Coating processes – Electrical product produced – Fuel cell part
Reexamination Certificate
2002-09-25
2004-09-28
Wu, David W. (Department: 1713)
Coating processes
Electrical product produced
Fuel cell part
C427S358000, C427S407100, C427S402000, C428S001100, C429S006000, C429S006000
Reexamination Certificate
active
06797316
ABSTRACT:
The present invention relates to a process for producing a coating film, a coating film produced by said process and a solid polymer electrolyte fuel cell having said coating film as an electrolyte membrane. Particularly, it relates to a process for producing a coating film which makes it possible to make strength properties of the film containing a reinforcing material comprising short fibrous fillers isotropic, a coating film produced by said process and a process for producing an electrolyte membrane for solid polymer electrolyte fuel cells by said coating process.
Fuel cells are expected to be widely used in the future since their power generation efficiency is high, and their load to the environment is light. Particularly solid polymer fuel cells are expected to be widely spread for movable bodies such as automobiles, or as a diversed power generation system or a cogeneration system for home use, since their power density is high and their operating temperature is low, whereby downsizing and cost cutting are easy as compared with other fuel cells.
In general, as illustrated in the sectional view of
FIG. 7
, a membrane-electrode assembly
101
for solid polymer electrolyte fuel cells comprises a polymer electrolyte membrane
103
comprising an ion exchange resin, catalyst layers
105
a
and
105
b
bonded to both sides of the polymer electrolyte membrane
103
, and e.g. carbon paper or carbon cloth as gas diffusion layers
107
a
and
107
b
disposed outside the catalyst layers.
Outside the gas diffusion layers
107
a
and
107
b
, an electrically conductive separator
109
is disposed. On the separator
109
, gas flow paths
111
a
and
111
b
, which face the gas diffusion layers
107
a
and
107
b
, are formed. A fuel gas and an oxidant gas are made to pass through the gas flow paths, and at the same time, electricity is transmitted from the gas diffusion layers
107
a
and
107
b
to the outside, and electric energy is taken out.
As described above, the membrane-electrode assembly
101
is formed by bonding the electrode catalyst layers
105
a
and
105
b
containing a noble metal on both sides of the polymer electrolyte membrane
103
. The electrode catalyst layers
105
a
and
105
b
are formed by a method of directly coating the polymer electrolyte membrane
103
with an ink for formation of an electrode catalyst layer, containing a catalyst-supported carbon and a dispersion of an ion exchange resin (such as a dispersion of a perfluorocarbon polymer having sulfonic acid groups) as the main solid contents or a method wherein catalyst layers
105
a
and
105
b
preliminarily formed in the form of a sheet are bonded to the polymer electrolyte membrane
103
by means of e.g. hot pressing.
In addition, a method of coating each of the coating layers
105
a
and
105
b
formed into a sheet with an ion exchange resin dispersion by cast film forming, laminating and bonding and the catalyst layers
105
a
and
105
b
with the coating films faced inside, may, for example, be mentioned.
In order to improve performances of the fuel cell, it is considered to decrease the electric resistance by making the polymer electrolyte membrane
103
thin. In a case where a polymer electrolyte membrane
103
in the form of a thin film is formed by cast film forming by using an ion exchange resin comprising a fluorine-containing polymer having sulfonic acid groups, a method of mixing short fibrous fillers with the ion exchange resin with a purpose of compensating for the decrease in mechanical strength, is considered.
In a conventional cast film forming, as illustrated in a perspective view of
FIG. 8
, a die
121
for discharging a coating liquid is equipped with a linear opening
123
in the form of a slit downward as an exit. A substrate
125
for coating disposed to face the linear opening
123
is relatively movable in at least one direction. For example, the substrate
125
for coating is movable in the longitudinal direction X for feeding operation.
The coating liquid discharged from the linear opening
123
of the die
121
is coated on the coating substrate
125
by a coating operation which relatively moves the die
121
in the longitudinal direction of the coating substrate
125
. By this cast film forming, a coating film consisting of a single coating layer
127
or a coating film consisting of a plurality of coating layers wherein a second coating layer
129
is further formed on the coating layer
127
formed in advance.
However, in a case where an ion exchange resin containing short fibrous fillers is coated by the cast film forming, the short fibrous fillers are likely to be orientated in one direction at the exit of the die, and anisotropy is generated such that the strength is different as between in the MD direction (the direction in which a film is formed, the direction of the arrow X in
FIG. 8
) and in the TD direction (the direction perpendicular to the MD direction). Namely, the reinforcing effect by the short fibrous fillers is restricted to one direction, and no adequate strength can be obtained depending upon the direction in the film plane.
Under these circumstances, it is an object of the present invention to provide a process for producing a coating film, which makes it possible to make strength properties of a film containing a reinforcing material comprising short fibrous fillers isotropic, a coating film produced by said process, and a process for producing an electrolyte membrane for solid polymer electrolyte fuel cells by said coating process.
The present invention provides a process for producing a coating film consisting of a single coating layer or a plurality of coating layers laminated, which comprises a coating operation of relatively moving at least one of a die for discharging a coating liquid containing short fibrous fillers from a linear opening with a predetermined length and a substrate for coating, on which the coating liquid discharged from the die is coated, to form a coating layer on the substrate for coating, wherein the direction in the coating operation includes at least two different angle directions with regard to the single coating layer or the plurality of coating layers of the coating film.
The coating film is formed by a coating operation in at least two angle directions. Here, the short fibrous fillers in the coating liquid are aligned mainly along the direction of the coating operation. Accordingly, the short fibrous fillers in the single or the plurality of coating layers are aligned in at least two different directions depending upon the coating operation. Namely, with regard to a cross section in an optional direction, the short fibrous fillers are present so that the short fibrous fillers in at least one direction cross the cross section.
Therefore, the coating film according to the production process of the present invention is free from such a drawback that mechanical properties such as a tensile modulus of elasticity and a tear strength are high only in one direction, and anisotropy in strength properties of a coating film such that the film is made to have a high strength only in one direction by short fibrous fillers, as in a conventional cast film obtained by moving the substrate for coating relatively to the die only in one direction along one line, can be decreased.
Further, in the present invention, the coating operation is preferably a composite operation comprising a feeding operation in one direction along one line and a reciprocating operation in a direction at right angles to the line of the feeding operation.
By the reciprocating operation under the process of the feeding operation, operations in at least different angle directions are continuously carried out, whereby a continuous film can be formed with coating operations in at least two directions. Further, the coating film can be formed by a simple construction comprising drive mechanism for the feeding operation and drive mechanism for the reciprocating operation.
Further, in the present invention, it is preferred that the direction in the feeding operation
Kinoshita Shinji
Mukoyama Atsushi
Shimoda Hiroshi
Asahi Glass Company Limited
Hu Henry S.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Wu David W.
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