WO2015063664A1

WO2015063664A1 - Metal oxide suspension, its manufacture and uses

Info

Publication number: WO2015063664A1
Application number: PCT/IB2014/065596
Authority: WO
Inventors: Björn OLOF LINDMAN; Jens OTTO NORRMAN; Ana Lúcia COSTA LAGOA
Original assignee: Innovnano – Materiais Avançados, Sa.
Priority date: 2013-10-30
Filing date: 2014-10-24
Publication date: 2015-05-07
Also published as: PT107263A; PT107263B

Abstract

The present disclosure relates to a metal oxide suspension, its manufacture and uses, in particular for the deposition of a metal oxide layer. The metal oxide suspension is a non-polluting, low-energy process for the deposition of metal-oxide layers. The suspension disclosed deposits the metal-oxide nanoparticles with the help of a cellulose-derived polymer as a stabiliser of a suspension for metal- oxide deposition by destabilisation of the suspension by heating. The present disclosure comprises a suspension for metal-oxide deposition comprising water; suspended metal-oxide nanoparticles; cellulose-derived polymer as a stabiliser, said polymer being suitable to be destabilised by heating; wherein the nanoparticles have been deagglomerated.

Description

D E S C R I P T I O N

"METAL OXIDE SUSPENSION, ITS MANUFACTURE AND USES"

Technical field

The present disclosure relates to a metal oxide suspension, its manufacture and uses, in particular for the deposition of a metal oxide layer.

Background Art

Document US20110027567A1 describes a process for covering a substrate with a polymer film, wherein, prior to the deposition of said polymer film, nanoparticles are adsorbed electrostatically onto the surface of said substrate to be coated.

Document US2009114124A1 describes a process for preparing a nanometric suspension of anatase Ti0₂, by reacting a titanium alkoxide with a polyethylene glycol; heating to remove at least a portion of any alcohol formed; adding water, a polyethylene glycol, and a polycondensation inhibitor, wherein the polycondensation inhibitor comprises a mixture of at least one mineral acid and at least one organic acid; and heating under reflux to obtain the nanometric suspension of anatase Ti0₂.

Document CN101554580A describes a preparation method of a photocatalyst layer containing titanium dioxide nano-crystal grains. The method comprises titrating TiOS0₄ and ammonia into a deionized water solution; precipitating the suspension by pH; stirring and aging; washing; separating solid from liquid; diluting precipitate; using a peptizing agent; heating and cooling to obtain the nano-crystalline titanium dioxide photocatalyst. Document WO2001025316A1 describes a method of forming a coherent nanoparticle film, by adding to a suspension of nanoparticles linker molecules which form crosslinks to start a cross-linking reaction; and separating the cross-linked nanoparticles from the suspension prior to completion of the cross-linking reaction to obtain a coherent nanoparticle film.

Summary

The present disclose is a non-polluting, low-energy process for the deposition of metal- oxide layers. The suspension disclosed deposit the metal-oxide nanoparticles with the help of a cellulose-derived polymer as a stabiliser of a suspension for metal-oxide deposition by destabilisation of the suspension by heating.

The present disclosure comprises a suspension for metal-oxide deposition comprising:

- water;

- suspended metal-oxide nanoparticles;

- cellulose-derived polymer as a stabiliser, said polymer being suitable to be destabilised by heating; wherein the nanoparticles have been deagglomerated. The suspension disclosed deposit the oxides with the help of a polymer.

In some embodiments the nanoparticles have been deagglomerated mechanically, in particular by milling the suspension, in further particular by bead-milling the suspension.

In some embodiments the cellulose-derived polymer is soluble in water, particularly selected from hydroxyethyl cellulose, hydrofobically modified hydroxyethyl cellulose, cationic hydroxyethyl cellulose, methyl cellulose, ethyl hydroxyl cellulose, methyl ethyl hydroxy ethyl cellulose or mixtures thereof, among others. Some embodiments comprise an anti-foaming agent, in particular tri-butyl phosphate.

In some embodiments the metal-oxide is selected from a group of Ti0₂, AZO, ZnO, ITO, GZO, IZO, or mixtures therefore, in particular titanium dioxide (Ti0₂), or aluminum- doped zinc oxide (AZO). In another embodiment the suspension disclosed includes a two-step phase for the preparing of the Ti0₂. In a first step, Ti0₂ is synthesized and in a second step is deposited by a dip-coating like procedure.

In some embodiments the metal-oxide nanoparticles are 1-6% w/w of the suspension, preferably 1-4% w/w of the suspension, and even more preferably 1-2% w/w of the suspension.

In some embodiments the cellulose-derived polymer is 0.1-12% w/w of the suspension, preferably 0.5-8% w/w of the suspension and even more preferably 0.5- 4% w/w of the suspension.

In some embodiments the metal-oxide proportion to the cellulose-derived polymer is 0.35-0.5, preferably 0.40-0.44 and even more preferably 0.42-0.43, depending on the oxide and their surface area.

The disclosure further comprises a dilute of the suspension for metal oxide deposition of any one of the above suspensions, in particular where the suspension is diluted 5-15 times.

The disclosure also comprises a freeze-dried suspension of any one of the above suspensions.

When trying to develop a process to prepare the inventive suspension, applicants found that existing processes did produce the desired suspension, but they were not cost-effective or not robust, i.e. suspension was not reproducible enough for economic production. Therefore it was a further object of the invention to provide a process to solve these problems. Surprisingly, applicants have found that this object is met by the following aspect of the invention which provides a process for the manufacture of any of the above suspensions for metal-oxide deposition, comprising mixing water and the metal-oxide nanoparticles prior to gradually incorporating the cellulose-derived polymer while mechanically deagglomerating, in particular by bead-milling.

However, in some of the tests made during the development of this technology, the applicants surprisingly have also found that the process for the manufacture of any of the above suspensions for metal-oxide deposition can start by preparing polymer solutions of a known concentration and then adding metal-oxide suspensions that were pre-treated with ultra-sound probe to break up larger aggregates.

The disclosure also comprises the use of a cellulose-derived polymer as a stabiliser of a suspension for metal-oxide deposition by destabilisation of the suspension by heating.

The disclosure also comprises a process for the deposition of a metal oxide layer on a substrate comprising:

- placing the substrate in any one of the above suspensions;

- disrupting the stability of the suspension by heating;

- letting the destabilised suspension deposit over the substrate.

In some embodiments the suspension nanoparticles are deagglomerated mechanically previous to the depositing, in particular by milling the suspension, in further particular by bead-milling the suspension.

In some embodiments the nanoparticles have been deagglomerated prior to incorporation in the suspension.

In some embodiments the destabilising heat is applied to the suspension at the region of the substrate or from below the substrate. In some embodiments the destabilising heat is applied to the suspension at the upper region of the suspension.

Some embodiments comprise subsequent sintering of the deposited metal oxide layer, in particular sintering to a temperature high enough for substantially full removal of the stabilising cellulose-derived polymer.

In some embodiments the process of depositing the metal-oxide layer is a continuous process comprising moving the substrate as it passes a deposition area of the destabilised suspension.

The disclosure also comprises a process for the deposition of multiple layers of metal- oxide by repeating any one of the above processes of metal-oxide layer deposition.

The disclosure comprises a product with a deposited layer of metal-oxide obtainable by any one of the above processes of metal-oxide layer or layers deposition, for example parts for solar cell, display or touchscreen devices.

Detailed Description

This application discloses subject-matter related to a metal oxide suspension for the deposition of thin films that can be easily prepared from pre-manufactured nanomaterials, not requiring in-situ synthesis.

In an embodiment, the nanometric metal oxide, with aprox. 4% massic concentration is placed in a water solution of a cellulose-derived polymer soluble in water, such as ethyl hydroxyethyl cellulose, methyl ethyl hydroxyethyl cellulose, among others, in a mass ratio between polymer and metal oxide of 0.35-0.5, preferably 0.40-0.44 and even more preferably 0.42-0.43, depending on the oxide and their surface area and mixed in order to make a pre-dispersion of the nanomaterial. This pre-dispersion is then subjected to a mechanically deagglomeration of the nanomaterials, in particular by milling the suspension, or further particular by bead-milling and allow the attachment of the polymer to the surface of the particle. This process lasts until the deagglomeration of the particles stabilizes, with a particle size distribution that remains identical. During or previously to the deagglomeration an anti-foaming agent might be added. The suspension thus obtained is stable for several weeks. If the nanoparticles of the metal oxide are already deagglomerated prior to addition to the polymer solution, this step might not be necessary.

The suspension thus obtained is superior to other similar suspensions in the sense that no organic solvents, toxic or otherwise, are used and the composition comprises only a nanomaterial, a polymer, water and optionally an anti-foaming agent that can be chosen among any kind that is water-soluble and does not prejudice the final application.

In some of the tests made during the development of this technology, the applicants surprisingly have also found that the process for the manufacture of any of the above suspensions for metal-oxide deposition can start by preparing polymer solutions of a known concentration and then adding metal-oxide suspensions that were pre-treated with ultra-sound probe to break up larger aggregates.

In the disclosed subject matter the producing of a suspension is based on steric stabilization in which the polymer attaches to the surface of the particle by one end of the chain, extending the rest of the chain perpendicularly to the surface. With the approach of the two particles, surprisingly the conformational freedom is reduced and the solvation is decreased, since the steric stabilization assumes a favorable polymer- solvent interaction. This surprisingly creates a particle with a "hairy" surface. In order for these particles to agglomerate, the polymer suffers a compression by the osmotic pressure of the solvent, which is energetically unfavorable leading to repulsion between the particles, mainly of an entropic origin, which, as a consequence, remain in suspension. The "compression" is caused by forcing the particles close to each other. Since this is not possible, the particles remain in suspension. The difference to other processes of steric stabilization of nanoparticles is that the polymers chosen for the stabilization contract their chain at a very well determined temperature, characteristic of each polymer, which allows the steric stabilization to be compromised and deposition to occur.

Depending on the kind and quality of the film required, the suspension can be used as prepared or further diluted by the simple addition of extra water. The lower the concentration, the better is the quality of the film, i.e. with a more uniform surface, since the probability of agglomeration during descend decreases.

To deposit the film in a surface, this should be placed inside a vessel and the suspension, diluted to the desired concentration, usually by diluting the initial suspension 10-15 times, is poured on top of it. The vessel, which is standing on top of a heating plate, is heated to the temperature of destabilization. Heating from the bottom will lead too highly uniform films. For higher roughness of the surface, the heating element should be placed on the top part of the suspension. After deposition of the film, which takes only a few minutes (in particular between 20 - 60 minutes, preferably 30-45 minutes), the upper part of the suspension is drained and the film is dried and/or sintered. The sintering process starts at room temperature and evolves in several heating steps until 500 °C. Temperatures above 500 °C can be used depending on the metal oxide nanoparticle and on the nature of the substrate, as well as on the desired degree of sintering. Bellow this temperature there will not be a full removal of the polymer, but the layer polymer metal oxide will have a good adhesion to the surface and can be used as a thin film as well, as long as the polymer presents no problem to the application.

The process of deposition can be done once or several times for multilayer films, with or without sintering in between depositions. The process can be automatized by making the substrate roll as the suspension is poured on top of it. The substrate will then enter a heated area in which the deposition occurs and will move out of it in an angle moving up so that it leaves the upper solution behind. The substrate will then move into a hoven where will be subjected to the several steps of the heat treatment for sintering or simple drying, according to the desired final application.

The residual solution is not environmentally hazardous since it is composed solely of water and cellulose-based polymers.

Embodiment 1:

5.4 g of nanostructured titanium dioxide with particles of an average size of 150- 200 nm was added to a water solution containing 2.28 g of methyl ethyl hydroxy ethyl cellulose and 392.32 g of water. The suspension was then homogenized in a highspeed laboratory mill for several hours, in particular between 3-6 hours. The obtained suspension was diluted by adding 15 g of water to 1 g of the prepared suspension. Around 1 cm³ of the diluted suspension was transferred to a bottomless circular vessel placed on top of a flat glass. The glass was heated up to 80 °C in order to destabilize the suspension and deposit the Ti0₂ nanoparticles in its surface. After particle deposition, first the remaining water and then the vessel were removed, leaving a thin film deposited on the glass.

Embodiment 2:

10.84 g of nanostructured titanium dioxide with particles of an average size of 150- 200 nm was added to a water solution containing 3.84 g of methyl ethyl hydroxy ethyl cellulose and 385.32 g of water. The suspension was then homogenized in a highspeed laboratory mill for several hours. The obtained suspension was diluted by adding 10 g of water to 2 g of the prepared suspension. Around 1 cm³ of the diluted suspension was transferred to a bottomless circular vessel placed on top of a flat glass. The glass was heated up to 80 °C in order to destabilize the suspension and deposit the Ti02 nanoparticles in its surface. After particle deposition, first the remaining water and then the vessel were removed, leaving a thin film deposited on the glass. The film was sintered at 500 °C for 15 min with a heating rate of 5 °C/min and 5 min dwell time at 125 °C, 325 °C, 375 °C and 450 °C in between.

Embodiment 3:

6.7 g of nanostructured aluminum-doped zinc oxide (AZO) with particles of an average size of 150-200 nm was added to a water solution containing 2.85 g of methyl ethyl hydroxy ethyl cellulose and 490.45 g of water. The suspension was then homogenized in a high-speed laboratory mill for several hours. The obtained suspension was diluted by adding 20 g of water to 2 g of the prepared suspension. Around 1 cm³ of the diluted suspension was transferred to a bottomless circular vessel placed on top of a flat glass. The glass was heated up to 80 °C in order to destabilize the suspension and deposit the AZO nanoparticles in its surface. After particle deposition, first the remaining water and then the vessel were removed, leaving a thin film deposited on the glass. The film was sintered at 500 °C for 15 min with a heating rate of 5 °C/min.

The above described embodiments are combinable.

The disclosure is of course not in any way restricted to the embodiments described and a person with ordinary skill in the art will foresee many possibilities to modifications thereof without departing from the disclosure as defined in the appended claims.

The following claims set out particular embodiments of the present disclosure.

Claims

C L A I M S

1. Suspension for metal-oxide deposition comprising:

• water;

• suspended metal-oxide nanoparticles;

• cellulose-derived polymer as a stabiliser, said polymer being suitable to be destabilised by heating;

wherein the nanoparticles are deagglomerated.

2. Suspension according to the previous claim wherein the nanoparticles are deagglomerated mechanically, in particular by milling the suspension, in further particular by bead-milling the suspension.

3. Suspension according to any one of the previous claims wherein the cellulose- derived polymer is soluble in water.

4. Suspension according to the previous claim wherein the cellulose-derived polymer is selected from a group of hydroxyethyl cellulose, hydrofobically modified hydroxyethyl cellulose, cationic hydroxyethyl cellulose, methyl cellulose, ethyl hydroxyl cellulose, methyl ethyl hydroxy ethyl cellulose or mixtures thereof.

5. Suspension according to any one of the previous claims further comprises an anti- foaming agent.

6. Suspension according to the previous claim wherein the foaming agent is a tri- butyl phosphate.

7. Suspension according to any one of the previous claims wherein the metal-oxide is selected from a group of Ti0₂, AZO, ZnO, ITO, GZO, IZO or mixtures thereof.

8. Suspension according to the previous claim wherein the metal-oxide is titanium dioxide, or aluminum-doped zinc oxide.

9. Suspension according to any one of the previous claims wherein the metal-oxide nanoparticles are in 1-6% w/w of the suspension.

10. Suspension according to any one of the previous claim wherein the metal-oxide nanoparticles are in 1-4% w/w of the suspension, preferably 1-2% w/w of the suspension.

11. Suspension according to any one of the previous claims wherein the cellulose- derived polymer is 0.1-12% w/w of the suspension.

12. Suspension according to any one of the previous claim, wherein the cellulose- derived polymer is 0.5-8% w/w, preferably 0.5-4% w/w of the suspension.

13. Suspension according to any one of the previous claims wherein the metal-oxide proportion to the cellulose-derived polymer is 0.35-0.5.

14. Suspension according to the previous claim, wherein said proportion is 0.40-0.44, preferably 0.42-0.43.

15. Dilute of the suspension for metal oxide deposition of any one of the claims 1-14, in particular where the suspension is diluted 5-15 times.

16. Freeze-dried suspension of any one of the previous claims.

17. Process for the manufacture of the suspension for metal-oxide deposition of any one of the claims 1-14, comprising mixing water and the metal-oxide nanoparticles prior to gradually incorporating the cellulose-derived polymer while mechanically deagglomerating, in particular by bead-milling.

18. Process for the manufacture of the suspension for metal-oxide deposition of any one of the claims 1-14, comprising mixing water and cellulose-derived polymer and then adding metal-oxide suspensions that were pre-treated with ultra-sound probe to break up larger aggregates.

19. Use of a cellulose-derived polymer as a stabiliser of a suspension for metal-oxide deposition by destabilisation of the suspension by heating.

20. Process for the deposition of a metal oxide layer on a substrate comprising:

a. placing the substrate in the suspension of any one of the claims 1-14; b. disrupting the stability of the suspension by heating;

c. letting the destabilised suspension deposit over the substrate.

21. Process according to the previous claim wherein the suspension nanoparticles are deagglomerated mechanically previous to the depositing, in particular by milling the suspension, in further particular by bead-milling the suspension.

22. Process according to any one of the claims 20-21 wherein the nanoparticles have been deagglomerated prior to incorporation in the suspension.

23. Process according to any one of the claims 20-22 wherein the destabilising heat is applied to the suspension at the region of the substrate or from below the substrate.

24. Process according to any one of the claims 20-23 wherein the destabilising heat is applied to the suspension at the upper region of the suspension.

Process according to any one of the claims 20-24 comprising subsequent sintering of the deposited metal oxide layer, in particular sintering to a temperature high enough for substantially full removal of the stabilising cellulose-derived polymer.

26. Process according to any one of the claims 20-25 wherein the process is a continuous process comprising moving the substrate as it passes a deposition area of the destabilised suspension.

Process for the deposition of multiple layers of metal oxide comprising repeat the process of any one of the claims 20-26.

28. Product with a deposited layer of metal-oxide obtainable by any one of the claims 20-27.