Thiol-ene printable resins for inkjet 3D printing

Abstract

A composition suitable for 3-D printing comprises, in one embodiment, a photopolymer including one or more thiol monomer, one or more alkene monomer, and a polymerization initiator. In another embodiment, the thiol monomer is selected from the group consisting of: glycol di(3-mercaptopropionate) [GDMP]; trimethylolpropane tris(3-mercaptopropionate) [TMPMP]; pentaerythritol tetrakis(3-mercaptopropionate) [PETMP] and 3,6-dioxa-1,8-octanedithiol [DODT]. In yet another embodiment, the alkene monomer comprises: an allyl-functional urethane/urea monomer synthesized from: an isocyanate moiety and a hydroxyl or amine functional allyl moiety. In still another embodiment, the hydroxyl or amine functional allyl moiety comprises 2-allyloxyethanol, allyl alcohol, and allylamine. In still yet another embodiment, the isocyanate moiety is selected from the group consisting of: isophorone diisocyanate (IDI), hexamethylene diisocyanate (HDI), trimethylhexamethylene diisocyanate (TMHDI), 1,3-bis(isocyanatomethyl)cyclohexane, and dicyclohexylmethane 4,4′-Diisocyanate (HMDI).

Claims

1. A composition comprising: 3,6-dioxa-1,8-octanedithiol (DODT), and one or more alkene monomer being selected from: ##STR00001##

2. The composition of claim 1, wherein the one or more alkene monomer is selected from: ##STR00002##

3. The composition of claim 1, wherein the alkene monomer is ##STR00003##

4. The composition of claim 1, wherein the alkene monomer is ##STR00004##

5. The composition of claim 1, wherein the alkene monomer is ##STR00005##

6. The composition of claim 1, wherein the alkene monomer is ##STR00006##

7. The composition of claim 1, wherein the alkene monomer is ##STR00007##

8. The composition of claim 1, wherein the alkene monomer is ##STR00008##

9. The composition of claim 1, further comprising a polymerization initiator.

10. A cured composition being prepared by a method comprising curing the composition of claim 1.

11. The cured composition of claim 10, wherein the composition is cured by UV or visible light irradiation.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The structure and function of the invention can be best understood from the description herein in conjunction with the accompanying figures. The figures are not necessarily to scale, emphasis instead generally being placed upon illustrative principles. The figures are to be considered illustrative in all aspects and are not intended to limit the invention, the scope of which is defined only by the claims.

(2) FIG. 1 is a depiction of the synthesis reaction of the di(2-allyloxyethyl carbamate) ester of isophorone diisocyanate.

(3) FIG. 2 is a graph of the tensile stress-strain behavior of thiol-ene printable resins made using commercial allyl monomers and synthesized allyl urethane monomers.

(4) FIG. 3 is a graph of the viscosity-temperature profiles of various synthesized allyl urethane monomers.

(5) FIG. 4 is a graph of the viscosity of a thiol-ene printable resin utilizing an allyl urethane monomer at 70° C. over an 18 hour period.

(6) FIGS. 5A-5F depict preferred embodiments of allyl urethane/urea monomers. HDI and TMHDI are reacted with allyloxyethanol, allyl alcohol, or allylamine

DESCRIPTION OF A PREFERRED EMBODIMENT

(7) In brief overview, the invention relates to the composition of a new 3D printable material comprising allyl urethanes that have increased strength upon curing.

(8) As will be described in greater detail below, compositions were formulated with essentially two functionality groups resulting in a material that acts as a chain extender (small amount of tri-functional monomer was added to crosslink the material). Thus, the polymer chain of the material is longer and does not connect to other polymer chains. This characteristic is particularly important for elastomeric materials, which are desired to be more stretchable, rather than more rigid. Such compositions will provide materials that have relatively low viscosity, desirable polymerization characteristics, better curing properties and with increased stability over longer periods of time.

(9) Urethane bonds have high degrees of hydrogen bonding due to containing both a proton donor and acceptor. Incorporation of urethane bonds into acrylic photopolymers is method of increasing toughness by increasing the degree of hydrogen bonding in the cured resin. Therefore, one method for increasing the toughness of thiol-ene photopolymer resins is to synthesize monomers or oligomers which contain urethane bonds.

(10) In one embodiment, allyl-functional urethane monomers are synthesized by the stoichiometrically balanced reaction between di-functional isocyanate monomers such as, but not limited to, isophorone diisocyanate (IDI), hexamethylene diisocyanate (HDI), trimethylhexamethylene diisocyanate (TMHDI), 1,3-bis(isocyanatomethyl)cyclohexane, dicyclohexylmethane 4,4′-Diisocyanate (HMDI), or N,N′,N″-Tris(6-isocyanatohexyl)isocyanurate and a hydroxyl or amine functional allyl monomer such as, but not limited to, 2-allyloxyethanol, allyl alcohol, and allylamine with or without the presence of a suitable catalyst such as, but not limited to, dibutyltin dilaurate (DBTDL). The reaction may be accelerated by heating, although temperatures above 70° C. risk the generation of undesirable side products. A representative reaction product between IDI and 2-allyloxyethanol is shown in FIG. 1.

(11) Such allyl urethanes are shown to significantly improve the tensile strength and maximum elongation without breaking of thiol-ene resins in comparison to printable resins made with commercially available allyl monomers and oligomers. Uniaxial tensile tests for cured thiol-ene resins containing commercial allyl monomers and the above-synthesized allyl urethane monomer are shown in FIG. 2. The tensile strength of the allyl urethane material is approximately 10 times higher and the elongation is 5 times higher than the commercial allyl material.

(12) Printable resins for use in inkjet printing require that the viscosity conform to certain specifications. The viscosity of the printable resins is highly dependent on the formulation and structure of the synthesized allyl monomer. The temperature-dependent viscosity of the raw allyl monomers are shown in FIG. 3. Viscosity decreases as the monomer becomes less sterically hindered, although monomers with too little hindrance are subject to crystallization at lower temperatures. None of the monomers measured thus far demonstrate viscosities less than 30 cP, although resin viscosities in the jettable range are achievable when mixed with thiol and/or alkene monomers. An embodiment of a printable resin comprising TMHDI-DA is shown in FIG. 4 with a viscosity in the range of 10 cP at 70° C. The viscosity remains in this range over the course of one day at 70° C.

(13) Viscosity measurements in which an isocyanate-functional monomer, trimethylhexamethylene diisocyanate (TMHDI), is reacted with three different alcohol or amine functional allyl monomers is shown in Table 1 below.

(14) TABLE-US-00001 TABLE 1 TMHDI-Allyl TMHDI-Allyloxy TMHDI-Allyl Temperature Alcohol Ethanol Amine 30 C. 1466.0 817.4 Not Measurable (High) 40 C. 608.2 383.8 Not Measurable (High) 50 C. 261.3 190.0 Not Measurable (High) 60 C. 129.3 104.4 Not Measurable (High) 70 C. 70.3 61.8 Not Measurable (High) *Viscosity in cP

(15) The same adducts with hexamethylene diisocyanate (HDI) instead of trimethylhexamethylene diisocyanate (TMHDI) are solids and would require a fully heated feed system for printing.

(16) Table 2 provides an embodiment of the composition of a printable resin comprising Glycol di(3-mercaptopropionate) (GDMP), Trimethylhexamethylene di(2-allyloxyethyl carbamate) (TMHDI-DA), Trimethylolpropane diallyl ether (TMPDAE) and Triallyl cyanurate (TAC).

(17) TABLE-US-00002 TABLE 2 Weight Fraction Material Name (%) Glycol di(3-mercaptopropionate) 41.93 Trimethylolpropane diallyl ether 1.89 Trimethylhexamethylene di(2-allyloxyethyl carbamate) 47.41 Triallyl cyanurate 8.77 Pyrogallol 0.05 Ebecryl 168 0.5 Omnirad 819 1.0

(18) Table 3 provides a list of mechanical properties, the applicable standards, and the measurements performed on the composition of a printable resin comprising Glycol di(3-mercaptopropionate) (GDMP), Trimethylhexamethylene di(2-allyloxyethyl carbamate) (TMHDI-DA), Trimethylolpropane diallyl ether (TMPDAE) and Triallyl cyanurate (TAC) shown in Table 2

(19) TABLE-US-00003 TABLE 3 MECHANICAL PROPERTIES STANDARD VALUE UNIT Ultimate Tensile Strength ASTM D412 1.11 ± 0.05 MPa Elongation at Break ASTM D412 256.25 ± 4.95  % Young's Modulus ASTM D412 0.38 ± 0.01 MPa Tear Propagation ASTM D624-B 3.68 ± 0.16 kN/m Strength Shore Hardness ASTM D2240 25 Shore A

(20) Table 4 provides an embodiment of the composition of a printable resin comprising a thiol-ene elastomer using the TMHDI-Allyl alcohol adduct

(21) TABLE-US-00004 TABLE 4 Material Name Weight Fraction (%) 3,6-dioxa-1,8-octanedithiol 36.41 TMHDI-Allyl Alcohol 61.93 Triallyl isocyanurate 1.66 Pyrogallol 0.05 Ebecryl 168 0.5 Omnirad 819 1.0

(22) Table 5 provides a list of mechanical properties, the applicable standards, and the measurements performed on the composition of a printable resin for the thiol-ene elastomer using the TMHDI-Allyl alcohol adduct shown in Table 4.

(23) TABLE-US-00005 TABLE 5 MECHANICAL PROPERTIES STANDARD VALUE UNIT Ultimate Tensile Strength ASTM D412-C 3.97 ± 0.06 MPa Elongation at Break ASTM D412-C 914 ± 26  % Elastic Modulus @ 100% ASTM D412-C  0.3 ± 0.15 MPa Tear Propagation Strength ASTM D624-B 6.26 ± 0.25 kN/m Shore Hardness ASTM D2240 28 Shore A

(24) The disclosed composition has a number of advantages over the current state of the art such as: (1) increased tensile strength, (2) increased elongation at break, (3) low susceptibility to oxygen inhibition, (4) low shrinkage and warping, and (5) high monomer conversion. These properties are highly desirable when considering materials for use in functional 3D printed parts, especially for medical applications.

(25) Referring to FIGS. 5A-5F, other embodiments are possible in which the photopolymer includes thiol monomers selected from the group consisting of: glycol di(3-mercaptopropionate) [GDMP]; trimethylolpropane tris(3-mercaptopropionate) [TMPMP]; pentaerythritol tetrakis(3-mercaptopropionate) [PETMP] and 3,6-dioxa-1,8-octanedithiol [DODT]. Further, the allyl-functional urethane monomer in other embodiments is synthesized from a di-functional isocyanate monomer selected from the group consisting of: isophorone diisocyanate (IDI), hexamethylene diisocyanate (HDI), trimethylhexamethylene diisocyanate (TMHDI), 1,3-bis(isocyanatomethyl)cyclohexane, and dicyclohexylmethane 4,4′-Diisocyanate (HMDI) and a hydroxyl or amine functional allyl monomer selected from the group consisting of 2-allyloxyethanol, allyl alcohol, and allylamine.

(26) A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. For example, various forms of the materials shown above may be used, with steps re-ordered, added, or removed. Accordingly, other implementations are within the scope of the following claims.

(27) The examples presented herein are intended to illustrate potential and specific implementations of the present disclosure. The examples are intended primarily for purposes of illustration of the invention for those skilled in the art. No particular aspect or aspects of the examples are necessarily intended to limit the scope of the present invention.

(28) The figures and descriptions of the present invention have been simplified to illustrate elements that are relevant for a clear understanding of the present invention, while eliminating, for purposes of clarity, other elements. Those of ordinary skill in the art may recognize, however, that these sorts of focused discussions would not facilitate a better understanding of the present disclosure, and therefore, a more detailed description of such elements is not provided herein.

(29) Unless otherwise indicated, all numbers expressing lengths, widths, depths, or other dimensions and so forth used in the specification and claims are to be understood in all instances as indicating both the exact values as shown and as being modified by the term “about.” As used herein, the term “about” refers to a ±10% variation from the nominal value. Accordingly, unless indicated to the contrary, the numerical parameters set forth in the specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Any specific value may vary by 20%.

(30) The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The foregoing embodiments are therefore to be considered in all respects illustrative rather than limiting on the invention described herein. Scope of the invention is thus indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are intended to be embraced therein.

(31) It will be appreciated by those skilled in the art that various modifications and changes may be made without departing from the scope of the described technology. Such modifications and changes are intended to fall within the scope of the embodiments that are described. It will also be appreciated by those of skill in the art that features included in one embodiment are interchangeable with other embodiments; and that one or more features from a depicted embodiment can be included with other depicted embodiments in any combination.