Radiation-curable resin composition used for manufacturing three-dimensional mold

Abstract

This disclosure relates to a radiation-curable composition comprising (a) at least one light polymerizable liquid; (b) at least one spherical inorganic particle having an average particle size D50 of from 50 to 2000 nm; (c) at least one photoinitiator.

Description

[0001] Radiation-curable Resin Composition used for manufacturing three-dimensional mold

[0002] Technology Field

[0003] The present invention relates to the technical field of chemical materials for three-dimensional (hereinafter referred to as “3D”) printing, and in particular relates to a radiation-curable composition comprising spherical inorganic particle. The present invention further relates to a process of forming 3D objects by using the composition, and to 3D objects formed by using the composition.

[0004] Background

[0005] 3D printing or additive manufacturing (AM) is a manufacturing method that seeks to avoid traditional manufacturing techniques that are either subtractive (i.e. machining and ablation) or formative (i.e. molding and casting), and in doing so leverages considerable benefits in terms of design freedom. Radiation curable photopolymer is a class of 3D printable materials which have been widely used in various applications including prototyping of plastic parts, metal investment casting, dental applications, etc. Up to date, the radiation curable photopolymers on the market are suitable in making prototypes and demonstrations but may not be adequate for real applications that require thermal and mechanical properties. To bridge the gap from prototyping to real manufacturing, it is critical to have advanced materials with specific properties dictated by targeted industrial applications.

[0006] 3D printing can be an effective way to manufacture molds, which usually requires the material to possess adequate thermal deflection temperature (HDT) and mechanical performances, which can hardly be achieved by traditional acrylate-based photopolymers. Therefore, it becomes crucial to employ new process in 3D material development for advanced performances that could match existing plastics fabricated with traditional manufacturing methods.

[0007] To solve this issue, attempts have been made to combine inorganic fillers with a light polymerizable liquid in a radiation 3D printing process. However, inorganic fillers would dramatically increase the viscosity of the liquid, making it not possible to be 3D printed. Although there are already some curable compositions containing inorganic fillers have been developed, either viscosities of the compositions are still so high, which limit the 3D printing process, or the mechanical properties of the 3D-printed object are not satisfied. Therefore, there is a strong need to provide a ceramic-like radiation-curable composition with good dispersion, which enables the development of a 3D printed object with high HDT and high rigidity as well as good printability and high accuracy. Summary of the Invention

[0008] It is an object of the present invention to provide a radiation-curable composition with good dispersion, which enables the development of a 3D object with high HDT and high rigidity, wherein the radiation-curable composition comprises (a) at least one light polymerizable liquid;

[0009] (b) at least one spherical inorganic particle having an average particle size D5o of 50 to 2000 nm; and (c) at least one photoinitiator.

[0010] Another object of the present invention is to provide a 3D printed object formed from the radiation-curable composition.

[0011] A further object of the present invention is to provide a process of forming the 3D printed object by using the radiation-curable composition of the present invention.

[0012] It has been surprisingly found that the above-mentioned objects can be achieved by following embodiments:

[0013] (a) at least one light polymerizable liquid;

[0014] (b) at least one spherical inorganic particle having an average particle size D5o of 50 to 2000 nm;

[0015] (c) at least one photoinitiator.

[0016] In one embodiment, the average particle size D5o of the spherical inorganic particle is in the range from 100 to 1500 nm, preferably from 300 to 1000 nm.

[0017] In another embodiment, the spherical inorganic particle is surface-treated by silane, preferably by alkoxysilane.

[0018] In a further embodiment, the spherical inorganic particle is spherical silica particle.

[0019] Another object of the present invention is to a 3D printed object formed for the radiation-curable composition.

[0020] The radiation-curable composition according to the present invention shows excellent stability and good printing accuracy and is easy to be 3D printed due to low viscosity. The object formed from the radiation-curable composition also shows high HDT value and adequate mechanical properties. Description of the Drawing

[0021] Figure 1 shows stability test of example 4-7 and comparative example 1 with a centrifuge at 25 °C

[0022] Figure 2(a) shows the picture of standard benchmark model and Figure 2(b) shows the picture of 3D-printed object obtained by printing the composition of example 10 according to the standard benchmark model.

[0023] Figure 3 shows the pictures of 3D-printed objects obtained by printing the composition of example 10.

[0024] Embodiment of the Invention

[0025] Unless defined otherwise, all technical and scientific terms used herein have the meaning commonly understood by a person skilled in the art to which the invention belongs. As used herein, the following terms have the meanings ascribed to them below, unless specified otherwise.

[0026] As used herein, the articles "a", "an" and "the" refer to one or more of the species designated by the term following said article.

[0027] The term “liquid“as used in the presnet invention is to be equated with "liquid at room temperature" which is, in general a temperature between about 5 °C and about 30 °C. In the context of the present disclosure, any specific values mentioned for a feature (comprising the specific values mentioned in a range as the end point) can be recombined to form a new range.

[0028] Light polymerizable liquid (a)

[0029] The radiation-curable composition of the present invention comprises at least one light polymerizable liquid as component (a).

[0030] In an embodiment of the present invention, the light polymerizable liquid (a) of the present invention comprises a monomer and / or oligomer containing at least one radiation-curable functional group.

[0031] The radiation-curable functional group of the light polymerizable liquid (a) of the present invention may be selected from the group consisting of an ethylenically unsaturated functional group, an epoxy group, and the mixture thereof. For example, the at least one radiation-curable functional group of the monomer and / or oligomer containing at least one radiation-curable functional group suitable as light polymerizable liquid (a) is selected from the group consisting of an ethylenically unsaturated functional group, an epoxy group, and the mixture thereof. Preferably, the number of the radiation-curable functional group in light polymerizable liquid (a) is in the range from 1 to 12, for example 1.2, 1.5, 1.8, 2, 2.2. 2.5, 3, 3.5,4, 5, 6, 7, 8, 9, 10, 11, preferably from 1 to 10, such as from 1 to 8, or 1.5 to 6, per molecule of light polymerizable liquid (a).

[0032] As light polymerizable liquid (a) containing at least one epoxy group, non-limiting examples may include epoxidized olefins, aromatic glycidyl ethers, aliphatic glycidyl ethers, or the combination thereof, preferably aromatic or aliphatic glycidyl ethers.

[0033] Examples of possible epoxidized olefins include epoxidized C2-Cw-olefins, such as ethylene oxide, propylene oxide, iso-butylene oxide, 1 -butene oxide, 2-butene oxide, vinyloxirane, styrene oxide or epichlorohydrin, preference being given to ethylene oxide, propylene oxide, isobutylene oxide, vinyloxirane, styrene oxide or epichlorohydrin, particular preference to ethylene oxide, propylene oxide or epichlorohydrin, and very particular preference to ethylene oxide and epichlorohydrin.

[0034] Aromatic glycidyl ethers are, for example, bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, bisphenol B diglycidyl ether, bisphenol S diglycidyl ether, hydroquinone diglycidyl ether, alkylation products of phenol / dicyclopentadiene, e.g., 2,5-bis[(2,3-epoxypropoxy)phenyl]octahy- dro-4,7-methano-5H-indene (CAS No. [13446-85-0]), tris[4-(2,3-epoxypropoxy)phenyl]methane isomers (CAS No. [66072-39-7]), phenol-based epoxy novolaks (CAS No. [9003-35-4]), and cresol-based epoxy novolaks (CAS No. [37382-79-9]).

[0035] Examples of aliphatic glycidyl ethers include 1 ,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane triglycidyl ether, pentaerythritol tetraglycidyl ether, 1, 1,2,2- tetrakis[4-(2,3-epoxypropoxy)phenyl]ethane (CAS No. [27043-37-4]), diglycidyl ether of polypropylene glycol (a,cu-bis(2,3-epoxypropoxy)poly(oxypropylene), CAS No. [16096-30-3]) and of hydrogenated bisphenol A (2,2-bis[4-(2,3-epoxypropoxy)cyclohexyl]propane, CAS No. [13410-58- 7]).

[0036] More preferably, light polymerizable liquid (a) of the present invention contains at least one ethylenically unsaturated functional group.

[0037] In an embodiment of the invention, the ethylenically unsaturated functional group contains a carbon-carbon unsaturated bond, such as those found in the following functional groups: allyl, vinyl, acrylate, methacrylate, acryloxy, methacryloxy, acrylamido, methacrylamido, acetylenyl, maleimido, and the like; preferably, the ethylenically unsaturated functional group contains acrylate or methacylate. In a preferred embodiment of the invention, light polymerizable liquid (a) of the present invention contains, in addition to the ethylenically unsaturated functional group and / or epoxy group, urethane groups, ether groups, ester groups, carbonate groups, and any combination thereof.

[0038] As light polymerizable liquid (a) of the present invention, the oligomer containing at least one radiation-curable functional group includes, for example, oligomers containing a core structure linked to the ethylenically unsaturated functional group, optionally via a linking group. The linking group can be an ether, ester, amide, urethane, carbonate, or carbonate group. In some instances, the linking group is part of the ethylenically unsaturated functional group, for instance an acryloxy or acrylamido group. The core group can be an alkyl (straight and branched chain alkyl groups), aryl (e.g. phenyl), polyether, polyester, siloxane, urethane, or other core structures and oligomers thereof. Suitable ethylenically unsaturated functional group may comprise groups containing carbon-carbon double bond, such as methacrylate groups, acrylate groups, vinyl ether groups, allyl ether groups, acrylamide groups, methacrylamide groups, or a combination thereof, preferably methacrylate or acrylate. In some embodiments, suitable oligomers comprise mono- and / or polyfunctional acrylate, such as mono (meth)acrylate, di(meth)acrylate, tri(meth)acrylate, or higher, or combination thereof. Optionally, the oligomer may include a siloxane backbone in order to further improve cure, flexibility and / or additional properties of the radiation-curable composition for 3D printing.

[0039] In some embodiments, the oligomer containing at least one ethylenically unsaturated functional group can be selected from the following classes: urethane (e.g. an urethane-based oligomer containing ethylenically unsaturated functional group), polyether (e.g. an polyether-based oligomer containing ethylenically unsaturated functional group), polyester (e.g. an polyester-based oligomer containing ethylenically unsaturated functional group), polycarbonate (e.g. an polycarbonate-based oligomer containing ethylenically unsaturated functional group), polyestercarbonate (e.g. an polyestercarbonate-based oligomer containing ethylenically unsaturated functional group), epoxy (e.g. an epoxy-based oligomer containing ethylenically unsaturated functional group), silicone (e.g. a silicone-based oligomer containing ethylenically unsaturated functional group) or any combination thereof. Preferably, the oligomer containing at least one ethylenically unsaturated functional group can be selected from the following classes: a urethane- based oligomer, an epoxy-based oligomer, a polyester-based oligomer, a polyether-based oligomer, polyether urethane-based oligomer, polyester urethane-based oligomer or a silicone- based oligomer, as well as any combination thereof.

[0040] In a preferred embodiment of the invention, the oligomer containing at least one ethylenically unsaturated functional group comprises a urethane-based oligomer comprising urethane repeating units and one, two or more ethylenically unsaturated functional groups, for example those containing carbon-carbon unsaturated double bond, such as (meth)acrylate groups, (meth)acrylamide groups, allyl groups and vinyl groups. Preferably, the oligomer contains at least one urethane linkage (for example, one, two or more urethane linkages) within the backbone of the oligomer molecule and at least one acrylate and / or methacrylate functional groups (for example, one, two or more acrylate and / or methacrylate functional groups) pendent to the oligomer molecule. In some embodiments, aliphatic, cycloaliphatic, or mixed aliphatic and cycloaliphatic urethane repeating units are suitable. Urethanes are typically prepared by the condensation of a diisocyanate with a diol. Aliphatic urethanes having at least two urethane moieties per repeating unit are useful. In addition, the diisocyanate and diol used to prepare the urethane comprise divalent aliphatic groups that may be the same or different.

[0041] In one embodiment, the oligomer containing at least one ethylenically unsaturated functional group comprises polyester urethane-based oligomer or polyether urethane-based oligomer containing at least one ethylenically unsaturated functional group. The ethylenically unsaturated functional group can be those containing carbon-carbon unsaturated double bond, such as acrylate groups, methacrylate groups, vinyl groups, allyl groups, acrylamide groups, methacrylamide groups etc., preferably acrylate groups and methacrylate groups.

[0042] Suitable urethane-based oligomers are known in the art and may be readily synthesized by a number of different procedures. For example, a polyfunctional alcohol may be reacted with a polyisocyanate (preferably, a stoichiometric excess of polyisocyanate) to form an NCO-termi- nated pre-oligomer, which is thereafter reacted with a hydroxy-functional ethylenically unsaturated monomer, such as hydroxy-functional (meth)acrylate. The polyfunctional alcohol may be any compound containing two or more OH groups per molecule and may be a monomeric polyol (e.g., a glycol), a polyester polyol, a polyether polyol or the like. The urethane-based oligomer in one embodiment of the invention is an aliphatic urethane-based oligomer containing (meth)acrylate functional group.

[0043] Suitable polyether or polyester urethane-based oligomers include the reaction product of an aliphatic or aromatic polyether or polyester polyol with an aliphatic or aromatic polyisocyanate that is functionalized with a monomer containing the ethylenically unsaturated functional group, such as (meth)acrylate group. In a preferred embodiment, the polyether and polyester are aliphatic polyether and polyester, respectively. In a preferred embodiment, the polyether and polyester urethane-based oligomers are aliphatic polyether and polyester urethane-based oligomers and comprise (meth)acrylate group.

[0044] In one embodiment, the viscosity of the oligomer containing at least one ethylenically unsaturated functional group at 60°C can be in the range from 200 to 200000 cP, for example 500 cP, 800 cP, 1000 cP, 2000 cP, 3000 cP, 4000 cP, 5000 cP, 6000 cP, 7000 cP, 8000 cP, 10000 cP, 20000 cP, 30000 cP, 40000 cP, 50000 cP, 60000 cP, 70000 cP, 80000 cP, 90000 cP, 95000 cP, preferably 500 to 60000cP, for example 1000 to 50000 cP, 2000 to 40000 cP, 3000 to 20000 cP, 4000 to 15000 cP, or 20000 cP to 60000 cP, as measured according to DIN EN ISO 3219.

[0045] The monomer can lower the viscosity of the composition. The monomer can be monofunctional or multifunctional (such as difunctional, trifunctional), preferably monofunctional. In one embodiment, the monomer can be selected from the group consisting of (meth)acrylate monomers, (meth)acrylamide monomers, vinylaromatics having up to 20 carbon atoms, vinyl esters of carboxylic acids having up to 20 carbon atoms, a,p-unsaturated carboxylic acids having 3 to 8 carbon atoms and their anhydrides, and vinyl substituted heterocycles,

[0046] In the context of the present disclosure, the term “(meth)acrylate monomer” means a monomer comprises a (meth)acrylate moiety. The structure of the (meth)acrylate moiety is as follows: wherein R is H or methyl.

[0047] The (meth)acrylate monomer can be monofunctional or multifunctional (such as difunctional, trifunctional) (meth)acrylate monomer. Exemplary (meth)acrylate monomer can include Ci to C20 alkyl (meth)acrylate, Ci to C10 hydroxyalkyl (meth)acrylate, C3 to C10 cycloalkyl (meth)acrylate, urethane acrylate, 2-(2-ethoxy)ethyl acrylate, tetrahydrofurfuryl (meth)acrylate, 2-phenoxyeth- ylacrylate, dicyclopentenyloxyethyl (meth)acrylate, dicyclopentadienyl (meth)acrylate, caprolactone (meth)acrylate, morpholine (meth)acrylate, ethoxylated nonyl phenol (meth)acrylate, (5- ethyl-1 ,3-dioxan-5-yl) methyl acrylate, phenyl (meth) acrylate, benzyl (meth)acrylate, phenethyl (meth)acrylate, dicyclopentanyl (meth)acrylate, 3,3,5-trimethylcyclohexyl (meth)acrylate and dicyclopentenyl (meth)acrylate.

[0048] Specific examples of Ci to C20 alkyl (meth)acrylate can include methyl (meth)acrylate, ethyl (meth)acrylate, isopropyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, sec-butyl (meth)acrylate, pentyl (meth)acrylate, n- hexyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, n-lauryl (meth)acrylate, n-tridecyl (meth)acrylate, n-cetyl (meth)acrylate, n-stearyl (meth)acrylate, isomyristyl (meth)acrylate, stearyl (meth)acry- late, and isostearyl (meth)acrylate (ISTA). C6to C alkyl (meth)acrylate, especially Ce to Cw alkyl (meth)acrylate or Cs to C12 alkyl (meth)acrylate is preferred.

[0049] Specific examples of Ci to C10 hydroxyalkyl (meth)acrylate, such as C2 to Cs hydroxyalkyl (meth)acrylate can include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3- hydroxypropyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6- hydroxyhexyl (meth)acrylate, or 3-hydroxy-2-ethylhexyl (meth)acrylate etc.

[0050] Specific examples of C3 to C cycloalkyl (meth)acrylate can include isobornyl acrylate, isobornyl methacrylate, cyclohexyl acrylate or cyclohexyl methacrylate.

[0051] Examples of monofunctional acrylate include such as methyl acrylate, ethyl acrylate, butyl acrylate, 2-(2-ethoxy)ethyl acrylate, tetrahydrofurfuryl acrylate, lauryl acrylate, isooctyl acrylate, isodecyl acrylate, 2-phenoxyethylacrylate, 2-ethylhexyl acrylate, isobornyl acrylate, dicyclopentenyloxyethyl acrylate, dicyclopentadienyl acrylate, 2-hydroxyethyl acrylate, 2- hydroxypropyl acrylate, 2-hydroxybutyl acrylate, 4-hydroxybutyl acrylate, caprolactone acrylate, morpholine acrylate, epoxy-acrylate hybrid monomers such as 3,4-epoxy-cyclohexyl-14 methyl acrylate.

[0052] In the context of the present disclosure, term “(meth)acrylamide monomer” means a monomer comprises a (meth)acrylamide moiety. The structure of the (meth)acrylamide moiety is as follows: CH2=CR1-CO-N, wherein R1is hydrogen or methyl. Specific example of (meth)acrylamide monomer can include acryloylmorpholine, methacryloylmorpholine, N-(hydroxymethyl)acryla- mide, N-hydroxyethyl acrylamide, N-isopropylacrylamide, N-isopropylmethacrylamide, N-tert- butylacrylamide, N,N’-methylenebisacrylamide, N-(isobutoxymethyl)acrylamide, N-(butoxyme- thyl)acrylamide, N-[3-(dimethylamino)propyl]methacrylamide, N,N-dimethylacrylamide, N,N-di- ethylacrylamide, N-(hydroxymethyl)methacrylamide, N-hydroxyethyl methacrylamide, N- isopropylmethacrylamide, N-isopropylmethacrylamide, N-tert-butylmethacrylamide, N,N’-meth- ylenebismethacrylamide, N-(isobutoxymethyl)methacrylamide, N-(butoxymethyl)methacryla- mide, N-[3-(dimethylamino)propyl]methacrylamide, N,N-dimethylmethacrylamide and N,N-dieth- ylmethacrylamide. The (meth)acrylamide monomer can be used alone or in combination.

[0053] Examples of monofunctional acrylamides or methacrylamides component include such as acryloylmorpholine (ACMO), methacryloylmorpholine, N-(hydroxymethyl)acrylamide, N- hydroxyethyl acrylamide, N- isopropylacrylamide, N-isopropylmethacrylamide, N-tert- butylacrylamide, N,N'- methylenebisacrylamide, N-(isobutoxymethyl)acrylamide, N- (butoxymethyl)acrylamide, N-[3-(dimethylamino)propyl]methacrylamide, N,N- dimethylacrylamide, N,N-diethylacrylamide, N-(hydroxymethyl)methacrylamide, N-hydroxyethyl methacrylamide, N-isopropylmethacrylamide, N-isopropylmethmethacrylamide, N-tert- butylmethacrylamide, N,N'-methylenebismethacrylamide, N-(isobutoxymethyl)methacrylamide, N-(butoxymethyl)methacrylamide, N-[3-(dimethylamino)propyl]methmethacrylamide, N,N- dimethylmethacrylamide and N,N-diethylmethacrylamide.

[0054] Examples of vinylaromatics having up to 20 carbon atoms can include, such as styrene and Ci- C4-alkyl substituted styrene, such as vinyltoluene, p-tert-butylstyrene and a-methyl styrene.

[0055] Examples of vinyl esters of carboxylic acids having up to 20 carbon atoms (for example 2 to 20 or 8 to 18 carbon atoms) can include vinyl laurate, vinyl stearate, vinyl propionate, and vinyl acetate.

[0056] Example of a,p-unsaturated carboxylic acids having 3 to 8 carbon atoms can be acrylic acid or methacrylic acid.

[0057] Examples of vinyl substituted heterocycles can include monovinyl substituted heterocycles, wherein the heterocycle is a 5- to 8-membered ring containing 2 to 7 carbon atoms, and 1 to 4 (preferably 1 or 2) heteroatoms selected from N, O and S, such as vinylpyridines, N-vinylpyrroli- done, N-vinylmorpholin-2-one, N-vinyl caprolactam and 1-vinylimidazole, vinyl alkyl oxazoli- dinone such as vinyl methyl oxazolidinone.

[0058] Preferred monomers are (meth)acrylate monomer and (meth)acrylamide monomer. More preferably, the monomers are mono-functional.

[0059] In a preferred embodiment, light polymerizable liquid (a) of the present invention comprises both the oligomer and the monomer containing at least one ethylenically unsaturated functional group. The weight ratio of the oligomer to the monomer can be in the range from 10: 1 to 1 : 10, preferably from 8:1 to 1 :8, or from 5:1 to 1:5, or from 3:1 to 1:5, or from 1:1 to 1 :4.

[0060] The amount of light polymerizable liquid (a) can be in the range from 20 to 90 wt.%, for example 25 wt.%, 30 wt.%, 35 wt.%, 40 wt.%, 50 wt.%, 60 wt.%, 70 wt.%, 80 wt.%, 90 wt.%, preferably from 25 to 80 wt.%, more preferably from 30 to 70 wt.% or from 30 to 60 wt.%, based on the total weight of the curable composition.

[0061] Spherical Inorganic Particle (b)

[0062] According to the present invention, the radiation-curable composition also comprises at least one spherical inorganic particle having an average particle size D50of 50 to 2000 nm. Examples of inorganic fillers are silica particles, glass or silica beads, calcium carbonate, barium sulfate, talc, mica, glass or silica bubbles, zirconium silicate, iron oxides, diatomaceous earth, dolomite, powdered metals, titanium oxides, pulp powder, kaoline, modified kaolin, hydrated kaolin metallic filers, ceramics and composites.

[0063] In the present invention, spherical inorganic particle is used so that a higher amount of inorganic particle can be added to the composition to achieve good mechanical properties while keeping good stability and low viscosity. The spherical inorganic particle has a sphericity of 0.7 to 1 , preferably 0.8 to 1 , more preferably 0.9 to 1.

[0064] In an embodiment, the spherical inorganic particle is silica particle, such as silica, fumed silica, precipitated silica, colloidal silica, Vaporized Metal Combustion (VMC) silica and mixture thereof.

[0065] In a preferred embodiment, the silica particles are Vaporized Metal Combustion (VMC) spherical silica particles. The VMC method provides fine spherical silica particles from metal powder by direct oxidation.

[0066] It is preferable to surface-treat the silica particle with a known surface treatment agent such as an organic silicon compound. More preferably, the silica particle is surface-treated with a silane coupling agent. The spherical silica particles, which can be treated to provide silica particles treated with silane in accordance with the invention, are generally commercially available, or can be prepared by known methods from various starting materials (e.g., wet-process type silica)..

[0067] The silica particle treated with silane can be obtained by reacting the silica particle with a silane coupling agent.

[0068] Silane coupling agent has the form R-SiXs, where R is an organic functional group, such as amino, methacryl, glycidoxy, mercapto, vinyl and X is a hydrolyzable group. Preferably silane coupling agent is alkoxysilane having a structure of the following formula:

[0069] R1nSi(OR2)4-n

[0070] Wherein R1can be selected from C1-C30 (preferably C1-C18, or C1-C12, or Ci-Ce or C1-C4) alkyl, amino C1-C30 (preferably C1-C18, or C1-C12, or Ci-Ce or C1-C4) alkyl, C2-C30 (preferably C2-C18, or C2-C12, or C2-Ce or C2-C4) alkenyl, amino C2-C30 (preferably C2-C18, or C2-C12, or C2-Ce or C2-C4) alkenyl and methacryl C4-C30 (preferably C4-C18, or C4-C12, or C4-Cs) alkyl, C3-C10 cycloalkyl, and CB-CW aryl; R2can be selected from C1-C18 alkyl (preferably C1-C15, C1-C10, Ci-Cs, Ci-Ce or C1-C4 alkyl); and n is an integer from 1 to 3. In an embodiment, the alkoxysilane is a trialkoxysilane. The trialkoxysilane can have the structure of the following formula: R1Si(OR2)3wherein R1can be selected from C1-C30 (preferably C1-C18, or C1-C12, or Ci-Ce or C1-C4) alkyl, amino C1-C30 (preferably C1-C18, or C1-C12, or Ci-Ce or C1-C4) alkyl, C2-C30 (preferably C2-C18, or C2-C12, or C2-Ce or C2-C4) alkenyl, amino C2-C30 (preferably C2-C18, or C2-C12, or C2-Ce or C2-C4) alkenyl and methacryl C4-C30 (preferably C4-C18, or C4-C12, or C4-Cs) alkyl, and C3-C10 cycloalkyl; R2can be selected from C1-C10 alkyl (preferably Ci-Cs or Ci-Ce or C1-C4 alkyl).

[0071] Specific example of the alkoxysilane can be selected from methyltrimethoxysilane, ethyltrimethoxysilane, propyltrimethoxysilane, butyltrimethoxysilane, pentyltriethoxysilane, hexyltriethoxysilane, heptyltriethoxysilane, octyltriethoxysilane, 3-aminopropyltriethoxysilane, 3-aminobu- tyltriethoxysilane, Methacryloxyethyltrimethoxysilane, Methacryloxypropyltrimethoxysilane, and combinations thereof.

[0072] The silica particle treated with silane can have an average particle size D50 in the range from 50 to 2000 nm, for example 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 120 nm, 140 nm, 160 nm, 180 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1000 nm, 1200 nm, 1500 nm, 1800 nm or 2000 nm, preferably from 100 to 1500 nm or from 300 to 1000 nm.

[0073] In the present invention, there is no need to add other type of inorganic particles with different particle size distribution to balance the viscosity of the radiation-curable composition and filler content, such as microparticle having average particle size D50 of 1 to 6 pm.

[0074] In the radiation-curable composition of the present invention, the amount of spherical inorganic particle can be in the range from 10 to 80 wt.%, for example 15 wt.%, 20 wt.%, 25 wt.%, 30 wt.%, 35 wt.%, 40 wt.%, 50 wt.%, 60 wt.%, 65 wt.%, 70 wt.%, preferably from 30 wt.% to 70 wt.%, or from 50 wt.% to 70 wt.%, based on the total weight of the radiation-curable composition.

[0075] Photoinitiator (c)

[0076] The radiation-curable composition comprises at least one photoinitiator as component (c). For example, the photoinitiator component (c) may include at least one free radical photoinitiator and / or at least one ionic photoinitiator, and preferably at least one (for example one or two) free radical photoinitiator. For example, it is possible to use all photoinitiators known in the art for use in compositions for 3D-printing, e.g., it is possible to use photoinitiators that are known in the art use with SLA, DLP or PPJ (Photo polymer jetting) processes. Exemplary photoinitiators may include benzophenone, acetophenone, chlorinated acetophenone, dialkoxyacetophenones, dialkylhydroxyacetophenones, dialkylhydroxyacetophenone esters, benzoin and derivative (such as benzoin acetate, benzoin alkyl ethers), dimethoxybenzion, dibenzylketone, benzoylcyclohexanol and other aromatic ketones, alpha-aminoketone compounds, phenylglyoxylate compounds, oxime ester, acyloxime esters, acylphosphine oxides, acylphosphonates, ketosulfides, dibenzoyldisulphides, diphenyldithiocarbonate, mixtures thereof and mixtures with alpha-hydroxy ketone compounds, or alpha-alkoxyketone compounds.

[0077] Examples of suitable acylphosphine oxide compounds are of the formula (XII), wherein

[0078] R50 is unsubstituted cyclohexyl, cyclopentyl, phenyl, naphthyl or biphenylyl; or is cyclohexyl, cyclopentyl, phenyl, naphthyl or biphenylyl substituted by one or more halogen, C1-C12 alkyl, Ci- 012 alkoxy, C1-C12 alkylthio or by NR53R54; or R50 is unsubstituted C1-C20 alkyl or is C1-C20 alkyl which is substituted by one or more halogen, C1-C12 alkoxy, C1-C12 alkylthio, NR53R54 or by -(CO)-O-Ci-C24 alkyl;

[0079] R51 is unsubstituted cyclohexyl, cyclopentyl, phenyl, naphthyl or biphenylyl; or is cyclohexyl, cyclopentyl, phenyl, naphthyl or biphenylyl substituted by one or more halogen, C1-C12 alkyl, Ci- 012 alkoxy, C1-C12 alkylthio or by NR53R54; or R51 is -(CO)R’52; or R51 is C1-C12 alkyl which is unsubstituted or substituted by one or more halogen, C1-C12 alkoxy, C1-C12 alkylthio, or by NR53R54; R52 and R’52 independently of each other are unsubstituted cyclohexyl, cyclopentyl, phenyl, naphthyl or biphenylyl, or are cyclohexyl, cyclopentyl, phenyl, naphthyl or biphenylyl substituted by one or more halogen, C1-C4 alkyl or C1-C4 alkoxy; or R52 is a 5- or 6-membered heterocyclic ring comprising an S atom or N atom;

[0080] R53 and R54 independently of one another are hydrogen, unsubstituted C1-C12 alkyl or C1-C12 alkyl substituted by one or more OH or SH wherein the alkyl chain optionally is interrupted by one to four oxygen atoms; or R53 and R54 independently of one another are C2-C12 alkenyl, cyclopentyl, cyclohexyl, benzyl or phenyl.

[0081] Specific examples of photoinitiators can include 1 -hydroxycyclohexyl phenylketone, 2-methyl-1- [4-(methylthio)phenyl]-2-morpholinopropan-1-one, 2-benzyl-2-N,N-dimethylamino-1-(4-morpho- linophenyl)-1-butanone, combination of 1-hydroxycyclohexyl phenyl ketone and benzophenone, 2,2-dimethoxy-2-phenyl acetophenone, bis(2,6-dimethoxybenzoy 1 -(2,4,4- trimethylpentyl)phosphine oxide, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, bis(2,4,6-trimethyl benzoyl) phenyl phosphine oxide, 2-hydroxy-2-methyl-1-phenyl-1-propane, combination of

[0082] 2.4.6-trimethylbenzoyldiphenyl-phosphine oxide, 2-hydroxy-2-methyl-1-phenyl-propan-1-one,

[0083] 2.4.6-trimethylbenzoyldiphenylphosphinate and 2,4,6-trimethylbenzoyldiphenyl-phosphine oxide and also any combination thereof.

[0084] In a particularly preferred embodiment, the photoinitiator (c) is a compound of the formula (XII), such as, for example, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide; 2,4,6- trimethylbenzyl- diphenyl-phosphine oxide; ethyl (2,4,6-trimethylbenzoyl phenyl) phosphinic acid ester; (2,4,6- trimethylbenzoyl)-2,4-dipentoxyphenylphosphine oxide and bis(2,6-dimethoxybenzoyl)-2,4,4- trimethylpentylphosphine oxide.

[0085] The amount of the photoinitiator (c) can be in the range from 0.1 to 10 wt.%, for example 0.2 wt.%, 0.5 wt.%, 0.8 wt.%, 1 wt.%, 2 wt.%, 3 wt.%, 5 wt.%, 8 wt.%, or 10 wt.%, preferably from 0.1 to 5 wt.% or 0.5 to 5 wt.% or from 0.5 to 3 wt.%, based on the total weight of the composition.

[0086] In one embodiment, the radiation curable resin composition comprising

[0087] (a) at least one light polymerizable liquid;

[0088] (b) at least one spherical inorganic particle having an average particle size D5o of from 50 to 2000 nm;

[0089] (c) at least one photoinitiator.

[0090] The amount of component (a) can be represented from 20 to 90 wt.% or 25 to 80 wt.% or 30 to 60 wt.%; the amount of component (b) can be represented from 10 to 80 wt.% or 30 to 70 wt.% or 50 to 70 wt.%; the amount of component (c) can be represented from 0.1 to 10 wt.% or 0.5 to 5 wt.% or 0.5 to 3 wt.%.

[0091] Auxiliaries

[0092] The composition of the present invention may further comprise one or more auxiliaries.

[0093] As auxiliaries, mention may be made by way of preferred example of surface-active substances, flame retardants, nucleating agents, lubricant wax, adhesion promoters, rheology modifiers, dyes, pigments, catalyst, UV absorbers and stabilizers, e.g. against oxidation, hydrolysis, light, heat or discoloration, inorganic and / or organic fillers, reinforcing materials and plasticizers. As hydrolysis inhibitors, preference is given to oligomeric and / or polymeric aliphatic or aromatic carbodiimides. To stabilize the material cured of the invention against aging and damaging environmental influences, stabilizers are added to system in preferred embodiments. If the composition of the invention is exposed to thermo-oxidative damage during use, in preferred embodiments antioxidants are added. Preference is given to phenolic antioxidants. Phenolic antioxidants such as Irganox® 1010 from BASF SE are given in Plastics Additive Handbook, 5th edition, H. Zweifel, ed., Hanser Publishers, Munich, 2001 , pages 98-107, page 116 and page 121.

[0094] If the composition of the invention is exposed to UV light, it is preferably additionally stabilized with a UV absorber. UV absorbers are generally known as molecules which absorb high-energy UV light and dissipate energy. Customary UV absorbers which are employed in industry belong, for example, to the group of cinnamic esters, diphenylcyan acrylates, formamidines, benzyli- denemalonates, diarylbutadienes, triazines and benzotriazoles. Examples of commercial UV absorbers may be found in Plastics Additive Handbook, 5th edition, H. Zweifel, ed, Hanser Publishers, Munich, 2001 , pages 116-122.

[0095] Further details regarding the abovementioned auxiliaries may be found in the specialist literature, e.g. in Plastics Additive Handbook, 5th edition, H. Zweifel, ed, Hanser Publishers, Munich, 2001.

[0096] According to the present invention, the auxiliary can be present in an amount of from 0 to 50% by weight, from 0.01 to 50% by weight, for example from 0.5 to 30% by weight, based on the total weight of the radiation-curable composition.

[0097] Preparation of the radiation-curable composition

[0098] One aspect of the present invention relates to a process of preparing the radiation-curable composition of the present invention for 3D-printing, comprising mixing the components of the composition. There is no special requirement of sequence of adding the components. The inorganic particle can be added to the light polymerizable liquid together and then the whole composition is mixed or the inorganic particle is added after the light polymerizable liquid is mixed firstly.

[0099] According to an embodiment of the invention, the mixing can be carried out at room temperature with stirring. There is no particular restriction on the time of mixing and rate of stirring, as long as all components are uniformly mixed together. In a specific embodiment, the mixing can be carried out by speed-mixture at 1000 to 3000 RPM, preferably 1500 to 2500 RPM for 5 to 60 min, more preferably 6 to 30 min.

[0100] The viscosity of the radiation-curable composition at 25 °C is less than 2000 mPa.s, preferably less than 1500 mPa.s, more preferably less than 1200 mPa.s. The radiation-curable composition of the present invention shows excellent stability. When the composition is centrifuged at 25 °C, there is only slight phase separation after 2 hours, preferably after 5 hours, more preferably after 16 hours.

[0101] 3D-printed object and preparation thereof

[0102] One aspect of the present invention relates to a process of forming 3D-printed object, comprising using the radiation-curable composition of the present invention.

[0103] In one embodiment of the present invention, the process of forming a 3D-printed object comprises the steps of:

[0104] (i) applying light to cure the curable composition layer by layer to form an intermediate 3D object;

[0105] (ii) curing the whole intermediate 3D-printed object by radiation to form a cured 3D-printed object; and

[0106] (iii) optionally thermally curing the whole cured 3D-printed object to form a final 3D-printed object.

[0107] According to the invention, the curing time in step (i) and (ii) may be determined respectively by a skilled person according to practical application. For example, in step (i) of the process, the curing time for each layer may be from 0.5 to 15s, such as from 1 to 10 s.

[0108] In step (ii) of the process, the curing time for the whole intermediate 3D-printed object may be in the range from 10 min to 500 min, for example 20 min, 30 min, 40 min, 60 min, 80 min, 100 min, 120 min, 180 min, 250 min, 300 min, 400 min, preferably from 10 min to 250 min.

[0109] There is no specific restriction on the temperature during step (i) or step (ii). Specifically, the temperature may be selected depending on the material and the 3D printer used.

[0110] Step (iii) of the process of forming a 3D-printed object of the present invention may be carried out at the temperature of 60 to180°C, preferably 80 to 150 °C, more preferably 100 to 140 °C, for such as 1 hour to 48 hours, for example 2 hours, 4 hours, 6 hours, 8 hours, 10 hours, 12 hours, 16 hours, 20 hours, 24 hours, 28 hours, 32 hours, 36 hours, 40 hours, 44 hours, 48 hours, preferably for 4 hours to 36 hours, 6 hours to 36 hours, 8 hours to 36 hours, 10 hours to 24 hours, 12 hours to 24 hours, 12 hours to 20 hours, 16 hours to 36 hours, 20 hours to 36 hours, 24 hours to 36 hours, 28 hours to 36 hours. The temperature during step (iii) may be changed as required. For example, in an embodiment of the present invention, step (iii) of the process of forming a 3D-printed object of the present invention may be carried out in two stages, with the first stage being carried out at the temperature of 80°C for one hour and the second stage being carried out at the temperature of 130°C for 2 hours.

[0111] Radiation used in steps (i) and (ii) of the process of forming a 3D-printed object of the present invention may be adopted by a skilled person according to the practical 3D-printing applications. For example, the radiation may be actinic ray that has sufficient energy to initiate a polymerization or cross-linking reaction. The actinic ray can include but is not limited to a-rays, y-rays, ultraviolet radiation (UV radiation), visible light, and electron beams, wherein UV radiation and electron beams, especially, UV radiation is preferred.

[0112] In a specific embodiment, the wavelength of the radiation light can be in the range from 350 to 480 nm, for example 365 nm, 385 nm, 395 nm, 405 nm, 420 nm, 440nm, 460nm, 480nm.

[0113] Stereolithography (SLA), digital light processing (DLP), photopolymer jetting (PPJ), LCD technology or other techniques known by a person skilled in the art can be employed in step (i) of the process of forming 3D-printed objects of the present invention. Preferably, the production of cured 3D objects of complex shape is performed for instance by means of digital light processing (DLP), which has been known for a number of years. In this technique, the desired shaped article is built up from a radiation-curable composition with the aid of a recurring, alternating sequence of three steps (1), (2) and (3). In step (1), the radiation-curable composition is filled into the build region between a carrier and an optically transparent membrane. In step (2), a layer of the radiation-curable composition is cured with the aid of appropriate imaging radiation, preferably imaging radiation from a computer-controlled UV light projector, which corresponds to the desired cross-sectional area of the shaped article to be formed, and in step (3), the cured radiation-curable composition and the carrier is moving away from the optically transparent membrane. The sequence of steps (1), (2) and (3) is repeated until the desired 3D shape is finished.

[0114] The present invention further relates to a 3D-printed object formed from the curable composition of the present invention or obtained by the process of the present invention.

[0115] Examples of the 3D-printed objects comprises functional parts with advanced properties for au- tomotive / mold application, or demonstration parts that require ceramic-like feelings. Examples

[0116] The present invention is further illustrated by the following examples, which are set forth to illustrate the present invention and is not to be construed as limiting thereof. Unless otherwise noted, all parts and percentages are by weight.

[0117] Materials and abbreviations

[0118] Component (a)

[0119] Miramer M370, Tris (2-hydroxy ethyl) isocyanurate triacrylate, available from Miwon;

[0120] Sartomer SR833S, tricyclodecane dimethanol diacrylate, available from Sartomer Co., Exton, PA;

[0121] ACMO, Acryloylmorpholine, available from RAHN;

[0122] Component (b)

[0123] TG-C100, spherical silica particles, average particle size D5o is 115 nm, surface treated with 1 , 1 , l-trimethyl-N-(trimethylsilyl)- (TMS), available from Cabot;

[0124] TPX-5110, spherical silica particles, average particle size D5o is115 nm, surface treated with methacrylic silane (Methacryloxypropyltrimethoxysilane (MPS)), available from Cabot;

[0125] SC2500-SMJ, spherical silica particles, average particle size D5o is 500nm, surface treated with methacrylic silane (Methacryloxypropyltrimethoxysilane (MPS)), available from Admatechs.

[0126] Component (c)

[0127] Omnicure TPO-L, Ethyl(2,4,6-trimethylbenzoyl)-phenyl phosphonate, available from IGM

[0128] Composition example 1

[0129] Formlabs Rigid 10K Resin, product code FLRG1001 , available from Formlabs, Inc

[0130] Methods

[0131] (1) Viscosity

[0132] The viscosity of the raditaion-curable composition was determined using a Brookfield AMETEK DV3T rheometer. For each test, approximately 0.65 ml of sample was used, and shear rates between 1 s’1and 30 s-1were selected according to the viscosities.

[0133] (2) Tensile test

[0134] Tensile tests were carried out according to ISO 527-5A:2009 with Zwick, Z050 Tensile equipment, wherein the parameters used include: Start position: 50 mm; Pre-load: 0.02 MPa; Test speed: 5 mm / min.

[0135] (3) Heat deflection temperature (HDT) Heat deflection temperature was determined in accordance with ASTM D648-07

[0136] (4) Stability

[0137] Resin stability was measured using a stability analyzer (LumiFuge, LUM). Liquid samples were loaded into plastic vials and centrifuged with designated spinning speed, duration and temperature, during which the particle sedimentation behavior was monitored by measuring the transmittance of a laser beam passing through the surface region of the liquid samples. And the resin stability can be directly compared by observing the phase separation after the test.

[0138] Examples 1-3

[0139] The light polymerizable liquid composition 1 was prepared by adding all components in amounts as listed in Table 1 into a plastic vial and mixing by speed-mixer at 2000RPM for 10 minutes at 50°C to obtain the liquid base composition.

[0140] Table 1

[0141] Example 1-3 were prepared by mixing composition 1 and three spherical silica particles in different filler loadings as listed in Table 2 into a plastic vial and mixing by speed-mixer at 2000RPM for 10 minutes to obtain homogeneous filler-containing resins. Filler loading means the weight percentage of the inorganic particles based on the total weight of the radiation-curable composition.

[0142] Viscosity of the radiation-curable composition containing different amount of inorganic particles are tested as shown in Table 2.

[0143] Table 2

[0144] For all three silica parties, there were dramatic increase in viscosity as the increase of filler loading. However the radiation-curable composition containing SC2500-SMJ silica particle showed the lowest viscosity, allowing a higher filler loading to be used in the composition to improve mechanical properties.

[0145] Examples 4-7, comparative example 1

[0146] The composition of examples 4-7 are the same but with different preparing method as shown in table 3. The composition consists of 35 g composition 1 and 65 g SC2500-SMJ.

[0147] Table 3

[0148] For each set of stability tests, 10ml - 20ml of liquid samples were loaded into plastic vials and sealed with a PP plug. Samples were then centrifuged with a spinning speed of 4000 RPM at 25°C for 16 hours, during which the particle sedimentation behavior was monitored by measuring the transmittance of a laser beam passing through the samples. Particle sedimentation during centrifuge would reduce particle contents on the surface region, leaving less particle to block the laser beam, and in turn leads to an increased light transmittance. After the tests, the resin stabilities were then directly compared by observing the phase-separation behavior of the tested samples.

[0149] The phase separation after 16 hours of examples 4-7 and comparative example 1 were shown in Figure 1. Examples 8-11

[0150] The curable compositions in example 8-11 were prepared by adding silica particles by amount as listed in Table 4 into a plastic vial and mixing with composition 1 by speed-mixer at 2000RPM for 10 minutes to obtain homogeneous filler-containing resins.

[0151] The curable compositions of examples 8-11 were printed using a MiiCraft 150 3D printer, which is a desktop Digital Light Processing (DLP) 3D printer with light wavelength at 405 nm. For a typical printing process, curable compositions were loaded into a vat within the printer. Detailed printing parameters are summarized as follows: UV energy 4.75 mW / cm2, base curing time 10.0 s, base layer 1 , curing time 2.0 s, buffer layer 5.

[0152] After a 3D printing process, the printed parts were soaked in isopropanol and shook for 10 seconds to remove uncured resin on the surface, followed by being dried using compressed air. Parts with smooth-dry surfaces can be obtained after being UV post-cured for 40 minutes using a NextDent post-curing unit (LC-3DPrint box). Thermal treatment was performed by heating samples at 120 °C for 2 hours.

[0153] The physical properties of the cured samples obtained from composition of examples 8-11 via 3D-printing were also shown in table 4, from which it can be concluded that example 11 showed much higher tensile modulus than the other three while keeping low viscosity for 3D printing.

[0154] Table 4 Example 12

[0155] The curable compositions in example 12 was prepared by adding all components in amounts as shown in table 5 into a plastic vial and mixing by speed-mixer at 2000RPM for 10 minutes at 50 °C to obtain the liquid curable compositions.

[0156] The curable compositions of examples 12 was printed using a MiiCraft 150 3D printer, which is a desktop Digital Light Processing (DLP) 3D printer with light wavelength at 405 nm. For a typical printing process, curable compositions were loaded into a vat within the printer. Detailed printing parameters are summarized as follows: UV energy 4.75 mW / cm2, base curing time 10.0 s, base layer 1 , curing time 2.0 s, buffer layer 5.

[0157] After a 3D printing process, the printed parts were soaked in isopropanol and shook for 12 seconds to remove uncured resin on the surface, followed by being dried using compressed air. Parts with smooth-dry surfaces can be obtained after being UV post-cured for 40 minutes using a NextDent post-curing unit (LC-3DPrint box). Thermal treatment was performed by heating samples at 120 °C for 2 hours.

[0158] The physical properties of the cured samples obtained from composition of example 12 via 3D- printing were shown in table 5, which showed both high rigidity and high HDT.

[0159] Table 5

[0160] The picture of 3D-printed object obtained by printing the composition of example 12 according to the standard benchmark model was shown in Figure 2(b). The comparison between the standard benchmark model (Figure 2(a)) and Figure 2(b) demonstrated that good printability and high accuracy could be achieved by the radiation-curable composition of the present invention.

[0161] The picture of 3D-printed objects obtained by printing the composition of example 12 were shown in Figure 3.

Claims

Claims1. A radiation curable resin composition comprising(a) at least one light polymerizable liquid;(b) at least one spherical inorganic particle having an average particle size D5o of 50 to 2000 nm;(c) at least one photoinitiator.

2. The radiation-curable composition according to claim 1, wherein the average particle size D5o of the spherical inorganic particle is in the range from 100 to 1500 nm, preferably from 300 to 1000 nm.

3. The radiation-curable composition according to claim 1 or 2, wherein the spherical inorganic particle is surface-treated by silane, preferably by alkoxysilane.

4. The radiation-curable composition according to any one of claims 1 to 3, wherein the spherical inorganic particle is silica particle.

5. The radiation-curable composition according to any one of claims 1 to 4, wherein the light polymerizable liquid contains at least one radiation-curable functional group, preferably the radiation-curable functional group is selected from the group consisting of an ethylenically unsaturated functional group, an epoxy group, or the mixture thereof, more preferably the radiation- curable functional group is an ethylenically unsaturated functional group.

6. The radiation-curable composition according to claim 5, wherein the light polymerizable liquid comprises at least one monomer and / or oligomer containing at least one ethylenically unsaturated functional groups.

7. The radiation-curable composition according to claim 6, wherein the monomer containing at least one ethylenically unsaturated functional group is mono-functional.

8. The radiation-curable composition according to claims 6 or 7, wherein the oligomer containing at least one ethylenically unsaturated functional groups is (meth)acrylate oligomer having 1 to 12, preferably 1 to 10, more preferably 1 to 8 ethylenically unsaturated functional groups.

9. The radiation-curable composition according to any one of claims 1 to 8, wherein the amount of the spherical inorganic particle is from 10 to 80% by weight, preferably from 40 to 70% by weight, based on the total weight of the radiation-curable composition.

10. The radiation-curable composition according to any one of claims 1 to 9, wherein the amount of the light polymerizable liquid is in the range from 20 to 90% by weight, preferably from 30 to 60% by weight, based on the total weight of the radiation-curable composition.

11. The radiation-curable composition according to any one of claims 1 to 10, wherein the viscosity of the radiation-curable composition at 25 °C is less than 1500 mPa.s, preferably less than 1200 mPa.s.

12. The radiation-curable composition according to claim any one of claims 1 to 11 , wherein the photoinitiator is a radical photoinitiator.

13. A process of forming 3D object, comprising:(i) applying light to cure the curable composition according to any of claims 1 to 12 layer by layer to form an intermediate 3D object;(ii) further applying light to cure the intermediate 3D object as a whole to form a cured 3D object; and(iii) optionally treating the cured 3D object as a whole by heating and / or microwave irradiating to form a final 3D object.

14. The process according to claim 13, wherein stereolithography, photopolymer jetting, digital light processing, or LCD technology is used in step (i) to form the intermediate 3D-printed object.

15. The process according to claim 13 or 14, wherein the radiation is UV radiation.

16. A 3D-printed object formed from the composition according to any one of claims 1 to 12 or obtained by the process according to any one of claims 13 to 15.

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