Patent Application
20220332648
The present invention relates to a curable composition for manufacturing green parts of ceramic or metallic material by stereolithography, such green parts being intended to be subjected to cleaning, debinding and sintering operations in order to obtain finished ceramic or metallic parts.
Stereolithography generally comprises the following steps, for obtaining these green parts:
Then, in order to obtain the finished part as indicated above, the green part is cleaned in order to remove the uncured composition; the cleaned green part is debinded; and the cleaned and debinded green part is sintered in order to obtain the finished part.
The part may be manufactured by a paste process or by a liquid process.
In a manufacturing by a paste process, the photocurable composition is in the form of a paste while the rigid support is a working tray that supports the different layers of the part under construction as well as the paste; each of the layers is generally formed by lowering the working tray and spreading paste with a predefined thickness. A paste stock is stored in tanks that are automatically emptied of a predefined amount of paste at each layer using a piston. This creates a bead of paste to be spread over the upper layer of the part being manufactured that has been previously lowered by the working tray. Each layer is generally spread by scraping using a “scraper” blade which sweeps over the working surface of the working tray, for example by advancing in a horizontal rectilinear direction.
In the case of a manufacturing by a liquid process, the photocurable composition is in the form of a low viscosity suspension.
The various ceramic or metallic powders that are used in stereolithography exhibit UV light absorption behaviors at the wavelength of the UV beam used (for example 355 nm), that may vary from one to the other.
Some powders are very absorbent, such as lanthanum strontium manganite (LSM) ceramic, silicon carbide (SiC) or silver (Ag) powders, while other powders are much less absorbent, such as alumina (Al2O3) and zirconia (ZrO2).
We may thus mention that the ZrO2 powder absorbs only 8% of UV light at 355 nm, while LSM and SiC each absorb more than 90%.
In these latter cases, the light absorbed by the powder is no longer available for the photoinitiator, and the photopolymerization reaction can, therefore, no longer take place.
In other words, the lack of reactivity of certain photosensitive ceramic or metallic pastes or suspensions to UV exposure makes it difficult, if not impossible, to construct an object by UV stereolithography.
To solve this problem, the Applicant has already filed a first French patent application FR3099079 reporting the use of a thermal initiator in a ceramic or metallic paste or suspension in order to use the thermal energy released by ceramic or metallic powders during their exposure to UV-visible light as well as IR light, so as to generate the controlled initiation of the thermal polymerization.
In this case, the absorbencance of the ceramic or metallic particles at the working wavelength is therefore favorable, as the light energy absorbed by the ceramic or metallic particles is converted into heat, and as this heat is then absorbed by a thermal initiator to allow polymerization of the resin.
However, it can be pointed out that thermal initiators are generally hazardous compounds that can cause difficulties in the production, storage, transport and use of suspensions, and that ceramic suspensions tend to polymerize spontaneously over a relatively short time scale.
To overcome these drawbacks, the Applicant has developed a new initiator system allowing the polymerization of ceramic or metallic pastes or suspensions during their exposure to UV-visible light as well as a IR light: the initiator system using an onium salt or a charge-transfer complex (CTC).
Patent application US2001/036591 A1 relates to the use of iodonium salt compounds as photoinitiators. Similarly, patent application US2005/070621A1 describes photoinitiators.
Charge-transfer complexes are electron donor (ED) and electron acceptor (EA) pairs. These complexes exhibit thermal and photochemical reactivity allowing the initiation of radical polymerization in two ways:
Since CTC complexes are more stable than conventional thermal initiators, the pot stability of suspensions is extended. In addition, the CTC complex is made up of molecules that are not listed as hazardous.
To this end, the present invention relates to a curable composition for the manufacture, by stereolithography, of a green part made of a ceramic or metallic material, said curable composition comprising:
The curable composition may be semi-liquid to pasty in consistency.
The ceramic powder(s) may be selected from:
The metal powder(s) may be selected from silver, copper, iron, tungsten and alloys thereof.
The monomer(s) and/or oligomer(s) may be selected from polyfunctional (meth)acrylates, such as diethoxylated bisphenol A dimethacrylate, 1,6-hexanediol diacrylate, 3-methyl-1,5-pentanediol diacrylate, trimethylolpropane triacrylate, and mixtures thereof.
The onium salts used in combination with at least one amine and/or at least one phosphine may be selected from iodonium, sulfonium and diazonium salts.
An iodonium salt, which may enter into the composition according to the invention, may be a diaryliodonium such as bis-(4-t-butylphenyl)-iodonium hexafluorophosphate.
A sulfonium salt, which may enter into the composition according to the invention, may be a triarylsulfonium such as triarylsulfonium hexafluoroantimonate in admixture with propylene carbonate, in particular in a proportion 50% of triarylsulfonium hexafluoroantimonate in the mixture.
The amines may be selected from primary, secondary and tertiary, aliphatic or aromatic amines. In particular, the amine may be selected from 2-[4-(dimethylamino)phenyl]ethanol, 2,2′-(4-methylphenylimino)diethanol, ethyl 4-(dimethylamino)benzoate and N-methyldiethanolamine.
The phosphines may be selected from primary, secondary and tertiary, aliphatic or aromatic phosphines. In particular, the phosphine may be selected from triphenylphosphine, 4-(diphenylphosphino)styrene, 4-(diphenylphosphino)benzoic acid, 2-(diphenylphosphino)benzoic acid 2-(diphenylphosphino)benzaldehyde, (1R,2R)-(+)-1,2-diaminocyclohexane-N,N′-bis(2-diphenylphosphino-1-naphthoyl) or (R,R)-DACH-naphthyl-Trost Ligand (a Trost ligand), bis[2-(diphenylphosphino)phenyl] ether.
The composition according to the invention may also comprise at least one plasticizer selected in particular from polyethylene glycol, dibutyl phthalate and glycerol.
The composition according to the invention may also comprise at least one dispersant selected in particular from phosphoric esters.
The composition according to the invention may comprise, relative to the total volume:
The present invention also relates to a method for manufacturing, by stereolithography, a green part made of a ceramic or metallic material, method according to which layers based on a composition which is curable by polymerization and comprises a ceramic or metallic powder, depending on whether it is desired to manufacture a ceramic or metallic green part respectively, are successively cured by the said polymerization according to a pattern defined for each layer, the first layer being formed on a working tray and each other layer being formed and then cured on the preceding layer, characterized by the fact that: a curable composition as defined above is used and a thermal polymerization is carried out on each layer under the exposure to at least one source of irradiation selected from UV, visible or IR irradiation sources.
The following Examples illustrate the present invention, without limiting its scope.
Suspensions were prepared, the composition of which is given in the following Tables in % by volume of the total volume, and stereolithography tests were carried out, at the wavelengths indicated in the Tables, at the power of 2 W and at the beam diameter of 300 μm. These experiments were carried out with a stereolithography machine of the CERAMAKER type equipped with different lasers.
The results are also shown in each of Tables 1 and 2.
C Ceramic powder: Silicon carbide
M Monomer: Diethoxylated bisphenol A diacrylate
| Number | Date | Country | Kind |
|---|---|---|---|
| 2103673 | Apr 2021 | FR | national |
