Process for the production of sintered moldings

• US 10,456,834 B2
• Filed: 06/01/2015
• Issued: 10/29/2019
• Est. Priority Date: 06/02/2014
• Status: Active Grant

• Current Assignee: BASF SE
• Original Assignee: BASF SE
• Inventors: Hermant, Marie-Claire, Von Bernstorff, Bernd-Steffen
• Primary Examiner(s): Walker, Keith
• Assistant Examiner(s): Hevy, John A
• Application Number:
  US15/315,594
• Publication Number:
  US 20180185919A1
• Time in Patent Office: 1,611 Days
• Field of Search: None
• CPC Class Codes: B22F 1/10 Metallic powder containing lubricating or binding agents; Metallic powder containing organic material
• CPC Class Codes: B22F 2302/45 Others, including non-metals
• CPC Class Codes: B22F 3/1025 not by heating only
• CPC Class Codes: B22F 3/16 in successive or repeated steps
• CPC Class Codes: B22F 3/225 by injection molding
• CPC Class Codes: C23F 1/12 Gaseous compositions
• CPC Class Codes: C23F 1/16 Acidic compositions C23F1/42 takes precedence

Abstract

The present invention relates to an improved process for the production of sintered moldings by molding a mixture of a sinterable ceramic or metallic powder and polyoxymethylene or a copolymer containing a majority of oxymethylene units as binder to give a compact, removing the binder from the compact by treatment with a gaseous acid, and sintering the resulting molding.

Claims

1. A process for the production of sintered moldings which comprises:

molding a mixture comprising

A. a sinterable metallic powder and

B. a binder comprising polyoxymethylene or a polyoxymethylene copolymer having at least 50 mol % of —

CH₂O—

repeat units in the main polymer chain

to give a compact;

removing the binder from the compact by treatment with a gaseous acid to obtain a molding; and

sintering the molding;

wherein the acid is selected from the group consisting of methanesulfonic acid, a mixture of methanesulfonic acid with oxalic acid, a solution of methanesulfonic acid in a solvent selected from the group consisting of water, C_1-4-carboxylic acids and mixtures thereof, a solution of a mixture of methanesulfonic acid and oxalic acid in a solvent selected from water, C_1-4-carboxylic acids and mixtures thereof, and a solution of oxalic acid in water,

wherein B is a thermoplastic composition comprising

from 10 to 90% by weight of a polyoxymethylene homo- or copolymer with a weight-average molar mass (M_w) in the range from above 60,000 to 200,000 g/mol as component B1.1 and

from 10 to 90% by weight of a polyoxymethylene copolymer with a weight average molar mass (M_w) in the range from 10,000 to 60,000 g/mol, as component B1.2, the molecular weights being determined by way of gel permeation chromatography.

2. The process of claim 1, wherein the amount of methanesulfonic acid, oxalic acid, or mixtures thereof, in the acid/solvent mixture is in the range of from 1 to 100 wt %.

3. The process of claim 1, wherein the C_1-4-carboxylic acid is selected from the group consisting of formic acid, acetic acid and propionic acid.

4. The process of claim 1, wherein the metallic powder is selected from the group consisting of Cu, Mg, Al, and MgAl-alloys.

5. The process of claim 1, wherein the mixture comprises

A. from 40 to 70% by volume of the sinterable pulverant metal, the sinterable pulverant metal alloy, or the mixture thereof;

B. from 30 to 60% by volume of the binder, the binder comprising;

B1.) from 50 to 98% by weight of the polyoxymethylene homopolymers or copolymers B1.1 and B1.2 based on the total amount of the component B;

B2.) from 2 to 35% by weight of one or more polyolefins, based on the total amount of component B;

B3.) from 0 to 40% by weight of poly-1,3-dioxolane, poly-1,3-dioxepane or polytetrahydrofuran or mixtures thereof, based on the total amount of component B,

wherein the sum of B1, B2, and B3 add up to 100% by weight of component B.

6. The process of claim 5, wherein at least 90% by weight of component B1.1, based on the polyoxymethylene homo- or copolymer, is derived from trioxane and optionally butanediol formal as monomers.

7. The process of claim 5, wherein at least 90% by weight of component B1.1, based on the polyoxymethylene homo- or copolymer, is derived from trioxane and butanediol formal as monomers, with a proportion of butanediol formal, based on the polymer, in the range from 1 to 5% by weight.

8. The process of claim 5, wherein at least 90% by weight of component B1.1, based on the polyoxymethylene homo- or copolymer, is derived from trioxane and butanediol formal as monomers, with a proportion of butanediol formal, based on the polymer, in the range from 2 to 3.5% by weight.

9. The process of claim 5, wherein at least 90% by weight of component B1.1, based on the polyoxymethylene homo- or copolymer, is derived from trioxane and butanediol formal as monomers, with a proportion of butanediol formal, based on the polymer, in the range from 2.5 to 3% by weight.

10. The process of claim 1, wherein the binder is removed at atmospheric pressure or under reduced pressure.

11. The process of claim 1, wherein the acid is selected from the group consisting of methane sulfonic acid, and a combination of methane sulfonic acid with formic acid or water.