Positive pressure drop-on-demand printing

• US 20040217186A1
• Filed: 04/10/2003
• Published: 11/04/2004
• Est. Priority Date: 04/10/2003
• Status: Active Grant

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Sachs, Emanuel M., Serdy, James G., Gleason, Blake W.
• Granted Patent: US 7,077,334 B2
• Time in Patent Office: Days
• US Class Current: 239/11
• CPC Class Codes: B33Y 10/00 Processes of additive manufacturing
• CPC Class Codes: B33Y 30/00 Apparatus for additive manufacturing; Details thereof or accessories therefor
• CPC Class Codes: B41J 2/1429 of tubular type
• CPC Class Codes: B41J 2002/14475 characterised by nozzle shapes or number of orifices per chamber

Abstract

A drop on demand printer has a nozzle with an orifice and a surrounding annular land. Surrounding the land is an edge, which is surrounded by a perimetrical surface that is inclined to the land at an angle α. A pressure controller maintains a positive overpressure on liquid to be printed such that a cap of liquid is substantially always present covering the orifice and the land. The edge between the land and the perimetrical surface prevents liquid from overflowing, and maintains the cap, if the pressure is maintained between lower and upper limits disclosed. The liquid to be printed preferably wets the orifice land, which may be alumina, glass, ceramic, and others. Liquids with very small, even zero, wetting angles relative to the land may be used, such as water and organic solvents, including, isopropyl and ethyl alcohol and chloroform. The liquid can be loaded with dissolved polymers, or particles, such as of polymer or ceramic. Very small drops can be printed, by using an orifice of about 40 microns effective diameter, with a land of about 90 microns effective diameter. The printer can be used for any drop dispensing application, such as ink jet, Three Dimensional printing, and also for depositing small amounts of pharmaceutical materials into a receptacle, or drug delivery vehicle. A means for establishing a temperature differential, with a higher upstream and lower downstream temperature, eliminates any gas bubbles at the orifice.

Claims

1. A method for printing drops of liquid, the method comprising the steps of:

a. providing a quantity of liquid to be printed;

b. providing a nozzle, the nozzle defining an orifice that is aligned along an axis, and having an annular land surrounding the orifice, the land being bounded perimetrically by an outer edge;

c. coupling the quantity of liquid hydraulically to the orifice;

d. filling the orifice with some of the quantity of liquid;

e. establishing within the liquid in the orifice, a steady state pressure that is greater than atmospheric by an overpressure, great enough to cause a cap of liquid to cover the annular land and the orifice;

f. selectively causing a single drop of liquid to detach from the cap of liquid and to be ejected from the orifice; and

g. allowing pressure at the orifice to return to the steady state pressure, such that a cap of liquid covers the annular land and the orifice.

2. The method of claim 1, the land being a circular annulus, having an outer radius of R_land.

3. The method of claim 1, the step of providing a quantity of liquid comprising providing a quantity of liquid in a reservoir, the step of hydraulically coupling the quantity of liquid comprising coupling the reservoir to the orifice through a conduit.

4. The method of claim 1, the step of providing a nozzle comprising providing a nozzle having a land comprising a material that is wetted by the liquid.

5. The method of claim 2, the step of establishing a steady state pressure comprising the step of establishing a pressure that is:

a. not so great as to cause the liquid to wet beyond the outer edge; and

b. not so great as to cause the liquid to form a cap having an outer surface that is larger than a hemisphere having a radius equal to R_land.

6. The method of claim 1, the step of providing a nozzle comprising providing a nozzle that further comprises a perimetrical surface that perimetrically bounds the outer edge, the perimetrical surface being inclined relative to the land by an edge angle α

>

180′

.

7. The method of claim 6, the step of providing a nozzle comprising providing a nozzle with a perimetrical surface inclined relative to the land by an edge angle α

of greater than about 210° and

less than about 315°

.

8. The method of claim 6, the step of providing a nozzle comprising providing a nozzle with a perimetrical surface inclined relative to the land by an edge angle α

of greater than about 225° and

less than about 270°

.

9. The method of claim 1, the liquid having a wetting angle with respect to the material of the orifice land that is less than about 50°

.

10. The method of claim 1, the liquid comprising an organic solvent.

11. The method of claim 1, the liquid comprising an alcohol based material.

12. The method of claim 11, the liquid comprising an ethyl alcohol based material.

13. The method of claim 11, the liquid comprising an isopropyl alcohol based material.

14. The method of claim 1, the liquid comprising a chloroform based material.

15. The method of claim 1, the land material comprising glass.

16. The method of claim 1, the land material comprising a ceramic.

17. The method of claim 1, the land comprising alumina.

18. The method of claim 1, the liquid comprising a liquid vehicle that is loaded with a material selected from the group consisting of:

dissolved polymer;

polymer particles; and

ceramic particles.

19. The method of claim 6, the liquid cap having a surface that defines at its perimeter, a contact angle γ

with the land, and the liquid on the orifice land material having a wetting angle, ω

, the step of establishing a steady state pressure comprising the step of establishing an over pressure that maintains the cap of a configuration that maintains the angle γ

to be less than ω

+α

−

180°

.

20. The method of claim 2, the liquid having a surface tension σ

and a wetting angle ω

with respect to the surface material, the step of providing an overpressure comprising the step of providing a pressure that is greater than

21. The method of claim 20, the step of providing an overpressure comprising the step of providing a pressure that is less than

22. The method of claim 6, the liquid on the orifice land material having a wetting angle ω

, the step of providing an overpressure comprising the steps of providing a pressure that is less than

23. The method of claim 1, the step of establishing an overpressure comprising the step of providing a reservoir of the liquid, hydraulically coupled to and gravitationally above the orifice, and maintaining a surface of the reservoir of the liquid a controlled distance above the orifice, to establish the overpressure.

24. The method of claim 23, further comprising the step of coordinating movement of the reservoir to coincide with any motion of the orifice, so that the middle of the reservoir always remains substantially directly above the orifice.

25. The method of claim 23, the step of maintaining the surface a controlled distance above the orifice comprising measuring the surface location, and replenishing liquid when necessary to maintain the surface within an established tolerance from the controlled distance.

26. The method of claim 1, further comprising the steps of:

a. providing a piezoelectric actuator, acoustically coupled to the liquid in the orifice through a conduit;

b. the step of selectively causing a single droplet of liquid to be ejected from the orifice comprising the step of energizing the actuator to change its shape and the shape of the conduit sufficiently to initiate in the liquid a pressure wave that travels to the orifice to cause a single droplet of liquid to be ejected from the orifice.

27. The method of claim 26, further comprising the step of providing the quantity of liquid at a temperature of between about ½

and about 10 degrees C. more than a temperature at which any liquid at the piezoelectric actuator is maintained.

28. The method of claim 27, the step of providing the quantity of liquid at a temperature that is more than the temperature of any liquid at the piezoelectric actuator comprising the step of heating the quantity of liquid.

29. The method of claim 27, the step of providing the quantity of liquid at a temperature that is more than the temperature of the liquid at the piezoelectric actuator comprising the step of cooling the liquid by when it reaches the piezoelectric actuator.

30. The method of claim 26, further comprising the step of providing the quantity of liquid at a temperature greater than that of any the liquid at the actuator by an amount that is sufficient to decrease the capacity of the warmer liquid to absorb atmospheric gas, relative to the absorption capacity of any the liquid at the actuator by an amount sufficient to substantially eliminate any gas bubbles in any the liquid at the actuator.

31. The method of claim 1, further comprising the steps of:

a. providing an evaporative heater, thermally coupled to the liquid;

b. the step of selectively causing a single droplet of liquid to be ejected from the orifice comprising the step of energizing the heater to heat sufficiently to cause a single droplet of liquid to be ejected from the orifice.

32. The method of claim 1, further comprising the step of, during times the nozzle is parked, ejecting a droplet of liquid at a relatively low frequency, as compared to a printing frequency.

33. The method of claim 1, the step of establishing a steady state pressure comprising the step of establishing a steady state pressure that is great enough to cause a cap of liquid to cover the land and orifice when the nozzle is quiescent.

34. The method of claim 1, the step of establishing a steady state pressure comprising the step of establishing a stead state pressure that is great enough to cause a cap of liquid to cover the land and orifice when the nozzle is static.

35. An apparatus for printing a liquid, the apparatus comprising:

a. a printhead nozzle comprising an annular body that defines an orifice aligned with an axis, and further comprises;

i. an annular orifice land having an outer effective diameter D=²R_land comprising a land material; and

ii. a perimetrical surface that meets the land at a perimetrical outer edge;

b. a liquid delivery unit, hydraulically coupled to the orifice;

c. a pressure controller, hydraulically coupled to the orifice, adapted to establish a steady state, positive overpressure, relative to surrounding atmosphere, to any liquid within the orifice, sufficient to cause the liquid to stably cover the orifice and the land; and

d. an excitation unit, coupled to the orifice and operative to selectively eject a single drop of any liquid within the nozzle from the orifice.

36. The apparatus of claim 35, the pressure controller being adapted to maintain any liquid in said orifice substantially fully covering the annular land and the orifice when the nozzle is quiescent.

37. The apparatus of claim 35, the pressure controller being adapted to maintain any liquid in said orifice substantially fully covering the annular land and the orifice when the nozzle is static.

38. The printing apparatus of claim 35, the land comprising a substantially flat surface.

39. The printing apparatus of claim 35, the land comprising a convex outward facing surface

40. The printing apparatus of claim 35, the excitation unit comprising a piezoelectric element that is acoustically coupled to the orifice.

41. The printing apparatus of claim 35, the excitation unit comprising a heating element that is thermally coupled to the orifice.

42. The printing apparatus of claim 35, the pressure controller comprising a reservoir and a fixture that maintains liquid within the reservoir gravitationally above the orifice.

43. The printing apparatus of claim 42, the fixture further comprising a fixture that maintains the middle of the reservoir substantially directly above and in line with the axis of the orifice.

44. The printing apparatus of claim 35, the land having an outer effective radius R_land, the liquid having surface tension σ

, and the liquid having a wetting angle ω

with respect to the land material, the pressure controller being adapted to pressurize any liquid at the orifice to at least

45. The printing apparatus of claim 44, the pressurizing unit being adapted to pressurize the liquid to less than

46. The printing apparatus of claim 35, further comprising a plurality of substantially identical nozzles, all hydraulically coupled to the liquid delivery unit and the pressure controller in substantially the same manner.

47. The printing apparatus of claim 46, further comprising, for each nozzle, an individual excitation unit.

48. The printing apparatus of claim 47, the individual excitation unit comprising an evaporative heater.

49. The printing apparatus of claim 46, further comprising a fixture that maintains all of the plurality of nozzles together in an array.

50. The printing apparatus of claim 35, the perimetrical surface meeting the orifice land at an outer edge.

51. The printing apparatus of claim 50, the outer edge being defined by a radius q, and being shaped and located at an effective radius R_land from the axis, such that q/R_land is much less than 10.

52. The printing apparatus of claim 51, the outer edge being shaped and located such that q/R_land is much less than 100.

53. The printing apparatus of claim 50, the edge being defined by an outer perimetrical surface that meets the orifice land at an angle α

of between about 225 degrees and about 315 degrees.

54. The printing apparatus of claim 53, the pressurizing unit being operative to pressurize the liquid to less than

55. The printing apparatus of claim 53, the edge being defined by a surface that meets the orifice land at an angle α

of between about 255 degrees and about 270 degrees.

56. The printing apparatus of claim 35, the nozzle for use with a liquid, the orifice land comprising a material that is wetted by the liquid.

57. The printing apparatus of claim 35, the orifice having an effective diameter d of less than about one hundred microns.

58. The printing apparatus of claim 35, the orifice having an effective diameter d of less than about sixty microns.

59. The printing apparatus of claim 35, the orifice outer edge having an effective diameter of less than about three hundred microns.

60. The printing apparatus of claim 35, the orifice outer edge having an effective diameter of less than about one hundred microns.

61. The printing apparatus of claim 35, the orifice land comprising a ceramic.

62. The printing apparatus of claim 35, the orifice land comprising alumina.

63. The printing apparatus of claim 35, the orifice land comprising a glass.

64. The printing apparatus of claim 40, further comprising means for establishing a temperature differential between any liquid in the liquid delivery unit and any liquid at the piezoelectric element, such that any liquid in the liquid delivery unit is warmer.

65. The printing apparatus of claim 64, the means for establishing a temperature differential comprising a heater that is configured to be thermally coupled to any liquid in the liquid delivery unit.

66. The printing apparatus of claim 64, the means for establishing a temperature differential comprising a cooler that is configured to be thermally coupled to any liquid such that the liquid is cooled by the time it reaches the piezoelectric element.

67. The printing apparatus of claim 40, further comprising, coupled to the orifice, a body comprising a thin-walled metal tube.

68. The printing apparatus of claim 67, the thin-walled metal tube comprising stainless steel, having an annular wall thickness of between approximately 25 microns (0.001 in) and approximately 75 microns (0.003 in).

69. The printing apparatus of claim 68, the piezoelectric actuator being acoustically coupled to the tube.

70. The printing apparatus of claim 69, the piezoelectric actuator being arranged concentric around the tube.

71. The printing apparatus of claim 70, further comprising solder that couples the piezoelectric actuator to the tube.

72. The printing apparatus of claim 71, the solder having approximately zero shrinkage upon solidification.

73. The printing apparatus of claim 71, the solder comprising a solder that has a melting temperature that is less than any Curie temperature of the piezoelectric actuator.

74. The printing apparatus of claim 71, the solder comprising Bismuth (49%), indium (21%), lead (18%) and tin (12%) all, by weight.

75. The printing apparatus of claim 72, the solder comprising a eutectic composition.

76. An apparatus for printing a liquid, the apparatus comprising:

a. a printhead nozzle comprising a body that defines an orifice;

b. a liquid delivery unit, hydraulically coupled to the orifice;

c. a piezoelectric excitation unit, arranged to be acoustically coupled to any liquid in the orifice nozzle and operative to selectively eject a single drop of liquid from the orifice; and

d. means for establishing a temperature differential between any liquid in the liquid delivery unit and any liquid at the excitation unit, such that any liquid at the liquid excitation unit is cooler.

77. A process for making a component comprising the steps of

a. depositing a layer of a powder material in a confined region;

b. applying to one or more selected regions of the layer of powder material a liquid containing a further material which will cause the layer of powder material to become bonded at the one or more selected regions, the applying step being conducted by drop-on-demand jet printing single drops of the liquid through a nozzle defining an orifice that is aligned along an axis, and having an annular land surrounding the orifice, the land having an outer effective radius R_land and bounded perimetrically by an outer edge;

c. maintaining the orifice and land covered by a cap of the liquid when the nozzle is quiescent;

d. repeating steps (a) (b) and (c) a selected number of times to produce a selected number of successive layers, the further material causing the successive layers to become bonded to each other;

e. removing unbonded powder material which is not at the one or more selected regions to provide the component.

78. The method of claim 77, further where the step of maintaining the orifice land covered comprising maintaining the orifice land covered while the nozzle is holding.

79. The method of claim 77, the liquid comprising a material selected from the group consisting of:

water, isopropyl alcohol, ethyl alcohol and chloroform.

80. The method of claim 77, the liquid comprising an organic solvent.

81. An apparatus for making a three dimensional part comprising:

a. a powder dispenser, that provides successive adjacent layers of powder;

b. a drop-on-demand liquid jet dispenser that dispenses single drops of a liquid that contains a further material that will cause grains of the powder to become bound to adjacent grains within a layer, and between adjacent layers, the dispenser comprising;

i. a nozzle, comprising an annular body that defines an orifice that is aligned with an axis, and having a perimetrical annular land, bounded by an outer orifice edge;

ii. a liquid delivery unit hydraulically coupled to the orifice by a conduit;

iii. a pressure controller, coupled to the orifice operative to maintain, in any liquid in the orifice a steady state positive pressure relative to surrounding atmosphere sufficient to maintain a cap of liquid that substantially completely covers the orifice and land; and

c. a positioner that positions the nozzle at selected positions adjacent the layer of powder.