GB2313561A

GB2313561A - Coating a plate with hydrophobic resin

Info

Publication number: GB2313561A
Application number: GB9708085A
Authority: GB
Inventors: Su Suk Choi; Jun Hyung Park; Bung Hyun Kang; Jong Wook Lee; Sang Bong Nam; Meen Seon Paik
Original assignee: Samsung Display Devices Co Ltd
Current assignee: Samsung SDI Co Ltd
Priority date: 1996-05-31
Filing date: 1997-04-22
Publication date: 1997-12-03
Also published as: NL1006184A1; SG71706A1; ES2125832A1; JPH1040905A; IT1291648B1; ITMI970955A0; KR0172229B1; DE19716704A1; CN1170247A; SE9701907L; ES2125832B1; KR970077787A; FR2749195A1; NL1006184C2; SE9701907D0; ITMI970955A1; GB9708085D0

Description

2313561 A METHOD OF PREPARING A HYDROPHOBIC PLATE

BACKGROUND OF THE INVENTION

1 Field of the invention

The present invention relates to a method of preparing, a hydrophobic 1 plate, and specifically, to a method of easily preparing a hydrophobic plate having good hydrophobic property by dipping a plate into dispersion solution.

lo 2. Description of the Related Arts

In general a sealed nickel-hydrogen cell that is an alkali storage battery uses metal oxide as an anode and hydrogenated alloy as a cathode. This cell is charged or discharged by storing the hydrogenated alloy hydrogen ions is produced by cleavage of water in the electrolyte during, the charging, process, C1 C) CI and releasing hydrogen ions into the electrolyte during the discharging process. The nickel-hydrogen cell uses hydrogenated alloy as a negative active material, Ni(OH)2 as a positive active material, and alkali aqueous solution as an electrolyte. When the nickel-hydrogen cell is represented by a general formula that is a Ni-MH (nickel-metalhydride) cell Electrical-chemical reactions of the nickel -hydrogen cells are as follows.

2 Anode: NI(OH)2 + OH- N100H + H-20 ----------- (1) Cathode: M + H,0 4--> MH + OH - --------------------- (2) In the above reactions, M is a hydrogenated alloy that can absorb and emit hydrogen ions.

A charge and discharge are performed according to the above reaction, oxygen gas is electrically-chemically generated in the anode during the charge and discharge. When the charge and discharge cycles are continuously performed, the oxygen gas generated causes the cathode to oxidize and the internal pressure of a cell to increase thereby decreasing the capacity of the cell.

lo Accordingly, in order to remove gas by transferring gas generated in the anode to the cathode, hydrophobic property gives to the cathode to extend the interface of the cathode in which cleavage or absorption of gas has occurred.

Fig, 2a shows a negative plate (7) being plated with fluoro-based resin powder as a hydrophobic material by spraying the plate (7) as it is moving in the direction of the arrow (11). Fig. 2b, shows a negative plate (7) being plated with a fluoro-based resin powder as a hydrophobic material by spraying the stationary plate (7) while the spray nozzle (9) is moving, in the direction of the arrow (1 3)). Alcohol that can be readily vaporized after spraying was used w as a medium for spraying, water was not used as a medium because it takes a 1 tp lone, time for water to vaporize thereby oxidizing the plate.

3 As described above, when fluoro resin powder is sprayed on the plate, a three-phase (vapor-liquid-solid) material is formed on the surface of the plate so that gas readily attaches on the plate. Therefore, gas is absorbed or decomposed on the plate so that internal pressure is decreased. However, the s disadvantages of the spray method is that it is difficult to uniformly coat the plate with the fluoro-based resin, and alcohol used as medium is vaporized so that it is harmful to humans and is extremely flammable. Furthermore, the spray method has problems when the hole of the spray nozzle clogs up with the resin of the spray solution, thereby decreasing the operation efficiency.

SUMMARY OF THEE INVENTION

In order to solve the above-mentioned problems of the conventional process, an object of the present invention is to provide a method of preparing is hydrophobic plates, which is not harmful to humans, poses no thereat of causing a fire, and has high operation efficiency.

The secondary object of the present invention Is to provide hydrophobic plates for a cell having low internal pressure and lone, life by using the hydrophobic plate.

While studying a. hydrophobic plate for a cell in order to solve the Z above-mentioned problems, the present inventor discovered that a plate having 1:1 4 good hydrophobic property can be easily prepared, in case of coating a dispersion solution made of hydroFhobic resin. Conventionally, a person havina the ordinary skills in the art thoucht that when a hydrophobic dispersion W is used, it is difficult to prepare a hydrophobic plate, and a plate having bad s hydrophobic property is prepared due to a hydrophilic agent added to promote dispersion, 1. e. interfacial active a ent. Therefore, a method of spraying 9 11.1 powder of a hydrophobic resin on the plate has been used in the conventional process. However, as like the present invention, the plate can be readily coated with hydrophobic resin when a hydrophobic plate is prepared by the io dipping the plate into hydrophobic dispersion solution. Moreover, a cell prepared using the plate has good hydrophobic property, when compared with a cell using a plate prepared by the spray method. Therefore, internal pressure of a cell is decreased, thereby preventing deficiency of an electrolyte in a cell. Furthermore, an electrolyte is uniformly distributed so that a cell having a long life can be prepared.

In order to achieve the object, the present invention provides a method of preparing a hydrophobic plate comprising the steps of coating a plate with a P dispersion solution including hydrophobic resin; and drying said coated plate.

In the present invention, the preferred hydrophobic resin is an aqueous e) to 10 % by weight of a copolymer solution includina fluoro-based resin, U-, - 1:7 of tetrafluoroethylene and hexafluoropropylene, and/or polytetrafluoroethylene.

When dispersion below 3 % by weight of fluoro-based resin is used as a dispersion solution including hydrophobic resin dispersion, a plate having sufficient hydrophobic property can not be produced. Furthermore, when dispersion above 10 % by weight of fluo 0-based is used as a dispersion solution including, hydrophobic resin, the hydrophobic property of a cathode increases. Therefore, it is not preferred to produce a cell using a plate having excess hydrophobic property since the permeation amount of an electrolyte is decreased.

Furthermore, in the present invention, the coatiner step is formed by lo dipping the plate into hydrophobic resin dispersion. It is preferred that the coatina step is carried out for 1 second to 5 minutes in order to obtain 0.2 to 3.0 Mg/CM2 of hydrophobic resin on the plate.

ck In the method of the present invention, it is preferred that b, ck 4 ZCA calendering step is after the drying step because the plate is having uniform thickness can be produced.

Moreover, the method of the present invention can be applied to general molded products as well as a plate of a cell in order to ive good hydrophobic 91 Z1 property.

BRIEF DESCRIPTION OF THE DRAWINGS

6 Fie. 1 (a) is a diagram showing a step of dip-coating a plate into an c C C> aqueous solution including fluoro-based resin to give good hydrophobic 0 1_1.

property to a plate accordina to one embodiment of the present invention; ing a Fit>. 1 (b) is a diagram showing a step of continuously dip-coat' 1-7 plate-roll into an aqueous solution including fluoro-based resin to give good 1 1 C.

hydrophobic property to a plate according to another embodiment of the present invention; Fig. 2 (a) is a diagram showing a step of spraying an aqueous solution lo including fluoro-based resin on plate moving to give hydrophobic property accordina to the conventional method; and Fig. 2 (b) is a diagram showing a step of spraying an aqueous solution includina fluoro-based resin on a plate with a spray nozzle moving accordine, to the conventional method.

is DETAILED DESCRIPTION OF THE INVENTION

The present invention is further explained in more detail with reference to the following example which is within the scope of this invention.

[Example 1]

A cathode of a nickel-hydrogen cell was dipped into 5 wt% of a 7 copolymer of tetra fl uoroethyl ene and hexafluoropropylene, ND-1 (1, Japan, Dikyn Co. Ltd.) for 5 sec. as shown in Fig. 1 (a), and dried in an oven at 601C.

The thickness of the dried plate is controlled by calendering with roller to prepare a hydrophobic plate.

[Example 2]

A hydrophobic plate was prepared by the same procedure as in Example 1 except that a dispersion solution including polytetrafluoroethylene, LDW-40 0 (1, Japan, Takedayakuhing Co, Ltd.) was used as a dispersion solution including fluoro-based resin instead of ND-1, and plate-roll (5) is continuously lo dipped into the dispersion as shown in Fig. 1 (b).

[Comparative example 1] Fluoro-based resin powder is sprayed on a plate while the plate (7) was moving (11) as shown in Fig. 2 (a) to prepare a hydrophobic plate.

[Comparative example 2] is Fluoro-based resin powder is sprayed on a plate while a spray'nozzle (9) was moving (13) as shown in Fig. 2 (b) to prepare a hydrophobic plate.

After the cells were prepared using hydrophobic plate obtained according to the above example and comparative example, the cells were char ed and discharged for 100 times, internal pressure and lifetime (ICY. 9 90% level of total capacity) of these cells were determined and the results thereof is shown in the followina table 1.

W 8 I. Table 1

Internal pressure Lifetime [atmospheric pressure] (When the cell was charged 1 and discharaed once) Z_ [CY] Example 1 5 3 50 Example 2 6

Comparative 20 250 Example 1

Comparative 20 250 Example 2

Conventionally, a person having ordinary skills in the art thought that when hydrophobic dispersion is used, it is difficult to prepare a hydrophobic -5 plate, and a plate having bad hydrophobic property is prepared due to hydrophilic agent added to promote dispersion, i. e. interfacial active agent. Therefore, a method of spraying powder of hydrophobic resin on the plate has been used in the conventional process. However, as like the present invention, the plate can be readily coated with tiydrophobic resin when a hydrophobic lo plate was prepared by dipping the plate into hydrophobic dispersion solution. Moreover, a cell prepared using, the plate has good hydrophobic property, when 9 compared with a cell using a plate prepared by a spray method. Therefore, internal pressure of a cell is decreased, thereby preventing deficiency of an electrolyte in a cell. Furthermore, an electrolyte is uniformly distributed so that a cell having a long life can be prepared.

As shown in the above table 1, the method of coating dispersion solution of the present invention can be effectively performed, when compared with the method of spraying powder. Furthermore, dust is not scattered thereby easily preparing a hydrophobic plate, and an amount of fluoro- based resin coated on a plate is easily controlled by controlling the concentration of io the dispersion aqueous solution.

The method of preparing hydrophobic plate of the present invention can be applied to a method of preparing plates for various fields, such as a condenser as well as a cell in preparing a plate with the object of increasing C1 contact area of a gas.

Moreover, the method of the present invention is a useful method to give hydrophobic property to certain objects.

Claims

CLAIMS:

1. A method of preparing a hydrophobic plate comprising the steps of:

coating a plate with a dispersion solution including hydrophobic resin; and drying said coated plate.

2. A method of preparing a hydrophobic molded product comprising the steps of:

coating a molded product with dispersion solution including hydrophobic resin; and drying said coated molded product.

3. A method according to claim 1 or claim 2, wherein the dispersion solution is an aqueous solution including 3 to 10 wt'i of hydrophobic resin.

4. A method according to any one of claims 1 to 3, wherein the hydrophobic resin is a fluoro-based resin.

5. A method according to claim 4, wherein the fluoro based resin comprises a copolymer of tetrafluoroethylene and hexafluoropropylene, and/or polytetrafluoroethylene.

6. A method according to any one of claims 1 to 5, wherein the coating is performed by dipping the plate into the dispersion solution.

7. A method according to claim 6, wherein the dipping is maintained until 0.2 to 3.0 Mg/CM2 of the hydrophobic resin is coated on the plate.

8. A method according to claim 6 or claim 7, wherein the dipping is performed for 1 second to 5 minutes.

9. A method according to any one of claims 1 to 8, further comprising a calendering step to uniform the thickness of the coated plate or molded product af ter the drying step.

10. A hydrophobic plate or a hydrophobic molded product produced by a method according to any one of claims 1 to 9.