Field

The present invention generally relates to polymeric surface coatings, and in particular polymeric coatings for stainless steel surfaces which are readily peelable and provide a surface protection function from contamination and physical scratching.

Background

Peelable coatings may provide conveniently removable surface coatings for a variety of objects. They may be presented as a sacrificial protector coating for the surface.

A popular form of peelable coating include rubber coatings, applied via aerosol sprays or dip coats, used to decorate car rims, bonnets and door panels. Peelable rubber coatings include rubbers such as styrene -butadiene dissolved in organic solvents such as xylene, ethylbenzene, acetone and methyl ethyl ketone. These solvents release volatile organic compounds (VOC) into the air and are potentially hazardous for both human health and the environment. Regulatory developments have led to stricter use of volatile organic solvents in paints.

As an alternative water-based emulsion coatings have been developed where water replaces organic solvents as the medium in which polymer particles are dispersed. Polyvinyl acetate and acrylic are examples of polymers capable of forming water-based emulsions. Coatings formed by casting a dispersion and allowing it to dry typically form a permanently adhered coating. To achieve peelability, the adhesion strength of the polymer coating often needs to be reduced. A technique employed in some coatings is to use a release agent such as paraffinic wax, animal or vegetable oils, all of which contain fatty acids, to reduce the adhesion of the polymer coating to the surface. Several problems associated with the inclusion of release agents containing fatty acids into a coating composition are their tendency to react with metal, stain masonry and wood, as well as its oily texture. Accordingly, those in the art appreciate that the peelability of a coating composition will be somewhat also dependent not only on the compositional make up of the coating composition but the substrate surface coating interaction which is primarily dependent on the nature of the substrate surface.

Other requirements of peelable coatings include having sufficient tensile strength in the coating so that no fracturing occurs either with weathering or upon peeling.

The use of stainless steel as a working surface has grown over the years with applications ranging from the kitchen setting to industrial working surfaces such as in factories for cutting, paint mixing and other chemical processing applications. Stainless steel is however susceptible to degradation and oxidation by harsh chemicals such as solvents and acids, as well as physical wear and tear which compromise the integrity of the surface by scratching. Providing a protective coating which may be sacrificed and easily peelable offers an attractive solution. Prior art approaches to this solution offer coating compositions having one or more of the following drawbacks: i) not curable at ambient temperature, ii) the requirement of multiple coating applications to achieve an effective thickness, iii) no/mild chemical resistance, iv) necessity of crosslinking agents, v) water dissolvable and/or vi) the application of heat for peel release.

It is therefore desirable to provide an easily peelable protector coating composition for stainless steel (and other substrates) without the use of release agents, one that is chemically and water robust, flexible, and capable of curing at ambient temperatures.

Summary of Invention

In part, the present invention is based on the discovery that a peelable polymer coating which is able to protect stainless steel (and other surfaces) and can be easily applied and cured at ambient temperature, can be prepared using a mixture of water dispersible polyurethane resins with different glass-transition temperatures (Tg).

Accordingly, in one aspect, there is provided a peelable polymer coating composition comprising a mixture of at least one low Tg water-dispersed polyurethane (low Tg PU) and at least one high Tg water-dispersed polyurethane (high Tg PU), wherein the low Tg PU has a low Tg PU solids content of about 30% to about 50% by weight and the high Tg PU has a high Tg PU solids content of about 30% to about 50% by weight, wherein the ratio of the high Tg PU : low Tg PU to form the coating composition is from 10:90 %(w/w) to about 90: 10 %(w/w).

In one embodiment the at least one low Tg PU has a Tg between about -5° - 10° C, such as -5°, -4°, -3°,-2°,-Γ, 0°, 1°, 2°, 3°, 4°, 5°, 6°, 7°, 8°, 9° or 10° C.

In one embodiment the at least one high Tg PU has a Tg between about 20° - 40° C, such as 20°, 21°, 22°, 23°, 24°, 25°, 26°, 27°, 28°, 29°, 30°, 31°, 32°, 33°, 34°, 35°, 36°, 37°, 38°, 39°, or 40° C.

As used herein "Tg water-dispersed polyurethane" refers to a polyurethane resin dispersed in water, wherein the polyurethane resin is characterized by a high or low Tg (or glass-transition temperature). Tg may be measured by ASTM E1356-08. Tg characterizes a temperature of the reversible transition of a polymer resin from a hard and relatively "glassy" state into a molten or rubber-like state as temperature increases. The Tg ranges shown above characterize the range of temperatures over which the glass transition occurs, which is always lower than the melting temperature, (Tm) of the crystalline or glassy state. The "low" therefore refers to a temperature range (-5° - 10°C) which is lower relative to a "high" Tg PU which is characterized with a higher Tg (i.e., a Tg between about 20° - 40°C). It will be appreciated that the term "water-dispersed polyurethane" refers to a polyurethane resin that forms a colloidal system in which particles of the polyurethane are dispersed in water which acts as the continuous phase. Examples of a low Tg water-dispersed PU include Neorez R1005, Neorez R1007, and Neorez R2190 available from DSM. Examples of a water dispersed high Tg PU includes Neorez R2180 and Neorez 2203 available from DSM and Alberdingk U9800 and U9380 available from Alberdingk Boley. The low Tg and high Tg polyurethane dispersions may also be further characterised by their elongation at break strain value. Elongation at break strain is expressed as a percentage and is the ratio of the initial length of a sample and the length at which the sample breaks. A low Tg PU may display an elongation at break strain percentage of between 1000% and 1500%, for example 1000%, 1100%, 1200%, 1300%, 1400% or 1500%. A high Tg PU may display an elongation at break strain percentage of between 100% and 700%, for example 100%, 200%, 300%, 400%, 500%, 600% or 700%.

In another aspect of the invention there is provided a method of forming a peelable polymer coating on a surface, the method comprising the steps of (i) mixing at least one water- dispersed low Tg PU and at least one water-dispersed high Tg PU, wherein the low Tg PU has a low Tg PU solids content of about 30% to about 50% by weight and the high Tg PU has a high Tg PU solids content of about 30% to about 50% by weight, and wherein the ratio range of high Tg PU : low Tg PU is from about 10:90 %(w/w) to about 90: 10 %(w/w), to form a coating composition; (ii) applying said coating composition from (i) to a surface; and (iii) curing of the coating composition at ambient temperature on said surface to form the peelable polymer coating.

In an embodiment the surface is a stainless steel surface.

In an embodiment the mixing step further comprises the addition of at least one coalescing agent.

In certain embodiments the mixing step further comprises the addition of one or more additives selected from the group consisting of coalescing agents, defoamers, levelling agents and thickeners.

As used herein, the term "polyurethane" may refer to a polyester-based polyurethane or a polyether-based polyurethane. A polyester-based polyurethane is a polyurethane comprising multiple ester functional groups. A polyether-based polyurethane is a polyurethane comprising multiple ether functional groups. The high Tg polyurethane of the present invention may be a polyester-based polyurethane. The low Tg polyurethane of the present invention may be a polyether-based polyurethane.

In a further aspect the invention provides a stainless steel based product wherein at least a portion of the product has been coated with a composition comprising a mixture of at least one low Tg water-dispersed polyurethane (low Tg PU) and at least one high Tg water-dispersed polyurethane (high Tg PU), wherein the low Tg PU has a low Tg PU solids content of about 30% to about 50% by weight and the high Tg PU has a high Tg PU solids content of about 30% to about 50% by weight, and where the ratio range of high Tg PU : low Tg PU is from about 10:90 %(w/w) to about 90: 10 %(w/w).

In still a further aspect of the invention there is provided a kit for forming a peelable polymer coating on a surface, the kit comprising (i) a coating composition comprising a mixture of at least one low Tg water-dispersed polyurethane (low Tg PU) and at least one high Tg water- dispersed polyurethane (high Tg PU), wherein the low Tg PU has a low Tg PU solids content of about 30% to about 50% by weight and the high Tg PU has a high Tg PU solids content of about 30% to about 50% by weight, and where the ratio range of high Tg PU : low Tg PU is from about 10:90 %(w/w) to about 90: 10 %(w/w); (ii) an applicator for applying the coating composition to the surface; and (iii) instructions for coating the surface with said composition and curing to form the peelable polymer coating.

Brief Description of the Drawings

Fig. 1 shows a graphic depiction of a peelable polymer coated stainless steel surface according to an embodiment of the present invention.

Fig. 2 shows photographs of the application of a coating composition according to one embodiment of the present invention to a stainless steel surface.

Fig. 3 shows photographs of performance testing of a coating composition according to one embodiment of the present invention as applied to a stainless steel surface.

Detailed Description

Various aspects of the invention as described herein provide for a peelable polymer coating composition suitable for application on stainless steel based products such as bench tops, whitegoods (i.e., kitchen and laundry stainless steel appliances), walls, etc., but may also be appropriate for use on other substrates such as other metal surfaces, powder coated surfaces, ceramics and glass.

Advantageously, the peelable polymer coating as presently disclosed can (i) add a non- permanent colour to any surface (where a colour component is introduced into the composition), (ii) protect surfaces against scratches, stains and harsh chemical and water degradation (iii) be easily removed by peeling without using chemicals, heat or mechanical stripping methods, leaving no residue or damage to the surface. In contemplated applications, the coating composition can be used to protect stainless steel work benches from harsh chemicals and paint (see for instance, Figure 1), or may be used as temporary protection, for instance, for protecting stainless steel kitchen appliances during storage, transport, delivery and installation. Other applications may include industrial applications, such as automotive paint booth surface protection, surface protection for transportation vehicles (such as buses, trains and trucks) and as a protective coating for complex surfaces, where adhesive films may not be sufficiently conformable to be laid down properly.

It will be appreciated that the coating composition according to the invention will be cured to form a coating on a surface. The term "coating" as used herein refers to the cured composition and the "coating composition" refers to the composition prior to curing. The peelable polymer coating composition according to the present invention comprises a mixture of at least one low Tg water-dispersed polyurethane (low Tg PU) and at least one high Tg water-dispersed polyurethane (high Tg PU), wherein the low Tg PU has a low Tg PU solids content of about 30% to about 50% by weight and the high Tg PU has a high Tg PU solids content of about 30% to about 50% by weight, and where the ratio range of high Tg PU : low Tg PU is from about 10:90 %(w/w) to about 90: 10 %(w/w). The ratio range includes mixtures of high Tg PU : low Tg PU from about 50:50, 51 :49, 52:48, 53:47, 54:46, 55:45, 56:44, 57:43, 58:42, 59:41, 60:40, 61 :39, 62:38, 63:37, 64:36, 65:35, 66:34, 67:33, 68:32, 69:31, 70:30, 71 :29, 72:28, 73:27, 74:26, 75:25, 76:24, 77:23, 78:22, 79:21, 80:20, 81 : 19, 82: 18, 83: 17, 84: 16, 85: 15, 86: 14, 87: 13, 88: 12, 89: 11 and to about 90: 10. Conversely the ratio range includes mixtures of high Tg PU : low Tg PU from about 50:50, 49:51, 48:52, 47:53, 46:54, 45:55, 44:56, 43:57, 42:58, 41 :59, 40:60, 39:61, 38:62, 37:63, 36:64, 35:65, 34:66, 33:67, 32:68, 31 :69, 30:70, 29:71, 28:72, 27:73, 26:74, 25:75, 24:76, 23:77, 22:78, 21 :79, 20:80, 19:81, 18:82, 17:83, 16:84, 15:85, 14:86, 13:87, 12:88, 11 :89, to about 10:90.

In an embodiment the ratio range of mixtures of high Tg PU : low Tg PU is about 90: 10 to

70:30.

In an embodiment the ratio range of mixtures of high Tg PU : low Tg PU is about 90: 10 to

50:50.

In an embodiment the ratio range of mixtures of high Tg PU : low Tg PU is about 10:90 to 30:70.

In an embodiment the ratio range of mixtures of high Tg PU : low Tg PU is about 10:90 to

50:50.

The term 'peelable' refers to the property of being removable by physical peeling by hand. Peel strength is a measure of adhesive bond strength. It can be defined by various measurements, such as the average load required to part two bonded materials per unit length separation (N/inch or N/m), or the average load per unit width of bond line required to part two bonded materials where the angle of separation is 90 degrees and separation rate is 50 millimeters per minute (ASTM D6862). For a coating to be peelable, its cohesive strength (i.e. breaking force) should be greater than its adhesive bond strength. Since the adhesive bond strength will vary depending on the nature of the substrate to which the coating is adhered, the coating may be peelable from some substrates and not from others. In an embodiment the compositions of the invention are specifically suitable for coating stainless steel. The peel strength is preferably between 1-10 N/inch, for instance 1-7 N/inch, 1-6 N/inch, 1-5 N/inch, or 1-4 N/inch, such as about 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5.0, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9, 6.0, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, 7.0, 7.1, 7.2, 7.3, 7.4, 7.5, 7.6, 7.7, 7.8, 7.9, 8.0, 8.1, 8.2, 8.3, 8.4, 8.5, 8.6, 8.7, 8.8, 8.9, 9.0, 9.1, 9.2, 9.3, 9.4, 9.5, 9.6, 9.7, 9.8 or 9.9 N/inch. The peelable coatings described herein have an elongation at break of at least about 100% as measured by ASTM D882, or at least about 150, 250, 350, 400, 450 or 500, or between about 300 and about 1200%, or between about 100 and 800, 100 and 500, 200 and 1200, 600 and 1200 or 400 and 600%, e.g. about 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, 1000, 1050, 1100, 1150 or 1200%.

The coating compositions according to the present invention may be prepared by the use of standard equipment in the art. The high and low Tg PUs may be mixed at ambient temperature (i.e., room temperature) in a container (e.g mixing tank) which is exposed to atmospheric conditions. Homogeneity of the mixture may be attained with medium stirring over a 2-10 min mixing period. In an embodiment any additional additives (such as coalescing agents, thickeners, defoamers and leveling agents) are added once homogeneity is attained.

Accordingly, in an embodiment the peelable polymer coating composition comprises: a mixture of at least one low Tg water-dispersed polyurethane (low Tg PU) and at least one high Tg water-dispersed polyurethane (high Tg PU), wherein the low Tg PU has a low Tg PU solids content of about 30% to about 50% by weight and the high Tg PU has a high Tg PU solids content of about 30% to about 50% by weight, and wherein the ratio range of high Tg PU : low Tg PU is from about 10:90 %(w/w) to about 90: 10 %(w/w); and at least one coalescing agent.

In another embodiment the peelable polymer coating composition comprises: a mixture of at least one low Tg water-dispersed polyurethane (low Tg PU) and at least one high Tg water- dispersed polyurethane (high Tg PU), wherein the low Tg PU has a low Tg PU solids content of about 30% to about 50% by weight and the high Tg PU has a high Tg PU solids content of about 30% to about 50% by weight, and wherein the ratio range of high Tg PU : low Tg PU is from about 10:90 %(w/w) to about 90: 10 %(w/w); at least one coalescing agent; at least one thickener; at least one defoamer; and/or at least one leveling agent.

Coalescing agents may be used for optimizing the film formation process of the polymeric binder particles by reducing the minimum film formation temperature (MFFT) of the dispersions. The film formation process in polymer dispersions involves the coalescence of the polymeric particles, during and after the evaporation of the water, thereby permitting contact and fusion of adjacent polymer dispersion particles. Coalescing agents typically reduce the MFFT and as a consequence may serve to improve film formation by avoiding crack formation on the film surface. Suitable coalescing agents include partially or moderately hydrophobic organic solvents and are less volatile (i.e. have a slower evaporation rate) than water. Examples of suitable coalescing agents include butoxydiglycol, butyl glycol, glycol ethyl ether, diethylene glycol ethyl ether, alkylene glycol ethers such as ethylene glycol monomethyl ether, ethylene glycol monohexyl ether, ethylene glycol monoethyl ether, ethylene glycol mono-n-butyl ether, diethylene glycol monomethyl ether, diethylene glycol mono-n-butyl ether, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol n-butyl ether, tripropylene glycol monomethyl ether, ethylene glycol monoisobutyl ether, diethylene glycol monoisobutyl ether, propylene glycol monoisobutyl ether, ethylene glycol monophenyl ether, propylene glycol monophenyl ether, ethylene glycol monomethyl ether acetate, ethyl diglycol, butyl diglycol and mixtures of any two or more thereof. In a preferred embodiment, the coalescing agent used in the coating composition is dipropylene glycol n-butyl ether.

The coalescing agent is preferably present in the coating composition at a concentration of between about 1 to 8% by weight, for example, 1%, 2%, 3%, 4%, 5%, 6% 7% or 8% by weight.

Suitable thickeners for the present application are those which are also sometimes described as rheology modifiers which are added to control the viscosity of the composition. A suitable rheology modifier should preferably serve both functions of building up the viscosity of the coating composition and improving its anti-sagging properties. Accordingly, anti-sagging agents are also interchangeably referred to herein and thickeners. For applications on non- horizontal surfaces, anti-sagging is an important property. It will be appreciated that the eventual thickness of the coating will depend on orientation of the surface to which the coating composition is applied. It will be appreciated that the viscosity of the coating composition will be determined by considering both the orientation of the surface to which the composition is to be applied and the method by which the composition is to be applied. For example, a coating composition to be applied to a vertical surface may have a viscosity of between about 4000 cPs to about 5400 cPs in order to provide a coating of a suitable thickness, where the method of application is by using a brush, a roller or an adhesive spreader. A coating composition to be applied to a horizontal surface may have a viscosity of between about 400 cPs to 1000 cPs, in order to provide a coating of a suitable thickness and smooth appearance. Where the method of application is by spraying on to a vertical or horizontal surface, a composition with lower viscosity is required. For example, a coating composition to be applied by spray application may have a viscosity of about 100 cPs to about 200 cPs.

A suitable thickener may be an associative thickener. Examples of a suitable thickener include Coapur 5035, Coapur 5535, Rheolate 278, Acrysol RM-8, and Coatex BR-100P. An example type of preferred thickener is hydrophobically modified ethoxylate urethanes (HMEU).

The thickener may be present in the composition in an amount of from 0.5% to about 5% (w/w).

When using a thickener the composition may be allowed to stand for a period of from 2hrs-30hrs to allow the viscosity to build up prior to application to a surface.

The compositions disclosed herein may also include a defoamer, which prevents the formation of bubbles in the coating and destroys any bubbles that do form. Examples of suitable defoamers include silicon-based defoamers such as polysiloxane defoamers. Particular defoamers include polydimethylsiloxane with a HLB value of about 1 to 3, BYK 094, BYK 024, BYK 029, Tegofoamex 825, Drewplus S-4386, Drewplus S-4287 and Drewplus S4288. The defoamer may be added to reduce the formation of foaming when the composition is applied to the surface.

The compositions disclosed herein may also include a levelling agent, which ensures that the surface of the coating obtained from the coating composition self levels. Examples of suitable levelling agents include silicon-based wetting agents such as polysiloxane wetting agents.

Particular levelling agents include polydimethylsiloxane, Tego Wet 250, BYK 333, BYK 346, BYK 348 and BYK 349.

Since the defoamer and the levelling agent are similar in both chemical structure and nature, they can be used interchangeably in the composition. In an embodiment, a composition of the present invention may comprise a defoamer or a levelling agent. In another embodiment, a composition of the present invention may comprise both a defoamer and a levelling agent.

The defoamer and the levelling agent may be present in the composition in a combined amount of from 0.05% to about 2.0% (w/w).

The peelable polymer coating may be formed as a single layer adhering directly to the stainless steel surface to be coated or a portion thereof, with no intermediate surface release agent required to facilitate peeling. The stainless steel surface or the portion thereof to be coated may be in a vertical orientation, a horizontal orientation or an orientation intermediate to the vertical and horizontal orientations.

The single layer coating may be formed through the application of one coat. The single layer coating may be applied by an adhesive spreader. In this regard, the coating thickness may range from a thin layer of about 100 microns, or 10 microns, or less, to a thick layer of 1000 microns, or 10000 microns, or more. In an embodiment the coating thickness is from 0.15 - 3.5 mm, such as about 1.6 mm, 1.7 mm, 1.8 mm, 1.9 mm, 2.0 mm, 2.1 mm, 2.2 mm, 2.3 mm, 2.4 mm, 2.5 mm, 2.6 mm, 2.7 mm, 2.8 mm, 2.9 mm, 3.0 mm, 3.1 mm, 3.2 mm, 3.3 mm, 3.4 mm or a range based on any two of these figures. In some embodiments for wall coatings, the typical thickness of a coating is in the range of several hundred microns or generally more than 100 microns.

The peelable polymer coating may also be formed from the application of more than one layer of the coating composition adhering directly to the stainless steel surface to be coated, or a portion thereof, with no intermediate surface release agent required to facilitate peeling. The coating may be formed through the application of multiple layers of the coating composition. The multiple layer coating may be applied by an aerosol, spray gun, an atomizer, adhesive spreader, a paint brush or roller.

One of the main advantages of the coating compositions of the present invention is that they are curable at ambient temperature and often within about 24 hrs after application.

As a further advantage the coatings produced by the coating compositions disclosed herein are both water and chemical resistant. Water resistance can be measured by a covered spot test (ASTM D 1308-02). Chemical resistance has been observed in relation to acids (e.g. isocyanic acid), and organic solvents (e.g. naptha, toluene, ethylene benzene, N-butyl acetate, etc.). Many of the chemicals mentioned above are used in the automotive aftermarket industry such as panel repair shops. Accordingly, the coatings formed by the compositions disclosed herein may have specific application in the protection of surfaces used in this industry.

In an embodiment, the coating compositions may also include additional polymers, such as a polyurethane-acrylate (PUA) or an acrylic resin. Examples of a polyurethane-acrylate (PUA) include NeoPac E- 122 and NeoPac R-9045. Polyurethane-acrylates may display an elongation at break strain percentage of between about 500% to about 750%, for example, 500%, 560%, 610%, 660% or 750%. An acrylic resin may also be a self-crosslinking acrylic. Examples of an acrylic resin include Neocryl XK-12 and Neocryl XK-14. Acrylic resins may display an elongation at break strain percentage of between about 100% to about 310%, for example, 100%, 150%, 200%, 250%, 300% or 310%. The polyurethane-acrylate and acrylic resin together, may be present in the composition in an amount of no greater than 50% of total resins. For example, the concentration of the polyurethane-acrylate and acrylic resin taken together may be 0%, 10%, 20%, 30%, 40 % or 50% of the coating composition.

In an embodiment the coating compositions may also include colouring agents. Colouring agents usable for the peelable coating comprises any variety of water soluble paints, pigments and dyes. Usable organic pigments include azo dyes (monoazo, diazo, azo condensation, azo salt, azo metal complex, and benzimidazolone) and polycyclic pigments (phthalocyanide, anthraquinone, quinacridone, dioazine, perylene, and thioindigo). Usable inorganic pigments include carbon black, titanium dioxide, zinc oxide, yellow or red iron oxides, zinc chromates, azurite, chromium oxides, cadmium sulphides, lithopone, raw and burnt sienna or umber, phthalocyanine green, phthalonitrile blue, ultramarine blue. Also possible is the use of matting agents such as silicas and of fillers such as calcium carbonate and/or talcum. Optionally, effect pigments such as aluminum or pearlescent flakes or dichroic pigments may be used, either alone or in combination with one or more other pigments. An example of an effect pigment may be a carbon-based pigment, which may have odour-absorbing properties. Another example of an effect pigment may be a pigment with fluorescent properties, which may provide a "glow-in-the-dark" effect.

In a further embodiment, the composition may also include a pH indicator compound which may be added to allow the user to detect the coating on the surface and/or to indicate that the coating has cured.

To provide the coatings with additional functionalities, additives such as biocides, fillers and anti-cratering agents, fragrance oils may also be added to the coating. SYNTHESIS EXAMPLES

Preparation of High Tg Polyurethane-Low Tg Polyurethane Blended Compositions

A first high Tg polyurethane dispersion (for instance, NeoRez R-2180, DSM NeoResins or Aberdingk U9800 and U9380) and second low Tg polyurethane dispersion (for instance NeoRez R-1005, DSM NeoResins) were mixed by 5 minute-mild stirring at room temperature (amounts were added based on the %w/w ratio's shown in Table 1). A small amount of a coalescing agent such as butoxydiglycol, butyl glycol, glycol ethyl ether, dipropylene glycol n-butyl ether, ester alcohol, and diethylene glycol ethyl ether, is added into the mixture of polymer dispersions. The mixture is stirred at 300 rpm for 5 minutes. Then, additives such as defoamers, leveling agents, and a thickener that is based on polyurethane, were incorporated into the mixture with the mild agitation. The agitation speed was maintained at 300 to 500 rpm for 5 minutes until a

homogeneous coating composition was obtained. The coating compositions were then applied to a horizontal stainless steel surface and left to dry at ambient temperature to form a coating. The coating formed displays a transparent film.

TESTS AND OBSERVATIONS

Peel strength of peelable polymer coating on stainless steel.

To evaluate the removable/peelable/aging properties of the peelable colour coating on stainless steel, the peel strength test was conducted (ASTM D6862) by aging the coating in a 50°C oven for up to 28 days. The same samples were also aged at room temperature (23°C) as a control. The test is based on 90 degree peel strength test with an Instron machine, head cell weight (5Kg), cell capacity (100N), head speed (50 mm/min), 15mm gauge length, and 3 measurements were made for each sample type. Table 1 shows the peel strength of various formulations and the corresponding comparative non-blended formulations. The successful formulations were further tested and exposed to a range of industrial spray painting chemicals (solvent-based, water-based paints, hardeners, thinners etc., (Table 1)), using a covered spot test, following ASTM D1308-02 (Figure 3). The spot tested coating was then peeled back to check for any film integrity lost and if the chemicals had penetrated through the polymer coating on to the stainless steel (SS) substrate. Similarly, SS panels were painted with car paint to stimulate residues on a SS bench top in a panel shop and the polymer coating was coated onto a "dirty" bench and the polymer coating is then removed (Figure 3).

Results.

The peel strength results showed blended formulations consistently had lower (easier to peel) peel strength when compared to, for instance, the neat high or low Tg PU coating, conforming the necessity to have the blend in for better peelability. These coated panels were then aged in a 50°C oven for up to 28 days to test the film peelability and tests for film brittleness over time (accelerate aging), which is important in order to know the durability limits of when the film is no longer peelable. All blended coatings tested were both water and chemical resistant.

Table 1 - Blended polymer formulation v the raw high or low Tg PU tested under accelerated heat aging test (at 50°C) and test results for 1) Peel Strength at 7 days on stainless steel substrate and coating 2) Days until coating is not peelable after accelerated heat aging on stainless steel substrate

Further robust testing of 'NeoRez R2180/ NeoRez R1005' and 'Alberdingk U9800/ NeoRez R1005' showed that this formulation was able to resist the harsh chemicals used in panel shops and the coating can still retain its film integrity when covered spot tested with these chemicals and protected the stainless steel substrate.

Applicator Testing

The choice of applicator design may be deemed advantageous to the final finish coating appearance and also the ease of use to the application. The following application methods have been tested and the results are summarized in the comparison table below, Table 2. The adhesive spreader is the recommended application method as it is quick and easy to apply and can achieve a good film build (0.2-0.3 mm) in one coat and also create a high gloss and smooth appearance in the cured coating. The 4mm V notch spacing on the adhesive spreader allows excess coating composition to be pushed along with the applicator to easily spread the coating, but the gaps between the V notches also leaves behind a thin layer of the coating composition to create the desired film build up, which a squeegee, brush or roller cannot readily achieve.

Table 2 - Comparison Table of Applicator Testing for stainless steel surface protect coating