US4250002A
Expired / Lapsed
US
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Polymeric microporous separators for use in electrolytic processes and devices
Assignee: Occidental Chemical Corp
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Filing: 1979-09-19
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Granted: 1981-02-10
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Expires: 1999-09-19
Abstract
Abstract The invention disclosed herein relates to a polymeric microporous electrolytic cell separators for producing alkali metal hydroxide at high current efficiencies, said separator having: a. porosity of at least about 60%; b. thickness of between 8 and 130 mils; c. hysteresis of from 0.30 to 0.99 wherein hysteresis is defined as the ratio of the amount of mercury trapped within the pore structure of the separator after release of pressure to 1 psi compared to the amount of mercury present when first subjected to total impregnation by mercury at 50,000 psi, and d. distribution of pore sizes in a range between 0.004 and 34 microns wherein at least 85% of said pores have a diameter of between 0.12 and 33 microns and at least 60% of said pores have a diameter between 0.59 and 33 microns; wherein the porosity, thickness, hysteresis, and pore size distribution are adapted to provide the separator with the property of exhibiting a high current efficiency including the property of a current efficiency of about 85% to about 98% when measured at a sodium hydroxide concentration of 150 gpl. The separator also possesses hydraulic properties which renders them suitable for use in a commercial scale cell. Also disclosed herein is a method for preparing the separators of this invention comprising the steps (a) forming a sheet comprising a fluorocarbon polymer, a pore forming additive and a fluorinated surface active agent; (b) sintering the sheet; and (c) removing the pore forming additive.
Inventors
- 👤 Christine A. Lazarz
- 👤 Edward H. Cook, Jr.
- 👤 Arthur C. Schulz
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-24 10:37
CPC Classifications
C; C08; C08J; C08J9/00; C08J9/26; C25; C25B; C25B13/00; C25B13/04; C25B13/08; H; H01; H01M; H01M50/00; H01M50/40; H01M50/409; H01M50/411; H01M50/414; H01M50/426; H01M50/489; H01M50/491; B; B29; B29C; B29C43/00; B29C43/006; C08J2327/00; C08J2327/02; C08J2327/12; C08J2327/18; Y; Y02; Y02E; Y02E60/00; Y02E60/10
Claims Analysis
Total Claims: 38
Claim 1
Independent Claim
184 words
A polymeric microporous electrolytic cell separator having: a. porosity of at least about 60%; b. thickness of between 8 and 130 mils; c. hysteresis of from 0.30 to 0.99 wherein hysteresis is defined as the ratio of the amount of mercury trapped within the pore structure of the separator after release of pressure to 1 psi compared to the amount of mercury present when first subjected to total impregnation by mercury at 50,000 psi, and d. distribution of pore sizes in a range between 0.004 and 34 microns wherein at least 85% of said pores have a diameter of between 0.12 and 33 microns and at least 60% of said pores have a diameter between 0.59 and 33 microns; wherein said porosity, thickness, hysteresis, and pore size distribution are adapted to provide said separator with the porperty of exhibiting a high current efficiency including the property of a current efficiency of about 85% to about 98% when measured in a chlor-alkali cell at a sodium hydroxide concentration of 150 gpl, and said separator having hydraulic properties adapted for use in a commercial scale cell.
Claim 2
Dependent Claim
184 words
A polymeric microporous electrolytic cell separator having: a. porosity of at least about 60%; b. thickness of between 8 and 130 mils; c. hysteresis of from 0.30 to 0.99 wherein hysteresis is defined as the ratio of the amount of mercury trapped within the pore structure of the separator after release of pressure to 1 psi compared to the amount of mercury present when first subjected to total impregnation by mercury at 50,000 psi, and d. distribution of pore sizes in a range between 0.004 and 34 microns wherein at least 85% of said pores have a diameter of between 0.12 and 33 microns and at least 60% of said pores have a diameter between 0.59 and 33 microns; wherein said porosity, thickness, hysteresis, and pore size distribution are adapted to provide said separator with the porperty of exhibiting a high current efficiency including the property of a current efficiency of about 85% to about 98% when measured in a chlor-alkali cell at a sodium hydroxide concentration of 150 gpl, and said separator having hydraulic properties adapted for use in a commercial scale cell.
Claim 3
Dependent Claim
110 words
The cell separator of claim 1 wherein said porosity, thickness, hysteresis and distribution of pore diameters are related to said current efficiency by the following formula: CE=A+Bx+Cx.sub.1 +Dx.sub.2 +Ex.sub.3 +Fx.sub.4 +Gx.sub.5 +Jx.sub.6 +Kx.sub.7 wherein: A=Constant=+116.4 Bx=-11.07 [(Porosity) (hysteresis)÷(thickness)] Cx 1 =+1.495 (Zone D+Zone F) Dx 2 =-0.9290 (Zone F+Zone G) Ex 3 =-1.153 (Zone E+Zone F) Fx 4 =-1.484 (Zone C+Zone D) Gx 5 =+92.37 (hysteresis) Jx 6 =-1.756 (thickness) (hysteresis) Kx 7 =+0.9026 (thickness) wherein Zones C-G represent percentages of pores having diameter ranges: Zone C=0.59 to 1.309 microns Zone D=1.31 to 2.949 microns Zone E=2.95 to 6.59 microns Zone F=6.60 to 14.759 microns Zone G=14.76 to 33 microns.
Claim 4
Dependent Claim
12 words
The cell separator of claim 2 wherein the polymeric material is fluorine-containing
Claim 5
Dependent Claim
13 words
The cell separator of claim 3 wherein the fluorine-containing polymeric material is polytetrafluorethylene.
Claim 6
Dependent Claim
13 words
The cell separator of claim 4 wherein the porosity is at least 70%.
Claim 7
Dependent Claim
17 words
The cell separator of claim 4 wherein the thickness is from about 20 to about 70 mils.
Claim 8
Dependent Claim
15 words
The cell separator of claim 4 wherein the hysteresis is from about 0.60 to 0.99.
Claim 9
Dependent Claim
34 words
The cell separator of claim 4 wherein said porosity is at least about 70% said thickness is from about 20 to about 70 mils, and said hysteresis is from about 0.60 to about 0.99.
Claim 10
Dependent Claim
32 words
The cell separator of claim 4, wherein at least about 10% of the pores are between 1.3 to 2.95 microns and about 10% of the pores are between 2.95 to 6.6 microns.
Claim 11
Dependent Claim
20 words
The separator according to claim 9, wherein at least about 10% of the pores are between 0.59 and 1.309 microns.
Claim 12
Dependent Claim
20 words
The separator according to claim 9, wherein at least about 5% of the pores are between 0.59 to 1.309 microns.
Claim 13
Dependent Claim
23 words
The separator according to claim 4, wherein the combined percent distribution of pores within zones D and E is at least about 20%.
Claim 14
Dependent Claim
22 words
The separator according to claim 4 or 9 wherein less than about 20% of the pores are between 14.76 and 33 microns.
Claim 15
Dependent Claim
62 words
The cell separator of claim 5, wherein said hydraulic properties, porosity, thickness, hysteresis and pore size distribution are adapted to provide said separator with the property of exhibiting a current efficiency of about 85 to 98% when measured at a sodium hydroxide concentration of 150 gpl in a chlor-alkali cell wherein the brine head height is from about 2 to 40 inches.
Claim 16
Dependent Claim
15 words
The cell separator of claim 4, wherein said thickness is from 8 to 100 mils.
Claim 17
Dependent Claim
25 words
The cell separator according to claim 4, wherein said porosity is from 60 to 90% and wherein said thickness is from 8 to 100 mils.
Claim 18
Dependent Claim
19 words
An electrolytic cell containing the cell separator as defined in claims 1, 2, 4, 8, 9, 10 or 14.
Claim 19
Dependent Claim
25 words
The electrolytic cell of claim 14, which is a chlor-alkali cell capable of producing alkali metal hydroxide at a concentration of at least 80 gpl.
Claim 20
Independent Claim
39 words
A method of producing chlorine and alkali metal hydroxide which comprises electrolyzing brine in an electrolytic cell equipped with a polymeric microporous electrolytic cell separator, said separator being defined in claims 1, 2, 4, 8, 9, 10 or 14.
Claim 21
Dependent Claim
46 words
The method of claim 19, wherein the separator produces sodium hydroxide at a current efficiency of about 90% to about 95% when measured at a sodium hydroxide concentration of 150 gpl in a chlor-alkali cell having a brine head height of from 2 to 40 inches.
Claim 22
Independent Claim
41 words
The method of making the microporous separator of claims 4, 8, 9, 10 or 14 which comprises: (a) forming a sheet comprising polytetrafluoroethylene, a pore forming additive and a lubricant; (b) sintering the sheet; and (c) removing the pore forming additive.
Claim 23
Dependent Claim
16 words
The method according to claim 18, wherein said lubricant is a nonionic fluorinated surface active agent.
Claim 24
Dependent Claim
26 words
The method according to claim 22, wherein said sheet is reduced to the desired thickness by milling said sheet between the rolls of a roll mill.
Claim 25
Independent Claim
275 words
A method for selecting from a group of porous diaphragms one which will be useful as a separator in an electrolytic cell for the manufacture of chlorine and caustic soda which comprises measuring porosity, thickness, hysteresis, and pore size distribution of such diaphragms and selecting such diaphragms as are within the characteristic ranges of: (a) porosity of at least about 60%; (b) thickness of between 8 and 130 mils; (c) hysteresis of from about 0.30 to about 0.99 wherein hysteresis is defined as the ratio of the amount of mercury trapped within the pore structure of the diaphragm after release of pressure to 1 psi compared to the amount of mercury present when first subjected to total impregnation by mercury at 50,000 psi, and (d) distribution of pore sizes in a range between 0.004 and 34 microns wherein at least 85% of said pores have a diameter of between 0.12 and 33 microns, and at least 60% of said pores have a diameter between 0.59 and 33 microns; wherein the relationship of properties a-d to the current efficiency of the diaphragm is expressed by the formula: A+Bx+Cx.sub.1 +DX.sub.2 +Ex.sub.3 +Fx.sub.4 +Gx.sub.5 +Jx.sub.6 +Kx.sub.7 =CE of at least 85% wherein: A=Costant=+116.4 Bx=-11.07 [(Porosity) (hysteresis)÷(thickness)] Cx 1 =+1.495 (Zone D+Zone F) Dx 2 =-9.9290 (Zone F+Zone G) Ex 3 =-1.153 (Zone E+Zone F) Fx 4 =-1.484 (Zone C+Zone D) Gx 5 =+92.37 (hysteresis) Jx 6 =-1.756 (thickness) (hysteresis) Kx 7 =+0.9026 (thickness) wherein Zones C-G represent percentages of pores having diameter ranges: Zone C=0.59 to 1.309 microns Zone D=1.31 to 2.949 microns Zone E=2.95 to 6.59 microns Zone F=6.60 to 14.759 microns Zone G=14.76 to 33 microns
Claim 26
Independent Claim
275 words
A method for selecting from a group of porous diaphragms one which will be useful as a separator in an electrolytic cell for the manufacture of chlorine and caustic soda which comprises measuring porosity, thickness, hysteresis, and pore size distribution of such diaphragms and selecting such diaphragms as are within the characteristic ranges of: (a) porosity of at least about 60%; (b) thickness of between 8 and 130 mils; (c) hysteresis of from about 0.30 to about 0.99 wherein hysteresis is defined as the ratio of the amount of mercury trapped within the pore structure of the diaphragm after release of pressure to 1 psi compared to the amount of mercury present when first subjected to total impregnation by mercury at 50,000 psi, and (d) distribution of pore sizes in a range between 0.004 and 34 microns wherein at least 85% of said pores have a diameter of between 0.12 and 33 microns, and at least 60% of said pores have a diameter between 0.59 and 33 microns; wherein the relationship of properties a-d to the current efficiency of the diaphragm is expressed by the formula: A+Bx+Cx.sub.1 +DX.sub.2 +Ex.sub.3 +Fx.sub.4 +Gx.sub.5 +Jx.sub.6 +Kx.sub.7 =CE of at least 85% wherein: A=Costant=+116.4 Bx=-11.07 [(Porosity) (hysteresis)÷(thickness)] Cx 1 =+1.495 (Zone D+Zone F) Dx 2 =-9.9290 (Zone F+Zone G) Ex 3 =-1.153 (Zone E+Zone F) Fx 4 =-1.484 (Zone C+Zone D) Gx 5 =+92.37 (hysteresis) Jx 6 =-1.756 (thickness) (hysteresis) Kx 7 =+0.9026 (thickness) wherein Zones C-G represent percentages of pores having diameter ranges: Zone C=0.59 to 1.309 microns Zone D=1.31 to 2.949 microns Zone E=2.95 to 6.59 microns Zone F=6.60 to 14.759 microns Zone G=14.76 to 33 microns
Claim 27
Independent Claim
277 words
The method of making a microporous separator having: a. porosity of at least about 60%; b. thickness of between 8 and 130 mils; c. hysteresis of from 0.30 to about 0.99 wherein hysteresis is defined as the ratio of the amount of mercury trapped within the pore structure of the separator after release of pressure to 1 psi compared to the amount of mercury present when first subjected to total impregnation by mercury at 50,000 psi, and d. distribution of sizes in a range between 0.004 and 34 microns wherein at least 85% of said pores have a diameter of between 0.12 and 33 microns and at least 60% of said pores have a diameter between 0.59 and 33 microns; which comprises: (a) forming a sheet comprising polytetrafluoroethylene, a pore forming additive and a nonionic fluorinated surface active agent; (b) milling the sheet; (c) sintering the sheet, and (d) removing the pore forming additive, wherein the size of the pore forming additive and the milling are adapted to provide a separator wherein said pore distribution, porosity, hysteresis are related to current efficiency by the following relationships: CE=A+Bx+Cx.sub.1 +Dx.sub.2 +Ex.sub.3 +Fx.sub.4 +Gx.sub.5 +Jx.sub.6 +Kx.sub.7 wherein: A=Constant=+116.4 Bx=-11.07 [(Porosity) (hysteresis)÷(thickness)] Cx 1 =+1.495 (Zone D+Zone F) CE=current efficiency between about 85 to 98% Dx 2 =-0.9290 (Zone F+Zone 6) Ex 3 =-1.153 (Zone E+Zone F) Fx 4 =-1.484 (Zone C+Zone D) Gx 5 =+92.37 (hysteresis) Jx 6 =-1.756 (thickness) (hysteresis) Kx 7 =+0.9026 (thickness) wherein Zones C-G represent percentages of pores having diameter ranges: Zone C=0.59 to 1.309 microns Zone D=1.31 to 2.949 microns Zone E=2.95 to 6.59 microns Zone F=6.60 to 14.759 microns Zone G=14.76 to 33 microns
Claim 28
Independent Claim
277 words
The method of making a microporous separator having: a. porosity of at least about 60%; b. thickness of between 8 and 130 mils; c. hysteresis of from 0.30 to about 0.99 wherein hysteresis is defined as the ratio of the amount of mercury trapped within the pore structure of the separator after release of pressure to 1 psi compared to the amount of mercury present when first subjected to total impregnation by mercury at 50,000 psi, and d. distribution of sizes in a range between 0.004 and 34 microns wherein at least 85% of said pores have a diameter of between 0.12 and 33 microns and at least 60% of said pores have a diameter between 0.59 and 33 microns; which comprises: (a) forming a sheet comprising polytetrafluoroethylene, a pore forming additive and a nonionic fluorinated surface active agent; (b) milling the sheet; (c) sintering the sheet, and (d) removing the pore forming additive, wherein the size of the pore forming additive and the milling are adapted to provide a separator wherein said pore distribution, porosity, hysteresis are related to current efficiency by the following relationships: CE=A+Bx+Cx.sub.1 +Dx.sub.2 +Ex.sub.3 +Fx.sub.4 +Gx.sub.5 +Jx.sub.6 +Kx.sub.7 wherein: A=Constant=+116.4 Bx=-11.07 [(Porosity) (hysteresis)÷(thickness)] Cx 1 =+1.495 (Zone D+Zone F) CE=current efficiency between about 85 to 98% Dx 2 =-0.9290 (Zone F+Zone 6) Ex 3 =-1.153 (Zone E+Zone F) Fx 4 =-1.484 (Zone C+Zone D) Gx 5 =+92.37 (hysteresis) Jx 6 =-1.756 (thickness) (hysteresis) Kx 7 =+0.9026 (thickness) wherein Zones C-G represent percentages of pores having diameter ranges: Zone C=0.59 to 1.309 microns Zone D=1.31 to 2.949 microns Zone E=2.95 to 6.59 microns Zone F=6.60 to 14.759 microns Zone G=14.76 to 33 microns
Claim 29
Dependent Claim
10 words
The cell separator made by the process of claim 25.
Claim 30
Independent Claim
137 words
A method for preparing a microporous separator for producing sodium hydroxide comprising the step of correlating the thickness, porosity, hysteresis and pore size distribution during the manufacture of a polytetrafluoroethylene film having an internal network of tortuous pores, to provide a separator exhibiting a current efficiency in the range of from 85% to 98% when measured in a chlor-alkali cell at a sodium hydroxide concentration of 150 gpl and wherein said porosity is at least about 60%, the thickness is between 8 and 30 mils, the hysteresis is from 0.30 to 0.99, and the distribution of pore diameters is between 0.004 to 34 microns wherein at least 85% of the pores have a diameter between 0.12 and 33 microns and at least 60% of the pores have a diameter in the range of 0.59 to 33 microns.
Claim 31
Independent Claim
137 words
A method for preparing a microporous separator for producing sodium hydroxide comprising the step of correlating the thickness, porosity, hysteresis and pore size distribution during the manufacture of a polytetrafluoroethylene film having an internal network of tortuous pores, to provide a separator exhibiting a current efficiency in the range of from 85% to 98% when measured in a chlor-alkali cell at a sodium hydroxide concentration of 150 gpl and wherein said porosity is at least about 60%, the thickness is between 8 and 30 mils, the hysteresis is from 0.30 to 0.99, and the distribution of pore diameters is between 0.004 to 34 microns wherein at least 85% of the pores have a diameter between 0.12 and 33 microns and at least 60% of the pores have a diameter in the range of 0.59 to 33 microns.
Claim 32
Dependent Claim
111 words
The method according to claim 27, wherein said porosity, hysteresis, thickness and pore size distribution are correlated to said current efficiency in accordance with the following relationship: CE=A+Bx+Cx.sub.1 +Dx.sub.2 +Ex.sub.3 +Fx.sub.4 +Gx.sub.5 +Jx.sub.6 +Kx.sub.7 wherein: A=Constant=+116.4 Bx=-11.07 [(Porosity) (hysteresis)÷(thickness)] Cx 1 =+1.495 (Zone D+Zone F) Dx 2 =-0.9290 (Zone F+Zone G) Ex 3 =-1.153 (Zone E+Zone F) Fx 4 =-1.484 (Zone C+Zone D) Gx 5 =+92.37 (hysteresis) Jx 6 =-1.756 (thickness) (hysteresis) Kx 7 =+0.9026 (thickness) wherein Zones C-G represent percentages of pores having diameter ranges: Zone C=0.59 to 1.309 microns Zone D=1.31 to 2.949 microns Zone E=2.95 to 6.59 microns Zone F=6.60 to 14.759 microns Zone G=14.76 to 33 microns
Claim 33
Dependent Claim
105 words
The method according to claim 28, wherein said polytetrafluoroethylene film is prepared by (a) forming a sheet comprising polytetrafluoroethylene, a nonionic fluorinated surface active agent, and a pore forming additive and (b) milling the sheet; (c) sintering the sheet and (d) removing the pore forming additive; and wherein said correlation is accomplished by adapting the size of the pore forming additive and the milling step to provide said separator with a porosity of at least 70%, a thickness of between 8 to 130 mils, a hysteresis of from 0.30 to 0.99 and a pore diamter distribution in the range of between 0.004 to 34 microns.
Claim 34
Dependent Claim
12 words
The product made by the method of claims 27, 28 or 29.
Claim 35
Dependent Claim
148 words
A polytetrafluoroethylene electrolytic cell separator for producing alkali metal hydroxide at about 95% current efficiency when measured in a clor-alkali cell at a sodium hydroxide concentration of 150 gpl, said separator having an internal network of pores with diameters ranging in size between about 0.004 and 34 microns, a porosity of about 80%, a hysteresis of about from 0.95 to 0.99, and a thickness of about from 20-40 mils, and wherein the percent distribution of pore diameters within zones C-G is defined by the areas bounded by the plot lines of FIG. I, wherein zones C-G are defined by the following pore diameter ranges: Zone C=0.59 to 1.309 microns Zone D=1.31 to 2.949 microns Zone E=2.95 to 6.59 microns Zone F=6.60 to 14.759 microns Zone G=17.46 to 33 microns and wherein about from 60-100% of the pores of said separator have diameters distributed within zones C through G.
Claim 36
Dependent Claim
148 words
A polytetrafluoroethylene electrolytic cell separator for producing alkali metal hydroxide at about 95% current efficiency when measured in a clor-alkali cell at a sodium hydroxide concentration of 150 gpl, said separator having an internal network of pores with diameters ranging in size between about 0.004 and 34 microns, a porosity of about 80%, a hysteresis of about from 0.95 to 0.99, and a thickness of about from 20-40 mils, and wherein the percent distribution of pore diameters within zones C-G is defined by the areas bounded by the plot lines of FIG. I, wherein zones C-G are defined by the following pore diameter ranges: Zone C=0.59 to 1.309 microns Zone D=1.31 to 2.949 microns Zone E=2.95 to 6.59 microns Zone F=6.60 to 14.759 microns Zone G=17.46 to 33 microns and wherein about from 60-100% of the pores of said separator have diameters distributed within zones C through G.
Claim 37
Dependent Claim
210 words
A polytetrafluoroethylene electrolytic cell separator for producing alkali metal hyroxide at about a 95% current efficiency when measured in a chlor-alkali cell at a sodium hydroxide concentration of 150 gpl, said separator having an internal network of pores with diameters ranging in size from 0.004 to 34 microns, a hysteresis of from 0.95 to 0.99, a porosity between 75 and 85%, and a thickness of 20, 30 or 40 mils, wherein the percent distribution of pore diameters within zones C-G for a thickness of 20 mils is defined by areas bounded by the plot lines of FIG. II, the percent distribution of pore diameters within zones C-G for a thickness of 30 mils is defined by the areas bounded by the plot lines of FIG. III, and the percent distribution of pores within zones C-G for a thickness of 40 mils is defined by the areas bounded by the plot lines of FIG. IV, wherein said zones C-G are defined by the following pore diameter ranges: Zone C=0.59 to 1.309 microns Zone D=1.31 to 2.949 microns Zone E=2.95 to 6.59 microns Zone F=6.60 to 14.759 microns Zone G=17.46 to 33 microns and wherein about from 60 to 100% of the pores of said separator have diameters distributed within zones C-G.
Claim 38
Dependent Claim
210 words
A polytetrafluoroethylene electrolytic cell separator for producing alkali metal hyroxide at about a 95% current efficiency when measured in a chlor-alkali cell at a sodium hydroxide concentration of 150 gpl, said separator having an internal network of pores with diameters ranging in size from 0.004 to 34 microns, a hysteresis of from 0.95 to 0.99, a porosity between 75 and 85%, and a thickness of 20, 30 or 40 mils, wherein the percent distribution of pore diameters within zones C-G for a thickness of 20 mils is defined by areas bounded by the plot lines of FIG. II, the percent distribution of pore diameters within zones C-G for a thickness of 30 mils is defined by the areas bounded by the plot lines of FIG. III, and the percent distribution of pores within zones C-G for a thickness of 40 mils is defined by the areas bounded by the plot lines of FIG. IV, wherein said zones C-G are defined by the following pore diameter ranges: Zone C=0.59 to 1.309 microns Zone D=1.31 to 2.949 microns Zone E=2.95 to 6.59 microns Zone F=6.60 to 14.759 microns Zone G=17.46 to 33 microns and wherein about from 60 to 100% of the pores of said separator have diameters distributed within zones C-G.
References Cited (Backward Citations)
US2573639A
Cited
US3556161A
Cited
US3281511A
Cited
US3506493A
Cited
GB1081046A
Cited
FR1491033A
Cited
US3518332A
Cited
US3817772A
Cited
US3661645A
Cited
GB1364683A
Cited
US3813461A
Cited
US3930886A
Cited
US3890417A
Cited
US3852224A
Cited
US4049589A
Cited
US4031000A
Cited
US3930979A
Cited
US4098672A
Cited
US3859402A
Cited
US3944477A
Cited
US4135996A
Cited
US4110153A
Cited
US4165271A
Cited
US4170540A
Cited
US4170538A
Cited
US4170537A
Cited
US4170539A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1984-02-10 | 1984-08-11 | 1985-02-10 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1988-02-10 | 1988-08-11 | 1989-02-10 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1992-02-10 | 1992-08-11 | 1993-02-10 | $7700.00 | Window Closed / Lapsed |