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• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D4/00—Coating compositions, e.g. paints, varnishes or lacquers, based on organic non-macromolecular compounds having at least one polymerisable carbon-to-carbon unsaturated bond ; Coating compositions, based on monomers of macromolecular compounds of groups C09D183/00 - C09D183/16
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  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F2/00—Processes of polymerisation
  • C08F2/46—Polymerisation initiated by wave energy or particle radiation
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C64/00—Additive manufacturing, i.e. manufacturing of three-dimensional [3D] objects by additive deposition, additive agglomeration or additive layering, e.g. by 3D printing, stereolithography or selective laser sintering
  • B29C64/10—Processes of additive manufacturing
  • B29C64/106—Processes of additive manufacturing using only liquids or viscous materials, e.g. depositing a continuous bead of viscous material
  • B29C64/124—Processes of additive manufacturing using only liquids or viscous materials, e.g. depositing a continuous bead of viscous material using layers of liquid which are selectively solidified
  • B29C64/129—Processes of additive manufacturing using only liquids or viscous materials, e.g. depositing a continuous bead of viscous material using layers of liquid which are selectively solidified characterised by the energy source therefor, e.g. by global irradiation combined with a mask
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C64/00—Additive manufacturing, i.e. manufacturing of three-dimensional [3D] objects by additive deposition, additive agglomeration or additive layering, e.g. by 3D printing, stereolithography or selective laser sintering
  • B29C64/10—Processes of additive manufacturing
  • B29C64/106—Processes of additive manufacturing using only liquids or viscous materials, e.g. depositing a continuous bead of viscous material
  • B29C64/124—Processes of additive manufacturing using only liquids or viscous materials, e.g. depositing a continuous bead of viscous material using layers of liquid which are selectively solidified
  • B29C64/129—Processes of additive manufacturing using only liquids or viscous materials, e.g. depositing a continuous bead of viscous material using layers of liquid which are selectively solidified characterised by the energy source therefor, e.g. by global irradiation combined with a mask
  • B29C64/135—Processes of additive manufacturing using only liquids or viscous materials, e.g. depositing a continuous bead of viscous material using layers of liquid which are selectively solidified characterised by the energy source therefor, e.g. by global irradiation combined with a mask the energy source being concentrated, e.g. scanning lasers or focused light sources
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B33—ADDITIVE MANUFACTURING TECHNOLOGY
  • B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
  • B33Y10/00—Processes of additive manufacturing
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B33—ADDITIVE MANUFACTURING TECHNOLOGY
  • B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
  • B33Y70/00—Materials specially adapted for additive manufacturing
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F2/00—Processes of polymerisation
  • C08F2/46—Polymerisation initiated by wave energy or particle radiation
  • C08F2/48—Polymerisation initiated by wave energy or particle radiation by ultraviolet or visible light
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F2/00—Processes of polymerisation
  • C08F2/46—Polymerisation initiated by wave energy or particle radiation
  • C08F2/48—Polymerisation initiated by wave energy or particle radiation by ultraviolet or visible light
  • C08F2/50—Polymerisation initiated by wave energy or particle radiation by ultraviolet or visible light with sensitising agents
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F222/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a carboxyl radical and containing at least one other carboxyl radical in the molecule; Salts, anhydrides, esters, amides, imides, or nitriles thereof
  • C08F222/10—Esters
  • C08F222/1006—Esters of polyhydric alcohols or polyhydric phenols
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F222/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a carboxyl radical and containing at least one other carboxyl radical in the molecule; Salts, anhydrides, esters, amides, imides, or nitriles thereof
  • C08F222/10—Esters
  • C08F222/1006—Esters of polyhydric alcohols or polyhydric phenols
  • C08F222/103—Esters of polyhydric alcohols or polyhydric phenols of trialcohols, e.g. trimethylolpropane tri(meth)acrylate
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F222/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a carboxyl radical and containing at least one other carboxyl radical in the molecule; Salts, anhydrides, esters, amides, imides, or nitriles thereof
  • C08F222/10—Esters
  • C08F222/1006—Esters of polyhydric alcohols or polyhydric phenols
  • C08F222/105—Esters of polyhydric alcohols or polyhydric phenols of pentaalcohols
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D135/00—Coating compositions based on homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a carboxyl radical, and containing at least another carboxyl radical in the molecule, or of salts, anhydrides, esters, amides, imides or nitriles thereof; Coating compositions based on derivatives of such polymers
  • C09D135/02—Homopolymers or copolymers of esters
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D7/00—Features of coating compositions, not provided for in group C09D5/00; Processes for incorporating ingredients in coating compositions
  • C09D7/40—Additives
  • C09D7/60—Additives non-macromolecular
  • C09D7/63—Additives non-macromolecular organic
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
  • B29K2033/00—Use of polymers of unsaturated acids or derivatives thereof as moulding material
  • B29K2033/04—Polymers of esters
  • B29K2033/08—Polymers of acrylic acid esters, e.g. PMA, i.e. polymethylacrylate
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
  • B29K2033/00—Use of polymers of unsaturated acids or derivatives thereof as moulding material
  • B29K2033/04—Polymers of esters
  • B29K2033/12—Polymers of methacrylic acid esters, e.g. PMMA, i.e. polymethylmethacrylate
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F2800/00—Copolymer characterised by the proportions of the comonomers expressed
  • C08F2800/20—Copolymer characterised by the proportions of the comonomers expressed as weight or mass percentages

Definitions

• the invention relates to a photopolymerizable composition activatable by two-photon absorption at nanometric resolution, and an associated 3D printing method.
• Document D2 B. Mettra, YY Liao, T. Gallavardin, C. Armagnat, D. Pitrat, P. Baldeck, T. Le Bahers, C. Monnereau and C. Andraud, “A combined theoretical and experimental investigation on the influence of the bromine substitution pattern on the photophysics of conjugated organic chromophores”, Phys. Chem. Chem. Phys., 2018, 20, 3768, describes molecules exhibiting a certain sensitivity to two-photon absorption, in particular molecules obtained by substitution of one or more heavy atoms on a central phenyl nucleus by a branch comprising an oligomer.
• the present invention aims to overcome at least one of the drawbacks of known initiator molecules, compositions and two-photon 3D printing methods.
• the invention proposes a new polymerization initiator molecule, able to be excited by two photons and to generate polymerization initiator free radicals, molecule characterized in that it comprises two branches grafted onto a central phenyl nucleus in position 1 and 3, each arm comprising an oligomer of the oligo-phenylenethynylene-yl type or of the oligo2,5-dihalogenophenylenethynylene-yl type.
• the initiator molecules according to the invention Compared to initiator molecules conventionally used in the context of photolithography by two-photon absorption in the visible range and more particularly 532 nm, for example known molecules having Pi-conjugated structures of small dimensions, the initiator molecules according to the invention have larger branches, better suited to obtaining strong non-linearities, which lead to much higher two-photon absorption (ADP) cross sections, as will be better seen later.
• ADP two-photon absorption
• the initiator molecules according to the invention are characterized by a very high sensitivity to ADP.
• the number and dimensions of the branches of the initiator molecules contribute to reducing their mobility in the photopolymerizable composition, which improves the resolution in 3D printing.
• the molecule according to the invention comprising branches grafted onto a central phenyl nucleus in position 1 and 3 has absorption and emission spectra much less shifted in the red or infrared while retaining nonlinear optical properties, including a high two-photon absorption cross section.
• the molecule according to the invention presents in this an ideal compromise between high non-linearity and transparency in the visible, making it possible to have a significant two-photon absorption in the visible, without residual single-photon absorption, which is not the case. on linear molecules of comparable conjugation length. Biphoton absorption in the visible makes it possible to use lasers that are easier to implement.
• each branch comprises an oligomer of the oligo2,5-dihalogenophenylenethynylene-yl type.
• the halogen substituents preferably correspond to two bromine atoms.
• This halogen is known to amplify intersystem crossing processes when incorporated into Pi-conjugated structures by heavy atom effect, bringing the molecule to a triplet-like excited state.
• the triplet state with a longer lifetime, is therefore more apt to generate photochemical reactions (typically photoinduced electron transfer) at the origin of the generation of radicals.
• photochemical reactions typically photoinduced electron transfer
• bromine generates a markedly more marked heavy atom effect, while possessing a lower sensitivity than that of iodine to parasitic chemical reactions, allowing a easier functionalization of the target molecule.
• each branch of an initiator molecule in accordance with the invention is terminated by a terminal phenylamine, preferably by a terminal phenylamine of the dialkylphenylamine type, and even more preferentially a dihexylphenylamine.
• the alkyl groups substituted on the terminal functions of the phenylamine make the initiator molecule according to the invention soluble in the composition. This makes it possible to avoid the addition of organic solvent during the formulation of the resin, a process that is generally tedious, expensive and potentially toxic. Also, the alkyl groups limit the crystallization of the initiator molecule, which is favorable for use in 3D printing where the presence of crystals is a problem.
• an initiator molecule in accordance with the invention comprises a halogen atom and two branches grafted onto the central phenyl ring, respectively in position 1, 3 and 5.
• the two-branched initiator molecule has good sensitivity and at the same time good solubility in the photopolymerizable composition, which allows good overall reactivity of said composition.
• the halogen atom is preferably a bromine atom, for its advantages explained above.
• the initiator molecule is associated with a co-initiator molecule, such as an amine-derived molecule or an iodonium-derived molecule, as will be better seen below.
• a co-initiator molecule such as an amine-derived molecule or an iodonium-derived molecule, as will be better seen below.
• the invention also provides a photopolymerizable composition according to the invention comprising:
• composition characterized in that the photoinitiator system comprises at least one initiator molecule as described above.
• photochemically effective amount is meant an “amount sufficient to allow the resin to polymerize”. Said quantity depends on the photoinitiator system, in particular on its reactivity and on its solubility in the composition.
• a measurement of the polymerization threshold and of the characteristics of the structures makes it possible to determine a minimum value and a maximum value of a “photochemically effective quantity” of the photoinitiator system; the said quantity, or the range of values of the said quantity can be, for example, expressed as a percentage of a quantity of total composition equal to 100%.
• the polymerizable resin comprises a main monomer of vinyl monomer type, preferably an acrylate monomer or methacrylate monomer.
• the main monomer is chosen to be highly crosslinkable, to obtain submicronic and preferably nanometric resolution.
• the main monomer is a multifunctional acrylate monomer, for example a dipentaerythritol penta-/hexa-acrylate (DPPHA) or a Pentaerythritol triacrylate (PETA).
• DPPHA dipentaerythritol penta-/hexa-acrylate
• PETA Pentaerythritol triacrylate
• the polymerizable resin may also include a solubilizing component, such as:
• a diacrylate with at least one alkyl chain for example a Poly(ethylene glycol) diacrylate (PEGDA), or a 1,10-decanediol diacrylate (DDA), or
• PEGDA Poly(ethylene glycol) diacrylate
• DDA 1,10-decanediol diacrylate
• dithiol for example a 1,10-decanedithiol (DDT).
• DDT 1,10-decanedithiol
• diacrylates or dithiols are also interesting for their moderate cross-linking properties, which help to complete the polymerization of the resin once the reaction of polymerization is initiated by the main monomer; the final degree of polymerization of the composition is thus improved.
• the composition may comprise from 0.1 to 10%, preferably 0.2 to 5% and even more preferably 0.5 to 1.5% by weight of photoinitiator system. These amounts are a compromise between the amount of photoinitiator that can be dissolved directly in the resin and the overall reactivity of the composition. The latter tends to increase for increasing concentrations of photoinitiator, but the benefit is less beyond 2% by weight.
• the composition may comprise 5 to 60%, and preferably 10 to 25% solubilizing component. These amounts are again a compromise between the amount of photoinitiator that the solubilizing component makes it possible to dissolve in the resin, and the overall reactivity of the composition.
• the invention also relates to a three-dimensional printing process comprising a step of transforming a volume of a photopolymerizable composition activatable by two-photon absorption, composition comprising a resin polymerizable by the radical route and a photoinitiator system in a photochemically effective quantity, system photoinitiator comprising at least one initiator molecule able to be excited by two photons and to generate free radicals polymerization initiator, the transformation step consisting in irradiating the volume of composition by an irradiation source emitting an irradiation signal having a wavelength L irr between 1 and 1.5 times, and preferably between 1.1 and 1.25 times, a cut-off wavelength L Cut o ff of the initiator molecule, L Cut o ff being defined as the wavelength beyond which the molar extinction coefficient of the photoinitiator is considered negligible because it is less than 1% of the maximum value of the molar absorption coefficient of said initiator molecule.
• the wavelength of the irradiation signal is between 1.1 and 1.25 times the cutoff wavelength Lcutoff- This makes it possible to eliminate the risk of residual single-photon absorption while ensuring the the most efficient reaction possible with the lowest possible irradiance.
• the photopolymerizable composition is a composition according to the invention, as described above.
• the three-dimensional irradiation step of the volume of composition can be carried out by a technique of direct writing by a laser-type irradiation source, technique implemented at a high speed, preferably at a speed greater than 50 mm/s, and even more preferably at a speed greater than 1 m/s.
• the three-dimensional irradiation step of the volume of composition can be carried out by a parallel projection technique, of the photolithography type or of the holographic projection type, with a high number of irradiation sources, preferably a number of irradiation sources greater than ten thousand, and even more preferably greater than one million.
• the three-dimensional irradiation step of the volume of composition can be carried out by a direct writing technique with a single beam or by a parallel projection technique with several beams.
• the invention also relates to a three-dimensional printing device comprising means arranged for the implementation of the method according to the invention and as described above.
• FIG. 1 presents examples of known initiator molecules
• FIG. 2 presents a first example of initiator molecules according to the invention
• FIG. 3 presents a variant of FIG. 2
• figure 4 presents a variant of figure 2
• figure 5 presents a variant of figure 2
• figure 6 presents an example of initiator molecules close to the example of figure 2
• 7 presents the evolution of the one-photon (OPA) and two-photon absorption of the molecule of figure 2, as a function of the wavelength of an excitation signal
• figure 8 presents results implementation of the method according to the invention
• FIG. 9 presents other results of implementation of the method according to the invention
• FIG. 10 presents other results of implementation of the method according to the invention.
• the invention relates to a photopolymerizable composition which can be activated by biphotonic absorption, composition
• a photopolymerizable composition which can be activated by biphotonic absorption, composition
• composition comprising:
• radical photoinitiator system in a photochemically effective quantity, capable of being excited by several photons and capable of generating free radicals.
• composition according to the invention is characterized in that the photoinitiator system comprises at least one initiator molecule comprising two branches grafted onto a central phenyl core in position 1 and 3, each branch comprising an oligomer of the oligo-phenylenethynylene-yl or oligo2 type, 5-dihalogen-phenylenethynylene-yl.
• FIG. 2 presents an example of a two-armed initiator molecule, according to the invention, which will be referred to below as PA2 for simplicity.
• Figures 3 to 5 show variants of the molecule of Figure 2.
• Figure 6 presents an example of an initiator molecule with three branches (which will be called PA3 hereafter), close to that of figure 2.
• each branch of a molecule according to the invention comprises (or begins with) a phenylenethynylene-yl such as:
• a phenylenethynylene-yl (fig. 2 ), and more generally an oligo2,5 - phenylenethynylene-yl (fig. 3 with n between 0 and 4)
• an oligo2,5-dibromo-phenylenethynylene-yl (figures 4-5 with n between 0 and 4), and more generally, an oligo2,5-dihalogeno-phenylenethynylene-yl with n between 0 and 4, and two halogens per group phenylenethynylene-yl, the halogens being for example bromine, chlorine, iodine, fluorine or astatine.
• halogens makes it possible to increase the spin-orbit coupling within the molecule and to optimize the photoinduced formation of the photoinitiator in its triplet state initially, and of radicals in a second stage (following a transfer of 'photoinduced electrons); initiator molecules with halogens are therefore more effective than similar molecules without halogens.
• the best results have been obtained with Bromine: tests with Bromine have in fact shown that the light-curing threshold can be reduced, compared to their unsubstituted analogues, by a factor of 1.5 to 2.
• the free end of each branch of the initiator molecule is terminated by a terminal phenylamine (aniline), preferably a terminal phenylamine of the dialkylaminophenyl type; in the example molecules figure 2 (molecule PA2) and figures 3-5, the phenylamine end is a dihexylaminophenylethynyl end group.
• aniline preferably a terminal phenylamine of the dialkylaminophenyl type
• the phenylamine end is a dihexylaminophenylethynyl end group.
• - R -[p-N, N-(dialkyl)aminophenylethynyl](oligo-phenylenethynylene-yl) or
• - R' -[p-N, N-(dialkyl)aminophenylethinyl](oligo2,5-dihalogenophenylenethynylene-yl).
• the initiator molecules of figures 2, 3 and 5 have two branches and include two R-type branches and a halogen atom (Bromine here) grafted onto the central phenyl ring, respectively in position 1, 3 and 5. They can be synthesized for example by the substitution by type R branches of two halogen atoms present on a phenyl ring comprising three halogen atoms in position 1, 3 and 5.
• the initiator molecule of FIG. 4 has two branches of the R 1 type grafted onto the central phenyl ring, respectively in position 1, 3, position 5 being occupied by a Hydrogen. It can be synthesized, for example, by the substitution by branches of the R' type of two hydrogen atoms present on a phenyl ring comprising three hydrogen atoms in position 1, 3 and 5.
• the PA3 initiator molecule in FIG. 6 has three R-type branches grafted onto the central phenyl nucleus, respectively in position 1, 3 and 5. It can be synthesized for example by the substitution by R-type branches of three hydrogen atoms present on a phenyl ring in position 1, 3 and 5.
• the absorption spectrum of the PA2 molecule was measured using conventional techniques, for a sample of molecules dissolved in dichloromethane.
• FIG. 7 is represented the molar extinction coefficient of the PA2 molecule.
• the molar extinction coefficient is an intrinsic parameter of a molecule, directly proportional to the absorbance of a composition containing said molecule; more precisely, the absorbance of the molecule is obtained by multiplying the molar extinction coefficient by the concentration of the molecule in the composition used to carry out the measurement and by the length of the cuvette containing the composition used for the measurement.
• PA2 we note:
• L 770 nm
• L absR 386 nm of the single-photon absorption resonance
• the two-photon absorption cross section for a wavelength of 532 nm is of the order of 77 +/- 11 GM.
• the sensitivity of the PA2 molecule is thus much greater than that of the BDEBP molecule commonly used today for two-photon absorption reactions, and a fortiori than those of the molecules specifically used at 532 nm (OXE2 type), of which the estimated cross section values generally vary between a few GM and a few tens of GM.
• the invention also relates to a polymerizable resin composition incorporating an initiator molecule as described above.
• the composition comprises a main monomer of the vinyl monomer type, preferably an acrylate monomer or a methacrylate monomer. These monomers are known for their high reactivity in radical polymerization.
• monomers of the triacrylate type such as Pentaerythritol triacrylate (PETA) gave good results and monomers of the dipentaerythritol penta-/hexa-acrylate (DPPHA) type gave the best results in combination with the initiator molecules of type PA2.
• PETA Pentaerythritol triacrylate
• DPPHA dipentaerythritol penta-/hexa-acrylate
• the initiator molecules according to the invention comprise, at the end of their branches, a terminal alkylphenylamine, one of the functions of which is to facilitate the dissolution of the molecule in the composition.
• a solubilizing comonomer can be added such as:
• a diacrylate with at least one alkyl chain for example a Poly(ethylene glycol) diacrylate (PEGDA), a 1,6-hexanediol diacrylate (HDODA), or a 1,10-decanediol diacrylate (DDA)
• PEGDA Poly(ethylene glycol) diacrylate
• HDODA 1,6-hexanediol diacrylate
• DDA 1,10-decanediol diacrylate
• dithiol for example a 1,10-Decanedithiol (DDT).
• DDT 1,10-Decanedithiol
• compositions produced and tested comprise 0.2 to 5% by weight of photoinitiator system and/or 10 to 25% by weight of solubilizing component.
• Example 1 compositions comprising dipentaerythritol penta-/hexa-acrylate (DPPHA) and 1,10-decanediol diacrylate (DDA) monomers and the PA2 molecule, with different mass proportions (% wt or % by weight):
• DPPHA dipentaerythritol penta-/hexa-acrylate
• DDA 1,10-decanediol diacrylate
• DDA makes it possible to improve the dissolution of the initiator molecule PA2 in the composition and also makes the composition less viscous, but DDA is less reactive than DPPHA during 3D printing. If all the compositions 1a to 1f give good results, composition 1c gives the best compromise.
• Example 2 composition comprising dipentaerythritol penta-/hexa-acrylate (DPPHA) monomers, 1,10-Decanedithiol (DDT) molecules and PA2 molecules, with the following mass proportions (% wt):
• DPPHA dipentaerythritol penta-/hexa-acrylate
• DDT 1,10-Decanedithiol
• PA2 PA2 molecules
• DDT also gives good results in terms of microfabrication (threshold comparable to similar compositions with DDA instead of DDT) but more DDT than DDA must be used to achieve equivalent solubility; the composition therefore remains the best compromise.
• Example 3 composition comprising dipentaerythritol penta-/hexa-acrylate (DPPHA) monomers, poly(ethylene glycol) diacrylate (PEGDA) monomers and PA2 molecules, with the following mass proportions (%wt):
• DPPHA dipentaerythritol penta-/hexa-acrylate
• PEGDA poly(ethylene glycol) diacrylate
• PA2 molecules with the following mass proportions (%wt):
• Example 4 compositions comprising Pentaerythritol triacrylate (PETA) and 1,10-decanediol diacrylate (DDA) monomers and the PA2 molecule, with different proportions mass (%wt):
• PETA Pentaerythritol triacrylate
• DDA 1,10-decanediol diacrylate
• composition 4a PETA/DDA/PA2, mass proportions: 59.7/39.8/0.5
• composition 4b PETA/DDA/PA2, mass proportions: 60/37/3
• composition 4c PETA/DDA/PA2, mass proportions: 60/35/5
• Example 5 composition comprising dipentaerythritol penta-/hexa-acrylate (DPPHA) monomers, 1,10-decanediol diacrylate (DDA) monomers and PA3 molecules, with the following mass proportions (% wt):
• DPPHA dipentaerythritol penta-/hexa-acrylate
• DDA 1,10-decanediol diacrylate
• the PA3 molecule dissolves more with difficulty in the composition, an amount of 20% wt of DDA making it possible to dissolve only 0.66% wt of PA3, whereas it makes it possible to dissolve at minus l%wt of PA2.
• the compositions with the PA3 molecules are thus less effective than those containing the PA2 molecules with the same proportions of DPPHA and DDA monomers.
• the most reactive compositions comprise 0.5 to 1.5% by weight of photoinitiator system and/or 10 to 25% by weight of solubilizing component.
• the photoinitiator system can also comprise a suitable co-initiator to improve the formation of radicals.
• a co-initiator, electron acceptor, of the diphenyliodonium type for example, decomposes by generating an aryl radical.
• Other coinitiators such as amines of the aliphatic amine type (generation of the radical by abstraction of hydrogen on the aliphatic carbon alpha to the nitrogen) or triarylamines (electronic transfer leading to the formation of a cation radical on the non-binding doublet of nitrogen) can also be considered.
• the invention finally relates to a two-photon three-dimensional printing process comprising a step of transforming a volume of a photopolymerizable composition comprising a resin polymerizable by the radical route and a photoinitiator system in a photochemically effective quantity capable of being excited by several photons and capable of generating free radicals, photoinitiator system comprising at least one initiator molecule, the transformation step consisting in irradiating said volume of composition by an irradiation source emitting an irradiation signal having a wavelength L irr between 1 and 1.5 times, and preferably between 1.1 and 1.25 times, a cutoff wavelength L Cut o ff of the initiator molecule beyond which the molar extinction coefficient of said initiator molecule is less than 1% of the maximum value of the molar extinction coefficient of said initiator
• the two-photon excitation is deliberately positioned close to the wavelength L absR of absorption resonance of a photon of the initiator molecule, that is to say in the zone where the sensitivity of the initiator molecule is at least as great as for a wavelength L irr close to 2 times the wavelength L absR of resonance d absorption of a photon (fig. 7), as shown by the analysis of the two-photon absorption cross sections.
• the reaction is voluntarily positioned in the zone where the sensitivity of the initiator molecule is much greater only for a wavelength L irr close to 2 times the wavelength L abSR of absorption resonance of a photon (fig. 7).
• the absorption cross section for L irr wavelengths below 578 nm is greater than around 1000 GM (see fig. 7), or greater than the absorption cross section for wavelengths L irr in the vicinity of twice the absorption resonance wavelength L absR of a photon of the initiator molecule (approximately 650 GM at the wavelength 770 nm- see fig. 7).
• the absorption cross section for L irr wavelengths below 532 nm is greater than about 1500 GM, and increases further when L irr decreases.
• the results are less interesting than for PA2; in fact, the effective absorption section, for a given wavelength, is substantially lower for PA3 compared to PA2; for example, the absorption cross section for PA3 only reaches about 740 gm at 532 nm.
• the laser used for the tests described below is a pulsed laser with a frequency of 11.7 kHz, producing pulses of irradiation with a duration of 560 ps (picosecond). Additional tests have shown the applicability of the system on pulsed lasers producing pulses of irradiation with a duration of the order of nanoseconds (ns) and femtoseconds (fs), at wavelengths between 515 and 532 nm, with similar conclusions. Specifically, the additional lasers used have the following characteristics:
• the polymerization threshold minimum power of the irradiation signal necessary for polymerization
• the minimum size of the objects that can be produced by the method according to the invention It is considered that the polymerization threshold is reached when the structures photogenerated by the irradiation step can withstand a final rinsing step of the monomer residues without undergoing significant distortion.
• a first test (Fig 8c-d) consists of printing a series of 20 ⁇ m lines spaced 4 ⁇ m apart on a substrate; the laser is focused exactly or very slightly above the substrate, for an accurate measurement of the line width while ensuring adhesion of the lines on the substrate.
• a second test (Fig.
• 8a-b consists of printing 13 ⁇ m lines suspended between two pads 5 ⁇ m apart, to ensure good mechanical stability of the line; the lines are positioned 1.5 ⁇ m above the substrate. This second test makes it possible to determine the height of the lines, a parameter not accessible with the first test.
• the lines are made with decreasing irradiation powers, up to the limit of the polymerization threshold and the printing speed is the same, 40 pm/s.
• Figures 8a to 8d show more precisely, for composition 1.e, DPPFIA/DDA/PA2 (79.2%/19.8%/1%):
• FIG. 8a an overview of a suspended line, obtained from composition l.e, irradiated by an irradiation signal of power 103 pW,
• FIG. 8b a top view of suspended lines, obtained from composition l.e irradiated by a power irradiation signal decreasing from top to bottom from 257 pW to 82 pW,
• FIG. 8c a top view of a line written on a substrate, from composition 1.e, irradiated by an irradiation signal of power 85 pW
• FIG. 8d a top view of a series of lines written on the surface of a substrate from composition 1.e, irradiated by an irradiation signal with a power increasing from left to right from 75 pW to 303 pW.
• compositions comprising one of the three initiator molecules BDEBP, ITX and OXE2, with compositions comprising:
• -Fig. 9a and Fig. 9b top view and enlarged top view of the periodic grid, produced by irradiating composition Ie with an irradiation signal with a power of 103 pW
• -Fig. 9c and Fig. 9d perspective view and overall view of a structure of the photonic crystal type, called a cubic “pile of wood”, produced by irradiating composition Ic with an irradiation signal of power 125 pW.
• the invention proposes a family of photoinitiating molecules for a photoinduced generation reaction with two photons of radicals, a composition comprising such molecules and a process for printing in three dimensions by irradiation of such photosensitive compositions, which in particular provide the following technical and economic benefits:
• the resins according to the invention for parallel writing, that is to say to simultaneously print several structures by means of several laser beams.
• the initial laser beam of the 3D printer can be separated into several beams by means of an optical diffractive element (EOD) placed on the optical path.
• EOD optical diffractive element

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