Additive manufacturing process for producing ceramic articles using a sol containing nano-sized particles

1. A process for producing a ceramic article, the process comprising:

providing a printing sol, wherein the printing sol comprising solvent, nano-sized particles, radiation curable monomer(s) and photoinitiator, and wherein the printing sol having a viscosity of less than 500 mPa*s at 23° C.;

processing the printing sol as construction material in an additive manufacturing process to obtain a 3-dimensional article being in a gel state, the 3-dimensional article having a Volume A,

transferring the 3-dimensional article being in a gel state to a 3-dimensional article being in a dry state, namely an aerogel or xerogel; and

applying a heat treatment step to obtain a sintered 3 ceramic article, the ceramic article having a Volume F;

wherein Volume A of the 3-dimensional article in a gel state being more than 500% of Volume F of the ceramic article in its sintered state.

2. The process of claim 1 , the transfer of the 3-dimensional article being in a gel state to a 3-dimensional article being in a dry state being conducted by applying a supercritical drying step.

3. The process of claim 1 , the additive manufacturing process being selected from: stereolithographic printing.

4. The process of claim 1 , the additive manufacturing processing comprising:

providing a layer of the construction material on a surface;

radiation curing those parts of the layer of construction material which will belong to the 3-dimensional article to be produced;

providing an additional layer of the construction material in contact with the radiation cured surface of the previous layer; and

repeating the previous steps until the 3-dimensional article is obtained.

5. The process of claim 1 , the process not comprising either or all of the following steps:

heating the construction material during the additive manufacturing processing step to a temperature above 70° C.;

applying pressure during the sintering step.

6. The process of claim 1 , the printing sol being characterized by at least one or all of the following features:

being translucent in a wavelength range from 420 to 600 nm for a path length of 10 mm;

showing a transmission of at least 5% at 420 nm determined for a path length of 10 mm;

pH value: from 1 to 6.

7. The process of claim 1 , the printing sol being characterized by at least one or more or all of the following features:

the nano-sized particles being present in an amount from 20 to 70 wt.-% with respect to the weight of the printing sol;

the average primary particle size of the nano-sized zirconia particles being in a range up to 50 nm.

8. The process of claim 1 , the nano-sized particles being characterized by at least one or all of the following features:

being crystalline;

being essentially spherical, cuboidal or a mixture thereof;

being non-associated;

comprising ZrO 2 in an amount of 70 to 100 mol-%;

comprising HfO 2 in an amount of 0 to 4.5 mol-%;

comprising a stabilizer selected from Y 2 O 3 , CeO 2 , MgO, CaO, La 2 O 3 or a combination thereof in an amount of 0 to 30 mol-%;

comprising Al 2 O 3 in an amount of 0 to 1 mol-%.

9. The process of claim 1 , the printing sol comprising in addition organic dye(s).

10. The process of claim 9 , the organic dye being characterized by at least one or all of the following features:

being present in an amount from 0.001 to 0.5 wt.-% with respect to the weight of the printing sol;

showing a radiation absorption in the range from 200 to 500 nm;

having a molecular weight in the range of 100 to 1,000 g/mol;

being soluble in the solvent;

being combustible without residues at a temperature below 800° C.;

not containing heavy metal ions with an atomic mass above 40.

11. The process of claim 1 , the printing sol in addition comprising inhibitor(s), preferably in an amount from 0.001 to 1 wt.-% with respect to the weight of the printing sol.

12. The process of claim 1 , the radiation curable monomer(s) being characterized by at least one or all of the following features:

being represented by a formula A-B with A comprising an acidic group, a silane group, an amine, amide or alcohol group and B comprising a vinyl group;

being present in the printing sol in an amount from 2 to 30 wt.-% with respect to the weight of the printing sol.

13. The process of claim 1 , the printing sol not comprising either or all of the following components:

wax(es) in an amount of more than 0.1 wt.-%;

insoluble pigment(s) in an amount of more than 0.5 wt.-%;

particles having a primary particle diameter larger than 100 nm in an amount of more than 1 wt.-%;

wt.-% with respect to the weight of the printing sol.

14. A ceramic article obtained by the process of claim 1 , the ceramic article being characterized by either or all of the following features:

density: more than 98.5% with respect to theoretical density;

translucency: more than 30% determined on a polished sample having a thickness of 1 mm;

flexural strength: at least 450 MPa according to ISO 6872;

phase content tetragonal phase: from 0 to 100 wt.-%;

phase content cubic phase: from 0 to 100 wt.-%;

dimension in either x, y or z direction: at least 0.25 mm.

15. The ceramic article of claim 14 , the ceramic article having the shape of a dental or orthodontic article.