Formulations for additive manufacturing of three-dimensional objects containing sinterable materials
A sinterable paste formulation usable as cast material in a cast-mold process, in combination with a mold material formulation, is provided. The sinterable paste formulation comprises a power of a sinterable material, in an amount of at least 85% by weight of the total weight of the formulation, a binder as described in the specification, and an aqueous solution which comprises water and a water-miscible organic solvent featuring an evaporation rate in a range of from 0.3 to 0.8 on an n-butyl acetate scale. Methods employing the formulation and objects and products obtained therefrom are also provided.
1 . A sinterable paste formulation usable as cast material in a cast-mold process in combination with a mold material formulation, the sinterable paste formulation comprising a powder of a sinterable material, a binder and an aqueous solution, wherein an amount of said powder is at least 85% by weight of the total weight of the formulation, and wherein said aqueous solution comprises water and a water-miscible organic solvent, wherein said organic solvent has an evaporation rate in a range of from 0.3 to 0.8 on an n-butyl acetate scale, wherein said sinterable material is a metal,
and wherein:
the formulation features a pH of at least 8; and/or
a total amount of said aqueous solution ranges from 6 to 10% by weight of the total weight of the formulation; and/or
an amount of said water-miscible organic solvent in said aqueous solution ranges from 20 to 80% by weight of the total weight of the aqueous solution.
2 . The formulation of claim 1 , wherein a total amount of said aqueous solution ranges from 6 to 10% by weight of the total weight of the formulation.
3 . The formulation of claim 1 , wherein an amount of said water-miscible organic solvent in said aqueous solution ranges from 20 to 60% by weight of the total weight of the aqueous solution.
4 . The formulation of claim 1 , wherein said water-miscible organic solvent and said binder are selected such that said binder is dissolvable and/or dispersible in said organic solvent.
5 . The formulation of claim 1 , wherein said organic solvent is an alkylene glycol.
6 . The formulation of claim 1 , wherein an amount of said binder is no more than 10% by weight of the total weight of said formulation.
7 . The formulation of claim 1 , wherein said binder is thermolizable at a temperature lower by at least 100° C. than a sintering temperature of said sinterable material.
8 . The formulation of claim 1 , wherein said binder has a Tg of at least 30° C.
9 . The formulation of claim 1 , wherein said binder is characterized by a film forming temperature (TMF) of at least 0° C.
10 . The formulation of claim 1 , featuring a pH in a range of from 8 to 10.
11 . The formulation of claim 1 , featuring a viscosity of in a range of from 10000 to 50000 centipoises.
12 . The formulation of claim 1 , featuring no shear-thinning behavior under reduced pressure of 5 mBar or of 10 mBar.
13 . The formulation of claim 1 , comprising:
from 85 to 95% by weight of said powder of said sinterable material;
from 6 to 10% by weight of an aqueous solution which comprises water and at least 20% of said organic solvent; and
from 1 to 2% by weight of said binder.
14 . The formulation of claim 1 , wherein:
(1) the formulation comprises:
said powder of said sinterable material in an amount of from 88 to 92% by weight;
said binder, in an amount of from 1 to 2% by weight;
an anti-foaming agent, in an amount of from 0.1 to 1% by weight;
a pH adjusting agent, in an amount of from 0.005 to 0.015% by weight; and
said aqueous solution, in an amount of from 8 to 9% by weight, wherein said aqueous solution comprises said water-miscible organic solvent in an amount of from 20 to 40% by weight of the weight of said aqueous solution; or
(2) wherein the formulation comprises:
said powder of said sinterable material in an amount of from 88 to 92% by weight;
a dispersion of a binder which comprises an emulsion containing 45% by weight an acrylic polymer in water, in an aqueous solution, in an amount of from 2.5 to 3.5% by weight;
a dispersion of a binder which comprises an emulsion containing 22-23% by weight an acrylic polymer, 53-54% water and 20-21% propylene glycol mono methyl ether, in an aqueous solution, in an amount of from 1.5 to 2.5% by weight;
an anti-foaming agent, in an amount of from 0.1 to 1% by weight;
a pH adjusting agent, in an amount of 0.01% by weight;
water, in an amount of from 2 to 3% by weight; and
said water-miscible organic solvent in an amount of from 1 to 3% by weight, or
(3) wherein the formulation comprises:
said powder of said sinterable material in an amount of from 88 to 92% by weight;
a dispersion of a binder which comprises an emulsion containing 45% by weight an acrylic polymer in water, in an aqueous solution, in an amount of from 1 to 1.1% by weight;
a dispersion of a binder which comprises an emulsion containing 22-23% by weight an acrylic polymer, 53-54% water and 20-21% propylene glycol mono methyl ether, in an aqueous solution, in an amount of from 3 to 4% by weight;
an anti-foaming agent, in an amount of from 0.2 to 0.3% by weight;
a pH adjusting agent, in an amount of from 0.01 to 0.1% by weight;
water, in an amount of 3% by weight; and
said water-miscible organic solvent in an amount of from 1 to 2% by weight.
15 . A method of forming a three-dimensional object which comprises a sintered material, the method comprising:
forming a mold according to a shape of the object, using a mold material formulation;
filling the mold with a sinterable formulation according to claim 1 , to thereby obtain a mold-cast product;
removing the mold from said mold-cast product, to thereby obtain a green body;
removing said binder from said green body to thereby obtain a brown body; and
subjecting the brown body to a sintering condition, thereby forming said object.
16 . The method of claim 15 , wherein said filling comprises pouring said sinterable formulation into said mold or injection molding of said sinterable formulation into said mold.
17 . The method of claim 15 , wherein removing said mold comprises at least one of applying heat and contacting the mold with an organic solvent.
18 . The method of claim 15 , further comprising, prior to removing said mold, hardening said mold-cast product.
19 . The method of claim 18 , wherein said hardening comprises subjecting the mold-cast layer or object to a reduced pressure for a pre-determined time period.
20 . The method of claim 19 , further comprising, prior to subjecting to a reduced pressure, applying hot air to said mold-cast layer or object.
21 . The method of claim 19 , wherein said reduced pressure ranges from 0.01 millibar to 100 milliBar.
22 . The method of claim 15 , wherein forming said mold comprises forming a layered mold by dispensing a plurality of layers of said mold material formulation in a configured pattern corresponding to the shape of the object.