CH714966A2 - Binder for injection molding composition. - Google Patents

Abstract

The invention relates to a binder for an injection molding composition comprising: from 40 to 55 vol. of a polymeric base, from 35 to 45 vol. a mixture of waxes or a mixture of wax and palm oil, and at least 5% vol. at least one surfactant, wherein the polymeric base is composed of copolymers of ethylene and methacrylic or acrylic acid, copolymers of ethylene and propylene and / or maleic anhydride grafted polypropylene, and polymers soluble in isopropyl alcohol, propyl alcohol and / or turpentine, and selected from the group consisting of cellulose acetate butyrate, polyvinyl butyral and copolyamide, the respective amounts of the binder components being such that their sum is equal to 100% by volume of the binder.The invention also relates to injection molding compositions comprising said binder and an inorganic powder, for example ceramic.

Description

Description Field of the Invention The invention relates to a binder composition for injection molding as well as an injection molding composition (feedstock) intended for the manufacture of metallic or ceramic shaped parts.

BACKGROUND OF THE INVENTION In the manufacture of hard materials for the jewelry industry and the watch industry, or also for technical applications such as medical, electronics, telephony, tools, wafers machining cutting, the consumer goods industry, and in particular with regard to hard materials generally designated by the generic name of inorganic "ceramics", powder metallurgy techniques are used. The “inorganic” synthetic material obtained, whatever the nature of this material, will be called “ceramic” here, sapphire, ruby, artificial diamond, sapphire glass, ceramic, micro-magnet, metal, alloy, or other.

The basic raw materials are of different nature, in general, and comprise at least on the one hand ceramic powder and on the other hand organic binders, such as resins or plastics or the like which allow the injection and good performance of the component produced with the mixture of all the raw materials. Other additives can be incorporated into the mixture. These raw materials can also be of different textures: solid, pulverulent, liquid, or even pasty. The mixture can also change its structure during its development, in particular, and not limited to, when complementary components of a resin undergo a polymerization reaction.

The overall process for manufacturing an inorganic ceramic component comprises at least the following steps:

- preparation of raw materials;

- mixture (s) of raw materials, or / and premix two by two (or more) if necessary;

- homogenization mixing;

- granulation;

- pressing, in particular in a molding chamber, of a quantity of feedstock powder or granules from kneading and granulation, for producing a component blank, called a green part. This pressing can be carried out by injection, under pressure, in particular in a screw injector comprising means for warming up this quantity of feedstock powder or granules resulting from the kneading and granulation;

- Baking of debinding for combustion (thermal debinding) or / and the dissolution of certain components of the mixture in an appropriate solvent (solvent debinding);

- heat treatment of the roughing at the debinding end, for a secondary thermal debinding and for sintering giving its final consistency to the finished component. This heat treatment results in dimensional shrinkage, which makes it possible to obtain a component in finished dimensions;

- component appearance finish treatment.

The invention more particularly aims to provide a binder for an optimized injection molding composition facilitating the kneading in powder metallurgy for obtaining ceramics or metals, so as to obtain a production of very reproducible quality, with a controlled shrinkage coefficient.

We already know for example the application WO 2014/191 304 from the applicant which describes an injection molding composition (feedstock) for the manufacture of ceramic or metallic molded parts which contains a sinterable inorganic powder and an organic binder, that this being essentially constituted by a mixture of copolymer of ethylene and methacrylic acid, of polyethylene, of polypropylene, of acrylic resins, and of waxes.

These feedstocks have many advantages. They have more particularly good homogeneity and good fluidity allowing the manufacture of metallic or ceramic parts of more complex shapes. They also make it possible to increase the mechanical resistance of green and debonding bodies to production constraints (handling and various recovery operations), as well as to perform a solvent debinding, to remove part of the organic binder, using a non-polluting solvent which can be removed by simple heat treatment.

Claims (16)

SUMMARY OF THE INVENTION The aim of the present invention is to overcome the drawbacks mentioned above by proposing new feedstocks making it possible in particular to further improve the viscosity of the composition injected, to obtain a more effective solvent debinding and to obtain components of better aesthetic quality. To this end, the subject of the invention is a binder for an injection molding composition comprising: - from 40 to 55% vol. of a polymer base, - from 35 to 45% vol. a mixture of waxes or a mixture of wax and palm oil, - and at least 5% vol. at least one surfactant, in which the polymer base consists of copolymers of ethylene and methacrylic or acrylic acid, of copolymers of ethylene and of propylene and / or of polypropylene grafted with maleic anhydride, and of polymers soluble in a solvent chosen from the group comprising iso alcohol CH 714 966 A2 propyl, propyl alcohol, turpentine, and mixtures thereof, and chosen from the group comprising a cellulose acetate butyrate, a poly (vinyl butyral) and a copolyamide, the respective amounts of the components of the binder being such that their sum is equal to 100% by volume of the binder. The present invention also relates to an injection molding composition (feedstock) intended for the manufacture of metallic or ceramic shaped parts comprising 76 to 96% by weight. of an inorganic powder and 4 to 24% wt. of the binder as defined above. The injection molding composition according to the invention makes it possible to improve the viscosity of the injected composition, to obtain a more effective solvent debinding and to obtain components of better aesthetic quality. Detailed description of the preferred embodiments [0012] According to the invention, the binder for injection molding composition comprises the following components: - from 40 to 55% vol., preferably 45 to 54% vol., of a polymer base, - 35 to 45% vol., preferably 39 to 42% vol., of a mixture of waxes or a mixture of wax and palm oil, - And at least 5% vol., preferably 5 to 15% vol., of at least one surfactant, in which the polymer base consists of copolymers of ethylene and methacrylic or acrylic acid, of copolymers of ethylene and propylene and / or polypropylene grafted with maleic anhydride, and polymers soluble in isopropyl alcohol and / or propyl alcohol and / or turpentine, and chosen from the group comprising a cellulose acetate butyrate, a poly (vinyl butyral) and a copolyamide, the respective amounts of the components of the binder being such that their sum is equal to 100% by volume of the binder. Preferably, the polymer base of the binder of the invention comprises from 2 to 7% vol. copolymers of ethylene and methacrylic or acrylic acid, from 0 to 40% vol. copolymers of ethylene and propylene, from 0 to 35% vol. of maleic anhydride grafted polypropylene, the overall amount of copolymer of ethylene and propylene and maleic anhydride grafted polypropylene being between 30% and 40% vol., and from 6 to 15% vol. of polymer soluble in isopropyl alcohol and / or propyl alcohol and / or turpentine, relative to 100% by volume of binder, the respective amounts of the components of the binder being such that their sum is equal to 100 % by volume of the binder. Preferably, the polymer base comprises a mixture of copolymers of ethylene and propylene and of polypropylene grafted with maleic anhydride. Preferably, the polymer base of the binder of the invention comprises from 2 to 7% vol. copolymers of ethylene and methacrylic or acrylic acid, from 25 to 30% vol. of copolymers of ethylene and propylene, from 5 to 10% vol. of polypropylene grafted with maleic anhydride and from 6 to 15% vol. of polymer soluble in isopropyl alcohol and / or propyl alcohol and / or turpentine, relative to 100% by volume of binder. More preferably, the polymer base of the binder of the invention comprises from 3 to 5% vol. copolymers of ethylene and methacrylic or acrylic acid, from 26 to 29% vol. copolymers of ethylene and propylene, from 6 to 8% vol. of polypropylene grafted with maleic anhydride and from 6 to 12% vol. of polymer soluble in isopropyl alcohol and / or propyl alcohol and / or turpentine, relative to 100% by volume of binder. Preferably, the ethylene and propylene copolymer is a random (random) copolymer of ethylene and propylene having a melting point between 140 ° C and 150 ° C, this melting point varying according to the percentage ethylene and propylene in said copolymer. For example, for oxide and nitride powders, the random copolymer of ethylene and propylene preferably contains more propylene in order to have a melting point of around 147 ° C. For metallic powders, the random copolymer of ethylene and propylene preferably contains more ethylene in order to have a melting point of approximately 140 ° C. Preferably, the copolymer of ethylene and methacrylic or acrylic acid contains from 3 to 10% by weight. methacrylic or acrylic comonomer. Preferably, the maleic anhydride grafted polypropylene has a grafting rate of between 1% and 2% and a melting point of between 100 ° C and 140 ° C. Preferably, the polymer soluble in isopropyl alcohol and / or propyl alcohol and / or turpentine is a cellulose acetobutyrate having a butyryl content of between 37% and 53% by weight. acetyl content between 2% and 13% by weight. relative to the weight of the polymer, a melting point between 125 ° C and 165 ° C and a molecular weight between 16,000 and 40,000. Advantageously, the wax is a Carnauba wax or a paraffin wax or a mixture of these elements. When the wax is mixed with palm oil, the wax is preferably Carnauba wax. According to another preferred characteristic, the surfactant is an NN'-ethylene-bis (stearamide) or a mixture of stearic and palmitic acids (stearin), or a mixture of these elements. According to another characteristic, the surfactant is soluble in isopropyl alcohol and / or propyl alcohol and / or turpentine. CH 714 966 A2 The invention also relates to an injection molding composition (feedstock) intended for the manufacture of metal or ceramic shaped parts comprising 76 to 96% by weight. of an inorganic powder and 4 to 24% wt. of the binder as defined above. According to a particular characteristic, the inorganic powder of the injection molding composition can be chosen from the group comprising an oxide, nitride, carbide, metal powder, or a mixture of these said powders and of preferably the inorganic powder is chosen from the group comprising an alumina powder, a zirconium oxide powder, a chromium carbide powder, a titanium carbide powder or a tungsten carbide powder, a tungsten powder metallic or silicon nitride, stainless steel powder, metallic titanium powder or a mixture of these powders. According to preferred embodiments of the injection molding composition, the latter contains in% by weight - 76 to 88% of alumina and 12 to 24% of binder according to the invention as defined above, or - 76 to 88% of alumina and 0.1 to 0.6% of magnesium oxide and 12 to 24% of binder of the invention, or - 58 to 86.5% of zirconium oxide and 3.9 to 4.6% of yttrium oxide and 0.18 to 18.5% of alumina and 9 to 22% of binder of the invention, or - 61.5 to 84% of zirconium oxide and 3.9 to 4.6% of yttrium oxide and 0.2 to 9% of alumina and 2 to 5.5% of inorganic pigments from a list comprising iron oxide, cobalt oxide, chromium oxide, titanium oxide, manganese oxide, zinc oxide or a mixture of said oxides and from 9 to 22% of binder the invention, or - from 88 to 91% of chromium or titanium carbide, and from 9 to 12% of binder of the invention, or - from 93 to 96% of tungsten carbide or of metallic tungsten and from 4 to 7% of binder of the invention, or - from 78 to 85% of silicon nitride and from 15 to 22% of binder of the invention. The injection molding composition (feedstock) intended for the manufacture of metal or ceramic shaped parts according to the invention has a lower viscosity than known feedstocks, for equivalent shear rates. As a result, the composition of the invention allows the parts to be better filled during the injection, especially in areas with thin walls. In addition, the composition according to the invention allows a more effective solvent debinding of the parts, in particular thanks to a better loss of the binder compounds in the solvent isopropyl alcohol and / or propyl alcohol and / or turpentine. Propyl alcohol, with a boiling point of 97 ° C allows to unbind at higher temperature for more efficiency, thanks in particular to better elimination of Carnauba wax (melting point of 82 ° C). The composition of the invention also makes it possible to obtain molded and sintered parts having an improved surface appearance, without apparent cracks or weld lines of material. The present invention will now be illustrated in more detail by the following nonlimiting examples. Examples The polymeric part of the binder is mixed with an inorganic powder at a temperature of around 150 ° C to form a premix. To this premix are added the waxes and the surfactant, and the temperature is again increased to about 180 ° C to form a sort of homogeneous paste, which is then cooled then granulated until solidification, then preserved to constitute the feedstock usable in the manufacture of a shaped part by injection using a known technique. This technique typically includes a hot injection molding operation under pressure in a mold with cavities. The part is cooled in the cavity then is ejected from the mold. The whole process takes place at around 170 ° C-180 ° C. The green part is then debonded in isopropyl alcohol before being sintered. By debinding, part of the organic binder is removed from the part, leaving only enough binder to maintain cohesion, or in other words the molded shape of the green part. The binder is typically extracted from the green part by heating the solvent in which the part is immersed. During this operation at least 40% of the binder compounds must dissolve. With the binder of the invention, the green part is typically immersed in the isopropyl alcohol solvent and heated to a temperature of the order of 70 ° C. At this temperature, the mixture of waxes and or the mixture of wax and oil decomposes thermally while the surfactants and the polymers soluble in isopropyl alcohol are dissolved chemically. Once the solvent debinding operation is completed, the part is porous. The part is then placed in a high temperature oven in order to firstly remove the remaining binder (thermal debinding, typically at a temperature below 400 ° C.), this operation being facilitated by the porosity left in the part during solvent debinding, then sinter the part at a high temperature. Parts are produced according to the method described above from different binders of the invention according to the compositions indicated in Table I below, depending on the nature of the inorganic powder: CH 714 966 A2 Table I components Example 1 (% Volume / 100% of binder) Oxides (Zirconia, Alumina, etc.) Example 2 (% by volume / 100% of the binder) Nitrides (SÌ3N4, TiN, etc.) Example 3 (% by volume / 100% of the binder) Carbides, cermets and metals (TiC, WC, W, Steel, etc.) Ethylene Propylene Copolymer (Polypropylene Random Copolymer) 28.5 28 27 Copolymers of ethylene and methacrylic acid 4.5 4.5 4.5 Polypropylene grafted maleic anhydride 7 7 7 Cellulose acetobutyrate 10.5 6.5 10.5 Carnauba wax 10.5 10 10 Paraffin wax 31 30 29 NN ’Etylène Bis Stéaramide 8 10 14 Stearine 4 % Powder mass ZrO ₂ : 86% SÌ3N4: 78% TiC: 89% The components are commercially available. The Polypropylene Random Copolymer is PPR 10232 distributed by Total Refining & Chemicals. The maleic anhydride grafted polypropylene is Fusabond® P353 distributed by DuPont ™. Cellulose acetobutyrate is CAB-551-0.01 distributed by Eastman ™. A composition was produced according to Example 1 above with, as inorganic powder, zirconia ZrO ₂ black St Gobain Zir Black powder. The viscosity of this composition was measured using an Instron Ceast SR20 capillary rheometer with a die 0 1 mm, length 20 mm. By way of comparison, the viscosity of the feedstock composition described in Example 1 of application WO 2014/191 304 was measured with the same inorganic zirconia powder ZrO ₂ black St Gobain Zir Black powder. The results are shown in Table II below: Table II Shear rate (1 / s) Viscosity Example ZrO ₂ black powder St Gobain Zir Black according to example 1 of WO 2014/191304 (Pa.s) at 172 ° C 0M Powder: 86.05% Viscosity Example ZrO ₂ black St Gobain Zir Black powder according to Example 1 of the invention (Pa.s) at 172 ° C0M Powder: 86.05% 10 8000 4300 100 1300 500 1000 120 75 The injection molding composition according to the invention has a lower viscosity than known feedstocks, for equivalent shear rates. In addition, the losses of binders during debinding in the solvent isopropyl alcohol are improved: about 45% of binder described in application WO 2014/191 304 were lost in the solvent while at least 50% of binder according to CH 714 966 A2 the invention are lost, in particular cellulose acetobutyrate. In the case of metallic powders, the percentage of loss can be up to 65%. The molded and sintered parts obtained have an improved surface appearance, without visible cracks or weld lines of material. claims 1. Binder for injection molding composition comprising as components: - from 40 to 55% vol. of a polymer base, - from 35 to 45% vol. a mixture of waxes or a mixture of wax and palm oil, - and at least 5% vol. at least one surfactant, in which the polymer base consists of copolymers of ethylene and methacrylic or acrylic acid, of copolymers of ethylene and of propylene and / or of polypropylene grafted with maleic anhydride, and of polymers soluble in a solvent chosen from the group comprising isopropyl alcohol, propyl alcohol, turpentine, and mixtures thereof, and chosen from the group comprising cellulose acetate butyrate, poly (vinyl butyral) and copolyamide, the amounts respective components of the binder being such that their sum is equal to 100% by volume of the binder. 2. Binder according to claim 1, characterized in that the polymer base comprises from 2 to 7% vol. copolymers of ethylene and methacrylic or acrylic acid, from 0 to 40% vol. copolymers of ethylene and propylene, from 0 to 35% vol. of maleic anhydride grafted polypropylene, the amount of copolymer of ethylene and propylene and maleic anhydride grafted polypropylene being between 30% and 40% vol., and from 6 to 15% vol. of polymer soluble in a solvent chosen from the group comprising isopropyl alcohol, propyl alcohol, turpentine and mixtures thereof, relative to 100% by volume of binder, the respective amounts of the components of the binder being such that their sum is equal to 100% by volume of the binder. 3. Binder according to one of the preceding claims, characterized in that the polymer base comprises a mixture of copolymers of ethylene and propylene and of polypropylene grafted with maleic anhydride. 4. Binder according to claim 3, characterized in that the polymer base comprises from 2 to 7% vol. copolymers of ethylene and methacrylic or acrylic acid, from 25 to 30% vol. of copolymers of ethylene and propylene, from 5 to 10% vol. of polypropylene grafted with maleic anhydride and from 6 to 15% vol. of polymer soluble in a solvent chosen from the group comprising isopropyl alcohol, propyl alcohol, turpentine and mixtures thereof, relative to 100% by volume of binder. 5. Binder according to one of the preceding claims, characterized in that the ethylene-propylene copolymer is a random (random) copolymer of ethylene and propylene having a melting point between 140 ° C and 150 ° C . 6. Binder according to one of the preceding claims, characterized in that the copolymer of ethylene and methacrylic or acrylic acid contains from 3 to 10% by weight. methacrylic or acrylic comonomer. 7. Binder according to one of the preceding claims, characterized in that the polypropylene grafted with maleic anhydride has a grafting rate of between 1% and 2% and a melting point of between 100 ° C and 140 ° C. 8. Binder according to one of the preceding claims, characterized in that the polymer soluble in a solvent chosen from the group comprising isopropyl alcohol, propyl alcohol, turpentine, and mixtures thereof, is an acetobutyrate of cellulose having a butyryl content of between 37% and 53% by weight, an acetyl content of between 2% and 13% by weight. relative to the weight of the polymer, a melting point between 125 ° C and 165 ° C and a molecular weight between 16,000 and 40,000. 9. Binder according to one of the preceding claims, characterized in that the wax is a Carnauba wax, a paraffin wax, or mixtures thereof. 10. Binder according to one of the preceding claims, characterized in that the wax in the mixture of wax and palm oil is Carnauba wax. 11. Binder according to one of the preceding claims, characterized in that the surfactant is an NN'-ethylenebis (stearamide), or a mixture of stearic and palmitic acids (stearin), or a mixture of these elements. 12. Binder according to one of the preceding claims, characterized in that the surfactant is soluble in a solvent chosen from the group comprising isopropyl alcohol, propyl alcohol, turpentine, and mixtures thereof. 13. Injection molding composition (feedstock) intended for the manufacture of metallic or ceramic shaped parts comprising 76 to 96% by weight. of an inorganic powder and 4 to 24% wt. of the binder according to one of claims 1 to 12. 14. A molding composition according to claim 13, in which the inorganic powder is chosen from the group comprising an oxide, nitride, carbide, metal powder, or a mixture of these. CH 714 966 A2 15. A molding composition according to claim 14, in which the inorganic powder is chosen from the group comprising an alumina powder, a zirconium oxide powder, a chromium carbide powder, a titanium carbide powder or a tungsten carbide powder, a metallic tungsten powder or silicon nitride, a stainless steel powder, a metallic titanium powder, or a mixture of these powders. 16. A molding composition according to claim 15, which contains in% by weight: - 76 to 88% of alumina and 12 to 24% of binder, - 76 to 88% of alumina and 0.1 to 0.6% of magnesium oxide and 12 to 24% of binder, - 58 to 86.5% of zirconium oxide and 3.9 to 4.6% of yttrium oxide and 0.18 to 18.5% of alumina and 9 to 22% of binder, - 61.5 to 84% of zirconium oxide and 3.9 to 4.6% of Yttrium oxide and 0.2 to 9% of alumina and 2 to 5.5% of inorganic pigments from a list comprising iron oxide, cobalt oxide, chromium oxide, titanium oxide, manganese oxide, zinc oxide or a mixture of said oxides and from 9 to 22% of binder, - from 88 to 91% of chromium or titanium carbide and from 9 to 12% of binder, - from 93 to 96% of tungsten carbide or metallic tungsten and from 4 to 7% of binder, or - from 78 to 85% of silicon nitride and from 15 to 22% of binder.