JP2019143082A - Dispersion and manufacturing method therefor - Google Patents

Abstract

To provide a dispersion having viscosity suitable for coating, and excellent in storage stability, and a method capable of stably manufacturing the dispersion having viscosity suitable for coating, and excellent in storage stability.SOLUTION: There is provided a manufacturing method of a dispersion including conducting a dispersion treatment on a target liquid containing a liquid medium, a carbon fiber, and an ion exchange resin, and having solid component concentration of 10 to 30 mass%, by using an ultrasonic dispersion machine under a condition with Pt calculated by the following formula 1 of 700 to 4000 W min. n: the number of the dispersion treatments and an integer of 1 or more. Pi: high frequency electric output of an ultrasonic dispersion machine in ith dispersion treatment (W). Ti: retention time of the target liquid in the ultrasonic dispersion machine in ith dispersion treatment (min.). i: an integer of 1 to n.SELECTED DRAWING: None

Description

  The present invention relates to a dispersion containing carbon fiber and an ion exchange resin, and a method for producing the same.

  In the polymer electrolyte fuel cell, a cell is formed by sandwiching a membrane electrode assembly between two separators, and a plurality of cells are stacked. The membrane / electrode assembly includes an anode and a cathode having a catalyst layer and a gas diffusion layer, and a polymer electrolyte membrane disposed between the anode and the cathode.

  In order to improve the electrical conductivity, gas diffusibility, drainage, etc. of the electrode, particularly the cathode, and improve the power generation performance of the membrane electrode assembly, an intermediate containing a carbon material and a polymer between the catalyst layer and the gas diffusion layer A layer may be provided (Patent Document 1).

JP-A-2015-195187

  The intermediate layer described in Patent Document 1 is formed by applying a dispersion liquid (intermediate layer forming paste) containing a carbon material, a polymer, and a liquid medium to the surface of a carrier film or a gas diffusion layer and drying it. The dispersion liquid is manufactured by supplying a treatment target liquid containing a carbon material, a polymer, and a liquid medium to an ultrasonic disperser and performing a dispersion treatment.

  However, when carbon fiber is used as the carbon material and an ion exchange resin is used as the polymer, the dispersion produced by the method described in Patent Document 1 has a viscosity suitable for coating depending on the conditions of the dispersion treatment. May come off. In addition, the viscosity may increase due to long-term storage.

  The present invention provides a dispersion having a viscosity suitable for coating and excellent storage stability, and a method capable of stably producing a dispersion having a viscosity suitable for coating and excellent storage stability. provide.

ただし、ｎは、分散処理の回数であって１以上の整数であり、Ｐｉは、ｉ回目の分散処理における前記超音波分散機の高周波電気出力（Ｗ）であり、Ｔｉは、ｉ回目の分散処理における前記超音波分散機における前記処理対象液の滞留時間（分）であり、ｉは、１〜ｎの整数である。
＜２＞前記処理対象液に含まれる炭素繊維に対するイオン交換樹脂の質量比が、０．２〜１．０である、前記＜１＞の分散液の製造方法。
＜３＞前記分散処理の回数が、２回以上である、前記＜１＞又は＜２＞の分散液の製造方法。
＜４＞最終の分散処理を行った直後の前記分散液の粘度が、２００〜５００ｍＰａ・ｓであり、最終の分散処理から１週間経過した前記分散液の粘度が、２００〜５００ｍＰａ・ｓである、前記＜１＞〜＜３＞のいずれかの分散液の製造方法。
＜５＞最終の分散処理を行った直後の前記分散液の粘度を基準としたときの、最終の分散処理から１週間経過した前記分散液の粘度の変化率が、２５％以内である、前記＜１＞〜＜４＞のいずれかの分散液の製造方法。
＜６＞液状媒体と炭素繊維とイオン交換樹脂とを含む分散液であり、前記分散液の固形分濃度が、１０〜３０質量％であり、調製直後の前記分散液の粘度が、２００〜５００ｍＰａ・ｓであり、調製から１週間経過した前記分散液の粘度が、２００〜５００ｍＰａ・ｓである、分散液。
＜７＞前記分散液に含まれる炭素繊維に対するイオン交換樹脂の質量比が、０．２〜１．０である、前記＜６＞の分散液。 The present invention has the following aspects.
<1> For a liquid to be treated containing a liquid medium, carbon fiber, and an ion exchange resin and having a solid content concentration of 10 to 30% by mass, PT obtained from the following formula 1 is 700 to 4000 W using an ultrasonic disperser. A method for producing a dispersion, characterized in that the dispersion treatment is performed under the condition of minutes.

Where n is the number of times of dispersion processing and is an integer equal to or greater than 1, Pi is the high-frequency electrical output (W) of the ultrasonic disperser in the i-th dispersion processing, and Ti is the i-th dispersion. It is the residence time (minutes) of the liquid to be treated in the ultrasonic disperser in the treatment, and i is an integer of 1 to n.
<2> The method for producing a dispersion according to <1>, wherein the mass ratio of the ion exchange resin to the carbon fiber contained in the treatment target liquid is 0.2 to 1.0.
<3> The method for producing a dispersion according to <1> or <2>, wherein the number of times of the dispersion treatment is 2 or more.
<4> The viscosity of the dispersion immediately after performing the final dispersion treatment is 200 to 500 mPa · s, and the viscosity of the dispersion after one week from the final dispersion treatment is 200 to 500 mPa · s. The method for producing a dispersion liquid according to any one of <1> to <3>.
<5> The rate of change in the viscosity of the dispersion after one week from the final dispersion treatment, based on the viscosity of the dispersion immediately after the final dispersion treatment, is within 25%. <1>-<4> The manufacturing method of the dispersion liquid in any one.
<6> A dispersion containing a liquid medium, carbon fiber, and an ion exchange resin, the solid content concentration of the dispersion is 10 to 30% by mass, and the viscosity of the dispersion immediately after preparation is 200 to 500 mPa A dispersion liquid that is s and has a viscosity of 200 to 500 mPa · s after one week from preparation.
<7> The dispersion according to <6>, wherein the mass ratio of the ion exchange resin to the carbon fiber contained in the dispersion is 0.2 to 1.0.

The dispersion of the present invention has a viscosity suitable for coating and is excellent in storage stability.
According to the method for producing a dispersion of the present invention, a dispersion having a viscosity suitable for coating and excellent in storage stability can be stably produced.

It is sectional drawing which shows an example of the membrane electrode assembly for polymer electrolyte fuel cells. It is sectional drawing which shows the other example of the membrane electrode assembly for polymer electrolyte fuel cells.

In the present specification, a unit represented by the formula u1 is referred to as a unit u1. Units represented by other formulas are also described in the same manner.
A monomer represented by the formula m1 is referred to as a monomer m1. The same applies to monomers represented by other formulas.

The following definitions of terms apply throughout this specification and the claims.
“Monomer” means a compound having a polymerization-reactive carbon-carbon double bond.
The “unit” is a general term for an atomic group directly formed by polymerizing one monomer molecule and an atomic group obtained by chemically converting a part of the atomic group.
The “ion exchange group” means a group having H ⁺ , a monovalent metal cation, an ammonium ion and the like. Examples of the ion exchange group include a sulfonic acid group, a sulfonimide group, and a sulfonemethide group.
The solid content concentration of the liquid to be treated and the dispersion is represented by the ratio of the sum of the masses of components (ion exchange resin, carbon fiber, etc.) solid at 25 ° C. in the total mass of the dispersion.
The viscosity of the dispersion is a viscosity at a rotor rotational speed of 10 rpm measured at 25 ° C. using an E-type viscometer.
“˜” indicating a numerical range means that numerical values described before and after the numerical value range are included as a lower limit value and an upper limit value.

<Dispersion>
The dispersion of the present invention (hereinafter also referred to as “the present dispersion”) includes a liquid medium, carbon fibers, and an ion exchange resin. The present dispersion may contain other components as necessary within a range not impairing the effects of the present invention.

  The solid content concentration of the dispersion is 10 to 30% by mass, and preferably 15 to 25% by mass. When the solid content concentration is within the above range, the viscosity of the dispersion liquid is easily set to a viscosity suitable for coating, and the viscosity suitable for coating is easily maintained for a long period of time. If the solid content concentration is not less than the lower limit of the above range, the dispersion can be applied to the surface of the substrate thickly. If the solid content concentration is not more than the upper limit of the above range, the present dispersion can be applied to the surface of the substrate without unevenness.

  The mass ratio of the ion exchange resin to the carbon fibers contained in the dispersion (ion exchange resin / carbon fiber) is preferably 0.2 to 1.0, and more preferably 0.3 to 0.7. If the mass ratio of the ion exchange resin to the carbon fiber is not less than the lower limit of the above range, the carbon fiber can be favorably dispersed in the liquid medium. In addition, the moisture retention of the intermediate layer formed using this dispersion is increased, and drying of the polymer electrolyte membrane can be suppressed. If the mass ratio of the ion exchange resin to the carbon fiber is not more than the upper limit of the above range, the gas permeability of the intermediate layer formed using this dispersion liquid will not be lowered.

  The viscosity of the dispersion immediately after preparation is 200 to 500 mPa · s, and preferably 250 to 450 mPa · s. If the viscosity immediately after the preparation of the present dispersion is within the above range, the viscosity of the dispersion after one week from the preparation is easily maintained at 200 to 500 mPa · s, preferably 250 to 450 mPa · s.

  Both the viscosity of the dispersion immediately after the preparation and the viscosity of the dispersion after one week from the preparation are 200 to 500 mPa · s, and preferably 250 to 450 mPa · s. If the dispersion has a viscosity equal to or higher than the lower limit of the above range, the dispersion will not easily spread in the surface direction along the surface of the substrate when the dispersion is applied to the surface of the substrate. The liquid can be applied to the surface of the substrate thickly. If the viscosity of the present dispersion is not more than the upper limit of the above range, the present dispersion can be applied evenly to the surface of the substrate.

The change rate of the viscosity of the dispersion after one week from the preparation, based on the viscosity of the dispersion immediately after the preparation, is preferably within 25%. When the rate of change is within the above range, the storage stability of the dispersion is further improved.
The viscosity of this dispersion can be set to the above range by appropriately selecting the solid content concentration, the mass ratio of the ion exchange resin to the carbon fiber, the dispersion treatment apparatus, the dispersion treatment conditions, and the like.

(Liquid medium)
As a liquid medium, the thing containing an organic solvent and water from the point which the dispersibility of carbon fiber and an ion exchange resin is further excellent is preferable.
As the organic solvent, alcohol is preferable because the dispersibility of the carbon fiber and the ion exchange resin is further improved.

  Examples of the alcohol include non-fluorine alcohols (methanol, ethanol, 1-propanol, 2-propanol, etc.), fluorine alcohols (2,2,2-trifluoroethanol, 2,2,3,3,3-penta). Fluoro-1-propanol, 2,2,3,3-tetrafluoro-1-propanol, 4,4,5,5,5-pentafluoro-1-pentanol, 1,1,1,3,3,3 -Hexafluoro-2-propanol, 3,3,3-trifluoro-1-propanol, 3,3,4,4,5,5,6,6,6-nonafluoro-1-hexanol, 3,3,4 4, 5, 5, 6, 6, 7, 7, 8, 8, 8-tridecafluoro-1-octanol, etc.).

  The mass ratio of the organic solvent to water (organic solvent / water) is preferably 70/30 to 30/70, and more preferably 50/50 to 40/60. When the organic solvent / water is within the above range, the dispersibility of the carbon fiber and the ion exchange resin is further improved.

(Carbon fiber)
Examples of the carbon fiber include vapor grown carbon fiber, carbon nanotube (single wall, double wall, multi-wall, cup laminated type, etc.), PAN-based carbon fiber, and pitch-based carbon fiber.
Examples of the PAN-based carbon fiber and pitch-based carbon fiber include chopped fiber and milled fiber.

  30-250 nm is preferable and, as for the average fiber diameter of carbon fiber, 50-200 nm is more preferable. If the average fiber diameter of the carbon fiber is equal to or greater than the lower limit of the above range, the gas diffusion property and drainage of the intermediate layer containing the carbon fiber and the ion exchange resin are excellent. If the average fiber diameter of the carbon fibers is not more than the upper limit of the above range, the carbon fibers can be favorably dispersed in the liquid medium.

  The fiber length of the carbon fiber is preferably 1 to 50 μm, and more preferably 5 to 30 μm. If the fiber length of the carbon fiber is not less than the lower limit of the above range, the gas diffusion property and drainage of the intermediate layer containing the carbon fiber and the ion exchange resin are excellent. If the fiber length of the carbon fiber is not more than the upper limit of the above range, the carbon fiber can be favorably dispersed in the liquid medium.

(Ion exchange resin)
The ion exchange resin is a polymer compound having an ion exchange group.
The ion exchange resin is preferably a fluorine-containing ion exchange resin from the viewpoint of durability, and more preferably a perfluorocarbon polymer having an ion exchange group (which may contain an etheric oxygen atom). As the perfluorocarbon polymer having an ion exchange group, for example, a unit based on a perfluoromonomer having an ion exchange group and a 5-membered ring described in Polymer A described later, Polymer B described later, International Publication No. 2011/013577, etc. Polymer A or polymer B is preferable from the viewpoint of availability and ease of production.

  The polymer A is a polymer having the unit u1 (except for the polymer B).

However, Q ¹ is a single bond or a perfluoroalkylene group which may have an etheric oxygen atom, R ^f1 is a perfluoroalkyl group which may have an etheric oxygen atom, and X ¹ Is an oxygen atom, a nitrogen atom or a carbon atom, a is 0 when X ¹ is an oxygen atom, ¹ when X ¹ is a nitrogen atom, 2 when X ¹ is a carbon atom, and Z ¹ is a fluorine atom or a monovalent perfluoro organic group, and s is 0 or 1. A single bond means that the carbon atom of CFZ ¹ and the sulfur atom of SO ₂ are directly bonded. An organic group means a group containing one or more carbon atoms.

When the perfluoroalkylene group of Q ¹ has an etheric oxygen atom, the etheric oxygen atom may be one or two or more. The etheric oxygen atom may be inserted between the carbon atom-carbon atom bonds of the perfluoroalkylene group or may be inserted at the carbon atom bond terminal.
The perfluoroalkylene group may be linear or branched. 1-6 are preferable and, as for carbon number of a perfluoroalkylene group, 1-4 are more preferable.

The perfluoroalkyl group for R ^f1 may be linear or branched, and is preferably linear. 1-6 are preferable, as for carbon number of a perfluoroalkyl group, 1-4 are more preferable, and 1 or 2 is further more preferable.

_{^{- (SO 2 X 1 (SO}} 2 R f1) a) - H + group is an ion-exchange group. _{^{- (SO 2 X 1 (SO}} 2 R f1) a) - The ^{H +} group, a sulfonic acid group _(-SO ³ - ^{H +} group), a sulfonimide group ^{_{(-SO 2 N (SO 2 R}} f1) - H ⁺ group), or a sulfonmethide group ^{_{(-SO 2 C (SO 2 R}} f1) 2) - H + group).
Z ¹ is preferably a fluorine atom or a trifluoromethyl group.

  As the unit u1, the unit u1-1, the unit u1-2, the unit u1-3 or the unit u1-4 is preferable because the production of the polymer A is easy and industrial implementation is easy.

The polymer A may further have units based on other monomers (hereinafter referred to as “other units”). What is necessary is just to adjust suitably the ratio of another unit so that the ion exchange capacity of the polymer A may become the preferable range mentioned later.
Other units are preferably units based on a perfluoromonomer from the viewpoint of mechanical strength and chemical durability, and more preferably units based on tetrafluoroethylene (hereinafter referred to as “TFE”).

The polymer A can be produced by polymerizing the compound m1 and, if necessary, another monomer to obtain a precursor polymer, and then converting the —SO ₂ F group in the precursor polymer into a sulfonic acid group. Conversion of the —SO ₂ F group to a sulfonic acid group is performed by hydrolysis and acidification treatment.
_{CF 2 = CF- (CF 2)} s OCF 2 -CFZ 1 -Q 1 -SO 2 F type m1

  The polymer B is a polymer having the unit u2.

However, Q ²¹ is a perfluoroalkylene group which may have an etheric oxygen atom, Q ²² is a perfluoroalkylene group which may have a single bond or an etheric oxygen atom, and R ^f2 Is a perfluoroalkyl group optionally having an etheric oxygen atom, X ² is an oxygen atom, a nitrogen atom or a carbon atom, b is 0 when X ² is an oxygen atom, and X ² Is 1 when X is a nitrogen atom, ² when X ² is a carbon atom, Z ² is a fluorine atom or a monovalent perfluoro organic group, t is 0 or 1, and u is 0 or 1. The single bond means that the carbon atom of CZ ² and the sulfur atom of SO ₂ are directly bonded. An organic group means a group containing one or more carbon atoms.

When the perfluoroalkylene group of Q ²¹ and Q ²² has an etheric oxygen atom, the etheric oxygen atom may be one or may be two or more. The etheric oxygen atom may be inserted between the carbon atom-carbon atom bonds of the perfluoroalkylene group or may be inserted at the carbon atom bond terminal.
The perfluoroalkylene group may be linear or branched, and is preferably linear. 1-6 are preferable and, as for carbon number of a perfluoroalkylene group, 1-4 are more preferable. If the number of carbon atoms is 6 or less, the boiling point of the raw material monomer becomes low, and distillation purification becomes easy.

Q ²² is preferably a C 1-6 perfluoroalkylene group which may have an etheric oxygen atom. When Q ²² is a perfluoroalkylene group having 1 to 6 carbon atoms which may have an etheric oxygen atom, when the polymer electrolyte fuel cell is operated over a long period of time compared to the case where Q ²² is a single bond In addition, it has excellent power generation performance stability.

The perfluoroalkyl group for R ^f2 may be linear or branched, and is preferably linear. 1-6 are preferable, as for carbon number of a perfluoroalkyl group, 1-4 are more preferable, and 1 or 2 is further more preferable.
When the unit u2 has two or more R ^{f2 s} , the R ^f2s may be the same group or different groups.

_{^{- (SO 2 X 2 (SO}} 2 R f2) b) - H + group is an ion-exchange group. _{^{- (SO 2 X 2 (SO}} 2 R f2) b) - as the ^{H +} group, a sulfonic acid group _(-SO ³ - ^{H +} group), a sulfonimide group ^{_{(-SO 2 N (SO 2 R}} f2) - H ⁺ group), or a sulfonmethide group ^{_{(-SO 2 C (SO 2 R}} f2) 2) - H + group).
Z ² is preferably a fluorine atom or a linear perfluoroalkyl group having 1 to 6 carbon atoms which may have an etheric oxygen atom.

  As the unit u2, the unit u2-1, the unit u2-2, the unit u2-3, or the unit u2-4 is more preferable because the production of the polymer B is easy and industrial implementation is easy.

The polymer B may further have other units. What is necessary is just to adjust suitably the ratio of another unit so that the ion exchange capacity of the polymer B may become the preferable range mentioned later.
The other unit is preferably a unit based on a perfluoromonomer, more preferably a unit based on TFE, from the viewpoint of mechanical strength and chemical durability.

The polymer B can be produced, for example, by the method described in International Publication No. 2007/013533.
The ion exchange capacity of the fluorine-containing ion exchange resin is preferably 0.5 to 2.0 meq / g dry resin, and 0.8 to 1.5 meq / g dry resin from the viewpoint of conductivity and gas permeability. Is more preferable.

(Mechanism of action)
The present dispersion described above is suitable for coating because both the viscosity immediately after the preparation and the viscosity after one week from the preparation are 200 to 500 mPa · s. Moreover, since solid content concentration is 10-30 mass% and the viscosity immediately after preparation is 200-500 mPa * s, it is excellent in storage stability. Specifically, the viscosity of the dispersion after one week from the preparation can be maintained at 200 to 500 mPa · s.

<Method for producing dispersion>
This dispersion is produced by subjecting a liquid to be treated, which includes a liquid medium, carbon fiber, and an ion exchange resin, to a dispersion treatment using a dispersion treatment device under conditions such that the viscosity of the dispersion falls within an appropriate range. it can.

Examples of the dispersion processing apparatus include an ultrasonic disperser, a thin film swirl type high speed mixer, and an ultra high speed homogenizer. As the dispersion treatment apparatus, an ultrasonic disperser or a thin-film swirl type high-speed mixer is preferable, and an ultrasonic disperser is particularly preferable from the viewpoint that carbon fibers can be favorably dispersed in a liquid medium.
As a commercial item of a thin-film swirl type high-speed mixer, for example, FILMIX (registered trademark) manufactured by Primix Corporation may be mentioned.

  As a manufacturing method of this dispersion liquid, a dispersion treatment is performed on a treatment target liquid having a solid content concentration of 10 to 30% by mass using an ultrasonic disperser under a condition that PT described later is 700 to 4000 W · min. The method is preferred.

(Processing liquid)
The liquid to be treated is prepared, for example, by adding carbon fiber to the resin liquid while stirring the resin liquid in which the ion exchange resin is dissolved or dispersed in the liquid medium.
The solid content concentration of the liquid to be treated is 10 to 30% by mass, and preferably 15 to 25% by mass. If the solid content concentration is within the above range, it is easy to produce this dispersion having a viscosity suitable for coating and capable of maintaining the viscosity suitable for coating for a long period of time.

  The mass ratio of the ion exchange resin to the carbon fibers contained in the liquid to be treated (ion exchange resin / carbon fiber) is preferably 0.2 to 1.0, and more preferably 0.3 to 0.7. When the mass ratio of the ion exchange resin to the carbon fiber is within the above range, the carbon fiber can be favorably dispersed in the liquid medium, and the present dispersion suitable for forming the intermediate layer can be easily produced.

(Distributed processing)
Examples of the ultrasonic disperser include an ultrasonic homogenizer, an ultrasonic mixer, and an ultrasonic stirrer.
The ultrasonic disperser may include one ultrasonic oscillator, or may include two or more ultrasonic oscillators connected in series.
The ultrasonic disperser may be a batch type that emits ultrasonic waves to the liquid to be processed contained in a storage tank, tank, autoclave, etc. It may be a flow type that irradiates ultrasonic waves to the liquid to be processed that flows through the piping or the like while ensuring. Further, in the flow type, a pipe may be connected so that the processing target liquid can be circulated, and the processing target liquid may be irradiated with ultrasonic waves while circulating the processing target liquid.

  The dispersion treatment using an ultrasonic disperser is preferably performed under the condition that the PT obtained from the following formula 1 is 700 W · min. PT is more preferably 800 W · min or more, and still more preferably 900 W · min or more. PT is preferably 4000 W · min or less.

  Here, n is the number of times of dispersion processing and is an integer equal to or greater than 1, Pi is the high-frequency electrical output (W) of the ultrasonic disperser in the i-th dispersion processing, and Ti is the i-th dispersion processing. Is the residence time (minutes) of the liquid to be treated in the ultrasonic disperser, and i is an integer of 1 to n.

  If PT is at least the lower limit of the above range, it is easy to stably produce the dispersion having a viscosity suitable for coating and capable of maintaining the viscosity suitable for coating for a long period of time. If PT is less than or equal to the upper limit of the above range, the viscosity of the dispersion does not become too low and the coating is not affected. Moreover, the productivity of this dispersion liquid is good.

The number of times of dispersion treatment is preferably 2 times or more from the viewpoint that carbon fibers can be sufficiently dispersed.
The number of dispersion treatments is preferably 4 times or less, more preferably 2 times or less, from the viewpoint of good productivity of the dispersion.

  The viscosity of the dispersion immediately after the final dispersion treatment is preferably 200 to 500 mPa · s, more preferably 250 to 450 mPa · s. If the viscosity of the dispersion immediately after the final dispersion treatment is within the above range, the viscosity of the dispersion after one week from the final dispersion treatment is easily maintained at 200 to 500 mPa · s, preferably 250 to 450 mPa · s.

  The viscosity of the dispersion immediately after the final dispersion treatment and the viscosity of the dispersion after one week from the final dispersion treatment are preferably 200 to 500 mPa · s, and more preferably 250 to 450 mPa · s. If the viscosity of the dispersion is equal to or greater than the lower limit of the above range, the dispersion is difficult to spread in the surface direction along the surface of the substrate when the dispersion is applied to the surface of the substrate. Can be thickly applied to the surface of the material. If the viscosity of the dispersion is not more than the upper limit of the above range, the dispersion can be applied uniformly to the surface of the substrate.

  The change rate of the viscosity of the dispersion after one week from the final dispersion treatment, based on the viscosity of the dispersion immediately after the final dispersion treatment, is preferably within 25%. When the rate of change is within the above range, the storage stability of the dispersion is further improved.

This dispersion liquid can be used as a coating liquid for forming an intermediate layer in a membrane electrode assembly for a polymer electrolyte fuel cell.
This dispersion may be used as it is as a coating solution, or a solution to which other components are further added may be used as a coating solution.
The coating liquid may be filtered with a filter, may be shaken with a shaker or the like, and may be defoamed with a non-bubbling kneader or the like.

(Mechanism of action)
In the method for producing a dispersion of the present invention described above, a dispersion having a viscosity suitable for coating and excellent in storage stability can be stably produced for the following reasons.
The liquid to be treated having a solid content concentration of 10 to 30% by mass cannot be dispersed well with a normal dispersing apparatus such as a bead mill, but is dispersed by irradiating with ultrasonic waves under conditions where PT is 700 to 4000 W · min. When the treatment is performed once or more, the entanglement of the carbon fibers can be loosened. As a result, a dispersion having a viscosity suitable for coating and excellent in storage stability can be stably produced.

<Membrane electrode assembly>
The membrane electrode assembly includes an anode having a catalyst layer and a gas diffusion layer, a cathode having a catalyst layer and a gas diffusion layer, and a polymer electrolyte membrane disposed between the anode catalyst layer and the cathode catalyst layer. And either one or both of the anode and the cathode have an intermediate layer between the catalyst layer and the gas diffusion layer.

The intermediate layer improves the conductivity, gas diffusibility, drainage and the like in the membrane electrode assembly.
In the membrane / electrode assembly, it is preferable that at least the cathode has an intermediate layer because pore clogging (flooding) is likely to occur due to condensation of water vapor at the cathode.

FIG. 1 is a cross-sectional view showing an example of a membrane electrode assembly.
The membrane electrode assembly 10 includes an anode 20 having a catalyst layer 22 and a gas diffusion layer 26, a cathode 30 having a catalyst layer 32, an intermediate layer 34, and a gas diffusion layer 36 in order, and the catalyst layer 22 and the cathode 30 of the anode 20. And a polymer electrolyte membrane 40 disposed between the catalyst layer 32 and the catalyst layer 32.

  The catalyst layer 22 and the catalyst layer 32 (hereinafter, collectively referred to as “catalyst layer”) are layers including a catalyst and an ion exchange resin. The catalyst layer 22 and the catalyst layer 32 may be layers having the same component, composition, thickness, or the like, or may be different layers.

  The catalyst is not particularly limited as long as it promotes the oxidation-reduction reaction in the polymer electrolyte fuel cell. A catalyst containing platinum is preferable, and a supported catalyst in which platinum or a platinum alloy is supported on a carbon support is particularly preferable.

  The ion exchange resin for the catalyst layer is preferably a fluorine-containing ion exchange resin from the viewpoint of durability, more preferably a perfluorocarbon polymer having an ion exchange group (which may contain an etheric oxygen atom), and polymer A. Or polymer B is particularly preferred.

The polymer electrolyte membrane 40 is an ion exchange resin membrane.
The ion exchange resin of the polymer electrolyte membrane 40 is preferably a fluorine-containing ion exchange resin from the viewpoint of durability, and more preferably a perfluorocarbon polymer having an ion exchange group (which may contain an etheric oxygen atom). Polymer A or polymer B is particularly preferred.

The membrane electrode assembly is not limited to that shown in FIG. For example, as shown in FIG. 2, the anode 20 may have an intermediate layer 24 between the catalyst layer 22 and the gas diffusion layer 26.
Further, the cathode 30 may have two or more intermediate layers, and the anode 20 may have two or more intermediate layers.
Further, the polymer electrolyte membrane 40 may be reinforced with a reinforcing material, and the catalyst layer may be reinforced with a reinforcing material. Examples of the reinforcing material include porous bodies, fibers, woven fabrics, and non-woven fabrics.
The polymer electrolyte membrane 40 may contain cerium ions or manganese ions, and the catalyst layer may contain cerium ions.

  The membrane electrode assembly is formed by using this dispersion liquid in the method for producing a membrane electrode assembly described in, for example, International Publication No. 2009/116630, International Publication No. 2011/114949, Patent Document 1, etc. Can be manufactured.

The membrane electrode assembly is used for a polymer electrolyte fuel cell. A polymer electrolyte fuel cell is manufactured, for example, by forming a cell by sandwiching a membrane electrode assembly between two separators and stacking a plurality of cells.
Examples of the separator include a conductive carbon plate in which a groove serving as a passage for an oxidant gas (air, oxygen, etc.) containing fuel gas or oxygen is formed.

  Examples of the polymer electrolyte fuel cell include a hydrogen-oxygen fuel cell and a direct methanol fuel cell (DMFC). The methanol or methanol aqueous solution used for the DMFC fuel may be a liquid feed or a gas feed.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples.

(Viscosity of dispersion)
The viscosity of the dispersion was measured at 25 ° C. at a shear rate of 200 (1 / s) using a viscometer for flow analysis (manufactured by Toki Sangyo Co., Ltd., RE550).

(Polymer A)
Polymer dispersion: Dispersion of polymer A having units u1-1 and units based on TFE (solid content concentration: 20% by mass, dispersion medium: mixed solvent of ethanol 60% by mass and water 40% by mass, polymer A ions Exchange capacity: 1.1 meq / g dry resin).

(Carbon fiber)
Vapor growth carbon fiber: VGCF-H manufactured by Showa Denko KK, fiber diameter: about 150 nm, fiber length: 10-20 μm.

(Example 1)
In a 2 L beaker, 220 g of distilled water, 180 g of ethanol, and 250 g of the polymer dispersion were added and stirred to obtain a resin solution. While stirring the resin solution, 100.0 g of vapor growth carbon fiber was added little by little to the resin solution. After the vapor growth carbon fiber was added, stirring was continued for 5 minutes to obtain a liquid to be treated.
Liquid to be treated at a rate of 100 g / min using a pump with an ultrasonic dispersion device (Nippon Seiki Seisakusho, US-600AT, high frequency electric output 600 W, oscillation frequency 19.5 kHz) connected in series to two ultrasonic dispersion devices. Supplied and distributed. The residence time of the liquid to be treated in the ultrasonic treatment apparatus, that is, the ultrasonic irradiation time T shown in the following formula was 0.8 minutes. Further dispersion treatment was performed under the same conditions, and dispersion treatment was performed twice in total to obtain a dispersion. PT is 960 W · min as shown in the following formula.
T = 2 units × 0.4 min / unit = 0.8 min PT = 600 W × 2 units × 0.4 min / unit × 2 times = 960 W · min The solid content concentration of the dispersion is 20% by mass, The mass ratio of the ion exchange resin to the carbon fibers contained in the dispersion (ion exchange resin / carbon fiber) was 0.5, and the viscosity of the dispersion was 350 mPa · s.
The dispersion was placed in a resin container, sealed, and allowed to stand at 25 ° C. for 1 week. The viscosity was measured to be 380 mPa · s.

(Example 2)
A liquid to be treated was obtained in the same manner as in Example 1.
Liquid to be treated at a rate of 100 g / min using a pump with an ultrasonic dispersion device (Nippon Seiki Seisakusho, US-1200AT, high frequency electrical output 1200 W, oscillation frequency 19.5 kHz) connected in series. Supply and dispersion treatment were performed to obtain a dispersion. The residence time of the liquid to be treated in the ultrasonic treatment apparatus, that is, the ultrasonic irradiation time T shown in the following formula was 0.8 minutes. PT is 960 W · min as shown in the following formula.
T = 2 units × 0.4 min / unit = 0.8 min PT = 1200 W × 2 units × 0.4 min / unit × one time = 960 W · min The solid content concentration of the dispersion is 20% by mass, The mass ratio of the ion exchange resin to the carbon fibers contained in the dispersion (ion exchange resin / carbon fiber) was 0.5, and the viscosity of the dispersion was 340 mPa · s.
The dispersion was put in a resin container, sealed, and allowed to stand at 25 ° C. for 1 week. The viscosity was measured to be 360 mPa · s.

(Example 3)
A liquid to be treated was obtained in the same manner as in Example 1.
The liquid to be treated was supplied to the same ultrasonic dispersion apparatus as in Example 1 at 80 g / min using a pump to perform dispersion treatment. The residence time of the liquid to be treated in the ultrasonic treatment apparatus, that is, the ultrasonic irradiation time T shown in the following formula, was 1.0 minute. Further dispersion treatment was performed under the same conditions, and dispersion treatment was performed twice in total to obtain a dispersion. PT is 1200 W · min as shown in the following formula.
T = 2 units × 0.5 min / unit = 1.0 min PT = 600 W × 2 units × 0.5 min / unit × 2 times = 1200 W · min The solid content concentration of the dispersion is 20% by mass, The mass ratio of the ion exchange resin to the carbon fibers contained in the dispersion (ion exchange resin / carbon fiber) was 0.5, and the viscosity of the dispersion was 300 mPa · s.
The dispersion was put in a resin container, sealed, and allowed to stand at 25 ° C. for 1 week. The viscosity was measured to be 320 mPa · s.

Example 4
A liquid to be treated was obtained in the same manner as in Example 1.
The liquid to be treated was supplied to the same ultrasonic dispersion apparatus as in Example 1 at 60 g / min using a pump to perform dispersion treatment. The residence time of the liquid to be treated in the ultrasonic treatment apparatus, that is, the ultrasonic irradiation time T shown in the following formula was 1.33 minutes. Further dispersion treatment was performed under the same conditions, and dispersion treatment was performed twice in total to obtain a dispersion. PT is 1600 W · min as shown in the following formula.
T = 2 units × 0.66 ·· min / unit = 1.33 min PT = 600 W × 2 units × 0.66 ·· min / unit × 2 times = 1600 W · min The solid content concentration of the dispersion is 20 mass. The mass ratio of the ion exchange resin to the carbon fibers contained in the dispersion (ion exchange resin / carbon fiber) was 0.5, and the viscosity of the dispersion was 250 mPa · s.
The dispersion was put in a resin container, sealed, and allowed to stand at 25 ° C. for 1 week. The viscosity was 260 mPa · s.

(Comparative Example 1)
A liquid to be treated was obtained in the same manner as in Example 1.
The liquid to be treated was supplied to the same ultrasonic dispersion apparatus as in Example 1 at a rate of 200 g / min using a pump, and dispersion treatment was performed. The residence time of the liquid to be treated in the ultrasonic treatment apparatus, that is, the ultrasonic irradiation time T shown in the following formula was 0.4 minutes. Further dispersion treatment was performed under the same conditions, and dispersion treatment was performed twice in total to obtain a dispersion. PT is 480 W · min as shown in the following formula.
T = 2 units × 0.2 min / unit = 0.4 min PT = 600 W × 2 units × 0.2 min / unit × 2 times = 480 W · min The solid content concentration of the dispersion is 20% by mass, The mass ratio of the ion exchange resin to the carbon fibers contained in the dispersion (ion exchange resin / carbon fiber) was 0.5, and the viscosity of the dispersion was 600 mPa · s.

(Comparative Example 2)
A liquid to be treated was obtained in the same manner as in Example 1.
Except that the indicated value of the output indicator of the ultrasonic oscillator is halved and the high frequency electrical output of the ultrasonic disperser is halved, the liquid to be treated is pumped into the same ultrasonic dispersing apparatus as in the first embodiment. Was supplied at 100 g / min for dispersion treatment. The residence time of the liquid to be treated in the ultrasonic treatment apparatus, that is, the ultrasonic irradiation time T shown in the following formula was 0.8 minutes. Further dispersion treatment was performed under the same conditions, and dispersion treatment was performed twice in total to obtain a dispersion. PT is 480 W · min as shown in the following formula.
T = 2 units × 0.4 min / unit = 0.8 min PT = 300 W × 2 units × 0.4 min / unit × 2 times = 480 W · min The solid content concentration of the dispersion is 20% by mass, The mass ratio of the ion exchange resin to the carbon fibers contained in the dispersion (ion exchange resin / carbon fiber) was 0.5, and the viscosity of the dispersion was 600 mPa · s.

(Comparative Example 3)
A liquid to be treated was obtained in the same manner as in Example 1.
The liquid to be treated was supplied to the same ultrasonic dispersion apparatus as in Example 1 at 160 g / min using a pump to perform dispersion treatment. The residence time of the liquid to be treated in the ultrasonic treatment apparatus, that is, the ultrasonic irradiation time T shown in the following formula was 0.5 minutes. Further dispersion treatment was performed under the same conditions, and dispersion treatment was performed twice in total to obtain a dispersion. PT is 600 W · min as shown in the following formula.
T = 2 units × 0.25 min / unit = 0.5 min PT = 600 W × 2 units × 0.25 min / unit × 2 times = 600 W · min The solid content concentration of the dispersion is 20% by mass, The mass ratio of the ion exchange resin to the carbon fibers contained in the dispersion (ion exchange resin / carbon fiber) was 0.5, and the viscosity of the dispersion was 470 mPa · s.
The dispersion was put in a resin container, sealed, and allowed to stand at 25 ° C. for 1 week. The viscosity was measured to be 560 mPa · s.

(Comparative Example 4)
A liquid to be treated was obtained in the same manner as in Example 1.
The liquid to be treated was supplied to the same ultrasonic dispersion apparatus as in Example 2 at 40 g / min using a pump, and dispersion treatment was performed. The residence time of the liquid to be treated in the ultrasonic treatment apparatus, that is, the ultrasonic irradiation time T shown in the following formula was 2.0 minutes. Further dispersion treatment was performed under the same conditions, and dispersion treatment was performed twice in total to obtain a dispersion. PT is 4800 W · min as shown in the following formula.
T = 2 units × 1.0 min / unit = 2.0 min PT = 1200 W × 2 units × 1.0 min / unit × 2 times = 4800 W · min The solid content concentration of the dispersion is 20% by mass, The mass ratio of the ion exchange resin to the carbon fibers contained in the dispersion (ion exchange resin / carbon fiber) was 0.5, and the viscosity of the dispersion was 170 mPa · s.
Although this dispersion was applied to the surface of the substrate, the dispersion was likely to spread in the surface direction along the surface of the substrate, and the dispersion could not be applied thickly on the surface of the substrate.

  The results of Examples 1 to 4 and Comparative Examples 1 to 4 are summarized in a table.

  The dispersion liquid of the present invention is useful as a coating liquid for forming an intermediate layer in a membrane electrode assembly.

10 Membrane electrode assembly,
20 anode,
22 catalyst layer,
24 middle layer,
26 Gas diffusion layer,
30 cathode,
32 catalyst layer,
34 Middle layer,
36 Gas diffusion layer,
40 Polymer electrolyte membrane.

Claims (7)

A processing target liquid containing a liquid medium, carbon fiber, and an ion exchange resin and having a solid content concentration of 10 to 30% by mass, using an ultrasonic disperser, PT obtained from the following formula 1 is 700 to 4000 W · min. Dispersion treatment is performed under the following conditions.

Where n is the number of times of dispersion processing and is an integer equal to or greater than 1, Pi is the high-frequency electrical output (W) of the ultrasonic disperser in the i-th dispersion processing, and Ti is the i-th dispersion. It is the residence time (minutes) of the liquid to be treated in the ultrasonic disperser in the treatment, and i is an integer of 1 to n.   The manufacturing method of the dispersion liquid of Claim 1 whose mass ratio of the ion exchange resin with respect to the carbon fiber contained in the said process target liquid is 0.2-1.0.   The manufacturing method of the dispersion liquid of Claim 1 or 2 whose frequency | count of the said dispersion process is 2 times or more. The viscosity of the dispersion immediately after the final dispersion treatment is 200 to 500 mPa · s,
The manufacturing method of the dispersion liquid as described in any one of Claims 1-3 whose viscosity of the said dispersion liquid which passed 1 week after the last dispersion process is 200-500 mPa * s.   The rate of change in the viscosity of the dispersion after one week from the final dispersion treatment, based on the viscosity of the dispersion immediately after the final dispersion treatment, is within 25%. 5. The method for producing a dispersion according to any one of 4 above. A dispersion containing a liquid medium, carbon fibers and an ion exchange resin;
The solid content concentration of the dispersion is 10 to 30% by mass,
The viscosity of the dispersion immediately after preparation is 200 to 500 mPa · s,
The dispersion having a viscosity of 200 to 500 mPa · s after one week from the preparation.   The dispersion liquid according to claim 6, wherein a mass ratio of the ion exchange resin to carbon fibers contained in the dispersion liquid is 0.2 to 1.0.

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