GB2283185A

GB2283185A - Siloxane coating composition

Info

Publication number: GB2283185A
Application number: GB9321991A
Authority: GB
Inventors: Anthony Condron
Original assignee: DELVEMADE Ltd
Current assignee: DELVEMADE Ltd
Priority date: 1993-10-26
Filing date: 1993-10-26
Publication date: 1995-05-03
Anticipated expiration: 2013-10-26
Also published as: GB2283185B; GB9321991D0

Abstract

An anti-corrosion coating for sealing seams between overlapping building panels. The coating is formed from a silicone-rubber based sealant such as a dimethylsiloxane composition which is thinned with a solvent such as cyclohexane to enable its brush application. Once applied, the sealant forms a flexible skin over the joint between the adjacent panels.

Description

ANTI-CORROSION COATING The present invention relates to an anti-corrosion coating, and in particular to an anti-corrosion coating which is suitable for use as a sealant for exposed edges at the joint between overlapping sheets of sheet material of, for example, steel.

It is conventional practice to clad steel-framed buildings in sheet steel which is generally corrugated. Adjacent steel sheets overlap and are secured together. Although the sheet surfaces are provided with a durable weather-proof coating during their production, severe corrosion problems are now being experienced in many of the steel-clad buildings that have been erected. In some environments, it is not unusual for the effects of corrosion to become visible in as little as four years after the erection of a building. The problem is particularly severe where the steel sheets form part of a roof, although problems also arise where the sheets form part of a vertical wall.

There are two reasons for this corrosion problem. Firstly, when coated sheet steel is produced it is produced in relatively long lengths. These lengths then have to be cut down to enable the easy transport of the products, and the cutting process must be effected after coating. Thus the cut edges of the sheets are not protected by the coating and are therefore exposed to corrosion. Secondly, the outer surface of overlapping edges of adjacent sheets are often found to corrode relatively rapidly. This may be the result of thermal expansion and contraction.

Cut edge corrosion tends to be the greater of the two problems and superficially it might be expected that it would be the easiest problem to solve using available coating materials. This has proved not to be the case.

When steel sheets are supplied for the erection of buildings in the United Kingdom, the manufacturers or suppliers of those sheets are expected to give guarantees with regard to the durability of the finish on the sheets. Given problems with cut edge corrosion that have occurred in the past, very strict procedures have been specified for the remedial treatment of the cut edges to prevent corrosion. In one case the cut edges must first be sandblasted, painted with a primer, and then painted with three successive coats of an anticorrosion coating paint. Even when such rigorous procedures are followed, however, it is not unusual for the effects of cut edge corrosion to become visible in only a few years after remedial treatment. Thus, remedial work must be carried out at regular intervals.This is of fundamental significance to the economics of maintaining such buildings, the durability of the main surfaces of the cladding sheets being of little value if the cut edges corrode rapidly.

Silicone rubber sealant is well known and widely used in a variety of applications to fill gaps between adjacent building components. Such sealants are used, for example, to effect seals between window frames and surrounding brickwork. The known sealants are, however, far too thick for brush application, being designed for injection into a cavity between two adjacent building components. Such sealants are suitable, therefore, for injection between overlapping sheets of cladding material, but not for the formation of an anti-corrosion coating on the edge of, for example, a sheet of steel. The edge of a sheet of steel is very narrow and it would clearly not be appropriate to try and coat such an edge with a known silicone rubber sealant.

It is an object of the present invention to provide an anticorrosion coating which obviates or mitigates the problems outlined above.

According to the present invention, there is provided an anticorrosion coating comprising a silicone-rubber based sealant thinned with a solvent to a consistency which enables brush-application, the sealant being selected to ensure that after application to a sound surface and evaporation of the solvent a flexible skin of sealant is formed which adheres securely to the surface.

Surprisingly, it has been discovered that where two adjacent building panels are secured together firmly such that the gap between them is relatively small, the coating of the present invention can be simply brushed over the edge of one panel, forming a continuous film which is adhered at one side to one panel and at the other side to the other panel. In the event that the two panels are not firmly secured together, or there is a substantial gap of for example 5mm or more between adjacent panels, the gap can be initially filled by injecting a conventional relatively thick silicone-rubber based sealant and then the seal can be completed by painting over the filled gap with a relatively thin sealant in accordance with the present invention.In both cases, a durable and effectively permanent film is formed protecting not only the exposed edge of one of the panels but also the adjacent portions of the two panel surfaces. Thus, in contrast to the conventional systems, a coating in accordance with the present invention can be applied in a relatively small number of steps and yet provide a far more durable and effective anti-corrosion coating.

Preferably the coating is an alcoxy neutral curing sealant thinned with cyclohexane. A conventional alcoxy neutral curing sealant which may be used is marketed by General Electric of the United States under the trade name "SILPRUF". Good results have been used using such a sealant mixed with from 20 to 45% by weight of cyclohexane, preferably 25 to 45% by weight of cyclohexane.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a sectional view through overlapping edges of two adjacent steel cladding sheets which are securely fixed together and to which an anti-corrosion coating in accordance with the present invention has been applied; and Fig. 2 is a sectional view through two overlapping building cladding sheets which are spaced apart and to which an anti-corrosion coating in accordance with the present invention has been applied.

Referring to Fig. 1, the lower edge of a first building panel 1 is shown overlapping a second building panel 2, the two panels being secured together tightly so that only a small gap is defined therebetween. A first layer 3 of an anti-corrosion coating in accordance with the present invention is then applied over the substantially horizontal lower edge of the building panel 1 and for a few tens of millimetres up the outer surface of the building panel 1 away from its lower edge and down the outer surface of the building panel away from the lower edge of the building panel 1. A small quantity of the sealant penetrates the gap between the two panels adjacent the lower edge of the building panel 1 as indicated generally by numeral 4. A second coating 5 of the same sealant is then applied over the seam.The result is a fully weather-proof seal which will protect the lower edge of a building panel 1 against corrosion even if before the application of the coatings 3 and 5 there was no anticorrosive coating at all on that lower edge.

Fig. 2 illustrates the application of the present invention to circumstances in which two adjacent panels are either not securely fixed together or are fixed together with a substantial gap therebetween. The same reference numerals are used for the same features of Fig. 2 as in Fig. 1. In the case of Fig. 2, however, before the application of the coatings 3 and 5 a body of sealant 6 is injected into the gap between the panels 1 and 2. This bridges the gap between those two panels and enables the coatings 3 and 5 to form a continuous film extending horizontally across the bottom edge of the building panel 1 and onto the front surfaces of the two building panels.

In tests of the effectiveness of the present invention, the material used for the coatings 3 and 5 was a building component sealant marketed by General Electric of the United States (GE) under the trade name "SILPRUF" mixed with a solvent carrier of cyclohexane.

Tests have proved that a mixture incorporating from 25 to 40% by weight of cyclohexane produces very good results. The material used for the sealant 6 shown in Fig. 2 was simply the SILPRUF product without any added cyclohexane, and accordingly the sealant 6 and the adjacent coating 3 were perfectly compatible. The coatings 3 and 5 could be readily applied using a simple paint brush, the product being supplied ready-mixed so that it was not necessary to mix constituents on site. Once applied the coatings provided full anti-corrosion protection. It was not significantly affected by sunlight, high humidity, sea salt, salt water or generally encountered airborne pollutants. The product when cured had exceptional weather resistance and was capable of withstanding temperatures as low as minus 400C or as high as plus 600C. Its flexibility also enabled it to accommodate relative movement between adjacent building panels that can result from thermal expansion.

The coatings 3 and 5 were found to have excellent adhesion to properly prepared surfaces. Of course, the surfaces to which the coatings are applied must be dry, sound, dust free and free from oils, water or proprietary anti-corrosion treatments.

The coatings were found to be suitable for the treatment of steel sheets coated with PVC or PUF2, aluminium, weathered steel, stainless steel, galvanised steel, glass, concrete, stone and asbestos.

Generally, providing the surface has been correctly prepared, no additional primer is required, although a primer could be used in the unlikely event that adhesion proved to be a problem. A suitable primer is marketed by GE under the trade name SS4179.

The SILPRUF product which was used with cyclohexane to produce the above-described brush-applied coating was methyltrimethoxysilane supplied by G.E. Silicones Europe, Plasticslaan 1, P.O. Box 117, 4600 AC Bergen Op Zoom, Netherlands. The product composition is as follows: Approx. Wgt. % a. Methyltrimethoxysilane 1-5 b. Polydimethylsiloxane Silanol/STPD 30-60 c. Dimethylpolysiloxane 10-30 d. Calcium Carbonate 30-60 e. Trade Secret Component 1-5 f. Titanium Dioxide 1-5 Tests have been conducted using the above-described coatings to seal cut edges of PVC coated steel. The following procedures were followed: 1. All loose PVC was removed from the surface to leave a firm edge with the remaining PVC tapering down in thickness towards the edge of the sheet of steel.

2. All red and white rust areas were removed by grit blasting or abrading to bright metal, ensuring that the surface was not as a result polished and that any pitted rust was removed.

3. A first coat of the anti-corrosion coating was applied using a paint brush ensuring complete coverage of all exposed and immediately adjacent surfaces.

4. After a delay of four hours, a second coat of the sealant was applied so as to cover the first coat, the second coat overlapping the first by approximately 12.5mm to avoid the build-up of a thick edge. The second coat was coloured to match the colour of the PVC on the exterior surface of the sheet steel being treated. The final dry film thickness per coat was 175 microns, the two coat dry film thickness being 350 microns.

Where a seal is required over heavily corroded areas, a reinforcing bonded polyester fleece may be applied to the first coat within 30 minutes of its application, ensuring full contact is made over the whole surface and providing approximately 50% coverage of the first coating. The second coat is then applied over the polyester fleece. The result is a very reliable and yet highly flexible seal.

Claims

CLAIMS 1. An anti-corrosion coating comprising a silicone-rubber based sealant thinned with a solvent to a consistency which enables brushapplication, the sealant being selected to ensure that after application to a sound surface and evaporation of the solvent a flexible skin of sealant is formed which adheres securely to the surface. 2. An anti-corrosion according to claim 1, wherein the sealant is an alcoxy neutral curing sealant. 3. An anti-corrosion coating according to claim 2, wherein the solvent is cyclohexane. 4. An anti-corrosion coating according to claim 3, wherein the solvent makes up from 20 to 45% by weight of the thinned sealant. 5. An anti-corrosion coating according to claim 4, wherein the cyclohexane makes up from 25 to 40% by weight of the thinned sealant. 6. An anti-corrosion coating substantially as hereinbefore described with reference to the accompanying drawings. 7. A method for sealing a seam between two overlapping sheets, substantially as hereinbefore described with reference to the accompanying drawings, using a sealant in accordance with any one of claims 1 to 6. Amendments to the claims have been filed as follows

1. An anti-corrosion coating comprising a silicone-rubber based sealant thinned with a solvent to a consistency which enables brushapplication, the sealant being selected to ensure that after application to a sound surface and evaporation of the solvent a flexible skin of sealant is formed which adheres securely to the surface.

2. An anti-corrosion according to claim 1, wherein the sealant is an alcoxy neutral curing sealant.

3. An anti-corrosion coating according to claim 2, wherein the solvent is cyclohexane.

4. An anti-corrosion coating according to claim 3, wherein the solvent makes up from 20 to 45% by weight of the thinned sealant.

5. An anti-corrosion coating according to claim 4, wherein the cyclohexane makes up from 25 to 40% by weight of the thinned sealant.

6. An anti-corrosion coating substantially as hereinbefore described with reference to the accompanying drawings.

7. A method of sealing a seam between two overlapping sheets of material formed where an edge of a first sheet of material overlaps a second sheet of material, the method comprising: (a) brushing a layer of an anti-corrosion coating as defined in any preceding claim over said seam and adjacent portions of both the first and second sheets of material; and (b) allowing the coating solvent to evaporate to thereby form a flexible sealant skin over said seam which is adhered to both the first and second sheets of material.

8. A method according to claim 7, wherein prior to step (a) a relatively thick silicone-rubber based sealant is injected into any gap which exists between said edge of the first sheet and the second sheet subsequent to which step (a) is performed so that the anticorrosion coating covers the sealant filled gap.

G A method according to either claim 7 or claim 8, wherein steps (a) and (b) are repeated so that more than one layer of said anti-corrosion coating is applied to the seam.

0. A method according to claim 9, wherein successive layers of anti-corrosion coating overlap any previous layers of coating to avoid the build-up of a thick edge.

11. A method according to any one of claims 7-10, wherein prior to step (a) the surfaces of the two sheets adjacent said seam are treated to remove any existing rust and unwanted or damaged coatings and to thereby prepare the surface of the sheets to receive said anticorrosion coating.

12. A method for sealing a seam between two overlapping sheets, substantially as hereinbefore described with reference to the accompanying drawings, using a sealant in accordance with any one of claims 1 to 6.