WO2022144918A1

WO2022144918A1 - A resin composition for use in three-dimensional (3d) printing

Info

Publication number: WO2022144918A1
Application number: PCT/IN2021/051209
Authority: WO
Inventors: Sarthak Patel; Yogesh BAGUL
Original assignee: Sarthak Patel; Bagul Yogesh
Priority date: 2020-12-28
Filing date: 2021-12-28
Publication date: 2022-07-07

Abstract

The presently claimed invention relates to the field of three-dimensional (3D) printing, specifically to photopolymerization-based 3D printing. In particular, the present invention provides a curable resin composition for use in 3D printing, which is washed in water for removal of excess resin post-curing, and provides excellent mechanical properties to the finished 3D objects, possesses low viscosity, requires lesser duration of light exposure during curing, and reduces printing time, a process of preparing said composition, and uses thereof.

Description

“A RESIN COMPOSITION FOR USE IN THREE-DIMENSIONAL (3D) PRINTING”

[001] The presently claimed invention relates to the field of three-dimensional (3D) printing, specifically to photopolymerization-based 3D printing. In particular, the present invention provides a curable resin composition for use in 3D printing, which is washed in water for removal of excess resin post-curing, and provides excellent mechanical properties to the finished 3D objects, possesses low viscosity, requires lesser duration of light exposure during curing, and reduces printing time, a process of preparing said composition, and uses thereof.

Background of the invention

[002] 3D printing also known as additive manufacturing, uses computer-aided design (CAD) to create three-dimensional objects through a layering method.

[003] A typical 3D photopolymerization (also known as photocuring or photo-cross- linking) technique involves using a resin composition comprising monomers or oligomers in a liquid state that can be cured or photopolymerized upon exposure to a light source. The surface of a photocurable resin composition is selectively irradiated with light of a specific wavelength based upon CAD data to form a cured resin layer having a specific pattern. Another layer of a resin composition is provided over this cured resin layer and the liquid surface is selectively irradiated to form a new cured resin layer integrally laminated over the cured resin layer. This step is repeated a certain number of times using the same or different irradiating patterns to obtain a 3D object consisting of integrally laminated cured resin layers. After it is rinsed with a liquid solvent to free it of excess resin, the object is baked in an ultraviolet oven to further cure the product.

[004] A number of photo-cured resin compositions have been disclosed in the prior art in the last few years, for use in 3D printing. However, the performance of objects printed by these compositions is limited due to their low mechanical strength because of which the printed objects cannot be directly used as structural parts. Generally, the objects which are printed by photocuring 3D printing technique are brittle, of poor toughness, and can't withstand impact.

[005] Another problem of the resin compositions and processes of the prior art is the application of washing agents to remove excess uncured resins. Washing agents, for example, ethanol, isopropanol and acetone, tend to be absorbed into the 3D object, causing swelling and deformation of the object leading to a significant decrease in the strength of the finished object.

[006] WO2021089313 Al relates to a photocurable composition comprising acroloylmorpholine. However, the final composition of the prior art does not have sufficient ductility and is susceptible to breakage. US 2021/0070921 Al relates to a water washable UV curing resin comprising Poly [oxy methyl (1,2 ethanediyl) ether glycol] but does not result in improved mechanical strength of the final printed object. US6685869 B2 discloses a photocurable resin composition that has improved coatability and uniformity without formation of bubbles. However, it maintains the need for an organic washing agent as water is deemed to have unfavorable consequences on the viscosity of the composition.

[007] Also, uncured and partially cured resins make the object tacky and difficult to clean, and, therefore, must be removed. However, most of the prior art resin compositions employ oligomers and monomers that are soluble only in certain organic solvents. 3D printed objects prepared using such compositions can only be washed with solvents such as isopropanol and acetone. These organic solvents are often volatile organic chemicals (VOC) which have health, safety and environment concerns.

[008] The growing need to reduce VOC emissions is slowly phasing out the use of organic solvents. Because of this trend, 3D printing formulators are making efforts to replace organic solvents with water as a washing agent.

[009] As the market for 3D printed objects continues to grow, there is an ongoing need to provide photo-cured resin compositions for developing 3D printed objects with improved mechanical strength while reducing the use of organic solvents for washing cured resins.

[010] Additionally, exposure time during the photo-curing process also affects the mechanical strength of the 3D printed object and printing time.

[Oi l] Therefore, it was an object of the presently claimed invention to provide a resin composition for preparing 3D printed objects which is washable with water and at the same time exhibits good physical and mechanical properties and strength, possesses low viscosity, requires lesser duration of light exposure during curing, and reduces printing time.

[012] Yet another object of the invention relates to the fabrication of orthodontic appliances. Studies of acrylated polymers for additive manufacturing have been extensive, examining conductivity, elasticity, and optical properties. Determining the composition of photosensitive inks, which may contain acrylic oligomers, acrylic monomers, reactive diluents, and photoinitiators, is essential for exploiting DLP-based 3D printing in dental applications. Although various printable resins have been developed, several inherent limitations inhibit their use in clinical applications. Polymethyl methacrylate (PMMA), for example, is a common light-curing resin used in the 3D printing industry. However, PMMA has a high shrinkage rate during light curing and poor mechanical properties. Bisphenol A-glycidyl methacrylate (Bis-GMA) and urethane dimethacrylate (UDMA) are also used as light-polymerized dental composite resins; however, they have high molecular weights and viscosities. Owing to their high wearability and inherent biocompatibility, polyurethanes have been widely used in biomedical devices such as dental aligners and artificial hearts. It has been observed that printable urethane acrylate (UA)-based photopolymer resins with tunable mechanical properties for DLP-based 3D printers may be used for the purpose of orthodontic material printing and scope of their use in this regard has not been fully exploited. Therefore, it is the object of this invention to come up with an inventive resin composition having the remarkable properties of urethane acrylate in the best manner.

Summary of the invention

[013] The present invention relates to resin 3D printing and, applies to methods, including but not limited to Digital Light Processing (DLP) and Liquid Crystal Display (LCD) projection, 2PP (two photon polymerization), continuous liquid interface production, material jetting, and micro stereolithography (pSLA).

[014] The present invention provides a composition of a photo curing resin comprising 4-(l-oxo-2 -propenyl)- morpholine (A) in the range of > 10 wt. % to < 70 wt. %; at least one acrylate resin (B) in the range of > 1 wt. % to < 15 wt. %; a diluent (C) selected from N, N-dimethyl acrylamide and N-(hydroxyethyl)acrylamide in the range of > 1 wt. % to < 20 wt. %; ethoxylated trimethylpropane triacrylate (D) in the range of > 5 wt. % to < 60 wt. %; and at least one photo-initiator (E) selected from ethyl phenyl(2,4,6-trimethylbenzoyl)phenyl phosphinate and bis(eta5-cyclopentadienyl)- bis(2,6-difluoro-3 -(pyrrol- l-yl)-phenyl) titanium, and diphenyl(2,4,6- trimethylbenzoyl)phosphine oxide, in the range of > 0.1 wt. % to < 5 wt. %.

Description of the invention

[015] All 3D polymerization techniques involve a photosensitive resin cured by a light source to produce solid layers and, eventually, whole parts. The resin is contained within a vat, or tank, and is cured against a build platform, which slowly rises out of the tank as the part is formed. The most well-known and oldest of the three is stereolithography (SLA). It uses a laser, directed by galvanometers, to cure the resin.

[016] Digital Light Processing (DLP) uses a digital light projector to cure the resin. It flashes images of whole layers onto the bottom of the vat. Light is selectively directed using a digital micromirror device (DMD), which is a component consisting of hundreds of thousands of tiny mirrors. Layers generated using DLP printers consist of voxels, the 3D equivalent of pixels.

[017] Yet another method in resin 3D printing is LCD 3D printing which is similar to DLP. It also flashes complete layers at the resin tank, but with the UV light coming from an array of LEDs shining through an LCD and not a projector. A screen acts as a mask, revealing only the pixels necessary for the current layer. As such, no special device is required to direct the light, as is the case in both SLA and DLP. Definitions

[018] Unless otherwise defined, all terms of art, notations and other scientific terminology used herein are intended to have the meanings commonly understood by those of skill in the art to which this invention pertains. In some cases, terms with commonly understood meanings are defined herein for clarity and/or for ready reference, and the inclusion of such definitions herein should not necessarily be construed to represent a substantial difference over what is generally understood in the art. The techniques and procedures described or referenced herein are generally well understood and commonly employed using conventional methodology by those skilled in the art.

[019] The term “alkyl” denotes a saturated moiety constituted solely of atoms of carbon and of hydrogen.

[020] The term “aliphatic alcohol” as used herein denotes organic compounds containing one or more hydroxyl groups attached to an alkyl radical.

[021] The term “difimctional urethane” denotes a urethane ester along with a difimctional isocyanate as monomers.

[022] The term “aliphatic urethane” which are also known as aliphatic polyurethane, are urethanes without any aromatic moiety.

[023] The term “speciality acrylate resin” generally denotes resins that are proprietary in nature and include products that are based on specific curing technologies or chemistries, orthose designed for specialized applications.

[024] The term “polyisocyanate compound” relates to organic compounds comprising at least two isocyanate groups which are used as a reactant to form polyurethane through urethane linkers.

[025] The term “urethane (meth) acrylate” means an oligomer that consists of urethane and methacrylate as monomers.

[026] The term “difimctional polyurethane” denotes polyurethanes (PU) made of oligomers consisting of urethane (carbamate) linkages between the monomers urethane and isocyanate, wherein the isocyanate group consists of more than one functional group.

[027] The term “polyol” denotes a compound having multiple hydroxyl groups. [028] The term “polyester polyol” relates to those polyols which are made by the polycondensation of multifunctional carboxylic acid and polyhydroxyl compounds.

[029] The term “polyvinyl alcohol” relates to a vinyl polymer joined by only carboncarbon linkages.

[030] The term “polyacid” is defined as an acid having more than one acidic hydrogen.

[031] The term “monomer” is to be understood to be a molecule of low molecular weight which may combine with other molecules to form a molecule in a chain or branched form having high molecular weight.

[032] The term “oligomer” relates to a molecule composed of a small number of linked monomer units; a short polymer; - compounds called oligomers have less than one hundred monomer units and usually less than thirty.

[033] The term “polymer” is used to denote a substance composed of macromolecules.

[034] The term “diluent” denotes any liquid substance that is mixed with a polymer composition to reduce its viscosity and increase its flow rate.

[035] The term “photoinitiator” denotes compounds that produce radicals when exposed to UV light which then react with monomers and/or oligomers to initiate polymer chain growth.

[036] The term “photopolymer” is understood to mean a polymeric material that is sensitive to light.

[037] The term “elongation @ break” is understood to be the percentage increase in length that the material will achieve before breaking. It is also known as “fracture strain” or “tensile elongation at break”.

[038] The term “flexural modulus” is understood to be the ratio of stress is to strain during flexural deformation.

[039] The term “tensile strength” is understood to be the ability of a material to withstand stress without breaking.

[040] The term “flexural strength” of a material is defined as its ability to resist deformation under load. [041] The term “viscosity” is understood to be the thickness of the liquid which is usually measured in centipoise(cP) or Pa.s.

[042] The term “Rockwell Hardness” is understood to be defined as ASTM E- 18 and measures the permanent depth of indentation produced by a force/load on an indenter.

[043] The term “exposure time” is defined as the amount of time that the light source will expose each layer during printing. Different SLA/DLP/LCD 3D printers have different exposure times for resins.

[044] The acronym “ASTM” denotes the standards set by the American Society for Testing and Materials that comprises of six types of standards relating to manufacturing processes such as testing, materials classification and operation. The six types are test method, specification, classification, practice, guide and terminology standards. The inventors have fully complied with ASTM D standards for testing of material properties.

ASTM D256- Standard test method for determining the izod pendulum impact resistance of plastics.

ASTM D790- Standard test method for determining flexural properties of unreinforced and reinforced plastics and electrical insulating materials.

ASTM D638- Standard test method for determining tensile properties of polymers.

ASTM D-4274C- Standard test method for determining molecular weight of polymers.

ASTM D445- Standard test method for determining viscosity of polymers.

[045] The present invention relates to a resin composition comprising 4-(l-oxo-2- propenyl)- morpholine (A) in the range of > 10 wt. % to < 70 wt. %

[046] The composition also comprises at least one acrylate resin (B) in the range of > 1 wt. % to < 15 wt. %.

[047] The acrylate resin is selected from speciality acrylate resins having outstanding properties based on specific curing technologies as per the applications of the present invention. The speciality resin may be made by a person skilled in the art with constituents which are well known in the art including urethane acrylate, difimctional polyurethane acrylate, polyethylene glycol, ethoxylated trimethylpropane triacrylate and water. [048] The urethane acrylate may be an aliphatic urethane methacrylate which may be selected from urethane (meth)acrylate, epoxy (meth)acrylate, polyester (meth)acrylate, (meth)acrylic (meth)acrylate, or a mixture thereof. The term "(meth)acryl" is to be understood as to encompass both acryl and methacryl compounds or derivatives as well as mixtures thereof.

[049] The (meth)acrylated urethane is generally obtained from the reaction of at least one polyisocyanate compound, at least one polyol, preferably a polyester polyol, comprising at least one polyethylene glycol segment and at least one pendant hydrophilic group, and at least one (meth)acrylated compound containing at least one reactive group capable to react with isocyanate groups. Preferred are partially water soluble (meth) acrylated aliphatic urethanes.

[050] The polyester polyol is preferably obtained from the reaction of at least one polyethylene glycol, at least one polyacid and at least one compound containing at least one hydrophilic group, and optionally at least one other polyol.

[051] By hydrophilic group it is meant to designate a group that is either ionic, such as for example a carboxylate or sulfonate group, or that becomes ionic after reaction with a neutralizing agent forming a salt, such as a carboxylic acid, sulfonic acid, amino group.

[052] The polyethylene glycol preferably has a molecular weight of from 200 to 2000, more preferably of at least 400. By the term "glycol" as used herein in (i) is meant any class of organic compounds belonging to the polyol family. In the molecule of a glycol, hydroxyl (-OH) groups are attached to different carbon atoms. Preferably, a glycol comprises two hydroxyl groups. This group also covers polyalkylene oxide polyols, such as polyethylene oxide and polycaprolactone polyols.

[053] Particularly preferred are polyester polyols which contain from 20 to 80 percent by weight, more preferably from 40 to 80 percent by weight, of polyethylene glycol segments and from 5 to 20 percent, more preferably from 5 to 15 percent, by weight of a compound containing at least one hydrophilic group, especially sodium sulfoisophthalic acid, 2,2-dimethylolpropionic acid and 2,2-dimethylolbutanoic acid and/or alpha, omega-polypropylenglycol-diamine-sulfopropylated, sodium salt. Suitable water-dilutable (meth)acrylates are for example those that have been commercialized under the name of UCECOAT® 6558, UCECOAT® 6559, EBECRYL® 2002 and EBECRYL® 2003. The proprietary chemicals with the trade name UCECOAT and EBECRYL are available from Allnex, in Frankfurt, Germany.

[054] Other preferred glycols are polyvinyl alcohols. Polyvinyl Alcohol (having acronyms PVOH, PVA or PVAL) are synthesized by hydrolysis of polyvinylacetate. It is classified into two classes namely partially hydrolysed and fully hydrolysed. These are commercially available from Kuraray under the tradename Poval. Preferred are partially hydrolysed polyvinyl alcohols.

[055] The (meth)acrylate functional urethane oligomer according to another preferred embodiment of the invention, has the structure: end group - polyisocyanate - backbone - polyisocyanate - end group.

[056] The difunctional urethane acrylate -based oligomer described above can be obtained, for example, by selecting a difunctional oligomer from urethane acrylate oligomers which are obtained by esterification with (meth)acrylic acid of polyurethane oligomers obtained by the reaction of a polyisocyanate with a polyether polyol or a polyester polyol.

[057] 4-(l -oxo-2 -propenyl)- morpholine, the acrylate resin as defined above, diluent and ethoxylated trimethylpropane triacrylate together achieve outstanding properties such as significantly improved mechanical strength, flexibility, ductility, and tensile strength, low viscosity, low exposure time during curing and reduced printing time.

[058] The inventive composition also comprises a diluent (C) selected from N, N, dimethyl acrylamide or N-hydroxy ethyl acrylamide, in the range of > 1 wt. % to < 20 wt. %.

[059] Diluents are low-molecular- weight, low-viscosity compounds that are used to reduce the viscosity or enhance the solubility of a resin and/or hardener. Diluents may be either reactive or non-reactive. However, the reactive species are more desirable since they combine chemically with the main resin during cure and are not free to outgas or leach, especially during thermal -vacuum exposure.

[060] Dimethylacrylamide (DMMA) can be polymerized very quickly by radical chain reaction initiators or copolymerized with the pre-polymers as claimed in the present invention. Copolymerization of DMAA improves tensile strength, impact strength, printing, dying and antistatic properties of resins in the claimed photocurable resin composition.

[061] The present invention also comprises a crosslinking agent (D) selected from ethoxylated trimethylpropane triacrylate (3), ethoxylated trimethylpropane triacrylate (6), or ethoxylated trimethylpropane triacrylate (9), in the range of > 5 wt. % to < 60 wt. %. The water insoluble reactive triacrylate helps in achieving a 3-dimensional (3D) polymer network thereby enhancing the mechanical properties of the claimed photocurable composition.

[062] The present composition further comprises at least one photoinitiator (E) selected selected from ethyl phenyl(2,4,6-trimethylbenzoyl)phenyl phosphinate, bis(eta5-cyclopentadienyl)-bis(2,6-difluoro-3-(pyrrol-l-yl)-phenyl) titanium and diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO), in the range of> 0.1 wt. %to < 5 wt. %.

[063] Photoinitiators suitable for use in the polymerizable liquid compositions of the invention include, but are not limited to photoinitiators activated by UV or visible light. In some embodiments, the photoinitiator is activated by long-wave length UV light or UVA (wavelength approximately 320 to 520 nm). Photoinitiators activated by long wavelength UV light include, but are not limited to, Ethyl (2, 4, 6-trimethylbenzoyl) phenyl phosphinate, acylgermanes, a bimolecular system of camphorquinone (CQ) and N, N-di methylaminobenzoic acid ethyl ester (DMAB), bisacylphos phine oxides and hydroxyalkylphenones and 1, 5 -diphenyl- l,4-diyn-3 -one for 320 to 405 nm and Bis(r|5- cyclopentadienyl)-bis(2,6-difluoro-3-[pyrrol-l-yl]-phenyl) titanium for 405 to 550 nm. Camphorquinone (CQ), N, N-dimethylaminobenzoic acid ethyl ester (DMAB) bisacylphosphine oxides, hydroxyalkylphenones and l,5-diphenyl-l,4-diyn-3-one (Dinone) are biocompatible.

[064] In further embodiments, the composition does not include a second type of initiator other than a photoinitiator.

[065] Examples of photoinitiators are known to the person skilled in the art and for example published by Kurt Dietliker in “A compilation of photoinitiators commercially available for UV today”, Sita Technology Textbook, Edinburgh, London, 2002.

[066] The photocurable resin composition of the present invention may further comprise additives to modify and enhance resin properties that become a part of the polymer matrix thereby improving both cost effectiveness and performance.

[067] The additives may be selected from thixotropes, pigments or colourants, solvents, fire retardants, suppressants, electricity conductors, UV inhibitors, fillers ceramic particles and dispersants.

[068] The additives may particularly be selected from thixotropes such as silica gel and materials containing contains various siloxane and silanol groups.

[069] The pigments and colourants may be selected any kind commonly used by those skilled in the art, such as black pigments and pigments of other colors including blue, black, brown, cyan, green, white, purple, magenta, red, orange or yellow pigments. They may also be mixtures of various pigments.

[070] The additives may also include solvents such as polyethylene glycol (200), polyethylene glycol (400), polyethylene glycol (500), polyethylene glycol (600), and polyethylene glycol (300). [071] The additives may also be a fire retardant selected from materials containing ATH (alumina trihydrate), bromine, chlorine, borate and phosphorus.

[072] Performance improving fillers may also be added in the resin composition as selected from a range of fillers commonly known in prior art including calcium carbonate, kaolin, alumina trihydrate and calcium sulphate.

[073] The additive may also be a UV stabilizers which protect the resin composition by absorbing the UV selected from commonly known stabilizers including benzophenones, hydroxybenzophenone, carbon black, enzotriazoles, hydroxyphenyltriazines and hydroxyphenylbenzotriazole.

[074] The terms and expressions which have been employed herein in the disclosure are used as terms of description and not of limitation, and there is no intention in the use of such terms of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed. Thus, it should be understood that although the present invention has been specifically disclosed by preferred embodiments, exemplary embodiments and optional features, modification and variation of the concepts herein disclosed may be resorted to by those skilled in the art, and that such modifications and variations are considered to be within the scope of this invention as defined by the appended claims. The specific embodiments provided herein are examples of useful embodiments of the present invention and it will be apparent to one skilled in the art that the present invention may be carried out using a large number of variations of the devices, device components, methods steps set forth in the present description. As will obvious to one of skill in the art, methods and devices useful for the present methods can include a large number of optional composition and processing elements and steps.

[075] In an embodiment of the composition according to the present invention, 4-(l- oxo-2 -propenyl)-morpholine (A) is present in an amount in the range of > 20 wt. % to

< 70 wt. %, based on the total weight of the composition.

[076] In an embodiment of the composition according to the present invention, 4-(l- oxo-2 -propenyl)-morpholine (A) is present in an amount in the range of > 30 wt. % to

< 70 wt. %, based on the total weight of the composition.

[077] In a particular embodiment of the composition according to the present invention, 4-(l-oxo-2-propenyl)-morpholine (A) is present in an amount in the range of > 40 wt. % to < 70 wt. %.

[078] In another embodiment of composition according to the present invention, 4-(l- oxo-2 -propenyl)-morpholine (A) is present in an amount in the range of > 40 wt. % to

< 65 wt. %, based on the total weight of the composition. [079] In still another embodiment of the composition according to the present invention, 4-(l-oxo-2-propenyl)-morpholine (A) is present in an amount in the range of > 40 wt. % to < 60 wt. %.

[080] In an embodiment of the composition according to the present invention, the at least one acrylate resin (B) is present in an amount in the range of > 2 wt. % to < 15 wt. %, based on the total weight of the composition.

[081] In another embodiment of the composition according to the present invention, the at least one acrylate resin (B) is present in an amount in the range of > 3 wt. % to < 10 wt. %, based on the total weight of the composition.

[082] In another embodiment of the composition according to the present invention, the at least one acrylate resin (B) is present in an amount in the range of > 3 wt. % to < 7 wt. %, based on the total weight of the composition.

[083] In another embodiment of the composition according to the present invention, the at least one acrylate resin (B) is present in an amount in the range of > 4 wt. % to < 7 wt.-%, based on the total weight of the composition.

[084] In an embodiment of the composition according to the present invention, the at least one diluent (C) is present in an amount in the range of > 2 wt. % to < 20 wt. %, based on the total weight of the composition.

[085] In another embodiment of the composition according to the present invention, the at least one diluent (C) is present in an amount in the range of > 2 wt. % to < 15 wt. %, based on the total weight of the composition.

[086] In another embodiment of the composition according to the present invention, the at least one diluent (C) is present in an amount in the range of > 5 wt. % to < 10 wt. %, based on the total weight of the composition.

[087] In another embodiment of the composition according to the present invention, least one diluent (C) is present in an amount in the range of > 3 wt. % to < 5 wt. %, based on the total weight of the composition.

[088] In an embodiment of the composition according to the present invention, the crosslinker ethoxylated trimethylpropane triacrylate (D) is present in an amount in the range of > 5 wt. % to < 50 wt. %, based on the total weight of the composition.

[089] In an embodiment of the composition according to the present invention, the crosslinker ethoxylated trimethylpropane triacrylate (D) is present in an amount in the range of > 15 wt. % to < 50 wt. %, based on the total weight of the composition. [090] In another embodiment of the composition according to the present invention, the crosslinking agent ethoxylated trimethylpropane triacrylate (D) is present in the range of > 20 wt. % to < 50 wt. %, based on the total weight of the composition.

[091] In another embodiment of the composition according to the present invention, the crosslinking agent, ethoxylated trimethylpropane triacrylate (D) is present in the range of > 20 wt. % to < 40 wt. %, based on the total weight of the composition.

[092] In another embodiment of the composition according to the present invention, the crosslinking agent, ethoxylated trimethylpropane triacrylate (D) is present in the range of > 25 wt. % to < 40 wt. %, based on the total weight of the composition.

[093] In another embodiment of the composition according to the present invention, the crosslinking agent, ethoxylated trimethylpropane triacrylate (D) is present in the range of > 5 wt. % to < 20 wt. %, based on the total weight of the composition.

[094] In an embodiment of the composition according to the present invention, the at least one photo-initiator (E) is present in an amount in the range of > 0. 1 wt. % to < 5 wt. %, based on the total weight of the composition.

[095] In an embodiment of the composition according to the present invention, the at least one photo-initiator (E) is present in an amount in the range of > 0.5 wt. % to < 5 wt. %, based on the total weight of the composition.

[096] In another embodiment of the composition according to the present invention, the at least one photoinitiator (E) is present in an amount in the range of > 1 wt. % to < 3 wt. %, based on the total weight of the composition.

[097] In an embodiment of the composition according to the present invention, weight average molecular weight M_w of the at least one acrylate resin (B) is in the range of > 120 g/mol to < 700 g/mol determined according to ASTM D-4274C.

[098] In another embodiment of the composition according to the present invention, weight average molecular weight M_w of the at least one acrylate resin (B) is in the range of > 150 g/mol to < 300 g/mol determined according to ASTM D-4274C.

[099] In an embodiment of the composition according to the present invention, 4-(l- oxo-2 -propenyl)-morpholine (A) has a viscosity in the range of > 0.001 Pa.s to < 2 Pa.s at a temperature of 25°C, determined according to ASTM D445.

[100] In an embodiment of the composition according to the present invention, 4-(l- oxo-2 -propenyl)-morpholine (A) has a viscosity in the range of > 0.001 Pa.s to < 0.015 Pa.s at a temperature of 25 °C, determined according to ASTM D445. [101] In an embodiment of the composition according to the present invention, 4-(l- oxo-2 -propenyl)-morpholine (A) has a viscosity in the range of > 0.009 Pa.s to < 0.015 Pa.s at a temperature of 25 °C, determined according to ASTM D445.

[102] In another embodiment of the composition according to the present invention, the at least acrylate resin (B) has a viscosity in the range of > 0.0001 Pa.s to < 1.5 Pa.s at a temperature of 25°C, determined according to ASTM D445.

[103] In another embodiment of the composition according to the present invention, the at least acrylate resin (B) has a viscosity in the range of > 0.8 Pa.s to < 1.5 Pa.s at a temperature of 25°C, determined according to ASTM D445.

[104] In another embodiment of the composition according to the present invention, the at least one diluent (C) has a viscosity in the range of > 0.0005 Pa.s to < 2 Pa.s at a temperature of 25°C, determined according to ASTM D445.

[105] In another embodiment of the composition according to the present invention, the at least one diluent (C) has a viscosity in the range of > 0.0005 Pa.s to < 0.001 Pa.s at a temperature of 25°C, determined according to ASTM D445.

[106] In another embodiment of the composition according to the present invention, wherein ethoxylated trimethylpropane triacrylate (D) has a viscosity in the range of > 0.09 Pa.s to < 0.13 Pa.s at a temperature of 25°C, determined according to ASTM D445.

[107] In another embodiment of the composition according to the present invention, the composition has a viscosity in the range of> 0.01 Pa.s to < 0.05 Pa.s at a temperature of 25°C, determined according to ASTM D445.

[108] In another embodiment of the composition according to the present invention, the composition has a viscosity in the range of> 0.01 Pa.s to < 0.02 Pa.s at a temperature of 25°C, determined according to ASTM D445.

[109] In an embodiment the present invention provides a method of preparing a composition comprising mixing (a) > 10 wt. % to < 70 wt. % of 4-(l-oxo-2 -propenylmorpholine (A); (b) adding > 1 wt. % to < 15 wt. % of at least one acrylate resin (B); (c) > 1 wt. % to < 20 wt. % of a diluent (C) selected from N, N-dimethyl acrylamide and N-(hydroxyethyl)acrylamide; (d) > 5 wt. % to < 60 wt. % of ethoxylated trimethylpropane triacrylate (D); and (e) > 0.1 wt. % to < 5 wt. % of at least one photoinitiator (E) selected from Ethyl phenyl(2,4,6-trimethylbenzoyl)phenyl phosphinate and Bis(eta5-cyclopentadienyl)-bis(2,6-difluoro-3-(pyrrol-l-yl)-phenyl) titanium, and diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO), in a mixer at a speed of 1200 rpm, at a temperature between 25°C to 60 °C, without vacuum, and photo-curing in the range of 320 nm to 550 nm, to obtain the cured resin composition.

[110] In a preferred embodiment, the present invention provides a composition consisting of 4-(l-oxo-2 -propenyl)- morpholine (A) in the range of > 40 wt. % to < 70 wt. %; at least one acrylate resin (B) in the range of > 1 wt. % to < 15 wt. %; a diluent (C) selected from N, N-dimethyl acrylamide and N-(hydroxyethyl)acrylamide in the range of > 1 wt. % to < 20 wt. %; ethoxylated trimethylpropane triacrylate (D) in the range of > 5 wt. % to < 20 wt. %; and at least one photo-initiator (E) selected from ethyl phenyl(2,4,6-trimethylbenzoyl)phenyl phosphinate and bis(eta5-cyclopentadienyl)- bis(2,6-difluoro-3 -(pyrrol- l-yl)-phenyl) titanium, and diphenyl(2,4,6- trimethylbenzoyl)phosphine oxide, in the range of > 0.1 wt. % to < 5 wt. %.

[111] The invention may be further understood by the following non-limiting examples as tabulated below:

Table 1

Table 1 provides different ingredients of composition I and their wt. %.

Table 2

Table 2 provides different ingredients of the composition II and their wt.%.

Table 3

Table 3 provides different ingredients of composition III and their wt. %.

Characteristic properties of composition III of table 3 have been provided in Table 4 below.

Table 4

Table 5

Table 5 provides different ingredients of composition IV and their wt. %.

Characteristic properties of composition IV of Table 5 have been provided in Table 6 below.

Table 6

Table 7

Table 10 provides different ingredients of composition V and their wt. %.

Characteristic properties of composition V of Table 7 have been provided in Table 8 below.

Table 8

Table 9

Table 9 provides different ingredients of composition VI and their wt. %.

Chemical compound

Concentration (% by weight)

Characteristic properties of composition VI of Table 9 have been provided in Table 10 below.

Table 10

Table 11

Table 11 provides different ingredients of composition VII and their wt. %.

Characteristic properties of composition VII of Table 11 have been provided in Table 12 below.

Table 12

Table 13

Table 15 provides different ingredients of composition VIII and their wt. %.

Characteristic properties of composition VIII of Table 13 have been provided in Table 14 below.

Table 14

Table 15 Table 15 provides different ingredients of composition IX and their wt. %.

Characteristic properties of composition IX of Table 15 have been provided in Table 16 below.

Table 16

Table 17 Table 17 provides different ingredients of composition X and their wt. %.

Characteristic properties of composition X of Table 17 have been provided in Table 18 below.

Table 18

The above exemplified compositions are merely reflective of the non-limiting range of inventive resin photocurable resin compositions that are possible based on the claimed inventive photocurable resin composition. The inventive composition has significant mechanical properties as reflected by the tensile strength, impact strength and flexural modulus values. The values are as desired for toughness, flexibility and structural integrity under stress.

The present invention is more ductile and resistant to breakage as reflected from the higher elongation at break values.

The values of properties of the photocured materials achieved from the claimed photocurable resin composition are the desired values for orthodontic material fabrication.

Table 19 below provides the comparative performance, in terms of the mechanical properties, of the representative compositions (III and X) of the present invention and commercially available model resins.

Table 19

It is clearly evident that the presently claimed resin compositions have tensile strength comparable to that of the commercially available resins, and at the same time display better elongation @ break % values that is critical for ductility and for other application purposes. Additionally, the present invention also possesses sufficient flexural modulus values necessary for application in 3-D printing and at the same time achieve enhanced impact strength.

The above results confirm that the presently claimed photocurable resin composition, which is a water washable composition, not only reduces the use of organic solvents for removing the excess uncured resins from the surface of finished 3 D objects, but also offers mechanical properties such as tensile strength and flexural strength comparable to commercially available solvent washable resin compositions and ever better values for elongation @ break %, which makes the present composition suitable for a wide range of applications. [112] Procedure

For 3D printing, samples were formulated as provided the compositions I to X above, in a mixer at a speed of 1200 rpm, at temperature between 25°C to 60°C, without vacuum. A Rapidshape® D40 II (dental fabrication unit) was utilized with a 385 nm LED projector and build plate with dimensions of 64 mm x 40 mm. The layer thickness was kept in the range of 25 pm to 200 pm and the exposure time was in the range of 1.5 to 2.8 seconds/layer. After printing, the parts were rinsed with water and post cured with the 385 Formcure® light for 15- 35 minutes for temperature between 40°C to 60°C and Rapid Shape’s RS Cure® machine with program name FotoDent® model 2, at 385nm. The final printed material was washed with water to remove the uncured resin.

Table 20 below provides printing time, photo-curing time and exposure time for different compositions of the present invention.

Table 20

As mentioned above, the printing time for the printed 3D product obtained using the compositions ofthe present invention is in the range of 19 minutes to 35 minutes, and exposure time is in the range of 1.5 to 2.5 seconds. These values demonstrate the advantages of the compositions of the of the present invention i.e. faster printing, and lesser duration of light exposure (i.e. exposure time) required during curing.

Further, surprisingly the inventors observed that the resin compositions as per the present invention possess a viscosity much lower than the model resin compositions known in the prior art. The viscosity of resin compositions of present invention is in the range from 0.01 Pa.s to 0.05 Pa.s. at a temperature of 25°C, determined according to ASTM D445, as compared to prior art model resin compositions for which viscosity is in the range of 0.2 Pa.s to 0.3 Pa.s.

The present invention is particularly inventive in that the significantly lower viscosity of the claimed resin compositions results in increased speed of printing as reflected in Table 20 and also in the reduction of exposure time i.e. in the range of 0.9 to 2 seconds as compared to the exposure time of resin compositions known in art which fall in the range of 2.8 to 7 seconds as demonstrated in Table 21 below.

Table 21

Comparison between exposure time for compositions of the present invention and commercially available model resin compositions of prior art.

[113] Applications

The applications of the presently claimed resin composition in additive manufacturing is vast especially in processes such as digital light processing (DLP), liquid crystal display (LCD), Polyjet and Stereolithography (SLA) projection technologies.

They can be utilised as a prototyping tool to make end products as well as final functional parts due to their significant mechanical properties and high-quality surface finish.

In Particular, the composition according to the present invention is useful as an inventive resin composition for printing a wide range of 3D objects such as orthodontic appliances, orthodontic models, surgical guides, crowns, bridges, dental splints, and denture bases, retainer and shell aligner and thus useful in orthodontic processes such as denture fabrication and subtractive milling. The present invention provides for such photocurable resin compositions that are compatible with the oral tissue, are non-toxic, and possess sufficient mechanical integrity in the oral environment during orthodontic treatment processes.

Claims

1. A composition comprising:

(A)> 10 wt. % to < 70 wt. % of 4-(l -oxo-2 -propenyl)-morpholine;

(B) > 1 wt. % to < 15 wt. % of at least one acrylate resin;

(C) > 1 wt. % to < 20 wt. % of a diluent selected from N, N-dimethyl acrylamide and N- (hydroxyethyl)acrylamide ;

(D)> 5 wt. % to < 60 wt. % of ethoxylated trimethylpropane triacrylate; and

(E) > 0.1 wt. % to < 5 wt. % of at least one photo-initiator selected from ethyl phenyl(2,4,6-trimethylbenzoyl)phenyl phosphinate and bis(eta5-cyclopentadienyl)- bis(2,6-difluoro-3-(pyrrol-l-yl)-phenyl) titanium, and diphenyl(2,4,6- trimethylbenzoyl)phosphine oxide, wherein wt. % is based on the total weight of composition.

2. The composition as claimed in claim 1, wherein the atleast one acrylate resin (B) comprises one or more of urethane acrylate, difunctional polyurethane acrylate, polyethylene glycol, ethoxylated trimethylpropane triacrylate and water.

3. The composition as claimed in claim 1 or 2, wherein the aliphatic urethane (meth) acrylate is selected from urethane (meth)acrylate, epoxy (meth)acrylate, polyester (meth)acrylate, and (meth)acrylic (meth)acrylate, or a mixture thereof.

4. The composition as claimed in one or more of claims 1 to 3, wherein the ethoxylated trimethylpropane triacrylate (C) is selected from ethoxylated(3)trimethylolpropane triacrylate, ethoxylated(6)trimethylolpropane triacrylate, and ethoxylated(9)trimethylolpropane triacrylate .

5. The composition as claimed in one or more of claims 1 to 4, wherein 4-(l-oxo-2- propenyl)-morpholine (A) is present in an amount in the range of > 20 wt. % to < 70 wt. %, based on the total weight of the composition.

6. The composition according to one or more of claims 1 to 5, wherein 4-(l-oxo-2- propenyl)-morpholine (A) is present in an amount in the range of > 40 wt. % to < 70 wt. %, based on the total weight of the composition.

7. The composition according to one or more of claims 1 to 6, wherein the at least one acrylate resin (B) is present in an amount in the range of > 2 wt. % to < 15 wt. %, based on the total weight of the composition.

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8. The composition according to one or more of claims 1 to 7, wherein the at least one acrylate resin (B) is present in an amount in the range of > 3 wt. % to < 10 wt. %, based on the total weight of the composition.

9. The composition according to one or more of claims 1 to 8, wherein the at least one diluent (C) is present in an amount in the range of > 2 wt. % to < 20 wt. %, based on the total weight of the composition.

10. The composition according to one or more of claims 1 to 9, wherein the at least one diluent (C) is present in an amount in the range of > 3 wt. % to < 5 wt. %, based on the total weight of the composition.

11. The composition according to one or more of claims 1 to 10, wherein ethoxylated trimethylpropane triacrylate (D) is present in an amount in the range of > 5 wt. % to < 50 wt. %, based on the total weight of the composition.

12. The composition according to one or more of claims 1 to 11, wherein ethoxylated trimethylpropane triacrylate (D) is present in an amount in the range of > 5 wt. % to < 20 wt. %, based on the total weight of the composition.

13. The composition according to one or more of claims 1 to 12, wherein the at least one photo-initiator (E) is present in an amount in the range of > 0.5 wt. % to < 5 wt. %, based on the total weight of the composition.

14. The composition according to one or more of claims 1 to 13, wherein the at least one photo-initiator (E) is present in an amount in the range of > 1 wt. % to < 3 wt. %, based on the total weight of the composition.

15. The composition according to one or more of claims 1 to 14, wherein the weight average molecular weight M_w of the at least one acrylate resin (B) is in the range of > 120 g/mol to < 700 g/mol, determined according to ASTM D-4274C.

16. The composition according to one or more of claims 1 to 15, wherein the weight average molecular weight Mw of the at least one acrylate resin (B) is in the range of> 150 g/mol to < 300 g/mol, determined according to ASTM D-4274C.

17. The composition according to one or more of claims 1 to 16, wherein 4-(l-oxo-2- propenyl) -morpholine (A) has a viscosity in the range of > 0.001 Pa.s to < 2 Pa.s at a temperature of 25°C, determined according to ASTM D445.

18. The composition according to one or more of claims 1 to 17, wherein the at least one acrylate resin (B) has a viscosity in the range of > 0.0001 Pa.s to < 1.5 Pa.s at a temperature of 25°C, determined according to ASTM D445.

19. The composition according to one or more of claims 1 to 18, wherein the at least one diluent (C) has a viscosity in the range of > 0.0005 Pa.s to < 2 Pa.s at a temperature of 25°C, determined according to ASTM D445.

20. The composition according to one or more of claims 1 to 19, wherein ethoxylated trimethylpropane triacrylate (D) has a viscosity in the range of > 0.09 Pa.s to < 0. 13 Pa.s at a temperature of 25°C, determined according to ASTM D445.

21. The composition according to one or more of claims 1 to 20, wherein said composition has a viscosity in the range of > 0.01 Pa.s to < 0.05 Pa.s at a temperature of 25°C, determined according to ASTM D445.

22. The composition according to one or more of claims 1 to 21, wherein said composition has a viscosity in the range of > 0.01 Pa.s to < 0.02 Pa.s at a temperature of 25°C, determined according to ASTM D445.

23. The composition according to one or more of claims 1 to 22, wherein said composition consists of 4-(l -oxo-2 -propenyl)- morpholine (A) in the range of > 40 wt. % to < 70 wt. %; at least one acrylate resin (B) in the range of > 1 wt. % to < 15 wt. %; a diluent (C) selected from N, N-dimethyl acrylamide and N-(hydroxyethyl)acrylamide in the range of > 1 wt. % to < 20 wt. %; ethoxylated trimethylpropane triacrylate (D) in the range of > 5 wt. % to < 20 wt. %; and at least one photo-initiator (E) selected from ethyl phenyl(2,4,6-trimethylbenzoyl)phenyl phosphinate and bis(eta5-cyclopentadienyl)- bis(2,6-difluoro-3-(pyrrol-l-yl)-phenyl) titanium, and diphenyl(2,4,6- trimethylbenzoyl)phosphine oxide, in the range of > 0. 1 wt. % to < 5 wt. %.

24. A method of preparing a composition according to one or more of claims 1 to 23, comprising mixing (a) > 10 wt. % to < 70 wt. % of 4-(l -oxo-2 -propenyl)-morpholine (A); (b) adding > 1 wt. % to < 15 wt. % of at least one acrylate resin (B); (c) > 1 wt. % to < 20 wt. % of a diluent (C) selected from N, N-dimethyl acrylamide and N- (hydroxyethyl)acrylamide; (d) > 5 wt. % to < 60 wt. % of ethoxylated trimethylpropane triacrylate (D); and (e) > 0. 1 wt. % to < 5 wt. % of at least one photo-initiator (E) selected from Ethyl phenyl(2,4,6-trimethylbenzoyl)phenyl phosphinate and Bis(eta5- cyclopentadienyl)-bis(2,6-difluoro-3-(pyrrol-l-yl)-phenyl) titanium, diphenyl(2,4,6- trimethylbenzoyl)phosphine oxide, in a mixer at a speed of 1200 rpm, at temperature between 25°C to 60°C, without vacuum, and photo-curing in the range of 320 nm to 550 nm, to obtain the cured resin composition.

25. The method according to claim 24, wherein the cured resin composition is washed with water to obtain the 3D printed object. Use of the composition according to one or more of claims 1 to 23 or the composition which is obtained according to the method of claim 24 or 25 in 3D printing applications using digital light processing (DLP), liquid crystal display (LCD), Polyjet and Stereolithography (SLA) projection technologies. A three-dimensional (3D) object made using the composition of 1 to 23, wherein said object is an orthodontic appliance, retainer and shell aligner.

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