GB2489990A

GB2489990A - Process for applying a coating to glass

Info

Publication number: GB2489990A
Application number: GB201106413A
Authority: GB
Inventors: Andrew Van Zwanenberg
Original assignee: Marks and Spencer PLC
Current assignee: Marks and Spencer PLC
Priority date: 2011-04-15
Filing date: 2011-04-15
Publication date: 2012-10-17
Also published as: GB201106413D0

Abstract

A process for coating a three-dimensional glass structure, such as tableware or homeware, is disclosed which comprises spraying a solvent-based hydrophobic silicon dioxide nano-coating composition. The coating imparts easy-clean and self-dry properties. The coating is applied to glass surface using as solvent based composition using a pump actuator that delivers less than 0.5 g of composition per spray.

Description

Process For Applying A Coating to Glass The present invention relates to a new process for applying a coating composition to a three-dimensional glass structure. The composition is a silicon dioxide nano-coating which makes the glass up to 80% easier to clean and dry. In particular, the coating composition may be applied to glass vases, glass drinking vessels etc..

Background to the Invention

Compositions of the type employed in the present invention are sometimes referred to as "easy-clean" or "self-clean" compositions/coatings. Such coatings have been employed in other industries, e.g. applied to ceramic materials. However, until now no-one has successfully applied these coatings to three-dimensional glass structures.

In principal, there are two methods by which easier, or self clean properties can be imparted to a glass surface: the development of a high energy hydrophilic surface, or the use of a low energy, hydrophobic surface. The differences are represented below by the three water droplets, on the 3 glass slides shown in figures 7A-7C. Figure 7A shows a normal glass 0 surface, Figure 7B shows a hydrophobic surface and Figure 7C shows a hydrophilic surface. r

A hydrophilic surface results in the water wetting, or completely covenng the surface of the glass. When placed on the vertical, as in windows, the water sheets' down the pane of glass when it rains, and coupled with some UV active metallic coatings, results in a self cleaning effect. This technology has previously been employed in self cleaning window glass.

A hydrophobic surface resists water contacting with it. The water does not wet the surface, it beads and forms droplets of minimum contact area with the glass. This contact area is a ratio of the surface tension of the water meniscus, and the surface energy of the glass.

After significant research, it has been discovered by the inventor of the present invention that hydrophobic coatings have advantages when used in the context of the present invention, i.e. application to three-dimensional glass structures. It has been discovered that the presence of static water in the glass vessel renders the hydrophilic technologies less effective since they rely on an active system, i.e. continual movement of water, for the usheeting approach to be effective. This does not work in the static environment of a three-dimensional glass structure, e.g. a vase.

Hydrophobic technologies have been employed in other industries however these predominantly rely on a process that involves applying the coating to the surface followed by a curing process at elevated temperature. These two-step processes are not desirable and require the use of a furnace. There is therefore a need to develop technologies that avoid this firing step and therefore reduce costs and process time.

Hydrophobic technologies that do not involve a firing process have also been employed in other industries. These generally involve applying the coating by dipping. The application of the coating is effective at room temperature and therefore no subsequent firing step is required. However, processes that involve dipping steps raise environmental, handling and storage problems. For example, dipping inherently requires the use of an open dipping tank and subsequently draining the item. The silicon dioxide nano-coatings are solvent based.

During the dipping and draining process the solvent will evaporate and when it evaporates in significant quantities special handling is required to avoid the adverse environmental and health effects this causes. Counteracting these effects inevitably leads to reduced production rates, increased production space requirements, significant VOC (volatile organic compound) issues, and increased costs, There is therefore a need to develop technologies that avoid such issues.

The present invention addresses these needs and provides an alternative process for applying a coating composition to a three-dimensional glass structure that is effective, efficient, cost-effective, easier to manage, and environmentally acceptable.

Summary of the Invention

According to a first aspect, the present invention provides a process for preparing a three-dimensional glass structure coated with a hydrophobic silicon dioxide nano-coating comprising applying a solvent-based hydrophobic silicon dioxide nano-coating composition to a three-dimensional glass structure, wherein said coating is applied by spraying said composition onto said three-dimensional glass structure using a pump actuator that delivers less than 0.5 g of said composition per spray.

According to a second aspect, the present invention provides a silicon dioxide nano-coated three-dimensional glass structure obtainable by the process of the first aspect described above.

Detailed Description of the Invention

The invention provides a cost-effective, efficient, efficacious process for coating three dimensional glass structures with an easy-cleaning/self-drying coating.

According to a first aspect of the invention, the invention provides a process for preparing a three-dimensional glass structure coated with a hydrophobic silicon dioxide nano-coating comprising applying a solvent-based hydrophobic silicon dioxide nano-coating composition to a three-dimensional glass structure, wherein said coating is applied by spraying said composition onto said three-dimensional glass structure using a pump actuator that delivers less than 0.5 g of said composition per spray.

Three dimensional glass structures useful in the context of the present invention include, but are not limited to, glass homeware and glass tableware, such as glass vases, glass drinking vessels etc. The process of the present invention is particularly useful when applied to glass vases. The three-dimensional glass structures, e.g. vases, may be transparent, translucent or opaque. Preferably, the structures are transparent or translucent, more preferably transparent. Also, the glass structures may be made up of colourless glass, coloured glass or a combination of both. In a most preferred embodiment, the three-dimensional glass structure, e.g. vase, is constructed from transparent colourless glass.

Three-dimensional glass structures, as opposed to two-dimensional structures such as glass panes, posses both an external glass surface area and an internal glass surface. This presents a unique challenge when developing processes for applying easyfself-clean coatings to these structures. The prior art processes are applicable only to two-dimensional glass structures (e.g. glass panes, architectural glass, ship windscreens, shower enclosures, car windscreens) and do not successfully address the problems associated with 3D-structures. However, the process of the present invention is suitable for applying to the external glass surface and/or the internal glass surface of a three-dimensional glass structure. In a preferred embodiment, the process of the present invention comprises applying the hydrophobic silicon dioxide nano-coating composition to both the external glass surface and the internal glass surface of the three dimensional glass structure, e.g. glass homeware, glass tableware, glass vase etc. The hydrophobic silicon dioxide nano-coating employed in the process of the invention provides a hydrophobic coating to the surface of the three-dimensional glass structure. The properties imparted to the glass surface provide a easy-cleaning/self-drying three- dimensional glass structure. Such coatings may be applied to a glass surface as a solvent-based composition comprising the silicon dioxide nano-coating. Once the coating composition has been applied to the glass surface the solvent evaporates leaving a silicon dioxide nano-coating bound to the surface of the glass. The solvent merely acts as a means for applying the nano-coating to the glass surface. In a preferred embodiment of the present invention, the process does not involve any step that is carried out at elevated temperature.

In particular, it is advantageous if once the solvent-based composition has been applied to the glass surface, the solvent carrier evaporates at ambient temperature leaving a layer of silicon dioxide hydrophobic nano-coating. The use of such a solvent-based composition avoids the need for a subsequent firing step. Solvent-based easy-clean/self-drying hydrophobic silicon dioxide nano-coating compositions are commercially available, such as from Signo. Typically, silicon dioxide coatings comprise a silicon dioxide matrix, deposited as a layer, of thickness on the nano-scale. This matrix contains an active ingredient, distributed as nano particles which modify the surface properties at the surface of the material being coated.

The process of the present invention highlights the potential associated with applying a solvent based composition by spraying onto a three-dimensional glass structure. The features of the process, in particular the use of pump actuator that delivers a required weight of composition per spray, allow adequate coverage of the composition on the surface(s) of the glass structure. However, it has also been discovered that coverage of the composition on the glass surface can be improved by wiping the surface after spraying to ensure complete coverage. Accordingly, in a preferred embodiment of the invention, the process further comprises wiping the surface of the three-dimensional glass structure after the hydrophobic solvent-based silicon dioxide nano-coating composition has been applied. Any such wiping step must take place before the composition has cured. A cotton cloth is a suitable, but not the only, means of carrying out such a wiping step.

In a further preferred embodiment, the process of the invention further comprises cleaning the surfaces of the three-dimensional glass structure before applying the hydrophobic silicon dioxide nano-coating composition.

The process of the present invention involves spraying the hydrophobic silicon dioxide nano-coating composition onto the glass surfaces using a pump actuator that delivers less than 0.5 g of composition per spray. Preferably, the process employs a pump actuator that delivers less than 0.4 g of composition per spray, more preferably less than 0.3 g, even more preferably about 0.2 g of composition per spray.

Surprisingly, it has been discovered that using a pump actuator as described above, allows the process of the present invention to be effective when applying only two or less sprays per area of glass, preferably one spray per area of glass. For example it has been found that the solvent-based composition can be spread out using a cloth more efficiently when the process of the present invention is employed. It has been discovered that typically you need the following number of sprays for coating a whole vase.

Sprays outside Sprays inside Simple small vase 1 1 Complicated small vase 2 1 Simple medium vase 2 1 Complicated medium vase 3 1 Simple largevase 3 2 Complicated large vase 1 2 Conventional spraying means for these types of applications deliver about 1.2-1.5 g of composition per spray. However for the purpose of the present invention, the application to three-dimensional structures such as tableware or homeware, such levels of delivery were surprisingly found to be inefficient and/or not cost-effective. The inventor found that reducing the amount of composition delivered per spray achieved significant improvements in atomisation of composition droplets which resulted in better spray coverage per spray.

Surprisingly, this reduction in spray volume was achieved without needing to increase the number of sprays per glass structure/vase, so increased the number of structures that could be coated per litre of composition. This led to a significant cost, resource and time reduction The invention will now be illustrated by reference to a number of examples. These examples should not be viewed as limiting the scope of the invention in any way. They are merely for illustrative purposes.

Examples

Example I

A number of glass tiles were subjected to testing in order to demonstrate the effectiveness of a hydrophobic silicon dioxide nano-coating applied in accordance with the process of the present invention. In total 64 glass tiles were tested: 32 coated in accordance with the process of the present invention, 32 uncoated. The procedure and results are presented below.

Sample Details Samples were received for assessment of the present invention.

Those samples were as follows: 32 x Glass Tiles 9cm x 7cm with Signo coating 32 x Glass Tiles 9cm x 7cm uncoated The tiles coated with Signo coating were prepared by spraying (using a pump extractor that delivers 0.2 g of spray per delivery) Signo material onto each tile. Each tile was sprayed once.

Procedure Testing was carried out in accordance with the Assessment Procedure (see below) to ascertain the efficacy of the present invention.

Results Based overall on the staining remaining on the test pieces after the test procedure, the outcome was assessed and categorized in the following table; Sample Identity Staining Remaining Very Severe Severe Slight Very Slight No stain Coated Tile -6 tiles 8 tiles 9 tiles 9 tiles Uncoated Tile 8 tiles 16 tiles 8 tiles --Comments On dropping the solution on to the surfaces the difference in the behaviour of the liquid on each different surface finish was evident with the solution "spreading" over the surface of the untreated tile, but remaining in the form of a small "bead" in the case of the coated tile. See Figures 1 and 2.

After baking in the oven, again the behaviour of the solution on each different surface finish was significant. See Figures 3 and 4. And finally the end result after abrasion testing is illustrated in Figures 5 and 6.

As an indication to the interpretation, the two samples illustrated, uncoated and coated, were categorized as slight and very slight staining respectively.

Example 2

A cylindrical glass vase having a height of 40 cm and a diameter of 20 cm was sprayed with a solvent-based hydrophobic silicon dioxide nano-coating composition (Signo), both internally and externally. The surface was wiped to ensure complete coverage, and the nano-coating was allowed to cure at room temperature. The resulting coated glass vase demonstrated overall hydrophobic easy-clean/self-dry properties. Thus confirming that the process of the invention provides an effective method of applying such a coating to a three-dimensional glass structure.

Assessment Procedure Purpose To determine the effectiveness of hydrophobic silicon dioxide nano-coating on Glassware Test Products Glass tile test pieces Apparatus Abrasion Resistance Test Machine complying with requirements of BS 7069:1988 Abrasive Pad 7 cm x 9 cm -Scotchbrite No 7447 Clear glass tiles 10.0 cm x 10.5 cm Blue food colouring diluted with water -50/50 Method Apply two drops of blue coloured solution to centre of a glass tile to stain.

Bake in an air circulating oven for 12 minutes at temperature of 75° C. Remove the tile from the over and cool to room temperature.

Load the automated reciprocating arm of the test rig with an abrasive pad and place tile under the arm.

Lower the arm on to the tile with a I SN loading.

One movement of the arm forward and back over a distance of 100 mm equates to I cycle.

10 cycles to be carried out and area of staining observed.

2 sets of 50 reciprocating cycles to be carried out with the abrasive pad being changed after each set.

The area of staining to be observed.

Results Observe the amount of dye removed and note.

Claims

CLAIMS1. A process for preparing a three-dimensional glass structure coated with a hydrophobic silicon dioxide nano-coating comprising applying a solvent-based hydrophobic silicon dioxide nano-coating composition to a three-dimensional glass structure, wherein said coating is applied by spraying said composition onto a three-dimensional glass structure using a pump actuator that delivers less than 0.5 g of said composition per spray.
2. The process of claim I wherein the three-dimensional glass structure is a glass vase or a glass drinking vessel, preferably a glass vase.
3. The process of claim I or claim 2, wherein said process excludes a subsequent firing process.
4. The process of any one of the preceding claims, wherein the process comprises applying the hydrophobic silicon dioxide nano-coating composition to both the external glass surface and the internal glass surface of the three-dimensional glass structure.
5. The process of any one of the preceding claims, wherein said process further comprises a step in which the hydrophobic silicon dioxide nano-coating composition is wiped over the surface of the three-dimensional glass structure before the solvent evaporates off.
6. The process of any one of the preceding claims, wherein said process further comprises cleaning the surfaces of the three-dimensional glass structure before applying the hydrophobic silicon dioxide nano-coating composition.
7. The process of any one of the preceding claims, wherein the pump actuator delivers less than 0.4 g of said composition per spray.
8. The process of claim 7, wherein the pump actuator delivers less than 0.3 g of said composition per spray.
9. The process of claim 8, wherein the pump actuator delivers about 0.2 g of said composition per spray.
10. A process for preparing a glass vase coated with a hydrophobic silicon dioxide nano-coating comprising applying a solvent-based hydrophobic silicon dioxide nano-coating composition to a glass vase, wherein said coating is applied by spraying said composition onto a glass vase using a pump actuator that delivers less than 0.5 g of said composition per spray.
11. A three-dimensional glass structure coated with a hydrophobic silicon dioxide nano-coating obtainable by a process as defined in any one of claims I to 9.
12. A glass vase coated with a hydrophobic silicon dioxide nano-coating obtainable by a process as defined in claim 10.