Curable formulations usable in forming transparent materials or objects featuring high mechanical strength

Abstract

Curable formulations that provide, when hardened, transparent materials, and uses thereof, are provided. The curable formulations include two or more urethane (meth)acrylate materials which differ from one another at least by the number average molecular weight lower than 2000 grams / mol and / or the Tg, and optionally by the number of blocks and / or the NCO / OH ratio in the urethane (meth)acrylate material, and optionally a material or substance that is capable of interfering with the formation of micron-sized clusters in a hardened material formed of the formulations.

Description

[0001] CURABLE FORMULATIONS USABLE IN FORMING TRANSPARENT MATERIALS OR OBJECTS FEATURING HIGH MECHANICAL STRENGTH

[0002] RELATED APPLICATION

[0003] This application claims the benefit of priority under 35 USC § 119(e) of U.S. Provisional Patent Application No. 63 / 666,345 filed on July 1, 2025, the contents of which are incorporated herein by reference in their entirety.

[0004] FIELD AND BACKGROUND OF THE INVENTION

[0005] The present invention, in some embodiments thereof, relates to material science and, more particularly, but not exclusively, to curable formulations which are usable in forming transparent hardened materials and to use thereof in additive manufacturing of three-dimensional objects such as orthodontic devices.

[0006] Additive manufacturing (AM) is a technology enabling fabrication of arbitrarily shaped structures directly from computer data via additive formation steps. The basic operation of any AM system consists of slicing a three-dimensional computer model into thin cross sections, translating the result into two-dimensional position data and feeding the data to control equipment which fabricates a three-dimensional structure in a layer- wise manner.

[0007] Additive manufacturing entails many different approaches to the method of fabrication, including three-dimensional (3D) printing such as stereolithography, DLP printing, 3D inkjet printing, electron beam melting, selective laser sintering, laminated object manufacturing, fused deposition modeling and others.

[0008] Some 3D printing processes, for example, 3D inkjet printing, are being performed by a layer-by-layer inkjet deposition of building materials. Thus, a building material is dispensed from a dispensing head having a set of nozzles to deposit layers on a supporting structure. Depending on the building material, the layers may then be cured or solidified. Other 3D printing processes are performed by a layer-by-layer selective curing or solidification of building materials in liquid form. Curing may be by exposure to a suitable condition, and optionally by using a suitable device.

[0009] The building material includes an uncured model material (also referred to as “uncured modeling material” or “modeling material formulation”), which is used to produce the desired object, and may optionally also include an uncured support material (also referred to as "uncured supporting material” or “support material formulation”) which provides, when hardened, temporary support to specific regions of the object during building and assures adequate vertical placement of subsequent object layers. The supporting structure is configured to be removed after the object is completed. In some additive manufacturing systems that are based on hardening or curing of a liquid building material, the uncured building (e.g., modeling) material typically comprises a photopolymerizable or photocurable material that is cured, hardened or solidified upon exposure to ultraviolet (UV) light. The uncured model material may be a photopolymerizable material formulation that has a composition which, after curing, gives a solid material with mechanical properties that permit the building and handling of the three-dimensional object being built. The modeling material formulation typically includes a reactive (curable) component and a photoinitiator. The solidified material may be rigid, or may have elastic properties.

[0010] Some modeling material formulations known as usable in additive manufacturing are designed so as to provide, when solidified, a transparent material.

[0011] The use of light emitting diodes (LED) as a source for electromagnetic irradiation has recently become more and more common and desirable in many fields, including additive manufacturing processes such as those that utilize UV-curable materials. Most of the commercially available UV LED light sources emit UVA radiation, at the higher wavelengths of 365 / 395 / 405 nm.

[0012] During the last decade, efforts have been made to use additive manufacturing such as 3D inkjet printing and digital light processing (DLP) in the denture field.

[0013] Dental aligners are plastic orthodontic appliances that fit over the teeth and are used to correct their alignment, among other uses. Dental aligners put gentle pressure on the teeth so as to effect gradual reposition of the teeth over time. Dental aligners can be clear or colored, and are typically transparent. Traditionally, dental aligners were prepared in a mold, however, in recent years, methodologies for preparing 3D-printed dental aligners are being developed.

[0014] Dental aligners are orthodontic devices designed to straighten and align teeth, providing an alternative to traditional braces. These aligners are typically made of clear, flexible plastic and are custom-fitted to the patient's teeth. Dental aligners are commonly made of a thermoplastic material, such as polyurethanes (e.g., TPU), polyesters (e.g., PETG) or multi-layers thereof. These materials are selected for exhibiting transparency, flexibility, durability, and resistance to deformation.

[0015] The process begins with the creation of a digital impression of the patient's teeth, often using intraoral scanners or other digital impression techniques. This digital model is then used to create a three-dimensional (3D) virtual representation of the teeth and surrounding structures. Advanced computer-aided design (CAD) software is employed to plan the step-by-step movement of teeth throughout the treatment. Each set of aligners is custom-designed based on the specific needs of the patient. The treatment plan involves a series of aligners, each slightly different from the previous one, to gradually move the teeth into the desired positions. The aligners are strategically fabricated to apply controlled forces to specific teeth, causing them to shift over time. The digital nature of the process enables precise control over tooth movement, contributing to the effectiveness of the treatment.

[0016] WO 2023 / 114740 describes photocurable formulations usable in 3D printing, which comprise urethane (meth) acrylate (UA) pre-polymers which contribute to the toughness (e.g., high elongation at break) of the hardened material, and which can be synthesized from a multifunctional polyol (e.g., diol), a diisocyanate, and a hydroxy-functional (meth)acrylate, or from a multi-functional polyol and an NCO-functional (meth)acrylate.

[0017] Additional background art includes U.S. Patent Application Publication No. 2018 / 0049954.

[0018] SUMMARY OF THE INVENTION

[0019] According to an aspect of some embodiments of the present invention there is provided a curable formulation, preferably a transparent curable formulation (e.g., a modeling material formulation usable in additive manufacturing of a three-dimensional object that comprises, in at least a portion thereof, a transparent material), the curable formulation comprising: a first curable material which is a first urethane (meth)acrylate material (pre-polymer) having an average number molecular weight (average Mn) lower than 2000 grams / mol and featuring Tg of at least 80 °C or of at least 100 °C, the first curable material being a first reaction product of a first cycloaliphatic diisocyanate, a first diol, and a first acrylic compound featuring a hydroxy group; a second curable material, which is a second urethane (meth)acrylate material (pre-polymer) having an average number molecular weight (average Mn) of from 2000 grams / mol to 10,000 grams / mol and featuring Tg lower than -20 °C, or lower than 40 °C, the second curable material being a second reaction product of a second cycloaliphatic diisocyanate, a second diol, and a second acrylic compound featuring a hydroxy group; a photoinitiator; optionally, a third curable material, which comprises a third (meth)acrylic compound; and a compound capable of interfering with the formation of micron-sized clusters in a hardened material formed of the formulation.

[0020] According to some of any of the embodiments described herein, the formulation further comprises the third curable material.

[0021] According to some of any of the embodiments described herein, the third curable material features, when hardened, Tg of at least 100 °C.

[0022] According to some of any of the embodiments described herein, the third curable material is a mono-functional curable material. According to some of any of the embodiments described herein, the third curable material is or comprises isobomyl (meth)acrylate.

[0023] According to some of any of the embodiments described herein, an amount of the third curable material ranges from 20 to 50, or from 30 to 50, or from 30 to 40, % by weight of the total weight of the formulation.

[0024] According to some of any of the embodiments described herein, the first reaction features NCO / OH ratio of about 2.

[0025] According to some of any of the embodiments described herein, the first cycloaliphatic diisocyanate is selected from cyclohexane- 1,3-diisocyanate, cyclohexane- 1,4-diisocyanate, 1- isocyanato-2-isocyanatomethyl cyclopentane, l-isocyanato-3-isocyanatomethyl-3,5,5- trimethylcyclohexane (isophorone diisocyanate; IPDI), bis-(4-isocyanatocyclohexyl)- methane (H12MDI), l,3-bis(isocyanatomethyl)-cyclohexane, l,4-bis(isocyanatomethyl)- cyclohexane, bis- (4-isocyanato-3-methyl-cyclohexyl)methane, 1-isocyanato- l-methyl-4(3)- isocyanatomethyl cyclohexane, 2,4-hexahydrotoluylene diisocyanate, 2,6-hexahydrotoluylene diisocyanate, and any combination thereof.

[0026] According to some of any of the embodiments described herein, the first cycloaliphatic diisocyanate is or comprises isophorone diisocyanate (IPDI).

[0027] According to some of any of the embodiments described herein, the first acrylic compound featuring a hydroxy group comprises a hydroxyalkyl (meth)acrylate, wherein the alkyl is of from 1 to 10, or from 2 to 10, or from 2 to 8, or from 2 to 6, carbon atoms in length, including any intermediate values and subranges therebetween.

[0028] According to some of any of the embodiments described herein, the hydroxyalkyl is hydroxyethyl.

[0029] According to some of any of the embodiments described herein, the first diol comprises is or comprises an aliphatic diol of from 2 to 12 carbon atoms, including any intermediate values and subranges therebetween.

[0030] According to some of any of the embodiments described herein, the first diol is selected from ethylene glycol, 1,2-propanediol, 1,3 -propanediol, glycerol, 1,3 -butanediol, 2,3-butanediol, 1,4-butanediol, 2-methyl-l,4-butanediol, 3-methyl-l,3-butanediol, 1,2,4-butanetriol, 1,5- pentanediol, 3 -methyl- 1,5-pentanediol (MPD), 3-methyl-2,4- pentanediol, 2-methyl-l,3- pentanediol, 2-methyl- 1,5-pentanediol, 1,2,5-pentanetriol, 1,6-hexanediol, 1,2-hexanediol, 1,5- hexanediol, 2-methyl- 1,6-hexanediol, 4-methyl-l,3-hexanediol, 5-methyl-2,4-hexanediol, 3- methyl- 1,6-hexanediol, 1,2,6-hexanetriol, 1,7-heptanediol, 2,5-heptanediol, 4-methyl-l,6- heptanediol, 3-methyl-2,4-heptanediol, 2-methyl-2,6-heptanediol, 5-methyl-2,4-heptanediol, 4- methyl-l,7-heptanediol, 1,2,7-heptanetriol, 1,8-octanediol, 2-methyl-l,8-octanediol, 7-methyl-l,7- octanediol, 6-methyl-l,7-octanediol, 3-methyl-l,4-octanediol, 1,2,8-octanediol, 1,9-nonanediol, 8- methyl-l-8-nonanediol, 1,2,9- nonanetriol, 1,10-decanediol, 2-methyl-l,10-decanediol, 2-methyl- 2,5-decanediol, 4,8-Bis(hydroxymethyl)tricyclo[5.2.1.02,6] decane (DCPDM), 1,11- undecanediol, 1,12-dodecanediol, and any combination thereof.

[0031] According to some of any of the embodiments described herein, the second reaction product is a multi-block co-polymer.

[0032] According to some of any of the embodiments described herein, the second reaction product features NCO / OH ratio lower than 2.

[0033] According to some of any of the embodiments described herein, the second reaction product features NCO / OH ratio in a range of from 1 to 1.8, or from 1 to 1.5, or from 1.33 to 1.5.

[0034] According to some of any of the embodiments described herein, the second reaction product features NCO / OH ratio of about 1.5 or of about 1.33.

[0035] According to some of any of the embodiments described herein, the second cycloaliphatic diisocyanate is selected from cyclohexane- 1,3-diisocyanate, cyclohexane- 1,4-diisocyanate, 1- isocyanato-2-isocyanatomethyl cyclopentane, l-isocyanato-3-isocyanatomethyl-3,5,5- trimethylcyclohexane (isophorone diisocyanate; IPDI), bis-(4-isocyanatocyclohexyl)- methane (H12MDI), l,3-bis(isocyanatomethyl)-cyclohexane, l,4-bis(isocyanatomethyl)- cyclohexane, bis- (4-isocyanato-3-methyl-cyclohexyl)methane, 1-isocyanato- l-methyl-4(3)- isocyanatomethyl cyclohexane, 2,4-hexahydrotoluylene diisocyanate, 2,6-hexahydrotoluylene diisocyanate, and any combination thereof.

[0036] According to some of any of the embodiments described herein, the second cycloaliphatic diisocyanate is or comprises isophorone diisocyanate (IPDI).

[0037] According to some of any of the embodiments described herein, the second acrylic compound featuring a hydroxy group comprises a hydroxyalkyl (meth)acrylate, wherein the alkyl is of from 1 to 10, or from 2 to 10, or from 2 to 8, or from 2 to 6, carbon atoms in length.

[0038] According to some of any of the embodiments described herein, the hydroxyalkyl is hydroxyethyl.

[0039] According to some of any of the embodiments described herein, the second diol is or comprises a polyether diol (e.g., a polyalkylene ether glycol) having average Mn of from 500 to 5,000, or from 1,000 to 5,000, or from 2,000 to 5,000, grams / mol, including any intermediate values and subranges therebetween.

[0040] According to some of any of the embodiments described herein, the second diol comprises polyTHF. According to some of any of the embodiments described herein, the second reaction product features NCO / OH ratio of about 2, and the second diol has an average number molecular weight (average Mn) higher than 2,000, or higher than 2,500, or higher of 2,900, or of at least 3,000, grams / mol.

[0041] According to some of these embodiments, the second diol is or comprises a polyether diol (e.g., a polyalkylene ether glycol) having average Mn of from 3,000 to 10,000, or from 3,000 to 8,000, or from 3,000 to 5,000, grams / mol, including any intermediate values and subranges therebetween.

[0042] According to some of these embodiments described herein, the second diol is or comprises polyTHF having an average Mn higher than 2,000, or higher than 2,500, or higher of 2,800, or of at least 3,000, grams / mol, or of from 3,000 to 10,000, or from 3,000 to 8,000, or from 3,000 to 5,000, grams / mol, including any intermediate values and subranges therebetween.

[0043] According to some of any of the embodiments described herein, an amount of the first curable material ranges from 20 to 50, or from 20 to 40, preferably from 25 to 35 or from 25 to 30, % by weight of the total weight of the formulation, including any intermediate values and subranges therebetween.

[0044] According to some of any of the embodiments described herein, an amount of the second curable material ranges from 25 to 50, or from 30 to 50, or from 30 to 40, % by weight of the total weight of the formulation, including any intermediate values and subranges therebetween.

[0045] According to some of any of the embodiments described herein, an amount of the photoinitiator ranges from 1 to 5, % by weight of the total weight of the formulation, including any intermediate values and subranges therebetween.

[0046] According to some of any of the embodiments described herein, each of the first and the second acrylic compound featuring a hydroxy group independently comprises a hydroxyalkyl (meth)acrylate, wherein the alkyl is of from 1 to 10, or from 2 to 10, or from 2 to 8, or from 2 to 6, carbon atoms in length; the first diol comprises an aliphatic diol of from 2 to 12 carbon atoms; the second diol comprises polyTHF having Mn of from 1,000 to 5,000, or from 2,000 to 5,000, grams / mol; and the second reaction product is a multiblock co-polymer (e.g., which comprises at least 2 blocks of the second diol).

[0047] According to some of any of the embodiments described herein, the second reaction product features NCO / OH ratio lower than 2, or from 1 to 1.5, or of about 1.5 or about 1.33.

[0048] According to some of any of the embodiments described herein, each of the first and the second acrylic compound featuring a hydroxy group independently comprises a hydroxyalkyl (meth)acrylate, wherein the alkyl is of from 1 to 10, or from 2 to 10, or from 2 to 8, or from 2 to 6, carbon atoms in length; the first diol comprises an aliphatic diol of from 2 to 12 carbon atoms; the second diol comprises polyTHF having Mn of at least 3,000 grams / mol, as described herein; and the second reaction product features NCO / OH ratio of about 2.

[0049] According to some of any of the embodiments described herein, an amount of the first curable material ranges from 25 to 35 or from 25 to 30, % by weight of the total weight of the formulation, including any intermediate values and subranges therebetween; an amount of the second curable material ranges from 25 to 40, or from 30 to 40, % by weight of the total weight of the formulation, including any intermediate values and subranges therebetween; and an amount of the third curable material ranges from 30 to 40, % by weight of the total weight of the formulation, including any intermediate values and subranges therebetween.

[0050] According to some of any of the embodiments described herein, the compound capable of interfering with the formation of micron-sized clusters is capable of interfering with intermolecular and / or intramolecular hydrogen bonds formed by the first urethane (meth) acrylate material.

[0051] According to some of any of the embodiments described herein, the compound capable of interfering with the formation of micron-sized clusters comprises at least one carboxylic acid moiety.

[0052] According to some of any of the embodiments described herein, the compound capable of interfering with the formation of micron-sized clusters is a photocurable material.

[0053] According to some of any of the embodiments described herein, the compound capable of interfering with the formation of micron-sized clusters comprises a (meth) acrylate featuring at least one carboxylic acid moiety.

[0054] According to some of any of the embodiments described herein, the compound capable of interfering with the hydrogen bonds comprises (meth)acrylic acid.

[0055] According to some of any of the embodiments described herein, an amount of the compound capable of interfering with the formation of micron-sized clusters ranges from 1 to 10, or from 2 to 10, % by weight of the total weight of the formulation, including any intermediate values and subranges therebetween.

[0056] According to some of any of the embodiments described herein, the formulation a shear viscosity of less than 1 Pa- second at 100 °C at a shear rate of 50 / second.

[0057] According to some of any of the embodiments described herein, the formulation is usable in additive manufacturing of a transparent three-dimensional object.

[0058] According to an aspect of some embodiments of the present invention there is provided a hardened material from upon exposing to irradiation the formulation as described herein in any of the respective embodiments and combination thereof. According to some of any of the embodiments described herein, the hardened material is a transparent hardened material.

[0059] According to some of any of the embodiments described herein, the hardened material features transparency of at least 85 % (e.g., when determined as described herein).

[0060] According to some of any of the embodiments described herein, the hardened material features a haze value of no more than 15 %, or no more than 10 %, or no more than 5 % (e.g., when determined as described herein).

[0061] According to some of any of the embodiments described herein, the hardened material features at least one of: Tg of at least 100, or at least 120, °C; Tensile modulus of at least 800, or at least 900, or at least 1,000 MPa; Yield Stress of at least 20 MPa; Elongation at break of at least 30 %.

[0062] According to an aspect of some embodiments of the present invention there is provided a three-dimensional object comprising, in at least a portion thereof, the hardened material as described herein in any of the respective embodiments and any combination thereof.

[0063] According to some of any of the embodiments described herein, the three-dimensional object is or forms a part of an orthodontic device.

[0064] According to some of any of the embodiments described herein, the orthodontic device is a dental aligner.

[0065] According to an aspect of some embodiments of the present invention there is provided a method of additive manufacturing a three-dimensional object featuring in at least a portion thereof a transparent material, the method comprising forming a plurality of layers in a configured pattern correspond to the shape the denture object, thereby forming the object, wherein at least a few of the layers are formed of the (curable) modeling material formulation as described herein in any of the respective embodiments and any combination thereof, upon exposing each of the layers to irradiation.

[0066] According to an aspect of some embodiments of the present invention there is provided a kit comprising the curable formulation as described herein in any of the respective embodiments and any combination thereof, wherein the first and second curable materials are each individually packaged within the kit.

[0067] According to an aspect of some embodiments of the present invention there is provided a curable formulation, or a curable transparent formulation, (e.g., a modeling material formulation usable in additive manufacturing of a three-dimensional object that comprises, in at least a portion thereof, a transparent material), the curable formulation comprising: a first curable material, as described herein in any of the respective embodiments and any combination thereof, which is a first urethane (meth) acrylate material (pre-polymer) having an average number molecular weight (average Mn) lower than 2000 grams / mol and featuring Tg of at least 80 °C or of at least 100 °C, the first curable material being a first reaction product of a first cycloaliphatic diisocyanate, a first diol, and a first acrylic compound featuring a hydroxy group, as described herein in any of the respective embodiments and any combination thereof; a second curable material, as described herein in any of the respective embodiments and any combination thereof, which is a second urethane (meth)acrylate material (pre-polymer) having an average number molecular weight (average Mn) of from 2000 grams / mol to 10,000 grams / mol and featuring Tg lower than -20 °C, or lower than 40 °C, the second curable material being a second reaction product of a second cycloaliphatic diisocyanate, a second diol, and a second acrylic compound featuring a hydroxy group, the second reaction product being a multi-block co-polymer (e.g., which comprises at least two blocks of the second diol), as described herein in any of the respective embodiments and any combination thereof; and optionally, a third curable material, as described herein in any of the respective embodiments and any combination thereof, which comprises a third (meth)acrylic compound, wherein an amount of the first curable material ranges from 20 to 35, or from 25 to 35, preferably from 25 to 30, % by weight of the total weight of the formulation, including any intermediate values and subranges therebetween; and an amount of the second curable material ranges from 25 to 50, or from 30 to 50, or from 30 to 40, % by weight of the total weight of the formulation, including any intermediate values and subranges therebetween.

[0068] According to some of any of the embodiments described herein, the formulation further comprises the third curable material, as described herein in any of the respective embodiments and any combination thereof.

[0069] According to some of any of the embodiments described herein, the third curable material comprises isobomyl (meth)acrylate.

[0070] According to some of any of the embodiments described herein, an amount of the third curable material ranges from 20 to 50, or from 30 to 50, or from 30 to 40, % by weight of the total weight of the formulation, including any intermediate values and subranges therebetween.

[0071] According to some of any of the embodiments described herein, the first reaction product features NCO / OH ratio of about 2.

[0072] According to some of any of the embodiments described herein, the second reaction product features NCO / OH ratio lower than 2.

[0073] According to some of any of the embodiments described herein, the second reaction product features NCO / OH ratio in a range of from 1 to 1.8, or from 1 to 1.5, or from 1.33 to 1.5; and According to some of any of the embodiments described herein, the second reaction product features NCO / OH ratio of about 1.5 or of about 1.33.

[0074] According to some of any of the embodiments described herein, each of the first and second cycloaliphatic diisocyanate is as described herein in any of the respective embodiments and any combination thereof.

[0075] According to some of any of the embodiments described herein, each of the first and second the second acrylic compound featuring a hydroxy group comprises a hydroxyalkyl (meth)acrylate, wherein the alkyl is of from 1 to 10, or from 2 to 10, or from 2 to 8, or from 2 to 6, carbon atoms in length, including any intermediate values and subranges therebetween.

[0076] According to some of any of the embodiments described herein, each of the first and second the second diol comprises a polyether diol (e.g., a polyalkylene ether glycol) having Mn of from 500 to 5,000, or from 1,000 to 5,000, or from 2,000 to 5,000, grams / mol.

[0077] According to some of any of the embodiments described herein, the second diol comprises polyTHF.

[0078] According to some of any of the embodiments described herein, the formulation further comprises a photoinitiator.

[0079] According to some of any of the embodiments described herein, an amount of the photoinitiator ranges from 1 to 5, % by weight of the total weight of the formulation, including any intermediate values and subranges therebetween.

[0080] According to some of any of the embodiments described herein, each of the first and the second acrylic compound featuring a hydroxy group independently comprises a hydroxyalkyl (meth)acrylate, wherein the alkyl is of from 1 to 10, or from 2 to 10, or from 2 to 8, or from 2 to 6, carbon atoms in length; the first diol comprises an aliphatic diol of from 2 to 12 carbon atoms; the second diol comprises polyTHF having Mn of from 1,000 to 5,000, or from 2,000 to 5,000, grams / mol; the first reaction product features NCO / OH ratio of about 2; and the second reaction product features NCO / OH ratio of about 1.5 or about 1.33.

[0081] According to some of any of the embodiments described herein, an amount of the first curable material ranges from 25 to 35 or from 25 to 30, % by weight of the total weight of the formulation, including any intermediate values and subranges therebetween; an amount of the second curable material ranges from 30 to 40, % by weight of the total weight of the formulation, including any intermediate values and subranges therebetween; and an amount of the third curable material ranges from 30 to 40, % by weight of the total weight of the formulation, including any intermediate values and subranges therebetween. According to an aspect of some embodiments of the present invention there is provided a curable formulation, or a curable transparent formulation, (e.g., a modeling material formulation usable in additive manufacturing of a three-dimensional object that comprises, in at least a portion thereof, a transparent material), the curable formulation comprising: a first curable material, as described herein in any of the respective embodiments and any combination thereof, which is a first urethane (meth) acrylate material (pre-polymer) having an average number molecular weight (average Mn) lower than 2000 grams / mol and featuring Tg of at least 80 °C or of at least 100 °C, the first curable material being a first reaction product of a first cycloaliphatic diisocyanate, a first diol, and a first acrylic compound featuring a hydroxy group, as described herein in any of the respective embodiments and any combination thereof; a second curable material, as described herein in any of the respective embodiments and any combination thereof, which is a second urethane (meth)acrylate material (pre-polymer) having an average number molecular weight (average Mn) of from 2000 grams / mol to 10,000 grams / mol and featuring Tg lower than -20 °C, or lower than 40 °C, the second curable material being a second reaction product of a second cycloaliphatic diisocyanate, a second diol featuring average Mn of 3,000 grams / mol or higher, or of at least 2,500, or at least 2,900, or at least 3,000, grams / mol, as described herein, and a second acrylic compound featuring a hydroxy group; and optionally, a third curable material, as described herein in any of the respective embodiments and any combination thereof, which comprises a third (meth)acrylic compound, wherein an amount of the first curable material ranges from 20 to 35, or from 25 to 35, preferably from 25 to 30, % by weight of the total weight of the formulation, including any intermediate values and subranges therebetween; and an amount of the second curable material ranges from 25 to 50, or from 30 to 50, or from 30 to 40, % by weight of the total weight of the formulation, including any intermediate values and subranges therebetween.

[0082] According to some of any of the embodiments described herein, the formulation further comprises the third curable material, as described herein in any of the respective embodiments and any combination thereof.

[0083] According to some of any of the embodiments described herein, the third curable material is or comprises isobomyl (meth)acrylate.

[0084] According to some of any of the embodiments described herein, an amount of the third curable material ranges from 20 to 50, or from 30 to 50, or from 30 to 40, % by weight of the total weight of the formulation, including any intermediate values and subranges therebetween.

[0085] According to some of any of the embodiments described herein, the first reaction product features NCO / OH ratio of about 2. According to some of any of the embodiments described herein, the second reaction product features NCO / OH of about 2.

[0086] According to some of any of the embodiments described herein, each of the first and second cycloaliphatic diisocyanate is as described herein in any of the respective embodiments and any combination thereof.

[0087] According to some of any of the embodiments described herein, each of the first and second the second acrylic compound featuring a hydroxy group comprises a hydroxyalkyl (meth)acrylate, wherein the alkyl is of from 1 to 10, or from 2 to 10, or from 2 to 8, or from 2 to 6, carbon atoms in length, including any intermediate values and subranges therebetween.

[0088] According to some of any of the embodiments described herein, the first diol is or comprises a polyether diol (e.g., a polyalkylene ether glycol) having Mn of from 500 to 5,000, or from 1,000 to 5,000, or from 2,000 to 5,000, grams / mol.

[0089] According to some of any of the embodiments described herein, the second diol is or comprises a polyether diol (e.g., a polyalkylene ether glycol) having average Mn of at least 3,000 grams / mol, as described herein.

[0090] According to some of any of the embodiments described herein, the second diol is or comprises polyTHF having average Mn of at least 3,000 grams / mol, as described herein.

[0091] According to some of any of the embodiments described herein, the formulation further comprises a photoinitiator.

[0092] According to some of any of the embodiments described herein, an amount of the photoinitiator ranges from 1 to 5, % by weight of the total weight of the formulation, including any intermediate values and subranges therebetween.

[0093] According to some of any of the embodiments described herein, each of the first and the second acrylic compound featuring a hydroxy group independently comprises a hydroxyalkyl (meth)acrylate, wherein the alkyl is of from 1 to 10, or from 2 to 10, or from 2 to 8, or from 2 to 6, carbon atoms in length; the first diol comprises an aliphatic diol of from 2 to 12 carbon atoms; the second diol comprises polyTHF having Mn of at least 3,000 grams / mol; the first reaction product features NCO / OH ratio of about 2; and the second reaction product features NCO / OH ratio of about 2.

[0094] According to some of any of the embodiments described herein, an amount of the first curable material ranges from 25 to 35 or from 25 to 30, % by weight of the total weight of the formulation, including any intermediate values and subranges therebetween; an amount of the second curable material ranges from 30 to 40, % by weight of the total weight of the formulation, including any intermediate values and subranges therebetween; and an amount of the third curable material ranges from 30 to 40, % by weight of the total weight of the formulation, including any intermediate values and subranges therebetween.

[0095] According to an aspect of some of any of the embodiments described herein, there is provided a hardened material from upon exposing to irradiation the curable formulation as described in any of the embodiments that relate to this aspect of embodiments of the present invention.

[0096] According to an aspect of some of any of the embodiments described herein, there is provided a three-dimensional object comprising, in at least a portion thereof, the hardened material as described in any of the embodiments that relate to this aspect of embodiments of the present invention.

[0097] According to an aspect of some of any of the embodiments described herein, there is provided a method of additive manufacturing a three-dimensional object featuring in at least a portion thereof a transparent material, the method comprising forming a plurality of layers in a configured pattern correspond to the shape the denture object, thereby forming the object, wherein at least a few of the layers are formed of the curable (e.g., modeling material) formulation as described in any of the embodiments that relate to this aspect of the present invention, upon exposing each of the layers to irradiation.

[0098] According to an aspect of some of any of the embodiments described herein, there is provided a kit comprising the curable (e.g., modeling material) formulation as described herein for any of the embodiments of this aspect of embodiments of the present invention, wherein the first and second curable materials are each individually packaged within the kit.

[0099] Unless otherwise defined, all technical and / or scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention pertains. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of embodiments of the invention, exemplary methods and / or materials are described below. In case of conflict, the patent specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and are not intended to be necessarily limiting.

[0100] Implementation of the method and / or system of embodiments of the invention can involve performing or completing selected tasks manually, automatically, or a combination thereof. Moreover, according to actual instrumentation and equipment of embodiments of the method and / or system of the invention, several selected tasks could be implemented by hardware, by software or by firmware or by a combination thereof using an operating system. For example, hardware for performing selected tasks according to embodiments of the invention could be implemented as a chip or a circuit. As software, selected tasks according to embodiments of the invention could be implemented as a plurality of software instructions being executed by a computer using any suitable operating system. In an exemplary embodiment of the invention, one or more tasks according to exemplary embodiments of method and / or system as described herein are performed by a data processor, such as a computing platform for executing a plurality of instructions. Optionally, the data processor includes a volatile memory for storing instructions and / or data and / or a non-volatile storage, for example, a magnetic hard-disk and / or removable media, for storing instructions and / or data. Optionally, a network connection is provided as well. A display and / or a user input device such as a keyboard or mouse are optionally provided as well.

[0101] BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

[0102] Some embodiments of the invention are herein described, by way of example only, with reference to the accompanying drawings. With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of embodiments of the invention. In this regard, the description taken with the drawings makes apparent to those skilled in the art how embodiments of the invention may be practiced.

[0103] In the drawings:

[0104] FIGs. 1A-C present photographs of a dental aligner printed using an exemplary modeling formulation as described in Example 1 herein, per se (FIG. 1A) and when immersed in isopropyl alcohol (IPA) (FIG. IB; reproduced from FIG. 4, right photograph) and of a 1 mm film prepared by casting an exemplary modeling formulation as described in Example 1 herein (FIG. 1C; reproduced from FIG. 5A).

[0105] FIGs. 2A-B present SEM images of a hardened material formed of an exemplary modeling formulation as described in Example 1 herein (FIG. 2A), and of an exemplary modeling formulation as described in Example 1 herein to which 4 wt.% methacrylic acid was added (FIG. 2B). Circles in FIG. 2A denote micron-sized clusters within the hardened material that are causing haze.

[0106] FIG. 3 presents comparative plots showing the tensile behavior as measured under low (5 mm / minute) and high (50 mm / minute) pulling speed at ambient conditions, for a tensile bar printed of an exemplary modeling formulation as described in Example 1 herein (denoted soft pTHF2000tri), to which 4 % by weight methacrylic acid was added.

[0107] FIG. 4 presents side-by-side photographs of a dental aligner printed of an exemplary modeling formulation as described in Example 1 herein (right), and of the same formulation to which 4 % by weight methacrylic acid was added, upon immersion in IPA to prove the absence of haze / opaqueness (left).

[0108] FIGs. 5A-E present photographs (FIGs. 5A-D) of a 1 mm film cast from an exemplary modeling formulation as described in Example 1 herein per se (FIG. 5A), and to which 1, 2.3 and 4 % by weight MA was added (FIGs. 5B-D, respectively), and a table (FIG. 5E) presenting the respective haze values as measured for each formulation.

[0109] DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION

[0110] The present invention, in some embodiments thereof, relates to material science and, more particularly, but not exclusively, to curable formulations which are usable in forming transparent hardened materials and the use thereof in additive manufacturing of three-dimensional objects such as orthodontic devices.

[0111] Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not necessarily limited in its application to the details of construction and the arrangement of the components and / or methods set forth in the following description and / or illustrated in the drawings and / or the Examples. The invention is capable of other embodiments or of being practiced or carried out in various ways.

[0112] The present inventors have designed and successfully prepared and practiced novel curable formulations that can be employed in additive manufacturing, e.g. DLP, of transparent objects. The newly designed formulations provide, typically upon exposure to a curing condition such as irradiation, hardened transparent materials that feature high mechanical strength and / or toughness (e.g., as described herein) and can be considered as usable in the manufacturing of transparent devices such as orthodontic devices (e.g., dental aligners).

[0113] According to some embodiments of any of the embodiments described herein, the newly designed formulations form (when harden or solidify, e.g., upon exposure to a curing condition as described herein) a hardened transparent material that features one or more of the following optical properties:

[0114] Color (CIE color space; C*) lower than 1.2;

[0115] Transparency (visible light transmittance) higher than 85 %; and

[0116] Haze value, denoting the percentage of incoming light scattered by more than 2.5° through the material, lower than 15 %, each determined as described herein.

[0117] According to some embodiments of any of the embodiments described herein, the newly designed formulations form (when harden or solidify, e.g., upon exposure to a curing condition as described herein) a hardened transparent material that features one or more of the optical properties as described herein, and, at the same time features one or more of the following mechanical properties:

[0118] Tg higher than 100 °C, or higher than 120 °C;

[0119] Tensile modulus higher than 1000 MPa;

[0120] Yield stress higher than 20 MPa; and

[0121] Strain at break higher than 30 %, each determined as described herein.

[0122] Herein and in the art, the term “haze” describes cloudiness or opacity of a transparent material and is determined as the percentage of light that is scattered at large angles as it passes through the material, causing a loss of transparency or clarity. Haze is typically measured using a haze meter or a spectrophotometer equipped with a haze measurement function, which directs a light beam through the material and measures the amount of light scattered at large angles relative to the incident light. The haze value is calculated as the ratio of the scattered light intensity to the total transmitted light intensity, expressed as a percentage. An exemplary method for measuring haze is provided in the Examples section that follows.

[0123] Elastic Modulus, which is also referred to as Modulus of Elasticity or as Young’s Modulus, or as Tensile modulus, or “E”, describes a material’ s resistance to elastic deformation when a force is applied, or, in other words, as the tendency of an object to deform along an axis when opposing forces are applied along that axis. Elastic modulus is typically measured by a tensile test (e.g., according to ASTM D 624) and is determined by the linear slope of a Stress-Strain curve in the elastic deformation region, wherein Stress is the force causing the deformation divided by the area to which the force is applied and Strain is the ratio of the change in some length parameter caused by the deformation to the original value of the length parameter. The stress is proportional to the tensile force on the material and the strain is proportional to its length. Tensile modulus represents the stiffness of a material, defined as the relationship between stress (force per unit area) and strain (proportional deformation) in a material in the linear elasticity regime of a uniaxial deformation. Tensile modulus may also be determined, for example, according to ASTM D-638-04. Tensile Strength describes a material’s resistance to tension, or, in other words, its capacity to withstand loads tending to elongate, and is defined as the maximum stress in MPa, applied during stretching of an elastomeric composite before its rupture. Tensile strength is typically measured by a tensile test (e.g., according to ASTM D 624) and is determined as the highest point of a Stress-Strain curve, as described herein and in the art. Tensile strength represents the maximum stress that a material can withstand while being stretched or pulled before breaking. Tensile strength may also be determined, for example, according to ASTM D-638-03.

[0124] Elongation, or elongation at break, is the extension of a uniform section of a material, expressed as percent of the original length as follows:

[0125] Final length - Original length

[0126] Elongation % = - x 100.

[0127] Original length

[0128] Elongation or elongation at break is typically determined according to ASTM D412.

[0129] By “Elongation at break” it is meant the percentage increase in length of a material specimen at the point of rupture or breakage compared to its original length. It represents the maximum amount of stretch or deformation the material can sustain before reaching its breaking point. It may be determined, for example, according to ASTM D-638-04.

[0130] Flexural strength or Flexural stress describes the stress in a material just before it yields in a flexure test. Flexural strength may be determined, for example, according to ASTM D-790-03, unless otherwise indicated.

[0131] Flexural modulus describes the ratio of stress to strain in flexural deformation, which is determined from the slope of a stress-strain curve produced by a flexural test such as the ASTM D790. Flexural modulus may be determined, for example, according to ASTM D-790-04, unless otherwise indicated.

[0132] The term “transparent” describes a property of a hardened material that reflects the transmittance of light therethrough. A transparent material is typically characterized as capable of transmitting at least 70 % of a light that passes therethrough, or by transmittance of at least 70 %. Transmittance of a material can be determined using methods well known in the art.

[0133] A transparent curable formulation as described herein can be transparent also before it is hardened.

[0134] By “Transparency” it is meant the % transmittance of light through a material. A transparent material is typically characterized as capable of transmitting at least 70 % of light that passes therethrough, or by transmittance of at least 70 %. Transmittance of a material can be determined using methods well known in the art. In some embodiments, transmission is determined at room temperature based on ASTM D1003 using a film having a thickness of 0.3 mm.

[0135] Yield stress, or yield strength, or Yield Point, is the amount of stress a material can withstand before it begins to deform plastically and undergoes permanent and irreversible changes in shape or size, and represents the point at which a material transitions from elastic deformation to plastic deformation. Yield stress or strength is typically measured by a standardized tensile test (e.g., according to ASTM D 624 or according to ASTM D-638-04.

[0136] Water absorption or water absorbance typically describes an amount of water that a material is capable of absorbing, relative to its weight, when immersed in water at room temperature, for 24 hours, and can be determined, for example, according to ASTM D57098.

[0137] The newly designed curable formulations are based on poly(urethane (meth)acrylate) chemistry and employ curable urethane (meth) acrylate materials that interact with one another when exposed to a curing condition (e.g., irradiation), to thereby provide a transparent hardened material featuring mechanical properties as described herein.

[0138] The newly designed formulations are based on combining curable urethane acrylate materials such as described in WO 2023 / 114740, while selecting a combination of materials that provide to the hardened material formed thereby the desired mechanical properties and transparency. According to some embodiments of the present invention, the newly designed formulations provide to the hardened material formed thereby the desired mechanical properties and transparency while solving the problem of substantially high haze values obtained while employing such formulations.

[0139] The newly designed formulations are usable in forming transparent objects, suitable for use in applications that require high mechanical strength, via additive manufacturing, by featuring properties that meet the requirements of additive manufacturing protocols.

[0140] Embodiments of the present invention relate to newly designed curable formulations, to three-dimensional objects formed therefrom and to methods of manufacturing the three- dimensional objects. The formulations and methods described herein are suitable, inter alia, for additive manufacturing of orthodontic devices such as dental aligners.

[0141] Herein throughout, the term “object” describes a final product of the additive manufacturing. This term refers to the product obtained by a method as described herein, after removal of the support material, if such has been used as part of the building material. The “object” therefore essentially consists (at least 95 weight percent) of a hardened (e.g., cured) modeling material or a combination of two or more hardened (e.g., cured) modeling materials.

[0142] The term "object" as used herein throughout refers to a whole object or a part thereof.

[0143] An object according to the present embodiments is such that at least a part or a portion thereof is transparent, and is also referred to herein as “a transparent object” or “an object having at least a portion thereof which is transparent”. The object may be such that several parts or portions thereof are made of a transparent material, or such that is entirely made of a transparent material. The transparent material can be the same or different in the different parts or portions, and, for each part, portion or the entire object made of a transparent material, the transparent material can be the same or different within the portion, part or object. When different transparent materials are used, they can differ in their chemical composition and / or mechanical properties.

[0144] Herein throughout, the phrase “building material” encompasses the phrases “uncured building material” or “uncured building material formulation” and collectively describes the materials that are employed during the sequential formation of the layers, as described herein. This phrase encompasses uncured materials which form the final object, namely, one or more uncured modeling material formulation(s), and optionally also uncured materials used to form a support, namely uncured support material formulations. The building material can also include non-curable materials that preferably do not undergo (or are not intended to undergo) any change during the process, as described herein.

[0145] An uncured building material can comprise one or more modeling material formulations, and can be utilized such that different parts of the object are made upon hardening (e.g., curing) of different modeling formulations, and hence are made of different hardened (e.g., cured) modeling materials or different mixtures of hardened (e.g., cured) modeling materials.

[0146] Herein throughout, the phrase “cured modeling material” or “hardened modeling material” describes the part of the building material that forms the object, as defined herein, upon exposing the formed layers to a curing condition, and, optionally, if a support material is sued, also upon removal of the cured support material, as described herein. The cured modeling material can be a single cured material or a mixture of two or more cured materials, depending on the modeling material formulations used in the method, as described herein.

[0147] The phrase “cured modeling material” or “cured modeling material formulation” can be regarded as a cured building material wherein the building material consists only of a modeling material formulation (and not of a support material formulation). That is, this phrase refers to the portion of the building material, which is used to provide the final object.

[0148] Herein throughout, the phrase “modeling material formulation”, which is also referred to herein interchangeably as “modeling formulation”, “model formulation” “model material formulation” or simply as “curable formulation” or “formulation”, describes a part or all of the building material which is used to form the object, as described herein. The modeling material formulation is an uncured, yet, curable, modeling formulation (unless specifically indicated otherwise), which, upon exposure to a curing condition such as curing energy, forms the object or a part thereof. In some embodiments of the present invention, a modeling material formulation is formulated for use in three-dimensional inkjet printing and is able to form a three-dimensional object on its own, without having to be mixed or combined with any other substance.

[0149] An uncured building material can comprise one or more modeling formulations, and can be employed such that different parts of the object are made, upon curing, of different cured modeling formulations or different combinations thereof, and hence are made of different cured modeling materials or different mixtures of cured modeling materials.

[0150] The formulations forming the building material (modeling material formulations and support material formulations) comprise one or more curable materials, which, when exposed to a curing condition (e.g., curing energy), form hardened (cured) material.

[0151] The formulations forming the uncured building material (modeling material formulations and support material formulations) are also referred to herein as curable formulations (e.g., a curable modeling material formulation or a curable support material formulation), which solidifies or hardens when exposed to a curing condition as described herein.

[0152] Herein throughout, a “curable material” is a compound (typically a monomeric or oligomeric compound, yet optionally a polymeric material) which, when exposed to a curing condition (e.g., curing energy), as described herein, solidifies or hardens to form a cured material. Curable materials are typically polymerizable materials, which undergo polymerization and / or cross-linking when exposed to a suitable energy source.

[0153] A curable material, according to the present embodiments, also encompasses materials which harden or solidify (cure) without being exposed to a curing energy, but rather to another curing condition (for example, upon exposure to a chemical reagent or simply upon exposure to the environment).

[0154] The terms “curable” and “solidifiable” as used herein are interchangeable.

[0155] The polymerization can be, for example, free-radical polymerization, cationic polymerization or anionic polymerization, and each can be induced when exposed to curing energy such as, for example, radiation, heat, etc., as described herein.

[0156] In some of any of the embodiments described herein, a curable material is a photocurable or photopolymerizable material, which polymerizes and / or undergoes cross-linking upon exposure to radiation, as described herein, and in some embodiments the curable material is a UV-curable material, which polymerizes and / or undergoes cross-linking upon exposure to UV radiation, as described herein.

[0157] In some embodiments, a curable material as described herein is a photopolymerizable or photocurable material that polymerizes via photo-induced free-radical polymerization. Alternatively, the curable material is a photopolymerizable material that polymerizes via photoinduced cationic polymerization.

[0158] In some of any of the embodiments described herein, a curable material can be a monomer, an oligomer or a short-chain polymer, each being polymerizable and / or cross -linkable as described herein.

[0159] In some of any of the embodiments described herein, when a curable material is exposed to curing energy (e.g., radiation), it hardens (cured) by any one, or combination, of chain elongation and cross-linking.

[0160] In some of any of the embodiments described herein, a curable material is a monomer or a mixture of monomers which can form a polymeric material upon a polymerization reaction, when exposed to curing energy at which the polymerization reaction occurs. Such curable materials are also referred to herein as monomeric curable materials.

[0161] In some of any of the embodiments described herein, a curable material is an oligomer or a mixture of oligomers which can form a polymeric material upon a polymerization reaction, when exposed to curing energy at which the polymerization reaction occurs. Such curable materials are also referred to herein as oligomeric curable materials.

[0162] In some of any of the embodiments described herein, a curable material, whether monomeric or oligomeric, can be a mono-functional curable material or a multi-functional curable material.

[0163] Herein, a mono-functional curable material comprises one functional group that can undergo polymerization when exposed to curing energy (e.g., radiation).

[0164] A multi-functional curable material comprises two or more, e.g., 2, 3, 4 or more, functional groups that can undergo polymerization when exposed to curing energy. Multi-functional curable materials can be, for example, di-functional, tri-functional or tetra-functional curable materials, which comprise 2, 3 or 4 groups that can undergo polymerization, respectively (also referred to herein as featuring a functionality of 2, 3, or 4, etc.). The two or more functional groups in a multifunctional curable material are typically linked to one another by a linking moiety, as defined herein. When the linking moiety is an oligomeric or polymeric moiety, the multi-functional group is an oligomeric or polymeric multi-functional curable material. Multi-functional curable materials can undergo polymerization when subjected to curing energy and / or act as cross -linkers.

[0165] The method of the present embodiments manufactures three-dimensional objects in a layerwise manner by forming a plurality of layers in a configured pattern corresponding to the shape of the objects, as described herein in any of the respective embodiments. The final three-dimensional object is made of the modeling material or a combination of modeling materials or a combination of modeling material / s and support material / s or modification thereof (e.g., following curing). All these operations are well-known to those skilled in the art of solid freeform fabrication.

[0166] According to an aspect of some embodiments of the present invention there is provided a method of additive manufacturing of a three-dimensional object, as described herein.

[0167] The method is generally effected or performed by sequentially forming a plurality of layers in a configured pattern corresponding to the shape of the object, such that formation of each of at least a few of said layers, or of each of said layers, comprises exposing a building material (uncured) which comprises one or more modeling material formulation(s), and optionally a support material formulation, to a curing condition (e.g., curing energy) to thereby form a cured modeling material, and optionally a cured support material, as described in further detail hereinafter.

[0168] According to some of any of the embodiments described herein, the curable modeling material formulation is a photocurable formulation, which comprises at least one, and preferably at least two or more photocurable materials that undergo polymerization and / or cross-linking upon exposure to radiation. The radiation can be electromagnetic radiation, or electron beam radiation, depending on the modeling material formulation being used. The radiation source can include any type of radiation emitting device, including, without limitation, light emitting diode (LED), digital light processing (DLP) system, resistive lamp and the like. Further details are provided hereinunder.

[0169] Curable formulations:

[0170] According to an aspect of some embodiments of the present invention, there is provided a curable formulation usable in preparing objects (e.g., three-dimensional objects) that comprise, in at least a portion thereof, a transparent material. According to some embodiments, the curable formulation is a photocurable formulation, which hardens upon exposure to radiation. According to some embodiments, the curable formulation is usable as a modeling material formulation in additive manufacturing of 3D objects. A curable formulation is therefore also referred to herein interchangeably as a modeling material formulation, and vice versa.

[0171] According to an aspect of some embodiments of the present invention, there is provided a modeling material formulation usable in additive manufacturing of a three-dimensional (3D) object that comprises, in at least a portion thereof, a transparent material. According to some embodiments, the 3D object is transparent in its entirety. According to some embodiments of any of the embodiments described herein, the modeling material formulation that provides, when hardened, a transparent material, is also transparent before being hardened, as described herein. According to some of any of the embodiments described herein, the 3D object is an orthodontic device such as a dental aligner and the formulation is designed so as to meet the respective requirements in terms of mechanical and visual properties, as delineated herein and / or known in the art.

[0172] According to some embodiments of any of the embodiments described herein, the modeling material formulation comprises curable urethane (meth)acrylate (e.g., pre-poly meric) materials, preferably a combination of one or more urethane (meth) acrylate (e.g., pre-polymeric) material(s) that provide, when hardened, high Tg and one or more urethane (meth) acrylate material(s) (e.g., pre-polymeric) that provide, when hardened, low Tg, optionally in combination with an additional curable material that imparts toughness to the formed hardened material (e.g., features high Tg when hardened) and a required viscosity, and which is also referred to herein as “reactive diluent”.

[0173] Herein, a urethane (meth)acrylate material is also referred to interchangeably as urethane (meth)acrylate pre-polymer, meaning that it can undergo polymerization and / or cross-linking, so as to form one or more polymeric networks, upon exposure to a suitable curing condition (e.g., irradiation).

[0174] According to some embodiments of any of the embodiments described herein, the formulation comprises a combination of a first curable material which is a first urethane (meth)acrylate material having a number average molecular weight (Mn) lower than 2000 grams / mol and featuring Tg of at least 80 °C or of at least 100 °C, and a second curable material, which is a second urethane (meth) acrylate material having a number average molecular weight (Mn) of from 2000 grams / mol to 10,000 grams / mol and featuring Tg lower than -20 °C, or lower than -40 °C.

[0175] Herein throughout, whenever molecular weight or its abbreviation MW is indicated with regard to polymeric or oligomeric materials, it is meant average number molecular weight, Mn, as determined by gel permeation chromatography (GPC), typically while employing polystyrene as a retention time standard.

[0176] Herein throughout, a number average molecular weight is also referred to interchangeably as average number molecular weight, average Mn, or simply as Mn.

[0177] According to some embodiments of any of the embodiments described herein, the first and second urethane (meth)acrylate materials are selected as substantially miscible or at least mixable with one another at the working temperature.

[0178] By “miscible” it is meant herein materials which form a clear, preferably homogeneous, solution when mixed in equal volumes or weights at an indicated temperature, as determined visually without optical instruments. In some embodiments, the temperature is room temperature. In some embodiments, the temperature is an elevated temperature, for example, 50, 60, 70, or 80

[0179] °C, or any other temperature in a range of 20 to 80 °C.

[0180] According to some embodiments of any of the embodiments described herein, the first urethane (meth) acrylate material has a number average molecular weight of less than 2000 grams / mol, or less than 1,800 grams / mol, or less than 1500 grams / mol, or less than 1200 grams / mol, or less than 1,100 grams / mol, or less than 1,000 grams / mol, or less than 900 grams / mol.

[0181] According to some embodiments of any of the embodiments described herein, the first urethane (meth) acrylate material has a number average molecular weight in a range of from 100 to 1,900, or from 100 to 1,800, or from 100 to 1,500, or from 100 to 1,200, or from 100 to 1,100, or from 100 to 1,000, or from 200 to 1,900, or from 200 to 1,800, or from 200 to 1,500, or from 200 to 1,200, or from 200 to 1,100, or from 200 to 1,000, or from 200 to 900, or from 200 to 800, or from 300 to 1,900, or from 100 to 1,800, or from 100 to 1,500, or from 100 to 1,200, or from 100 to 1,100, or from 100 to 1,000, or from 300 to 900, or from 300 to 800, or from 400 to 1,900, or from 400 to 1,800, or from 400 to 1,500, or from 400 to 1,200, or from 400 to 1,100, or from 400 to 1,000, or from 400 to 900, or from 400 to 800, or from 500 to 1,900, or from 500 to 1,800, or from 500 to 1,500, or from 500 to 1,200, or from 500 to 1,100, or from 500 to 1,000, or from 500 to 900, or from 500 to 800, or from 600 to 1,900, or from 600 to 1,800, or from 600 to 1,500, or from 600 to 1,200, or from 600 to 1,100, or from 600 to 1,000, or from 800 to 1,900, or from 800 to 1,800, or from 800 to 1,500, or from 800 to 1,200, or from 800 to 1,100, or from 800 to 1,000, including any intermediate values and subranges therebetween.

[0182] According to some embodiments of any of the embodiments described herein, the first urethane (meth)acrylate material features, when hardened (as a homopolymer), Tg in a range of from 80 to 200, or from 80 to 180, or from 80 to 150, or from 80 to 120, or from 100 to 200, or from 100 to 180, or from 100 to 150, °C, including any intermediate values and subranges therebetween.

[0183] According to some embodiments of any of the embodiments described herein, an amount of the first urethane (meth)acrylate material ranges from 20 to 60, or from 20 to 50, or from 20 to 40, preferably from 25 to 35 or from 25 to 30, % by weight of the total weight of the formulation, including any intermediate values and subranges therebetween.

[0184] According to some embodiments of any of the embodiments described herein, the second urethane (meth) acrylate material has a number average molecular weight of at least 2000 grams / mol, or at least 2,500 grams / mol, or at least 3,000 grams / mol, or at least 4,000 grams / mol. According to some embodiments of any of the embodiments described herein, the second urethane (meth)acrylate material has a number average molecular weight has a number average molecular weight in a range of from 2,000 to 10,000, or from 2,500 to 10,000, or from 3,000 to 10,000, or from 4,000 to 10,000, or from 2,000 to 8,000, or from 2,500 to 8,000, or from 3,000 to 8,000, or from 4,000 to 8,000, or from 2,000 to 6,000, or from 3,000 to 6,000, or from 2,000 to 4,000, including any intermediate values and subranges therebetween.

[0185] According to some embodiments of any of the embodiments described herein, the second urethane (meth) acrylate material features, when hardened (as a homopolymer), Tg lower than 0 °C, preferably lower than -10, or lower than -20, or lower than -40, °C.

[0186] According to some of any of the embodiments described herein, the second urethane (meth)acrylate material features, when hardened (as a homopolymer), Tg in a range of from -20 to -100, or from -40 to than -100, or from -50 to -100, or from -60 to -100, °C, including any intermediate values and subranges therebetween.

[0187] According to some embodiments of any of the embodiments described herein, an amount of the second urethane (meth) acrylate material is at least 20 %, preferably at least 25 %, or preferably at least 30 %, by weight of the total weight of the formulation.

[0188] According to some of any of the embodiments described herein, an amount of the second urethane (meth) acrylate material ranges from 20 to 60, preferably from 25 to 60, or from 25 to 50, or from 25 to 40, more preferably from 30 to 60, or from 30 to 50, or from 30 to 40, or from 35 to 40 or from 30 to 35, % by weight of the total weight of the formulation, including any intermediate values and subranges therebetween.

[0189] According to the present embodiments, the first and second curable materials comprised in the formulation are based on urethane acrylate chemistry, and are designed accordingly, by selecting suitable isocyanate, (meth)acrylate and isocyanate-reactive component, and ratios thereof, that provide a urethane (meth) acrylate material featuring the indicated MW and Tg values.

[0190] Generally speaking, the first and second urethane (meth) acrylate materials are first and second reaction products, respectively, of the following synthetic pathway:

[0191] As a first stage, a multi-functional, for example, di-functional, isocyanate (e.g., diisocyanate), is reacted with an isocyanate reactive component, that is, any multi-functional (e.g., di-functional) component that can react with isocyanate to form a respective urethane bond. By “functional” in this context it is meant the reactive groups that participate in a covalent-bond formation reaction; in this case - the formation of a urethane bond.

[0192] Examples of isocyanate reactive components include compounds featuring two or more of a hydroxy, thiol and amine groups. According to exemplary embodiments, the isocyanate reactive component is a polyol, that is, a material that comprises two hydroxy groups (also referred to as diol), or three or more hydroxy groups (referred to herein also as polyol).

[0193] In the following stage, the obtained urethane material is reacted with a reactive (meth)acrylate, that is, a (meth)acrylic compound that features a reactive group that is capable of reacting with the flanking isocyanate groups of the urethane material to provide a respective urethane (meth)acrylic material. According to exemplary embodiments, the reactive group is hydroxy, and the (meth)acrylic compound is a hydroxy-containing (meth)acrylic material, for example, a (meth)acrylic compound such as (meth)acrylate, that features a group that has a free hydroxy substituent, for example, a terminal hydroxy group.

[0194] Scheme 1 below presents a simplified, exemplary, schematic representation of the synthetic pathway:

[0195] Scheme 1

[0196] X represents the moiety to which two (and optionally more) cyanate moieties are linked in a polyisocyanate (exemplified in Scheme 1 as diisocyanate).

[0197] Y represents the moiety to which two (and optionally more) hydroxy moieties are linked in a polyol (exemplified in Scheme 1 as diol). n represents the number of urethane blocks in the curable material.

[0198] Z represents a moiety that comprises (e.g., terminates by) the reactive group. The reactive group is preferably hydroxy, such that Z is a moiety that comprises a hydroxy. An exemplary reactive (meth) acrylate is a hydroxy -containing (meth)acrylate, for example, a hydroxyalkyl (meth)acrylate.

[0199] Ra is hydrogen when the (meth) acrylate is an acrylate; and methyl when the (meth) acrylate is a methacrylate. The nature of the multi-functional isocyanate (polyisocyanate; e.g., of X in Scheme 1 above), of the polyol (e.g., of Y in Scheme 1 above), and of the (meth) acrylate (e.g., of Z in scheme 1 above), as well as the number of blocks (n is Scheme 1 above), all determine the chemical composition and accordingly the properties of the obtained first and second curable materials.

[0200] The number of blocks, n, can be manipulated by determining the isocyanate / hydroxy (NCO / OH) ratio during the reaction and controlling the reaction so as to obtain the desired number of blocks. In case of a diisocyanate and a diol, NCO / OH ratio of 2 typically results in a monoblock (n is Scheme 1 being 1); NCO / OH ratio of 1.5 typically results in a di-block (n in Scheme 1 being 2); NCO / OH ratio of 1.33 typically results in a tri-block (n is Scheme 1 being 3); and so forth.

[0201] It is to be noted that Scheme 1 presents the formation of the urethane (meth)acrylate in its most simplified configuration and that more complex configurations, resulting from various intramolecular and intermolecular interactions between the components are typically also present in the reaction products.

[0202] The multi-functional isocyanate (also referred to as polyisocyanate) is a material that features two or more isocyanate groups, and which can be aromatic, aliphatic or alicyclic (cycloaliphatic) polyisocyanate. In exemplary embodiments, as shown in Scheme 1 above, the multi-functional isocyanate is a diisocyanate. When the polyisocyanate is a diisocyanate, X in Scheme 1 above can be aromatic (for an aromatic diisocyanate), aliphatic (for an aliphatic diisocyanate) or alicyclic (cycloaliphatic) for a cycloaliphatic diisocyanate.

[0203] Thus, in some embodiments, a diisocyanate can include an aliphatic linear diisocyanate, a cycloaliphatic diisocyanate, an aromatic diisocyanate, or a combination thereof.

[0204] In some embodiments of any of the embodiments described herein, the diisocyanate is or comprises a cycloaliphatic diisocyanate. Representative examples of cycloaliphatic diisocyanates include, but are not limited to, cyclohexane- 1,3 -diisocyanate, cyclohexane- 1,4-diisocyanate, 1- isocyanato-2-isocyanatomethyl cyclopentane, IPDI, H12MDI, l,3-bis(isocyanatomethyl)- cyclohexane, l,4-bis(isocyanatomethyl)-cyclohexane, bis-(4-isocyanato-3-methyl- cyclohexyl)methane, l-isocyanato-l-methyl-4(3)-isocyanato methyl cyclohexane, 2,4- hexahydrotoluylene diisocyanate, 2,6-hexahydrotoluylene diisocyanate, and any combination thereof. In exemplary embodiments, a cycloaliphatic diisocyanate includes IPDI, H12MDI, or a combination thereof. In exemplary embodiments, a cycloaliphatic diisocyanate includes IPDI (isophorone diisocyanate). In some embodiments of any of the embodiments described herein, the diisocyanate includes at least 80 %, or at least 85 %, or at least 90 %, or at least 95 %, or at least 99 %, or 100 %, by weight, of one or more cycloaliphatic diisocyanate(s), as described herein.

[0205] In some embodiments of any of the embodiments described herein, the diisocyanate is devoid of aromatic diisocyanate(s), or comprises no more than 20 %, preferably no more than 15 %, or no more than 10 %, or no more than 5 %, or no more than 2 %, or no more than 1 %, by weight, of one or more aromatic diisocyanate(s).

[0206] Exemplary aromatic diisocyanates include, but are not limited to methylene diphenyl diisocyanate (MDI) (e.g., 2,4’-MDI, 4,4’-MDI, or a mixture thereof), toluene diisocyanate (TDI) (e.g., 2,4-TDI, 2,6-TDI, or a mixture thereof), or a combination thereof.

[0207] As used herein, an “isocyanate-reactive component” describes a compound (which can be monomeric, oligomeric or polymeric) featuring one or more of a hydroxy group, an amino group and a thiol group. The isocyanate-reactive component can typically have a functionality of at least 2, such that it includes two or more of the groups that are capable of reacting with the isocyanate to form a urethane bond (two or more groups selected from hydroxy, amine and thiol, and a combination of two or three thereof). Non-limiting examples of isocyanate reactive components include polyols (e.g., diols, triols, etc.), polyamines (e.g., diamines, triamines, etc.), polythiols (e.g., dithiols, trithiols, etc.), and the like, or a combination thereof. In Scheme 1 above, the isocyanate reactive material is exemplified as a diol, although higher polyols and / or diamine and / or dithiols and / or materials featuring a combination of these groups are also contemplated (forming the respective bonds). The moiety Y to which the functional groups (hydroxy, amine and / or thiol) are linked, and the chemical nature and number of functional groups, determine the chemical nature and accordingly the properties of the obtained urethane material.

[0208] The isocyanate reactive material can therefore be represented by the Formula Y(F)q, wherein Y is the backbone of the isocyanate -reactive component, F is a functional group as described herein (e.g., hydroxy, amine and / or thiol), and q is the number of functional groups. When q is 2 or more, the functional groups can be the same or different.

[0209] Y can be a hydrocarbon, as defined herein, which can be linear or branched, substituted or unsubstituted, saturated or unsaturated, and which can optionally be interrupted by one or more heteroatoms.

[0210] In exemplary embodiments, the isocyanate-reactive component is a polyol, represented by the formula Y(F)q in which F is hydroxy and q is at least 2. When q is 2, this component is referred to herein as a diol.

[0211] In exemplary embodiments Y is a diol, as defined herein. The moiety Z in the hydroxy-containing (meth) acrylate can be aliphatic, cycloaliphatic (alicyclic) or aromatic. In exemplary embodiments, Z is an aliphatic moiety, which can be linear or branched, preferably saturated, hydrocarbon (e.g., alkylene), which is substituted, preferably terminated, at least by hydroxy. In some embodiments, the alkyl is of 1 to 10, or 1 to 8, preferably 1 to 6, or 1 to 4, carbon atoms in length. In some embodiments, the hydroxy-containing (meth)acrylate is of from 3 to 12, or from 3 to 10 or from 3 to 8 or from 3 to 6, carbon atoms in length.

[0212] According to some embodiments of any of the embodiments described herein, both the first and the second reaction products are prepared in accordance with Scheme 1 as described hereinabove, to provide the respective urethane (meth)acrylate materials. According to some of these embodiments, the polyisocyanate is a diisocyanate, preferably an alicyclic diisocyanate, such that X is an alicyclic moiety, as described herein in any of the respective embodiments. According to some of these embodiments, the isocyanate reactive component is a diol, as described herein in any of the respective embodiments and any combination thereof. According to some of these embodiments, the polyisocyanate is a diisocyanate, preferably an alicyclic diisocyanate, such that X is an alicyclic moiety, as described herein in any of the respective embodiments, and the isocyanate reactive component is a diol, as described herein in any of the respective embodiments and any combination thereof. According to some of any of these embodiments, Z is an alkylene, terminated by hydroxy, as described herein in any of the respective embodiments and any combination thereof.

[0213] According to some embodiments of any of the embodiments described herein, each of the first and second polyurethane acrylate (the first and second urethane (meth)acrylate materials) independently has a simplified structure as described in Scheme 1 herein.

[0214] According to some embodiments of any of the embodiments described herein, the first urethane (meth)acrylate (the first curable urethane (meth)acrylate material) is or comprises a first reaction product formed of a cycloaliphatic (alicyclic) diisocyanate as described herein in any of the respective embodiments, a first diol, and a first hydroxy-containing (meth)acrylate, as described herein in any of the respective embodiments and any combination thereof.

[0215] According to some embodiments of any of the embodiments described herein, the first urethane (meth) acrylate curable material (first pre-polymer) is a first reaction product formed upon reacting, as described herein, a first cycloaliphatic (alicyclic) diisocyanate, as described herein in any of the respective embodiments, a first (meth)acrylic compound featuring a hydroxy group (a hydroxy-containing (meth)acrylate), as described herein in any of the respective embodiments, and a first diol. According to some embodiments of any of the embodiments described herein, the first urethane (meth) acrylate curable material (first pre-polymer) is or comprises a mono-block material, and is or comprises a first reaction product featuring NCO / OH ratio of 2.

[0216] According to some embodiments of any of the embodiments described herein, the first cycloaliphatic (alicyclic) diisocyanate used to form the first urethane (meth)acrylate material is as described herein in any of the respective embodiments, and in exemplary embodiments, it is or comprises IPDI (isophorone diisocyanate).

[0217] According to some embodiments of any of the embodiments described herein, the first acrylic compound featuring a hydroxy group is a first hydroxyalkyl (meth)acrylate. In schemes 1 and 2 above, Z is a hydroxyalkyl, which, upon reacting with the urethane, forms an alkoxy. In some embodiments, the hydroxy alkyl in the first (meth)acrylic compound featuring a hydroxy group is of from 1 to 10, or from 2 to 10, or from 2 to 8, or from 2 to 6, or from 2 to 4, carbon atoms in length, including any intermediate values and subranges therebetween. The selection of a hydroxyalkyl (meth) acrylate determines the chemical composition of moiety Z in the formed first urethane (meth) acrylate material.

[0218] Non-limiting examples of a first hydroxyalkyl (meth)acrylate include hydroxymethyl acrylate, hydroxymethyl methacrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, hydroxypentyl acrylate, hydroxypentyl methacrylate, hydroxyhexyl acrylate, hydroxyhexyl methacrylate, the like, and any combination thereof. In exemplary embodiments, the first hydroxyalkyl (meth)acrylate is or includes hydroxyethyl acrylate and / or hydroxyethyl methacrylate. In exemplary embodiments, the first hydroxy alkyl (meth)acrylate is or includes hydroxyethyl acrylate.

[0219] In exemplary embodiments, the first hydroxyalkyl (meth) acrylate is or includes hydroxy ethyl methacrylate (HEM A).

[0220] According to some embodiments of any of the embodiments described herein, the first diol is such that Y is a hydrocarbon, as defined herein, for example, an alkyl (alkylene), which can be linear or branched, is preferably saturated, and is preferably of 2 to 20, or from 2 to 12, or from 2 to 10, or from 2 to 8, or from 4 to 20, or from 4 to 12, or from 4 to 10, or from 4 to 8, carbon atoms in length, including any intermediate values and subranges therebetween, and which includes at least two hydroxy substituents available to react with the isocyanate, for example, two terminal hydroxy substituents. Upon reacting with the other components forming the urethane (meth)acrylate material, the Y moiety is bound to the X moiety via a urethane bond. Exemplary compounds usable as first diols include, without limitation, a C2-C8 linear or branched aliphatic polyol; a C4-C10 linear or branched aliphatic polyol; a C6-C12 linear or branched aliphatic polyol; or a mixture of any of these. Non-limiting examples of a first diol include ethylene glycol, 1,2-propanediol, 1,3-propanediol, glycerol, 1,3 -butanediol, 2,3- butanediol, 1,4-butanediol, 2-methyl-l,4-butanediol, 3-methyl-l,3-butanediol, 1,2,4-butanetriol, 1,5-pentanediol, 3 -methyl- 1,5-pentanediol, 3-methyl-2,4-pentanediol, 2-methyl-l,3-pentanediol, 2-methyl- ,5-pentanediol, 1,2,5-pentanetriol, 1,6-hexanediol, 1,2-hexanediol, 1,5-hexanediol, 2- methyl-l,6-hexanediol, 4-methyl-l,3-hexanediol, 5-methyl-2,4-hexanediol, 3-methyl- 1,6- hexanediol, 1,2,6-hexanetriol, 1,7-heptanediol, 2,5-heptanediol, 4-methyl-l,6-heptanediol, 3- methyl-2,4-heptanediol, 2-methyl-2,6-heptanediol, 5-methyl-2,4-heptanediol, 4-methyl-l,7- heptanediol, 1,2,7-heptanetriol, 1,8-octanediol, 2-methyl-l,8-octanediol, 7-methyl-l,7-octanediol, 6-methyl-l,7-octanediol, 3- methyl-l,4-octanediol, 1,2,8-octanediol, 1,9-nonanediol, 8-methyl-l-8- nonanediol, 1,2,9- nonanetriol, 1,10-decanediol, 2-methyl- 1,10-decanediol, 2-methyl-2,5- decanediol, 4,8-Bis(hydroxymethyl)tricycle [5.2.1.02, 6]decane (DCPDM), 1,11 -undecanediol, 1,12-dodecanediol, the like.

[0221] In exemplary embodiments, the first diol is or includes 3-methyl- 1,5-pentanediol (MPD).

[0222] The first urethane (meth) acrylate material according to some embodiments of any of the embodiments described herein can have a simplified chemical structure as depicted in Scheme 1 above, in which X is a cycloaliphatic moiety derived from a cycloaliphatic diisocyanate as described herein in any of the respective embodiments (e.g., IPDI); Y is derived from a first diol as described herein in any of the respective embodiments, n is 1 and Z is derived from the first hydroxyalkyl of a hydroxy-containing (meth)acrylate, as described herein in any of the respective embodiments.

[0223] An exemplary first urethane (meth) acrylate material is a (first) reaction product of HEMA, MPD and IPDI, with NCO / OH ratio of 2.

[0224] According to some embodiments of any of the embodiments described herein, the second urethane (meth)acrylate curable material (second pre-polymer) is or comprises a second reaction product formed upon reacting, as described herein, a second cycloaliphatic (alicyclic) diisocyanate, as described herein in any of the respective embodiments, a second acrylic compound featuring a hydroxy group (a hydroxy-containing (meth)acrylate, as described herein in any of the respective embodiments), and a second diol.

[0225] According to some embodiments of any of the embodiments described herein, the second cycloaliphatic (alicyclic) diisocyanate used to form the second urethane (meth)acrylate material is as described herein in any of the respective embodiments for the first diisocyanate, and is preferably

[0226] IPDI (isophorone diisocyanate).

[0227] The second cycloaliphatic diisocyanate can be the same or different from the first diisocyanate.

[0228] In exemplary embodiments, both the first and second cycloaliphatic diisocyanate are each IPDI (isophorone diisocyanate) or each comprise IPDI.

[0229] According to some embodiments of any of the embodiments described herein, the second acrylic compound featuring a hydroxy group is a second hydroxyalkyl (meth)acrylate. In scheme

[0230] 1 above, Z is a hydroxyalkyl, which, upon reacting with the urethane, forms an alkoxy. The hydroxyalkyl can be a linear or branched hydroxyalkyl, and can be of from 1 to 10 carbon atoms in length or in total. In some embodiments, the hydroxyalkyl in the second acrylic compound featuring a hydroxy group is of from 1 to 10, or from 2 to 10, or from 2 to 8, or from 2 to 6, or from

[0231] 2 to 4, carbon atoms in length, including any intermediate values and subranges therebetween.

[0232] Non-limiting examples of a second hydroxyalkyl (meth)acrylate include hydroxymethyl acrylate, hydroxymethyl methacrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, hydroxypentyl acrylate, hydroxypentyl methacrylate, hydroxyhexyl acrylate, hydroxyhexyl methacrylate, the like, and any combination thereof. In exemplary embodiments, the second hydroxyalkyl (meth)acrylate is or includes hydroxyethyl acrylate and / or hydroxyethyl methacrylate.

[0233] In exemplary embodiments, the second hydroxy alkyl (meth)acrylate is or includes hydroxyethyl acrylate.

[0234] In exemplary embodiments, the second hydroxy alkyl (meth)acrylate is or includes hydroxy ethyl methacrylate (HEM A).

[0235] The first hydroxyalkyl (meth)acrylate and the second hydroxyalkyl (meth)acrylate can be the same or different.

[0236] According to some embodiments of any of the embodiments described herein, the second diol comprises a polyether diol (e.g., a polyether glycol) having Mn of from 500 to 5,000, or from 1,000 to 5,000, or from 2,000 to 5,000, or from 2,000 to 4,000, or from 2,000 to 3,000, or from 2,500 to 5,000, or from 3,000 to 5,000, or from 3,000 to 4,000, or from 2,500 to 4,000, or from 2,500 to 3,500, or from 2,500 to 3,000, or from 3,000 to 3,500, grams / mol, including any intermediate values and subranges therebetween.

[0237] Exemplary polyether diols usable as the second diol include, but are not limited to, polyalkylene adipate diols such as polyethylene adipate diol (PEA), polybutylene adipate diol (PBA), and polypropylene adipate diol (PPA); polycaprolactone diol (PCL), polyalkylene succinate diols such as polyethylene succinate diol; polyalkylene sebacate diols such as polyethylene sebacate diol; polyalkylene ether glycol such as polytrimethylene ether glycol and polytetramethylene ether glycol (PTMEG; also known and referred to herein as polyTHF); and polyolefin polyol such as hydroxyl-terminated polybutadiene and hydroxyl-terminated polyisoprene.

[0238] Exemplary polyether diols usable as the second diol include also those marketed by Covestro under the tradename Desmophen®.

[0239] The second urethane (meth) acrylate material according to some of any of the embodiments described herein can have a simplified chemical structure as depicted in Scheme 1 above, in which X is a cycloaliphatic moiety derived from a cycloaliphatic diisocyanate as described herein in any of the respective embodiments (e.g., IPDI); Y is derived from a second diol as described herein in any of the respective embodiments, and Z is derived from the second hydroxyalkyl of a hydroxycontaining (meth)acrylate, as described herein in any of the respective embodiments.

[0240] In some embodiments, n is 2 or more, for example, 2 to 6, or 2 to 5, or 2 to 4, or 2 or 3, such that the second material is a multiblock urethane (meth) acrylate material. In some embodiments, the second urethane (meth)acrylate material is such that an NCO / OH ratio targeted during its preparation is lower than 2 or is no more than 1.5.

[0241] According to some of any of the embodiments described herein, the second urethane (meth)acrylate material is or comprises a second reaction product of a cycloaliphatic diisocyanate as described herein in any of the respective embodiments (e.g., IPDI); a second diol as described herein in any of the respective embodiments, and a second hydroxy -containing (meth)acrylate, as described herein in any of the respective embodiments, in which the NCO / OH ratio ranges from 1 to 1.8, or from 1 to 1.5, or from 1.2 to 1.8, or from 1.2 to 1.5, or from 1.3 to 1.8, or from 1.3 to 1.5, including any intermediate values and subranges therebetween.

[0242] An exemplary second urethane (meth)acrylate material is or comprises a second reaction product of HEMA, polyTHF and IPDI, at NCO / OH ratio of 1.5 (a di-block) or of 1.33 (a tri-block).

[0243] In alternative embodiments, n is 1, such that the second material is a mono-block urethane (meth)acrylate material.

[0244] In alternative embodiments, the second urethane (meth) acrylate material is such that an NCO / OH ratio targeted during its preparation is about 2.

[0245] According to some of these alternative embodiments, n is 1 and / or a NCO / OH ratio targeted during the preparation of the second urethane (meth)acrylate material is about 2, and the second diol is or comprises a polyether diol (e.g., a polyether glycol) having Mn of at least 2,000, preferably of at least 2,500, or at least 2,800, or at least 2,900, or at least 3,000, for example, of from 2,900 to 6,000, or from 2,900 to 5,000, or from 2,900 to 4,000, or from 3,000 to 6,000, or from 3,000 to 5,000, or from 3,000 to 4,000, or from 3,000 to 3,500, grams / mol, including any intermediate values and subranges therebetween.

[0246] According to some of these alternative embodiments, the second diol is or comprises a polyTHF having Mn of at least 2,000, preferably of at least 2,500, or at least 2,800, or at least 2,900, or at least 3,000, for example, of from 2,900 to 6,000, or from 2,900 to 5,000, or from 2,900 to 4,000, or from 3,000 to 6,000, or from 3,000 to 5,000, or from 3,000 to 4,000, or from 3,000 to 3,500, grams / mol, including any intermediate values and subranges therebetween.

[0247] According to some of these alternative embodiments, the second urethane (meth)acrylate material is or comprises a second reaction product of a cycloaliphatic diisocyanate as described herein in any of the respective embodiments (e.g., IPDI); a second diol as described herein in any of the respective embodiments, and a second hydroxy-containing (meth)acrylate, as described herein in any of the respective embodiments, in which the NCO / OH ratio is about 1.

[0248] An exemplary second urethane (meth)acrylate material is or comprises a second reaction product of HEM A, polyTHF having Mn as described herein in the respective embodiments, and IPDI, at NCO / OH ratio of about 2.

[0249] The first and / or second curable urethane (meth) acrylate materials can be selected from commercially available products, or can be synthetically prepared, in accordance with the general synthetic procedure described in the Examples section that follows, while selecting suitable reactants (first and second diisocyanate, diol and hydroxy-containing (meth)acrylate).

[0250] According to some of any of the embodiments described herein, the curable formulation further comprises a third curable component.

[0251] In some embodiments of any of the embodiments described herein, the third curable component is added to the first and / or second (meth) acrylate urethane curable materials in order to provide the formulation with a desired viscosity and / or to provide the hardened material with desired mechanical properties.

[0252] In some embodiments, the third curable material is considered as a reactive diluent, for example, as a curable material in which both the first and second curable materials are miscible or soluble.

[0253] According to some embodiments of any of the embodiments described herein, the third curable material is a mono-functional (meth)acrylate.

[0254] According to some embodiments of any of the embodiments described herein, the third curable material is a mono-functional (meth)acrylate monomeric material. According to some embodiments of any of the embodiments described herein, the third curable material is a mono-functional methacrylate monomeric material.

[0255] According to some embodiments of any of the embodiments described herein, the third curable material features, when hardened to form a homopolymer, a high Tg, for example, Tg higher than 50, or higher than 70, or higher than 80, or higher than 100, °C.

[0256] According to some embodiments of any of the embodiments described herein, the third curable material features, when hardened to form a homopolymer, Tg in a range of from 50 to 200, or from 50 to 180, or from 50 to 150, or from 50 to 130, or from 50 to 120, or from 80 to 200, or from 80 to 180, or from 80 to 130, or from 80 to 120, or from 100 to 200, or from 100 to 180, or from 100 to 150, °C, including any intermediate values and subranges therebetween.

[0257] Non-limiting examples of suitable (meth) acrylate monomeric materials (a third material) include isobomyl acrylate, isobornyl methacrylate, cyclohexyl methacrylate, 4-tert-butyl- cyclohexylmethacrylate, 4-tert-butylcyclohexyl acrylate, 3,3,5-trimethylcyclohexyl acrylate,

[0258] 3.3.5-trimethylcyclohexyl methacrylate, dicyclopentanyl acrylate, dicyclopentanyl methacrylate,

[0259] 3.5-dimethyl-l-adamantyl acrylate, 3,5-dimethyl-l-adamantyl methacrylate, tert-butyl methacrylate, 2 -decahydronap thy 1 methacrylate, 1-adamantyl acrylate, 1-adamantyl methacrylate, 2-ethylhexyl methacrylate, 3-tetracyclo[4.4.0.1.1]dodecyl methacrylate, tetrahydrofurfuryl methacrylate, 2-phenoxyethyl methacrylate, vinyl pyrrolidone, carboxyethyl acrylate, acryloyl morpholine, the like, and any combination thereof.

[0260] An exemplary third curable material is isobomyl acrylate (IBOA), or isobomyl methacrylate (IBOMA).

[0261] According to some embodiments of any of the embodiments described herein, the curable formulation comprises the first, second and third curable materials as described herein in any of the respective embodiments and any combination thereof.

[0262] According to some of any of the embodiments described herein, when the formulation further comprises the third curable material, an amount of the third curable material ranges from 20 to 50, or from 30 to 50, or from 30 to 40, % by weight of the total weight of the formulation, including any intermediate values and subranges therebetween.

[0263] According to some embodiments of any of the embodiments described herein, an amount of the first curable material ranges from 25 to 35 or from 25 to 30, % by weight, of the total weight of the formulation, including any intermediate values and subranges therebetween.

[0264] According to some embodiments of any of the embodiments described herein, an amount of the first curable material is no more than 35, preferably no more than 30, % by weight, of the total weight of the formulation. According to some embodiments of any of the embodiments described herein, an amount of the second curable material is at least 25 %, or at least 30 %, by weight, of the total weight of the formulation. According to some embodiments of any of the embodiments described herein, an amount of the second curable material ranges from 30 to 40 or from 32 to 38, or from 34 to 36, % by weight, of the total weight of the formulation, including any intermediate values and subranges therebetween.

[0265] According to some embodiments of any of the embodiments described herein, an amount of the first curable material ranges from 25 to 35 or from 25 to 30, % by weight of the total weight of the formulation; an amount of the second curable material ranges from 30 to 40, % by weight of the total weight of the formulation; and an amount of the third curable material ranges from 30 to 40, % by weight of the total weight of the formulation, including any intermediate values and subranges therebetween.

[0266] According to some embodiments of any of the embodiments described herein, the formulation comprises: a first curable material which is a first reaction product of a cycloaliphatic diisocyanate as described herein in any of the respective embodiments and any combination thereof, for example, IPDI, a hydroxy-containing methacrylate, as described herein in any of the respective embodiments and any combination thereof, for example, HEMA, and a first diol which is an aliphatic or alicyclic diol of from 2 to 12 carbon atoms such as 3-Methyl-l,5-pentanediol (1,5-MPD); 1,4-Butanediol (1,4-BDO); 4,8-Bis(hydroxymethyl)tricycle [5.2.1.02, 6]decane (DCPDM); and 1,9-Nonanediol, for example, 1,5-MPD (also referred to as MPD), and is a mono-block urethane (meth) acrylate and / or features NCO / OH ratio of about 2), in an amount of from 25 to 35 or from 25 to 30, % by weight of the total weight of the formulation, including any intermediate values and subranges therebetween; a second curable material which is a second reaction product of a cycloaliphatic diisocyanate as described herein in any of the respective embodiments and any combination thereof, for example, IPDI, a hydroxy-containing methacrylate, as described herein in any of the respective embodiments and any combination thereof, for example, HEMA, and a second diol which is polyalkylene ether glycol such as polyTHF, featuring average Mn of from 2,000 to 5,000 grams / mol, in accordance with any of the respective embodiments, is a multi-block such as a diblock or a tri-block urethane (meth)acrylate and / or features NCO / OH ratio lower than 2, or lower than 1.8, or 1.5 or lower, as described herein, in an amount of from 25 to 40, or from 30 to 40, or from 35 to 40, or from 32 to 38, %, by weight of the total weight of the formulation, including any intermediate values and subranges therebetween; and optionally, a third curable material, which is a monomeric mono-functional (meth) acrylate which is hydrophilic or amphiphilic and / or features high Tg as described herein in any of the respective embodiments and any combination thereof, in an amount of from 30 to 40, % by weight of the total weight of the formulation, including any intermediate values and subranges therebetween.

[0267] According to some embodiments of any of the embodiments described herein, the formulation comprises the third curable material as described herein in any of the respective embodiments and any combination thereof.

[0268] According to some embodiments of any of the embodiments described herein, the second reaction product is a di-block or a tri-block urethane (meth)acrylate, respectively, e.g., it features NCO / OH ratio of about 1.5 (di-block) or of about 1.33 (tri-block). Higher number of blocks and / or lower NCO / OH ratios are also contemplated.

[0269] According to alternative embodiments, the formulation comprises: a first curable material which is a first reaction product of a cycloaliphatic diisocyanate as described herein in any of the respective embodiments and any combination thereof, for example, IPDI, a hydroxy-containing methacrylate, as described herein in any of the respective embodiments and any combination thereof, for example, HEMA, and a first diol which is an aliphatic or alicyclic diol of from 2 to 12 carbon atoms such as 3-Methyl-l,5-pentanediol (1,5-MPD); 1,4-Butanediol (1,4-BDO); 4,8-Bis(hydroxymethyl)tricycle [5.2.1.02, 6]decane (DCPDM); and 1,9-Nonanediol, for example, 1,5-MPD (also referred to as MPD), and is a mono-block urethane (meth) acrylate and / or features NCO / OH ratio of about 2), in an amount of from 25 to 35 or from 25 to 30, % by weight of the total weight of the formulation, including any intermediate values and subranges therebetween; a second curable material which is a second reaction product of a cycloaliphatic diisocyanate as described herein in any of the respective embodiments and any combination thereof, for example, IPDI, a hydroxy-containing methacrylate, as described herein in any of the respective embodiments and any combination thereof, for example, HEMA, and a second diol which is polyalkylene ether glycol such as polyTHF, featuring average Mn higher than 2,000, preferably higher than 2,500, or higher than 2,900, or of at least 3,000, grams / mol, for example, from 3,000 to 5,000 grams / mol, in accordance with any of the respective embodiments, is a monoblock urethane (meth) acrylate and / or features NCO / OH ratio of about 2, as described herein, in an amount of from 25 to 40, or from 30 to 40, or from 35 to 40, or from 32 to 38, %, by weight of the total weight of the formulation, including any intermediate values and subranges therebetween; and optionally, a third curable material, which is a monomeric mono-functional (meth) acrylate which is hydrophilic or amphiphilic and / or features high Tg as described herein in any of the respective embodiments and any combination thereof, in an amount of from 30 to 40, % by weight of the total weight of the formulation, including any intermediate values and subranges therebetween.

[0270] According to some embodiments of these alternative embodiments, the formulation comprises the third curable material as described herein in any of the respective embodiments and any combination thereof.

[0271] According to some embodiments of any of the embodiments described herein, each of the first and the second acrylic compounds featuring a hydroxy group independently comprises a hydroxyalkyl (meth)acrylate, wherein the alkyl is of from 1 to 10, or from 2 to 10, or from 2 to 8, or from 2 to 6, carbon atoms in length.

[0272] According to some embodiments of any of the embodiments described herein, each of the first and the second acrylic compounds featuring a hydroxy group is HEA or HEMA.

[0273] According to some embodiments of any of the embodiments described herein, each of the first and the second cycloaliphatic diisocyanate is IPDI.

[0274] According to some embodiments of any of the embodiments described herein, each of the first and the second acrylic compounds featuring a hydroxy group is HEA or HEMA; each of the first and the second cycloaliphatic diisocyanate is IPDI; the first diol is or comprises an aliphatic or alicyclic diol of from 2 to 12 carbon atoms, as described herein in any of the respective embodiments and any combination thereof; and the second diol is or comprises polyTHF having Mn of from 1,000 to 5,000, or from 2,000 to 5,000, grams / mol, as described herein in any of the respective embodiments. According to some of these embodiments, the first curable material is a mono-block urethane (meth)acrylate and the second curable material is a di-block or tri-block urethane (meth)acrylate. According to some of these embodiments, the first reaction product features NCO / OH ratio of about 2 and / or is a mono-block and the second reaction features NCO / OH ratio of about 1.5 or about 1.33 and / or is a di-block or tri-block, respectively. According to some of these embodiments, the third curable material is or comprises IBOMA. According to some of these embodiments, an amount of each of the first, second and third curable materials is as described herein in any of the respective embodiments and any combination thereof.

[0275] According to alternative embodiments, each of the first and the second acrylic compounds featuring a hydroxy group is HEA or HEMA; each of the first and the second cycloaliphatic diisocyanate is IPDI; the first diol is or comprises an aliphatic or alicyclic diol of from 2 to 12 carbon atoms, as described herein in any of the respective embodiments and any combination thereof; and the second diol is or comprises polyTHF having Mn of at least 2,000, or of at least 2,500, or of at least 2,900, or of at least 3,000, grams / mol, as described herein in any of the respective embodiments. According to some of these embodiments, the first curable material is a mono-block urethane (meth) acrylate and the second curable material is a mono-block urethane (meth)acrylate. According to some of these embodiments, the first reaction product features NCO / OH ratio of about 2 and / or is a mono-block and the second reaction features NCO / OH ratio of about 2 and / or is a mono-block, respectively. According to some of these embodiments, the third curable material is or comprises IBOMA. According to some of these embodiments, an amount of each of the first, second and third curable materials is as described herein in any of the respective embodiments and any combination thereof.

[0276] As discussed and demonstrated herein, the curable formulations as described herein in any of the respective embodiments and any combination thereof meet the process requirements, by featuring rheological properties suitable for additive manufacturing such as DLP or 3D inkjet printing (as discussed in further detail hereinafter), and by providing hardened material that exhibits mechanical properties suitable for, for example, orthodontic devices, as described herein.

[0277] According to some embodiments of any of the embodiments described herein, the curable formulation features a shear viscosity of less than 1 Pa- second at 100 °C at a shear rate of 50 / second.

[0278] In some embodiments, the curable formulation can have a shear viscosity of less than 1 Pa- second at 80 °C or lower temperature at a shear rate of 50 / second. In some embodiments, the formulation can have a shear viscosity of less than 1 Pa- second at 70 °C or lower temperature at a shear rate of 50 / second.

[0279] Without being bound by any particular theory, it is assumed that the curable formulation as described herein forms, when hardened, at least two polymeric networks; one formed of the first curable material and optionally the third curable material, and features high Tg, and one formed of the second curable material and optionally the third curable material, and features low Tg. The miscibility of these polymeric networks with one another, at the micron-scale and at the nano-scale, which is determined by the chemical composition and MW of the first and second curable materials and the ratio between the first and second curable materials, affects the mechanical and visual properties of the hardened material.

[0280] Without being bound by any particular theory, it is assumed that a phase separation at the sub-micron scale (e.g., nanoscale), that is, within the sub-micron (e.g., nano) structure of the hardened material) contributes to the toughness of the hardened material, so as to achieve high modulus, high Yield and high tensile strength. However, a phase separation at the microscale, that is, within the micro structure of the hardened material, which can be reflected, for example, by micron-sized clusters that form a non-homogenous microstructure, may adversely affect the visual properties of the hardened material, by causing haze, as discussed in further detail and demonstrated in the Examples section that follows.

[0281] According to some embodiments of any of the embodiments described herein, the curable formulation further comprises a material or substance which is capable of reducing or preventing the formation of the micron-sized clusters in the hardened material, preferably without affecting the nanoscale structure of the hardened material, so as to reduce haze without affecting the mechanical performance.

[0282] The presence or absence of micron-sized clusters in a hardened material can be determined by common microscopic means, for example, by SEM measurements.

[0283] In some embodiments, the micron-sized clusters constitute a minor portion of the hardened, for example, of from 0.1 to 5 %, or from 0.1 to 3 %, or from 0.1 to 2 %, by volume, of the hardened material.

[0284] By “micron-size clusters” it is meant that a phase separation between the two polymeric networks as described herein is reflected by the formation of clusters of one polymeric network within a continuous phase formed of the other polymeric network, whereby the clusters feature at least one dimension (e.g., average diameter) at the micron scale, that is, from 1 micron to 1,000 microns, or from 1 micron to 500 microns, or from 1 micron to 200 microns, or from 1 micron to 100 microns, or from 1 micron to 50 microns, or from 1 micron to 20 microns or from 1 micron to 10 microns, including any intermediate values and subranges therebetween.

[0285] Without being bound by any particular theory, the present inventors have conceived that the formation of the micron-sized clusters is associated with, or results from, intermolecular and / or intramolecular hydrogen bonds formed mainly by the first curable material, due to the relatively high density of urethane groups that are known to form hydrogen bonds, within the first polymeric network.

[0286] According to some embodiments of any of the embodiments described herein, the material or substance that reduces or eliminates the formation of the micron-sized clusters is capable of interfering with intermolecular and / or intramolecular hydrogen bonds formed mainly by the first curable material.

[0287] According to some embodiments of any of the embodiments described herein, the modeling material formulation further comprises a compound capable of interfering with intramolecular and / or intermolecular hydrogen bonds formed by the first curable material. According to some of these embodiments, such a compound reduces or eliminates the formation of micron-sized clusters in the hardened material formed of the curable formulation (e.g., upon exposure to a curing condition as described herein).

[0288] According to some embodiments of any of the embodiments described herein, such a compound reduces the haze value of the hardened material formed of the formulation.

[0289] As used herein and known in the art, a “hydrogen bond” is a non-covalent bond that forms a type of dipole-dipole attraction which occurs when a hydrogen atom bonded to a strongly electronegative atom exists in the vicinity of another electronegative atom with a lone pair of electrons.

[0290] The hydrogen atom in a hydrogen bond is partly shared between two relatively electronegative atoms.

[0291] Hydrogen bonds are typically formed between a hydrogen bond donor group and a hydrogen bond acceptor group.

[0292] A hydrogen-bond donor, which is also referred to herein as a hydrogen bond-forming donor group, is a group that includes both the atom to which the hydrogen is more tightly linked and the hydrogen atom itself, whereas a hydrogen-bond acceptor, which is also referred to herein as a hydrogen bond-forming acceptor group, is an electronegative atom capable of being linked to a hydrogen atom of another group. The relatively electronegative atom to which the hydrogen atom is covalently bound pulls electron density away from the hydrogen atom so that it develops a partial positive charge (5+). Thus, it can interact with an atom having a partial negative charge (S’) through an electrostatic interaction.

[0293] Atoms that typically participate in hydrogen bond interactions, as donors and / or acceptors, include oxygen, nitrogen and fluorine. These atoms typically form a part of a chemical group or moiety such as, for example, carbonyl, carboxylate, amide, hydroxyl, amine, imine, carbamate, ether, alkyl fluoride, F2, and more. However, other electronegative atoms and chemical groups or moieties containing same may participate in hydrogen bonding.

[0294] Exemplary hydrogen bond-forming groups include, but are not limited to, amide, carboxylate, hydroxy, alkoxy, aryloxy, ether, amine, carbamate, urethane, hydrazine, a nitrogencontaining heteroalicyclic (e.g., piperidine, oxalidine), nitrile, and an oxygen-containing heteroalicyclic (e.g., tetrahydrofuran, morpholine), and any other chemical moiety that comprises one or more nitrogen and / or oxygen atoms.

[0295] In the context of the present embodiments, the present inventors have assumed that relatively strong hydrogen bonds are formed by the plurality of urethane moieties that are present in the hardened material, particularly in the polymeric network formed of the first curable material, where, due to the relatively short diol moiety, the density of the urethane moieties (the number of urethane moieties per mol of the formed polymer) is higher. Without being bound by any particular theory, it has been further assumed that, in addition to these hydrogen bonds, phase separation may be due to the relatively high MW second curable material, which may affect its capability to be homogeneously dispersed within a continuous polymeric network that is formed of the first material or of the first and third curable materials. Without being bound by any particular theory, phase separation may be due to the relatively high MW second curable material, which renders it chemically incompatible with the continuous polymeric network that is formed of the first material or of the first and third curable materials. Without being bound by any particular theory, the incompatibility or incapability to be homogeneously dispersed, of the second curable material is attributed to the nature of the second diol. Without being bound by any particular theory, the phase separation results from the second material being a multi-block (e.g., di-block or triblock), and formed using a second diol of high MW as described herein, but can also occur when the second material is a mono-block formed using a second diol of even higher MW as described herein in any of the respective embodiments.

[0296] According to some embodiments of any of the embodiments described herein, a compound that is capable of interfering with the intermolecular and / or intramolecular hydrogen bonds of urethane moieties is a compound that is capable of forming hydrogen bonds that are thermodynamically favored over the urethane hydrogen bonds, that is, is capable of competing with urethane in forming hydrogen bonds, thereby reducing the amount of hydrogen bonds formed by the first curable material.

[0297] According to some embodiments of any of the embodiments described herein, the compound capable of interfering with the hydrogen bonds and / or capable of interfering with the formation of micron-sized clusters, comprises at least one carboxylic acid moiety or group. As demonstrated in the Examples section that follows, it has been uncovered that a compound featuring a carboxylic group exhibits improved performance in the context of these embodiments, compared, for example, to phosphonic acid, amide, amine, and like polar groups.

[0298] According to some embodiments of any of the embodiments described herein, the compound capable of interfering with the hydrogen bonds and / or capable of interfering with the formation of micron-sized clusters is a photocurable material.

[0299] According to some embodiments of any of the embodiments described herein, the compound capable of interfering with the hydrogen bonds and / or capable of interfering with the formation of micron-sized clusters is a photocurable material, featuring one or more photocurable groups as described herein and one or more groups that are capable of forming thermodynamically favored hydrogen bonds over those formed by the oxygen atoms derived from the first diol, as described herein.

[0300] According to some embodiments of any of the embodiments described herein, the compound capable of interfering with the hydrogen bonds and / or capable of interfering with the formation of micron-sized clusters is a photocurable material, featuring one or more photocurable groups as described herein and one or more carboxylic acid groups.

[0301] According to some embodiments of any of the embodiments described herein, the compound capable of interfering with the hydrogen bonds and / or capable of interfering with the formation of micron-sized clusters is a (meth)acrylate, featuring one or more photocurable groups as described herein and one or more groups that are capable of forming thermodynamically favored hydrogen bonds over those formed by the oxygen atoms derived from the first diol, as described herein.

[0302] According to some embodiments of any of the embodiments described herein, the compound capable of interfering with the hydrogen bonds and / or capable of interfering with the formation of micron-sized clusters is a (meth)acrylate, featuring one or more photocurable groups as described herein and one or more carboxylic acid groups. An exemplary such a compound is or comprises (meth)acrylic acid. An exemplary such a compound is or comprises methacrylic acid.

[0303] Additional examples include, but are not limited to, those represented by the formula: (CH2=C(Ra)-C(=O)-O)q-L, with L being a moiety, for example, a hydrocarbon, an alkyl, a cycloalkyl, an aryl, an alkylene glycol, and the like, or a combination thereof, which is substituted by one or more carboxylic acid or carboxylic acid-terminated substituents, and q being the number of (meth)acrylate moieties. When q is greater than 1, L is or comprises a branching unit as defined herein.

[0304] Non-limiting examples include pyromellitic glycerol dimethacrylate, hydroxyethyl methacrylate succinate adduct, 1,3-glycerol dimethacrylate / maleate adduct and 1,3-glycerol dimethacrylate succinate adduct.

[0305] According to some embodiments of any of the embodiments described herein, an amount of the compound capable of interfering with the hydrogen bonds and / or capable of interfering with the formation of micron-sized clusters, as described herein in any of the respective embodiments and any combination thereof, ranges from 1 to 10, or from 2 to 10, or from 2 to 8, or from 2 to 6, or from 3 to 10, or from 3 to 8, or from 3 to 6, or from 4 to 10, or from 4 to 8, or from 4 to 6, or from 2 to 5, or from 3 to 5, or from 4 to 5, % by weight of the total weight of the formulation, including any intermediate values and subranges therebetween. According to some embodiments of any of the embodiments described herein, a curable formulation comprises a first curable material, a second curable material, and a compound capable of interfering with the formation of micron-sized clusters and / or hydrogen bonds as described herein, as these compounds and their respective amounts are described in any of the respective embodiments and any combination thereof.

[0306] According to some embodiments of any of the embodiments described herein, a curable formulation comprises a first curable material, a second curable material, a third (e.g., curable) material and a compound capable of interfering with the formation of micron-sized clusters and / or hydrogen bonds as described herein, as these compounds and their respective amounts are described in any of the respective embodiments and any combination thereof.

[0307] According to some embodiments of any of the embodiments described herein, the curable formulation further comprises at least one photoinitiator.

[0308] According to some embodiments of any of the embodiments described herein, an amount of the photoinitiator ranges from 1 to 5, % by weight of the total weight of the formulation, including any intermediate values and subranges therebetween.

[0309] Non-limiting examples of suitable photoinitiators include benzophenones (aromatic ketones) such as benzophenone, methyl benzophenone, Michler's ketone and xanthones; acylphosphine oxide type photo-initiators such as 2,4,6-trimethylbenzolydiphenyl phosphine oxide (TMPO), 2,4,6-trimethylbenzoylethoxyphenyl phosphine oxide (TEPO), and bisacylphosphine oxides (BAPO's); benzoins and bezoin alkyl ethers such as benzoin, benzoin methyl ether and benzoin isopropyl ether and the like. Examples of photoinitiators are alpha-amino ketone, bisacylphosphine oxide (BAPO's), and those marketed under the tradename Irgacure®.

[0310] A photo-initiator may be used alone or in combination with a co-initiator. Benzophenone is an example of a photoinitiator that requires a second molecule, such as an amine, to produce a free radical. After absorbing radiation, benzophenone reacts with a ternary amine by hydrogen abstraction, to generate an alpha-amino radical which initiates polymerization of acrylates. Nonlimiting examples of a class of co-initiators are alkanolamines such as triethylamine, methyldiethanolamine and triethanolamine.

[0311] According to some embodiments, the photoinitiator is, for example, of the Irgacure® family.

[0312] Non-limiting examples of photoinitiators include those of the Irgacure® family and of the Darocur® family, marketed by BASF, such as 1-hydroxycyclohexyl phenyl ketone (IRGACURE 184), 2,2-dimethoxy-l,2-diphenylethan-l-one (IRGACURE 651), bis(2,4,6- trimethylbenzoyl)phenylphosphineoxide (IRGACURE 819), l-[4-(2-hy droxy ethoxy )phenyl] -2- hydroxy-2-methyl-l -propane- 1 -one (IRGACURE 2959), 2-benzyl-2-dimethylamino-l-(4- morpholinophenyl)butanone (IRGACURE 369), 2-methyl-l-[4-(methylthio)phenyl]-2- morpholinopropan-l-one (IRGACURE 907), Oligo[2-hydroxy-2-methyl-l[4-(l- methylvinyl)phenyl]propanone] (ESACURE ONE), 2-hydroxy-2-methyl- 1 -phenyl propan- 1 -one (DAROCUR 1173), 2,4,6-trimethylbenzoyldiphenylphosphine oxide (IRGACURE TPO), and

[0313] 2.4.6-trimethylbenzoylphenyl phosphinate (IRGACURE TPO-L), and similar photoinitiators, and any a combination thereof. Additional non-limiting examples of photoinitiators include, benzyl dimethyl ketal, 2-methyl-2-hydroxypropiophenone, benzoin methyl ether, benzoin isopropyl ether, anisoin methyl ether, aromatic sulfonyl chlorides, photoactive oximes, the like, and any combination thereof.

[0314] According to some embodiments of any of the embodiments described herein, the photoinitiator(s) comprises, or consists essentially of, a phosphine oxide-type (e.g., mono-acrylated (MAPO) or bis-acrylated phosphine oxide-type (BAPO) photoinitiator.

[0315] Exemplary monoacyl and bisacyl phosphine oxides include, but are not limited to, 2,4,6- trimethylbenzoyldiphenyl phosphine oxide, bis(2,4,6-trimethylbenzoyl) phenylphosphine oxide, dibenzoylphenylphosphine oxide, bis(2,6-dimethoxybenzoyl)phenyl phosphine oxide, tris(2,4- dimethylbenzoyl) phosphine oxide, tris(2-methoxybenzoyl)phosphine oxide, 2,6- dimethoxybenzoyldiphenyl phosphine oxide, 2,6-dichlorobenzoyldiphenyl phosphine oxide,

[0316] 2.3.5.6-tetramethylbenzoyldiphenyl phosphine oxide, benzoyl-bis(2,6-dimethylphenyl) phosphonate, and 2,4,6-trimethylbenzoylethoxyphenyl phosphine oxide. Commercially available phosphine oxide photoinitiators capable of free-radical initiation when irradiated at wavelength ranges of greater than about 380 nm to about 450 nm include 2,4,6-trimethylbenzoyldiphenyl phosphine oxide (TPO), bis(2,4,6-trimethylbenzoyl)phenyl phosphine oxide (marketed as IRGACURE® 819), bis(2,6-dimethoxybenzoyl)-(2,4,4-trimethylpentyl) phosphine oxide (marketed as CGI 403), 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 (marketed as IRGACURE® 1700), a 1: 1 mixture, by weight, of bis(2,4,6-trimethylbenzoyl)phenyl phosphine oxide and 2-hydroxy-2-methyl-l -phenylpropane- 1 -one (marketed as DAROCUR® 4265), and ethyl 2,4,6-trimethylbenzylphenyl phosphinate (LUCIRIN LR8893X).

[0317] In an exemplary embodiment, the photoinitiator is or comprises 2,4,6- trimethylbenzoyldiphenyl phosphine oxide (marketed as TPO).

[0318] In some embodiments of any of the embodiments described herein, the modeling material formulation further comprises one or more additional materials, which are referred to herein also as non-reactive materials (e.g., non-curable materials). Such agents include, for example, surface active agents (surfactants), inhibitors, antioxidants, fillers, pigments, dyes, impact modifiers, thickeners, UV-absorbers, flame retardants and / or dispersants.

[0319] Surface-active agents may be used to reduce the surface tension of the formulation to the value required for jetting or for printing process. Such agents include silicone materials, for example, organic polysiloxanes such as PDMS and derivatives therefore, such as those commercially available as BYK type surfactants.

[0320] Suitable dispersants (dispersing agents) can be silicone materials, for example, organic polysiloxanes such as PDMS and derivatives therefore, such as those commercially available as BYK type surfactants.

[0321] Suitable stabilizers (stabilizing agents) include, for example, thermal stabilizers, which stabilize the formulation at high temperatures.

[0322] The term “filler” describes an inert material that modifies the properties of a polymeric material and / or adjusts a quality of the end products. The filler may be an inorganic particle, for example calcium carbonate, silica, and clay.

[0323] Fillers may be added to the modeling formulation in order to reduce shrinkage during polymerization or during cooling, for example, to reduce the coefficient of thermal expansion, increase strength, increase thermal stability, reduce cost and / or adopt rheological properties. Nanoparticle fillers are typically useful in applications requiring low viscosity such as inkjet applications.

[0324] In some embodiments, a concentration of each of a surfactant and / or a dispersant and / or a stabilizer and / or a filler, if present, ranges from 0.01 to 2 %, or from 0.01 to 1 %, by weight, of the total weight of the respective formulation, including any intermediate values and subranges therebetween. Dispersants are typically used at a concentration that ranges from 0.01 to 0.1 %, or from 0.01 to 0.05 %, by weight, of the total weight of the respective formulation, including any intermediate values and subranges therebetween.

[0325] In some embodiments, the modeling material formulation further comprises an inhibitor, for example, a polymerization inhibitor. The inhibitor is included for preventing or reducing curing before exposure to curing energy. Suitable inhibitors include, for example, those commercially available as the Genorad™ type, or as MEHQ. Any other suitable inhibitors are contemplated.

[0326] The pigments can be organic and / or inorganic and / or metallic pigments, and in some embodiments the pigments are nanoscale pigments, which include nanoparticles.

[0327] Exemplary inorganic pigments include nanoparticles of titanium oxide, and / or of zinc oxide and / or of silica. Exemplary organic pigments include nano-sized carbon black. In some embodiments, the pigment’s concentration ranges from 0.1 to 2 % by weight, or from 0.1 to 1.5 %, by weight, of the total weight of the respective formulation, including any intermediate values and subranges therebetween.

[0328] In some embodiments, combinations of white pigments and dyes are used to prepare colored cured materials.

[0329] The dye may be any of a broad class of solvent soluble dyes. Some non-limiting examples are azo dyes which are yellow, orange, brown and red; anthraquinone and triarylmethane dyes which are green and blue; and azine dye which is black.

[0330] According to some embodiments of any of the embodiments described herein, the modeling material formulation is a clear (e.g., transparent), colorless formulation, which is devoid of a coloring agent.

[0331] According to some embodiments of any of the embodiments described herein, the modeling material formulation further comprises one or more coloring agent(s).

[0332] The coloring agent can be a pigment or a dye and is preferably a pigment.

[0333] The pigments can be organic and / or inorganic and / or metallic pigments, and in some embodiments the pigments are nanoscale pigments, which include nanoparticles.

[0334] Exemplary inorganic pigments include nanoparticles of titanium oxide, and / or of zinc oxide and / or of silica. Exemplary organic pigments include nano- sized carbon black.

[0335] In some embodiments, combinations of white and color pigments are used to prepare colored cured materials.

[0336] Kits:

[0337] In some embodiments of any of the embodiments described herein there is provided a kit comprising one or more modeling material formulations as described herein in any of the respective embodiments and any combination thereof.

[0338] In exemplary embodiments, the formulations are packaged within the kit in a suitable packaging material, preferably, an impermeable material (e.g., water- and gas-impermeable material), and further preferably an opaque material. In some embodiments, the kit further comprises instructions to use the formulations in an additive manufacturing process, as described herein. The kit may further comprise instructions to use the formulations in the additive manufacturing process in accordance with the method as described herein.

[0339] According to some embodiments of any of the embodiments that relate to a kit, the kit may further comprise a support material formulation. Any support material formulation that is usable, for example, in AM is contemplated. According to some embodiments of any of the embodiments described herein, when the formulation further comprises a photoinitiator, the photoinitiator is packaged in the kit separately at least from the curable material. In some of these embodiments, the kit may further comprise a photoinitiator, and / or instructions to add the photoinitiator to the formulation.

[0340] According to some embodiments, the first and second curable materials, and optionally the third curable material, if present, are each packaged individually within the kit. In some of these embodiments, the kit may further comprise instructions to mix the components before use.

[0341] According to some embodiments, the kit is such that it comprises the materials used to provide each of the first and / or second curable materials, and optionally other reagents required to prepare the first and / or second curable materials (e.g., catalysts). In some of these embodiments, the kit may further comprise instructions on how to prepare the first and / or second materials. In some of these embodiments, the kit may further comprise the third curable material, or instructions to mix the formed first and second curable materials with the third curable material. In some of these embodiments, the kit may further comprise a photoinitiator, and / or instructions to add the photoinitiator to the formulation.

[0342] Method, Hardened Material and Object:

[0343] According to an aspect of some embodiments of the present invention, there is provided a hardened material formed upon exposing a curable formulation as described herein in any of the respective embodiments and any combination thereof, to a curing condition such as radiation, preferably electromagnetic radiation, to thereby effect polymerization and / or cross-linking of the curable materials.

[0344] According to some embodiments of any of the embodiments described herein, the hardened material is devoid of micron-sized clusters as described herein.

[0345] By “devoid of’ it is meant an amount that does not exceed 0.1 %, or 0.05 %, or 0.01 %, or 0.005 %, by volume, of the total volume of the hardened material, or is nullified.

[0346] According to an aspect of some embodiments of the present invention there is provided a method of forming a hardened material, which is effected by exposing the curable formulation as described herein to radiation, preferably electromagnetic radiation, to thereby effect polymerization and / or cross-linking of the curable materials.

[0347] In some embodiments, forming the hardened material comprises applying the curable formulation on a substrate, and exposing the formulation to radiation as described herein. In some embodiments, applying the formulation and exposing it to radiation are effected sequentially, such that the exposing is performed after applying. In some embodiments, such as in additive manufacturing processes, applying and exposing are performed substantially at the same time. Any suitable substrate can be employed, such as wood, plastic, ceramic, metal, glass, etc.

[0348] Applying the curable formulation to a substrate can be effected by casting, coating, painting, rolling, dipping, spraying, depositing, etc., and by any combination of the foregoing. Once the hardened material is obtained, it can remain on the substrate or be separated therefrom, to form a stand-alone object. The object can be a two-dimensional or a three-dimensional object.

[0349] The substrate can be a mold, shaped as desired, such that the obtained hardened material features the desired shape, and the method comprises coasting and / or molding. Alternatively, in some examples, the substrate is coated by the hardened material.

[0350] The relatively low viscosity of the formulation allows applying it at relatively low temperatures. In some embodiments, applying the formulation is performed at a temperature lower than 100, or lower than 90, or lower than 80, or lower than 70, or lower than 60, or lower than 50, or lower than 40, or lower than 30, °C, for example, at room temperature (e.g., of from 15 to 25, or from 30 to 25, °C). In some embodiments, applying the formulation is performed at a temperature in a range of from 20 to 100, or from 20 to 80, or from 20 to 60, or from 20 to 40, or from 20 to 30, or from 20 to 25, or from 25 to 30, °C, including any intermediate values and subranges therebetween.

[0351] In some embodiments, exposing the formulation to electromagnetic radiation is performed at a temperature lower than 100, or lower than 90, or lower than 80, or lower than 70, or lower than 60, or lower than 50, or lower than 40, or lower than 30, °C, for example, at room temperature. In some embodiments, exposing the formulation to electromagnetic radiation is performed at a temperature in a range of from 20 to 100, or from 20 to 80, or from 20 to 60, or from 20 to 40, or from 20 to 30, or from 20 to 25, or from 25 to 30, °C, including any intermediate values and subranges therebetween.

[0352] As used herein throughout, the term “hardening”, which is also referred to herein as “curing” describes a process in which a formulation is hardened. The hardening of a formulation typically involves an increase in a viscosity of the formulation and / or an increase in a storage modulus of the formulation (G’).

[0353] The terms “hardening” or “curing” as used herein encompass, for example, polymerization of monomeric and / or oligomeric materials and / or cross-linking of polymeric chains (either of a polymer present before curing or of a polymeric material formed in a polymerization of the monomers or oligomers). The hardened material is therefore typically a polymeric material and / or a cross-linked material. This term, as used herein, encompasses also partial curing, for example, hardening of at least 20 % or at least 30 % or at least 40 % or at least 50 % or at least 60 % or at least 70 %, or at least 80 % of the formulation, in addition to hardening of 100 % of the formulation. The radiation can be electromagnetic radiation (e.g., ultraviolet or visible light), or electron beam radiation, or ultrasound radiation or microwave radiation, depending on the materials to be cured. The application of radiation (irradiation) is effected by a suitable radiation source. For example, an ultraviolet or visible or infrared or Xenon or mercury or lamp, or LED source, can be employed, as described herein.

[0354] A curable material or system that undergoes curing upon exposure to radiation is referred to herein interchangeably as “photopolymerizable” or “photoactivatable” or “photocurable”.

[0355] As used herein, the phrase “electromagnetic radiation” describes any type of electromagnetic radiation that is suitable to facilitate or induce photopolymerization of the photocurable composition. In some examples, the polymerizing electromagnetic radiation is or comprises ultraviolet electromagnetic radiation (e.g., electromagnetic irradiation at a wavelength from 10 nm to 400 nm). In some examples, the electromagnetic radiation is or includes visible electromagnetic radiation (e.g., electromagnetic irradiation at a wavelength from 380 nm to 750 nm). In some examples, the electromagnetic radiation is or includes infrared electromagnetic irradiation (e.g., electromagnetic radiation at a wavelength from 700 nm to 1 mm).

[0356] Exposing the curable formulation to electromagnetic radiation can be performed during a time period sufficient to induce polymerization and / or cross-linking of at least 20 %, at least 30 %, at least 40 %, preferably at least 50 %, at least 60 %, at least 70 %, or at least 80 %, of the curable materials. The time period during which the formulation is exposed to radiation depends on the wavelength of the electromagnetic radiation, the intensity of the electromagnetic radiation, the dimensions of the exposed curable composition (e.g., thickness), and the like. Exposing to the electromagnetic radiation can be effected by means of multiple doses, such that the formulation is exposed to multiple cycles of irradiation.

[0357] In some embodiments, the exposure to radiation (irradiation) is for a short time period, for example, a time period of less than 3 minutes, less than 300 seconds, for example, of from 10 seconds to 240 seconds, or from 10 seconds to 120 seconds, to from 10 seconds to 60 seconds, including an intermediate values and subranges therebetween.

[0358] In some embodiments, exposing to radiation (irradiation) is for a time period that ranges from 1 second to 120 seconds.

[0359] In some embodiments, the irradiation is at wavelength within the UV-vis range.

[0360] In some embodiments, the irradiation is at a wavelength in a range of from about 300 to about 800, or from about 300 to about 600, or from about 300 to about 500, or from about 350 to about 350, nm, including any intermediate values and subranges therebetween. In exemplary embodiments, the irradiation is at 385 nm. In some embodiments, the irradiation is at a level that ranges from about 1 to about 150, or from about 1 to about 130, or from about 1 to about 100, or from about 10 to about 150, or from about 10 to about 130, or from about 10 to about 100, or from about 50 to about 150, or from about 50 to about 130, or from about 50 to about 100, or from about 1 to about 50 or from about 1 to about 30 or from about 1 to about 20, from about 1 to about 10, from about 1 to about 9, from about 1 to about 10, mW / cm2, including any intermediate values and subranges therebetween.

[0361] In some embodiments of any of the embodiments described herein, the exposure controls the amount of energy delivered by the light source to the applied, deposited or printed layer. In some embodiments, the exposure is at a level that ranges from about 1 to about 150, or from about 1 to about 130, or from about 1 to about 100, or from about 10 to about 150, or from about 10 to about 130, or from about 10 to about 100, or from about 50 to about 150, or from about 50 to about 130, or from about 50 to about 100, or from about 1 to about 50 or from about 1 to about 30 or from about 1 to about 20, from about 1 to about 10, from about 1 to about 9, from about 1 to about 10 mJ / cm2, including any intermediate values and subranges therebetween.

[0362] According to some embodiments of any of the embodiments described herein, preparing a hardened material or an object comprising same is effected by introducing the curable formulation to a container. The container can be positioned to allow the curable formulation to sufficiently contact or cover a substrate or a build platform. The portion of the substrate or build platform that is contacted or covered with the curable formulation can depend on the direction(s) from which the formulation will be exposed to the electromagnetic radiation.

[0363] According to some embodiments of any of the embodiments described herein, the hardened material is formed at least of a curable formulation as described herein in any of the respective embodiments by additive manufacturing and the method is of additive manufacturing of a three- dimensional object.

[0364] According to an aspect of some embodiments of the present invention, there is provided a process (a method) of additive manufacturing (AM) of a three-dimensional object. According to embodiments of this aspect, the method is effected by sequentially forming a plurality of layers in a configured pattern corresponding to the shape of the object, thereby forming the object. According to some embodiments of this aspect, formation of each layer is effected by exposing at least one uncured building material formulation, as defined described herein in any of the respective embodiments (for example, an uncured building material that comprises at least a modeling material formulation as described herein in any of the respective embodiments), to a curing condition, to thereby form a hardened (cured) material. According to some embodiments of this aspect, the method is effected by sequentially exposing, in a layer-wise manner, an uncured building material as described herein to a curing condition, whereby the exposure to the curing condition is effected in a configured pattern corresponding to the shape of the object. According to these embodiments, the uncured building material comprises the curable formulation as described herein in any of the respective embodiments and any combination thereof, optionally two or more of such a curable formulation, and the curing condition comprises exposing the layers to electromagnetic radiation as described herein in any of the respective embodiments.

[0365] The method of these embodiments manufactures three-dimensional objects in a layer- wise manner by forming a plurality of layers in a configured pattern corresponding to the shape of the object.

[0366] Each layer is formed by an additive manufacturing apparatus which scans a two- dimensional surface and patterns it. While scanning, the apparatus visits a plurality of target locations on the two-dimensional layer or surface, and decides, according to a pre-set algorithm, for each target location or a group of target locations, whether or not the target location or group of target locations is to be occupied by a hardened building material, and which type of building material is to be hardened therein. The decision is made according to a computer image of the surface.

[0367] The formed three-dimensional object is made of the hardened modeling material or a combination of hardened modeling materials or a combination of hardened modeling material / s and support material / s or modification thereof (e.g., following curing). All these operations are well-known to those skilled in the art of additive manufacturing (also known as solid freeform fabrication). The final three-dimensional object can be made of the hardened modeling material or a combination of hardened modeling materials, upon removal at least a portion or all of the hardened support material(s), if such has been formed.

[0368] An exemplary process according to some embodiments of the present invention starts by receiving 3D printing data corresponding to the shape of the object. The data can be received, for example, from a host computer which transmits digital data pertaining to fabrication instructions based on computer object data, e.g., in a form of a Standard Tessellation Language (STL) or a StereoLithography Contour (SLC) format, Virtual Reality Modeling Language (VRML), Additive Manufacturing File (AMF) format, Drawing Exchange Format (DXF), Polygon File Format (PLY), Digital Imaging and Communications in Medicine (DICOM) or any other format suitable for Computer-Aided Design (CAD).

[0369] When the AM is by three-dimensional inkjet printing, an uncured building material, as defined herein, is dispensed from a dispensing head having a set of nozzles to deposit building material in layers on a supporting structure. The AM apparatus thus dispenses building material formulation(s) in target locations which are to be occupied and leaves other target locations void. The apparatus typically includes a plurality of dispensing heads, each of which can be configured to dispense a different building material formulation (for example, different modeling material formulations, each containing a different biological component; or each containing a different curable material; or each containing a different concentration of a curable material, and / or different support material formulations). Thus, different target locations can be occupied by different building materials (e.g., a modeling formulation and / or a support formulation, as defined herein).

[0370] In some exemplary embodiments of the invention an object is manufactured by dispensing uncured building material that comprises two or more different modeling material formulations, each modeling material formulation from a different dispensing head of the AM apparatus. The modeling material formulations are optionally and preferably deposited in layers during the same pass of the dispensing heads. The modeling material formulations and / or combination of formulations within the layer are selected according to the desired properties of the object.

[0371] The process comprises dispensing the building material as described herein in layers, on a receiving medium, using one or more dispensing (e.g., printing) heads, according to the printing data.

[0372] The dispensing can be in a form of droplets, or a continuous stream, depending on the additive manufacturing methodology employed and the configuration of choice.

[0373] The receiving medium can be a tray of a printing system, or a supporting article or medium made of, or coated by, a biocompatible material, such as support media or articles commonly used in bioprinting, or a previously deposited layer.

[0374] Once the uncured building material is dispensed on the receiving medium according to the 3D data, the method optionally and preferably continues by hardening the dispensed formulation(s). In some embodiments, the process continues by exposing the deposited layers to a curing condition. Preferably, the curing condition is applied to each individual layer following the deposition of the layer and prior to the deposition of the previous layer.

[0375] Some embodiments contemplate the fabrication of an object by dispensing different formulations from different dispensing heads. These embodiments provide, inter alia, the ability to select formulations from a given number of formulations and define desired combinations of the selected formulations and their properties.

[0376] According to some embodiments, the spatial locations of the deposition of each formulation with the layer are defined, either to effect occupation of different three-dimensional spatial locations by different formulations, or to effect occupation of substantially the same three- dimensional location or adjacent three-dimensional locations by two or more different formulations so as to allow post deposition spatial combination of the formulations within the layer.

[0377] The present embodiments thus enable the deposition of a broad range of material combinations, and the fabrication of an object which may consist of multiple different combinations of modeling material formulations, in different parts of the object, according to the properties desired to characterize each part of the object.

[0378] A system utilized in 3D-inkjet printing may include a receiving medium and one or more dispensing heads. The receiving medium can be, for example, a fabrication tray that may include a horizontal surface to carry the material dispensed from the printing head.

[0379] The dispensing head may be, for example, a printing head having a plurality of dispensing nozzles arranged in an array of one or more rows along the longitudinal axis of the dispensing head. The dispensing head may be located such that its longitudinal axis is substantially parallel to the indexing direction.

[0380] The additive manufacturing system may further include a controller, such as a microprocessor to control the AM process, for example, the movement of the dispensing head according to a pre-defined scanning plan (e.g., a CAD configuration converted to a Standard Tessellation Language (STL) format and programmed into the controller). The dispensing head may include a plurality of jetting nozzles. The jetting nozzles dispense material onto the receiving medium to create the layers representing cross sections of a 3D object.

[0381] In addition to the dispensing head, there may be a source of curing energy, for curing the dispensed building material. The curing energy is typically radiation, for example, UV radiation or heat radiation.

[0382] Additionally, the AM system may include a leveling device for leveling and / or establishing the height of each layer after deposition and at least partial solidification, prior to the deposition of a subsequent layer.

[0383] According to some of any of any of the embodiments described herein, the additive manufacturing is by SLA or DLP.

[0384] SLA and DLP are additive manufacturing technologies in which an uncured building material in a bath or vat is converted into hardened material(s), layer by layer, by selective curing using a light source while the uncured material is later separated / washed from the hardened material. SLA is widely used to create models, prototypes, patterns, and production parts for a range of industries. DLP differs from laser-based SLA in that DLP uses a projection of ultraviolet (UV) light (or visible light) from a digital projector to flash a single image of the layer across the entire uncured material at once. One of the key components of DLP is a digital micromirror device (DMD) chip, which is typically composed of an array of reflective aluminum micromirrors that redirect incoming light from the UV source to project an image of a designed pattern. For achieving a high-resolution structure, parameters such as the curing time of each layer, layer thickness, and intensity of the UV light should be tuned, for example, by controlling the concentration and types of the curable materials, the photoabsorber and / or the photoinitiator.

[0385] According to an aspect of some embodiments of the present invention, there is provided a process (or method) of additive manufacturing using DLP technology, wherein a three-dimensional object as described herein is prepared. In some embodiments, a 3D digital model is created or obtained through the use of computer-aided design (CAD) software, as described herein. In an embodiment, specialized slicing software is employed, slicing the 3D model into distinct cross- sectional layers, or "slices" as described herein, with varying layer thickness and slicing parameters. In accordance with some embodiments, an uncured building material which comprises one or more modeling material formulations and optionally support material formulations is placed in the vat. In some embodiments, the DLP 3D printing process is implemented by following the method steps as described herein in any of the respective embodiments. In an embodiment, the digital light projector, through the projection of highly detailed images onto the curable formulation surface, ensures precision and accuracy in layer-by-layer additive printing.

[0386] According to some embodiments, post-processing procedures are carried out after the completion of printing, including rinsing to remove excess, uncured formulations and optional post-curing (e.g., by application of electromagnetic irradiation and / or heat).

[0387] According to some embodiments of any of the embodiments described herein, the additive manufacturing is effected by sequentially exposing in a layer-wise manner a curable formulation as described herein in any of the respective embodiments and any combination thereof to a curing condition such as UV irradiation, as described herein in any of the respective embodiments and any combination thereof, and the exposing is performed in a configured pattern corresponding to the shape of the object (in accordance with a pre-determined computerized software as described herein), such that the curable formulation is hardened in each layer at locations exposed to the curing condition, as typically performed in DLP processes. In some embodiments of any of these embodiments, the thickness of each layer, the level of irradiation (energy dose) and / or the time of exposing each layer to irradiation are determined or manipulated so as to provide the optimal resolution for a curable formulation of choice. According to some embodiments of any of the embodiments described herein, the level of irradiation and the time of exposure to irradiation is as described herein in any of the respective embodiments and any combination thereof. According to some embodiments of any of the embodiments described herein, the uncured building material is applied to a build platform and is selectively exposed to electromagnetic radiation to form a crosslinked interface layer that interfaces with the build platform. Based on the 3D object model, additional uncured building material can be applied to the interface layer and / or additional hardened layers and selectively exposed to electromagnetic radiation to form one or more additional hardened layers until the 3D object is complete based on the 3D object model. In some embodiments, applying an additional formulation to the interface layer and / or additional hardened layer(s) can include moving the build platform by a distance of from 1 pm to 2000 pm.

[0388] The additive manufacturing methods as described herein in any of the respective embodiments and any combination thereof provide a three-dimensional object that comprises, in at least a portion thereof, a hardened material formed of the curable formulation as described herein in any of the respective embodiments and any combination thereof.

[0389] According to some embodiments of any of the embodiments described herein, the hardened material formed of the curable formulation of the present embodiments is a transparent material, as described herein (featuring transparency of at least 80, or at least 85 %). The objects comprising the hardened material is therefore also transparent, at least in a respective portion thereof that is made of the curable formulation.

[0390] According to some embodiments of any of the embodiments described herein, the hardened material or object comprising same or a portion thereof (e.g., a 3D object obtained by AM as described herein, for example, DLP) features transparency of at least 85 %.

[0391] According to some embodiments of any of the embodiments described herein, the hardened material or object comprising same or a portion thereof (e.g., a 3D object obtained by AM as described herein, for example, DLP) features a haze value, as defined and described herein, of no more than 15 %, or no more than 10 %, or no more than 5 %, preferably of from 0.1 to 5, or from 0.1 to 4, %, or null.

[0392] According to some embodiments of any of the embodiments described herein, the hardened material or object comprising same or a portion thereof (e.g., a 3D object obtained by AM as described herein, for example, DLP) features at least one of:

[0393] Tg of at least 100, or at least 120, °C;

[0394] Tensile modulus of at least 800, or at least 900, or at least 1,000 MPa;

[0395] Yield Stress of at least 20 MPa; and

[0396] Elongation at break of at least 30 %, as these parameters are described and defined herein. According to some embodiments of any of the embodiments described herein, the hardened material or object comprising same or a portion thereof (e.g., a 3D object obtained by AM as described herein, for example, DLP) features at least one of:

[0397] Color (CIE color space; C*) lower than 1.2, representing the chroma component in a CIE lab color space, as determined, for example, according to SO 11664-4 (CIE Lab) and related standards;

[0398] Transparency (visible light transmittance) higher than 85 %; and

[0399] Haze value, denoting the percentage of incoming light scattered by more than 2.5° through the material, lower than 15 %.

[0400] According to some embodiments of any of the embodiments described herein, a 3D object obtained by AM as described herein, for example, DLP, is or forms a part of a medical device.

[0401] Non-limiting examples of medical devices can include an orthodontic appliance (e.g., a dental aligner, a dental retainer, a surgical guide, or the like), an auditory appliance (e.g., a hearing aid, a cochlear implant, or the like), an orthopedic appliance (e.g., a brace, a cast, a cranial plate, a prosthesis, or the like). In exemplary embodiments, the 3D object can be or include or from a part of a dental aligner, a surgical guide, a hearing aid, or a cochlear implant.

[0402] In exemplary embodiments, the 3D object is or forms a part of a dental aligner.

[0403] As discussed hereinabove, dental aligners are orthodontic devices used to straighten teeth and correct various dental misalignments. Dental aligners are typically formed in accordance with a model of a patient’s teeth, so as to adapt closely to the teeth' contours and apply controlled forces to achieve tooth movement. The stress applied by the aligner is crucial for ensuring proper fit and effectiveness of the aligner. Stress retention in dental aligners is an important consideration for their effectiveness and durability.

[0404] The desired mechanical properties of dental aligners are crucial for their effectiveness in orthodontic treatment. These properties ensure that the aligners can apply appropriate forces to the teeth, withstand the stresses of daily use, and maintain their shape throughout the treatment period. Some of the key mechanical properties include flexibility, so as to exert the desired force yet maintain shape during the prolonged treatment period; elasticity, so as to assure withstanding repeated cycles of bending and stretching without permanent deformation; an adequate strength to withstand the forces exerted during chewing, speaking, and other daily activities without breaking or deforming and withstand occlusal forces and other stresses encountered in the oral cavity; toughness, sufficient to resist cracking or fracturing under normal usage conditions, thereby ensuring durability throughout the treatment period; transparency, so as to provide invisibility for aesthetic reasons; biocompatibility; dimensional stability; and ease of fabrication and adjustment. Dental aligners should also at least meet the requirements of ISO 10993-1 (Biological evaluation of medical devices (for mucosal membrane contact with long term exposure)).

[0405] According to some embodiments, formulations that form dental aligners and other orthodontic devices are selected so as to meet the requirements of ISO 10993, iso 13485, ISO 20795-dentistry, ISO 4049-Dentistry and / or ISO 7405-Dentistry.

[0406] As used herein the term “about” refers to ± 10 % or ± 5 %.

[0407] The terms "comprises", "comprising", "includes", "including", “having” and their conjugates mean "including but not limited to".

[0408] The term “consisting of’ means “including and limited to”.

[0409] The term "consisting essentially of" means that the composition, method or structure may include additional ingredients, steps and / or parts, but only if the additional ingredients, steps and / or parts do not materially alter the basic and novel characteristics of the claimed composition, method or structure.

[0410] As used herein, the singular form "a", "an" and "the" include plural references unless the context clearly dictates otherwise. For example, the term "a compound" or "at least one compound" may include a plurality of compounds, including mixtures thereof.

[0411] Throughout this application, various embodiments of this invention may be presented in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the invention. Accordingly, the description of a range should be considered to have specifically disclosed all the possible subranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range.

[0412] Whenever a numerical range is indicated herein, it is meant to include any cited numeral (fractional or integral) within the indicated range. The phrases “ranging / ranges between” a first indicate number and a second indicate number and “ranging / ranges from” a first indicate number “to” a second indicate number are used herein interchangeably and are meant to include the first and second indicated numbers and all the fractional and integral numerals therebetween.

[0413] Herein the terms "method" and “process” are used interchangeably and refer to manners, means, techniques and procedures for accomplishing a given task including, but not limited to, those manners, means, techniques and procedures either known to, or readily developed from known manners, means, techniques and procedures by practitioners of the chemical, pharmacological, biological, biochemical and medical arts.

[0414] Herein throughout, whenever the phrase “weight percent”, or “% by weight” or “% wt.”, is indicated in the context of embodiments of a formulation (e.g., a modeling formulation), it is meant weight percent of the total weight of the respective uncured formulation.

[0415] Herein throughout, an acrylic material is used to collectively describe material featuring one or more acrylate, methacrylate, acrylamide and / or methacrylamide group(s).

[0416] Similarly, an acrylic group is used to collectively describe curable groups which are acrylate, methacrylate, acrylamide and / or methacrylamide group(s), preferably acrylate or methacrylate groups (referred to herein also as (meth)acrylate groups).

[0417] Herein throughout, the term “(meth) acrylic” encompasses acrylic and methacrylic materials.

[0418] The term “branching unit” as used herein throughout describes a multi-radical linking moiety, which can be aliphatic, alicyclic, aromatic, heteroaromatic or heteroalicyclic. By “multiradical” it is meant that the linking moiety has two or more attachment points such that it links between two or more atoms and / or groups or moieties.

[0419] That is, the branching unit is a chemical moiety that, when attached to a single position, group or atom of a substance, creates two or more functional groups that are linked to this single position, group or atom, and thus "branches" a single functionality into two or more functionalities.

[0420] In some embodiments, the branching unit is derived from a chemical moiety that has two, three or more functional groups.

[0421] Herein throughout, the phrase “linking moiety” or “linking group” describes a group that connects two or more moieties or groups in a compound. A linking moiety is typically derived from a bi- or tri-functional compound, and can be regarded as a bi- or tri-radical moiety, which is connected to two or three other moieties, via two or three atoms thereof, respectively.

[0422] Exemplary linking moieties include a hydrocarbon moiety or chain, optionally interrupted by one or more heteroatoms, as defined herein, and / or any of the chemical groups listed below, when defined as linking groups.

[0423] When a chemical group is referred to herein as “end group” it is to be interpreted as a substituent, which is connected to another group via one atom thereof.

[0424] Herein throughout, the term “hydrocarbon” collectively describes a chemical group composed mainly of carbon and hydrogen atoms. A hydrocarbon can be comprised of alkyl, alkene, alkyne, aryl, and / or cycloalkyl, each can be substituted or unsubstituted, and can be interrupted by one or more heteroatoms. The number of carbon atoms can range from 2 to 30, and is preferably lower, e.g., from 1 to 10, or from 1 to 6, or from 1 to 4. A hydrocarbon can be a linking group or an end group.

[0425] As used herein, the term “amine” describes both a -NR’R” group and a -NR'- group, wherein R’ and R" are each independently hydrogen, alkyl, cycloalkyl, aryl, as these terms are defined hereinbelow.

[0426] The amine group can therefore be a primary amine, where both R’ and R” are hydrogen, a secondary amine, where R’ is hydrogen and R” is alkyl, cycloalkyl or aryl, or a tertiary amine, where each of R’ and R” is independently alkyl, cycloalkyl or aryl.

[0427] Alternatively, R' and R" can each independently be hydroxyalkyl, trihaloalkyl, cycloalkyl, alkenyl, alkynyl, aryl, heteroaryl, heteroalicyclic, amine, halide, sulfonate, sulfoxide, phosphonate, hydroxy, alkoxy, aryloxy, thiohydroxy, thioalkoxy, thioaryloxy, cyano, nitro, azo, sulfonamide, carbonyl, C-carboxylate, O-carboxylate, N-thiocarbamate, O-thiocarbamate, urea, thiourea, N-carbamate, O-carbamate, C-amide, N-amide, guanyl, guanidine and hydrazine.

[0428] The term “amine” is used herein to describe a -NR'R" group in cases where the amine is an end group, as defined hereinunder, and is used herein to describe a -NR'- group in cases where the amine is a linking group or is or part of a linking moiety.

[0429] The term "alkyl" describes a saturated aliphatic hydrocarbon including straight chain and branched chain groups. Preferably, the alkyl group has 1 to 30, or 1 to 20 carbon atoms. Whenever a numerical range; e.g., " 1-20", is stated herein, it implies that the group, in this case the alkyl group, may contain 1 carbon atom, 2 carbon atoms, 3 carbon atoms, etc., up to and including 20 carbon atoms. The alkyl group may be substituted or unsubstituted. Substituted alkyl may have one or more substituents, whereby each substituent group can independently be, for example, hydroxyalkyl, trihaloalkyl, cycloalkyl, alkenyl, alkynyl, aryl, heteroaryl, heteroalicyclic, amine, halide, sulfonate, sulfoxide, phosphonate, hydroxy, alkoxy, aryloxy, thiohydroxy, thioalkoxy, thioaryloxy, cyano, nitro, azo, sulfonamide, C-carboxylate, O-carboxylate, N-thiocarbamate, O-thiocarbamate, urea, thiourea, N-carbamate, O-carbamate, C-amide, N-amide, guanyl, guanidine and hydrazine.

[0430] The alkyl group can be an end group, as this phrase is defined hereinabove, wherein it is attached to a single adjacent atom, or a linking group, as this phrase is defined hereinabove, which connects two or more moieties via at least two carbons in its chain. When the alkyl is a linking group, it is also referred to herein as “alkylene” or “alkylene chain”.

[0431] Alkene and Alkyne, as used herein, are an alkyl, as defined herein, which contains one or more double bond or triple bond, respectively. The term "cycloalkyl" describes an all-carbon monocyclic ring or fused rings (z.e., rings which share an adjacent pair of carbon atoms) group where one or more of the rings does not have a completely conjugated pi-electron system. Examples include, without limitation, cyclohexane, adamantine, norbomyl, isobomyl, and the like. The cycloalkyl group may be substituted or unsubstituted. Substituted cycloalkyl may have one or more substituents, whereby each substituent group can independently be, for example, hydroxyalkyl, trihaloalkyl, cycloalkyl, alkenyl, alkynyl, aryl, heteroaryl, heteroalicyclic, amine, halide, sulfonate, sulfoxide, phosphonate, hydroxy, alkoxy, aryloxy, thiohydroxy, thioalkoxy, thioaryloxy, cyano, nitro, azo, sulfonamide, C- carboxylate, O-carboxylate, N-thiocarbamate, O-thiocarbamate, urea, thiourea, N-carbamate, O-carbamate, C-amide, N-amide, guanyl, guanidine and hydrazine. The cycloalkyl group can be an end group, as this phrase is defined hereinabove, wherein it is attached to a single adjacent atom, or a linking group, as this phrase is defined hereinabove, connecting two or more moieties at two or more positions thereof.

[0432] The term "heteroalicyclic" describes a monocyclic or fused ring group having in the ring(s) one or more atoms such as nitrogen, oxygen and sulfur. The rings may also have one or more double bonds. However, the rings do not have a completely conjugated pi-electron system. Representative examples are piperidine, piperazine, tetrahydrofurane, tetrahydropyrane, morpholino, oxalidine, and the like.

[0433] The heteroalicyclic may be substituted or unsubstituted. Substituted heteroalicyclic may have one or more substituents, whereby each substituent group can independently be, for example, hydroxyalkyl, trihaloalkyl, cycloalkyl, alkenyl, alkynyl, aryl, heteroaryl, heteroalicyclic, amine, halide, sulfonate, sulfoxide, phosphonate, hydroxy, alkoxy, aryloxy, thiohydroxy, thioalkoxy, thioaryloxy, cyano, nitro, azo, sulfonamide, C-carboxylate, O-carboxylate, N-thiocarbamate, O-thiocarbamate, urea, thiourea, O-carbamate, N-carbamate, C-amide, N-amide, guanyl, guanidine and hydrazine. The heteroalicyclic group can be an end group, as this phrase is defined hereinabove, where it is attached to a single adjacent atom, or a linking group, as this phrase is defined hereinabove, connecting two or more moieties at two or more positions thereof.

[0434] The term "aryl" describes an all-carbon monocyclic or fused-ring polycyclic (z.e., rings which share adjacent pairs of carbon atoms) groups having a completely conjugated pi-electron system. The aryl group may be substituted or unsubstituted. Substituted aryl may have one or more substituents, whereby each substituent group can independently be, for example, hydroxyalkyl, trihaloalkyl, cycloalkyl, alkenyl, alkynyl, aryl, heteroaryl, heteroalicyclic, amine, halide, sulfonate, sulfoxide, phosphonate, hydroxy, alkoxy, aryloxy, thiohydroxy, thioalkoxy, thioaryloxy, cyano, nitro, azo, sulfonamide, C-carboxylate, O-carboxylate, N-thiocarbamate, O-thiocarbamate, urea, thiourea, N-carbamate, O-carbamate, C-amide, N-amide, guanyl, guanidine and hydrazine. The aryl group can be an end group, as this term is defined hereinabove, wherein it is attached to a single adjacent atom, or a linking group, as this term is defined hereinabove, connecting two or more moieties at two or more positions thereof.

[0435] The term "heteroaryl" describes a monocyclic or fused ring (z.e., rings which share an adjacent pair of atoms) group having in the ring(s) one or more atoms, such as, for example, nitrogen, oxygen and sulfur and, in addition, having a completely conjugated pi-electron system. Examples, without limitation, of heteroaryl groups include pyrrole, furan, thiophene, imidazole, oxazole, thiazole, pyrazole, pyridine, pyrimidine, quinoline, isoquinoline and purine. The heteroaryl group may be substituted or unsubstituted. Substituted heteroaryl may have one or more substituents, whereby each substituent group can independently be, for example, hydroxyalkyl, trihaloalkyl, cycloalkyl, alkenyl, alkynyl, aryl, heteroaryl, hetero alicyclic, amine, halide, sulfonate, sulfoxide, phosphonate, hydroxy, alkoxy, aryloxy, thiohydroxy, thioalkoxy, thioaryloxy, cyano, nitro, azo, sulfonamide, C-carboxylate, O-carboxylate, N-thiocarbamate, O-thiocarbamate, urea, thiourea, O-carbamate, N-carbamate, C-amide, N-amide, guanyl, guanidine and hydrazine. The heteroaryl group can be an end group, as this phrase is defined hereinabove, where it is attached to a single adjacent atom, or a linking group, as this phrase is defined hereinabove, connecting two or more moieties at two or more positions thereof. Representative examples are pyridine, pyrrole, oxazole, indole, purine and the like.

[0436] The term "halide" and “halo” describes fluorine, chlorine, bromine or iodine.

[0437] The term “haloalkyl” describes an alkyl group as defined above, further substituted by one or more halide.

[0438] The term “phosphonate” describes a -P(=O)(OR’)(OR”) end group or a -P(=O)(OR’)(O)- linking group, as these phrases are defined hereinabove, with R’ and R” as defined herein.

[0439] The term “thiophosphonate” describes a -P(=S)(OR’)(OR”) end group or a -P(=S)(OR’)(O)- linking group, as these phrases are defined hereinabove, with R’ and R” as defined herein.

[0440] The term “phosphinyl” describes a -PR'R" end group or a -PR’- linking group, as these phrases are defined hereinabove, with R’ and R" as defined hereinabove.

[0441] The term “phosphine oxide” describes a -P(=O)(R’)(R”) end group or a -P(=O)(R’)- linking group, as these phrases are defined hereinabove, with R’ and R” as defined herein.

[0442] The term "carbonyl" or "carbonate" as used herein, describes a -C(=O)-R’ end group or a -C(=O)- linking group, as these phrases are defined hereinabove, with R’ as defined herein. The term "thiocarbonyl" as used herein, describes a -C(=S)-R’ end group or a -C(=S)- linking group, as these phrases are defined hereinabove, with R’ as defined herein.

[0443] The term “oxo” as used herein, describes a (=0) group, wherein an oxygen atom is linked by a double bond to the atom (e.g., carbon atom) at the indicated position.

[0444] The term “thiooxo” as used herein, describes a (=S) group, wherein a sulfur atom is linked by a double bond to the atom (e.g., carbon atom) at the indicated position.

[0445] The term “oxime” describes a =N-0H end group or a =N-0- linking group, as these phrases are defined hereinabove.

[0446] The term “hydroxyl” describes a -OH group.

[0447] The term "alkoxy" describes both an -O-alkyl and an -O-cycloalkyl group, as defined herein. The term alkoxide describes -R’0“ group, with R’ as defined herein.

[0448] The term "aryloxy" describes both an -O-aryl and an -O-heteroaryl group, as defined herein.

[0449] The term "thiohydroxy" or “thiol” describes a -SH group. The term “thiolate” describes a -S’ group.

[0450] The term "thioalkoxy" describes both a -S-alkyl group, and a -S-cycloalkyl group, as defined herein.

[0451] The term "thioaryloxy" describes both a -S-aryl and a -S-heteroaryl group, as defined herein.

[0452] The “hydroxyalkyl” is also referred to herein as “alcohol”, and describes an alkyl, as defined herein, substituted by a hydroxy group.

[0453] The term "cyano" describes a -C=N group.

[0454] The term “isocyanate” describes an -N=C=0 group.

[0455] The term “isothiocyanate” describes an -N=C=S group.

[0456] The term "nitro" describes an -NO2 group.

[0457] The term “acyl halide” describes a -(C=0)R"" group wherein R"" is halide, as defined hereinabove.

[0458] The term "azo" or “diazo” describes an -N=NR’ end group or an -N=N- linking group, as these phrases are defined hereinabove, with R’ as defined hereinabove.

[0459] The term “carboxylate” as used herein encompasses C-carboxylate and O-carboxylate.

[0460] The term “C-carboxylate” describes a -C(=0)-0R’ end group or a -C(=0)-0- linking group, as these phrases are defined hereinabove, where R’ is as defined herein.

[0461] The term “O-carboxylate” describes a -0C(=0)R’ end group or a -0C(=0)- linking group, as these phrases are defined hereinabove, where R’ is as defined herein. A carboxylate can be linear or cyclic. When cyclic, R’ and the carbon atom are linked together to form a ring, in C-carboxylate, and this group is also referred to as lactone. Alternatively, R’ and O are linked together to form a ring in O-carboxylate. Cyclic carboxylates can function as a linking group, for example, when an atom in the formed ring is linked to another group.

[0462] The term “thiocarboxylate” as used herein encompasses C-thiocarboxylate and O- thiocarboxylate.

[0463] The term “C-thiocarboxylate” describes a -C(=S)-OR’ end group or a -C(=S)-O- linking group, as these phrases are defined hereinabove, where R’ is as defined herein.

[0464] The term “O-thiocarboxylate” describes a -OC(=S)R’ end group or a -OC(=S)- linking group, as these phrases are defined hereinabove, where R’ is as defined herein.

[0465] A thiocarboxylate can be linear or cyclic. When cyclic, R’ and the carbon atom are linked together to form a ring, in C-thiocarboxylate, and this group is also referred to as thiolactone. Alternatively, R’ and O are linked together to form a ring in O-thiocarboxylate. Cyclic thiocarboxylates can function as a linking group, for example, when an atom in the formed ring is linked to another group.

[0466] The term “carbamate” as used herein encompasses N-carbamate and O-carbamate.

[0467] The term “N-carbamate” describes an R”OC(=O)-NR’- end group or a -OC(=O)-NR’- linking group, as these phrases are defined hereinabove, with R’ and R” as defined herein.

[0468] The term “O-carbamate” describes an -OC(=O)-NR’R” end group or an -OC(=O)- NR’- linking group, as these phrases are defined hereinabove, with R’ and R” as defined herein.

[0469] A carbamate can be linear or cyclic. When cyclic, R’ and the carbon atom are linked together to form a ring, in O-carbamate. Alternatively, R’ and O are linked together to form a ring in N-carbamate. Cyclic carbamates can function as a linking group, for example, when an atom in the formed ring is linked to another group.

[0470] The term “carbamate” as used herein encompasses N-carbamate and O-carbamate..

[0471] The term “thiocarbamate” as used herein encompasses N-thiocarbamate and O- thiocarbamate.

[0472] The term “O-thiocarbamate” describes a -OC(=S)-NR’R” end group or a -OC(=S)-NR’- linking group, as these phrases are defined hereinabove, with R’ and R” as defined herein.

[0473] The term “N-thiocarbamate” describes an R”OC(=S)NR’- end group or a -OC(=S)NR’- linking group, as these phrases are defined hereinabove, with R’ and R” as defined herein.

[0474] Thiocarbamates can be linear or cyclic, as described herein for carbamates. The term “dithiocarbamate” as used herein encompasses S -dithiocarbamate and N- dithiocarbamate.

[0475] The term “S -dithiocarbamate” describes a -SC(=S)-NR’R” end group or a -SC(=S)NR’- linking group, as these phrases are defined hereinabove, with R’ and R” as defined herein.

[0476] The term “N-dithiocarbamate” describes an R”SC(=S)NR’- end group or a -SC(=S)NR’- linking group, as these phrases are defined hereinabove, with R’ and R” as defined herein.

[0477] The term “amide” as used herein encompasses C-amide and N-amide.

[0478] The term “C-amide” describes a -C(=O)-NR’R” end group or a -C(=O)-NR’- linking group, as these phrases are defined hereinabove, where R’ and R” are as defined herein.

[0479] The term “N-amide” describes a R’C(=O)-NR”- end group or a R’C(=O)-N- linking group, as these phrases are defined hereinabove, where R’ and R” are as defined herein.

[0480] An amide can be linear or cyclic. When cyclic, R’ and the carbon atom are linked together to form a ring, in C-amide, and this group is also referred to as lactam. Cyclic amides can function as a linking group, for example, when an atom in the formed ring is linked to another group.

[0481] The term “hydrazine” describes a -NR’-NR”R’” end group or a -NR’ -NR”- linking group, as these phrases are defined hereinabove, with R’, R”, and R'" as defined herein.

[0482] As used herein, the term “hydrazide” describes a -C(=O)-NR’-NR”R”’ end group or a - C(=O)-NR’-NR”- linking group, as these phrases are defined hereinabove, where R’, R” and R’” are as defined herein.

[0483] As used herein, the term “thiohydrazide” describes a -C(=S)-NR’-NR”R”’ end group or a -C(=S)-NR’-NR”- linking group, as these phrases are defined hereinabove, where R’, R” and R’” are as defined herein.

[0484] As used herein, the term “alkylene glycol” describes a -O-[(CR’R”)Z-O]y-R’” end group or a -O-[(CR’R”)Z-O]y- linking group, with R’, R” and R’” being as defined herein, and with z being an integer of from 1 to 10, preferably, from 2 to 6, more preferably 2 or 3, and y being an integer of 1 or more. Preferably R’ and R” are both hydrogen. When z is 2 and y is 1, this group is ethylene glycol. When z is 3 and y is 1, this group is propylene glycol. When y is 2-4, the alkylene glycol is referred to herein as oligo(alkylene glycol).

[0485] As used herein, the phrase “impact resistance”, which is also referred to interchangeably, herein and in the art, as “impact strength” or simply as “impact”, describes the resistance of a material to fracture by a mechanical impact, and is expressed in terms of the amount of energy absorbed by the material before complete fracture. Impact resistance can be measured using, for example, the ASTM D256-06 standard Izod impact testing (also known as “Izod notched impact”, or as “Izod impact”), and / or as described hereinunder, and is expressed as J / m.

[0486] As used herein, HDT refers to a temperature at which the respective formulation or combination of formulations deforms under a predetermined load at some certain temperature. Suitable test procedures for determining the HDT of a formulation or combination of formulations are the ASTM D-648 series, particularly the ASTM D-648-06 and ASTM D-648-07 methods. In various exemplary embodiments of the invention the core and shell of the structure differ in their HDT as measured by the ASTM D-648-06 method as well as their HDT as measured by the ASTM D-648-07 method. In some embodiments of the present invention the core and shell of the structure differ in their HDT as measured by any method of the ASTM D-648 series. In the majority of the examples herein, HDT at a pressure of 0.45 MPa was used.

[0487] Without wishing to be bound to any particular theory, it is assumed that the state of a polymeric material gradually changes from the glassy state into the rubbery within the Tg range as defined above. The lowest temperature of the Tg range is referred to herein as Tg(low) and the highest temperature of the Tg range is referred to herein as Tg(high).

[0488] Herein throughout, whenever a curable material is defined by a property of a hardened material obtained therefrom, it is to be understood that this property is for a hardened material obtained from this curable material per se.

[0489] Herein throughout, unless otherwise indicated, viscosity values are provided for a viscosity of a material or a formulation when measured at 25 °C on a Brookfield’s viscometer. Measured values are provided in centipoise units, which correspond to mPa- second units, or in Pa- second.

[0490] It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination or as suitable in any other described embodiment of the invention. Certain features described in the context of various embodiments are not to be considered essential features of those embodiments, unless the embodiment is inoperative without those elements.

[0491] Various embodiments and aspects of the present invention as delineated hereinabove and as claimed in the claims section below find experimental support in the following examples.

[0492] EXAMPLES

[0493] Reference is now made to the following examples, which together with the above descriptions illustrate some embodiments of the invention in a non-limiting fashion. MATERIALS AND EXPERIMENTAL METHODS

[0494] 3D printing was mainly performed using Envisiontec HT system (5 mW / cm2 @ 385 nm) at 60 °C. Exposure time was 4 seconds.

[0495] Washing / cleaning was performed using tripropylene glycol monomethyl ether (TPM) for 4 minutes in pre-heated (40 °C) vat (600 rpm), followed by two washings with isopropanol (IPA) for 4 minutes (RapidShape Wash (RSW) apparatus).

[0496] Printed objects were optionally subjected to post-curing UV-irradiation and / or thermal treatment. Post-curing using UV irradiation was typically performed for 20 minutes at room temperature (apparatus Formcure); Post-curing thermal treatment comprised heating at 120 °C for 20 minutes; followed by gradual slow cooling.

[0497] Castings were prepared by placing a rubber spacer (1 mm) onto a glass plate to control the thickness of the specimen. To lower the viscosity, the formulation was heated in the oven at 80 °C. After the formulation was poured on the glass in the spacer, the second glass plate was carefully placed on top of the spacer. The glass plates were clamped together using office binder clips. The glass plates used in the making of castings were fluorosilane-coated, so as to provide a hydrophobic surface and reduce adherence to the formulation.

[0498] For curing with high intensity, a Heraeus P300MT in combination with a V-bulb was used. The distance between the glass and the lamp was 27 cm, resulting in an intensity of 150 mW / cm2. Samples were cured for 1 minute.

[0499] Tensile Modulus, Yield stress, Strain at break and Tg (calculated as max tan delta; tan6) were determined in accordance with ISO 527-2 specimen 5A using 5 or 50 mm / minute pulling speed under ambient conditions.

[0500] Transparency was determined visually before and after curing.

[0501] Haze was determined using Byk Haze gard i instrument calibrated with Standard 4776.

[0502] Exemplary first and second curable polyurethane acrylate materials were each prepared by reacting a diol (first and second diol, respectively), a diisocyanate (first and second diisocyanate, respectively) and a hydroxy-containing (meth) acrylate (first and second, respectively), in the presence of a catalyst, according to the following general procedure.

[0503] Generally, a catalyst (e.g., Coscat 83 10 wt. %) solution in an organic solvent, optionally a reactive diluent (e.g., a third mono-functional curable material as described herein, for example, isobomyl (meth)acrylate), and a 10 wt. % butylated hydroxytoluene (BHT) solution in an organic solvent (preferably a reactive diluent as used for the catalyst solution) were prepared, respectively. At room temperature, a diol was mixed in an organic solvent (preferably a reactive diluent as used for the catalyst solution) in a three-neck reactor fitted with a reflux condenser, a thermocouple, and mechanical stirrer until a homogeneous solution was achieved. The catalyst (100 ppm) solution was added into the mixture. The stirring rate was set at 500 rpm and reaction was blanketed with a mixture of lean air and nitrogen. After raising the temperature to 60 °C, the diisocyanate was added dropwise into the reactor within approximately 15 minutes. A dry-ice bath was used to cool the reactor to maintain the solution temperature as lower than 70 °C, while monitoring the NCO content. Then, phenothiazine (50 ppm) and additional catalyst (400 ppm) were added into the reactor. Once the desired NCO content was reached, the hydroxy-containing (meth)acrylate was added into the solution within 15 minutes in order to further reduce the NCO- content to less than 0.2 %, and the reaction mixture was thereafter cooled down to room temperature.

[0504] Representative, non-limiting examples of hydroxy-containing (meth)acrylates include hydroxyethyl methacrylate (HEMA), hydroxyethyl acrylate (HEA), caprolactones-modified HEMA (such as marketed by DIACEL under the tradename PLACCEL FM1).

[0505] Representative, non-limiting examples of diisocyanates include Isophorone diisocyanate (IPDI) and 4’-diisocyanato dicyclohexylmethane (H12MDI).

[0506] In exemplary curable materials, the selected hydroxy-containing (meth) acrylate was hydroxy ethyl methacrylate (HEMA), and the selected diisocyanate was Isophorone diisocyanate (IPDI).

[0507] Different diols were used for providing the first curable material and the second curable material. Representative, non-limiting examples of diols include 3-Methyl-l,5-pentanediol (1,5- MPD); 1,4-Butanediol (1,4-BDO); 4,8-Bis(hydroxymethyl)tricycle [5.2.1.02, 6]decane (DCPDM); 1,9-Nonanediol; DESMOPHEN C2202, commercially available from COVESTRO; DESMOPHEN C1200, commercially available from COVESTRO; ARCOL PPG 2000, commercially available from COVESTRO; VELVETOL H2000, commercially available from ALLESSA; Poly(tetrahydrofuran) (PTMEG) 1000; Poly (tetrahydrofuran) (PTMEG) 2000 (pTHF2000); Poly(tetrahydrofuran) (PTMEG) 2900 (pTHF2900).

[0508] Generally, for the first curable material, low Mn diols (e.g., of 2 to 10 carbon atoms in length) were selected; and for the second curable material, higher Mn diols (e.g., oligomeric or polymeric having Mn of at least 1,000 grams / mol) were selected.

[0509] Exemplary first and second curable polyurethane acrylate materials were each prepared by reacting isophorone as diisocyanate, hydroxy ethyl methacrylate, and 3 -methyl- 1,5-pentanediol as a diol in the first material or pTHF2000 as diol in the second material, in the presence of a catalyst, and isobornyl (meth) acrylate as a reactive diluent solvent, according to the general procedure as described hereinabove.

[0510] In an exemplary procedure, a catalyst (e.g., Coscat 83; 10 wt. %) solution in isobornyl methacrylate, and a butylated hydroxy toluene (BHT ; 10 wt. %) solution in isobomyl methacrylate, were prepared. At room temperature, the selected diol was mixed in isobomyl methacrylate in a three-neck reactor fitted with a reflux condenser, a thermocouple, and mechanical stirrer until a homogeneous solution was achieved. The catalyst (100 ppm) solution was added into the mixture. The stirring rate was set at 500 rpm and the reaction was blanketed with a mixture of lean air and nitrogen. After raising the temperature to 60 °C, isophorone diisocyanate was added dropwise into the reactor within approximately 15 minutes. A dry-ice bath was used to cool the reactor to maintain the solution temperature as lower than 70 °C, while monitoring the NCO content. Then, phenothiazine (50 ppm) and additional catalyst (400 ppm) were added into the reactor. Once the desired NCO-content was reached, the hydroxy ethyl methacrylate was added into the solution within 15 minutes in order to reduce the NCO-content to less than 0.2%. The reaction mixture was thereafter cooled down to room temperature.

[0511] The following describes an exemplary procedure for preparing a modeling material formulation:

[0512] The first and second curable materials (e.g., prepared as described hereinabove, in the presence of the third curable material (e.g., 25% IBOMA) as a reactive diluent) and an additional amount of the third curable material (e.g., IBOMA) were mixed at 60 °C in a reaction vessel equipped with a cooler and nitrogen flow. After about 1 hour, a photoinitiator (e.g., TPO-L; 3 wt. %) was added and the mixture was allowed to homogenize for about 30 minutes, and the obtained mixture was stored in dark containers.

[0513] EXAMPLE 1 Modeling Formulation Design

[0514] The present inventors have sought after curable formulations which are usable for additive manufacturing, particularly, DLP printing, of transparent objects, such as, for example, dental aligners.

[0515] Transparent objects should preferably exhibit the following optical properties:

[0516] Color (CIE color space; C*) lower than 1.2;

[0517] Transparency (visible light transmittance) higher than 85 %;

[0518] Haze value, denoting the percentage of incoming light scattered by more than 2.5° through the material, lower than 15 %. Besides transparency, objects such as dental aligners and other objects usable in dentistry, should typically also exhibit sufficient mechanical strength, for example, sufficiently high Tg, Tensile modulus, strain at break, and other mechanical properties.

[0519] Objects that are intended for contacting a mucosal membrane with long term exposure should also preferably meet the requirements of ISO 10993-1 (Biological evaluation of medical devices).

[0520] The present inventors have realized that curable formulations as described in WO 2023 / 114740 feature properties that are suitable for forming transparent objects such as dental aligners and others.

[0521] WO 2023 / 114740 describes photocurable formulations (compositions) which comprise: a first curable material (pre-polymer) having an average molecular weight (Mn) of up to 2000 grams / mol, which is a reaction product of a cycloaliphatic diisocyanate, a hydroxy-functional (meth)acrylate, and a diol, which can optionally co-polymerize with the second curable material, and which features Tg higher than 80 or higher than 100, °C; a second curable material (pre-polymer) having an average molecular weight (Mn) of from 2000 grams / mol to 10,000 grams / mol, which is a reaction product of a cycloaliphatic diisocyanate, a hydroxy-functional (meth)acrylate, and a diol, and which features Tg lower than -20 or lower than -40, °C; and a third curable material (monomer or pre-polymer) which is a mono-functional curable material featuring Tg of at least 25 °C, or at least 40 °C, and which can optionally co-polymerize with the first and second curable material.

[0522] While studying various combinations of the above-described curable materials, and their effect on the mechanical properties of the obtained hardened material, it was uncovered that manipulating the relative amounts of the curable materials, and the type and amount of the second curable material, substantially affects the mechanical properties of the hardened material.

[0523] Table 1 below presents a set of exemplary formulations that were preliminary tested.

[0524] In all of the exemplary formulations that were tested, the third curable material (III) was IBOMA, as an exemplary mono-functional curable material as described herein for a third curable component III (e.g., a reactive diluent); the first curable material I is a pre-polymer prepared using a short diol as described herein (I mono, for a mono-block, and I di for a di -block); and the second curable material II is a pre-polymer preparing using a longer diol as described herein, and using diols of different MW (1000 or 2000 grams / mol) and / or different number of blocks (II mono 1000; II di 1000; II mono 2000 or II di 2000). Numbers represent the % by weight of each curable material out of the total weight of curable materials in the formulation. Table 1

[0525] The mixability of the formulations at 60 °C was determined visually. While formulations 1-6 and 8 were all clear, formulation 7 was opaque (hazy).

[0526] The transparency of printed objects (tensile and DMA bars) prepared from each formulation was determined visually and all formulations provided clear objects, as can be seen in the exemplary bar shown in FIG. 1A (the bottom object), which was made of formulation 7.

[0527] However, when soaking such objects in e.g., isopropanol, haziness is visible, as can be seen in FIG. IB for a dental aligner prepared from formulation 7.

[0528] Moreover, it was uncovered that while all formulations provided brittle hardened material (manually), formulation 7 was the only formulation that provided a tough material (both manually and via tensile testing). Therefore, investigations were continued with formulation 7.

[0529] Further studies were performed while studying the effect of the amount of II di 2000, and of using various amounts of a second curable material that comprises triblocks of a diol featuring average Mn of 2000 grams / mol, ; e.g., polyTHF2000 (II tri 2000), and of using a second curable material with comprises a 2900 grams / mol diol component, e.g., polyTHF2900, as monoblock (II mono 2900) and diblock (II di 2900) on the mechanical properties, particularly elongation at break, also at high pulling speed, and on the physical properties, particularly Tg, of printed tensile and DMA bars.

[0530] Table 2 below presents the tested formulations and Table 3 below presents the mechanical properties of the hardened material prepared therefrom. Table 2

[0531] Table 3

[0532] Additional studies were performed with formulations in which a diblock diol was used to form the first curable material. These formulations provided hardened materials with Tg lower than 130, or even lower than 120 °C, and lower Tensile Strength (data not shown).

[0533] Further studies were performed while replacing the polyTHF diol by polypropylene glycol (PPG) or polyhexamethylene carbonate, featuring various MW and various number of blocks. Both types of alternative polyol are examples of low Tg polyols, that could act as an alternative for polyTHF. The obtained hardened materials exhibited different mechanical properties (data not shown). The obtained data indicate that formulations that provide desired compatibility with the printing process and desired mechanical properties of the hardened material should employ as a preferred second curable material a urethane acrylate polymer made of a multi-block (e.g., of at least 2, 3 or more blocks; or obtained at NCO / OH ratio lower than 2, for example, of 1.5 or 1.33) of polyTHF, each block having Mn of at least 2000 grams / mol, when used in an amount of from 30 to 35 % by weight; as a preferred first curable material a urethane acrylate polymer made of a short diol (e.g., of 2 to 8 carbon atoms in length), in an amount of from 25 to 30 % by weight; as a preferred third curable material a mono-functional (meth)acrylate, preferably featuring, when hardened, high Tg (e.g., of at least 40, at least 50, at least 60, or preferably at least 80, °C), in an amount of from 30 to 40 % by weight; and a photoinitiator, in an amount of from 1 to 5 % by weight.

[0534] While practicing exemplary formulations as described herein, the present inventors have uncovered that a hardened material formed upon exposing such formulations to irradiation, which features the required mechanical properties and features transparency of over 90 %, also features a haze value higher than 50 % (see, Table 2 above and accompanying data description), which affects at least its aesthetical properties, as exemplified by the photographs presented in FIGs. 1B-C and 5A.

[0535] The hardened material obtained from an exemplary formulation as described herein was observed using SEM, in order to understand the source of the high haze of such a formulation.

[0536] As shown in FIG. 2A, SEM images revealed that micron-sized domains (microclusters; marked by circles) are formed in the hardened material, presumably, but without being bound to any particular theory, due to the high Mn of the second material and the intermolecular and / or intramolecular hydrogen bonds formed by the first material, which prevent the formation of a homogenous mixture. Without being bound by any particular theory, it is assumed that these microclusters or microdomains contribute to the mechanical performance of the hardened material, and, at the same time, are the source of the high haze values. The nano-sized morphology, shown in the left inset in FIG. 2A, cannot cause this haze since its size, being much lower than 100 nm is outside the visual range of the human eye.

[0537] Without being bound by any particular theory, it is assumed that such microclusters or microdomains are also obtained when the second diol is a high molecular weight diol, either as a multi-block (e.g., 2, 3, or more blocks), or as a mono-block, for example, when the second diol has an average number molecular weight higher than 2,500, or higher than 2,900, or higher than 3,000, grams / mol. The present inventors have therefore sought for novel formulations that exhibit haze values that meet the desired optical performance (haze value lower than 15 %), without affecting the mechanical properties.

[0538] EXAMPLE 2

[0539] The present inventors have conceived including in the formulation a compound that interferes with the formation of the micron-sized clusters or domains discussed in Example 1 hereinabove, without affecting the submicron structure (e.g., nanoscale structure such as nanoscale clusters). The present inventors have further hypothesized that the formation of these micron-sized domains is related to the high amount of intermolecular and / or intramolecular hydrogen bonding formed by the first curable material (which exhibits a high density of urethane moieties such as carbamate moieties that participate in the formation of hydrogen bonds). The present inventors have therefore realized that influencing the hydrogen bonding could affect the micro sc ale structure significantly, without influencing the submicron (e.g., nanoscale) structure, and have accordingly conceived including in the formulation a compound that interferes with the formation of hydrogen bonds.

[0540] The present inventors have therefore tested the effects of various polar compounds that may affect the polarity of the composition and thereby affect, preferably reduce, the level of hydrogen bonds.

[0541] Table 4 below presents the effect of including 5 % by weight of each of the tested polar compounds in an exemplary formulation as depicted in Example 1 hereinabove on the transparency of the liquid formulation (uncured). Transparency was determined visually.

[0542] Table 4

[0543] As can be seen, only the addition of MA provided the desired transparency of the formulation, suggesting that a suitable compound should feature one or more carboxylic acid groups for effectively interfering with the hydrogen bonds formed by urethane moieties.

[0544] EXAMPLE 3

[0545] Further studies were performed in order to evaluate the effect of MA on the performance of the formulation.

[0546] 3D Printing:

[0547] First, the effect of adding 5 % by weight of MA to the curable formulation was investigated by SEM imaging.

[0548] As can be seen in FIG. 2B, the SEM image revealed that in the presence of methacrylic acid, the micron-sized domains shown in FIG. 2A disappeared completely, without affecting the nanoscale structure, as desired.

[0549] The effect of adding 4 % by weight MA to an exemplary formulation as described in Example 1 hereinabove, containing 35 % of the second curable component, on the mechanical performance of the hardened material formed upon 3D printing was also tested, under low and high pulling speeds, and the obtained data is shown in FIG. 3. As can be seen, toughness of the hardened material remained substantially the same at both pulling speeds, with only a minor drop in elongation at break observed at the higher speed.

[0550] MA-containing exemplary formulations as described herein were successfully practiced in 3D-printing of dental aligners. The haze magnitude was established visually upon soaking the obtained aligner in isopropanol (IPA).

[0551] FIG. 4 presents photographs of IPA- soaked dental aligners formed of an exemplary formulation as described in Example 1, without MA (right photo), and the same formulation to which 4% by weight MA was added (left photo). The effect of the presence of MA on the haze is clearly visible.

[0552] Casting:

[0553] The optical properties of the hardened material formed upon casting a 1 mm film of an exemplary formulation as described in Example 1 hereinabove, containing 35 % of the second curable component, with and without addition of different loadings of MA were tested. Especially the effect of the concentration of MA on haze was studied.

[0554] FIGs. 5A-E present images (FIGs. 5A-D) and a respective table (FIG. 5E) presenting the haze values as determined for casted films obtained from the exemplary formulation as described herein, without MA (FIG. 5A), and from the exemplary formulation with increasing concentrations of MA (FIGs. 5B-D), clearly showing the effect of the addition of MA in reducing the haze.

[0555] As can be clearly observed, the haze value drops significantly already upon the addition of 1 % MA. Further increase results in haze values that approach zero already between 2.3% and 4%.

[0556] Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims.

[0557] It is the intent of the applicant(s) that all publications, patents and patent applications referred to in this specification are to be incorporated in their entirety by reference into the specification, as if each individual publication, patent or patent application was specifically and individually noted when referenced that it is to be incorporated herein by reference. In addition, citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the present invention. To the extent that section headings are used, they should not be construed as necessarily limiting. In addition, any priority document(s) of this application is / are hereby incorporated herein by reference in its / their entirety.

Claims

WHAT IS CLAIMED IS:

1. A curable formulation comprising: a first curable material which is a first urethane (meth) acrylate material (pre-polymer) having a number average molecular weight lower than 2000 grams / mol and featuring Tg of at least 80 °C or of at least 100 °C, said first curable material being a first reaction product of a first cycloaliphatic diisocyanate, a first diol, and a first acrylic compound featuring a hydroxy group; a second curable material, which is a second urethane (meth)acrylate material (prepolymer) having a number average molecular weight of from 2000 grams / mol to 10,000 grams / mol and featuring Tg lower than -20 °C, or lower than -40 °C, said second curable material being a second reaction product of a second cycloaliphatic diisocyanate, a second diol, and a second acrylic compound featuring a hydroxy group, wherein said second reaction product is a multi-block copolymer; a photoinitiator; optionally, a third curable material, which comprises a third (meth)acrylic compound; and a compound capable of interfering with the formation of micron-sized clusters in a hardened material formed of the formulation.

2. The formulation of claim 1, further comprising said third curable material.

3. The formulation of claim 1 or 2, wherein said third curable material features, when hardened, Tg of at least 100 °C.

4. The formulation of any one of claims 1 to 3, wherein said third curable material is a mono-functional curable material.

5. The formulation of any one of claims 2 to 4, wherein an amount of said third curable material ranges from 20 to 50, or from 30 to 50, or from 30 to 40, % by weight of the total weight of the formulation.

6. The formulation of any one of claims 1 to 5, wherein said first reaction product features NCO / OH ratio of about 2.

7. The formulation of any one of claims 1 to 6, wherein said first cycloaliphatic diisocyanate is selected from cyclohexane- 1,3-diisocyanate, cyclohexane- 1,4-diisocyanate, 1-isocyanato-2-isocyanatomethyl cyclopentane, l-isocyanato-3-isocyanatomethyl-3,5,5- trimethylcyclohexane (isophorone diisocyanate; IPDI), bis-(4-isocyanatocyclohexyl)- methane (H12MDI), l,3-bis(isocyanatomethyl)-cyclohexane, l,4-bis(isocyanatomethyl)- cyclohexane, bis- (4-isocyanato-3-methyl-cyclohexyl)methane, 1-isocyanato- l-methyl-4(3)- isocyanatomethyl cyclohexane, 2,4-hexahydrotoluylene diisocyanate, 2,6-hexahydrotoluylene diisocyanate, and any combination thereof.

8. The formulation of any one of claims 1 to 7, wherein said first acrylic compound featuring a hydroxy group comprises a hydroxyalkyl (meth)acrylate, wherein said alkyl is of from 1 to 10, or from 2 to 10, or from 2 to 8, or from 2 to 6, carbon atoms in length.

9. The formulation of any one of claims 1 to 8, wherein said first diol comprises an aliphatic diol of from 2 to 12 carbon atoms.

10. The formulation of claim 9, wherein said first diol is selected from ethylene glycol, 1,2-propanediol, 1,3-propanediol, glycerol, 1,3 -butanediol, 2,3-butanediol, 1,4-butanediol, 2- methyl-l,4-butanediol, 3 -methyl-1, 3 -butanediol, 1,2,4-butanetriol, 1,5-pentanediol, 3-methyl-l,5- pentanediol (MPD), 3-methyl-2,4- pentanediol, 2-methyl-l, 3 -pentanediol, 2-methyl- 1,5- pentanediol, 1,2,5-pentanetriol, 1,6-hexanediol, 1,2-hexanediol, 1,5-hexanediol, 2-methyl- 1,6- hexanediol, 4-methyl-l,3-hexanediol, 5-methyl-2,4-hexanediol, 3 -methyl- 1,6-hexanediol, 1,2,6- hexanetriol, 1,7-heptanediol, 2,5-heptanediol, 4-methyl-l,6-heptanediol, 3-methyl-2,4-heptanediol, 2-methyl-2,6-heptanediol, 5-methyl-2,4-heptanediol, 4-methyl-l,7-heptanediol, 1,2,7-heptanetriol, 1,8-octanediol, 2-methyl-l, 8-octanediol, 7-methyl-l,7-octanediol, 6-methyl-l,7-octanediol, 3- methyl-l,4-octanediol, 1,2, 8-octanediol, 1,9-nonanediol, 8-methyl-l-8-nonanediol, 1,2,9- nonanetriol, 1,10-decanediol, 2-methyl- 1,10-decanediol, 2-methyl-2,5-decanediol, 4,8- Bis(hydroxymethyl)tricyclo[5.2.1.02,6]decane (DCPDM), 1,11 -undecanediol, 1,12-dodecanediol, and any combination thereof.

11. The formulation of any one of claims 1 to 10, wherein said second reaction product features NCO / OH ratio lower than 2, or in a range of from 1 to 1.8, or from 1 to 1.5, or from 1.33 to 1.5.

12. The formulation of any one of claims 1 to 11, wherein said second reaction product features NCO / OH ratio of about 1.5 or of about 1.33.

13. The formulation of any one of claims 1 to 12, wherein said second cycloaliphatic diisocyanate is selected from cyclohexane- 1,3-diisocyanate, cyclohexane- 1,4-diisocyanate, 1- isocyanato-2-isocyanatomethyl cyclopentane, l-isocyanato-3-isocyanatomethyl-3,5,5- trimethylcyclohexane (isophorone diisocyanate; IPDI), bis-(4-isocyanatocyclohexyl)- methane (H12MDI), l,3-bis(isocyanatomethyl)-cyclohexane, l,4-bis(isocyanatomethyl)- cyclohexane, bis- (4-isocyanato-3-methyl-cyclohexyl)methane, 1-isocyanato- l-methyl-4(3)- isocyanatomethyl cyclohexane, 2,4-hexahydrotoluylene diisocyanate, 2,6-hexahydrotoluylene diisocyanate, and any combination thereof.

14. The formulation of any one of claims 1 to 13, wherein said second acrylic compound featuring a hydroxy group comprises a hydroxyalkyl (meth)acrylate, wherein said alkyl is of from 1 to 10, or from 2 to 10, or from 2 to 8, or from 2 to 6, carbon atoms in length.

15. The formulation of any one of claims 1 to 14, wherein said second diol comprises a polyether diol having average Mn of from 500 to 5,000, or from 1,000 to 5,000, or from 2,000 to 5,000, grams / mol.

16. The formulation of any one of claims 1 to 15, wherein said second diol comprises a polyTHF.

17. The formulation of any one of claims 1 to 16, wherein: an amount of said first curable material ranges from 20 to 50, or from 20 to 40, preferably from 25 to 35 or from 25 to 30, % by weight of the total weight of the formulation; and / or an amount of said second curable material ranges from 25 to 50, or from 30 to 50, or from 30 to 40, % by weight of the total weight of the formulation; and / or an amount of said photoinitiator ranges from 1 to 5, % by weight of the total weight of the formulation.

18. The formulation of any one of claims 1 to 17, wherein: each of said first and said second acrylic compound featuring a hydroxy group independently comprises a hydroxy alkyl (meth)acrylate, wherein said alkyl is of from 1 to 10, or from 2 to 10, or from 2 to 8, or from 2 to 6, carbon atoms in length; said first diol comprises an aliphatic diol of from 2 to 12 carbon atoms;said second diol comprises a polyTHF having average Mn of from 1,000 to 5,000, or from 2,000 to 5,000, grams / mol; and said second reaction product is a multiblock co-polymer.

19. The formulation of claim 18, wherein: said second reaction product features NCO / OH ratio lower than 2, or from 1 to 1.5, or of about 1.5 or about 1.33; an amount of said first curable material ranges from 25 to 35 or from 25 to 30, % by weight of the total weight of the formulation; an amount of said second curable material ranges from 25 to 40, or from 30 to 40, % by weight of the total weight of the formulation; and an amount of said third curable material ranges from 30 to 40, % by weight of the total weight of the formulation.

20. The formulation of any one of claims 1 to 19, wherein said compound capable of interfering with the formation of said micron-sized clusters is a photocurable material.

21. The formulation of any one of claims 1 to 20, wherein said compound capable of interfering with the formation of said micron-sized clusters comprises a (meth)acrylate featuring at least one carboxylic acid moiety.

22. The formulation of any one of claims 1 to 21, wherein said compound capable of interfering with said hydrogen bonds comprises (meth)acrylic acid.

23. The formulation of any one of claims 1 to 22, wherein an amount of said compound capable of interfering with the formation of said micron-sized clusters ranges from 1 to 10, or from 2 to 10, % by weight of the total weight of the formulation.

24. A hardened material from upon exposing the formulation of any one of claims 1 to23 to irradiation.

25. The hardened material of claim 24, being a transparent material.

26. The hardened material of claim 24 or 25, featuring a haze value of no more than 15 %, or no more than 10 %, or no more than 5 %.

27. The hardened material of any one of claims 24 to 26, featuring at least one of:Tg of at least 100, or at least 120, °C;Tensile modulus of at least 800, or at least 900, or at least 1,000 MPa;Yield Stress of at least 20 MPa;Elongation at break of at least 30 %.

28. A three-dimensional object comprising, in at least a portion thereof, the hardened material of any one of claims 24 to 27.

29. The three-dimensional object of claim 28, being or forming a part of an orthodontic device such as a dental aligner.

30. A method of additive manufacturing a three-dimensional object featuring in at least a portion thereof a transparent material, the method comprising forming a plurality of layers in a configured pattern correspond to the shape the denture object, thereby forming the object, wherein at least a few of said layers are formed of the modeling material formulation as defined in any one of claims 1 to 23, upon exposing each of said layers to irradiation.

31. A kit comprising the curable formulation as defined in any one of claims 1 to 23, wherein said first and second curable materials, and optionally said third material, if present, are each individually packaged within the kit.

32. A curable formulation comprising: a first curable material which is a first urethane (meth)acrylate material having an average number molecular weight lower than 2000 grams / mol and featuring Tg of at least 80 °C or of at least 100 °C, said first curable material being a first reaction product of a first cycloaliphatic diisocyanate, a first diol, and a first acrylic compound featuring a hydroxy group; a second curable material, which is a second urethane (meth) acrylate material having an average number molecular weight of from 2000 grams / mol to 10,000 grams / mol and featuring Tg lower than -20 °C, or lower than -40 °C, said second curable material being a second reaction product of a second cycloaliphatic diisocyanate, a second diol, and a second acrylic compoundfeaturing a hydroxy group, said second reaction product being a multi-block co-polymer which comprises at least two blocks of said second diol; and optionally, a third curable material, which comprises a third (meth)acrylic compound, wherein an amount of said first curable material ranges from 20 to 35, or from 25 to 35, preferably from 25 to 30, % by weight of the total weight of the formulation; and an amount of said second curable material ranges from 25 to 50, or from 30 to 50, or from 30 to 40, % by weight of the total weight of the formulation.

33. The formulation of claim 32, further comprising said third curable material.

34. The formulation of claim 32 or 33, wherein said third curable material features, when hardened, Tg of at least 100 °C.

35. The formulation of any one of claims 32 to 34, wherein said third curable material is a mono-functional curable material.

36. The formulation of any one of claims 33 to 35, wherein an amount of said third curable material ranges from 20 to 50, or from 30 to 50, or from 30 to 40, % by weight of the total weight of the formulation.

37. The formulation of any one of claims 32 to 36, wherein said first reaction product features NCO / OH ratio of about 2.

38. The formulation of any one of claims 32 to 37, wherein said first acrylic compound featuring a hydroxy group comprises a hydroxyalkyl (meth)acrylate, wherein said alkyl is of from 1 to 10, or from 2 to 10, or from 2 to 8, or from 2 to 6, carbon atoms in length.

39. The formulation of any one of claims 32 to 38, wherein said first diol comprises an aliphatic diol of from 2 to 12 carbon atoms.

40. The formulation of any one of claims 32 to 39, wherein said second reaction product features NCO / OH ratio lower than 2, or in a range of from 1 to 1.8, or from 1 to 1.5, or from 1.33 to 1.5.

41. The formulation of any one of claims 32 to 40, wherein said second acrylic compound featuring a hydroxy group comprises a hydroxyalkyl (meth)acrylate, wherein said alkyl is of from 1 to 10, or from 2 to 10, or from 2 to 8, or from 2 to 6, carbon atoms in length.

42. The formulation of any one of claims 32 to 41, wherein said second diol comprises a polyether diol having Mn of from 500 to 5,000, or from 1,000 to 5,000, or from 2,000 to 5,000, grams / mol.

43. The formulation of any one of claims 32 to 42, wherein said second diol comprises a polyTHF.

44. The formulation of any one of claims 32 to 43, further comprising a photoinitiator.

45. The formulation of claim 44, wherein an amount of said photoinitiator ranges from 1 to 5, % by weight of the total weight of the formulation.

46. The formulation of any one of claims 32 to 45, wherein: each of said first and said second acrylic compound featuring a hydroxy group independently comprises a hydroxy alkyl (meth)acrylate, wherein said alkyl is of from 1 to 10, or from 2 to 10, or from 2 to 8, or from 2 to 6, carbon atoms in length; said first diol comprises an aliphatic diol of from 2 to 12 carbon atoms; said second diol comprises polyTHF having Mn of from 1,000 to 5,000, or from 2,000 to 5,000, grams / mol; said first reaction product features NCO / OH ratio of about 2; and said second reaction product features NCO / OH ratio of about 1.5 or about 1.33.

47. The formulation of claim 46, wherein: an amount of said first curable material ranges from 25 to 35 or from 25 to 30, % by weight of the total weight of the formulation; an amount of said second curable material ranges from 30 to 40, % by weight of the total weight of the formulation; and an amount of said third curable material ranges from 30 to 40, % by weight of the total weight of the formulation.

48. A hardened material from upon exposing the formulation of any one of claims 32 to 47 to irradiation.

49. A three-dimensional object comprising, in at least a portion thereof, the hardened material of claim 48.

50. A method of additive manufacturing a three-dimensional object featuring in at least a portion thereof a transparent material, the method comprising forming a plurality of layers in a configured pattern corresponding to the shape of the denture object, thereby forming the object, wherein at least a few of said layers are formed of the modeling material formulation as defined in any one of claims 32 to 47, upon exposing each of said layers to irradiation.

51. A kit comprising the curable formulation as defined in any one of claims 32 to 47, wherein said first and second curable materials, and optionally said third curable material, if present, are each individually packaged within the kit.

Images