WO2017216544A1

WO2017216544A1 - Coating

Info

Publication number: WO2017216544A1
Application number: PCT/GB2017/051719
Authority: WO
Inventors: Jas Pal Singh Badyal; Rebekah Catherine FRASER
Original assignee: Surface Innovations Limited
Priority date: 2016-06-14
Filing date: 2017-06-13
Publication date: 2017-12-21
Also published as: CN109923949A; GB201610481D0; TW201811931A

Abstract

A coating comprising: (i) a first layer, and (ii) a second layer, wherein the first and second layers are cross-linked by a crosslinking group, and wherein at least one of the first and second layers is self cross-linked.

Description

Coating

Field of the invention

This invention relates to coatings. In particular, though not exclusively, the invention relates to substrates with protective coatings formed thereon , as well as methods of forming coatings on substrates.

Background of the invention

It is well known that electronic and electrical devices are very sensitive to damage caused by contamination of liquids such as environmental liquids, in particular water. Contact with liquids, either in the course of normal use or as a result of accidental exposure, can lead to short circuiting between electronic components, corrosion, degradation, and irreparable damage to circuit boards, electronic chips etc.

This problem is particularly acute in relation to small portable and wearable electronic equipment such as mobile phones, smartphones, pagers, radios, hearing aids, laptops, notebooks, tablet computers, phablets and personal digital assistants (PDAs), which can be exposed to significant liquid contamination when used outside or when used inside in close proximity to liquids.

Such devices are also prone to accidental exposure to liquids, for example if dropped in liquid or splashed. There is a continual drive towards smaller portable electronic and electrical devices with greater functionality, leading to even more stringent demands for device performance, for example operation during immersion in water.

Other types of electronic or electrical devices may be prone to damage, due to their location, for example outdoor lighting systems, radio antenna and other forms of communication equipment.

Known coating techniques and coatings include spraying, dip coated polystyrene, gas phase processing systems such as parylene, urethane modified polybutadiene, polymer composites, amorphous hydrocarbon films (a-C:H), and plasma deposited coatings (e.g . WO2007/083122 and WO2006/109014). Often, these coatings are problematic in that they do not provide enough environmental protection, or the coatings are so thick that they undesirably increase the size and bulk of the electronic or electrical devices. To obtain increased protection from water damage, multilayering has been used. However, multilayering tends to involve multiple and lengthy steps, as well as elevated temperatures. Multiple and lengthy steps add to the cost of manufacture, and the high temperatures may damage sensitive components present in electronic or electrical devices.

Therefore, there remains a need in the art for effective protective coatings that can provide high wet electrical barrier performance, and which can be applied in a simple and efficient manner. It is an object of the present invention to address this need.

Summary of the invention

In a first aspect of the invention, there is provided a coating comprising:

(i) a first layer, and

(ii) a second layer, wherein the first and second layers are cross-linked by a crosslinking group, and wherein at least one of the first and second layers is self cross-linked.

The coating of the invention provides exceptionally high wet electrical barrier performance. The first layer and the second layer synergistically combine to provide an exceptionally high wet electrical barrier. Without wishing to be bound by theory, it is believed that crosslinking of the first and second layers, and the self cross-linking of one of the layers, securely fixes the two layers together, and provides high wet electrical barrier performance of the coating.

Wet electrical barrier performance is a measure of how resistant a coated electronic device is to liquid damage. In this test, the ease with which aqueous ions diffuse through a barrier layer towards an underlying electronic circuit determines the overall level of device protection. Hence, electrical resistance measurements of a coated circuit during water immersion can be taken as an indicator of wet electrical barrier performance. Compared to modern

smartphones, which have cell voltages ranging from 3.70-3.85 V (however amplifiers within the device can obtain voltages of up to 20V, and even higher), the much higher voltages employed in the present test represent very demanding conditions. The coatings of the invention show a very good level of performance.

The coatings of the invention can be made very thin while still retaining the exceptionally high wet electrical barrier performance. Thin coatings are desirable on electronic or electrical devices, as the devices are less bulky they are therefore more appealing to consumers. Very thin coatings would also advantageously not be expected to impede the performance of any moveable parts, such as buttons, switches or the moving parts in microphones/speakers.

The methods used to make the coatings of the invention are easily scalable and suitable for high throughput electronic device assembly lines.

The coating of the invention may consist of the first and second layers, or it may comprise additional layers. For example, it may comprise more than one set of first and second layers, as previously described. Where more than one additional layer is provided, the additional layers may be the same or different. An example of an additional layer is a liquid repellent layer, particularly an oil and/or water repellent layer. Any appropriate oil and/or water repellent layer may be used, such as an oil and/or water repellent layer that forms a water repellent surface defined by a static water contact angle (WCA) of at least 90°. The oil and/or water repellent layer may be highly halogenated, optionally highly fluorinated. The oil and/or water repellent layer may comprise a polymer from a pulsed plasma perfluoro acrylate monomer, optionally, a perfluorooctyl acrylate monomer.

When the coating comprises one or more additional layers, the first and second layers are generally adjacent, so as to allow cross-linking. The additional layers may be found on one or both sides of the cross-linked first and second layers. For example, the cross-linked first and second layers may be under and/or overcoated by the one or more additional layers.

In an embodiment, a multilayer comprises the coating of the invention. The multilayer may comprise more than one coating of the invention, which optionally may be interspaced with one or more other layers. Optionally, the coating of the invention may be overcoated and/or undercoated with one or more other layers. Such other layer might include an oil and/or water repellent layer.

In an embodiment, a substrate may comprise the first layer. As such, the first layer is the surface portion of the substrate. In an embodiment the first layer and second layer are different. Where two different layers contact each other, there will be an interface/interface region. In the present invention, crosslinking generally occurs at the interface/interface region.

In most embodiments, the first and second layers are generally different. Whilst the layers are referred to as first and second, the terms first and second are not indicative of the relative positioning of the layers within the coating. For example, the first layer may be found above or below the second layer. When the coating is provided on a substrate, the first layer may be found between the surface of the substrate and the second layer. Alternatively, the first layer may be part of the substrate. In another embodiment, the second layer may be found between the surface of the substrate and the first layer. Or, the second layer may be part of the substrate.

The layers may be deposited by any appropriate means and the method of deposition may be selected according to the particular layers in the coating. Without being bound by theory, though, it is understood that the cross-linking of the layers to each other and of the self cross- linking of one of the layers occurs under excitation conditions. Accordingly, one layer may be deposited in such a manner that cross-linking between the layers occurs. Alternatively, both layers may be deposited and then cross-linked post-deposition. In one embodiment, at least one of the layers is deposited under excitation conditions, such as by plasma deposition, beam grafting, chemical vapour deposition, initiated chemical vapour deposition, heating or photon source. In that embodiment, the other layer may be deposited by any other means, such as spin, dip or spray coating. In the electronics industry, thin coatings are generally desirable, particularly those that can be manufactured easily on a large scale. Spin coating allows very thin layers to be applied to electronic or electrical devices, or components thereof, in a reasonably easy and cost effective manner. In other situations, other techniques might be more suitable. In the case of coating non-planar circuit boards spray or dip coating may be preferred. It may or may not be deposited under excitation conditions. In another embodiment, both layers may be deposited without excitation, such as by spin, dip or spray coating, and then both layers subject to excitation by plasma, chemical or other excitation means.

In an embodiment, cross-linking of the layers occurs at or is found in an interface region between the first and second layers.

In an embodiment, the first layer is a polymeric layer. In an embodiment, the first layer comprises a polymer. Polymers are particularly useful materials and can be made conveniently and cost effectively on an industrial scale.

In an embodiment, the first layer may comprise a polymer comprising a reactive group, the reactive group being reactive to a thiol group. In particular, the reactive group may be reactive under the conditions of plasma deposition. The reactive group may also be reactive to radical species produced during plasma deposition, such as thiyl radicals.

The first layer is provided with reactive groups, those groups being reactive to groups present in the second layer. Not wishing to be bound by theory, it is believed that this leads to effective crosslinking of the layers. The coatings of the invention give rise to a synergistic increase in the resultant electrical barrier performance, an increase that is beyond that provided by simply increasing the thickness of the coating alone. It is unexpected that the first layer could have such a profound effect on the electrical barrier performance.

In an embodiment the reactive group may be a non-aromatic unsaturated chemical group, particularly a double or triple bond. In an alternative embodiment, the reactive group may be selected from a double bond group, a triple bond group, a halide group, and an epoxide group. In an embodiment, the first layer comprises a polymer, comprising at least one double or triple bond group. The inventors have surprisingly found that the presence of a non- aromatic unsaturated group allows for significantly improved electrical barrier performance. Examples of non-aromatic unsaturated chemical groups include C=C; C=N; N=N and C≡C. The reactivity of the first layer can be adjusted by changing the types of unsaturated bonds in that layer. In an embodiment, the first layer comprises a polymer comprising C=C groups.

In the process of reacting, at least some of the reactive groups of the first layer are typically consumed. This leaves few (or none) of these reactive groups at the interface/interface region of the first layer, as when compared to the bulk portion of the first layer (or when compared to the first layer prior to the plasma deposition). In the case of the reaction of a thiol group (or thiyl radical) with a double bond, this is expected to lead to saturation of the double bond.

In an embodiment, the first layer comprises a polymer comprising a poly-1 ,3-diene, such as polybutadiene or polyisoprene. In an embodiment, the first layer comprises a polymer comprising polybutadiene, or is polybutadiene. In an embodiment, the first layer comprises a polymer comprising polyisoprene, or is polyisoprene.

In an embodiment, the first layer comprises a polymer comprising repeating units of formula (I):

-[WR³C=CR⁴Z]-

(I) where W may independently be a bond, or is one or more of O, S, CO, C(0)0, CH₂0 or (CR¹R²)_P, and Z may independently be a bond, or is one or more of O, S, CO, C(0)0, CH₂0 or (CF^R⁶)^ where p and q are independently an integer from 1 to 6, and wherein W, Z, R³ to R⁴ are substantially inert groups. Optionally, W consists of up to 40, 30, 20, 15, 10, 9, 8, 7, 6, 5, 4, 3, 2 or 1 atom(s). Optionally Z consists of up to 40, 30, 20, 15, 10, 9, 8, 7, 6, 5, 4, 3, 2 or 1 atom(s).

In an embodiment, R¹ to R⁶ are independently selected from a hydrogen atom, optionally substituted straight or branched alkane chain(s) or optionally substituted aryl group(s). In an embodiment, R³ and R⁴ are H, and W and Z are CH₂ (i.e. p and q are 1 and R¹ , R², R⁵ and R⁶ are H). In an embodiment, R³ is H, R⁴ is methyl, W and Z are CH₂.

The term "alkane" refers to straight or branched chains of carbon atoms, suitably of from 1 to 20 carbon atoms in length. The term "aryl" refers to aromatic cyclic groups such as phenyl or naphthyl. Suitable optional substituents are groups that are substantially inert during the methods of the invention. They may include alkane or halo groups such as fluoro, chloro, bromo and/or iodo. Particularly preferred halo substituents are fluoro.

A polymer is usually made of a number of repeating units, such as the repeating unit shown in formula (I). In this case, the part of the polymer that repeats is shown in square brackets, and the lines that extend from the brackets are the points where the repeats can connect. A polymer may be made of a number of different repeating units. In formula (I) there is a carbon- carbon double bond between the WR³C group and the CR⁴Z group. Changing the nature of W, R³, R⁴ and Z will change the nature of the double bond. For example, it can be made more or less electron rich. W, R³, R⁴ and Z could also be used to control the space around the double bond, and hence access to the double bond by any reactive groups.

In an embodiment, the unsaturated group is electron rich. In an embodiment, the substituents on, or close to, the unsaturated group could contribute to the stabilization of a radical.

In an embodiment, at least one of W, Z, R³ or R⁴ is an electron donating group. In an embodiment, at least one of W, Z, R³ or R⁴ is capable of stabilising a radical. In an embodiment, at least one of R³ and R⁴ is an electron donating group. The electron donating group may be selected from optionally substituted straight or branched alkane chain(s) or optionally substituted aryl group(s). In an embodiment, R³, W and Z are hydrogen and R⁴ is a methyl group.

Without wishing to be being bound by theory, it is believed that the methyl group increases the electron density at the double bond and it is this that is providing the synergistic increase in the electrical barrier performance of the resultant coating. Alternatively, or in addition, the methyl groups of the polymer may affect the space around the double bond, and so control the way the plasma deposited layer crosslinks to the first layer. Alternatively, or in addition, the methyl groups may stabilize radical groups during crosslinking.

In an embodiment the second layer comprises a polymer prepared by deposition of a monomer compound of formula (II):

K-L-[-M-H]_m

(II) wherein:

K is a group comprising a non-aromatic unsaturated bond; L is a linker group linking groups K and M;

M is a group capable of reacting with a non-aromatic unsaturated bond; H is a hydrogen atom; and m is an integer greater than 0; optionally m is 1 , 2, 3, 4, 5 or 6.

Without wishing to be bound by theory, it is believed that the second layer fulfills two roles. Firstly, the second layer crosslinks with the first layer. Secondly, the second layer is capable of self cross-linking.

To fulfill these two roles, the second layer is prepared from a monomer that comprises two reactive groups. The monomer has a group that provides effective binding to the first layer, by crosslinking to that layer (hetero-crosslinking). The monomer also has a group that permits self-polymerisation and self cross-linking.

In an embodiment, M is selected from S; O; NH; NR⁷; PH; PR⁸; POR⁸; P(0)R⁹ and P(0)OR⁹; wherein R⁷ to R⁹ are independently selected from optionally substituted straight or branched alkane chain(s), or optionally substituted aryl group(s). In an embodiment, M is an S atom. When M is S, the M-H is a mercaptan group. A mercaptan group is capable of reacting with groups such as carbon double bonds. Under excitation conditions, radicals of the monomer will also form, e.g. thiyl radicals (S ) from the mercaptan groups. Radicals are also capable of reacting with groups such as carbon double bonds, permitting self cross-linking. In an embodiment, group K comprises double or triple bonds. In an embodiment, K comprises a group selected from C=C; C=N; N=N; or C≡C groups. In an embodiment, K comprises a C=C group.

In an embodiment, L is substantially inert. In an embodiment, L is selected from a bond, optionally substituted straight or branched alkane chain(s) or optionally substituted aryl group(s). Group L separates groups K and M. Without being bound by theory, L is not understood to be directly involved in crosslinking reactions. However, by changing the length and shape of L, the crosslinking reactions of K and M may be optimised. L may also be used to activate or deactivate groups K and M, by increasing or decreasing the electron density at K and/or M. In an embodiment, L might be branched and/or include one or more additional K and/or M groups. Additional crosslinking groups would be expected to result in additional crosslinking during plasma deposition of the monomer.

In an embodiment, the second layer comprises a polymer prepared by the deposition of a monomer compound of formula (lla):

R^1UR¹¹C=CR¹ -L-I-S-H] m

(lla) wherein L is as defined above and R¹⁰ to R¹² are independently selected from optionally substituted straight or branched alkane chain(s), optionally substituted aryl group(s), or hydrogen atom and m is an integer greater than 0; optionally m is 1 , 2, 3, 4, 5 or 6.

In an embodiment, L is a CH₂ group. The compound of formula (lla) is a thiol-ene compound, and corresponds to the monomer of formula (II) where K is an olefin and group R¹⁰R^{1 1}C=CR¹², and M is S. In an embodiment, the monomer of Formula (II) or (lla) is allyl mercaptan. In an embodiment, L comprises one or more additional K and/or M groups.

In an embodiment, the second layer comprises a polymer comprising repeating units of formula (III):

(III) wherein:

X is selected from the group CR^AR^B or NR^C;

Y is selected from the group CR^D or N; or X and Y together are a group CR^E =C;

R^A to R^E are independently selected from a hydrogen atom, optionally substituted straight or branched alkane chain(s) or optionally substituted aryl group(s);

L and M are as defined above.

The second layer may be made of a number of repeating units of formula (III). The lines that extend from the brackets are the points where the repeating units may connect.

Group X-Y corresponds to the saturated form of K in formula (II), after polymerisation and/or crosslinking during plasma deposition of the monomer. Likewise Group X-Y corresponds to the saturated form of R¹⁰R^{1 1}C=CR¹² in formula (lla), after polymerisation during plasma deposition of the monomer. With reference to Figure 8 it can be seen that when allyl mercaptan monomer (spectrum (c)) is plasma deposited to give the second layer (spectrum (d)) the peak (at about 3080 cm^"1) corresponding to the =CH₂ group is lost. This would suggest that group K in the monomer of formula (II) has become fully saturated by reaction in the plasma deposition to give the group corresponding to X-Y in formula (III).

Group L-M corresponds to L-M in formula (II), and L-S in formula (lla) (i.e. where M is S), after crosslinking during plasma deposition of the monomer. Crosslinking may occur between the first layer and second layer, or optionally internally within the second layer. With reference to Figure 8 it can be seen that when allyl mercaptan monomer (spectrum (c)) is plasma deposited to give the second layer (spectrum (d)) the peak (at about 2550 cm^"1) corresponding to the SH group is mostly lost. This would suggest that the crosslinking group M-H, in L-M-H of the monomer of formula (II), has mostly been consumed. The M-H group being consumed by forming crosslinks in the plasma deposition. The crosslinks correspond to L-M- in formula (III). This indicates a highly crosslinked coating.

In an embodiment, X is CH₂; Y is CH; L is CH₂ and M is an S atom. In an embodiment, the crosslinking group comprises a group M, wherein M is as defined above. In an embodiment, the crosslinking group comprises a group L-M, wherein M and L are as defined above. In an embodiment, the crosslinking group comprises an S; CH₂ or a CH₂-S group. In an embodiment, the coating comprises units of formula (IV):

-[WR³HC-C ⁴Z]-

(IV) wherein X, Y, L, M, W, Z, R³ and R⁴ are as defined above.

The repeating unit of formula (IV) corresponds to formula (III), where M is crosslinked to repeating unit of formula (I) of the first layer. The units of formula (IV) may in effect define an interface, or interface region, between layers (i) and (ii).

In an embodiment, there are fewer unsaturated bonds at the interface/interface region between layers (i) and (ii) than in the bulk of the first layer. In an embodiment, there are substantially no unsaturated bonds at the interface/interface region between layers (i) and (ii). In an embodiment, the second layer is substantially free of non-aromatic unsaturated double bonds.

In an embodiment, the coating is substantially pin-hole free. This property leads to better electrical barrier performance. In an embodiment, the coating is electrically insulating. In an embodiment, the coating has a resistance of 0.6 M Ω nm-1 or higher when submerged in water and a voltage of 10V is applied for 13 minutes. This is a high electrical barrier.

In an embodiment, the first layer has a thickness of 50nm-10,000nm; optionally a thickness greater than 200nm, 400nm, 500nm, 1000nm, 2000 nm or 5000nm.

In an embodiment, the second layer has a thickness of 10nm-10,000nm, optionally a thickness greater than 50nm, 100nm, 200nm, 300nm, 500nm, 1000nm, 2000nm or 5000nm.

With reference to Figure 12, it can be seen that for a combination of the first layer and second layer there is a region in which increased electrical barrier performance is obtained. This is the region in which the gradient of the line on the graph increases markedly.

In an embodiment of the first aspect of the invention, the first or second layer may be part of or comprised by a substrate to be coated. In a second aspect of the invention, there is provided a method of preparing a coating, comprising providing

(i) a first layer, and

(ii) a second layer, and cross-linking the layers under excitation conditions, such that the layers are cross-linked to each other and at least one of the layers is self cross-linked.

A third aspect of the invention provides a method of preparing a coating according to the first aspect of the invention, comprising the steps of the second aspect of the invention.

The first and second layers may be as defined in relation to the first aspect of the invention.

In an embodiment, the first layer is provided prior to providing the second layer. In another embodiment the second layer is provided prior to providing the first layer. In a further embodiment, a substrate comprises the first layer. In another embodiment a substrate comprises the second layer. In an additional embodiment, the first layer is formed on a substrate. Alternatively, the second layer may be formed on a substrate. The substrate may be any substrate to be coated, including but not limited to, an electronic or electrical device, or component thereof.

In the methods of the second and third aspects of the invention, the first and second layers are cross-linked during excitation. This may occur either by providing one of the layers under excitation conditions, or by providing both layers and then subjecting them to excitation conditions. For example, one layer may be provided by deposition, particularly deposition without excitation, such as spin, dip or spray coating. The other layer may then be deposited under excitation conditions, for example by plasma deposition, beam grafting, chemical vapour deposition or by initiated chemical vapour deposition. In one embodiment, the first layer is provided under excitation conditions. In another embodiment the second layer is provided under excitation conditions. The first layer may be deposited before or after the second layer, in other words it may be the former or latter layer to be deposited. The second layer may be deposited before or after the first layer, in other words it may be the former or latter layer to be deposited. Generally, the latter layer to be deposited, is deposited under excitation conditions, whereas the former layer is deposited without excitation. Alternatively, the first and second layers may be deposited and then two layers subjected to excitation conditions. For example, one layer may be deposited by spin, dip or spray coating. The other layer may then be deposited by spin, dip or spray coating. The two layers may be then be placed under excitation conditions, such as those previously described.

The method may be for coating a substrate. The step of providing the first layer or the step of providing the second layer may comprise providing the layer on a substrate to be coated. The substrate may be any substrate that it is desirable to be coated with a coating, but is particularly an electronic or electrical device, or a component thereof. In some embodiments, the substrate is a personal electronic or electrical device, especially a telephone or other communication device, a tablet, a computer, headphones or a watch.

The method may also comprise providing one or more additional layers, such as a liquid repellent layer, as described previously. The one or more additional layers may be provided prior to and/or after the first and second layers.

In a fourth aspect of the invention, there is provided a coating obtainable by the second or third aspect of the invention, or a substrate having a coating obtainable by the second or third aspect of the invention.

In a fifth aspect of the invention, there is provided a method for treating an electronic or electrical device or component thereof, comprising: exposing the electronic or electrical device or component thereof to a plasma comprising one or more monomer compounds for a sufficient period of time to allow a protective coating to form on the electronic or electrical device or component thereof, the protective coating forming a physical barrier over a surface of said electronic or electrical device or component thereof; wherein each monomer is a compound of formula (II) or (I la), is as defined above; and wherein the electronic or electrical device or component thereof comprises a substrate, the substrate comprising a first layer, the first layer being as defined above. In an embodiment the first layer is the surface portion of a substrate.

In an alternative embodiment, there is provided a method for treating an electronic or electrical device or component, comprising providing on the device first and second layers and cross- linking the layers under excitation conditions, such that the first and second layers are cross- linked and at least one of the layers is self cross-linked. The first and second layer may be as described in relation to other aspects of the invention.

In an alternative, there is provided a method for treating an electronic or electrical device or component thereof, comprising exposing the electronic or electrical device or component thereof to a plasma comprising one or more monomer compounds for a sufficient period of time to allow a protective coating to form on the electronic or electrical device or component thereof, the protective coating forming a physical barrier over a surface of said electronic or electrical device or component thereof; wherein each monomer is a compound of formula (II) or (lla), as defined above; and wherein the plasma deposited layer is provided with a first layer as defined above.

In a further alternative, there is provided a method for treating an electronic or electrical device or component thereof, comprising: providing the electronic or electrical device with a first layer, to form a protective coating on the electronic or electrical device or component thereof, the protective coating forming a physical barrier over a surface of said electronic or electrical device or component thereof; wherein the first layer is as defined above, and wherein the electronic or electrical device or component thereof comprises a substrate, the substrate comprising a second layer, the second layer being as defined above. In an embodiment the second layer is the surface portion of a substrate.

In an embodiment of the fifth aspect of the invention, the barrier is a conformal physical barrier.

The methods of the invention may comprise the step of plasma deposition, or the step of exposing a device or component thereof to a plasma . Those steps may comprise a continuous wave (CW) deposition step or a pulsed (PW) deposition step; or optionally a CW step followed by a PW step, or a PW step followed by a CW step. By pulsed plasma, it is meant that the plasma is applied in pulses of power on and power off. In one embodiment, the pulses of the pulsed plasma are applied in a sequence which yields a ratio of time on : time off in the range of from 0.001 to 1 . In an embodiment of the fifth aspect of the invention, the pulsing conditions are time on = 10-500 and time off = 0.1 to 30 ms. In an embodiment of the fifth aspect of the invention, the monomer is introduced during the pulsing at a flow rate of between 1 .5 to 2500 seem. In an embodiment of the fifth aspect of the invention, the power to monomer flow ratio during the pulsed plasma is between 2-60 W/sccm.

By continuous wave plasma, it is meant that plasma is applied continuously. The plasma may be applied at a steady power level, or the power applied may be changed throughout the step. For example, the power may be raised and lowered, so as to approximate pulsed plasma conditions. The increase and decrease in power may be cyclic.

In an embodiment of the fifth aspect of the invention, the compound of formula (lla) is allyl mercaptan.

In an embodiment of the fifth aspect of the invention, the first layer comprises polybutadiene or polyisoprene.

In an embodiment of the fifth aspect of the invention, the method further comprises a preliminary activation step of applying a CW plasma in the presence of an inert gas.

In an embodiment of the invention, the electronic or electrical device or component thereof, or substrate, is selected from mobile phones, smartphones, pagers, radios, sound and audio systems such as loudspeakers, microphones, ringers and/or buzzers, headphones, headsets, and other on-ear or in-ear devices, hearing aids, personal audio equipment such as personal CD, tape cassette or MP3 players, televisions, DVD players including portable DVD players, Blu-ray players including portable Blu-ray players, video recorders, digi and other set-top boxes, media streaming devices, computers and related components such as laptop, notebook, tablet, phablet or palmtop computers, personal digital assistants (PDAs), keyboards, or instrumentation, printers, games consoles, data storage devices, outdoor lighting systems, radio antennae and other forms of communication equipment, cameras and other optical devices, electronic toys including remote control toys.

In a sixth aspect of the invention, there is provided an electronic or electrical device or a component thereof obtainable by any one of the methods of the fifth aspect of the invention.

In a seventh aspect of the invention, there is provided an electronic or electrical device or a component thereof comprising a coating of the first or fourth aspects of the invention.

In an embodiment of the seventh aspect of the invention the coating is a physical barrier; optionally a conformal physical barrier.

In an embodiment of the seventh aspect of the invention the electronic or electrical device or component comprises a housing and wherein the coating forms a conformal physical barrier over an internal surface of the housing.

In an embodiment of the seventh aspect of the invention the electronic or electrical device or component thereof is selected from mobile phones, smartphones, pagers, radios, sound and audio systems such as loudspeakers, microphones, ringers and/or buzzers, headphones, headsets, and other on-ear or in-ear devices, hearing aids, personal audio equipment such as personal CD, tape cassette or MP3 players, televisions, DVD players including portable DVD players, Blu-ray players including portable Blu-ray players, video recorders, digi and other set- top boxes, media streaming devices, computers and related components such as laptop, notebook, tablet, phablet or palmtop computers, personal digital assistants (PDAs), keyboards, or instrumentation, printers, games consoles, data storage devices, outdoor lighting systems, radio antennae and other forms of communication equipment, cameras and other optical devices, electronic toys including remote control toys.

In an embodiment of the seventh aspect of the invention the electronic or electrical device or component thereof can withstand immersion in up to 1 m of water for over 30 minutes without failure or corrosion whilst power is applied to the electronic or electrical device or component.

In an eighth aspect of the invention, there is provided a use of a monomer compound of formula (II) or (Ma):

K-L-[-M-H]_m

(II)

R⁷R⁸C=CR⁹-L-[-S-H]_m

(lla) as a monomer in a plasma deposition process; to treat a layer comprising a reactive group, the reactive group being reactive to a thiol group; optionally the reactive group is selected from a double bond group, a triple bond group, halide group, epoxide group; optionally the layer is the surface portion of a substrate; wherein the monomer of formula (II) or (lla) is as defined above.

In a ninth aspect of the invention, there is provided a method of coating a substrate, wherein the substrate comprises a first polymer comprising at least one non-aromatic double bond; the method comprising the step of plasma depositing a monomer onto the substrate, the monomer comprising a thiol group capable of reacting with the double bond in the first polymer. Optionally, the thiol group is capable of reacting with a monomer molecule. Optionally the first polymer comprises polybutadiene or polyisoprene. Optionally the monomer is allyl mercaptan.

Plasma deposition and other conditions may be as defined in relation to other aspects of the invention.

The present invention will now be further described with reference to the following non-limiting examples and the accompanying illustrative drawings, of which:

Brief description of the drawings

Figure 1 is a schematic representation of an embodiment of the invention

Figure 2 is a schematic representation of a crosslinking reaction at a polymer layer interface with mercaptan; and reaction at a polymer layer interface with 1 -propanethiol

Figure 3 is a photograph of a separated copper track micro-circuit board

Figure 4 is a schematic representation of the method of fabrication of the copper track micro- circuit board

Figure 5 is a schematic representation of the circuit diagram used in the barrier measurement of the coated copper track micro-circuit board

Figure 6 is a photograph of the apparatus used in the barrier measurement of the coated copper track micro-circuit board

Figure 7 is high resolution XPS spectra of 2 W plasma deposited layers: (a) 1 -propanethiol; and (b) allyl mercaptan. The sulfur spectra are fitted to S(2p3/2) and S(2p1/2) components (separation 1.18 eV, and 2:1 relative peak area ratio).

Figure 8 Infrared spectra of: (a) liquid 1 -propanethiol; (b) 2 W plasma deposited

1 -propanethiol; (c) liquid allyl mercaptan; and (d) 2 W plasma deposited allyl mercaptan. Dashed lines indicate allyl CH₂ (3080 cm-1) and thiol S-H (2555 cm-1) stretches respectively.

Figure 9 is a graph of the final wet electrical barrier whilst immersed in water for 13 min under an applied electric field of 10 V mm-1 , for a range of plasma polymers deposited onto a spin coated polybutadiene base layer (thickness 1872 ± 39 nm): 1 H ,1 H,2H,2H-perfluorooctyl acrylate (PFAC-6, pulsed duty cycle 20 ton, 20 ms toff, and 40 W peak power); glycidyl methacrylate (GMA, 5 W); tetramethylsilane (TMS, 3 W); 1 -propanethiol (PT, 2 W); and allyl mercaptan (AM, 2 W) precursors. Polybutadiene base layer (PBD) and following H2S plasma exposure (PBD H₂S, 2 W) are controls. Samples marked within dashed boxes reached the instrument detection limit of 8 x 108 Ω.

Figure 10 is photographs of the micro-circuit board taken after wet electrical barrier testing (10 V mm^"1 electric field applied for 13 min): (a) allyl mercaptan plasma polymer on polyisoprene base layer; and (b) 1 -propanethiol plasma polymer on polyisoprene base layer. Plasma polymer thickness of 555 ± 23 nm, and polyisoprene base layer thickness of 1353 ± 40 nm. Similar results were obtained for polybutadiene base layer.

Figure 11 is a graph of final wet electrical barrier whilst immersed in water for 13 min under an applied electric field of 10 V mm^"1 , for variable thickness plasma deposited allyl mercaptan (2 W) onto a range of fixed thickness spin coated polymer base layers: polybutadiene (▲ thickness 1872 ± 39 nm); polyisoprene (■ thickness 1681 ± 35 nm); and polystyrene (· thickness 2037 ± 195 nm). Samples above the dashed line reached the instrument detection limit of 8 x 10⁸ Ω.

Figure 12 is a graph of final wet electrical barrier whilst immersed in water for 13 min under an applied electric field of 10 V mm-1 , for fixed thickness allyl mercaptan plasma polymer coatings (2 W, 613 ± 71 nm) deposited onto varying thickness polyisoprene base layers. Samples above the dashed line reached the instrument detection limit of 8 x 108 Ω.

Figure 13 is a graph of final wet electrical barrier whilst immersed in water for 13 min as a function of applied electric field, for fixed thickness allyl mercaptan plasma polymer (2 W, 507 ± 14 nm) and polyisoprene base layer (1353 ± 40 nm). Samples above the dashed line reached the instrument detection limit.

Detailed description of the invention

EXPERIMENTAL

Micro-Circuit Board Fabrication

Single sided copper clad microcircuit boards were prepared using a photoresist board (manufacturer part code 141300, Kelan Circuits Ltd., comprising epoxy woven glass laminate base (National Electrical Manufacturers Association grade FR4 and British Standard BS4584) coated with 35 μιτι copper foil and a photoresist top layer (Photoposit SP24, Dow Chemical Company). The Micro-Circuit Board is shown in Figure 3. A scheme showing the method of fabrication of the copper track micro-circuit board is shown in Figure 4. A negative image mask (designed using Easy-PC 2000 (version 19) software, Number One Systems Ltd.) was printed onto 100 μιτι thickness transparent polymer sheets (product code 0224010460, Ryman UK Ltd) using black ink (product number PGI-520BK, Canon Inc.) and an inkjet printer (model IP3600, Canon Inc.). This negative image mask was then placed on top of the photoresist board, and exposed to UV irradiation (368 nm, 15 W, 2 min exposure, model LV204, Mega Electronics Inc.). The UV degraded photoresist regions were dissolved off by immersion in a developer solution for 30 s (1 .5% w/v NaOH and 1 .5% w/v KOH in water, product code AZ303, GSPK Circuits Ltd.) revealing underlying copper, which was then etched away by dipping into 50% w/v ferric chloride solution for 5 min (ferric chloride pellets (product code 3205022, Mega Electronics Inc.) mixed with 40-50 °C tap water (Northumbrian Water), contained in a bubble etch tank, (model PA104, Mega Electronics Inc.)). Next the circuit board was rinsed in tap water to wash away any remaining ferric chloride solution. Finally, the remaining unexposed protective photoresist regions were removed by gently rinsing the surface in acetone (>99.8 wt%, Fisher Scientific Ltd.), followed by soaking in propan-2-ol (>99.5 wt%, Fisher Scientific Ltd.) for 20 min.

The fabricated circuit board layout consisted of two copper contact pads connected to respective copper tracks (separated by 0.8 mm) on top of the epoxy glass laminate substrate, Figure 3. A small strip of single-sided adhesive tape (product code 1443170, Henkel Ltd.) was applied to the contact pads prior to film deposition in order to mask them (i.e. keep them clean for subsequent electrical test connection).

Polymer Base Layer Spin Coating

Polybutadiene

A 5% w/v polybutadiene solution was prepared by dissolving 2.5 g polybutadiene (Mw -200,000, Sigma-Aldrich Co.) in toluene (99.99 wt%, Fisher Scientific Ltd.) in a 50 mL volumetric flask. The solution was agitated for 3 days (sample shaker Vibrax-VXR Model No. VX 2, IKA-Werke GmbH) to ensure the polybutadiene had completely dissolved. Each masked circuit board was fixed onto a glass plate using double sided adhesive tape (product code 1445293, Henkel Ltd.), which in turn was attached to the chuck of a spincoater (model No PRS14E, Cammax Precima Ltd.). 6 drops (~480 μί) of the polybutadiene solution were spin coated at 3000 rpm onto the prepared micro-circuit boards.

Polyisoprene

A 10% w/v polyisoprene solution was prepared by dissolving 2 g polyisoprene (Mw ~40,000, Sigma-Aldrich Co.) in toluene (99.99 wt%, Fisher Scientific Ltd.) to make up to 20 mL total volume. The solution was agitated for 2 days to ensure the polyisoprene had completely dissolved. 6 drops (~480 μΙ_) of the polyisoprene solution were spin coated at 3000 rpm onto the prepared micro-circuit boards.

Polystyrene

A 10% w/v polystyrene solution was prepared by dissolving 1 g polystyrene (Mw ~280,000, Sigma-Aldrich Co.) in toluene (99.99 wt%, Fisher Scientific Ltd.) in a 10 ml volumetric flask. The solution was agitated for 2 days on the sample shaker to ensure the polystyrene was completely dissolved. 3 drops (~240 μί) of the polystyrene solution were spin coated onto the prepared micro-circuit boards at 2000 rpm.

Following spin coating of the respective polymer layers, the circuit boards were left to dry in a vacuum oven at 60 °C for 60 min in order to remove any trapped solvent. Then the back face of each circuit board was carefully cleaned using a cotton bud soaked in acetone, in order to remove any remaining traces of double sided tape which was previously used to hold the micro-circuit board in place during spin coating. Care was taken to ensure that no acetone came into contact with the coating surface. Prior to further testing, the coatings were visually inspected for the absence of defects.

Plasma Deposition

Plasma treatments were carried out in a cylindrical glass reactor (5 cm diameter, 470 cm³ volume) connected to a two stage rotary pump (model E2M2, Edwards Vacuum Ltd.) via a liquid nitrogen cold trap, (base pressure of 4 x10^"3 mbar and a leak rate better than 1 x 10^"9 mol s^"1). An L-C matching unit was used to minimize the standing wave ratio (SWR) of the power transmitted from a 13.56 MHz radio frequency generator (model ACG-3, ENI Power Systems Inc.) to a copper coil (4 mm diameter, 10 turns, spanning 8 cm) externally wound around the glass reactor. A signal generator (model TG503, Thurlby Thandar Instruments Ltd.) was used to trigger the RF power supply. Prior to each plasma treatment, the chamber was scrubbed with detergent, rinsed with propan-2-ol (+99.5 wt%, Fisher Scientific Ltd.), and further cleaned using a 50 W air plasma for at least 30 min. The precursors used for plasma deposition were allyl mercaptan (2-propene-1 -thiol, +80 wt% purity, Tokyo Chemical Industry Ltd.), 1 -propanethiol (+99 wt% purity, Sigma-Aldrich Co.), 1 H,1 H,2H,2H-perfluorooctyl acrylate (PFAC-6, +95% wt purity, Fluorochem Ltd.), tetramethylsilane (TMS, 99.9 wt% purity, Alfa Aesar Co. Ltd.) and glycidyl methacrylate (GMA, 97 wt% purity, Sigma-Aldrich Co.) Control plasma surface modification using H₂S (+99.5% purity, Aldrich Chemical Co.) was also carried out. Samples were placed into the centre of the plasma reactor and 0.2 mbar of precursor was then introduced into the chamber via a fine control needle valve (model LV10K, Edwards Vacuum Ltd.) at a flow rate of 1 .7 x 10^"7 mol s^"1, followed by ignition of the electrical discharge. Film deposition was allowed to proceed for the required time, and then the power supply was switched off whilst maintaining precursor flow through the reactor for 5 min in order to quench any remaining active sites.

Film Thickness

Film thickness measurements were carried out on coated silicon pieces using a

spectrophotometer (model nkd-6000, Aquila Instruments Ltd.). The obtained transmittance- reflectance curves (350-1000 nm wavelength range, using a parallel (P) polarised light source at a 30° incident angle) were fitted to a Cauchy model for dielectric materials, using a modified Levenberg-Marquardt method (version 2.2 software modified upgrade, Pro-Optix, Aquila Instruments Ltd.). The coated circuit boards lacked sufficient reflectivity for thickness measurements, and therefore silicon wafer pieces (1 cm², 5-20 Ω cm^"1 resistivity, Silicon Valley Microelectronics Inc.) were used instead and placed alongside the circuit boards during plasma deposition.

Wet Electrical Barrier Measurement

The immersion in water of coated circuit boards is a realistic test and used instead for electrical barrier. Tap water (156 cm^"1 conductivity, Northumbrian Water), representing a "real world" scenario for water damage to consumer electronics, was allowed to equilibrate to room temperature (20 °C) prior to usage. A multimeter (with a lower detection limit of 10 nA, Keithley 2000, Tektronix UK Ltd.) was used to measure the current flow for each coated micro-circuit board connected to a voltage supply (Model PS-6010, Instek Ltd.). Figure 5 shows a schematic representation of the circuit diagram used in this barrier measurement and Figure 6 shows the apparatus used.

The voltage applied across the circuit was checked using a handheld multimeter (model 72- 770, TENMA Ltd.). Standard wires and connectors were employed (Flexiplast 2V, stranded wire, cross sectional area: 0.75 mm², 129 strands, 0.07 mm diameter, negligible internal resistance, Multi-Contact UK Ltd.)

A fixed voltage was then applied across the 0.8 mm gap between the micro-circuit board copper tracks whilst immersed in water (e.g. 8 V corresponds to an electric field of 10 V mm^"1). Current measurements were taken every 30 s over a 13 min period. At this stage, the final electrical resistance was calculated using Ohm's law. This resistance value was then divided by the total coating thickness (plasma polymer and polymer base layer combined) in order to yield the electrical barrier performance (units Ω m^"1).

X-Rav Photoelectron Spectroscopy

XPS analysis of the plasma deposited allyl mercaptan and 1 -propanethiol layers was carried out using a VG ESCALAB II electron spectrometer equipped with a non-monochromated Mg Ka X-ray source (1253.6 eV) and a concentric hemispherical analyser. Photoemitted electrons were collected at a take-off angle of 20° from the substrate normal, with electron detection in the constant analyser energy mode (CAE, pass energy = 20 eV). See Figure 7. The instrument sensitivity (multiplication) factors used were experimentally determined using a polysulfone standard (0.005 in film, Westlake Plastics Company Inc.) to be C(1s):S(2p):0(1 s) equals 1 .00:0.57:0.35. All binding energies were referenced to the C(1 s) hydrocarbon peak at 285.0 eV. A linear background was subtracted from each core level spectrum and then fitted using fixed full width half maximum (FWHM) Gaussian peaks.

Infrared Spectroscopy

Fourier transform infrared (FTIR) analysis of the allyl mercaptan and 1 -propanethiol precursors was performed using a FTIR spectrometer (Spectrum Two, PerkinElmer Inc.) fitted with a transmission cell and a DTGS detector. See Figure 8. A drop of precursor was dispensed between two KBr plates and spectra taken. The spectra were acquired across the 450-4000 cm^"1 range, averaged over 16 scans at a resolution of 4 cm^"1. Reflection-absorption infrared spectroscopy (RAIRS) analysis of the plasma polymers deposited onto silicon wafer (Silicon Valley Microelectronics, Inc.) was carried out using a liquid nitrogen cooled MCT detector (Spectrum One, PerkinElmer Inc.) operating across the 450-4000 cm^"1 range.

Measurements were performed using a variable angle accessory (Specac Ltd.), with the mirrors aligned at an angle of 66° to the sample normal. The spectra were averaged over 285 scans at a resolution of 4 cm^"1.

RESULTS

Wet Electrical Barrier

The ease with which aqueous ions diffuse through a barrier layer towards an underlying electronic circuit determines the overall level of device protection. Hence, coating electrical resistance measurements during water immersion can be taken as an indicator of wet electrical barrier performance. Compared to modern smartphones, with cell voltages ranging from 3.70-3.85 V the much higher voltages employed in the present study during wet electrical barrier measurements demonstrate a very good level of performance.

A range of precursors containing different functional groups were screened for plasma deposition onto a polybutadiene base layer: 1 H,1 H,2H,2H-perfluorooctyl acrylate, glycidyl methacrylate, tetramethylsilane, 1 -propanethiol, and allyl mercaptan, see Figure 9 and Figure 10. The general trend observed was an improvement in wet electrical barrier with increasing plasma polymer layer thickness; for instance in the case of both glycidyl methacrylate and tetramethylsilane precursors, an absence of current flow was achieved at thicknesses exceeding 1.4 μιτι. The thinnest plasma deposited layers displaying high electrical barrier were obtained for allyl mercaptan precursor, whilst in contrast structurally related 1 - propanethiol (contains no carbon-carbon double bond) was found to be poor at comparable thicknesses. H₂S plasma modification of polybutadiene was employed as a control to demonstrate that surface sulfonation alone is insufficient to attain good wet electrical barrier performance. The wet electrical barrier against water contact angle values are shown in Table 2.

The specific role of the polymer base layer was explored by measuring the wet electrical barrier performance of allyl mercaptan plasma layers deposited onto polybutadiene, polyisoprene, and polystyrene, see Figure 11. All of these polymers contain unsaturated carbon-carbon bonds, however only the former two contain isolated alkene bonds necessary for thiol-ene reactions with plasma generated reactive sulfur species. Despite polystyrene base layer displaying the best uncoated wet electrical barrier, no significant improvement was observed following allyl mercaptan plasma polymer deposition. Whereas in the case of polybutadiene, the electrical barrier showed a marked improvement with increasing plasma polymer thickness; and polyisoprene was found to be the best performing polymer base layer, with the wet electrical barrier rising sharply beyond 100 nm plasma polymer layer thicknesses to reach an absence of current flow above 300 nm. The role of polyisoprene base layer thickness was investigated by maintaining a fixed plasma deposited allyl mercaptan layer thickness, see Figure 12. This indicated a significant improvement in electrical barrier beyond 500 nm polyisoprene thickness, to achieve high electrical barrier performance at

approximately 900 nm.

The wet electrical barrier performance of the optimised thickness allyl mercaptan plasma polymer and polyisoprene layers was then investigated in relation to the magnitude of the applied electric field, see Figure 13. This showed that the multilayer barrier was stable and resilient up to an applied electric field of 20 V mm^"1 , beyond which there was some indication of deterioration. Even then, the drop in performance was not severe, with a final wet electrical barrier of 2 x 10⁴ Ω nm^"1 , when measured at an applied field of 27.5 V mm^"1.

For the polymer base layers investigated, comparison of the obtained wet electrical barrier values with standard bulk polymer resistivity values shows that despite polystyrene possessing a high bulk resistivity value, (> 1 x 10¹⁶ Ω cm), its measured wet electrical barrier value is poor, as was also observed for polyisoprene and polybutadiene. This is most likely due to the relatively high water vapour transmission rates (the mass of water moving through a specified coating area, over a predetermined length of time, normalised to the coating thickness) of polystyrene (1.60-3.37 g mm m^"2 day^"1), polybutadiene (17.7 g mm m^"2 day^"1), and vulcanised (crosslinked) polyisoprene (2.4 g mm m^"2 day^"1). Therefore, conventional bulk electrical resistivity values cannot be taken as an indication of how well a polymer coating will perform as a wet electrical barrier.

X-Ray Photoelectron Spectroscopy

XPS detected the presence of elemental carbon, sulfur, and a low amount of oxygen for both allyl mercaptan and 1 -propanethiol plasma polymers,

Table 1 and Figure 7. The low level of oxygen can be attributed to some aerial surface oxidation during sample transfer from the plasma deposition chamber. The C(1 s) spectra demonstrated consistent hydrocarbon (285.0 eV) and carbon-sulfur (286.9 eV) environments, see Figure 7. There was no significant difference in the measured sulfur concentration between the 1 -propanethiol and allyl mercaptan plasma polymer layers. The S(2p_3/2) and S(2p_1/2) component peak binding energies are consistent with C-S-C or C-S-H (thiol) environments, and not oxidised sulfur (S(2p_3/2) binding energy range 166-168 eV).

Sample C(1s) S(2p) 0(1s)

Peak

Main S(2p_3/2) S(2p_1/2)

% % % Maximum Peak / eV Peak / eV Peak / eV

/ eV

1 -Propanethiol

75.0 - 25.0 - - 0.0 - Theoretical

1 -Propanethiol 65.3 ± 32.2 ± 2.7 ±

285.0 164.0 165.2 532.2 Plasma Polymer 0.8 2.2 1 .5

Allyl Mercaptan

75.0 - 25.0 - - 0.0 - Theoretical

Allyl Mercaptan 62.4 ± 35.1 ± 2.6 ±

285.0 163.6 164.8 531 .7 Plasma Polymer 0.8 2.5 1 .6

Table 1 : Elemental XPS compositions for 1-propanethiol and allyl mercaptan plasma polymer layers (2 W).

Infrared Spectroscopy

The infrared spectrum of allyl mercaptan precursor displays a strong allyl CH₂ stretching (3080 cm^"1) absorbance, which is lost upon plasma deposition, see Figure 8. As expected, this feature was absent for both 1-propanethiol monomer and its corresponding plasma polymer. A weak S-H stretch (2555 cm^"1) was discernible for both 1-propanethiol and allyl mercaptan precursors, as well as for plasma deposited allyl mercaptan; however it was missing for plasma deposited 1 -propanethiol.

Contact Angle Measurements

Microliter sessile drop contact angle analysis was carried out with a video capture system (VCA2500XE, AST Products Inc.) using a 1.0 μΙ_ dispensation of ultra-high purity water (BS 3978 grade 1) droplets onto the surface of the sample. The measured sessile water contact angles showed no obvious correlation to the wet electrical barrier performance. The most hydrophobic coating, pulsed plasma perfluorooctyl acrylate, had a relatively poor wet electrical barrier performance, whilst the best performing coating, allyl mercaptan, had a comparatively low water contact angle.

Table 2 - Sessile water contact angle measurements of the plasma deposited precursors and the polybutadiene and H2S plasma treated polybutadiene control samples.

Some aspects and embodiments of the invention are set out in the following clauses:

Clause 1 . A coating comprising:

(i) a first layer, and

Clause 2. A coating according to clause 1 , wherein the first layer is a polymeric layer. Clause 3. A coating according to clause 1 or 2, wherein the first layer comprises a polymer.

Clause 4. A coating according to any preceding clause, wherein the first layer is not made by a plasma deposition process.

Clause 5. A coating according to any preceding clause, wherein the first layer is made by spin, dip or spray coating.

Clause 6. A coating according to any one of clauses 1 to 3, wherein the first layer is made by a plasma deposition process or by chemical vapour deposition, initiated-chemical vapour deposition, radiation initiated grafting, radiation beam curing, electron beam initiated grafting, electron beam curing or self-assembled layer.

Clause 7. A coating according to any preceding clause, wherein the first layer comprises a polymer comprising a non-aromatic unsaturated chemical group.

Clause 8 A coating according to any preceding clause, wherein the first layer comprises a polymer comprising a reactive group, the reactive group being reactive to a thiol group; optionally the reactive group is selected from a double bond group, a triple bond group, a halide group, and an epoxide group.

Clause 9. A coating according to any preceding clause, wherein the first layer comprises a double or triple bond group.

Clause 10. A coating according to any preceding clause, wherein the first layer comprises a group selected from C=C; C=N; N=N or C≡C.

Clause 1 1 . A coating according to any preceding clause, wherein the first layer comprises a C=C group.

Clause 12. A coating according to any preceding clause, wherein the first layer comprises a polymer comprising a poly-1 ,3-diene.

Clause 13. A coating according to any preceding clause, wherein the first layer comprises a polymer comprising polybutadiene.

Clause 14. A coating according to any preceding clause, wherein the first layer comprises a polymer comprising polyisoprene. Clause 15. A coating according to any preceding clause, wherein the first layer comprises a polymer comprising repeating units of formula (I):

-[WR³C=CR⁴Z]-

(I) where W may independently be a bond, or is one or more of O, S, CO, C(0)0, CH₂0 or (CR¹R²)_p, and Z may independently be a bond, or is one or more of O, S, CO, C(0)0, CH₂0 or (CR⁵R⁶)_q, where p and q are independently an integer from 1 to 6, and wherein W, Z, R³ and R⁴ are substantially inert groups; optionally, R¹ to R⁶ are independently selected from a hydrogen atom, optionally substituted straight or branched alkane chain(s) or optionally substituted aryl group(s).

Clause 16. A coating according to any one of clauses 7 to 15, wherein the unsaturated group is electron rich.

Clause 17. A coating according to clause 15 or 16, wherein at least one of W, Z, R³ or R⁴ is an electron donating group.

Clause 18. A coating according to clause 17, wherein at least one of R³ and R⁴ is an electron donating group.

Clause 19. A coating according to clause 17 or 18, wherein the electron donating group is selected from optionally substituted straight or branched alkane chain(s) or optionally substituted aryl group(s).

Clause 20. A coating according to any one of clauses 15 to 19, wherein W, Z and R³ are hydrogen and R⁴ is a methyl group.

Clause 21 . A coating according to any preceding clause, wherein the second layer comprises a polymer prepared by deposition of a monomer compound of formula (II):

K-L-[-M-H]_m

(II) wherein: K is a group comprising a non-aromatic unsaturated bond;

L is a linker group linking groups K and M;

Clause 22. A coating according to clause 21 , wherein group K comprises double or triple bonds.

Clause 23. A coating according to clause 21 or 22, wherein K comprises a group selected from C=C; C=N; N=N; or C≡C groups.

Clause 24. A coating according to any one of clauses 21 to 23, wherein K comprises a C=C group.

Clause 25. A coating according to any one of clauses 21 to 24, wherein M is selected from S; O; NH; NR⁷; PH ; PR⁸; POR⁸; P(0)R⁹ and P(0)OR⁹; wherein R⁷ to R⁹ are

independently selected from optionally substituted straight or branched alkane chain(s), or optionally substituted aryl group(s).

Clause 26. A coating according to any one of clauses 21 to 25, wherein M is an S atom.

Clause 27. A coating according to any one of clauses 21 to 26, wherein L is substantially inert.

Clause 28. A coating according to any one of clauses 21 to 27, wherein L is selected from a bond, optionally substituted straight or branched alkane chain(s) or optionally substituted aryl group(s).

Clause 29. A coating according to any preceding clause, wherein the second layer comprises a polymer prepared by deposition of a monomer compound of formula (lla):

R¹⁰R C=CR¹²-L-[-S-H]_m

(lla) wherein L is as defined in clause 27 or 28, and R¹⁰ to R¹² are independently selected from optionally substituted straight or branched alkane chain(s), optionally substituted aryl group(s), or a hydrogen atom and m is an integer greater than 0; optionally m is 1 , 2, 3, 4, 5 or 6.

Clause 30. A coating according to any one of clauses 27 to 29, wherein L is a CH₂ group.

Clause 31 . A coating according to any one of clauses 21 to 30, wherein the monomer of Formula (II) or (lla) is a thiol-ene.

Clause 32. A coating according to any one of clauses 21 to 31 , wherein the monomer of Formula (II) or (lla) is allyl mercaptan.

Clause 33. A coating according to any one of clauses 21 to 32, wherein L comprises one or more additional K and/or M groups.

Clause 34. A coating according to any one of clauses 1 to 20, wherein the second layer comprises a polymer comprising repeating units of formula (III):

(III) wherein:

X is selected from the group CR^AR^B or NR^C;

L is as defined in any one of clauses 21 , 27 or 28; and

M is as defined in any one of clauses 21 , 25 or 26.

Clause 35. A coating according to clause 34, wherein X is CH₂; Y is CH; L is CH₂ and M is an S atom. Clause 36. A coating according to any preceding clause, wherein the crosslinking group comprises a group M, wherein M is as defined in any one of clauses 21 , 25 or 26.

Clause 37. A coating according to any preceding clause, wherein the crosslinking group comprises a group L-M, wherein M and L are as defined in any one of clauses 21 and 25 to 28.

Clause 38. A coating according to any preceding clause, wherein the crosslinking group comprises a S; a CH₂ or a CH₂-S group.

Clause 39. A coating according to any one of clauses 1 to 20, comprising units of formula (IV):

-[X-Y]-

-[ R³HC-CR Z1-

(IV) wherein X, Y, L and M are as defined in any one of clause 34 to 38 and W, Z, R³ to R⁴ are as defined in any one of clauses 15 to 20.

Clause 40. A coating according to clause 39, wherein units of formula (IV) define an interface, or interface region, between layers (i) and (ii).

Clause 41 . A coating according to any preceding clause, wherein there are fewer unsaturated bonds at the interface/interface region between layers (i) and (ii) than in the bulk of the first layer; and optionally wherein there are substantially no unsaturated bonds at the interface/interface region between layers (i) and (ii).

Clause 42. A coating according to any preceding clause, wherein the second layer is deposited under excitation.

Clause 43. A coating according to any preceding clause, wherein the coating is substantially pin-hole free. Clause 44. A coating according to any preceding clause, wherein the coating is electrically insulating, particularly wherein the coating has a resistance of 0.6 M Ω nm-1 or higher when submerged in water and a voltage of 8V is applied for 13 minutes.

Clause 45. A coating according to any preceding clause, wherein the coating comprises at least one additional layer, particularly a liquid repellent layer.

Clause 46. A coating according to any preceding clause, wherein the first layer has a thickness of 50nm-10,000nm; optionally a thickness greater than 200nm, 400nm, 500nm, 1000nm, 2000 nm or 5000nm.

Clause 47. A coating according to any preceding clause, wherein the second layer has a thickness of 10nm-10,000nm, optionally a thickness greater than 50nm, 100nm, 200nm, 300nm, 500nm, 1000nm, 2000nm or 5000nm.

Clause 48. A method of coating a substrate, wherein the substrate comprises a first polymer comprising at least one non-aromatic double bond; the method comprising the step of plasma depositing a monomer onto the substrate, the monomer comprising a thiol group capable of reacting with the double bond in the first polymer; optionally the first polymer comprises polybutadiene or polyisoprene; optionally the monomer is a mercaptan.

Clause 49. A method of preparing a coating, comprising providing

(i) a first layer, and

Clause 50. A method of preparing a coating according to clause 49, wherein the first layer is as defined in any one of clauses 2 to 20.

Clause 51 . A method of preparing a coating according to clause 49 or 50, wherein the second layer is as defined in any one of clauses 21 to 38.

Clause 52. A method of preparing a coating according to any one of clauses 49 to 51 , wherein the crosslinking groups is as defined in any one of clauses 36 to 38. Clause 53. A method of preparing a coating according to any one of clauses 49 to 52, wherein the first layer is formed prior to providing the second layer.

Clause 54. A method of preparing a coating according to any one of clauses 49 to 52, wherein the second layer is formed prior to providing the first layer.

Clause 55. A method of preparing a coating according to any one of clauses 49 to 53, wherein a substrate comprises the first layer.

Clause 56. A method of preparing a coating according to any one of clauses 49 to 52 and 54, wherein a substrate comprises the second layer.

Clause 57. A method of preparing a coating according to clause 55, wherein the first layer is formed on the substrate.

Clause 58. A method of preparing a coating according to clause 56, wherein the second layer is formed on the substrate.

Clause 59. A method of preparing a coating according to any one of clauses 55 to 58, wherein an electronic or electrical device, or component thereof, comprises the substrate.

Clause 60. A method for coating a substrate, comprising providing on the substrate:

(i) a first layer, and

Clause 61 . A coating obtainable by any one of the processes of clauses 49 to 60.

Clause 62. A method for treating an electronic or electrical device or component thereof, comprising: exposing the electronic or electrical device or component thereof to a plasma comprising one or more monomer compounds for a sufficient period of time to allow a protective coating to form on the electronic or electrical device or component thereof, the protective coating forming a physical barrier over a surface of said electronic or electrical device or component thereof; wherein each monomer is a compound of formula (II) or (lla), as defined in any one of clauses 21 to 33; and wherein the electronic or electrical device or component thereof comprises a substrate, the substrate comprising a first layer as defined in any one of clauses 2 to 20; optionally the first layer is the surface portion of a substrate.

Clause 63. A method for treating an electronic or electrical device or component thereof, comprising: exposing the electronic or electrical device or component thereof to a plasma comprising one or more monomer compounds for a sufficient period of time to allow a protective coating to form on the electronic or electrical device or component thereof, the protective coating forming a physical barrier over a surface of said electronic or electrical device or component thereof; wherein each monomer is a compound of formula (II) or (lla), as defined in any one of clauses 21 to 33; and wherein the plasma deposited layer is provided with a first layer as defined in any one of clauses 2 to 20.

Clause 64. A method according to clause 62 or 63 wherein the barrier is a conformal physical barrier.

Clause 65. A method according to any one of clauses 62 to 64, wherein the step of exposing said electronic or electrical device or component thereof to a plasma comprises a continuous wave (CW) deposition step or a pulsed (PW) deposition step; or optionally a CW step followed by a PW step or optionally a PW step followed by a CW step.

Clause 66. A method according to clause 65 wherein the pulses of the pulsed plasma are applied in a sequence which yields a ratio of time on : time off in the range of from 0.001 to 1 .

Clause 67. A method according to clause 65 or 66, wherein the pulsing conditions are time on = 10-500 and time off = 0.1 to 30 ms.

Clause 68. A method according to any one of clauses 65 to 67, wherein the monomer is introduced during the pulsing at a flow rate of between 1.5 to 2500 seem.

Clause 69. A method according to any one of clauses 65 to 68, wherein the power to monomer flow ratio during the pulsed plasma is between 2-60 W/sccm. Clause 70. A method according to any one of clauses 62 to 69 wherein the compound of formula (lla) is a mercaptan, particularly allyl mercaptan.

Clause 71 . A method according to any one of clauses 62 to 70 wherein the first layer comprises polybutadiene or polyisoprene.

Clause 72. A method according to any one of clauses 65 to 71 , further comprising a preliminary activation step of applying a CW plasma in the presence of an inert gas.

Clause 73. A method according to any one of clauses 65 to 72, wherein the electronic or electrical device or component thereof is selected from mobile phones, smartphones, pagers, radios, sound and audio systems such as loudspeakers, microphones, ringers and/or buzzers, headphones, headsets, and other on-ear or in-ear devices, hearing aids, personal audio equipment such as personal CD, tape cassette or MP3 players, televisions, DVD players including portable DVD players, Blu-ray players including portable Blu-ray players, video recorders, digi and other set-top boxes, media streaming devices, computers and related components such as laptop, notebook, tablet, phablet or palmtop computers, personal digital assistants (PDAs), keyboards, or instrumentation, printers, games consoles, data storage devices, outdoor lighting systems, radio antennae and other forms of communication equipment, cameras and other optical devices, electronic toys including remote control toys.

Clause 74. An electronic or electrical device or a component thereof obtainable by any one of the methods of clauses 62 to 73.

Clause 75. An electronic or electrical device or a component thereof comprising a coating of any one of clauses 1 to 47 and 61 .

Clause 76. An electronic or electrical or component according to clause 74 or 75, wherein the coating is a physical barrier; optionally a conformal physical barrier.

Clause 77. An electronic or electrical device or component thereof according to any one of clauses 74 to 76, wherein the electronic or electrical device or component comprises a housing and wherein the coating forms a conformal physical barrier over an internal surface of the housing.

Clause 78. An electronic or electrical device or component thereof according to any one of clauses 74 to 77, wherein the electronic or electrical device or component is selected from mobile phones, smartphones, pagers, radios, sound and audio systems such as

loudspeakers, microphones, ringers and/or buzzers, headphones, headsets, and other on-ear or in-ear devices, hearing aids, personal audio equipment such as personal CD, tape cassette or MP3 players, televisions, DVD players including portable DVD players, Blu-ray players including portable Blu-ray players, video recorders, digi and other set-top boxes, media streaming devices, computers and related components such as laptop, notebook, tablet, phablet or palmtop computers, personal digital assistants (PDAs), keyboards, or

instrumentation, printers, games consoles, data storage devices, outdoor lighting systems, radio antennae and other forms of communication equipment, cameras and other optical devices, electronic toys including remote control toys.

Clause 79. An electronic or electrical device or component thereof according to any one of clauses 74 to 78, wherein the electronic or electrical device or component thereof can withstand immersion in up to 1 m of water for over 30 minutes without failure or corrosion whilst power applied to electronic or electrical device or component.

Clause 80. Use of a monomer compound of formula (II) or (I la):

K-L-[-M-H]_m

(II)

R⁷R⁸C=CR⁹-L-[-S-H]_m

(lla) as a monomer in a plasma deposition process; to treat a layer comprising a reactive group, the reactive group being reactive to a thiol group; optionally the reactive group is selected from a double bond group, a triple bond group, halide group, epoxide group; optionally the layer is the surface portion of a substrate; wherein the monomer of formula (II) or (lla) is as defined in any one of clauses 21 to 33.

Claims

1 . A coating comprising:

(i) a first layer, and

2. A coating according to claim 1 , wherein the first layer comprises a polymer comprising a non-aromatic unsaturated chemical group.

3 A coating according to claim 1 or 2, wherein the first layer comprises a polymer comprising a reactive group, the reactive group being reactive to a thiol group; optionally the reactive group is selected from a double bond group, a triple bond group, halide group, epoxide group.

4. A coating according to any preceding claim, wherein the first layer comprises a polymer comprising repeating units of formula (I):

-[WR³C=CR⁴Z]-

5. A coating according to claim 4, wherein at least one of W, Z, R³ or R⁴ is an electron donating group; optionally the electron donating group is selected from optionally substituted straight or branched alkane chain(s) or optionally substituted aryl group(s).

6. A coating according to claim 4 or 5, wherein W, Z and R³ are hydrogen and R⁴ is a methyl group.

7. A coating according to any preceding claim, wherein the second layer comprises a polymer prepared by deposition of a monomer compound of formula (II):

K-L-[-M-H]_m

(II) wherein:

8. A coating according to claim 7, wherein K comprises a group selected from C=C; C=N; N=N; or C≡C groups.

9. A coating according to claim 7 or 8, wherein M is selected from S; O; NH; NR⁷; PH; PR⁸; POR⁸; P(0)R⁹ and P(0)OR⁹; wherein R⁷ to R⁹ are independently selected from optionally substituted straight or branched alkane chain(s), or optionally substituted aryl group(s).

10. A coating according to any one of claims 7 to 9, wherein L is substantially inert.

1 1 . A coating according to any one of claims 7 to 10, wherein L is selected from a bond, optionally substituted straight or branched alkane chain(s) or optionally substituted aryl group(s).

12. A coating according to any preceding claim, wherein the second layer comprises a polymer prepared by deposition of a monomer compound of formula (Ila):

R¹⁰R C=CR¹²-L-[-S-H]_m

(Ila) wherein L is as defined in claim 10 or 11 , and R¹⁰ to R¹² are independently selected from optionally substituted straight or branched alkane chain(s), optionally substituted aryl group(s), or a hydrogen atom and m is an integer greater than 0; optionally m is 1 , 2, 3, 4, 5 or 6.

13. A coating according to any one of claims 7 to 12, wherein the monomer of Formula (II) or (lla) is a thiol-ene; optionally the monomer of Formula (II) or (lla) is allyl mercaptan.

14. A coating according to any one of claims 1 to 16, wherein the second layer comprises a polymer comprising repeating units of formula (III):

(III) wherein:

X is selected from the group CR^AR^B or NR^C;

L is as defined in any one of claims 7, 10 or 1 1 ; and

M is as defined in claim 7 or 9.

15. A coating according to claim 14, wherein X is CH₂; Y is CH; L is CH₂ and M is an S atom.

16. A coating according to any preceding claim, wherein the crosslinking group comprises a group M, wherein M is defined in claim 7 or 9.

17. A coating according to any preceding claim, wherein the crosslinking group comprises a group L-M, wherein M and L are defined in any one of claims 7 and 9 to 11 .

18. A coating according to any preceding claim, wherein the crosslinking group comprises a S; CH₂ or a CH₂-S group.

19. A coating according to any one of claims 1 to 6, comprising units of formula (IV):

-[X-YJ- I

-[WR³HC-CR Z;

(IV) wherein X, Y, L and M are as defined in any one of claim 14 to 18 and W, Z, R³ to R⁴ are as defined in any one of claims 4 to 6.

20. A coating according to any preceding claim, wherein the coating comprises at least one additional layer, particularly a liquid repellent layer.

21 . A method of preparing a coating, comprising providing

(i) a first layer, and

22. A method of preparing a coating according to claim 21 , wherein the first layer is as defined in any one of claims 2 to 6.

23. A method of preparing a coating according to claim 21 or 22, wherein the second layer is as defined in any one of claims 7 to 18.

24. A method of preparing a coating according to any one of claims 21 to 23, wherein the first layer is formed prior to providing the second layer.

25. A method of preparing a coating according to any one of claims 21 to 24, wherein a substrate comprises the first layer.

26. A method of preparing a coating according to claim 25, wherein the first layer is formed on the substrate.

27. A method of preparing a coating according to any one of claims 21 to 23, wherein the second layer is formed prior to providing the first layer.

28. A method of preparing a coating according to any one of claims 21 to 23 and 27, wherein a substrate comprises the second layer.

29. A method of preparing a coating according to claim 28, wherein the second layer is formed on the substrate.

30. A method of preparing a coating according to any one of claims 25, 26, 28 and 29, wherein an electronic or electrical device, or component thereof, comprises the substrate.

31 . A coating obtainable by any one of the methods of claims 21 to 30.

32. A method for treating an electronic or electrical device or component thereof, comprising: exposing the electronic or electrical device or component thereof to a plasma comprising one or more monomer compounds for a sufficient period of time to allow a protective coating to form on the electronic or electrical device or component thereof, the protective coating forming a physical barrier over a surface of said electronic or electrical device or component thereof; wherein each monomer is a compound of formula (II) or (I la), as defined in any one of claims 7 to 13; and wherein the electronic or electrical device or component thereof comprises a substrate, the substrate comprising a first layer as defined in any one of claims 2 to 6; optionally the first layer is the surface portion of a substrate.

33. A method for treating an electronic or electrical device or component thereof, comprising: exposing the electronic or electrical device or component thereof to a plasma comprising one or more monomer compounds for a sufficient period of time to allow a protective coating to form on the electronic or electrical device or component thereof, the protective coating forming a physical barrier over a surface of said electronic or electrical device or component thereof; wherein each monomer is a compound of formula (II) or (I la), as defined in any one of claims 7 to 13; and wherein the plasma deposited layer is provided with a first layer as defined in any one of claims 2 to 6.

34. A method according to claim 32 or 33 wherein the compound of formula (lla) is a mercaptan, particularly allyl mercaptan.

35. A method according to any one of claims 32 to 34 wherein the first layer comprises polybutadiene or polyisoprene.

36. An electronic or electrical device or a component thereof obtainable by any one of the methods of claims 32 to 35.

37. An electronic or electrical device or a component thereof comprising a coating of any one of claims 1 to 20 and 31 .

38. An electronic or electrical device or component thereof according to claim 36 or 37, wherein the electronic or electrical device or component comprises a housing and wherein the coating forms a conformal physical barrier over an internal surface of the housing.

39. An electronic or electrical device or component thereof according to any one of claims 36 to 38, wherein the electronic or electrical device or component thereof is selected from mobile phones, smartphones, pagers, radios, sound and audio systems such as

40. Use of a monomer compound of formula (II) or (lla):

K-L-[-M-H]_m

(II)

R⁷R⁸C=CR⁹-L-[-S-H]_m

(lla) as a monomer in a plasma deposition process; to treat a layer comprising a reactive group, the reactive group being reactive to a thiol group; optionally the reactive group is selected from a double bond group, a triple bond group, halide group, epoxide group; optionally the layer is the surface portion of a substrate; wherein the monomer of formula (II) or (lla) is as defined in any one of claims 7 to 13.