TECHNICAL FIELD

The present disclosure broadly relates to articles including a urethane component and at least one monofunctional reactive diluent, and methods of making the articles, such as additive manufacturing methods.

BACKGROUND

The use of stereolithography and inkjet printing to produce three-dimensional articles has been known for a relatively long time, and these processes are generally known as methods of so called 3D printing (or additive manufacturing). In vat polymerization techniques (of which stereolithography is one type), the desired 3D article is built up from a liquid, curable composition with the aid of a recurring, alternating sequence of two steps: in the first step, a layer of the liquid, curable composition, one boundary of which is the surface of the composition, is cured with the aid of appropriate radiation within a surface region which corresponds to the desired cross-sectional area of the shaped article to be formed, at the height of this layer, and in the second step, the cured layer is covered with a new layer of the liquid, curable composition, and the sequence of steps is repeated until a so-called green body (i.e., gelled article) of the desired shape is finished. This green body is often not yet fully cured and must, usually, be subjected to post-curing. The mechanical strength of the green body immediately after curing, otherwise known as green strength, is relevant to further processing of the printed articles.

Other 3D printing techniques use inks that are jetted through a print head as a liquid to form various three-dimensional articles. In operation, the print head may deposit curable photopolymers in a layer-by-layer fashion. Some jet printers deposit a polymer in conjunction with a support material or a bonding agent. In some instances, the build material is solid at ambient temperatures and converts to liquid at elevated jetting temperatures. In other instances, the build material is liquid at ambient temperatures.

One particularly attractive opportunity for 3D printing is in the direct creation of orthodontic clear tray aligners. These trays, also known as aligners or polymeric or shell appliances, are provided in a series and are intended to be worn in succession, over a period of months, in order to gradually move the teeth in incremental steps towards a desired target arrangement. Some types of clear tray aligners have a row of tooth-shaped receptacles for receiving each tooth of the patient's dental arch, and the receptacles are oriented in slightly different positions from one appliance to the next in order to incrementally urge each tooth toward its desired target position by virtue of the resilient properties of the polymeric material. A variety of methods have been proposed in the past for manufacturing clear tray aligners and other resilient appliances. Typically, positive dental arch models are fabricated for each dental arch using additive manufacturing methods such as stereolithography described above. Subsequently, a sheet of polymeric material is placed over each of the arch models and formed under heat, pressure and/or vacuum to conform to the model teeth of each model arch. The formed sheet is cleaned and trimmed as needed and the resulting arch-shaped appliance is shipped along with the desired number of other appliances to the treating professional.

An aligner or other resilient appliance created directly by 3D printing would eliminate the need to print a mold of the dental arch and further thermoform the appliance. It also would allow new aligner designs and give more degrees of freedom in the treatment plan. Exemplary methods of direct printing clear tray aligners and other resilient orthodontic apparatuses are set forth in PCT Publication Nos. WO2016/109660 (Raby et al.), WO2016/148960 (Cinader et al.), and WO2016/149007 (Oda et al.) as well as US Publication Nos. US2011/0091832 (Kim, et al.) and US2013/0095446 (Kitching).

SUMMARY

Existing printable/polymerizable resins tend to be too brittle (e.g., low elongation, short-chain crosslinked bonds, thermoset composition, and/or high glass transition temperature) for a resilient oral appliance such as an aligner. An aligner or other appliance prepared from such resins could easily break in the patient's mouth during treatment, creating material fragments that may abrade or puncture exposed tissue or be swallowed. These fractures at the very least interrupt treatment and could have serious health consequences for the patient. Thus, there is a need for curable liquid resin compositions that are tailored and well suited for creation of resilient articles using 3D printing (e.g., additive manufacturing) method. Preferably, curable liquid resin compositions to be used in the vat polymerization 3D printing process have low viscosity, a proper curing rate, and excellent mechanical properties in both the final cured article. In contrast, compositions for inkjet printing processes need to be much lower viscosity to be able to be jetted through nozzles, which is not the case for most vat polymerization resins.

Urethane (meth)acrylates are a class of raw materials that have interesting properties, for example an elongation of over 100% when cured, and very high toughness. But these resins also have a very high viscosity; at room temperature they are basically solids. Therefore, they only have been used in small amounts in photosensitive resin formulations for vat polymerization or stereolithography, and the properties of these resins are dominated by the other components.

In a first aspect, a photopolymerizable composition is provided. The photopolymerizable composition includes a blend of (a) 30 to 70 wt. %, inclusive, of at least one urethane component and (b) 25 to 70 wt. %, inclusive, of at least one monofunctional reactive diluent. The at least one monofunctional reactive diluent includes at least one monofunctional reactive diluent having a Tgof up to but not including 25 degrees Celsius. The photopolymerizable composition further includes (c) optionally at least one multifunctional reactive diluent in an amount of 1 to 30 wt. %, inclusive, if present, based on the total weight of the photopolymerizable composition; (d) 0.1 to 5 wt. %, inclusive, of at least one initiator; and (e) an optional inhibitor in an amount of 0.001 to 1 wt. %, inclusive, if present, based on the total weight of the photopolymerizable composition.

In a second aspect, an article is provided including a reaction product of a photopolymerizable composition. The photopolymerizable composition includes a blend of (a) 30 to 70 wt. %, inclusive, of at least one urethane component and (b) 25 to 70 wt. %, inclusive, of at least one monofunctional reactive diluent. The at least one monofunctional reactive diluent includes at least one monofunctional reactive diluent having a Tgof up to but not including 25 degrees Celsius. The photopolymerizable composition further includes (c) optionally at least one multifunctional reactive diluent in an amount of 1 to 30 wt. %, inclusive, if present, based on the total weight of the photopolymerizable composition; (d) 0.1 to 5 wt. %, inclusive, of at least one initiator; and (e) an optional inhibitor in an amount of 0.001 to 1 wt. %, inclusive, if present, based on the total weight of the photopolymerizable composition.

In a third aspect, a method of making an article is provided. The method includes (a) providing a photopolymerizable composition and (b) selectively curing the photopolymerizable composition to form an article. Optionally, the method further includes (c) curing unpolymerized urethane component and/or reactive diluent remaining after step (b). The photopolymerizable composition includes a blend of (a) 30 to 70 wt. %, inclusive, of at least one urethane component and (b) 25 to 70 wt. %, inclusive, of at least one monofunctional reactive diluent. The at least one monofunctional reactive diluent includes at least one monofunctional reactive diluent having a Tgof up to but not including 25 degrees Celsius. The photopolymerizable composition further includes (c) optionally at least one multifunctional reactive diluent in an amount of 1 to 30 wt. %, inclusive, if present, based on the total weight of the photopolymerizable composition; (d) 0.1 to 5 wt. %, inclusive, of at least one initiator; and (e) an optional inhibitor in an amount of 0.001 to 1 wt. %, inclusive, if present, based on the total weight of the photopolymerizable composition.

In a fourth aspect, a non-transitory machine readable medium is provided. The non-transitory machine readable medium has data representing a three-dimensional model of an article, when accessed by one or more processors interfacing with a 3D printer, causes the 3D printer to create an article. The article includes a reaction product of a photopolymerizable composition including a blend of (a) 30 to 70 wt. %, inclusive, of at least one urethane component and (b) 25 to 70 wt. %, inclusive, of at least one monofunctional reactive diluent. The at least one monofunctional reactive diluent includes at least one monofunctional reactive diluent having a Tgof up to but not including 25 degrees Celsius. The photopolymerizable composition further includes (c) optionally at least one multifunctional reactive diluent in an amount of 1 to 30 wt. %, inclusive, if present, based on the total weight of the photopolymerizable composition; (d) 0.1 to 5 wt. %, inclusive, of at least one initiator; and (e) an optional inhibitor in an amount of 0.001 to 1 wt. %, inclusive, if present, based on the total weight of the photopolymerizable composition.

In a fifth aspect, a method is provided. The method includes (a) retrieving, from a non-transitory machine readable medium, data representing a 3D model of an article; (b) executing, by one or more processors, a 3D printing application interfacing with a manufacturing device using the data; and (c) generating, by the manufacturing device, a physical object of the article. The article includes a reaction product of a photopolymerizable composition including a blend of (a) 30 to 70 wt. %, inclusive, of at least one urethane component and (b) 25 to 70 wt. %, inclusive, of at least one monofunctional reactive diluent. The at least one monofunctional reactive diluent includes at least one monofunctional reactive diluent having a Tgof up to but not including 25 degrees Celsius. The photopolymerizable composition further includes (c) optionally at least one multifunctional reactive diluent in an amount of 1 to 30 wt. %, inclusive, if present, based on the total weight of the photopolymerizable composition; (d) 0.1 to 5 wt. %, inclusive, of at least one initiator; and (e) an optional inhibitor in an amount of 0.001 to 1 wt. %, inclusive, if present, based on the total weight of the photopolymerizable composition.

In a sixth aspect, another method is provided. The method includes (a) receiving, by a manufacturing device having one or more processors, a digital object comprising data specifying a plurality of layers of an article; and (b) generating, with the manufacturing device by an additive manufacturing process, the article based on the digital object. The article includes a reaction product of a photopolymerizable composition including a blend of (a) 30 to 70 wt. %, inclusive, of at least one urethane component and (b) 25 to 70 wt. %, inclusive, of at least one monofunctional reactive diluent. The at least one monofunctional reactive diluent includes at least one monofunctional reactive diluent having a Tgof up to but not including 25 degrees Celsius. The photopolymerizable composition further includes (c) optionally at least one multifunctional reactive diluent in an amount of 1 to 30 wt. %, inclusive, if present, based on the total weight of the photopolymerizable composition; (d) 0.1 to 5 wt. %, inclusive, of at least one initiator; and (e) an optional inhibitor in an amount of 0.001 to 1 wt. %, inclusive, if present, based on the total weight of the photopolymerizable composition.

In a seventh aspect, a system is provided. The system includes (a) a display that displays a 3D model of an article and (b) one or more processors that, in response to the 3D model selected by a user, cause a 3D printer to create a physical object of an article. The article includes a reaction product of a photopolymerizable composition including a blend of (a) 30 to 70 wt. %, inclusive, of at least one urethane component and (b) 25 to 70 wt. %, inclusive, of at least one monofunctional reactive diluent. The at least one monofunctional reactive diluent includes at least one monofunctional reactive diluent having a Tgof up to but not including 25 degrees Celsius. The photopolymerizable composition further includes (c) optionally at least one multifunctional reactive diluent in an amount of 1 to 30 wt. %, inclusive, if present, based on the total weight of the photopolymerizable composition; (d) 0.1 to 5 wt. %, inclusive, of at least one initiator; and (e) an optional inhibitor in an amount of 0.001 to 1 wt. %, inclusive, if present, based on the total weight of the photopolymerizable composition.

Clear tray aligners and tensile bars made according to at least certain embodiments of this disclosure were found to show low brittleness, high elongation, good resistance to water, and good toughness.

The above summary of the present disclosure is not intended to describe each disclosed embodiment or every implementation of the present disclosure. The description that follows more particularly exemplifies illustrative embodiments. In several places throughout the application, guidance is provided through lists of examples, which examples can be used in various combinations. In each instance, the recited list serves only as a representative group and should not be interpreted as an exclusive list.

