METHOD AND APPRATUS FOR MANUFACTURE OF 3D OBJECTS

Abstract

The current three-dimensional object manufacturing technique relies on the deposition of a pseudoplastic material in gel aggregate state. The gel flows through a deposition nozzle because the applied agitation and pressure shears the bonds and induces a breakdown in the material elasticity. The elasticity recovers immediately after leaving the nozzle, and the gel solidifies to maintain its shape and strength.

Claims

1. A pseudoplastic material for manufacture of three-dimensional objects comprising: 20-96 weight-% of epoxy resin; 0-30 weight % of oxetane; 0-30 weight-% of polyol; 0.5-6 weight-% of at least one cationic photoinitiator; 0-30 weight-% of at least one rheology modifier; and 0-30 weight-% of at least one performance additive/filler; and wherein the pseudoplastic material is formulated to form the three-dimensional objects by extruding a layer of the pseudoplastic material and curing the extruded layer to form a cured extruded layer, and successively extruding and curing layers of the pseudoplastic material upon the cured extruded layer; and wherein the pseudoplastic material is formulated to be cured by cationic curing.

2. The pseudoplastic material according to claim 1, wherein the epoxy resin is at least one of a group of resins consisting cycloaliphatic epoxies.

3. The pseudoplastic material according to claim 1, wherein the epoxy resin comprises at least one of modified and unmodified Bisphenol A, Oxiranes oxides of alkadienes, alkenes, cycloalkadienes and cycloalkenes.

4. The pseudoplastic material according to claim 1, wherein the oxirane comprises at least one selected from a group consisting of Cyclohexanol, 4,4-(1-methylethylidene)bis, polymer with (chloromethyl) oxirane, hydrogenated Bisphenols A, 3,4-Epoxycyclohexane)methyl 3,4-epoxycyclohexylcarboxylate, Bis(7-oxabicyclo[4.1.0]hept-3-ylmethyl) adipate.

5. The pseudoplastic material according to claim 1, wherein the oxetane comprises at least one selected from a group consisting of vinyl ethers, TMPO-3-ethyl-3-hydroxymethyloxetane, 2-Oxepanone, polymer with 2-ethyl-2-(hydroxymethyl)-1,3-propanediol, 2-oxepanone, polymer with 2,2-bis(hydroxymethyl)-1,3-propanediol.

6. The pseudoplastic material according to claim 1, wherein the polyol comprises at least one selected from a group consisting of chain extenders such as 2-Oxepanone, polymer with 2-ethyl-2-(hydroxymethyl)-1,3-propanediol, 2-oxepanone, polymer with 2,2-bis(hydroxymethyl)-1,3-propanediol.

7. The pseudoplastic material according to claim 1, wherein the cationic photoinitiator comprises at least one of a group of cationic photoinitiators consisting of Iodonium (4-methylphenyl)[4-(2-methylpropyl)phenyl]-, hexafluorophosphate(1-) (1:1) (4-methylphenyl)[4-(2-methylpropyl) phenyl]-, hexafluorophosphate in propylene carbonate, triarylsulfonium hexafluorophosphate with sensitizer, 4,4-dimethyl-diphenyl iodonium hexafluorophosphate, and 3-ethyl-3-hydroxymethloxetane.

8. The pseudoplastic material according to claim 1, wherein the cationic photoinitiator sensitizer comprises at least one of a group of sensitizers consisting of 9,10-Dibutoxyanthracene and Isopropylthioxanthone to enhance reactivity of the cationic photoinitiator and extend curing radiation range to longer wavelengths.

9. The pseudoplastic material according to claim 1, wherein the rheology modifier comprises at least one of a group of rheology modifiers consisting of attapulgite clays, bentonite clays, organoclays, treated and untreated synthetic silicas, and fumed silica.

10. The pseudoplastic material according to claim 1, wherein the performance additive/filler comprises at least one of a group of filers consisting of pigments, glass beads, Kevlar fibers, nylon fibers, flame retardants, impact modifiers clay and silica.

11. The pseudoplastic material according to claim 1, wherein a first viscosity of the material before extrusion is in a range of about 120,000.00 mPa.Math.s to about 500,000.00 mPa.Math.s at atmospheric pressure; and/or wherein a second viscosity of the material when a force is applied is in a range of about 250 to about 700 mPa.Math.s.

12. The pseudoplastic material according to claim 1, wherein the psuedoplastic material is extruded in layers to form the three-dimensional objects having a cantilever ratio of at least 1:4.

13. The pseudoplastic material according to claim 1, wherein the pseudoplastic material is curable by ultraviolet radiation with a wavelength in a range of 360 to 485 nm.

14. The pseudoplastic material according to claim 1, wherein the pseudoplastic material can be extruded onto an earlier extruded layer of cured pseudoplastic material and then cured to form a bond between the cured layers of pseudoplastic material.

15. The pseudoplastic material according to claim 1, wherein a bond is strong enough to support a later extruded layer of the pseudoplastic material in a suspended state.

16. The pseudoplastic material according to claim 1, wherein the psuedoplastic material can form a three-dimensional object free of any conventional support structures when extruded in layers and cured.

17. The pseudoplastic material according to claim 1, wherein the pseudoplastic material can recover at least 30% of a first viscosity immediately upon being extruded and exposed to atmospheric pressure.

18. The pseudoplastic material according to claim 1, wherein the pseudoplastic material can recover at least 40% of the first viscosity immediately upon being extruded and exposed to atmospheric pressure.

19. The pseudoplastic material according to claim 1, wherein the pseudoplastic material can recover at least 50% of the first viscosity immediately upon being extruded and exposed to atmospheric pressure.

20. The pseudoplastic material according to claim 1, wherein the pseudoplastic material can recover 60% to 90% of the first viscosity immediately upon being extruded and exposed to atmospheric pressure.

21. The pseudoplastic material according to claim 1, wherein the psuedoplastic material can be extruded in layers to form the three-dimensional objects including cantilever objects having a cantilever ratio of at least 1:4 without use of structures to support uncured pseudoplastic material.

22. The pseudoplastic material according to claim 1, wherein the psuedoplastic material can be extruded in layers to form the three-dimensional objects including cantilever objects having a cantilever ratio of at least 1:5 without use of structures to support uncured pseudoplastic material.

23. The pseudoplastic material according to claim 1, wherein the psuedoplastic material can be extruded in layers to form the three-dimensional objects including cantilever objects having a cantilever ratio of 1:5 to 1:200 without use of structures to support uncured pseudoplastic material.

24. The pseudoplastic material according to claim 1, wherein a second viscosity is in a range of 250 to 700 mPa.Math.s.

25. The pseudoplastic material according to claim 1, wherein a second viscosity is in a range of 250 to 700 mPa.Math.s at a pressure of 0.1 to 30 bar.

26. The pseudoplastic material according to claim 1, wherein the first viscosity is in a range of 100,000 to 400,000 mPa.Math.s at atmospheric pressure.

27. A pseudoplastic material for manufacture of three-dimensional objects comprising: 0-30% acrylate oligomer; 0-30% acrylate monomer; 0.5-10% free radical photoinitiator; 30-70% epoxy resin; 0-30% oxetane; 0-30% polyol; 0.1-5% cationic photoinitiator; 0-5% sensitizer; 1-10% rheology modifier; and 0-30% performance improving additives/fillers; and wherein the pseudoplastic material is formulated to form three-dimensional objects by extruding a layer of the pseudoplastic material and curing the extruded layer to form a cured extruded layer, and successively extruding and curing layers of the pseudoplastic material upon the cured extruded layer, the pseudoplastic material having a first viscosity when under atmospheric pressure and a second viscosity when under an extrusion pressure during extrusion, the second viscosity being less than the first viscosity, the second viscosity allowing the psuedoplastic material to flow when extruded from a three-dimensional printer, and the first viscosity allowing uncured psuedoplastic material to form the three-dimensional object including a cantilever object; and wherein the pseudoplastic material is a hybrid curable formulation.

28. A method of forming a three-dimensional object comprising: a) providing a highly viscous pseudoplastic material having a first viscosity and agitating the material to shear the pseudoplastic material and cause it to flow through a delivery system to an extrusion unit; b) employing an extrusion unit to extrude a first strip of the pseudoplastic material in image-wise manner; c) extruding a second strip of the pseudoplastic material, the second strip adjacent to the first strip and contacting the first strip at at least one contact point; d) continuously illuminating the first and the second strip to harden the pseudoplastic material; e) continue to extrude the pseudoplastic material in an image-wise manner and continuously illuminate extruded material to form a three-dimensional object; and wherein the pseudoplastic material is a hybrid curable formulation material.

29. A method of forming a three-dimensional object comprising: a) providing a highly viscous pseudoplastic material formulated for hybrid curing and having a first viscosity and agitating the material to shear the pseudoplastic material thereby decreasing viscosity to a second viscosity and to cause it to flow through a delivery system to an extrusion unit; b) employing an extrusion unit to extrude a first portion of the pseudoplastic material in image-wise manner, the first portion having a cross section with a diameter; c) illuminating the first extruded portion to harden the pseudoplastic material; d) extruding a second portion of the pseudoplastic material adjacent to the first portion and contacting the first portion at at least one contact point, wherein a cross section of the second portion is shifted in an axis perpendicular to a gravitational force compared to the cross section of the first portion; e) obtaining a common contact section between surfaces of the first and second extruded portions by forming an envelope into which a segment of the first portion protrudes by sliding, due to a gravitational force, of the second portion along circumference of surface of the first portion hardened in step c), wherein surface of the second portion wets surface of the first portion at the common contact section; f) illuminating the extruded second portion to harden the pseudoplastic material and to form a bond between the first and second portions of pseudoplastic material at the common contact section; g) adjusting relative position between extrusion unit and extruded second portion such that the second portion obtains location of extruded first portion of step b); and h) repeating steps d) to g) until the three-dimensional object has been formed.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] FIG. 1 is a schematic illustration of an example of an apparatus for manufacture of a three-dimensional object.

[0040] FIGS. 2A and 2B are examples of a three-dimensional object manufactured using the present apparatus.

[0041] FIGS. 3A-3C are illustrations explaining printing or manufacture of a 3D object with the present pseudoplastic material/gel.

[0042] FIG. 4 is an example of a hollow rectangular prism with 90 degrees angles.

[0043] FIG. 5 is a graph that demonstrates the variations of viscosity vs shear rate.

DETAILED DESCRIPTION OF THE INVENTION

[0044] The invention will be described with reference to the attached non-limiting drawings. The present invention is concerned with methods for the manufacture of three-dimensional structures by printing, i.e. by so-called 3D-printing, a material and an apparatus useful therefore, and the use of a pseudoplastic material for 3D printing.

[0045] It has been found that using pseudoplastic material, i.e. a composition with decreasing viscosity when shear force is applied, allows to produce sophisticated and complex three-dimensional structures by 3D printing, in particular hollow structures and structures that are cantilever-like, without the need for supporting elements during manufacture.

[0046] The pseudoplastic material used according to the present invention shows shear-thinning in a range such that the starting composition having high viscosity when it is transferred to and through an extrusion unit has a viscosity low enough for the transfer and for creating a portion of a 3D structure, such as a strip, or a layer or an image, but has an increased viscosity within short term when it arrives at its predetermined position. Viscosity of the starting composition is also called first viscosity and viscosity after application of a force, such as at the outlet of the extrusion unit, is also called second viscosity. In one embodiment a gel is used which viscosity decreases to about 700-250 mPa.Math.s at a pressure higher than atmospheric pressure. A number of pseudoplastic material compositions that are useful for this purpose is as defined below. Some of the compositions or formulations are suitable for radical curing processes. Other of the compositions could be better cured by cationic curing processes and still other compositions are more suitable for hybrid curing processes.

[0047] One three-dimensional object manufacturing technique relies on the deposition of material in gel aggregate state. The gel flows through a deposition nozzle because the applied agitation and pressure shears the inter-particle bonds and induces a breakdown in the elasticity of the material. The material recovers immediately after leaving the nozzle, and the pseudoplastic material or gel almost immediately solidifies to maintain its shape.

[0048] A method of forming a three-dimensional object is provided which comprises the following steps: [0049] a. providing a highly viscous pseudoplastic material having a first viscosity and agitating the material to shear the pseudoplastic material and cause it to flow through a delivery system to an extrusion unit; [0050] b. employing an extrusion unit to extrude a strip of the pseudoplastic material in image-wise manner; [0051] c. extruding a second strip of the pseudoplastic material, the second strip adjacent to the first strip and contacting the first strip at at least one contact point; [0052] d. continuously illuminating the first and the second strip to harden the pseudoplastic material; and [0053] e. continue to extrude the pseudoplastic material in an image-wise manner and continuously illuminate extruded material to form a three-dimensional object.

[0054] Furthermore a method of forming a three-dimensional object is provided comprising: [0055] a. providing a highly viscous pseudoplastic material having a first viscosity and agitating the material to shear the pseudoplastic material thereby decreasing viscosity to a second viscosity and to cause it to flow through a delivery system to an extrusion unit; [0056] b. employing an extrusion unit to extrude a first portion of the pseudoplastic material in image-wise manner, the first portion having a cross section with a diameter; [0057] c. illuminating the first extruded portion to harden the pseudoplastic material; [0058] d. extruding a second portion of the pseudoplastic material adjacent to the first portion and contacting the first portion at at least one contact point, wherein a cross section of the second portion is shifted in an axis perpendicular to the gravitational force compared to the cross section of the first portion; [0059] e. obtaining a common contact section between the surfaces of the first and second extruded portions by forming an envelope into which a segment of the first portion protrudes by sliding, due to the gravitational force, of the second portion along the circumference of the surface of the first portion hardened in step c), wherein the surface of the second portion wets the surface of the first portion at the common contact section; [0060] f. illuminating the extruded second portion to harden the pseudoplastic material and to form a bond between the first and second portions of pseudoplastic material at the common contact section; [0061] g. adjusting the relative position between extrusion unit and extruded second portion such that the second portion obtains the location of the extruded first portion of step b); and [0062] h. repeating steps d) to g) until the three-dimensional object has been formed.

[0063] The present application also discloses a method of additive manufacture of a three-dimensional object which comprises the following steps: [0064] a. providing a tank with a high viscosity pseudoplastic material and acting to reduce the material viscosity in the tank to shear thin the material; [0065] b. applying to the pseudoplastic material pressure exceeding atmospheric pressure to cause the pseudoplastic material to flow through a delivery system to an extrusion nozzle; [0066] c. extruding in an image-wise manner a first portion of the pseudoplastic material; [0067] d. extruding in an image-wise manner at least a second portion of the pseudoplastic material; and [0068] e. wherein the second portion of pseudoplastic material has at least one common contact section with the first portion of the pseudoplastic material; and [0069] f. wherein the pseudoplastic material immediately upon extrusion from the nozzle changes the viscosity to a viscosity substantially higher than the viscosity at the pressure exceeding atmospheric pressure.

[0070] A three-dimensional object can be obtained with any of the above mentioned methods and by use of any of the disclosed material formulations and the objects obtained are also part of the present invention.

[0071] An apparatus that is useful for manufacture of a three-dimensional object comprises a tank for storing a pseudoplastic material at atmospheric pressure; a pump configured to apply agitation to the pseudoplastic material to shear thin the pseudoplastic material and reduce the pseudoplastic material viscosity such as to cause the material to flow; an extrusion unit comprising an extrusion nozzle, an extrusion head, an extrusion die, or another extrusion outlet, configured to extrude in image-wise manner the pseudoplastic material at a pressure exceeding atmospheric pressure; and an X-Y-Z movement system configured to move at least the extrusion nozzle in a three coordinate system.

[0072] The present apparatus is described in detail by reference to FIG. 1 which is a schematic illustration of an example of an apparatus suitable for manufacture of three-dimensional objects or structures. The apparatus comprises at least a container such as a tank to receive the pseudoplastic material, a pump to apply a force to the pseudoplastic material, an extrusion unit comprising a nozzle to extrude the pseudoplastic material, and a movement system comprising a control unit, such as a computer.

[0073] Apparatus 100 includes a container for pseudoplastic material, such as a storage or material supply tank 102 adapted to store a pseudoplastic high viscosity material 104, a pump 108 configured to apply a force to the gel, for example by agitating and shear thinning the pseudoplastic high viscosity material or gel 104, to reduce material 104 viscosity to cause the material to flow. Pumps for such purpose are well-known in the art and any pump that can apply shear to the gel to be extruded is useful. Pump 108 could be such as Graco S20 supply system commercially available from Graco Minneapolis, Minn. U.S.A., or a barrel follower dispensing pump Series 90 commercially available from Scheugenpflug AG, 93333 Neustadt a.d. Donau, Germany. Pump 108 in addition to agitation also develops a pressure higher than atmospheric pressure such that the pseudoplastic material 104 flows through a delivery tubing or system 112 to an extrusion (unit) nozzle 116. The higher than atmospheric pressure developed by the pump is communicated to the dispenser and could be such as 0.1 bar to 30.0 bar and typically from 1.0 bar to 20.0 bar and sometimes 2.0 bar to 10.0 bar.

[0074] Apparatus 100 includes an X-Y-Z movement system 124 configured to move the extrusion nozzle 116 in a three coordinate system. Alternatively, a table 120 could be made to move in a three coordinate system. In another example, the movement in three directions (X-Y-Z) could be divided between the extrusion nozzle 116 and table 120. Apparatus 100 also includes a control unit, such as computer 128 configured to control operation of movement system 124, pump 108 pseudoplastic material steering operation and value or magnitude of the pressure higher than atmospheric pressure. The control unit, computer 128 is further adapted to receive the three-dimensional object 132 data and generate from the received data the X-Y-Z movement commands and distance such that the pseudoplastic material 104 is extruded through extrusion unit 114 and nozzle 116 in an image wise manner. The X-Y-Z movement could be performed in a vector mode or raster mode, depending on the object to be printed. Computer 128 could also be configured to optimize the decision on the printing mode.

[0075] Apparatus 100 further includes a source of radiation for curing or hardening the pseudoplastic material. Any source of radiation providing radiation that is useful for curing can be used. The source of radiation could provide ultraviolet radiation, infrared radiation, heat, microwave radiation and other types of radiation suitable for curing the material.

[0076] In FIG. 1 a UV LED based source of radiation 136 is used for curing the extruded material. An example for a source of radiation 136 is a FireJet FJ200 commercially available from Phoseon Technology, Inc., Hillsboro Oreg. 97124 USA. A suitable source of radiation 136 provides UV radiation with total UV power of up to 900 W and with a wavelength that normally is in the range of 230-420 nm, but can also be in the range of 360-485 nm, for example a wavelength in the range of 380-420 nm. Alternatively, a UV lamp such as for example, mercury vapor lamp model Shot 500 commercially available from CureUV, Inc., Delray Beach, Fla. 33445 USA can be used, or any other UV lamp that is available. In one embodiment the source of UV radiation 136 operates in a continuous manner and the UV radiation is selected to harden the pseudoplastic material 104. Computer 128 could also be configured to control operation of source of UV radiation 136 and synchronize it with the printing mode.

[0077] Manufacture or formation of a three-dimensional object 132 takes place by extrusion. Initially, a highly viscous pseudoplastic material 104, such as the one that will be described below under test name BGA 0, is provided in tank 102. The pseudoplastic material has a first viscosity or starting viscosity before the material is conveyed to the extruder unit. By application of shear the viscosity is reduced so that the material has a second viscosity which is in a range such that the material easily flows. After extrusion the material rests and regains at least a percentage of the first viscosity.

[0078] A suitable first or starting viscosity for the pseudoplastic material 104 could be in the range of about 40,000 to 500,000 mPa.Math.s, and typically such as 100,000 to 400,000 mPa.Math.s at a low shear rate. The viscosity after application of shear can decrease as low as 250 mPa.Math.s. As is shown in FIG. 1, Pump 108 is operative to agitate and deliver material 104 through the delivery system 112 to the extrusion unit 114 and to nozzle 116 and apply to it a varying pressure exceeding the atmospheric pressure. The tested pseudoplastic material formulation has shown different degrees of shear thinning properties and viscosity under different pressure. The pressure applied would typically be in range of 1.0 bar to 5.0 bar. Application of agitation and pressure to material 104 reduces the viscosity of material 104 by a shear thinning process to about 250-700 mPa.Math.s and typically to about 450 to 550 mPa.Math.s. The pressure higher than atmospheric pressure applied to the pseudoplastic material with reduced viscosity is sufficient to shear the pseudoplastic material 104 and cause it to flow through a delivery system 112 to extrusion unit 114 to be extruded through nozzle 116.

[0079] In some examples the agitation intensity and application of higher than atmospheric pressure could vary. Extrusion unit 114 or nozzle 116 extrudes a strip or a portion of the pseudoplastic material 104 in image-wise manner. The system can comprise one extrusion unit or more than one unit and one unit can comprise one nozzle or more. There could be one or more extrusion units 114 or nozzles 116 and their diameter could be set to extrude a strip or a layer of the pseudoplastic material 104 with a diameter of 0.5 to 2.0 mm. The diameter of a nozzle can have different forms as is known in the art. Other than round nozzle 116 cross sections are possible and generally a set of exchangeable nozzles with different cross sections could be used with apparatus 100.

[0080] The control unit, such as computer 128, is adapted to receive the three-dimensional object 132 data and generate from the received data the X-Y-Z movement commands and length of strips of pseudoplastic material 204-1, 204-2 (FIG. 2B) and so on, such that the pseudoplastic material 104 extruded through extrusion (unit) nozzle 116 in an image wise manner resembles a slice of object 132. In a similar manner a second strip or a portion of the pseudoplastic material 104 is extruded.

[0081] FIGS. 3A-3C are illustrations explaining printing or manufacture of a 3D object with the present pseudoplastic material or gel. As shown in FIG. 3 B, when producing horizontally oriented segments of a three-dimensional object, each next or adjacent strip or portion of pseudoplastic material 204-4 or 204-5 is extruded or printed. Strip or drop 204-5 could slightly shift or slide in a direction indicated by arrow 312 at about the boundary 304 of the previously extruded strip or layer, for example 204-4 or 204-3. The shift or slide 308 could be in a range of 1/5 to 1/35, such as 1/10 or 1/30 of the extruded strip diameter and the shift or slide value could vary in the process of the three-dimensional object manufacture. Drop or strip 204-5 slides as shown by arrow 312 from its unstable position to a more stable position dictated by the solidification rate of the pseudoplastic material that could be attributed to the material viscosity increase and gravitational forces. The cross-section of the second strip or drop 204-5 is shifted (304) in an axis perpendicular to the gravitational force compared to the cross-section of the first strip or drop 204-4.

[0082] Without being bound by theory it is assumed that in the course of a sliding movement of drop or strip 204-5 along the circumference of the adjacent strip surface, drop or strip 204-5 wets the surface of the adjacent strip 204-4 and the still at least partially liquid drop or strip 204-5 is forming an envelope into which a segment of the previously printed drop or strip 204-4 protrudes. Furthermore, it is assumed that the large contact surface between earlier printed drop/strip or layer and the later extruded drop/strip or layer contributes to extraordinary strength of the bond between the strips/drops or layers. In addition to this, viscosity of the extruded drop/strip is rapidly increasing limiting to some extent the slide of the drop and further contributing to the bond strength. Curing radiation sources 136 are operative in course of printing and by the time drop/strip 204-5 reaches its stable position drop/strip 204-5 solidifies or hardens. In some examples, a shift of a drop/strip can be intentionally introduced.

[0083] The bond between the later and earlier extruded strips of pseudoplastic material 104 becomes strong enough to support in a suspended state the later extruded and additional strips of the present pseudoplastic material until the later extruded strip of pseudoplastic material has dropped into a horizontal position alongside the earlier extruded strip or layer of pseudoplastic material.

[0084] This bond is sufficiently strong to support printing of hollow and/or cantilever-like structures or three-dimensional objects with a cantilever ratio of at least 1:5 and up to 1:200 and even more without any conventional support structures. Objects of FIGS. 2A and 2B have been printed by strips with diameter of 1.3 mm. Objects of FIGS. 2A and 2B had a cantilever ratio from 1:5 up to more than 1:200. No support structures have been required.

[0085] FIG. 3C illustrates manufacture or printing of a vertical segment of a 3D object. In the example of FIG. 3C drops 204 are positioned on top of each other and before the pseudoplastic material solidifies the later printed strip 204-5 wets the surface of the adjacent strip 204-4 and the still, at least partially liquid strip 204-5, is forming an envelope into which a segment of the previously printed strip 204-4 protrudes. Without being bound by theory it is assumed that concurrently to the increase in the viscosity of the extruded drop/strip and the solidification of the pseudoplastic material there is an increase in surface tension of the later extruded drop/strip that further contributes to the bond strength.

[0086] The present method and apparatus are useful for manufacturing hollow articles in a size not available until now without support structures. With the new system it is possible to prepare hollow figures of big size for example 100010001000 mm.sup.3 or even 100001000010000 mm.sup.3 that are stable. FIG. 4 is an example of a hollow rectangular prism with 90 degrees angles. The dimensions of prism 404 cross section are 150150 mm.sup.2. The extruded strips 408 has a square cross section with dimensions of 1.81.8 mm.sup.2. No internal support structures are required.

[0087] The source of radiation that is used according to the present invention can be operated in a continuous mode or a discontinuous mode. The skilled person can choose the mode that is best suited for a specific object and material, respectively. In a continuous mode the source of radiation 136 irradiates the strips of the three-dimensional object 132 being manufactured to harden or cure the extruded layer of material 104. Concurrently, extrusion unit 114 can continue to extrude layers of the pseudoplastic material in an image-wise manner and source of radiation 136 could operate to continuously illuminate or irradiate extruded layers of pseudoplastic material 104 to form a cured extruded layer of a three-dimensional object. In a discontinuous mode the source of radiation is adapted to irradiate the extruded layer of material when it is necessary.

[0088] The pseudoplastic material has a first viscosity at atmospheric pressure and a second viscosity at a pressure exceeding atmospheric pressure. The second viscosity is lower than the first viscosity and as the material 104 is leaving the extrusion unit (nozzle) it immediately upon leaving the extrusion nozzle recovers a significant fraction of the first viscosity, such as at least 30%, suitably at least 40%, in particular at least 50% of the first viscosity. The recovered viscosity in a preferred embodiment is between 60 to 90% or even more of the first viscosity.

[0089] The formulation of the pseudoplastic gel material will now be described. In some examples, the radical curable pseudoplastic gel material used for the present 3D objects printing comprises at least one curable oligomer, at least one reactive diluent, at least one curing agent, at least one rheology modifier, and optionally at least one performance improving additive and/or further additives. In some examples, the cationic curable pseudoplastic gel material used for the present 3D objects printing comprises at least one epoxy or vinyl ether compound, at least one cationic curing agent, at least one rheology modifier, and optionally at least one performance improving additive and/or further additives. The curable oligomers used in the present curable composition can be oligomers having at least one ethylenically unsaturated group and can be comprised for example of urethane, epoxy, ester and/or ether units. Oligomers such as acrylated and methacrylated oligomers such as acrylated epoxies, polyesters, polyethers and urethanes are useful. Examples of oligomers useful in the present invention are acryl based or methacryl based oligomers, olefine based oligomers, vinyl based oligomers, styrene oligomers, vinyl alcohol oligomers, vinyl pyrrolidone oligomers, diene based oligomers, such as butadiene or pentadiene oligomers, addition polymerization type oligomers, such as oligoester acrylate based oligomers, for example oligoester (meth)acrylate or oligoester acrylate, polyisocyanate oligomers, polyether urethane acrylate or polyether urethane methacrylate oligomers, epoxy oligomers among others. Those oligomers are known in the art and are commercially available.

[0090] The use of a UV or visible light induced cationic curing mechanism provides the following advantages: [0091] a. Epoxy resins that undergo cationic polymerization show lower shrinkage, insensitive to oxygen inhibition and undergo dark reaction-post cure effect, where areas that are not exposed to UV irradiation or thick layers can also be cured. [0092] b. The printing material may further include an epoxide compound (A cationic reagent typically includes at least one cyclic ether group (e.g., one or more epoxide groups (e.g., a three member cyclic ether), (e.g., at least one of a siloxane epoxide compound, a cylcoaliphatic epoxide compound, or a glycidyl ether epoxide compound), one or more oxetane groups (e.g., a four member cyclic ether), or a combination of such groups). [0093] c. Polymerization of the cationic reagent typically includes a ring-opening reaction of the cyclic ether group(s) of the reagent (e.g., cationic ring opening polymerization). The polymerization can be initiated by, for example, an initiating species (e.g., a cation) formed by a photoinitiator upon absorption of light by the photoinitiator. The cationic reagent can be a monomer or an oligomer (e. g., a compound having multiple repeat units, at least some of which (e.g., most or all) typically have at least one cyclic ether group). In some embodiments, the cationic reagent is an oxetane compound having at least one oxetane group (e. g., at least two oxetane groups or more). The printing material may include a combination of such oxetane compounds. [0094] d. As disclosed in U.S. Pat. No. 5,889,084 to Roth and U.S. Pat. No. 7,889,084 to Jang incorporated herein by reference, examples of cationic reagents including at least one epoxide group include cycloaliphatic epoxy compounds such as bis-(3,4-epoxycyclohexyl)adipate, 3,4-epoxycyclohexyl methyl-3,4-epoxycyclohexane carboxylate, and 7-Oxa-bicyclo[4.1.0]heptane-3-carboxylic acid 7-oxabicyclo[4.1.0] hept-3-ylmethyl ester; ether derivatives including diol derivatives such as 1,4-butanediol diglycidylether and neo pentyl glycol diglycidylether; and glycidyl ethers such as n-butyl glycidyl ether, distilled butyl glycidyl ether, 2-ethyl hexyl glycidyl ether, C8-C10 aliphatic glycidyl ether, C12 C14 aliphatic glycidyl ether, O-cresyl glycidyl ether, P-tertiary butyl phenyl glycidyl ether, nonyl phenyl glycidyl ether, phenyl glycidyl ether, cyclohexanedimethanol diglycidyl ether, polypropylene glycol diglycidyl ether, poly glycol dig lycidyl ether, dibromo neopentyl glycol diglycidyl ether, trimethylopropane triglycidyl ether, castor oil triglycidyl ether, propoxylated glycerin triglycidyl ether, sorbitol polyglycidyl ether, glycidyl ester of neodecanoic acid, and glycidyl amines such as epoxidized meta-xylenediamine. In some embodiments, the ink includes at least two (e.g., at least three or more) cationic reagents. For example, the ink can include at least one oxetane compound in combination with one or more other cationic reagents (e.g., in combination with at least one other oxetane compound, at least one cationic reagent. [0095] e. Additional examples for an epoxide group containing reagents are cycloaliphatic epoxies such as (3,4-Epoxycyclohexane)methyl 3,4-epoxycyclohexylcarboxylate; 3,4-Epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate modified epsilon-caprolactone; cyclohexanol, 4,4-(1-methylethylidene)bis-, polymer with (chloromethyl) oxirane: epoxidized polybutadiene; Epsilon-caprolactone modified tetra(3,4-epoxycyclohexylmethyl)butanetetracarboxylate, modified and unmodified Bisphenol A didiglycidyl ether epoxy resins etc.

[0096] The reactive diluents used for the radical curable pseudoplastic composition of the present invention are low molecular weight mono- or multifunctional compounds, such as monomers carrying one, two, three or more functional groups that can react in a curing reaction. A useful reactive diluent is for example a low molecular compound having at least one functional group reactive with the oligomer in the presence of a curing agent. Typical examples are low molecular weight acrylate esters including mono-, di-, and tri-(meth)acrylates or mixtures thereof. Reactive materials used in cationic curable formulations may be low molecular weight monomer and co-monomers that are used as diluents. Vinyl ethers such as methyl vinyl ether, styrene, alpha olefins and oxetanes could provide faster material curing speed. In some embodiments, the oxetane compound includes at least one of 3-ethyl-3-hydroxymethyloxetane, 3,3-oxybis(methylene)bis(3-ethyloxetane), 1,4-bis[(3-ethyl-3-oxetanylmethoxy)methyl]benzene and 3-ethyl-3-[(2-ethylhexyloxy)methyl]oxetane.

[0097] Diols and polyols are used as chain extenders and usually increase the flexibility of the system and the curing speed. Examples of those materials are 2-Oxepanone, polymer with 2-ethyl-2-(hydroxymethyl)-1,3-propanediol, 2-oxepanone, polymer with 2,2-bis(hydroxymethyl)-1,3-propanediol.

[0098] The rheology modifier acts as thickening agent, it can be an organic or inorganic rheology modifier, both of which are well-known in the art. The most common types of modified and unmodified inorganic rheology modifiers that are useful for the present invention, are attapulgite clays, bentonite clays, organoclays, and treated and untreated synthetic silicas, such as fumed silica. Most inorganic thickeners and rheology modifiers are supplied as powders. If they are properly dispersed into a coating, they usually function as suspending or gelling agents and, thus, help to avoid sedimentation. Inorganic rheology modifiers tend to have high yield values and are characterized as thixotropes.

[0099] Organic rheology modifiers that are useful for the present invention can be subdivided into products based on natural raw materials, like cellulose or xanthan, and products based on synthetic organic chemistry, like polyacrylates, polyurethanes or polyamides. Other rheology modifiers and thickeners such as polyamides, organoclays etc., can also be used.

[0100] In one example, the curing agent used for the present invention suitably is at least one photoinitiator. It can be another initiator that is known for this type of reactions, i.e. a compound that generates radicals under predetermined conditions.

[0101] A useful curing agent can be selected depending for example on the UV source or other reaction condition. It has been found that photoinitiators, such as -hydroxyketone, -aminoketone, phenylglyoxylate, benzyldimethyl-ketal, etc., are suitable. In one embodiment for a specific formulation phosphine oxide is used.

[0102] Examples for photoinitiators suitable for radical curing formulations of the present invention are 1-hydroxy-cyclohexyl-phenylketone, available as Irgacure 184, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1, available as Irgacure 369 from BASF Ludwigshafen, Germany, bis(2,4,6-trimethylbenzoyl)-phenylphosphinoxide, available as Irgacure 819, diphenyl-(2,4,6-trimethylbenzoyl)phosphinoxide, available as TPO.

[0103] A photoinitiating system includes at least one photoinitiator capable of absorbing light (e.g., ultraviolet light) to provide an initiating species capable of initiating polymerization of a cationic reagent or combination of such reagents. For example, a photoinitiator may generate a strong acid upon absorbing light. The strong acid is an initiating species that initiates a ring opening reaction of a cyclic ether of a cationic reagent, which can then react (e.g., polymerize) with the cyclic ether of another cationic reagent. Examples of photoinitiators include arylsulfonium salts (e.g., PL 6992 and PL 6976) such as mixed triarylsulfonium hexafluoroantimonate salts triarylsulfonoumhexafluoroantimonate or hexafluorophosphate, iodonium salts (e.g., Deuteron UV 2275 available from Deuteron GmbH, Achim Germany; Rhodorsil 2076 available from Rhodia, Lyon, France; LV9385C available from General Electric, Waterford, N.Y.; Bis(t-butylphenyl)iodonium hexafluorophosphate) available from Hampford Research, Inc. of Stratford, Conn.; and Irgacure 250 available from Ciba Specialty Chemicals Corp. of Basel, Switzerland), ferrocenium salts, and diazonium salts. In some embodiments, the photoinitiating system includes a sensitizer in combination with the photoinitiator. The sensitizer absorbs light (e.g., ultraviolet light and/or visible light) and transfers energy to the photoinitiator, which provides an initiating species (e.g., a strong acid) capable of initiating polymerization of a cationic reagent or combination of such reagents as disclosed in U.S. Pat. No. 7,845,785 included herein by reference. For a given light flux, the sensitizer can enhance the rate of photoinitiation. Alternatively or in combination, the sensitizer can provide a photoinitiator with the ability to initiate polymerization of cationic reagents upon exposure to longer wavelength light than in the absence of the sensitizer. Sensitizers can be useful in, for example, inks including particles (e. g., pigment particles such as rutile titania used to color the ink and/or provide opacity) which can decrease the penetration depth of ultraviolet light absorbed by the photo initiator. Light having a longer wavelength than ultraviolet (e.g., visible light) can penetrate more deeply through ink including the colorant particles to provide more uniform curing of the ink. Sensitizers typically absorb the longer wave length light more efficiently than the photoinitiator itself thereby enhancing curing of the ink. The concentration of photoinitiator and the optional sensitizer of an ink can be selected as desired. In some embodiments, the ink includes photoinitiator in the amount of at least about 0.5% by weight (e.g., at least about 1%). The total amount of photoinitiator of the ink may be about 3% or less by weight (e. g., about 2% or less). In some embodiments, the ink includes sensitizer in the amount of at least about 0.01% by weight (e. g., at least about 0.05%). The total amount of sensitizer of the ink may be about 0.5% or less by weight (e.g., about 0.1% or less). Exemplary sensitizers include at least one aromatic group and include compounds such as 9,10-diethoxy anthracene, 2-ethyl-9,10-dimethoxyanthracene, isopropylthioxanthone, or perylene. Photoinitiators that are used for cationic curable materials are of type of the onium salts as sulfonium, iodonium or diazonium salts. The onium salt absorbs UV light and undergoes cleavage to form protonic acid. Cationic photoinitiators suitable for the present invention are Iodonium (4-methylphenyl)[4-(2-methylpropyl)phenyl]-, hexafluorophosphate(1-) (1:1) (4-methylphenyl)[4-(2-methylpropyl) phenyl]-, hexafluorophosphate in propylene carbonate (Irgacure 250 from BASF), triarylsulfonium hexafluorophosphate with sensitizer (H-Nu C390 from Spectra), 4,4-dimethyl-diphenyl iodonium hexafluorophosphate & 3-ethyl-3-hydroxymethloxetane (Omnicat 445 from IGM).

[0104] Antharacene or thioxantone sensitizers may be needed to enhance the reactivity of the photoinitiator and extend the curing range to a longer wavelengths. The common sensitizers are 9,10-Dibutoxyanthracene (Anthracure UVS-1331, and Isopropylthioxanthone (Genocure ITX).

[0105] In one example, the radical curable pseudoplastic material or gel 104 comprises: [0106] Curable oligomer: 30-70% [0107] Reactive diluent: 30-70% [0108] Curing agent: 0.2-7% [0109] Rheology modifier: 1-10% [0110] Performance improving additive/filler 0-30%

[0111] The oligomer typically is one of the family of curable oligomers as described above, for example one having at least one ethylenically unsaturated bond such as acrylated and methacrylated oligomers and in particular acrylated epoxies, polyesters, polyethers and urethanes. The oligomer typically is present be in a proportion of 30-70% by weight.

[0112] The reactive diluent can be a substance as described above and typically can be a mono, di and tri functional monomer and the proportion would be about 30-70% by weight. The reactive diluents or monomers would typically be low molecular weight acrylate esters including methacrylates, monoacrylates, diacrylates and triacrylates.

[0113] The rheology modifier can be one or more of the substances described above and suitable for use in the current material composition is a filler that provides for a suitable viscosity of the material to be extruded and enhances the shear-thining properties, such as fumed silica or clay.

[0114] The curing agent can be a compound as described above, in particular a photo initiator, and a useful initiator is an alpha cleavage type unimolecular decomposition process photo initiator that absorbs light between 230 and 420 nm, to yield free radical(s). Examples of such alpha cleavage photo initiators could be 1-hydroxycyclohexyl phenyl ketone (Irgacure 184 from BASF), 2-Benzyl-2-dimethylamino1-(4-morpholinophenyl) (Irgacure 369 from BASF), Bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide (Irgacure 819 from BASF) or Diphenyl(2,4,6-trimethylbenzoyl) phosphineoxide (Irgacure TPO from BASF).

[0115] Examples for further useful additives are performance improving additives and/or fillers. Fillers are well-known in the art and can be used in amounts that are commonly used. Suitable performance improving additives and fillers are for example pigments, glass beads, different fibers (glass, Kevlar, nylon etc), surfactants, wetting and dispersing additives, flame retardants and toughening materials and impact modifiers such as core shells, polymer modifiers, clay, silica and others.

[0116] In one example, the cationic curable pseudoplastic material or gel 104 comprises (all ingredients are given by weight percentage): [0117] 20-96% epoxy resin [0118] 0-30% oxetane [0119] 0-30% polyol [0120] 0.5-6% cationic photoinitiator [0121] 0-5% sensitizer [0122] 1-10% rheology modifier [0123] 0-30% performance improving additives/fillers

[0124] In order to combine the benefits of both curing mechanisms: curing speed of radically cured materials with low shrinkage and tack free surface of cationicaly cured materials, the hybrid material was formulated containing both radically and cationically cured materials.

[0125] An example of a pseudoplastic material for use as a hybrid curable formulation for 3D printing is below (all ingredients are given by weight percentage): [0126] 0-30% acrylate oligomer [0127] 0-30% acrylate monomer [0128] 0.5-10% free radical photoinitiator [0129] 30-70% epoxy resin [0130] 0-30% oxetane [0131] 0-30% polyol [0132] 0.1-5% cationic photoinitiator [0133] 0-5% sensitizer [0134] 1-10% rheology modifier [0135] 0-30% performance improving additives/fillers

Example 1 Radical Curing Pseudoplastic Material

[0136] In the following example some commercially available materials have been used: [0137] BR 144 and BR 441-B are polyether and polyester urethane acrylates available from a number of suppliers. [0138] CN 981 is urethane acrylate. [0139] Ebecryl 3300 is epoxy acrylate. [0140] 03-849 is polyester acrylate. [0141] TPO is phosphine oxide photo initiator. [0142] SR 506D, SR 238, SR 833S, SR 351 are mono, di and tri functional reactive diluents. [0143] Aerosil 200 is fumed silica such as Evonic-Aerosil 200.

[0144] Tables 1 and 2 provide four tested suitable for radical curing formulations of the pseudoplastic material or gel. 104. All percentages refer to weight parts of component or compound per weight of the total composition. Table 1 has the formulations 1-4 without performance additives and Table 2 has formulations 5-8 with the performance additives to demonstrate how different UV curable ingredients, including urethane, polyester and epoxy acrylates together with mono, di and tri functional monomers can be combined in the formulation.

TABLE-US-00001 TABLE 1 Formula- Formula- Formula- Formula- Ingredient tion #1 tion #2 tion #3 tion #4 BR741 36 16 35 (Urethane acrylate) CN9001 20 (Urethane acrylate) BR 930D 16 (Urethane acrylate) Ebecryl 3300 20 (epoxy acrylate) CN2266 12 (polyester acrylate) TPO 0.5 1 2 3 (phoshine oxide photoinitiator) SR506D 56 55 10 (monofunctional acrylate monomer) SR 423D 20 (monofunctional methacrylate monomer) SR217 45 12.5 (monofunctional acrylate monomer) SR833S 10 (difunctional acrylate monomer) Aerosil 200HV 7.5 8 7 7.5 (fumed silica)

TABLE-US-00002 TABLE 2 Formula- Formula- Formula- Formula- Ingredient tion #5 tion #6 tion #7 tion #8 Urethane acrylate 36 36 37.5 35 Epoxy acrylate 20 Polyester acrylate 12 Photoinitiator 0.5 3 2 1 Mono, di and tri 56 33 37.5 44.5 functional reactive diluent Filler (Flame retardant) 15 Fumed Silica 7.5 8 6 7 Surfactant 2 Mechanical strength 0.5 additive

[0145] The formulations were prepared by dissolving the curing agent, which could be a photoinitiator, in the reactive diluent and then adding the solution to the oligomer. Performance additives, such as surfactants, fillers, and pigments, could be added at the mixing stage and rheology modifiers could be added close to the end of the mixing stage. Different mixing orders have been tested, but no significant changes in the pseudoplastic material properties have been noted.

[0146] The mix was prepared by using a mixer and under reduced pressure or vacuum to accomplish simultaneous formulation degassing. The prepared formulation of the pseudoplastic material had a viscosity of about 100000.00 mPa.Math.s to 400,000 mPa.Math.s at atmospheric pressure. The viscosity was measured at room temperature (25 C.) by using a Brookfield RVDV-E viscometer available from Brookfield AMETEK 11 Commerce Boulevard Middleboro, Mass., U.S.A. 02346.

[0147] The pseudoplastic material formulation has shown different degrees of shear thinning properties under different degrees of agitation and pressure. FIG. 5 is a graph that demonstrates the variations of viscosity at different shear rates.

[0148] Examples of cationic curable (Formulations #9 and #10) and hybrid curable (Formulations #11 and #12) pseudoplastic materials formulations are shown in Table 3. All numbers refer to weight parts of component or compound per weight of the total composition.

[0149] Cationic formulation will contain at least one epoxide reagent, at least one cationic photoinitiator, at least one sensitizer, at least one rheology modifier and optionally a performance improving additive/filler.

[0150] Hybrid formulation will typically contain at least one acrylate reagent, at least one cationic reagent, both cationic and radical photoinitiators, at least one rheology modifier and optionally a performance improving additive/filler.

TABLE-US-00003 TABLE 3 Formula- Formula- Formula- Formula- Ingredient tion #9 tion #10 tion #11 tion #12 Liquid diglycidyl ether of 62.38 49.9 43.67 Bisphenol A Diepoxide of 62.38 cycloaliphatic alcohol, hydrogenated Bisphenol A Cycloaliphatic epoxide 19.05 19.05 15.24 13.33 triglycidyl ether of 9.52 9.52 7.62 6.67 propoxylated glycerin Cationic photoinitiator 3.81 3.81 3.05 2.67 Sensitizer 0.48 0.48 0.38 0.33 Di and tetra functional 18.67 28 reactive acrylate diluent Acrylate photoinitiator 0.38 0.57 Fumed silica 4.76 4.76 4.76 4.76

[0151] While the claimed invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one of ordinary skill in the art that various changes and modifications can be made to the claimed invention without departing from the spirit and scope thereof.