WO2002020676A1

WO2002020676A1 - Coating compositions containing perfluoropolyether surfactants

Info

Publication number: WO2002020676A1
Application number: PCT/NL2001/000662
Authority: WO
Inventors: Maarten Johannes Krupers; Franky Flory Vercauteren; Renz Jeroen Van Ee
Original assignee: Nederlandse Organisatie Voor Toegepast-Natuurwetenschappelijk Onderzoek Tno
Priority date: 2000-09-07
Filing date: 2001-09-07
Publication date: 2002-03-14
Also published as: AU2001294391A1

Abstract

The present invention relates to a coating composition, comprising: at least one polymeric binder; at least one dispersion medium; at least one (per) fluorosurfactant; and optionally one or more further components of coating compositions known per se; which composition is characterised in that said (per) fluorosurfactant is a perfluoroether surfactant, and in particular a perfluoropolyether surfactant. The coating composition is preferably in the form of an aqueous dispersion, and may for instance be a paint or coating for household or industrial use, or a specialized coating composition. The coating compositions thus obtained have low surface energy (less than 30 Nm-1, preferably 20 Nm-1, in particular 16-18 Nm-1), excellent physical and/or chemical resistance, and good stability. The coatings can also be cured at low(er) temperatures, compared to conventional PTFE-based coatings.

Description

Coating compositions containing perfluoropolyether surfactants.

The present invention relates to a coating composition comprising a polymeric binder, a dispersion medium and at least one fluorosurfactant.

Such a coating composition is known from the European application 0 070 498, which describes a heat-curable coating composition comprising an aqueous dispersion of an acrylate-based copolymer, which composition is stabilised using a fluorosurfactant.

The dispersion of EP 0 070 498 is prepared by emulsion polymerisation of a suitable monomer mixture in an aqueous medium, preferably in the presence of the fluorosurfactant used. The dispersion thus obtained can be applied to a substrate or surface and is then cured, e.g. for 10-30 minutes at 80-180 °C. The resulting coatings are described as having good flow properties, gloss, elasticity, adhesion, coverage, evenness, weathering resistance and resistance to yellowing.

As the fluorosurfactant, EP 0 070 498 generally mentions fluorosurfactants comprising a perfluoroalkyl residue with 2 to 20 carbon atoms or a perfluoroaralkyl residue with 7 to 30 carbon atoms, such as perfluoroalkylsulfonic acids, perfluoroaralkylsulfonic acids, long chain perfluoroalkanoic acids, perfluoroalkylphosphonic acids, perfluoroalkylphosphonic acids, perfluoroalkylsulfates, perfluoroaralkylsulfates and/or perfluoroalkylphosphates, or mixtures of two or more thereof. More specifically, in the Examples of EP 0 070 498, either perfluorooctylsulfonate or a mixture of perfluorophosphonic acids and perfluorophosphinic acids with 6 to 10 carbon atoms in the alkyl group is used. Thus, EP 0 070 498 does not specifically disclose the use of perfluoro(poly)ether surfactants.

However, during further research by applicant, it was found that by the use of the perfluorosurfactants described in EP 0 070 498, it is not possible to obtain - i.e. in a (commercially) satisfactory manner - coating compositions that can provide final coatings with very low surface energies, e.g. in the range of 20 mNm^"1 or less, and in particular in the range of 10-18 mNm^"1. hi addition, it was found that when linear perfluoroalkanoic acids of fluorinated chain lengths longer than than C₆, and in particular longer than C 8 are used in the preparation of coating compositions, in practice problems may occur with respect to the compatibility of the components used and/or with respect to the stability of the compositions obtained, such as the formation of precipitates, phase separation, and defects of the applied coatings. Also, it may be very difficult to dissolve such long(er) chained perfiuorosurfactants in aqueous media, such as the aqueous media used in the (emulsion or suspension) polymerisation of the coating compositions.

Furthermore, whereas of the long(er) chain fluorosurfactants mentioned in EP 0 070 498, the fluorosurfactants with 6 to 10 carbon atoms used in the Examples of EP 0 070 498 are commercially available, the perfiuorosurfactants described in EP 0 070 498 with even longer chain lengths - e.g. of C12, C16, C20 or oligomeric species or more - are not commercially available and also are difficult to prepare synthetically.

WO 00/40633 describes a coating composition for manufacturing coatings having a low surface energy as well as a method for preparing such a coating composition. The coating compositions described in this document comprise a curable coating system consisting of a cross-linkable resin and a cross-linking agent, as well as a functional fluorine compound capable of reacting with the cross-linkable resin and/or the cross-linking agent. The two- component coating compositions as described in WO 00/40633 may be used to coat a substrate, provided that curing conditions are applied under which cross-linking will occur between the cross-linkable resin and the cross linking agent as well as covalent binding between the fluorine compound and the cross-linkable resin and/or the cross linking agent. EP-A 0 361 346 describes coating compositions comprising a film forming material and a fluoroalkyl ether having an amide bond. It is observed in EP-A 0 361 346 that the coating compositions described therein may suitably be used in the preparation of coatings that display durable water and oil repellency as well as lubricity. It is an object of the invention to provide a coating composition that can be used, i.e. dried, to provide a coating with the favourable properties described herein, and in particular with a low surface energy, good non-stick properties and good physical and/or chemical resistance. More specifically, it is an object of the invention to provide such a coating composition that (also) has the stability and the further properties desired/required for marketing said composition as a commercial product, and that can readily be prepared without any problems of solubility and/or of compatibility.

Currently, coatings with low surface energies are applied using coating compositions based upon polymeric binders that are highly - and usually fully - substituted with fluorine atoms. Of these so-called (per)fluorocarbon polymers, polytetrafluoroethylene (PTFE,

Teflon^®) is most commonly used.

However, the use of PTFE in coating compositions has a number of disadvantages. For instance, PTFE is relatively expensive and difficult to process; also, it has a high melting point, hi addition, PTFE-based coating layers are usually coated onto a substrate or surface by applying an aqueous dispersion of small PTFE particles. However, after removal/evaporation of the aqueous phase, this generally does not lead to a contiguous, uniform film/coating, but rather to a layer of PTFE droplets on the substrate. To convert these droplets to a uniform coating, the substrate with the PTFE-layer applied thereon has to be sintered - e.g. at temperatures of 380-400 °C - which means that known PTFE-based coatings cannot be applied on temperature-sensitive substrates, but only e.g. on metallic substrates. Thus, it is a further object of the invention to provide a coating composition that can be used to impart upon a surface or substrate properties comparable to the favourable properties provided by known PTFE-based coating compositions/coatings, but without the disadvantages of PTFE-based coating compositions mentioned above. More specifically, it is an object of the invention to provide such a coating composition that is cheaper and easier to prepare, to process and/or to apply than known fluorocarbon-based coating compositions, and that also does not require high sintering or curing temperatures (i.e. for film formation), so that it can (also) be applied onto temperature- sensitive substrates. It has now been found that the mentioned objects can be achieved by the use, in (the preparation of ) a coating composition comprising a polymeric binder and a dispersion medium, of at least one perfluoroether surfactant, and in particular of at least one perfluoropolyether surfactant.

More in particular, it was found that by the use of at least one perfluoro(poly)ether surfactant, it is possible to prepare/formulate a coating composition that can be used to provide a final coating with a surface energy of less than 20 Nm^"1, and in particular with a surface energy in the range of 10 to 18 mNm^"1, without any problems of stability, compatibility and/or solubility of the coating composition thus obtained.

Also, it was found that by the use of at least one perfluoro(poly)ether surfactant, it is possible to provide a coating composition and/or a final coating with (surface) properties comparable to those provided by known fluoropolymer-based coatings.

More specifically, and with particular advantage, it was found that by the use of at least one perfluoro(poly)ether surfactant, it is possible to attain these favourable properties without the use of a (per)fluorinated polymeric binder such as PTFE. Accordingly, the present invention in its broadest sense now makes it possible to attain the favourable (surface) properties of known PTFE-based coatings with any desired polymeric binder or combination of polymeric binders, including but not limited to conventional binder systems, such as poly(meth)acrylics and other vinylics. Also, the present invention in its broadest sense now makes it possible to impart upon conventional coating compositions known per se one or more of the favourable properties, i.e. by the use of at least one perfluoro(poly)ether in (the preparation of) such a coating composition, for instance by adding one or more perfluoro(poly)ether surfactants to said coating composition and/or by replacing (at least part of) the conventional surfactants used in the preparation of these coating compositions with at least one (per)fluoropolyether surfactant described below.

Thus, in its broadest sense, the present invention now makes available an entire range of different coating compositions, from paints intended for household use to industrial coatings and/or to speciality products, which can all be used to provide coatings with low surface energies, non-stick properties and good physical and/or chemical resistance. Preferably, however, the invention is used to provide coating compositions based upon aqueous systems, e.g. aqueous emulsions or dispersions, for instance based upon (meth)acrylate binders, polyurethanes, polyisocyanates and/or epoxy resins, as described in more detail below.

Accordingly, in a first aspect, the invention relates to a coating composition which comprises: at least one polymeric binder; a suitable dispersion medium, which is preferably an aqueous dispersion medium, such as water or a mixture of water and one or more water-miscible solvents; at least one (per)fluorosurfactant; and optionally - one or more further components of coating compositions known per se; characterised in that said (per)fluorosurfactant is a (per)fluoroether surfactant, and in particular a perfluoropolyether surfactant.

In another aspect, the invention relates to the use of at least one perfluoroether surfactant, and in particular of at least one perfluoropolyether surfactant, in (the preparation of) a coating composition.

The invention also relates to a coating, formed from a coating composition as described above; and to a substrate or surface that has been coated with a coating composition as described above.

The invention also relates to a method for preparing a coating composition of the invention, said method generally comprising at least one step of polymerising a suitable monomer or mixture of monomers to form a polymeric binder, in which said polymerisation is carried out in a suitable (dispersion) medium - which again preferably is an aqueous medium such as water or a mixture of water and one or more water-miscible solvents - and in the presence of at least one perfluorosurfactant, characterised in that said perfluorosurfactant is a perfluoroethersurfactant, and in particular a perfluoropolyether surfactant.

Other aspects and embodiments will become clear from the further description below.

It is an important object of the present invention to provide coating compositions that are capable of forming a coating on a substrate without the need to cure said composition at highly elevated temperatures, i.e. temperatures exceeding 100°C. This an important difference between the coating compositions according to the present invention and the coating compositions disclosed in WO 00/40633. Hence in a particularly preferred embodiment the present coating composition does not include a curable coating system consisting of a cross- linkable resin and a cross-linking agent as well as a (perfluorosurfactant capable of reacting with the cross-linkable resin and/or the cross-linking agent when subjected to curing. In an even more preferred embodiment the coating composition does not comprise a cross-linkable resin which is capable of reacting with the (perfluorosurfactant when the composition is subjected to curing conditions.

The perfluorosurfactant used in the invention can most generally be described as a (per)fluorocarbon compound - i.e. a compound consisting essentially of carbon atoms and fluorine atoms - which fluorocarbon compound comprises at least one ether bond and at least one covalently attached (functional) group which confers surfactant properties to the fluorocarbon compound. Some non-limiting examples of such a functional group - also referred to hereinbelow as "ionizable group R" - are a -COOH group, a phosphonic acid group, a phosphinic acid group, a sulfonic acid group, an amino-group, an amine-group, or another group which can be ionized, e.g. in an aqueous medium and depending upon the pH. hi particular, the perfluoroether surfactant used in the invention can be described as a linear or branched fluorocarbon compound comprising n carbon atoms - in which n is an integer of between 3 and 500 - and (2n+l) fluorine atoms, which further contains at least one oxygen atom bound to two of the carbon atoms so as to form an ether bond (i.e. a bond C - O - C), and in which at least one of the fluorine atoms is replaced by an ionizable group R as defined above.

Usually, the total number of carbon atoms n of the perfluoroether used in the invention will be no more than 300, in particular no more than 150, and more in particular no more than 75. Also, usually, the amount of carbon atoms n will be more than 3, in particular more than 4, and more in particular more than 9.

More in particular, (in) the perfluoroether surfactant used: comprises a total of between 4 and 150 carbon atoms, and in particular between 9 and about 60 carbon atoms; and/or - comprises at total of between 1 and 150, and more preferably between 1 and 75, oxygen atoms/ether bonds; and/or

- only one of the fluorine atoms is replaced by an ionizable group R, so that the fluoroether surfactant comprises n carbon atoms, (2n) fluorine atoms, and one ionizable group R; or a combination of two or more of such perfluoroether surfactants.

Usually, in the perfluoroether surfactants used in the invention, the ratio of [the total number of oxygen atoms in the perfluoroether group] divided by [total number of carbon atoms in the perfluoroether group] will be less than 1. For instance , for the preferred perfluoropolyethers mentioned below, this ratio may be in the range of between 0.7 and 0.1, and in particular between 0.5 and 0.25, for instance about 0.5 for a perfluoropolyether group made up mainly of (CF₂-CF₂-O)-units; or about 0.33 for a perfluoropolyether group made up mainly of (CF(CF₃)-CF₂-O)-units. However, this ratio may also be much smaller than 0.1, depending upon the total number of oxygen atoms/ether bonds that are present in the perfluoropolyether group. Also, in the perfluoroether surfactants of the invention, the ionizable group R may be

(covalently) linked directly to the perfluoroether group, or via a suitable linking group, which is preferably a linear or branched perfluoroalkyl group with no more than 6 carbon atoms, and in particular only 1, 2 or 3 carbon atoms, such as a -CF₂- , CF₂-CF₂- or C(CF )-CF₂- group. Besides such a perfluoroalkyl group, this linking group may also be another suitable group, such as a hydrocarbon residue or an SO or SO2 group. In a preferred embodiment of the invention the (perfiuorosurfactants employed are different from the amide bond containing (perfiuorosurfactants disclosed in EP-A 0 361 346, i.e the (per)fluorosurfactant applied in accordance with the invention, preferably does not contain an amide bond. Preferably, the perfluoroether surfactant used at least comprises a ( linear or branched) "backbone" of between 3 and about 150 carbon atoms, preferably between 3 and about 75 carbon atoms, in which:

- said backbone is substituted with at least one, and preferably only one, ionizable group R; more preferably at (only) one end of said backbone, optionally via a linker group as mentioned above;

- said backbone is interrupted with between 1 and about 150, and preferably between 2 and about 75 oxygen atoms/ether bonds;

- said backbone may or may not be substituted with one or more "fluorocarbon residues", by which is generally meant herein a perfluoroalkyl groups with nor more than 4 carbon atoms, such as -CF₃ or -CF₂CF₃.

Again, in these preferred perfluoroether surfactants, the ratio of [the total number of oxygen atoms in the perfluoroether group] divided by [total number of carbon atoms in the perfluoroether group] will be less than 1 , and may in particular be in the range of 0.7 and 0.1 (or less), and more in particular in the range of 0.5 and 0.25.

Preferably, in the invention, a perfluoropolyether surfactant is used, by which is generally meant a perfluoroether surfactant as described above in which the "backbone" is formed by a perfluoropolyether residue. Such a perfluoropolyether surfactant may for instance be represented by formula (I) below:

F - [ (CQ₂)_P - O ]_q- (CQ₂)_r - CQ₂ -R (I)

in which:

- each group Q is independently a fluorine atom or a fluorocarbon residue as defined above; - R is an ionizable group as defined above;

- p is an integer of between 1 and 3, and is preferably 1 or 2;

- q is an integer such that the product [p times q] is between 1 and 75, and preferably between 4 and 60; - r is 0 or an integer between 1 and 3, and is preferably 0 or 1; or a combination of two or more such perfluoropolyether surfactants.

Some preferred, but non-limiting examples of suitable perfluoro(poly)ether surfactants are given in Formula's II and III below:

F - [ CF(CF₃) -CF₂-O)]_n - CF₂ - CF₂ - COOH (II, in which n = > 3)

F - [ CF(CF₃) -CF₂-O)]₃ - CF(CF₃)- COOH (III)

These and other suitable perfluoro(poly)ether surfactants may be prepared synthetically and/or are commercially available, for instance from DuPont and Ausimont

under the trade names Krytox^® and Galden^® MF Series, respectively; of which Krytox 157

FSL and Galden MF 300, MF 310, MF 420, MF 201, MF 418, MF 430, MF 431 and MF 103 are some particularly preferred but non-limiting examples. In the art, these commercially available perfluoro(poly)ether surfactants have ter alia been used as lubricants; they have not yet been proposed for use in coating compositions.

Also, preferably, the perfluoro(poly)ether surfactants used in the invention will have a molecular weight of between about 350 and about 5000, preferably between about 350 and about 2500. The perfluoro(poly)ether surfactants mentioned above will generally be used in amounts of between 0.01 and 10 wt.%, and in particular in amounts of between 0.1 and 4 wt.%, of the total coating composition.

Also, suitable mixtures of two or more of the perfluoro(poly)ether surfactants mentioned above may also be used.

Generally, by the use of one or more perfluoro(poly)ether surfactants as defined hereinabove in (the preparation of) a coating composition, one or more of the following advantages will be obtained: the coating compositions can be used to provide final coatings with low surface energies, i.e. of 20 mNm^"1 or less, and in particular of between 10 and 18 mNm^"1;

- the coating compositions can be used to provide coatings with excellent non-stick properties (which may also depend on the matrix polymer used); the coating compositions can be used to provide coatings with excellent physical and/or chemical resistance (which again may also depend upon the matrix polymer used); - the coating compositions of the invention can be cured at relatively low temperatures, e.g. of between RT (e.g. about 20 °C) and 100 °C ;

- the coating compositions of the invention will usually be cheaper and easier to prepare/formulate than conventional PTFE-based coating compositions; the coating compositions will have good stability, with for instance a shelf life of more than 6 months, preferably more than 18 months.

Also, as already mentioned above, another major advantage of the invention is that the perfluoro(poly)ether surfactants can be incorporated into almost any desired coating composition, including but not limited to any conventional coating composition known per se, as long as the perfluoro(poly)ethersurfactant is compatible with the further components of such a composition. As such, the perfluoro(poly)ether surfactants may be used in addition to, and/or may be used to replace part and/or all of, the surfactant(s) commonly used in (the preparation of) such coating compositions known per se.

Thus, by means of the invention, an entire range of coating compositions can be provided, which compositions will have one or more of the advantages mentioned above and which in addition will usually have one or more properties that have specifically been chosen/adapted for the intended final use of the coating composition.

For instance, the invention may be used in the preparation/manufacture of: paints or other coating compositions for household use paints or other coating compositions for industrial use, including but not limited to anti- fouling coatings, heavy duty industrial coatings, coatings for OEM applications; specialised coating compositions including but not limited to indoor and outdoor decoration paints, for the do-it-yourself and professional market.

In this respect, it will be clear to the skilled person that such a range of different coating compositions cannot be provided by the use of a PTFE-based binder system. hi accordance with the above, the invention is not particularly limited as to the type of coating composition into which the perfluoro(poly)ether surfactants are incorporated, e.g. the type of binder(s), dispersion medium and/or further components that are present in said coating composition; nor in the amounts thereof, as long as a practicable coating composition suited for the intended final use is obtained. In a particularly preferred embodiment of the present invention the coating composition is capable of forming a coating on a solid substrate as a result of drying at temperatures below 100°C. The coating obtained after drying will typically display a surface energy of less than 30 Nm^"1, preferably a surface energy of less than 20 Nm^"1. Especially preferred are coating compositions that can be dried at a temperature between 5 and 80°C to form a coating with such a low surface energy. The present coating compositions are generally capable of forming a coating on a substrate under the aforementioned drying conditions without the occurrence of any cross-linking.

For instance, the polymeric binder may be any polymeric binder for coating compositions known per se, or any suitable combination of such polymeric binders. Some particularly preferred, but non-limiting, polymeric binders include:

- polymeric binders based upon one or more unsaturated monomers such as acrylate monomers, methacrylate monomers, vinyl monomers, or mixtures thereof;

- polyurethanes; epoxyresins; - alkyds; or suitable combinations thereof.

These binders will generally be used in conventional amounts, e.g. of between 10 and 90 wt.%, and in particular between 20 and 70 wt.%, of the total coating composition.

The dispersion medium may be any suitable medium (e.g. liquid) that can be used to keep the components of the coating composition is dispersion, and that can be used as such in the preparation/formulation of a coating composition (i.e. dispersion). Usually, an aqueous dispersion system will be used, by which is generally meant water or a mixture of water and one or more water-miscible solvents such as e.g. an alcohol. In a particularly preferred embodiment of the invention the coating composition contains from 25 to 90 wt.% water, more preferably from 30 to 90 wt.% water and most preferably from 40 to 80 wt.% water.

Even more in particular, the coating compositions of the invention may be in the form of an aqueous emulsion or dispersion, with aqueous emulsions being particularly preferred, especially in the form of an essentially fully water-borne system.

The dispersion medium will generally comprise between 30 and 90 wt.%, and in particular between 80 and 40 wt.%, of the total coating composition. The coating compositions of the invention may further contain one or more further components for coating compositions known per se, in amounts known per se, depending upon the desired properties/characteristics of the final composition and the intended use thereof. Such components may for instance include, but are not limited to:

- pigments such as TiO₂, which may for instance be added in amounts between 0 and 60 wt.%;

- fillers such as clay, which may for instance be added in amounts of between 0 and 40 wt.%; - further additives such as rheology modifying additives (including but not limited to thickeners), flow modifying additives, levelling additives, wetting agents, and anti- fungicidal additives, which may for instance be added in amounts of up to 10 wt.%; or a suitable combination thereof, in which the wt.% are based on the total composition.

Preferably, the amount of further components (i.e. pigments, fillers and further additives) will make up no more than 60 wt.% of the total coating composition.

The perfluoro(poly)ether surfactant(s), the binder(s) and the one or more further components used should be compatible with each other and with the dispersion medium used. Also, the components should be such that a coating formulation is obtained that is stable enough to be stored until its final use, e.g. at least 6 months, and preferably > 18 months. As mentioned above, such compatibility and/or stability cannot be achieved when conventional perfluoroalkyl or perfluoroaralkyl surfactants are used, such as the surfactants described in EP 0 070 498.

Also, according to the invention, the presence of at least one surfactant, stabiliser, emulsifier or dispersant - i.e. in addition to the at least one perfluoro(poly)ether surfactant - is not excluded, although the presence thereof is not be required. If one or more further surfactants are present in addition to the one or more perfluoro(poly)ether surfactants, the total amount of surfactants (including perfluoro(poly)ether surfactants) is preferably between 0.01 and 10 wt.%, and in particular between 0.5 and 5 wt.% of the total composition.

Generally, the coating compositions of the invention can be prepared by mixing the abovementioned components in the amounts indicated. However, as mentioned above, the coating compositions of the invention are preferably in the form of an aqueous emulsion or dispersion, the preparation of which will now be discussed in more detail.

Generally, the aqueous emulsions/dispersions of the invention are prepared by a method that at least comprises the polymerisation, in water or a mixture of water and one or more water-miscible solvents and in the presence of at least one perfluoro(poly)ether surfactant as described above, of a suitable monomer or a suitable mixture of monomers, such as one or more monomers chosen from acrylate monomers, methacrylate monomers, or vinyl monomers.

Preferably, this polymerisation is carried out by emulsion polymerisation or suspension polymerisation, with emulsion polymerisation being particularly preferred, as it may lead to less coagulate being fonned during polymerisation, and leading to smaller dispersed particle sizes favouring the resulting paints quality .

Generally, the polymerisation will also involve the use of a suitable initiator, such as 2,2'-azo-bis-wo-butyronitrile (AIBN) for suspension polymerisation; or ammonium persulfate or potassium persulfate for emulsion polymerisation.

The polymerisation mixture may optionally also contain one or more further components for such polymerisation(s) known per se, such as e.g. cosolvents and catalysts.

The starting mixtures for the polymerisation may be prepared by mixing/adding the monomer(s), the perfluoro(poly)ether surfactant(s), the one or more further components and the initiator with/to the aqueous medium in a manner known per se and in suitable amounts. For instance, such a polymerisation mixture may contain:

- monomer(s): 10 - 60 wt.%

- medium: 30 - 90 wt.% - perfluoro(poly)ether surfactant(s): 1 - 5 wt.%

- initiator 0.5 - 5 wt %> to a total of 100 wt.% of the above components. Such polymerisation mixtures containing at least one perfluoro(poly)ether surfactant as described above also form a further aspect of the invention. After mixing of the starting components, the monomers are polymerised in a manner known per se, for instance, suitable polymerisation conditions may for instance comprise: a temperature of between 50 and 90 °C, and in particular between 60 and 80 °C; and a time of 30 to 720 minutes, in particular 60 to 360 minutes; and optionally under stirring or agitation. The polymerisation is usually carried out until (essentially) full conversion. Usually, the resulting emulsion or dispersion will have a mean particle size of between 10 and 10000 nm, and in particular between 100 and 1000 nm.

After polymerisation is completed, the emulsions/dispersions may be formulated into the final coating compositions, e.g. by adding the pigments, fillers and further components mentioned above. Optionally, the coating compositions of the invention may also be packaged in a suitable container, such as a tin or a drum.

Although the invention is not limited to any specific explanation or mechanism of the manner in which the use of the perfluoro(poly)ether surfactants according to the invention leads to the advantages indicated above, it is assumed that the perfluoro(poly)ether surfactants may function as schematically shown in Figure 1. As can be seen from this Figure, the perfluoro(poly)ether surfactants used in the present invention may be considered as comprising a polar "functional head" and an apolar fluorocarbon "tail". During the (emulsion) polymerisation, the surfactants stabilise the dispersion, as shown in "Step 1". Thereafter, upon application of the coating and film formation, the perfluoro(poly)ether surfactants migrate to the coating/air-interface, to provide a final coating in which the apolar fluorocarbon tails of the surfactants "stick out" of the coating layer, thus forming a "boundary layer" of fluorocarbon groups as schematically shown in "Step 2". This layer of fluorocarbon groups provides the coating with surface properties comparable to those provided by fluorocarbon polymers in conventional fluorocarbon coatings.

In this respect, it should be noted that it was very unexpected that during the emulsion polymerisation, the fluorocarbon "tails" are incorporated into the polymerised particles so as to stabilise the dispersions. This was considered unlikely because in general the perfluorinated tails of the surfactant are highly incompatible with common organic moieties, i.e. aliphatic, ester, etc..

In addition, it was surprisingly found that during application of the coating onto a substrate, the perfluoro(poly)ether surfactants migrate to the coating/air-interface so as to provide a "boundary layer" of perfluoro(poly)ether "tails". This migration, with the advantages it entails, has not yet been described or suggested in the art. Furthermore, in both the above respects, it may be that the use of surfactants comprising a perfluoro(poly)ether "tail" may have advantages over the use of surfactants having a linear fluorocarbon tail (i.e. without ether-bonds (and pendant side groups such as - CF2-CF3 and in particular -CF3), such as the perfiuorosurfactants described in EP 0 070 498. Also, in one embodiment, to improve the coatings obtained according to the invention even further, perfluoro(poly)ether surfactants may be used that contain one or more, and preferably only one, functional group(s) that allow the ("functional head" of) the perfluoro(poly)ether surfactant used to be "chemically incorporated" into the hardened coating composition, i.e. during film formation. Such functional groups may for instance include groups such as carboxylic acids, sulphonic acids and/or amine groups; and are preferably groups that also (can be used to) confer surfactant properties upon the ρerfluoro(poly)ether, so that they also function as a "ionizable group" R as defined above. Also, for this purpose, one or more compounds that can covalently (cross-)link the fluorosurfactant to the binder - e.g. via the one or more functional groups mentioned above - may be added to the compositions of the invention. Some preferred, but non-limiting examples of such compounds include, but are not limited to, polycarbodiimides, isocyanates and/or epoxide-compounds or functionally similar types of compounds (e.g. as known per se for the preparation of other and/or conventional coating compositions), as will be clear to the skilled person. These crosslinking compounds may be added to the compositions of the invention in suitable amounts known per se, for instance between 1 and 30 wt.% , based on the total weight of the composition. One very convenient way of incorporating these crosslinking compounds into the compositions of the invention may involve mixing (a small amount of) a dispersion of the crosslinking composition to the dispersion of the invention, e.g. after the polymerisation.

Another aspect of the invention relates to a method of coating a solid substrate by applying a thin layer of the coating composition as described herein before onto the solid substrate and by drying said coating composition at a temperature below 100°C, preferably below 80°C. Preferably essentially no cross-linking occurs under these conditions. The invention also encompasses coated substrates obtainable from the aforementioned method. The coating compositions of the invention can be applied to any suitable substrate or surface. These may include metallic substrates or surfaces, including but not limited to those currently coated with known fluoropolymer-based coatings. However, as mentioned above, the invention also makes it possible to coat temperature-sensitive substrates or surfaces, including but not limited to substrates or surfaces such as wood, paper, and plastics.

The coating compositions of the invention may be applied using any coating technique known per se, such as pouring, dipping, brushing, rolling, spraying, spin casting or coating with a coating knife or doctor blade.

After the coating composition has been applied, the coating is hardened to form a film, which generally will involve removal/evaporation of the dispersion medium used, e.g. at room temperature or at elevated temperatures. Suitable conditions may for instance comprise: - a temperature of between RT and 100 °C, and in particular between 40 and 80 °C; - a time of 1 to 120 minutes, in particular 5 to 60 minutes.

The coating (layer) thus obtained can generally have any desired thickness, for instance between 5 and 300 μm, and in particular between 20 and 150 μnι, depending upon the intended use of the coating. As mentioned above, the coating compositions/coatings of the invention can be used to provide a surface or substrate with (improved) non-stick properties, (improved) physical or chemical resistance . Also, the coatings obtained from the coating compositions of the invention will usually have very low surface energies, e.g. of 30 mNm^"1 or less, preferably of 20 mNm^"1 or less, and in particular in the range of between 10 and 18 mNm^"1, as determined by the method described in the Experimental Part below. (By comparison, acrylate-based coatings without perfluoro(poly)ether surfactants will usually have surface energies of 40 mNm^"1 or more).

As mentioned above, the coating compositions of the invention may be formulated to provide a range of products, from conventional household paints with improved non-stick properties and improved resistance, to specialised coatings that can be used as an alternative to currently used coating compositions based upon fluoropolymers.

For instance, the invention may be used to provide household or industrial coatings which are easy to clean, which repel dirt and grease, which are oil- and/or water-resistant, which are solvent resistant, and which have excellent durability, both for indoor and outdoor use. As such, the coatings of the invention may also provide advantages over conventional silicone-based coatings, which are usually not dirt- or grease-repellent.

Some specific applications of the coating compositions of the invention include, but are not limited to: - anti-stick coatings, for instance for appliances, kitchen equipment and paints subjected to pollution ; - anti-fouling coatings, both for household as well as industrial use; anti-graffiti coatings;

The invention will now be illustrated by means of the following non-limiting Experimental Part and the non-limiting Figures, in which:

Figure 1 schematically shows the proposed (non-limiting) mechanism of action of the perfluoroether surfactants according to the invention during the emulsion polymerisation (Step 1) and during/after coating application (Step 2);

Figure 2 is a graph showing surface energy as a function of the Krytox/HFPO-COOH ratio, as further described in Example 2 below.

EXPERIMENTAL PART

Acrylic dispersions based on common hydrocarbon monomers and using fluorosurfactants were prepared, which were then utilized to prepare low surface energy coatings. Emulsion polymerization with butyl methacrylate as monomer, sodium persulphate as initiator and a fluorosurfactant resulted in better dispersions than suspension polymerization with the same monomer/fluorosurfactant but AIBN as initiator. In the case of the suspension polymerization a significant amount of coagulate (12-40 %) was formed during the reaction. In contrary, emulsion polymerization gave coagulate levels less than 1 %. All dispersions were stable for prolonged periods of time (several months). The HFPO-COOH surfactant gives the most stabile dispersions and the smallest dispersed particles (as obtained from centrifugal sedimentation experiments).

Dispersions with solid contents up to 30 % could be prepared. The best results were obtained when a surfactant mix consisting of Krytox 157 FSL and carboxylic acid endcapped oligo(hexafluoropropene oxide) (HFPO-COOH) was used. These high solid dispersions could be applied without using a thickening agent.

Transparant low surface energy coatings were be prepared from the acrylic emulsions. The value of the surface energy depended on the type of fluorosurfactant used. Krytox surfactants reduced the surface energy (determined by contact angle measurement using water and diiodomethane as wetting liquids; the data were processed by means of the Owen-Wendt- Rabel-Kaelble method) down to 15-18 mN/m, whereas HFPO-COOH reduced to 20-27 mN/m. Perfluoroheptanoic acid (F(CF2)6-COOH) performed worst, giving surface energies of about 27 mN/m. The use of F(CF2)6-COOH also led to coatings with bad properties (visual inspection). Without any fluorosurfactant surface energies ranging between 28 and 38 were observed.

The addition of the fluorosurfactant before the polymerization was shown to be of great importance. When the fluorosurfactant was added after the polymerization had been finished, usually coatings with bad properties resulted. Also mixing a fluorosurfactant based dispersion with a dispersion (different size of dispersed particles) without any fluorinated material usually did not give good coating properties.

One non-limiting purpose of the invention described herein aims at designing an environmentally friendly waterborne fluorocoating system. Therefore, the undesired characteristics inherent to existing fluoropolymers have to be surmounted. The approach chosen includes the reduction of the fluorine content and at the same time retain the surface characteristics of competetive coating systems with a high fluorine content.

The strategy involves the usage of a two-step process in which a fluoro-type surfactant is used. Figure 1 schematically outlines the role of the fluorosurfactant as emulsifier in step one and as functional surface additive in step two.

In step one a conventional emulsion polymerization is carried out using conventional hydrocarbon monomers typically used in emulsion polymerizations, e.g. (meth)acrylates. A fluorosurfactant stabilizes the monomer in water dispersion. The fluorosurfactant constitutes of an apolar segment having a perfluorinated linear or branched chain. The polar head has an ionic nature being very well soluble in water.

Step two comprises the formation of a coating layer. During the film formation process the fluorosurfactant migrates to the coating-air interface due to its strong surface activity. There, the fluorinated chains excert special surface properties, i.e. low surface energy and high water and oil repellency. Following basic characterization of the fluorodispersions, they were implemented into a coating system by taking into account the following variables: solid content, dispersion time and dispersion temperature, latex particle size and particle size distribution, pH, wettability and coagulation properties of the coating, processability of the dispersion into a coating formulation, stability of the coating system, etc.. Hereinbelow, the invention will be discussed in more detail with reference to experiments on this non-limiting two-step process. The results of step one will be discussed in Example 1, and the results of step two will be given in Example 2.

Example 1 : Fluorosurfactant stabilized Polymethacrylate Dispersions

In this example results of an investigation of step one of the two-step process are presented. The dissolution method used the get the fluorosurfactant into the aqueous phase is described. Also the emulsion and suspension polymerizations are described in detail. Three different types of fluorosurfactants were used, i.e. Krytox 157 FSL, carboxylic acid terminated oligo(hexafluoropropene oxide) (HFPO-COOH), and perfluoroheptanoic acid.

1.1 Preparation of Oligofhexafluoropropene oxide) carboxylic acid fHFPO-COOH) Oligo(hexafluoropropene oxide) carboxylic acid (Official name: perfluoro-2,5,8- trimethyl 3,6,9-trioxadodecanoic acid) was prepared by the saponification of the corresponding methyl ester. 5.02 g (7.38 mmol) Oligo(hexafluoropropene oxide) carboxylic acid methyl ester, 25 mL 1,1,2-trichlorotrifluoroethane, and 25 niL potassium hydroxide solution (10 wt % in ethanol) were weighed into a 100 mL round bottomed flask. While being stirred at 300 rpm, the clear solution was heated above the boiling point of 1,1,2- trichlorotrifluoroethane (being 48°C) at a temperature of about 75°C fot 6 hrs resulting in a brownish/yellow colored liquid. The liquid was titrated with hydrochloric acid until a pH of about 4 was obtained. During titration two phases appeared. Both phases were extracted three times: the upper one (mostly aqueous) was extracted with 1,1,2-trichlorotrifluoroethane while the lower phase (mostly 1,1,2-trichlorotrifluoroethane) was extracted with water. The 1,1,2- trichlorotrifluoroethane phases were collected and the solvent evaporated. The slightly brownish/yellow liquid product (viscosity a litle bit higher then water) was obtained in yields >91%. IR: The peak at 1795 cm-1 (ester) disappeared and apeak at 1755-1775 (acid) appeared. NMR: HFPO-ester one peak (singulet) at 3.92 ppm. HFPO-COOH occurrence of one peak (singulet) at 9.68 ppm. Peak at 3.92 became quartet and occurrence of peak (triplet) at 1.13 ppm indicating the presence of a small amount of ethanol. TLC: A concentrated HFPO-ester solution in 1,1,2-trichlorotrifluoroethane had an Rf-value of 0.13-0.26 and the HFPO-COOH had an Rf-value of 0.6-0.8. In both cases only one dot was observed indicating the absence of impurities with different chemical nature.

1.2 Preparation of the fluorosurfactant base solution (1) Aqueous Krytox 157 FSL (carboxylic acid terminated perfluoropolyether) solution 1.02 g (ca. 0.408 mmol) Krytox 157/fsl, 5.28 g demineralised water and 1.31 g 2- propanol were weighed into a small glass flask. This two-phase mixture was titrated while being stirred with an aqueous 0.1 M sodium hydroxide solution. The titration was stopped when a clear one-phase solution appeared being lightly opaque. The titrated Krytox 157 FSL solution had a pH of ca. 7.5. About 4.8 mL of the sodium hydroxide had been used.

(2) Aqueous carboxylic acid terminated oligo(hexafluoropropene oxide) (HFPO-COOH) solution

0.50 g HFPO-COOH and 2.59 g demineralised water were weighed into a small glass flask. This two-phase mixture was titrated while being stirred with an aqueous 0.1 M sodium hydroxide solution. The titration was stopped when a clear one-phase solution appeared. The titrated HFPO-COOH solution had a pH of ca. 7.5. About 7.1 mL of the sodium hydroxide had been used.

(3) Aqueous perfluoroheptanoic acid solution 1 g perfluoroheptanoic acid and 5.186 g demineralised water were weighed into a 50 mL erlenmeyer. Thereafter, this two-phase mixture was titrated while being stirred with an aqueous 0.1 M sodium hydroxide solution. The titration was stopped when a clear one-phase solution appeared. The titrated HFPO-COOH solution had a pH of ca. 7.5. About 27.5 mL of the sodium hydroxide had been used.

1.3 Emulsion polymerization of Butylmethacrylate (BuMA) by using fluorosurfactants In the following preparation Krytox 157 FSL was used as fluorosurfactant.(l) 5.97 g (0.2 mmol) Krytox 157 FSL solution (1), 8.71 g (61.3 mmol) BuMA, and 60.58 g demineralised water were weighed into a 250 mL three necked round bottomed flask. The mixture was sonified fro 30 s at 30 rpm upon which an emulsion is formed. While being stirred at 180 rpm nitrogen gas was passed through the emulsion for 43 min at room temperature (RT). Subsequently, the nitrogen flow was stopped and the temperature was raised to 73°C (oil bath temperature: 80°C). When the temperature reached 73°C 100 μL of an ammonium persulphate solution (3 %) was added under nitrogen and the stirring speed was increased to 270 rpm. After 8 min the stirring speed was reduced to 206 rpm. About 10 min after addition of the ammonium persulphate solution the dispersion became a blueish opaque appearance. After a total polymerization time of 1.5 hrs the emulsion was cooled and filtered. When HFPO-COOH was used as fluorosurfactant the composition of the polymerization mixture was: 10.26 g (0.76mmol) HFPO solution, 56.26 g demineralised water, and 8.71 g (61.3 mmol) BuMA.

When perfluoroheptanoic acid was used as fluorosurfactant the composition of the polymerization mixture was: 17.04 g (1.37 mmol) perfluoroheptanoic acid solution, 49.52 g demineralised water, and 8.71 g (61.3 mmol) BuMA. 1.4 Suspension polymerization of Butylmethacrylate (BuMA) by using fluorosurfactants In the following preparation Krytox 157 FSL was used as fluorosurfactant. 5.97 g (0.2 mmol) Krytox 157 FSL solution(l) and 60.58 g demineralised water were weighed into a 250 mL three necked round bottomed flask. To this solution a solution was added containing 0.0832 g (0.507 mmol) 2,2'-azobisisobutyronitrile (AIBN) in 8.71 g (61.3 mmol) BuMA. The mixture was sonified for 30 s at 30 rpm upon which an emulsion is formed. While being stirred at 700 rpm nitrogen gas was passed through the emulsion for 20 min at room temperature (RT). Subsequently, the nitrogen flow was stopped and the temperature was raised to 60°C (oil bath temperature: 80°C). When the temperature reached 60°C the stirring speed was increased to 900 rpm. After about 20 min the dispersion became a blueish opaque appearance and the stirring speed was readjusted to 700 rpm. After a total polymerization time of 1 hr some coagulated material could be observed. After a total polymerization time of 3 hrs the emulsion was cooled and filtered.

The aqueous Krytox 157 FSL solution was prepared by the following procedure: 0.50 g (0.2 mmol) Krytox 157/fsl, 2.59 g demineralised water, and 0.65 g methanol were weighed into a small glass flask. This two-phase mixture was titrated while being stirred with an aqueous 0.1 M sodium hydroxide solution. The titration was stopped when a clear one- phase solution appeared being lightly opaque. The titrated Krytox 157 FSL solution had a pH of ca. 7.5. About 2.2 g of the sodium hydroxide solution had been used.

1.5 Particle size and distribution measurement

The particle size and particle size distribution of the dispersions was determined by means of a Brookliaven Instruments Corporation BI-DCP particle sizer. A 5% aqueous sucrose solution was used as spin fluid. 1.6 Aqueous fluorosurfactant solutions

For the suspension and emulsion polymerizations several fluorosurfactants were used as emulsifier. Table 1 lists the fluorosurfactants with abbreviation, chemical fomula and molecular weight. The fluorosurfactant had to be dissolved in water, for which a titration with sodium hydroxide was used. In alkaline solution the ionic nature of the acid head group is sufficient to dissolve the apolar hydrophobic fluoroalkyl tail of the surfactant molecule. In the case of Krytox 157 FSL the resulting solution was blueish opaque indicating the presence of a colloidal system. The other two fluorosurfactants were colorless in aqueous solution at the concentration used.

Table 1. Used fluorosurfactants: abbreviation, formula, and molecular weight.

(1) Official name: perfluoro-2,5,8-trimethyl 3,6,9-trioxadodecanoic acid

The Krytox surfactant was dissolved by using methanol or 2-propanol as cosolvent. The perfluoropolyether with the lower molecular weight could be dissolved in water without using any cosolvent at all.

1.7 Suspension polymerization

Suspension polymerization allows the use of an apolar initiator which is very soluble in the monomer droplets. In emulsion polymerization weater soluble initiators are used. Residues of the water soluble initiator molecule often contain ionic groups. These groups provide additional stability to the dispersed polymer particles. From the other side the presence of ionic groups disturb the formation of a low surface energy coating layer, i.e. polarity and hydrophilicity are enhanced. For this reason suspension polymerization was tried first.

For the preparation of dispersions based on common hydrocarbon polymers stabilized by means of fluorosurfactants (both the higher molecular weight perlfuoropolyether: Krytox, and the low molecular weight perfluoropolyether: HFPO-COOH were used), suspension polymerization techniques were utilized. Butyl methacrylate (BuMA) was chosen as monomer. Azobisisobutyronitrile (AIBN) was used as monomer soluble initiator. A series of experiments were carried out. The used amounts of monomer, fluorosurfactant, as well as all other ingredients are given in Tables 2 and 3. Furthermore, are typical dispersion characteristics such as amount of formed coagulate, pH of the fluorosurfactant solution, solid content and theoretical solid content listed in Tables 2 and 3.

All suspension polymerizations resulted in the formation of a significant amount of coagulate during reaction (12-40 wt %). It seemed that suspension polymerization by using fluorosufactants as dispersants is not a suitable method for the preparation of poly(butyl methacrylate) (PBuMA) dispersions. In contrast, an experiment was conducted with sodium dodecyl sulphate (SDS) as surfactant, which resulted in a dispersion with only 3% coagulate. It is very likely that the incompatibility of the perfluoro chains causes the insufficient stabilization of the dispersed PBuMA. Perfluoroheptanoic acid has not been tested due to an even greater incompatibility with the PBuMA compared to the perfluoropolyether based surfactants.

It was also attempted to increase the dispersion stability by adding an amount of Triton xlOO (commercially available non-fluorine containing surfactant). However, the addition of Triton xlOO did not improve dispersion stability. Table 2. Experimental data on suspension polymerizations using butyl methacrylate CBuMA) as monomer and AIBN as initiator. Several typical dispersion characteristics are listed: amount of fonned coagulate, pH of the fluorosurfactant solution, solid content and theoretical solid content.

Table 3. Experimental data on suspension polymerizations using butyl methacrylate (BuMA) as monomer and AIBN as initiator. Several typical dispersion characteristics are listed: amount of formed coagulate. pH of the fluorosurfactant solution, solid content and theoretical solid content.

1.8 Emulsion polymerization

Because the fluorsurfactants were not nor fully satisfactory in stabilizing the dispersed polymer particles during and after suspension polymerization, emulsion polymerization was evaluated, using a slightly changed experimental procedure in which a water soluble ammonium persulphate initiator was employed. Three different fluorosurfactants, i.e. Krytox, HFPO-COOH and F(CF2)6-COOH were tested. Furthermore, were variables such as solid content and additives investigated.

Butyl methacrylate (BuMA) was chosen as monomer. Ammonium persulphate was used as water soluble initiator. A series of experiments was carried out. The used amounts of monomer, fluorosurfactant, as well as all other ingredients are given in Tables 4-7.

Furthermore, are typical dispersion characteristics such as amount of formed coagulate, pH of the fluorosurfactant solution, solid content and theoretical solid content listed in Tables 4-7.

The first striking difference with the suspension polymerizations is the low amount of formed coagulate (often < 1 wt %). Initially, polymerizations were carried out with about 10 % solid content. For practical application this is too low. Therefore, polymerizations were performed with higher solid contents (up to 34 %). Even for these high solid content dispersions the amount of coagulate formed was very low. The best dispersions were obtained when two types of fluorosurfactants were employed: the low and the high molecular weight perfluoropolyethers, i.e. krytox and HFPO-COOH. High solid content dispersions based on only one surfactant were prone to coagulation.

All dispersions were stable for prolonged periods of time. Also copolymerization of other methacrylate monomers like methacrylic acid was possible. The use of 2-propanol seemed to be essential for the reduction of coagulate. In a series of experiments in which the 2-propanol content was varied, it was shown that for low 2-propanol concentrations (0.066 g) a high amount of coagulate was formed (14 %). Table 4. Experimental data on suspension polymerizations using butyl methacrylate (BuMA) as monomer and hydrogen periode or ammonium persulphate as initiator. Several typical dispersion characteristics are listed: amount of formed coagulate, pH of the fluorosurfactant solution, solid content and theoretical solid content.

Emulsion polymerizations could be carried out with low amounts of fluorosurfactant (down to 0.3 wt % relative to monomer content). On the other hand can emulsion polymerizations be conducted without any surfactant at all. The ionic sulphate groups are the polar heads and the oligoBuMA chains are the apolar tails of the in situ formed surfactants.

Table 5. Experimental data on suspension polymerizations using butyl methacrylate (BuMA) as monomer and ammomum persulphate as initiator. Several typical dispersion characteristics are listed: amount of formed coagulate, pH of the fluorosurfactant solution, solid content and theoretical solid content.

Sample name RJ-126 RJ-128 RJ-131 RJ-135(1)

Water (g) 65.890 66.540 66.030 60.600

BuMA (g) 8.700 8.720 8.710 8.760

Krytox (g) 0.498 0.498

HFPO-COOH (g) 0.479

F(CF2)6-COOH (g) 0.492

2-Propanol (g) 0.660 0.660

NaOH (g) 0.067 0.028 0.009 0.009

Ammonium persulphate (g) 0.006 0.006 0.003 0.003

Total (g) 75.149 75.767 75.907 70.707

Coagulate (g) 0.00 0.00 0.010 0.034

Coagulate (wt %) 0.00 0.00 0.115 0.392

PH fluorosurfactant solution 7.520 7.680 7.840 7.840

PH dispersion 4.370 6.690 6.670 4.300

Solid content (wt %) 12.210 11.700 11.430 11.570

Theor. solid content (wt %) 12.321 12.178 13.012 14.294

(1) + 0.180 g methacrylic acid (2 wt % of total monomer amount)

(2) + 0.59 g SDS Table 6. Experimental data on suspension polymerizations using butyl methacrylate (BuMA) as monomer and ammonium persulphate as initiator. Several typical dispersion characteristics are listed: amount of formed coagulate, pH of the fluorosurfactant solution, solid content and theoretical solid content.

Sample name RJ-142 RJ-145 RJ-146 RJ-153

Water (g) 54.160 50.850 66.080 52.120

BuMA (g) 22.490 22.500 8.890 22.490

Krytox (g) 0.498 1.000 0.051 0.253

HFPO-COOH (g) 0.109 0.206

F(CF2)6-COOH (g)

Isopropanol (g) 0.660 1.320 0.066 0.330

NaOH (g) 0.015 0.030 0.015 0.015

Ammonium persulphate (g) 0.003 0.003 0.003 0.006

Total (g) 77.932 75.700 75.102 75.414

Coagulate (g) 0.040 0.080 1.210 0.080

Coagulate (wt %) 0.178 0.356 13.611 0.356

PH fluorosurfac- tant 7.130 7.130 7.130 7.00 solution.

PH dispersion 7.600 6.370 6.600 5.740

Solid content (wt %) 33.700 31.100 10.140 32.300

Theor. solid content (wt %) 30.504 32.827 12.013 30.888

(1) + 1.280 g methacrylic acid Table 7. Experimental data on suspension polymerizations using butyl methacrylate (BuMA) as monomer and ammonium persulphate as initiator. Several typical dispersion characteristics are listed: amount of fonned coagulate, pH of the fluorosurfactant solution, solid content and theoretical solid content.

Sample name RJ-154 RJ-127(1)

Water (g) 52.030 235.61

BuMA (g) 22.500 62.550

Krytox (g) 0.750

HFPO-COOH (g) 0.068

F(CF2)6-COOH (g)

Isopropanol (g) 0.330

NaOH (g) 0.015

Ammonium persulphate (g) 0.003 1.350

Total (g) 75.693 299.44

Coagulate (g) 0.160 2.670

Coagulate (wt %) 0.711 4.269

PH fluorosurfactant solution. 7.00

PH dispersion 7.260 2.780

Solid content (wt %) 30.680 22.160

Theor. solid content (wt %) 31.262 21.316 1.9 Dispersion characterization

Dispersions were characterized with respect to the dispersed particle size and particle size distribution by means of centrifugal sedimentation, essentially as described under 1.5 above. The particles were produced roughly in the range 100-200 nm.

Example 2: Coatings

2.1 Introduction

The dispersion prepared as described in the previous sections were used to make coating layers. Different substrates were tested including glass, metal and wood. Problems encountered due to insufficient wettability and inadequate film formation were attempted to solve by using additives.

2.2 Coating application

The dispersions of Example 1 above were applied onto the substrate which was tilted so that all the redundant solvent was removed immediately. The substrate was put into the oven in a vertical position and dried for 2 hrs at 80°C. This method resulted in good homogeneous films. For 12% dispersions this method gives good results. For the 30%

dispersions a 100 or 150 μm casting knife was used.

3.3 Coating characteristics The prepared coatings were subjected to surface energy measurements by means of the

Owen-Wendt-Rabel-Kaelble method, using water and diiodomethane as wetting liquids. Table 8 shows the results of both contact angle measurements and surface energy determinations. Table 8. Diiodomethane and water contact angles (θ), surface energy (SE) data (total, disperse

part and polar part) as determined by the Owens- Wendt-Rabel-Kaelble method.

Table 8. (continued).

(1) Total surface energy. (2) Disperse part of surface energy.

(3) Polar part of surface energy.

Some samples (e.g. 142, 145, 153, and 154) showed a low surface energy. Here the concept of selective surface enrichment seems to be sucessful.

The increase in solid content (from 12 to 30 %) as described earlier resulted in significantly better coating layers. The resulting coatings were more homogeneous due to an improved film formation. The best coatings were based on dispersions with two types of fluorosurfactants: the low and the high molecular weight perfluoropolyethers, i.e. Krytox and HFPO-COOH. Figure 2 shows the relation between surface energy and the ratio of krytox/HFPO-COOH. The total amount of fluorosurfactant used was 0.4 mmol.

2.4 Addition of thickeners

Initially, coating layers showed some defects, such as craters. It was attempted to improve the coating quality by using dispersions with higher solid contents. However, this was only partially successful. To overcome this problem a thickener was added. By the addition of 10% (relative to total solid content) Texanol. Thus much better coatings could be prepared. Natrosol 250 could not be used because addition to the PBuMA dispersion lead to coagulation.

2.5 Preparation of cross linked coatings by using a polycarbodiimde cross linking agent In order to prepare coatings with increased mechanical properties as well as better chemical resistance, dispersion based on fluorosurfactants were mixed with a polycarbodiimde (PCDI). Carbodiimides (XR-5560; Stahl) react with carboxylic acid containing components and thus introduce cross linking. The PCDI could be introduced into the dispersion without any coagulation problems. As shown in Table 9 the surface energy increased upon increasing PCDI content. However, when 1.4 wt % of PCDI was added still a surface energy comparable to poly(tetrafluoroethene) (ca. 19 mN/m) could be obtained. Tabel 9. Poly(butyl methacrylate) stabilized by Krytox and cured with a poly(carbodiimide) (PCDI).

Sample PCDI(l) PCDI(2) θ CH2I2 θ water Total SE(3) d-SE(4) p-SE(5)

name (wt %) (wt %) (°) (°) (mN/m) (mN/m) (mN/m)

RJ-135 0 100.0 91.6 17.51 8.86 8.83

RJ-135 1.4 50 95.6 88.3 19.83 10.36 9.47

RJ-135 3.4 100 89.8 86.4 21.74 12.78 8.96

RJ-135 6.8 200 86.8 81.2 25.27 14.17 11.09

(1) Relative to dispersion.

(2) Relative to COOH (3) Total surface energy

(4) Disperse part of surface energy

(5) Polar part of surface energy

2.6 Mixing dispersions In an attempt to reduce the total amount of fluorosurfactant and improve the film formation process, two dispersions were mixed. By taking a dispersion based on a fluorosurfactant and mix this dispersion with a dispersion without fluorosurfactant (Jongcryl 77; SC Johnson Polymer; solid content: 45.5 %; particle size 60 nm) a new dispersion was prepared. Nevertheless, it was not possible to prepare a stable dispersion. In the mixed dispersions coagulation occureed.

3. Comparative Experiments

Experiments were carried out in which the dispersion was prepared without the use of fluorosurfactants. After the dispersion had been prepared an amount of dissolved fluorosurfactant was added to the dispersion. Coatings from these dispersions performed much worse than coatings from dispersions where the fluorosurfactant had been added before the polymerization was started. Diiodomethane drops on the former coating were stable but the contact angles varied between 70 and 104°. No homogeneous coatings could be prepared.

4. Conclusions

Acrylic dispersions based on common hydrocarbon monomers can be prepared which can be applied to form low surface energy coatings. Therefore, fluorosurfactants can be used.

Emulsion polymerization with butyl methacrylate as monomer, sodium persulphate as initiator and a fluorosurfactant resulted in better dispersions than suspension polymerization with the same monomer/fluorosurfactant but AIBN as initiator. In the case of the suspension polymerization a significant amount of coagulate (12-40 %) was fonned during the reaction. In contrary, emulsion polymerization gave coagulate levels less than 1 %. All dispersions were stable for prolonged periods of time (several months). The HFPO-COOH surfactant gives the most stabile dispersions and the smallest dispersed particles. However, it takes longer to prepare such a dispersion.

Dispersions with solid contents up to 30 % could be prepared. The best results were obtained when a surfactant mix consisting of krytox and carboxylic acid endcapped oligo(hexafluoropropene oxide) (HFPO-COOH) was used. These high solid dispersions could be applied without using a thickening agent.

Transparant low surface energy coatings can be prepared from the acrylic emulsions. The value of the surface energy depended on the type of fluorosurfactant used. Krytox surfactants were able to reduce the surface energy down to 15-18 mN/m, whereas HFPO- COOH reduces to 20-27. Perfluoroheptanoic acid (F(CF2)6-COOH) performed worst, giving surface energies of about 27 mN/m. Besides, leads the use of F(CF2)6-COOH to coatings with bad properties (visual inspection). Without any fluorosurfactant surface energies ranging between 28 and 38 were observed.

The addition of the fluorosurfactant before the polymerization was shown to be essential. When the fluorosurfactant was added after the polymerization had been finished, coatings with bad properties resulted. Also mixing a fluorosurfactant based dispersion with a dispersion (different size of dispersed particles) without any fluorinated material did not give good coating properties.

Claims

C LA IM S

1. Coating composition, comprising: at least one polymeric binder; - at least one dispersion medium;

- at least one (per)fluorosurfactant; and optionally

- one or more further components of coating compositions known per se; characterised in that said (ρer)fluorosurfactant is a perfluoroether surfactant.

2. Coating composition according to claim 1, but not including a curable coating system consisting of a cross-linkable resin and a cross-linking agent as well as a (per)fluorosurfactant capable of reacting with the cross-linkable resin and/or the cross-linking agent when subjected to curing.

3. Coating composition according to claim 1 or 2, in which the perfluoroether surfactant is a perfluoropolyether surfactant.

4. Coating composition according to any one of claims 1-3, in which the perfluoro(poly)ether surfactant comprises between 3 and 500 carbon atoms, preferably between 3 and 300 carbon atoms, more preferably between 4 and 150 carbon atoms, and even more preferably between 9 and 60 carbon atoms; and between 1 and 150 ether bonds, preferably between 1 and 75 ether bonds.

5. Coating composition according to any one of claims 1-3, in which the perfluoro(poly)ether surfactant has a molecular weight of between 350 and 5000, preferably between 350 and 2500.

6. Coating composition according to any of the preceding claims, in which the

(per)fluorosurfactant does not comprise an amide bond.

7. Coating composition according to any of the preceding claims, in which the perfluoro(poly)ether surfactant has the general formula

F - [ (CQ₂)_P - O ]_q- (CQ₂)_r - CQ₂ -R (I)

in which: each group Q is independently a fluorine atom or a fluorocarbon residue as defined above;

- R is an ionizable group as defined above;

- p is an integer of between 1 and 3, and is preferably 1 or 2;

- q is an integer such that the product [p times q] is between 1 and 75, and preferably between 4 and 60; - r is 0 or an integer between 1 and 3, and is preferably 0 or 1 ; or a combination of two or more such perfluoropolyether surfactants.

8. Coating composition according to any of the preceding claims, in which the at least one polymeric binder is chosen from: polymeric binders based upon one or more unsaturated monomers such as acrylate monomers, methacrylate monomers, vinyl monomers, or mixtures thereof; polyurethanes; epoxyresins; - alkyds; or a suitable combination thereof

9. Coating composition according to any of the preceding claims, in which the dispersion medium is an aqueous dispersion medium, such as water or a mixture of water and one or more water-miscible solvents.

10. Coating composition according to any one of the preceding claims, containing from 25 to 90 wt.% water.

11. Coating composition according to any of the preceding claims, in which the one or more further components are chosen from:

- pigments such as TiO₂, which may for instance be added in amounts between 0 and 60 wt.%; fillers such as clay, which may for instance be added in amounts of between 0 and 40 wt.%;

- further additives such as rheology modifying additives, flow modifying additives, levelling additives, wetting agents, and anti-fungicidal additives, which may for instance be added in amounts of up to 10 wt.%; or a suitable combination thereof, in which the wt.% are based on the total composition, and in which the total amount of further components makes up no more than 60 wt.% of the total coating composition.

12. Coating composition according to any of the preceding claims, having the following composition:

- binder(s): 10 - 90 wt.%, preferably 20 - 70 wt.%;

- dispersion medium: 30 - 90 wt.%, preferably 40 - 80 wt.%;

- perfluoro(poly)ether surfactant(s): 0.01 - 10 wt.%, preferably 0.1 - 4 wt.%; - one or more further components: 0 - 60 wt.%; to a total of 100 wt.% of the total composition.

13. Use of at least one perfluoroether surfactant in (the preparation of) a coating composition.

14. Use according to claim 13, in which the resulting coating composition does not comprise a curable coating system consisting of a cross-linkable resin and a cross-linking agent as well as a (per) fluorosurfactant capable of reacting with the cross-linkable resin and/or the cross-lining agent.

15. Use according to claim 13 or 14, in which perfluoroether surfactant is a perfluoropolyether surfactant.

16. Use according to any one of claims 13-15, in which the perfluoro(poly)ether surfactant comprises between 3 and 500 carbon atoms, preferably between 3 and 300 carbon atoms, more preferably between 4 and 150 carbon atoms, and even more preferably between 9 and 60 carbon atoms; and between 1 and 150 ether bonds, preferably between 1 and 75 ether bonds.

17. Use according to any of claims 13-16, in which the perfluoro(poly)ether surfactant has a molecular weight of between 350 and 5000, preferably between 350 and 2500.

18. Use according to any of claims 13-17, in which the perfluoro(poly)ether surfactant has the general formula:

F - [ (CQ₂)_P - O ]_q- (CQ₂)_r - CQ₂ -R (I)

in which:

- each group Q is independently a fluorine atom or a fluorocarbon residue as defined above;

- R is an ionizable group as defined above;

- p is an integer of between 1 and 3, and is preferably 1 or 2;

19. Use according to any of claims 13-18, in the preparation of a coating composition which is in the form of an aqueous dispersion or emulsion.

20. Use according to any of claims 13-19, in which the perfluoro(poly)ether surfactant(s) are used in amounts of between 0.01 and 10 wt.%, and in particular in amounts of between 0.1 and 4 wt.%, of the total coating composition.

21. Method for preparing a coating composition, in particular a coating composition according to any of claims 1-12, comprising at least one step of polymerising a suitable monomer or mixture of monomers to form a polymeric binder, in which said polymerisation is carried out in a suitable dispersion medium and in the presence of at least one perfluorosurfactant, characterised in that said perfluorosurfactant is a perfluoroether surfactant.

22. Method according to claim 21, in which the perfluorosurfactant is a perfluoropolyether surfactant.

23. Method according to claim 21 or 22, in which the perfluoro(poly)ether surfactant comprises between 3 and 500 carbon atoms, preferably between 3 and 300 carbon atoms, more preferably between 4 and 150 carbon atoms, and even more preferably between 9 and 60 carbon atoms; and between 1 and 150 ether bonds, preferably between 1 and 75 ether bonds.

24. Method according to any of claims 21-23, in which the perfluoro(poly) ether surfactant has a molecular weight of between 350 and 5000, preferably between 350 and 2500.

25. Method according to any of claims 21-24, in which the perfluoro(poly)ether surfactant has the general formula:

F - [ (CQ₂)_P - O ]_q- (CQ₂)_r - CQ₂ -R (I)

in which: each group Q is independently a fluorine atom or a fluorocarbon residue as defined above; - R is an ionizable group as defined above; - p is an integer of between 1 and 3, and is preferably 1 or 2; q is an integer such that the product \p times q] is between 1 and 75, and preferably between 4 and 60; r is 0 or an integer between 1 and 3, and is preferably 0 or 1; or a combination of two or more such perfluoropolyether surfactants.

26. Method according to any of claims 21-25, in which said polymerisation is carried out in an aqueous medium by suspension- or emulsion-polymerisation, and preferably emulsion polymerisation.

27. Method according to any of claims 21-26, in which the perfluoro(poly)ether surfactant(s) are used in amounts of between 0.01 and 10 wt.%, and in particular in amounts of between 0.1 and 4 wt.%, of the total coating composition.

28. Method of coating a solid substrate by applying a thin layer of a coating composition according to any of claims 1-12 onto the solid substrate and by drying said coating composition at a temperature below 100°C, preferably below 80°C.

29. Coated substrate obtainable from the method according to claim 28.

30. Coated substrate according to claim 29, wherein the coating has a surface energy of less than 30 mNm^"1, preferably 20 mNm^"1, in particular 10-18 mNm^"1.