler, thermometer and dropping funnel. The mixture was first refluxed for 1 hour and then hydrolyzed with 263 g water (approx. 20% excess) at a temperature of 90 to 100’C.

The mixture was then stirred for 2 h at 100’C and neutralized for 1 h at 100’C with 21.7 g (0.265 mol) sodium acetate. 1,600 ml xylene were then distilled off and the product was filtered. 1,580 g of a 75% solution of the silicone resin are obtained.

In its solventless state, the silicone resin (4) is a solid having 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%. 2H NMR (300 MHz, CDC13, ppm): S 0.15 (s, SiCH3, int: 149.8), 1.20 (br. s, OCH2CH3, int: 21.5), 3.80 (br. s, OCHaCHa, int: 14.5). IR (KBr, cm1): 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). A molecular formula of (CH3)! 46Si (OCH2CH3) 0.2ΐθι.ΐ6 can be calculated from these 10 values.

The ceramic yield after pyrolysis at up to 1,000 °C (heating rate 2°C/min.) in air was 75.3%.

Example 5 (silicone resin 5) Production of a QM silicone resin As in Example 4, 1,542 g (10.28 mol SiO2) Dynasil 40 and 583 g (7.2 mol Me3SiO1/2) hexamethyl disiloxane were hydrolyzed with 270 g water, neutralized with sodium acetate, concentrated and filtered. 1,600 g of a 75% solution of the silicone resin are obtained.

In its solventless state, the silicone resin (5) is a solid with a softening temperature of 100 to 110*0, an SiOH content (Karl Fischer) of less than 0.01% and an ethoxy content (Zeisel) of 11.8%. XH NMR (300 MHz, CDC13, ppm): δ 0.15 (s, SiCH3, int: 149.2), 1.20 (br. s, OCH2CH3, int: 21), 3.80 (br. s, OCH2CH3, int: 14.5). IR (KBr, cm1): 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). A molecular formula of (CH3) r45Si(Oet)0.2oOi.i7 can be calculated from these values.

The ceramic yield after pyrolysis at up to 1,000°C (heating rate 2*C/min.) in air was 76.7%.

Example 6 (silicon resin 6) Production of a QM silicone resin As in Example 4, 1,154 g (7.69 mol SiO2) Dynasil 40, 311.5 g (3.85 mol Me3SiO1/2) hexamethyl disiloxane and 428 g (5.77 mol Me2SiO) octamethyl cyclotetrasiloxane were hydrolyzed with 202 g water, neutralized with sodium acetate, concentrated and filtered. 1300 g of a 54% solution of the silicone resin were obtained.

In its solventless state, the silicone resin (6) is a solid having 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%. NMR (300 MHz, CDC13, ppm): 6 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 1,000’C (heating rate 2’C/min.) in air was 76.5%.

Example 7 (silicone resin 7) Production of a Qm silicone resin As in Example 4, 1,500 g (10.0 mol SiO2) Dynasil 40 and 516 g (6.4 mol Me3SiO1/2) hexamethyl disiloxane were hydrolyzed with 290 g water, neutralized with sodium acetate, concentrated and filtered. 1600 g of a 75% solution of the silicone resin are obtained.

In its solventless state, the silicone resin (7) is a solid having a softening temperature of 220 °C, an SiOH content (Karl Fischer) of less than 0.01% and an ethoxy content (Zeisel) of 12.5%. JH NMR (300 MHz, CDC13, ppm): δ 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) , 1050-1200 (br, vs), 870 (sh, s), 850 (sh, s), 760 (sh, m). A molecular formula of (CH3) 115Si (OCH2CH3) 021O131 can be calculated from these data.

The ceramic yield after pyrolysis at up to 1,000°C (heating rate 2°C.min.) in air was 78.7%.

Example 8 (molding compound of silicone resin 1) 395 g A12O3 powder, 100 g of the above 64% resin solution of Example 1 (64 g resin), 4 g calcium stearate and 8 g polyethylene oxide were introduced into a twinscrew kneader. The mixture was kneaded under reduced pressure for 15 minutes at 110°C to remove the solvent. The mixture was then kneaded for another 15 minutes without the vacuum. A plastic molding compound with good flow properties which solidified on cooling was formed. The molding compound contains approximately 61.5% by volume A12O3· The molding compounds was press molded to pellets at around 120°C/500 bar. A pellet measuring 13 x 2.0 mm was fired in air for 6.0 h at up to 1000°C in accordance with the following program: 25-150°C/25 mins.; 150-400°C/250 mins.; 400-600°C/65 mins.; 600-1,000°C/20 mins.. The fired pellet was of high strength and was free from macroscopic defects. The weight loss during firing was 5.5%.

Examples 9-13 Various molding compounds were produced in a kneader as in Example 8 from A12O3 powder and silicone resin solution 1. The compositions of these molding compounds are shown in Table 1. The molding compounds were press molded to pellets and fired in air, Table 2.

Table 1: Composition of the molding compounds No. Temp. •cAl2°3 g Resin solution g Ca stearate g Others 9 105 415 94 5 8 g Hard paraffin I 10 105 435 100 5 2 g Polyethylene oxide 11 105 415 100 5 8 g Siloxane copolymer 12 130 415 86 5 9 8.5 g g Hard paraffin I Polystyrene 13 120 375 100 9 g Polar polyolefin wax Table 2: Results of firing8 No. Size mm Temp. program Firing time h % Weight loss Appearance 8 10 X 4.5 l°C/min. to 1,000’C 16.25 5.1 Defect-free 9 13 X 2.5 l’C/min. to l,000°C 16.25 5.9 Defect-free 10 13 X 2.5 l°C/min. to 1,000’C 16.25 4.2 Defect-free 11 13 X 2.5 25-150’C/ 25 mins. 150-400’C/ 250 mins. 400-600°C/ 65 mins. 600-1,000’C 20 mins. 6.0 3.5 Defect-free 12 13 X 2.5 l°C/min. to 1,000’C 16.25 7.1 Defect-free 13 13 X 2 l’C/min. to 1,000’C 5.5 Defect-free 8 Kneader temperature Example 14 (molding compound of silicone resin 2) 32.5 g (25 g resin) silicone resin solution 2, 22.5 g montan wax and 2.5 g stearic acid amide were introduced into a kneader and heated to 120 °C. 222.5 g A12O3 powder were then mixed in and the solvent was removed by purging with nitrogen. Another 85 g A12O3 powder were gradually incorporated. The mixture was then kneaded for another 60 minutes. A plastic molding compound having good flow properties which solidified on cooling was formed. The molding compound contained approximately 62.3% by volume A12O3.

The molding compound was press molded to pellets at around 120°C. A pellet measuring 13 x 2.0 mm was fired in air by heating at l’C/min. to l,000°C. The fired pellet was of high strength and was free from macroscopic defects. The weight loss during firing was 8.4%.

Example 15 (molding compound of silicone resin 4) 41.7 g (25 g resin) of a 60% silicone resin solution 20 of Example 4, 24.5 g montan wax and 0.5 g sodium stearate were introduced into a kneader and mixed for 5 minutes at 120°C. 220 g A12O3 powder were then added and the mixture was kneaded for 30 minutes while purging continuously with nitrogen in order to evaporate the xylene. Another 117 g A12O3 powder was then added in portions and the mixture was kneaded for a total of 1 h. A plastic molding compound with good flow properties which solidified on cooling was obtained. The molding compound contained approximately 64.9% by volume A12O3.

The molding compound was press molded to pellets at around 120°C/100 bar. A pellet measuring 13 x 2.0 mm was calcined in air by heating in accordance with the following program: l’C/min. to 100°C, 0.5°C/min. to 400°C, l’C/min. to 600°C and 5°C/min. to 1,000°C. The calcined pellet was of high strength and was free from macroscopic defects.

The weight loss during firing was 9.0%.

Examples 16 to 19 Various molding compounds were produced from A12O3 5 powder, silicone resin and auxiliaries in a kneader in the same way as in Example 15. The compositions of the molding compounds are shown in Table 3. The molding compounds were press molded to pellets and calcined in air, Table 4.

Table 3: Composition of the molding compounds No.Ai°3 Silicone No. resin g Others 16 328 4 35 10 5 g Montan wax g Stearic acid amide 17 246 4 35 5 g Copolymer wax 5 g Paraffin II 5 g Stearic acid amide 18 311 5 35 5 g Paraffin II 9.5 g Montan wax 0.5 g Sodium stearate 19 252 6 35 5 g Copolymer wax 9.5 g Montan wax 0.5 g Sodium stearate Table 4: Results of firing No. Size mm Firing time h % Weight loss Appearance 15 13 x 2 16:20 9.0 Defect-free 16 13 X 2 16:20 6.8 Defect-free 17 13 X 2 16:20 8.3 Defect-free 18 13 X 2 16:20 7.0 Defect-free 19 13 X 2 16:20 8.3 Defect-free Heating program: l’C/min. 25-100’C, 0.5’C/min. 100-400’C, l’C/min. 400-600’C and 5’C/min. 600-1,000’C Example 20 A soft resin and a hard resin were mixed in accordance with Table 5 to show the properties of the mixture.

Example 21 Production of a molding compound from the mixture of silicone resins (1) and (3) 39.1 g (25 g resin) of a 64% resin solution from Example 1, 6.0 g (5.25 g resin) of an 88% resin solution from Example 2, 12.5 g montan wax and 2.5 g stearic acid amide were introduced into a kneader and mixed for 5 minutes at 120’C. 200 g A12O3 powder were then added and the mixture was heated for 30 minutes while purging con15 tinuously with nitrogen in order to evaporate the solvent. Another 76 g A12O3 powder were added in portions to the mixture which was then kneaded for a total of 1 h. A plastic molding compound having good flow properties which solidified on cooling was obtained.

The molding compound was press molded to pellets at approx. 120° C/100 bar. The pellets were easy to demold and were of high strength. A pellet measuring 13 x 2.0 mm was fired in air by heating in accordance with the following program: l°C/min. to 100 °C, 0.5°C/min. to 400°C, l°C/min. to 600°C and 5°C/min. to l,000°C. The fired pellet was of high strength and was free from macroscopic defects. The weight loss during firing was 7.2%.

Examples 22-26 Various molding compounds were produced in a kneader as in Example 21 from A12O3 powder and various silicone resin mixtures. The compositions of these molding compounds are shown in Table 6. The molding compounds were press molded to pellets at around 120°C. The molding compounds were easy to demold and did not adhere to the walls of the mold. The press-molded compounds varied in hardness. They became harder and more brittle with increasing content of the silicone resins (3), (4) and (7).

The press-molded compounds could be fired in a short time without any defects, Table 7.

Table 5 ϊ Properties of the silicone resin mixtures Resin 1 (Ex. 1) Hard Ex. resin No. % by wt. Softening perature, tem- •c Viscosity mPa.s, 130' Hard’C ness* 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 ++ “Hardness scale: ++: very hard, brittle, + plastic, +/-: hard, plastic, -: soft, —: : hard, slightly very soft.

Table 6: Composition of the molding compounds Ex. Ai ° Silicone resin Others No. 3 3 No. g 22 276 1 17.5 12.5 g Montan wax 3 17.5 2.5 g Stearic acid amide 23 276 1 17.5 17.5 g Montan wax 4 17.5 2.5 g Stearic acid amide 24 276 1 29.75 12.5 g Montan wax 7 5.25 2.5 g Stearic acid amide 25 414 1 27.4 18.25 g Montan wax 7 27.4 26 414 1 18.3 36.5 g Montan wax 7 18.3 Table 7: Results of firing EX. No. Size mm Firing time’ h % Weight loss Appearance 21 13 x 2 16:20* 7.2 Defect-free 22 13 x 2 16:20 7.2 Defect-free 23 13 X 2 16:20 7.3 Defect-free 24 13 X 2 16:20 7.3 Defect-free 25 13 X 2 ll:00b 5.8 Defect-free 26 13 X 2 11:00 9.4 Defect-free “Heating program: l’C/min. 25-100’C, 0.5’C/min. 100-400’C, l’C/min. 400-600’C and 5’C/min. 600-1,000’C. bHeating program l’C/min. 25-600’C, 4’C/min. 600-1000’C.

Example 27 Production of molding compound from porcelain powder As in Example 21, 39.1 g of a 64% resin solution (25 g resin) from Example 1, 10 g montan wax, 10 g copolymer wax and 5 g stearic acid amide were mixed with 253 g porcelain powder and the resulting mixture was kneaded for a total of 1 hour. A plastic molding compound with good flow properties which solidified on cooling was obtained.

The molding compound contained approximately 62% by volume powder.

The molding compound had a density of 1.97 g/cm3 and a viscosity of 700 Pa.s at a shear rate of 100 s'1 and of 350 Pa.s at 700 s'1. The molding compound was injection molded at a melt temperature of 130 to 140’C, a mold temperature of 35’C and a pressure of 900 bar to form bars measuring 80 x 20 x 5 mm. The moldings were free from macroscopic defects. They could be fired without defects in less than 30 hours. The percentage weight loss was 17.7%.

Claims

1. Binders for thermoplastic molding compounds containing at least one thermoplastic silicone resin which has a softening temperature of 30 to 200°C and corresponds to the 5 following average formula: RiSi(OH) b (OR 2 ) c O (4 ..^ )/2 (I) in which 10 the sum (a+b+c) is 1.05 to 1.7, the sum (b+c) is at most 0.3, R 1 represents one or more of the substituents H, Cj., 8 alkyl, allyl, vinyl or phenyl, R 2 represents one or more organic C,. ]8 alkyl radicals, with the proviso that the average molecular weight (arithmetic mean) of the organic radicals (including the alkoxy radicals) should be at most 50 divided by the sum (a+c).

2. A thermoplastic molding compound containing at least 20 one sinterable powder and at least one thermoplastic binder according to claim 1.

3. A thermoplastic molding compound as claimed in claim 2 containing another thermoplastic silicone resin according to claim 1, the first silicone resin having a softening 25 temperature of 30 to 120°C and the other silicone resin having a softening temperature of at least 60°C.

4. A thermoplastic molding compound as claimed in claim 2 or 3 additionally containing another thermoplastic binder on an organic basis or based on a copolymer with siloxanes. 3 0

5. A process for the production of the thermoplastic molding compounds claimed in any of claims 2 to 4 by mixing sinterable powder with binders, sintering aids and other auxiliaries at temperatures above the softening temperature of the silicone resin or silicone resin mixture. 35

6. A process for the production of sintered compacts, characterized in that, after injection molding, extrusion or hot pressing, thermoplastic molding compounds according to any of claims 2 to 4 are first fired at a temperature of 200 to l,000°C and then sintered at temperatures of 1,000 to 2,000°C.

7. A binder as claimed in claim 1, substantially as hereinbefore described and exemplified.

8. A thermoplastic molding compound according to claim 2, substantially as hereinbefore described and exemplified.

9. A process for the production of a thermoplastic molding compound according to claim 2, substantially as hereinbefore described and exemplified.

10. A thermoplastic molding compound according to claim 2, whenever produced by a process claimed in claim 5 or 9.

11. A process according to claim 6 for the production of a sintered compact, substantially as hereinbefore described and exemplified.

12. A sintered compact, whenever produced by a process claimed in claim 6 or 11.