AU2017258972B2

AU2017258972B2 - Fastenings and other components for use with treated timber

Info

Publication number: AU2017258972B2
Application number: AU2017258972A
Authority: AU
Inventors: Desmond Mark EBEJER; Yizheng Gong
Original assignee: Illinois Tool Works Inc
Current assignee: Illinois Tool Works Inc
Priority date: 2011-08-18
Filing date: 2017-11-10
Publication date: 2019-07-04
Anticipated expiration: 2031-08-18
Also published as: AU2016247115A1; AU2017258971B2; AU2016247115B2; AU2017258972A1; AU2011213775A1; AU2011213775B2; NZ601854A; AU2017258971A1; NZ711830A; NZ621296A

Abstract

A fastening or other steel component for use in building construction, the component being coated with a base layer of zinc by hot-dip galvanising, and the component having at least one polymer coating applied over the base layer to provide the component with a resistance to corrosion from copper based preservative in treated timber, wherein the polymer coating is a thermosetting polymer in the form of an epoxy resin.

Description

FASTENINGS AND OTHER COMPONENTS FOR USE WITH TREATED TIMBER

This application is a divisional application derived from Australian Patent Application No.2016247115 (which was derived from Australian Patent No. 2011213775), the entire contents of which, as originally filed and accepted, is incorporated herein by reference.

The present invention relates to fastenings and other components for use with treated timber, treated pine for example, in building construction.

In building construction using external timber exposed to the weather, it is common to use timber treated with a preservative to improve its weather-resistance. Pine, a commonly used timber for building construction, is widely available both in raw form and in a form in which it is treated with a wood preservative and this is usually referred to as treated pine. A widely used preservative for this purpose is chromated copper arsenate (CCA) and preserves the wood from decay, fungi and wood-attacking insects. It has been used for many decades and is a very effective treatment although other copper-based treatments which avoid the use of arsenic are now available. The copper primarily acts to protect the wood against decay and fungi, with other compounds acting as an insecticide (in CCA, it is the arsenic which provides the insecticidal function). An arsenic and chromium free alternative to CCA is available which uses copper and a quaternary ammonium compound (known as 'ACQ'). ACQ is also useful in protecting wood against fungi, termites and other wood-boring insects.

Conventionally, timber fastenings such as bolts or screws or other steel components for use in an external environment are coated against corrosion unless fabricated from stainless steel. A widely used anti-corrosion coating for components such as these is galvanising involving the application of a zinc coating. A widely practised method of applying the zinc coating is to use a hot dip method which produces a thicker and less porous zinc coating than that which can be applied by other current methods such as mechanical pounding or electroplating.

For galvanised components which have been used with pine or other timber treated with a copper based preservative, the copper present in the preservative tends to attack the zinc coating and the rate of attack can be quite severe in certain environmental conditions for example moist or damp conditions and in some coastal situations. Although a hot dip zinc coating can be quite robust, such zinc coated products break down over a period of time as a consequence of attack from the copper used in the timber treatment (i.e., for instance, either CCA or ACQ), the underlying metal being subject to corrosion damage, and often quite severe damage.

2017258972 31 May 2019

In order to overcome this shortcoming in the art the present invention relates to a polymer coating(s) to be applied to the zinc coating which thereby acts as a base layer, to shield that zinc layer against attack by the copper in the treated timber. This additional coating does not adversely affect the ordinary performance of the fastening component and in some embodiments actually enhances the performance of the fastening component.

The present invention provides a fastening or other steel component for use in building construction, the component being coated with a base layer of zinc by hot-dip galvanising, and the component having a polymer coating applied over the base layer to provide the component with a resistance to corrosion from copper based preservative in treated timber, wherein the polymer coating is a thermosetting polymer in the form of an epoxy resin, and wherein the application of the polymer coating over the base layer involves multiple coating/curing processes.

The epoxy resin may comprise crosslinking components selected from amines or other nucleophilic nitrogen based compounds.

The crosslinking components may be selected from triethylenetetraamine, hexamethylene, tetramine, methoxymethyl melamine and mixtures thereof.

The ratio of epoxy resin crosslinker components may be about 3:1 to 4:1.

The ratio of epoxy resin crosslinker components may be about 3.5:1 to about 4:1.

The polymer coating may comprise one or more of pigments or opacifers; modifiers to control floating, flooding and silking, or to enhance and improve flow and levelling, or to provide scratch and mar resistance; defoamers; and solvents.

The thickness of the polymer coating may be 15-20 microns.

The polymer coating may comprise a first polymer coating layer that is applied directly onto the base layer.

The component may have at least one primer layer applied over the base layer.

There is disclosed a fastening or other steel component for use in building construction, the component being coated with a base layer of zinc, and the zinc base layer having at least one polymer coating.

2017258972 31 May 2019

There is disclosed a method of forming a copper resistant zinc coated fastening or other steel component for use in association with copper treated wood; said method comprising the step of coating the zinc coated fastening or other steel component with a polymer.

Advantageously the polymer used for the coating is a thermosetting polymer preferably based on an epoxy resin system.

Embodiments will now be described in detail by way of example only.

Preferred embodiments will be described in relation to a steel bolt coated with a base layer of zinc by a conventional hot dip process. Although for convenience the embodiment is being described in relation to a coating applied to a bolt, it is to be understood that an embodiment is applicable to a range of other fasteners and other components as may be used in the building construction industry, such as nuts, washers, screws, nails, staples, nail plates, brackets, joist hangers, metal strap ties and so forth. It will be understood that in each case the component is basically fabricated from steel and after fabrication is coated with a zinc base layer using the hot dip coating method and then the polymer coating as will be described in detail.

Accordingly, preferred examples provide a method of forming a copper resistant zinc coated fastening or other steel component comprising:

(i) subjecting the fastening or other steel component to hot-dip galvanising in order to prepare a zinc coated fastening or other steel component; and (ii) coating the zinc coated fastening or other steel component with a polymer.

The thickness of such a zinc coating achieved by the hot dip process in step (i) above is typically many times that which can be achieved by other galvanising methods and could be as high as 80 microns. The polymer coating is preferably applied over the entirety of the zinc coating, although it will be appreciated that depending on the end use of the component, only part of the component may need to be polymer coated, for instance, any part which comes into contact with copper treated timber.

Although a primary use of the bolt is with treated pine or other treated timber, nevertheless the bolt with a polymer outer coating and zinc base layer also has significant utility in environments where an exposed outer coating layer of zinc would be exposed to salt-laden moist air as would typically be encountered in a coastal environment. In either case, the outer coating acts to shield

2017258972 31 May 2019 the zinc base layer and thereby improves the corrosion resistance of the bolt.

In an embodiment the polymer coated fastening or other steel component is used in conjunction with copper treated timber, and in particular either CCA or ACQ treated timber.

The Polymer Coating

In an embodiment the polymer coating is based on a thermosetting polymer, for example, epoxy resins or phenol formaldehyde resins.

In an embodiment the polymer coating is a polymer composition comprising an epoxy resin based coating system.

In the system described above the epoxy resins may be produced from a reaction between epichlorohydrin and bisphenol-A (or derivatives or analogues thereof). Other systems involve the use of hardener or cross-linking components based on amines, guanidines, ureas, glycouril, or other nucleophilic nitrogen based compounds. Examples of suitable crosslinking/hardening components include triethylenetetraamine, hexamethylene, tetramine, methoxymethyl melamine as well as mixtures of the above.

It will be appreciated by those in the art that in relation to the aforementioned embodiment the curing step to form the epoxy resin based coating system can be controlled through temperature, choice of resin and hardener/crosslinking components and the ratio of resin to hardener/crosslinker.

Typically the ratio of epoxy resin: hardener/crosslinker is about 3:1 to about 4:1, and preferably about 3.5:1 to about 4:1.

The curing process is typically conducted in an oven at temperatures between 180°-250 °C. Curing times may vary but are typically in the range of 7-20 mins.

The polymer coating compositions may include additional components including: pigments and opacifers such as metal based pigments derived from aluminium, cadmium, cobalt, lead, mercury, titanium (e.g., TiO₂), zinc (e.g., zinc phosphate), and iron (e.g., sanguine, caput mortuum, oxide red, Venetian red, Prussian blue, and iron oxide (clay earth) including yellow ochre, burnt and raw sienna, and burnt and raw umber; surface modifiers to control floating, flooding and silking, to enhance and improve flow and levelling, and to provide scratch and mar resistance, etc., such

2017258972 31 May 2019 modifiers including polyether modified polydimethylsiloxanes, polyacrylates, polyesters, waxes (e.g., polyethylene, polypropylene, and mono- and bis amide based waxes), urea and amide based modifiers, and so on; defoamers (such as siloxanes); and solvents (such as propylene glycol monomethyl ether acetate (PMA); 2-butoxyethanol (or BCS), dibenzyl ether, butyl alcohol, butyl acetate, xylene, toluene, trimethylbenzene, and the like which may also function as viscosity modifiers.

In a preferred embodiment a bolt coated with a base layer of zinc is coated with the polymer such that the resultant polymer coating does not impede the performance of the bolt. Preferably the coating is of a thickness of 10-40 microns, and preferably 25-30 microns.

In relation to the embodiment where the polymer coating is a epoxy resin based coating system, the resin components are mixed and shortly thereafter a bolt is coated with the coating composition. The coating process may involve dipping or immersing the bolt into the composition or spraying the bolt with the composition. Once coated the bolt is subjected to heat or UV curing.

In order to control coating thickness, there may be provided a double dipping (or immersion) method, whereby the zinc coated bolt is dipped into the polymer coating composition ('a primer coating') and subsequently cured, this sequence being repeated a further time to achieve the required coating thickness. In the first dip and cure process it is preferred that a coating thickness of between 8-10 microns is achieved. The inventors have found that this double dipping technique with two layers of a primer coating ensures increased adhesion of the coating composition to the zinc surface of the bolt. In this embodiment, the primer coating (which is applied twice) is an epoxy resin based coating as described above.

A further process step between the coating and curing steps may involve a step to remove any unwanted coating on a bolt after the dipping (coating) process. For instance, this may involve subjecting the bolt to centrifugal forces at high speed. Such a process may better ensure uniformity in coating thickness.

Modifications of the above double dipping process would be apparent to the skilled person. For instance, the first coating/curing step may be performed with a primer coating composition with slight variations compared to the subsequent coating composition which is used in the second coating/curing step. One of the variations may be the addition of polymer components (or differing amounts of polymer components) to aid in the adhesion quality of the primer coating

2017258972 31 May 2019 composition to the zinc surface of the bolt.

In a preferred embodiment the coating/curing step is repeated a further third time with a finishing coat. As this third finishing coat is intended to be the outer coating, it may be modified (relative to the first two coatings) by including components which, for example, provide enhancement in relation to wear (e.g., scratch resistance), weathering, colour (which may be used to identify, for example, a particular sized bolt), and so on. Preferably the finishing coat is also an epoxy resin based coating.

It will also be appreciated that the finishing coat may be applied in the same manner as the primer coating layer(s) described above.

Accordingly, in a further aspect there is provided a method of forming a copper resistant zinc coated fastening or other steel component comprising:

(i) coating a zinc coated fastening or other steel component with a polymer;

(ii) subjecting the resultant polymer coated zinc coated fastening or other steel component from step (i) to a further polymer coating process;

(iii) applying a finishing polymer coat to the resultant polymer coated zinc fastening or other steel component from step (ii).

In relation to the above aspect it is preferred that at each stage the thickness of each coating does not exceed 10 microns.

In a further preferred embodiment, which is based on the above aspect, the first two polymer coating layers in steps (i) and (ii) are based on the same epoxy resin based coating ('primer coating'), and the third finishing polymer coat is a modified epoxy resin based coating (i.e., modified in relation to the primer coating).

In other preferred embodiments, the second primer coating referred to earlier could form the outer finishing coat, or the finishing coat referred to earlier could be applied just to a single primer coating whereby in either case, the bolt has just two polymer layers over its galvanised base layer.

As a further recognised advantage the polymer coating on the fastening or other steel component functions to reduce friction when driving the fastener into timber, for instance, (i) into predrilled timber holes for fixing bolts or (ii) into pilot holes or directly into the timber with self-drilling

2017258972 31 May 2019 screws.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word comprise, and variations such as comprises and comprising, will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not by way of limitation. It will be apparent to a person skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. Thus, the present invention should not be limited by any of the above described exemplary embodiments.

Examples

Formulation of epoxy coating

	Raw Materials	%
1	Epoxy Resin	20-40
2	Solvent	1.0-5.0
3	Wetting and dispersing Additives	0-2.0
4	TiO2 Pigment	5.0-15.0
5	Yellow Pigment	1.0-3.0
6	Chemical Resistance Pigment	5.0-15.0
7	Sealant	0-1.0
8	Solvent	1.0-5.0
9	Epoxy Resin	20-40
10	Amine Resin I	2.0-12.0

2017258972 31 May 2019

	Raw Materials	%
11	Amine Resin II	2.0-12.0
12	Surface Additives	0-2.0
13	Leveling Additives	0-2.0
14	Solvent	0.1-5.0
15	Solvent	1.0-5.0
16	Color Paste	0-3.0
	Total	100

Preparation of epoxy coating

Process

1) Add the following raw materials U 2_X 3_X 4_X 5_X 6_X 7 with middle speed 200~400 r/min, high speed 600-1000 r/min disperate 10-15min, send to three-roller mill in order to get thickness <30 um, use 8 to clean

2) Add the following raw materials 9_X 10_x 1U 12_x 13_x 14 with middle speed disperation about 10-20 min.

3) Use 15 to adjust viscosity, use 16 to adjust color, check viscosity and color, filtrate and packing.

Coating Process

1) Bolts are dipped into coating formulation.

2) Excess coating is removed.

3) Coated bolts are cured in an oven at elevated temperatures for 5-20 mins.

4) The process (i.e., steps 1) - 3)) is repeated a further time.

5) The bolts are dipped into a finishing coat formulation which is a slightly modified

2017258972 31 May 2019 version of the coating formulation of 1).

6) Excess coating is removed.

7) Coated bolts are cured in an oven at elevated temperatures for 5-20 mins.

8) The total thickness of the combined polymer coats (i.e., resultant polymer coating) is between about 25-30 microns.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A fastening or other steel component for use in building construction, the component being coated with a base layer of zinc by hot-dip galvanising, and the component having a polymer coating applied over the base layer to provide the component with a resistance to corrosion from copper based preservative in treated timber, wherein the polymer coating is a thermosetting polymer in the form of an epoxy resin, and wherein the application of the polymer coating over the base layer involves multiple coating/curing processes.
2. A component according to claim 1 wherein the epoxy resin comprises crosslinking components selected from amines or other nucleophilic nitrogen based compounds.
3. A component according to claim 2 wherein the crosslinking components are selected from triethylenetetraamine, hexamethylene, tetramine, methoxymethyl melamine and mixtures thereof.
4. A component according to claim 3 wherein the ratio of epoxy resin crosslinker components is about 3:1 to 4:1.
5. A component according to claim 4 wherein the ratio of epoxy resin crosslinker components is about 3.5:1 to about 4:1.
6. A component according to any one of claims 1 to 5 wherein the polymer coating comprises one or more of pigments or opacifers; modifiers to control floating, flooding and silking, or to enhance and improve flow and levelling, or to provide scratch and mar resistance; defoamers; and solvents.
7. A component according to any one of claims 1 to 6 wherein the thickness of the polymer coating is 15-20 microns.
8. A component according to any one of claims 1 to 7, wherein the polymer coating comprises a first polymer coating layer that is applied directly onto the base layer.
9. A fastening or other steel component according to any one of claims 1 to 7 wherein the component has at least one primer layer applied over the base layer.