AU776513B2

AU776513B2 - A pre-coated metal sheet having enhanced thermal resistance properties

Info

Publication number: AU776513B2
Application number: AU25202/00A
Authority: AU
Inventors: Graeme K Stark; Cat V Tu
Original assignee: BlueScope Steel Ltd
Current assignee: BlueScope Steel Ltd
Priority date: 1999-03-31
Filing date: 2000-03-31
Publication date: 2004-09-09
Anticipated expiration: 2020-03-31
Also published as: AU2520200A

Description

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AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

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Name of Applicant: Actual Inventors: Address for Service: Invention Title: BHP eStol (JLA) Pty Ltd SEC p%,e Stee ,104 Cat V Tu and Graeme K Stark TA/ O BALDWIN SHELSTON WATERS 60 MARGARET STREET SYDNEY NSW 2000 'A PRE-COATED METAL SHEET HAVING ENHANCED THERMAL RESISTANCE PROPERTIES' Details of Associated Provisional Application No. PP9554 dated 31 Mar 1999 The following statement is a full description of this invention, including the best method of performing it known to me/us:- File: 27311AUP00 -2- A PRE-COATED METAL SHEET HAVING ENHANCED THERMAL RESISTANCE PROPERTIES Field Of The Invention The present invention relates to pre-coated metal sheet particularly but not exclusively, suitable for insulation purposes. There is also described a method of making the strip. The strip finds particular use in the building and construction industries.

Backaround Of The Invention Pre-coated metal sheet comprising a metal strip painted on both its upper and :underside faces and which is provided for use in cladding and roofing purposes, is known in the art. The thickness of the paint on each face of the strip is generally less than about 25 micron. The purpose of the paint is to protect the metal and to provide a desired coloured finish.

The painted metal sheet provides only a relatively low degree of resistance to transfer of external ambient temperatures in use. Accordingly, in instances where ooooo insulation of a building structure is desired or necessary, it is common to locate discrete sheet and/or bulk insulation materials such as natural or synthetic fibres or other such materials under the metal sheet, and to use air-conditioning to regulate the temperature within the structure. The use of insulation materials and air-conditioning to regulate temperature can be costly.

Summary Of The Invention It is an aim of the present invention to provide an alternate painted metal sheet to that known in the art. Broadly stated, the invention relates to a pre-coated metal sheet with enhanced thermal resistance properties.

More particularly, in one aspect there is provided a method of manufacturing a pre-coated metal sheet having enhanced thermal resistance properties, comprising the steps of: providing a metal strip with an upperside face and an opposite underside face each having a metallic coating of a metal alloy thereon; coating the upperside face of the strip over the metallic coating with a primer and drying the primer, wherein the underside face of the metal strip is left substantially free of the primer; applying a layer of paint to the dried primer, on the upperside face of the metal strip such that the metallic coating on the underside face of the metal strip is left substantially paint free for inhibiting transfer of heat; and drying the paint; *o .i .wherein the dried paint has a substantially constant thickness of at least 15 microns and a thermal reflectivity value in a range of from about 0.59 to about 0.67, and wherein the metallic coating on the underside face of the strip has a thermal emissivity value of less S 20 than about 0.30.

S.In addition, the method may comprise one or both of roll forming the metal strip once the paint is substantially dry and cutting the metal strip to desired lengths.

00oo In yet another aspect, there is provided a pre-coated metal sheet with enhanced th a thermal resistance properties, comprising a metal strip having an upperside face and an opposite underside face each with a metallic coating thereon, wherein the metallic coating on the upperside face of the metal strip is coated with a layer of paint having a thickness of at least 15 microns and the exterior surface of the metallic coating on the underside face of the metal strip is substantially paint free for inhibiting transfer of heat.

In still another aspect there is provided the use of a pre-coated metal sheet of the present invention as an insulation material to inhibit transfer of incident heat into a space for being shielded by the sheet, and wherein the use involves arranging the sheet such that the substantially paint free metallic coating is directed toward the space.

In a further aspect there is provided a method of insulating a building structure comprising the step of fixing a plurality of pre-coated metal sheets of the present invention to a frame of the building structure such that adjacent said sheets overlap one another and the substantially paint free metallic coating of each is directed toward the interior of the building structure.

The metal strip will usually be made of a ferrous metal and most usually, will be a steel strip.

Preferably, the metallic coating will be achieved by the step of hot dip coating the .i metal strip involving dipping the metal strip into molten metal, although any other suitable coating process such as electro-galvanising may be used to provide the metallic coating.

20 The metallic coating will typically be an aluminium or zinc coating, or a coating of an alloy of aluminium and zinc. It has been found that these coatings have relatively low thermal emissivity and accordingly, are particularly suitable for inhibiting radiation of oo o heat from the underside of the present metal sheet. An example of a metal strip with a ol metallic coating on its upperside and underside faces and which is suitable for use in 4a making the pre-coated metal sheet of the invention is commnercially available in Australia under the trade mark Zincalumne.

OP I It has surprisingly been found that by providing paint of increased thickness on the upperside of the metal strip and leaving the exterior surface of the metallic coating on the underside thereof substantially paint free, markedly enhanced thermal resistance properties relative to those of known metal sheet painted on both its upper and undersides may be achieved.

As such, pre-coated metal sheet as described herein is suitable for fixing directly to the frame of a building structure for cladding or roofing purposes to provide enhanced insulation of the structure against external ambient temperatures and accordingly, may S. provide a number of significant advantages including achieving substantial cost reductions by reducing or eliminating the need for installation of other insulation materials to provide adequate insulation of the structure.

Elimination or reduced use of other insulating materials can also lead to increased speed of construction and a reduction in costs associated with the building of such structures. Moreover, by having enhanced thermal resistance properties, use of precoated metal sheet of the invention to clad or roof a structure may result in lower airconditioning usage to regulate temperature within the structure leading to further cost S-savings due to reduced energy usage.

In addition, by needing to only paint the upperside face of the metal strip in the making of the pre-coated metal sheet, significant manufacturing costs may be realised.

The invention, therefore, provides a simple, convenient and economical material suitable for building and insulation purposes.

The features and advantages of pre-coated metal sheet of the invention will be further described hereinafter in relation to a number of preferred embodiments.

-6- Detailed Description Of Preferred Embodiments Of The Invention The paint may be applied to metal strip stock by conventional wet film or dry powder coating processes or alternatively, by melting the paint onto heated metal strip from a solid block of a paint composition while the strip is in forced contact with the block and is moved relative thereto.

Dry powder coating processes usually comprise spraying electrostatically charged, dry particles of the desired paint composition onto an oppositely charged substrate and then heating the powder to form a film, and if applicable, to thermoset the paint. A solid block paint application process suitable for use in the manuacture of the pre-coated metal sheet of the invention is described in Australian Patent No. 644928. Thermosetting •polymer based paint compositions are particularly suitable for application by that method. Preferably, the paint is applied by a wet film application process involving roll coating the paint onto the strip.

Typically, steel strip stock having a substantially constant thickness in a range of o0° from 0.3 mm to 0.8 mm and provided with a metallic coating consisting of a zincaluminium alloy of about 20 microns thickness on both its upperside and underside faces will be fed from a coil of the strip to roll coating apparatus for coating only the metallic coating on the upperside face of the strip with paint as the strip travels along the processing line, and subsequently to a drying furnace for drying the paint following application thereof. Care is taken to ensure that the metallic coating on the opposite underside face of the strip remains substantially paint free. Preferably, the thickness of the steel strip will be between about 0.30 mm to about 0.60 mm and more preferably, -7about 0.30 mm to about 0.48 mm. As will be appreciated, substantially the entire upperside surface of the metal strip is coated by the layer of paint.

The exposed surface of the zinc-aluminium alloy coating on the upperside face of the strip can be primed prior to the application of the finishing paint. The priming may be achieved with the use of a solvent based primer composition in the known manner prior to the steel strip being passed through a drying furnace to dry off the solvent and cure the primer. That drying furnace may be the same or a different furnace to the one used for drying the finishing paint layer.

S. The thickness of the primer coat will usually be within a range of about 3 to about 10 microns and usually, will have a thickness of about 5 microns. Preferably, the priming and subsequent application of the finishing paint will be achieved in the one production run.

Once the layer of finishing paint has dried sufficiently, the steel strip may be taken up by a conventional re-coiler and stored before being roll formed to provide the steel strip with a desired sectional profile and cut to desired lengths at a later date.

Alternatively, rather than being re-coiled, the steel strip may be further processed S-.•.immediately prior being cut and stacked downline. The steel strip will usually be roll formed to a desired sectional profile by any suitable cold rolling process.

The finishing paint may be any suitable commercially available paint composition and typically, will have relatively high thermal reflectivity value when dry. Preferably, the thermal reflectivity of the paint will be greater than about 0.50 and more preferably, greater than about 0.55. Most preferably, the thermal reflectivity of the paint will be in a range from about 0.59 to about 0.67.

-8- Accordingly, the paint will also generally have relatively low thermal absorptivity when dry. In addition, the conductivity of the paint will typically be relatively low to inhibit the transfer of heat to the underlying steel strip. Most usually, the paint will have a thermal conductivity value lower than 75W/mK and most usually, the thermal conductivity of the paint will be about 69 W/mK. The absorptivity of the paint will preferably be lower than 0.45, more preferably lower than about 0.41 and most preferably, will be in a range from about 0.33 to about 0.41.

The paint will generally have a thermal emissivity value of up to about 0.90 when dry. Usually, the thermal emissivity value of the paint will be greater than about 0.70 and more usually, about 0.85.

The thickness of the finishing paint will normally be limited by the paints ability to withstand cold forming of the metal strip substantially without suffering damage to its integrity. Preferably, the layer of paint will have a substantially constant thickness in a range of from about 15 microns to about 100 microns more preferably in a range of from about 20 microns to about 70 microns and most preferably, in a range of from about microns to about 50 microns.

Indeed, while it is desirable that the external surface of the zinc-aluminium coating on the upperside face of the steel strip be primed it is not necessary and the finishing paint layer can be applied directly onto the zinc-aluminium alloy coating if desired.

Generally, however, the thickness of the primer if any will be taken into account when determining the thickness of the outer paint layer to be coated onto the steel strip.

The thermal emissivity of the metallic coating on the upperside and underside faces of the steel strip will most usually be lower than about 0.30. Preferably, the S4 -9thermal emissivity will be lower than about 0.25 and most preferably, in a range of from about 0.05 to about 0.20. The zinc-aluminium alloy forming the metallic coating in the preferred embodiment will generally comprise about 55% aluminium and about zinc.

As the thermal reflectivity of the paint layer is relatively high while the absorptivity and conductivity of the paint layer are relatively low as is the emissivity of the exposed zinc-aluminium coating on the underside face of the steel strip in the preferred embodiment, the transfer of incident heat through the sheet into the interior of a building structure to which the sheet is fixed in use is minimised. In use, the sheet may be fixed to a frame of a building structure such as a warehouse or shed by any conventional means such that adjacent sheets partially overlap in the manner of the prior art, and the exposed metallic coating of each sheet is directed toward the interior space of the structure.

Although the present invention has been described hereinbefore with reference to a number of preferred embodiments, the skilled addressee will appreciate that numerous variations and modifications are possible without departing from the scope of the invention. •.invention.

Claims

1. A method of manufacturing a pre-coated metal sheet having enhanced thermal resistance properties, comprising the steps of: providing a metal strip with an upperside face and an opposite underside face each having a metallic coating of a metal alloy thereon; coating the upperside face of the strip over the metallic coating with a primer and drying the primer, wherein the underside face of the metal strip is left substantially free of the primer; applying a layer of paint to the dried primer, on the upperside face of the metal strip such that the metallic coating on the underside face of the metal strip is left substantially paint free for inhibiting transfer of heat; and drying the paint; wherein the dried paint has a substantially constant thickness of at least 15 microns and a thermal reflectivity value in a range of from about 0.59 to about 0.67, and wherein the metallic coating on the underside face of the strip has a thermal emissivity value of less than about 0.30.

2. A method according to claim 1 wherein the pre-coated metal sheet is in a form suitable for use to insulate a space from incident heat.

3. A method according to claim 1 wherein the pre-coated metal sheet is adapted for being fixed to a frame of a building structure. :o 4. A method according to any one of claims 1 to 3 wherein the layer of paint is applied -oo• as the strip travels along a processing line. *•o -11- A method according to any one of claims 1 to 4 further comprising feeding the strip from a coil of the strip to a location where the layer of paint is applied to the upperside face of the strip as the strip continues to travel along.

6. A method according to any one of claims 1 to 5 wherein the metal strip is progressively coiled following the application of the layer of paint, for later processing of the strip into the pre-coated metal strip.

7. A method according to any one of claims 1 to 5 further comprising roll forming the metal strip to a desired sectional profile following the application of the layer of paint.

8. A method according to any one of claims 1 to 5, further comprising cutting the metal strip into desired lengths following the application of the layer of paint.

9. A method according to any one of claims 1 to 8 wherein the dried paint has a thickness greater than about 20 microns. A method according to claim 9 wherein the dried paint has a thickness greater than about 30 microns.

11. A method according to claim 10 wherein the dried paint has a thickness in a range of from about 20 microns to about 70 microns. S ae

12. A method according to any one of claims 1 to 11 wherein the dried paint has a o• S°thermal conductivity value lower than about 75 W/mk.

13. A method according to claim 12 wherein the dried paint has a thermal conductivity 20 value lower than about 69 W/mnk. ooo

14. A method according to any one of claims 1 to 13 wherein the dried paint has a .0 thermal absorbtivity value lower than about 0.45. 0o••

15. A method according to claim 14 wherein the dried paint has a thermal absorbtivity value lower than about 0.41. -12-

16. A method according to claim 14 or 15 wherein the dried paint has a thermal absorbtivity value in a range of from about 0.33 to about 0.41.

17. A method according to any one of claims 1 to 16 wherein the dried paint has a thermal emissivity value greater than about 0.70.

18. A method according to claim 17 wherein the dried paint has a thermal emissivity value of about 0.85 or greater.

19. A method according to any one of claims 1 to 18 wherein the strip has a substantially constant thickness greater than about 0.3 mm. A method according to claim 19 wherein the thickness of the strip is in a range of from about 0.3 mm to about 0.6 mm.

21. A method according to claim 20 wherein the metal alloy is an alloy of zinc and aluminium.

22. A method according to claim 21 wherein the alloy comprises about 45% zinc and aluminium.

23. A method according to any one of claims 1 to 20 wherein the metallic coating on each of the upperside face and the underside face of the strip is a zinc or an aluminium go o," o coating.

24. A method according to any one of claims 1 to 23 wherein the metallic coating on the underside face of the strip has a substantially lower thermal emissivity value than the 0200 20 dried paint.

25. A method according to claim 24 wherein the metallic coating on the underside face of the strip has a thermal emissivity value of less than about 0.25.

26. A method according to any one of claims 1 to 25 wherein the strip is made of a ferrous material. 13

27. A method according to claim 26 wherein the strip is made of steel.

28. A pre-coated metal sheet manufactured by a method as defined in any one of claims 1 to 27.

29. Use of a pre-coated metal sheet as defined in claim 28 as an insulation material to inhibit transfer of incident heat into a space for being shielded by the sheet, wherein the use involves arranging the sheet such that the substantially paint free metallic coating is directed towards the space. A method of insulating a building structure comprising the step of fixing a plurality of pre-coated metal sheets as defined in claim 28 to a frame of the building structure such that adjacent said sheets overlap one another and the substantially paint free metallic coating of each is directed toward the interior of the building structure.

31. A method of manufacturing a pre-coated metal sheet substantially as hereinbefore described.

32. A pre-coated metal sheet substantially as hereinbefore described. 15 33. A method of insulating a building structure comprising fixing a plurality of pre- coated metal sheets to a frame of the building structure, substantially as hereinbefore described.

34. Use of a pre-coated metal sheet as an insulation material, substantially as hereinbefore described. DATED this 20th Day of May, 2004 RA BALDWIN SHELSTON WATERS Attorneys for: B-P Steel (JLA) Pty Ltd- SEC B\AeScoe S tee\ beA a 104 -r *og go.