BINDER FOR INJECTION MOULDING COMPOSITIONS

Abstract

Binder for injection moulding composition including: from 45 to 50 volume percent of a polymeric base, at least 34 volume percent of a mixture of waxes or a mixture of wax and palm oil, and from 11 to 16 volume percent of a surfactant, wherein the polymeric base contains ethylene and methacrylic or acrylic acid copolymers, or ethylene copolymers comprising a maleic anhydride or a mixture of such copolymers, in addition to polyethylene, polypropylene and an acrylic resin, the respective quantities of the binder components being such that added together, they do not exceed 100 volume percent.

Claims

1. A binder composition, comprising: from 45 to 50 volume percent of a polymeric base, at least 34 volume percent of a mixture of waxes or a mixture of at least one wax and palm oil, and from 11 to 16 volume percent of a surfactant, wherein the polymeric base comprises ethylene and methacrylic or acrylic acid copolymers, or ethylene copolymers comprising a maleic anhydride or a mixture of said copolymers, in addition to polyethylene, polypropylene and an acrylic resin, respective quantities of the binder components being such that added together, a total amount of the binder components do not exceed 100 volume percent.

2. The binder composition of claim 1, including comprising: 4 to 5 volume percent of one of said copolymers or of a mixture of said copolymers, between 25 and 30 volume percent of polyethylene, 3 to 5 volume percent of polypropylene, and 8 to 10 volume percent of acrylic resin.

3. The binder composition of claim 1, wherein the copolymer of ethylene and methacrylic or acrylic acid, if present, comprises 3 to 10 wt. % of methacrylic or acrylic comonomer, and the copolymer of ethylene and anhydride, if present, is a statistical (random) copolymer of ethylene and maleic anhydride with a melting point of 100 to 110 C. or a copolymer of HD polyethylene and a modified anhydride with a melting point of 130 to 134 C.

4. The binder composition of claim 1, wherein the acrylic resin has a molecular weight of between 50000 and 220000 and an inherent viscosity of between 0.21 and 0.83 and the acrylic resin is a polymer and/or copolymer, which is at least one selected chosen from the group consisting of isobutyl methacrylate, methyl methacrylate, ethyl methacrylate and N-butyl methacrylate polymers, and copolymers of isobutyl methacrylate and N-butyl methacrylate and methyl methacrylate.

5. The binder composition of claim 1, wherein the wax mixture comprises a Carnauba wax and a paraffin wax, or the wax mixture comprises a Carnauba wax and a palm oil.

6. The binder composition of claim 1, wherein the surfactant is an N,N-ethylene bis(stearamide) or a mixture of a stearic acid and a palmitic acid, or a mixture an N,N-ethylene bis(stearamide), a stearic acid and a palmitic acid.

7. The binder composition of claim 1, wherein the surfactant and the acrylic resin are soluble in isopropyl alcohol and/or turpentine.

8. An injection moulding composition, comprising: 70 to 80 volume percent of a metal powder and 20 to 30 volume percent of a binder composition wherein the binder composition comprises: from 45 to 50 volume percent of a polymeric base, at least 34 volume percent of a mixture of waxes or a mixture of at least one wax and palm oil, and from 11 to 16 volume percent of a surfactant, wherein the polymeric base comprises ethylene and methacrylic or acrylic acid copolymers, or ethylene copolymers comprising a maleic anhydride or a mixture of said copolymers, in addition to polyethylene, polypropylene and an acrylic resin, respective quantities of the binder components being such that added together, a total amount of the component do not exceed 100 volume percent.

9. The injection moulding composition according to claim 8, wherein the metal powder is at least one selected from the group consisting of a tungsten metal powder, a stainless steel powder, a titanium metal powder, and a noble metal powder chosen from the group consisting of gold, platinum, silver, palladium, rhodium and ruthenium.

Description

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

[0036] The present invention will now be illustrated in more detail by the following non-limiting example.

[0037] The polymeric part of the binder is mixed with a stainless steel powder (typically a 316L steel powder) at a temperature of around 150 C. to create a premix. The waxes and surfactant are added to this premix, and the temperature is increased again to around 180 C. to form a kind of homogeneous paste. This paste is then simultaneously ground and cooled to ambient temperature to form a powder. This powder is then fed into a calender which cuts and granulates the premix. The product of this last step is kept to form feedstock for use in the manufacture of a shaped part by injection moulding in accordance with a known technique.

[0038] In this example, more specifically, 46.5 kg of (316L) stainless steel metal powder (78 volume percent) and 3.5 kg of binder (approx. 22 volume percent) were used having the following volume composition: [0039] 28% of HD polyethylene [0040] 4% of polypropylene [0041] 4.5% of copolymer of ethylene and methacrylic acid (with 6.5 wt. % of methacrylic acid, for example a type such as Nucrel by DuPont) [0042] 8.5% of an isobutyl methacrylate polymer resin having a molecular weight of 195,000 (for example a type such as Elvacite 2045 by Lucite International) [0043] 1% of an n-butyl and isobutyl methacrylate polymer resin having a molecular weight of 165,000 (for example a type such as Elvacite 2046 by Lucite International) [0044] 9% of Carnauba wax [0045] 31% of a paraffin wax (for example a type such as Carisma 56T by Alpha Wax BV) [0046] 14% of N, N Ethylene-bis(stearamide)