DE4134694A1 - Binder for thermoplastic moulding compsn. contg. sintered metal or ceramic prods. - Google Patents

Abstract

Binders (I) for thermoplastic moulding materials (II) are claimed, contg. thermoplastic silicone resin(s) of formula (III) with softening pt. (T) = 30-200 deg.C; RaSi(OH)b(OR')cO(4-a-b-c)/2 (III) R = H, 1-18C alkyl, allyl, vinyl or Ph; R' = independently 1-18C alkyl; a + b + c = 1.05.1-7; b + c = not above 0.3; mean mol.wt. of organic residues (including alkoxy gps.) = not above 50/(a + c). Also claimed are thermoplastic materials (II) contg. a sinterable powder (IV) and binder(s) (I); and a process for the prodn. of (II), by mixing (IV) with (I), sintering aids and other additives at temps. above T. Pref. (II) contain a mixt. of silicone resin with T = 30-200 deg.C and another silicone resin with T = at least 60 deg.C, and pref. also another thermoplastic binder based on organic substances or siloxane copolymers.

Description

The present invention relates to new thermoplastic Molding compounds for the production of molded parts Ceramic or metal from appropriate ceramic or Metal powders. Thermoplastic molding compounds can be found at other application in processes such as injection molding, Extrude or hot press, where a tempera flow behavior is necessary.

It is known that sinterable ceramic or metal powder together with thermoplastic binders and other auxiliaries by injection molding, extrusion or hot pressing can be processed into molded parts (F. Aldinger and H.-J-Kalz Angew. Chem. 99 (1987) 381- 391; P. Glutz Feinwerktechnik & Meßtechnik 97 (1989) (383-385); M.J. Edirisinghe, J.R.G. Evans: Inter. J. High Technology Ceramics 2 (1986) 1-31; W. Michaeli, R. Bieler; Ind. 113 (1991) 12-14). After shaping  the binder is used at temperatures between 200 and 1000 ° C removed from the molded part (called green body) or burned out.

Then the green body is usually at tem temperatures of more than 1000 ° C sintered, one partially or complete phase change can and a compression of the body takes place.

As a rule, purely organic binders are used used this method. Examples are polystyrene, Polyethylene, polypropylene, polybutyl acrylates and Paraffin waxes. However, organic binders do Disadvantage that burning out slowly and with great Care should be taken in temperature control must, otherwise green bodies with gross defects such as cracks or pores can be obtained. Sometimes green too body with lack of firmness after burnout receive. Adequate strength of the green body is for the further processing of the green body as well as that error-free sintering necessary.

Silicone resins are already used several times as binders for the production of ceramics has been described. However are the silicone resins for process described so far ren who use a thermoplastic processing, such as injection molding, not suitable.

US 30 90 691 describes a method of manufacture development of molded parts made of ceramic, which is achieved by firing a Mixture of an organosiloxane and a ceramic powder  is marked. The organosiloxane has a total collects 1 to 3 organic groups per silicon atom. The mixtures are fired at 500 to 1550 ° C usually contain a curing catalyst, such as for example lead oxide or lead stearate.

DE-A 21 42 581 describes compositions for the manufacture of alumina ceramics, which are suitable for the selection ter inorganic additional components due to low Shrinkage during sintering are marked. Several Binding agents are described, but are heat-hardened bare silicone resins preferred. For shaping through Injection molding is used as a binder, polyethylene, Polyvinyl chloride or a polyamide is preferred.

DE-A 21 06 128 and DE-A 22 11 723 describe heat curable molding compounds made of inorganic solids and solvent-free liquid organosiloxanes, the 1.3 have up to 1.6 organic residues per silicon atom and consist of at least 22 mol% phenylsiloxy units, and organic peroxides as curing catalysts. The Molding compounds are brought into a mold by pressing and during the pressing process at elevated temperature hardened. The green bodies are then 2 to 4 Cured for hours at 200 ° C and then over 32 hours sintered to solid ceramics up to 1510 ° C. As anorga alumina becomes a niche solid in the examples described.

US-A 48 88 376 and US-A 49 29 573 describe a Process for the production of molded silicon carbide parts with thermosetting polyorganosiloxanes as a binder.  

The polysiloxanes are highly viscous to solid at room temperature and consist of 10 to 90 mole% PhSiO _3/2 -Einhei ten, 0 to 50 mole% CH ₃ SiO _3/2, and 10 to 90 mol% of Ph (CH ₂ = CH ) SiO _2/2 units and are characterized in that at least 0.2% by weight of free carbon, based on the weight of the silicon carbide powder, is formed in the pyrolysis of the polysiloxane. In US-A 48 88 376 an organic peroxide is additionally added as a curing catalyst. The polysiloxanes according to these processes have ceramic yields of only 39 to 50.8% by weight in the pyrolysis in an inert gas atmosphere.

The silicone resins described have one or more Disadvantage. Many of the silicone resins are liquid and must be hardened in the mold. to a sufficient To cause strength of the molded part. The hardening in the Form leads to long cycle times and therefore longer ones Unit cost. Solid silicone resins that are used at higher temperatures temperatures, d. H. Processing temperatures, not him switches are also for thermoplastic processing processing not suitable. Other silicone resins only have low ceramic yields during pyrolysis up to 1000 ° C on. However, a high ceramic yield is an advance setting for a fast, flawless burning. Out of this the technical desire for molding compounds results Ceramics or metal powders and binders, which are good possess thermoplastic processing properties and Fired in a short time without additional hardening stages can be.  

It has now surprisingly been found that certain Silicone resins have excellent thermoplastic properties as well as high ceramic yields in pyrolysis up to Have 1000 ° C. Made with these silicone resins Thermoplastic molding compositions have excellent Properties for thermoplastic processing and can be molded within a short period of time be burned.

The thermoplastic molding compositions according to the invention consist of a general wording homogeneous mixture of at least one sinterable Ceramic or metal powder and at least one thermoplastic silicone resin. In addition, the Molding compositions according to the invention other auxiliaries, such as Sintering aids, flow and separation aids contain.

In another embodiment of the present Invention, the thermoplastic molding compositions in addition Lich other thermoplastic polymers to the silicone resin re on an organic basis or their copolymers with Si contain loxanes. In the present invention is based the advantage of fast burning mainly on the chosen silicone resin. However, other thermopla stische Polymer properties of the molding material in the Improve shape without significantly reducing the burning time to extend.

The sinterable powders according to the invention are preferably made of oxide ceramic, non-oxide ceramic, or hard metal, alloy steel or pure metal. Examples of preferred oxide ceramics are Al₂O₃, MgO, ZrO ₂ , Al ₂ TiO ₅ , BaTiO ₃ and silicate ceramics, such as por cellan. Examples of non-oxide ceramics are SiC, Si ₃ N ₄ , BN, B ₄ C, AlN, TiN, and TiC among others. Examples of sinterable hard metals are WC or TaC alloys. An example of a sinterable metal is silicon, which can be converted to silicon nitride with nitrogen at high temperatures. The powders can be used alone or as a mixture of different powders.

In general, depending on the ceramic or metal various sintering aids added by Bil formation of low-melting phases the phase change development or compression during sintering at lower temperatures accelerate temperatures. Have these sintering aids usually no significant influence on the thermo plastic properties of the molding compounds.

The in the thermoplastic molding materials according to the invention sen contained silicone resins correspond to the general formula

R ¹ _a Si (OH) _b (OR ² ) _c O ( _4-abc ) _{/ 2}

wherein R ¹ = C1 to C18 alkyl, allyl, vinyl or phenyl, R ² = C1 to C18 alkyl, a has a value of 0.95 to 1.5 and the sum b + c less than 0.3 is. Preferred are thermoplastic silicone resins, which consist essentially of

• a) 50 to 90 mol% of CH ₃ SiO _3/2 units,
• b) 0 to 20 mole% PhSiO _3/2 units, and ViSiO _3/2 - units
• c) 5 to 30 mol% (CH ₃ ) ₂ SiO _2/2 units,
• d) 0 to 20 mol% of Ph ₂ SiO _2/2 units and CH ₃ (R ³ ) SiO _2/2 units,
• e) 0 to 5 mole% SiO _4/2 units, and
• f) 0 to 5 mol% of (CH _{3) 3} SiO _1/2 units, wherein R ³ = C2 to C18 alkyl, allyl, vinyl or phenyl, are made and an average of 1.05 to 1.3 organic substituents have per silicon atom. Thermoplastic silicone resins, which essentially consist of, are very particularly preferred
• a) 80 to 95 mol% of CH ₃ SiO _3/2 units,
• b) 5 to 20 mol% (CH ₃ ) ₂ SiO _2/2 units,
• g) 0 to 5 mol% of PhSiO _3/2 units and
• d) 0 to 5 mol% (CH ₃ ) ₃ SiO _1/2 units exist.

The silicone resins of the invention are, for example by cohydrolysis of an appropriate chlorosilange  mixed manufactured. The hydrolysis is carried out according to the methods carried out, as in W. Noll Chemie and Technology of silicones (Weinheim: Verlag Chemie, 1968, s. 162-169). For example it will Chlorosilane mixture together with an organic solvent to an excess of water and possibly one aliphatic alcohol added. The phases are ge separates and the organic phase washed neutral. The Silicone resin is used either as a solution or after peeling it off of the solvent as a solid to produce the Molding compositions according to the invention used.

The silicone resins of the invention are in solution medium-free state at room temperature until waxy rubbery solids, the softening temperatures between between 40 and 200 ° C. Above this temperature the silicone resins are liquid to highly viscous. The sili conharze are amorphous in the solid state. Hence the Temperature at which plastic flow begins in the Usually only imprecise. Be particularly preferred Silicone resins with softening temperatures between 50 and 120 ° C.

The silicone resins according to the invention are characterized by high ceramic yields in pyrolysis up to 1000 ° C., for example more than 60% by weight. The ceramic yield is defined as the residue in% by weight after pyrolysis. The ceramic yield is usually deteriorated with increasing proportions of PhSiO _3/2 and Ph ₂ SiO _2/2 units and siloxy units with long-chain alkyl residues, so the sum of these units should not exceed 40 mol%.

The thermoplastic polymers according to the invention All organic polymers are the organic basis a softening temperature between 40 and 200 ° C point. Examples are polyethylene, polypropylene, poly styrene, polyacrylates, polyester and ethylene vinyl acetate Copolymers, as well as polar and non-polar waxes, preferred polar polyolefin waxes and their mixtures with un polar thermoplastic polymers. To be favoured Polyethylene, polypropylene and their copolymers. Also thermoplastic copolymers are more organic Polymers with polydimethylsiloxanes or silicone resins used. Examples are polyester siloxane copoly merisate, so-called combination resins.

The polar polyols to be used according to the invention Finaxes are waxes, the acid numbers according to DIN 53 402 between 5 and 60 mg KOH / g and saponification numbers DIN 53 401 between 10 and 115 mg KOH / g. Examples are the commercial products Hostalub H 22 and Hostamont TP EK 581 from Hoechst AG (Augsburg) and the products No. 19.191-4 and 19.192-2 of Aldrich Chemie GmbH + Co. KG (Steinheim). The polar Polyolefin waxes can either be low or low be highly viscous in the melt. Waxes are preferred, viscosities between 10 and 200,000 mPa-s at 140 ° C exhibit.  

The thermoplastic organic according to the invention Polymers and their copolymers with siloxanes are described in the amount used that is still an improvement in Properties in the design or the properties of the molded part still causes a short burning time allow. As previously described, orga thermoplastic completely when burning from the Green bodies are removed. Therefore have too big Portions of organic polymers in the molding compound negative influence on the burning time. To be favoured Molding compositions in which at least 10% by weight of the sum of all Binder and excipients from the invention Silicone resins exist. Molding compounds with relatively little Silicone resin is particularly suitable for the production of molded parts, in which the ceramic residue of the silicone resin has a negative influence on the properties of the Can have molded parts, such as molded parts non-oxide ceramic. Molding compositions, in which at least 50% by weight of the total of all binders and auxiliary substances Silicone resins exist, are preferably used if the shortest possible burning time is desired.

The thermoplastic molding compositions according to the invention ent usually hold in addition to the silicone resin (and preferably the thermoplastic polymer) or several flow aids or separation aids, one Lowering the viscosity of the molding compound at the Shaping as well as a clean and easy demolding guarantee. Examples are aliphatic fatty acids  and their salts, such as stearic acid, calcium stearate, Magnesium stearate or the like, oils such as polydime thylsiloxanes, polyethylene oxides, polypropylene oxides, or Copolymers of polydimethylsiloxane and polyethylene oxide or polypropylene oxide and the like. Are preferred Molding compositions containing 0.25 to 3 wt .-% stearic acid and / or their salts and 0.25 to 3% by weight paraffin wax, Polyethylene oxide, polypropylene oxide or silicone oil contain. In general, only so much flow aid added as necessary to the viscosity to bring the shape into the desired area and to improve the wetting of the powder.

The thermoplastic molding compositions according to the invention ent hold at least as much silicone resin, thermoplastic organic polymers and other auxiliaries, as necessary dig is to a thermoplastically processable mass too receive. Usually binders have to be used together with the other auxiliaries at least the free volume fill in between the powder particles in the molded part. Each by powder type and their grain shape and grain size ver division, different quantities are necessary. Experience has shown that 25 to 60% by volume of binder is required agile. Molding compositions with 50 to 70% by volume are preferred Powder and 30 to 50 vol .-% binder and auxiliary fen.

The thermoplastic molding compositions according to the invention are solid at room temperature, but at temperatures above half the softening temperature of the silicone used  resin plastically deformable. In a preferred embodiment the molding compositions have viscosities of less than 10,000 Pa · s in the range between 50 and 200 ° C. Especially molding compositions with viscosities between are preferred 100 and 5000 Pa · s in the range between 100 and 200 ° C.

The thermoplastic molding compositions according to the invention are made by mixing the components mentioned in a Temperature above the softening temperature of the sili conharzes produced, with any remaining solution is removed from silicone resin production. It it is advantageous to use high shear forces when mixing the to crush powder aggregates and thereby a to obtain a homogeneous mixture. Suitable mixing units are kneaders, twin-screw extruders or Rolling mills. The molding compounds can then either directly used or first to powder or granules are processed.

The thermoplastic molding compositions according to the invention be sit excellent properties for the thermoplas table shape, such as by injection molding, Extrude or hot press. The molding compounds can Temperatures above the softening temperature of the Si licon resin processed plastically and under pressure in forms whose temperature is below the softening point temperature of the silicone resin is introduced. The molding compound solidifies again by cooling. The one there  the green parts created have good strength and can, for example, by grinding, drilling or sowing edited or reworked. Leftovers from the Shapes can be used again.

The thermoplastic molding compositions according to the invention are particularly suitable for the production of complicated Parts for engine or mechanical engineering by Formge practice methods such as thermoplastic injection molding. The molding compounds have good flow properties Temperatures of at least 30 ° C above the softening point temperature of the silicone resin used. The formmas sen can contain high levels of solids. The greens can also be burned in a short time. The ge burnt green bodies have high strength and high Poetry.

The produced from the molding compositions according to the invention Green bodies can either be in the air or in a Inert gas atmosphere free of defects within a short time be burned.

Burning is preferred at a temperature rise program from 0.5 to 5 ° C / min to 1000 ° C carried out. It can also be between 0.5 to 5 ° C / min in stages up to a temperature between 200 and 800 ° C can be heated at this temperature for so long be held until no weight change is observed and then heated at 5 to 50 ° C / min to 1000 ° C will. The burned green body can then depending on powder and sintering aids used  sintered at temperatures between 1000 and 2000 ° C the.

The produced from the molding compositions according to the invention Green bodies demonstrate low weight loss burning up to 1000 ° C. Depending on the proportion of Silicone resin and the proportions of additional thermoplas organic polymers and others Auxiliary substances, the weight loss is different. However, with an increasing proportion of those according to the invention Silicone resins in the sum of all auxiliary substances as well as decreasing proportion of all auxiliaries in the molding compounds weight loss when burning is reduced. Before molding compounds are less than 11% by weight desire to burn. Are particularly preferred Molding compounds that lose less than 6% in weight Have a burning sensation.

The invention is further illustrated by the following examples described.

Examples As a general rule

The following substances were used in the examples used

Al₂O₃ powder from Martinswerk GmbH with the name Martinoxid ZPS-402 with an average particle size of 2.0-3.0 microns, a density of approx. 3.95 g / cm³, an α-Al₂O₃ content of <95% and a loss on ignition of approximately 0.2% by weight,
Hard paraffin with a softening temperature of 52-54 ° C,
Hostyren N 2000 polystyrene from Hoechst AG,
Polyethylene oxide with a viscosity of 160 mPas at 25 ° C,
Polydimethylsilioxane with a viscosity of 5000 mPas at 25 ° C,
Siloxane copolymer a 76% solution in toluene of a block copolymer of (40:60) polydimethylsiloxane and polyethylene oxide with an average molecular weight of 4230 g / mol.
Polar polyolefin wax from Hoechst AG with the name Hostalub H 22 and 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 approx. 300 mPas at 120 ° C.

example 1

Production of the silicone resin from CH ₃ SiCl ₃ , (CH ₃ ) ₂ Si ₂ and (CH ₃ ) ₃ SiCl.

A mixture of 880 g CH ₃ SiCl ₃ , 90 g (CH ₃ ) ₂ SiCl ₂ and 12 g (CH ₃ ) ₃ SiCl slowly became a stirred mixture of 3.8 l noble water, 650 g xylene and 650 g n-butanol dripped. The water phase was separated and the solution washed three times with water. Then, xylene-n-butanol was distilled off from the resin solution to obtain an 80% solution and then diluted with toluene to obtain a resin solution with 64% by weight solid and a viscosity of 45 mPa · s at 25 ° C .

In the solvent-free state, the silicone resin is a solid with a softening temperature of 60-65 ° C. and a density of 1.18 g / cm ³ . According to ²⁹ Si-NMR, the silicone resin contains 1.15 methylene groups per silicon atom. The ceramic yield after pyrolysis up to 1000 ° C (heating rate 1 ° C / min) in air was 76% by weight.

Production of the molding compound

395 g of Al ₂ O ₃ powder, 100 g of the above 64% silicone resin solution, 4 g of calcium stearate and 8 g of polyethylene oxide were placed in a two-shaft kneader. The mixture was kneaded at 95 ° C and vacuum for 15 min to remove the solvent. The mass was then kneaded for a further 15 minutes without vacuum. The result was a plastic putty-like molding compound with good flow properties that solidified on cooling. The Al ₂ O ₃ volume fraction of the molding compound is calculated to be approximately 61.5%.

The molding compound became pills at about 120 ° C. and 500 bar pressed. A 13 × 2.0 mm pill was used in one gradual heating program (25-150 ° C / 25 min; 150- 400 ° C / 250 min; 400-600 ° C / 65 min; 600-1000 ° C / 20 min) over Burned in air for 6.0 h to 1000 ° C. The burned one Pill was of high strength and free of macrosco errors. Weight loss when burning was 4.0%.

Examples 2-5

Different molding compositions were produced in a kneader as in Example 1 from Al ₂ O ₃ powder and the silicone resin solution from Example 1. The compositions of these molding compositions are listed in Table 1. The molding compounds were pressed into pills and fired in air, Table 2.

Table 1

Composition of the molding compounds

Table 2

Burning Results)

Claims (11)

1. Thermoplastic molding composition, characterized in that it consists essentially of a homogeneous mixture of at least one sinterable powder of ceramic or metal and at least one thermoplastic silicone resin of the general formula R¹ _a Si (OH) _b (OR²) _c O _{(4- abc) / 2} , in which R ¹ = C1 to C18-alkyl, allyl, vinyl or phenyl, R ² = C1- to C18-alkyl, a has a value from 0.95 to 1.5 and the sum b + c is less than 0.3, which has a softening temperature between 40 and 200 ° C and the ceramic yield of the silicone resin in the pyrolysis is up to 1000 ° C at least 60 wt .-%. 2. Thermoplastic molding composition according to claim 1, characterized in that the silicone resin consists essentially of

• a) 50 to 95 mol% of CH ₃ SiO _3/2 units,
• b) 0 to 20 mol% of PhSiO _3/2 units and ViSiO _3/2 units
• c) 5 to 30 mol% (CH ₃ ) ₂ SiO _2/2 units,
• d) 0 to 20 mol% of Ph ₂ SiO _2/2 units and CH ₃ (R ³ ) SiO _2/2 units,
• e) 0 to 5 mol% of SiO _4/2 units, and
• f) 0 to 5 mol% (CH ₃ ) ₃ SiO _1/2 units, in which R ³ = C2 to C14-alkyl, allyl, vinyl or phenyl, and on average between 1.05 and 1.3 organic Has substituents per silicon atom.

3. Thermoplastic molding composition according to one of claims 1 or 2, characterized in that the sinterable powder consists essentially of Al ₂ O ₃ , MgO, ZrO ₂ , Al ₂ TiO ₅ , BaTiO ₃ , porcelain, SiC, Si ₃ N ₄ , BN , B ₄ C, AlN, TiN, TiC, TiB ₂ , ZrN, ZrB ₂ , WC, TaC, Si or alloy steel. 4. Thermoplastic molding composition according to one of the claims 1 to 3, characterized in that the molding compound additionally at least one thermoplastic polymer on an organic basis or their copolymers Contains siloxanes. 5. Thermoplastic molding compositions according to one of the An Proverbs 1 to 4, characterized in that they a polar polyolefin wax that has an acid number between 5 and 60 mg KOH / g and a saponification number has between 10 and 150 mg KOH / g. 6. Thermoplastic molding composition according to one of the claims 1 to 5, characterized in that the molding compound additionally contains inorganic sintering aids.   7. Thermoplastic molding composition according to one of the claims 1 to 6, characterized in that the molding compound in addition aids that improve Cause flow properties and demoldability, contains. 8. Thermoplastic molding composition according to one of the claims 1 to 7, characterized in that the molding compound a weight loss when burning up to 1000 ° C less than 11%. 9. A process for the preparation of thermoplastic molding compositions, characterized in that at least one sinterable powder made of ceramic or metal with at least one thermoplastic silicone resin of the general formula R¹ _a Si (OH) _b (OR²) _c O ( _4-abc ) / ₂ wherein R ¹ = C1 to C18-alkyl, allyl, vinyl or phenyl, R ² = C1 to C18-alkyl, a has a value from 0.95 to 1.5 and the sum b + c is less than 0.3, which has a softening temperature of between 40 and 200 ° C and the ceramic yield of the silicone resin in pyrolysis is up to at least 60% by weight up to 1000 ° C, mixes at a temperature above the softening temperature of the silicone resin to a homogeneous mass. 10. The method according to claim 9, characterized in that the molding compounds after mixing to a powder or granules are processed. 11. Process for the production of molded articles Ceramic or metal, characterized in that thermoplastic molding compositions according to one of the Claims 1 to 10 after molding by spray pour, extrude or hot press at one Temperature between 200 ° C and 1000 ° C burns and then at a temperature between 1000 and 2000 ° C sinters into a solid body.