WO2024099798A1

WO2024099798A1 - Radiation curable compositions for additive manufacturing of high toughness articles

Info

Publication number: WO2024099798A1
Application number: PCT/EP2023/080047
Authority: WO
Inventors: Erwin PENG; Yili WU; Soumya Sarkar; Dinesh Kumar BASKER; Ma Monica Carlos DELA CRUZ
Original assignee: Evonik Operations GmbH
Current assignee: Evonik Operations GmbH
Priority date: 2022-11-08
Filing date: 2023-10-27
Publication date: 2024-05-16
Anticipated expiration: 2025-05-08
Also published as: TW202440661A

Abstract

A liquid radiation curable composition comprising component a) (30) to (50) weight percent of one or more reactive oligomer(s), said reactive oligomer(s) containing at least two urethane and/or urea linkages in the backbone and two ethylenic unsaturated group(s) which can form polymeric crosslink networks in the presence of radicals, anions, nucleophiles or combinations thereof, with a weight average molecular weight (Mw) of greater than 5000 g/mol; component b) (5) to (40) weight percent of one or more reactive monomer(s), said reactive monomer(s) containing one ethylenic unsaturated group capable of forming polymeric crosslinked networks in the presence of radicals, anions, nucleophiles or combinations thereof, the said reactive monomer(s) having at least one bicyclic non-aromatic hydrocarbon moiety and a glass transition temperature (Tg) of the cured reactive monomer(s) of greater than (80) °C; component c) (20) to (50) weight percent of one or more reactive monomer(s), said reactive monomer(s) containing at least one N-substituted (meth)acrylamide group capable of forming polymeric crosslinked networks in the presence of radicals, anions, nucleophiles or combinations thereof and the said monomer having a glass transition temperature (Tg) of the cured monomer(s) greater than (80) °C; component d) 0.01 to 10 weight percent of one or more photoinitiator(s) capable of producing radicals when irradiated with actinic radiation, component e) 0 to 30 weight percent of one or more additive(s) selected from the group consisting of filler(s), pigment(s), thermal stabilizer(s) or antioxidant(s), non-reactive diluent or solvent(s), UV light stabilizer(s), UV light absorber(s), radical inhibitor(s); with the provision that the composition has a viscosity of 8000 mPa.s at 25°C or less and that component c) of the liquid radiation curable composition is different from component b).

Description

Radiation Curable Compositions for Additive Manufacturing of High Toughness Articles

The present invention pertains to liquid radiation curable compositions suitable for additive manufacturing processes to obtain three dimensional objects with high toughness and good heat resistant properties.

Additive manufacturing (AM) technology through a photopolymerization process in which layer-by-layer solidification of liquid resinous materials by means of radiation curing (e.g. UV) to manufacture three- dimensional solid polymeric objects has tremendous potential for direct manufacturing of end-use parts.

VAT photopolymerization is a subset of additive manufacturing (AM) processes that builds three- dimensional objects or articles by selectively curing liquid resin through radiation or an actinic light source.

Liquid photopolymer resins generally are a class of thermoset material. Through the formulation chemistry, the liquid photopolymer resin is designed to mimic thermoplastic materials behavior after polymerization.

In the past, VAT photopolymerization relied on highly cross-linked materials that would result in objects or articles that are brittle network and are considered to have low toughness. Such brittleness and low toughness hindered VAT photopolymerization materials to be used for broader applications when compared with the thermoplastic materials.

High toughness materials are required to ensure that the printed objects or articles are able to absorb more energy before breaking and have the flexibility to be deformed with higher strain before breaking and are able to withstand moderate to high mechanical stress to deform.

Several attempts have been described in the prior art to achieve such high level of toughness with VAT photopolymerization processes.

WO2019213585A1 discloses a curable composition for use in a VAT photopolymerization process which comprises a toughness modifier that is a reactive or polymerizable oligomer with an average molecular weight greater than 5000 Da and a reactive diluent that is a reactive or polymerizable compound having a molecular weight of 100-1000 Da. Such combination will result in a solid or highly viscous resin formulation (1 K system) with a viscosity of 1 -70 Pa.s at 90°C-110°C. The polymerization process of such a composition can only be carried out in a high temperature lithography-based photopolymerization process (temperature range of 50°C - 120°C) which limits the use in typical VAT photopolymerization at room temperature.

US9453142B2, US9598606B2, US9676963B2 and US10350823B2 disclose the use of multiple cure mechanisms of hardening to obtain a three-dimensional object or articles. The resin composition comprises polyurethane or polyurea copolymer, silicone resin, epoxy resin or cyanate ester resin. These references rely on the use of polymerizable liquid resins that comprise at least one of a blocked or reactive blocked prepolymer or diisocyanate or chain extender. During the VAT photopolymerization, such reactive blocked component will be cured during the article formation, resulting in the first network formation. The solid objects or articles will undergo a secondary re-solidifying or curing step upon second radiation exposure (e.g. thermal) that results in the first network degradation, forming the necessary constituent for the second solidifiable component polymerization. While such dual-curing mechanism allow the formation of printed articles or objects with high toughness, the VAT photopolymerization process is often hindered by relative low pot-life of the resin composition and the lengthy processing workflow for the second polymerization process to be completed (e.g. oven baking).

US10316213B1 discloses a dual-cure resin technology that includes a photo-curable component configured to cure when subjected to actinic radiation and a secondary component that comprises a plurality of encapsulants containing a first and second secondary precursor species. The encapsulants are designed to degrade upon correct stimuli, releasing the secondary species for secondary curing to produce secondary polymer. The first secondary precursor species comprises of one of the chain extenders for polyurea or polyurethane formation, e.g. polyamine or polyol species while the second secondary precursor species comprises of diisocyanate or polyisocyanate species. While the encapsulation technology allows printed articles or objects to possess good toughness and impact resistant properties, the resin formulation and the encapsulants are sensitive to various stimuli such as humidity and elevated temperature which complicates the VAT photopolymerization process.

The prior art references demonstrate that 3D printed objects can possess high toughness and good thermomechanical properties. However, there are some limitations or challenges with these approaches presented in the prior art. For example, VAT photopolymerization and its post-processing process and resin composition shelf-life are often sacrificed to obtain high toughness and good thermomechanical materials performance. Alternative routes towards such high toughness and good thermomechanical materials performance therefore continue to be much needed.

It is therefore an object of the present invention to provide a liquid radiation curable composition suitable for VAT photopolymerization processes in which the disadvantages of prior art compositions are at least reduced and which provides a high degree of toughness and elongation at break of the manufactured three dimensional objects while still maintaining the simplicity of the VAT photopolymerization process without the need for sophisticated elevated temperature printing or multiple-curing mechanism.

This object is achieved with a liquid radiation curable composition comprising: component a) 30 to 50 weight percent of one or more reactive oligomer(s), said reactive oligomer(s) containing at least two urethane and/or urea linkages in the backbone and two ethylenic unsaturated group(s) which can form polymeric crosslink networks in the presence of radicals, anions, nucleophiles or combinations thereof, with a weight average molecular weight (/ T) of greater than 5000 g/mol; component b) 5 to 40 weight percent of one or more reactive monomer(s), said reactive monomer(s) containing one ethylenic unsaturated group capable of forming polymeric crosslinked networks in the presence of radicals, anions, nucleophiles or combinations thereof, the said reactive monomer(s) having at least one bicyclic non-aromatic hydrocarbon moiety and a glass transition temperature (T_g) of the cured reactive monomer(s) of greater than 80 °C; component c) 20 to 50 weight percent of one or more reactive monomer(s), said reactive monomer(s) containing at least one N-substituted (meth)acrylamide group capable of forming polymeric crosslinked networks in the presence of radicals, anions, nucleophiles or combinations thereof and the said monomer having a glass transition temperature (T_g) of the cured monomer(s) greater than 80 °C; component d) 0.01 to 10 weight percent of one or more photoinitiator(s) capable of producing radicals when irradiated with actinic radiation; component e) 0 to 30 weight percent of one or more additive(s) selected from the group consisting of filler(s), pigment(s), thermal stabilizer(s) or antioxidant(s), non-reactive diluent or solvents), UV light stabilizer(s), UV light absorber(s), radical inhibitor(s); with the provision that the composition has a viscosity of 8000 mPa.s at 25°C or less and that component c) of the liquid radiation curable composition is different from component b).

The sum of components a) to e) equals 100 weight percent.

The term “ethylenic unsaturated group” as used herein means a vinyl, allyl, itaconate or a (meth)acrylate group.

The term “(meth)acrylate group” means either a methacrylate group, an acrylate group or a mixture of both.

The term “N-substituted (meth)acrylamide group” means an acrylamide group, a methacrylamide group or a mixture of both in which either one or both hydrogen atoms attached to the nitrogen atom in the amide group of the (meth)acrylamide is substituted with an alkyl group.

As used herein oligomer means an intermediate of a polymerization reaction that involves two or more components.

The weight average molecular weight (M_w) is determined by gel permeation chromatography (GPC) measurement using tetrahydrofuran (THF) as eluent with PS/DVB (polystyrene divinylbenzene) column (size: 4.6mm I.D. x 15cm, particle size: 3pm) and PS/DVB (polystyrene divinylbenzene) guard column (size: 4.6mm I.D. x 2cm, particle size: 4pm) at a temperature of 40°C and a flow rate of 0.35 mL/min with refractive index detector. The sample concentration is 5 to 6 mg/mL in THF with injection amount of 20 pL. The weight average molecular weights are calculated relative to polystyrene standard.

The glass transition temperature (T_g) is determined in accordance with ASTM D3418.

The viscosity is measured using a rotational rheometer equipped with a cone plate (2°) at 25°C and reading is obtained at 1 Hz shear rate.

Various engineering applications such as automotive or aerospace demand for 3D printed objects or articles to exhibit excellent thermomechanical properties as close as possible to the thermomechanical properties of commodity and engineering thermoplastic obtained from conventional injection molding. VAT photopolymerization technology which commonly utilizes (meth)acrylate-based and/or (meth)acrylamide-based thermoset resin chemistry often experience auto-acceleration during the early phase of chain growth (free radical) polymerization whereby the termination reactions are mobility restricted. As such, the resultant networks are inhomogeneous, exhibit high brittleness, are high in crosslink density and are less efficient in dissipating stress (Bagheri, A, Jin, J.: Photopolymerization in 3D Printing. ACS Appl. Polym. Mater. 2019, 1 , 4, 593-611).

Surprisingly it could be shown that the liquid radiation curable composition according to the invention containing (meth)acrylate and (meth)acrylamide photocrosslinkable moieties can attain printed three- dimensional objects with a high tensile toughness of greater or equal than 45 J/m³ while having high flexibility shown as an elongation at break of greater or equal than 150% and a high heat deflection temperature (HDT) at 0.455MPa of greater or equal than 45°C.

The liquid radiation curable composition according to the invention allows for the first time to produce three-dimensional objects with high tensile toughness that are not brittle, have high flexibility, good resistance to load at elevated temperatures without the need for multiple curing steps and a viscosity of the composition allowing processing at room temperature. Such properties were not possible to achieve in the prior art.

Preferably the liquid radiation curable composition according to the invention has a viscosity of 5000 mPa.s at 25°C or less.

Component a):

Preferably the weight average molecular weight (M_w) of component a) ranges from 5000 g/mol to 50000 g/mol, more preferably 5000 g/mol to 30000 g/mol and most preferably 5000 g/mol to 25000 g/mol.

Component a) of the liquid radiation curable composition according to the invention comprises one or more reactive oligomers containing at least two urethane and/or urea linkages in the backbone. Said urethane and/or urea linkages in the reactive oligomer(s) of component a) are preferably obtained by reacting aliphatic or aromatic diisocyanate with polyesters polyols, polyether polyols or polyamines to form an amine-Zhydroxyl-terminated or isocyanate-terminated polyurethane/urea intermediate. The urethane and/or urea linkages in the reactive oligomer(s) of component a) can also be obtained by reacting aliphatic or aromatic diisocyanate with mixtures of two or more of polyesters polyols, polyether polyols and/or polyamines.

The amine-Zhydroxyl-terminated polyurethane/urea intermediate is preferably reacted with an isocyanate-functionalized (meth)acrylate or the isocyanate-terminated polyurethane/urea intermediate is reacted with a hydroxyl-functionalized (meth)acrylate to form component a).

Component a) obtained from that reaction preferably has the following structure:

With Ri being a hydrocarbon residue from the reaction of aliphatic or aromatic diisocyanate with polyester or polyether polyol or polyamine, R2 is a hydrocarbon residue formed by the reaction of aliphatic or aromatic diisocyanate with a polyester polyol or a polyether polyol, R3 is a hydrocarbon residue formed by the reaction of aliphatic or aromatic diisocyanate with polyester polyol, polyether polyol or diamine. X is either H or CH3, Y is O and Z is either O or NH and Y can be the same or different than Z, n is an integer ranging from 1 to 100 and m is an integer ranging from 0 to 100.

More preferably component a) of the liquid radiation curable composition according to the invention comprises one or more reactive oligomers containing only urethane linkages and no urea linkages in the backbone. Said urethane linkages in the reactive oligomer(s) of component a) are preferably obtained by reacting polyester polyol with aliphatic or aromatic diisocyanate to form a hydroxyl-terminated or isocyanate-terminated polyurethane intermediate. The hydroxyl-terminated polyurethane intermediate is reacted with an isocyanate-functionalized (meth)acrylate or the isocyanate-terminated polyurethane intermediate is reacted with a hydroxyl-functionalized (meth)acrylate to form component a).

Component a) obtained from the reaction of the hydroxyl-terminated or isocyanate-terminated polyurethane intermediate with isocyanate-functionalized or hydroxyl-functionalized (meth)acrylate has the following structure:

With R4 being a hydrocarbon residue from the reaction of aliphatic or aromatic diisocyanate with polyester polyol. R5 is a hydrocarbon residue formed by the reaction of a polyester polyol with aliphatic or aromatic organic difunctional acids or anhydrides. Re is a hydrocarbon residue formed by aliphatic or aromatic organic difunctional acids or anhydrides after reaction with a polyol. X is either H or CHs, n is an integer ranging from 1 to 100, p is an integer ranging from 1 to 100.

The polyester polyol is preferably obtained from the reaction of aliphatic or aromatic organic difunctional acids or anhydrides or mixtures thereof with a polyol. The polyol is preferably a short chain polyol. The term “short chain polyols” as used herein means polyols with a molecular weight of less than 2000 g/mol. The short chain polyol preferably carries two primary OH groups.

The aliphatic or aromatic difunctional organic acid(s) or anhydrides used to prepare the polyester-polyol may be cycloaliphatic or heterocyclic in nature. The aliphatic or aromatic organic difunctional acid(s) or anhydrides can be optionally substituted with halogen atoms and/or be unsaturated. The preferred aliphatic or aromatic organic difunctional acids or anhydrides are selected from the group consisting of succinic acid, adipic acid, suberic acid, azelaic acid, sebacic acid, phthalic acid, terephthalic acid, isophthalic acid, dichlorophthalic acid, glutaric acid, 1 ,4-cyclohexanedicarboxylic acid, and — where obtainable — their anhydrides or esters.

The polyols used to prepare the polyester-polyol are preferably selected from the group consisting of monoethylene glycol, 1 ,2- and 1 ,3-propylene glycol, 1 ,4- and 2,3-butylene glycol, di-p- hydroxyethylbutanediol, 1 ,5-pentanediol, 1 ,6-hexanediol, 1 ,8-octanediol, decanediol, dodecanediol, neopentyl glycol, cyclohexanediol, 3(4),8(9)-bis(hydroxymethyl)tricyclo[5.2.1 .02,6]decane (Dicidol), 1 ,4- bis(hydroxymethyl)cyclohexane, 2,2-bis(4-hydroxycyclohexyl)propane, 2,2-bis[4-(p- hydroxyethoxy)phenyl]propane, 2-methylpropane-1 ,3-diol, 2-methyl-pentane-1 ,5-diol, 2, 2, 4(2, 4,4)- trimethylhexane-1 ,6-diol and also diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, polypropylene glycols, polybutylene glycols, xylylene glycol, and neopentyl glycol hydroxy pivalate.

In another preferred embodiment the urethane linkages in the reactive oligomer(s) of component a) are obtained by reacting polyether polyol, with aliphatic or aromatic diisocyanate to form a hydroxylterminated or isocyanate-terminated polyurethane intermediate. The polyether polyols are preferably selected from the group consisting of polyethylene glycol, polypropylene glycol, polypropylene glycolethylene glycol copolymer, polytetramethylene glycol, polyhexamethylene glycol, polyheptamethylene glycol and polydecamethylene glycol.

The hydroxyl-terminated polyurethane intermediate is reacted with an isocyanate-functionalized (meth)acrylate or the isocyanate-terminated polyurethane intermediate is reacted with a hydroxylfunctionalized (meth)acrylate to form component a).

Component a) of that reaction has the following structure:

With the provision that Rz is a hydrocarbon residue after the reaction of aliphatic or aromatic diisocyanate with polyether polyol, Rs is a hydrocarbon residue formed by the reaction of aliphatic or aromatic diisocyanate with polyether polyol, X is either H or CHs, Y is O, q is an integer ranging from 1 to 100.

Preferably the aliphatic and aromatic diisocyanates are selected from the group consisting of 5- lsocyanato-1-(isocyanatomethyl)-1 ,3,3-trimethylcyclohexane (isophorone diisocyanate), 1 ,6- diisocyanatohexane, 1 ,3-Bis(2-isocyanatopropan-2-yl)benzene, 2,2,4-trimethylhexane diisocyanate, 2,4,4-trimethylhexane diisocyanate, pentane diisocyanate, 4,4’- methylene bis(cyclohexyl isocyanate), 4-Methyl-1 ,3-phenylene diisocyanate, 2,2'-methylenebis(phenyl isocyanate), 2,4'-methylenebis(phenyl isocyanate), 4,4'-methylenebis(phenyl isocyanate) and mixtures thereof.

The polyamines used for obtaining component a) preferably have two primary amine groups at the terminus. Said polyamines according to the invention can be of low(er) molecular weight such as aromatic amine (e.g. diethyl-toluenediamine, dimethylthio-toluenediamine, N,N’-di(sec.butyl)- aminobiphenyl methane) or aliphatic amines (e.g. diethylenetriamine, triethylene tetraamine) which usually act as chain extender. The polyamines used for obtaining component a) can also be of high(er) molecular weight such as amine-terminated ethylene or propylene oxide based polyethers (e.g. Jeffamines®).

Component b):

Component b) of the liquid radiation curable composition according to the invention comprises one or more reactive monomer(s) with a glass transition temperature (T_g) of the cured reactive monomer(s) of greater than 80 °C. Preferably the glass transition temperature (T_g) of the cured reactive monomer(s) ranges from 80°C - 250°C, more preferably from 80°C - 220°C and most preferably from 80°C - 190°C.

The reactive monomer(s) of component b) are preferably selected from the group consisting of isobornyl acrylate, isobornyl methacrylate, isoborncyclohexyl acrylate, and isoborncyclohexyl methacrylate.

Component c):

Component c) of the liquid radiation curable composition according to the invention comprises one or more reactive monomer(s) with a glass transition temperature (T_g) of the cured reactive monomer(s) of greater than 80°C. Preferably the glass transition temperature (T_g) of the cured reactive monomer(s) ranges from 80°C - 200°C, more preferably from 80°C - 180°C and most preferably from 80°C - 160°C.

The reactive monomer(s) of component c) contain at least one A/-substituted (meth)acrylamide group capable of forming polymeric crosslinked networks in the presence of radicals, anions, nucleophiles or combinations thereof. Preferably the reactive monomer(s) contain at least one A/-substituted (meth)acrylamide group in which both hydrogen atoms attached to the nitrogen atom in the amide group of the (meth)acrylamide are substituted with alkyl groups forming a ring.

In another preferred embodiment of the invention component c) of the radiation curable liquid composition is selected from the group consisting of 4-acrylolmorpholine, A/,A/-dimethyl acrylamide, N,N- diethyl acrylamide, A/-isopropyl acrylamide, A/,A/-dimethylaminopropyl acrylamide, A/-hydroxyethyl acrylamide, diacetone acrylamide and mixtures thereof.

Component d):

Component d) of the liquid radiation curable composition is a photoinitiator or a mixture of photoinitiators capable of producing radicals when irradiated with actinic radiation. The amount of photoinitiator added to the liquid radiation curable composition according to the invention ranges from 0.01 % to 10% weight of the total liquid formulation. Preferably the actinic radiation source irradiating the said photoinitiator(s) is a mercury lamp or a LED source that has an emission wavelength between 230 nm to 600 nm, more preferably 300nm to 460nm.

Preferably component d) is a free radical photoinitiator, more preferably the free radical photoinitiator is an aromatic ketone type photoinitiator or a phosphine oxide type photoinitiator.

Aromatic ketone type photoinitiators are preferably selected from the group consisting of 1- hydroxycyclohexyl phenyl ketone, 2-hydroxy-l-(4-(4-(2-hydroxy-2- methylpropionyl) benzyl)phenyl-2- methylpropan- 1 -one, 2-hydroxy-2-methyl- 1 - phenylpropanone, 2-hydroxy-2-methyl-l-(4- isopropylphenyl)propanone, oligo (2- hydroxy -2 -methyl- 1 -(4-(l -methylvinyl)phenyl)propanone, 2- hydroxy-2-methyl- 1 -(4- dodecylphenyl)propanone, 2-hydroxy-2-methyl-l-[(2- hydroxyethoxy)phenyl]propanone, benzophenone, substituted benzophenones, 2,2 -Dimethoxy-1 ,2- diphenylethanone or mixtures thereof.

Phosphine type photoinitiators are preferably selected from the group consisting of diphenyl(2,4,6- trimethylbenzoyl) phosphine oxide (TPO), phenylbis(2,4,6-trimethylbenzoyl) phosphine oxide (BAPO) or Ethyl phenyl(2,4,6-trimethylbenzoyl)phosphinate (TPO-L) or mixtures thereof.

Component e):

The liquid, radiation curable composition according to the invention may comprise one or more additive(s) selected from the group consisting of filler(s), pigment(s), thermal stabilizer(s) or antioxidant(s), non-reactive diluent or solvents), UV light stabilizer(s), UV light absorber(s), radical inhibitor(s). Filler(s) may be inorganic or organic particles or mixtures of both. Preferably filler(s) are nano-sized to micron-sized inorganic particles selected from the group consisting of silica, alumina, zirconia, titania or mixtures thereof. In case the filler(s) include organic particles, such nano-sized to micron-sized organic particles are selected from the group consisting of poly (methyl methacrylate), poly(vinyl alcohol), poly(vinyl butyrate), polyamide, polyimide or mixtures thereof.

Solvents) or non-reactive diluent(s) that may be present are for example n- hexane, n- heptane, n- octane, cyclohexane, cyclopentane, toluene, xylene, ethylbenzene, methanol, ethanol, n- butanol, ethylene glycol monomethyl ether, propylene glycol monomethyl ether, ethyl acetate, n- butylacetate, n- amyl acetate, ethylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, acetone, methyl ethyl ketone, methyl isobutyl ketone, methyl n- amyl ketone, cyclohexanone, diethylene glycol dimethyl ether, diethylene glycol dibutyl ether, 1 , 2 -dimethoxyethane, tetrahydrofuran, dioxane, N- methylpyrrolidone, dimethylformamide, dimethylacetamide, ethylene carbonate and water.

Suitable thermal stabilizers) or antioxidants are preferably selected from the group consisting of phenolic primary antioxidant (e.g. Pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), 3,5- Bis(1 ,1-dimethylethyl)-4-hydroxybenzenepropanoic acid thiodi-2,1 -ethanediyl ester, octadecyl-3-[3,5-di- tert-butyl-4-hydroxyphenyl]propionate], Diethyl 3,5-di-tert-butyl-4-hydroxybenzylphosphonate or mixture thereof).

Suitable UV light absorbers are preferably selected from the group consisting of 2-isopropylthioxanthone, 1-phenylazo-2-naphtol as well as optical brightener such as 2,5-bis- (5-tert-butyl-2-benzoxazolyl) thiophene, 4, 4'-bis(2-methoxystyryl)-1 ,1 '-biphenyl.

Suitable UV light stabilizers are preferably selected from the group consisting of 2,2,6, 6-Tetramethyl-4- piperidinol; bis(2,2,6,6,-tetramethyl-4-piperidyl)sebaceate; bis (1 , 2, 2, 6, 6-pentamethyl-4-piperidyl) sebacate and Methyl 1 , 2, 2, 6, 6- pentamethyl-4- piperidyl sebacate; decanedioic acid, bis (2, 2,6,6- tetramethyl-1- (octyloxy)-4-piperidinyl) ester; bis (1 ,2,2,6, 6-pentamethyl-4-piperidinyl)-[[3, 5-bis (1 , 1- dimethylethyl)-4- hydroxyphenyl]methyl] butylmalonate or mixtures thereof.

A radical inhibitor can be added to provide additional thermal stability. Suitable radical inhibitors are methoxyhydroquinone (MEHQ) or various aryl compounds like butylated hydroxytoluene (BHT).

The liquid radiation curable composition according to the invention is especially suitable to be used in additive manufacturing processes especially in VAT photopolymerization processes. Such additive manufacturing processes usually comprise the repeated steps of deposition or layering and irradiating the composition to form a three-dimensional object.

Irradiation can be provided by an actinic light source that has an emission wavelength between 230 nm to 600 nm. The irradiation during printing can be in the form of laser (e.g. in stereolithography or SLA), projection (e.g. in digital light processing or DLP) or mask-projection/illumination (e.g. when liquid crystal display or LCD is used as a mask). In a preferred embodiment of the invention, the total actinic irradiation dose required for the curing of the liquid radiation curable composition per layer is greater than 5 mJ/cm² per layer 100 pm layer thickness. The total actinic irradiation dose can be up to 100 mJ/cm² for a 100 pm layer thickness print setting. Preferably if the total actinic irradiation is between 5 mJ/cm² and 70 mJ/cm² at 100 pm layer thickness. More preferably if the total actinic irradiation is between 5 mJ/cm² and 40 mJ/cm² at 100 pm layer thickness. For a commercial DLP 3D printer that has light intensity of 4 mW/cm², 10 mJ/cm² per layer is equivalent to 2.5 seconds of total irradiation process per layer curing. When other layer thickness print setting is used (e.g. 10 pm, 20 pm and 50 pm), the total actinic irradiation dose required for the curing of the liquid radiation curable composition per layer must be scaled accordingly.

The additive manufacturing process that uses the liquid radiation curable composition according to the invention may comprise additional process steps like cleaning, washing, sonication, additional dosage of radiation, heating, polishing, coating or combinations thereof.

As mentioned above it was unexpectedly found that the liquid radiation curable composition can attain printed three-dimensional objects with unique properties having high tensile toughness and at the same time high elongation at break and a high heat deflection temperature.

Thus, the invention also encompasses a three-dimensional object formed by an additive manufacturing process using the liquid radiation curable composition according to the invention. Such a three- dimensional object printed using the liquid radiation curable composition according to the invention exhibits an elongation at break of 150% to 400% according to ASTM D638, a tensile toughness of 45 J/m³ to 100 J/m³ according to ASTM D638, a heat deflection temperature (HDT) at 0.455MPa of 45°C to 100°C according to ASTM D648.

Preferably, the elongation at break of the three-dimensional object formed by an additive manufacturing process using the liquid radiation curable composition according to the invention in XY direction differs no more than 30% from the elongation at break and tensile toughness in Z direction.

Examples

The subject matter of the present invention is illustrated in more detail in the following examples and without any intention that the subject matter of the present invention be restricted to these examples.

The liquid radiation curable resin composition was prepared by mixing the ingredients as mentioned in the tables below in a mixing equipment. The thus prepared resin composition was used to generate three-dimensional test specimens through a DLP 3D printing process (Asiga Max 62 with light source of either 385 nm or 405 nm wavelength) with an actinic irradiation between 5 and 40 mJ/cm²) per 100 micron layer thickness. 3D printing was carried out at temperatures between 25°C to 45°C. Where applicable, lowest possible processing temperature is preferred. Elongation at break, heat deflection temperature and tensile toughness are determined using said printed, washed and UV post-cured three-dimensional test specimen with dimension and shape in accordance with the respective ASTM standards.

Table A summarizes the abbreviations used for ingredients in the following examples.

Table A: Abbreviations of the ingredients used for liquid radiation curable compositions Table B list the components a) used for the liquid radiation curable compositions in the following examples. Functionality means the number of ethylenic unsaturated groups in component a).

Table B. List of component a)

Component a) designated as EP01 is an aliphatic urethane diacrylate synthesized in accordance with the procedure described in WO 2021/122058 A1 . EP02 to EP08 are commercially available oligomers used as component a) in the liquid radiation curable compositions as described in the following examples. For component a) denominated as EP07 the molecular weight Mw was not determined as oligomers with four acrylates are already out of scope for component a) of a composition according to the invention.

Elongation at break of the printed, washed and UV post-cured specimen was determined according to ASTM D638 (Type V specimen).

All specimens’ dimensions were in accordance with the standard dimension recommended in the respective ASTM documents. All specimens were subjected to identical post-curing condition: (i) simultaneous UV and thermal post-curing condition at 80°C for 120 minutes with minimal combined light intensity of 10 mW/cm² at 405nm wavelength, followed by (ii) thermal post-treatment in the oven at 80°C for 3 hours.

The tensile toughness was determined from the area under the stress-strain curve of the specimen measured according to ASTM D638 (Type V specimen). A tensile testing machine from Instron, 3300 series with automatic extensometer was used to record the stress-strain curve of the specimen.

Heat deflection temperature (HDT) of the printed, washed and UV post-cured specimen is measured at an applied stress of 0.45 MPa (66 psi) according to ASTM D648 Method B.

The viscosity of the final liquid radiation curable composition is measured using rotational rheometer equipped with cone plate (2°) and reading is obtained at 1 Hz shear rate. Unless otherwise indicated viscosity is measured at a temperature of 25°C.

Example 1

Example 1 encompasses liquid radiation curable composition 1A, 1 B, 1C, 1 D, 1 E, 1 F and 1 G. All liquid radiation curable compositions comprise TPO (Diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide) as component d).

Composition 1A comprises as component a) an aliphatic urethane diacrylate (EP01) with a weight average molecular weight of 18700 g/mol, component b) IBoA and component c) ACMO.

Composition 1 B comprises as component a) an aliphatic urethane diacrylate (EP01) with a weight average molecular weight of 18700 g/mol, component b) IBoMA and component c) ACMO.

Composition 1 C comprises as component a) a commercially available aliphatic urethane diacrylate (EP02) with a weight average molecular weight of 5020 g/mol, component b) IBoA and component c) ACMO.

Composition 1 D comprises as component a) an aliphatic urethane diacrylate (EP03) with a weight average molecular weight of 9993 g/mol, component b) IBoMA and component c) ACMO. Composition 1 E comprises as component a) an aliphatic urethane diacrylate (EP04) with a weight average molecular weight of 10820 g/mol, component b) IBoA and component c) ACMO.

Composition 1 F comprises as component a) an aliphatic urethane diacrylate (EP05) with a weight average molecular weight of 14832 g/mol, component b) IBoA and component c) ACMO. Composition 1 G comprises as component a) an aliphatic urethane diacrylate (EP06) with a weight average molecular weight of 30524 g/mol, component b) IBoA and component c) ACMO.

Table 1 : Liquid radiation curable compositions 1A - 1 G and properties of printed specimens

The viscosity of the compositions 1A, 1 B, 1C, 1 D, 1 E, 1 F and 1G were 1550 mPa.s, 1490 mPa.s, 788 mPa.s, 322 mPa.s, 602 mPa.s, 1310 mPa.s, 4660 mPa.s at 25°C and therefore within the required range of less than 5000 mPa.s at 25°C.

Printed specimens of Composition 1A, 1 B, 1C, 1 D, 1 E, 1 F and 1G according to the invention show an elongation at break between 150% to 400% measured according to ASTM D638, a heat deflection temperature (HDT) at 0.455MPa between 45°C to 100°C according to ASTM D648 and a tensile toughness of greater than 45 J/m³ measured according to ASTM D638. Example 2

Example 2 is a comparative example encompassing liquid radiation curable compositions 2A and 2B. All liquid radiation curable compositions of Example 2 comprise TPO (Diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide) as component d).

Composition 2A comprises component a) an aliphatic urethane tetraacrylate (EP07), component b) IBoA and component c) ACMO.

Composition 2B comprises component a) an aliphatic urethane tetraacrylate (EP07), component b) IBoMA and component c) ACMO.

Table 2: Liquid radiation curable compositions 2A and 2B and properties of printed specimens

The viscosity of the composition 2A was 1150mPa.s and 2B 1120 mPa.s at 25°C and therefore within the required range of less than 5000 mPa.s at 25°C.

Printed specimens of composition 2A and 2B are in the required range of heat deflection temperature of between 45°C to 100°C but neither specimen reaches the required elongation at break of 150% to 400% nor the tensile toughness of 45 J/m³ to 100 J/m³. Comparative examples 2A and 2B show the criticality of having a component a) with two ethylenic unsaturated groups. EP07 used as component a) has four acrylate groups and it is therefore out of the inventive range of two ethylenic unsaturated groups.

Example 3

Example 3 encompasses liquid radiation curable composition 3A. Composition 3A comprises as component a) an aliphatic urethane diacrylate (EP08) with a weight average molecular weight of 3060 g/mol, component b) IBoMA and component c) ACMO.

Table 3: Composition 3A for liquid radiation curable resin for 3D printing

The viscosity of the composition 3A was 1100 mPa.s at 25°C and therefore within the required range of less than 5000 mPa.s at 25°C.

A printed specimen of composition 3A lies in the required range of heat deflection temperature of between 45°C to 100°C but does neither reach the required elongation at break of 150% to 400% nor the tensile toughness of 45 J/m³ to 100 J/m³. Comparative Example 3 shows the criticality of the weight average molecular weight Mw of component a. While EP08 has two acrylate groups the weight average molecular weight Mw lies below the required 5000 g/mol according to the invention.

Example 4

Example 4 encompasses liquid radiation curable compositions 4A to 4E.

Composition 4A and 4B comprises as component a) an aliphatic urethane diacrylate (EP06) with a weight average molecular weight of 30524 g/mol, component b) IBoA and either CTFA orTMCHA as component c). Neither CTFA nor TMCHA are N-substituted.

Composition 4C comprises as component a) an aliphatic urethane diacrylate (EP06) with a weight average molecular weight of 30524 g/mol, component b) IBoA and component c) ACMO. Component c) which is below the claimed range of 20 wt% - 50 wt %.

Composition 4D and 4E comprise as component a) an aliphatic urethane diacrylate (EP06) with a weight average molecular weight of 30524 g/mol, component b) IBoA and component c) ACMO. Component a) below the claimed range of 30 wt% - 50 wt % and component c) is above the claimed range of 20 wt % - 50 wt%.

Table 4: Liquid radiation curable compositions 4A to 4E and properties of printed specimens

The viscosity of the composition 4A was 5530 mPa.s at 25°C and did not meet the required range of less than 5000 mPa.s at 25°C. The viscosity of the composition 4B, 4C, 4D and 4E were 3960 mPa.s, 4930 mPa.s, 1310 mPa.s and 499 mPa.s at 25°C and therefore within the required range of less than 5000 mPa.s at 25°C.

A printed specimen of composition 4A neither reaches the required range of heat deflection temperature of between 45°C to 100°C, nor the required elongation at break of 150% to 400% and also not the tensile toughness of 45 J/m³ to 100 J/m³.

A printed specimen of composition 4B lies in the required range of elongation at break of 150% to 400% and the required heat deflection temperature of between 45°C to 100°C but does not reach the required tensile toughness of 45 J/m³ to 100 J/m³.

Printed specimens of composition 4C, 4D and 4E are in the claimed range of heat deflection temperature of between 45°C to 100°C but neither reach the required elongation at break of 150% to 400% and nor the required tensile toughness of 45 J/m³ to 100 J/m³.

Example 5

For example 5 composition 1 F was used which was printed in XY direction (parallel to the printer platform direction) and another specimen was printed in Z direction (perpendicular to the printer platform direction).

Table 5: Properties of printed specimens printed in XY and in Z direction).

Printed specimens of composition 1 F printed in XY direction and printed in Z direction are in the required range of elongation at break of 150% to 400%, tensile toughness of 45 J/m³ to 100 J/m³ and heat deflection temperature of 45°C to 100°C. Neither elongation at break nor tensile toughness or heat deflection temperature differ more than 30% between printing in XY direction and printing in Z direction.

Claims

Claims:

1 . A liquid radiation curable composition comprising: component a) 30 to 50 weight percent of one or more reactive oligomer(s), said reactive oligomer(s) containing at least two urethane and/or urea linkages in the backbone and two ethylenic unsaturated group(s) which can form polymeric crosslink networks in the presence of radicals, anions, nucleophiles or combinations thereof, with a weight average molecular weight (M_w) of greater than 5000 g/mol; component b) 5 to 40 weight percent of one or more reactive monomer(s), said reactive monomer(s) containing one ethylenic unsaturated group capable of forming polymeric crosslinked networks in the presence of radicals, anions, nucleophiles or combinations thereof, the said reactive monomer(s) having at least one bicyclic non-aromatic hydrocarbon moiety and a glass transition temperature (T_g) of the cured reactive monomer(s) of greater than 80 °C; component c) 20 to 50 weight percent of one or more reactive monomer(s), said reactive monomer(s) containing at least one N-substituted (meth)acrylamide group capable of forming polymeric crosslinked networks in the presence of radicals, anions, nucleophiles or combinations thereof and the said monomer having a glass transition temperature (T_g) of the cured monomer(s) greater than 80°C; component d) 0.01 to 10 weight percent of one or more photoinitiator(s) capable of producing radicals when irradiated with actinic radiation, component e) 0 to 30 weight percent of one or more additive(s) selected from the group consisting of filler(s), pigment(s), thermal stabilizers) or antioxidant(s), non-reactive diluent or solvents), UV light stabilizer(s), UV light absorber(s), radical inhibitors); with the provision that the composition has a viscosity of 8000 mPa.s at 25°C or less and that component c) of the liquid radiation curable composition is different from component b).

2. The liquid radiation curable composition according to claim 1 , characterized in that the viscosity of the composition 5000 mPa.s at 25°C or less.

3. The liquid radiation curable composition according to claim 1 , characterized in that the urethane and/or urea linkages in the reactive oligomer(s) of component a) are obtained by reacting aliphatic or aromatic diisocyanate with polyester polyol, polyether polyol or polyamine to form amine-Zhydroxyl-terminated or isocyanate-terminated polyurethane/urea intermediate. The liquid radiation curable composition according to claim 3, characterized in that the amine- /hydroxyl-terminated polyurethane/urea intermediate is reacted with an isocyanate- functionalized (meth)acrylate or the isocyanate-terminated polyurethane/urea intermediate is reacted with a hydroxyl-functionalized (meth)acrylate to form component a). The liquid radiation curable composition according to claim 4, characterized in that component a) has the following structure:

With Ri being a hydrocarbon residue from the reaction of aliphatic or aromatic diisocyanate with polyester polyol or polyether polyol or polyamine, R2 is a hydrocarbon residue formed by the reaction of aliphatic or aromatic diisocyanate with a polyester polyol or a polyether polyol, R3 is a hydrocarbon residue formed by the reaction of aliphatic or aromatic diisocyanate with polyester polyol, polyether polyol or diamine. X is either H or CH3, Y is O and Z is either O or NH and Y can be the same or different than Z, n is an integer ranging from 1 to 100 and m is an integer ranging from 0 to 100. The liquid radiation curable composition according to claim 1 , characterized in that the urethane linkages in the reactive oligomer(s) of component a) are obtained by reacting polyester polyol with aliphatic or aromatic diisocyanate to form a hydroxyl-terminated or isocyanate-terminated polyurethane intermediate. The liquid radiation curable composition according to claim 6, characterized in that the hydroxyl- terminated polyurethane intermediate is reacted with an isocyanate-functionalized (meth)acrylate or the isocyanate-terminated polyurethane intermediate is reacted with a hydroxyl-functionalized (meth)acrylate to form component a). The liquid radiation curable composition according to claim 7, characterized in that component a) has the following structure:

With R4 being a hydrocarbon residue from the reaction of aliphatic or aromatic diisocyanate with polyester polyol, R5 is a hydrocarbon residue formed by the reaction of a polyester polyol with aliphatic or aromatic organic difunctional acids or anhydrides, Re is a hydrocarbon residue formed by aliphatic or aromatic organic difunctional acids or anhydrides after reaction with a polyol, X is either H or CHs, n is an integer ranging from 1 to 100, p is an integer ranging from 1 to 100. The liquid radiation curable composition according to claim 1 , characterized in that the urethane linkages in the reactive oligomer(s) of component a) are obtained by reacting polyether polyol with aliphatic or aromatic diisocyanate to form a hydroxyl-terminated or isocyanate-terminated polyurethane intermediate. The liquid radiation curable composition according to claim 9, characterized in that the hydroxyl- terminated polyurethane intermediate is reacted with an isocyanate-functionalized (meth)acrylate or the isocyanate-terminated polyurethane intermediate is reacted with a hydroxyl-functionalized (meth)acrylate to form component a). The liquid radiation curable composition according to claim 10, characterized in that component a) has the following structure:

With the provision that R is a hydrocarbon residue after the reaction of aliphatic or aromatic diisocyanate with polyether polyol, Rs is a hydrocarbon residue formed by the reaction of aliphatic or aromatic diisocyanate with polyether polyol, X is either H or CHs, Y is O, q is an integer ranging from 1 to 100. The liquid radiation curable composition according to any one of claims 3 to 11 , characterized in that the aliphatic and aromatic diisocyanates are selected from the group consisting of 5- lsocyanato-1-(isocyanatomethyl)-1 ,3,3-trimethylcyclohexane (isophorone diisocyanate), 1 ,6- diisocyanatohexane, 1 ,3-Bis(2-isocyanatopropan-2-yl)benzene, 2,2,4-trimethylhexane diisocyanate, 2,4,4-trimethylhexane diisocyanate, pentane diisocyanate, 4,4’- methylene bis(cyclohexyl isocyanate), 4-Methyl-1 ,3-phenylene diisocyanate, 2,2'-methylenebis(phenyl isocyanate), 2,4'-methylenebis(phenyl isocyanate), 4,4'-methylenebis(phenyl isocyanate) and mixtures thereof. The liquid radiation curable composition according to claim 1 , characterized in that component b) is selected from the group consisting of isobornyl acrylate, isobornyl methacrylate, isoborncyclohexyl acrylate, isoborncyclohexyl methacrylate and mixtures thereof. 14. The liquid radiation curable composition according to claim 1 , characterized in that component c) is selected from the group consisting of 4-acrylolmorpholine, A/,A/-dimethyl acrylamide, N,N- diethyl acrylamide, A/-isopropyl acrylamide, A/,A/-dimethylaminopropyl acrylamide, N- hydroxyethyl acrylamide, diacetone acrylamide and mixtures thereof.

15. Use of the liquid radiation curable composition of claims 1 to 14 in an additive manufacturing process that comprises the repeated steps of deposition or layering and irradiating the composition to form a three-dimensional object.

16. Use of the liquid radiation curable composition according to claim 15, characterized in that the additive manufacturing process comprises the additional steps of cleaning, washing, sonication, additional dosage of radiation, heating, polishing, coating or combinations thereof.

17. A three-dimensional object formed by an additive manufacturing process using a liquid radiation curable composition according to any one of claims 1 to 14, characterized in that the three- dimensional object has: an elongation at break of 150% to 400% according to ASTM D638, a tensile toughness of 45 J/m³ to 100 J/m³ according to ASTM D638, a heat deflection temperature (HDT) at 0.455MPa of 45°C to 100°C according to ASTM D648.

18. The three-dimensional object according to claim 17, characterized in that the elongation at break, tensile toughness and heat deflection temperature of the three-dimensional object measured according to ASTM D638 in XY direction and in Z direction differs not more than 30% from each other.