FI127329B

FI127329B - Fluoropolymer sludge and fluoropolymer coating

Info

Publication number: FI127329B
Application number: FI20165159A
Authority: FI
Inventors: Vesa Myllymäki; Perttu Rintala
Original assignee: Carbodeon Ltd Oy
Priority date: 2016-03-01
Filing date: 2016-03-01
Publication date: 2018-03-29
Also published as: WO2017149202A1; FI20165159A

Abstract

The present invention relates to a slurry composition comprising a fluoropolymer, nanodiamond particles having zeta potential higher than + 30 mV and a liquid medium comprising an organic solvent or a mixture of organic solvents. The present invention further relates to use of the slurry composition in manufacturing of a fluoropolymer coating, and to a fluoropolymer coating.

Description

Field of the invention

The present invention relates to a fluoropolymer slurry containing nano5 diamonds and to a fluoropolymer coating containing nanodiamonds.

Background art

Fluoropolymers (FP) are known for their excellent non-stick properties but also for their low friction, excellent corrosion and chemical resistance and resistance to galling. They withstand very high temperatures and are electrically insulating. Moreover, they do not absorb water. The most well-known fluoropolymer is polytetrafluoroethylene (PTFE) having the formula -(F2CCF2)n-. The fluorine in a fluoropolymer is electrically negative, which gives it the property of not bonding easily with other materials. That is what makes a fluoropolymer non-stick. Fluoropolymers are applied in a variety of industries, including automotive, aerospace, food industries, cook- and cutting ware, forestry appliances, pharmaceutical sector, chemical industries but also within machinery and other industries. Applications within electronic industries include high temperature electronic parts but also optically clear, dirt repellant and protective coatings. Fluoropolymer coatings can be applied both on metallic and non-metallic surfaces. The coatings can be applied as single coating layer or as a system of plural coatings. One way of manufacturing fluoropolymer coatings is applying fluoropolymer material containing slurry as a spray coat. In such an approach said fluoropolymer slurry is sprayed on the surface, the coating being cured by baking it at selected temperature. Fluoropolymer slurries can also be applied substrate by coil method, by dipping or spinning but also other methods. The applied fluoropolymer containing slurry can be aqueous or solvent based. Typically, solvent-based fluoropolymers exhibit better wear resistance than their aqueous versions.

Main drawbacks of, for example polytetrafluoroethylene are its still low wear resistance and thermal conductivity, although it possesses very low friction coefficient. The low friction coefficient of the PTFE is due to its molecular structure. It has un-branched chain-like molecular structure. The chains are

20165159 prh 08 -03- 2018 linked only with weak Van der Waals forces. Thus the chains slide easily past each other. This results in transfer film formation. However, as the formation and removal cycle is repeated continuously, the wear rate increases and this procedure results in a high wear rate typical to PTFE.

It has been suggested in the art that nanoparticles have an effect on fluoropolymer, such as PTFE, properties such as wear. In the art PTFE composite coatings loaded with various substances have been studied. Such substances include silica, metallic nanoparticles, nanodiamond, titanium oxide, Kevlat fabric, and graphene.

Nanodiamonds can be produced by synthetic or detonation processes.

Synthetic nanodiamonds may be produced by several known methods, such as chemical vapour deposition or high pressure high temperature (HPHT) method, followed by crushing and sieving of resulting diamond particles. Such particles have wide particle size distribution (PSD) and the particle size (D50) varies from tens of nanometers to several hundred micron size. Nanodiamonds produced this way don’t exhibit surface functionalization, nor can their surface be functionalized with covalently bound surface functions. Moreover, their shape is irregular and the particles exhibit hard edges.

Nanodiamonds produced by detonation synthesis are called detonation nanodiamonds. That is, detonation nanodiamonds originate from detonation process.

Detonation nanodiamond, also referred to as ultrananocrystalline diamond or ultradispersed diamond (UDD), is a unique nanomaterial, which can be produced in thousands of kilograms by detonation synthesis.

Detonation nanodiamonds, or nanodiamonds originating from detonation process, were first synthesized by researchers from the USSR in 1963 by explosive decomposition of high-explosive mixtures with negative oxygen balance in a non-oxidizing medium. A typical explosive mixture is a mixture of trinitrotoluene (TNT) and hexogen (RDX), a preferred weight ratio of TNT/RDX is 40/60.

As a result of the detonation synthesis, diamond-bearing soot also referred to as detonation blend is obtained. This blend comprises spherical nanodiamond

20165159 prh 08 -03- 2018 particles, which typically have an average particle size of about 2 to 8 nm, and different kinds of non-diamond carbon contaminated by metals and metal oxide particles coming from the material of the detonation chamber and used explosives. The content of nanodiamonds in the detonation blend is typically between 30 and 75% by weight.

The nanodiamond-containing blends obtained from the detonation contain same hard agglomerates, typically having a diameter of above 1 mm. Such agglomerates are difficult to break. Additionally the particle size distribution of the blend is very broad, ranging typically from several to tens of microns.

The diamond carbon comprises sp³ carbon and the non-diamond carbon mainly comprises sp² carbon species, for example carbon onion, carbon fullerene shell, amorphous carbon, graphitic carbon or any combination thereof. In addition, the nanodiamond blend contains metallic impurities originating mainly from the detonation chamber but sometimes also from the applied explosives.

There are number of processes for the purification of the detonation blends. The purification stage is considered to be the most complicated and expensive stage in the production of nanodiamonds.

For isolating the end diamond-bearing product, use is made of a complex of chemical operations directed at either dissolving or gasifying the impurities present in the material. The impurities, as a rule, are of two kinds: non-carbon (metal ions, metal oxides, salts etc.) and non-diamond forms of carbon (graphite, black, amorphous carbon).

Chemical purification techniques are based on the different stability of the dia25 mond and non-diamond forms of carbon to oxidants. Liquid-phase oxidants offer an advantage over gas or solid systems, because they allow one to obtain higher reactant concentrations in the reaction zone and, therefore, provide high reaction rates.

The usability of the detonation nanodiamonds is based on the fact that the outer surface of detonation nanodiamond, as opposite to for example nanodiamonds derived from micron diamonds by crushing and sieving, is covered with various surface functions. Typically detonation nanodiamond surface contains mixture of oppositely charged functions and exhibits thus high

20165159 prh 08 -03- 2018 agglomeration strength at low overall zeta-potential properties. With agglomeration it is meant the single nanodiamond particles tendency to form clusters of nanodiamond particles, these clusters sizing from tens of nanometers into millimetre-sized agglomerates.

The zeta potential value can be related to the stability of colloidal dispersions. The zeta potential indicates the degree of repulsion between adjacent, similarly charged particles in dispersion or suspension. For molecules and particles that are small enough, a high zeta potential will confer stability, i.e., the solution or dispersion will resist aggregation. When the potential is low, attraction exceeds repulsion and the dispersion will break and flocculate. So, colloids with high zeta potential (negative or positive) are electrically stabilized while colloids with low zeta potentials tend to coagulate or flocculate. If the zeta potential is 0 to ±5 mV, the colloid is subjected to rapid coagulation or flocculation. Zeta potential values ranging from ±10 mV to ±30 mV indicate incipient instability of the colloid (dispersion), values ranging from ±30 mV to ±40 mV indicate moderate stability, values ranging from ±40 mV to ±60 mV good stability as excellent stability is reached only with zeta potentials more than ±60 mV. One of the common ways to measure the material zeta potential is laser Doppler Micro-Electrophoresis method. An electric field is applied to a solution of molecules or a dispersion of particles, which then move with a velocity related to their zeta potential. This velocity is measured using laser interferometric technique called M3-PALS (Phase analysis Light Scattering). This enables the calculation of electrophoretic mobility, and from this the zeta potential and zeta potential distribution.

Document US 2010/233371 A1 relates a PTFE coating agent obtained by dispersing nanodiamond powder in a polar organic solvent, mixing the dispersion with a silane coupling agent and finally mixing the mixture with an oily PTFE coating solution. The silane coupling agent is essential to obtain improved friction and wear resistance properties.

Document CN 101613511 A discloses a PTFE composite material and a preparation method thereof. The composite material comprises polyether ether ketone (PEEK) powder, PTFE powder and nanodiamond powder. The method comprises steps of: 1) using a stirring ball mill to disperse the nanodiamond powder and dispersing agent polyvinylpyrrolidone (PVP) in ethanol medium to obtain nanodiamond dispersal liquid; 2) adding PEEK powder and PTFE

20165159 prh 08 -03- 2018 powder into nanodiamond dispersal liquid, drying the stirred mixture to obtain mixed powder; 3) cold press molding; and 4) high-temperature sintering to obtain the PTFE composite material.

Document WO 2015042555 A1 discloses nanodiamond coating composition, 5 wherein the nanodiamond coating composition is comprised of a nanodiamond material, a fluoropolymer, a liquid solvent for the fluoropolymer and at least one additive selected from the group consisting of dispersing agents, adhesion promoters, and coupling agents. The composition can be applied on a substrate and dried to form a coating the substrate.

Document US 2014086776 A1 discloses a surface treating agent comprising an organic solvent; nanodiamond powder and carbon nanotube powder dispersed in the organic solvent; and a polytetrafluoroethylene (PTFE) solution mixed with the organic solvent, wherein the organic solvent is an amide-based organic solvent.

Publication ’’Wear Resistant, low friction coatings”, http://www.carbodeon.net/index.php/en/applications/wearresistantlow-friction-coatings, available on Internet from November 2014, discloses that hydrogen functionalized nanodiamonds can be used in fluoropolymer coatings which may be used as wear resistant coatings. Nanodiamond dispersion is added as a liquid dispersion and the composition is mixed.

In view of the above, there still exists a demand for new and cost-efficient fluoropolymer coating compositions and coatings having improved properties which are obtainable with simpler methods.

Summary of the invention

An object of the present invention is to provide a slurry composition comprising fluoropolymer and nanodiamonds.

Another object of the present invention is to provide a slurry composition comprising fluoropolymer and nanodiamonds wherein the nanodiamonds are evenly distributed in the slurry.

Yet, a further object of the present invention is to provide a slurry composition comprising fluoropolymer and nanodiamonds wherein the slurry is in form of a dispersion.

20165159 prh 08 -03- 2018

A further object of the present invention is to provide a fluoropolymer coating comprising nanodiamond particles.

Yet, a further object of the present invention is to provide a fluoropolymer coating comprising nanodiamond particles wherein wear resistance of the coating is improved.

Yet, a further object of the present invention is to provide a fluoropolymer coating comprising nanodiamond particles wherein kinetic friction of the coating is reduced.

It has now been surprisingly found that a fluoropolymer coating comprising nanodiamonds having zeta potential higher than + 30 mV shows improved wear resistance. Additionally, amount of the nanodiamonds can be kept low which renders the coating economically feasible.

It was surprisingly found that the fluoropolymer coating having low nanodiamond content can be produced from a slurry comprising a fluoropolymer and nanodiamonds having zeta potential higher than + 30 mV by dying and/or curing the slurry. It was additionally found that the slurry can be in a form of a dispersion. That is, substantially all the nanodiamond particles are in a single digit form evenly distributed in the dispersion. Hence, the nanodiamonds are also evenly distributed in the coating, and thus, wear resistance of the coating is improved.

The present invention provides a slurry composition as depicted by claim 1.

The present invention provides a use of the slurry composition as depicted by claim 7.

The present invention provides a fluoropolymer coating as depicted by claim 8.

The present invention provides a coated article as depicted by claim 16.

Brief description of the figures

Figure 1 shows wear resistance of a reference coating and coatings according to the present invention.

Figure 2 shows wear resistance of a reference coating and coatings according to the present invention.

Figure 3 shows kinetic friction properties of a reference coating and coatings according to the present invention.

20165159 prh 08 -03- 2018

Detailed description

According to first aspect of the present invention there is provided a slurry composition comprising fluoropolymer and nanodiamonds. More particularly there is provided a slurry composition comprising at least one fluoropolymer, nanodiamond particles having zeta potential higher than + 30 mV and a liquid medium comprising an organic solvent or a mixture of organic solvents.

The composition may comprise one, two or more different fluoropolymer(s). The fluoropolymer can be any suitable fluoropolymer. Such fluoropolymers comprise polyvinylfluoride, polyvinylidene fluoride, polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene, perfluoroalkoxy polymer, fluorinated ethylene-propylene, polyethylenetetrafluoroethylene, polyethylenechlorotrifluoroethylene, perfluoroelastomer, fluorocarbon, perfluoropolyether, perfluorosulfonic acid, fluorinated polyimide and perfluoropolyoxetane.

In one embodiment the fluoropolymer is selected from a group consisting of polyvinylfluoride, polyvinylidene fluoride, polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene, perfluoroalkoxy polymer, fluorinated ethylenepropylene, polyethylenetetrafluoroethylene, polyethylenechlorotrifluoroethylene, perfluoroelastomer, fluorocarbon, perfluoropolyether, perfluorosulfonic acid, fluorinated polyimide or perfluoropolyoxetane or mixtures thereof, preferably PTFE.

Fluoropolymer materials for coating use are sold under different brand names, including but not limited to Teflon®, Nafion®, Zonyl®, Xylan®, Resilon, Enternitex®, Dykor®, Xylar®, Eterna®, Eclipse®, Halo®, Quantanium®, Quantum2®, Skandia®, Solaflon™, Xylac®, Fusion®, Kynar®, MaxCoat®,

Excalibur®, Algoflon®, Solef®, Fluon®, FTONE™, OPTOOL™, UNIDYNE™, DAIFREE™, ZEFFLE™, Cytop™, Lumiflon™ and Bonnflon™’. For example Xylan is generally used to reduce friction, improve wear resistance, and for non-stick applications. Additionally, it can be used to protect a metal from

20165159 prh 08 -03- 2018 corrosion. Xylan is made of low friction composites of fluoropolymers and reinforcing binder resins.

The nanodiamonds are detonation nanodiamonds.

Precursor nanodiamond material may be substantially pure detonation nano5 diamond material, preferably having a nanodiamond content of at least 87% by weight, more preferably at least 97% by weight. The detonation nanodiamond may contain graphite and amorphous carbon originating from the production of the detonation nanodiamonds. They may also contain some residual metal impurities, either as metals, metal salts or in metal oxide, nitride or halogenate form.

Zeta potential of the nanodiamond particles is higher than + 30 mV, preferably higher than + 35 mV, more preferably higher than + 40 mV, and even more preferably higher than + 50 mV. The zeta potential is measured with Laser Doppler Micro-Electrophoresis.

In one embodiment the nanodiamond particles are substantially free of negatively charged functionalities. By term “substantially free of negatively charged functionalities” is meant that the applied nanodiamond material acid value is less than 5.0. A comprehensive description on determining the acid value can be found in example section.

The detonation nanodiamond surface contained acidic terminal group can be determined by Boehm titration method. Boehm titration is a widely used method to determine acidic terminal groups on carbon materials. The basic principle of the method is that the surface oxygen groups of carbon material with acidic properties (carboxyl, lactone and phenol) can be identified by neutralizing them with bases of different strengths. The method is most often used to determine the amount of surface carboxyl groups, which can be neutralized with a weak base, sodium bicarbonate (NaHCOs).

In one embodiment the detonation nanodiamond acid value is less than 4.0, preferably less than 3.5, such as 0-3.5.

Examples of negatively charged functionalities include but are not limited to carboxylic acid, sulfonic and nitric acid functionalities and their various salts.

20165159 prh 08 -03- 2018

In a preferred embodiment the detonation nanodiamonds are free of negatively charged functionalities, that is, the acid value is 0.

The absence of the nanodiamond surface contained acidic, negatively charged functionalities can be measured and secured by Boehm titration, which method is more comprehensively described in “Rivka Fidel, Evaluation and implementation of methods for quantifying organic and inorganic components of biochar alkalinity, Iowa State University, Digital Repository at Iowa State University, 2012”. The method is based on the principle that strong acids and bases will react with all bases and acids, respectively, whereas the conjugate bases of weak acids will accept protons only from stronger acids (i.e. acids with lower pKa values).

Examples of functionalities on detonation nanodiamond that are not negatively charged are hydrogen, amine and hydroxyl termination. In a preferred embodiment the nanodiamond particles in the slurry are amine functionalized nanodiamond particles, hydrogen functionalized nanodiamond particles, hydroxyl functionalized nanodiamond particles, or a mixture thereof, preferably amine functionalized nanodiamond particles. Functionalized nanodiamond particles are commercially available, or can be produced with known methods.

In one embodiment of the present invention the detonation nanodiamond may include detonation soot such as graphitic and amorphous carbon, the content of oxidisable carbon preferably being at least 5 wt.-%, more preferably at least 10 wt.-%.

Preferably the detonation nanodiamonds are in single digit form. In one embodiment the detonation nanodiamond particles in single digit form have an average primary particle size of from 1 nm to 10 nm, preferably from 2 nm to 8 nm, more preferably from 3 nm to 7 nm, and most preferably from 4 nm to 6 nm. Such particle size can be determined for example by TEM (Tunneling Electron Microscope).

In one embodiment particle size distribution D90 of the detonation nano30 diamond dispersion is not more than 100 nm, such as 1-100 nm, preferably not more than 20 nm, such as 1-20 nm, most preferably not more than 12 nm, such as 1-12 nm. Such particle size distribution can be measured for example by dynamic light scattering method.

20165159 prh 08 -03- 2018

The concentration of the nanodiamond particles is preferably at most 2 wt.% as calculated from the slurry composition dry material content. If the nanodiamond concentration is above 2 wt.% usability of the slurry worsens and expenses rises. Preferably the concentration of the nanodiamond particles is less than 1 wt%. More preferably the concentration of the nanodiamond particles is 0.001 wt.%-1 wt.%, even more preferably 0.01 wt.%-1 wt.%, even more preferably 0.01 wt.%-0.8 wt.%, even more preferably 0.01 wt.%-0.4 wt.%, further even more preferably 0.01 wt.%-0.15 wt.%, and most preferably 0.03 wt.%-0.1 wt.%, as calculated from the slurry composition dry material content.

With the range of 0.03 wt.%-0.1 wt.% best performance is obtained, the slurry is cost-effective and usability of the slurry is advantageous.

The liquid medium comprises an organic solvent or a mixture of organic solvents. The organic solvent can be any suitable solvent. In one embodiment the organic solvent is selected from a group consisting of:

alcohols such as methanol, ethanol, isopropanol, butanol;

linear aliphatic diols such as ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,8-octanediol;

branched diols such as 1,2-propanediol, 1,3-butanediol, 2,3-butanediol, 1,3butanediol, 1,2-pentanediol, etohexadiol, p-menthane-3,8-diol, 2-methyl-2,420 pentanediol;

carboxylic acids such as formic acid and acetic acid;

tetrahydrofuran;

propylene carbonate;

lactams such as N-methyl-2-pyrrolidone (NMP) and N-ethyl-2-pyrrolidone 25 (NEP);

ketones such as acetone and methyl ethyl ketone (MEK) and propylene glycol monomethyl ester acetone (PGMEA);

esters such as methyl acetate and ethyl acetate;

lactones such as gamma-butyrolactone (GBL);

20165159 prh 08 -03- 2018

Ν,Ν-methylformamide, dimethyl sulfoxide (DMSO);

aromatic solvents such as toluene, xylenes and benzene such as ethyl benzene;

chlorinated solvents such as dichloromethane, trichloroethylene and chloro5 form;

ionic liquids such as 1-ethyl-3-methylmidazolium chloride, 1-butyl-3-methylmidazolium chloride, 1-ethyl-3-methyl-imidazolium ethylsulfate, 1 -ethyl-3methyl imidazolium diethylphosphate, 1-ethyl-3-methyl-imidazolium dicyanamide, tris-(2-hydroxyethyl)-methylammonium methylsulfate, 1-ethyl-3-methyl10 imidazolium thiocyanate, 1-ethyl-3-methyl-imidazolium tetrafluoroborate, 1ethyl-3-methyl-imidazolium trifluoromethanesulfonate, 1 -ethyl-3-methyl-imidazolium bis (trifluoromethanesulfonyl)imide, 1-ethyl-3-methyl-imidazolium methylcarbonate and 1-butyl-3-methyl-imidazolium methylcarbonate;

or mixtures thereof.

In one embodiment the liquid medium is selected from the above list of organic solvents or mixtures thereof.

In another embodiment the organic solvent is a mixture of NMP, xylene, GBL and ethyl benzene.

Preferably the organic solvent is selected from a group consisting of GBL,

NMP, or a mixture thereof. More preferably the liquid medium is GBL, NMP, or a mixture thereof.

In one embodiment the liquid medium may comprise additionally water, preferably only traces of water. In a preferred embodiment the liquid medium is substantially free of water, preferably the liquid medium is free of water.

In one embodiment the nanodiamond particles are included into the slurry in form of a suspension or dispersion, preferably dispersion. Particle size distribution (D90) of nanodiamond dispersion is generally considered as less than 20 nm (D90).

In a preferred embodiment the slurry composition consists of a fluoropolymer, nanodiamond particles having zeta potential higher than + 30 mV and an

20165159 prh 08 -03- 2018 organic solvent or a mixture of organic solvents. In another preferred embodiment the slurry composition is free of coupling agents, such as silane coupling agents, and/or dispersing agents, such as polyvinylpyrrolidone.

In a second aspect of the present invention there is provided a fluoropolymer 5 coating. More particularly there is provided a fluoropolymer coating comprising at least one fluoropolymer and nanodiamond particles in an amount of at most wt.% and zeta potential of the nanodiamond particles is higher than +30 mV.

The fluoropolymer coating is prepared from a solvent based fluoropolymer slurry. The fluoropolymer coating is so called solvent based coating because the slurry of which the coating is made of comprises organic solvents. There is preferably only a minor amount of water present in the slurry, more preferably the slurry is water free.

The fluoropolymer coating is obtained by drying and/or curing a slurry composition comprising at least one fluoropolymer, nanodiamond particles in an amount of at most 2 wt.% having zeta potential higher than +30 mV and a liquid medium comprising an organic solvent or a mixture of organic solvents.

The composition may comprise one, two or more different fluoropolymer(s). The fluoropolymer can be any suitable fluoropolymer. Such fluoropolymers comprise polyvinylfluoride, polyvinylidene fluoride, polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene, perfluoroalkoxy polymer, fluorinated ethylene-propylene, polyethylenetetrafluoroethylene, polyethylenechlorotrifluoroethylene, perfluoroelastomer, fluorocarbon, perfluoropolyether, perfluorosulfonic acid, fluorinated polyimide, and perfluoropolyoxetane.

In one embodiment the fluoropolymer is selected from a group consisting of polyvinylfluoride, polyvinylidene fluoride, polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene, perfluoroalkoxy polymer, fluorinated ethylenepropylene, polyethylenetetrafluoroethylene, polyethylenechlorotrifluoroethylene, perfluoroelastomer, fluorocarbon, perfluoropolyether, perfluorosulfonic acid, fluorinated polyimide, or perfluoropolyoxetane or mixtures thereof, preferably PTFE.

Fluoropolymer materials for coating use are sold under different brand names, including but not limited to Teflon®, Nafion®, Zonyl®, Xylan®, Resilon, Enternitex®, Dykor®, Xylar®, Eterna®, Eclipse®, Halo®, Quantanium®,

20165159 prh 08 -03- 2018

Quantum2®, Skandia®, Solaflon™, Xylac®, Fusion®, Kynar®, MaxCoat®, Excalibur®, Algoflon®, Solef®, Fluon®, FTONE™, OPTOOL™, UNIDYNE™, DAIFREE™, ZEFFLE™, Cytop™, Lumiflon™ and Bonnflon™’. For example Xylan is generally used to reduce friction, improve wear resistance, and for non-stick applications. Additionally, it can be used to protect a metal from corrosion. Xylan is made of low friction composites of fluoropolymers and reinforcing binder resins.

The nanodiamonds are detonation nanodiamonds.

Precursor nanodiamond material may be substantially pure detonation nano10 diamond material, preferably having a nanodiamond content of at least 87% by weight, more preferably at least 97% by weight. The detonation nanodiamond may contain graphite and amorphous carbon originating from the production of the detonation nanodiamonds. They may also contain some residual metal impurities, either as metals, metal salts or in metal oxide, nitride or halogenate form.

20165159 prh 08 -03- 2018

The absence of the nanodiamond surface contained acidic, negatively charged functionalities can be measured and secured by Boehm titration, which method is more comprehensively described in “Rivka Fidel, Evaluation and implementation of methods for quantifying organic and inorganic components of biochar alkalinity, Iowa State University, Digital Repository at Iowa State University, 2012”. The method is based on the principle that strong acids and bases will react with all bases and acids, respectively, whereas the conjugate bases of weak acids will accept protons only from stronger acids (i.e.

acids with lower pKa values).

Examples of functionalities on detonation nanodiamond that are not negatively charged are hydrogen, amine and hydroxyl termination. In a preferred embodiment the nanodiamond particles in the slurry are amine functionalized nanodiamond particles, hydrogen functionalized nanodiamond particles, hydroxyl functionalized nanodiamond particles, or a mixture thereof, preferably amine functionalized nanodiamond particles. Functionalized nanodiamond particles are commercially available.

20165159 prh 08 -03- 2018

In one embodiment particle size distribution D90 of the detonation nanodiamond dispersion is not more than 100 nm, such as 1-100 nm, preferably not more than 20 nm, such as 1-20 nm, most preferably not more than 12 nm, such as 1-12 nm. Such particle size distribution can be measured for example by dynamic light scattering method.

The concentration of the nanoparticles is preferably at most 2 wt.%, as calculated from the total weight of the coating. If the amount is more than 2 wt.% wear resistance of the coating deteriorates. More preferably the concentration of the nanodiamond particles is 0.001 wt.%-1 wt.%, even more preferably 0.01 wt.%-1 wt.%, even more preferably 0.01 wt.%-0.8 wt.%, even more preferably

0.01 wt.%-0.4 wt.%, further even more preferably 0.01 wt.%-0.15 wt.%, and most preferably 0.03 wt.%-0.1 wt.%, as calculated from the total weight of the coating. The wear resistance is improved when the concentration is at most 2 wt.%. Additionally, optical properties of the coating can be maintained in applications in which such property is needed.

alcohols such as methanol, ethanol, isopropanol, butanol;

branched diols such as 1,2-propanediol, 1,3-butanediol, 2,3-butanediol, 1,3butanediol, 1,2-pentanediol, etohexadiol, p-menthane-3,8-diol, 2-methyl-2,4pentanediol;

carboxylic acids such as formic acid and acetic acid;

tetrahydrofuran;

propylene carbonate;

lactams such as N-methyl-2-pyrrolidone (NMP) and N-ethyl-2-pyrrolidone (NEP);

20165159 prh 08 -03- 2018 ketones such as acetone and methyl ethyl ketone (MEK) and propylene glycol monomethyl ester acetone (PGMEA);

esters such as methyl acetate and ethyl acetate;

lactones such as gammabutyrolactone (GBL);

Ν,Ν-methylformamide, dimethyl sulfoxide (DMSO);

aromatic solvents such as toluene, xylenes and benzene such as ethyl benzene;

chlorinated solvents such as dichloromethane, trichloroethylene and chloroform;

ionic liquids such as 1-ethyl-3-methylmidazolium chloride, 1-butyl-3-methylmidazolium chloride, 1-ethyl-3-methyl-imidazolium ethylsulfate, 1 -ethyl-3methyl imidazolium diethylphosphate, 1-ethyl-3-methyl-imidazolium dicyanamide, tris-(2-hydroxyethyl)-methylammonium methylsulfate, 1-ethyl-3-methylimidazolium thiocyanate, 1-ethyl-3-methyl-imidazolium tetrafluoroborate, 115 ethyl-3-methyl-imidazolium trifluoromethanesulfonate, 1-ethyl-3-methyl-imidazolium bis (trifluoromethanesulfonyl)imide, 1-ethyl-3-methyl-imidazolium methylcarbonate and 1-butyl-3-methyl-imidazolium methylcarbonate;

or mixtures thereof.

Preferably the organic solvent is selected from a group consisting of GBL, NMP, or a mixture thereof. More preferably the liquid medium is GBL, NMP, or a mixture thereof.

In one embodiment the liquid medium may comprise additionally water, preferably only traces of water. In a preferred embodiment the liquid medium is substantially free of water, preferably the liquid medium contains no water.

20165159 prh 08 -03- 2018

In one embodiment the nanodiamond particles are included into the slurry in form of a suspension or dispersion, preferably dispersion.

In a preferred embodiment the slurry composition consists of a fluoropolymer, nanodiamond particles having zeta potential higher than + 30 mV and an organic solvent or a mixture of organic solvents. In another preferred embodiment the slurry composition is free of coupling agents, such as silane coupling agents, and dispersing agents, such as polyvinylpyrrolidone.

Wear resistance of the fluoropolymer coating is preferably improved when compared to a fluoropolymer coating without nanodiamond particles. Prefer10 ably the wear resistance is improved by more than 20%, preferably more than 40%, more preferably more than 60%, and even more preferably more than 80% when compared to a fluoropolymer coating without nanodiamond particles. The wear resistance is measured as loss of mass by the Taber Abrasion Test, applying standard SFS-EN 13523-16.

Typically, the test is conducted by placing a coated test panel on a rotating disc under a set of two abrasive wheels mounted in parallel and symmetrically on opposite sides of centre rotating in the reverse direction. The loss of material, i.e. difference in mass, in combination with the number of revolutions is a measure of the abrasion resistance. The test can be interrupted after 100, 250,

500, 1000 or more revolutions. The results are expressed either by the mean of mass loss after every specified number of revolutions or the mean number of the revolutions until the substrate is just exposed. The weight loss is measured by applying an analytical balance, accurate to 0.1 mg. The wear resistance is measured at ambient temperature.

Kinetic friction of the fluoropolymer coating is preferably not impaired when compared to a fluoropolymer coating without nanodiamond particles. Preferably the kinetic friction of the fluoropolymer coating is same or reduced as compared to a fluoropolymer coating without nanodiamond particles. With term reduced is meant the kinetic friction is lower than that of a fluoropolymer coat30 ing without nanodiamond particles and said reduced kinetic friction should be considered as a positive and beneficial property. The kinetic friction is measured by Pin on Disk system, following the standard ASTM G99, as Coefficient Of Friction (COF).

20165159 prh 08 -03- 2018

With kinetic friction is meant friction when two surfaces are moving with respect to one another, the frictional resistance being almost constant over a wide range of low speeds. The coefficient is typically less than the coefficient of static friction, reflecting the common experience that it is easier to keep something in motion across horizontal surface that to start it in motion from rest. The coefficient of friction (COF), often symbolized by the Greek letter μ, is a dimensionless scalar value, which describes the ratio of the force of friction between two bodies and the force pressing them together. The coefficient of friction depends on the materials used; for example, ice on steel has a low coefficient of friction, while rubber on pavement has a high coefficient of friction. Coefficients of friction range from near zero to greater than one.

Yet in another embodiment kinetic friction (COF) of the fluoropolymer coating is less than 0.11, preferably less than 0.10, more preferably less than 0.09.

Yet in another embodiment the fluoropolymer coating has an optical trans15 mission higher than 89% as measured at visible wavelength. The visible wavelength ranges between 400 nm - 800 nm. It is also possible to improve the current optically clear fluoropolymer coatings mechanical and thermal properties without deteriorating the fluoropolymer coating properties. As nanodiamonds exhibit very high refractive index, it is also possible to tailor said fluoropolymer coatings refractive index properties. Optically clear fluoropolymer coating applications include but are not limited to dirt-repellant coatings, anti-reflective coatings, photo mask covers, dielectric coatings for semiconductors, protective coatings on steel, building concrete and glass structures, greenhouses, solar cells, interior design, wearable textiles, leather, carpets, seats and linen, hats, gloves, ties, handbags, surgical gowns, luggage, sportswear, heavy duty water repellency on filters, partitions and tents.

The fluoropolymer coating is obtained by drying, or curing, or drying and curing the slurry composition. The drying and the curing may occur simultaneously, or first drying and subsequently curing. After the drying and/or curing the formed coating is free of the liquid medium.

In another aspect, there is also provided a use of the slurry composition of the present invention for production of a fluoropolymer coating.

20165159 prh 08 -03- 2018

There is also provided a method for producing a fluoropolymer coating comprising at least one fluoropolymer and nanodiamond particles in an amount of at most 2 wt.% having zeta potential higher than + 30 mV, wherein a slurry composition comprising at least one fluoropolymer, nanodiamond particles in an amount of at most 2 wt.% having zeta potential higher than + 30 mV and a liquid medium comprising an organic solvent or a mixture of organic solvents is dried, or cured, or dried and cured to produce the fluoropolymer coating. Preferably the fluoropolymer coating and the slurry composition are according to the present invention.

The drying and curing may occur simultaneously, or first drying and then curing. The drying can be any suitable drying method known by a skilled person, such as drying at elevated temperature. The curing can be any suitable curing method known by a skilled person, such as curing/baking at elevated temperature, IR and UV.

The slurry composition can be applied both on metallic and non-metallic surfaces such as ceramics, plastic, leather, glass, concrete, wood based material, textile and the like. The slurry composition can be applied as single coating layer or as a system of plural coatings. One way of manufacturing fluoropolymer coatings is applying the slurry composition as a spray coat. In such an approach said slurry composition is sprayed on the surface, the coating being cured preferably by baking it at selected temperature. The slurries can also be applied on a substrate by coil method, by dipping or spinning, but with also other methods.

In a preferred embodiment the method for producing the fluoropolymer coating comprises (i) applying the slurry composition on a metallic or non-metallic surface, preferably by spraying, by coil method, by dipping or by spinning; and (ii) drying and/or curing the slurry composition to produce the fluoropolymer coating.

Preferably the slurry composition is applied by spraying and cured by baking it at an elevated temperature suitable for curing the composition.

Yet in another aspect, there is also provided a coated article, wherein at least a part of at least one surface of the article is coated, and wherein the coating comprises the fluoropolymer coating according to the present invention.

20165159 prh 08 -03- 2018

The coated article is obtainable by coating at least a part of at least one surface of an article with the slurry composition of the present invention and drying and/or curing the slurry composition to form the fluoropolymer coating according to the present invention on the surface.

Hereafter, the present invention is described in more detail and specifically with reference to the examples, which are not intended to limit the present invention.

Examples

Materials

The applied fluoropolymer material was Whitford commercial polytetrafluoroethylene (PTFE) coating slurry Xylan 1010. Said product is comprised of 26.9 wt.% solid materials, including PTFE, binder materials and proprietary fillers.

Xylan 1010 product is applied as one-coat solution, and this coating doesn’t require the use of primer coating before its application. The slurry contained solvents include N-methylpyrrolidone (NMP), gamma-butyrolactone (GBL), xylene and ethylbenzene.

The applied nanodiamond material was Carbodeon Ltd Oy produced uDiamond Amine D dispersion in GBL (Gamma-butyrolactone) solvent (3wt.% nanodiamond content). Said material zeta potential exceeds + 50 mV and applied product lot particle size distribution (as measured from 3 wt.% nanodiamond dispersion) was less than 15 nm (D90). The degree applied nanodiamond material amine surface termination was determined by measuring the nanodiamond material contained surface nitrogen with Kjeldahl method and exceeded the specified value of 2000 mg/kg of nanodiamonds. Particle size and zeta potential measurements were carried out with Malvern Zetasizer Nano ZS tool.

Preparation of nanodiamond containing fluoropolymer slurries (according to the present invention)

The nanodiamonds were mixed to fluoropolymer slurry by shaking to create nanodiamond containing fluoropolymer composition slurries. The nanodiamond concentrations were adjusted to prepare the nanodiamond containing

20165159 prh 08 -03- 2018 fluoropolymer coatings with the following nanodiamond concentrations: 0.05 wt.%, 0.1 wt.%, 0.2 wt.% and 0.5 wt.%. The concentrations were calculated from below:

_x . ITirary c_composite (wt. %) =----100% m-ND I m_FP ^-NDdispersion^-NDdispersion . _nnn/ —- 1UU% ^-NDdispersion^NDdispersion + ^-FPslurry^FPslurry

The fluoropolymer slurry had a theoretical solid content of 26.9% (CFPsiurry) and the coating was calculated to form from the solids only. Each slurry sample mass was 150 g per concentration (mFPsiun-y). The concentration of the original nanodiamond dispersion in GBL (CNDdispersion) was 3.0wt.%

The slurry sample preparation was carried out as follows: the 3 wt.% nanodiamond dispersion in GBL was diluted into 1.5 wt.% nanodiamond dispersions by diluting applied nanodiamond dispersion with additional GBL solvent. As initial step, the employed Xylan 1010 fluoropolymer slurry samples were subjected to shaking by applying Edmund BOhler KS-15 shaking device for 60 minutes period and Heidolph RZR 2061 control-blade mixer for a period of 60 minutes, each. This was followed by administrating selected volume of diluted, 1.5 wt.% uDiamond Amine D in GBL nanodiamond additive with Brand accu-jet pro electronic pipette controller and mixing resulting slurries with IKA RW 11 B Lab-Egg blade mixer, by creating a vortex during mixing.

Spraying and curing of the composite coatings

The applied substrates were made of 4 mm aluminium plates sizing 10 cm x 10 cm. The substrates were degreased and sand-blasted prior to coating procedure. The reference and nanodiamond containing fluoropolymer slurry samples according to the present invention were gently shaked by hand before the coating. The coatings were prepared by manual spraying and curing by thermal treatment according to Table 1.

Table 1: Curing: thermal treatments

	Temperature (°C)	Time (min)
Drying 1	80	15
Drying 2	100	15
Drying 3	120	15
Curing	230	25

20165159 prh 08 -03- 2018

Wear resistance measurements

The wear resistance is measured as loss of mass by the Taber Abrasion Test, 5 applying standard SFS-EN 13523-16. The prepared samples (reference and samples according to the present invention) wear resistances were measured by using commercial Taber Abraser 5135 by applying 250 g load and CS-10 discs. The prepared coatings were initially subjected to a 100 cycle Taber screening test. The Taber Wear Indexes (TWI’s) for those initial 100 cycles are depicted in Figure 1. The data is indicating that the coating wear resistance is improved most with the lowest nanodiamond additive concentrations and adding more of zeta positive nanodiamond additive results in lower performance in terms of wear resistance.

As subjecting both reference sample (without any nanodiamond additive) and coating samples containing 0.05 and 0.1 wt.% of nanodiamond particles according to the present invention for 500 and 1000 cycles Taber Wear Index measurement, it was evident that the highest improvement in wear resistance was gained with the lowest amount of nanodiamond additive (0.05 wt.%) and that these results were concordant regardless the applied number of wear cycles. If applying only 0.05 wt.% of nanodiamond additive, the composite coating wear resistance is almost doubled (90.5%) as compared to standard sample (Reference sample TWI: 28 mg; 0.05 wt.% nanodiamond composite sample TWI: 14.7; 1000 cycles). Applying double concentration of nanodiamonds (0.1 wt.%) gives a 67% improvement in wear resistance ((Reference sample TWI: 28 mg; 0.05 wt.% nanodiamond composite sample TWI: 16.8;

1000 cycles). The Taber Wear Indexes (TWI’s) for 500 and 1000 cycles are depicted in Figure 2.

Kinetic friction measurements

The kinetic friction properties were tested with ball-on-plate method with CSM

Instruments Tribometer, following the standard ASTM G99, as Coefficient Of Friction (COF). The tests were carried out at room temperature (21.8 °C), with air humidity of 44%. The applied counterpart was a 6 mm steel ball. Rotation of the plate resulted in speed of 3.9 cm/s and the normal force was 3 N. The results are presented in Figure 3.

It could be shown that the nanodiamond addition does not alter or is improving the solvent based fluoropolymer coating kinetic friction properties slightly. The same applies for all the tested nanodiamond containing fluoropolymer coatings, containing 0.05 wt.%, 0.1 wt.%, 0.2 wt.% and 0.5 wt.% of nanodiamond particles, as calculated from the cured coating solids.

Claims

A slurry composition comprising at least one fluoropolymer, nanoparticle particles and a liquid medium, characterized in that said nanoparticle particles have a zeta potential higher than +30 mV.

And said liquid medium contains an organic solvent or mixture of organic solvents.

The slurry composition of claim 1, wherein the nanoparticle particles have a zeta potential greater than +35 mV, more preferably higher than +40 mV, and even more preferably higher than +50 mV.

10

The slurry composition according to claim 1 or 2, wherein the content of nanoparticle particles is up to 2% by weight, preferably 0.001% by weight to 1% by weight, more preferably 0.01% by weight to 1% by weight, more preferably 0.01% to 0.8% by weight, and most preferably 0.01% by weight - 0.4% by weight of the slurry composition

15 based on the dry matter content.

The slurry composition according to any one of claims 1 to 3, wherein the organic solvent is selected from the group consisting of alcohols such as methanol, ethanol, isopropanol, butanol;

linear aliphatic diols such as ethylene glycol, 1,3-propanediol,

1,4-butanediol, 1,5-pentanediol, 1,8-octane diol;

branched diols such as 1,2-propanediol, 1,3-butanediol, 2,3-butanediol, 1,3-butanediol, 1,2-pentanediol, etohexadiol, pmentane-3,8-diol, 2-methyl-2,4-pentanediol ;

carboxylic acids such as formic acid and acetic acid;

Tetrahydrofuran;

propylene carbonate;

lactams such as N-methyl-2-pyrrolidone (NMP) and N-ethyl-2-pyrrolidone (NEP);

20165159 prh 08 -03-2018 ketones such as acetone and methyl ethyl ketone (MEK) and propylene glycol monomethyl ester acetone (PGMEA);

esters such as methyl acetate and ethyl acetate;

lactones such as gamma-butyrolactone (GBL);

5?,? -Methylformamide, dimethylsulfoxide (DMSO);

aromatic solvents such as toluene, xylenes and benzene such as ethylbenzene;

chlorinated solvents such as dichloromethane, trichlorethylene and chloroform;

10 ionic liquids such as 1-ethyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium ethyl sulfate, 1 ethyl 3-methylimidazolium diethyl phosphate, 1-ethyl-3-methylimidazole, 2-hydroxyethyl) -methylammonium methylsulfate, 1-ethyl-3-methylimidazolium thiocyanate, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium trifluoromethanesulfonimide, 1-ethylimidazolide , 1-ethyl-3-methylimidazolium methyl carbonate and 1-butyl-3-methylimidazolium methyl carbonate;

or mixtures thereof.

20 5. any one of claims 1 to 4 slurry composition, wherein the fluoropolymer comprises polyvinyl fluoride, polyvinylidene fluoride, polytetrafluoroethylene, polychlorotrifluoroethylene, perfluoroalkoxy, fluorinated ethylene, polyeteenitetrafluorieteenin, polyeteeniklooritrifluorieteenin, perfluoro elastomers, fluorocarbon, perfluoropolyether, perfluorisulfonihapon, fluora25 tun polyimide, perfluoripolyoksetaanin of these polymers or two or more of mixture.

The slurry composition according to any one of claims 1 to 5, wherein the nanoparticle particles are amine-functionalized nanoparticle particles, hydrogen-functionalized nanoparticle particles, hydroxyl-functionalized nano30 diamond particles, or a mixture thereof, preferably amine-functionalized nanotime particles.

20165159 prh 08 -03- 2018

Use of a slurry composition according to any one of claims 1 to 6 for the preparation of a fluoropolymer coating.

8. A fluoropolymer coating made from a solvent-based fluoropolymer slurry, characterized in that the fluoropolymer coating contains at least one fluorine polymer and nanoparticle particles in an amount of up to 2% by weight, and the nanoparticle particles have a zeta potential higher than +30 mV.

The fluoropolymer coating of claim 8, wherein the nanoparticle particles have a zeta potential greater than +35 mV, more preferably higher than +40 mV, even more preferably higher than +50 mV.

The fluoropolymer coating according to claim 8 or 9, wherein the amount of nanoparticle particles in the coating is up to 1% by weight, preferably from 0.001% to 1% by weight, more preferably from 0.01% to 1% by weight, even more preferably from 0.01% to 0.8% by weight, and most preferably 0 , 01% by weight to 0.4% by weight

15 based on the total weight of the coating.

The fluoropolymer coating according to any one of claims 8 to 10, wherein the fluoropolymer comprises polyvinyl fluoride, polyvinylidene fluoride, polytetrafluoroethylene, polychlorotrifluoroethylene, perfluoroalkoxy copolymer, fluorinated ethylene propylene, polyethylene tetrafluoroethylene, polyethylene tetrafluoroethylene,

20 perfluoro elastomer, fluorocarbon, perfluoropolyether, perfluorosulfonic acid, fluorinated polyimide, perfluoropolyoxetane, or mixtures of two or more of these polymers.

The fluoropolymer coating according to any one of claims 8 to 11, wherein the nanoparticle particles are amine-functionalized nanoparticle particles,

25 hydrogen-functionalized nanoparticle particles, hydroxyl-functionalized nanoparticle particles, or a mixture thereof, preferably amine-functionalized nanoparticle particles.

The fluoropolymer coating according to any one of claims 8 to 12, wherein the fluoropolymer coating has an improved wear resistance of more than 20%, preferably more than

40%, more preferably more than 60%, and even more preferably more than 80% compared to a non-nanoparticulate fluoropolymer coating.

The fluoropolymer coating according to any one of claims 8 to 13, wherein the kinetic friction of the fluoropolymer coating is the same or reduced as compared to the fluoropolymer coating without nanoparticle particles.

The fluoropolymer coating according to any one of claims 8 to 14, wherein the fluoropolymer coating has an optical transmission of greater than 89% as measured at an apparent wavelength.

Coated article, characterized in that at least part of the at least one surface of the article is coated, and in that the coating comprises a fluoropolymer coating according to any one of claims 8 to 15.