Binder for injection moulding compositions

Abstract

A binder for an injection moulding composition including: from 40 to 55 volume percent of a polymeric base, from 35 to 45 volume percent of a mixture of waxes or a mixture of wax and palm oil, and at least 5 volume percent of at least one surfactant, wherein the polymeric base is formed 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 chosen from the group including a cellulose acetate butyrate, a polyvinyl butyral and a copolyamide, the respective quantities of the binder components being such that their sum is equal to 100 volume percent of the binder.

Claims

1. A binder suitable for an injection molding composition, the binder comprising, based on total binder volume: a polymeric base, in a range of from 40 to 55 vol. %; a mixture of waxes, or a mixture of wax and palm oil, in a range of from 35 to 45 vol. %; and a surfactant, in at least 5 vol. %, wherein the polymeric base of comprises (i) a copolymer ethylene and methacrylic or acrylic acid, (ii) a copolymer of ethylene and propylene and/or maleic anhydride-grafted polypropylene, and (iii) a solvent-soluble polymer, soluble in isopropyl alcohol, propyl alcohol, turpentine, or a mixture thereof, and wherein the solvent-soluble polymer (iii) is a cellulose acetate butyrate, a polyvinyl butyral, and/or a copolyamide, and wherein the binder has a lower viscosity, measured with a capillary rheometer with a 1 mm diameter and 20 mm length die, at 172° C. and shear rates of 10, 100, and 1000 Hz, than a binder lacking the solvent-soluble polymer (iii).

2. The binder of claim 1, wherein the polymeric base comprises the copolymer (i) of ethylene and methacrylic or acrylic acid in a range of from 2 to 7 vol. %, the copolymer (ii-a) of ethylene and propylene in a range of from 0 to 40 vol. %, the copolymer (ii-b) of maleic anhydride-grafted polypropylene in a range of from 0 to 35 vol. %, and the solvent-soluble polymer (iii) in a range of from 6 to 15 vol. %, wherein the copolymer of ethylene and propylene and the maleic anhydride-grafted polypropylene are present in a range of from 30 to vol. %, and wherein a total of the copolymer (i), copolymer (ii-a), copolymer (ii-b), and solvent-soluble polymer (iii) make up 100 vol. % of binder.

3. The binder of claim 1, wherein the polymeric base comprises a plurality of the copolymer (ii) of ethylene and propylene and maleic anhydride-grafted polypropylene as a mixture of copolymers (ii).

4. The binder of claim 3, wherein the polymeric base comprises the copolymer (i) of ethylene and methacrylic or acrylic acid in a range of from 2 to 7 vol. %, the copolymer (ii-a) of ethylene and propylene in a range of from 25 to 30 vol. %, the copolymer (ii-b) of maleic anhydride-grafted polypropylene in a range of from 5 to 10 vol. %, and the solvent-soluble polymer (iii) in a range of from 6 to 15 vol. %, wherein a total of the copolymer (i), copolymer (ii-a), copolymer (ii-b), and solvent-soluble polymer (iii) make up 100 vol. % of binder.

5. The binder of claim 1, wherein the copolymer (ii) comprises a copolymer (ii-a) of ethylene and propylene, which is a random statistical copolymer of ethylene and propylene with a melting point in a range of from 140 to 150° C.

6. The binder of claim 1, wherein the copolymer (i) comprises methacrylic or acrylic comonomer from 3 to 10 wt. % of methacrylic or acrylic comonomer.

7. The binder according to claim 1, wherein the copolymer (ii) comprises a copolymer (ii-b) of maleic anhydride-grafted polypropylene having a grafting rate in a range of from 1 to 2% and a melting point in a range of from 100 to 140° C.

8. The binder of claim 1, wherein the solvent-soluble polymer (iii) is a cellulose acetate butyrate having, relative to total solvent-soluble polymer (iii) weight, a butyryl content in a range of from 37 to 53 wt. %, and an acetyl content in a range of from 2 to 13 wt. %, wherein the solvent-soluble polymer (iii) has a melting point in a range of from 125 to 165° C. and wherein the solvent-soluble polymer (iii) has a molecular weight in a range of from 16000 to 40000.

9. The binder of claim 1, wherein the wax is a Carnauba wax, a paraffin wax, or a mixture thereof.

10. The binder of claim 1, wherein the wax and palm oil mixture is present, and wherein the wax is a Carnauba wax.

11. The binder of claim 1, wherein the surfactant is an N,N′-ethylene bis(stearamide).

12. The binder of claim 1, wherein the surfactant is soluble in isopropyl alcohol, propyl alcohol, turpentine, or a mixture thereof.

13. An injection molding composition feedstock suitable for abricating one or more shaped metal or ceramic parts, the injection molding composition comprising: an inorganic powder in a range of from 76 to 96 wt. %, and the binder of claim 1 in a range of from 4 to 24 wt. %.

14. The molding composition of claim 13, wherein the inorganic powder comprises an oxide powder, nitride powder, carbide powder, and/or metal powder.

15. The molding composition of claim 14, wherein the inorganic powder comprises an alumina powder, a zirconium oxide powder, a chromium carbide powder, a titanium carbide powder, a tungsten carbide powder, a metallic tungsten powder, a silicon nitride powder, a stainless steel powder, a metallic titanium powder, or a mixture thereof.

16. The molding composition of claim 13, comprising, in weight percentage: alumina in a range of from 76 to 88% and the binder in a range of from 12 to 24%; or alumina in a range of from 76 to 88%, magnesium oxide in a range of from 0.1 to 0.6%, and the binder in a range of from 12 to 24%, zirconium oxide in a range of from 58 to 86.5%, yttrium oxide in a range of from 3.9 to 4.6%, alumina in a range of from 0.18 to 18.5%, and the binder in a range of from 9 to 22%; or zirconium oxide in a range of from 61.5 to 84%, yttrium oxide in a range of from 3.9 to 4.6%, alumina in a range of from 0.2 to 9%, organic pigment in a range of from 2 to 5.5% of inorganic pigments from a list including iron oxide, cobalt oxide, chromium oxide, titanium oxide, manganese oxide, zinc oxide or a mixture of said oxides and in a range of from 9 to 22% of binder, the inorganic pigment comprising iron oxide, cobalt oxide, chromium oxide, titanium oxide, manganese oxide, and/or zinc oxide; or chromium or titanium carbide in a range of from 88 to 91%, and the binder in a range of from 9 to 12%; or tungsten carbide or metallic tungsten in a range of from 93 to 96%, and the binder in a range of from 4 to 7%; or silicon nitride in a range of from 78 to 85%, and the binder in a range of from 15 to 22%.

17. The binder of claim 1, wherein the surfactant is a mixture of stearic and palmitic acids.

18. The binder of claim 1, wherein the surfactant comprises an N,N′-ethylene bis(stearamide), stearic acid, and palmitic acid.

19. The binder of claim 1, having a viscosity, measured with a capillary rheometer with a 1 mm diameter and 20 mm length die, at 172° C. and a shear rate of 10 Hz of no more than 4300 Pa•s.

20. The binder of claim 1, having a viscosity, measured with a capillary rheometer with a 1 mm diameter and 20 mm length die, at 172° C. and a shear rate of 100 Hz of no more than 500 Pa•s.

Description

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(1) According to the invention, the binder for injection moulding compositions includes the following components: from 40 to 55 volume percent, preferably 45 to 54 volume percent of a polymeric base, from 35 to 45 volume percent, preferably 39 to 42 volume percent of a mixture of waxes or a mixture of wax and palm oil, and at least 5 volume percent, preferably 5 to 15 volume percent of at least one surfactant,
wherein the polymeric base is formed 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 and/or propyl alcohol and/or turpentine, and chosen from the group including a cellulose acetate butyrate, a polyvinyl butyral and a copolyamide, the respective quantities of the binder components being such that their sum is equal to 100 volume percent of the binder.

(2) Preferably, the polymeric base of the binder of the invention includes from 2 to 7 volume percent of copolymers of ethylene and methacrylic or acrylic acid, from 0 to 40 volume percent of copolymers of ethylene and propylene, from 0 to 35 volume percent of maleic anhydride-grafted polypropylene, the overall quantity of copolymer of ethylene and propylene and maleic anhydride-grafted polypropylene being comprised between 30 and 40 volume percent, and from 6 to 15 volume percent of polymer soluble in isopropyl alcohol and/or propyl alcohol and or turpentine, to 100 volume percent of binder, the respective quantities of the binder components being such that their sum is equal to 100 volume percent of binder.

(3) Preferably, the polymeric base includes a mixture of copolymers of ethylene and propylene and maleic anhydride-grafted polypropylene.

(4) Preferably, the polymeric base of the binder of the invention includes from 2 to 7 volume percent of copolymers of ethylene and methacrylic or acrylic acid, from 25 to 30 volume percent of copolymers of ethylene and propylene, from 5 to 10 volume percent of maleic anhydride-grafted polypropylene and from 6 to 15 volume percent of polymer soluble in isopropyl alcohol and/or propyl alcohol and/or turpentine, to 100 volume percent of binder.

(5) More preferably, the polymeric base of the binder of the invention includes from 3 to 5 volume percent of copolymers of ethylene and methacrylic or acrylic acid, from 26 to 29 volume percent of copolymers of ethylene and propylene, from 6 to 8 volume percent of maleic anhydride-grafted polypropylene and from 6 to 12 volume percent of polymer soluble in isopropyl alcohol and/or propyl alcohol and/or turpentine, to 100 volume percent of binder.

(6) Preferably the ethylene-propylene copolymer is a (random) statistical copolymer of ethylene and propylene with a melting point comprised between 140° C. and 150° C., this melting point varying according to the percentage of ethylene and propylene in said copolymer. For example, for oxide and nitride powders, the statistical copolymer of ethylene and propylene preferably contains more propylene to have a melting point of around 147° C. For metal powders, the statistical copolymer of ethylene and propylene preferably contains more ethylene to have a melting point of around 140° C.

(7) Preferably, the copolymer of ethylene and methacrylic or acrylic acid contains from 3 to 10 wt % of methacrylic or acrylic comonomer.

(8) 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.

(9) Preferably, the polymer soluble in isopropyl alcohol and/or propyl alcohol and/or turpentine is a cellulose acetate butyrate having a butyryl content of between 37 wt. % and 53 wt. %, an acetyl content of between 2 wt. % and 13 wt. % to the weight of polymer, a melting point of between 125° C. and 165° C. and a molecular weight of between 16000 and 40000.

(10) Advantageously, the wax is a Carnauba wax or a paraffin wax or a mixture of these elements. When the wax is a mixture with palm oil, the wax is preferably Carnauba wax.

(11) According to another preferred feature, the surfactant is an N,N′-ethylene bisstearamide or a mixture of stearic and palmitic acids (stearin), or a mixture of these elements.

(12) According to another feature, the surfactant is soluble in isopropyl alcohol and/or propyl alcohol and/or turpentine.

(13) The invention also concerns an injection moulding composition (feedstock) intended for fabrication of shaped metal or ceramic parts including 76 to 96 wt. % of an inorganic powder and 4 to 24 wt. % of the binder defined above.

(14) According to a particular feature, the inorganic powder of the injection moulding composition can be chosen from the group including an oxide powder, nitride powder, carbide powder, metal powder, or a mixture of said powders and preferably the inorganic powder is chosen from the group including 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 powder, a stainless steel powder, a metallic titanium powder or a mixture of said powders.

(15) According to preferred embodiments of the injection moulding composition, the latter contains in weight percent: 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 the 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 the 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 including iron oxide, cobalt oxide, chromium oxide, titanium oxide, manganese oxide, zinc oxide or a mixture of said oxides and 9 to 22% of the binder of the invention, or 88 to 91% of chromium or titanium carbide, and 9 to 12% of the binder of the invention, or 93 to 96% of tungsten carbide or metallic tungsten and 4 to 7% of the binder of the invention, or 78 to 85% of silicon nitride and 15 to 22% of the binder of the invention.

(16) The injection moulding composition (feedstock) intended for fabrication of shaped metal or ceramic parts according to the invention has lower viscosity than known feedstocks, for equivalent shear rates. Consequently, the composition of the invention makes it possible to better fill the parts during injection moulding, especially in areas with thin walls. Further, the composition according to the invention makes possible more efficient solvent debinding of parts, particularly through improved elimination of the binder components in the isopropyl alcohol and/or propyl alcohol and/or turpentine solvent. Propyl alcohol, with a boiling point of 97° C. makes it possible to debind at a higher temperature for improved efficiency, especially through improved elimination of Carnauba wax (melting point of 82° C.).

(17) The composition of the invention also makes it possible to obtain moulded and sintered parts having an improved surface appearance, without visible cracks or lines of weld.

(18) This invention will now be illustrated in more detail by means of the following non-limiting examples.

EXAMPLES

(19) The polymeric part of the binder is mixed with an inorganic powder at a temperature of around 150° C. to create a premix. To said premix are added the waxes and surfactant, and the temperature is further increased to around 180° C. to form a kind of homogeneous paste, which is then cooled and granulated to solidification, and then kept to form feedstock that can be used for fabrication of a shaped part by a known injection moulding technique.

(20) This technique typically includes a high pressure, hot injection moulding operation in a mould with cavities. The part is cooled inside the cavity and then ejected from the mould. All the processes are carried out at around 170°-180° C. The green part is then subjected to debinding in isopropyl alcohol before being sintered. Debinding eliminates part of the organic binder from the part and leaves just enough binder to maintain cohesion, or, in other words, the moulded shape of the green part. The binder is typically removed 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 be dissolved. With the binder of the invention, the green part is typically immersed in the isopropyl alcohol solvent and heated to a temperature of around 70° C. At this temperature, the wax mixture or wax and oil mixture thermally decomposes while the surfactants and the isopropyl alcohol soluble polymers are chemically dissolved. Once the solvent debinding operation is complete, the part is porous. The part is then placed in a high temperature furnace in order, firstly, to eliminate the remaining binder (thermal debinding, typically at a temperature of less than 400° C.), this operation being facilitated by the porosity left in the part during solvent debinding, and then, secondly, to sinter the part at a high temperature.

(21) Parts are made according to the method described above from various binders of the invention with the compositions indicated in Table I below, as a function of the nature of the inorganic powder:

(22) TABLE-US-00001 TABLE I Example 3 Example 1 Example 2 (volume %/100% (volume %/100% (volume %/100% of binder) Carbides, of binder) Oxides of binder) Nitrides cermets and metals Components (zironia, alumina etc.) (Si.sub.3N.sub.4, TiN, etc.) (TiC, WC, W, steel, etc.) Ethylene-propylene copolymer 28.5 28 27 (random polypropylene copolymer) Copolymers of ethylene and 4.5 4.5 4.5 methacrylic acid Polypropylene grafted maleic 7 7 7 anhydride Cellulose acetate butyrate 10.5 6.5 10.5 Carnauba wax 10.5 10 10 Paraffin wax 31 30 29 N,N′-ethylene bis(stearamide) 8 10 14 Stearin 4 Mass percentage of powder ZrO.sub.2: 86% Si.sub.3N.sub.4: 78% TiC: 89%

(23) The components are commercially available. The ethylene-propylene copolymer (random polypropylene copolymer) is PPR 10232 distributed by Total Refining & Chemicals. The maleic anhydride-grafted polypropylene is Fusabond® P353 distributed by DuPont™. The cellulose acetate butyrate is CAB-551-0.01 distributed by Eastman™.

(24) A composition was made according to Example 1 above with Saint-Gobain Zir Black black zirconium oxide ZrO.sub.2 powder as the organic powder. The viscosity of this composition was measured with an Instron Ceast SR20 capillary rheometer with a 1 mm diameter and 20 mm length die.

(25) By way of comparison, the viscosity of the feedstock composition disclosed in Example 1 of Patent Application No. WO 2014/191304 with the same Saint-Gobain Zir Black black inorganic zirconium oxide ZrO.sub.2 powder was measured.

(26) The results are set out in Table II below:

(27) TABLE-US-00002 TABLE II Viscosity example Viscosity example Saint-Gobain Zir Saint-Gobain Zir Black black ZrO.sub.2 Black black ZrO.sub.2 powder according powder according to Example I of to Example I of WO2014/191304 the invention Shear rate (Pa .Math. s) at 172° C. ØM (Pa .Math. s) at 172° C. ØM (1/s) Powder: 86.05% Powder: 86.05% 10 8000 4300 100 1300 500 1000 120 75

(28) The injection moulding composition according to the invention has lower viscosity than known feedstocks, for equivalent shear rates.

(29) Further, elimination of the binder during debinding in the isopropyl alcohol solvent is improved: around 45% of the binder described in Patent Application WO2014/191304 was eliminated in the solvent whereas at least 50% of binder of the invention is eliminated, notably the cellulose acetate butyrate. In the case of metal powders, the percentage of elimination can be up to 65%.

(30) The moulded and sintered parts obtained have an improved surface appearance, without visible cracks or lines of weld.