Photohardenable epoxy composition

Abstract

A photohardenable composition especially suitable for use in solid imaging. The compositions are characterized by their improved photospeed in combined with excellent initial green strength. The compositions allows for the production of articles by solid imaging processing techniques that show little or no distortion, high accuracy, excellent clarity. The compositions are low in toxicity and have low sensitivity to water.

1. In an improved photohardenable composition composed of a cationically polymerizable and free radical polymerizable organic substance, a photo-generated photo- generating  acid precursor, a sensitizer for the photo-generated photo- generating  acid precursor and a free radical polymerization initiator wherein the improvement comprises:
 a) a mixture of photopolymerizable resins consisting essentially of 
 at least two epoxy resins one of which polymerizes , said at least two epoxy resins including a first epoxy resin polymerizing at a slower rate and has a having a higher neat viscosity than at least one other epoxy resin present and the , said first epoxy resins are being present at a concentration in the mixture of from 5 to 25% by weight, and  
 at least one monoacrylic monomer and at least one multi-acrylic monomer wherein the concentration of the monoacrylic monomer is from 0.12 to 0.90 parts by weight that of the multilayer monomer and wherein the ratio of the weight of the epoxy resins to that of the acrylic monomers is between 3 to 10; and  
 
 b) a combination of a free radical initiator and a photo-generating acid precursor characterized by optical molar extinction coefficient and optimized for use with a multi-wavelength argonion laser operating in the UV and producing two major wavelengths of 351 nm and 364 nm such that a normalized ratio of the extinction coefficients of the precursor and the initiator at one major wavelength is less than 3 times the ratio of extinction coefficient at a second major wavelength.  
 
     
     
       2. A method for accurately fabricating an integral three dimensional article having improved green strength by controlling the diffusion of photoactivated molecular species in the regions of a photohardenable liquid composition exposed to actinic radiation, the method comprising the steps of:
 (a) forming a layer of the photohardenable liquid composition;  
 (b) imagewise exposing areas of at least a portion of the layers to actinic radiation at wavelengths of 351 nm and 364 nm;  
 (c) introducing a new layer of liquid on to the layer previously exposed imagewise in step (b);  
 (d) imagewise exposing at least a portion of the new liquid layer to actinic radiation, wherein the improvement comprises use of photohardenable liquid composition comprising: 
 a) a mixture of photopolymerizable resins consisting essentially of 
 at least two epoxy resins one of which polymerizes , said at least two epoxy resins including a first epoxy resin polymerizing at a slower rate and has having a higher neat viscosity than at least one other epoxy resin present and the , said first epoxy resins are being present at a concentration in the mixture of from 5 to 25% by weight, and  
 at least one monoacrylic monomer and at least one multi acrylic monomer wherein the concentration of the monoacrylate monomers if from 0.12 to 0.90 parts by weight that of the multi-acrylate monomer and wherein the ratio of the weight of the epoxy resins to that of the acrylic monomers is between 3 to 10; and  
 
 b) a combination of a free radical initiator and a photo-generating acid precursor characterized by optical molar extinction coefficients and optimized for use with a multi-wavelength argon ion laser operating in the UV and producing two major wavelengths of 351 nm and 364 nm such that a normalized ratio of the extinction coefficients of the precursor and the initiator at one major wavelength is less than 3 times the ratio of extinction coefficient at a second major wavelength.  
 
 
     
     
       3. A photohardenable composition comprising:
 ( i )  a mixture of cationically polymerizable components having at least two epoxy resins, said at least two epoxy resins including a first epoxy resin polymerizing at a slower rate and having a higher neat viscosity than at least one other epoxy resin present,      ( ii )  a blend of radically polymerizable components;      ( iii )  at least one photo - generating acid precursor;      ( iv )  at least one free radical initiator; and      ( v )  water;      
       
         wherein said first epoxy resin has a viscosity of greater than  1000  poise @  25 ° C. and a viscosity greater than  200  poise @  52 ° C.  
       
     
     
       4. The composition of  claim 3  wherein said first epoxy resin has a softening point below  40 ° C.  
     
     
       5. The composition of  claim 3  wherein said mixture of cationically polymerizable components comprises, relative to the total weight of said at least two epoxy resins, from  5  to  25 %  by weight of said first epoxy resin.    
     
     
       6. The composition of  claim 3  wherein said blend includes at least one mono- acrylate monomer and at least one multi - acrylate monomer.    
     
     
       7. The composition of  claim 6  wherein the total amount of mono- acrylate monomers to the total amount of multi - acrylate monomers present in the composition, on a parts by weight basis, is  0 . 12 - 0 . 9  parts of mono - acrylate monomers to  1  part of multi - acrylate monomers.    
     
     
       8. The composition of  claim 6  wherein the total amount of mono- acrylate monomers to the total amount of multi - acrylate monomers present in the composition, on a parts by weight basis, is  0 . 27 - 0 . 58  parts of mono - acrylate monomers to  1  part of multi - acrylate monomers.    
     
     
       9. The composition of  claim 6  wherein said at least one multi- acrylate monomer includes at least one tri - acrylate monomer.    
     
     
       10. The composition of  claim 9  wherein the total amount of mono- acrylate monomers to the total amount of tri - acrylate monomers present in the composition, on a parts by weight basis, is  0 . 12 - 0 . 9  parts of mono - acrylate monomers to  1  part of tri - acrylate monomers.    
     
     
       11. The composition of  claim 9  wherein the total amount of mono- acrylate monomers to the total amount of tri - acrylate monomers present in the composition, on a parts by weight basis, is  0 . 27 - 0 . 58  parts of mono - acrylate monomers to  1  part of tri - acrylate monomers.    
     
     
       12. The composition of  claim 3 , wherein the ratio, on a parts by weight basis, of said mixture of cationically polymerizable components to said blend of radically polymerizable components is from  3 - 10  parts of said mixture to  1  part of said blend.  
     
     
       13. The composition of  claim 3  wherein said first epoxy resin includes an epoxy phenolic novolac resin and/or an epoxy cresol novolac resin.  
     
     
       14. The composition of  claim 13  wherein said epoxy phenolic novolac resin has on average  3 . 6  or more epoxy groups.  
     
     
       15. The composition of  claim 3  wherein said at least one other epoxy resin includes at least one cycloaliphatic epoxy.  
     
     
       16. The composition of  claim 3  wherein said composition further comprises a sensitizer for the photo- generating acid precursor.    
     
     
       17. The composition of  claim 3  wherein said blend of radically polymerizable components includes tetrahydrofurfuryl acrylate, isobornyl acrylate, lauryl acrylate and/or caprolactone acrylate.  
     
     
       18. The composition of  claim 3  wherein said blend of radically polymerizable components includes caprolactone acrylate.  
     
     
       19. The composition of  claim 3 , comprising, relative to the total weight of the composition,  0 . 2 - 3  wt %  of said water.    
     
     
       20. A photohardenable composition comprising:
   a mixture of at least two epoxy resins wherein a first epoxy resin polymerizes at a slower rate and has a higher neat viscosity than a second epoxy resin,        at least one mono - acrylate monomer and at least one multi - acrylate monomer,        a photo - generating acid precursor,        a free radical polymerization initiator, and        water;      
       
         wherein said first epoxy resin comprises an epoxy phenolic novolac resin and/or an epoxy cresol novolac resin.  
       
     
     
       21. The photohardenable composition of  claim 20  wherein the total amount of mono- acrylate monomers to the total multi - acrylate monomers present in the composition, on a parts by weight basis, is  0 . 12 - 0 . 9  parts of mono - acrylate monomers to  1  part of multi - acrylate monomers.    
     
     
       22. The photohardenable composition of  claim 20  wherein the total amount of mono- acrylate monomers to the total amount of multi - acrylate monomers present in the composition, on a parts by weight basis, is  0 . 27 - 0 . 58  parts of mono-acrylate monomers to  1  part of multi - acrylate monomers.    
     
     
       23. The photohardenable composition of  claim 20  wherein the ratio, on a parts by weight basis, of said mixture to said mono- acrylate and multi - acrylate monomers is from  3 - 10  parts of said mixture to  1  part of said mono - acrylate and multi - acrylate monomers.    
     
     
       24. The photohardenable composition of  claim 20  wherein said epoxy phenolic novolac resin has on average  3 . 6  or more epoxy groups.  
     
     
       25. The photohardenable composition of  claim 20  wherein said second epoxy resin comprises at least one cycloaliphatic epoxy.  
     
     
       26. The photohardenable composition of  claim 20  wherein said composition comprises a tri- acrylate monomer.    
     
     
       27. The photohardenable composition of  claim 20  wherein said at least one mono- acrylate monomer includes tetrahydrofurfuryl acrylate, isobornyl acrylate, lauryl acrylate and/or caprolactone acrylate.    
     
     
       28. The photohardenable composition of  claim 20  wherein said at least one mono- acrylate monomer includes caprolactone acrylate.    
     
     
       29. The photohardenable composition of  claim 20  wherein said composition further comprises a sensitizer for the photo- generating acid precursor.    
     
     
       30. The composition of  claim 20 , comprising, relative to the total weight of the composition,  0 . 2 - 3  wt %  of said water.    
     
     
       31. A method for fabricating a three- dimensional article comprising:      a. forming a layer of a photohardenable composition comprising,    (   1   )  a mixture of cationically polymerizable components having at least two epoxy resins, said at least two epoxy resins including a first epoxy resin polymerizing at a slower rate and having a higher neat viscosity than at least one other epoxy resin present,      (   2   )  a blend of at least one mono - acrylate monomer and at least one multi - acrylate monomer;      (   3   )  at least one photo - generating acid precursor; and      (   4   )  at least one free radical initiator;          b. imagewise exposing areas of at least a portion of the layer to actinic radiation; and        c. introducing a new layer of said composition on to the layer previously exposed imagewise in step  ( b )  and repeating step  ( b ) .      
     
     
       32. The method of  claim 31  wherein said first epoxy resin has a viscosity of greater than  1000  poise @  25 ° C.  
     
     
       33. The method of  claim 31  wherein said first epoxy resin has a viscosity of greater than  200  poise @  52 ° C.  
     
     
       34. The method of  claim 31  wherein said first epoxy resin has a softening point below  40 ° C.  
     
     
       35. The method of  claim 31  wherein said mixture of cationically polymerizable components comprises, relative to the total weight of said at least two epoxy resins, from  5  to  25 %  by weight of said first epoxy resin.    
     
     
       36. The method of  claim 31  wherein said first epoxy resin has a viscosity of greater than  1000  poise @  25 ° C.  
     
     
       37. The method of  claim 31  wherein the total amount of mono- acrylate monomers to the total amount of multi - acrylate monomers present in the composition, on a parts by weight, is  0 . 12 - 0 . 9  parts of mono - acrylate monomers to  1  part of multi - acrylate monomers.    
     
     
       38. The method of  claim 31  wherein the total amount of mono- acrylate monomers to the total amount of multi - acrylate monomers present in the composition, on a parts by weight basis, is  0 . 27 - 0 . 58  parts of mono - acrylate monomers to  1  part of multi - acrylate monomers.    
     
     
       39. The method of  claim 31  wherein said blend includes at least one tri- acrylate monomer.    
     
     
       40. The method of  claim 39  wherein the total amount of mono- acrylate monomers to the total amount of tri - acrylate monomers present in the composition, on a parts by weight basis, is  0 . 12 - 0 . 9  parts of mono - acrylate monomers to  1  part of tri - acrylate monomers.    
     
     
       41. The method of  claim 39  wherein the total amount of mono- acrylate monomers to the total amount of tri - acrylate monomers present in the composition, on a parts by weight basis, is  0 . 27 - 0 . 58  parts of mono - acrylate monomers to  1  part of tri - acrylate monomers.    
     
     
       42. The method of  claim 31  wherein the ratio, on a parts by weight basis, of said mixture of cationically polymerizable components to said blend is from  3 - 10  parts of said mixture to  1  part of said blend.  
     
     
       43. The method of  claim 31  wherein said first epoxy resin includes an epoxy phenolic novolac resin and/or an epoxy cresol novolac resin.  
     
     
       44. The method of  claim 43  wherein said epoxy phenolic novolac resin has on average  3 . 6  or more epoxy groups.  
     
     
       45. The method of  claim 43  wherein said at least one other epoxy resin includes at least one cycloaliphatic epoxy.  
     
     
       46. The method of  claim 31  wherein said at least one other epoxy resin includes at least one cycloaliphatic epoxy.  
     
     
       47. The method of  claim 31  wherein said composition further comprises a sensitizer for the photo- generating acid precursor.    
     
     
       48. The method of  claim 31 , wherein said composition further comprises water.  
     
     
       49. The method of  claim 31 , wherein said composition comprises, relative to the total weight of the composition,  0 . 2 - 3  wt %  of water.    
     
     
       50. A method of forming a photohardenable composition comprising:
   a. forming a mixture of epoxy resins having a first epoxy resin which polymerizes at a slower rate and has a higher neat viscosity than a second epoxy resin, said first epoxy resin having a softening point below  40 ° C.,        b. mixing in at least one monoacrylic monomer and at least one multiacrylic monomer, and        c. adding a photo - generating acid precursor and a free radical polymerization.      
     
     
       51. The method of  claim 50  further comprising admixture a sensitizer for the photo- generating acid precursor.    
     
     
       52. The method of  claim 50  wherein said at least one multi- acrylate monomer includes a tri - acrylate monomer.   
     
     
       53. The method of  claim 50  wherein the total amount of mono- acrylate monomers to the total amount of multi - acrylate monomers present in the composition, on a parts by weight basis, is  0 . 12 - 0 . 90  parts of mono - acrylate monomers to  1  part of multi - acrylate monomer.    
     
     
       54. The method of  claim 50  wherein the total amount of mono- acrylate monomers to the total amount of multi - acrylate monomers present in the composition, on a parts by weight basis, is  0 . 27 - 0 . 58  parts of mono - acrylate monomers to  1  part of multi - acrylate monomers.    
     
     
       55. The method of  claim 50  wherein the ratio, on a parts by weight basis, of said mixture of epoxy resins to said at least one mono- acrylate monomer and said multi - acrylate monomer is from  3 - 10  parts of said mixture to  1  part of said mono - acrylate and multi - acrylate monomer.    
     
     
       56. The method of  claim 50  wherein said first epoxy resin comprises an epoxy phenolic novolac resin and/or an epoxy cresol novolac resin.  
     
     
       57. The method of  claim 55  wherein said epoxy phenolic novolac resin has on average  3 . 6  or more epoxy groups.  
     
     
       58. The method of  claim 50  wherein said second epoxy resin comprises at least one cycloaliphatic epoxy.  
     
     
       59. The method of  claim 50  wherein said first epoxy resin has a viscosity of greater than  1000  poise @  25 ° C.  
     
     
       60. The method of  claim 59  wherein said mixture of epoxy resins comprises from  5  to  25 %  by weight of said first epoxy resin.    
     
     
       61. The method of  claim 50  wherein said first epoxy resin has a viscosity of greater than  200  poise @  52 ° C.  
     
     
       62. The method of  claim 50  wherein said mixture of epoxy resins comprises from  5  to  25 %  by weight of said first epoxy resin.    
     
     
       63. The composition of  claim 50 , further comprising adding water to form said composition.  
     
     
       64. A photohardenable composition comprising:
 ( a )  a mixture of at least two epoxy resins, said at least two epoxy resins including a first epoxy resin polymerizing at a slower rate and having a higher neat viscosity than at least one other epoxy resin present, said first epoxy resin being present, relative to the total weight of said mixture, in an amount of from  5  to  25   %  by weight, said first epoxy resin having a viscosity of greater than  1000  poise @  25 ° C. and a softening point below  40 ° C.,      ( b )  a blend of acrylate functional monomers comprising at least one multi - acrylate monomer and at least one mono - acrylate monomer, wherein the ratio of said at least one mono - acrylate monomer to said at least one multi - acrylate monomer, on a parts by weight basis, is  0 . 12 - 0 . 90  parts of mono - acrylate monomers to  1  part of multi - acrylate monomers,      ( c )  at least one photo - generating acid precursor, and      ( d )  at least one free radical initiator,        wherein the ratio, on a parts by weight basis, of said mixture of epoxy resins to said blend of acrylate functional monomers is from  3 - 10  parts of said mixture to  1  part of said blend.      
     
     
       65. A method of forming a three- dimensional article comprising:      a. forming a layer of the composition of    claim 64   ,        b. imagewise exposing areas of at least a portion of the layer to actinic radiation; and        c. introducing a new layer of said composition on to the layer previously exposed imagewise in step  ( b )  and repeating step  ( b ) .      
     
     
       66. A method of forming the composition of  claim 64  comprising:
   forming said composition by combining said mixture of epoxy resins, said blend of acrylate functional monomers, said at least one photo - generating acid precursor, and said at least one free radical initiator.      
     
     
       67. An article formed by solid imaging the composition of  claim 64 .  
     
     
       68. An object comprising the article of  claim 67 .  
     
     
       69. The composition of  claim 64 , wherein said composition further comprises water.  
     
     
       70. The composition of  claim 64 , wherein said composition comprises, relative to the total weight of the composition,  0 . 2 - 3  wt %  of water.    
     
     
       71. A photohardenable composition comprising:
 ( i )  a mixture of cationically polymerizable components having at least two epoxy resins, said at least two epoxy resins including a first epoxy resin polymerizing at a slower rate and having a higher neat viscosity than at least one other epoxy resin present,      ( ii )  a blend of radically polymerizable components;      ( iii )  at least one photo - generating acid precursor; and      ( iv )  at lest one free radical initiator;        wherein said first epoxy resin is selected from the group consisting of epoxy phenolic novolac resins and epoxy cresol novolac resins.      
     
     
       72. A method of forming a three- dimensional article comprising:      a. forming a layer of the composition of    claim 71   ;        b. imagewise exposing areas of at least a portion of the layer to actinic radiation; and        c. introducing a new layer of said composition on to the layer previously exposed imagewise in step  ( b )  and repeating step  ( b ) .      
     
     
       73. The composition of  claim 71 , wherein said at least one other epoxy resin includes a cycloaliphatic epoxy.  
     
     
       74. A method of forming a three- dimensional article comprising:      a. forming a layer of a photohardenable composition comprising    ( i )  a mixture of cationically polymerizable components having at least two epoxy resins, said at least two epoxy resins including a first epoxy resin polymerizing at a slower rate and having a higher neat viscosity that at least one other epoxy resin present,      ( ii )  a blend of radically polymerizable components;      ( iii )  a polyol;      ( iv )  at least one photo - generating acid precursor;      ( v )  at least one free radical initiator; and        vi )  above  0 . 75  wt  %  water;        wherein the composition has an equivalent weight ratio of epoxy to polyol of above  3 . 5 ;          b. imagewise exposing areas of at least a portion of the layer to actinic radiation; and        c. introducing a new layer of said composition on to the layer previously exposed imagewise in step  ( b )  and repeating step  ( b );    
         wherein said three - dimensional article is being formed at a room relative humidity in the range of about  40  to  80   % .    
     
     
       75. The method of  claim 74 , wherein said composition comprises, relative to the total weight of the composition, up to  3  wt %  of water.    
     
     
       76. A method of forming a three- dimensional article at a relative humidity in the range of about  40   %  to  80   % , comprising:    ( a )  equilibrating a photoformable composition to said relative humidity by adding, relative to the total weight of the composition, above  0 . 75  wt  %  and up to  3  wt  %  of water to a photoformable composition, said photoformable composition comprising  
 ( i )  a mixture of cationically polymerizable components having at least two epoxy resins, said at least two epoxy resins including a first epoxy resin polymerizing at a slower rate and having a higher neat viscosity than at least one other epoxy resin present,    
 ( ii )  a blend of radically polymerizable components;    
 ( iii )  a polyol;    
 ( iv )  at least one photo - generating acid precursor; and    
 ( v )  at least one free radical initiator;    
   wherein the composition has an equivalent weight ratio of epoxy to polyol of above  3 . 5 ;    
   ( b )  forming a layer of the photoformable composition comprising the added water;      ( c )  imagewise exposing areas of at least a portion of the layer to actinic radiation; and      ( d )  introducing a new layer of said composition on to the layer previously exposed imagewise in step  ( c )  and repeating step  ( c ) .