Coating process by ion exchange

Abstract

A process for coating a product by ion exchange including: a) providing a product that contains a surface segregating species (SSS) having a low surface energy component and an ionic component wherein the SSS has segregated to an outer surface of the product to form an activated surface; and b) treating the activated surface of the product with a liquid containing a surface modifying agent comprising one or more polyionic species, wherein the polyionic species is attracted to and deposits on the activated surface through a process of ion exchange.

Claims

1. A process for coating a product by ion exchange comprising: a) providing a product with a mixture comprising a polymer and a surface segregating species (SSS), wherein the SSS is an electroactive compound having a low surface energy component and an ionic component, and wherein the SSS has segregated to an outer surface of the product to form an activated surface; and b) treating the activated surface of the product with a liquid comprising a surface modifying agent comprising one or more polyionic species, wherein the polyionic species is attracted to and deposits on the activated surface through a process of ion exchange.

2. The process of claim 1, wherein step b) further includes the formation of a superhydrophilic layer from the deposited polyionic species; the process further including the step: c) drying the superhydrophilic layer to form said coating.

3. The process of claim 1, wherein the mixture is a paint, and wherein the polymer and the SSS is provided within the paint, and wherein the SSS has segregated to an outer surface of the paint.

4. The process of claim 3, wherein the SSS has a concentration in the paint selected from the group consisting of: at least 0.5 wt %, between 0.5 wt % and 10 wt %, between 0.5 wt % and 5 wt %, and between 2 wt % and 5 wt %.

5. The process of claim 3, wherein the paint is a polyester-melamine based, thermally cured paint system.

6. The process of claim 3, wherein the SSS is added to the paint when the paint is still liquid and subsequently segregates to the surface of the paint layer.

7. The process of claim 1, wherein the low surface energy component of the SSS comprises one or more of the following: a siloxane derivative, a long chain alkyl group, a branched structure, a nonionic surfactant of the alkylene oxide oligomer or polymer type, a fluorocarbon or a dendrimer.

8. The process of claim 1, wherein the ionic component of the SSS is comprised of an organic cation covalently bound to the low surface energy component, in association with a mobile additive counterion.

9. The process of claim 8, wherein the cation comprises a quaternary ammonium ion.

10. The process of claim 1, wherein the ionic component of the SSS is comprised of an anion, preferably wherein the anion comprises part of the low surface energy group, more preferably part of a long chain alkyl group.

11. The process of claim 1, wherein the SSS comprises a salt of an organic cation, or a precursor of a salt of an organic cation.

12. The process of claim 11, wherein the salt of an organic cation comprises a quaternary ammonium cation, a quaternary phosphonium ion, or a thiouronium cation.

13. The process of claim 1, wherein the SSS comprises a quaternary ammonium cation (QAS) having low charge shielding.

14. The process of claim 13 wherein the SSS comprises one or more of N-(3-trimethoxysilylpropyl)-N,N,N-trimethyl ammonium chloride, N-(trimethoxysilyl) propyl-tetradecyldimethyl-ammonium chloride, a benzyltrimethylammonium chloride, N-(3-trimethoxysilylethyl)benzyl-N,N,N-trimethylammonium chloride, cetyl trimethylammonium bromide (CTAB), and a silicone quaternary surfactant containing a quaternary ammonium functional group.

15. The process of claim 1, wherein the surface modifying agent comprises one or more of an electrostatically stabilized colloidal suspension, a metal or non-metal oxide, material held in suspension through use of an ionic dispersant or as an emulsion, or a soluble polyionic organic polymer.

16. The process of claim 1, wherein the surface modifying agent comprises surface modifying ionic materials in association with their corresponding mobile phase counter ions, further wherein the surface modifying ionic materials are dissolved in the liquid or held in suspension in the liquid by electrostatic stabilisation.

17. The process of claim 1, wherein the surface modifying agent comprises one or more of: silica colloids; mixtures of silicas of various sizes; mixtures of functionalised silicas and polymer latexes; functionalised polymer latexes and their mixtures; layered double hydroxides; phyllosilicates; graphene oxide; particles suspended in water using electro steric dispersants; polyionic polymers; conductive polymers and cyclodextrins.

18. The process of claim 17, wherein the silica colloid has a concentration in the liquid selected from the group consisting of: at least 0.05 wt %, at least 0.25 wt %, and at least 0.5 wt %.

19. The process of claim 17, wherein the surface modifying agent is a smectic phyllosilicate present at a concentration of at least 0.05 wt %, preferably at least 0.4 wt %.

20. The process of claim 17, wherein the surface modifying agent comprises a silica colloid.

21. The process of claim 20, wherein the silica colloid comprises silica particles having a size from 5 nm to over 100 nm.

22. The process of claim 17, wherein the surface modifying agent comprises a functionalised silica colloid.

23. The process of claim 1, wherein the liquid has a pH selected from the group consisting of: less than or equal to 10, less than or equal to 9, and less than or equal to 7.

24. The process of claim 23, wherein the liquid has a basic pH.

25. The process of claim 1, wherein in step (b), the ionic strength of the liquid is adjusted.

26. The process of claim 1, wherein step (b) is conducted in a single pass.

27. The process of claim 1, wherein the product comprises steel.

28. The process of claim 27, wherein the product is steel coil.

29. The process of claim 1, wherein the surface modifying agent comprises an aqueous suspension of a synthetic smectic phyllosilicate clay, preferably laponite at a concentration of at least 0.5 wt %.

30. The process of claim 1, wherein the water contact angle of the coated product is selected from the group consisting of: less than 30°, less than 25°, and less than 20°.

31. The process of claim 1, wherein the low surface energy component of the SSS comprises polyethylene oxide.

32. The process of claim 1, wherein the low surface energy component comprises an organosilane derivative.

33. The process of claim 1, wherein the low surface energy component comprises an alkoxy silane.

34. The process of claim 1, wherein the low surface energy component comprises a trialkoxysilane.

35. A process for coating a product by ion exchange comprising: a) providing a product that with a mixture comprising a polymer and a surface segregating species (SSS), wherein the SSS is an electroactive compound having a low surface energy component and an ionic component, and wherein the surface segregating species SSS has segregated to an outer surface of the product to form an activated surface; and b) treating the activated surface of the product with a liquid comprising a surface modifying agent which comprises a surface modifying ionic material, wherein the surface modifying ionic material is attracted to and deposits on the activated surface in a process of ion exchange.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Notwithstanding any other forms which may fall within the scope of the apparatus and method as set forth in the Summary, specific embodiments will now be described, by way of example only, with reference to the accompanying drawings in which:

(2) FIGS. 1a to 1d shows a proposed physical model for the present process. FIG. 1a shows the initial attraction of suspended colloids (10) to the activated surface (20) and the quasi-equilibrium that may develop. FIG. 1b depicts cases where colloids in proximity to the activated surface lose part of their hydration sphere and become irreversibly bound to the substrate surface. This step is driven entropically by the release of bound water and by the dispersion of mobile counterions into the water layer. FIG. 1c depicts the formation of a superhydrophilic layer on the surface of the substrate as the density of adsorbed particles (10) reaches a critical limit. The water layer (30) sitting above the superhydrophilic surface contains additional material(s) which can now be deposited by drying of the water layer. FIG. 1d depicts the result of drying of the water film above the superhydrophilic surface where materials suspended in the water film are deposited randomly on the surface. This serves as a means to vary coating weight and to provide complex mixtures in the coating.

(3) FIG. 2 depicts the depth profile populations of elements in the immediate surface of Sample SM-13, (having paint without the electroactive additive) as measured by glow discharge optical emission spectroscopy (GDOS).

(4) FIG. 3 depicts the depth profile populations of elements in the immediate surface of Sample SM-20, (having paint with the electroactive additive) as measured by glow discharge optical emission spectroscopy (GDOS). Comparison to FIG. 2 shows that the population of silicon in the immediate surface region is enhanced, presumably due to segregation of the silicon containing SSS to the surface of the paint.

(5) FIG. 4 is a GDOS trace of Sample SM-20 that shows the presence of a chlorine signal in the immediate surface region of the paint containing the electroactive additive.

(6) FIG. 5 depicts the elemental depth profiles for Sample SM-21: a paint containing 5% N-(3-trimethoxysilylpropyl)-N,N,N-trimethyl ammonium after treatment with 6% Ludox suspension at pH 8, as measured by GDOS.

(7) FIG. 6 depicts the depth profile populations of elements in the immediate surface of Sample SM-21, (having paint with the electroactive additive) as measured by GDOS.

(8) FIG. 7 shows EPMA maps of the Mg signal at varying concentrations of Laponite suspensions as described in Example 16. The Mg signal is a proxy for Laponite concentration.

(9) FIG. 8: Graph showing relationship between Ludox® AM30 silica suspension concentration and silica coating thickness.

(10) FIG. 9: Graph showing relationship between Ludox® HS40 silica suspension concentration and silica coating thickness.

(11) FIG. 10: Graph showing correlation between silica thickness determined via EPMA versus SiO IR absorption peak area at 1200 cm.sup.−1.

(12) FIG. 11: EPMA analysis of the surface of a sample paint panel SM-21 coated with a silver/zinc oxide nanoparticle in silica mixture (5%).

(13) FIG. 12: EPMA silver distribution map of the surface of a sample paint panel SM-21 coated with a silver/zinc oxide nanoparticle in silica mixture (5%).

(14) FIG. 13: EPMA zinc distribution map of the surface of a sample paint panel SM-21 coated with a silver/zinc oxide nanoparticle in silica mixture (5%).

(15) FIG. 14: Photomicrograph of an area of the coating formed from Kynar ARC PVDF latex and Ludox HS40 mixture.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

Examples

(16) Non-limiting Examples of a process for coating a product by ion exchange will now be described.

Example 1 (Comparative): Water does not Wet the Standard Paint Surface

(17) A panel of a commercial coil coating was prepared according to standard laboratory methods. The paint used was a solvent-borne thermal cure system comprised of hydroxyl functional polyester, alkylated melamine formaldehyde, titanium dioxide pigment, acid catalyst, and miscellaneous additives (PPG Industries). The paint was coated at a nominal thickness of 40 microns on a preprimed steel panel using a wire drawdown bar and cured for 45 s in an oven set to 300 C to reach a Peak Metal Temperature (PMT) of 235 C and a final thickness of approximately 20 microns. The panel was cooled to room temperature immediately on removal from the oven by quenching in a water bath. A sample cut from this panel was dipped into water. The interaction of the water with the paint surface was hydrophobic i.e. no wetting was observed and no water was retained on the panel. The contact angle of a droplet of water with this surface was 83°.

Example 2 (Comparative): Aqueous Ludox Suspension does not Wet the Standard Paint Surface

(18) A sample of the paint panel from Example 1 was dipped into a 5% w/w aqueous suspension of Ludox HS-40® colloidal silica. The interaction of the Ludox suspension with the paint surface was hydrophobic i.e. no wetting was observed and the aqueous suspension was not retained on the panel when withdrawn from the liquid.

Example 3 (Comparative): Aqueous Laponite S482 Suspension does not Wet the Standard Paint Surface

(19) A sample of the paint panel from Example 1 was dipped into a 2% w/w aqueous suspension of Laponite S482 synthetic phyllosilicate clay. The interaction of the Laponite suspension with the paint surface was hydrophobic i.e. no wetting was observed and the aqueous suspension was not retained on the panel when withdrawn from the liquid.

Example 4: Preparation of Active Paint

(20) A liquid sample of the paint from example 1 (100 g) was mixed with a solution of electroactive deposition additive comprising N-(3-trimethoxysilylpropyl)-N,N,N-trimethyl ammonium chloride, 50% in methanol, (Gelest Industries) (6.8 g) to form a 5% w/w mixture of the additive in paint. The paint was coated on a primed steel panel and cured according to standard procedures as described in Example 1.

Example 5: Water does not Wet Activated Paint

(21) A sample of the paint panel from Example 4 was dipped into water. The interaction of the water with the paint surface was hydrophobic i.e. no wetting was observed and no water was retained on the panel when withdrawn from the liquid. The contact angle of a droplet of water with this surface was 82°.

Example 6: Salt Solution does not Wet the Activated Paint

(22) A sample of the paint panel from Example 4 was dipped into 1 M NaCl solution. The interaction of the solution with the paint surface was hydrophobic i.e. no wetting was observed and no water was retained on the panel when withdrawn from the solution. This shows that it is not sufficient that the wetting solution only contains an anion in order to induce hydrophilicity of the activated surface. It is inferred that the anionic species must be capable of irreversible attachment to the activated paint surface in order for superhydrophilicity to be manifested.

Example 7: Aqueous Ludox® Suspension does Wet the Activated Paint Panel

(23) A sample of the steel panel from Example 4 was dipped into an aqueous suspension of 5% w/w Ludox HS-40® colloidal silica (Grace Chemical Industries). On removal of the panel from the aqueous suspension it was observed that the entire paint surface was covered in liquid film, i.e. the wetting of the liquid on this surface was superhydrophilic. The superhydrophilic film on the surface of the paint was allowed to dry. The contact angle of a droplet of water on this modified paint surface was below the measurement capability of the Goniometer (i.e. less than 10°).

Example 8: Establish Effect of Variable Ludox HS-40 Concentration

(24) A sample of the steel panel from Example 4 was dipped into an aqueous suspension of Ludox HS-40® colloidal silica (Grace Chemical Industries) at concentrations of 0.5%, 0.25%, 0.1%, and 0.05% w/w. The panel was held in the Ludox® suspension for 5 seconds, then removed and the wetting of the suspension on the surface was observed. The panel was then dipped into each Ludox® suspension for a second period of 5 seconds and the wetting of the suspension on the surface was observed. Results are summarised in Table 1. Under these conditions the critical Ludox® concentration for complete wetting on the first dip is between 0.25 and 0.5% w/w. Critical concentration for wetting on a second dip is between 0.05 and 0.1% w/w. It is inferred from this example that particles are deposited irreversibly on the activated surface from suspensions with low concentrations of silica but the density of coverage is too low to provide superhydrophilic wetting without additional exposure.

(25) TABLE-US-00001 TABLE 1 Ludox ® Concentration Wetting After Wetting After (% w/w) 1.sup.st Dip, 5 s 2.sup.nd Dip, 5 s 0.5 0.25 0.1 0.05 Superhydrophilic wetting-  ; Incomplete wetting-  ; Non-wetting- 

Example 9 (Establish Effect of Variable Additive Concentration)

(26) The paint from example 1 was formulated with variable amounts of the additive N-(3-trimethoxysilyl-propyl)-N,N,N-trimethyl ammonium chloride, 50% in methanol, (Gelest Industries). The resulting paints were applied to primed steel panels and cured as per the panels in example 1. Panels incorporating each lot of paint were dipped in a 6% w/w Ludox® suspension at pH≅9 for a period of 5 seconds. Wettability of the panel increases with increasing additive concentration in the paint. Results are summarised in Table 2.

(27) TABLE-US-00002 TABLE 2 Additive concentration Wetting after in paint (% w/w) dip, 5 s 5 3 2 1 Superhydrophilic wetting-  ; Non-wetting- 

Example 10: Effect of Alternative Quaternary Ammonium Additive Benzyltrimethylammonium Chloride

(28) The paint from Example 1 was mixed with 5% w/w benzyltrimethylammonium chloride, drawn down on a primed steel panel and cured according to standard practices. The resultant paint film surface showed some disruption. Panel samples were dipped in Ludox® HS-40 suspensions prepared according to the specifications in Table 3. These results show that decreasing pH results in improved particle deposition (as measured by induction of surface wettability) even as the particle concentration decreases.

(29) TABLE-US-00003 TABLE 3 Ludox ® HS-40 concentration (% w/w) pH Wetting Comments 6.0 8-9 1.0 5-6 0.5 4 Patchy film after drying

Example 11: Establish Effect of Variable Ionic Strength

(30) The paint from Example 1 was mixed with 5% w/w benzyltrimethylammonium chloride, drawn down on a primed steel panel and cured according to standard practices. The resultant paint film surface showed some disruption. Panel samples were dipped in 6% w/w Ludox® HS-40 suspensions prepared according to the specifications in Table 3 where ionic strength was varied with additions of sodium chloride. These results show that increasing ionic strength results in improved particle deposition, as measured by the induction of surface wetting.

(31) TABLE-US-00004 TABLE 4 NaCl Concentration Wetting after (mol L.sup.−1) dip, ? s Comments 1.0 Drying produces patchy Ludox film; Ludox suspensions begins to gel at this ionic strength 0.75 0.5 0.25 0 Superhydrophilic wetting-  ; Incomplete wetting-  ; Non-wetting- 

Example 12: Establish Effect of Alternative Additives

(32) The paint from Example 1 was formulated with alternative additives incorporating the some or all of the structural features descriptive of the additive N-(3-trimethoxysilyl-propyl)-N,N,N-trimethyl ammonium chloride, namely organic cation part, low surface energy (surfactant) part, trialkoxysilyl part. Results are summarised in Table 5. The optimum performance is exhibited by N-(3-trimethoxysilyl-propyl)-N,N,N-trimethyl ammonium chloride. A cationic centre is required for deposition of a Ludox® HS-40 suspension, rather than hydrolysed alkoxy silane. Hydrophobic shielding of the cation reduces the effective of deposition. A low surface energy group is necessary to manifest the effect. Low surface energy groups vary in their effectiveness. Some low surface energy groups lead to disruption of the paint surface.

(33) TABLE-US-00005 TABLE 5 Hydrolysable Concentration Additive Cation type Surfactant type alkoxy silane in paint N-(trimethoxysilyl)- Monoalkyltrimethyl Alkoxysilane Yes  >3% propyl-N,N,N-trimethyl QAS ammonium chloride N-(trimethoxysilyl)propyl- Dialkyldimethyl Alkoxysilane Yes .sup. 5% tetradecyldimethyl- QAS .sup. 5% ammonium chloride .sup. 5% 2-[methoxy(polyethyleneoxy) None Alkoxysilane, Yes .sup. 5% propyl]trimethoxysilane oligomeric (6-9 EO units) ethylene oxide CTAB Monoalkyltrimethyl Long chain alkyl No .sup. 5% QAS Didocyldimethylammonium Dialkyldimethyl QAS Long chain alkyl No .sup. 5% bromide BYK 163 Secondary None No 3.0% Ammonium Ion 20.0%  BYK 2000 Dialkyldimethyl None No 3.0% QAS 20.0%  Benzyl Monoalkyltrimethyl None No 5.0% trimethylammonium QAS chloride Octyl Monoalkyltrimethyl Short chain No 5.0% trimethylammonium QAS alkyl chloride Silquat AO (Hydrophilic) Dialkyldimethyl Siloxane No 5.0% QAS 3.0% Silquat AO-B Dialkyldimethyl Siloxane No 5.0% (Hydrophobic) QAS 3.0% 1.0% Silquat J15 Dialkyldimethyl Siloxane No 3.0% (Hydrophobic) QAS Silquat J2-B Dialkyldimethyl Siloxane No 1.2% (Hydrophobic) QAS Silquat Di-10 Dialkyldimethyl Siloxane No 3.0% (Hydrophilic) QAS 3.0% (Difunctional) 1.0% Silquat MO-25 Dialkyldimethyl Siloxane No 3.0% (Hydrophobic) QAS Silquat 3150 Dialkyldimethyl Siloxane, Long No 5.0% (Hydrophobic) QAS chain alkyl 5.0% 3.0% Bis(3- Ammonium (in Alkoxysilane Yes 5.0% trimethoxysilylpropyl)amine water, exposure below pH 9) Ludox ® HS-40 Additive suspension Wetting Comments/Observations N-(trimethoxysilyl)- Various As per descriptions propyl-N,N,N-trimethyl given in examples ammonium chloride above (see Table 1) N-(trimethoxysilyl)propyl- 2% tetradecyldimethyl- 1% Initial wetting, ammonium chloride followed by dewetting at edges 0.25%   2-[methoxy(polyethyleneoxy) 6.0%.sup.  propyl]trimethoxysilane (6-9 EO units) CTAB 6.0%.sup.  Addition to paint results in surface disruption Didocyldimethylammonium 6.0%.sup.  Addition to paint bromide results in surface disruption BYK 163 6.0%.sup.  6.0%.sup.  Loading at this level results in disruption of surface quality BYK 2000 6.0%.sup.  6.0%.sup.  Loading at this level results in disruption of surface quality Benzyl 6.0%.sup.  Surface disruption trimethylammonium chloride Octyl 6.0%.sup.  trimethylammonium chloride Silquat AO (Hydrophilic) 1% 1% Silquat AO-B 6% (Hydrophobic) 1% 6% Silquat J15 1% (Hydrophobic) Silquat J2-B 1% (Hydrophobic) Silquat Di-10 1% (Hydrophilic) 6% Initial panel wetting followed by dewetting 6% Silquat MO-25 1% (Hydrophobic) Silquat 3150 1% Initial wetting (Hydrophobic) 6% followed by dewetting at edges 6% Bis(3- 6% trimethoxysilylpropyl)amine Superhydrophilic wetting-   ; Incomplete wetting-   ; Non-wetting-  These results suggest that quaternary ammonium ions are generally useful for this process, more heavily alkylated QAS (more charge shielding) show lower activity, and alkoxy silanes are most effective within this group.

Example 13: Effect of Concentration on Laponite S482 Coating

(34) Concentration of surface active ion was varied in the paint at levels of 1, 3, 4, and 5% w/w. Concentration of Laponite S482 in aqueous suspension was varied at levels of 0.01, 0.05, 0.1, 0.5, 1 and 2% w/w. The boundary level for film formation is defined as the point at which the aqueous suspension shows superhydrophilic wetting of the paint surface.

(35) TABLE-US-00006 TABLE 6 Laponite concentration Electroactive additive concentration in paint (% w/w) w/w in water 1 3 4 5 .01 .05 .1 .5 1 2 Superhydrophilic wetting-  ; Non-wetting- 

(36) These results show that both the electroactive additive and Laponite S482 concentrations need to be at optimal levels in order for superhydrophilic wetting of the substrate surface to occur, where superhydrophilic wetting indicates that surface modifying particles are bound to the substrate in a dense array.

Example 14: Detection of the Additive at the Paint Surface

(37) The presence of the electroactive additive in the paint film was monitored according to the depth profile populations of silicon and chlorine as measured by glow discharge optical emission spectroscopy (GDOS). A commercial coil coating formulated by PPG Australia was used to demonstrate the activity of the electroactive additive. The composition of this paint system can be described generically according to the typical characteristics of this class of materials, as follows. It is a solvent borne paint of approximately 50% volume solids. Approximately 40% of the solids are pigments, predominantly titanium dioxide. Of the remaining 60% of solids, approximately 80% of that amount is a hydroxyl-functional polyester resin and 20% is an alkylated melamine formaldehyde crosslinking resin. The mixture includes small amounts of additives including an acid catalyst for curing. GDOS measurements were performed on an unmodified control and on a modified paint containing 5% w/w of the electroactive additive N-(3-trimethoxysilylpropyl)-N,N,N-trimethyl ammonium chloride.

(38) FIGS. 2 and 3 depict the populations of elements in the immediate surface of two examples: Sample SM-13 and Sample SM-20, paints without and with the electroactive additive, respectively. The GDOS trace illustrates the atomic percent of silicon in the top one micron of paint volume. Comparison of the data for the two cases shows that the silicon population at the immediate surface is higher (10% versus 4%) for the paint containing the electroactive additive, and that the integrated intensity of the signal through a depth of 0.2 microns is significantly greater. (The source of silicon in the unmodified paint is a silicon containing surfactant.)

(39) FIG. 4 is a GDOS measurement of the elemental depth profile of a sample of paint containing 5% of the additive N-(3-trimethoxysilylpropyl)-N,N,N-trimethyl ammonium chloride. It shows the presence of a chlorine signal in the immediate surface region of the paint containing the electroactive additive. These results show that the electroactive additive has migrated to the surface of the paint and is localised in the immediate surface region. It is inferred that as a result of localisation in this manner the additive is available to interact electrostatically with ionic materials in a supernatant liquid in the manner described in the disclosure.

Example 15: Detection of the Ludox® Colloidal Silica Layer at the Surface of the Paint and Estimation of Thickness

(40) A paint sample panel SM-21 containing the electroactive additive (5% w/w) was exposed to an aqueous suspension of Ludox colloidal silica (5% w/w). The aqueous suspension completely wet the surface of the paint. The panel was allowed to dry in air. The dried panel was analysed by GDOS to reveal the depth profile of elements (FIGS. 5 and 6). FIG. 5 is a crude measurement which illustrates that the treatment results in formation of a layer of silica colloid on the surface. FIG. 6 is a finer measurement that allows an estimate of the average thickness of the deposited silica layer, at ca. 100 nm.

(41) The GDOS results in FIG. 6 show that the immediate surface region of the paint is composed entirely of silicon and oxygen. With increasing depth, the silicon concentration population decreases as the carbon (from the paint) concentration increases. This behaviour is typical of low resolution measurements on rough surfaces where the signals corresponding to layers of different elemental composition are mixed, due to non-uniform etching caused by surface roughness.

(42) In general the surfaces of coil coating paints such as this one with moderate surface gloss have an Ra surface roughness on the order of one micron with numerous spikes and discontinuities. In such cases the thickness of a surface layer is approximated as being equal to the half-height of an element known to have a stable concentration in the matrix but zero concentration in the surface layer. Therefore by using the half height of the nitrogen signal we can make a rough estimate a thickness of the colloidal silica layer of approximately 100 nm.

(43) This result supports the inference that drying of the aqueous layer formed by superhydrophilic wetting of the Ludox® suspension on the electroactivated paint surface results in deposition of all of the material in the supernatant liquid film. Without being bound by theory it is reasonable to suggest that the electrostatic attraction between the surface active ion in the paint and the surface modifying ionic material suspended in the aqueous phase will reach an equilibrium state of charge neutralisation where the immediate surface of the paint is covered in a layer of the surface modifying ionic material approximating a monolayer in thickness, and as a result any of the surface modifying ionic material remaining freely suspended In the aqueous phase will be electrostatically repelled from this surface.

(44) As illustrated in FIGS. 1a to 1d, the forces of repulsion between nanoparticulate materials at relative large distances from each other increase exponentially as the distance between the particles is reduced. However at a critical point in the very close approach of the particles attractive forces increase rapidly and become dominant such that the particles now experience a strong attraction. Once nanoparticles establish adhesion to each other it becomes very difficult to counter the forces holding them together.

(45) In this way the electroactive deposition method can be used to deposit a thin coating of controlled thickness and good structural integrity.

Example 16: Detection of the Laponite Phyllosilicate Particle Distribution on the Paint Surface

(46) Paint panels containing 5% w/w of the electroactive additive N-(3-trimethoxysilylpropyl)-N,N,N-trimethyl ammonium chloride were dipped into aqueous suspensions of Laponite® S482 phyllosilicate of varying concentrations at levels of 0.05, 0.1, 0.2, 0.4, 0.6, 0.8 and 1.0% w/w. The panels were dried and analysed by EPMA, mapping the Mg signal and the results are presented in FIG. 7. Mg is unique to Laponite in this formulation and therefore is diagnostic of the presence of Laponite on the surface. The size of the mapping area of the paint coupons is 512 μm by 512 μm. The presence of Mg is mapped on a scale of 0 (blue) to 32 (red), where 32 is the maximum value recorded. In these results it is clear that the surface approaches complete coverage (as observable under the resolution of this technique) at a Laponite concentration between 0.4 and 0.6% which is in keeping with the results in the example for the determination of boundary conditions.

Example 17: Evidence of Improved Adhesion

(47) Samples of paint containing the SSS were treated with suspensions of commercial silica products according to the specifications given in Table 7. Control samples include a standard paint with no SSS and no silica, and a paint where a silica coating was applied on a standard paint panel without the SSS additive. The water contact angle and carbon absorption resistance, using the procedure below, was measured for each sample.

(48) Each sample was subjected to a “water double rub” procedure. In this procedure the surface of the paint is rubbed both forward and reverse with 10 repetitions with a wet cotton pad. The water contact angle and carbon absorption resistance tests were repeated on the panel after the water rubbing test. An increase in the water contact angle indicates removal of the silica. An increase in ΔL (i.e. darkening) of the panel due to carbon absorption also indicates removal of the silica coating where presence of a silica layer acts as a barrier to absorption of carbon dust on the paint surface.

(49) These results show that presence of the SSS dramatically improves the adhesion of the silica to the surface as reflected in the maintenance of the original contact angle and carbon absorption resistance.

(50) TABLE-US-00007 TABLE 7 ΔL (after 6 + 10 brushing Water Contact Angle (°) cycles) Additive Level Coating After initial After 10 After initial After 10 in Paint system/conditions silica coating water DRs silica coating water DRs 5% 6% w/w Bindzil C8 15.33    10 to 12.74 −3.73 −4.48 5% 6% w/w Bindzil 23.77 28.62 −9.48 −11.94 C50 5% 6% w/w Bindzil <10 <10 to 10 −4.31 −5.45 cc301 5% 6% w/w Bindzil 18.38 21.11 −5.88 −8.72 cc151 3% 6% w/w Ludox <10 10.17 −6.35 −6.78 HS-40 4% 6% w/w Ludox    10 to 16.96 18.11 −9.2 −9.35 HS-40 5% 6% w/w Ludox <10 to 10 23.79 −6.19 −7.59 HS-40 5% 3% w/w Bindzil C8 +  10.64 to 23.82 34.49 −10.07 −10.04 3% w/w Bindzil C50 5% 5.05% w/w <10 to 10 14.54 −9.21 −7.77 Bindzil C8 + 0.94% w/w Bindzil C50 5% 5.5% w/w Bindzil <10 to 10 15.79 −10.94 −9.81 C8 + 0.5% w/w Bindzil C50 No additive Ludox HS-40 37.16 84.71 −2.07 −22.64 No additive No coating 80.24 — −37.8
Carbon Absorption Resistance Procedure:

(51) The carbon used is Special Black 4 Powder, from Evonik Degussa Australia Pty. Ltd. The initial “L” colour data of the panel is recorded using the Hunter Lab system. A 15 w/w % carbon slurry in water is applied on the sample surface (about 4 cm diameter area) and the sample is dried at 70° C. for 1 hr. After removal from the oven the sample is allowed to cool. Loosely adhered carbon powder is tipped gently from the surface. The sample is placed under running water and additional carbon is removed from the surface by brushing six times with a soft paint brush. The sample is dried and colour reading “L” value is recorded. The sample is again placed under running water and additional carbon is removed from the surface by brushing a further ten times with a soft paint brush. The sample is dried and colour reading “L” value is recorded.

Example 18. Variation of the Silica Coating Thickness

(52) A paint sample panel SM-21 containing N-(3-trimethoxysilylpropyl)-N,N,N-trimethyl ammonium chloride (5% w/w) was exposed to an aqueous suspension of Ludox HS40 colloidal silica (6% w/w) for 5 seconds. After removal from the mixture the panel was dried in an oven at 100 C for 60 seconds. The silica coating thickness was estimated by EPMA to be 510 nm.

(53) Variable coating thicknesses can be obtained by using more dilute silica suspensions. A drawdown bar technique was used with silica suspensions of varying concentration. Ludox® HS40 and Ludox® AM30 silica suspensions were applied to a paint sample panel SM-21 containing the electroactive additive (5% w/w) using a #0003 drawdown bar (Gardiner). The panel was dried in an oven at 100 C for 20 seconds. Silica coating thickness estimates were obtained by EPMA (Table 8). FIGS. 8 and 9 show that the silica coating thickness is proportional to the silica concentration for a given liquid film thickness for Ludox® HS40 and Ludox® AM30 respectively.

(54) TABLE-US-00008 TABLE 8 Area of SiO Silica Silica Coating absorption Concentration Thickness (nm, envelope (ca Silica Type (% w/w in water) EPMA Estimate) 1200 cm.sup.−1) Ludox HS40 0.5 15 — (drawdown) 1 33 158 2 48 196 4 137 440 Ludox AM30 0.5 14 101 (drawdown) 1 27 133 2 50 189 4 103 384 6 125 593 Ludox HS40 (dip 6 513 — coating)

(55) FTIR (Fourier transform infrared spectroscopy) spectroscopy was used to establish a correlation between EPMA (Electron Probe Microanalyser) thickness determination versus the integrated intensity of the silica absorption peak in the region of 1200 cm-1 in the mid IR. The sample panels used for EPMA were measured by ATR (Attenuated total reflection) spectroscopy on a Perkin Elmer Spectrum instrument using a diamond crystal. The digital difference spectrum was obtained for the silica peak of a coated versus uncoated paint panel. The area of this peak was determined by digital integration (Table 8) and these values were correlated to EPMA thickness (FIG. 10). Accordingly, FTIR can be used to detect the presence of a silica coating applied using the method of the present disclosure and to estimate its thickness using this correlation.

Example 19. Incorporation of Metal/Metal Oxide Nanoparticles into the Silica Colloid Deposition Layer

(56) Silver/zinc oxide nanoparticle mixtures (courtesy of the Polymer CRC, U.S. Pat. No. 8,673,367, “Nano silver-zinc oxide composition”) were suspended in Ludox HS40 silica suspensions (6% w/w in water) at concentrations of 1%, 5% and 10% w/w relative to silica using a high speed mixer using BYK2010 polymeric dispersant (BYK Additives & Instruments, Altana). The suspensions were not stable to settling. The suspensions were dip coated onto paint sample panels SM-21 [containing N-(3-trimethoxysilylpropyl)-N,N,N-trimethyl ammonium chloride]. The surfaces of the panel were analysed by EPMA to reveal the presence of silver and zinc oxide incorporated into the silica coating. Results are presented for the case of a 5% w/w silver/zinc oxide nanoparticle in silica coating where the silver/zinc oxide nanoparticle composition by mass is approximately 30% silver and 58% zinc with the remainder being oxygen. The results refer to the same analysis area. The only source of silver and zinc in these systems is from the incorporated nanoparticle mixture. The silver/zinc oxide mixture is reported to have antibacterial properties. Therefore the disclosed process can be used to prepare a surface treatment where the silica effectively functions as a binder for other materials that may alter the chemical properties of the surface.

(57) FIGS. 11, 12 and 13 show EPMA distribution maps of silica, silver and zinc, respectively, of the surface of the sample paint panel SM-21 (containing N-(3-trimethoxysilylpropyl)-N,N,N-trimethyl ammonium chloride) coated with a silver/zinc oxide nanoparticle in silica mixture (5%). The map area is 512 microns by 512 microns. In each case, the white areas indicate higher concentrations of the mapped element [please confirm]. Comparison of FIGS. 12 and 13 indicate the correspondence between silver and zinc maps, that is, the observed signals are due to the silver/zinc oxide mixed nanoparticle.

Example 20. Incorporation of Polymer Latex into the Silica Colloid Deposition Layer

(58) Two PVDF (polyvinylidene difluoride)/acrylic resin latexes were used, including Kynar Aquatec® ARC and Kynar Aquatec® CRX, both obtained from Arkema. These are both anionic latex suspensions with particle sizes of approximately 100 nm. Ludox HS40 was mixed with the Kynar latex in water according to the mass ratios given in Table 9 to give stable suspensions, where the total mass of suspended solids was 2% of the mixture. Paint sample panels SM-21 with 5% w/w electroactive additive in the paint were coated with the colloid mixtures using a #0003 drawdown bar. Water contact angle data (for Kynar CRX systems) illustrates that the contact angle increases as the proportion of Kynar resin latex increases. That is, as the proportion of hydrophobic fluorocarbon Kynar increases the surface becomes more hydrophobic. In this way the silica acts as a binder to allow surface modification with latexes and in that way to manifest the latex properties on the surface of the paint, thereby to alter the physical properties of the surface.

(59) TABLE-US-00009 TABLE 9 Kynar CRX/Silica Water contact mass ratio angle (deg) 0 (100% silica) <10 0.2 39 0.4 48 0.6 58 0.8 59 1.0 55 1.2 64

(60) FIG. 14 is a FEGSEM photomicrograph at 50,000 times magnification of an area of the coating formed from the Kynar ARC PVDF latex and Ludox HS40 mixture. The Kynar:Ludox mass ratio was 0.4 in a total 2% solids aqueous suspension. As shown in FIG. 14, the larger Kynar ARC latex particles are distributed throughout in the mass of smaller Ludox silica colloid particles.

(61) Hydrophobic/hydrophilic segregation in the system is largely avoided as the surfaces of the particles are anionic while suspended.

Example 21. Use of Silica Suspensions in Water/Alcohol Mixtures

(62) A 3% Ludox® HS40 v/v suspension in water (6% w/w) was diluted with methanol to a 1% v/v mixture. The suspension is stable and clear with no evidence of particle coalescence. Sample paint panels with varying levels of electroactive additive were dipped into this suspension. The suspension was also applied to sample panels with varying levels of electroactive additive using a #0003 drawdown bar. Observations are recorded in Table 10. The presence and thickness of a silica coating was determined by FTIR spectroscopy using the relationship illustrated in FIG. 10 above. This data illustrates that suspensions in solvent mixtures can be used to prepare silica coating by ion exchange by the method of this disclosure. Solvent mixtures change the ability to wet the hydrophobic paint surface. It is believed that solvent mixtures affect the many aspects of the mechanisms of the processes at work that are influenced by hydrogen bonding among water molecules.

(63) TABLE-US-00010 TABLE 10 Silica coating thickness estimate Conditions Observations (FTIR) 0% Initial panel wetting. On drying the liquid beads 0 electroactive up rapidly. No permanent silica coating formed. additive; dip Contact angle same as uncoated paint surface. coating 1% Initial panel wetting. On drying the liquid beads 0 electroactive up slowly. No permanent silica coating formed. additive; dip Contact angle same as uncoated paint surface. coating 2% Initial panel wetting. Wetting is persistant on  41 nm electroactive drying. Contact angle <10 degrees. additive; dip SiO peak area = 173 coating 5% nitial panel wetting. Wetting is persistant on  38 nm electroactive drying. Contact angle <10 degrees. additive; dip SiO peak area = 162 coating 0% Panel doesn't wet. No permanent silica coating 0 electroactive formed. Contact angle same as uncoated paint additive; surface. drawdown 1% Initial panel wetting. On drying it is revealed 0 electroactive that no permanent silica coating formed. additive; Contact angle same as uncoated paint surface. drawdown 2% Initial panel wetting. Wetting is persistant on 490 nm electroactive drying. Contact angle <10 degrees. additive; SiO peak area = 1925 drawdown 5% Initial panel wetting. Wetting is persistant on 268 nm electroactive drying. Contact angle <10 degrees. additive; SiO peak area = 1058 drawdown

(64) Whilst a number of specific process embodiments have been described, it should be appreciated that the process may be embodied in many other forms.

(65) In the claims which follow, and in the preceding description, except where the context requires otherwise due to express language or necessary implication, the word “comprise” and variations such as “comprises” or “comprising” are used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the apparatus and method as disclosed herein.

(66) Further patent applications may be filed in Australia or overseas on the basis of, or claiming priority from, the present application. It is to be understood that the following provisional claims are provided by use of example only and are not intended to limit the scope of what may be claimed in any such future applications. Features may be added to or omitted from the provisional claims at a later date so is to further define or re-define the invention or inventions.