WO2023166446A1

WO2023166446A1 - Timber coating composition and method

Info

Publication number: WO2023166446A1
Application number: PCT/IB2023/051917
Authority: WO
Inventors: Philip Kenneth COVENY; Robert James COUNSELL; David Gordon KENNEDY
Original assignee: Coveny Philip Kenneth; Counsell Robert James; Kennedy David Gordon
Priority date: 2022-03-01
Filing date: 2023-03-01
Publication date: 2023-09-07

Abstract

Described is a method of priming timber with a coating formulation that comprises PVDC. Also described is a coating formulation for use as a primer on timber, the coating formulation comprising about 30 to 90% by weight of a polyvinylidene dichloride (PVDC) polymer, about 0.1 to 1% of a non-ionic dispersant, about to about 25% by weight of a pigment, the pigment being non-reactive in an acidic environment, a non-ionic rheological modifier, and about 0.5 to about 3% by weight of a silane.

Description

TIMBER COATING COMPOSITION AND METHOD

FIELD OF THE INVENTION

[0001] The present invention relates to a composition for coating timber and the method of use thereof. More particularly the present invention relates to the use of a coating formulation containing PVDC for use as a primer on finished timber.

Background to the Invention

[0002] Wood has long been a vital commodity for many industries. It has provided humanity with structures for domicile and commerce, means for early and contemporary transportation, as well as many other useful devices and apparatuses, ranging from furniture to fence posts.

[0003] The social usefulness of wood is however undermined by its vulnerability to deterioration. Specifically, wood deteriorates when it is exposed to certain woodconsuming organisms, in particular species of fungi and insects. This is particularly true of softwoods like pine and spruce.

[0004] To overcome this problem, industry has developed the practice of incorporating chemical preservatives into wood. Such preservatives are designed to repel the activity of wood-consuming organisms, and thereby increase the lifetime of the wood. This reduces the need to replace wood, which in turn decreases costs for consumers, and decreases the burden on the world's forests.

[0005] The effectiveness of protection depends upon many factors, from the inherent nature of the wood, to the environment that the wood is exposed to. The field of wood preservation focuses in particular on two factors: the type of preservative; and the mode of application.

[0006] There are broadly two modes of application for wood preservatives: nonpressure processes, and pressure processes. Non-pressure processes involve the incorporation of preservatives in wood under standard conditions, typically by coating or immersing the wood within a preservative solution. Pressure processes involve forcing preservatives into wood through the application of high pressures. Whilst pressure processes are generally more effective, as they ensure a deep and consistent saturation of preservatives, they require more energy and equipment, and are therefore more expensive.

[0007] There are two broad classes of preservative: water based, and oil based. The water based class refers to preservatives that are water-soluble; they hence tend to be provided in an aqueous solution. The oil based class refers to hydrophobic preservatives, which tend to be provided within an organic solvent.

[0008] Water based preservatives are typically cheaper, and less environmentally harmful than oil based preservatives. Most oil based preservatives are dissolved in volatile organic compounds, which have well documented environmental and toxicity issues. While there are examples of oil based preservatives that are dissolved in more benign organic solvents, for instance dearomatised solvents, these tend to be more expensive. A typical example of the latter is light oil solvent preservation or LOSP.

[0009] Water based preservatives are typically more economic and environmentally friendly. There is however the issue that when water based preservatives are applied to wood, the wood fibres will absorb the water, which will cause the wood to swell. As the wood dries, the wood fibres will contract, but in doing so will not necessarily return to their original shape. As a result the wood will become disfigured and lose dimensional stability.

[0010] In order to prevent subsequent water absorption the industry has begun to develop primer technology. Primers are coatings that are applied to preservative-treated wood, with an aim to limit the rate of moisture vapour penetration. The primers that are currently available do however suffer from a multitude of flaws.

[0011] For example, solvent based long oil alkyd primers penetrate timber well, and seal the timber surface giving acceptable substrate dimensional stability. However, they have a slow drying speed, and hence provide a handling issue since they cannot be immediately stacked upon preparation. They may also have poor UV stability which creates the need for prompt overcoating. UV cured primers provide a faster cure system but tend to suffer from poor adhesion due to their relative inflexibility. They are more rigid systems that don't tolerate unstable substrates (the substrate being the wood), as have a high crosslink density and poor longer term UV resistance as they are unpigmented so require pigmented primer overcoats. Their moisture vapour resistance is higher than water based acrylics but lower than alkyds. Powder coating timber provides electrical conductivity to wood so that the timber can be powder coated. While the MVTR may be at acceptable levels, the timber tends to crack, that is, it cannot withstand dimensional instability. Water based primers can be pure acrylic or styrene acrylic based and tend to dry fairly quickly, although it can take a number of hours for the co-solvent to evaporate. These primers offer high UV resistance, but have poor penetration and poor adhesion. The adhesion is further compromised when LOSP treatment is used, due to the residual solvent levels. These factors, plus the acrylic backbone mean a high MVTR, so provide a poor option as this process does not assist dimensional stability of the timber. Additionally, the polymers used generally have poor block resistance, which means stacks of wood treated with acrylic primers can cement together

[0012] It is therefore an object of the present invention to overcome any of the above-mentioned disadvantages, or to at least provide the public with a useful choice.

SUMMARY OF THE INVENTION

[0013] In a first aspect there is described a method of coating finished treated timber comprising applying an aqueous composition that comprises a polyvinylidene dichloride (PVDC) polymer to the finished treated timber.

[0014] In a further aspect there is described a method of coating finished treated timber comprising applying an aqueous composition that comprises a polyvinylidene dichloride (PVDC) polymer to the finished treated timber, wherein the coating provides the timber with a water vapour permeability of less than 30%.

[0015] In a further aspect there is described a method of coating finished treated timber comprising applying an aqueous composition that comprises a polyvinylidene dichloride (PVDC) polymer to the finished treated timber, wherein the coating provides the timber with a water vapour permeability of less than 25%.

[0016] In a further aspect there is described a method of coating finished treated timber comprising applying an aqueous composition that comprises a polyvinylidene dichloride (PVDC) polymer to the finished treated timber, wherein the coating provides the timber with a water vapour permeability of less than 20%.

[0017] In a further aspect there is described a method of coating finished treated timber comprising applying an aqueous composition that comprises a polyvinylidene dichloride (PVDC) polymer to the finished treated timber, wherein the coating provides the timber with a water vapour permeability of less than 15%.

[0018] In a further aspect there is described a coating for finished treated timber comprising

• about 30 to 90% by weight of a polyvinylidene dichloride (PVDC) polymer,

• about 0.1 to 1% of a non-ionic dispersant,

• about 15 to about 25% by weight of a pigment, the pigment being non- reactive in an acidic environment, a non-ionic rheological modifier, and about 0.5 to about 3% by weight of a silane. [0019] In a further aspect there is described a coating for finished treated timber comprising

• a polyvinylidene dichloride (PVDC) polymer,

• a non-ionic dispersant,

• an extender pigment,

• a defoamer,

• a coalescent solvent,

• a non-ionic rheological modifier,

• a wax,

• a silane,

• titanium dioxide, and

• a wetting agent.

[0020] In a further aspect there is described finished timber that contains a preservative, and wherein the timber comprises a coating of a composition that comprises polyvinylidene dichloride (PVDC) polymer.

[0021] Any one or more of the following embodiments may relate to any of the above aspects.

[0022] In one configuration the PVDC is applied to finger jointed timber.

[0023] In one configuration the PVDC is factory applied.

[0024] In one configuration polyvinylidene dichloride (PVDC) polymer is in an acidic form.

[0025] In one configuration the composition is applied to the timber to form a wet thickness of about 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145 or 150 pm, and useful ranges may be selected between any of these values.

[0026] In one configuration the composition is applied to the timber to form a dry thickness of about 30, 35, 40, 45 or 50 pm, and useful ranges may be selected between any of these values.

[0027] In one configuration the composition is applied to the timber at a rate of about 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 155, 160, 165, 170, 175, or 180 g/m², and useful ranges may be selected between any of these values. [0028] In one configuration the timber is selected from any finished timber that has been treated with a preservative.

[0029] In one configuration substantially all of the surface of the finished timber is coated.

[0030] In one configuration the coating is applied to the finished timber by spraying, brushing or dipping.

[0031] In one configuration the coated finished timber is dried by force drying.

[0032] In one configuration the coated finished timber is dried by ambient drying.

[0033] It is intended that reference to a range of numbers disclosed herein (for example, 1 to 10) also incorporates reference to all rational numbers within that range (for example, 1, 1.1, 2, 3, 3.9, 4, 5, 6, 6.5, 7, 8, 9 and 10) and also any range of rational numbers within that range (for example, 2 to 8, 1.5 to 5.5 and 3.1 to 4.7).

[0034] This invention may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, and any or all combinations of any two or more of said parts, elements or features, and where specific integers are mentioned herein which have known equivalents in the art to which this invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth.

[0035] The term "comprising" as used in this specification means "consisting at least in part of". When interpreting statements in this specification which include that term, the features, prefaced by that term in each statement, all need to be present but other features can also be present. Related terms such as "comprise" and "comprised" are to be interpreted in the same manner.

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The invention will now be described by way of example only and with reference to the drawings in which:

[0037] Figure 1 is a graph showing the white spirits loss from timber coated with the coating formulation as a primer coat.

[0038] Figure 2A is a picture showing the cross hatching of timber that has been primed with the coating formulation with no topcoat. [0039] Figure 2B is a picture showing the cross hatching of timber that has been primed with the coating formulation and subsequently top coated with a water based enamel topcoat.

[0040] Figure 2C is a picture showing the cross hatching of timber that has been primed with the coating formulation and subsequently coated with a water based exterior paint.

DETAILED DESCRIPTION OF THE INVENTION

[0041] Described is a method of coating a finished treated timber. The method comprises applying an aqueous composition that comprises a polyvinylidene dichloride (PVDC) polymer to the finished treated timber. Also described is a formulation for treating timber. The coating formulation comprises about 30 to 90% by weight of a polyvinylidene dichloride (PVDC) polymer, about 0.1 to 1% of a non-ionic dispersant, about 15 to about 25% by weight of a pigment, the pigment being non-reactive in an acidic environment, a non-ionic rheological modifier, and about 0.5 to about 3% by weight of a silane.

[0042] Advantages of the present coating formulation include, and are not limited to the following.

• Being a water based Primer.

• Using the PVDC as binder.

• Being applied to finger jointed, treated softwood timber

• Restricts short term water vapour absorption to 2% by weight over 6 days at 95% RH with a single coat (e.g. ~100 ji wet) and 1% by weight with 2 coats (e.g. at ~100 g wet each coat).

[0043] An additional benefit may include providing an effecting method for application to softwood timber.

[0044] An additional benefit may include providing an effective method for application to timber in a factory for high throughput processing.

[0045] Broadly speaking, the coating formulation may contain 30, 40, 50, 60, 70, 80 or 90% by weight PVDC, and useful ranges may be selected between any of these values (for example, about 30 to about 90, about 30 to about 80, about 30 to about 60, about 30 to about 50, about 40 to about 90, about 40 to about 80, about 40 to about 70, about 40 to about 50, about 50 to about 90, about 50 to about 80, about 50 to about 70, about 60 to about 90 or about 60 to about 80% by weight PVDC). [0046] In some embodiments the coating formulation may contain 50, 52, 54, 56, 58, 60, 62, 64, 66, 68 or 70% by weight PVDC, and useful ranges may be selected between any of these values (for example, about 50 to about 70, about 50 to about 66, about 50 to about 62, about 52 to about 70, about 52 to about 68, about 52 to about 64, about 52 to about 60, about 54 to about 70, about 54 to about 66, about 54 to about 60, about 56 to about 70, about 56 to about 68, about 56 to about 64, about 56 to about 60, about 58 to about 70, about 58 to about 66, about 58 to about 62, about 60 to about 70 or about 60 to about 66% by weight PVDC.

[0047] In some embodiments the coating formulation may contain about 60% by weight PVDC.

[0048] The formulation is prepared to coat finished timber (sometimes also referred to as "dressed timber"). Finished timber generally refers to timber that is used for finishing construction and as such the visual appearance of that timber is important.

This visual appearance is typically achieved by passing the timber through a machine that achieves the smoothed finished surface. Dressed timber is a type of finished timber, in that it is generally the most finished of all of the types of finished timber providing an extremely smooth and consistent finish.

[0049] Finished timber needs to remain dimensionally stable as it has been machined to a profile and merchantable quality. Examples of such timber includes any finished treated timber such as window reveals, doors, weatherboards, structural beams, made from any finger jointed softwood timber such as pine and spruce. As used herein, the term "finger jointed timber" refers to a board of timber that is created by using small, individual pieces joined together with glue and small interlocking ’fingers'". The joins typically create a neat zig zag effect at the join site. A benefit of finger jointed timber is that it assists in removing knots from the timber.

[0050] Finished timber is generally prepared in a factory as it is processed by machines to achieve its finish. The finished timber may also be assembled into structures such as window frames or door frames. The present process may provide the ability to mass treat the finished timber to achieve high throughput of the finished timber.

[0051] The finished timber for treatment with PVDC may be treated finished timber that has been treated with a water based or solvent based (e.g. CCA [copper chrome arsenate] or LOSP [light organic solvent-based preservative]) preservative formulation.

[0052] The timber to be treated by PVDC may have a hazard rating of H2, H3, or H4. H codes (Hl to H5) are conditional use codes representing appropriate levels of preservative treatments (against biological decay) that are required for using a specific timber in a specific application and location. Each code (Hl, H2, H3, H4, H5) represents a different, required minimum preservative treatment. The minimum level of preservative treatment required to protect the timber from attack by insects, including termites. H2 preservative treatments are suitable in above to about ground, well to about ventilated situations protected from weather and wetting. H3 preservative treatment offers protection in situations above to about ground, exposed to the weather or periodic wetting. H4 treatments are suitable for use in situations where the timber is in contact with the ground or is continually damp. The coating may be used on timber with a hazard rating of H2.1. The coating may be used on timber with a hazard rating of H3.

[0053] When applied to the timber the formulation may be applied to a wet film thickness of about 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145 or 150 pm, and useful ranges may be selected between any of these values (for example, about 75 to about 150, about 75 to about 135, about 75 to about 100, about 75 to about 80, about 90 to about 150, about 90 to about 125, about 90 to about 100, about 100 to about 150, about 100 to about 120, about 110 to about 150 or about 110 to about 140 pm).

[0054] One or more coats of the presently described PVDC treatment may be applied to the finished timber.

[0055] In terms of the loading of the coating on the timber, the coating may be applied at a loading of about 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190 or 200 g/m² and useful ranges may be selected between any of these values (for example, about 80 to about 200, about 80 to about 180, about 80 to about 160, about 80 to about 100, about 90 to about 200, about 90 to about 180, about 110 to about 160, about 100 to about 200, about 100 to about 170, about 100 to about 150, about 110 to about 200, about 110 to about 18 to about , about 110 to about 150, about 120 to about 200, about 120 to about 180, about 120 to about 150 or about 150 to about 200, about 150 to about 180 g/m²).

[0056] Once applied to the timber in wet form, the coating then dries to a dry film. The coating may have a dry film thickness of about 30, 32, 34, 36, 38, 40, 42, 44, 46, 48 or 50 pm, and useful ranges may be selected between any of these values (for example, about 30 to about 50, about 30 to about 46, about 30 to about 40, about 32 to about 50, about 32 to about 46, about 32 to about 40, about 34 to about 50, about 34 to about 48, about 34 to about 44, about 34 to about 40, about 36 to about 50, about 36 to about 46, about 36 to about 40 or about 40 to about 50 pm). [0057] Once applied to the timber some of the coating will penetrate into the timber. The present coating formulation may not include low surface tension solvents and thus this together with its polymer particle morphology may limit penetration into the timber. For example, about 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29 or 30% of the coating formulation may penetrate the timber to be treated.

[0058] Without wishing to be limited by theory, the polymer particle morphology of the described formulations may contribute to the prevention of penetration since the evaporation of only a small amount of water on drying causes a sharp increase in viscosity preventing the coating from further movement into the substrate.

[0059] The coating formulation can be applied through a range of techniques such as painting, spraying or dipping. The use of a spray gun may allow the application rate to be more effectively controlled since the application pressure can be controlled with the use of a spray gun. The application thickness of the coating formulation before it dries is called the wet film thickness (WFT). The WFT can be measured with a wet film comb gauge or wet film wheel.

[0060] Once applied to the timber the coating formulation may be dried. The coated timber may be dried in ambient conditions or force dried. Force drying may include a heated airflow that circulates about the coated timber. Force drying may also include cooking the timber in ovens.

[0061] The timber coated with the coating formulation may dry more rapidly than other industry treatment approaches.

[0062] The coating formulation may comprise a non-ionic dispersant. The non-ionic dispersant may be selected from one or more of DISPERBYK-190, Additol VXW 6208, Stepsperse 250 and Uniqsperse 730U. DISPERBYK-190 is a VOC and solvent-free wetting and polymeric dispersing additive for aqueous coating systems. The non-ionic dispersant may be present in the coating formulation at about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1.0% by weight, and useful ranges may be selected between any of these values (for example, about 0.1 to about 1.0, about 0.1 to about 0.8, about 0.1 to about 0.5, about 0.2 to about 1.0, about 0.2 to about 0.9, about 0.2 to about 0.7, about 0.2 to about 0.5, about 0.3 to about 1.0, about 0.3 to about 0.7, about 0.3 to about 0.5, about 0.4 to about 1.0, about 0.4 to about 0.9, about 0.4 to about 0.7 or about 0.4 to about 0.5% by weight). Without intending to be limited by theory, the presence of the non-ionic dispersant may enhance or promote in-can stability of the coating formulation. This may assist in preventing or reducing pigment particles in the can from agglomerating. [0063] The coating formulation may comprise an extender pigment. A pigment adds colour and opacity whereas the extender pigment in the coating formulation provides bulk and block resistance. Without wishing to be limited by theory, the extender pigment may assist in providing a hard layer (not a soft polymer) of coating.

[0064] The extender pigment may be a water soluble dye. An example of an extender pigment for use with the coating formulation is nepheline syenite. The pigment may be present in the coating formulation at about 15, 16, 17, 8, 19, 20, 21, 22, 23, 24 or 25% by weight, and useful ranges may be selected between any of these values (for example, about 15 to about 25, about 15 to about 23, about 15 to about 20, about 15 to about 19, about 16 to about 25, about 16 to about 24, about 16 to about 23, about 16 to about 19, about 17 to about 25, about 17 to about 22, about 17 to about 19, about 18 to about 25, about 18 to about 24, about 18 to about 22, about 18 to about 20 or about 19 to about 25% by weight). The pigment may include a characteristic of being non-reactive in an acidic environment. The pigment may also include the characteristic of block resistance. Preferably the pigment is not calcium carbonate since the pigment cannot be chemically reactive in an acidic environment. As such basic pigments also cannot be used. Thus the pigment for use in the coating formulation is any pigment that does not react at a low pH, for example, is inert at low pH such as calcined clays, kaolin clays, talc, bentonite clays, silicates or any combination thereof.

[0065] The coating formulation may comprise a defoamer.

[0066] The coating formulation may comprise a coalescent solvent. In some embodiments the coalescent solvent may be selected from long chain alcohols or plasticisers. For example, the coalescent solvent may be glycol ether. The coalescent solvent may be present in the coating formulation at about 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4 or 1.5% by weight, and useful ranges may be selected between any of these values. The coalescent solvent may assist in allowing smaller particles in the formulation to fuse together.

[0067] In some embodiments the coating formulation may not include a coalescent solvent, in which case the coating formulation may need to be exposed to heat.

[0068] The coating formulation may comprise a rheological modifier. The rheological modifier may not be an alkali sensitive rheological modifier. That is, the rheological modifier may be effective at a low pH of about 2 to about 4.5. The effectiveness at low pH may provide the required characteristics to the formulation for wet state stability and application properties. The rheological modifier preferably provides for the coating formulation to have an application viscosity of about 2500, 3000, 2500, 4000, 4500 or 5000 cP, and useful ranges may be selected between any of these values. Such a viscosity may ensure in-can stability and specified coverage rate during application. In some embodiments the rheological modifier is not an alkali activated compound.

[0069] The coating formulation may comprise about 0.5, 0.1, 1.5, 2.0, 2.5, or 3% by weight of a wax or wax equivalent, and useful ranges may be selected between any of these values. The wax equivalent may be selected from polyethylene, polypropylene, halogen containing waxes or a combination thereof. The wax does not include paraffin wax. The wax may provide for a performance characteristic that the coating can be readily over coated without inter-coated adhesion.

[0070] The coating formulation may comprise about 0.5, 0.1, 1.5, 2.0, 2.5, or 3% by weight silane, and useful ranges may be selected between any of these values. The silane may be a functionally modified silane with a ratio of between 10:90 to 90: 10.

[0071] If the coating formulation comprises a pigment, the coating formulation may comprise titanium dioxide. The titanium dioxide may be present at about 0.75: 1 to 1 :0.75 to the extender pigment. The titanium dioxide may be present at about 1 : 1 to the pigment.

[0072] The coating formulation may comprise a wetting agent. Preferably the wetting agent is a non-ionic wetting agent. The wetting agent may be selected from an ethoxylate, such as a fatty alcohol or acid ethoxylate. The wetting agent may provide for a specific hydrophilic to lipophilic balance, which may help to keep clumps of powder apart in the formulation.

[0073] The coating formulation may be used at ambient temperature. In the event that the coating formulation does not include a coalescent solvent the coating formulation can be used if it is cured at an elevated temperature relative to ambient.

[0074] The coating formulation may have a solids content of about 25, 30, 35, 40, 45, 50 or 55% by volume, and useful ranges may be selected between any of these values.

[0075] The coating formulation may have a solids content of about 30, 40 or 50% by volume.

[0076] The coating formulation may have a solids content of about 30, 35, 40, 45, 50, 55, 60 or 65% by weight, and useful ranges may be selected between any of these values. [0077] The coating formulation may be formed by first dispersing pigments separately in water. The raw materials are then all combined to form a first mixture and then that first mixture is then combined with the PVDC resin.

[0078] The coating formulation may demonstrate good block resistance. Block resistance is the ability of paint, when applied to a painted surface, to not stick to other painted surfaces when pressure is applied. For instance, when a painted door frame is pushed against a painted door, the block resistance of the respective paints can be understood as the degree to which the paint on the frame does not stick to the paint on the door.

[0079] The coating formulation may demonstrate adhesion for subsequent paint layers. Good adhesion means that a top coat(s) of paint applied to the coating formulation (primer) do not lift from the primer coat.

EXAMPLES

Example 1

[0080] The purpose of this example was to measure various performance characteristics of the coating formulation that contains PVDC once applied to the timber as a primer coat. The characteristics measured included:

• block resistance, and

• low Moisture Vapour Transition Rate (MVTR).

Block resistance

[0081] This test was run to measure the block resistance of the primer coat (i.e. the coating formulation containing PVDC). The experiment was designed as follows.

[0082] Blocks of timber were first soaked in low aromatics petroleum distillate at ambient temperature for two minutes and left overnight to dry. The soaked blocks were then coated in primer and left for 24 hours at ambient to dry.

[0083] Coated blocks were stacked on top of each other and subjected to 1 kg/cm² of pressure for 24 hours.

[0084] After 24 hours the blocks came apart with no stick or coating removal. Low Moisture Vapour Transition Rate (MVTR)

[0085] The MVTR was measured for primed wood with both single and double coatings. The results were comparable to the performance of alkyds, which as discussed is currently the industry leader with regards to MVTR.

[0086] The experiment was designed as follows.

[0087] Weatherboards formed from finger jointed Pinus radiata from a provincial timber mill were coated by spraying with an airless sprayer at lOOOpsi using a 0.019" tip with a primer coating containing PVDC.

Table 1.

[0088] The coating thicknesses of the single primed boards was 100 pm (wet). The coating of the primer was uniform across the timber with a wet film thickness of about 90 to 100 pm per coat. For multiple coats each coating was allowed to dry for 20 min at ambient (18-25°C) and relative humidity of less than 80%. Coating thickness was measured wet using a comb gauge or a wet film wheel. Stability test

[0089] Dimensional stability can be assessed by soak tests whereby the wood is immersed in water for defined periods and the dimensional increases are observed. However, soak methods are not necessarily useful in determining dimensional stability of primed or painted timber because shrinkage or swelling is due to the passage of water vapour through the coating. In addition, the soak test does not yield information on the shrinkage of timber in dry atmospheres, an area of importance to the industry.

[0090] The dimensional stability test used herein measures rates of water vapour transfer in both directions through the coating. This is achieved by conditioning boards (typically 300mm x 200mm and end sealed) in two separate chambers conditioned to 20% and 95% relative humidity environments. Unprimed LOSP treated boards are used for reference.

[0091] A 4-5 day period is chosen for the comparisons. Shorter periods are not preferred as the dimensional or weight changes may be too small for clear differentiation of the samples. Longer periods (weeks) are also not desired as the controlling factor may be the rate of diffusion of water through the wood matrix, rather than the passage through the coating.

[0092] The ratio of total dimensional (or weight) change compared to the reference uncoated samples (as a percentage) is denoted %WVP (%Water Vapour Permeability). Weight changes rather than dimensional changes are preferred for calculations as greater measurement sensitivity is obtainable.

[0093] We obtained measurements for the rate of water absorption and water desorption within high and low humidity environments. The 300mm long PVDC treated boards were tested in duplicate (i.e. two pieces in each humidity chamber). Two reference samples of commercially treated boards were tested in triplicate. The samples were conditioned in the humidity chambers for five days. Individual test pieces were measured for both weight and dimension (board width) before and after conditioning.

[0094] Reference results (typical results) are given below:

• Uncoated Boards WVP = 100%

• Acrylic Primers (two coat) WVP = 65-75%

• Single coat alkyd - (90pm wet) WVP = 30-50%

• Two coat alkyd (2 x 90 pm wet) WVP = 10-15% Results

[0095] The results of the PVDC tested boards are given below for both single and double coats of the PVDC coating.

• WVP (water vapour permeability) = 30.3% for single coat.

• WVP= 5.7% for a double coat

[0096] The PVDC single coated board yielded a result WVP of 30.3% indicating a performance as good as the best reported one coat alkyd primer WVP which is considered to be the "gold standard " for the industry

[0097] The PVDC double coated board yielded a result WVP= 5.7% indicating even less water vapour permeability than generally expected from the two coat alkyd primer which is considered to be the "gold standard " for the industry.

[0098] WVP was in the range of, and lower than, the WVP achieved with alkyd primer. Hence, the results were as good, if not better, than the industry leader for MVTR. Therefore, the coating formulation containing PVDC provides excellent dimensional stability to the substrate.

[0099] Weight gain as a measure of WVP was recorded for coated weatherboards, ends sealed with epoxy, suspended in a 95% RH chamber at ambient temperature. Results were:

• Alkyd single coat at 90pm wet, weight gain 1.8% over 6 days

• PVDC primer single coat at 100pm wet, weight gain 1.9% over 6 days

• Alkyd 2 coats each 90pm wet, weight gain 0.9% over 6 days

• PVDC primer 2 coats each 100pm wet, weight gain 0.7% over 6 days

[0100] Timber is commonly treated with organic solvents bearing treatment chemicals and thus it is useful to examine the adhesion of the primer and the ability of the solvent to evaporate from the timber after the timber is treated with a primer, such as the coating formulation as described that contains PVDC. Residual solvent compatibility therefore refers to the ability of the primer to allow residual solvent to evaporate.

[0101] A test was conducted to determine the compatibility of the coating formulation primer in question. Three samples were soaked in white spirits for two minutes. One of the samples was then coated with primer. The weight of the three samples was then recorded over eight days. The results are shown in Figure 1.

[0102] Another characteristic of a primer for consideration is that any subsequent coating on top of the primer coat has good adhesion to the primer coat. The adhesion of the PVDC coating was tested as shown in Figures 2A to 2C. That is, the timber was coated with the coating formulation containing PVDC as a primer coat. The primer was then coated with no topcoat as shown in Figure 2A, WB (water based) enamel as shown in Figure 2B, and WB exterior paint as shown in Figure 2C. The coating was allowed to dry and then tested as per ASTM D3359 for inter-coat adhesion using the cross hatch method. 25 by 2mm squares are cut into the surface through to the timber below and then adhesive tape is applied diagonally and removed. If the paint layer of the primer does not adhere well, then it is expected that some of the squares will be removed. If there is good adhesion then all that will show is the cross hatching cut into the coating top layer with no coating dislodged next to the cut.

[0103] As shown in Figures 2A to 2C the paint adhered well to the PVDC coating.

[0104] Although embodiments have been described with reference to a number of illustrative embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

[0105] Many modifications will be apparent to those skilled in the art without departing from the scope of the present invention as herein described with reference to the accompanying drawings.

Claims

WE CLAIM:

1. A method of coating finished treated timber comprising applying an aqueous composition that comprises a polyvinylidene dichloride (PVDC) polymer to the finished treated timber.

2. A method of claim 1 wherein the timber is finger jointed softwood timber.

3. A method of claim 1 or 2 wherein the aqueous composition is factory applied to the finished treated timber.

4. A method of any one of claims 1 to 3 wherein the coating limits the 6 day weight gain to less than 2%.

5. A method of any one of claims 1 to 4 wherein the coating provides the timber with a water vapour permeability rate of less than 30%.

6. A method of claim 5 wherein the coating provides the timber with a water vapour permeability rate of less than 30%.

7. A method of claim 5 wherein the coating provides the timber with a water vapour permeability rate of less than 25%.

8. A method of claim 5 wherein the coating provides the timber with a water vapour permeability of less than 20%.

9. A method of claim 5 wherein the coating provides the timber with a water vapour permeability rate of less than 15%.

10. A method of any one of claims 1 to 9 wherein the coating for the finished treated timber comprises

• about 30 to 90% by weight of a polyvinylidene dichloride (PVDC) polymer,

• about 0.1 to 1% of a non-ionic dispersant,

• about 15 to about 25% by weight of a pigment, the pigment being non-reactive in an acidic environment,

• a non-ionic rheological modifier, and

• about 0.5 to about 3% by weight of a silane.

11. A method of any one of claims 1 to 10 wherein the coating for the finished treated timber comprises a polyvinylidene dichloride (PVDC) polymer, a non-ionic dispersant, an extender pigment, a defoamer, a coalescent solvent, a non-ionic rheological modifier, a wax, a silane, titanium dioxide, and a wetting agent.

12. A method of any one of claims 1 to 11 wherein the finished timber contains a preservative.

13. A method of any one of claims 1 to 12 wherein the coating is applied to the timber to form a wet thickness of about 75 to 150 pm.

14. A method of any one of claims 1 to 13 wherein the coating is applied to the timber to form a dry thickness of about 30 to 50 pm.

15. A method of any one of claims 1 to 14 wherein the coating is applied to the timber at a rate of about 100 to 180 g/m².

16. A method of any one of claims 1 to 15 wherein the timber is selected from any finished timber that has been treated with a preservative.

17. A method of any one of claims 1 to 16 wherein substantially all of the surface of the finished timber is coated.

18. A method of any one of claims 1 to 17 wherein the coating is applied to the finished timber by spraying, brushing or dipping.

19. A method of any one of claims 1 to 18 wherein the coated finished timber is dried by force drying.

20. A method of any one of claims 1 to 19 wherein the coated finished timber is dried by ambient drying.

21. A coating formulation suitable for finished treated timber comprising • about 30 to 90% by weight of a polyvinylidene dichloride (PVDC) polymer,

• about 0.1 to 1% of a non-ionic dispersant,

• a non-ionic rheological modifier, and

• about 0.5 to about 3% by weight of a silane.

22. A formulation of claim 21 wherein the polyvinylidene dichloride (PVDC) polymer is in an acidic form.