CH709100B1 - Binder for injection molding composition. - Google Patents

Abstract

The invention relates to a binder for injection molding composition comprising: - from 35 to 54% vol. a polymeric base, - from 40 to 55% vol. a mixture of waxes, and about 10% vol. a surfactant, wherein the polymeric base contains copolymers of ethylene and methacrylic or acrylic acid, or copolymers of ethylene and vinyl acetate, or copolymers of ethylene comprising maleic anhydride or a mixture thereof of these copolymers, as well as polyethylene, polypropylene and an acrylic resin.

Description

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

In the manufacture of hard materials for jewelry and the watch industry, or for technical applications such as medical, electronics, telephony, tooling, machining cutting inserts, consumer goods industry, and in particular with regard to hard materials generally referred to under the generic name of inorganic “ceramics”, powder metallurgy techniques are used. The inorganic synthetic material obtained will be called “ceramic” here, regardless of the nature of this material, sapphire, ruby, artificial diamond, sapphire crystal, ceramic, micro-magnet, metal, alloy, or other.

[0003] 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 structure during its preparation, in particular, and not limited to, when complementary components of a resin undergo a polymerization reaction.

[0004] The overall process for manufacturing an inorganic ceramic component comprises at least the following steps:

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

[0006] For example, US Pat. No. 5,145,900, thermoplastic materials (feedstock) are already known for the manufacture of ceramic molded parts which contain a sinterable inorganic powder and a polymeric organic binder, the latter essentially consisting of a blend of polyoxymethylene and copolymers of polyoxymethylene and polyoxolanes.

[0007] However, these feedstocks have revealed numerous drawbacks, such as for example insufficient fluidity in injection molding, and problems with the holding of molded shaped parts which have cracks and lamination, this especially when the shape of the parts is complex. ; they are also responsible for environmental problems due to the need to use aggressive products, such as nitric acid, more particularly for the final elimination of the organic phase. In addition, the use of water in this organic binder removal process is problematic in the event that the feedstocks contain metallic materials which may be oxidized.

[0008] Consequently, the aim of the present invention is to provide a binder for a molding composition which obviates the aforementioned drawbacks, and more particularly which aims to improve the homogeneity and the fluidity of the feedstock to allow the manufacture of metal parts or ceramics of more complex shapes, to reduce cycle times in production, to increase the mechanical resistance of green bodies and debinding to production constraints (handling and various recovery operations), and finally which eliminates the need to use products aggressive for the environment for the elimination of the organic binder, by replacing them with non-polluting solvents which can be eliminated by simple heat treatment.

[0009] To this end, the subject of the invention is a binder for an injection molding composition comprising:

[0010] Preferably, the binder of the invention comprises from 2 to 7% vol. of one of said copolymers or mixtures thereof, approximately 25% vol. polyethylene, from 2 to 15% vol. polypropylene and 6 to 15% vol. of acrylic resin.

[0011] According to a preferred embodiment, the copolymer of ethylene and methacrylic or acrylic acid contains from 3 to 10% by weight. of methacrylic or acrylic comonomer, the ethylene-vinyl acetate copolymer contains 7-18% by weight. of vinyl acetate comonomer, and the ethylene anhydride copolymer is a random (random) copolymer of ethylene and maleic anhydride having a melting point of 100 to 110 ° C or a copolymer of polyethylene HD and d a modified anhydride having a melting point of 130 to 134 ° C.

Preferably, the acrylic resin has a molecular weight of between 50,000 and 220,000 and an inherent viscosity of 0.21 to 0.83, and is chosen from the group comprising polymers of isobutyl methacrylate, methyl, ethyl and N-butyl, and copolymers of isobutyl and N-butyl methacrylates and methyl and N-butyl methacrylates or a mixture of these polymers and / or copolymers.

[0013] Advantageously, the wax is a Carnauba wax or a paraffin wax, or a palm oil, or a mixture of these elements.

[0014] 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.

[0015] The subject of the invention is also an injection molding composition (feedstock) intended for the manufacture of shaped metallic or ceramic parts comprising 76 to 96% by weight. of an inorganic powder and 4 to 24% wt. of binder comprising:

[0016] According to one particular characteristic, the inorganic powder of the injection molding composition can be chosen from the group comprising an oxide, nitride, carbide or metal powder, or a mixture of these said powders and 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, a stainless steel powder, a 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% alumina and 12 to 24% of binder according to the invention as defined above, or • 76 to 88% 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 oxide of yttrium and 0.18 to 18.5% 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 of the invention, or • from 88 to 91% of chromium or titanium carbide, and from 9 to 12% of binder of invention, or • from 93 to 96% of tungsten carbide or metallic tungsten and from 4 to 7% of binder of the invention, or • from 78 to 85% silicon nitride and 15-22% binder of the invention.

[0018] The present invention will now be illustrated in more detail by the non-limiting examples which follow.

Example 1

[0019] The polymeric part of the binder is mixed with a black zirconium oxide powder (of the St. Gobain Zir Black type) at a temperature of about 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 kind of homogeneous paste, which is then cooled and then granulated until solidification, then stored to constitute the feedstock. usable in the manufacture of a shaped part by injection according to a known technique.

In this example, was used more particularly 17.2 kg of zirconia powder (86% wt.) And 2.8 kg of the binder (approx. 14% wt) having the following volume composition:

Example 2

[0021] The same type of feedstock as in Example 1 above is prepared by replacing black zirconium oxide with white zirconium oxide, and using slightly different values of the various components of the binder, plus particularly:

Example 3

Still with the same components of the organic binder, with slightly different volume proportions, other feedstocks can be prepared with various ceramic or metal powders, more particularly alumina, with a shrinkage index of 1.19 or 1 , 30 (translucent), chromium carbide or titanium carbide, tungsten carbide (of various qualities) and metallic tungsten, according to the following Table.

[0023]

Claims (12)

1. Binder for injection molding composition comprising: - from 35 to 54% vol. of a polymer base, - from 40 to 55% vol. a mixture of waxes or a mixture of wax and palm oil, - and about 10% vol. a surfactant, wherein the polymeric base contains copolymers of ethylene and methacrylic or acrylic acid, or copolymers of ethylene comprising maleic anhydride or a mixture of these copolymers, as well as polyethylene, polypropylene and acrylic resin, the amounts the respective components of the binder being as added together, they do not exceed 100%. 2. Binder according to claim 1 comprising from 2 to 7% vol. of one of said copolymers or mixtures thereof, approximately 25% vol. polyethylene, from 2 to 15% vol. polypropylene and 6 to 15% vol. of acrylic resin. 3. Binder for injection molding composition comprising: - from 35 to 54% vol. of a polymer base, - from 40 to 55% vol. a mixture of waxes or a mixture of wax and palm oil, - and about 10% vol. a surfactant, in which the polymeric base contains 2 to 7% vol. of ethylene vinyl acetate copolymer, about 25% vol. polyethylene, from 2 to 15% vol. polypropylene and 6 to 15% vol. of acrylic resin, the respective amounts of the components of the binder being as added together, they do not exceed 100%. 4. A binder according to claim 1, wherein the copolymer of ethylene and methacrylic or acrylic acid contains 3 to 10 wt%. of methacrylic or acrylic comonomer, and the copolymer of ethylene and anhydride is a random copolymer of ethylene and maleic anhydride having a melting point of 100 to 110 ° C or a copolymer of polyethylene and a modified anhydride having a melting point of 130 to 134 ° C. 5. The binder of claim 3, wherein the ethylene vinyl acetate copolymer contains 7 to 18 wt%. of vinyl acetate comonomer. 6. Binder according to one of the preceding claims, in which the acrylic resin has a molecular weight of between 50,000 and 220,000 and an inherent viscosity of 0.21 to 0.83, and is chosen from isobutyl methacrylate polymers. , methyl, ethyl and n-butyl, and copolymers of isobutyl and n-butyl methacrylates and methyl and n-butyl methacrylates or a mixture of these polymers and / or copolymers. 7. Binder according to one of the preceding claims, wherein the mixture of waxes comprises a Camauba wax and a paraffin wax or the wax mixture comprises a Camauba wax and a palm oil. 8. Binder according to one of the preceding claims, in which the surfactant is an NN'-ethylene-bis (stearamide), or a mixture of stearic and palmitic acids, stearin, or a mixture of these elements. 9. Feedstock injection molding composition intended for the manufacture of shaped metallic or ceramic parts comprising 76 to 96% by weight. of an inorganic powder and 4 to 24% wt. binder according to one of claims 1 to 8. 10. A molding composition according to claim 9, wherein the inorganic powder is selected from the group comprising an oxide, nitride, carbide, metal powder, or a mixture thereof. 11. A molding composition according to claim 9, wherein the inorganic powder is selected 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 or silicon nitride powder, a stainless steel powder, a metallic titanium powder, or a mixture of these powders. 12. A molding composition according to claim 10 or 11, which contains in% by weight: • 76 to 88% alumina and 12 to 24% binder, • 76 to 88% alumina and 0.1 to 0.6% magnesium oxide and 12 to 24% binder, • 58 to 86.5% zirconium oxide and 3.9 to 4.6% yttrium oxide and 0.18 to 18.5% alumina and 9 to 22% binder, • 61.5 to 84% zirconium oxide and 3.9 to 4.6% Yttrium oxide and 0.2 to 9% alumina and 2 to 5.5% 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 of metallic tungsten and from 4 to 7% of binder, or • from 78 to 85% of silicon nitride and from 15 to 22% of binder