Substrate-based additive fabrication process

1. A method for forming a three-dimensional object comprising:

1) coating a layer of liquid radiation curable resin comprising from 30 to 80 wt % of at least one cationically curable compound on a substrate;

2) contacting the layer of liquid radiation, curable resin with a previously cured layer;

3) selectively exposing the layer of liquid radiation curable resin to actinic radiation, provided by a source of actinic radiation, thereby forming a cured layer which adheres to the previously cured layer;

4) allowing a separation delay time to occur and after the conclusion of the separation delay time separating the cured layer and the substrate; and

5) repeating steps 1-4 a sufficient number of times in order to build up a three-dimensional object;

wherein the separation delay time is the time from first exposure of the layer of liquid radiation curable resin to actinic radiation to the time that the storage shear modulus (G′) of the liquid radiation curable resin is measured to have achieved a (G′) value of greater than about 9.0×10 5 Pa, as measured from the beginning of light exposure, when the storage shear modulus (G′) of the liquid radiation curable resin is measured on a Real Time Dynamic Mechanical Analyzer as the liquid radiation curable resin is cured with a light intensity of 50 mW/cm 2 for 1.0 second light exposure time.

2. The method of claim 1 wherein the storage shear modulus of the liquid radiation curable resin is measured at an ambient temperature of from 20° C. to 23° C. and a percent relative humidity of from 25% to 35%.

3. The method of claim 1 wherein the Real Time Dynamic Mechanical Analyzer is set up with an 8 mm plate and a sample gap of 0.10 mm.

4. The method of claim 1 wherein the storage shear modulus of the liquid radiation curable resin is measured at a frequency of 10 Hz and a 10 second equilibrium time.

5. The method of claim 1 wherein the cured layer does not adhere to the substrate and adheres to the previously cured layer.

6. The method of claim 1 wherein the liquid radiation curable resin is able to achieve a storage shear modulus of greater than about 7.5×10 5 2.0 seconds after light exposure begins when measured on a Real Time Dynamic Mechanical Analyzer.

7. The method of claim 1 wherein the light intensity of 50 mW/cm 2 has a spectral output with a peak at about 365 nm.

8. The method of claim 1 wherein the light intensity of 50 mW/cm 2 and the source of actinic radiation have the same spectral output.

9. The method of claim 1 wherein the source of actinic radiation is one or more LEDs.

10. The method of claim 1 wherein the one or more LEDs emit light at a wavelength of from 340-400 nm.

11. The method of claim 1 wherein the separation delay time does not exceed 15.0 seconds.

12. The method of claim 1 wherein the liquid radiation curable resin further comprises: from about 0.5 to about 10 wt % of at least one cationic photoinitiator; from 15 to 40 wt % of at least one free radical polymerizable component; and from about 1 to about 10 wt % of at least one free radical photoinitiator.

13. The method of claim 12 wherein the at least one cationic photoinitiator comprises a triaryl sulfonium salt.

14. The method of claim 13 wherein the triarly sulfonium salt is a triaryl sulfonium tetrakis(pentafluorophenyl)borate.

15. The method of claim 14 wherein the triaryl sulfonium tetrakis(pentafluorophenyl)borate is tris(4-(4-acetylpheny])thiophenyl)sulfonium tetrakis(pentafluorophenyl)borate.

16. The method of claim 1 wherein the liquid radiation curable resin comprises more than one free radical photoinitiator.

17. The method of claim 16 wherein a free radical photoinitiator is bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide and is present in an amount less than 0.5 wt % of the liquid radiation curable resin.

18. The method of claim 1 wherein the substrate is substantially inelastic.

19. The method of claim 1 wherein the substrate is less than 250 microns thick.

20. The method of claim 1 wherein the amount of cationically polymerizable compounds is from about 40 wt % to about 60 wt %.

21. The method of claim 1 wherein a cationically polymerizable component is an epoxidized polybutadiene present in an amount from about 5 wt % to about 20 wt %.

22. The method of claim 1 wherein the layer of liquid radiation curable resin is from about 25 microns to about 250 microns in thickness.

23. The method of claim 1 wherein the actinic radiation must travel through the substrate to reach the liquid radiation curable resin.

24. A method for forming a three-dimensional object comprising:

1) coating a layer of liquid radiation curable resin comprising from 35 to 70 wt % of at least one cationically curable compound on a substrate;

2) contacting the layer of liquid radiation curable resin with a previously cured layer;

3) selectively exposing the layer of liquid radiation curable resin to actinic radiation, provided by a source of actinic radiation, thereby forming a cured layer which adheres to the previously cured layer;

4) separating the cured layer and the substrate; and

5) repeating steps 1-4 a sufficient number of times in order to build up a three dimensional object; wherein the storage shear modulus (G′) of the liquid radiation curable resin is measured to have achieved a (G′) value of greater than 9.5×10 5 Pa at 2.0 seconds from the beginning of light exposure when the storage shear modulus (G′) of the liquid radiation curable resin is measured on a Real Time Dynamic Mechanical Analyzer as the liquid radiation curable resin is cured with a light intensity of 50 mW/cm 2 for 1.0 second light exposure time.