Microporous filter membrane, method of making microporous filter membrane and separator employing microporous filter membranes

• US 20050263452A1
• Filed: 08/02/2005
• Published: 12/01/2005
• Est. Priority Date: 12/08/1999
• Status: Active Grant

• Current Assignee: James D. Jacobson
• Original Assignee: James D. Jacobson
• Inventors: Jacobson, James D.
• Granted Patent: US 7,442,303 B2
• Time in Patent Office: Days
• US Class Current: 210/484
• CPC Class Codes: B01D 2323/42 Details of membrane preparation apparatus
• CPC Class Codes: B01D 2325/028 Microfluidic pore structures
• CPC Class Codes: B01D 63/16 Rotary, reciprocated or vibrated modules
• CPC Class Codes: B01D 67/0032 by elimination of segments of the precursor, e.g. nucleation-track membranes, lithography or laser methods
• CPC Class Codes: B01D 67/0034 by micromachining techniques, e.g. using masking and etching steps, photolithography
• CPC Class Codes: B01D 69/02 characterised by their properties
• CPC Class Codes: B01D 69/106 Membranes in the pores of a support, e.g. polymerized in the pores or voids
• CPC Class Codes: B01D 69/107 Organic support material
• CPC Class Codes: B23K 26/384 of specially shaped holes
• CPC Class Codes: B26F 1/31 by radiation by laser beam B23K26/00
• CPC Class Codes: Y10S 55/05 Methods of making filter
• CPC Class Codes: Y10T 428/249953 Composite having voids in a component [e.g., porous, cellular, etc.]

Abstract

A filter membrane, methods of making such filter membrane and apparatus employing such filter membrane are disclosed, in which the filter membrane is a monolithic polymeric membrane that includes a polymeric filter layer including a micron-scale precision-shaped pores and a polymeric support layer that has a precision-shaped porous support structure for the filter layer. Several methods are disclosed for making such a membrane using micromachining techniques, including lithographic, laser ablation and x-ray treatment techniques. Several filter apparatus employing such a membrane are also disclosed.

Claims

1-64. -64. (canceled)

65. A method for making a monolithic polymeric filter membrane comprising at least a filter layer including micron-scale precision-shaped pores and a support layer including a precision-shaped support structure for the filter layer, the method comprising:

forming the filter membrane layer by removing selected material from one side of a polymeric film to define the precision-shaped micron-scale pores of the filter layer; and

forming the support structure layer by removing selected material from the other side of said membrane to define the precision-shaped porous support structure, the pores communicating with the porous support structure to allow the passage of filtrate therethrough.

67. The method of claim 65 or 66 in which at least one of said filter layer and support layer is formed by:

providing a polymeric film that is of polyimide material

applying a metallic film to one surface of said polyimide film,

applying a photoresist material to said metallic film,

creating a first pattern on said photoresist layer to define micron scale pores or support structure and removing selected material from said photoresist layer;

removing material from said metallic film in the areas where said photoresist material has been removed; and

removing selected material from the polyimide film in the areas where the metallic film has been removed to define the pores or support structure;

removing any remaining photoresist material and the metallic film from the polyimide film.

68. The method of claim 65 or 66 in which at least one of said filter layer and said support layer comprises a photoimageable polymeric film and the at least one layer is formed by exposing the film to light through a mask defining a pattern and removing selected portions of said polymeric film defined by pattern to form the pores or support layer.

69. The method of claim 67 in which said polymeric film is a negative-acting photoimagable film and said removing is carried out by removing the non-exposed portions of said film.

70. The method of claim 67 in which said film is a positive-acting photoimagable film and said removing is carried out by removing the exposed portions of said film.

71. The method of claim 67 in which the removing of selected material from the polyimide film is carried out by dry etching.

72. The method of claim 65 or 66 in which at least one of the steps of removing material includes ablating the film by laser or treating the film with ionizing radiation.

73. The method of claim 72 employing an excimer laser to ablate said film.

74. The method of claim 65 or 66 in which the support layer is thicker than the filter layer.

75. The method of claim 74 wherein the support layer is thicker than the filter layer by a factor of between about 2 and 250.

76. The method of claim 68 wherein a continuous web of the photoimageable polymeric film is continuously supplied and the pattern is progressively created on said film and selected material is progressively removed to define the pores or support structure.

77. The method of claim 65 or 66 in which a continuous web of laser ablatable polymeric film is continuously supplied and selected material is progressively removed to define the pores or support structure.

78. The method of claim 68 in which said photoimageable polymeric film comprises a polyimide.

79. The method of claim 65 or 66 in which the support structure comprises a first plurality of spaced apart support struts in which said struts are spaced apart a distance substantially greater than the size of said micron-scale pores.

80. The method of claim 79 in which said support structure comprises a second plurality of spaced apart struts intersecting said first plurality of struts to define a support grid.

81. The method of claim 79 in which said struts are spaced apart a distance in the range of about 50 to 1000 microns.

82. The filter membrane of claim 79 in which the struts are between about 10 and 100 microns in width.

83. The method of claim 65 or 66 in which the support structure comprises a grid.

84. The method of claim 65 or 66 in which the support structure comprises at least two sublayers, a first sublayer of a selected porosity and a second sublayer of different porosity than the first sublayer and disposed between the first sublayer and the filter layer.

85. The method of claim 83 in which the support grid comprises at least two subgrids, a first subgrid comprising struts of selected width and spaced apart a selected distance and a second subgrid disposed between the first subgrid and the filter layer, the second subgrid including support struts of different width or spacing than the struts in the first subgrid.

86. The method of claim 83 in which the grid comprises a plurality of intersecting walls, said walls being curved at least at the intersections.

87. The method of claim 86 in which the grid comprises a plurality of intersecting walls defined by spaced apart, generally cylindrically or elliptically shaped pores.

89. The method of claim 65 or 66 in which the filter membrane is flexible.

90. The method of claim 89 in which the filter membrane is sufficiently flexible to be disposed along a radius of curvature of ½

inch.

66. A method for making a monolithic polymeric filter membrane comprising at least a filter layer including micron-scale precision-shaped pores therethrough and a support layer including a porous support structure for said filter layer, the method comprising:

forming the filter layer by removing selected material from a first polymeric film to define a plurality of micron-scale precision-shaped pores therethrough;

forming the support structure layer by removing selected material from a second polymeric film to define a precision-shaped porous support structure; and

joining the filter and support layers together in overlying relationship to form a monolithic filter membrane.

88. The method of claim 66 in which support structure layer is formed by removing material from two non-fully cured polymeric films, one film having material removed to define a support structure of selected porosity, and another film having material removed to define a support structure of greater porosity than the one film, said filter layers film and support films being bonded together to form an integral filter membrane.

96. The method of claim 66 in which the first and second films are not fully cured at the time of the removal step, and the joining step includes curing the first and second films.

91. A method for making a monolithic polymeric filter membrane of a predetermined thickness, the filter membrane comprising at least one filter layer with micron-scale precision-shaped pores and a support layer including a precision-shaped support structure for said filter layer, the method comprising:

providing a substrate;

spinning a first polyimide layer onto the substrate;

applying a metal layer to the first polyimide layer;

applying photoresist to the metal layer;

developing the photoresist to define a first pattern of one of the micron-scale pores or support structure;

transferring the first pattern from said photoresist to said metal layer;

transferring the first pattern from the metal layer to said first polyimide layer so as to create one of said micron-scale pores or said support structure;

sequentially removing the photoresist and the metal layer;

spinning a second polyimide layer onto the first layer polyimide so as to create an interface therebetween;

creating a second pattern on the second polyimide layer to define the other of the micron-scale pores or the support structure;

removing selected material from the second polyimide layer to define the other of the micron-scale pores or support structure;

curing the first and second polyimide layers so as to remove the interface therebetween and create a monolithic filter layer-support structure; and

removing the integral filter layer-support structure from said substrate.

101. The method of claim 91 in which the substrate comprises a silicon wafer.

92. A method for making a monolithic polymeric filter membrane of a predetermined thickness, the filter membrane comprising at least one filter layer with micron-scale precision-shaped pores and a support layer including a precision-shaped support structure for said filter layer, the method comprising:

providing a silicon wafer substrate;

spinning a first polyimide layer onto the silicon wafer;

exposing the first polyimide layer to light through a mask defining a first pattern of one of the micron-scale pores or support structure;

spinning a second polyimide layer onto the first layer polyimide so as to create an interface therebetween;

exposing the second polyimide layer to light through a mask defining a second pattern of the other of the micron-scale pores or the support structure;

removing selected material from the first and second polyimide layers to define the micron-scale pores and support structure;

curing the first and second polyimide layers so as to remove the interface therebetween and create a monolithic filter layer-support structure; and

removing the monolithic filter layer-support structure from said silicon wafer substrate.

93. The method of claim 92 in the removing of selected material from the first polyimide later is carried out before the second layer is spun onto the first layer.

94. A method for making a filter membrane comprising:

providing a flexible film having opposed, generally planar surfaces and a thickness between the surfaces;

ablating selected areas of one of the surfaces to a first selected depth to define a plurality of micron-scale precision-shaped pores on the one surface; and

ablating selected areas of the other of the surfaces to a second selected depth to define a porous precision-shaped support structure, the pores communicating with the porous support structure to allow the passage of filtrate therethrough.

95. The method of claim 94 in which the ablation is carried out by laser.

97. A method for making a monolithic polymeric filter membrane comprising at least a filter layer including micron-scale precision-shaped pores and a support layer including a precision-shaped support structure for the filter layer, the method comprising:

providing a polymeric film including a support structure defined on one side of the film;

forming the filter layer by removing selected material from the other side of the polymeric film to define precision-shape micron-scale pores of the filter layer.

98. The method of claim 97 wherein said support structure is embossed on said one side of said film.

99. The method of claim 97 in which said support structure is pre-cast on said one side of said film.

100. The method of claim 97 in which said forming step is carried out by etching, laser ablation, photoimaging or radiation.

102. (canceled)