WO2018150056A1

WO2018150056A1 - Surface activation

Info

Publication number: WO2018150056A1
Application number: PCT/EP2018/054183
Authority: WO
Inventors: Mohamed Oubaha; Muhammad MORSHED; Brendan Duffy; Mary O'SULLIVAN
Original assignee: Technological University Dublin
Current assignee: Technological University Dublin
Priority date: 2017-02-20
Filing date: 2018-02-20
Publication date: 2018-08-23
Anticipated expiration: 2019-08-20
Also published as: GB201702740D0

Abstract

A method to treat the surface of a substrate or a portion thereof, the method comprising applying air-plasma to said surface or a portion thereof and applying a silane composition to said surface or a portion thereof.

Description

Title

Surface activation Field of the Invention

The current invention relates to treatment of substrate surfaces using air-plasma treatment and silane treatment. Also contemplated is a treatment composition and uses thereof.

Background of the Invention

Exposed surfaces of materials are responsible for all mechanical, thermal, chemical, and electrochemical interaction with the environment. For this reason, functional coatings are often used on such surfaces, in particular metal surfaces, to provide the required properties such as aesthetic properties or protective properties, including protection against corrosion, fouling, graffiti, fingerprints or contamination of any type. Activation, or functionalisation, of the surface of the substrate (often referred to as "surface treatment") is required to enable irreversible anchorage of these coatings, be they organic, inorganic or hybrid coatings, to the substrate surface. Generally speaking, surface treatment is implemented at an early stage of the product development in a wide variety of industries including, but not limited to, transport (automotive, aerospace, railway), electronics, military and medical industries. In the automotive and aerospace industries, in particular, surface treatments are needed to enable adhesion of organic primers and paints on aluminium, steel, composites and plastics. In the electronic and military industries surface treatments are needed to enable the adhesion of insulating coatings, and in the medical industry surface treatments are used to enable the irreversible binding of biocompatible coatings on a variety of implants.

Currently, the most widely used surface treatment strategy to functionalise metal and other surfaces, such as plastics, glass and ceramics, is organic-inorganic hybrid silanes (OIHS). The OIHS is used as a thin film (mono or multiple layer) that is deposited onto the metal surface, and acts as an adhesion promoter to other inorganic, organic or hybrid coatings. This process is generally sufficient if the substrate to be coated exhibits high energy surfaces with hydroxyl groups that can act as an anchoring point for the OIHS adhesion promoter. This adhesion promoter forms a stable and homogenous surface for the top coating to be applied. However, an issue can arise if the substrate to be coated exhibits low surface energy properties. This can often be seen with metal and plastic surfaces. It then becomes almost impossible to fully immobilise the OIHS on the low energy surface, which results in poor binding of the OIHS reflected in the overall adhesion of the top coating, with delamination and cracking taking place. Acid etching performed in a liquid state is a well-established method for treating metal surfaces for better adhesion. Different acid treatments can be applied to different metal substrates, for example, chromic acid is used when the metal is aluminium, sulphuric acid can be utilised for stainless steel and nitric acid is often used on copper substrates. However, there are numerous drawbacks to this approach as it can be a time consuming and costly process, and can also cause damage to the surface being treated. Wet chemical treatments are also problematic under environmental consideration because of issues with waste disposal, with pressure mounting in the industry to completely phase out chromate conversion coatings.

At present some industries are making use of silanes, such as 3-(trimethoxysilyl)propyl methacrylate (Methacryloxypropyltrimethoxysilane) (MAPTMS) or TEOS, as an intermediate layer for coating adhesion on metal surfaces. The process involves either washing of the samples with the silanes solutions or introduction of the silanes solutions within a chamber followed by the plasma irradiation of the silane vapour, which is subsequently deposited on the metal substrates by vacuum. In the latter, the plasma is used to decompose the silane vapour into active species that become able to chemically bind on some metal surfaces. The main disadvantages of this process include the fact that the aforementioned silane compositions are not versatile enough, i.e. they do not contain all of the required chemical functionalities to be employed for a wide variety of metals. In addition, large and irregularly shaped substrates cannot be processed within the standard plasma chambers used. Furthermore, the process being currently employed can lead to contamination and deterioration of the plasma system, with a direct effect on the reproducibility and maintenance costs.

Aluminium has been the substrate material of choice in the automotive and aerospace industries in recent years due to its high strength to weight ratio, excellent fatigue resistance and good machinability. It is also widely used in microelectronics, food and packaging, home furnishing, marine, medical and dental industries. This is a very reactive metal, quickly forming an aluminium oxide layer upon exposure to the ambient atmosphere. It is this layer that protects the metal substrate against corrosion and adverse environmental effects. However, for commercial identity purposes this layer has to be removed, the surface anodized, primed and, in some cases, painted. Anodising has been exploited extensively by the aerospace and automotive industries as a surface pre-treatment for aluminium, and other metals, to create a more structured and corrosion resistant base for primers and paints. Any exposure to the environment either chemical, physical or mechanical can damage the anodised layer and subsequently expose the base substrate, which will lead to corrosion. In order to avoid this, protective coatings are employed as a top layer. However, because of the inherent non-polar character of anodised aluminium, surface treatment to promote wetting to ensure good adhesion of a top coat, such as a paint, to the surface for a range of manufacturing applications is necessary.

OIHS prepared by the sol-gel process, also called sol-gel materials, are one family of materials that are applied to anodised metal surfaces, such as anodised aluminium surfaces, in order to increase adhesion of organic systems such as paints and primers, in addition to providing uniformity, chemical, physical and mechanical resistance, as well as the necessary environmental and health requirements. Sol-gel coatings bond well to metallic substrates and are easily deposited via dip-coating, spin coating or spray coating methods, and can be cured at low temperatures, typically below 150^°C. However, the main challenge for adopting these materials is the poor adhesion of primer and top-coat layers to the sol-gel surface due to the lack of mechanical bonding between sol-gel and the top layer. Acid or wet chemical processing is not suitable for the activation of the sol-gel coated anodised surface, due to the possible damage induced by the corrosive effect of the reactions taking place in this process.

US20160102406 describes a method of coating a surface using sol-gel precursors of alkoxysilane type. This document is concerned with aluminium only. It does not disclose the amounts the precursors used in the composition.

US2012/01 18436 discloses a method of treating a substrate. This document is concerned with substrates comprising nitinol only. The composition disclosed for use in the method comprises APTES only. GB2498356 describes a treatment of the surface of an implantable medical device. The composition disclosed for use in the method comprises APTES only. The silane is not hydrolysed prior to deposition.

WO201 1/018707 relates to improved packaging. This document discloses layer on layer adhesion and air plasma application in a chamber before coating. The silane layer is composed of vinyl trichlorosilane in either xylene, isopropyl alcohol or a chlororfluorocarbon gas. Alternatively, gammamethacryloxypropyltrimethoxysilane (MAPTMS) in a methanol- water solvent is used.

Karakoy et al (2014) discloses increasing adhesion strength of SEMS (self-expandable metal stents) to the surrounding tissue by modifying the stent surface with silane coupling agents. The composition disclosed for use in the method comprises one silane only, namely GPTMS or APTES.

Fiorilli S et al (2008) discloses a vacuum system equipped with a plasma source for deposition of APTES on a silicon surface. Therefore, there is a need to develop a method, which is low-cost and high throughput, to treat a surface, in particular a metal surface, and enable binding of primers and other inorganic, organic or hybrid coatings, while avoiding the above-discussed problems. The current invention offers an alternative to chemical surface treatment using an environmentally friendly, rapid and inexpensive method that can be used for surface treatment without damaging the surface.

Summary of the Invention

One aspect of the current invention provides a method to treat the surface of a substrate or a portion thereof, the method comprising - applying air-plasma to said surface or a portion thereof, and

- applying a silane composition to said surface or a portion thereof.

Preferably, the silane composition comprises 3-aminopropyltriethoxysilane (APTES).

Typically, the silane composition comprises a combination of at least two silanes, in which one of said at least two silanes is APTES. Preferably, the composition further comprises (3- (Trimethoxysilyl)propyl methacrylate) Methacryloxypropyltrimethoxysilane (MAPTMS).

Still preferred, the silane composition has from about 20% to about 90% w/w APTES.

Suitably, the silane composition comprises about 50% w/w APTES and 50% w/w MAPTMS.

Typically, the air plasma is applied in ambient air.

Preferably, the air plasma is applied by an air plasma treatment apparatus, for example, an air gun.

Preferably, the silane composition is applied by vapour or by liquid immersion. Preferably, the substrate comprises metal.

Typically, the metal is selected from the group comprising zinc, stainless steel, carbon steel, tin, aluminium and magnesium alloy. Preferably, the substrate is anodised. Still preferred, the substrate is anodised aluminium or anodised steel.

Preferably, the substrate is a sol-gel coated metal, anodised metal, plastics, glass or ceramics.

Preferably, the silane(s), or silane composition, is hydrolysed. Typically, the silane(s) has a degree of hydrolysis of between 10% and 100%, preferably 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, typically substantially 100% hydrolysis. Preferably, the silane composition is diluted in a water solution.

Typically, the silane composition is a solution. Typically, the silane composition is diluted in an alcohol/ water solution at a concentration comprised between 0.1 and 5% volume, preferably at 0.5%. Suitably, the alcohol/water ratio of the diluting solution is in the range of 10/90 to 90/10, preferably 90/10.

Preferably, the alcohol is isopropyl alcohol. For instance, in a total volume of 100 ml of silane wash (including diluent), 0.5ml of silane in 89.55ml of IPA and 9.95ml of water is present.

Typically, the pH of the solution is from about 1 to about 10, preferably from about 6.5 to about 7.5.

A further aspect of the current invention provides a treatment composition comprising APTES and MAPTMS.

The treatment composition may comprise the silane composition as described herein.

Preferably, the treatment composition has from about 20% to about 90% w/w APTES. Suitably, the treatment composition comprises about 50% w/w APTES and 50% w/w MAPTMS

Also provided by an aspect of the current invention is the use of the treatment composition of the invention to treat (or activate) a surface of a substrate or a portion thereof.

A further aspect of the current invention provides a method to treat an anodised surface comprising applying air plasma to said surface or a portion thereof. Preferably, the method further comprises applying a silane composition to the surface or a portion thereof.

A further aspect of the current invention provides a method of applying a coat to a surface or a portion thereof, the method comprising

- applying air-plasma to said surface or a portion thereof,

- applying a silane composition to said surface or a portion thereof, and - applying a coating.

A surface treated or produced by the method(s) of the current invention is also provided.

A further aspect provides a method to treat the surface of a substrate or a portion thereof, the method comprising

- applying air-plasma to said surface or a portion thereof, and - applying a silane composition to said surface or a portion thereof, in which the silane composition comprises APTES, MAPTMS and water, in which the ratio of APTES and MAPTMS in the composition is from 90:10 to 50:50.

Typically the composition comprises hydrolysed APTES and MAPTMS. Preferably, the composition further comprises alcohol.

The silane composition of this method is as described herein.

Definitions

Where used herein and unless specifically indicated otherwise, the following terms are intended to have the following meanings in addition to any broader (or narrower) meanings the terms might enjoy in the art:

Unless otherwise required by context, the use herein of the singular is to be read to include the plural and vice versa. The term "a" or "an" used in relation to an entity is to be read to refer to one or more of that entity. As such, the terms "a" (or "an"), "one or more," and "at least one" are used interchangeably herein. As used herein, the term "comprise," or variations thereof such as "comprises" or "comprising," are to be read to indicate the inclusion of any recited integer (e.g. a feature, element, characteristic, property, method/process step or limitation) or group of integers (e.g. features, element, characteristics, properties, method/process steps or limitations) but not the exclusion of any other integer or group of integers. Thus, as used herein the term "comprising" is inclusive or open-ended and does not exclude additional, unrecited integers or method/process steps.

As used herein, the term "sol-gel coating composition" means a composition formed by a sol- gel process where a solution evolves gradually towards the formation of a solid phase. The process involves conversion of monomers into a colloidal solution (sol) that acts as the precursor for the formation of an integrated solid network upon full thermal or UV radiation stabilisation. In one embodiment, the sol-gel coating composition of the current invention comprises of nanomaterials composed of interpenetrating networks of organosilanes and transition metal complexes.

The term "wetting" when used herein is taken to mean the ability of a liquid to maintain contact with as much of the liquid or solid substrate area as possible. The angle between the surface of the liquid and the outline of the contact surface is called the "contact angle". This can be used interchangeably with "wetting angle". It is a measure of the wettability or likely affinity of a solid by a liquid. For example, in one embodiment, contact angles were measured using the sessile drop method on the FTA 200 instrument and FTA 32 software. Calibration was performed on a 90 ± 1 ° standard prior to each set of measurements, with the contact angle of each water droplet being taken approximately 5 seconds following contact of the droplet with the sample surface. A number of measurements taken for each sample and an average value calculated based on these.

The term "surface" when used herein is understood to mean the outside or uppermost layer of the substrate. It will be appreciated that this may include any part of a substrate that requires application of a coating.

The terms "ambient air" when used herein refers to ambient atmosphere. The term "silane" when used herein is understood to mean an inorganic compound with the formula R_xSi(OR" )4-_x, where x varies between 0 and 4 and R and R^" are either organic groups or the hydrogen atom.

When used herein the terms "anodised" or "anodising", mean the formation of an oxide layer on the surface of a metallic substrate by an electrochemical process. When used herein the term "coating" is understood to mean a micron scale layer or a sub- nanometer surface treatment, which covers the entire substrate or part of the same substrate, respectively.

The phrase "treat" when used herein means to modify a surface by introducing functional groups to the surface which are the same or different to those originally found on the surface of a material, but provide a certain desired functionality to the substrate. This phrase can be used interchangeably herein with "functionalised" and "activated ".

The term "cooling" as used herein is defined as allowing the substrate / material to cool to ambient/room temperature, i.e. approximately between 10 °C and 25 °C.

Air plasma is generated when enough energy is supplied to air (in the form an electrical discharge in all references to "air plasma" described herein) to ionise the gas to form a "fourth state of matter"; namely a plasma. In one embodiment, the plasma treatment apparatus utilised consists of the application of a high voltage power supply to ambient air under pressure to form a plasma jet for the plasma treatment of substrates. One example is by use of an air gun, but any suitable device may be used. Such devices are known in the art. Brief Description of the Figures

The invention will be more clearly understood from the following description of an embodiment thereof, given by way of example only, with reference to the accompanying drawings, in which: Figure 1 illustrates the effect of air-plasma treatment on test metals;

Figure 2 displays the percentage change of contact angle as a function of plasma irradiation time for the test metals of Figure 1 ;

Figure 3 illustrates the contact angle measurements (n = minimum 6 measurements, with outliers removed using Median Absolute Deviation methodology) for air-plasma treated anodized substrates measured at indicated time intervals pre-and post-air-plasma treatment.

Figure 4 illustrates the contact angle measurements (n = 3) for air-plasma treated anodized substrates measured at indicated time intervals pre-and post-air-plasma treatment.

Figure 5 illustrates cross hatch results carried out on anodised aluminium substrates, which had been plasma activated for 2 minutes at a distance of ~ 2 cm from the plasma nozzle. Figure 6 illustrates the contact angle measurements (n = 6) for air-plasma treated sol-gel coated aluminium substrates (same sample exposed for initial plasma treatment time monitored over time) measured at indicated time intervals pre-and post air-plasma treatment;

Figure 7 displays contact angle values of dual treated (air-plasma/silane treated) metal substrate samples (AL=aluminium; MG=magnesium; SS=stainless steel). Figure 8 illustrates cross hatch results carried out on sol-gel coated anodised aluminium substrates, which were plasma treated, washed with 0.5 % vol silane in a 90:10 ratio of IPA:H₂0 (immersion for 30 seconds and allowed to air dry for 5 minutes), and then spin-coated with a primer.

Figure 9 illustrates cross hatch results carried out on sol-gel coated anodised aluminium substrates, which were plasma treated and then spin-coated with a primer.

Detailed Description of the Invention

All publications, patents, patent applications and other references mentioned herein are hereby incorporated by reference in their entireties for all purposes as if each individual publication, patent or patent application were specifically and individually indicated to be incorporated by reference and the content thereof recited in full. In its broadest sense, the current invention provides a method to treat the surface of a substrate to enable attachment of a coating. The method reduces the contact angle of the surface. This decrease in contact angle corresponds to a significant increase in surface energy. It provides the necessary level of wetting for enhanced adhesion of coatings onto the treated surface and, in some cases, the chemical groups required for enhanced bonding.

In this manner, the method provides a surface onto which a primer or coating can be bound, preferably irreversibly bound. The method of the current invention provides an alternative to currently used chemical surface treatment using an environmentally friendly, rapid and inexpensive method to enhance adhesion of a coating without surface damage. In an embodiment, the current invention provides a method to treat the surface of a substrate or a portion of a surface of a substrate comprising applying air-plasma to said surface.

In an embodiment, the air plasma is applied by an air plasma treatment apparatus.

In an embodiment, the air plasma is generated by a high voltage power supply and applied with ambient air to the surface via a compressor and by any other means in the art that generates air plasma.

Preferably, the air plasma is applied by an air gun (or similar means).

In an embodiment, said air-plasma is applied in ambient air. It will be understood that in an embodiment the air plasma is applied outside a chamber or similar apparatus.

This step serves to form or deposit a sub-nanometre, i.e. from about 0 nm to about 1 nm, uniform and oxygen-rich layer on the surface of the substrate.

The method also cleans or removes any surface contaminants or organic residues without changing the bulk properties of the substrate. This provides a surface onto which a coating can be stably adhered or bound.

There is no limitation to the substrate size or shape. This further illustrates the method's suitability to industrial scale applications.

In an embodiment of the method of the invention the substrate is held in place by a clamp or a similar attachment member known in the art and the air-plasma is applied to the substrate or to a portion thereof by an air-plasma treatment apparatus. Typically, the air-plasma treatment apparatus is stationary and the substrate being treated is fed, preferably manually, under the air-plasma spray generated by the air-plasma treatment apparatus. In a typical embodiment, the substrate is held at a distance of from about 10 mm to about 40 mm, preferably about 15 mm, 20 mm, 25 mm, 30 mm, to about 35 mm, ideally, from about 20mm to about 25 mm, from the air-plasma treatment apparatus.

The feed rate of the substrate under the air-plasma spray is between about 0.5 m/min to about 5 m/min, typically about 1 m/min, 2 m/min, 3 m/min or 4 m/min. It will be understood that this feed rate can be adjusted as a function of the pressure and power applied. The pressure of the air-plasma applied is from about 1 bar to 5 bar, ideally, about 3 bar.

The air-plasma is applied to the surface of the substrate or a portion thereof for a time of from about 1 seconds to about 2 minutes. Preferably, from about 30 seconds to about 2 minutes, preferably about 1 minute. It will be appreciated that the exposure time will depend on the power/pressure used to apply the air-plasma. For instance, an increase in the power/pressure application could result in a decrease in the exposure time. The feed rate is adjusted to ensure that the exposure time on the sample falls within the parameters outlined above.

The treated surface may then be allowed to cool for a period of time. Preferably, the surface is allowed to cool at room temperature, i.e. between Ι Ο 'Ό and 25^qC. This step may be for a time of from about 1 to about 10 minutes, preferably, about 1 to about 5 minutes, typically about 5 minutes.

The surface may be any surface of a substrate, or a portion of a surface of a substrate. It will be appreciated that this includes any part of the substrate which requires activation and application or adhesion of a coating.

In an embodiment of the invention, the substrate comprises of a metal or metallic alloys. The metal may be selected from, but not limited to, the group comprising zinc, stainless steel, carbon, steel, tin, aluminium and magnesium alloys. In an embodiment, the substrate may be selected from, but not limited to, the group comprising plastics, glass, ceramics and composite materials.

The substrate may be anodised. Preferably, the substrate may be anodised aluminium and anodised steel and any other metallic surfaces that can be anodised, e.g. titanium and magnesium.

The substrate may be a sol-gel coated substrate. In an embodiment, the substrate comprises sol-gel coated anodised aluminium.

The coating may comprise any suitable material known in the art to be used as a coating material. The coating may be selected from, but not limited to, the group comprising a paint, a primer, other organic, inorganic or hybrid coatings required for specific aesthetic, anti- corrosion, anti-icing, self-cleaning or anti-reflective functionalities and other purposes. Anticorrosion and anti-icing coatings are required for the transport industry including automotive, aerospace and railway. Anti-reflective coatings are employed in the optical and telecommunications industries. In an embodiment, following the air-plasma treatment step, the substrate is subjected to silane treatment. This step involves applying a silane composition to said surface or a portion thereof. This may be applied as a layer of silane to said surface. The uniformity and chemical functionality of the layer avoids delamination of the coating to be applied thereon. This step forms a functional nanometre monolayer that exhibits both organic and inorganic reactive groups capable of fully and irreversibly immobilising both organic, inorganic and hybrid coatings. Silane treatment provides a low contact angle on the treated surface.

This step involves applying a silane composition to the surface of a substrate or a portion of a surface of a substrate. It will be understood that any suitable means of application may be used and such means are known in the art. The silane composition may be applied by spray, spin or dip-coating the substrate. In one embodiment, the means immersion in a bath containing the aforementioned silane composition. In a typical embodiment, the bath may contain 0.5% volume in a ratio of 90:10 alcohol: H₂0 e.g. IPA:H₂0. Preferably for a silane wash of from about 0.1 % to 2.5% silane, the alcohol :water ratio may be from about 5:95 to 95:5. Alternatively, the silane can be applied on the surface of the substrate by other means such as spray-coating, dip-coating and spin-coating.

The application time may be for any suitable period of time. Preferably, the application time is for a period from about 1 second to about 2 minutes. The application time may be for 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 1 10, seconds. For instance, in an embodiment wherein the substrate is immersed, the substrate may be dipped or immersed and immediately removed, or may remain in the bath for a period of time of between 1 second to 2 minutes or as stated above. The substrate may be fully or partially immersed, depending on the area of the substrate that requires treatment.

The substrate can be left to air dry at room temperature. The drying process may be accelerated using drying with a hot air gun. This may be for about 5 to 30 seconds. The time required for drying, e.g. air-drying or accelerated drying using a hot air gun, is to be understood as one sufficient for the substrate to be free from moisture or liquid. It will be understood that the time taken to dry will vary depending on the size, area and type of substrate.

The silane composition may comprise any silane known in the art. In a preferred embodiment, the silane composition comprises 3-aminopropyltriethoxysilane (APTES). In a still preferred embodiment, the silane composition comprises a combination of at least two silanes, in which one of said at least two silanes is 3-aminopropyltriethoxysilane (APTES). In another of these embodiments at least one of the two silanes may be MAPTMS.

The composition comprises from about 10% to about 90% w/w APTES, at least about 20%, 30%, 40%, 50%, 60%, 70% or 80%, w/w of the composition , preferably at least about 50% APTES. The composition may comprise an amount of MAPTMS. Preferably the remainder of the composition (i.e. to bring the total % to 100%) comprises MAPTMS. For example, if the composition comprises about 60% w/w APTES, the composition comprises 40% w/w MAPTMS. Suitably, APTES and MAPTMS are present in a ratio of 50:50. Suitably, the APTES and MAPTMS are present in a ratio of 90:10, 80:20, 70:30, 60:40, 50:50, or vice versa.

In a preferred embodiment, the silane composition comprises about 50% w/w APTES and about 50% w/w MAPTMS. Other silanes that can be substituted for MAPTMS are: tetraethoxysilane, tetramethoxysilane, 3-trimethoxypropylmethoxysilane, 3- triethoxypropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, 3-glycidyloxypropyltrimethoxysilane, 3-glycidyloxypropyltriethoxysilane, 3-(triethoxysilyl)propyl isocyanate, trimethoxyphenylsilane, triethoxyphenylsilane, methyltrimethoxysilane and methyltriethoxysilane. In an embodiment, the silane composition is hydrolysed. In an embodiment, the degree of hydrolysis, typically to the reactive alkoxide groups of the silanes in the composition, is from 10% to 100%. Typically, 50%, 60%, 70%, 80%, 90%, 91 %, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99%. Preferably, there is between 90% and 100% hydrolysis.

In an embodiment, the silane composition is hydrolysed by diluting the silane composition in a water solution. In one embodiment the silane composition is diluted water solution at a concentration of from 0.1 and 5% volume, preferably 0.5%. Typically, this step is carried out at room temperature. In an embodiment, the solution may be an alcohol/water solution. In one embodiment the silane composition is diluted in an alcohol/water solution at a concentration of from 0.1 and 5% volume, preferably 0.5%. Suitably, the alcohol/water ratio of the diluting solution is in the range of 10/90 to 90/10, preferably 90/10, preferably 95/5. Typically, this step is carried out at room temperature.

The hydrolysis of the silanes composition, prior to deposition enables formation of reactive Si- OH groups onto a rich OH surface to form covalent oxide bonds with the surface. This step avoids the necessity to catalyse the condensation reaction with the surface by heating or other curing methodologies. The silane(s) are hydrolysed, preferably completely. In an embodiment in which the silane composition comprises MAPTMS and APTES the complete hydrolysis of the methoxy and ethoxy groups on the MAPTMS and APTES, respectively, is seen.

In an embodiment, the silane composition is within a silane-based solution, in which said silane combination is present in an amount of between about 0.1 % to 5% vol, preferably, about 0.5%, 1 %, 1 .5%, 2%, 2.5%, 3%, 3.5%, 4%, or 4.5% preferably 0.5% vol, preferably in a solution of water (H₂0). The silane composition may be in any suitable formulation. In an embodiment, the silane composition is within a silane-based solution, in which said silane combination is present in an amount of between about 0.1 % to 5% vol, preferably, about 0.5%, 1 %, 1 .5%, 2%, 2.5%, 3%, 3.5%, 4%, or 4.5% preferably 0.5% vol, preferably in a solution of alcohol and water (alcohol/H₂0). The ratio of alcohol/H₂0 is comprised between about 5/95 and 95/5, preferably 90/10. The pH of the solution is comprised between about 1 and 10, preferably between 6.5 and 7.5. The formulation may further contain buffers that are known in the art.

In an embodiment, the current invention provides a treatment composition comprising at least two silanes, wherein one of said at least two silanes is APTES. The second of the at least two silanes may be MAPTMS. The composition has between 20% and 90% w/w APTES, at least about 20%, 30%, 40%, 50%, 60%, 70% or 80%, preferably at least 50% w/w APTES. In a preferred embodiment, the silane composition comprises of 50% APTES and 50% MAPTMS. Other silanes that can be substituted for MAPTMS are: propyltrimethoxysilane, propyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane 3- aminopropyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, 3- glycidyloxypropyltrimethoxysilane, 3-(triethoxysilyl)propyl isocyanate, 3-

(trimethoxysilyl)propyl isocyanate, trimethoxyphenylsilane, triethoxyphenylsilane, methyltrimethoxysilane, methyltriethoxysilane, mercaptopropyltrimethoxysilane and mercaptopropyltriethoxysilane

Preferably, 1 , 2, 3, 4, or 5 layers of the silane composition is applied to the surface of a substrate or a portion thereof.

In an embodiment, the treatment composition comprises hydrolysed silanes. In an embodiment, the treatment composition is a solution comprising water and at least two silanes. In an embodiment, the treatment composition further comprises alcohol.

Also provided is the use of the treatment composition of the invention to treat or activate a surface of a substrate or a portion thereof. Preferably, 1 , 2, 3, 4, or 5 layers of the treatment composition is applied to the surface of a substrate or a portion thereof. The treatment composition may be used alone or in combination with a prior air-plasma treatment step. It will be appreciated that this depends on the chemical composition of the coating layer to be applied.

The treatment composition may be used to treat any suitable surface, such as the surfaces described herein.

In an embodiment of the invention there is provided a method to treat a surface of a substrate or a portion thereof comprising

- applying air-plasma to said surface or a portion thereof,

- allowing said surface to cool,

- applying a treatment composition to said air-plasma treated surface, wherein said composition comprises APTES,

- allowing said surface to dry.

The surface is allowed to cool to room temperature.

A further aspect of the current invention provides a method to treat an anodised surface comprising applying air plasma to said surface or a portion thereof. This step is as described herein. Preferably, the method further comprises applying a silane composition to the surface or a portion thereof. This step is as described herein. The anodised surface may be anodised aluminium or steel or any other metallic surface that can be anodised, as described herein.

A further embodiment of the invention provides a method to apply a top coating to a substrate comprising

- applying air-plasma to said surface,

- allowing said surface to cool;

- applying a coating to said surface.

The substrate is preferably an anodised substrate. The air-plasma treatment is as described above and herein.

The method may further comprise application of a silane composition to said surface prior to the step of applying a coating. This silane treatment step is as described above and herein.

In an embodiment, the invention provides a method to treat the surface of a substrate or a portion thereof, the method comprising - applying air-plasma to said surface or a portion thereof, and - applying a silane composition to said surface or a portion thereof, in which the silane composition comprises hydrolysed APTES, MAPTMS and water and alcohol, in which the ratio of APTES and MAPTMS in the composition is from 90:10 to 50:50. The silane composition and the amounts of the silane(s) in the composition of this method may be any composition and amounts as described herein.

The invention will now be described with reference to specific Examples. These are merely exemplary and for illustrative purposes only: they are not intended to be limiting in any way to the scope of the monopoly claimed or to the invention described. These examples constitute the best mode currently contemplated for practicing the invention.

EXAMPLE 1

Air-Plasma treatment

Materials and Methods

Six metals were used in this study, namely, zinc, stainless steel, carbon steel, tin, aluminium and magnesium. Each surface was subjected to air-plasma treatment for either five or 60 seconds. The percentage change in contact angle for each surface was calculated.

Results

The effect of treatment is illustrated in Figure 1 and the percentage change of contact angle for each metal is plotted in Figure 2. As displayed by these Figures, air-plasma treatment of 5 seconds reduced the contact angle of the metals in the range of 17% (stainless steel) to 61 % (magnesium alloy). Exposure to air-plasma treatment for a duration of 60 seconds enabled to decrease the contact angle in the range of 57% (Zinc) to 85% (Tin). The contact angle was measured as described previously herein.

EXAMPLE 2 Air-plasma treatment of anodised aluminium surfaces

Materials and Methods

Contact angle measurements were conducted on untreated anodized aluminium samples. This established the level of wettability of the untreated surface. The anodized aluminium samples were air-plasma treated as outlined in Example 1 , with an atmospheric plasma system. The sample were retested immediately once cool. Separate untreated anodized aluminium samples were plasma treated for 15, 30, 60 and 120 second time periods, respectively. At least six measurements taken for all data points, and outliers removed using the Median Absolute Deviation (MAD) statistical method. The contact angle measurements were taken again 24 hours and 1 week after treatment.

To ensure that the results were not due to differences across the surface of the original sample substrates and to eliminate any variation in contact angle values due to the use of different substrates, the experiment was repeated, with a new site on a single substrate was plasma treated for each plasma exposure time and subsequently tested following each time interval.

Results

Figure 3 illustrates a significant decrease in contact angle for all treated surfaces immediately after plasma treatment, with a decrease of almost 30 ° i.e. 75% in contact angle for samples treated for 120 seconds. This decrease in contact angle corresponds to a significant increase in surface energy. It provides the necessary level of wetting for enhanced adhesion of protective coatings onto the activated anodized substrate.

While there was some variation across the samples in terms of hydrophobic recovery due to unavoidable variations in the initial contact angles of the samples tested, it is clear that none of the treated samples have recovered to the original value of approximately 40⁰ contact angle after 24 hours, with all samples having a contact angle of 25° or less, demonstrating promising stability of the method of the invention.

At 1 week following treatment, the samples exposed for 60 seconds and 120 seconds had contact angles of 18° and 14°, respectively, further indicating the excellent surface activation stability.

Figure 4 illustrates the results for the repeated experiment, with plasma activation and contact angle monitoring carried out on a single substrate for each treatment time, rather than separate untreated substrates for each set of contact angle measurements as in Figure 3. The results of Figure 4 confirm the decrease in contact angle (from 40° to 17° and 16° for the 60 second and 120 second samples, respectively) and good wetting stability over a four-hour time interval (all values range within error bars).

These results demonstrate that the method of the invention provides activation of anodized aluminium substrates for improved surface adhesion.

EXAMPLE 3 Cross Hatch adhesion tests

Materials and Methods Anodised aluminium substrates were air-plasma treated for two minutes at a distance of approximately 2 cm from the plasma nozzle. The substrate was moved manually under the nozzle with the nozzle fixed into place. The samples were then immediately spin coated with an epoxy based protective primer coating, e.g. SP350 of ~8 microns thickness and cured according to manufacturer's specifications. Adhesion testing was carried out according to the ASTM D3359 -09 standard test (e.g. https://www.astm.org/Standards/D3359.htm) at three blemish free points on the substrate.

Sol-gel coated anodised aluminium substrates were air-plasma treated for two minutes at a distance of approximately 2 cm from the plasma nozzle. This was then washed with 0.5% vol. of the silane composition (MATPMS/APTES silane) in a 90:10 ratio of IPA:H₂0 (immersion for 30 seconds and allowed to air dry for 5 minutes), and then spin-coated with a primer. Adhesion testing was carried out according to the ASTM D3359 -09 standard testat three blemish free points on the substrate.

An adhesion test was also carried out on a sol-gel coated anodised aluminium substrate that was air-plasma treated only. Air plasma treatment was as described above, i.e. two minutes at a distance of approximately 2 cm from the plasma nozzle. Adhesion testing was carried out according to the ASTM D3359 -09 standard test.

Results

Figure 5 illustrates cross hatch results carried out on anodised aluminium substrates. The results indicated excellent adhesion, with the results rating 4B - 5B according to the ASTM D3359-09 standard of the primer to the substrate following plasma treatment.

Figure 8 illustrates cross hatch results carried out on sol-gel coated anodised aluminium substrates, which were plasma treated, washed with 0.5% vol silane composition in a 90:10 ratio of I PA: H₂0. Figure 9 illustrates cross hatch results carried out on sol-gel coated anodised aluminium substrates, which were plasma treated only and then spin-coated with a primer.

The results indicate excellent adhesion.

EXAMPLE 4

Activation of Sol-gel coated aluminium surface

Materials and Methods

Contact angle measurements were taken for untreated sol-gel samples which had been coated onto 2024-T3 aluminium substrates and cured at 120 °C for 2 hours. One sample was used for each treatment time and six contact angle measurements were taken to calculate an average and cured at 120 °C for 2 hours.

The sol-gel coated anodised aluminium surface was air-plasma treated as explained in Example 1 . The irradiation times were 5, 15, 30, 60 and 120 seconds, and the initial measurements recorded immediately after air plasma treatment. Samples were set at a distance of approximately 2.5 cm from the plasma nozzle under continuous irradiation. The contact angles were monitored for 24 hours according to the intervals outlined in Figure 6.

Results As shown in Figure 6 a significant decrease in contact angle for all treated surfaces immediately after plasma treatment is observed.

Immediately after the air plasma treatment, it can be seen that all samples undergo a dramatic decrease of contact angle of between 73% and 90%, as recorded for the samples exposed for durations ranging from 5 to 120 seconds, respectively. Also, it is important to note that, excluding the sample irradiated for 5 seconds, contact angle values remain close to 30° and 45° after 4 and 24 hours, respectively. This demonstrates the good stability of the hydrophilic character of the treated surfaces following air plasma irradiation, providing an ideal platform for further application of a top organic coating within a 24-hour time period.

EXAMPLE 5 Silane Formulation

Materials and Methods

Six metal substrates were subjected to air-plasma treatment according to the procedure as outlined in Example 1 and subsequently treated with the silane formulations of Table 1 .

Table 1 : Formulations of the current invention. The silanes were applied by immersing the metal samples within a silane-based solution at 0.5% volume in IPA/H₂0 at a ratio of 90/10. The samples were then left to dry at room temperature for 5 minutes before contact angle measurement. The percentage change in contact angle for each surface was calculated. Results

Contact angle values of the dual plasma/silane treated metal samples were calculated and the results are displayed in Figure 7. It is shown that of the individual silane treatments, APTES provides the lowest contact angle regardless of the metal substrate. This is due to its double binding capability facilitated by the amino and ethoxysilane functionalities available at each extremity of the propyl chain.

As the MAPTMS silane shows high contact angle values when employed as a coating on its own, it is possible to conclude that the hydrophobic organic chain would be situated at the air- coating interface, while the ethoxysilane hydrophilic group would be linked to the oxygen-rich substrate interface via condensation reactions. This result confirms the availability of the functional organic group at the top surface of the base monolayer as an anchoring point for irreversible immobilisation of organic-based top-coatings.

The combined silane / plasma treatment results in high surface energy (i.e. a low contact angle) on the substrate by attaching polar groups in the form of homogenous adhesion promoters such as silane coupling agents.

Claims

1 . A method to treat the surface of a substrate or a portion thereof, the method comprising

- applying air-plasma to said surface or a portion thereof, and

- applying a silane composition to said surface or a portion thereof, in which the silane composition comprises 3-aminopropyltriethoxysilane (APTES) and 3-(Trimethoxysilyl)propyl methacrylate (MAPTMS), and in which the amount of APTES is from 20% and 90% w/w.

2. The method of Claim 1 , wherein said silane composition comprises about 50% w/w APTES and 50% w/w MAPTMS.

3. The method of Claim 1 or 2, in which the silane composition is hydrolysed.

4. The method of Claim 3, in which the silane composition is diluted in a water solution.

5. The method of Claim 3 or 4, in which the silane composition is diluted in an alcohol/ water solution.

6. The method of Claim 5, in which the silane composition is diluted in an alcohol/water solution at a concentration comprised between 0.1 and 5% volume.

7. The method of Claim 5 or 6, in which the alcohol/water ratio of the diluting solution is in the range of 15/95 to 95/5, preferably 95/5.

8. The method of any one of claims 5 to 7, wherein the alcohol is isopropyl alcohol.

9. The method of any one of the preceding Claims, wherein the air-plasma is applied in ambient air.

10. The method of any one of the preceding Claims, in which the air-plasma is applied by an air plasma treatment apparatus.

1 1 . The method of Claim 10, in which the air plasma treatment apparatus is an air gun.

12. The method of any one of the preceding Claims, wherein said silane composition is applied by vapour or by liquid immersion.

13. The method of any one of the preceding Claims, wherein said air-plasma is applied for a time from about 1 second to about 2 minutes.

14. The method of any one of the preceding claims wherein said substrate comprises metal.

15. The method of claim 14, wherein said metal is selected from the group comprising zinc, stainless steel, carbon steel, tin, aluminium, magnesium and titanium alloys.

16. The method of Claim 14 or 15, wherein said substrate is anodised.

17. The method of Claim 16, wherein the substrate is anodised aluminium or any other metallic surface that can be anodised.

18. The method of any one of the preceding Claims, wherein said substrate is a sol-gel coated metal, anodised metal, plastics, glasses and ceramics.

19. The method of any one of Claims 4 to 18, wherein the pH of the solution is comprised between 1 and 10, preferably between 6.5 and 7.5.

20. A method to treat the surface of a substrate or a portion thereof, the method comprising

- applying air-plasma to said surface or a portion thereof, and

- applying a silane composition to said surface or a portion thereof, in which the silane composition comprises hydrolysed APTES, hydrolysed MAPTMS, water and alcohol, and in which the ratio of APTES and MAPTMS in the composition is from 90:10 to 50:50.

21 . A treatment composition comprising APTES and MAPTMS in which the composition comprises from 20% to 90% w/w APTES.

22. The treatment composition of Claim 21 wherein said silane composition comprises about 50% w/w APTES and 50% w/w MAPTMS.

23. Use of the treatment composition of Claim 21 or 22, to treat or activate a surface of a substrate or a portion thereof.

24. A method to treat an anodised surface comprising applying air plasma to said surface or a portion thereof.

25. The method of Claim 24, wherein said method further comprises applying a silane composition to the surface or a portion thereof.

26. A method to apply a coating to a substrate comprising the method of any one of the preceding Claims and applying a coating to said surface.