Method for debubbling an ink

Information

  • Patent Grant
  • 6558450
  • Patent Number
    6,558,450
  • Date Filed
    Thursday, March 22, 2001
    23 years ago
  • Date Issued
    Tuesday, May 6, 2003
    21 years ago
Abstract
The present invention is directed to a method for debubbling an ink. The method comprises the steps of: providing an ink having an entrained gas; providing a membrane contactor comprising a plurality of integrally asymmetric hollow fiber microporous membranes; a membrane defining within the contactor a lumen side and a shell side; providing a vacuum source; passing the gas entrained ink through the shell side of the contactor; applying the vacuum source to the lumen side of the contactor; and debubbling the gas entrained ink across the membrane.
Description




FIELD OF THE INVENTION




This invention is directed to a method of debubbling an ink by using a membrane contactor.




BACKGROUND OF THE INVENTION




It is known to use hollow fiber membrane contactors to degas liquids. See, for example, the LIQUI-CEL® SemiPer™ membrane contactor commercially available from Celgard Inc. of Charlotte, N.C. This contactor utilizes a homogeneous, nonskinned, symmetric, polypropylene microporous hollow fiber membrane coated with a fluoropolymer and has been used to remove gases from photoresist developer solutions, lithographic printing plate solutions, and photographic film and paper emulsions. In this contactor, the foregoing liquids flow over the exterior surfaces of the hollow fibers.




Inks, for example, inks for ink jet printers, are sensitive to bubble formation. Formation of the bubbles, as the ink is discharged, can be detrimental to, among other things, quality printing applications or cartridge filling operations. See, for example, European Publication 1,033,163, Paragraph 0014, which is incorporated herein by reference.




Several membrane-based solutions have been proposed for bubble-in-ink problems. See, for example, Japanese Kokai's 517712; 10-60339; 10-298470; European Publications 1,033,162; 1,052,011; and U.S. Pat. No. 6,059,405. Also, please note European Publication 1,033,162, Paragraph 0007 which categorizes additional techniques for removing dissolved gases from chemical liquids by use of a membrane.




Japanese Kokai 5-17712 discloses the use of membranes made from polyethylene, polypropylene, poly(tetrafluoroethylene), polystyrene, or polymethyl methacrylate resins (Paragraph 0008), and the ink flows on the lumen side of the membrane (Paragraph 0007).




Japanese Kokai 10-60339 discloses the use of membranes made from a fluororesin (claim 2), and the ink flows on the lumen side of the membrane (abstract).




Japanese Kokai 10-298470 (and its related case European Publication 1,052,011) discloses the use of composite (or conjugate or multi-layered) membranes with porous and nonporous layers, and suggests, among other things, the use of polymethylpentene (or PMP or poly(4-methylpentene-1)) (Paragraphs 0018-0020), and the ink flows on the lumen side of the membrane (abstract).




European Publication 1,033,162 discloses the use of composite membranes, with porous and nonporous layers and suggests, among other things, the use of PMP (Paragraphs 0026 and 0048) for both layers, and the ink flows on the lumen side of the membrane (Paragraph 0054).




U.S. Pat. No. 6,059,405 discloses the use of a membrane, a hollow fiber membrane, and the ink flows on the lumen side of the membrane (column 3, lines 55-65).




While each of the foregoing had a measured success in accomplishing the debubbling goal, there is still a need for a method of removing entrained gases from inks in a simple and cost effective manner.




SUMMARY OF THE INVENTION




The present invention is directed to a method for debubbling (or degassing) an ink. The method comprises the steps of: providing an ink having an entrained gas; providing a membrane contactor comprising a plurality of integrally asymmetric hollow fiber microporous membranes; a membrane defining within the contactor a lumen side and a shell side; providing a vacuum source; passing the gas entrained ink through the shell side of the contactor; applying the vacuum source to the lumen side of the contactor; and debubbling the gas entrained ink across the membrane.











DESCRIPTION OF THE DRAWINGS




For the purpose of illustrating the invention, there is shown in the drawings a form which is presently preferred; it being understood, however, that this invention is not limited to the precise arrangements and instrumentalities shown.





FIG. 1

is a schematic illustration of an ink debubbling system.





FIG. 2

is a schematic illustration of the first embodiment of a membrane contactor made according to the instant invention.





FIG. 3

is a schematic illustration of a second embodiment of the membrane contactor.





FIG. 4

is a schematic illustration of a third embodiment of the membrane contactor.





FIG. 5

is a graph illustrating the performance of the CELGARD SemiPer contactor to the instant invention.











DETAILED DESCRIPTION OF THE INVENTION




Referring to the drawings wherein like numerals indicate like elements, there is shown in

FIG. 1

an ink debubbling system


10


. Ink debubbling system


10


comprises an ink reservoir


12


. A membrane contactor


14


is in fluid communication with the reservoir


12


. An end use application


16


is in fluid communication with membrane contactor


14


. End use application may be, but is not limited to, an ink jet printing head (thermal or piezoelectric), an ink cartridge filling station, or the like.




Ink, as used herein, is a fluid containing pigments or dyes. Inks, preferably, have a surface tension less than water at room temperature (i.e., about 72.75 dynes/cm at 20° C. and 71.20 dynes/cm at 30° C.). These inks are, preferably, used in computer printers or other ink jet type printers. Such inks, preferably, have a viscosity of 0.8 to 10 centipoises (CPS), a specific gravity of 0.7 to 1.5 grams per milliliter (g/ml), and a surface tension of 20 to 40 dynes per centimeter (dynes/cm).




The membrane contactor


14


, which is discussed in greater detail below, is an external flow, hollow fiber membrane module. Hollow fiber membrane contactors are known. For example see: U.S. Pat. Nos. 3,228,877; 3,755,034; 4,220,535; 4,940,617; 5,186,832; 5,264,171; 5,284,584; 5,449,457, each is incorporated herein by reference. The membrane contactor


14


has a lumen side and a shell side. The lumen side, also known as the internal side, is defined, in large part, by the lumen of the hollow fiber. The shell side, also known as the external side, is defined, in part, by the external surface of the hollow fiber. The ink travels through the shell (or external) side, while the vacuum (or vacuum and sweep gas) is applied to the lumen (or internal) side. Thereby, entrained gases from the ink pass from the shell side through the membrane to the lumen side. The contactor


14


is made of components that are inert to or non-reactive with the ink (or other liquid). Preferably, these components are plastic, but metals may be used.




The membrane is preferably a semi-permeable, gas selective, heterogeneous, integrally asymmetric, and liquid impermeable membrane. The membrane has a permeability of less than 100 Barrers (10


−8


standard cm


3


.cm/sec.cm


2


.cm(Hg)). The membrane preferably has an active surface area of 0.1 to 20 meters


2


. The membrane is, preferably, a skinned membrane and the skin is on the shell side. The membrane is, preferably, a single layer membrane (e.g., not a composite or multi-layered membrane) and is made from a homopolymer of polymethylpentene. For example, see U.S. Pat. No. 4,664,681, incorporated herein by reference.




Referring to

FIG. 2

, ink


22


enters contactor


14


via ink inlet


24


of core tube


26


. Core tube


26


includes a perforated


28


area immediately ahead of block


30


. Ink


22


travels through the inlet


24


of core tube


26


and exits tube


26


via perforations


28


when it is diverted by block


30


. Ink


22


then travels over the exterior surfaces of hollow fibers


34


. Ink


22


re-enters core tube


26


via perforations


28


on the other side of block


30


and exits tube


26


via ink outlet


32


. The hollow fibers


34


surround core tube


26


and are maintained generally parallel to tube


26


's axis via tube sheets


36


. Hollow fibers


34


extend through tube sheet


36


and are in communication with headspaces


38


on either end of contactor


14


, so that vacuum


44


drawn at ports


40


and


42


is in communication with the lumen side via headspaces


38


. Port


40


, for example, may also be used to introduce a sweep gas, which facilitates entrained gas removal.




Referring to

FIG. 3

, contactor


14


′ is the same as shown in

FIG. 2

but for a flow diverting baffle


46


located within the shell side, and port


40


has been moved. The baffle


46


is added to promote distribution of ink over all exterior surfaces of the hollow fibers


34


. Port


40


is moved to illustrate the non-criticality of port location.




Referring to

FIG. 4

, contactor


14


″ differs from contactors


14


and


14


′ by moving ink outlet


32


from the terminal end of core tube


26


to the contactor shell, as illustrated. Vacuum


44


is in communication with headspace


38


which, in turn, is in communication with the lumens of hollow fibers


34


. The second headspace illustrated in the previous embodiments has been eliminated. Ink


22


enters ink inlet


24


of core tube


26


. Ink


22


exits tube


26


via perforations


28


, travels over the exterior surfaces of hollow fibers


34


, and exits the shell side via outlet


32


. Outlet


32


may be placed at other locations on the exterior of the contactor so that it maintains communication with the shell side.




In operation, entrained gases, which form bubbles, are removed from the ink by a concentration difference across the membrane, that is by diffusion. Vacuum, ranging from 25 to 200 torr, is placed on lumen side of the membrane, and the gas entrained ink is in contact with the shell side (or exterior surface) of the membrane. The concentration (partial pressure of the gas) difference drives the gas from the ink on the shell side, through the membrane to the lumen side. Furthermore, by routing the ink through the shell (or exterior) side, versus the lumen side, the pressure drop of the ink through the contactor is greatly reduced. This is because passage through the lumens provides a much greater resistance to flow than the shell side space. In

FIG. 5

, the performance of a contactor according to the present invention is compared to CELGARD's SemiPer contactor. The graph illustrates ‘Dissolved Oxygen (DO) Removal Efficiency’ (%) as a function of water flow rate (liters/minute) at 20° C. and 35 torr of vacuum. Water was used, instead of ink, but contactor performance is deemed analogous to the foregoing inks at the stated conditions. The upper curve represents performance of the instant invention (2.5″ diameter), and the lower curve represents performace of the SemiPer contactor (2.5″ diameter).




The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof, and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification, as indicating the scope of the invention.



Claims
  • 1. A method for debubbling an ink comprising the steps of:providing an ink having a gas entrained therein; providing a membrane contactor comprising a plurality of single layered, skinned, polymethylpentene hollow fiber microporous membranes, the membrane defining within the contactor a lumen side and a shell side and the skin being on the shell side; providing a vacuum; passing the gas entrained ink through the shell side of the contactor; applying the vacuum to the lumen side of the contactor; and debubbling the gas entrained ink across the membrane.
  • 2. The method of claim 1 wherein the ink has a surface tension less than the surface tension of water at room temperature.
  • 3. The method of claim 1 wherein the ink has a viscosity of 0.8 to 10 centipoises, a specific gravity of 0.7 to 1.5 grams per milliliter, and a surface tension of 20 to 40 dynes per centimeter.
  • 4. The method of claim 1 wherein the membrane has an active surface area of 0.1 to 20 meters2.
  • 5. The method of claim 1 wherein the membrane has a permeability of less than 100 Barrers.
  • 6. The method of claim 1 wherein the membrane is a semi-permeable, gas selective, heterogeneous, liquid impermeable membrane.
  • 7. The method of claim 1 wherein polymethylpentene being a homopolymer.
  • 8. The method of claim 1 wherein the module includes a baffle.
  • 9. The method of claim 1 wherein the vacuum ranges from 25 to 200 torr.
  • 10. A method for debubbling an ink comprising the steps of:providing an ink having a gas entrained therein, the ink having a viscosity of 0.8 to 10 centipoises, a specific gravity of 0.7 to 1.5 grams per milliliter, and a surface tension of 20 to 40 dynes per centimeter; providing a membrane contactor comprising a plurality of single layered, skinned, polymethylpentene hollow fiber microporous membranes, the membrane defining within the contactor a lumen side and a shell side and the skin being on the shell side, the membrane having an active surface area of 0.1 to 20 meters2; providing a vacuum, the vacuum ranging from 25 to 200 torr; passing the gas entrained ink through the shell side of the contactor; applying the vacuum to the lumen side of the contactor; and debubbling the gas entrained ink across the membrane.
US Referenced Citations (22)
Number Name Date Kind
3228877 Mahon Jan 1966 A
3755034 Mahon et al. Aug 1973 A
4220535 Leonard Sep 1980 A
4421529 Revak et al. Dec 1983 A
4664681 Anazawa et al. May 1987 A
4707267 Johnson Nov 1987 A
4752305 Johnson Jun 1988 A
4788556 Hoisington et al. Nov 1988 A
4869732 Kalfoglou Sep 1989 A
4940617 Baurmeister Jul 1990 A
5186832 Mancusi et al. Feb 1993 A
5211728 Trimmer May 1993 A
5254143 Anazawa et al. Oct 1993 A
5264171 Prasad et al. Nov 1993 A
5284584 Huang et al. Feb 1994 A
5449457 Prasad Sep 1995 A
5522917 Honda et al. Jun 1996 A
5695545 Cho et al. Dec 1997 A
5701148 Moynihan et al. Dec 1997 A
5808643 Tracy et al. Sep 1998 A
6059405 Mochizuki et al. May 2000 A
6168648 Ootani et al. Jan 2001 B1
Foreign Referenced Citations (16)
Number Date Country
1033162 Sep 2000 EP
1052011 Nov 2000 EP
58-219067 Dec 1983 JP
02-102714 Apr 1990 JP
02-107317 Apr 1990 JP
02-135117 May 1990 JP
02-290201 Nov 1990 JP
03-080983 Apr 1991 JP
03-109904 May 1991 JP
03-118802 May 1991 JP
04-007003 Jan 1992 JP
05-017712 Jan 1993 JP
06-134446 May 1994 JP
06-327905 Nov 1994 JP
10-060339 Mar 1998 JP
10-298470 Nov 1998 JP