WO2025104550A1

WO2025104550A1 - Radiation curable composition for additive manufacturing processes

Info

Publication number: WO2025104550A1
Application number: PCT/IB2024/060982
Authority: WO
Inventors: Joachim W. Zech; Hendrik Grupp; Ralf M. PAEHL; Dietmar Blees; Malte Korten
Original assignee: Solventum Intellectual Properties Co
Current assignee: Solventum Intellectual Properties Co
Priority date: 2023-11-13
Filing date: 2024-11-06
Publication date: 2025-05-22
Anticipated expiration: 2026-05-13

Abstract

The invention relates to a radiation-curable composition for additive-manufacturing processes, the composition comprising (meth)acrylate component A1 comprising a polyalkylene oxide backbone, with at least two (meth)acrylate moieties, not comprising a urethane moiety, and having a molecular weight Mw of at least 2,000 g/mol, (meth)acrylate component A1 being present in an amount of 50 to 85 wt.%, (meth)acrylate component A2 with at least two (meth)acrylate moieties, comprising in addition at least two urethane moieties, and having a molecular weight Mw of at most 1,000 g/mol, (meth)acrylate component A2 being present in an amount of 5 to 20 wt.%, (meth)acrylate component A3 with only one (meth)acrylate moiety, and having a molecular weight of at most 500 g/mol, (meth)acrylate component A3 being present in an amount of 5 to 20 wt.%, photo-initiator, and optionally stabilizer, wt.% with respect to the amount of the whole composition. The invention also relates to a process of producing an elastomeric 3-dim article by processing the radiation-curable composition, an elastomeric 3-dim article obtainable by such a process.

Description

RADIATION CURABLE COMPOSITION FOR ADDITIVE MANUFACTURING PROCESSES

Field of the Invention

The invention relates to a radiation-curable composition which can be used in an additive manufacturing process. The radiation curable composition is particularly useful for producing transparent and elastomeric 3 -dim articles, which can be further used i.a. in the dental and orthodontic field, e.g., for the transfer and fixation of brackets.

Background

In the area of orthodontics teeth are often moved using brackets and wires which apply force to the teeth. Manual placement of brackets onto patients’ teeth is typically time consuming and failure prone towards inaccurate positioning.

For addressing this issues so-called Indirect Bonding Trays (IBT) have been developed which act as a template in which all brackets can be inserted and thus transferred in one step into a patient 's mouth.

IBTs increase robustness and precision of the positioning procedure, enabling a successful orthodontic procedure, and safe time by placing all brackets at once. With the reduced chair time and ease of use patient comfort is increased.

IBTs are sometimes produced in a multiple step procedure using a harder outer shell which can be produced in a thermoforming process and which is combined with an elastomeric and softer inner shell which takes up and releases the brackets afterwards.

This procedure, however, is labor-intensive and time-consuming.

As an alternative it has been suggested to produce IBTs by 3D-printing using an “IBT-resin”.

US 6,855,748 (Hatton) describes UV-curable compositions containing oxetane- and epoxycompounds in combination with multifunctional hydroxyl-compounds which can contain additional (meth)acrylates and which can be used for laser initiated stereolithographic procedures.

US 2014/0035202 Al (Southwell et al.) describes radiation curable resin compositions and rapid 3D imaging processes using them. The resins are based on cycloaliphatic epoxides in combination with oxetanes and (meth-)acrylates and cationic and free radical photo-initiators.

One class of suitable free radical photo-initiators comprises the ionic dye-counter ion compounds, which are capable of absorbing actinic rays and producing free radicals.

WO 2014/078537 Al (Dentsply) describes 3D fabricating material systems for producing dental products like artificial teeth, dentures, splints, veneers, inlays, onlays, copings, frame patterns, crowns, bridges, and the like. DLP procedures are used. The materials are (meth)acrylate based and can contain pigments. US 2007/0205528 Al (Patel et al.) and US 2007/0256781 Al (Johnson et al.) describe photocurable compositions for rapid prototyping techniques which can contain dyes.

WO 2014/078537 Al (Sun et al.) describes a three-dimensional fabrication material system for producing dental products. The composition for making a three-dimensional dental prosthesis comprises a mixture of (meth)acrylate, an inorganic filler, an organic filler, a silicone-acrylic-based rubber impact modifier, pigments and light initiators.

WO 2013/153183 A2 (Wachter et al.) describes a composite resin composition and method for producing dental components by means of stereo-lithography. The composite resin composition contains a) at least one poly-reactive binder, b) a first photo-polymerization initiator with an absorption maximum at a wavelength of less than 400 nm, c) a second photo polymerization initiator with an absorption maximum of at least 400 nm, and d) an absorber with an absorption maximum at a wavelength of less than 400 nm for the SLA production of a dental formed component on the basis of a composite resin.

US 2008/0287564 Al (Klare et al.) describes a biocompatible, low-viscosity radiation-curable formulation for producing medical products, in particular adaptive ear pieces, otoplastic parts, shells or ear parts, by means of PNP methods or stereolithographic methods, wherein the critical energy to penetration depth is adjusted by adding small quantities of anaerobic inhibitors such as phenothiazine or DPPH.

US 2014/0072712 Al (Xu) describes opaque inks for use with a three-dimensional printing system comprising 10-95 wt.% polymerizable component and 3-25 wt.% non-reactive wax component.

US 2010/0056661 Al (Xu) relates to a radiation-curable composition useful for the production of 3-dim solid articles. The composition comprises a hyperbranched poly(meth)acylate compound, a light sensitizer and an initiator. UV light sensitizers containing a thioxanthone moiety are said to be preferred. The composition may also contain pigments as additives.

US 2004/0170923 Al (Steinmann et al.) describes a liquid colored radiation-curable composition comprising a cationically polymerizing organic substance, a free-radical polymerizing organic substance, a cationic polymerization initiator, a free-radical polymerization initiator and an effective color-imparting amount of a soluble dye selected from diarylmethane and triarylmethane dyes, rhodamine dyes, azo dyes, thiazole dyes, anthraquinone dyes and safranine dyes. The resin composition is said to be particularly useful in the jewelry industry which requires good color contrast in thin layers.

WO 2018/234898 Al (3M) relates to a radiation curable composition for additive-manufacturing processes, the composition comprising (methjacrylate component(s) not comprising a urethane moiety, the (methjacrylate component s) having a molecular weight Mw of at least 1,000 as Component Al, photo-initiator as Component B, red, yellow or orange dye or combination thereof as Component C, blue dye having a light absorption band in the range of 350 to 420 nm as Component D, and optionally stabilizer as Component E. The radiation curable composition is said to be useful for producing transparent and elastomeric 3 -dim articles, which can be further used i.a. in the dental and orthodontic field e.g., for the fixation of brackets.

WO 2009/005576 (DSM IP Assets) describes a radiation curable liquid resin that can be used to make a clear and colorless, three-dimensional article by stereolithography process.

Summary of Invention

However, there is still a need for a radiation-curable composition which can be processed in an additive-manufacturing technique (in particular using a stereolithographic 3d-printing process) to obtain a transparent elastomeric 3 -dimensional-article (3 -dim article) having high surface resolution.

The 3-dim-article should also have an adequate Shore hardness.

In particular, the radiation-curable composition should be suitable to produce an elastomeric 3 -dim article, which can be used in the dental or orthodontic field.

Further, if possible, the radiation-curable composition should enable the production of a so-called indirect bonding positioning tray (IBT) based on data obtained from e.g., an intraoral scan of the dental situation in the mouth of a patient.

The material of such a 3-dim article should have good elastomeric and translucent properties, in particular in the region of 420 to 500 nm.

It would be advantageous if other dental or orthodontic article like orthodontic brackets can be snapped into the IBT in order to give the practitioner a good sense of control while loading the brackets into the IBT, prevent the brackets from falling out of the IBT while handling it, and finally release the brackets from the IBT without being damaged.

One or more of the above-mentioned objects are addressed by the invention described in the present text and claims.

A 3d-printable resin was developed which facilitates the manufacturing of 3-dim article in a 3d- printing process more easily and at lower costs.

In one embodiment the present invention features a radiation-curable composition for additivemanufacturing processes, the composition comprising

(meth)acrylate component Al comprising a polyalkylene oxide backbone, with at least two (meth)acrylate moieties, not comprising a urethane moiety, having a molecular weight Mw of at least 2,000 g/mol, in an amount of 50 to 85 wt.%,

(meth)acrylate component A2 with at least two (methjacrylate moieties, comprising in addition at least two urethane moieties, having a molecular weight Mw of at most 1,000 g/mol, in an amount of 5 to 20 wt.%,

(methjacrylate component A3 with only one (methjacrylate moiety, having a molecular weight of at most 500 g/mol, in an amount of 5 to 20 wt.%, photo-initiator, and optionally stabilizer, wt.% with respect to the amount of the whole composition.

The invention also relates to a process of producing a 3 -dim elastomeric article, the process comprising the step of processing the radiation-curable composition described in the present text in an additive-manufacturing process comprising a radiation-curing step, preferably using light with a wavelength in the range of 350 to 420 nm.

The invention is also directed to a 3 -dim elastomeric article obtained or obtainable by the process described in the present text, the 3 -dim elastomeric article comprising the radiation-curable composition as described in the present text in its cured state.

The invention is also related to the use of the radiation-curable composition for producing fittings, shock absorbers, seals, masks and medical products.

The invention also relates to a process of curing a radiation-curable Composition II, the process comprising the steps of providing a radiation-curable Composition I, the radiation-curable Composition I being the radiation-curable composition as described in the present text, processing the radiation-curable Composition I in an additive-manufacturing process using radiation for curing radiation-curable Composition I to obtain a transparent elastomeric 3 -dim article having an outer side and an inner side, placing the radiation-curable Composition II on the inner side of the transparent 3 -dim article, radiation-curing the radiation-curable Composition II from the outer side of the transparent 3- dim article, the radiation-curable Composition II being different from the radiation-curable Composition I with respect to its chemical formulation, radiation-curable Composition II comprising (meth)acrylate components, photo -initiator, and optionally filler.

Moreover, the invention features a kit of parts comprising a radiation-curable Composition I, the radiation curable Composition I being the radiation-curable composition as described in the present text, and a radiation-curable Composition II, the radiation-curable Composition II being characterized by the following features alone or in combination: being different in its chemical composition from the radiation-curable Composition I, being the radiation-curable Composition II as described in the present text.

Unless defined differently, for this description the following terms shall have the given meaning: The term "compound" or “component” is a chemical substance which has a certain molecular identity or is made of a mixture of such substances, e.g., polymeric substances.

A “hardenable or curable or polymerizable component” is any component which can be cured or solidified in the presence of a photo-initiator by radiation-induced polymerization. A hardenable component may contain only one, two, three or more polymerizable groups. Typical examples of polymerizable groups include unsaturated carbon groups, such as a vinyl group being present i.a. in a (methyl)acrylate group.

As used herein, "(meth)acryl" is a shorthand term referring to "acryl" and/or "methacryl”. For example, a "(meth) acryloxy" group is a shorthand term referring to either an acryloxy group (i.e., CH₂=CH-C(O)-O-) and/or a methacryloxy group (i.e., CH2=C(CH₃)-C(O)-O-).

As used herein, "hardening" or "curing" a composition are used interchangeably and refer to polymerization and/or crosslinking reactions including, for example, photo -polymerization reactions and chemical-polymerization techniques (e. g., ionic reactions or chemical reactions forming radicals effective to polymerize ethylenically unsaturated compounds) involving one or more materials included in the composition.

A “photo-initiator” is a substance being able to start or initiate the curing process of a hardenable composition in the presence of radiation, in particular light with a wavelength in the range of 300 to 700 nm.

“UV light” means light having a wavelength in the range of 300 to 420 nm.

A “monomer” is any chemical substance which can be characterized by a chemical formula, bearing polymerizable groups (including (meth)acrylate groups) which can be polymerized to oligomers or polymers thereby increasing the molecular weight. The molecular weight of monomers can usually simply be calculated based on the chemical formula given.

The term “dental or orthodontic article” means any article which is to be used in the dental or orthodontic field, especially for producing a dental restoration, orthodontic devices, a tooth model and parts thereof.

A dental or orthodontic article has typically two different surface portions, an outer surface and an inner surface. The outer surface is the surface which is typically not in permanent contact with the surface of a tooth. In contrast thereto, the inner surface is the surface which is used for attaching or fixing the dental article to a tooth.

Examples of dental articles include crowns, bridges, inlays, onlays, veneers, facings, copings, crown and bridged framework, implants, abutments, dental milling blocks, monolithic dental restorations and parts thereof.

Examples of orthodontic articles include brackets, buccal tubes, cleats and buttons and parts thereof.

A dental or orthodontic article should not contain components which are detrimental to the patient's health and thus free of hazardous and toxic components being able to migrate out of the dental or orthodontic article.

A “transparent article” is an article which is transparent if inspected with the human eye, in particular an article which has a light transmission of at least 50 % for a path length of 2 mm for light having a wavelength of 500 nm. A “particle” means a substance being a solid having a shape which can be geometrically determined. The shape can be regular or irregular. Particles can typically be analysed with respect to e.g. particle size and particle size distribution.

“Additive manufacturing” or “3d-printing” means processes comprising a radiation-curing step used to make 3 -dimensional articles. An example of an additive manufacturing technique is stereolithography (SLA) in which successive layers of material are laid down under computer control. The articles can be of almost any shape or geometry and are produced from a 3 -dim model or other electronic data source.

Other examples are digital light processing (DLP), continuous liquid interface production (CLIP), and volumetric additive manufacturing (VAM), robocasting (RC).

“Ambient conditions” mean the conditions which the composition described in the present text is usually subjected to during storage and handling. Ambient conditions may, for example, be a pressure of 900 to 1,100 mbar, a temperature of 10 to 40 °C and a relative humidity of 10 to 100 %. In the laboratory ambient conditions are typically adjusted to 20 to 25 °C and 1,000 to 1,025 mbar (at maritime level).

As used herein, “a”, “an”, “the”, “at least one” and “one or more” are used interchangeably. Also herein, the recitations of numerical ranges by endpoints include all numbers subsumed within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc.).

Adding an “(s)” to a term means that the term should include the singular and plural form. E.g., the term “additive(s)” means one additive and more additives (e.g. 2, 3, 4, etc.).

Unless otherwise indicated, all numbers expressing quantities of ingredients, measurement of physical properties such as described below and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about”.

The terms “comprise” or “contain” and variations thereof do not have a limiting meaning where these terms appear in the description and claims. “Consisting essentially of’ means that specific further components can be present, namely those which do not materially affect the essential characteristic of the article or composition. “Consisting of’ means that no further components should be present. The term “comprise” shall include also the terms “consist essentially of’ and “consists of’.

A composition is “essentially or substantially free of’ a certain component, if the composition does not contain said component as an essential feature. Thus, said component is not wilfully added to the composition either as such or in combination with other components or ingredient of other components. A composition being essentially free of a certain component usually does not contain that component at all. However, sometimes the presence of a small amount of the said component is not avoidable e.g. due to impurities contained in the raw materials used. Detailed Description

It has been found that the composition and processes described in the text are advantageous for a couple of reasons.

The radiation-curable composition described in the present text can be processed as manufacturing material in an additive-manufacturing process, in particular a so-called SLA process.

The radiation-curable composition has a viscosity which is low enough for enabling a fast 3d- printing of a 3 -dim article and high enough for enabling the production of a sufficiently hard and robust product.

Further, the 3 -dim article obtained by curing the radiation-curable composition described in the present text is sufficiently elastic, flexible and transparent in the visible light region.

The 3-dim article also shows an adequate Shore hardness.

Due to its mechanical properties, the invention provides a solution for the simultaneous transfer and release of individual parts from a transfer device made from the radiation-curable composition described in the present text to another surface.

Due to its optical properties, the invention provides a solution for the rapid curing of another radiation-curable composition or article which is stored or fixed in the translucent 3-dim article obtained by curing the radiation-curable composition described in the present text.

Thus, the invention facilitates e.g., the light-curing of a dental composition like an adhesive or cement by irradiating light through the elastomeric and transparent 3-dim article obtained by curing the radiation-curable composition described in the present text and the removing of the elastomeric transparent 3-dim article afterwards.

Thus, the radiation-curable composition described in the present text is in particular useful for producing medical products, in particular dental and orthodontic products including IBTs.

In was also found that once cured, the 3-dim article is also not sticky.

Thus, other articles which are attached to or fixed in the elastomeric 3-dim article can easily be released therefrom.

It was also found that the elastomeric 3-dim article obtained from the curable composition described in the present text usually does not stick to surfaces of other (meth)acrylate containing compositions. That is, the elastomeric 3-dim article can be easily removed from the surface of (meth)acrylate composite articles or compositions, including dental adhesives and dental cements.

This is surprising as both articles, the elastomeric 3-dim article and the (meth)acrylate composite article, are based on the same crosslinking chemistry.

Instead, one would have expected that the curing of a radiation-curable (meth)acrylate composition being located on the surface of another (meth)acrylate article will result in an adhesion of that radiation curable (meth)acrylate composition to the other (meth)acrylate article. It was also found that the 3 -dim article obtained from the curable composition described in the present text remains sufficiently storage stable and does not show undesired discoloration and/or changes in its physical-mechanical properties (e.g., E-modulus, elongation at break) over time.

The invention relates to a radiation-curable composition, in particular for use in an additivemanufacturing process.

The radiation-curable composition comprises a (meth)acrylate component Al.

The (meth)acrylate component Al is or can be characterized by the following properties: it comprises a polyalkylene oxide backbone, it comprises at least at least two (meth)acrylate moieties; it does not comprise a urethane moiety; it has a molecular weight Mw of at least 2,000 g/mol, it is present in the radiation-curable composition in an amount of 50 to 80 wt.%.

It was found that a (meth)acrylate component where the (meth)acrylate moieties are attached or connected through other moieties to a polyalkylene oxide backbone of a sufficiently high molecular weight is particularly suitable for producing rubber-elastic materials.

A molecular weight in this range may help to improve properties like elasticity, elongation at break, Young's modulus and/or elastic modulus.

(Meth)arylate component Al typically has a viscosity in the range of 0.1 to 100 Pa*s or 1 to 50

Pa*s measured at 23°C and a shear rate of 50 s’¹.

The average molar weight (Mw) of Component Al is typically within a range from 1,000 to 20,000 g/mol.

A molecular weight in this range may help to improve properties like elasticity, elongation at break, Young's modulus and/or elastic modulus of the resulting cured 3-dim article.

Preferred representatives of Component Al include

R-[(CH₂)„-(CHR’)-O]_k-[(CH₂)_m-(CHR")-O]i-(CH₂)_m-(CHR")-R with: n = 1 to 6, preferably 1 to 4, in particular 1, m = 1 to 6, preferably 1 to 4, in particular 3, k, 1 = 2 to 500, preferably 4 to 250, in particular 10 to 200,

R',R" = independently selected from H, methyl, ethyl, preferably R'=R"=H,

R = CH₂=CH-C(O)-O- or CH₂=C(CH₃)-C(O)-O-, the bracketed expressions indexed by the symbols k and 1 being able to be arranged regularly or irregularly alternating or in block form.

Appropriate polyethers or polyether groups which may form the polyalkylene oxide backbone of Component Al can be produced in a manner known to the person skilled in the art e.g. by the reaction of a starting compound having a reactive hydrogen atom with alkylene oxides, e.g., ethylene oxide, propylene oxide, butylene oxide, styrene oxide, tetrahydro furane (THF) or epichlorohydrin or mixtures of two or more thereof.

Especially suitable are polyether compounds which are obtainable by polyaddition of ethylene oxide, 1,2-propylene oxide, 1,2-butylene oxide or tetrahydrofuran or of mixtures of two or more of the mentioned compounds with the aid of a suitable starting compound and a suitable catalyst. The reaction products of low-molecular-weight polyfunctional alcohols having at least two hydroxyl groups with alkylene oxides, so-called polyethers, may also be used as polyols. The alkylene oxides preferably have from 2 to 4 carbon atoms. Suitable polyols are, for example, the reaction products of ethylene glycol, propylene glycol, butanediol or hexanediol isomers with one or more of the following alkylene oxides: ethylene oxide, propylene oxide or butylene oxides like tetrahydrofuran. Furthermore, the reaction products of polyfunctional alcohols such as glycerol, trimethylolethane or trimethylolpropane, pentaerythritol or sugar alcohols, or mixtures of two or more thereof, with the mentioned alkylene oxides, forming polyether polyols are also suitable.

Suitable starting compounds are, for example, water, ethylene glycol, 1,2- or 1,3-propylene glycol, 1,4- or 1,3-butylene glycol, 1,6-hexanediol, 1,8-octanediol, neopentyl glycol, 1,4- hydroxymethylcyclohexane, 2-methyl-l,3-propanediol, glycerol, trimethylolpropane, 1,2,6- hexanetriol, 1,2,4-butanetriol, trimethylolethane, pentaerythritol, mannitol, sorbitol, or mixtures of two or more thereof.

Especially suitable are polyether compounds as are obtainable by polyaddition of ethylene oxide, 1,2-propylene oxide, 1,2-butylene oxide or tetrahydrofuran or of mixtures of two or more of the mentioned compounds with the aid of a suitable starting compound and a suitable catalyst.

For example, polyether polyols which are prepared by copolymerisation of tetrahydrofuran and ethylene oxide in a molar ratio of from 10 : 1 to 1 : 1, preferably to 4 : 1, in the presence of strong acids, for example boron fluoride etherates, are suitable as well.

Specific examples of Component Al include (meth)acrylated ethylene oxide, propylene oxide, ethylene / propylene oxide copolymers, ethylene oxide / tetrahydrofuran copolymers, polypropylene glycol and mixtures thereof.

Component Al is typically present in the following amounts: 50 to 85 wt.% or 55 to 80 wt.% with respect to the whole composition.

The radiation-curable composition further comprises (meth)acrylate component A2.

The (meth)acrylate component A2 is or can be characterized by the following properties: it comprises at least two (meth)acrylate moieties, it comprises in addition at least one urethane moiety, it has a molecular weight Mw of at most 1,000 g/mol, it is present in the radiation-curable composition in an amount of 5 to 20 wt.%. Component A2 typically has a viscosity of 0.1 to 100 Pa*s or 1 to 50 Pa*s at 23 °C and a shear rate of 50 s’¹.

Component A2 typically has a molecular weight (Mw) in the range of 200 to 1,000 g/mol or 300 to 800 g/mol.

Component A2 may comprise at least 2 or 3 or 4 (meth)acrylate moieties.

Further, component A2 may comprise at least 2 or 3 or 4 urethane moieties.

Further, component A2 may comprise a C2 to C20 linear or branched alkyl moiety to which the (meth)acrylate moieties are attached via a spacer comprising the urethane moieties.

Thus, the urethane moieties are typically located between the (meth)acrylate moieties and the linear or branched alkyl backbone.

Suitable urethane (meth)acrylates may be obtained by a number of processes known to the skilled person.

The urethane(meth)acrylates are typically obtained by reacting an NCO-terminated compound with a suitable monofunctional (meth)acrylate monomer such as hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, preferably hydroxyethyl- and hydroxypropyl methacrylate.

For example, a polyisocyanate and a polyol may be reacted to form an isocyanate-terminated urethane prepolymer that is subsequently reacted with a (meth)acrylate such as 2-hydroxy ethyl(meth)acrylate. These types of reactions may be conducted at room temperature or higher temperature, optionally in the presence of catalysts such as tin catalysts, tertiary amines and the like.

Polyisocyanates which can be employed to form isocyanate-functional urethane prepolymers can be any organic isocyanate having at least two free isocyanate groups. Included are aliphatic cycloaliphatic, aromatic and araliphatic isocyanates.

Any of the known polyisocyanates such as alkyl and alkylene polyisocyanates, cycloalkyl and cycloalkylene polyisocyanates, and combinations such as alkylene and cycloalkylene polyisocyanates can be employed.

Preferably, diisocyanates having the formula X(NCO)2 can be used, with X representing an aliphatic hydrocarbon radical with 2 to 12 C atoms, a cycloaliphatic hydrocarbon radical with 5 to 18 C atoms, an aromatic hydrocarbon radical with 6 to 16 C atoms and/or an araliphatic hydrocarbon radical with 7 to 15 C atoms.

Examples of suitable polyisocyanates include 2,2,4-trimethylhexamethylene-l,6-diisocyanate, hexamethylene- 1,6-diisocyanate (HDI), cyclohexyl-l,4-diisocyanate, 4,4'methylene-bis(cyclohexyl isocyanate), l,l'-methylenebis(4-isocyanato) cyclohexane, isophorone diisocyanate, 4,4'-methylene diphenyl diisocyanate, 1,4-tetramethylene diisocycanate, meta- and para-tetramethylxylene diisocycanate, 1,4-phenylene diisocycanate, 2,6- and 2,4-toluene diisocycanate, 1,5 -naphthylene diisocycanate, 2,4' and 4,4'-diphenylmethane diisocycanate and mixtures thereof. It is also possible to use higher-functional polyisocyanates known from polyurethane chemistry or else modified polyisocyanates, for example containing carbodiimide groups, allophanate groups, isocyanmate groups and/or biuret groups. Particularly preferred isocyanates are isophorone diisocyanate, 2,4,4-trimethyl-hexamethylene diisocyanate and higher-functional polyisocyanates with isocyanurate structure.

The isocyanate terminated urethane compound is capped with a (meth)acrylate to produce a urethane(meth)acrylate compound. In general, any (meth)acrylate-type capping agent having a terminal hydroxyl group and also having an acrylic or methacrylic moiety can be employed, with the methacrylic moiety being preferred.

Examples of suitable capping agents include 2-hydroxyethyl(meth)acrylate, 2-hydroxypropyl (meth)acrylate, glycerol di(meth)acrylate and/or trimethylolpropane di(meth)acrylate. Particularly preferred are 2-hydroxyethyl methacrylate (HEMA) and/or 2-hydroxyethyl acrylate (HEA).

The equivalence ratio of isocyanate groups to compounds reactive vis-a-vis isocyanate groups is 1.1:1 to 8:1, preferably 1.5:1 to 4:1.

The isocyanate polyaddition reaction can take place in the presence of catalysts known from polymethane chemistry, for example organotin compounds such as dibutyltin dilaurate or amine catalysts such as diazabicyclo[2.2.2]octane. Furthermore, the synthesis can take place both in the melt or in a suitable solvent which can be added before or during the prepolymer preparation. Suitable solvents include e.g. acetone, 2-butanone, tetrahydrofuran, dioxane, dimethylformamide, N-methyl-2 -pyrrolidone (NMP), ethyl acetate, alkyl ethers of ethylene and propylene glycol and aromatic hydrocarbons and mixtures thereof. The use of ethyl acetate as solvent is particularly preferred.

Suitable examples of urethane (meth)acrylates include 7,7,9-trimethyl-4,13-dioxo-3,14-dioxa-5,12- diazahexadecane-l,16-dioxy -dimethacrylate (e.g. Plex 666-1, Rohm), 7,7,9-trimethyl-4,13-dioxo- 5, 12-diazahexadecane-l,16-dioxy -dimethacrylate (UDMA), urethane (methacrylates) derived from 1,4 and l,3-Bis(l-isocyanato-l-methylethyl)benzene (e.g., as described in EP 0934926 Al) and mixtures thereof.

A suitable urethane dimethacrylate can be characterized e.g., by the following formula:

wherein

R¹ is a hydrogen atom or a methyl group, and

R² is a linear or branched alkylene group of 1 to 8 carbon atoms or

Specific examples of Component A2 also include di(acryloxyethyl)dimethylene diurethane, di(methacryloxyethyl)-dimethylene diurethane, di(acryloxyethyl)tetramethylene diurethane, di(methacryloxyethyl)-tetramethylene diurethane, di(acryloxyethyl)-trimethylhexamethylene diurethane, and di(methcryloxyethyl)-trimethylhexanmethylene dimethane, and mixtures thereof. According to one embodiment the methane dimethacrylate of the following formula is preferred:

Other suitable urethane(meth)acrylates which may be present in the radiation cmable composition described in the present text are characterized as follows: having the structure A-(-Sl-U-S2-MA)_n, with

A being a connector element comprising at least one unit,

51 being a spacer group comprising at least 4 units connected with each other,

52 being a spacer group comprising at least 4 units connected with each other, the units of A, SI and S2 being independently selected from CH₃-, -CH₂-, -O-, -S-, -NR¹-, -CO-

with R¹ and R² being independently selected from hydrogen, alkyl, substituted alkyl, alkenyl, cycloalkyl, substituted cycloalkyl, arylalkyl, aryl or substituted aryl, wherein these units can form linear, branched or cyclic structures such as alkyl, cycloalkyl, aryl, ester, urethane or amide groups,

U being a urethane group connecting spacer groups SI and S2,

MA being an acrylate or methacrylate group and n being 3 to 6.

According to one embodiment the methane(meth)acrylate is represented by the structure

A-(-Sl-U-S2-MA)_n with

A being a connector element comprising at least 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20 units,

SI being a spacer group comprised of units connected with each other and comprising at least 4, 5,

6, 7, 8, 9 or 10 units, S2 being a spacer group comprised of units connected with each other and comprising at least 4, 5, 6, 7, 8, 9, 10, 12, 15, 20 or 25 units,

U being a urethane group connecting spacer groups S 1 and S2,

MA being an acrylate or methacrylate group and n being 3 to 6 or 4 to 6 or 5 to 6.

It can be preferred, if A has a cyclic structure and comprises at least 6 units.

It can further be preferred, if SI has a linear or branched structure and comprises at least 4 or 6 units.

It can further be preferred, if S2 has a linear or branched structure and comprises at least 6 or 8 units.

A urethane(meth)acrylate wherein A has a cyclic structure and comprises at least about 6 units and SI has a linear structure and comprises at least 4 units and S2 has a linear structure and comprises at least 8 units and U is a urethane group can also be preferred.

Neither the atoms of the urethane group connecting SI and S2 nor the atoms of the (meth)acrylgroup belong to the spacer group SI or S2. Thus, the atoms of the urethane group do not count as units of the spacer groups SI or S2.

The nature and structure of the connector element is not particularly limited. The connector element can contain saturated (no double bonds) or unsaturated (at least one or two double bonds) units, aromatic or hetero aromatic units (aromatic structure containing atoms including N, O and S).

Specific examples of connector element A having a cyclic structure include:

Specific examples of connector element A having a non-cyclic but branched structure include:

unit)

The dotted lines indicate bondings to the spacer group SI.

The nature and structure of the spacer groups SI or S2 is not particularly limited, either. The spacer groups are comprised of units connected with each other. Typical units include: CH3-, -

CR'R²-. with R¹ and R² independently selected from hydrogen, alkyl, substituted alkyl, alkenyl, cycloalkyl, substituted cycloalkyl, arylalkyl, aryl or substituted aryl.

These units can form linear, branched or cyclic structures such as alkyl, cycloalkyl, aryl, ester, urethane or amide groups.

The structure of SI can be identical to the structure of S2. However, in some embodiments the structure of SI is different from S2. In a specific embodiment the number of units being present in SI is less or equal than the number of units being present in S2.

In a specific embodiment, SI may have a saturated hydrocarbon structure.

In another specific embodiment, S2 may have a saturated hydrocarbon structure.

Typical examples of useful spacer groups for SI include:

The dotted lines indicate the chemical bonding to either the group A or the group U.

Typical examples of useful spacer groups for S2 include:

The dotted lines indicate the chemical bonding to either the (meth)acrylate group or the group U.

The number of the units to be counted according to the invention is given in brackets.

Specific examples of hardenable component (B) include

Further suitable urethane(meth)acrylates are based on alpha-omega-terminated poly(meth)acrylatdiols (e.g. as described in EP 1 242 493 Bl) or can be a polyester, poly ether, polybutadiene or polycarbonate urethane(meth)acrylate (e.g. as described in US 6,936,642 B2). Component A2 is typically present in the following amounts: 5 to 20; or from 3 to 18; or from 8 to

15 wt.%; wt.% with respect to the whole composition.

The radiation-curable composition further comprises (meth)acrylate component A3.

The (meth)acrylate component A3 is or can be characterized by the following properties: it comprises only one (meth) aery late moiety, is has a molecular weight of at most 500 g/mol, or of at most 400 g/mol, or of at most 350 g/mol, it is present in the radiation-curable composition in an amount of 5 to 20 wt.%.

Contrary to (meth)acrylate components Al and A2, (meth)acrylate component A3 has a lower molecular weight.

Further, as (meth)acrylate component A3 comprises only one (meth)acrylate moiety, component A3 cannot act as a crosslinking agent.

Without wishing to be bound to a particular theory, it is believed that during the radiation-curing and resulting polymerization of the components, (meth)acrylate component A3 hampers the formation of a too dense network and thus contributes to achieving the elastomeric properties of the resulting 3 -dim article.

Further, it was found that adding a low viscous component to the other components of the radiation-curable composition contributes to the reducing of the overall viscosity of the radiation- curable composition which may facilitate the processing of the composition in an additivemanufacturing process.

In particular low viscous and low molecular weight components were found to be useful.

In this respect suitable (meth)acrylate components A3 can be further characterized by the following features alone or in combination: a) molecular weight (Mw): 85 to 500 g/mol, or 130 to 500 g/mol, or 130 to 400 g/mol; b) viscosity: 0.01 to 20 Pa*s, or 1 to 50 Pa*s at 23°C at a shear rate of 50 s’¹.

Component A3 does not comprise an aromatic moiety.

Component A3 does typically not comprises more than 25 or more than 22 or more than 20 carbon atoms.

Examples for component A3 include hydroxyethyl(meth)acrylate (HEMA), hydroxypropyl(meth)acrylate (HPMA), butyl(meth)acrylate, isobomyl(meth)acrylate, lauryl(meth)acrylate, stearyl(meth)acrylate, tetrahydrofurfurylmethacrylate and mixtures thereof.

Component A3 is typically present in the following amounts: 5 to 20 or from 3 to 18 or from 8 to 15 wt.% with respect to the whole composition.

The radiation-curable composition described in the present text comprises one or more photo- initiator(s).

The nature and structure of the photo-initiator is not particularly limited unless the desired result cannot be achieved.

Suitable photo-initiator(s) can typically be characterized by the following features alone or in combination: showing a light absorption band in a wavelength range of 300 to 450 nm; solubility: at least 2 g in 100 g of triethylenglycol di(meth)acrylate (TEGDMA) at 23°C.

The photo-initiator typically absorbs light in the blue spectral range, e.g., in the range of 350 to 450 nm.

The photo-initiator should be soluble in the radiation-curable components of the radiation-curable composition described in the present text.

The photo-initiator is capable of generating free radicals for polymerization upon exposure to light energy having a wavelength in the range of 350 to 450 nm.

Photo-initiator(s) where two radicals are generated by cleavage were found to be particular useful. Examples of photo-initiators according to this type typically contain a moiety selected form benzoin ether, acetophenone, benzoyl oxime, 1,2-diketone or acyl phosphine oxide.

A particularly suitable class of photo-initiators include the class of acylphosphine oxides, as described e.g. in US 4,737,593 (Elrich et al.).

Such acylphosphine oxides can be characterized by the following formula

(R⁹)₂ — P(=O) — C(=O)— R¹⁰ wherein each R⁹ individually can be a hydrocarbyl group such as alkyl, cycloalkyl, aryl, and aralkyl, any of which can be substituted with a halo-, alkyl- or alkoxy -group, or the two R⁹ groups can be joined to form a ring along with the phosphorous atom, and wherein R¹⁰ is a hydrocarbyl group, an S-, O-, or N-containing five- or six-membered heterocyclic group, or a -Z-C(=O)- P(=O)- (R⁹)₂ group, wherein Z represents a divalent hydrocarbyl group such as alkylene or phenylene having from 2 to 6 carbon atoms.

Preferred acylphosphine oxides are those in which the R⁹ and R¹⁰ groups are phenyl or lower alkyl- or lower alkoxy-substituted phenyl. By “lower alkyl” and “lower alkoxy” is meant such groups having from 1 to 4 carbon atoms.

Exemplary UV photo-initiators include 1 -hydroxy cyclohexyl benzophenone (available, e.g., under the previous trade designation “IRGACURE™ 184” from Ciba Specialty Chemicals Corp.), 4-(2- hydroxyethoxy)phenyl-(2-hydroxy-2-propyl) ketone (available, for example, under the previous trade designation “IRGACURE™ 2529” from Ciba Specialty Chemicals Corp.), 2-hydroxy-2- methylpropiophenone (available, for example, under the previous trade designation “DAROCURE™ Dill” from Ciba Specialty Chemicals Corp.) and bis(2,4,6-trimethylbenzoyl)- phenyl phosphine oxide (available, for example, under the previous trade designation “IRGACURE™ 819” from Ciba Specialty Chemicals Corp.), which is often preferred.

Tertiary amine reducing agents may be used in combination with an acylphosphine oxide.

Illustrative tertiary amines include ethyl 4-(N,N-dimethylamino)benzoate and N,N- dimethylaminoethyl methacrylate.

Commercially-available phosphine oxide photo-initiators capable of free-radical initiation when irradiated at wavelengths of greater than 400 nm to 1200 nm include a 25:75 mixture, by weight, of bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentyl phosphine oxide and 2-hydroxy-2-methyl-l- phenylpropan-l-one (previously available as IRGACURE™ 1700, Ciba Specialty Chemicals), 2- benzyl-2-(N,N-dimethylamino)-l-(4-morpholinophenyl)-l-butanone (previously available as IRGACURE™ 369, Ciba Specialty Chemicals), bis(r]5-2,4-cyclopentadien-l-yl)-bis(2,6-difluoro- 3-(lH-pyrrol-l-yl)phenyl) titanium (previously available as IRGACURE™ 784 DC, Ciba Specialty Chemicals), a 1:1 mixture, by weight, of bis(2,4,6-trimethylbenzoyl)phenyl phosphine oxide and 2- hydroxy-2-methyl-l-phenylpropane-l-one (previously available as DAROCUR™ 4265, Ciba Specialty Chemicals), and ethyl-2,4,6-trimethylbenzylphenyl phosphinate (LUCIRIN™ LR8893X, BASF Corp., Charlotte, NC).

Also useful are photo-initiators comprising an alpha, beta-triketon moiety or comprising an alphadiketon dialkyl ketal moiety.

The photo-initiator(s) is typically present in the following amounts: at least 0.01 or at least 0.05 or at least 0.1 wt.%; at most 5 or at most 3 or at most 2 wt.%; from 0.01 to 5 or from 0.01 to 3 wt.% or 0.01 to 2 wt.%; wt.% with respect to the weight of the whole composition.

The radiation curable composition described in the present text may also comprise one or more stabilizer(s).

A stabilizer may extend the shelf life of the radiation-curable composition, help prevent undesired side reactions, discoloration and adjust the polymerization process of the radiation-curable component(s) present in the radiation-curable composition.

Adding one or more stabilizers) to the radiation-curable composition may further help to improve the accuracy or detail resolution of the surface of the 3 -dim article to be produced.

Stabilizers which can be added may function as oxygen-scavenger, as UV-absorber and/or storage stabilizer.

The radiation-curable composition may comprise an oxygen-scavenger. One or more oxygenscavengers may be present.

Using an oxygen-scavenger may contribute to reducing the risk of an undesired discoloration of the 3d-printed article.

A discoloration of the 3d-printed article later might be disadvantageous as the 3d-printed article will become less transparent and thus less aesthetic.

Aside from that, a discoloration of the 3d-printed article might also have a negative impact on a possible future use of the 3d-printed article for acting as a kind of template or mould for storing and curing other radiation-curable compositions located in this template or mould.

Due to the reduced transparency and depending on the wavelength used for curing, the curing of the other radiation-curable compositions stored in such a template or mould might not be as effective as desired.

Using an oxy gen-scavenger may also contribute to improving the reactivity of the radiation-curable composition. It was found that in particular stabilizers comprising at least one or two prenyl moieties, i.e. at least one or more CH=C(CH₃)2 moieties, are suitable.

Examples of stabilizers which may act as oxygen scavenger include components comprising a glycerin ether moiety, in particular a diprenyl-glycerin ether moiety (DPNG).

These stabilizers do not contain a (meth)acrylate moiety and so do not take part in a radical polymerization reaction.

Further, it was found that these stabilizers do not migrate out of the 3d-printed article during storage or later use.

It was found that using these stabilizers in an amount of at least 0.5 wt.% or in the range of 1 to 3 wt.% with respect to the radiation-curable composition can be advantageous for avoiding an undesired discoloration.

The radiation-curable composition may comprise in addition an UV-absorber. One or more UV absorbers can be present.

In particular adding a UV-absorber to the radiation-curable composition may help to enhance the resolution and accuracy of the SLA process by attenuating or avoiding unwanted scattering effects, as well as increase the shelf life of the radiation-curable composition.

Using UV-absorbers comprising a triazine or (benzo)triazole moiety are sometime preferred.

Examples of UV-absorbers which can be used include 2-(2'-Hydroxy-3'-tert-butyl-5'- methylphenyl)-5-chlorobenzortriazole (Tinuvin™ 326), 2-(tert-Butyl)-6-(5-chloro-2H- benzo[d][l,2,3]triazol-2-yl)-4-methylphenol (Bumetrizole™), 2-[3-(2H-Benzotriazol-2-yl)-4- hydroxyphenyl] ethyl methacrylate and mixtures thereof.

If present, UV-absorbers are typically used in an amount of less than 0.5 wt.% or in a range of 0.01 to 0.3 wt.% each with respect to the radiation-curable composition.

The radiation-curable composition may comprise also in addition storage stabilizers. One or more storage stabilizers can be present.

A storage stabilizer may help to improve the storage stability of the radiation-curable composition, that is, avoid a premature polymerization of the composition and an undesired increase of viscosity during storage and use.

Examples of storage stabilizers which can be used include stabilizers comprising one or more of the following moieties: phenol, quinone, phenothiazine, free radicals.

Specific examples of such stabilizer(s) include: p-methoxyphenol (MOP), hydroquinone monomethylether (MEHQ), 2,6-di-tert-butyl-4-methyl-phenol (BHT; Ionol), phenothiazine, Irganox™ 1010 (CAS: 6683-19-8; available from BASF), 2,2,6,6-tetramethyl-piperidine-l-oxyl radical (TEMPO) and mixtures thereof. If present, storage stabilizers are typically used in an amount of less than 0.5 wt.% or in a range of 0.01 to 0.4 wt.% each with respect to the radiation-curable composition.

Sometimes, the combined use of different kinds of stabilizers is preferred.

Using a combination of stabilizers may help to provide a radiation-curable composition which is not only sufficiently storage stable storage, which can be 3d-printed with the desired accuracy, and where the 3d-printed article does not show an undesired discoloration afterwards.

The radiation-curable composition may comprise one or more of the following stabilizers in combination: oxygen scavenger, preferably in an amount of 0.5 to 3 wt.%,

UV-absorber, preferably in an amount of 0.01 to 0.5 wt.%, storage stabilizer, preferably in an amount of 0.01 to 0.5 wt.%, wt.% with respect to the weight of the curable composition.

If a combination of stabilizers is present, the stabilizers are present in the following amounts: at least 1 or at least 1.5 wt.%; at most 3, or at most 2.5 wt.%; from 1 to 3 or from 1.5 to 3 wt.%; wt.% with respect to the weight of the curable composition.

The radiation-curable composition may also contain additive(s).

Additive(s) which can be added include diluents, surfactants, and mixtures thereof.

If present, additive(s) are present in an amount of not more than 5 wt.% with respect to the weight of the composition.

In certain embodiments, the radiation-curable composition described in the present text is characterized by the following properties alone or in combination: a) viscosity: less than 50 Pa*s or less than 20 Pa*s at 23°C and a shear rate of 50 s'¹; b) pH value: 2 to 8 e.g., if the radiation-curable composition is brought in contact with wet pH sensitive paper; c) light transmission: at least 50 % for a path length of 2 mm using light having a wavelength of 500 nm; d) radiation-curable with light having a wavelength in the range of 350 to 420 nm; e) appearance: transparent; f) color: colorless.

In certain embodiments, the combination of the following features is sometimes desirable: a), c) and d); or e) and f).

The radiation-curable composition may comprise, essentially consists of or consists of the following components in the respective amounts: (meth)acrylate component Al: 50 to 85 wt.%,

(meth)acrylate component A2: 3 to 20 wt.%,

(meth)acrylate component A3: 3 to 20 wt.%, photo-initiator: 0.01 to 5 wt.%, stabilizers: 0.5 to 4 wt.%, additives: 0 to 5 wt.%, wt.% with respect to the radiation-curable composition.

Alternatively, the radiation-curable composition may comprise, essentially consists of or consists of the following components in the respective amounts:

(meth)acrylate component Al: 55 to 80 wt.%,

(meth)acrylate component A2: 3 to 18 wt.%,

(meth)acrylate component A3: 3 to 18 wt.%, photo-initiator: 0.01 to 3 wt.%, stabilizer: 1 to 4 wt.%, additives: 0 to 5 wt.%, wt.% with respect to the radiation-curable composition.

All components used in the radiation-curable composition described in the present text should be sufficiently biocompatible, that is, the radiation-curable composition should not produce a toxic, injurious, or immunological response in living tissue.

The radiation-curable composition does typically not comprise or are essentially free of the following component(s) alone or in combination: cationically curable component(s); organic or inorganic pigment(s); dye(s), in particular perylene dye(s); fdler, in particular fdler particles having a refractive index which differs by more than 0.5 from the refractive index of the resin composition; wt.% with respect to the whole composition.

The radiation-curable composition described in the present text can be produced by mixing the respective components, in particular under save light conditions. If desired, a speed mixer can be used.

Typically, component Al is provided first. The other components are added as desired.

During storage, the radiation-curable composition described in the present text is typically packaged in a suitable packaging device.

The radiation-curable composition described in the present text is typically stored in container. Suitable containers include vessels, foil bags, cartridges, etc.

The volume of the respective containers is not particularly limited, but is typically in a range from 10 to 200,000 ml or from 500 to 10,000 ml. The radiation-curable composition is in particular useful for being processed in an additivemanufacturing process.

As a result, a transparent, elastomeric 3 -dim article is obtained.

Such an additive-manufacturing process typically comprises the following steps in the following order: providing a layer of the radiation-curable composition on a surface, radiation curing those parts of the layer of the radiation-curable composition which will belong to the 3 -dim article to be produced, providing an additional layer of the radiation-curable composition in contact with the radiation- cured surface of the previous layer, repeating the previous steps until a 3 -dim article is obtained.

Such a process comprises the step of applying radiation to the surface of a radiation-curable material, wherein the radiation is applied only to those parts of the surface which will later form a part of the article to be produced.

Radiation can be applied by using e.g., a laser beam or by mask-image projection. Using a maskimage projection based stereolithography process (MIP-SL) is sometimes preferred, as it allows a more rapid manufacturing of the article.

Projecting the mask image on the radiation-curable material can be done either top-down or bottom-up with respect to the orientation of the vat.

Using the bottom-up technique can be beneficial as less radiation-curable material is needed.

If desired, the obtained 3 -dim article can be further post-processed.

Suitable post-processing steps include cleaning the 3 -dim article, and/or conducting a further curing step.

If desired, the cleaning can be done by either using a cleaning solution (such as iso-propanol) or conducting a so-called spin-cleaning process as described e.g., in WO 2019/023120 Al (3M) or using a post-processing device as described in US 63/477,687 (3M).

If desired, further curing or post-curing can be done by applying radiation and/or heat, e.g., by applying radiation with wavelength in the range of 200 to 500 nm.

The radiation-curable composition described in the present text can be used for producing a 3 -dim article.

The 3 -dim article obtained by curing the radiation-curable composition can typically be characterized by the following features alone or in combination: a) tensile strength: 0.5 to 50 MPa, or 1.0 to 30 MPa according to ISO/DIN 53504 (2015-8); b) elongation at break: 100 to 500 %, or 150 to 400 % according to ISO/DIN 53504 (2015-8); c) E-modulus: 1 to 10 MPa, or 1 to 5 MPa according to ISO/DIN 53504 (2015-8); d) elastic recovery: at least 99% determined according to the process described in the description; e) Shore hardness A: 50 to 90 according to ISO/DIN 53505 (2000-8); f) light transmission: at least 50 % for a path length of 2 mm using light having a wavelength of 500 nm; g) water contact angle: < 100°; h) not sticky to surfaces of cured (meth)acrylates; i) colorless to the human eye.

In particular, the 3 -dim article is rubber-elastic and transparent.

A combination of the features a) and b); or b) and c); or a), b), c) and d); or a), b), e) and 1) can sometimes be preferred.

Good elastic properties can be beneficial as it may allow an easy placing and release of other articles in recesses of the 3-dim article.

A good light transmission may allow not only a good inspection of other articles in recesses of the 3-dim article, but also facilitates the curing of a radiation-curable composition placed in recesses of the 3-dim article.

A sufficiently high Shore hardness can be beneficial as it allows a firm fixation of other articles (such as orthodontic brackets in recesses of an individual bonding tray).

A water contact angle as outlined below can be beneficial, in particular if the 3-dim article should be used as a mold in a moist or humid environment.

The 3-dim article may have the shape of a medical product, in particular the shape of an orthodontic or dental article.

According to one embodiment, the 3-dim article has the shape of a dental impression or indirect bonding tray (IBT).

The radiation-curable composition described in the present text and the 3d-printed articles obtained therefrom may be used for producing various items and technical parts like transparent fittings, shock absorbers, seals, masks, shoe sols etc.

The radiation-curable composition described in the present text is in particular useful for producing medical products such as dental and/or orthodontic products including indirect bonding trays (IBT).

The radiation-curable composition can in particular be used in a process of treating the dental situation in the mouth of a patient, the process comprising the steps of a) processing the radiation-curable composition in an additive -manufacturing process for obtaining a 3-dim article having the shape of a customized IBT containing recesses for receiving orthodontic brackets, the shape of the customized IBT being based on patient-specific digital data, b) optionally post-processing the 3-dim article (e.g., by conducting a cleaning step, post-curing step, etc.), c) inserting orthodontic brackets in the recesses of the customized IBT, the orthodontic brackets comprising radically curable components, wherein the radically curable components a. can be present already on the orthodontic brackets before the insertion step, or b. are applied on the surface of the orthodontic brackets in a separate step, d) inserting the customized IBT with the inserted orthodontic brackets into the mouth of a patient so that the orthodontic brackets are in contact with the surfaces with the opposing teeth, e) fixing the orthodontic brackets to the surface of the opposing teeth, e.g. by applying radiation or with the aid of a redox-curing dental adhesive, f) removing the customized IBT from the mouth of the patient, wherein the individual steps can be done at different locations by different practitioners. For example, steps a) and b) are done at one location such as a 3d-printing company or an orthodontic office, and/or step c) is done at a different location such as a dental lab, an orthodontic office and/or steps d) to f) are done at an even further different location such as a dental surgery or an orthodontic office.

Patient-specific data can be obtained or information associated with the dental situation of a patient can be obtained and provided by means known to the skilled person, e.g., by photographing or scanning the dental situation in the mouth of a patient or by using information stored in a database. Various intraoral scanners are meanwhile commercially available on the market (e.g., from 3 Shape, Planmeca, and others).

The radiation-curable composition described in the present text can also be used in a process of curing a further radiation-curable composition.

Such a process may comprise the steps of a) providing a radiation-curable Composition I, the radiation-curable Composition I being the radiation-curable composition as described in the present text, b) processing the radiation-curable Composition I in an additive-manufacturing process using radiation for curing radiation-curable Composition I to obtain a transparent elastomeric 3-dim article having an outer side and an inner side, c) placing a radiation-curable Composition II on the inner side of the transparent 3-dim article, d) radiation-curing the radiation-curable Composition II from the outer side of the transparent 3- dim article, the radiation-curable Composition II being different from the radiation-curable Composition I with respect to its chemical formulation, radiation-curable Composition II comprising (meth)acrylate components, photo-initiator, and optionally filler.

The radiation-curing in step b) and step d) is typically done at different wavelengths, preferably the radiation-curing in step b) is done at a wavelength in the range of 350 to 420 nm and the radiationcuring in step d) is done at a wavelength in the range of 430 to 500 nm.

The nature of radiation-curable Composition II is not particularly limited. Any kind of radiation- curable composition can be used as long it is different in its composition from the radiation-curable Composition I.

According to one embodiment, radiation-curable Composition II is selected from a dental cement, a dental adhesive, or a dental composite material.

The invention also relates to a kit of parts comprising the radiation-curable Composition I described in the present text, being radiation-curable by applying radiation having a wavelength in the range of 300 to 400 nm, and a radiation-curable Composition II being different from the radiation-curable Composition I and being radiation-curable by applying radiation having a wavelength in the range of 420 to 500 nm.

Such a kit of parts is in particular useful for producing 3 -dim cured articles based on the radiation- curable Composition II with the aid of radiation-curable Composition I from which a transparent mould or transparent cover has been produced by means of an additive manufacturing process.

According to one embodiment, the kit comprises the radiation-curable Composition I described in the present text typically contained in a packaging device, and orthodontic brackets comprising a layer of a radiation-curable dental adhesive or cement.

The complete disclosures of the patents, patent documents, and publications cited herein are incorporated by reference in their entirety as if each were individually incorporated. Various modifications and alterations to this invention will become apparent to those skilled in the art without departing from the scope and spirit of this invention.

The above specification, examples and data provide a description of the manufacture and use of the compositions and methods of the invention.

The invention is not limited to the embodiments disclosed herein. One skilled in the art will appreciate that many alternative embodiments of the invention can be made without departing from the spirit and scope of thereof.

The following examples are given to illustrate the invention. Examples

Unless otherwise indicated, all parts and percentages are on a weight basis, all water is de-ionized water, and all molecular weights are weight average molecular weight. Moreover, unless otherwise indicated all experiments were conducted at ambient conditions (23 °C; 1013 mbar).

Methods

Molecular Weight (Mw)

If desired, the molecular weight (Mw) of the polymeric (meth)acrylate components described in the present text can be determined by titration of terminal groups, e.g. by titration of the OH number of the starting OH-terminated polyether using the method described e.g. in DIN EN ISO 4692-2 (2016). The molar mass can then be calculated by mathematically adding the molecular weight of the molecules used for any chain extension and/or to introduce a (meth)acrylate functionality.

Viscosity

If desired, the viscosity can be measured using a Physica Rheometer MCR 301 device with a plateplate system (diameter 20 mm) and a slit of 0.2 mm. The viscosity values (Pa*s) can be recorded at 23 °C for each shear rate (starting from 10 1/s to 100 1/s). pH value

If desired, the pH value of can be determined as follows: 1.0 g of a component (e.g., resin) is dispersed in 10 ml de-ionized water and stirred for about 5 min. A calibrated pH electrode is dipped into the suspension and the pH value is determined during stirring.

Tensile Strength (TS), Elongation at Break (EaB), and E-Modulus (EM)

If desired, tensile strength, elongation at break and E-modulus can be determined according to DIN 53505 (2015-8). 3d-printed and cured specimens can be used for testing (2x2x25mm).

Elastic Revocery (ER)

If desired, the elastic recovery [%] or the 3d-printed and cured specimen can be determined as described in ISO 4823. In section 7.7.3 of the ISO the test procedure of the prepared specimen is given.

After 3D-printing and post-processing the specimen is measured as follows:

- gently lower the dial indicator spindle contact point to rest on the test plate on top of the specimen;

- after 10 sec.: read the dial indicator and record the reading as hl;

- after 15 sec.: deform the specimen (6,0 ± 0,1) mm, as limited by the stop on the test apparatus, within 1 s, release the deforming force slowly over a period of 5 s and then lift and hold the contact point from contact with the test plate remaining at rest on the specimen;

- after 110 sec. : gently return the contact point to rest on the test plate;

- after 120 sec.: record this dial indicator reading as h2. The calculation of the result is done using the following formula ER = 100 - (hl - h2) * 5), wherein hl is the dial indicator reading after 10 sec. (preferably immediately before the specimen is deformed) and h2 is the dial indicator reading after 120 sec.

Shore Hardness (SHA)

If desired, the Shore hardness can be determined according to DIN 53505 (2000-8) 24 h after curing of the 3d-printed specimens. Specimens are prepared by filling the formulations into a metal mold (cylindrical 15x6mm) covered with plastic foil sheets, pressed and cured in a Visio™ Beta (3M) device with program 2 without vacuum.

Light Transmission (LT)

If desired, the light transmission (contrast ratio mode) can be measured using a Color i7 spherical spectrophotometer (available from x-rite Inc., Grand Rapids, MI, USA).

The 3 -printed and cured test specimen is printed in the shape of a cylinder with approximate dimensions: diameter of 30 ± 0.5mm and thickness of 2 ± 0.05mm and processed as described in the present text.

For the measurement, the spectrometer parameters are: D65 illuminant (light source; day light; 6,500 K) and 10° observer. The white and black background is determined as followed: for the black background the sphere is closed and thereby no light is detected by the sensors of the Color i7. As white (or 100% D65 light) a measurement, without anything between sphere and sensors of the Color i7, is necessary. For measurement of the sample, the specimen is placed with a sample holder between sphere and lens of the Color i7. The specimen is thereby directly placed onto the aperture of the sphere.

Transmission (%T) is calculated using the Software Color iControl V7.5.10 at 450, 470 and 500 nm wavelength.

Stickiness (S)

If desired, the stickiness can be determined as follows: A 3d-printed and cured mold is filled with a light curable cement, e.g. RelyX™ Unicem 2 Automix (A2) (3M Oral Care).

Immediately after that, through the mold the cement in the mold is exposed to the light of an Elipar™ S10 light device for 20 sec. This resulted in an immediate cure of the RelyX™ Unicem 2 material which indicates good curability of the cement through the cured elastomer.

The stickiness can be determined by visually and manually inspecting the adhesion of a sample of a light-cured material X in a mold consisting of light-cured composition Y.

Additive Manufacturing Process (3DP)

In a MiiCraft™ 50X device all specimen used for the described methods were manufactured with the following printing parameters: 10 Base layers with an exposure time of about 100 sec; 10 Buffer layers; 10 sec exposure time per printing layer; 0.00 mm gap adjustment; 100% power; - 9.90% resin shrinkage compensation.

Post Processing (PP)

The specimens were cleaned in a beaker filled with Loctite™ Cleaner C (Henkel), put on a magnetic stirrer and heated up to 50 °C, and then stirred for 5 minutes. The specimen were dried with a kitchen paper and post-cured in an experimental UV curing device using 385 nm LED's and a vacuum pump. The conditions were as follows: about 1 min exposure to light with no vacuum; about 15 min exposure to light and vacuum (<1 mbar).

Materials

The following materials were used:

Table 1

Compositions

All compositions Cx of Table 2 were prepared by combining the respective components and stirring the composition using a magnetic stirrer for about 2 h (all amounts are given in parts by weight; pbw). Compositions C2 to C5 are inventive compositions, whereas Composition Cl is a comparative or reference composition.

Table 2; n.m. = not measured

The radiation-curable compositions according to the invention have a low viscosity before curing and show a very good elastic recovery behaviour (ER), adequate Shore hardness (SHA), adequate tensile strength (TS) and a high elongation at break (EaB) after curing.

Claims

1. A radiation-curable composition for additive -manufacturing processes, the composition comprising

(meth)acrylate component Al comprising a polyalkylene oxide backbone, with at least two (meth)acrylate moieties, not comprising a urethane moiety, and having a molecular weight Mw of at least 2,000 g/mol, (meth)acrylate component Al being present in an amount of 50 to 85 wt.%, (meth)acrylate component A2 with at least two (meth)acrylate moieties, comprising in addition at least two urethane moieties, and having a molecular weight Mw of at most 1,000 g/mol, (meth)acrylate component A2 being present in an amount of 5 to 20 wt.%,

(meth)acrylate component A3 with only one (meth)acrylate moiety, not-comprising an aromatic moiety, and having a molecular weight of at most 500 g/mol, (meth)acrylate component A3 being present in an amount of 5 to 20 wt.%, photo-initiator, and optionally stabilizer, wt.% with respect to the amount of the whole composition.

2. The radiation-curable composition according to any of the preceding claims being characterized by the following properties alone or in combination: a) viscosity: less than 50 Pa*s at 23°C and a shear rate of 50 s'¹; b) pH value: 2 to 8 if the radiation-curable composition is brought in contact with wet pH sensitive paper; c) light transmission: at least 50 % for a path length of 2 mm using light having a wavelength of 500 nm; d) radiation-curable with light having a wavelength in the range of 350 to 420 nm; e) appearance: transparent; f) color: colorless.

3. The radiation-curable composition according to any of the preceding claims, (meth)acrylate component Al being characterized by the following features alone or in combination: a) comprising a polyalkylene oxide backbone; b) comprising a polyalkylene oxide backbone to which the (meth)acrylate moieties are attached; c) molecular weight (Mw): 2,000 to 20,000 g/mol determined according to the description; d) viscosity: 0.1 to 100 Pa*s at 23°C and a shear rate of 50 s’¹.

4. The radiation-curable composition according to any of the preceding claims, (meth)acrylate component A2 being characterized by the following features alone or in combination: a) comprising a C2 to C20 linear or branched alkyl backbone; b) comprising a C₂ to C20 linear or branched alkyl backbone to which the (meth)acrylate moieties are attached via a spacer comprising the urethane moieties; c) molecular weight (Mw): 200 to 1,000 g/mol; d) viscosity: 0.1 to 100 Pa*s, or 1 to 50 Pa*s at 23°C at a shear rate of 50 s’¹.

5. The radiation-curable composition according to any of the preceding claims, (meth)acrylate component A3 being characterized by the following features alone or in combination: a) molecular weight (Mw): 85 to 500 g/mol; b) viscosity: 0.01 to 20 Pa*s, or 1 to 50 Pa*s at 23°C at a shear rate of 50 s’¹; c) being selected from hydroxyethyl(meth)acrylate, hydroxypropyl(meth)acrylate, butyl(meth)acrylate, isobomyl(meth)acrylate, lauryl(meth)acrylate, stearyl(meth)acrylate, tetrahydrofurfurylmethacrylate and mixtures thereof.

6. The radiation-curable composition according to any of the preceding claims comprising at least one stabilizer, the stabilizer being selected from oxygen scavengers, UV-absorbers, storage stabilizers and mixtures thereof.

7. The radiation-curable composition according to any of the preceding claims comprising at least one stabilizer, the stabilizer being selected from components comprising an iso-prenyl moiety, preferably a diprenylglycerin ether moiety, and mixtures thereof; and being preferably present in an amount of at least 0.5 wt.% with respect to the weight of the radiation-curable composition.

8. The radiation-curable composition according to any of the preceding claims not comprising the following components alone or in combination: perylene dye; epoxy functional component; silicone component; filler.

9. A process of producing an elastomeric 3-dimensional article, the process comprising the step of processing the radiation-curable composition described in any of the preceding claims in an additive-manufacturing process comprising a radiation-curing step, preferably using light with a wavelength in the range of 350 to 420 nm.

10. An elastomeric 3-dim article obtained or obtainable by the process of the preceding claim comprising the radiation-curable composition as described in any of the preceding claims in its cured state.

11. The elastomeric 3-dim article of the preceding claim being characterized by the following features alone or in combination: tensile strength: 0.5 to 50 MPa according to ISO/DIN 53504 (2015-8); elongation at break: 100 to 500 % according to ISO/DIN 53504 (2015-8);

E-modulus: 1 to 10 MPa according to ISO/DIN 53504 (2015-8); elastic recovery: at least 99.0% determined according to the process described in the description;

Shore hardness A: 50 to 90 according to ISO/DIN 53505 (2000-8); light transmission: at least 50 % for a path length of 2 mm using light having a wavelength of 500 nm; water contact angle: < 100°; not sticky to surfaces of cured (meth)acrylates; color: colorless.

12. The radiation-curable composition according to any of the preceding claims for use in a process of treating a dental situation in the mouth of a patient, the process comprising the steps of a) processing the radiation-curable composition in an additive -manufacturing process for obtaining a 3-dim article having the shape of a customized indirect bonding tray containing recesses for receiving orthodontic brackets, the shape of the customized indirect bonding tray being based on patient-specific digital data, b) optionally post-processing the 3-dim article, c) inserting orthodontic brackets in the recesses of the customized indirect bonding tray, the orthodontic brackets comprising radiation-curable components, wherein the radiation- curable components can be present already on the orthodontic brackets before the insertion step, or are applied on the surface of the orthodontic brackets in a separate step, d) inserting the customized indirect bonding tray with the inserted orthodontic brackets into the mouth of a patient so that the orthodontic brackets are in contact with the surfaces with the opposing teeth, e) fixing the orthodontic brackets to the surface of the opposing teeth by applying radiation, f) removing the customized indirect bonding tray from the mouth of the patient, wherein the individual steps can be done at different locations by different practitioners.

13. Use of the radiation-curable composition according to any of the preceding claims for producing fittings, shock absorbers, seals, masks and medical products.

14. A process of curing a radiation-curable Composition II, the process comprising the steps of a) providing a radiation-curable Composition I, the radiation-curable Composition I being the radiation-curable composition as described in any of claims 1 to 8, b) processing the radiation-curable Composition I in an additive-manufacturing process using radiation for curing radiation-curable Composition I to obtain a transparent elastomeric 3- dim article having an outer side and an inner side, c) placing the radiation-curable Composition II on the inner side of the transparent 3 -dim article, d) radiation-curing the radiation-curable Composition II from the outer side of the transparent 3 -dim article, the radiation-curable Composition II being different from the radiation-curable Composition I with respect to its chemical formulation, radiation-curable Composition II comprising (meth)acrylate components, photo-initiator, and optionally filler.

15. A kit of parts comprising a radiation-curable Composition I, the radiation curable Composition I being the radiation- curable composition as described in any of claims 1 to 8, and a radiation-curable Composition II, the radiation-curable Composition II being characterized by the following features alone or in combination: being different in its chemical composition from the radiation-curable Composition I, being the radiation- curable Composition II as described in claim 14.