FIELD AND BACKGROUND OF THE INVENTION

The present invention, in some embodiments thereof, relates to three-dimensional printing and, more particularly, but not exclusively, to methods of three-dimensional inkjet printing employing a thermally-curable cyanate ester, and to objects obtained by these methods.

Three-dimensional (3D) inkjet printing is a known process for building three dimensional objects by selectively jetting building material formulation(s), via ink-jet printing head nozzles, onto a printing tray in consecutive layers, according to pre-determined image data. 3D inkjet printing is performed by a layer by layer inkjet deposition of building material formulation(s). Thus, one or more formulations are dispensed in droplets from a dispensing head having a set of nozzles to form layers on a receiving medium. Each of the dispensed layers may then be cured or solidified independently using a suitable methodology, to form solidified or partially solidified layers of the building material.

The building material formulation(s) may be initially liquid and subsequently harden (cured or solidified) to form the required layer shape. The hardening may be effected, for example, by exposing the building material to a curing condition, for example, to a curing energy such as thermal energy (e.g., by heating the building material) or to irradiation (e.g., UV or other photo-irradiation), or to chemical activation, for example, by exposure to a chemical reagent that promotes curing (e.g., an acid or base activation).

The formulations utilized in 3D inkjet printing processes are therefore selected so as to meet the process requirements, namely, exhibiting a suitable viscosity during jetting (thus being non-curable under jetting conditions) and rapid curing or solidification (e.g., within milliseconds or seconds), typically upon exposure to a stimulus (a curing condition) on the receiving medium. The building materials may include modeling materials and support materials, which form the object and optionally the temporary support constructions supporting the object as it is being built, respectively. The modeling material (which may include one or more material(s)) makes up the desired object/s and the support material (which may include one or more material(s)) is used, with or without modeling material elements, to provide support structures for specific areas of the object during building and assure adequate vertical placement of subsequent object layers, e.g., in cases where objects include overhanging features or shapes such as curved geometries, negative angles, voids, and so on.

Both the modeling and support materials are preferably formed from respective formulations which are liquid at the working temperature at which they are dispensed, and which subsequently harden, typically upon exposure to a condition that affects curing of the materials, to form the required layer shape. After printing completion, support structures, if present, are removed to reveal the final shape of the fabricated 3D object.

In order to be compatible with most of the commercially-available print heads utilized in a 3D inkjet printing system, the uncured building material should feature the following characteristics: a relatively low viscosity (e.g., Brookfield Viscosity of up to 50 cps, or up to 35 cps, preferably from 8 to 25 cps) at the working (e.g., jetting) temperature; Surface tension of from about 25 to about 55 Dyne/cm, preferably from about 25 to about 40 Dyne/cm; and a Newtonian liquid behavior and high reactivity to a selected curing condition, to enable fast solidification of the jetted layer upon exposure to a curing condition, of no more than 1 minute, preferably no more than 20 seconds.

The hardened modeling material which forms the final object should preferably exhibit heat deflection temperature (HDT) which is higher than room temperature, in order to assure its usability. Desirably, the hardened modeling material should exhibit HDT of at least 35° C. For an object to be stable at variable conditions, a higher HDT is desirable. In most cases, it is also desirable that the object exhibits relatively high Izod Notched impact, e.g., higher than 50 or higher than 60 J/m.

Various three-dimensional inkjet printing techniques exist and are disclosed in, e.g., U.S. Pat. Nos. 6,259,962, 6,569,373, 6,658,314, 6,850,334, 7,183,335, 7,209,797, 7,225,045, 7,300,619, 7,479,510, 7,500,846, 7,962,237 and 9,031,680, all of the same Assignee, the contents of which are hereby incorporated by reference.

Several additive manufacturing (AM) processes, including three-dimensional inkjet printing, allow additive formation of objects using more than one modeling material, also referred to as “multi-material” AM processes. For example, U.S. Patent Application having Publication No. 2010/0191360, of the present Assignee, discloses a system which comprises a solid freeform fabrication apparatus having a plurality of print heads, a building material supply apparatus configured to supply a plurality of building materials to the fabrication apparatus, and a control unit configured for controlling the fabrication and supply apparatus. The system has several operation modes. In one mode, all print heads operate during a single building scan cycle of the fabrication apparatus. In another mode, one or more of the print heads is not operative during a single building scan cycle or part thereof.

In a 3D inkjet printing process such as Polyjet™ (Stratasys® Ltd., Israel), the building material is selectively jetted from one or more inkjet print heads and deposited onto a fabrication tray in consecutive layers according to a pre-determined configuration as defined by a software file.

U.S. Pat. No. 9,227,365, by the present assignee, discloses methods and systems for solid freeform fabrication of shelled objects, constructed from a plurality of layers and a layered core constituting core regions and a layered shell constituting envelope regions.

The Polyjet™ technology allows control over the position and composition of each voxel (volume pixel), which affords enormous design versatility and digital programming of multi-material structures. Other advantages of the Polyjet™ technology is the very high printing resolution, up to 14 μm layer height, and the ability to print multiple materials simultaneously, in a single object. This multi-material 3D printing process often serves for fabrication of complex parts and structures that are comprised of elements having different stiffness, performance, color or transparency. New ranges of materials, programmed at the voxel level, can be created by the PolyJet™ printing process, using only few starting materials.

International Patent Application Publication No. WO 2013/128452, by the present Assignee, discloses a multi-material approach which involves separate jetting of two components of a cationic polymerizable system and/or a radical polymerizable system, which intermix on the printing tray, leading to a polymerization reaction similar to pre-mixing of the two components before jetting, while preventing their early polymerization on the inkjet head nozzle plate.

Until today, most 3D inkjet methodologies have utilized photopolymerizable materials, and photo-induced curing, typically UV curing, thus narrowing the choice of materials and chemical reactions that can be utilized in this technology. Exemplary photopolymerizable building materials that are currently used in, for example, a “PolyJet™” technology (Stratasys® Ltd., Israel), are acrylic-based materials.

Current PolyJet™ technology offers the capability to use a range of curable (e.g., polymerizable) materials that provide polymeric materials featuring a variety of properties, ranging, for example, from stiff and hard materials (e.g., curable formulations marketed as the Vero™ Family materials) to soft and flexible materials (e.g., curable formulations marketed as the Tango™ and Agilus families), and including also objects made using Digital ABS, which contain a multi-material made of two starting materials (e.g., RGD515™ & RGD535/531™), and simulate properties of engineering plastic. Most of the currently practiced PolyJet™ materials are curable materials which harden or solidify upon exposure to radiation, mostly UV radiation and/or heat, with the most practiced materials being acrylic-based materials.

Acrylic-based materials typically feature non-optimal thermal stability (resistance to thermal deformation). For example, acrylic-based materials such as multi-functional acrylic materials, which feature, when hardened, Tg above 200° C., exhibit high volume shrinkage which often results in curling and/or deformation of the printed object.

Curable materials which feature low volume shrinkage when hardened include, for example, epoxides, polyurethanes, polyamides, benzoxazine and cyanate esters (CE). However, most of these materials are not compatible with the PolyJet™ methodology due to technological restrictions such as high viscosity of the modeling formulation containing same at the inkjet printing heads' working temperature, instability, and toxicity.

Cyanate esters are known to provide polymeric materials featuring high thermal stability and good mechanical properties, are available at various grades, while some cyanate esters also meet the system requirements of PolyJet™. However, cyanate esters are curable only upon application of heat at elevated temperatures (e.g., higher than 180° C.) and are further characterized by slow curing kinetics (minutes scale versus milliseconds scale that typically characterize PolyJet™ materials), and hence their use in PolyJet™ is restricted.

U.S. Pat. Nos. 9,780,440 and 9,873,761 describe a thermosetting resin composition usable in additive manufacturing, formed by a two-stage curing of a curable component that can be photo-curable, peroxide-curable, EB-curable and/or cationic curable and another curable component that is thermally curable, and can include a cyanate ester.

WO 2017/040883 also describes dual cure resin compositions which are cured by exposure to light and then by exposure to heat or microwave irradiation, and their use in additive manufacturing.

Additional background art includes WO2009/013751; WO 2016/063282; WO 2016/125170; WO 2017/134672; WO2017/134673; WO 2017/134674; WO 2017/134676; WO 2017/068590; WO2017/187434; WO2018/055521; and WO2018/055522, all to the present assignee.

SUMMARY OF THE INVENTION

In a search for performing 3D-inkjet printing using modeling material formulations that provide hardened materials that exhibit high thermal stability, while meeting the requirements of the 3D-inkjet printing system and methodology, the present inventors have designed and successfully practiced a formulation system composed of a cyanate ester curable material and an activating agent that promotes its polymerization when exposed to thermal curing, which exhibits a desired viscosity, surface tension and other requirements of a 3D-inkjet printing system, and good printability, while providing objects featuring high thermal stability and other improved mechanical properties. The newly designed formulation system is relatively stable (remains uncured) when jetted, undergoes a partial curing upon being dispensed, and an additional post-printing curing of the obtained green body.

According to an aspect of some embodiments of the present invention there is provided a method of fabricating a three-dimensional object by three-dimensional inkjet printing, the object comprising, in at least a portion thereof, a cyanate ester-containing polymeric network, the method comprising sequentially forming a plurality of layers in a configured pattern corresponding to the shape of the object, thereby fabricating the object,

wherein a formation of at least a portion of the layers comprises dispensing a first modeling material formulation which comprises a first curable material being a thermally-curable cyanate ester and a second modeling material formulation which comprises an activating agent for promoting polymerization of the cyanate ester and is devoid of the first curable material, the at least two modeling material formulations further comprise a second curable material being different from the first curable material, and optionally an agent for promoting hardening of the second curable material,

thereby fabricating the three-dimensional object.

According to some of any of the embodiments described herein, a viscosity of each of the first and second modeling material formulations does not exceed 50 cps, or 40 cps, or 30 cps, at 68° C.

According to some of any of the embodiments described herein, the method further comprises exposing each of the layers to a first curing condition for effecting hardening of the second curable material.

According to some of any of the embodiments described herein, the first curing condition does not comprise application of heat energy.

According to some of any of the embodiments described herein, the first curable material and the first curing condition are such that a degree of polymerization of the cyanate ester is no more than 20%.

According to some of any of the embodiments described herein, the method further comprises exposing the layers to a second curing condition to thereby effect polymerization of the thermally-curable cyanate ester, the second curing condition comprising heat energy.

According to some of any of the embodiments described herein, a formation of the at least a portion of the layers comprises:

repeating the dispensing of the at least two modeling material formulations, and the exposing of each of the layers to the first curing condition; and

collectively exposing the plurality of layers to the second curing condition.

According to some of any of the embodiments described herein, the second curing condition comprises heating the layers at a temperature of at least 80° C., for a time period of at least 1 hour.

According to some of any of the embodiments described herein, the first formulation comprises the first curable material and the agent for promoting polymerization of the second curable material.

According to some of any of the embodiments described herein, the second formulation comprises the second curable material and the agent for promoting polymerization of the cyanate ester.

According to some of any of the embodiments described herein, the second curable material is a photocurable material, preferably a UV-curable material.

According to some of any of the embodiments described herein, the first curing condition comprises irradiation, preferably UV irradiation.

According to some of any of the embodiments described herein, the agent for promoting hardening of the second curable material is a photoinitiator.

According to some of any of the embodiments described herein, the photocurable material features, when hardened, Tg of at least 150° C.

According to some of any of the embodiments described herein, the second curable material is an acrylic material.

According to some of any of the embodiments described herein, the acrylic material comprises a di-functional and/or a multi-functional acrylic material.

According to some of any of the embodiments described herein, the second curable material features, when hardened, Tg higher than 100° C. or higher than 150° C.

According to some of any of the embodiments described herein, the agent for promoting polymerization of the cyanate ester is activatable upon the exposing to the first curing condition and/or to the second curing condition.

According to some of any of the embodiments described herein, the agent for promoting polymerization of the cyanate ester is inactive or is partially active towards promoting polymerization of the cyanate ester prior to the exposing to the first curing condition and/or to the second curing condition.

According to some of any of the embodiments described herein, the at least two formulations further comprise an agent that activates the agent for promoting polymerization of the cyanate ester.

According to some of any of the embodiments described herein, the agent activates the agent for promoting polymerization of the cyanate ester upon exposure to the first curing condition and/or to the second curing condition.

According to some of any of the embodiments described herein, the agent for promoting polymerization of the cyanate ester comprises a nucleophilic group.

According to some of any of the embodiments described herein, the nucleophilic group is thiol.

According to some of any of the embodiments described herein, the nucleophilic group is amine.

According to some of any of the embodiments described herein, the amine is selected from a primary amine, a secondary amine and a combination thereof.

According to some of any of the embodiments described herein, the agent for promoting polymerization of the cyanate ester is an aromatic amine.

According to some of any of the embodiments described herein, the agent for promoting polymerization of the cyanate ester is an aromatic secondary amine.

According to some of any of the embodiments described herein, the second formulation further comprises a metal species that promotes polymerization of the cyanate ester.

According to some of any of the embodiments described herein, the at least two modeling material formulation further comprise an additional curable material which is capable of interacting with the cyanate ester to thereby form a co-polymeric network.

According to some of any of the embodiments described herein, the additional curable material is capable of interacting with the cyanate ester upon exposure to the first and/or the second curing condition.

According to some of any of the embodiments described herein, the additional curable material is or comprises an epoxy-containing curable material.

According to some of any of the embodiments described herein, the additional curable material features a viscosity lower than 1,000, or lower than 500, centipoises, at room temperature.

According to some of any of the embodiments described herein, a weight ratio of the first and the second modeling material formulations in each of the layers ranges from 50:50 to 70:30.

According to some of any of the embodiments described herein, dispensing the first and second formulations is in a voxelated manner, and wherein voxels of the first modeling formulation are interlaced with voxels and the second modeling formulation.

According to some of any of the embodiments described herein, a weight ratio of the voxels of the first modeling formulation and the voxels of the second modeling formulation ranges from 50:50 to 70:30.

According to some of any of the embodiments described herein, the first formulation comprises the first curable material and a photoinitiator and the second formulation comprises a multi-functional acrylic material that features, when hardened, a Tg of at least 150° C., and an aromatic amine.

According to some of any of the embodiments described herein, a total amount of the multi-functional acrylic material ranges from 20 to 40, or from 20 to 30, or from 25 to 30, % by weight, of the total weight of the first and second formulations.

According to some of any of the embodiments described herein, an amount of the aromatic amine ranges from 2 to 4, % by weight of the total weight of the first and second formulations.

According to some of any of the embodiments described herein, an amount of the photoinitiator ranges from 0.5 to 1.5%, by weight, of the total weight of the first and second formulations.

According to some of any of the embodiments described herein, the aromatic amine is an aromatic secondary amine.

According to some of any of the embodiments described herein, the at least two formulations further comprise an additional curable material that is capable of interacting with the cyanate ester.

According to some of any of the embodiments described herein, the first formulation is devoid of the additional curable material.

According to some of any of the embodiments described herein, the additional curable material is included in the second modeling material formulation.

According to some of any of the embodiments described herein, a total amount of the first curable material and the additional curable material, if present, ranges from 50 to 80, or from 60 to 80, or from 60 to 70, %, by weight, of the total weight of the at least two formulations.

According to some of any of the embodiments described herein, forming the plurality of layers further comprises dispensing a third modeling material, the dispensing being configured such that the at least two formulations form an inner region and the third formulation forms an outer region enveloping at least a portion of the inner region.

According to some of any of the embodiments described herein, the third modeling material formulation comprises a third curable material which is curable upon exposure to the first curing condition.

According to some of any of the embodiments described herein, forming the plurality of layers further comprises dispensing a support material formulation.

According to some of any of the embodiments described herein, the method further comprises removing a (hardened, solidified) support material formed of the support material formulation.

According to an aspect of some embodiments of the present invention there is provided a three-dimensional object obtainable by the method as described herein in any of the respective embodiments and any combination thereof.

According to an aspect of some embodiments of the present invention there is provided a formulation system usable in additive manufacturing of a three-dimensional object that comprises, in at least a portion thereof, a cyanate ester-containing polymeric network or material, the formulation system comprising a first modeling material formulation which comprises a first curable material being a thermally-curable cyanate ester, as described herein in any of the respective embodiments and a second modeling material formulation which comprises an activating agent for promoting polymerization of the cyanate ester, as described herein in any of the respective embodiments, and is devoid of the first curable material, the formulation system further comprises a second curable material being different from the first curable material, and optionally an agent for promoting hardening of the second curable material, as these are described herein in any of the respective embodiments and any combination thereof.

According to an aspect of some embodiments of the present invention there is provided a kit comprising the formulation system as described herein in any of the respective embodiments, wherein the first and the second modeling material formulations are separately packaged within the kit.

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.

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.

