BIOCIDAL COATINGS

The invention relates to a polymer with an incorporated biocidal component. The invention also relates to a crosslinker with an incorporated biocidal component, the invention further relates to a composition comprising either the biocidal polymer or crosslinker or both, to a substrate fully or partially coated with a biocidal composition and its use in coatings.

There is an increasing interest world wide to use biocidal / hygienic materials, due to the increasing attention in the Western world for health issues, for example because of epidemic events like SARS and because of increasing resistance of bacteria against antibiotics. It is not only fear that stimulates this interest but it is a necessity to use them because in the Western world alone thousands of people die yearly in hospital due to infections, for instance it is estimated that each year 5000 people die in hospitals due to infections in the UK, it is estimated that in the USA each year 76 million people fall ill due to food-borne contacts, in the Netherlands yearly more than 1 million people become ill due to bacteria.

Biocidal is here and hereinafter used in its broad sense, so as to encompass anti-bacterial as well as anti-fungal and anti-algae.

Although biocidal additives are widely used in household cleaning products and in cosmetics, their application in plastics and coatings is so far limited. However the potential application area is very broad and covers coatings, engineering plastics as well as fibres. Especially important are the industrial applications in drinking water industry, food and paper industry and in hospitals and other public buildings, outdoor building panels, glass and so forth. Another important area for these materials is biomedical applications. Additionally biocidal additives can advantageously be used in products that everybody touches, for example door handles, telephones and money, because these products are responsible for the fast transfer of bacteria and thus for the transfer of illnesses. Although biocidal coatings can of course not prevent all bacterial infections they can reduce the risk substantially. Often used techniques to obtain biocidal materials are the addition of low molecular weight biocidal additives or photoactive chemicals. An example of a low molecular weight biocidal additive is the addition of transition metal ions, in particular silver ions. An example of a photoactive chemical is non-coated titanium dioxide.

A disadvantage of the use of photoactive chemicals in coatings is that they tend to degrade the organic polymer as well, thereby degrading the integrity of the

coating.

A disadvantage of the use of low molecular weight biocidal additives in coating compositions is that they have a higher ability to leach out when the coating is in contact with for example (rain)water compared to other biocidal additives (see for example "Biomimetic and supramolecular systems", (2002), C20 (1-2), 167-173). This leaching-out gives rise to several problems such as for example the end of the desired biocidal activity but also to environmental problems. Worldwide about 1500 antibacterial products exist. However many of them are toxic and it is expected that many of them will be and need to be abandoned due to legislation. A disadvantage of silver ions is that they are leachable just as the other transition metal ions. Moreover, silver ions do not only kill bacteria, but they also denaturize essential human proteins, which is a toxic action. Furthermore, silver ions are easily reduced, forming a grey colour, which is not acceptable in many coating applications.

The object of the present invention is to overcome one or more of the above-mentioned problems. Thus the object is to make available a polymer with biocidal properties and which polymer can be used in coating compositions that have biocidal properties and from which coatings can be obtained from which the biocidal component does not leach after contact with water. By "does not leach" is herein meant that the biocidal product in an aqueous solution maintain the biocidal property. This object has been reached by a polymer with an incorporated biocidal component. With polymer is here and hereinafter meant a compound in which at least two repeating units are available, thus comprising the generally referred polymers as well as dimers and oligomers. With incorporated is thus meant that the biocidal component is chemically built-in in the polymer by covalent bonding or electrostatical bonding.

The kind of polymer that is chosen is not particularly critical. Its choice will generally be dictated by the requirements that must be met by the final coating. For example, a coating that is going to be used on a substrate that will be used outdoors needs to fulfil different requirements than a coating on a substrate that will be used indoors. In this respect the polymers that will be used in the two kinds of coatings will most probably be different. Thus the requirements that the final coating must meet will dictate the choice of polymer. Although the choice is not particularly critical, the polymer used in the biocidal coating composition must be obtained by a condensation reaction. The reason for this is that low viscous coating compositions are preferred since they giver better antibacterial properties. Low viscous and thus low molecular

weight polymers suitable for the coating composition are more conveniently made by a step-growth polymerisation technique than with a chain-growth polymerisation technique. As a consequence, polycondensates are most suitable. Polymers that can be obtained via a condensation reaction are for example polyesters, copolyesters, polyethers, polyamides, polyesteramides, polyurethanes and polycarbonates.

Preferably polyesters or polyesteramides are used. Most preferably polyesters are used as they have excellent properties for fulfilling the requirements of the final coating.

It is also possible within the scope of the invention to use a combination of two or more polymers with biocidal properties. Any combination can be made between different types of polymers with biocidal properties, as long as the polymers are obtained by a condensation reaction. For example it is possible to use a combination of a polyester with biocidal properties with a polyamide with biocidal properties, or a polyester with a polyurethane when both have biocidal properties. It is also possible within the scope of the invention to use a combination of two polymers of the same kind, for example two different polyesters with biocidal properties or two polyamides with biocidal properties. With different is in this context meant that the two polymers of the same kind have different chemical or physical properties. An example of two polymers of the same kind with different chemical properties is two polyesters wherein the alcohols and/or acids used in the synthesis are different, for example one polyester based on an aliphatic alcohol and the other polyester based on an aromatic alcohol, or one aliphatic acid and the other polyester is synthesized with an aromatic acid. An example of two polymers of the same kind with different physical properties is two polyesters wherein the acid values or the glass transition temperatures are different. Within the scope of the invention it is also possible to use a combination of at least one polymer with biocidal properties with one or more polymers that are not specifically adapted to display biocidal properties. These last ones will generally be referred to as "non-biocidal polymers". The choice of non-biocidal polymer is not critical and can be made so as to fulfil the final requirements of the coating, however the biocidal polymer must be chosen from between the polymers obtained by a condensation reaction. When a combination of polymers is used, either all of them having biocidal properties or only some of them having biocidal properties, it can sometimes be convenient to refer to the polymer that is present in the largest amount as to the "matrix polymer". Although in principle any polymer is suitable, it has been found

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advantageous to use polymers with a relatively low molecular weight as it was found that with higher molecular weights the biocidal activity decreased or could not even be measured anymore. The molecular weight used here is expressed as the number average molecular weight M _n . The number average molecular weight is determined by size exclusion chromatography (SEC). The columns used are 3 ^* PSS, the solvent is hexafluoro isopropanol (HFIP) and the detection is done with refraction index (Rl), ultra violet light (UV), deferential vsicosimetry (DP) and RALLS (light scattering). The data were collected and processed with ThSEC software. The molecular weight of the polymer should be less than 10.000 g/mol. Preferably the molecular weight is less than 8.000, most preferably less than 5.000 g/mol. The lower limit of the molecular weight is governed by the mechanical properties, when the crosslink density becomes too high the coating becomes too brittle. Preferably the molecular weight is at least 500, more preferably at least 1.000 g/mol. A preferred range for the molecular weight is between 500-8.000 g/mol, more preferably 1.000-5.000 g/mol. The resin will generally have some functional groups through which the resin can react with an optionally present crosslinker upon which a network will be formed. Examples of suitable functional groups are carboxyl-, hydroxyl-, epoxy-, amino groups and combinations of any of them. Preferably carboxyl- or hydroxyl functional groups are present in the resin. The coating composition comprising the biocidal polymer will generally comprise at least one crosslinker so as to form a network. The crosslinker present in the coating composition is not particularly critical. The nature of the crosslinker is determined by the nature of the functional groups in the polymer. The functional groups on the crosslinker must be able to react with the functional groups in the polymer. Examples of crosslinkers are epoxy resins, polyamines, (blocked) isocyanates, aminoresins, polycarboxylic acids, acid anhydrides, polyphenols, Primid®- like compounds and combinations of any of them. (Primid®-like compounds are based on β- hydroxyl alkyl amide). The man skilled in the art knows which suitable crosslinkers are available and he knows how to determine the best option. The present invention can be used in various ways. In one embodiment of the invention the biocidal component is incorporated as a cation of one of the monomers covalent bonding to the polymer is derived from. Thus the biocidal component is chemically incorporated in the polymer. In another embodiment of the invention the biocidal component is incorporated as one of the monomers as described under the first embodiment. However in this embodiment it is the anion that is built-in in

the polymer, the cation being the counter ion and bonded electrostatically to the polymer. In again another embodiment of the invention the biocidal component is incorporated in a crosslinker and hence being bonded either electrostatically or covalently to the final cured coating. In again another embodiment a combination of embodiments is used.

In the first embodiment of the invention the biocidal component is incorporated as a cation of one of the monomers the polymer is derived from. Thus the biocidal component is chemically incorporated in the polymer. As stated above the polymer must be obtained by a condensation reaction. An example of how the biocidal component can be incorporated in the polymer is the following. Where the biocidal polymer is a polyester and the polyester is formed in the reaction between an alcohol component and an acid component, the biocidal component can be either in the form of the alcohol component (see left-hand side of Formula I) or in the form of the acid component (see right-hand side of Formula I). Thus the polyester with incorporated biocidal component can for example be represented, without being limited to the exact structure, by one of the versions of Formula I. It is also possible within the scope of the invention that both versions of Formula I are present within one polyester polymer, thus that both part of the alcohol components and part of the acid components are used to incorporate the biocidal component.

Formula I

With "alcohol component" is here and hereinafter meant the component in the polyester synthesis that is an alcohol or behaves functionally the same as an alcohol in the polyester synthesis. Examples of suitable alcohol components are quaternary onium salts of alcohols, hydroxy-functional derivatives, such as for example di-(2-hydoxy ethyl) amine, di-(2-hydroxy propyl) amine, di-(3- hydroxy propyl) amine, tri-(2-hydroxy ethyl) amine. Alcohol components should have at least two hydroxyl groups to be able to react to a polyester as defined above. The "alcohol" could also be hidden in an ester of a low molecular weight acid and one of the

alcohols mentioned above. The low molecular weight acid could be removed during the polycondensation.

With "acid component" is here and hereinafter meant the component in the polyester synthesis that is an acid or behaves functionally the same as an acid in the polyester synthesis. Examples of suitable acid components are acids, acid anhydrides, esters, for example quaternary onium salts of imino acetic acid, 3,5- pyridine dicarboxylic acid, 2,6-pyridine dicarboxylic acid, 3,4 -pyridine dicarboxylic acid. Acid components should have at least two acid (or acid derived) groups to be able to react to a polyester as defined above. As known to the man skilled in the art of polyester synthesis, the exact nature of the components that are used in the polyester synthesis depends on the requirements the polyester must meet. He also knows how to vary the exact amount of the components to meet the requirements and how to choose the, by its chemical nature, most suitable components. As generally known in the art of polyester synthesis, although most of the components used are di- or higher functional, it is also possible to use certain amounts of mono-functional components. It is well-known to use combinations of alcohol components and combinations of acid components. The use of combinations for one or more of the components gives the skilled man additional possibilities to tailor-make the polyester as required. For more information and details regarding polyester synthesis reference is made to well-known and widely available handbooks on this subject.

Other polymers (than polyesters as described above) that are obtainable by a condensation reaction and that are thus suitable to incorporate a biocidal component are for example copolyesters, polyamides, polyesteramides, polyurethanes, polyethers, polycarbonates and combinations of any of them. For the preparation of these different polymers reference is made to the generally available information.

The biocidal component has a structure that can be represented by formula II:

Wherein:

Z ₁ , Z ₂ , Z ₃ may independently of one another, be the same or different functional endgroups at the branches, a,b,c may independently of one another, be the same or different integers and represent the number of functional endgroups per branch,

R ₁ , R _2, may, independently of one another, be the same or different hydrogen, alkyl- or alkenyl groups with 1-10 carbon atoms, R ₃ is hydrogen, alkyl- or alkenyl groups with 1-10 carbon atoms or the same as R ₄ , R ₄ is an alkyl- or alkenyl group with 6-36 carbon atoms, X ⁺ is a quaternary nitrogen- or phosphorus-containing cation, Y ^' is a counter ion of the quaternary cation.

Z ₁ , Z ₂ , Z ₃ are functional endgroups at the branches. These functional endgroups make it possible to build in the biocidal component covalently in the polymer. At least one of X ⁺ or Y ^" should be covalently bonded to the polymer. If X ⁺ is covalently bonded to the polymer, then at least one of the branches of X ⁺ should have a functional endgroup that is capable to react with groups in the polymer. If a + b + c = 1 , then X+ is capable of being connected to the polymer covalently at the end of the polymer. In a preferred embodiment a, b, c, may independently of one another be chosen to be the same or different integers, with the proviso that at least one of them has a value greater than 0. Preferably a + b + c is at least two (i.e. at least two functional endgroups in one branch or at least two branches each having at least one functional endgroup). Preferably at least two of them have a value greater than 0, as this allows to be covalently bonded twice and hence take other positions than only a polymer end position corresponding to a+b+c=1.

With "functional endgroup" is meant a group that is different from the alkyl- or alkenyl groups R and that is capable to react with groups in the polymer. The nature of the functional endgroups can vary widely as long as they are able to react

with groups on the polymer. Examples of functional endgroups are hydroxyl-, carboxyl-, amine-, (blocked) isocyanate, β-hydroxy alkyl amide, and epoxy groups. Preferably the functional endgroups are hydroxyl- or carboxyl- groups.

The R ₄ group in the biocidal component according to formula Il can be an alkyl- or alkenyl group with 6-36 carbon atoms. Generally the maximum length of this kind of groups is 36 carbon atoms. Preferably the length is at least 10 carbon atoms long and preferably the maximum length is 24 carbon atoms. Most preferably the length is between 12 and 20 carbon atoms. Generally the number of carbon atoms in R ₄ will be even. The group R ₃ can be the same as R ₄ . In that case two relatively long branches are available. However it is preferred to have only one "relatively long" group R ₄ . In that case R ₃ is a hydrogen, alkyl- or alkenyl group with 1-10 carbon atoms.

The groups R ₁ , R _2, are independently from each other either hydrogen or alkyl- or alkenyl groups with 1-10 carbon atoms. Preferably the length of the alkyl- or alkenyl- groups is at most 8 carbon atoms, more preferably at most 4 carbon atoms. R ₃ is either the same as R ₁ or as R ₄ . Thus R ₃ is either hydrogen or alkyl- or alkenyl groups with 1-10 carbon atoms or an alkyl- or alkenyl group with 6-36 carbon atoms. It is highly preferred that no more that one of R ₁ , R ₂ , R ₃ are hydrogen, since this was found to provide the strongest biocidal effect. Most preferably the groups R ₁ , R _2, R ₃ are independently from each other methyl, methylene, ethyl or ethylene. Preferably R ₁ , R _2, and R ₃ are all an alkyl- or alkylene group, thus it is preferred not to have hydrogen as one of the R ₁ , R _2, and R ₃ groups or in other words it is preferred not to have a protonated quaternary cation as they are less effective than the tetra alkyl biocidal component.

X ⁺ in formula Il is a quaternary nitrogen- or phosphorus-containing cation. The nitrogen or phosphorus can be present as such or in an organic moiety.

With "in an organic moiety" is meant that the nitrogen or phosphorus is part of a organic structure. Preferably the organic moiety has an aromatic character. An example of a moiety with an aromatic character is pyridine. Preferably X ⁺ is a quaternary phosphorus-containing cation as the quaternary P-cation is more thermally stable than the quaternary N-cation and can therefore more easily be used in a polymer synthesis, such as for example a polyester synthesis. Additionally it was found that under certain conditions the quaternary P-cation is more effective in its biocidal activity than the quaternary N-cation.

The counter ion of the quaternary cation is represented by Y ^" in formula II. The nature of the anion Y is not particularly critical. Suitable examples for Y

in the embodiment where the cation is covalently bonded to the polymer can be chosen from the list halogenide, carboxylate, phosphate, phosphonate, nitrate, hydroxide. Preferably iodide, chloride, bromide or a combination of any of them is used as the synthesis of the biocidal polymer appeared to be more successful with a halogenide. Most preferably bromide is used as the counter ion.

In another embodiment of the invention the biocidal component is still incorporated as one of the monomers as described under the first embodiment. However in this embodiment it is the anion that is built-in covalently in the polymer, the cation being the counter ion. Thus the biocidal component is also in this embodiment chemically incorporated in the polymer by electrostatically means. As stated above the polymer must be obtained by a condensation reaction.

An example of how the biocidal component can be incorporated in the polymer is the following. Where the biocidal polymer is a polyester and the polyester is formed in the reaction between an alcohol component and an acid component, the biocidal component can be either in the form of the alcohol component (see left-hand side of Formula III) or in the form of the acid component (see right-hand side of Formula III). Thus the polyester with incorporated biocidal component can for example be represented, without being limited to the exact structure, by one of the versions of Formula III. It is also possible within the scope of the invention that both versions of Formula III are present within one polyester polymer, thus that both part of the alcohol components and part of the acid components are used to incorporate the biocidal component.

Pζ§ — U ⁰ — ø _* w Y _W Q — ° Il p£2 PES — o — I lfL _* w-γ.v _* λjH — o — PES

I Formula III

For the meaning of "alcohol component" and "acid component" reference is made to what is described before under Embodiment I.

Other polymers (than polyesters as described above) that are obtainable by a condensation reaction and that are thus suitable to incorporate a biocidal component are for example copolyesters, polyamides, polyesteramides, polyurethanes, polyethers, polycarbonates and combinations of any of them. For the

preparation of these different polymers reference is made to the generally available information.

The biocidal component under this embodiment has a structure that can be represented by formula IV:

(Zi)a

R ₈ ^R 1

(Z ₄ ) _d R ₆ Q R ₇ (Z ₅ ) _e R4 X ⁺ R ₂ (Z ₂ ) _b

R ₅ R.

A ^" ( ^Z 3)c Formula IV

Wherein: a, b, c, Z ₁ , Z ₂ , Z ₃ , R ₁ , R ₂ , R ₃ , R ₄ are the same as described above, d, e may independently of one another, be the same or different integers and represent the number of functional endgroups per branch,

R ₅ is alkyl chain or aromatic ring,

R ₆ , R ₇ , is, independently of one another, the same or different hydrogen, alkyl- or alkenyl groups with 1-10 carbon atoms,

R ₈ is hydrogen, alkyl- or alkenyl groups with 1-10 carbon atoms or the same as R ₄ Z ₄ , Z ₅ is, independently of one another, the same or different functional endgroups at the branches,

Q is carbon or aromatic ring,

A ^' is SO ₃ ^" , COO ^" , O ^" , P(O)(OR ₉ )O ^" , P(O)(O) ₂ ^" , and

Rg is alkyl group with 1-6 carbon atoms or phenyl. It should be observed that even though a, b, c, d and e for the individual unit is an integer, the average values of these constants are typically not an integer for a practical resin consisting of a high number of individual units.

A suitable component to be used in the synthesis of the biocidal polymer under this embodiment is the anion of sulfo-isophthalic acid, neutralized with an onium cation. Other suitable acids are the mono anion of phosphoric acid with the onium ion as counter ion. An example of a suitable alcohol is the anion of 2,2-diethylol propionic acid, which is neutralized with an onium ion.

In another embodiment of the invention the biocidal component is

incorporated in a crosslinker. A crosslinker is a component that is used in the binder of a coating composition, next to the film forming resin. "Binder" is generally defined as the resinous part of a paint consisting of polymer and crosslinker. The function of the crosslinker is to react with the resin in the binder upon which a crosslinked network is formed. To obtain a three-dimensional network it is necessary that the resin and crosslinker are equal to or more than 2-functional. With "more than 2-functional" is meant that the resin or crosslinker, just as the case may be, has at least partly three groups available for reaction with the other component in the binder composition. As the functionality of a compound is an average value for the functionality of all separate molecules, the functionality need not be an integer. With "more than 2-functional" is thus meant that at least part of the molecules have a functionality higher than 2. Preferably the average value for the functionality is at least 2,1. More preferably the average functionality is at least 2,3. A higher value is preferred as with a higher value for the functionality the properties of the coating finally obtained are better. Thus for example when the resin is two-functional, the crosslinker should at least be more than 2-functional to obtain a three-dimensional network. Where the crosslinker is two- functional, the resin should at least be more than 2-functional to realise a three- dimensional network. It is preferred that the crosslinker is at least three-functional. In the case that the crosslinker is more than 2-functional the in the crosslinker incorporated biocidal component can be represented by formula V:

Formula Va Formula Vb Formula Vc

In formula Va, the three functional groups of the crosslinker that are available for reaction with the resin are represented by Z, which need not be the same but can be different. X is the quaternary cation and Y is the counter anion. It is also possible that Y is in the centre and that X is the counter ion as shown in Formula Vb. The functional groups need not be arranged on separate branches as shown in Formula Va and Vb but may alternatively be arranged with two functional groups on one branch as shown in Formula Vc or even more functional groups on one of the branches (not shown). X

and Y can be the same as described under Embodiment I or II. Then the value of the functionality could be considered as the sum of a + b + c or a + b + c + d + e, respectively. Preferred embodiments then corresponds to a + b + c >1 and 4 > a + b + c > 2 or a + b + c + d + e >1 and 4 > a + b + c + d + e > 2, respectively. In another embodiment of the invention it is possible to combine different biocidal components into one coating composition. Thus it is for example possible to combine two kinds of biocidal polymers. An example hereof is the combination of a biocidal polymer according to Formula I (incorporated cation) with a biocidal polymer of Formula III (incorporated anion). Or another example is the combination of a biocidal polymer of Formula I (incorporated cation) with a biocidal crosslinker according to Formula V. Again another example is the combination of a biocidal polymer of Formula III (incorporated anion) with a biocidal crosslinker according to Formula V.

The polymer or crosslinker with the biocidal component incorporated as described in the various embodiments above can be used in the preparation of one or more coating compositions. A coating composition or paint composition will generally comprise a binder composition (or short a binder) and additives. With additive is here and hereinafter meant a substance that is generally added in a small quantity and that has a particular chemical or technological effect. Sometimes also pigments and/or colorants and/or other additives will be present in the coating or paint composition. The pigment present in the coating composition can be of an inorganic or organic nature. With pigment is here and hereinafter meant a substance consisting of particles, which is practically insoluble in the binder and is used as a colorant (DIN 55943). A colorant is a color-imparting substance. The binder composition is generally defined as the resinous part of the coating or paint composition consisting of polymer and crosslinker.

The coating composition is then generally applied to a suitable substrate and subsequently cured to form a coating on the substrate. The substrate can be fully or partially coated with the coating composition and thus after curing fully or partially be coated with the coating. The curing process to obtain a cured coating can proceed in various stages. It is possible to fully cure the coating composition at once or it is possible to first partially cure and in a second stage complete the curing process. In the last situation, where the cure is effected in two or even more stages, it is possible to use different curing mechanisms. The curing process is well known to the man skilled in the art of making coatings. Examples of curing processes are thermal

curing, curing with electromagnetic radiation, such as for example UV- or electron beam curing. It is also possible to use two (dual-cure) or more types of curing processes.

The substrate is not particularly critical and can be chosen depending on the mechanical and/or aesthetical requirements. Examples of suitable substrates are organic and inorganic materials such as for example wood, metal, plastic, paper, cardboard, brick, stone and composite material.

The biocidal polymers and the biocidal coating compositions can be used in all kinds of coatings, such as for example can and coil coatings, powder coatings as well as in dispersions and emulsions.

Testing of non-leaching biocides

To evaluate the biocidal activity of the polymers and crosslinkers with incorporated biocidal component, a test method was developed, as no standard test seemed available to test non-leaching biocidal components. The biocidal activity was determined based on the results that were obtained with two kinds of bacteria: Escherichia CoIi (E-coli) and Staphylococcus Aureus. The E-coli bacteria (E.coli ATCC 11105) was supplied by ATCC (Middlesex, UK) and stored in a refrigerator at -18 ⁰ C. A stock solution containing 2-5 ^* 10 ⁹ bacteria/ml was prepared. Tests are performed by immersing coatings obtained from the polymers and crosslinkers with incorporated biocidal component, in a diluted buffer solution containing 2-5 ^* 10 ⁶ bacteria/ml. A buffer solution (KH ₂ PO ₄ / K ₂ HPO ₄ ; pH=7,0) is needed to protect the bacteria from acid or basic conditions, and to have suitable ionic strengths (0,5 mmol/l) to prevent killing by osmotic pressure. The concentration of the buffer solution is important as well. The ion concentration should not be too low to create the right conditions for bacteria to survive, and not too high to mask the action of antibacterial agents. The substrate on which the coating is applied must be inert. We found that this is not always the case. For instance aluminium panels A-46 and Alcan can be used but AI-36 not, since then all the bacteria are killed due to the specific treatment of the substrate. After having applied the coatings on substrate, parts of them are immersed in 25 ml of the bacteria solution (in a plastic centrifuge vial) containing 2-5*10 ⁶ bacteria/ml and incubated at 25 ⁰ C while gently shaking. After several time intervals samples are taken out of the vial, diluted with buffer solution (1000 times) and spread over an agar breeding medium in a petri dish (LB-agar per liter: 1O g Bacto Trypton, 5 g Bacto Yeast extract, 5 g NaCI, 15 g Agar). After the petri dishes are stored at 37 ⁰ C overnight the number of

bacteria colonies was counted (every single bacteria forms one colony). When all bacteria survive one can count about 1000 colonies, when all bacteria die a log 3 reduction is obtained. A log 3 reduction is often taken as measure for good antibacterial behaviour. If all the bacteria are killed 10 ⁵ bacteria/ml are used in a next experiment. If then all these bacteria are killed a log 5 reduction is obtained, which is an excellent result.

The effectiveness of this test method was determined with a number of well-known biocides (antibacterial agents). It appeared that all the used biocides, when used as an additive, were effective in killing bacteria according to the developed test.

The invention will be further elucidated by the following, non-limiting Examples.

Examples Materials

The phosphonium compounds: (dimethyl sulfoisophthalic acid salt of (tributyl, dodecyl- phosphonium)) and (dimethyl sulfoisophthalic acid salt of (tributyl, cetyl-phosphonium)) (referred to respectively as C12 SIP-P and C16 SIP-P compounds) were obtained from Nippon Kagaku Kogyo Co. The ammonium compound (dimethyl sulfoisophthalic acid salt of cetyl trimethyl ammonium compound; C12 SIP-N) were prepared as follows:

Synthesis of dimethyl sulfoisophthalic acid salt of cetyl thmethyl ammonium

Commercial CETAB (cetyl trimethyl ammonium bromide) was reacted in water with dimethyl 5-sulfoisophthalic acid sodium salt (DM-SIP) CAS [3965-55-7] (commercially available from DuPont) in the following way:

To 29,6 grams (lOOmmol) DM-SIP dissolved in 400 ml water 36,4 grams (100 mmol) CETAB in 400 g of water was added while vigorously stirring. The reaction mixture was stirred for one hour at 30°C and left overnight at room temperature. After adding 400grams of diethylether the water layer (with NaBr) was removed and the ether layer was evaporated. To the waxy solid 150 g of acetone were added and heated until reflux. After cooling the dispersion was filtered and dried. 39 g (70% yield) DM-SIP-N were obtained.

The polyester resins were prepared following a standard polyester synthesis recipe. In this case modified polyester resins were prepared that resembled

the commercially available resins Uralac® SN844 or Uralac® P5263 (powder) resin wherein part of the normally used acid was replaced with the ammonium- or phosphonium- salt. The polyester synthesized can be schematically represented by the following structure, without being limited to the exact structure:

The coatings were applied on aluminium panels.

Procedure for antibacterial tests

In most of the biocidal tests Echerichia CoIi (E-coli) bacteria were used and in some of the tests Staphylococcus Aureus were used. The test is similar to the ASTM E2149-01 standard test method for "Determining the biocidal activity of immobilized antimicrobial agents under dynamic contact conditions". The bacteria (E CoIiATCC 11105) are supplied by ATCC and stored in the refrigerator at -80 ⁰ C. A stock solution containing 2-5*10 ⁹ bacteria per ml was prepared. The coatings were immersed in a diluted buffer solution, containing 2-5 ^* 10 ⁶ bacteria/ml. A buffer solution (KH ₂ PO4/K ₂ HPO ₄ ; pH = 7.0; 0,5 mmol/l) was used to protect the bacteria from acid or basic conditions, and to have suitable ion strengths to prevent killing by osmotic pressure.

Coated substrates (2*5 cm; 5 samples) were immersed in 25 ml of the bacteria solution (in a plastic centrifuge vial) containing 2-5 ^* 10 ⁶ bacteria/ml and incubated at 25 ⁰ C for 24 hours while gently shaking. After several selected time intervals, samples were taken out of the vial, diluted with buffer solution (1000 times) and spread over an agar breeding medium in a petri dish (LB-agar per liter: 10g Bacto Trypton; 5gr Bacto Yeast extract; 5gr. NaCI; 15gr Agar). After the petri dishes were stored at 37 ⁰ C overnight the number of bacteria colonies were counted (every single bacteria forms one colony). When all bacteria survive one can count > 1000 colonies, when all bacteria die a log 3 reduction is obtained. A log 3 reduction is often taken as a measure for good antibacterial behaviour, and a log 5 reduction as an excellent behaviour.

Coating preparation

All the coil coatings were dissolved in Solvessa 150 (72 wt % dry weight) and applied on A-46 aluminium panels. Either Cymel 303 (melamine crosslinker) or Uradur YB147 (blocked isocyanate) were used as crosslinker.

Results with Echerichia CoIi bacteria 1. Results first series

The results are shown in Table 1.

Table 1 : 1 ^st series of experiments with 20 wt % C12- or C16 SIP-P-polyesters. (Number of bacteria surviving the test; starting with 3-5*10 ³ E coli bacteria.) Coatings contain common 30 wt% pigments (coated TiO ₂ ).

n.d. = not determined

SN844 stands for Uralac® SN844 polyester resin commercially available from DSM

Coating Resins, the Netherlands.

Cat stands for the catalyst PTSA, Paratoluensulphonic acid

SIP-P stands for sulfo isophthalic acid with tributyl alkyl (C ₁₂ or C ₁₆ ) quaternary phosphonium ion as counter ion. The reference samples did not kill any bacteria, as expected. The coatings containing the phosphonium ions were all biocidal. The C12 phosphonium cations (with C ₁₂ alkyl tail) are more effective than the C16 (with C ₁₆ alkyl tail). It should be emphasized that these biocidal compounds are built-in, and still active.

2. Results second series

In a second series of experiments clear coats were tested (no pigments). The results are given in table 2. The clear coats give a better performance that the pigmented systems (table 1). One could speculate that the biocide is absorbed on the surface of the TiO ₂ particles, or that the viscosity of these coatings is higher, which hampers the diffusion of the biocides to the surface.

Table 2: 2 ^nd series of experiments with clear SIP-polyester coats (Number of bacteria surviving the test; starting with 3-5*10 ³ E coli bacteria)

3. Leaching-out

The major advantage of built-in biocides is their non-depleting behaviour. Therefore biocidal tests were done with coatings that have been immersed in a buffer solution for several weeks. In the present system the anion (sulfonate) of the biocide is built-in in the polymer, while the cation (quaternary phosphonium ion) is coupled by means of Coulomb forces (salts). Thus, it is impossible to leach out the quaternary phosphonium ion with pure water since it would violate the electrostatic rules.

In order to test the teachability of the quaternary ion in that medium the coated panels were immersed for one month at room temperature in a aqueous buffer solutions. In another series of experiments the panels were immersed in an aqueous solution for 20 minutes at 121 ⁰ C. The results are collected in table 3.

Table 3: Antibacterial properties of coatings panels before and after immersing them in an aqueous buffer system (Number of bacteria surviving the test; starting with 3-5*10 ³ E coli bacteria).

4. Quaternary ammonium ion containing resins

The ammonium salt of sulfoisophthalic acid (C12-SIP-N) was prepared by starting from the sodium salt of dimethylisophthtalic acid and trimethyl- cetyl ammonium bromide (see above). Both starting compounds are commercially available. This biocide was built-in in a SN844 recipe. The synthesis was comparable with the phosphonium salts. The results are given in table 4.

Table 4: Antibacterial properties of C12-SIP-N 844 coating (Number of bacteria surviving the test; starting with 3-5 ^* 10 ³ E coli bacteria).

The coatings containing quaternary ammonium ions performed very well.

5. Results with Staphylococcus Aureus

Phosphonium containing coatings (C12-SIP-P SN844) have also been tested. Figure 1 shows that these coatings kill the Staphylococcus Aureus effectively. It can be seen that the panel is free of bacteria and that there is no halo around the panel, indicating that no biocidal compound is depleted into the solution.

The coatings were tested with Staphylococcus Aureus according to the procedure as described above and the results are given in Table 5. The panels coated with C12-SIP-P SN844 are also biocidal for Staphylococcus Aureus bacteria according to that test. The coated panels remain biocidal after an aqueous

extraction at 121 ⁰ C.

Table 5: Antibacterial properties of C12-SIP-P SN844 coated panels with Staphylococcus Aureus (Number of bacteria surviving the test; starting with 3-5 ^* 10 ³ Staphylococcus Aureus).

6, Powder coatings

Resins with more mobile biocidal compounds have been prepared and tested. The structures of these resins are as below.

They are mixed with Uralac® P2260 resin, a commercial product of DSM Coating Resins, the Netherlands, and Primid® XL552 as crosslinker. The results obtained with these compositions are shown in Table 6.

Table 6. Antibacterial properties of powder coatings containing C12 SIP-P (Number of bacteria surviving the test; starting with 3-5 ^* 10 ³ E coli bacteria).

_ = Clear powder coating; = Clear coil coating; = Pigmented powder coating.

From table 6 it can be seen that biocidal properties are obtained in powder coatings as

well.

R

n = 0 - 20