WO2012156199A1

WO2012156199A1 - Metal oxide dispersion based on organic solvent

Info

Publication number: WO2012156199A1
Application number: PCT/EP2012/057968
Authority: WO
Inventors: Wolfgang Lortz; Gabriele Perlet; Uwe Diener
Original assignee: Evonik Degussa Gmbh
Priority date: 2011-05-16
Filing date: 2012-05-02
Publication date: 2012-11-22
Also published as: DE102011075918A1; EP2709751A1; KR20140038409A

Abstract

Dispersion comprising metal oxide particles, in which a) the metal oxide particles a1) are selected from one or more oxides from the group consisting of titanium dioxide, cerium oxide, zinc oxide and zirconium dioxide, a2) are present in the dispersion with a proportion of at least 25% by weight, a3) have a mean aggregate diameter of 20 to 120 nm, and b) the liquid phase comprises b1) 90 to 99.5% by weight of one or more alkanols C_nH_2n+1OH where n = 2 to 4, b2) 0.5 to 10% by weight of one or more a,ß-unsaturated carboxylic acids having 4 to 12 carbon atoms, b3) 0 to 2% by weight of one or more alkanediols HO(CH₂)_xOH where x = 2 to 4, b4) a maximum of 5% by weight of water and b5) a maximum of 2% by weight, in total, of dispersing additives from the group consisting of polyoxyethylenated alkyl ether phosphates, polyoxyethylenated aryl ether phosphates; alkylolammonium salts of block copolymers having acidic groups; polyalkylene glycols, polyalkylene imines, polyalkylene alcohols. Use of the dispersion for production of dye solar cells.

Description

Organic solvent-based metal oxide dispersion

The invention relates to a dispersion containing metal oxide particles, an alkanol and an α, β-unsaturated carboxylic acid, their preparation and their use in the preparation of dye solar cells.

The use of metal oxide dispersions, in particular of titanium dioxide dispersions, represents an important step in the production of

Dye solar cells. The dispersion is applied to a conductive glass and subsequently the liquid phase of the dispersion is removed thermally.

WO93 / 18532 discloses that suitable solvents for such dispersions are alcohols, ethers, carboxylic acids or amines and the

Dispersions can be sterically stabilized by the addition of chelating agents such as acetylacetone.

In addition, propanol, 2-methyl-2-propanol and hexanol are mentioned in WO2005 / 071704. Preferably, a mixture of water and alcohol is used.

Mori et al. reveal in J. Mater. Be. 46 (2010) 1341-1350 organic solvent based titanium dioxide dispersions. They report that the most suitable dispersions for the preparation of dye-sensitized solar cells are those in which terpineol acts as a solvent and as a dispersant

Alkylolammonium salt of a block copolymer with acidic, phosphorus-containing groups is used.

Geng et al. describe in Journal of Electronic Materials 39 (2010) 1 -7

Dispersions of with lauric acid, caproic acid or sorbic acid

surface modified titanium dioxide particles in chlorobenzene, without the

Reveal the production of the particles. They conclude that dispersions surface-modified with caproic acid or sorbic acid Contain particles having a low stability with respect to a sedimentation and therefore are less suitable in the production of a dye solar cell.

The dispersions disclosed in the prior art should all be suitable for the preparation of dye-sensitized solar cells. However, it has been found that these dispersions have at least one of the following disadvantages:

- poor sedimentation stability

- a high viscosity with non-uniform particle distribution

- contain substances that are at a subsequent thermal

Treatment step can not be completely removed, especially inorganic components

- Contain substances that lead to cracks in the layer during the thermal treatment.

The object of the present invention was therefore a dispersion

to provide that avoids these disadvantages. Another object of the invention was to provide a process for producing this dispersion.

The invention relates to a dispersion containing metal oxide particles, in which

a) the metal oxide particles

a1) are selected from one or more oxides of the group

consisting of titanium dioxide, cerium oxide, zinc oxide and zirconium dioxide,

a2) in a proportion of at least 25% by weight, preferably 25 to 50

Wt .-%, particularly preferably 30 to 40 wt .-%, in the dispersion,

a3) have an average aggregate diameter of 20 to 120 nm, preferably 30 to 100 nm, more preferably 40 to 90 nm, and b) the liquid phase

b1) 90 to 99.5 wt .-%, preferably 95 to 99 wt .-%, of one or more alkanols C _n H _{2n +} iOH with

n = 2 to 4, b2) from 0.5 to 10% by weight, preferably from 1 to 5% by weight, of one or more α, β-unsaturated alkylcarboxylic acids having 4 to 12 C atoms,

b3) 0 to 2% by weight of one or more alkanediols HO (CH ₂ ) _x OH where x = 2 to 4, preferably x = 2,

b4) at most 5% by weight, preferably less than 1% by weight of water and b5) at most 2% by weight, preferably less than 1% by weight, in each case in

Sum of dispersing additives selected from the group consisting of polyoxyethylenated alkyl ether phosphates, polyoxyethylenated aryl ether phosphates; Alkylolammonium salts of block copolymers with acidic groups; Polyalkylene glycols, polyalkyleneimines,

Contains polyalkylene alcohols.

The metal oxide particles of the present invention are preferably aggregated primary particles whose surfaces have hydroxyl groups and which are largely free from micropores. The BET surface area of these particles is generally between 20 and 200 m ² / g, with values between 40 and 100 m ² / g being particularly preferred. Such aggregated primary particles can be obtained by pyrogenic methods such as flame hydrolysis or flame oxidation. Pyrogenic

Metal oxide particles in the context of the invention also include doped particles. Particularly suitable as doping component are the oxides of aluminum or silicon. The proportion of doping component, based on the doped

Metal oxide particles can be between 10 ppm and 5 wt .-%.

Titanium dioxide particles are preferred. Are commercially available, for example, ^® AEROXIDE _TiO2 P25 having a BET surface area of about 50 m ² / g and

AEROXIDE ^® TiO ₂ P90 with a BET surface area of approx. 90 m ² / g, both Evonik Degussa.

The titanium dioxide particles present in the dispersion according to the invention can be present in the rutile or anatase form or as a mixture of the two forms. When using pyrogenically prepared titanium dioxide powder, rutile and anatase modification are generally present. The anatase / rutile content can be in range from 2:98 to 98: 2. Most preferably, the range can be from 70:30 to 95: 5.

The dispersion according to the invention may also contain cerium oxide particles, preferably pyrogenically prepared cerium oxide particles. Particularly preferred may be the ceria particles disclosed in EP-A-1757560 which have carbonate groups on their surface and in a near-surface layer.

The average aggregate diameter of the metal oxide particles is 20 to 120 nm, preferably 30 to 100 nm and particularly preferably 40 to 90 nm. The values are determined by dynamic light scattering, for example by means of

Zetasizer ^® 3000 HS from Malvern Instruments is determined. In a particular embodiment of the invention, the dispersion contains no particles with a diameter of more than 200 nm, determined for example by means of

AccuSizer ^®, Gainco, Inc ..

The main constituent of the liquid phase is one or more alkanols C _n H _2n + iOH with n = 2 to 4. Preferred is an embodiment in which at least 90% by volume, more preferably an embodiment in which at least 99% by volume of the Alkanoles is isopropanol or the alkanol is exclusively ispropanol.

As a further constituent, the liquid phase contains one or more α, β-unsaturated carboxylic acids having 4 to 12 C atoms. They are completely soluble in the stated concentrations of 0.5 to 10 wt .-% at room temperature (23 ° C) in the liquid phase of the dispersion. An α, β-unsaturated carboxylic acid is to be understood as meaning a carboxylic acid with the unit C =C-CO ₂ H. The α, β-unsaturated carboxylic acid may be monounsaturated or polyunsaturated. For a multiple α, β-unsaturated carboxylic acid, the additional multiple bond may be in conjugation to the C = C-CO ₂ H moiety. The alkyl chain of the α, β-unsaturated carboxylic acids may be linear or branched. It can be a monocarboxylic acid or dicarboxylic acid. The α, β-unsaturated carboxylic acid contains no further functional group, such as a hydroxy, alkoxy or amino group. It was found, that α, β-unsaturated carboxylic acids with trans-configured double bonds provide the best results in terms of sedimentation stability and viscosity. Particularly preferred may be trans-2-hexenoic acid and sorbic acid. Very particular preference is given to sorbic acid. With dispersions containing sorbic acid, a weight ratio of metal oxide particles / sorbic acid 20: 1 to 40: 1 has proved to be ideal.

Besides the essential ingredients alkanol and a, ß-unsaturated

Carboxylic acids, the liquid phase of the dispersion 0 to 2 wt .-% of one or more alkanediols of the general formula HO (CH ₂ ) _x OH with x = 2 to 4, preferably x = 2, included. The alkanediols can improve the physico-chemical properties with the addition of said small amounts. In the event that the dispersion of the invention contains alkanediols, their proportion is preferably 0.01 to 1 wt .-% and particularly preferably 0.1 to 0.5 wt .-%, each based on the liquid phase.

In addition, the liquid phase of the dispersion is still maximum

5 wt .-% water and at most 2 wt .-% dispersing additives. Neither water nor dispersing additives are preferred components of the dispersion. However, in the stated amounts they have no adverse effects on the dispersion. Preferably, their concentration in the dispersion is as low as possible. In general, the proportion of water is less than 1 wt .-% and dispersing additive less than 0.1 wt .-%. Ideally, the dispersion is free of water and of dispersing additives within the detection limit.

As dispersing additives are those from the group consisting of

polyoxyethylenated alkyl ether phosphates, polyoxyethylenated

Aryletherphosphaten; Alkylolammonium salts of block copolymers with acidic groups; Polyalkylene glycols, polyalkyleneimines, polyalkylene understood.

Furthermore, the dispersion of the invention should be free of binders.

Binder means those substances which, in the absence of the liquid phase of the dispersion, the metal oxide particles, for example on a Substrate, fix. It is known to use such binders in the production of dye solar cells. You can the invention

Dispersion can be added after their preparation. These may be inorganic or organic binders. Suitable organic binders such as polyacrylamide, styrene-butadiene copolymers, poly-N-vinylacetamide, poly-N-vinylformamide, polytetrafluoroethylene, polyvinyl fluoride, polyvinylidene fluoride or polyvinylpyridine. Inorganic binders can also be used. These may be, for example, alkoxysilanes, partially hydrolyzed by acids alkoxysilanes, alkoxides of aluminum or titanium or zirconium salts.

In a particular embodiment of the invention, the dispersion having a proportion of isopropanol of 95 to 99 wt .-% and sorbic acid of 1 to 5 wt .-%, each based on the liquid phase, and a proportion of metal oxide particles in the form of titanium dioxide particles with a BET surface area of 50 + 5 m ² / g of 40 wt .-%, based on the dispersion, a viscosity of less than 750 mPas, more preferably less than 200 mPas, each at 23 ° C and a shear rate of 10 s ^"1 on.

In a further particular embodiment of the invention, the

Dispersion with a proportion of isopropanol of 95 to 99 wt .-% and sorbic acid of 1 to 5 wt .-%, each based on the liquid phase, and a proportion of metal oxide particles in the form of titanium dioxide particles having a BET surface area of 90 + 10 m ² / g of 30 wt .-%, based on the dispersion, a viscosity of less than 750 mPas, more preferably less than 200 mPas, each at 23 ° C and a shear rate of 10 s ^"1 on.

Another object of the invention is a process for the preparation of the dispersion according to the invention, in which first a predispersion is prepared by

a) metal oxide particles which are selected from one or more oxides of the group consisting of titanium dioxide, cerium oxide, zinc oxide and zirconium dioxide, with a proportion of at least 25 wt .-%, based on the predispersion, in a liquid phase, the b1) from 90 to 99.5% by weight of one or more alkanols C _n H ₂ n + iOH where n = 2 to 4,

b2) 0.5 to 10 wt .-% of one or more α, β-unsaturated carboxylic acids with

4 to 12 C atoms,

b3) 0 to 2 wt .-% of one or more alkanediols HO (CH ₂ ) _x OH with

x = 2 to 4,

b4) at most 5% by weight of water and

b5) at most 2 wt .-%, in total, dispersing additives from the group

consisting of polyoxyethylenated alkyl ether phosphates,

polyoxyethylenated aryl ether phosphates; Alkylolammonium salts of block copolymers with acidic groups; polyalkylene

Polyalkyleneimines, polyalkylene alcohols

contains

the predispersion feeds a high-pressure milling by dividing it into at least two partial streams, these partial streams under a pressure of at least 500 bar, preferably 2000 to 4000 bar, depressurized via a nozzle and in a gas- or liquid-filled reaction space

If necessary, repeat the high pressure milling several times if necessary.

Due to the high pressure in the high pressure milling low boiling points of the components of the liquid phase is not a problem. The preparation of the predispersion is not critical. Usually rotor / stator assemblies are used. The predispersion does not have to be special

Have properties, for example, with respect to the sedimentation or viscosity.

Another object of the invention is the use of the

Dispersion according to the invention for the preparation of dye solar cells. Examples

Determination of the mean aggregate diameter by means of dynamic

Light scattering: about 0.1 to 1 ml of the dispersion are dissolved in about 50 ml of a solution of 50 g of deionized water, 0.5 g of citric acid, 0.7 g of 2-amino-2-methyl-propanol and one drop of a ordinary hand dishwashing detergent, such as Palmolive ^®, Colgate-Palmolive by ultrasound at low power (20 W) dispersed. By means of the Zetasizer ^® 3000, Malvern Instruments, the mean aggregate diameter is determined.

Example 1: To a solution of 41 kg of isopropanol, 770 g of sorbic acid and 56 g of ethylene glycol, 28 kg of AEROXIDE® TiO ₂ P 25, Evonik Degussa, are added to the receiving container while the rotor / stator assembly (Ystral Conti-TDS 3) is being used. one hour added. After the addition, shear was carried out for a further 10 minutes at 3000 rpm. This predispersion is ground twice using a high-energy mill, Sugino Ultimaizer HJP-25050, at a pressure of 2500 bar, each 0.25 mm in diameter.

The dispersion has a solids content of 40% by weight. The viscosity, determined by means of the Physica MCR 300 rheometer, Anton Paar, at a temperature of 23 ° C. and a shear rate of 11.5 s ^-1 is 398 mPas and a shear rate of 108 s ^-1 is 97.8 mPas. The average aggregate diameter determined by means of dynamic light scattering is 91 nm.

Example 2: To a solution of 47.9 kg of isopropanol, 1, 04 kg of sorbic acid and 76 g of ethylene glycol 21 kg of AEROXIDE ^® TiO ₂ P 90, Evonik Degussa, with the rotor / stator assembly (Ystral Conti- TDS 3) in the reservoir. added within about an hour. After the addition, shear was carried out for a further 10 minutes at 3000 rpm. This predispersion is ground three times using a high-energy mill, Sugino Ultimaizer HJP-25050, at a pressure of 2500 bar, each 0.25 mm in diameter.

The dispersion has a solids content of 30% by weight. The viscosity, determined by means of the rheometer Physica MCR 300, Anton Paar, at a temperature of 23 ° C and a shear rate of 1 1, 7 s ^"1 is 501 mPas and a shear rate of 108 s ^-1 is 154 mPas The mean aggregate diameter determined by means of dynamic light scattering is 33 nm.

The examples show that the dispersions of the invention have a low viscosity at high solids concentration and low particle size. Their liquid components can be easily removed thermally.

The dispersion according to the invention is thus ideally suited for further processing in the production of dye-sensitized solar cells, for example by adding binders additionally to the dispersions. The binder-containing dispersions then still have very good properties due to the excellent properties of the dispersion according to the invention

Processing properties on.

Further attempts have been made to prepare dispersions with other than α, β-unsaturated carboxylic acids having 4 to 12 carbon atoms.

For example, caproic acid, adipic acid or malic acid were tested. Either not sufficient amounts of these a, ß-unsaturated

Carboxylic acids are dissolved in the liquid phase or the dispersions show high viscosities and are not sedimentation-stable.

Claims

claims

1 . Dispersion containing metal oxide particles,

characterized in that

a) the metal oxide particles

a1) are selected from one or more oxides of the group consisting of titanium dioxide, cerium oxide, zinc oxide and zirconium dioxide

a2) with a proportion of at least 25 wt .-% in the dispersion

present

a3) have a mean aggregate diameter of 20 to 120 nm and

b) the liquid phase

b1) from 90 to 99.5% by weight of one or more alkanols C _n H ₂ n + iOH where n = 2 to 4,

b2) 0.5 to 10 wt .-% of one or more α, ß-unsaturated

Carboxylic acids with 4 to 12 carbon atoms,

b3) 0 to 2% by weight of one or more alkanediols HO (CH ₂ ) _x OH where x = 2 to 4,

b4) at most 5% by weight of water and

b5) at most 2% by weight, in total, dispersing additives from the group consisting of polyoxyethylenated alkyl ether phosphates, polyoxyethylenated aryl ether phosphates; Alkylolammonium salts of block copolymers with acidic groups; Polyalkylene glycols, polyalkyleneimines, polyalkylene alcohols

contains.

2. Dispersion according to claim 1, characterized in that

the metal oxide particles are titanium dioxide particles.

3. Dispersion according to claims 1 or 2, characterized in that at least 90 vol .-% of the alkanol is isopropanol.

4. Dispersion according to claims 1 to 3, characterized in that the α, β-unsaturated carboxylic acid is sorbic acid.

5. Dispersion according to claim 4, characterized in that

the weight ratio of metal oxide particles / sorbic acid is 20: 1 to 40: 1.

6. A dispersion according to claims 4 or 5, characterized in that it contains at a proportion of isopropanol of 95 to 99 wt .-% and

Sorbic acid of 1 to 5 wt .-%, each based on the liquid phase, and a proportion of metal oxide particles in the form of titanium dioxide particles having a BET surface area of 50 + 5 m ² / g of 40 wt .-%, based on the dispersion , a viscosity of less than 750 mPas at 23 ° C and a shear rate of 10 s ^"1 has.

7. A dispersion according to claims 4 or 5, characterized in that it contains at a proportion of isopropanol of 95 to 99 wt .-% and

Sorbic acid from 1 to 5 wt .-%, each based on the liquid phase, and a proportion of metal oxide particles in the form of titanium dioxide particles having a BET surface area of 90 + 10 m ² / g of 30 wt .-%, based on the dispersion , a viscosity of less than 750 mPas at 23 ° C and a shear rate of 10 s ^"1 has.

8. A process for the preparation of the dispersion according to claims 1 to 7, characterized in that

to prepare a predispersion by

a) metal oxide particles selected from one or more

Oxides of the group consisting of titanium dioxide, cerium oxide, zinc oxide and zirconium dioxide, in a proportion of at least 25 wt .-%, based on the predispersion, brings in a liquid phase, the

b1) 90 to 99.5 wt .-% of one or more alkanols C _n H _2n + iOH with

n = 2 to 4,

b2) from 0.5 to 10% by weight of one or more α, β-unsaturated carboxylic acids having 4 to 12 C atoms,

b3) 0 to 2 wt .-% of one or more alkanediols HO (CH ₂ ) _x OH with

x = 2 to 4,

b4) at most 5% by weight of water and b5) at most 2% by weight, in total, dispersing additives from the group consisting of polyoxyethylenated alkyl ether phosphates,

Polyalkyleneimines, polyalkylene alcohols

contains

the predispersion feeds high-pressure milling by dividing it into at least two partial streams, pressurizing these partial streams under a pressure of at least 500 bar, preferably 2000 to 4000 bar, depressurizing via a nozzle and meeting one another in a gas- or liquid-filled reaction space, optionally high-pressure milling repeated several times.

9. Use of the dispersion according to claims 1 to 7 for the preparation of dye solar cells.