THIOL-ISOCYANATE-EPOXIDE FORMULATIONS FOR ADDITIVE MANUFACTURING

Abstract

The present invention refers to a photocurable composition comprising at least one polythiol having at least two thiol groups, at least one polyisocyanate having at least two isocyanate groups, at least one epoxy compound having at least one epoxy group, and at least one photolatent base catalyst. Furthermore, the present invention pertains to a method of photo-curing the photo-curable composition according to the present invention as well as to a method of three dimensional printing an object with the photocurable composition according to the present invention. Moreover, the present invention refers to a cross-linked polymer or a three-dimensional object obtained by the methods according to the present invention, and use of the polymer or the object as an antireflective coating, encapsulant for LEDs, microlense for CMOS image sensors, as optical material, as biomedical functional coating, packaging and textile, stents, scaffolds, dental applications, and as reversible adhesive for debond on demand applications.

Claims

1. A photo-curable composition comprising A) at least one polythiol having at least two thiol groups; B) at least one polyisocyanate having at least two isocyanate groups; C) at least one epoxy compound having at least one epoxy group; D) at least one photolatent base catalyst; and E) optionally at least one additive.

2. The photo-curable composition according to claim 1, wherein the at least one polythiol i) has two to six thiol groups; ii) is selected from primary and secondary aliphatic and oligomeric thiols having a molecular weight up to 5,000 g/mol; or iii) is selected from di-pentaerythritol tetra(3-mercapto-propionate), pentaerythritol tetra(3-mercaptopropionate), trimethylol-propane tris(3-mercaptopropionate), glycol di(3-mercaptopropionate), pentaerythritol tetramercaptoacetate, trimethylol-propane trimercaptoacetate, glycol dimercaptoacetate, ethoxylated trimethylolpropane tri(3-mercaptopropionate), propylene glycol-2,4,6-triallyloxy-1,3,5-triazine 3-mercaptopropionate, tris[2-(3-mercaptopropionyloxy)ethyl]isocyanurate, polycaprolactone tetra 3-mercaptopropionate, pentaerythritol tetrakis(3-mercaptobutylate), 1,4-bis(3-mercaptobutylyloxy)butane, 1,3,5-tris(3-mercaptobutyloxethyl)-1,3,5-triazine-2,4,6(IH,3H,5H)-trione, trimethylolpropane tris(3-mercarptobutyrate) or mixtures thereof.

3. The photo-curable composition according to claim 1, wherein the at least one polyisocyanate i) has two to six isocyanate groups; ii) has a number average molecular weight of 500 to 25,000 g/mol; or iii) is selected from 1,3,5-tris(6-isocyanatohexyl)-1,3,5-triazinane-2,4,6-trione, (E)-3,5-bis(6-isocyanatohexyl)-6((6-isocyanatohexyl)imino)-1,3,5-oxadiazinane-2,4-dione or a mixture thereof.

4. The photo-curable composition according to claim 1, wherein the at least one epoxy compound i) has one to five epoxy groups; ii) is an aliphatic or aromatic compound with a molecular weight of up to 5,000 g/mol; or iii) is selected from 1,4-cyclohexane dimethanol diglycidyl ether, dipropylene glycol diglycidyl ether, ethylene glycol diglycidyl ether, trimethylolpropane triglycidyl ether, trimethylol ethane triglycidyl ether, propoxylated glycol triglycidyl ether, neopentyl glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, polypropylene glycol diglycidyl ether or mixtures thereof.

5. The photo-curable composition according to claim 1, wherein the thiol groups:NCO groups:epoxy groups are present in an equivalent ratio of 0.7:0.05:1.3 to 1.3:1.3:0.05.

6. The photo-curable composition according to claim 1, wherein the at least one photolatent base catalyst i) is present in 0.01 to 5 wt.-%, based on the total weight of the composition; ii) is selected from 1,8-diazabicyclo[5.4.0]undec-7-ene-anthracene-tetraphenyl borate, 1,5,7-triazabicyclo[4.4.0]dec-5-ene hydrogen tetraphenyl borate, 2-benzyl-2-(dimethylamino)-1-(4-methoxyphenyl)butan-1-one, 2-benzyl-2-dimethylamino-4′-morpholinobutyrophenone, 2-dimethylamino-2-(4-methyl-benzyl)-1-(4-morpholin-4-yl-phenyl)-butan-1-one, 1-(anthracen-9-ylmethyl)-2,3,4,6,7,8,9,10-octahydropyrimido[1,2-a]azepin-1-ium tetraphenyl borate, 1-(anthracen-9-ylmethyl)-9-ethyl-3,4,6,7,8,9-hexahydro-2H-pyrimido[1,2-a]pyrimidin-1-ium tetraphenyl borate, 2-benzyl-2-(dimethylamino)-1-(4-methoxyphenyl)butan-1-one, 2-benzyl-2-dimethylamino-4′-morpholinobutyrophenone, 2-dimethylamino-2-(4-methyl-benzyl)-1-(4-morpholin-4-yl-phenyl)-butan-1-one or mixtures thereof; or iii) the photolatent base catalyst releases a basic component, of which its protonated counterpart has a pKa of above 10.

7. The photo-curable composition according to claim 1, wherein the at least one additive i) is present in up to 10 wt.-%, based on the total weight of the composition; ii) comprises (E1) at least one inhibitor selected from acid boric esters or phosphoric acid esters; and/or iii) comprises (E2) at least one compound selected from solvents, fillers, fire retardants, UV-stabilizer, pigments, dyes; or iv) comprises (E3) at least one sensitizer.

8. The photo-curable composition according to claim 1, wherein the composition has a viscosity of 1 to 5,000 m*Pas measured with a AR2000 rheometer from TA instruments equipped with a Peltier plate and a 40 mm parallel plate at 25° C. in the shear stress range of 100 to 500 Pa

9. A method of photo-curing the photo-curable composition according to claim 1, comprising the steps: i) providing the photo-curable composition by i.a) mixing the components A) to D) and optionally E) or i.b) mixing A), D) and optionally E) and separately mixing B) and C) before mixing the mixture containing A), D) and optionally E) and the mixture containing B) and C); ii) transferring the photo-curable composition of step i) to a mould; iii) exposing the photo-curable composition to UV-light to obtain a cross-linked polymer; and iv) optionally post-curing the obtained polymer by thermal or UV treatment.

10. A method of three dimensional printing an object with the photo-curable composition according to claim 1, comprising of the steps: i) providing the photo-curable composition; ii) forming a layer of the photo-curable composition with a three dimensional printer; iii) exposing the layer under a suitable light source following a pattern of cross-sectional layer of the model to cure the layer; iv) providing a further layer of the photo-curable composition with the three dimensional printer upon the cured layer obtained after step iii); v) exposing the layer of step iv) under a suitable light source following a pattern of cross-sectional layer of the model in order to cure the layer and bond with the layer of step iii); and vi) optionally repeating steps iv) and v) until the three-dimensional object is obtained.

11. A cross-linked polymer obtained by the method according to claim 9.

12. A three-dimensional object obtained by the method according to claim 10.

13. The cross-linked polymer according to claim 11 having i) a glass transition temperature Tg of 0 to 200° C., measured according to 11357-2:2014-07 or ASTM E1356-08 (2014); and/or ii) a refractive index of 1.50 to 1.80, measured with an Electronic Abbe Refractometer AR 2008 from A.Krüss Optronic at 21° C. and at standard wavelength of 589 nm.

14. The three-dimensional object according to claim 12 having i) a glass transition temperature Tg of 0 to 200° C., measured according to 11357-2:2014-07 or ASTM E1356-08 (2014); and/or ii) a refractive index of 1.50 to 1.80, measured with an Electronic Abbe Refractometer AR 2008 from A.Krüss Optronic at 21° C. and at standard wavelength of 589 nm.

Description

EXAMPLES

[0085] Glass transition temperature:

[0086] The Tg of the samples was determined using a DSC Q2000 equipped with a Refrigerated Cooling System 90, both from TA instruments. The DSC experiments comprised two cooling/heating cycles at a scanning rate of 10° C./min using N.sub.2 as a purge gas. The Tg can be measured in accordance with ISO 11357-2:2014-07 or ASTM E1356-08 (2014).

[0087] Refractive index (n.sub.D.sup.21):

[0088] The refractive index of the samples was measured using an Electronic Abbe Refractometer AR 2008 from A.Krüss Optronic. All measurements were performed at 21° C. and at standard wavelength of 589 nm.

[0089] Abbe's number (v.sub.D.sup.21)

[0090] The Abbe's number of the samples was measured using a Metricon 2010/M Prism Coupler equipped with three lamps emitting at 402, 511 and 687 nm. All measurements were performed at 21° C. and the value at λ=589 nm was interpolated by the software.

[0091] Initial viscosity:

[0092] The initial viscosity of the formulations was measured using an AR2000 rheometer from TA instruments equipped with a Peltier plate and a 40 mm parallel plate. The viscosity of the formulations was checked at 25° C. in the shear stress range of 100-500 Pa.

[0093] Pot-life:

[0094] The pot-life of the formulations is defined as the time during which the viscosity remains below the viscosity limit of 3000 m*Pas. The pot-life was checked by monitoring the viscosity over time as above described.

Example 1 and Comparative Example 1

[0095] The SH:NCO:epoxy equivalent ratio was set at 1.1:0.9:0.1. 2.0221 g of tris(6-isocyanatohexyl)-1,3,5-triazinane-2,4,6-trione (Desmodur® N3600) are added to a mixture of 1.8316 g of dipentaerythritol hexa(3-mercaptopropionate) (Thiocure® DiPETMP) and 0.1463 g of ethylene glycol diglycidyl ether (Erisys® EGDGE). The mixture was mixed for 1 min at 3500 rpm and stored at room temperature. The formulation viscosity was checked over time with a rheometer. A formulation containing the same monomers but with a 1,8-diazabicyclo[5.4.0]undec-7-ene-anthracene-tetraphenyl borate (DBU-Ant-BPh4) as a photolatent base catalyst was UV cured. Firstly, 0.0020 g (0.05 wt.-%) of DBU-Ant-BPh4 were added to 1.8306 g of Thiocure® DiPETMP and mixed for 1 min at 3500 rpm. Afterwards, 2.0211 g of Desmodur N3600 and 0.1463 g of Erisys® EGDGE were added to the previous mixture and were mixed for 1 min at 3500 rpm (Example 1). The formulation was degassed under vacuum if there were bubbles present. Then the mixture was casted in the appropriate mould and placed in a UV curing chamber equipped with a Hg lamp. The mixture was irradiated 3 times for 10 seconds. The reaction conversion was monitored by the disappearance of the NCO peak (˜2260 cm.sup.−1) and the epoxy ring vibration peak (around 900 cm.sup.−1) by ATR-FTIR. If the reaction was not completed upon UV light exposure the sample was thermally post-cured. The fully cured sample was characterized by DSC and refractometry.

[0096] For comparison, a formulation with a SH:NCO:epoxy equivalent ratio of 1.1:1.0:0.0 is prepared by adding 2.1901 g of tris(6-isocyanatohexyl)-1,3,5-triazinane-2,4,6-trione (Desmodur® N3600) to 1.8079 g of dipentaerythritol hexa(3-mercaptopropionate) (Thiocure® DiPETMP). The mixture was mixed for 1 min at 3500 rpm and stored at room temperature. The formulation viscosity was checked over time with a rheometer.

[0097] A formulation containing the same monomers but with a 1,8-diazabicyclo[5.4.0]undec-7-ene-Anthracene-Tetraphenyl borate (DBU-Ant-BPh4) as a photolatent base catalyst was UV cured. Firstly, 0.0020 g (0.05 wt.-%) of DBU-Ant-BPh4 were added to 1.8079 g of Thiocure® DiPETMP and mixed for 1 min at 3500 rpm. Afterwards, 2.1901 g of Desmodur® N3600 were added to the previous mixture and were mixed for 1 min at 3500 rpm. The formulation was degassed under vacuum if there were bubbles present. Then the formulation was casted in the appropriate mould and placed in a UV curing chamber equipped with a Hg lamp. The formulation was irradiated 3 times for 10 seconds. If the reaction was not completed upon UV light exposure the sample was thermally post-cured. The fully cured sample was characterized by DSC and refractometry (Comparative example 1).

TABLE-US-00001 Refractive Abbe's SH:NCO:epoxy Initial η Pot-life T.sub.g index number equivalent ratio (cP) (h) (° C.) (n.sub.D.sup.21) (v.sub.D.sup.21) Comp. 1.1:1:0 1157 ~8 70 1,548 43.7 Ex. 1 Ex. 1 1.1:0.9:0.1 1001 ~12 39 1,561 43.8

[0098] Comparative example is a binary formulation containing a multi-functional thiol and a multi-functional isocyanate which yields a viscous reactive formulation. In contrast, Example 1 is a ternary formulation containing three main components: a multi-functional thiol, a multi-functional isocyanate and a multi-functional epoxy monomer. This formulation is less viscous and less reactive as seen by the extension of the pot-life. Regarding the optical properties, the refractive index can be boosted as seen with Example 1 whereas the Abbe's number is not affected. Thus, the main improvement of compositions according to the present invention is the reduction of the viscosity and the extension of the pot-life. Additionally, other desired properties such as the refractive index can be improved as well.