WO2005077556A1

WO2005077556A1 - Surface cleaning system

Info

Publication number: WO2005077556A1
Application number: PCT/SE2005/000228
Authority: WO
Inventors: Claes-Göran GRANQVIST
Original assignee: Accelerator I Linköping Ab
Priority date: 2004-02-17
Filing date: 2005-02-17
Publication date: 2005-08-25
Also published as: SE0400380D0

Abstract

Surface cleaning system (80, 200) comprising a photocatalytic layer (120) provided on an exposed surface (90) of the system, and at least one source (130) of electromagnetic radiation that emits radiation that activates the photocatalytic layer (120) wherein the photocatalytic layer (120) is provided on a radiation guide (70), and that the source (130) of electromagnetic radiation is arranged so that emitted radiation is transferred into the radiation guide (70) guiding the radiation to the photocatalytic layer (120).

Description

SURFACE CLEANING SYSTEM

The present invention relates to a surface cleaning system, and in particular to a system with a photocatalytic surface capable of removing stains and the like through a photocatalytic process.

Background of the Invention

A vast majority of all ovens, including microwave ovens, for domestic and professional use are provided with at least one window. The window is e.g. used for inspection of the cooking process in the oven. All surfaces in an oven, such as the walls and the window, tend to be fouled by drops of foodstuff that may splash during the cooking process or by vaporized organic compounds that are deposited on said surfaces. In many ovens, the walls are provided with a pyrolytic layer that burns away such deposits in order to avoid the need for excessive cleaning, and are therefore referred to as self cleaning. However, as such pyrolytic layers are not transparent they cannot be used to provide self cleaning windows.

One example of a self cleaning oven window system is shown in DE 20021904 UI, wherein an inner surface of a window is provided with a photocatalytic layer and a source of ultraviolet (UV) radiation is arranged in the oven compartment or in between the window panes in a window with two or more window panes. When the source of UN radiation is arranged in the oven compartment, it will be subjected to the fouling process, whereby the emitted intensity decreases with time. Moreover, big opaque spots on the window must be decomposed from their periphery and inwards as no UN radiation reaches the photocatalytic layer underneath the spot, and as the decomposition process is relatively slow, this process requires long time to be completed. When the source of UN radiation is arranged in front of the inner window pane (in between the window panes), the UN radiation reaches the photocatalytic layer through the window pane. Hence, the UN radiation is not obstructed by spots or the like and it can reach all fouled or spotted areas on the photocatalytic layer, whereby the decomposition process is enhanced. However, arranging the source of radiation in between the window panes may lead to decreased visibility through the window or unwanted visual effects, as particles or the like that may enter the space in between the panes may give rise to optical scattering. Moreover only a small part of the emitted light will reach the photocatalytic layer due to reflection on the surface of the window pane, especially as the source(s) of UN radiation has to be arranged in the area of the edges of the window pane to avoid that it blocks the view into the oven. Besides this, the oven may emit undesired UN- radiation outside the oven.

Further, fouled window surfaces is a problem in many other applications where windows are provided for shielding and/or inspection purposes etc.. Examples of such applications include industrial ovens or heat treatment equipment, surface treatment equipment, scientific equipment, etc.

Still further, other surfaces that frequently are fouled may be provided with a photocatalytic layer in order to be self cleaning. However, such applications require that the surface is illuminated either by natural light from the sun or by UN-light provided by a dedicated light- source, the former being essentially restricted to outdoor surfaces and the latter resulting in emission of undesired UN-radiation to the surroundings.

JP 09023120 Al discloses a flexible film of a UN-transparent polymeric material with a photocatalytic layer on at least one surface thereof. UV emitting means are arranged at an end face of the film to introduce UN-radiation into the film, whereby the film functions as a light conductor, distributing UN-light to the photocatalytic layer. Disclosed areas of use include environmental purification by deodorization, sterilization, etc., e.g. in air or water purification units, refrigerators, shoes, automobiles etc.

JP,08-196898,A discloses a water purification unit with a number of light guide plates provided with photocatalytic layer.

Summary of the Invention

The object of the invention is to provide a new surface cleaning system, which system overcomes one or more drawbacks of the prior art. This is achieved by the surface cleaning system as defined in the appended claims.

One advantage with such a surface cleaning system is that essentially all supplied radiation is available for decomposition of organic deposits, and essentially no supplied radiation is emitted from the system. Another advantage is that practically no unwanted visual effects due to optical scattering or the like may occur.

Brief Description of the Drawings

The invention will be described in detail below with reference to the drawings, in which

Fig. 1 shows a schematic cross sectional view of an embodiment of a surface cleaning system according to the present invention.

Fig. 2 shows examples of absorption spectra for photocatalytic TiO₂ of two different structures, anatase and rutile.

Fig. 3 shows the ultraviolet transmittance for a standard glass and a low Fe₂O₃ glass.

Fig. 4 schematically shows a side view of an oven with a window with a surface cleaning system according to an embodiment of the present invention.

Fig. 5 shows a schematic front view of an embodiment of a window with a surface cleaning system according to the present invention.

Figs. 6a to 6c show alternative embodiments of the window with a surface cleaning system according to the present invention.

Fig. 7 shows another embodiment of the window with a surface cleaning system of fig. 1.

Detailed Description of Preferred Embodiments

The present invention relates to a surface cleaning system 200, as is shown in fig. 1, comprising a photocatalytic layer 120 provided on an exposed surface 90 thereof, and at least one source of electromagnetic radiation 130 that emits radiation that activates the photocatalytic layer 120. By activating the photocatalytic layer 120, any fouling deposits 180 on the surface 90 are fully or partly decomposed, and. either vanishes or can easily be transported away by ventilation, wiping off or the like. In the surface cleaning system 200 according to the present invention, the photocatalytic layer 120 is provided on a radiation guide 70, and the source of electromagnetic radiation 130 is arranged so that emitted radiation is transferred into the radiation guide 70 guiding the radiation to the photocatalytic layer 120. The radiation guide 70 maybe comprised of any suitable transparent material, such as a glass or a polymer material.

In the surface cleaning system according to the present invention, at least 50%, more preferably at least 75%, still more preferably at least 90%, still more preferably at least 95%, still more preferably at least 98% and most preferably essentially all of the radiation emitted from the source of radiation is transferred into and guided by the radiation guide 70.

The process of photocatalysis is well known in the art, and no detailed description is given herein. One well-known photocatalyst is titanium dioxide (TiO₂), and other known photocatalysts are ZnO, CdS, WO₃, SnO₂, ZrO₂, Sb₂O₄, CeO₂ and Fe₂O₃. All these materials can be deposited as thin transparent films that are chemically stable and that shows good photocatalytic activity over a temperature range of use, e.g. from 20°C up to 500°C depending on the type of application. The electromagnetic radiation emitted from the source of electromagnetic radiation 130 is preferably adapted to match the characteristics of the photocatalytic material 120. In general, the resulting photocatalytic activity of these materials is higher when the irradiated light is of high energy (short wavelength), such as light in the ultraviolet spectrum, i.e. light of wavelengths less than approximately 380 nm. Fig. 2 shows examples of absorption spectra for photocatalytic Ti0₂ of two different structures, anatase and rutile. As can be seen in fig. 2, the lower absorption limit is about 370 nm for anatase and 400 nm for rutile. Therefore, it is of great importance that the irradiated light that reaches the photocatalytic surface in the surface cleaning system 200 comprises as much ultraviolet irradiation as possible, to achieve optimum efficiency for the decomposition process.

In order to avoid unnecessary absorption losses in the radiation guide 70, it is preferably made of a material with low absorbance of the selected radiation spectra that is emitted by the source. Hence, if the emitted electromagnetic radiation is light in the UN-range, then the radiation guide 70 is preferably comprised of a material with low UN absorbance, such as a low Fe glass or the like. The absorbance of ultraviolet light for glass is highly dependent on the Fe₂O₃ content. Fig. 3 shows a comparison between a standard glass with a normal Fe₂O₃ content and a low Fe₂O₃ glass. The importance of the difference in transmittance (high transmittance means low absorbance) in the ultraviolet spectra is clear when fig. 3 is compared with the absorption spectra in fig. 2. Fig. 2 shows that the photocatalytic activity of TiO₂ increases significantly for wavelengths shorter than 350 nm, whereas fig 3 shows that the transmittance for standard glass drops significantly below 350 nm. One example of a commercially available low Fe₂O₃ glass is Optiwhite by Pilkington.

The surface cleaning system 200 can be used to provide essentially self cleaning surfaces in a large number of applications. The surface cleaning system 200 can preferably be used as self cleaning windows in any applications where windows are provided for shielding and/or inspection purposes and where fouling may be a problem. Examples of such applications include self cleaning oven windows as is described in detail below, industrial ovens or heat treatment equipment, surface treatment equipment, scientific equipment, etc.

Still further, the surface cleaning system according to the present invention can be incorporated in or applied to other surfaces where fouling may be a problem. For such surfaces, the radiation guide may form a structural part, such as a window pane or a body of a door knob etc., or it may be arranged as a surface layer on a support structure, such as on a working surface in a laboratory, as on a touch button keyboard etc.. Depending on the application, the radiation guide can be rigid or flexible, planar or non-planar and it can virtually be made of any material that is apt to guide UN-light, such as glass, UV-transparent polymers etc. As is discussed in the detailed example below, the radiation guide may be provided with reflecting layers in order to avoid loss of UN-radiation.

The efficiency of the surface cleaning system can be further enhanced by incorporating a fluorescent compound in the radiation guide, which compound emits electromagnetic radiation in the desired range.

Fig. 4 schematically shows a sectional view of an oven 10 with, a housing 20 and an oven door 30, together defining an oven compartment 40. The oven door 30 comprises a frame 50, an outer window pane 60, and an inner window pane 70 in the form of an oven window with a surface cleaning system 80 according to one embodiment of the present invention. In the disclosed embodiment, the oven window with the surface cleaning system 80 is arranged in an oven door 30, but the oven window 80 could also be arranged directly in the housing 20. Moreover the oven window 80 may be used in a single glazing configuration or together with one or more additional windows to form double (like fig. 4) or multiple glazing configurations.

The oven window with the surface cleaning system 80 comprises a window pane 70 in the form of an essentially flat sheet of transparent material with an inner surface 90 facing the oven compartment 40, an outer surface 100 and an edge 110. The expression edge 110, is herein defined as the transverse surface that extends between the outer 100 and the inner 90 surface along the periphery of the window pane 70. A photocatalytic layer 120 is provided on the inner surface 90, and at least one source of electromagnetic radiation 130, that emit radiation that activates the photocatalytic layer 120, is arranged so that emitted radiation is transferred into the window pane 70 at an edge 110 thereof. To achieve the improved oven window with the surface cleaning system 80 according to the present invention, the window pane 70 is arranged to function as a radiation guide, guiding the radiation to the photocatalytic layer 120. To achieve optimum performance and to avoid the discussed problems a substantial part of the radiation emitted from the source of radiation 130 is transferred into and guided by the window pane 70. Preferably at least 50%, more preferably 75%, still more preferably 90%, still more preferably at least 95%, still more preferably at least 98% and most preferably essentially all of the emitted radiation is transferred into the window pane 70.

In one specific embodiment TiO₂ is used as photocatalytic layer 120, and the source of electromagnetic radiation 130 is selected to emit radiation in the UN range. A suitable source 130 can be a fluorescent UN lamp or a UN light emitting diode (UN-LED). Further, as is schematically illustrated in fig. 5, the source 130 may be comprised of a plurality of sources to increase the emitted intensity, such as a plurality of UN-LEDs arranged along one or more of the edges 110 of the window pane 70.

In the embodiment shown in fig. 4 the source of radiation 130 is arranged directly at an edge 110 of the window pane 70 to achieve maximum transmission of radiation from the source 130 into the window pane 70. To achieve this, the source 130 can be provided in a slit or a bore at the edge of the window pane 70. Moreover the source 130 can be provided with reflecting means that reflects the radiation from the source 130 into the window pane 70. Figs. 6a to 6c show three different configurations of the source 130 with respect to the window pane 70. In fig 6a the source 130 is arranged in the same manner as in fig 4, i.e. in a slit or bore in the window pane 70. In fig 6b the source 130 is arranged along the edge 110 of the pane and is provided with reflecting means 140 to direct as much as possible of the emitted radiation into the window pane 70. The embodiment shown in fig. 6c is similar to the embodiment of fig. 6b, but the radiation from the source 130 is directed into the window pane 70 by a prism 150.

In figs. 6a to 6c the outer surface 100 of the window pane 70 is provided with a reflection layer 160 in order to preserve as much radiation as possible inside the window pane 70, i.e. to improve the radiation guide characteristics of the window pane 70. Furthermore, as is shown in figs. 5 and 6a to 6c, the edges 110 of the window pane can be provided with a "mirror layer" 170 that reflects essentially all incident radiation, in order to further lower the losses. When the radiation is in the UN range, the mirror layer 170 preferably is comprised of metallic aluminum that is deposited onto the edges 110. Furthermore a second photocatalytic layer can be provided on the outer surface 100 of the window pane 70, whereby this surface also will turn self cleaning, which may be of great interest in many oven applications.

It has been shown that a configuration where the light is provided in the window pane 70, where the pane 70 functions as a radiation guide, compared with the configuration shown in DE 20021904 UI, yields substantially better performance over the whole inner surface 90 of the window pane 70. Moreover, as is schematically shown in figs. 6a to 6c, it has been found that the fouled areas 180 locally reduces the reflectivity of the photocatalytic layer 120, whereby the radiation intensity that reaches the photocatalytic layer 120 at such areas 180 is increased. Hence, the photocatalytic activity at said areas 180 is increased, whereby the over all efficiency for the self cleaning window system 80 is increased even more.

Fig. 7 shows an alternative embodiment of the present invention wherein the source 130 is arranged in the main housing 20 of the oven 10 and the door 30 is so designed that the radiation from the source 130 enters the edge 110 of the inner window pane 70 when the door 30 is closed. By this embodiment, electrical connections to the source of radiation can be made in a simple manner, compared to the above embodiments where the source is arranged in the door. The surface cleaning system according to the present invention is advantageously incorporated in any surfaces that are frequently touched by bare hands and the like, such as light switches and door knobs etc.

The surface cleaning system according to the present invention is advantageously incorporated in any surface of electronic devices such as mobile phones, computers, especially keyboards and pointer control devices such as mice, PDA:s, remote controls, cash registers etc.

The surface cleaning system according to the invention may be used in the field of industrial food processing, such as: slaughterhouses, bakeries, institutional kitchens. In this field the system may be used to enhance the hygiene in general by providing the system as surface layers for working surfaces, housings for tools or other equipment, walls, floors., i.e. essentially any surface possible. Moreover handles on tools such as knives may be provided with the system. The surface cleaning system according to the invention may also be used in the field of domestic kitchen surfaces and appliances, such as bench surfaces, protective surfaces by stoves, glass top stoves, refrigerators, hand held appliances etc. The system according to the invention may also be used to increase the hygiene and cleanness of sale counters in super markets and the like, especially counters for fresh, chilled, or deep-frozen foodstuff.

The surface cleaning system according to the invention may be used in the field of public and domestic sanitary surfaces, such as bath tubs, shower cabins etc., whereby a high level of hygiene and cleanness can be provided. It may further be excessively used in the pharmaceutical process industry, for medical devices in hospital environment, and at laboratory facilities as working surfaces, in fume cupboards, on floors etc.

The surface cleaning system according to the invention may be used to reduce the need of cleaning surfaces that frequently are exposed to heavy fouling in the general field of industry, such as in industrial painting facilities, and process industry, etc.

The surface cleaning system according to the invention may be used to provide self cleaning hand tools such as screwdriver handles, drilling machines etc, where the handle surfaces often are exposed to and fouled with oil and fat. By forming the handle or at least a surface layer of the handle in a light guide material covered by a photocatalytic layer, and arranging a UN- light source in contact with the light guide, the tool handle will effectively be self cleaning and the grip will be improved.

Other surfaces that can be made self cleaning using the surface cleaning system according to the invention comprises: interior surfaces in automobiles, such as dashboard, steering wheel etc., internal and external surfaces of aquarium, surfaces below the waterline on boats, etc.

Claims

CLAIMS:

1. Surface cleaning system (200, 80) comprising a photocatalytic layer (120) provided on an exposed surface (90) of the system, and at least one source (130) of electromagnetic radiation that emits radiation that activates the photocatalytic layer (120) characterized in that the photocatalytic layer (120) is provided on a radiation guide (70), and that the source (130) of electromagnetic radiation is arranged so that emitted radiation is transferred into the radiation guide (70) guiding the radiation to the photocatalytic layer (120).

2. System according to claim 1 characterized in that at least 50%, more preferably at least 75%, still more preferably at least 90%, still more preferably at least 95%, still more preferably at least 98% and most preferably essentially all of the radiation emitted from the source (130) of radiation is transferred into and guided by the radiation guide (70).

3. System according to claim 1 or 2 characterized in that the electromagnetic radiation is light in the ultraviolet range.

4. System according to claim 3 characterized in that the radiation guide (70) is comprised of a material with low UN absorbance.

5. System according to claim 4 characterized in that the radiation guide (70) is comprised of a low Fe glass.

6. System according to any of the claims 1 to 5 characterized in that the source (130) is provided with reflecting means (140) that reflects the radiation from the source (130) into the radiation guide (70).

7. System according to any of the claims 1 to 6 characterized in that a fluorescent compound is incorporated in the radiation guide (70).

8. Self cleaning window system characterized in that it incorporates a surface cleaning system according to any of the claims 1 to 7.

9. Self cleaning oven window system characterized in that it incorporates a surface cleaning system according to any of the claims 1 to 7.