JP5164569B2 - Proton conductive membrane reinforcing material, proton conductive membrane using the same, and fuel cell - Google Patents

Description

  The present invention relates to a reinforcing material for reinforcing a proton conductive membrane used as an electrolyte membrane of a fuel cell, and further relates to a proton conductive membrane reinforced by this reinforcing material, and a fuel cell using the same.

  In recent years, fuel cells are attracting attention as environmentally friendly new energy sources because of their high power generation efficiency and low environmental impact. Fuel cells are generally classified into several types according to the type of electrolyte. Above all, the polymer electrolyte fuel cell (PEFC) is easy to make high output, small size and light weight, and can be expected to reduce the cost by mass production effect. As a fuel cell, it is considered as the next generation mainstay.

  At present, what is mainly used as a proton conductive membrane for PEFC is perfluoroalkylene as a main skeleton, and a part of the perfluorovinyl ether side chain is an ion exchange group such as a sulfonic acid group or a carboxylic acid group. For example, Nafion (registered trademark) membrane (Du Pont), Dow membrane (Dow Chemical), Aciplex (registered trademark) membrane (Asahi Kasei Kogyo), Flemion (registered trademark) A membrane (manufactured by Asahi Glass Co., Ltd.) is known.

  When these fluorine-based membranes contain water, the sulfonic acid groups in the polymer are ionized to become hydrophilic, and the ionized molecules gather to form clusters, which serve as proton passages. However, this proton conductive membrane swells with moisture, causing an increase in dimensions, a decrease in mechanical strength, and creep during long-time operation. Furthermore, the handleability at the time of stack assembly and the durability after the start of operation are lowered.

  In order to solve this, attempts have been made to reinforce the proton conductive membrane with various reinforcing materials. For example, in Japanese Patent Application Laid-Open No. 10-31815, dimensional stability and handling are improved by forming a porous support of randomly oriented individual fibers and impregnating the support with an ion conductive polymer material. Is disclosed. Here, examples of suitable fibers include fibers of glass, polymer, ceramic, quartz, silica, carbon, and metal, and it is shown that fibers of glass, ceramic, and quartz are preferable.

  The present applicant also discloses a glass fiber cloth in which a silica layer is coated on a surface layer whose surface has been made porous in JP 2004-047450 A, and has an average fiber diameter of 0.2 to 20 μm. It discloses that a proton conductive membrane is reinforced with a reinforcing material made of a cloth formed of glass fibers.

  As an improvement in the reinforcing material, for example, in Japanese Patent Application Laid-Open No. 2003-253010, “a composition mainly composed of a three-dimensional crosslinked structure (A) having a metal-oxygen bond and a proton conductivity-imparting agent (B)” is disclosed. , A proton conductive membrane reinforced with a short fiber material (C) and a long fiber material (D) is disclosed.

  In addition, the applicant also disclosed in Japanese Patent Application Laid-Open No. 2004-319421 by using a glass fiber nonwoven fabric in which two or more kinds of glass fibers having different average fiber diameters are combined as a reinforcing material for the proton conductive film. It discloses that deformation due to shrinkage during curing can be suppressed.

  On the other hand, the applicant of the present invention also discloses a separator for a lead-acid storage battery, for example, in Japanese Patent Application Laid-Open No. 2003-308818, “a separator for a sealed lead-acid battery mainly composed of fine glass fibers and containing inorganic powder. Then, a sealed lead-acid battery separator characterized in that the inorganic powder is an inorganic powder having a primary particle diameter of 15 nm or less has been proposed.

  Consider a case where the proton conductive membrane is reinforced with a glass fiber nonwoven fabric as described in JP-A-10-31815 and JP-A-2004-047450. In this case, if the glass fiber nonwoven fabric is simply impregnated with the proton conductive material, the filter effect of the nonwoven fabric may impede the permeation of the material, and a minute gap may be generated in the membrane. The minute gaps generated in this way do not have proton conductivity, and may reduce proton conductivity as a membrane.

  In order to eliminate such minute gaps, reduce the thickness of the membrane to improve proton conductivity, and further improve the uniformity and flatness of the thickness of the membrane, in the process of forming the proton conductive membrane, Alternatively, hot pressing using a press plate is often performed. In this hot pressing, in order to eliminate the minute gaps, it is preferable to carry out at a pressure as high as possible and at a high temperature within a range where the proton conductive membrane does not melt.

  However, when an inorganic material such as glass fiber is used as a reinforcing material, when hot pressing is performed at a high pressure, the pressure concentrates on a portion where the glass fibers intersect with each other, and the glass fiber at that portion is broken. As a result, the thickness as the reinforcing material cannot be maintained, and the gap for filling the proton conductive material is reduced. Even in such a case, the conductivity of the proton conductive membrane is lowered.

  In the above-mentioned Japanese Patent Application Laid-Open No. 2003-253010, when a proton conductive material is reinforced with a three-dimensional cross-linked structure and a fiber material, it is excellent in heat resistance, heat and moisture dimensional stability, and swelling resistance. However, the purpose of reinforcement is dimensional stability against heat and humidity, and the reason for using the short fiber material and the long fiber material together is not described.

  In the technique disclosed in Japanese Patent Application Laid-Open No. 2004-319421 by the present applicant, deformation due to shrinkage during proton conductive membrane curing is suppressed by combining glass fibers having different average fiber diameters. However, nothing is said about the compression resistance during the production of the proton conductive membrane.

  On the other hand, the technique disclosed by the present applicant in Japanese Patent Application Laid-Open No. 2003-308818 is a sealed lead-acid battery separator, and has an inorganic primary particle size of 15 nm or less in order to improve short-circuit resistance in the lead-acid battery. It contains powder.

  As described above, there is still a reinforcing material for a proton conductive membrane that can maintain a sufficient gap under high pressure and high temperature conditions required in a hot press process in the production of a proton conductive membrane. Did not exist.

  Therefore, the present invention is capable of maintaining a sufficient gap even when subjected to compression in a hot press process at a high pressure and high temperature, and a proton that can maintain high proton conductivity when used as a reinforcing material for a proton conductive membrane. It is in providing the reinforcing material for conductive films. A further object is to provide a proton conductive membrane and a fuel cell using the same.

  The reinforcing material for proton conductive membranes of the present invention is a reinforcing material for proton conductive membranes comprising a nonwoven fabric containing glass fibers and inorganic particles supported on the nonwoven fabric, with respect to the volume occupied by the reinforcing material. When the percentage of the volume excluding the volume of the glass fiber from the volume occupied by the reinforcing material is regarded as the assumed porosity, at least a part of the inorganic particles is set so that the assumed porosity is 90% by volume. It has a particle size equal to or greater than the thickness when the reinforcing material is deformed (hereinafter sometimes referred to as thickness T). The content rate of the said inorganic particle in the reinforcing material for proton conductive membranes of this invention can be 2-10 mass%, for example. Moreover, it is preferable that the particle size of the said inorganic particle is 2 times the thickness T (2T) or less. The particle size range of at least a part of the inorganic particles (inorganic particles having a particle size equal to or greater than the thickness T) is, for example, in the range of 15 μm to 200 μm.

In the present invention, the assumed porosity is a percentage of a volume obtained by removing the volume of the glass fiber from the volume occupied by the reinforcing material with respect to the volume occupied by the reinforcing material. That is, the assumed porosity is a value obtained by the following formula.
Considered porosity (%) = (V _R −V _G ) × 100 / V _R
V _R : Volume of reinforcing material V _G : Volume of glass fiber

In the present invention, the volume occupied by the reinforcing material (volume of the reinforcing material) V _R can be obtained using the following equation.
V _R = t × A
A: Area of the reinforcing material t: Thickness of the reinforcing material measured with a dial gauge after pressurizing the reinforcing material at 20 kPa

  Moreover, the volume of glass fiber can be calculated | required with the density and mass of glass fiber.

  The thickness of the reinforcing material when the reinforcing material is deformed so that the assumed porosity is 90% by volume is a value obtained when the reinforcing material is compressed in the thickness direction and the assumed porosity becomes 90% by volume. This value is obtained by measuring the thickness of the reinforcing material. Further, the compression of the reinforcing material in the thickness direction is performed without changing the area of the reinforcing material (in a state where the area is fixed).

  In addition, the particle size of the inorganic particles is expressed by the equivalent circle diameter by a microscopic method when the inorganic particles can be considered to be almost spherical, and by the opening size of the test sieve measured by the sieving method when the inorganic particles cannot be considered spherical. It is what you did. The microscope method is described in JIS Z 8901, and the sieving method is described in JIS Z 8815.

  The proton conductive membrane reinforcing material of the present invention includes inorganic particles having a predetermined particle diameter determined as described above, thereby reducing proton conductivity in a hot press process when producing a proton conductive membrane. In addition to eliminating the minute gaps that cause the gap, the gap for filling the proton conductive material can be left. Furthermore, since the reinforcing material for proton conductive membrane of the present invention has high strength, the mechanical strength of the proton conductive membrane can be further improved.

  The proton conductive membrane of the present invention includes the above-described reinforcing material for proton conductive membrane of the present invention and a proton conductive material fixed to the reinforcing material for proton conductive membrane.

  From another point of view, the proton conductive membrane of the present invention is a proton conductive membrane reinforcing material including a nonwoven fabric containing glass fibers and inorganic particles supported on the nonwoven fabric, and the proton conductive membrane. And a proton conductive material fixed to the reinforcing material.

  According to the proton conductive membrane of the present invention, it is possible to realize high strength while having proton conductivity equivalent to that of a proton conductive membrane not using a reinforcing material.

  The method for producing a proton conductive membrane of the present invention comprises a step of impregnating the above-described reinforcing material for a proton conductive membrane of the present invention with a proton conductive material, and the proton conductive membrane impregnated with the proton conductive material. And pressurizing the reinforcing material in the thickness direction.

  In the method for producing a proton conductive membrane of the present invention, a proton conductive reinforcing material containing inorganic particles having a predetermined particle diameter at a predetermined content is used. Even when the reinforcing material is compressed in the pressurizing step, the reinforcing material can maintain a gap necessary for filling the proton conductive material. Therefore, according to the method of the present invention, it is possible to manufacture a proton conductive membrane having high strength while realizing proton conductivity equivalent to that of a proton conductive membrane not using a reinforcing material.

  The fuel cell of the present invention uses the proton conductive membrane of the present invention described above. According to the fuel cell of the present invention, a fuel cell with high power generation efficiency can be provided.

1A and 1B are cross-sectional views schematically showing a state where the proton conductive reinforcing material of the present invention is compressed in the thickness direction. 2A and 2B are cross-sectional views schematically showing a state in which a conventional proton conductive reinforcing material is compressed in the thickness direction. It is a figure which shows the state observed about the proton-conductive reinforcement material of Example 1 using the scanning electron microscope. It is sectional drawing which shows an example of the proton conductive film | membrane of this invention. It is a disassembled perspective view which shows an example of the fuel cell of this invention.

  Hereinafter, embodiments of the present invention will be described in detail.

  First, an embodiment of the proton conductive membrane reinforcing material of the present invention will be described.

  The proton conductive membrane reinforcing material of the present embodiment (hereinafter referred to as a reinforcing material) includes a nonwoven fabric made of glass fiber and inorganic particles having a predetermined particle size carried on the nonwoven fabric. The reinforcing material of the present embodiment contains 2 to 10% by mass of inorganic particles having a predetermined particle size. For the nonwoven fabric, for example, a nonwoven fabric using glass fibers having a C glass composition as a main material can be used. Here, the main material is a material contained in an amount of 50% by mass or more, preferably 70% by mass or more.

  The predetermined particle size in the inorganic particles can be determined as follows.

  The volume excluding the volume of the glass fiber forming the nonwoven fabric is determined from the volume occupied by the reinforcing material, and the percentage of the volume with respect to the entire volume of the reinforcing material is not defined and defined as the porosity. The particle size of the inorganic particles contained in the reinforcing material is determined by using the thickness (T μm) of the reinforcing material when the reinforcing material is deformed so that the assumed porosity is 90% by volume. That is, the reinforcing material includes inorganic particles having a particle size of T μm or more.

  The reason for using this deemed porosity is to eliminate the influence of inorganic particles contained in the reinforcing material. The assumed porosity is different from the actual porosity described later. Moreover, since the reinforcing material of this embodiment should just contain the inorganic particle which has a particle size of Tmicrometer or more with the predetermined content rate (here 2-10 mass%), the inorganic particle diameter is less than Tmicrometer. Particles may further be included.

  In consideration of the thickness of generally used proton conductive membranes and reinforcing materials, the particle size range of inorganic particles suitably used for the reinforcing material is, for example, in the range of 15 μm to 200 μm (as an example, in the range of 20 μm to 75 μm). ) And can.

  The shape of the inorganic particles is not particularly limited as long as it is a shape that can maintain a sufficient gap when subjected to compression. In addition, it is preferable if the inorganic particles are substantially spherical, since stress concentration is not extreme when subjected to compression. Moreover, a reinforcing material using inorganic particles having a substantially spherical shape and a predetermined particle diameter is preferable because a desired thickness can be easily obtained when a proton conducting membrane is produced using the reinforcing material.

  The material of the inorganic particles is not particularly limited, and for example, silica, titania, alumina, glass, ceramics and the like can be used, but the inorganic particles used here preferably have high acid resistance, Since it is easily available and inexpensive, particles mainly composed of silica are preferably used. Accordingly, examples of such particles include particles made of silica and particles made of glass having a C glass composition.

  The inorganic particles are more preferably dense and hard. Even with porous or soft particles, it is possible to achieve the object of the present invention to ensure sufficient voids. However, if the pressure applied to the inorganic particles exceeds the allowable limit during the hot pressing process, the inorganic particles are destroyed or deformed and cannot fully fulfill their roles.

  In addition, when a predetermined amount of inorganic particles having a particle diameter of T μm or more is not included, the ability to secure voids may be reduced. On the other hand, when many inorganic particles having a particle size that is too large are contained, for example, when the content of inorganic particles having a particle size exceeding 2 Tμm is high, the reinforcing material is compressed to a predetermined thickness by hot pressing, and proton conductivity It may be difficult to produce a film. As a result, the above-mentioned minute gap remains inside the proton conductive membrane, and proton conductivity may be lowered. Therefore, the particle size of the inorganic particles contained in the reinforcing material is preferably 2 Tm or less. In addition, when the inorganic particle over 2 Tmicrometer is contained, the content rate of the inorganic particle is 5 mass% or less, and 3 mass% or less is more preferable.

  Moreover, when the particle size of the inorganic particles is too large, local protrusions are generated in the reinforcing material. When a proton conductive membrane is produced using a reinforcing material having such a convex portion and a fuel cell is further formed, the current collector adjacent to the proton conductive membrane is locally pressed and damaged. Sometimes. Accordingly, the upper limit of the particle size of the inorganic particles is preferably 2 Tμm, and more preferably 1.5 Tμm.

  When the content of the inorganic particles is less than 2% by mass, the ability to secure voids as a reinforcing material is reduced, and a locally convex portion is generated. When the content rate of an inorganic particle exceeds 10 mass%, the ratio of the glass fiber which forms the frame | skeleton of a nonwoven fabric reduces relatively, and the mechanical strength as a nonwoven fabric falls. For this reason, in the step of impregnating the reinforcing material with the proton conductive material, the reinforcing material is easily damaged, which is not preferable. Therefore, as described above, in the reinforcing material of the present embodiment, the content of inorganic particles having a particle size of T μm or more is preferably 2 to 10% by mass, and more preferably 3 to 8% by mass.

  Silica particles that can be used as inorganic particles are generally classified and marketed. In the reinforcing material of the present embodiment, a commercially available product can be used as it is as inorganic particles as long as it has a predetermined particle size distribution. However, in order to efficiently counteract the pressure in the hot pressing step, it is preferable to further classify the particles to have a sharp particle size distribution near a predetermined particle size. In particular, it is preferable to remove small particles.

  1A and 1B are diagrams for explaining the principle of the reinforcing material of the present embodiment, and are sectional views schematically showing how the reinforcing material of the present embodiment is compressed. 2A and 2B are cross-sectional views schematically showing how a conventional reinforcing material is compressed. FIG. 1A shows a reinforcing material 1 in which inorganic particles 12 having a predetermined particle size (T μm or more) are supported on a nonwoven fabric 11. FIG. 2A shows a conventional reinforcing material 100 that does not include inorganic particles and is composed only of the nonwoven fabric 11. FIG. 1B and FIG. 2B show a state in which the respective reinforcing members 1 and 100 are pressed in the thickness direction (the direction indicated by the arrow in the drawing) by the press plates 2 arranged above and below. .

  As shown in FIG. 1B, the reinforcing material 1 includes the inorganic particles 12 (supported by the nonwoven fabric 11) even when pressed in the thickness direction, so that the particle size (T μm) or less of the inorganic particles. Is not compressed. On the other hand, as shown in FIG. 2B, the conventional reinforcing material 100 does not contain inorganic particles, and thus is further compressed as compared with the reinforcing material 1 shown in FIG. 1B. That is, in the conventional reinforcing material 100, the space of the nonwoven fabric 11 is crushed by being compressed, whereas the reinforcing material 1 of the present embodiment is necessary for filling the proton conductive material even if compressed. It can be confirmed that the voids can be maintained.

  On the other hand, as a composition of the glass fiber which comprises a nonwoven fabric, C glass composition is preferable. This is because the C glass composition has the highest acid resistance among the known glass compositions for fibers. For this reason, the nonwoven fabric formed with the glass fiber of C glass composition is widely used in acidic atmospheres, such as a lead acid battery.

  Furthermore, the reinforcing material in the present embodiment is preferably subjected to an appropriate coating treatment on the surface of the glass fiber in order to improve the reinforcing effect. Specifically, a treatment for coating a glass fiber surface with a silane coupling agent or a binder is effective.

  In addition, you may perform coating processes, such as forming a film, such as a silica, in glass fiber. The surface treatment method is not particularly limited as long as it does not impair the heat resistance and acid resistance of the glass fiber.

  In order to ensure the function as a proton conductive membrane of the polymer electrolyte fuel cell, the thickness of the proton conductive membrane is preferably 100 μm or less, more preferably 50 μm or less. In order to obtain such a thickness, the average diameter of the glass fibers constituting the reinforcing material nonwoven fabric is preferably 0.1 to 20 μm. Similarly, the thickness of the reinforcing material is preferably 100 μm or less.

  If the average diameter of the glass fiber is less than 0.1 μm, the production cost becomes extremely high, which is not practical. On the other hand, if the average diameter exceeds 20 μm, the number of fibers per unit volume as a reinforcing material decreases, and sufficient tensile strength cannot be obtained.

  Furthermore, as an average fiber length of the glass fiber which comprises a reinforcing material, it is preferable that it is 0.5-20 mm. When the average fiber length is less than 0.5 mm, the mechanical strength of the reinforcing material is remarkably lowered, so that the reinforcing effect of the proton conductive membrane is reduced and the handleability is deteriorated. On the other hand, when the average fiber length of glass fiber exceeds 20 mm, the dispersibility of the glass fiber at the time of nonwoven fabric formation will fall. As a result, it becomes difficult to obtain the uniformity of the thickness necessary for the reinforcing material and the uniformity of the basis weight.

  The basis weight is the mass per unit area.

  Thickness uniformity required as a reinforcing material refers to the degree of unevenness of thickness in each part of the nonwoven fabric, and that there is thickness uniformity, the thickness in each part of the nonwoven fabric is relative to the average thickness. + 5% to -15%, more preferably in the range of + 0% to -10%.

  Uniformity of basis weight means the degree of unevenness of mass per unit area in each part of the nonwoven fabric. Uniformity of basis weight means that the basis weight in each part of the nonwoven fabric is the average basis weight. On the other hand, it is in the range of + 5% to -15%, more preferably + 0% to -10%.

Further, when the thickness of the proton conductive membrane is 100 μm or less as described above, the basis weight of the reinforcing material is preferably ² to 50 g / m ² , and preferably 3 to 25 g / m ^2. More preferred.

When the basis weight is 2 g / m ² or less, the number of fibers per unit volume as a reinforcing material decreases, and sufficient tensile strength may not be obtained. On the other hand, if the basis weight exceeds 50 g / m ² , the thickness as the reinforcing material may be too thick to obtain the proton conductive membrane having the above thickness. In order to make this a practical thickness, if the thickness is reduced by increasing the density with a press or the like, the glass fiber breaks and shortens at the crossing point, and the tensile strength of the reinforcing material significantly decreases. May occur.

  Moreover, it is preferable that the substantial porosity of a reinforcing material is 60-98 volume%. The substantial porosity is a porosity in consideration of the volume of inorganic particles and the volume of binder contained in the reinforcing material.

  If the actual porosity exceeds 98% by volume, the strength may be significantly reduced and it may be difficult to play a role as a reinforcing material. In addition, the rigidity is significantly lowered, and it may be difficult to play a role of suppressing deformation due to shrinkage of the proton conductive material. On the other hand, when the substantial porosity is less than 60% by volume, the proton conductivity may decrease. A more preferable substantial porosity is 80-98 volume%, and a still more preferable substantial porosity is 90-95 volume%.

  By the way, when short glass fibers with an average diameter of about 0.7 μm and an average length of about 3 mm are wet-made without a mechanical compression step to a thickness of 50 μm, a glass fiber nonwoven fabric with a substantial porosity of about 94 volume% is produced. can do.

In addition, the value of the substantial porosity V can be calculated | required by following Formula.
V (%) = (1−W / t × k) × 100
k = (1−c _A −c _B ) / ρ _G + c _A / ρ _A + c _B / ρ _B
t: pressure of the reinforcing material at 20 kPa, thickness of the reinforcing material measured with a dial gauge W: mass per unit area of the reinforcing material ρ _G : density of glass fiber (about 2.5 × 10 ³ kg / m ³ ( = 2.5 g / cm ³ ))
ρ _A : Density of inorganic particles ρ _B : True density of binder (density that does not include voids and uses only the volume occupied by the substance itself as the volume for density calculation)
c _A : mass ratio of inorganic particles c _B : mass ratio of solid content of binder

  According to the reinforcing material described above, the proton conductive membrane can be sufficiently reinforced. However, minute separation may be formed at the interface between the glass fiber and the proton conductive material due to the difference in thermal expansion coefficient or the stress during the formation of the proton conductive film. In the vicinity of the portion where minute peeling occurs, the effect of suppressing the deformation of the proton conductive material by the glass fiber is reduced. For this reason, the actual reinforcing effect is generally lower than the original effect of the reinforcing material.

  As a means for solving this problem and further improving the reinforcing effect, a coating treatment of the reinforcing material surface with a silane coupling agent is effective. By coating the surface of the reinforcing material with a silane coupling agent under appropriate conditions, the adhesion between the reinforcing material and the proton conductive material is improved, and the formation of the above-described minute separation is suppressed, and the reinforcing material The reinforcement effect by becomes very high.

In addition, as an adhesion amount of a silane coupling agent, it is preferable that it is 0.5-200 mg / m < ² > with respect to a reinforcing material surface area. If the adhesion amount is less than 0.5 mg / m ² , the silane coupling agent cannot sufficiently cover the surface of the reinforcing material, and the effect of improving the adhesion between the reinforcing material and the proton conductive material may be reduced. Moreover, if the adhesion amount exceeds 200 mg / m ² , a low-strength layer made of only silane is formed between the reinforcing material and the proton conductive material. For this reason, breakdown in the low-strength layer is likely to occur, and the effect of improving the adhesive force between the reinforcing material and the proton conductive material may be apparently reduced.

  The silane coupling agent used in the present embodiment is not limited as long as it exhibits an effect of improving the adhesion between the reinforcing material and the proton conductive material. From the viewpoint of easy handling, the silane coupling agent is preferably aminosilane or acrylic silane.

  Further, the glass fiber nonwoven fabric is not bonded to each other, and the mechanical strength is maintained by the entanglement of the fibers. That is, with the deformation of the proton conductive material, the glass fiber adhered to it also moves.

  Therefore, if the glass fibers are restrained using a binder, the movement between the glass fibers is reduced. Specifically, when a liquid binder is used, the intersections of the glass fibers may be bonded, and when a fibrous binder is used, the glass fibers and the binder fibers may be bonded or entangled. As a result, the reinforcing effect in the reinforcing material of the present embodiment is improved.

  The material of the binder is not particularly limited as long as it has good heat resistance and acid resistance. For example, beaten cellulose fiber, acrylic fiber, acrylic resin emulsion, fluororesin dispersion, colloidal silica and the like can be mentioned.

  In the case of a liquid binder, the solid content addition amount is preferably 0.5 to 10% by mass with respect to the glass fiber mass. When the addition amount is less than 0.5% by mass, the bonding effect between the glass fibers by the binder may be lowered. If the addition amount exceeds 10% by mass, a film may be formed between the glass fibers to inhibit proton conduction. As this liquid binder, it is more preferable to use colloidal silica which is particularly excellent in acid resistance and heat resistance.

  In the case of a fibrous binder, it is preferable that it is 1-40 mass% with respect to glass fiber mass as solid content addition amount. When the addition amount is less than 1% by mass, the bonding effect of the glass fiber by the binder may be lowered. If the addition amount exceeds 40% by mass, the glass fiber is remarkably fixed, and the glass fiber opening is reduced, and sufficient penetration between the fibers during impregnation with the polymer solution may be hindered.

  In addition, when the glass fiber diameter exceeds 20 μm, local protrusions are generated in the nonwoven fabric having a thickness of 50 μm or less, and the formation of a uniform nonwoven fabric may be inhibited. Therefore, the glass fiber diameter is preferably 20 μm or less. . However, this does not apply to cases where deformation or dissolution occurs during the formation of the nonwoven fabric or the proton conductive membrane and no convex portions are produced after the preparation of the nonwoven fabric.

  Since the above-mentioned silane coupling agent treatment and the above-mentioned binder addition exert a reinforcing effect by an independent mechanism, they can be used in combination, and the effects are synergistic.

  An embodiment of the proton conductive membrane of the present invention will be briefly described.

  The proton conductive membrane of the present embodiment uses the above-described reinforcing material of the present invention, and is formed by fixing a proton conductive material to the reinforcing material. The proton conductive material may have any composition as long as it is of a proton conductive type. For example, a perfluorosulfonic acid polymer such as Nafion (registered trademark) (manufactured by Du Pont) may be used. it can. The proton conductive membrane can be manufactured by first impregnating a reinforcing material with a proton conductive material and then pressurizing the reinforcing material impregnated with the proton conductive material in the thickness direction. FIG. 4 shows an example of the configuration of the proton conductive membrane of the present embodiment. In the proton conductive membrane 21, the proton conductive material 22 is filled in the void portion of the proton conductive membrane reinforcing material 1, and the proton conductive material 22 is fixed to the reinforcing material 1. In FIG. 4, hatching of the proton conductive material 22 is omitted.

  The proton conductive membrane of the present embodiment can be used as an electrolyte membrane of a fuel cell using known means. Further, the fuel cell according to the present embodiment may have any configuration as long as it is a proton conductive polymer solid electrolyte fuel cell. FIG. 5 is an exploded perspective view showing an example (cell) of the fuel cell according to the present embodiment. As an example of the fuel cell of this embodiment, for example, the proton conductive membrane 21 of this embodiment is sandwiched between an anode 32 and a cathode 33, and this is hot-pressed in the stacking direction to form a joined body 34. Cells 31 are formed by laminating separators 36 on both sides of the joined body 34 via gaskets 35 respectively. The anode 32 and the cathode 33 are formed by adhering carbon black carrying a platinum-based catalyst dispersed in a proton conductive polymer to carbon paper (paper made of carbon fiber) by a method such as screen printing. It has been done. Further, a number of these cells are stacked and stacked (a plurality of cells are connected in series) to form a stack. The number of stacked cells in the stack is determined from the output voltage of the fuel cell and the single cell voltage (about 0.7 to 1 V).

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. The present invention is not limited to the following examples as long as the gist of the present invention is not exceeded.

(Glass fiber)
The glass fibers used in Examples and Comparative Examples had the C glass composition shown in Table 1, those having an average diameter of 0.7 μm and an average length of about 3 mm.

  In Examples 1 to 6 and Comparative Examples 2 to 7, glass fiber nonwoven fabrics were composed of glass fibers having the compositions shown in Table 1. This glass composition is an example of a C glass composition. Needless to say, the general C glass composition shown in Table 1 may be used without being limited thereto.

Example 1
80% by mass of glass fiber, 15% by mass of fused-type spherical silica particles, 5% by mass of beating cellulose fiber as a binder, and simultaneously added to a pulper for unraveling the fiber and adjusted to pH 2.5 with sulfuric acid The paper was fully dissociated and dispersed therein to prepare a papermaking slurry.

  Table 2 shows the contents of glass fibers, silica particles, and beaten cellulose fibers together with Examples and Comparative Examples described below. The content rate of the beaten cellulose fiber was 5% by mass in any of the examples and comparative examples. In addition, about the silica particle, the content rate of the particle | grains whose particle size is more than Tmicrometer (thickness in which the porosity is considered to be 90%) is also shown in parentheses. Further, the average particle diameter is also shown.

Using these glass fiber dispersions, glass fiber nonwoven fabrics were prepared by a wet papermaking machine. The obtained glass fiber nonwoven fabric contained the above-described two types of fibers in the above-mentioned blending ratio, the thickness was 50 μm, and the basis weight was 7 g / m ² . This glass fiber nonwoven fabric can be used as a reinforcing material for proton conductive membranes. The substantial porosity of this glass fiber nonwoven fabric (reinforcing material) was about 94% by volume. The thickness at which the assumed porosity was 90% was 29 μm. The thickness T of the reinforcing material when the assumed porosity is 90% by volume was calculated from the following equation.
T = 10 × W / ρ _G
W: mass per unit area of reinforcing material ρ _G : density of glass fiber (about 2.5 × 10 ³ kg / m ³ (= 2.5 g / cm ³ ))

  In Example 1, 5 mass% of spherical silica particles having a particle size of 29 μm or more are included in the entire reinforcing material.

  The obtained reinforcing material was observed with a scanning electron microscope (SEM, manufactured by JEOL Ltd., model number: JSM-T330A). The shooting conditions were an acceleration voltage of 15 kV and a shooting magnification of 2000 times. The observation results are shown in FIG.

  From the observation results, it can be seen that silica particles are present between the glass fibers in the glass fiber nonwoven fabric.

  Next, a proton conductive membrane was produced using this reinforcing material. This reinforcing material was impregnated with a solution obtained by diluting a fluorine-based polymer electrolyte dispersion Nafion (registered trademark) DE2020 (manufactured by Du Pont) with isopropyl alcohol, and air-dried for 12 hours or more. Then, after heat-processing at 120 degreeC for 1 hour, it pressed in the thickness direction at 120 degreeC and 10 Mpa with the hot press apparatus, and the proton-conductive film | membrane was obtained. The concentration of the electrolyte dispersion and the amount of impregnation were adjusted so that the proton conductive membrane after pressing had a thickness of 30 μm.

  The proportion of glass fibers in the proton conductive membrane was calculated to be about 10% by mass. For the calculation, data on the density of the glass fiber and the proton conductive material, the substantial porosity of the reinforcing material, the thickness before pressing, and the thickness after pressing of the proton conductive membrane were used.

(Example 2)
The reinforcing material of Example 2 is obtained by changing the particle size distribution and content of silica particles with respect to the reinforcing material of Example 1 (see Table 2). Otherwise, a reinforcing material and a proton conductive membrane were obtained in the same procedure as in Example 1. Silica particles are a melt type.

  In Example 2, 8 mass% of the entire reinforcing material was included in the spherical silica particles having a particle size of 29 μm or more.

(Example 3)
The reinforcing material of Example 3 is made by making silica particles porous with respect to the reinforcing material of Example 1 by a sedimentation method. Otherwise, a reinforcing material and a proton conductive membrane were obtained in the same procedure as in Example 1.

  In Example 3, 5 mass% of porous silica particles having a particle size of 29 μm or more were included in the entire reinforcing material.

Example 4
In Example 4, a reinforcing material was produced using aminosilane as a silane coupling agent, and a proton conducting membrane with improved adhesion between glass fiber and proton conducting material was produced using this reinforcing material.

The reinforcing material prepared in Example 1 was impregnated with an aqueous solution in which aminosilane was dissolved in ion-exchanged water, and then heat-treated in an oven at 120 ° C. for 1 hour to prepare the reinforcing material of Example 4. At this time, the concentration and impregnation amount of the aminosilane aqueous solution were adjusted so that the solid content adhesion amount per glass fiber surface area was 10 mg / m ² .

  Using this reinforcing material, a proton conductive membrane was obtained in the same procedure as in Example 1.

  In Example 4, similar to Example 1, spherical silica particles having a particle size of 29 μm or more are included in 5% by mass of the reinforcing material.

(Example 5)
The reinforcing material of Example 5 is one in which colloidal silica is further used as a binder to further strengthen the restraint between glass fibers.

  The reinforcing material produced in Example 1 was impregnated with a diluted solution of pure water of colloidal silica, and then dried in an oven at 100 ° C. for 30 minutes to produce the reinforcing material of Example 5. At this time, the concentration and impregnation amount of the colloidal silica diluted solution were adjusted so that the solid content adhesion amount per mass of the glass fiber was 5% by mass. Using this reinforcing material, a proton conductive membrane was obtained in the same procedure as in Example 1.

  In Example 5, similarly to Example 1, 5% by mass of the spherical silica particles having a particle size of 29 μm or more was included in the entire reinforcing material.

(Example 6)
In Example 6, a reinforcing material was obtained by performing the silane coupling agent treatment described in Example 4 on the reinforcing material produced in Example 5. That is, in Example 6, a reinforcing material in which the restraint between the glass fibers was strengthened was produced, and a proton conducting membrane with improved adhesion between the glass fiber and the proton conducting material was produced using this reinforcing material. The proton conductive membrane was produced by the same procedure as in Example 1.

  In Example 6, as in Example 1, 5% by mass of spherical silica particles having a particle size of 29 μm or more is included in the entire reinforcing material.

(Comparative Example 1)
Comparative Example 1 is an example in which a proton conductive membrane was produced without using a glass fiber nonwoven fabric. The electrolyte dispersion used in Example 1 was placed in a glass petri dish with good flatness at the bottom and allowed to air dry for 12 hours or more. Then, after heat-processing at 120 degreeC for 1 hour, it pressed in the thickness direction at 120 degreeC and 10 Mpa with the hot press apparatus, and the proton-conductive film | membrane was obtained. The concentration of the electrolyte dispersion was the same as in Example 1, and the amount of the liquid was adjusted so that the thickness after the heat treatment was 30 μm.

(Comparative Example 2)
Comparative Example 2 is an example in which silica particles that are inorganic particles are not included in the reinforcing material. The mixing ratio of short glass fibers and beaten cellulose fibers was as shown in Table 2, and a papermaking slurry was prepared. Using this glass fiber dispersion, a reinforcing material and a proton conductive membrane were obtained in the same procedure as in Example 1.

(Comparative Example 3)
In Comparative Example 3, the particle size distribution and content of silica particles are changed with respect to the reinforcing material of Example 1, and the content of particles having a particle size of T μm or more is very small (see Table 2). . Other than that was the same procedure as in Example 1 to obtain a reinforcing material and a proton conductive membrane. Silica particles are a melt type.

(Comparative Example 4)
In Comparative Example 4, the particle size distribution and content of silica particles are changed with respect to the reinforcing material of Example 1, and the content of particles that are T μm or more is extremely large (see Table 2). . Other than that, in the same procedure as in Example 1, an attempt was made to obtain a reinforcing material and a proton conductive membrane. However, the tensile strength of the nonwoven fabric was extremely low, and it broke during the impregnation process. Silica particles are a melt type.

(Comparative Example 5)
In Comparative Example 5, the particle size distribution of the silica particles is changed with respect to the reinforcing material of Example 1, and the content ratio of particles having a particle size of T μm or more is very small (see Table 2). Other than that was the same procedure as in Example 1 to obtain a reinforcing material and a proton conductive membrane. Silica particles are a melt type.

(Comparative Example 6)
In Comparative Example 6, the particle size distribution of the silica particles is changed with respect to the reinforcing material of Example 1, and the content of particles having a particle size of T μm or more is large (see Table 2). Other than that was the same procedure as in Example 1 to obtain a reinforcing material and a proton conductive membrane. Silica particles are a melt type.

  The following tests were conducted on the proton conductive membranes prepared in Examples 1 to 6 and Comparative Examples 1 to 6. The results of the test are shown in Table 3.

[Thickness of reinforcing material before compounding (before being used to produce proton conducting membrane)]
The thickness was measured with a thickness gauge under a pressure of about 20 kPa.

[Proton conductive membrane thickness]
Measured with a micrometer.

[Thickness of reinforcing material in proton conducting membrane]
The cross section of the film was observed by SEM and measured.

[Measurement of tensile strength of reinforcing material and proton conductive membrane]
Both the reinforcing material and the proton conductive membrane were cut into a width of 20 mm and a length of 80 mm to prepare a test piece, a tensile test was performed at a chuck interval of 30 mm at a speed of 10 mm / min, and a load (N) at break was measured. . The tensile strength (MPa) was calculated by dividing this by the measured values of the sample thickness and width. Here, the sample thickness was measured with a thickness gauge under a pressure of about 20 kPa.

  As is clear from the results of the above Examples and Comparative Examples, the proton conductive membranes of Examples 1 to 6 using the reinforcing material according to the present invention are compared with the proton conductive membrane of Comparative Example 1 using no reinforcing material. Thus, the tensile strength was increased while having the same proton conductivity, and the reinforcing effect was confirmed.

  Further, Comparative Example 2 does not include inorganic particles, and Comparative Example 3 and Comparative Example 5 are insufficient in the ability to secure the voids of the nonwoven fabric by the inorganic particles, so in the film after hot pressing, compared to Examples 1-6. The thickness of the reinforcing material decreased, and the substantial porosity decreased. For this reason, the filling amount of the proton conductive material is small, and it is considered that proton conduction is inhibited.

  In Comparative Example 4, the tensile strength of the nonwoven fabric alone was remarkably lowered, the handling property in the step of impregnating the proton conductive material was poor, and it was difficult to obtain a proton conductive membrane practically.

  In Comparative Example 6, since the ability to secure the voids of the nonwoven fabric with inorganic particles is excessive, it is considered that the minute gaps could not be crushed by hot pressing, and proton conduction was significantly inhibited.

  The reinforcing material for proton conductive membrane of the present invention can improve the strength of the proton conductive membrane without reducing the proton conductivity. Therefore, it is suitably used as a reinforcing material for proton conductive membranes that require high strength and proton conductivity. The proton conductive membrane of the present invention is useful as a proton conductive membrane that requires high durability and high proton conductivity. The fuel cell of the present invention is useful as a fuel cell that requires high durability and high power generation efficiency.

Claims (15)

A reinforcing material for a proton conductive membrane comprising a nonwoven fabric containing glass fibers and inorganic particles carried on the nonwoven fabric,
When the percentage of the volume excluding the volume of the glass fiber from the volume occupied by the reinforcement relative to the volume occupied by the reinforcement is regarded as a void ratio,
At least a part of the inorganic particles has a particle diameter equal to or greater than the thickness of the reinforcing material when the reinforcing material is deformed so that the assumed porosity is 90% by volume,
A reinforcing material for proton conductive membrane, wherein the content of inorganic particles having the particle diameter is 2 to 10% by mass.   2. The proton conductivity according to claim 1, wherein the inorganic particles have a particle size equal to or less than twice the thickness of the reinforcing material when the reinforcing material is deformed so that the assumed porosity is 90% by volume. Membrane reinforcement.   2. The proton conductive membrane reinforcing material according to claim 1, wherein at least a part of the inorganic particles has a particle size in a range of 15 μm to 200 μm.   The proton conductive membrane reinforcing material according to claim 1, wherein the inorganic particles are particles containing silica as a main component.   The reinforcing material for proton conductive membrane according to claim 4, wherein the inorganic particles are made of silica or glass having a C glass composition.   2. The proton conductive membrane reinforcing material according to claim 1, wherein an average fiber diameter of the glass fibers is 0.1 μm to 20 μm, and an average fiber length of the glass fibers is 0.5 mm to 20 mm.   The proton conductive membrane reinforcing material according to claim 1, wherein the glass fiber has a C glass composition. The proton conductive membrane reinforcing material according to claim 1, wherein the basis weight is ² to 50 g / m ² .   The reinforcing material for proton-conductive membrane according to claim 1, wherein the thickness is 15 μm to 100 μm. When the percentage of the void volume with respect to the volume occupied by the reinforcing material is the substantial void ratio,
The reinforcing material for proton conductive membrane according to claim 1, wherein the substantial porosity is 60 to 98% by volume.   The proton conductive membrane reinforcing material according to claim 1, wherein a silane coupling agent is attached to a surface of the reinforcing material.   The reinforcing material for proton conductive membrane according to claim 1, wherein the glass fibers are constrained by a binder in the nonwoven fabric. A proton conductive membrane comprising: the proton conductive membrane reinforcing material according to claim 1; and a proton conductive material impregnated in the proton conductive membrane reinforcing material. A method for producing a proton conducting membrane comprising:
Impregnating the proton conductive membrane reinforcing material according to claim 1 with a proton conductive material;
Pressurizing the proton conductive membrane reinforcing material impregnated with the proton conductive material in the thickness direction; and
A method for producing a proton conductive membrane comprising: Fuel cell using the proton conducting membrane according to claim 1 3.