Ink for 3D printing with low print-through depth

Abstract

To provide an ink for use with a three-dimensional (3D) printing system.SOLUTION: There is provided an ink that comprises: based on a total weight of the ink, up to 80 wt.% of an oligomeric curable material; up to 80 wt.% of a monomeric curable material; up to 10 wt.% of a photo-initiator; up to 1 wt.% of a non-curable absorber material; and up to 10 wt.% of one or more additional components, where a total amount of the foregoing components is equal to 100 wt.%. Additionally, the photo-initiator is workable to initiate curing of the oligomeric curable material and / or the monomeric curable material when the photo-initiator is exposed to incident curing radiation having a peak wavelength λ. Moreover, the ink has a penetration depth (Dp), a critical energy (Ec), and a print through depth (DPT) at the wavelength λ of 2×Dp or less.SELECTED DRAWING: None

Description

Cross - Reference to Related Applications

[0001] This application claims priority under 35 U.S.C. § 119 to U.S. Provisional Patent Application No. 62 / 582,631, filed on November 7, 2017, which is hereby incorporated by reference in its entirety.

Technical Field

[0002] The present invention relates to inks for use in three - dimensional (3D) printing systems.

Background Art

[0003] Some commercially available 3D printers or additive manufacturing systems, such as the ProJect™ 3D printers manufactured by 3D Systems of Rock Hill, South Carolina, use inks (also known as build materials) that are jetted through a print head as a liquid to form various 3D objects, articles, or parts. Other 3D printing systems also use inks that are jetted through a print head or dispensed onto a substrate in other ways. In some examples, the ink is solid at ambient temperature and changes to a liquid at a high jetting temperature. In other examples, the ink is liquid at ambient temperature. Further, in some examples, the ink can be cured after being dispensed and / or deposited onto a substrate. Curing can be achieved using a laser or other electromagnetic radiation source.

[0004] Other 3D printers form 3D articles from reservoirs, vats, or containers of fluid inks or build materials, or powder inks or build materials. In some examples, a binder material, or a laser or other energy source, is used to selectively solidify or consolidate layers of the ink or build material in a step - by - step manner to provide a 3D article.

[0005] In a 3D printing system that uses curing radiation, the curing radiation can penetrate deeper into the ink than intended or desired. More specifically, the radiation can penetrate deeper than the portion of the ink that is intended to be cured or solidified as part of the printed article structure. Such an undesirable excessive curing depth can be referred to as "print through" or "print through depth". The occurrence of print through can be problematic for several reasons. First, print through can cause an undesirable "gummy" layer of partially cured ink or build material to form on certain surfaces (such as one or more "down surfaces") of the additive manufacturing system. Second, print through wastes build material. Third, even at best, print through generally requires correction in the build process to account for the fact that a layer or other layers of the printed article will be different from what was intended (e.g., different from the instructions of the corresponding computer-aided design or "CAD" file). For example, such a deviation can be accounted for or corrected when creating or selecting the specific CAD file used to form the printed article. However, such corrections can be inaccurate and lead to part distortion and an overall loss of print accuracy. Finally, when print through occurs, generally more unknown or inaccurate values are introduced into the build process. Moreover, the greater the print through, the greater the introduction of errors and / or uncertainties. Such uncertainties are, of course, undesirable in the additive manufacturing process.

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0006] Accordingly, there is a need for improved methods and inks for 3D printing with improved print through characteristics.

MEANS FOR SOLVING THE PROBLEMS

[0007] In one aspect, an ink for use in a 3D printer is described herein, which in some embodiments can have one or more advantages over conventional inks, particularly radiation-curable inks for use in additive manufacturing. For example, using the inks described herein, articles can be printed with improved accuracy and / or precision. The inks described herein can also reduce the amount of waste associated with the additive manufacturing process. The inks described herein can also, in some instances, provide one or more of the aforementioned advantages without sacrificing the speed of the additive manufacturing process, without sacrificing the energy efficiency of the additive manufacturing process, and / or without sacrificing the desired mechanical properties of the printed article. Further, the inks described herein can be used in a variety of different 3D printers or additive manufacturing systems, such as systems based on stereolithography (SLA), digital light processing (DLP), and multi-jet printing (MJP).

[0008] In some embodiments, the ink for use in the 3D printing system described herein comprises, based on the total weight of the ink, up to 80 wt% oligomeric curable material; up to 80 wt% monomeric curable material; up to 10 wt% photoinitiator; up to 10 wt% non-curable absorber material; and up to 10 wt% one or more additional components. Of course, it should be understood that the total amount of oligomeric curable material, monomeric curable material, photoinitiator, non-curable absorber material, and one or more additional components is equal to 100 wt%. The one or more additional components may include colorants, inhibitors, and / or stabilizers.

[0009] Further, the photoinitiator of the ink described herein is operable to initiate curing of the oligomeric curable material and / or the monomeric curable material when the photoinitiator is exposed to incident curing radiation having a Gaussian distribution of wavelengths and a peak wavelength λ. Further, the ink has a penetration depth (D p ) at wavelength λ and a critical energy (E c) Term D p and E c The ink is also 2xD p Less than or equal to 1.5xD p Print-through depth (D PT ) Term D PT Further, in some examples, the inks described herein may be PT D at wavelength λ corresponding to the value p Value and E c For example, in some embodiments, the inks described herein have a density of at least 10 or at least 15 (μm cm 2 DP / E in units of ) / mJ c In some cases, the ratio (μm cm 2 D in units of ) / mJ p / E c The ratio is between 10 and 50, between 10 and 25, between 10 and 15, between 10 and 13, between 15 and 50, between 15 and 30, between 15 and 25, or between 19 and 25. As described in more detail below, it is believed that inks having such properties can provide improved print performance, including through improved interaction with incident curing radiation.

[0010] In some exemplary embodiments, the inks described herein have a D of 60 to 100 μm. p and 2 to 4 mJ / cm 2 E c In another example, the ink has a D p is 101 to 150 μm, and the E of the ink c is 4~20mJ / cm 2 In yet another example, the ink D p is 151 to 200 μm, and the E of the ink c is 8~15mJ / cm 2 It is.

[0011] As described further below, the amount of photoinitiator and / or non-curable absorber material included in the ink, in combination with the other components of the ink, determines the desired D p , Ec and / or D PT Values can be selected to obtain. In some embodiments, for example, the inks described herein include up to 5 wt% photoinitiator and up to 2 wt% or up to 1 wt% non-curable absorber material. Further, in some examples, the total absorbance of the non-curable absorber material at wavelength λ is about 0.1 to 10 times the total absorbance of the photoinitiator at wavelength λ. Further, in some examples, both the non-curable absorber material and the photoinitiator of the inks described herein have an absorption peak within 30 nm of wavelength λ.

[0012] In another aspect, a method of forming a 3D article by additive manufacturing is described herein. In some embodiments, such a method includes providing an ink as described herein and selectively curing a portion of the ink using incident curing radiation having a Gaussian distribution of wavelengths and a peak wavelength at wavelength λ. For example, in some examples, the ink has a print-through depth (D p at the following wavelength λ PT ), and / or a D 2 ratio in units of (μm cm p / E c between 10 and 50. Further, in some embodiments of the methods described herein, the ink is selectively cured according to preselected computer-aided design (CAD) parameters, and D p corresponds to the voxel depth of the CAD parameters.

[0013] Further, in some examples, the step of providing the ink includes selectively depositing a layer of the ink in a fluid state onto a substrate to form a three-dimensional article. Alternatively, in other embodiments, the step of providing the ink includes holding the ink in a fluid state within a container, and the step of selectively curing a portion of the ink includes selectively applying curing radiation to the ink within the container to solidify or consolidate at least a portion of a first fluid layer of the ink, thereby forming a first solidified or consolidated layer that defines a first cross-section of the article. Such a method may further include raising or lowering the first solidified layer to provide a second fluid layer of the ink onto the surface of the fluid ink within the container, and selectively applying curing radiation to the ink within the container to solidify at least a portion of the second fluid layer of the ink, thereby forming a second solidified layer that defines a second cross-section of the article, wherein the first cross-section and the second cross-section are joined to each other in the z-direction. As further described below, the foregoing steps may be repeated any desired number of times necessary to complete the 3D article.

[0014] In yet another aspect, a printed 3D article is described herein. Such an article can be formed from any ink and using any method described herein. Such a printed 3D article, in some cases, has superior accuracy compared to some other 3D articles.

[0015] These and other embodiments are described in more detail in the following detailed description.

DETAILED DESCRIPTION OF THE INVENTION

[0016] The embodiments described herein can be more readily understood by reference to the following detailed description and examples. However, the elements, apparatus, and methods described herein are not limited to the specific embodiments presented in the detailed description and examples. It should be recognized that these embodiments are merely illustrative examples of the principles of the present disclosure. Numerous modifications and adaptations will be readily apparent to those skilled in the art without departing from the spirit and scope of the present disclosure.

[0017] Furthermore, it should be understood that all ranges disclosed herein include all sub-ranges subsumed therein. For example, the described range "1.0 to 10.0" should be interpreted to include any and all sub-ranges starting with a minimum value of 1.0 or more and ending with a maximum value of 10.0 or less, such as 1.0 to 5.3, or 4.7 to 10.0, or 3.6 to 7.9. Similarly, the described range "1 to 10" is considered to include any and all sub-ranges starting with a minimum value of 1 or more and ending with a maximum value of 10 or less, such as 1 to 5, or 4 to 10, or 3 to 7, or 5 to 8, etc.

[0018] Also, all ranges disclosed herein should be considered to include the endpoints of the range, unless specifically stated otherwise. For example, a range of "between 5 and 10", "from 5 to 10" or "5 - 10" should generally be considered to include the endpoints 5 and 10.

[0019] Furthermore, when the phrase "up to" is used in relation to an amount or quantity, that amount should be understood to be at least a detectable amount or quantity. For example, a substance present in an amount "up to" a particular amount can be present in an amount from a detectable amount up to (and including) that particular amount.

[0020] Terms such as "three-dimensional printing system", "three-dimensional printer", "print", etc. generally describe various solid freeform manufacturing techniques for creating three-dimensional articles or objects by stereolithography, selective deposition, jetting, fused deposition modeling, multi-jet modeling, and other additive manufacturing techniques now known or that may become known in the art for manufacturing three-dimensional objects using build materials or inks.

[0021] I. Ink for 3D printing In one aspect, an ink for use in a 3D printer is described herein. In some embodiments, the ink described herein comprises up to 80 wt% oligomeric curable material, up to 80 wt% monomeric curable material, up to 10 wt% photoinitiator, up to 10 wt% non-curable absorber material, and up to 10 wt% one or more additional components. The foregoing weight percentages are based on the total weight of the ink. Further, as will be understood by those skilled in the art, the total amount of the oligomeric curable material, monomeric curable material, photoinitiator, non-curable absorber material, and one or more additional components is equal to 100 wt%. Further still, the photoinitiator is operable to initiate curing of the oligomeric curable material and / or the monomeric curable material when the photoinitiator is exposed to incident curing radiation having a peak wavelength λ. That is, the photoinitiator is a photoinitiator for curing of the oligomeric curable material and / or the monomeric curable material. Further, the ink has a penetration depth (D p ) and a critical energy (E c ) at wavelength λ. The ink also has a print-through depth (D p ) at a wavelength λ of 2xD PT or less.

[0022] As will be understood by those skilled in the art, D PT refers to the difference between the total cure depth and the layer thickness, where the "total cure depth" refers to the depth at which any curing or polymerization of the ink occurs in response to the incident curing radiation. The "layer thickness" refers to the thickness of the region where "complete" curing or polymerization or curing of the ink occurs in response to the incident curing radiation. Such "complete" curing refers to the maximum curing brought about by the incident radiation. For example, "complete" curing corresponds to 80 - 100% curing, 80 - 95% curing, 80 - 90% curing, 85 - 100% curing, 85 - 99% curing, 85 - 95% curing, 90 - 100% curing, 90 - 99% curing, or 90 - 95% curing, where the percentage (%) is based on the total number of available curable moieties (functional groups).

[0023] In some examples, the ink described herein is 1.5xD p or less, 1.3xDp The following, 1.2xD p The following, or 1.1xD p D at the following wavelength λ PT has. In some examples, D at wavelength λ PT is 0.8xD p and 2xD p between, 0.8xD p and 1.5xD p between, 0.9xD p and 2xD p between, 0.9xD p and 1.8xD p between, 0.9xD p and 1.5xD p between, 0.9xD p and 1.3xD p between, 1xD p and 2xD p between, 1xD p and 1.7xD p between, 0.1xD p and 1.5xD p between, 1.1xD p and 2xD p between, 1.1xD p and 1.5xD p between, 1.2xD p and 2xD p between, 1.2xD p and 1.8xD p between, 1.3xD p and 2xD p between, 1.3xD p and 1.7xD p , or 1.5xD p and 2xD p is between.

[0024] Although not intended to be bound by theory, such D PTInks having values are believed to provide improved consistency, accuracy, and resolution when used as build materials in additive manufacturing processes such as those described herein. The inks described herein are further believed to reduce waste of build materials and / or reduce or eliminate the occurrence of undesirable "build-up" or "rubbery" residues or layers on the surface of the additive manufacturing system after completion of the additive manufacturing process. Such residues can be particularly undesirable on the so-called "down surface" of a 3D printing system.

[0025] Further, in some examples, the inks described herein have a D PT value at a wavelength λ corresponding to the above D p value and an E c value. For example, in some examples, the inks described herein have a D 2 / E p ratio in units of at least 10 or at least 15 (μm cm c ). In some embodiments, the D 2 / E p ratio in units of (μm cm c ) / mJ is between 10 and 50, between 10 and 25, between 10 and 15, between 10 and 13, between 15 and 50, between 15 and 30, between 15 and 25, or between 19 and 25. Such a D p / E c value can provide a D PT value corresponding to the above value.

[0026] For example, in one "regime", the D p of the ink is 60 - 100 μm and the E c of the ink is 2 - 4 mJ / cm 2 . In other exemplary embodiments, the D p of the ink is 101 - 150 μm and the E c of the ink is 4 - 20 mJ / cm 2 . In yet other examples, the D p of the ink is 151 - 200 μm and the E c of the ink is 8 - 15 mJ / cm2 is as follows.

[0027] Furthermore, in some embodiments, the inks described herein use the ink as a build material to enable energy-efficient and / or rapid additive manufacturing c value. For example, in some examples, the inks described herein have an E 2 of 60 mJ / cm or less, 50 mJ / cm 2 or less, 40 mJ / cm 2 or less, 20 mJ / cm 2 or less, or 10 mJ / cm 2 or less. In some examples, the inks described herein have an E c of 1 to 30 mJ / cm, 1 to 20 mJ / cm 2 1 to 15 mJ / cm, 1 to 10 mJ / cm 2 1 to 15 mJ / cm, 2 to 25 mJ / cm 2 2 to 20 mJ / cm, 2 to 15 mJ / cm 2 2 to 10 mJ / cm, 2 to 15 mJ / cm 2 2 to 10 mJ / cm, 2 to 15 mJ / cm 2 2 to 10 mJ / cm, 2 to 15 mJ / cm 2 2 to 10 mJ / cm, 2 to 15 mJ / cm 2 2 to 15 mJ / cm, 2 to 15 mJ / cm 2 of E c has.

[0028] Similarly, the inks described herein, in some examples, have a D p value that enables high-resolution and / or rapid additive manufacturing using the ink. In some examples, for example, the inks described herein have a D p of 50 to 200 μm, 60 to 150 μm, 70 to 150 μm, or 70 to 100 μm.

[0029] Furthermore, the parameter or property D p E c and D PTIt is to be understood that these are the structural parameters or properties of the inks described herein. Discussion of the "structural" or "compositional" nature of these values can be found, for example, in Chapter 4 of Paul F. Jacobs, Rapid Prototyping & Manufacturing: Fundamentals of Stereolithography (Society of Manufacturing Engineers, McGraw-Hill, 1992) (1st Edition) (hereinafter referred to as "Jacobs" in this specification). As will be understood by those skilled in the art, the value D p is the penetration depth of the ink defined as the depth of the ink that results in a reduction in irradiance to a level equal to 1 / e of the surface irradiance, where e is the base of the natural logarithm (equal to 2.7182818...). As described on page 86 of Jacobs, E c is the critical energy that is the energy required to obtain the gelation point of the ink. Further, as further explained in Jacobs (pages 86-89), the metric E c is equal to the intercept of the working curve corresponding to a semi-log plot of the cured depth on the vertical axis and the logarithm of the maximum radiation exposure on the horizontal axis. E c is specified at the intercept where the cured depth is zero.

[0030] The amount of photoinitiator and / or non-curable absorber material included in the inks described herein, in combination with the other components of the ink, can be selected to obtain the desired D p , E c , and / or D PT values. However, in some examples, the desired D p , E c , and / or D PTIt should be understood that the type and / or amount of other components of the ink, such as oligomeric and monomeric curable materials, can be changed without substantially changing the value. For example, in some instances, changing the type and / or amount of oligomeric and monomeric curable materials (within the currently disclosed types and ranges of amounts) will affect the D p and E c values, and / or the D PT value by no more than 5%, 4%, 3%, 2%, or 1%. More specifically, such minimal changes in the D p and E c values, and / or the D PT value can be obtained when components of the ink other than photoinitiators and non-curable absorber materials (such as oligomeric curable materials and / or monomeric curable materials) do not absorb (or refract or reflect) light of wavelength λ, or absorb (or refract or reflect) it minimally. Alternatively, such minimal changes in the D p and E c values, and / or the D PT value can also be obtained when components of the ink other than photoinitiators and non-curable absorber materials (such as oligomeric curable materials and / or monomeric curable materials) absorb (or refract or reflect) light of wavelength λ to approximately the same extent, regardless of which exact component species or amounts (within the range of currently disclosed species and amount options) are selected. That is, in the context of the compositions and methods described herein, the components of the ink described herein other than photoinitiators and non-curable absorber materials can be essentially (and generally) optically "spectator" species at wavelength λ, and thus these "spectator" species do not substantially affect the D p and E c values, and / or the D PT value of the overall ink. Thus, as will be described in more detail below, oligomeric and monomeric curable materials can be changed (with respect to the exact species and / or amounts) as desired for each ink such that the exact species and / or amounts used for each ink have similar light absorption profiles and / or refractive indices.

[0031] For the purposes of reference in this specification, a "non-curable absorber material" is a material or species that cannot be cured or is not substantially curable by the curing radiation described herein and that absorbs at least a portion of the curing radiation without causing substantial curing of other components of the ink. Thus, a "non-curable" absorber material can also be referred to as a "non-curing" or "non-reactive" absorber material. Further, a non-curable or non-curing absorber material described herein that is "not substantially" curable or that does not cause "substantial" curing is understood to convert less than 5%, less than 1%, less than 0.5%, or less than 0.1% of the absorbed curing radiation photons into a curing event (or use in a curing event). For example, in some embodiments, a non-curable (or non-curing) absorber material described herein can convert less than 2%, less than 1%, less than 0.5%, or less than 0.1% of the absorbed photons into free radical species, which can initiate or participate in (meth)acrylate polymerization or other curing processes.

[0032] It should be further understood that the non-curable or non-curing absorber materials described herein can still be polymerization "spectator" (i.e., non-polymerizable or non-polymerization initiating) species that "compete" with the ink photoinitiator with respect to absorption of photons of the incident curing radiation. Thus, in some examples, the non-curable absorber material and the photoinitiator of the ink described herein have substantially overlapping photon absorption profiles, particularly in the region of the electromagnetic spectrum corresponding to or including the peak wavelength λ described above. In some examples, for instance, both the non-curable absorber material and the photoinitiator have an absorption peak within 30 nm, within 20 nm, within 15 nm, within 10 nm, or within 5 nm of the wavelength λ.

[0033] However, it should be understood that the non-curable absorber material and photoinitiator described herein need not have the same absorbance, optical density, attenuation coefficient, and / or molar extinction coefficient at wavelength λ or any other arbitrary specific wavelength. Rather, the non-curable absorber material and photoinitiator can have different absorbances, optical densities, attenuation coefficients, and / or molar extinction coefficients at wavelength λ as well as at other wavelengths.

[0034] Furthermore, in some examples, the amounts of the photoinitiator and non-curable absorber material included in the inks described herein are selected based on the similarity or difference in the absorbance, optical density, attenuation coefficient, and / or molar extinction coefficient of those species, including at wavelength λ. For example, in some examples, the amounts of the photoinitiator and non-curable absorber material are selected to provide a desired ratio of the total absorbance of the various species at wavelength λ and / or to provide the desired D PT 、D p 、or D p / E c value. In some such embodiments, the total absorbance of the non-curable absorber material at wavelength λ is about 0.1 to 10 times, about 0.2 to 5 times, or about 0.5 to 2 times the total absorbance of the photoinitiator at wavelength λ, and the "total absorbance" of the various species at wavelength λ is understood to be the amount (moles) of each species multiplied by its molar extinction coefficient at wavelength λ.

[0035] Furthermore, it should be noted that wavelength λ can be any wavelength that is not inconsistent with the objectives of the present disclosure. For example, in some examples, λ is a wavelength in the ultraviolet (UV) or visible region of the electromagnetic spectrum. In some examples, the peak wavelength λ is in the infrared (IR) region of the electromagnetic spectrum. In some embodiments, wavelength λ is between 250 nm and 400 nm, or between 300 nm and 385 nm. In other examples, wavelength λ is between 600 nm and 800 nm, or between 900 nm and 1.3 μm. However, the exact wavelength λ is not particularly limited.

[0036] Any non-curable absorber material that does not conflict with the objectives of the present disclosure may be used in the inks described herein. For example, in some embodiments, the non-curable absorber material includes polycyclic aromatic compounds such as pyrene. The non-curable absorber material may be a "dye" having an absorption profile consistent with the above description. Such a "dye" may more particularly be a hydrophobic or oil-soluble dye. For example, in some instances, the non-curable absorber material is a yellow dye such as an oil-soluble yellow dye. Other yellow dyes may also be used. In other instances, the non-curable absorber material includes blue or green dyes such as KEYPLAST dyes commercially available from Keystone, Inc. Further, although less preferred, in some embodiments, the non-curable absorber material may have a broader absorption profile rather than a narrower absorption profile. For example, in such cases, the non-curable absorber material includes a black dye. In some embodiments, carbon black or another carbon allotrope may also be used as the non-curable absorber material.

[0037] As described above, the non-curable absorber material component can be present in the inks described herein in an amount up to 10% by weight, based on the total weight of the ink. For example, in some examples, the ink comprises up to 7%, up to 5%, up to 3%, up to 2%, or up to 1% by weight of the non-curable absorber material. In some embodiments, the ink comprises from 0.01 to 10%, from 0.01 to 5%, from 0.01 to 3%, from 0.01 to 2%, from 0.01 to 1%, from 0.05 to 10%, from 0.05 to 5%, from 0.05 to 3%, from 0.05 to 1%, from 0.1 to 10%, from 0.1 to 7%, from 0.1 to 5%, from 0.1 to 3%, from 0.1 to 1%, from 0.5 to 10%, from 0.5 to 7%, from 0.5 to 5%, from 0.5 to 2%, from 0.5 to 1%, from 1 to 10%, from 1 to 7%, from 1 to 5%, or from 1 to 3% by weight of the non-curable absorber material, based on the total weight of the ink. In some particularly preferred embodiments, the amount of the non-curable absorber material is about 1% by weight or less. For example, in some preferred embodiments, the inks described herein comprise from 0.0001 to 1%, from 0.0001 to 0.5%, from 0.0001 to 0.1%, from 0.001 to 1%, from 0.001 to 0.5%, from 0.001 to 0.1%, from 0.001 to 0.05%, from 0.01 to 1%, from 0.01 to 0.5%, from 0.01 to 0.1%, or from 0.01 to 0.05% by weight of the non-curable absorber material. The use of a relatively small amount of the non-curable absorber material, such as the amounts described above, can be particularly advantageous in some instances for maintaining or achieving the desired mechanical properties of an article formed from a given ink, since the "inert" non-curable absorber material not only serves as a material optically relevant during curing, but can also serve as a non-reactive "filler".

[0038] The inks described herein also include one or more photoinitiators. Any photoinitiator that is not inconsistent with the purposes of the present disclosure can be used in the inks described herein. In some embodiments, for example, the photoinitiator is an α-cleavage type (single molecule decomposition process) photoinitiator or a hydrogen abstraction type photosensitizer-tertiary amine synergist that is operable to absorb light between about 250 nm and about 400 nm, or between about 300 nm and about 385 nm, to generate free radicals. Examples of α-cleavage type photoinitiators are Irgacure 184 (CAS 947-19-3), Irgacure 369 (CAS 119313-12-1), and Irgacure 819 (CAS 162881-26-7). An example of a photosensitizer-amine combination is the combination of Darocur BP (CAS 119-61-9) and diethylaminoethyl methacrylate.

[0039] Furthermore, in some examples, the photoinitiator includes benzoins such as benzoin, benzoin ethers (e.g., benzoin methyl ether, benzoin ethyl ether, and benzoin isopropyl ether, etc.), benzoin phenyl ether, and benzoin acetate; acetophenones such as acetophenone, 2,2-dimethoxyacetophenone, and 1,1-dichloroacetophenone; benzyl, benzyl ketals (e.g., benzyldimethyl ketal and benzyldiethyl ketal, etc.); anthraquinones such as 2-methylanthraquinone, 2-ethylanthraquinone, 2-tert-butylanthraquinone, 1-chloroanthraquinone, and 2-amylanthraquinone; triphenylphosphine; benzoylphosphine oxides (e.g., 2,4,6-trimethylbenzoyldiphenylphosphine oxide (Lucirin TPO), etc.); benzophenones such as benzophenone and 4,4'-bis(N,N'-dimethylamino)benzophenone; thioxanthone and xanthone; acridine derivatives; phenazine derivatives; quinoxaline derivatives or 1-phenyl-1,2-propanedione; 2-O-benzoyloxime; 1-aminophenyl ketone; or 1-hydroxy phenyl ketones such as 1-hydroxycyclohexyl phenyl ketone, phenyl 1-hydroxyisopropyl ketone, and 4-isopropylphenyl 1-hydroxyisopropyl ketone.

[0040] The photoinitiator may also include a photoinitiator operable for use with a HeCd laser radiation source, and such photoinitiators include acetophenone, 2,2-dialkoxybenzophenone, and 1-hydroxy phenyl ketones (e.g., 1-hydroxy cyclohexyl phenyl ketone or 2-hydroxy isopropyl phenyl ketone (=2-hydroxy-2,2-dimethyl acetophenone), etc.). Further, in some examples, the photoinitiator includes a photoinitiator operable for use with an Ar laser radiation source, and such photoinitiators include benzyl ketals such as benzyldimethyl ketal. In some embodiments, the photoinitiator includes an α-hydroxy phenyl ketone, benzyldimethyl ketal or 2,4,6-trimethyl benzoyl diphenyl phosphine oxide, or a mixture thereof.

[0041] Another class of photoinitiators that can be included in the inks described herein includes ionic dye-counterion compounds that can absorb actinic radiation to generate free radicals for polymerization initiation. Some ionic dye-counterion compounds, and their mode of operation, are disclosed in European Patent Application Publication No. 0223587, U.S. Patent Nos. 4,751,102, 4,772,530, and 4,772,541. The photoinitiator described herein may be a cationic photoinitiator such as a triphenylsulfonium photoinitiator.

[0042] The photoinitiator may be present in the inks described herein in any amount not inconsistent with the purposes of the present disclosure. In some embodiments, the photoinitiator is present in the ink in an amount up to about 10 wt%, up to about 8 wt%, up to about 7 wt%, up to about 5 wt%, up to about 3 wt%, or up to about 2 wt% based on the total weight of the ink. In some examples, the photoinitiator is present in an amount of about 0.1 to 10 wt%, 0.1 to 5 wt%, 0.1 to 3 wt%, 0.1 to 2 wt%, 0.5 to 5 wt%, 0.5 to 3 wt%, 0.5 to 2 wt%, 1 to 10 wt%, 1 to 8 wt%, 1 to 5 wt%, 1 to 4 wt%, or 1 to 3 wt%. In some particularly preferred embodiments, the inks described herein contain a photoinitiator in an amount up to about 5 wt%. For example, in some examples, the photoinitiator component is present in the ink in an amount of 0.1 to 5 wt%, or 0.5 to 5 wt%, or even more preferably 1 to 5 wt%, 2 to 5 wt%, or 2 to 4 wt% based on the total weight of the ink.

[0043] Furthermore, it should be understood that the amounts (weight percentages) described in the immediately preceding paragraph refer to photoinitiators that are non-oligomeric and non-polymeric. That is, the above amounts refer to "monomer" or "molecular" photoinitiators having, for example, a molecular weight of less than 400. However, it should also be understood that oligomeric or polymeric photoinitiators can also be used in the inks and methods described herein. However, in such cases (when an oligomeric or polymeric photoinitiator is used), the above amounts (weight percentages) should be calculated without considering the weight of the oligomeric or polymeric portion of the oligomeric or polymeric photoinitiator. That is, to determine the total amount (weight percentage) of the oligomeric or polymeric photoinitiator present in the ink, the calculation (specifically, the numerator of the fraction) should be based only on the molecular weight of the photoactive portion of the photoinitiator (for the purposes of the present disclosure) and not on the molecular weight of the remaining portion or repeating units of the oligomeric or polymeric photoinitiator.

[0044] Furthermore, as described above, the amount of photoinitiator and the amount of non-curable absorber material can be selected with reference to each other. For example, in some examples, the inks described herein include up to 5 wt% photoinitiator and up to 1 wt% non-curable absorber material. In other examples, the inks described herein include up to 4 wt% photoinitiator and up to 0.5 wt% non-curable absorber material, or up to 5 wt% photoinitiator and up to 0.05 wt% non-curable absorber material. In some particularly preferred embodiments, the inks described herein include at least 1 wt% photoinitiator in combination with an amount of non-curable absorber material as described herein, such as an amount of up to 0.5 wt% non-curable absorber material. As further described herein, a composition with too little photoinitiator (especially compared to the amount of non-curable absorber) cannot sufficiently react to the curing radiation within distance D p and as a result, sufficient polymerization does not occur within the spatial region defined by D p . In some examples, the preferred (weight) ratio of photoinitiator to non-curable absorber material is 1 or more, 5 or more, or 10 or more. In some embodiments, the preferred (weight) ratio of photoinitiator to non-curable absorber material is 1-200, 1-100, 5-100, 1-200, 10-150, 10-100, 25-200, 25-100, 50-200, 50-150, or 50-100 (where the weight of the photoinitiator is the numerator and the weight of the non-curable absorber material is the denominator). Such ratios can, in some examples, result in the desired curing effect (e.g., achievement of the desired D p , E c , or D p / E c ratio) while minimizing the amount of other non-functional or non-curing "filler" materials with respect to the formation of the cured polymer network.

[0045] Furthermore, as noted above, the relative amounts of photoinitiator and non-curable absorber material can be based, at least in part, on the respective total (optical) absorbances of the photoinitiator and non-curable absorber material at wavelength λ (as opposed to being based only on weight percent or mass). For example, if the non-curable absorber material absorbs relatively weakly at wavelength λ, a relatively large amount (in moles or weight percent) of non-curable absorber material may be required to achieve the desired “photon competition” with the photoinitiator compared to a situation where the non-curable absorber material absorbs relatively strongly at wavelength λ (in which case a relatively small amount (in moles or weight percent) of non-curable absorber material may be required to achieve the same desired “photon competition”). Thus, in some embodiments, the ratio of the photoinitiator to the non-curable absorber material described herein (such as the weight-based ratio above) is used when the photoinitiator and non-curable absorber material have absorbance (or optical density) values within a factor of two of each other at wavelength λ. Additionally, in some examples, the ratio described in the previous paragraph (such as a ratio of photoinitiator to non-curable absorber material in the range of 10 to 100) is a ratio of total absorbances at wavelength λ rather than a weight-based ratio.

[0046] Here, with respect to other specific components of the inks described herein, the inks described herein may include one or more oligomeric curable materials and / or one or more monomeric curable materials. For reference purposes herein, curable materials include chemical species that include one or more curable or polymerizable moieties. For reference purposes herein, a "polymerizable moiety" includes a moiety that can polymerize or cure to provide a printed 3D article or object. Such polymerization or curing can be carried out in any manner that is not inconsistent with the purposes of the present disclosure. In some embodiments, for example, polymerization or curing includes irradiating the polymerizable or curable material with electromagnetic radiation having sufficient energy to initiate a polymerization or crosslinking reaction. For example, in some instances, ultraviolet (UV) radiation can be utilized. Thus, in some instances, the polymerizable moiety includes a photopolymerizable or photocurable moiety such as a UV polymerizable moiety. In some embodiments, the curable materials described herein are photopolymerizable or photocurable at wavelengths in the range of about 300 nm to about 400 nm or about 320 nm to about 380 nm. Alternatively, in other instances, the curable materials are photopolymerizable at visible wavelengths of the electromagnetic spectrum. Further, the curing radiation generally includes curing radiation having a peak wavelength of λ as described above.

[0047] Further, in some instances, the polymerization reaction includes a free radical polymerization reaction such as a reaction between unsaturation points that includes ethylenic unsaturation points. Other polymerization reactions may be used. As will be understood by those skilled in the art, the polymerization reactions used to polymerize or cure the curable materials described herein may include the reaction of a plurality of "monomers" or chemical species having one or more functional groups or moieties that can react with each other to form one or more covalent bonds.

[0048] A non-limiting example of a polymerizable moiety of the curable materials described herein is an ethylenic unsaturated moiety such as a vinyl moiety, an allyl moiety, or a (meth)acrylate moiety, and the term "(meth)acrylate" includes acrylate or methacrylate, or mixtures or combinations thereof.

[0049] The "oligomer" species contained in the oligomer-curable materials described herein are themselves polymers or oligomers and have a relatively high molecular weight or relatively high viscosity. These species can also undergo additional polymerization, such as via one or more unsaturation points described herein. The population of oligomer species in the oligomer-curable materials described herein can have various molecular structures and / or formulas across the population (which can be represented, for example, by a particular mass of urethane acrylate having a non-uniform molecular weight distribution or by a particular mass of ethoxylated polyethylene glycol having a distribution of ethylene glycol units and / or a distribution of ethoxy units within the population). The weight average molecular weight of the oligomer-curable materials described herein can generally range from 400 to 10,000, from about 600 to 10,000, from about 500 to 7,000, or from about 500 to 5,000.

[0050] In contrast to the "oligomer" species, the "monomer" species contained in the monomer-curable materials described herein are not themselves polymers or oligomers and have a relatively low molecular weight or relatively low viscosity. The "monomer" species contained in the monomer-curable materials can have a consistent or clearly defined molecular structure and / or formula across the population (which can be represented, for example, by a particular mass of ethoxylated (4) bisphenol A diacrylate or by a particular mass of the curable monomers described above). Further, in some embodiments, the monomer-curable materials described herein have a viscosity of 500 centipoise (cP) or less at 25 °C when measured in accordance with ASTM D2983, while the "oligomer" curable materials have a viscosity of 1000 cP or more at 25 °C when measured in accordance with ASTM D2983.

[0051] A non-limiting example of the polymerizable moiety of the oligomer-curable materials or monomer-curable materials described herein is an ethylenically unsaturated moiety such as a vinyl moiety, an allyl moiety, or a (meth)acrylate moiety, and the term "(meth)acrylate" includes acrylate or methacrylate, or mixtures or combinations thereof.

[0052] Furthermore, the oligomerizable materials and monomerizable materials described herein can include monofunctional, difunctional, trifunctional, tetrafunctional, pentafunctional, or higher-functionalizable species. For purposes of reference herein, "monofunctional" functionalizable species include chemical species that include one functionalizable or polymerizable moiety. Similarly, "difunctional" functionalizable species include chemical species that include two functionalizable or polymerizable moieties; "trifunctional" functionalizable species include chemical species that include three functionalizable or polymerizable moieties; "tetrafunctional" functionalizable species include chemical species that include four functionalizable or polymerizable moieties; "pentafunctional" functionalizable species include chemical species that include five functionalizable or polymerizable moieties. Thus, in some embodiments, the monofunctional monomerizable materials of the inks described herein include mono(meth)acrylates, the difunctional monomerizable materials of the inks described herein include di(meth)acrylates, the trifunctional monomerizable materials of the inks described herein include tri(meth)acrylates, the tetrafunctional monomerizable materials of the inks described herein include tetra(meth)acrylates, and the pentafunctional monomerizable materials of the inks described herein include penta(meth)acrylates. Other monofunctional, difunctional, trifunctional, tetrafunctional, and pentafunctional monomerizable materials can also be used.

[0053] In addition, the monofunctional, difunctional, trifunctional, tetrafunctional, and pentafunctional monomerizable materials can, in some instances, include relatively low molecular weight species, i.e., monomer species, or relatively high molecular weight species, i.e., oligomer species.

[0054] Generally, any oligomer-curable material or combination of oligomer-curable materials that is not inconsistent with the objectives of the present disclosure can be used in the inks described herein. For example, in some examples, oligomer-curable materials suitable for use in the inks described herein have a similar wavelength absorption profile and / or refractive index that includes the absorption profile and / or refractive index described above in relation to a wavelength λ or a wavelength close to wavelength λ (within 30 nm). In some examples, the oligomer-curable materials described herein have a photon absorption profile that is outside of or does not include the curing radiation having a peak wavelength λ.

[0055] In some examples, the oligomer-curable material includes a polyester (meth)acrylate oligomer, a urethane (meth)acrylate oligomer, or an epoxy (meth)acrylate oligomer. Further, in some embodiments, the oligomer-curable materials described herein include an aliphatic polyester urethane acrylate oligomer and / or an acrylate amine oligomer resin such as EBECRYL 7100. In some examples, the oligomer-curable materials described herein include polypropylene glycol mono(meth)acrylate or polyethylene glycol mono(meth)acrylate. In some embodiments, the oligomer-curable material includes a monofunctional aliphatic urethane (meth)acrylate. Further, in some examples, the oligomer-curable material includes diacrylates and / or dimethacrylate esters of aliphatic, cycloaliphatic or aromatic diols, including polyethylene glycol, ethoxylated or propoxylated neopentyl glycol, ethoxylated or propoxylated bisphenol A, ethoxylated or propoxylated bisphenol F, ethoxylated or propoxylated bisphenol S, ethoxylated or propoxylated 1,1,1-trimethylolpropane tri(meth)acrylate, or ethoxylated or propoxylated glycerol tri(meth)acrylate. The oligomer material may also include cycloaliphatic epoxies.

[0056] Some non-limiting examples of commercially available oligomer curable materials useful in some embodiments described herein include the following: alkoxylated tetrahydrofurfuryl acrylate commercially available under the trade name SR 611 from SARTOMER; monofunctional urethane acrylate commercially available under the trade name GENOMER 1122 from RAHN USA; aliphatic urethane diacrylate commercially available under the trade name EBECRYL 8402 from ALLNEX; multifunctional acrylate oligomer commercially available under the trade name BR-952 from DYMAX; aliphatic polyether urethane acrylate commercially available under the trade name BR-371S from DYMAX. Other commercially available oligomer curable materials may be used.

[0057] The urethane (meth)acrylates suitable for use in the inks described herein can, in some examples, typically be prepared by known methods such as reacting a hydroxyl-terminated urethane with acrylic acid or methacrylic acid to obtain the corresponding urethane (meth)acrylate, or reacting an isocyanate-terminated prepolymer with a hydroxyalkyl acrylate or methacrylate to obtain a urethane (meth)acrylate. Suitable processes are disclosed, inter alia, in European Patent Application Publications Nos. 114982 and 133908. The weight average molecular weight of such (meth)acrylate oligomers can, in some examples, be from about 400 to 10,000, or from about 500 to 7,000. Urethane (meth)acrylates are also commercially available under the product names CN980, CN981, CN975 and CN2901 from Sartomer, or under the product name BR-741 from BOMAR Specialties. In some embodiments described herein, the urethane (meth)acrylate oligomer has a viscosity in the range of from about 140,000 centipoise (cP) to about 160,000 cP at about 50 °C, or from about 125,000 cP to about 175,000 cP at about 50 °C, as measured by a method compliant with ASTM D2983. In some examples, the urethane (meth)acrylate oligomer has a viscosity in the range of from about 100,000 cP to about 200,000 cP at about 50 °C, or from about 10,000 cP to about 300,000 cP at about 50 °C, as measured by a method compliant with ASTM D2983.

[0058] The oligomerizable material can be present in the inks described herein in any amount that is not inconsistent with the purposes of the present disclosure. In some examples, the oligomerizable material is present in the ink in an amount of up to about 80 wt%, up to about 70 wt%, up to about 60 wt%, up to about 50 wt%, up to about 40 wt%, up to about 30 wt%, or up to about 20 wt% in total, based on the total weight of the ink. In some examples, the inks described herein contain from about 10 to 80 wt% or 10 to 70 wt% of the oligomerizable material, based on the total weight of the ink. In some embodiments, the ink contains from about 10 to 60 wt%, 10 to 50 wt%, 10 to 40 wt%, 10 to 30 wt%, 10 to 20 wt%, 15 to 40 wt%, 15 to 30 wt%, 20 to 60 wt%, 20 to 50 wt%, 20 to 40 wt%, 30 to 60 wt%, 30 to 50 wt%, or 40 to 60 wt% of the oligomerizable material, based on the total weight of the ink. In some particularly preferred embodiments, the amount of the oligomerizable material is 60 wt% or less, based on the total weight of the ink. In some examples, for instance, the inks described herein contain from 10 to 60 wt%, 10 to 55 wt%, 15 to 60 wt%, 15 to 55 wt%, 15 to 50 wt%, 20 to 60 wt%, 20 to 55 wt%, 20 to 50 wt%, 25 to 60 wt%, 25 to 55 wt%, 25 to 50 wt%, 30 to 60 wt%, 30 to 55 wt%, 30 to 50 wt%, 35 to 60 wt%, 35 to 55 wt%, 40 to 60 wt%, 40 to 55 wt%, 40 to 50 wt%, 45 to 60 wt%, 45 to 55 wt%, or 50 to 60 wt% of the oligomerizable material, based on the total weight of the ink.

[0059] Furthermore, it is understood that when the amount of the oligomer curable material in the ink described herein exceeds 60% by weight, relatively low molecular weight oligomers are generally used and generally preferred. For example, if the ink described herein contains 65-80% by weight of the oligomer curable material, the average molecular weight (e.g., weight average molecular weight) of the oligomer curable material can be less than 1000 rather than exceeding 1000. Alternatively, in other examples, when the amount of the oligomer curable material in the ink described herein exceeds 60% by weight, an oligomer curable material having a weight average molecular weight higher than 1000 can be used on condition that the ink is used at a high temperature during the additive manufacturing process so that the viscosity of the ink is similar to that of the other inks described in this paragraph.

[0060] Furthermore, any monomer curable material or combination of monomer curable materials that is not inconsistent with the objectives of the present disclosure can be used as the monomer curable material component. For example, in some examples, the monomer curable material suitable for use in the inks described herein has a similar wavelength absorption profile and / or refractive index, including the absorption profile and / or refractive index described above in relation to a wavelength λ or a wavelength close to wavelength λ (within 30 nm). In some examples, the monomer curable material described herein has a photon absorption profile that is outside or does not include the curing radiation having the peak wavelength λ.

[0061] In some examples, the monomer-curable materials of the inks described herein include one or more (meth)acrylates, such as, for example, one or more monofunctional (meth)acrylates, difunctional (meth)acrylates, trifunctional (meth)acrylates, tetrafunctional (meth)acrylates, and / or pentafunctional (meth)acrylates. In some embodiments, for example, the monomer-curable material includes methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, n-decyl (meth)acrylate, n-dodecyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2- or 3-hydroxypropyl (meth)acrylate, 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 2- or 3-ethoxypropyl (meth)acrylate, tetrahydrofurfuryl methacrylate, isobornyl (meth)acrylate, 2-(2-ethoxyethoxy)ethyl acrylate, cyclohexyl methacrylate, 2-phenoxyethyl acrylate, glycidyl acrylate, isodecyl acrylate, 2-phenoxyethyl (meth)acrylate, lauryl methacrylate, or a combination thereof. In some embodiments, the monomer-curable material includes one or more of allyl acrylate, allyl methacrylate, triethylene glycol di(meth)acrylate, tricyclodecane dimethanol diacrylate, and cyclohexane dimethanol diacrylate.Furthermore, in some examples, the monomer-curable material includes aliphatic, cycloaliphatic, or aromatic diol diacrylates and / or dimethacrylate esters, including 1,3- or 1,4-butanediol, neopentyl glycol, 1,6-hexanediol, diethylene glycol, triethylene glycol, tetraethylene glycol, tripropylene glycol, 1,4-dihydroxymethylcyclohexane, 2,2-bis(4-hydroxycyclohexyl)propane or bis(4-hydroxycyclohexyl)methane, hydroquinone, 4,4'-dihydroxybiphenyl, bisphenol A, bisphenol F, or bisphenol S. The monomer-curable materials described herein may also include 1,1-trimethylolpropane tri(meth)acrylate, pentaerythritol monohydroxy tri(meth)acrylate, dipentaerythritol monohydroxy penta(meth)acrylate, and / or bis(trimethylolpropane) tetra(meth)acrylate. Further, in some examples, the monomer-curable material may include ethoxylated or propoxylated species such as ethoxylated or propoxylated neopentyl glycol, ethoxylated or propoxylated bisphenol A, ethoxylated or propoxylated bisphenol F, ethoxylated or propoxylated bisphenol S, ethoxylated or propoxylated 1,1,1-trimethylolpropane tri(meth)acrylate, or ethoxylated or propoxylated glycerol tri(meth)acrylate. In some examples, the monomer-curable material includes cycloaliphatic epoxies.

[0062] Additional non-limiting examples of commercially available monomer-curable materials useful in some embodiments described herein include the following: isobornyl acrylate (IBOA) commercially available under the trade name SR 506 from Sartomer; isobornyl methacrylate commercially available under the trade name SR 423A from Sartomer; triethylene glycol diacrylate commercially available under the trade name SR 272 from Sartomer; triethylene glycol dimethacrylate commercially available under the trade name SR 205 from Sartomer; tricyclodecane dimethanol diacrylate commercially available under the trade name SR 833S from Sartomer; tris(2-hydroxyethyl) isocyanurate triacrylate commercially available under the trade name SR 368 from Sartomer; 2-phenoxyethyl acrylate commercially available under the trade name SR 339 from Sartomer; ethoxylated (3 mol) bisphenol A diacrylate commercially available under the trade name SR 349 from Sartomer; cyclic monofunctional acrylate commercially available under the trade name GENOMER 1120 from Rahn USA; and dipentaerythritol pentaacrylate commercially available under the trade name SR 399LV from Sartomer. Other commercially available monomer-curable materials can also be used.

[0063] The monomer-curable material can be present in the inks described herein in any amount that is not inconsistent with the purposes of the present disclosure. In some examples, the monomer-curable material is present in an amount of up to about 80 wt%, up to about 70 wt%, up to about 60 wt%, or up to about 50 wt% in total, based on the total weight of the ink. In some examples, the inks described herein contain from about 0 to 80 wt% or from 10 to 80 wt% of a monomer-curable material, based on the total weight of the ink. In some embodiments, the ink contains from about 0 to 75 wt%, 0 to 70 wt%, 0 to 60 wt%, 0 to 50 wt%, 0 to 40 wt%, 0 to 35 wt%, 0 to 30 wt%, 0 to 25 wt%, 0 to 20 wt%, 0 to 15 wt%, 0 to 10 wt%, 0 to 5 wt%, 10 to 75 wt%, 10 to 70 wt%, 10 to 60 wt%, 10 to 50 wt%, 10 to 40 wt%, 10 to 35 wt%, 10 to 30 wt%, 10 to 25 wt%, 10 to 20 wt%, 20 to 80 wt%, 20 to 60 wt%, or 20 to 40 wt% of a monomer-curable material, based on the total weight of the ink.

[0064] Regarding possible additional components of the inks described herein, the inks described herein can further include one or more photosensitizers. Generally, such sensitizers can be added to the ink to enhance the effectiveness of one or more photoinitiators that may be present. In some examples, the sensitizer includes isopropylthioxanthone (ITX) or 2-chlorothioxanthone (CTX).

[0065] The sensitizer can be present in the ink in any amount that is not inconsistent with the purposes of the present disclosure. In some embodiments, the sensitizer is present in an amount in the range of from about 0.1 wt% to about 2 wt% or from about 0.5 wt% to about 1 wt%, based on the total weight of the ink. However, in other examples, the inks described herein exclude sensitizers as described above.

[0066] Regarding another possible component of the ink described herein, the ink described herein can also include at least one colorant that may be different from the non-curable absorber material of the ink. Such a colorant of the ink described herein can be a particulate colorant such as a particulate pigment or a molecular colorant such as a molecular dye. Any such particulate or molecular colorant that does not conflict with the objectives of the present disclosure can be used. In some examples, for instance, the colorant of the ink includes inorganic pigments such as TiO 2 and / or ZnO. In some embodiments, the colorant of the ink includes colorants for use in RGB, sRGB, CMY, CMYK, L * a * b * , or Pantone® color schemes. Further, in some examples, the particulate colorant described herein has an average particle size of less than about 5 μm or less than about 1 μm. In some examples, the particulate colorant described herein has an average particle size of less than about 500 nm, for example, less than about 400 nm, less than about 300 nm, less than about 250 nm, less than about 200 nm, or less than about 150 nm. In some examples, the particulate colorant has an average particle size of about 50 - 5000 nm, about 50 - 1000 nm, or about 50 - 500 nm.

[0067] The colorant can be present in the ink described herein in any amount that does not conflict with the objectives of the present disclosure. In some examples, the colorant is present in the ink in an amount up to about 2 wt%, or in an amount of about 0.005 - 2 wt%, 0.01 - 2 wt%, 0.01 - 1.5 wt%, 0.01 - 1 wt%, 0.01 - 0.5 wt%, 0.1 - 2 wt%, 0.1 - 1 wt%, 0.1 - 0.5 wt%, or 0.5 - 1.5 wt% based on the total weight of the ink.

[0068] Furthermore, in some embodiments, the inks described herein further comprise one or more polymerization inhibitors and / or stabilizers. The polymerization inhibitors can be added to the ink to provide additional thermal stability to the composition. Any polymerization inhibitor that is not inconsistent with the objectives of the present disclosure can be used. Furthermore, the polymerization inhibitor can delay or reduce the polymerization rate and / or prevent polymerization from occurring for a certain period or “induction time” until the polymerization inhibitor is consumed. Further, in some examples, the polymerization inhibitors described herein are “additive” inhibitors. The inhibitors described herein may also be “chain transfer type” inhibitors. In some examples, suitable polymerization inhibitors include methoxyhydroquinone (MEHQ).

[0069] In some embodiments, the stabilizer comprises one or more antioxidants. The stabilizer may include any antioxidant that is not inconsistent with the objectives of the present invention. In some examples, suitable antioxidants include various aryl compounds such as butylated hydroxytoluene (BHT), which can also be used as polymerization inhibitors in some of the embodiments described herein. More generally, a single species may serve both as a stabilizer and a polymerization inhibitor. In some examples, it is also possible to use multiple inhibitors and / or stabilizers, where different inhibitors and / or stabilizers have different effects and / or function synergistically.

[0070] The polymerization inhibitor and / or stabilizer can be present in the ink in any amount that is not inconsistent with the objectives of the present disclosure. In some embodiments, the polymerization inhibitor is present in an amount in the range of about 0.01 wt% to about 2 wt% or about 0.05 wt% to about 1 wt% based on the total weight of the ink. Similarly, in some examples, the stabilizer is present in the ink in an amount in the range of about 0.1 wt% to about 5 wt%, about 0.5 wt% to about 4 wt%, or about 1 wt% to about 3 wt% based on the total weight of the ink.

[0071] In some embodiments, the inks described herein can include a viscosity modifier. Non-limiting examples of viscosity modifiers include saturated fatty acids or combinations of saturated fatty acids, or oils such as vegetable oils. The inks described herein may include up to 5 wt%, up to 3 wt%, up to 1 wt%, up to 0.5 wt%, or up to 0.1 wt% of a viscosity modifier that is not inconsistent with the purposes of the present disclosure.

[0072] The inks described herein can exhibit various desirable properties. For example, the inks described herein can have any freezing point, melting point, and / or other phase transition temperatures that are not inconsistent with the purposes of the present disclosure. In some examples, the ink has a freezing point and a melting point that are compatible with the temperatures used in some 3D printing systems, such as 3D printing systems designed to be used with phase change inks. In some embodiments, the freezing point of the ink is higher than about 40°C. In some examples, for instance, the ink has a freezing point centered around a temperature in the range of about 45°C to about 55°C or about 50°C to about 80°C. In some examples, the ink has a freezing point lower than about 40°C or lower than about 30°C.

[0073] Furthermore, in some embodiments described herein, the ink exhibits a sharp freezing point or other phase transition. In some examples, for instance, the ink freezes within a narrow temperature range, such as in the range of about 1 to 10°C, about 1 to 8°C, or about 1 to 5°C. In some embodiments, an ink having a sharp freezing point freezes within a temperature range of X ± 2.5°C, where X is the temperature at the center of the freezing point (e.g., X = 65°C).

[0074] Furthermore, in some examples, the inks described herein are fluids at the jetting temperatures faced in some 3D printing systems. Further still, in some embodiments, the ink solidifies as soon as it is deposited on a surface during the manufacture of a three-dimensionally printed article or object. Alternatively, in other examples, the ink remains substantially fluid upon deposition on a surface. The solidification of the ink, in some embodiments, occurs through a phase change of the ink or an ink component. The phase change can include a phase change from liquid to solid or from liquid to semi-solid. Further still, in some examples, the solidification of the ink includes an increase in the viscosity of the ink, such as an increase in viscosity from a low viscosity state to a high viscosity state. The solidification of the ink can also occur by curing of the ink.

[0075] Furthermore, in some embodiments, the inks described herein have a viscosity profile that matches the requirements and parameters of one or more 3D printing systems, such as MJP or SLA systems, when uncured. For example, in some examples, the inks described herein have a dynamic viscosity of 1600 centipoise (cP) or less, 1200 cP or less, or 800 cP or less at 30°C. In a preferred embodiment, the inks described herein have a dynamic viscosity of 500 cP or less at 30°C when measured in accordance with ASTM standard D2983 (e.g., using a Brookfield model DV-II+ viscometer). In some examples, the inks described herein exhibit a dynamic viscosity of about 200 to 1600 cP, about 200 to 1200 cP, about 200 to 800 cP, about 200 to 500 cP, or about 200 to 400 cP at 30°C when measured in accordance with ASTM standard D2983.

[0076] The inks described herein can also exhibit various desirable properties in the cured state, in addition to those described above. As used herein, "cured" inks include inks containing curable materials or polymerizable components that are at least partially cured, i.e., at least partially polymerized and / or crosslinked. For example, in some instances, the cured ink is at least about 70% polymerized or crosslinked, or at least about 80% polymerized or crosslinked. In some embodiments, the cured ink is at least about 85%, at least about 90%, at least about 95%, at least about 98%, or at least 99% polymerized or crosslinked. In some examples, the cured ink is about 80% to about 99% polymerized or crosslinked.

[0077] In some examples, the inks described herein, when cured, have an elongation at break of about 10 - 70%, about 10 - 60%, about 15 - 50%, or about 20 - 50% when measured in accordance with ASTM D638. Further, the cured inks described herein can, in some examples, have a tensile strength of about 40 - 70 MPa, about 40 - 60 MPa, or about 45 - 55 MPa when measured in accordance with ASTM D638. Additionally, the cured inks described herein can, in some embodiments, have a tensile modulus of about 1800 - 2100 MPa, about 1900 - 2100 MPa, or about 1950 - 2050 MPa when measured in accordance with ASTM D638. Also, the cured inks described herein can have an impact resistance of 1 - 4 ft·lb / in (about 53 - 214 J / m) (notched), 1 - 3 ft·lb / in (about 53 - 160 J / m) (notched), or 1 - 2 ft·lb / in (about 53 - 107 J / m) (notched) when measured in accordance with ASTM D256. Finally, in some examples, the cured inks described herein have a flexural modulus of 2000 - 2500 MPa, 2100 - 2400 MPa, or 2100 - 2200 MPa when measured in accordance with ASTM D790.

[0078] Furthermore, in some examples, the inks described herein can exhibit a plurality of the above properties when cured. For example, in some embodiments, the ink, when cured, has a tensile strength of about 40 to 70 MPa when measured in accordance with ASTM D638; an impact resistance of 1 to 4 ft·lb / in (about 53 to 214 J / m) when measured in accordance with ASTM D256; and an elongation at break of about 10 to 70% when measured in accordance with ASTM D638.

[0079] The inks described herein can be manufactured by any method that is not inconsistent with the objectives of the present disclosure. In some embodiments, for example, the method for preparing the inks described herein includes the steps of mixing the components of the ink, melting the mixture, and filtering the melted mixture. The melting of the mixture is, in some examples, carried out at a temperature of about 75°C or in the range of about 75°C to about 85°C. In some embodiments, the inks described herein are manufactured by placing all of the components of the ink in a reaction vessel and heating the resulting mixture to a temperature in the range of about 75°C to about 85°C while stirring. The heating and stirring are continued until the mixture reaches a substantially homogenized molten state. Generally, the molten mixture can be filtered while in a fluid state to remove large undesirable particles that may interfere with the jetting or ejection or other printing processes. The filtered mixture is then cooled to ambient temperature and stored until ready to be used in a 3D printing system.

[0080] The inks described herein can include, have, or exhibit the above-described combinations of components and / or properties, provided that the combinations of components and / or properties do not conflict with the principles and objects of the present invention. For example, in some preferred embodiments, the inks described herein include, based on the total weight of the ink, up to 60 wt% oligomeric curable material; up to 80 wt% monomeric curable material; up to 5 wt% photoinitiator; up to 1 wt% non-curable absorber material; and up to 10 wt% of one or more additional components, where the total amount of the oligomeric curable material, monomeric curable material, photoinitiator, non-curable absorber material, and one or more additional components is equal to 100 wt%; the photoinitiator is operable to initiate curing of the oligomeric curable material and / or monomeric curable material when the photoinitiator is exposed to incident curing radiation having a Gaussian distribution of wavelengths and a peak wavelength λ; the ink has a penetration depth (D p ) and a critical energy (E c ) at wavelength λ; the ink has a print-through depth (D p ) at wavelengths λ of 2×D PT or less, or a D 2 / E p value of 10 - 50 (μm cm c / mJ). In other preferred embodiments, the inks described herein include, based on the total weight of the ink, 40 - 60 wt% oligomeric curable material, 40 - 60 wt% monomeric curable material, 1 - 5 wt% photoinitiator%, and 0.001 - 0.1 wt% non-curable absorber material, where the total amount of the oligomeric curable material, monomeric curable material, photoinitiator, non-curable absorber material, and one or more additional components is equal to 100 wt%; the photoinitiator is operable to initiate curing of the oligomeric curable material and / or monomeric curable material when the photoinitiator is exposed to incident curing radiation having a Gaussian distribution of wavelengths and a peak wavelength λ; the ink has a penetration depth (D p ) and a critical energy (E c ) at wavelength λ; the ink has a print-through depth (D p ) at wavelengths λ of 1.5×D PT or less; and E c is 15 mJ / cm2 is less than. In yet another preferred embodiment, the ink described in this paragraph further has one, at least two, or in particularly preferred embodiments all of the following characteristics: (1) D in units of (μm cm 2 ) / mJ is between 10 and 50; (2) the weight ratio of the photoinitiator to the non-curable absorber material is between 5 and 100; (3) D p / E c ratio is between 5 and 100; (3) D p is 200 μm or less or 100 μm or less. Inks having such properties can be particularly preferred for improving the accuracy and / or precision of stereolithography while maintaining the normal (or faster) speed of the stereolithography process, maintaining (or improving) the normal energy efficiency (with respect to the energy required for curing) of stereolithography, and / or maintaining (or improving) the desired mechanical properties of the printed article. It should be understood that the above "normal" or "maintained" properties are compared to inks that are comparable to the inks of the present invention according to the present disclosure / preferred embodiments but are not within the measurement criteria of the present invention identified above. Similarly, it should be further understood that the "desired mechanical properties" can vary based on a given selection of ink components. Again, however, inks such as the above preferred inks can provide the advantages contemplated in the present disclosure without substantially impairing the mechanical properties provided by the ink if they are outside the scope of the parameters of the present invention described herein. For example, an ink formulated to have high elongation or tensile strength (e.g., through the selection of specific monomer and / or oligomer curable materials) can maintain such elongation or tensile strength despite including a photoinitiator and a non-curable absorbent material in the formulation in a manner consistent with the above preferred embodiments (e.g., the elongation or tensile strength can be achieved using the preferred inks described herein, where the elongation or tensile strength does not deviate by more than 5% from the desired elongation or tensile strength value using the desired value as the denominator for calculating the percent deviation).

[0081] II. Method for forming 3D articles In another aspect, a method of forming or "printing" a 3D article or object by additive manufacturing is described herein. The method of forming a 3D article or object described herein may include forming a 3D article from multiple layers of the inks described herein in a layer-by-layer fashion. The method of forming an object by additive manufacturing may include forming the object in a manner other than a layer-by-layer fashion. Any of the inks described above in Section I can be used in the methods described herein.

[0082] For example, in some examples, the method described herein provides an ink having a penetration depth (D p ) and a critical energy (E c ) at a wavelength λ; and further includes selectively curing a portion of the ink using incident curing radiation having a Gaussian distribution of wavelengths and a peak wavelength of wavelength λ, the ink having a print-through depth (D p ) at wavelengths λ of 2xD PT or less and / or a D 2 / E p ratio in units of (μm cm c ) / mJ of 0 to 50. Further, in some embodiments described herein, the ink is selectively cured according to preselected computer-aided design (CAD) parameters, and D p corresponds to the voxel depth of the CAD parameters. Further, in some examples, one or more layers of the inks described herein have a thickness of from about 10 μm to about 100 μm, from about 10 μm to about 80 μm, from about 10 μm to about 50 μm, from about 20 μm to about 100 μm, from about 20 to about 80 μm, or from about 20 to about 40 μm. Other thicknesses are possible.

[0083] Furthermore, it should be understood that the method of printing a 3D article described herein can include, for example, MJP or SLA 3D printing methods. For example, in some examples, the MJP method of printing a 3D article includes selectively depositing the layers of ink described herein in a fluid state onto a substrate such as a build pad of a 3D printing system. Further, in some embodiments, the method described herein further includes supporting at least one of the layers of ink with a support material. Any support material that does not conflict with the objectives of the present disclosure can be used.

[0084] The method described herein can also include curing the layers of ink, including using the above-described curing radiation (such as curing radiation having a peak wavelength λ). Further, curing can include polymerizing one or more polymerizable moieties or functional groups of one or more components of the ink. In some examples, the deposited layer of ink is cured prior to the deposition of another or adjacent layer of ink. Further, in some embodiments, the curing of one or more layers of deposited ink is performed by exposing the one or more layers to electromagnetic radiation such as UV light, visible light, or infrared light as described above.

[0085] Further details regarding various methods, including "material deposition" methods (such as MJP) or "vat polymerization" methods (such as SLA), are described below.

[0086] A. Material deposition method In the material deposition method, one or more layers of ink described herein are selectively deposited onto a substrate and further cured. Curing of the ink can occur after the selective deposition of one layer, each layer, some layers, or all layers of the ink.

[0087] In some examples, the inks described herein are selectively deposited in a fluid state onto a substrate such as a build pad of a 3D printing system. Selective deposition may include, for example, depositing the ink according to preselected CAD parameters. For example, in some embodiments, a drawing of a CAD file corresponding to the desired 3D article to be printed is created and sliced into a sufficient number of horizontal slices. Thereafter, the ink is selectively deposited layer by layer according to the horizontal slices of the drawing of the CAD file to print the desired 3D article. A "sufficient" number of horizontal slices is, for example, the number required to successfully print the desired 3D article in order to manufacture it accurately and precisely.

[0088] Furthermore, in some embodiments, a preselected amount of the inks described herein is heated to an appropriate temperature and ejected through one or more print heads of a suitable inkjet printer to form a layer on a print pad within a print chamber. In some examples, each layer of ink is deposited according to preselected CAD parameters. A print head suitable for depositing the ink is, in some embodiments, a piezoelectric print head. Additional print heads suitable for depositing the inks and support materials described herein are commercially available from various inkjet printer manufacturing manufacturers. For example, in some examples, print heads from Xerox, Hewlett Packard, or Ricoh can be used.

[0089] Furthermore, in some embodiments, the inks described herein remain substantially fluid when deposited. Alternatively, in other examples, the ink exhibits a phase change immediately upon deposition and / or solidifies immediately upon deposition. Additionally, in some examples, the temperature of the printing environment can be controlled such that the ejected droplets of ink solidify upon contact with the receiving surface. In other embodiments, the droplets of ejected ink do not solidify upon contact with the receiving surface and remain substantially in a fluid state. Further, in some examples, after each layer is deposited, the deposited material is flattened and cured using electromagnetic radiation (e.g., UV light, visible light, or infrared light) prior to the deposition of the next layer. Optionally, several layers may be deposited before flattening and curing, or after depositing and curing a number of layers, one or more additional layers may be deposited and then flattened without curing. Flattening corrects the thickness of one or more layers before curing of the material by flattening the dispensed material to remove excess material and creating a uniformly smooth exposed surface or flat upward-facing surface on the printer's support platform. In some embodiments, flattening is achieved using a wiper device, such as a roller that can rotate in a reverse direction in one or more print directions but not in one or more other print directions. In some examples, the wiper device includes a roller and a wiper that removes excess material from the roller. Additionally, in some examples, the wiper device is heated. It should be noted that in some embodiments, the viscosity of the ejected inks described herein prior to curing is desirably sufficient to hold its shape and not receive excessive viscous resistance from the flattening device.

[0090] Furthermore, when used, the support material can be deposited in a manner compliant with what was described above for the ink. The support material can be deposited, for example, according to preselected CAD parameters such that the support material is adjacent to or continuous with one or more layers of the ink. The droplets of the ejected support material solidify or coagulate upon contact with the receiving surface in some embodiments. In some examples, the deposited support material also undergoes flattening, curing, or both flattening and curing. Any support material that does not conflict with the objectives of the present disclosure can be used.

[0091] The laminated deposition of the ink and the support material can be repeated until the 3D article is formed. In some embodiments, the method of printing a 3D article further includes removing the support material from the ink.

[0092] Curing of the ink can occur after selective deposition of one layer of ink, each layer of ink, some layers of ink, or all layers of ink necessary to print the desired 3D article. In some embodiments, partial curing of the deposited ink is performed after selective deposition of one layer of ink, each layer of ink, some layers of ink, or all layers of ink necessary to print the desired 3D article. For reference purposes herein, an ink that is "partially cured" is one that can undergo further curing. For example, a partially cured ink is polymerized or crosslinked up to about 30%, or up to about 50%. In some embodiments, a partially cured ink is polymerized or crosslinked up to about 60%, up to about 70%, up to about 80%, up to about 90%, or up to about 95%.

[0093] Partial curing of the deposited ink may include irradiating the ink with an electromagnetic radiation source or photocuring the ink (including using the curing radiation described above). For example, any electromagnetic radiation source that does not conflict with the objectives of the present disclosure can be used, such as an electromagnetic radiation source that emits ultraviolet rays, visible light, or infrared rays. For example, in some embodiments, the electromagnetic radiation source may emit light having a wavelength of from about 300 nm to about 900 nm, such as a xenon (Xe) arc lamp.

[0094] Furthermore, in some embodiments, post-curing is performed after partial curing. For example, in some cases, post-curing is performed after selectively depositing all the layers of ink required to form the desired 3D article, after partially curing all the layers of ink, or after performing both of the above steps. Additionally, in some embodiments, post-curing includes photocuring, including using the above-described curing radiation having a peak wavelength λ. Again, any electromagnetic radiation source that does not conflict with the objectives of the present disclosure may be used in the post-curing step described herein. For example, in some embodiments, the electromagnetic radiation source may be a light source having higher energy, lower energy, or the same energy as the electromagnetic radiation source used for partial curing. In some examples where the electromagnetic radiation source used for post-curing has higher energy (i.e., a shorter wavelength) than that used for partial curing, a xenon (Xe) arc lamp can be used for partial curing and a mercury (Hg) lamp can be used for post-curing.

[0095] Furthermore, after post-curing, in some cases, at least about 80% of the deposited ink layer is polymerized or crosslinked, or at least about 85% is polymerized or crosslinked. In some embodiments, at least about 90%, at least about 95%, at least about 98%, or at least about 99% of the deposited ink layer is polymerized or crosslinked. In some examples, from about 80% to 100%, from about 80% to 99%, from about 80% to 95%, from about 85% to 100%, from about 85% to 99%, from about 85% to 95%, from about 90% to 100%, or from about 90% to 99% of the deposited ink layer is polymerized or crosslinked.

[0096] B. Batch polymerization method It is also possible to form a 3D article from the inks described herein using a vat polymerization method such as the SLA method. Thus, in some examples, the method of printing a 3D article described herein involves holding the ink described herein in a fluid state within a container and selectively applying energy (in particular, for example, curing radiation having a peak wavelength λ) to the ink within the container to solidify at least a portion of the fluid layer of the ink, thereby forming a solidified layer that defines a cross-section of the 3D article. Further, the method described herein may further include raising or lowering the solidified layer of the ink to provide a new or second fluid layer of unsolidified ink on the surface of the fluid ink within the container, and then selectively applying energy again to the ink within the container to solidify at least a portion of the new or second fluid layer of the ink to form a second solidified layer that defines a second cross-section of the 3D article. Further, by applying energy to solidify the ink, the first and second cross-sections of the 3D article can be joined or adhered to each other in the z-direction (or the build direction corresponding to the upward or downward direction described above). Further still, in some examples, the electromagnetic radiation has an average wavelength of 300 to 900 nm, and in other embodiments, the electromagnetic radiation has an average wavelength of less than 300 nm. In some examples, the curing radiation is provided by a computer-controlled laser beam. Further, in some examples, raising or lowering the solidified layer of the ink is performed using a lifting platform disposed within the container of the fluid ink. The method described herein may also include flattening the new layer of fluid ink brought about by raising or lowering the lifting platform. Such flattening can be performed, in some examples, by a wiper or a roller.

[0097] Furthermore, it should be further understood that the aforementioned process may be repeated a desired number of times to provide a 3D article. For example, in some instances, this process can be repeated “n” times, where n can be up to about 100,000, up to about 50,000, up to about 10,000, up to about 5000, up to about 1000, or up to about 500. Thus, in some embodiments, the method of printing a 3D article described herein comprises selectively applying energy (e.g., curing radiation of peak wavelength λ) to ink within a container to solidify at least a portion of the nth fluid layer of the ink, thereby forming an nth solidified layer that defines an nth cross-section of the 3D article; raising or lowering the nth solidified layer of the ink to provide, on the surface of the fluid ink within the container, an (n + 1)th layer of unsolidified ink; selectively applying energy to the (n + 1)th layer of ink within the container to solidify at least a portion of the (n + 1)th layer of the ink, thereby forming an (n + 1)th solidified layer that defines an (n + 1)th cross-section of the 3D article; raising or lowering the (n + 1)th solidified layer of the ink to provide, on the surface of the fluid ink within the container, an (n + 2)th layer of unsolidified ink; and continuing to repeat the aforementioned steps to form the 3D article. Further, it should be understood that one or more steps of the methods described herein, such as selectively applying energy (e.g., the curing radiation described herein) to a layer of ink, can be performed in accordance with an image of the 3D article in computer-readable format. General methods of 3D printing using stereolithography are further described, in particular, in U.S. Patent Nos. 5,904,889 and 6,558,606.

[0098] By performing the above-described printing process, a printed 3D article having a high feature resolution can be provided from the inks described herein. For reference purposes herein, the “feature resolution” of an article can be the smallest controllable physical feature size of the article. The feature resolution of an article can be described in units of distance such as micrometers (μm) or dots per inch (dpi). As will be understood by those skilled in the art, a higher feature resolution corresponds to a higher dpi value and also to a shorter distance in μm. In some examples, an article formed by depositing or solidifying the inks described herein can have a feature resolution of about 500 μm or less, about 200 μm or less, about 100 μm or less, or about 50 μm or less, including resolution at high temperatures. In some embodiments, the article can have a feature resolution between about 50 μm and about 500 μm, between about 50 μm and about 200 μm, between about 50 μm and about 100 μm, or between about 100 μm and about 200 μm. Correspondingly, in some examples, an article described herein can have a feature resolution of at least about 100 dpi, at least about 200 dpi, at least about 250 dpi, at least about 400 dpi, or at least about 500 dpi. In some examples, the feature resolution of the article is between about 100 dpi and about 600 dpi, between about 100 dpi and about 250 dpi, or between about 200 dpi and about 600 dpi.

[0099] In the above-described vat polymerization method, as described in Section IIA above, the ink can be partially cured. For example, in some embodiments, selectively applying energy to the ink in the container to solidify at least a portion of the fluid layer of the ink can include partially curing at least a portion of the fluid layer of the ink. In other embodiments, partial curing of at least a portion of the fluid layer of the ink can occur before or after providing and solidifying a first layer of ink and before or after providing or solidifying a second layer of ink, or before or after providing or solidifying one, some, or all subsequent layers of ink.

[0100] Furthermore, in some embodiments of the vat polymerization method described herein, post-curing as described in Section IIA above may be performed after partial curing or after the desired 3D article has been formed. The desired 3D article may be, for example, an article corresponding to the design of a CAD file.

[0101] III. Printed 3D article In another aspect, printed 3D articles are described herein. In some embodiments, the printed 3D articles are formed from the inks described herein. Any of the inks described in Section I above of this specification may be used. For example, in some examples, the ink comprises up to 60 wt% oligomer curable material; up to 80 wt% monomer curable material; up to 5 wt% photoinitiator; up to 1 wt% non-curable absorber material; and up to 10 wt% one or more additional components, based on the total weight of the ink, and the total amount of said components is equal to 100 wt%. Further, the photoinitiator is operable to initiate the curing of the oligomer curable material and / or the monomer curable material when the photoinitiator is exposed to incident curing radiation having a peak wavelength λ. Furthermore, the ink has a penetration depth (D p ) at wavelength λ, a critical energy (E c ) and a print-through depth (D p ) of 2×D PT or less.

[0102] Some embodiments of the 3D printing ink are further illustrated in the following non-limiting examples.

Examples

[0103] Example 1 Method for preparing the ink The ink according to some embodiments described in this specification was prepared as follows. Specifically, to prepare various inks, the components in Tables I - VI below were mixed in a reaction vessel to form the specific inks shown in the tables. The amounts of the various components in Tables I - VI represent the weight percentages of each component of the specified ink based on the total weight of the ink. For each ink, the appropriate mixture was heated to a temperature of about 75 - 85 °C while stirring. Heating and stirring were continued until the mixture reached a substantially homogenized molten state. Thereafter, the molten mixture was filtered. Next, the filtered mixture was allowed to cool to ambient temperature.

[0104] Example 2 Different amounts of oligomer and monomer curable materials Inks 1 and 2 in Table 1 were prepared according to the procedure of Example 1. While keeping the amounts of the photoinitiator and non - curable absorber material constant, the amounts of the oligomer curable material and monomer curable material were varied. The oligomer curable material and monomer curable material of Ink 1 and Ink 2 are of the same chemical identity and consist of (meth)acrylates that are non - absorbent at a wavelength λ (which was 405 nm). The photoinitiator is the same for Inks 1 and 2 and consists of Irgacure 819. The non - curable absorber material is the same for Inks 1 and 2 and consists of a 1:1 weight mixture of Keystone's Oil Yellow and Blue B. The amounts of the various components of Inks 1 and 2 in Table I are provided as weight percentages (wt%) based on the total weight of each ink. The values of D p and E c are also shown in Table I for each ink. The units of these values in Table I (and subsequent tables) are as follows: D p (μm), E c (mJ / cm 2 ), and the D p / E c ratio ((μm cm 2 ) / mJ).

Table 1

[0105] As shown in Table I, D p , E c , and the D p / E c ratio (and thus D PT ) remains substantially constant over different concentrations of oligomer and monomer curable materials, indicating that the amounts of photoinitiator and non-curable absorber material primarily control the D p , E c , and D PT of these compositions (and other compositions where the curable material is an optical spectrator, as further explained in Example 3 above and below).

[0106] Example 3 Different oligomer and monomer curable materials Inks 3 - 6 in Table II were prepared according to the procedure of Example 1 (again, components are provided as weight % in Table II). In Inks 3 and 4, the concentrations of oligomer and monomer curable materials, photoinitiator, and non-curable absorber material remained substantially constant, and the oligomer curable material, photoinitiator, and non-curable absorber material were the same. However, the type or species of monomer curable material differed between Ink 3 and Ink 4. Specifically, they contained different species of (meth)acrylate monomers. However, both monomer curable materials in Inks 3 and 4 were optical spectrator species that were substantially non-absorbing at wavelength λ (405 nm).

[0107] In Inks 5 and 6, the concentrations of oligomer and monomer curable materials, photoinitiator, and non-curable absorber material remained substantially constant. Further, the materials of the photoinitiator and non-curable absorber were the same species in both inks. However, the type or species of oligomer curable material differed between Ink 5 and Ink 6. Specifically, they contained different species of aliphatic urethane acrylates (Ink 6 contained a triacrylate, while Ink 5 contained only a diacrylate). Both oligomer curable materials in Inks 5 and 6 were optical spectrator species that were substantially non-absorbing at wavelength λ (405 nm).

Table 2

[0108] As shown in Table II for Inks 3 and 4, since the monomer curable material is essentially an optical spectral species, changing the type of monomer curable material results in a slight change in D p , E c , and the D p / E c ratio (and thus D PT ). Similarly, for Inks 5 and 6, changing the type of oligomer curable material also results in only a slight change in the D p , E c , and the D p / E c ratio.

[0109] Example 4 Additional changes Inks 7 - 14 in Table III were prepared according to the procedure of Example 1 (again, components are provided as weight % in Table III). Table IV shows the various components used in the various inks of Table III. In Tables III and IV, a dash (--) indicates that the component is absent or the value is not reported here. However, for clarity, all of Inks 7 - 14 are "inks according to the present invention" as broadly described herein (the same is true for all of Inks 1 - 6). Further, Inks 1 - 12 are particularly preferred embodiments of the present invention. All components of Inks 7 - 12 in Table III below, except for the photoinitiator and non-curable absorber material, are substantially non-absorbing at wavelength λ, and these species were essentially optical spectral species as described above.

Table 3

Table 4-1

[0110] As shown in Table III, different concentrations and types of photoinitiators and non-curable absorber materials were used in the inks described herein to adjust D p , E c , and the D p / E c ratio (and thus D PT ) can be adjusted.

[0111] Example 5 Comparative data Inks 15-17 and Comparative Inks 1 and 2 were prepared according to the procedure of Example 1. As shown in Table IV, Inks 15 and 16 are compared with Comparative Ink 1. Inks 15 and 16 have comparable amounts of the same types of oligomer and monomer curable materials as Comparative Ink 1. All three inks also contain the same photoinitiator and non-curable absorber materials. However, the ratio of photoinitiator to non-curable absorber in Comparative Ink 1 is too low, and in particular, due to the high E c , the desired results (such as print efficiency and speed) described herein cannot achieve the D p / E c ratio. Ink 17 and Comparative Ink 2 compared to each other contain comparable amounts of the same oligomer and monomer curable materials. Both inks contain the same photoinitiator and non-curable absorber materials. However, the amount of non-curable absorber material in Comparative Ink 2 is too high. For further comparison purposes, it should also be noted that Inks 1-12 showed improved print-through characteristics while maintaining desirable mechanical properties when compared to inks that were similar in other respects except for the combination of photoinitiator and non-curable absorber of Inks 1-12 (data not shown).

Table 4-2

[0112] It should be understood that the inks described and claimed herein are not limited to only the exact embodiments of Inks 1-17. Rather, based on the teachings of this disclosure, one of ordinary skill in the art can formulate other specific inks.

[0113] Example 6 Additional Exemplary Ink Compositions In addition to the above inks 1 to 17, other inks according to the present disclosure are provided using the amounts in Table V below. The amounts in Table V indicate the weight % of each component of a particular ink based on the total weight of the ink, and in certain cases the total amount is equal to 100 weight %. Further, "PI" is an abbreviation for "photoinitiator". [Table 5]

[0114] Some additional non-limiting exemplary embodiments are provided below.

[0115] Embodiment 1 An ink for use in a three-dimensional printing system, based on the total weight of the ink, Up to 80 wt% oligomer curable material, Up to 80 wt% monomer curable material, Up to 10 wt% photoinitiator, Up to 1 wt% non-curable absorber material, and Up to 10 wt% one or more additional components comprising, the total amount of oligomer curable material, monomer curable material, photoinitiator, non-curable absorber material, and one or more additional components is equal to 100 wt%, the photoinitiator is operable to initiate the curing of the oligomer curable material and / or the monomer curable material when the photoinitiator is exposed to incident curing radiation having a Gaussian distribution of wavelengths and a peak wavelength λ, the ink has a penetration depth (D p ) and a critical energy (E c ) at wavelength λ, and further the ink has a print-through depth (D p ) at a wavelength λ of 2×D PT or less, and / or a D 2 / E p value of 10 to 50 (μm cm c / mJ), the ink.

[0116] Embodiment 2 1.5×D p The printed-through depth (D PT ) at the following wavelength λ, of the ink of Embodiment 1.

[0117] Embodiment 3 D of the ink p is 60 to 100 μm, and E of the ink c is 2 to 4 mJ / cm 2 of the ink of Embodiment 1 or Embodiment 2.

[0118] Embodiment 4 D of the ink p is 101 to 150 μm, and E of the ink c is 4 to 20 mJ / cm 2 of the ink of Embodiment 1 or Embodiment 2.

[0119] Embodiment 5 D of the ink p is 151 to 200 μm, and E of the ink c is 8 to 15 mJ / cm 2 of the ink of Embodiment 1 or Embodiment 2.

[0120] Embodiment 6 (μm cm 2 ) / mJ unit between 10 and 50 of D p / E c ratio of the ink of any of the preceding embodiments.

[0121] Embodiment 7 The ink of any of the preceding embodiments, containing a photoinitiator up to 5% by weight.

[0122] Embodiment 8 Contains a photoinitiator up to 5% by weight and a non-curable absorber material up to 0.5% by weight, and An ink according to any of the preceding embodiments, wherein the weight ratio of the photoinitiator to the non-curable absorber is between 5 and 100.

[0123] Embodiment 9 An ink according to any of the preceding embodiments, wherein both the non-curable absorber material and the photoinitiator have an absorption peak within 30 nm of the wavelength λ.

[0124] Embodiment 10 An ink according to any of the preceding embodiments, wherein the total absorbance of the non-curable absorber material at the wavelength λ is about 0.1 to 10 times the total absorbance of the photoinitiator at the wavelength λ.

[0125] Embodiment 11 An ink according to any of the preceding embodiments, wherein the non-curable absorber material contains pyrene.

[0126] Embodiment 12 An ink according to any of the preceding embodiments, wherein the non-curable absorber material contains an oil-soluble yellow dye.

[0127] Embodiment 13 A method of forming a three-dimensional article by additive manufacturing, comprising: providing an ink according to any of Embodiments 1 to 12, and selectively curing a portion of the ink using an incident curing radiation having a Gaussian distribution of wavelengths and a peak wavelength at the wavelength λ comprising a method.

[0128] Embodiment 14 The ink is selectively cured according to preselected computer-aided design (CAD) parameters, D p is the method of Embodiment 13 corresponding to the voxel depth of the CAD parameters.

[0129] Embodiment 15 The step of providing the ink includes selectively depositing a layer of the ink in a fluid state on a substrate to form a three-dimensional article, the method of Embodiment 13 or Embodiment 14.

[0130] Embodiment 16 The step of providing the ink includes holding the ink in a fluid state within the container, The step of selectively curing a portion of the ink is, selectively applying curing radiation to the ink within the container to solidify at least a portion of a first fluid layer of the ink, thereby forming a first solidified layer that defines a first cross-section of the article, raising or lowering the first solidified layer to provide a second fluid layer of the ink on the surface of the fluid ink within the container, and selectively applying curing radiation to the ink within the container to solidify at least a portion of the second fluid layer of the ink, thereby forming a second solidified layer that defines a second cross-section of the article The method according to any one of Embodiments 13 to 15, wherein the first cross-section and the second cross-section are joined to each other in the z-direction.

[0131] Embodiment 17 A printed three-dimensional article formed from any one of the inks of Embodiments 1 to 12 and / or using any one of the methods of Embodiments 13 to 16.

[0132] All patent documents referred to herein are incorporated by reference in their entirety. Various embodiments of the present invention have been described in the context of achieving various objects of the present invention. It should be recognized that these embodiments are merely illustrative examples of the principles of the present invention. Numerous modifications and adaptations thereof will become readily apparent to those skilled in the art without departing from the spirit and scope of the present invention.

Claims

1. 1. An ink for use in a three dimensional printing system, comprising, based on a total weight of the ink, 10 to 80 weight percent of an oligomeric curable material; 10-80% by weight of a monomeric curable material; 0.1 to 5 wt. % of a photoinitiator; 0.01 to 0.5 weight percent of a non-hardening absorbent material, and Up to 10% by weight of one or more additional ingredients Including, the total amount of said oligomeric hardenable material, monomeric hardenable material, photoinitiator, non-curable absorber material, and one or more additional components equals 100% by weight; the photoinitiator is operable to initiate curing of the oligomeric and / or monomeric curable materials upon exposure of the photoinitiator to incident curing radiation having a Gaussian distribution of wavelengths and a peak wavelength λ; The ink has a penetration depth (D ｐ ) and the critical energy (E ｃ ) The weight percentage of each component of the ink is ｃ is 10 to 30 mJ / cm ２ and (μm cm ２ D in units of mJ ｐ / E ｃ The ratio is chosen to be between 10 and 50, an ink wherein the weight ratio of said photoinitiator to said non-curable absorber material is between 5 and 100;

2. Ink E ｃ is 20 mJ / cm ２ 2. The ink of claim 1, wherein:

3. (μm cm ２ D in units of mJ ｐ / E ｃ The ink of claim 1 , wherein the ratio is between 15 and 30.

4. Ink D ｐ The ink of claim 1, wherein the particle size is 151 to 200 μm.

5. An ink for use in a three dimensional printing system, comprising, based on a total weight of the ink, 10 to 80 weight percent of an oligomeric curable material; 10-80% by weight of a monomeric curable material; 0.1 to 5 wt. % of a photoinitiator; 0.01 to 0.5 weight percent of a non-hardening absorbent material, and Up to 10% by weight of one or more additional ingredients Including, the total amount of said oligomeric hardenable material, monomeric hardenable material, photoinitiator, non-curable absorber material, and one or more additional components equals 100% by weight; the photoinitiator is operable to initiate curing of the oligomeric and / or monomeric curable materials upon exposure of the photoinitiator to incident curing radiation having a Gaussian distribution of wavelengths and a peak wavelength λ; The ink has a penetration depth (D p ) and a critical energy (E c ) at a wavelength λ, the weight percentages of each component of the ink are selected such that the ink has an E c of 10-30 mJ / cm 2 and a D p / E c ratio in units of (μm cm 2 ) / mJ between 10 and 50; An ink, wherein both the non-curable absorber material and the photoinitiator have an absorption peak within 30 nm of a wavelength λ.

6. 2. The ink of claim 1, wherein the total absorbance of the non-curable absorber material at wavelength λ is about 0.1 to 10 times the total absorbance of the photoinitiator at wavelength λ.

7. An ink for use in a three dimensional printing system, comprising, based on a total weight of the ink, 10 to 80 weight percent of an oligomeric curable material; 10-80% by weight of a monomeric curable material; 0.1 to 5 wt. % of a photoinitiator; 0.01 to 0.5 weight percent of a non-hardening absorbent material, and Up to 10% by weight of one or more additional ingredients Including, the total amount of said oligomeric hardenable material, monomeric hardenable material, photoinitiator, non-curable absorber material, and one or more additional components equals 100% by weight; the photoinitiator is operable to initiate curing of the oligomeric and / or monomeric curable materials upon exposure of the photoinitiator to incident curing radiation having a Gaussian distribution of wavelengths and a peak wavelength λ; The ink has a penetration depth (D p ) and a critical energy (E c ) at a wavelength λ, the weight percentages of each component of the ink are selected such that the ink has an E c of 10-30 mJ / cm 2 and a D p / E c ratio in units of (μm cm 2 ) / mJ between 10 and 50; The ink, wherein the non-curable absorber material comprises a polycyclic aromatic compound.

8. The ink of claim 1 , wherein the non-curable absorber material comprises pyrene.

9. The ink of claim 1 , wherein the non-hardening absorber material comprises an oil soluble yellow dye.

10. An ink for use in a three dimensional printing system, comprising, based on a total weight of the ink, 10 to 80 weight percent of an oligomeric curable material; 10-80% by weight of a monomeric curable material; 0.1 to 5 wt. % of a photoinitiator; 0.01 to 0.5 weight percent of a non-hardening absorbent material, and Up to 10% by weight of one or more additional ingredients Including, the total amount of said oligomeric hardenable material, monomeric hardenable material, photoinitiator, non-curable absorber material, and one or more additional components equals 100% by weight; the photoinitiator is operable to initiate curing of the oligomeric and / or monomeric curable materials upon exposure of the photoinitiator to incident curing radiation having a Gaussian distribution of wavelengths and a peak wavelength λ; The ink has a penetration depth (D p ) and a critical energy (E c ) at a wavelength λ, the weight percentages of each component of the ink are selected such that the ink has an E c of 10-30 mJ / cm 2 and a D p / E c ratio in units of (μm cm 2 ) / mJ between 10 and 50; The ink, wherein the photoinitiator comprises an alpha-cleavage type photoinitiator.

11. The ink of claim 1 , wherein the oligomeric curable material comprises a (meth)acrylate moiety.

12. The ink of claim 1 , wherein the monomeric curable material comprises a (meth)acrylate moiety.

13. The ink of claim 1 , wherein the one or more additional components comprises a photosensitizer.

14. The ink of claim 1 , wherein the one or more additional components comprises a colorant different from the non-hardenable absorber material.

15. The ink of claim 1 , wherein the one or more additional components comprises a polymerization inhibitor.

16. The ink of claim 1 , wherein the one or more additional components comprises a stabilizer.

17. The ink of claim 1 , wherein the one or more additional components comprises a viscosity modifier.

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