WO2025155200A1

WO2025155200A1 - A method of rapid curing with energized curing vapour and a substrate produced by the method

Info

Publication number: WO2025155200A1
Application number: PCT/NO2025/050003
Authority: WO
Inventors: Kingsley Odinaka IWU; Macdonald Elochukwu NWAMMA
Original assignee: Nanize AS
Current assignee: Nanize AS
Priority date: 2024-01-15
Filing date: 2025-01-14
Publication date: 2025-07-24
Anticipated expiration: 2026-07-15
Also published as: NO20240042A1

Abstract

The present invention relates to a method of curing a layer of a coating formulation deposited on a substrate, the coating formulation containing hydrolysable Si-X groups wherein X is selected from a halogen, C₁-C₆ alkoxy, hydrogen, -NH-Si or -NH₂: The method comprising the steps of energizing a curing vapour, and subjecting the layer to the energized curing vapour. The present invention also relates to a substrate comprising a coating made using the method.

Description

A method of rapid curing with energized curing vapour and a substrate produced by the method

Technical Field

The present invention relates to a method for rapidly curing a layer of a coating formulation deposited on a substrate, the coating formulation containing hydrolysable Si-X groups wherein X is selected from a halogen, Ci-Ce alkoxy, hydrogen, -NH-Si or -NH2. and a substrate comprising a coating made using the method.

Background Art

Compounds containing hydrolysable Si-X groups are commonly used in coating formulations, either as the main component or as additives. Curing of such coatings involves the hydrolysis of the Si-X group to form silanols, followed by condensation reaction between the silanol groups to form Si-O-Si bond. Since they do not require or involve toxic curing agents or groups - either as part of the molecule or separate additives - they are considered environmentally friendly. Furthermore, the Si-O-Si bond is highly stable to LIV and other environmental factors, as well as to a large variety of chemicals.

The Si atoms of the Si-X or other Si atoms in the molecules can also be bonded to organic groups, for example methyl, ethyl, phenyl, vinyl (CH=CH2), etc. These Si- organic groups, being highly inert, confer good hydrophobicity and even oleophobicity to the coating. This is the reason for use of such compounds as antisoiling coatings or modification of surfaces to confer anti-soiling behaviour. Examples of compounds containing hydrolysable Si-X include (poly)alkoxysilanes, (poly)halosilanes, and (poly)silazanes.

Quite often coatings containing hydrolysable Si-X groups are left to cure in ambient atmosphere, that is their curing is effected by atmospheric moisture. Such a curing method is simple and environmentally friendly, since it does not utilize toxic curing agent, such as tin based compounds. However, such curing is usually top down, that is the top surface of the coating cures first or faster than the interior of the coating. The consequences of this are: Curing will generally slow down with time, since the cured top surface can act to slow down penetration of moisture to the interior. This is especially the case when Si atoms are bonded to organic groups, e.g., methyl and vinyl in polysilazane. These Si- alkyl groups (e.g., Si-CHs) or Si-aryl (Si-phenyl groups) are hydrophobic and inert and therefore can impede moisture ingress. In fact, in organic chemistry, they are only second to carbon-fluorine bonds (e.g., CF2 or CF3) in inertness and hydrophobicity. This is the reason polydimethylsiloxane (PDMS) is widely used as a water repellent surface.

Depending on weather conditions, curing may stall, leading to an uncured interior and a cured top surface and hence varying properties across the width of the coating.

Among compounds with hydrolysable Si-X groups which are used in coating formulations, organic polysilazane (OPSZ) is popular and widely used for coating vehicles in order to impact dirt repellence and protection of car paint from LIV. OPSZ coatings are also applied to solar PV glass, windows, eyewears, touchscreen, etc. as anti-soiling or easy to clean surfaces.

The commonly recommended curing method for OPSZ is to keep and cure in ambient environment, with curing (up to 95%) taking as long as 7 days. The inventors have noted that OPSZ coatings, whether commercially available or formulated inhouse, showed very limited or poor curing even after heating at 200°C for 1-2 hours. Therefore, the use of such high temperatures, which may not be practicable for some substrates, for example plastics, does not necessarily lead to satisfactory curing. Even after raising the relative humidity to more than 50%, the inventors found out that curing, as evidenced by the disappearance of N-H (or expressed as Si-NH or Si- NH-Si) FT-IR peak at about 900 cm^-1, is still poor or limited at elevated temperature, as well as low temperatures - as low as room temperature.

The only advantage high temperature treatment (e.g. > 150 °C) seems to bring is reducing dry-to-touch time, but usually a significant portion of the coating is not cured. It should be noted that reference is made to the FT-IR spectra of N-H peak in assessing curing because it is more sterically hindered than the Si-H functional groups. However, any process which leads to rapid consumption (hydrolysis to form Si-OH) of the N-H groups will normally have same or similar effect on the Si-H groups.

Therefore, a need for a cost effective and timely process which leads to (near) complete curing of polysilazane and other compounds containing hydrolysable Si-X groups remains. By curing we mean the consumption of N-H and Si-H groups via hydrolysis to lead to Si-O-Si as the final reaction product.

The patent application WO2023/282768 A1 teaches an improved curing method for polysilazane which involves the following process: a) drying in an oven maintained at 80°C for 10 mins, followed by; b) curing in a high humidity atmosphere containing H2O2 vapour. The authors noted that for coating formulation which does not contain the cross-linking catalyst, tetrabutylammonium fluoride (TBAF), curing - hydrolysis of Si-NH to form silanols and subsequent condensation to yield Si-O-Si - is limited, just like a TBAF-containing coating left to cure in ambient conditions. Tetrabutylammonium chloride (TBAC) is also known to enhance curing of polysilazane. TBAC and TBAF belong to a group called quaternary ammonium salts (QAS). QAS are easily hydrated, and this may be the reason they are able to enhance the curing of polysilazanes.

A polysilazane coating method is also described in WO 2022/002844 A1 . In that method, polysilazanes, catalysts (TBAF), and reactive nanomaterials and/or reactive molecules are introduced into a coating composition vessel and the solution is mixed for a predetermined time period. Then, within a further predetermined time after the mixing step, the mixed solution is applied to a substrate, and a coating layer is formed thereon, and subsequently cured.

It is the objective of the current invention to improve the curing method and achieve rapid curing of coatings containing hydrolysable Si-X groups. Summary of invention

The present invention provides a method for rapid curing a layer of a coating formulation deposited on a substrate, the coating formulation containing hydrolysable Si-X groups wherein X is selected from a halogen, Ci-Ce alkoxy, hydrogen, -NH-Si or -NH2, the method comprising the steps of: a) energizing a curing vapour, and b) subjecting the layer to the energized curing vapour.

Further, the present invention provides a substrate made using the inventive method.

Figures

Figure 1 shows an exemplary embodiment of a curing set up with a medium wave infra-red lamp as the energizer and sample locations A to K inside in the curing compartment.

Figure 2 shows the curing process ongoing with carrier fully inserted in the curing compartment.

Detailed description of the invention

The present invention provides an improved and rapid method of curing a layer deposited on a substrate, wherein the layer comprises a coating formulation containing hydrolysable Si-X groups, wherein X is selected from a halogen, Ci-Cs alkoxy, hydrogen, NH-Si and NH2. Examples of compounds containing hydrolysable Si-X groups include (poly)alkoxysilanes, (poly)halosilanes, and (poly)silazane. Their hydrolysis and condensation reaction can be summarised as follows:

Si-X + H2O = Si-OH + HX . (1 )

Si-OH + Si-OH = Si-O-Si + H2O . (2) where X may be a halogen, preferably chlorine or bromine (e.g., chlorine in dimethyldichlorosilane), alkoxy group - e.g. ethoxy in (3-aminopropyl)triethoxysilane APTES), methoxy in methyltrimethoxysilane or hydrogen e.g. in polysilazane and NH-Si or NH2, e.g. in polysilazane. The hydrolysis of Si-NH-Si in polysilazane has a different stoichiometry and leads to formation of two silanol molecules and ammonia:

Si-NH-Si + H2O = Si-OH + Si-NH₂. (3)

Si-NH₂ + H2O = Si-OH + NH₃ . (4)

The combined equation is therefore:

Si-NH-Si + 2H₂O = 2Si-OH + NH₃ . (5)

X in equations 3 and 4 are therefore NH-Si and NH2, respectively. The latter is normally not present in pristine polysilazane but can be realised if the polymer comes in contact with water, e.g. atmospheric moisture.

The coating formulation comprising hydrolysable Si-X groups wherein X is selected from a halogen, an C1-C6 alkoxy group, hydrogen, NH-Si or NH2, may be dissolved in one or more solvents. The solvent may be a polar aprotic solvent and/or a non-polar solvent. The solvent may be an anhydrous solvent. In some embodiments, all coating formulation components are completely dissolved or suspended as a stable suspension before their introduction into the coating composition vessel. In other embodiments, one or more liquid components is introduced neat, that is without the presence of a solvent, into the coating composition vessel, whereas all other components are completely dissolved or suspended as a stable suspension before their introduction into the coating composition vessel. In some embodiments, all components are dissolved or suspended in the same solvent. In other embodiments, different solvents are used for two or more of the components, and the resulting solutions combined to form the coating formulation. In some embodiments, a solvent is chosen from the list comprising, but not limited to, dimethyl sulfoxide (DMSO), n- butyl acetate, tertiary butyl acetate, secondary butyl acetate, propyl acetate, ethyl acetate, methyl acetate, methyl ethyl ketone (MEK), tetrahydrofuran (THF), 2-methyl- tetrahydrofuran (MTHF), dimethylformamide (DMF), dibutyl ether (DBE), xylene. In preferred embodiments, coating compositions comprising substantial amounts of PHPS comprise only non-polar solvents such as dibutyl ether and xylene. The choice of solvent depends on several factors such as solubility of coating components, stability of the solvent, especially for reactive formulations, and safety or economic considerations.

The method of curing includes in a first step a) energizing a curing vapour.

The curing vapour may be energized substantially remotely from the layer, that is the energy source for energizing is not directly interacting with the coating layer. For example, as shown in Figure 1 , samples in locations A to E are not under the infrared light. So, the curing vapour is energized remotely from the coatings. Remote energizing has the advantage of separating the coating and/or substrate from the energy of the energizer, for example it may be desirable to keep the temperature experienced by the substrate or coating to below 100°C.

The curing vapour may be energized in the same zone as the coating layer (not fully remote). A common energy source is used in energizing the curing vapour and heating the coating layer. For example, samples in locations G to K are being heated directly by or absorbing the infra-red light which is also being used to energize the curing vapour.

Energizing a curing vapour means imparting energy to the curing vapour in order to raise its energy level and/or temperature. Energizing may be carried out by means of exposure to electromagnetic radiation, for example infra-red light, LIV light or microwave. Exposure to electromagnetic radiation may be performed at wavelengths in which the curing vapour absorbs. For example, with a curing vapour comprising H2O2, infra-red wavelength of 2 to 12 pm may be used for energizing. Referring to Figure 1 , heat generated by the infra-red light may energize the vapour, as opposed to direct absorption of the light. The infra-red lamp heats up the chamber which in turn energizes the curing vapour by transferring thermal energy to it. Thus, energizing of the vapour in this exemplary embodiment may be due to direct absorption of the infra-red and/or indirect heating of the curing vapour. Increasing temperature with time detailed in Table 1 below suggest that the curing vapour is in part being energised though heat transfer from the chamber, which heats gradually upon being irradiated by the infra-red lamp. Therefore, energizing the curing vapour may involve heating it in order to raise its thermal energy, evidenced by rise in temperature. The thermal energy may be transferred directly from the energizer (energy source) to the curing vapour or indirectly by heating a container containing the curing vapour or through which the curing vapour flows on the way to interacting with coating which needs curing. The temperature of the energized curing vapour is preferably in the range from 30°C to 120°C, more preferred in the range from 35 °C to 80 °C.

Figure 1 is only an exemplary embodiment of the rapid curing process to enable a person skilled in the art to understand the concept. Other configurations may be implemented to cater to substrate type and dimensions or to required industry process, e.g. batch or continuous operation. Between the energizing zone and the location of the uncured coating, the curing vapour may lose some of its energy. It may then be desirable to counter this and keep the curing vapour at a certain energy level, for example at a certain temperature or temperature range. Examples of methods to achieve this may include insulating the system to avoid loss of energy and heating the compartment containing the uncured coating.

The length, shape and other characteristics of the energizing zone and the space (flow path) between the energizing zone and the coating may be optimised for efficient energizing of the curing vapour and optimum curing of the coating.

Heating of the curing vapour to energize it may be accomplished by methods other than use of infra-red lamp. For example, a heating element may be used. In another embodiment, air may be heated, and then mixed with the curing vapour in order to energize it. The air may act as both a diluent for the curing vapour and also to uniformly spread and direct the curing vapour towards all the surfaces of the uncured coating layer comprising hydrolysable Si-X.

Absorption of the energizer may cause the molecules of a component of the curing vapour to vibrate and increase their thermal energy. Energizing the curing vapour may comprise ionisation, that is the gas molecules may be ionised. They may therefore exist in part or whole as plasma. This may be achieved by ionising the molecules of the curing vapour, for example using a plasma generating system consisting of an anode and a cathode, or indirectly by subjecting the curing vapour to already generated plasma. Ionising may also be accomplished with high energy electromagnetic radiation, for example UV and Gamma rays. In this case the curing vapour molecules may absorb the energy directly.

In step b) the layer deposited on a substrate is subjected to the energized curing vapour, whereby the layer is cured by hydrolysing the Si-X groups of the coating formulation. The substrate may be glass, ceramic, metal, polymer (plastic), wood or a composite. The substrate may be rigid or flexible.

The duration of exposure to the energized curing vapour may be less than 10 minutes, preferably less than 5 minutes, more preferably less than 3 minutes and even more preferably less than 1 minute.

Prior to subjecting the layer to the energized vapour, the layer may be dried for a period of not more than 30 minutes at a temperature not greater than 20 °C above the boiling point of the solvent. Alternatively, the temperature may be equal to the boiling point. Preferably, the layer is dried at temperatures below the boiling point of the solvent. When e.g., butyl acetate with a boiling point of 126 °C is used as the solvent, the temperature may be 30 to 60 °C lower than the boiling point of the solvent. The drying may be performed in a period of not more than 5 minutes, and in some embodiments not more than 1.5 minutes.

The curing vapour comprises compounds known in the art to hydrolyse or promote the hydrolysis of Si-X groups. The curing vapour may comprise water, H2O2, NH3, or organic/inorganic acids or a combination of two or more compounds.

The curing compound may exist originally as a liquid and therefore will have to be transformed to the vapour phase. Generation of the vapour may be accomplished by any suitable process, for example using heat. Generation of vapour may be accomplished using any other known process known in the art, such as processes used in generating water vapour from water - for example for the purpose of humidification. Examples include ultrasonic and impeller humidifiers.

A preferred embodiment is generation of the curing vapour using an ultrasonic humidifier. An ultrasonic humidifier uses ultrasonic frequency to atomize (vaporize) liquid into fine mist and may be referred to in this patent document as ultrasonic vaporizer.

An impeller vapour generator uses a disc (impeller) rotating at high speed to break liquid into fine droplets which can float in air and may be referred to in this patent document as impeller vaporizer.

The curing vapour may comprise a mixture of water and H2O2. The curing vapour may comprise from 1 to 30 wt% H2O2 in water, preferably from 5 to 25 wt% H2O2 in water. Preferably, the concentration of H2O2 in water is 10 wt% or above. In another embodiment, the concentration of H2O2 in water may be greater than 30 wt% to obtain even more rapid curing.

The curing vapour may comprise a mixture of ammonia and water. The curing vapour may comprise from 0.25 to 30 wt% NH3 in water, preferably from 2 to 20 wt% NH3 in water.

The aforementioned percentages (of H2O2 and NH3) in water refer to the compositions of the liquid from which the curing vapour is generated. It is assumed that the generated vapour will have the same concentrations as the liquid.

After the coating layer is subjected to the energized curing vapour, it may be heated to complete or further enhance the curing process or to improve coating properties, e.g., mechanical properties. Heating may also be accomplished by the thermal energy of the curing vapour, that is it may be accomplished at the same time as exposure of the coating to the curing vapour. In this case the same energy source is used to energize the curing vapour as well as heat the coating. Alternatively, the energy source used in energizing the curing vapour may be different from that used in heating the coating during or after the curing process.

In the curing experiments described below, the coating formulations contain polysilazanes, with (3-aminopropyl)triethoxysilane (APTES) as curing agent. The curing method can also be performed on coating formulations containing hydrolysable Si-X groups wherein X is primarily selected from a halogen or an C-i-Cs alkoxy group.

EXPERIMENTS

General notes for the experiments:

• Except otherwise indicated, the curing vapour is 20 wt% H2O2 in water.

• For the sake of simplicity, wt% H2O2 vapour means a vapour generated from an aqueous solution containing same percentage of H2O2. That is, the concentration of H2O2 in the liquid and vapour phases are considered to be the same. This vapour may be simply referred to as energized H2O2 vapour.

• The H2O2 vapour is generated from an ultrasonic humidifier and redirected or uniformly distributed by flowing air - from a compressor.

• Curing vapour is any vapour capable of hydrolysing the polar groups in polysilazane to form silanols (Si-OH).

• The hydrolysable polar groups in polysilazane are Si-H and N-H, with the latter being a short form of Si-NH or Si-NH2

• Curing is rated from 6.75 (practically no curing) to 1 : 1-1.125 (excellent curing, EC); 1 .25-1 .5 (very very good curing, WGC); 1 .75-2 (very good curing, VGC); 2.25-2.75 (good curing, GC); 3-3.5, (fair curing, FC); 3.75 (borderline curing, BC); 4-4.5 (poor curing, PC); 4.75-5.5 (very poor curing, VPC) and 5.75-6.75 (extremely poor curing, EPC).

• Curing rating is based on FT-IR measurement of the NH (from Si-NH-Si) of polysilazane peak centred around 900 cm^-1. • D1500RC is an organic polysilazane with APTES to promote curing. Structure is believed to be (APTES covalently bonded to the polymer backbone):

(a, b and c are proprietary information)

• 7640 Permanent Profi Protect (PP) is a commercial formulation of organic polysilazane from Creative Chemical Manufacturers, CCM. According to CCM, it contains APTES. n-butyl acetate is the main solvent and accounts for 35% - <55% of the composition while organic polysilazane accounts for 15% - <35% and APTES accounts for 5% - <10%.

• Boiling point of n-butyl acetate is 126 °C.

• TBAF is a solution of tetrabutylammonium fluoride in THF (0.5 wt%). TBAF acts as cross-linking catalyst to prevent or minimize fragmentation.

• TG4 is a solution of TEGO® Glide 410, (from Evonik) in THF (5.5 wt%). TG4 is a polyether modified siloxane and acts as a levelling agent.

• Boiling point of THF is 66 °C.

• B17 is a solution of a dumbbell POSS (10 wt% in THF). The structure is shown below:

A85 is a solution of an open cage POSS (trisilanol isobutyl POSS, sourced from HybridPlastics) - 10 wt% in THF. The structure is shown below:

R = isobutyl

Coating formulations:

• B 17-66:

A: 2000 pl D1500RC + 1000 pl TG4

B: 2000 pl B17 POSS + 660 pl TBAF + 250 pl THF

• B 17-80

A: 1182 pl D1500RC + 590 pl TG4

B: 1420 pl B17 POSS + 400 pl TBAF + 2318 pl THF

• A85-8

A: 1182 pl D1500RC + 590 pl TG4

B: 1182 pl A85 + 400 pl TBAF + 2550 pl THF

• PP-1 :

3940 pl PP + 3940 pl n-butyl acetate

• D1500-R2:

2000 pl D1500RC + 3910 pl THF

• D1500-R9:

2000 pl D1500 RC + 9820 pl n-butyl acetate

The energizing zone is the region in which the H2O2 vapour is directly impacted by and absorbs infra-red light or any other source of energy. Otherwise referred to as the hot region of the infrared lamp. The infra-red lamp has a peak wavelength between 2.2 and 3.5 pm.

The curing set-up and ongoing curing process are shown in Figures 1 and 2. Figure 1 shows the IR lamp and sample locations inside the curing compartment. The expression ”... xx cm from the energizing zone” means the distance from the end of the energizing zone to the sample location. For example, a sample in location D in Figure 1 lies > 2.5 cm from the energizing zone.

The curing process starts when the carrier is partially inserted into the curing compartment (such that it is partially under the lamp) in the direction indicated in Figure 1.

Coated samples are placed on the carrier and identified by their locations (A-K).

Some samples are placed under the energizing zone, which means the infra-red light is being used to heat them and also energize the curing vapour at the same time.

Figure 2 shows the curing process with carrier and samples inserted in curing compartment. Hydrogen peroxide (H2O2) vapour is introduced from the top of the box and cold air from right corner which help redirect and distribute the H2O2 vapour uniformly. The H2O2 vapour is generated from a 20 wt% H2O2 solution in water by an ultrasonic humidifier.

X1 and X2, shown in Figure 1 , are the cold regions of the infra-red lamp. In between them is the region with emission of infrared radiation (hot zone of infrared lamp), and it is in this region that the curing vapour is energized. This region is called the energizing zone. There are sample locations in this zone, while a small part of the zone (indicated as Y) has no sample under it.

The carrier is partitioned into 11 parts represented by letters (A-K), each part having a length of 2.5 cm, to easily identify sample location.

Samples in the energizing zone are directly under the lamp while those placed in remote zones are not exposed to direct radiation from the lamp - their increased temperature is due to interaction with the energized H2O2 vapour/air. A small part of the remote zone is likely under the infra-red light (e.g. the part of F close to E), since infrared light may not strictly be emitted in a strictly straight line. Table 1 below shows temperature values in degrees Celsius at various durations for different sample locations in Figure 1 during a typical curing process. The measurements were made with 20 wt% H2O2 vapour after air flow and the infra-red lamp are turned on.

Table 1 : Curing vapour temperature in °C

A 29 41 58

B 33 50 71

C 34 51 73

D 35 55 78

E 42 65 95

F 50 81 114

Experiments 1 to 3

• Coating formulation (D1500-R2): 2000 pl D1500RC + 3910 pl THF

• The formulation was applied to glass slide substrates with the ultrasonic spray coater thus: flow rate 0.3 ml/min, line spacing 7 mm, air pressure 0.45 bar, height 50 mm and run power 36 %. Velocity for Exp. 1 was 40 mm/s while it was 50 mm/s for Exp. 2 and 3 which were applied in two layers (sprayed twice).

• Samples in locations A, C and G were dried at 70 °C for 1 .5 minutes while the rest were dried at 55 °C for same duration. There is no significant difference in curing with drying at these temperatures.

• After drying, the samples were introduced in the curing set-up (Figure 1 ) and exposed to energized H2O2 vapour for 1 .5 minutes.

• Average thickness of cured coatings was 3.4 pm for Exp.1 and 5.6 pm for Exp. 2 and 3.

• The curing levels attained are indicated in Table 2. The results indicate that in 1 .5 minutes exposure of energized H2O2 vapour, all samples in Exp. 1 achieved at least a curing level of good curing, GC, with the exception of sample H which showed a lower curing level of 3, FC.

• Samples in location C showed the best curing, indicating that at curing is optimum up to a distance of 5-7.5 cm from the energizing zone.

• In Exp. 2 where samples are about 2 pm thicker than Exp. 1 , only samples in locations C and E were cured (WGC and VGC respectively) after 1 .5 minutes of energized H2O2 vapour exposure. In Exp. 3 where samples have similar thickness as Exp. 2, longer exposure duration (3 minutes) lead to improved curing.

• Samples in locations G and H, even though experiencing a higher temperature are less cured than samples in locations B, C and E in Exp. 1 and C and E in Exp. 2. This may indicate that the curing vapour is not optimally energized and/or that at higher temperature, the curing vapour has a poorer interaction with the coating layer.

• With a higher flux of energized H2O2 vapour, for example by increasing flow of H2O2 vapour into the energizing zone and or more energetic H2O2, for example by increasing the irradiance of the infra-red lamp and/or increasing the length of the energizing zone, curing of thicker samples may be accomplished in less time, e.g., lower than 3 minutes.

A higher flux of energized H2O2 vapour or more energetic H2O2 vapour may work to extend the remote curing distance beyond (A), that is more than 10- 12.5 cm from the energizing zone.

Experiment 4

• Coating formulation (B17-80) was prepared by mixing A and B for 5 minutes: A: 1182 pl D1500 RC + 590 pl TG4 B: 1420 pl B17 + 400 pl TBAF + 2318 pl THF

• The formulation was applied on glass slides with the following parameters: First two layers (applied twice) - 0.30 ml/min flow rate, 50 mm/s velocity, 7 mm line spacing, 0.45 bar air pressure, 50 mm height, 36% run. A third layer was applied with same parameters except for flow rate of 0.5 ml/min, velocity of 30 mm/s and height of 40 mm.

• The coatings were dried at 70 °C for 1 .5 minutes, followed by exposure to energized H2O2 vapour for 1.5 minutes.

• The average thickness of the cured coating is 10 pm.

• The curing levels of the samples are listed in Table 3 and indicates that curing was best in location D and that locations longer than 7.5 cm from the energizing zone is not ideal for curing such a thick coating under the current conditions.

Experiment 5

• Coating formulation (PP-1): 3940 pl PP + 3940 butyl acetate.

• The formulation was applied on glass slides with the following parameters: 0.80 ml/min flow rate, 35 mm/s velocity, 7 mm line spacing, 0.45 bar air pressure, 50 mm height, 36% run.

• The coatings were dried at 60 °C for 5 min, followed by exposure to energized H2O2 vapour for 1 .5 minutes.

• The average thickness of the cured coating is 6.3 pm.

• The curing levels of the samples are listed in Table 3 and indicates that as far away as location B, which is about 7.5 to 10 cm from the energizing zone, curing level of WGC is achieved. Samples in locations C and D were cracked which could be a pointer to a better curing than in B. The authors have found out that FT-IR measurement tends to be erroneous or lower than expected for cracked samples and that cracking is mostly associated with a high degree of curing, especially for thicker samples.

Experiments 6 and 7

• Coating formulation (D1500-R9): 2000 pl D1500RC + 9820 pl THF.

• Coating formulation was sprayed onto glass slide with the following: flow rate 0.3 ml/min, velocity 40 mm/s, line spacing 7 mm, air pressure 0.45 bar, height 50 mm and run power 36 %. Formulation was sprayed twice.

• Samples of Exp. 6 were dried at 100 °C while those of Exp. 7 were dried at 55 °C, both for 10 minutes.

• After drying, the samples were cured with energized H2O2 vapour for 1 .5 min.

• The average thickness for Exp. 6 and 7 were 2 and 2.6 pm, respectively.

• The curing levels attained are listed in Table 4. They show that higher temperature drying for more than 10 minutes is not ideal for optimum curing when the samples are located further away from the energizing zone (location C and beyond).

• With 55 °C drying, the best cured sample is the sample in location B, which is about 10-12.5 cm from the energizing zone.

Experiments 8-10

• Coating formulation (D1500-R9): 2000 pl D1500RC + 9820 pl THF.

• Coating formulation was sprayed onto glass slides with spray parameters as in Exp. 6 and 7.

• Samples were dried at 70 °C for 1 .5 minutes and then cured with energized H2O2 vapour for different durations: Exp.8 for 1 .5 minutes; Exp. 9 for 1 minute and Exp.10 for 0.5 minutes.

• The average thickness after curing was 2.5, 2.7 and 3.3 pm for Exp. 8, 9 and 10, respectively. • The curing levels attained are listed in Table 5. Except for location A, they show that curing for 1 .5 minutes under the present conditions is only slightly better than curing for 1 minute and that for both duration, optimum curing may be obtained at up to > 10 cm from the energizing zone.

• At temperatures as low as 55-50 °C (Samples in location B to D) of Exp. 9, curing level of 1 .5 to 2 (VGC to WGC) is achieved.

• Exp. 10 shows that curing is virtually non-existent for 0.5 minute of energized H2O2 exposure at locations A, B and C where (with reference to Table 1 ) curing vapour temperatures are at or below 34°C. However, even at curing vapour temperatures as low as 35 °C (locations D, E and F) some curing is achieved. A more energetic or hotter curing vapour, for example with a higher irradiance infrared light or longer energizing zone, or a higher flux of curing vapour, for example with an increased flow rate of the curing vapour, may be used to achieve better curing. For a shorter curing vapour exposure duration such as 30 seconds or less, a more energetic or hotter curing vapour, for example with a higher irradiance infrared light or longer energizing zone, may be used to improve curing, e.g. to at least GC.

• Comparing Exp.8 with Exp. 7, it is obvious that for lower temperature drying, a short duration of 1 .5 minutes or less is sufficient.

• It should be noted that the best curing level in Exp. 8 (samples in location C and D) is the same for sample in location C of Exp. 2, even though Exp. 2 is on average twice the thickness of Exp. 8.

• This may be an indication that for a certain thickness range curing may not be strongly dependent on thickness.

Table 5; Experiments 11 - 13

• Coating formulation (D1500-R9): 2000 pl D1500RC + 9820 pl THF

• The formulation was sprayed onto glass slides with spray parameters as in Exp. 6 and 7.

• Samples were dried at 70 °C for 1.5 minutes and then cured with energized H2O2 vapour of different concentrations: 10, 5 and 2.5 wt% for Exp.11 , 12 and 13, respectively. Curing time was 1.5 minutes.

• The curing levels attained are listed in Table 6. They show that for 10 wt% H2O2, curing level was generally good, with samples in locations B to F having a rating of 1 .75-2.5, very good to good. In comparison, 20 wt% H2O2 (Exp. 8.) has a rating of 1 .5 to 2.

• With 5 wt% H2O2, curing was generally poor to extremely poor except for samples/locations C to E with a rating of 3-3.5 (FC)

• Curing however is generally non-existent for 2.5 wt% H2O2.

• The curing results with 5 or less wt% H2O2 vapour may indicate that a longer exposure duration and/or a higher flux of energized curing vapour and/or a more energetic curing vapour may be needed for satisfactory curing at lower H2O2 concentrations.

Control experiment 1

• Coating formulation and spray parameters were the same for Exp. 1

• Samples were dried at 70 °C for 1 .5 min.

• Curing was carried out under 20% H2O2 vapour for 1.5 minutes (same as Exp. 1 ). The only difference between Control exp. 1 and Exp. 1 is that curing took place inside an oven into which the H2O2 vapour was pumped, with the oven temperature maintained at 70 °C. • This curing oven temperature is similar to the temperature experienced by samples in locations B and C and higher than that of the sample in location A of Exp. 1 .

• The curing level attained ranged from 5 (very poor) to 6 (extremely poor), in contrast to samples in locations A, B, C of Exp. 1 which ranged from 1 .25 (WGC) to 2 (VGC)

Control experiment 2

• Coating formulation, spray parameters and drying conditions were the same as with Exp. 5

• Curing was carried out under 20% H2O2 vapour for 1.5 minutes (same as Exp. 5). The only difference between Control exp. 2 and Exp. 5 is that curing took place inside an oven into which the H2O2 vapour was pumped, with the oven temperature maintained at 70 °C.

• This curing oven temperature is similar to the temperature experienced by samples B and C and higher than that of the sample in locations A of Exp. 5

• The curing level attained ranged from 5.5 (VPC) to 6 (EPC), in contrast to samples in locations A, B, C of Exp. 5 which ranged from 1.5 WGC) to 2.75 (GC).

Control experiment 3

• Coating formulation, spray parameters and drying conditions were the same as with Exp. 8.

• Curing was carried out under 20% H2O2 vapour for 1.5 minutes (same as Exp. 8). The only difference between Control exp. 3 and Exp. 8 is that curing took place with the infra-red lamp off, that is the H2O2 was not energized.

• The curing level attained is between 6.5 and 6.75 (extremely poor) for samples in location A to D. Samples in locations E and F showed a slight but negligible improvement, with curing of 4.75 to 5.5 (very poor). These stand in contrast to samples of Exp. 8 which ranged from 1 .5 to 2. As can be seen from the experiments above, the curing method according to the invention shows that rapid curing of a coating comprising hydrolysable Si-X deposited as a layer on a substrate can be obtained using energized curing vapour, without an additional post-curing vapour treatment heating. The cured coatings include coatings which do not contain a quaternary ammonium salt (QAS), which normally require a heat treatment after exposure to a curing vapour in order to achieve an acceptable level of curing.

The curing process is advantageous in several ways.

1 . Curing may be achieved at low temperatures, for example below 80 °C and as low as 55 °C or less. This is important for temperature sensitive substrates or processes.

2. The curing speed (duration of exposure of energized curing vapour) of the curing method of the present invention is compatible with fast and large volume processes, for example a roll-to-rol I coating process. It should be noted that the infra-red lamp used has a response time of 5-10 seconds, which indicates achieving at least good curing (GC) under less than 1 minute with this exemplary curing set-up. This places the speed of this rapid curing method close to or about the same of UV curable coatings.

3. The curing method of the present invention gives more flexibility on the design and implementation of the curing set-up. For example, coating on a complex and large substrate may be cured by keeping the curing setup stationary and passing the coated substrate through/under it or by keeping the coated substrate stationary and passing the curing setup over or around or under it in order to expose the coating layer to the curing vapour.

Claims

1) A method for curing a layer of a coating formulation deposited on a substrate, the coating formulation containing hydrolysable Si-X groups wherein X is selected from a halogen, Ci-Ce alkoxy, hydrogen, -NH-Si or -NH2, the method comprising the steps of: a) energizing a curing vapour, and b) subjecting the layer to the energized curing vapour.

2) The method of claim 1 , wherein the temperature of the energized curing vapour is greater than or equal to 35 °C

3) The method of claim 1 or 2, wherein the curing vapour is energized substantially remotely from the layer.

4) The method of claim 1, 2 or 3, wherein the layer is heated during or after being subjected to the energized curing vapour.

5) The method of claim 4, wherein energizing the curing vapour and heating the layer is carried out with a common energy source.

6) The method of any of the preceding claims, wherein energizing the curing vapour is carried out with electromagnetic radiation.

7) The method of claim 6, wherein one or more compounds in the curing vapour absorbs in wavelengths of the electromagnetic radiation.

8) The method of claim 6 or 7, wherein the electromagnetic radiation is selected from infrared light, UV light or microwave.

9) The method of any of the preceding claims, wherein the curing vapour comprises one or more of water, H2O2, NH3, organic and inorganic acids. 10)The method of claim 9, wherein generation of the curing vapour is carried out with an ultrasonic vapourizer or an impeller vapourizer.

11) The method of claim any of the preceding claims, wherein the curing vapour contains from 1 to 30 wt% H2O2 in water. 12) The method of any claims 1 to 10, wherein the curing vapour contains from 0.25 to

30 wt% NH3 in water.

13) The method of any one of the preceding claims, wherein prior to subjecting the layer to the energized vapour, the layer is dried.

14) A substrate made using the method of any one of the preceding claims.