AU773964B2

AU773964B2 - Pre-coated metal sheet materials

Info

Publication number: AU773964B2
Application number: AU33364/01A
Authority: AU
Inventors: Edward M Boge
Original assignee: BHP Steel JLA Pty Ltd
Current assignee: BlueScope Steel Ltd
Priority date: 2000-03-31
Filing date: 2001-03-30
Publication date: 2004-06-10
Anticipated expiration: 2021-03-30
Also published as: AU3336401A

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Applicant(s): BHP STEEL (JLA) PTY LTD A.C.N. 000 011 058 Invention Title: PRE-COATED METAL SHEET MATERIALS The following statement is a full description of this invention, including the best method of performing it known to me/us: 2 PRE-COATED METAL SHEET MATERIALS The present invention relates to a pre-coated metal sheet material and to a method of forming a precoated metal sheet material. In particular, the present invention relates to a pre-coated metal sheet material having advantageous thermal emissivity characteristics combined with good handling characteristics.

A variety of different materials are currently used in constructing the roofs and walls of building structures. One type of material used for this purpose comprises a metal sheet material such as steel which is coated with an organic coating such as paint on both sides.

15 The painted surfaces of the sheet material serve a number .of purposes, including corrosion resistance, UV resistance, passivation protection, resistance to "galling", resistance 46 00to dulling and finger marking and abrasion resistance.

Another purpose of the paint is to provide a desired 20 coloured finish to the product for aesthetic appeal.

.os.oi These organic coatings are applied in layers of various thicknesses to both sides of the sheet material.

The typical nominal thickness of the primer coat is The primer coat is applied to both surfaces of the sheet material. Typically weather side or upper face finish coat **has a nominal thickness of 20pm. The underside or reverse face backing coat has a nominal thickness of Approximately three quarters of all heat enters an uninsulated building through the roof and walls of the building. Some of the heat energy striking the exterior surface of the building such as the roof is reflected and some is absorbed. The greater the level of reflection of heat energy, the less heat energy will be absorbed into the exterior surface of the building. Accordingly, highly reflective materials are to a certain extent desirable.

3 The absorbed energy heats the walls and roof of the building and is spread to both sides of the walls and roof by air convection and radiation. It is desirable when developing new materials for use in the roofing and cladding of buildings to provide materials that maximise radiation of heat towards the outside of the building and minimiseradiation of heat towards the inside of the building. At the same time, it is necessary that both sides of the building material have the qualities of abrasion resistance and corrosion resistance.

In known pre-coated sheet materials, the level of emittance towards the outside of the building and towards the inside of the building is roughly equal, even with the use of different (standard) paint compositions on either face of the sheet material. The level of emittance is relatively high for both faces of these pre-coated sheet materials.

It is an object of the present invention to provide a pre-coated sheet material suitable for use in building-applications which has good thermal emissivity properties together with good handling characteristics.

S* 25 It is also an object of the present invention to provide a method of manufacturing such a pre-coated sheet material.

According to the present invention there is provided a method of manufacturing sheet material comprising the steps of: providing a metal sheet having an upper face and a reverse face; applying an organic coating to the upper face of the metal sheet, and curing the organic coating on the upper face; and applying an organic coating to the reverse face of the 4 metal sheet, and curing the organic coating on the reverse face, wherein the cured organic coating on the upper face has a thickness of at least 15gm, and the cured organic coating on the reverse face has a thickness of between 0.5 and 2mn.

According to the present invention there is also provided a pre-coated sheet material comprising: a metal sheet having an upper face and a reverse face, an organic coating on the upper face of the metal sheet having a thickness of at least 15pm; and an organic coating on the reverse face having a thickness of between 0.5 and 2gm.

it has been found by the applicant that pre- **coated metal sheet materials having a relatively thick organic coating on an upper face and a very thin coating on the reverse face provides high radiation of absorbed energy from the upper face of the material and surprisingly very low radiation of absorbed energy through the reverse face of the material. Accordingly, when used in building applications with the upper face facing outwardly, an *extremely energy efficient and yet easy to handle building S. 25 material is provided. Specifically, since the sheeting material has an organic coating on the reverse face, this *face retains significant abrasion resistance and resistance to corrosive media which is very important for ease of handling and longevity of the material.

Preferably, the organic coating is a paint.

The metal sheet may be formed from any suitable metal material, such as an iron-based or aluminium-based material. Preferably, the metal sheet is an iron-based metal sheet. More preferably, the metal sheet is formed from steel.

5 The metal sheet may include an alloy coating.

Preferably, the alloy coating includes zinc. The alloy coating may alternatively, or additionally, include aluminium. Most preferably, the alloy coating includes zinc and aluminium. One suitable metal sheet material for this purpose is known by the trade mark ZINCALUME®.

The same or different organic coatings may be applied to the upper face and the reverse face of the metal sheet. The organic coatings may be applied at the same time or separately. Preferably, the organic coatings are applied separately to the upper face and the reverse face of the metal sheet.

Preferably, a pretreatment conversion coat for assisting paint adhesion to the upper face of the metal sheet is applied to the upper face prior to application of the organic coating. It is also preferred that a conversion coat be applied to the reverse face of the metal sheet prior to application of the organic coating thereto.

Preferably, a primer is applied to the upper face of the metal sheet prior to application of the organic coating, and the organic coating forms a finish coat. The primer is preferably applied at a thickness of about Preferably, the organic coatings are applied to the upper and reverse faces by roller coating techniques.

Suitable roller coating techniques include the use of a paint feed tray and transfer rollers for transferring a layer of paint of a suitable thickness to the particular face of the metal sheet.

Preferably, the organic coatings are thermosetting polymer-based paint compositions.

Preferably, the organic coating applied to the 6 reverse face contains between 10 and 50 vol./vol.% solids in solvent. More preferably, the organic coating applied to the reverse face contains between 10 and 30 vol./vol.% solids in solvent.

It has been found by the applicant that control of the thickness of the cured coating on the reverse face is facilitated by applying an organic coating having a high solvent content. For example, an organic coating having a solids content of 10% applied at a wet thickness of will cure to a thickness of approximately lm. In contrast, an organic coating having a solids content of will need to be applied at a thickness of about 2Jim to give approximately the same cured coating thickness. It will be appreciated by persons skilled in the art that it would be much more difficult to apply a 2pm thick layer of organic coating than a 10 pm thick layer of organic coating to achieve the desired cured coating thickness.

Preferably, the metal sheet is between 0.3mm andi 0.60mm thick.

Preferably, the cured organic coat on the upper face has a thickness of between 15im and 30pm. More preferably, the cured organic coat on the upper face has a thickness of about The same organic coating maybe applied to both the upper face and the reverse face. It has been found by the applicant that, even with the same organic coating applied to both the upper and reverse faces of the metal sheet, there is a differentiation in the level of radiation or emission of heat from either side of the pre-coated sheet material. Paints showing the best results in reducing emission at low film thickness (0.5 2gm) compared to high film thickness (15gm -30pm) are polyesters, water based acrylics, solvent based acrylics, 7 epoxy resins, polyvinylidenefluoride/acrylic resins and polyethylene films.

The pre-coated sheet materials of the present invention are suitable for fixing directly to the frame of a building structure for cladding or roofing purposes to provide enhanced insulation of the structure against solar radiation. Such pre-coated sheeting materials provide a number of significant advantages, including substantial cost reduction in the insulation of the structure by enabling the use of insulation materials to be reduced or eliminated. In addition, as a result of the enhanced thermal properties of the sheeting material, air conditioning usage as a means of regulating temperature within the structure can be reduced leading to further cost savings.

The present invention will now be described in further detail with reference to the following example of one embodiment of the invention.

Manufacture of Sheet Material The pre-coated sheet material is produced by 25 coating a suitable metal sheet material or substrate with an organic coating of the required thickness on either side.

The metal substrate used according to the preferred embodiment of the invention is ZINCALUME zinc/aluminium alloy coated steel which is a sheet metal product commercially available from the applicant of the present invention. The steel sheet strip product has a thickness of 0.42mm.

A coiled roll of ZINCALUME steel strip is unwound and fed through a pre-treatment vessel in which the metal 8 substrate is thoroughly cleaned. The steel strip is then fed through a chemical pre-treatment stage in which a conversion coat for assisting paint adhesion to the upper and reverse faces of the metal sheet is applied.

The steel strip is then fed through a primer coating station in which the upper face of the steel strip is coated with a primer, only. After coating with the primer coat, the steel strip is passed through a primer curing oven.

Following this stage, the steel strip is passed through a painting station in which paint is applied to the upper face of the steel strip by a series of rollers and oven cured. Paint is applied to the upper face of the sheet material so that the dried finish coat is approximately 201.i thick. Paint is also applied using similar techniques to the reverse face of the steel strip so that the dried backer paint layer on the reverse face is approximately lgm thick.

Testing of the Sheet Material Product A number of different sheet materials having different paint compositions were manufactured according to the method outlined above. These sheet materials included *paint compositions based on polyester, epoxy, water based acrylics, solvent based acrylics and polyvinylidinefluoride/acrylic resins. Some of the paint coatings included pigmentation.

The thickness of the reverse coat on the product was calculated on the basis of mass loss. The total mass of a sample of known area was measured. The paint coating on the reverse side of the sample was then removed using a solvent (eg. methyl ethyl ketone) and a mild abrasive, (eg.

sugar). The mass of the sample was measured again and the 9 mass of the reverse coating was calculated from the difference in sample mass before and after reverse coat removal. The volume of the reverse coating present was then calculated by dividing its mass by its dry specific gravity (from supplier's data). The thickness of the coating was then calculated by dividing the volume of the coating by the area of the sample, using the same units for both quantities.

Dry film thicknesses ranging from approximately O.lpm 2.4pm were tested. It was found that the emissivity for film thicknesses ranging between 0.5pm and 2 pm was within en emissivity range of 0.15 0.45. Whilst the emissivity for dry film thickness of less than 0.5pm was even lower, it was considered that the film coating was not sufficient to provide an adequate level of abrasion and corrosion resistance.

Many modifications may be made to the examples 20 without departing from the spirit and scope of the i* i. invention. For example, the metal substrate may be formed .from a metal sheet other than ZINCALUME. In addition, a variety of different organic coating materials other than those described in the examples above may be applied with similar results.

Since modifications within the spirit and scope of the invention may readily be effected by persons skilled within the art, it is to be understood that this invention 0 30 is not limited to the particular embodiment described by way of example hereinabove.

In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, H:\shirleyp\specis\P41722 BHP.doc 19/04/04 9a i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.

H: \shirleyp\specis\P41722 BHP.doc 19/04/04

Claims

1. A pre-coated sheet material comprising: a metal sheet having an upper face and a reverse face, an organic coating on the upper face of the metal sheet having a thickness of at least 15m; and an organic coating on the reverse face having a thickness of between 0.5 and 2pm.

2. The pre-coated sheet material according to claim 1, wherein the organic coating is a paint. S3. The pre-coated sheet material according to claim 1 or claim 2, wherein the metal sheet is formed from steel.

4. The pre-coated sheet material according to any one of claims 1 to 3, wherein the metal sheet includes a S..zinc and/or aluminium-containing coating. The pre-coated sheet material according to any one of claims 1 to 4, wherein the metal sheet is between 25 0.3mm and 0.60mm thick.

6. The pre-coated sheet material according to any one of claims 1 to 5, wherein the cured organic coat on the upper face has a thickness of between 15tim and

7. The pre-coated sheet material according to claim 6, wherein the cured organic coat on the upper face has a thickness of about

8. The pre-coated sheet material according to any one of claims 1 to 7, wherein the organic coatings are thermosetting polymer-based paint compositions. 11

9. The pre-coated sheet material according to any one of claims 1 to 8, wherein the organic coatings are selected from the group consisting of polyesters, water based acrylics, solvent based acrylics, epoxy resins, polyvinylidenefluoride/acrylic resins and polyethylene. The pre-coated sheet material according to any one of claims 1 to 9, wherein the sheet material includes a conversion coat between the upper face of the metal sheet and the organic coating on the upper face.

11. The pre-coated sheet material according to any one of claims 1 to 10, wherein the sheet material includes 15 a conversion coat between the reverse face of the metal sheet and the organic coating on the reverse face.

12. The pre-coated sheet material according to any one of claims 1 to 11, wherein the sheet material includes a primer coat immediately underneath the organic coating on the upper face of the metal sheet. s

13. A method of manufacturing sheet material comprising the steps of: 0 providing a metal sheet having an upper face and S. a reverse face; applying an organic coating to the upper face of the metal sheet, and curing the organic coating on the upper face; and applying an organic coating to the reverse face of the metal sheet, and curing the organic coating on the reverse face, wherein the cured organic coating on the upper face has a 12 thickness of at least 15pm, and the cured organic coating on the reverse face has a thickness of between 0.5 and 2pm.

14. The method according to claim 13, wherein a pretreatment conversion coat for assisting paint adhesion to the upper face of the metal sheet is applied to the upper face prior to application of the organic coating. The method according to claim 14, wherein a conversion coat is applied to the reverse face of the metal sheet prior to application of the organic coating thereto.

16. The method according to any one of claims 13 to wherein a primer is applied to the upper face of the 15 metal sheet prior to application of the organic coating, and the organic coating forms a finish coat.

17. The method according to claim 16, wherein the i *"*primer is applied at a thickness of about

18. The method according to any one of claims 13 to 17, wherein the organic coatings are applied to the upper and reverse faces by roller coating techniques.

19. The method according to any one of claims 13 to 18, wherein the organic coating is applied to the reverse face at a solids content of between 10 and 50 vol./vol.% solids in solvent solids in solvent. 13 The method according to claim 19, wherein the organic coating applied to the reverse face contains between and 30 vol./vol.% solids in solvent.

21. Pre-coated sheet materials or methods substantially as herein described with reference to the examples. Dated this 19th day of April 2004. BHP STEEL (JLA) PTY LTD By their Patent Attorneys GRIFFITH HACK Fellows Institute of Patent and Trade Mark Attorneys of Australia 0 0 0 0 0 0 H:\shirleyp\specis\P41722 BHP.doc 19/04/04