AU2021201287A1

AU2021201287A1 - Coloured Fibre-Cement Panels

Info

Publication number: AU2021201287A1
Application number: AU2021201287A
Authority: AU
Inventors: Ling Meng Wong
Original assignee: CSR Building Products Ltd
Current assignee: CSR Building Products Ltd
Priority date: 2020-02-26
Filing date: 2021-02-26
Publication date: 2021-09-09
Also published as: AU2021101063A4; AU2021101063B4

Abstract

A method for manufacturing a coloured, autoclaved fibre-cement panel is disclosed. The method comprises providing a pigment-bearing slurry and a fibre cement slurry. The method also comprises agitating the pigment-bearing slurry to 5 disperse the pigment within the pigment-bearing slurry, prior to introducing the pigment-bearing slurry to the fibre-cement slurry in a batching operation. The batched slurry is passed to a Hatschek fibre-cement forming process to obtain a coloured fibre-cement panel. The fibre-cement panel is pressed and auto-claved. 12145308_1 (GHMatter) P112870.AU.1 10 34 ~32 16 18 56 F4 6 28 30 24_ _ _ _ _ 40 20 22 38 42 66 i 860 52 50 70 )tL/ 46 H '64 _ I48 5I-M -No -* FWarehouse 72 73 74 Figure 1 1/8

Description

34

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Figure 1

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COLOURED FIBRE-CEMENT PANELS TECHNICAL FIELD

This disclosure relates to fibre-cement panels for building applications that are coloured in the mass and also relates to a method for making such coloured fibre-cement panels.

BACKGROUND ART

Coloured fibre-cement panels for building facades are known in the art, but are typically produced by applying coloured paints or other pigmented surface coatings to conventional, uncoloured fibre-cement panels.

Through-thickness or integral colouring of fibre-cement panels (where a colouring additive or pigment is distributed throughout the panel), though less common, can be achieved by the addition of pigments to thefibre-cement slurry during production of the panels, with such pigments including a range of materials such as metal oxide inorganic pigments and carbon-based organic pigments. Suitable pigments must be stable in the highly alkaline environment typical of setting concrete, be able to remain evenly distributed throughout thefibre-cement slurry during production and also be able to withstand any thermal curing treatments applied to the panels after forming.

Such coloured fibre-cement panels may be more aesthetically pleasing than conventional cement-coloured panels and may be produced using a number of methods known in the art for uncoloured fibre-cement panels, including the Hatschek process for example. The Hatschek process employs one or more rotating sieves within a fibre-cement slurry to accumulate de-watered layers of fibre-cement to form solid panels. Coloured fibre-cement panels produced in this way are typically subjected only to air-curing processes after forming, as thermally-assisted curing processes (such as autoclaving, for example) that are more commonly used for uncoloured panels may affect the pigments added during production of the panels. As such, coloured fibre-cement products containing

12145308_1 (GHMatter) P112870.AU.1 pigments that are not stable at elevated temperatures are typically restricted to slower production runs (as a result of longer air-curing times), lower dimensional stability and/or lower strengths than uncoloured fibre-cement panels, which can be autoclaved during production.

In order to achieve mass or through-thickness coloured panels that may be subjected to autoclaving processes, one or more thermally stable pigments must be selected. Carbon black is an example of one such thermally stable pigment that may be added to fibre-cement slurries to colour autoclaved fibre-cement panels in the mass. Carbon black also has the advantage of being chemically stable in highly alkaline cementitious environments but, due to its extremely low wettability in water, can be difficult to evenly disperse in water-based fibre cement slurries. Poor distribution and or agglomeration/settling of the carbon black pigment can lead to uneven colouration of the slurry and thus uneven colouration of the finished panel.

Dispersion agents such as surfactants can be used to improve the dispersion of carbon black in water, however such dispersants may lead to unwanted foaming of the slurry during production of thefibre-cement panel, resulting in increased porosity and reduced strength of the final product.

Attempts have been made in the art to address the poor dispersibility of carbon black in fibre-cement slurries without the use of additional dispersants. For example, JP2000226243A discloses a method of surface modification of carbon black particles using hydrophilic functional groups, which can be used to improve carbon black dispersion within the slurry.

In other attempts to incorporate well-dispersed pigments infibre-cement slurries, coal ash (such as fly ash), has been employed in place of pure carbon black (see for example JP2000327447A). This approach can avoid the need for additional dispersants, because the coal ash particles act as carriers for finer carbon particles (acting as the pigment) adhered to the surface of the coal ash, while the coal ash itself can be more easily mixed through the fibre-cement slurry than the fine

12145308_1 (GHMatter) P112870.AU.1 carbon black particles. However, coal ash, as a carrier for the carbon pigment, can introduce unwanted impurities in the fibre-cement slurry.

Known methods for incorporating carbon black into fibre-cement slurries are considered inefficient.

The above references to the background art do not constitute an admission that the art forms part of the common general knowledge of a person of ordinary skill in the art. The above references are also not intended to limit the application of the method and panel as disclosed herein.

SUMMARY

Disclosed herein is a method of manufacturing a coloured, autoclaved fibre cement panel. The method comprises providing a pigment-bearing slurry and a fibre-cement slurry.

The method also comprises agitating the pigment-bearing slurry to disperse the pigment within the pigment-bearing slurry, prior to introducing the pigment bearing slurry to the fibre-cement slurry in a batching operation. Provision of a separate, pre-mixed pigment-bearing slurry, as opposed to adding pigment directly to a fibre-cement slurry (such as in the form of a powder for example), can enable more efficient distribution of the pigment throughout thefibre-cement slurry, and can thus provide enhanced colouration of the resulting fibre-cement panel. In this regard, the pigment-bearing slurry may be mixed more vigorously (and hence effectively) than would be possible for pigments added directly to a more viscous fibre-cement slurry. By agitating the pigment-bearing slurry prior to batching, or combining, of the fibre-cement slurry and the pigment-bearing slurry, an optimum dispersion of pigment within the pigment-bearing slurry may be achieved. The optimum dispersion may be achieved without the need for dispersion agents such as surfactants (the use of which may lead to unwanted foaming of the slurry during production of thefibre-cement panel). This dispersion of pigment, resulting from agitation of the pigment-bearing slurry in

12145308_1 (GHMatter) P112870.AU.1 isolation from the fibre-cement slurry, can result in a corresponding optimal dispersion of pigment when the pigment-bearing and fibre-cement slurries are batched. Thus, separate mixing of each isolated slurry prior to the batching operation may enhance pigment distribution in the resulting combined slurry and in the finished autoclaved fibre-cement panel.

The fibre-cement slurry may be any of a number of compositions known in the art, having a cementitious component (such as Portland cement for example), a reinforcing fibre component, such as natural cellulose fibres and any number of additives known in the art including silica, a nucleating agent such as an aluminium hydrate, flocculants, dispersants and other additives.

The method further comprises passing the batched slurry resulting from the batching operation to a Hatschek fibre-cement forming process to obtain fibre cement panels; pressing the fibre-cement panels; and autoclaving thefibre-cement panels. The Hatschek process is a well-known method in the art for the production of laminated fibre-cement sheet material from fibre-cement slurries. The Hatschek process typically employs rotating sieve cylinders partially immersed in fibre cement slurries to produce 'green' fibre-cement sheets or panels by means of a solids accumulation process. The efficiency of such a process is strongly affected by the consistency of the slurry through which the sieve cylinders rotate.

In particular, air entrainment within, or foaming of the fibre-cement slurry, can have a detrimental impact on the efficiency of the Hatschek process. In this regard, foam present in the fibre-cement slurry, by nature of its relatively low density, will naturally rise toward the surface of the slurry. Surface foam may segregate the various solid components of the fibre-cement slurry (for example, separating the reinforcing fibres or pigment particles from the cement particles, etc.), stratifying the composition of the slurry and reducing the effectiveness of solids accumulation through the sieves of the Hatschek process. This can significantly impact the consistency and quality of the resulting fibre-cement panels. Vigorous mixing of fibre-cement slurries intended for use in a Hatschek

12145308_1 (GHMatter) P112870.AU.1

(or similar) process is therefore to be avoided, as such mixing may cause the unwanted entrainment of air within the relatively viscous fibre-cement slurry and the production of foam. This places a constraint over the degree and/or speed with which the fibre-cement slurry for panel production may be mixed or the slurry homogenised, which can be particularly problematic for the production of coloured fibre-cement articles, where a well-mixed, even distribution of pigment is required.

It has been surprisingly found that provision of a pre-mixed pigment-bearing slurry, in accordance with the present disclosure, can provide even colouration whilst avoiding unwanted foaming of coloured fibre-cement slurries intended for use in a Hatschek process. This may be achieved by a portion of the necessary mixing and dispersion of the pigment taking place in the absence of thefibre cement slurry. In this regard, vigorous mixing of the relatively less viscous pigment-bearing slurry can achieve a good suspension of pigment (without significant air entrainment, such as where the pigment-bearing slurry has a low viscosity), prior to combining the pigment-bearing and fibre-cement slurries in the batching process. Once batched, relatively gentle (i.e. laminar) mixing may be employed to mix the pigment-bearing and fibre-cement slurries, where the already good suspension of pigment within the pre-mixed pigment-bearing slurry can contribute to enhanced dispersion of pigment throughout the batched slurry, whilst avoiding unwanted foam production. Such enhanced pigment dispersion can result in fibre-cement panels produced by the Hatschek process which are evenly coloured in the mass by the pigment.

The homogeneous, through-thickness colouration produced by the enhanced pigment distribution of panels according to the present disclosure may serve to compensate for colouration effects of other components present in the fibre cement panels, such as reinforcing fibres for example. In this regard, the need for supplementary pigmentation or dyeing of the reinforcing fibres, added during production of the panels, may be obviated. Further, such panels may be cut after production (e.g. on-site during construction of a building), with the freshly cut

12145308_1 (GHMatter) P112870.AU.1 surfaces exhibiting a similar surface appearance to that of the original panel surfaces, without requiring the additional steps of painting/coating the freshly cut surfaces. The integral coloration may also aid in concealing damage to the panels, that may be suffered during installation or in later use.

Each of the surfaces of panels produced according to the present disclosure, in particular the major (i.e. larger) panel faces, will also exhibit the same colour and/or texture combination. This may allow for the panels to be mounted in any suitable orientation during installation (for example, in an orientation to conceal surface scratches and/or defects on one face of a given panel), without regard for differing colour treatments applied to a particular face of the panel during production. The consistent appearance of the panels over each surface may be of particular use where multiple surfaces of a given panel may be left visible after installation (for example portions of both the front and back of the panel).

Such panels may find use in facade, cladding and covering applications for buildings, including as coverings for internal and external wall members. The present disclosure provides fibre-cement panels for building applications which are mechanically suitable, environmentally durable and aesthetically pleasing.

In an embodiment of the method, the pigment-bearing slurry may comprise carbon black and water. Carbon black can be an effective pigment for autoclaved fibre-cement panels, as it is stable within the highly-alkaline environment of setting cement and under the elevated temperatures of autoclaving processes. Carbon black is also stable in conditions of prolonged exposure to ultraviolet light, which may contribute to enhanced durability of the coloured fibre-cement panels in outdoor applications.

The provision of carbon black in the form of a slurry (as opposed to dry powder for example) can enable the pigment to be employed with greater safety, reducing the risk of inhalation by plant operators and contamination of surrounding equipment, and simplifying cleaning operations where spillage occurs. The use of water, as opposed to other dispersants such as surfactants, may provide a pigment

12145308_1 (GHMatter) P112870.AU.1 bearing slurry with reduced propensity to foaming, thereby contributing to the efficient manufacture of coloured fibre-cement panels using a Hatschek process.

In some embodiments of the method, the pigment-bearing slurry may comprise 0.1% to 30% carbon black by weight of the pigment-bearing slurry, the balance of the pigment-bearing slurry comprising water. It has been found that as much as about 30% carbon black by weight of the slurry (with about 70% water, by weight of the slurry) may be used to produce a suitable pigment-bearing slurry, but that above around 20% carbon black 'loading' of the slurry may lead to less efficient dispersion of the carbon black within the pigment-bearing slurry. This is because high loadings of carbon black (i.e. above around 23 to 25% for example) may lead to significantly more viscous slurries and increased likelihood of agglomeration of pigment particles. Pigment-bearing slurries of such high loadings may require significantly more mixing than is required for lower loadings, which can reduce production efficiency.

In contrast, slurries containing below around 10% carbon black (including slurries containing anywhere from around 0.1 to 10% carbon black, or 'low-loading' pigment-bearing slurries), while also suitable for the production of coloured fibre cement panels according to the present disclosure, may lead to less efficient panel production than can be achieved using higher pigment loadings. This is because a relatively larger volume of a low-loading pigment-bearing slurry is required to be batched with a fibre-cement slurry to produce panels containing a given amount of carbon black, in comparison to the required volume of a higher loading pigment bearing slurry (e.g. around 10 to 25% carbon black loading).

Pigment-bearing slurries having carbon black loadings of approximately 10% to 20% by weight of slurry (for example, around 15% by weight of slurry) have been found to produce effective pigment-bearing slurries, which may be added in suitable amounts to fibre-cement slurries to produce coloured fibre-cement panels, according to the present disclosure, in an efficient manner. The person of skill in the art will understand that the desired carbon black loading of the pigment

12145308_1 (GHMatter) P112870.AU.1 bearing slurry may be any suitable amount (including for example greater than 30% by weight carbon black), provided that the pigment-bearing slurry is sufficiently mixed to ensure a good suspension of carbon black, prior to mixing the pigment-bearing slurry with fibre-cement slurry. Herein, the term 'loading' refers to the weight percentage of carbon black in the pigment-bearing slurry.

Pigment-bearing slurries according to the present disclosure may be produced by mixing a suitable pigment powder (e.g. carbon black) with water. Such mixing may be achieved by manual application of stick-style mixers (where open containers of pigment-bearing slurry are employed), or may be by way of mixing units fitted to closed vessels, such as an intermediate bulk container (IBC) for example.

In some embodiments of the method, the pigment-bearing slurry may comprise particles suspended in the slurry, the particles having a maximum size of less than 0.1mm. Carbon black particles, being virtually insoluble in water, have a tendency to agglomerate/flocculate and/or settle when dispersed in a liquid medium. It has been found that use of pigment-bearing slurries containing particles or agglomerates of carbon black of sizes exceeding about 0.1mm may lead to less than optimal distribution of pigment within the batched fibre-cement slurry. The use offinely milled carbon black, sufficiently mixed with water such that particle and/or agglomerate size of the carbon black does not exceed ~ 0.1mm in size, has been found to provide even colouration offibre-cement panels, produced in accordance with the present disclosure.

In some embodiments of the method, the pigment-bearing slurry may be agitated immediately prior to the batching operation. As noted above, carbon black particles may exhibit a tendency to agglomerate or flocculate within the pigment bearing slurry. In some cases, a portion of the suspended carbon black particles present in an already mixed pigment-bearing slurry may also settle (i.e. to the bottom of the pigment-bearing slurry), thereby reducing the amount of carbon

12145308_1 (GHMatter) P112870.AU.1 black pigment effectively dispersed or suspended within the pigment-bearing slurry.

Both flocculation/agglomeration and settling of the carbon black particles may lead to less than optimal dispersion of carbon black pigment within the batched fibre-cement slurry and the autoclaved panels. Flocculation/agglomeration and settling of suspended carbon black particles are time-dependent processes, particularly in relatively low-viscosity, water-based pigment-bearing slurries in accordance with the present disclosure. It has been found that additional agitation or mixing of the pigment-bearing slurry immediately prior to introduction of the fibre-cement slurry, can serve to re-suspend carbon black particles that may have flocculated, agglomerated or settled out of suspension. As above, such mixing may be achieved by manual application of stick-style mixers (where open containers of pigment-bearing slurry are employed), or by use of mixing units fitted to closed vessels, such as an intermediate bulk container (IBC) for example.

The expression "immediately prior to the batching operation" should be understood to indicate that the additional or supplementary mixing of the pigment-bearing slurry is carried out as close to the time of the batching operation as possible, in order to ensure that the pigment is adequately dispersed throughout the pigment-bearing slurry and/or that the pigment is suspended throughout the pigment-bearing slurry, whereby the pigment becomes distributed throughout the cementitious slurry, and whereby the autoclaved fibre-cement panel is coloured in the mass by the pigment. In this regard, mixing of the pigment-bearing slurry may be carried out continuously until the pigment-bearing slurry is passed to the batching operation (where less vigorous, but continuous mixing may be maintained) and/or may be conducted in the batching stage of the process, prior to the introduction of the cement. The pigment-bearing slurry may be mixed or stirred for at least about 15 minutes to 20 minutes for example, prior to batching with the fibre-cement slurry, to ensure optimal pigment suspension. It will be understood by a person of skill in the art that the optimal time for supplemental mixing of the pigment-bearing slurry, prior to batching, will depend on a range of

12145308_1 (GHMatter) P112870.AU.1 factors including pigment-bearing slurry composition or loading, fibre-cement slurry composition, temperature, downstream Hatschek processing speed, etc.

In some embodiments of the method, the autoclaved panel may comprise 0.1 to 3% carbon black by weight of the panel. By varying the amount of pigment bearing slurry that is batched with the fibre-cement slurry in the batching process (and/or the pigment loading of the pigment-bearing slurry), the amount of carbon black pigment present in the autoclaved panels may be controlled. This level of control may allow panels exhibiting a range of depths of colour to be produced, for example from the 'off-white' or cream colour typical ofuncoloured fibre cement panels, through various shades of grey and even black. The colour of the panels may be assessed or measured by any means known in the art, for example, by use of a colourimeter.

In some embodiments of the method, the fibre-cement slurry may comprise cellulose fibres. The cellulose fibres may be batched with the pigment-bearing slurry prior to the addition of cement, which may cause the pigment within the pigment-bearing slurry to substantially adhere to the cellulose fibres, whereby the cellulose fibres may act as carriers for the pigment. In this regard, the pigment carrying fibres may aid in the distribution of pigment within the batched fibre cement slurry.

In some embodiments of the method, the fibre-cement slurry may comprise aluminium trihydrate. Aluminium trihydrate may act as a nucleating agent during curing of the fibre-cement panels. In this regard, where the panels are autoclaved, aluminium trihydrate may act as a nucleation site for crystals forming in the fibre cement panel during curing at elevated temperature. Such crystals may include tobermorite crystals for example. The presence of aluminium trihydrate may increase the number of such nucleating crystals, whereby the movement and/or ingress of water within the finished fibre-cement panels in use may be impeded. This may in turn mitigate deleterious effects of exposure of the panels to the elements (i.e. particularly for external use, where rain, dew etc. may be

12145308_1 (GHMatter) P112870.AU.1 encountered), such as unwanted expansion, contraction and/or warping of the panels. Aluminium trihydrate may also react with the cement during production of the panels, thereby improving the strength of the cured fibre-panels.

In some embodiments, the method may further comprise the step of surface finishing the fibre-cement panel by means of a sanding process. The sanding process may serve to remove a portion (or all) of any efflorescence product that may have formed during curing of the fibre-cement panels i.e. during air curing and/or autoclave curing. Curing of the formed fibre-cement panels involves both the hardening of the cementitious matrix and a removal of excess process water from the panels, via evaporation through the panel surfaces. Both air-cured and autoclave-cured fibre-cement panels may be prone to the effects of efflorescence during curing, generally resulting from the deposition of crystalline salts on the surfaces of the fibre-cement panel by the drying water, which can produce a white, powdery appearance on the panel surfaces. This effect is typically considered visually unappealing, and is often removed by sanding or other surface finishing processes. In this regard, the mass or integral colour of panels produced in accordance with the present disclosure can allow for improved flexibility in such sanding or finishing processes, as the even colouration throughout the panel may permit removal of surface material to various depths, exposing underlying material of similar colouration to that of material nearer the panel surfaces.

In some embodiments, the sanding process may be performed so as to leave a portion of the panel un-sanded. In this regard, the various grey to black colouration that may be achieved with panels produced according to the present disclosure may provide an aesthetically pleasing contrasting effect with the typically white/cream-coloured efflorescence products that form on the panel surfaces during curing. Sanding and other finishing processes may be employed to enhance this contrast by more lightly removing only portions of efflorescence products, as opposed to more deep/complete sanding or finishing to remove substantially all of the efflorescence product, as is typical for conventional fibre cement panels.

12145308_1 (GHMatter) P112870.AU.1

In some embodiments, the method may further comprise the step of applying a silane-based coating to the panel. Silane-based coatings may be applied to all surfaces of the panel (i.e. both major and minor panel surfaces), whereby the coating can penetrate into the surfaces of the panel (for example, to a depth of around 3mm from the panel surfaces). The silane-based coating may act as a waterproofing agent for the panels, acting to impede the ingress of water into the panels in use and thereby limiting unwanted shrinkage, expansion or warping of the panels. The silane-based coating may further be UV resistant.

Also disclosed is an autoclaved fibre-cement panel produced by a method in accordance with the present disclosure.

In a further aspect, there is disclosed an autoclaved fibre-cement panel, the panel formed from a cementitious slurry comprising a cementitious matrix, cellulose fibres and a pigment. The pigment can be distributed throughout the cementitious slurry by means of a pigment-bearing slurry, such that the autoclaved fibre cement panel is coloured in the mass by the pigment.

In some embodiments, the pigment-bearing slurry may comprise 0.1% to 30% carbon black by weight of the pigment-bearing slurry, the balance of the pigment bearing slurry comprising water.

In some embodiments, the pigment-bearing slurry may comprise particles suspended in the slurry, the particles having a maximum size of less than 0.1mm.

In some embodiments, the autoclaved panel may comprise 0.1 to 3% carbon black by weight of the panel.

In some embodiments, the autoclaved panel may be surface finished.

In some embodiments, the panel may comprise 7% to 9% cellulose fibres by weight of the panel.

12145308_1 (GHMatter) P112870.AU.1

In some embodiments, the panel may comprise cement 33-36%, silica 50-55%, aluminium trihydrate 24% by weight of the panel.

In some embodiments, the panel may have a modulus of rupture of at least 18MPa, as determined according to AS2908.2.

In a yet further aspect, there is disclosed a coloured, autoclaved fibre-cement panel, the panel formed from a cementitious slurry comprising a cementitious matrix, reinforcing fibres and pigment, wherein the pigment is present in the panel in an amount equivalent to 0.1 to 3%, by weight of the panel.

The coloured, autoclaved fibre-cement panel of the yet further aspect can be otherwise as set forth above, and can be produced according to the method of manufacturing as set forth above.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described, by way of example only, with reference to the accompanying drawings in which:

Fig. 1 shows a flow diagram for an embodiment of a method for manufacturing coloured fibre-cement panels;

Fig. 2 shows various embodiments of pigment-bearing slurries, produced in accordance with the present disclosure;

Fig. 3 shows an embodiment of mixing arrangements for the pigment bearing slurry;

Fig. 4 shows an embodiment of the batched fibre-cement slurry;

Fig. 5 shows a further embodiment of the batched fibre-cement slurry;

Fig. 6 shows an embodiment of a part of the Hatschek process unit, including the forming roller;

12145308_1 (GHMatter) P112870.AU.1

Fig. 7 shows an embodiment of a press for the pressing of green Hatschek sheets;

Fig. 8 shows an embodiment offibre-cement blocks, produced in accordance with the present disclosure;

Fig. 9 shows an embodiment offibre-cement panels, produced in accordance with the present disclosure;

Figs. 10 and 11 show experiment results for mechanical testing of panels produced according to embodiments of the present disclosure; and

Fig. 12 shows embodiments of panels produced according to the present disclosure, having been subjected to various sanding procedures.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

In the following detailed description, reference is made to accompanying drawings which form a part of the detailed description. The illustrative embodiments described in the detailed description, depicted in the drawings and defined in the claims, are not intended to be limiting. Other embodiments may be utilised and other changes may be made without departing from the spirit or scope of the subject matter presented. It will be readily understood that the aspects of the present disclosure, as generally described herein and illustrated in the drawings can be arranged, substituted, combined, separated and designed in a wide variety of different configurations, all of which are contemplated in this disclosure.

Disclosed herein is a method of manufacturing a coloured, autoclaved fibre cement panel. Also disclosed is a coloured, autoclaved fibre-cement panel.

An exemplary formulation for preparing fibre-cement panels according to the present disclosure, including various ranges of additives in weight percent of dry ingredients, is set out in Table 1. The general formulation provided in Table 1 can be used in the manufacture offibre-cement panels or boards of approximately

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10mm thickness for example, in accordance with the process flow diagram shown in Figure 1. More specific example compositions are set out in the Examples below.

Table 1

Component Indicative wt.% Range

Silica 50-55

Cement 33-36

Cellulose Fibre 7-9

Aluminium Trihydrate - Al(OH) 3 2-4

Carbon Black 0-3

The ranges provided in Table 1 are indicative ranges of additives suitable for inclusion in a fibre-cement slurry for manufacturing a coloured fibre-cement product, such as fibre-cement panels for building facades. Those skilled in the art will readily appreciate that different additives may interact in the fibre-cement slurry in different ways, and that processing conditions may alter the amount of a specific additive required. For example, it is known that the type of cement and the way in which the cement is prepared imparts different properties to the resulting slurry. It has been found that silicafineness should be closely monitored during production, as coarse silica particles may limit the maximum strength of the finished boards. Typically, the silica should meet afineness standard of>85% of the silica particles able to be passed through a 45pm sieve.

As a consequence of different properties, the amount of e.g. silica, aluminium trihydrate, carbon black, water, etc., required can vary. Further, those skilled in

12145308_1 (GHMatter) P112870.AU.1 the art will appreciate that further additives such as flocculants, defoamers, clays (including kaolin clay for example) etc. may be employed.

Those skilled in the art will also readily understand that the amount of the different additives may also be varied depending on the specific properties required of the resultant fibre-cement panels.

Figure 1 details a flow diagram of afibre-cement production line 10. Raw material inputs include cement 12 (such as Portland cement), silica or fine grain sand 14, other additives 16 and process water 18, which are passed to a batching tank 22. The sand 14 is milled in a ball mill 20, before being passed to the batching tank 22, such that approximately 85% of the milled sand particles are able to be passed through a 45pm sieve. Cellulose fibres are prepared in a pulping mill 24, from a source of wood pulp 26. One suitable cellulose fibre precursor is an unbleached Kraft fibre cement pulp feed, commercially available from Oji Fibre Solutions under the trade name K25

The cellulose fibres are fibrilised in a refiner 28 to improve fibre adherence to the cement slurry, then transferred to a holding tank or pulp chest 30 before being passed to the batching tank 22 as required. A pigment-bearing slurry, such as a carbon black slurry at 15wt% solids in water, without other dispersants, is held in a slurry tank 32 or other suitable intermediate bulk container (IBC). The carbon black slurry is continually mixed with a mixer 34 (described in further detail below, with reference to Figures 2 and 3), before being passed to the batching tank 22. With the cellulose fibres and carbon black slurry batched, silica and alumina (in the form of aluminium trihydrate) are passed to the batching tank 22.

In practice, the cement may be the final component to be added to the batching tank 22, which may be an advantage in the event ofunexpected stoppages of the production line (i.e. reducing the risk of cement setting in various parts of the process).

The carbon black slurry used may be any suitable commercially available water/carbon black slurry, such as supplied by Cathay Industries Australasia

12145308_1 (GHMatter) P112870.AU.1 under the trade name Cathaytint Black 15, which is an aqueous slurry of ball milled elemental carbon supplied at approximately 15% carbon by weight of the slurry. The slurry is prepared such that the maximum particle/agglomerate size present in the slurry is below 0.1mm, prior to addition in the batching operation.

Where a carbon black slurry is produced by mixing dry carbon black and water, the carbon black may be in any suitable form such as a fine powder, for example as supplied by Cathay Industries Australasia under the trade name PowCarbon 5319F. Such powders may be used to produce carbon black slurries having a range of carbon black loadings, such as 0.1% to around 30% carbon black by weight of the slurry. The person of skill in the art will understand that the desired carbon black loading of the pigment-bearing slurry may be any suitable amount, and will depend on the particular processing parameters used to mix the pigment bearing slurry.

Figure 2 a. illustrates a 15wt% carbon black slurry, exhibiting a poor suspension of carbon black pigment due to settling-out of the carbon black particles, with a portion of the carbon black particles 76 having settled to the bottom of the container, reducing the amount ofuseful carbon black 78 remaining in suspension. In accordance with the present disclosure, carbon black slurries are stirred to suspend settled carbon black, prior to batching of the pigment-bearing slurry. Referring to Figure 3, for open-top vessels containing the carbon black slurry, a stick-style mixer 80, such as the Ultramix Ul supplied by Silverson, may be used to vigorously mix the slurry prior to batching (Figure 3 a.). For closed vessels such as an intermediate bulk container or IBC 82, a mixing unit 84 fitted to the container 82 is preferred (Figure 3 b.), allowing the pigment-bearing slurry to be continuously mixed, even while in transit to the batching tank (e.g. while being transported via a forklift).

Such stick-style mixers 80 and mixing units 84 may also be used to produce carbon black slurries of various loadings, using dry carbon black and water as described above. In this regard, carbon black powder and water may be added

12145308_1 (GHMatter) P112870.AU.1 directly to the batching tank 22 illustrated in Figure 1 and mixed to a produce a suitable suspension, prior to introducing further components (e.g. cement, fibre, silica, etc).

Figures 2 b. to 2 d. illustrate examples of mixed carbon black slurries having various loadings of carbon black. Figures 2 b. and 2 c. illustrate well-mixed carbon black slurries, having carbon black loadings of 15% and 23% by weight, respectively. In contrast, Figure 2 d. illustrates an insufficiently mixed slurry with a carbon black loading of 33% by weight. The carbon black slurry illustrated in Figure 2 d. has a lumpy/grainy appearance, indicative of large agglomerates of carbon black particles. Such large agglomerates (for example, agglomerates greater than 0.1mm in size) have been found to lead to inefficient distribution of carbon black in fibre-cement slurries and resulting panels, producing uneven colouration and/or 'black spotting' in thefinished panels.

The carbon black slurry should be continuously mixed before batching (for example, prior to being passed to the batching operation), and preferably immediately prior to batching with the cement, to ensure a suitable suspension of carbon black is maintained in the fibre-cement slurry. For an approximately 15 wt.% carbon black slurry, the slurry should be stirred/mixed for a minimum mixing time of around 15 minutes, prior to being pumped to the batching tank 22.

Referring again to Figure 1, gentle mixing of the combined ingredients is carried out in the batching tank 22 by means of a batch mixer 36 (further illustrated in Figure 4), to produce a homogeneous mixture of the pigment-bearing and fibre cement slurries. Mixing conditions within the batching tank 22 are controlled so as to maintain laminar mixing of the batched slurry (illustrated in Figure 5), preventing unwanted air entrainment. The batched slurry is mixed to produce and maintain a relatively homogenous fibre-cement mixture (i.e. significant agglomeration or settling is avoided), whilst air entrainment is minimised. In this regard, good dispersion of the carbon black pigment in the pigment-bearing

12145308_1 (GHMatter) P112870.AU.1 slurry, prior to passing of the pigment-bearing slurry to the batching tank 22, is important.

Referring again to Figure 1, the batcher 22 can provide 'just-in-time' delivery of slurry for the continuous production of green fibre-cement sheet by the downstream Hatschek process unit 42. Typical solids density of the batched slurry may be approximately 20 wt.% to 30 wt.%. Batching may be conducted by means of weight batching, volume batching or a combination of both methods.

The batched fibre-cement slurry is passed to a feed agitator 38 for short-term storage prior to use in the downstream Hatschek process unit 42 for panel formation. The feed agitator 38 comprises a ribbon mixer 40 which gently maintains a homogeneous suspension of the slurry, preventing for example agglomeration of the less-dense carbon black pigment or cellulose fibres, or settling of the relatively more-dense cement or silica. Batch residence time within the feed agitator 38 may typically be in the order of minutes, for example up to around 20 to 45 minutes, but should not exceed about 90 minutes. Beyond this residence time, the binding effect of the cement may degrade to unacceptable levels and reduce the strength of the finished fibre-cement panels. In order to form green fibre-cement panels, the fibre-cement slurry is passed through a series of pre-mixers 44, 46 to ensure optimum homogeneity of the slurry prior to passing the slurry to the Hatschek process unit 42. Afirst pre-mixer 44 mixes recycled water (from upstream within the Hatschek process) with the batched slurry, the recycled water passed along with a solids underflow from separation tank 56 as described below. Sufficient recycled water is added in the first pre-mixer 44 to reduce the solids loading of the slurry from about 20-30% to about 5-10% by weight of the slurry. A second pre-mixer 46 maintains the consistency of the fibre-cement slurry to be passed to the Hatschek process unit 42. The second pre mixer 46 may be positioned so as to allow thefibre-cement slurry to be passed to the Hatschek process unit 42 under gravity, providing consistent pressure and flow rate of the slurry.

12145308_1 (GHMatter) P112870.AU.1

The homogenised slurry is then passed to the Hatschek process unit 42, which includes a series of slurry tanks 48. Cylindrical sieves 50 partially immersed in the slurry tanks 48 are rotated to accumulate solid material from thefibre-cement slurry (i.e. a substantially homogeneous mixture of cement, cellulose fibres, carbon black pigment, etc.) and pass this material to a conveyor belt 52. The conveyor belt 52 may be of a felt or felt-like material to aid adherence of the solid fibre-cement mixture to the belt. Excess water is drained from the accumulating solid portions of the fibre-cement slurry through both the rotating sieves 50 and the conveyor belt 52, with this excess water draining to form an underflow stream 54. The underflow stream 54, which also contains some amount of cement, cellulose fibre, carbon black pigment and other solids is passed to a separation tank 56 which separates solids from the process water, allowing the filtered water to be passed back to the process water tank 18 and recycled for following batches of fibre-cement slurry, with the solids underflow from tank 56 passed to the first pre-mixer 44.

The draining solid material collected by the belt 52 is then passed onto a forming roller 58, where multiple layers offibre cement material are progressively accumulated and further dewatered. A layer cutter 60 may be employed to facilitate cutting of the green fibre-cement sheet 62. Cutting of the green fibre cement sheet 62 by layer cutter 60 may also aid in continuous pick up of the following thin layers of fibre-cement material to the forming roller 58 (as further illustrated in Figure 6). When sufficient material or layers offibre-cement have been accumulated on the forming roller 58 to achieve a desired thickness (around 6mm for example), a wire cutter 64 sections the green fibre-cement sheet 62, which may have a green sheet moisture content of approximately 28-34% water by mass of the sheet. The sectioned green fibre-cement sheets are trimmed to a suitable size by means of a trimming stacker operation 66 and passed to a press 68, where stacked green sheets 70 are pressed to remove further water (illustrated in Figure 7) and to form greenfibre-cement panels 72. Suitable pressing conditions include loads of 1.7 - 3.0 kN/m2 for approximately 30 to 45 minutes.

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Multiple green sheets may be stacked between steel templates prior to pressing, such that the stacked green sheets are compressed together in the pressing operation to form a single, laminated fibre-cement panel. In this way, the thickness of the resulting green panel may be varied by varying the number of green sheets stacked between the templates. For example, 9mm thick compressed green fibre-cement panels can be formed by pressing a stack of two 6mm thick green fibre-cement sheets between the steel templates (and 18mm thick panels can be produced by compressing four 6mm green fibre-cement sheets, etc), where a volume reduction of about 20% is employed.

The green panels are compressed to have a 'bone dry density' of around 1.65g/cm 3 and are pre-cured at 50 to 55°C for 8 to 12 hours, allowing the cement to partially harden and the panels to gain a portion of theirfinal strength. Herein, the term 'bone dry density' refers to a density measured for a panel in which substantially all of the free water (i.e. water not chemically bonded within the fibre-cement) has been evaporated. The pre-cured panels are then passed to an autoclaving process 73 for further thermally-assisted curing at 180°C for 8 to 14 hours.

The autoclaved fibre-cement panels are then passed to a finishing line 74, where the panels are trimmed to final dimension using a water saw. Surface treatments including sanding and application of any surface coatings (such as clear silane based coatings) is also carried out. Where a silane coating or sealer is applied, the coating is applied to all surfaces of the panel and allowed to cure for 3 to 7 days prior to storage or shipping of thefinished panel.

Examples

Non-limiting examples will now be described. Example 1 outlines exemplary coloured fibre-cement compositions of the present disclosure and Example 2 describes the physical properties of panels according to the present disclosure that are produced using the compositions of Example 1, to exemplify their suitability to form coloured fibre-cement panels that meet relevant building

12145308_1 (GHMatter) P112870.AU.1 standards. Example 3 outlines an exemplary surface finishing process for autoclaved panels of the present disclosure.

Example 1

Fibre-cement slurry compositions 0 to 4 (as shown in Table 2) were prepared in accordance with the present disclosure. Sample fibre-cement panels were also produced using slurry compositions 0 to 4, in accordance with the present disclosure. Suitable amounts of carbon-black slurry, prepared in accordance with the present disclosure, were batched with fibre-cement slurries to produce panels containing the amounts of carbon black indicated in Table 2.

In accordance with the present disclosure, the carbon black slurry was mixed as close as possible in time to the batching stage (e.g. immediately prior to being added/pumped to the batching tank). Typically, the carbon black slurry was mixed for at least 15 minutes prior to batching. It was observed that this resulted in an optimal suspension of the carbon black in thefibre-cement slurry.

Where the carbon-black slurry was prepared in an open-top vessel, a stick style mixer (e.g. the Silverson Ultramix U1) was used to vigorously mix the slurry prior to batching.

Conversely, where the carbon-black slurry was supplied in a closed vessel (e.g. an intermediate bulk container), a mixing unit was fitted to the IBC and the pigment-bearing slurry was vigorously mixed, even while in transit to the batching tank, and even during pumping to the batching tank.

The compositions shown in Table 2 below indicate the weight percentage of each component, given as a percentage of the total dry weight of the components.

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Table 2

Designation Cellulose Fibre Cement Silica Al(OH) 3 Carbon wt. % wt. % wt. % wt. % Black wt.%

0 8.5 35.2 54.1 2.0 0.0

1 8.5 35.2 53.9 2.0 0.2

2 8.5 35.2 53.7 2.0 0.6

3 8.5 35.2 52.3 2.0 2.0

4 8.5 35.2 51.1 2.0 3.0

Fibre-cement slurry compositions within the ranges outlined above were observed to be suitable to produce fibre-cement panels that were coloured in the mass, in accordance with the present disclosure. Such compositions were able to produce fibre-cement panels having both sufficient colour depth/homogeneity and adequate strength characteristics (refer Example 2).

With regard to colour characteristics, illustrative examples of fibre-cement blocks (Figure 8) and panels (Figure 9) produced using compositions 0 to 4 indicate that an aesthetically pleasing range of colours may be produced.

Example 2

The mechanical properties of approximately 9mm-thick panels made from compositions 1 to 4 were tested according to AS2908.2, with the panels conforming to the Type A, Category 5 requirement for 'wet condition sheet strength', exhibiting a minimum modulus of rupture (MOR) of greater than 18 MPa, as illustrated in Figures 10 and 11. As indicated in Figures 10 and 11, the

12145308_1 (GHMatter) P112870.AU.1 panels were tested in both the perpendicular and parallel directions, relative to the long-axis of Hatschek fibre-cement sheet formation for the panels.

Example 3

Coloured, autoclaved fibre-cement panels produced in accordance with the present disclosure were surface finished by a sanding process to selectively remove portions of efflorescence products that formed on the major surfaces of the panels during the air and autoclave curing steps. Referring to Figure 12, the stacked autoclaved panels (Figure 12 a.) were passed to a conveyor belt which carried the panels to pass under an online roller belt sander. The panels were passed under the belt sander multiple times, with varying grades of sanding media/paper used to obtain the desired surface finish. In some cases, it was desirable to remove substantially all of the efflorescence product by thorough sanding of the panels. Figure 12 d. for example, illustrates a typical 'fully sanded' panel which has undergone an initial five to six pass sanding step using 40 grit sand paper for each pass, followed by a final pass sanding step using 60 grit sand paper. 'Fully sanded' panels, having a smoother surface finish, were found to reflect a higher proportion of diffuse light, thereby altering the appearance of the panels. Sanding of the panels typically reduced the panel thickness from around 10mm thickness to around 9mm thickness.

Figures 12 b. and 12 c. illustrate panels that were sanded so as to leave a portion of the efflorescence product intact on the surface of the panel. The panel of Figure 12 b. underwent two passes using 30 grit paper for each pass, while Figure 12 c. illustrates a panel that underwent two passes using 36 grit sand paper for each pass. In Figure 12 c., it can be seen that regions of darker sanded areas 80 and pockets of light-coloured un-sanded regions 82 are present on the panel surfaces. The more heavily sanded, darker regions exhibit more closely the mass or through thickness colour of the panels, imparted by the carbon black pigment. The contrast between the darker panel and the lighter coloured efflorescence product can give an aesthetically pleasing natural or 'bark-like' appearance.

12145308_1 (GHMatters) P112870.AU.1

A person of skill in the art will appreciate that many intermediate levels of sanding may be applied, on order to produce panels of a desired surface finish.

Variations and modifications may be made to the parts previously described without departing from the spirit or ambit of the disclosure.

In the claims which follow and in the preceding description, 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, 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 method and panel.

12145308_1 (GHMatter) P112870.AU.1

Claims

1. A method of manufacturing a coloured, autoclaved fibre-cement panel, the method comprising the steps of:

a. providing a pigment-bearing slurry and a fibre-cement slurry;

b. agitating the pigment-bearing slurry to disperse the pigment within the pigment-bearing slurry, prior to introducing the pigment bearing slurry to the fibre-cement slurry in a batching operation;

c. passing the batched slurry resulting from the batching operation to a Hatschek fibre-cement forming process to obtain a coloured fibre-cement panel;

d. pressing the fibre-cement panel; and

e. autoclaving the fibre-cement panel.

2. A method according to claim 1, wherein the pigment-bearing slurry comprises carbon black and water.

3. A method according to claim 1 or claim 2, wherein the pigment-bearing slurry comprises 0.1% to 30% carbon black by weight of the pigment-bearing slurry, the balance of the pigment-bearing slurry comprising water.

4. A method according to any one of the preceding claims, wherein the pigment-bearing slurry comprises particles suspended in the slurry, the particles having a maximum size of less than 0.1mm.

5. A method according to any one of the preceding claims, wherein the pigment-bearing slurry is agitated immediately prior to the batching operation.

6. A method according to any one of the preceding claims, wherein the autoclaved panel comprises 0.1 to 3% carbon black by weight of the panel.

12145308_1 (GHMatter) P112870.AU.1

7. A method according to any one of the preceding claims, wherein the fibre cement slurry comprises cellulose fibres.

8. A method according to any one of the preceding claims, wherein the fibre cement slurry comprises aluminium trihydrate.

9. A method according to any one of the preceding claims, further comprising the step of surface finishing the coloured, autoclaved fibre-cement panel by means of a sanding process.

10. A method according to claim 9, wherein the sanding process is performed so as to leave a portion of the panel un-sanded.

11. A method according to any one of the preceding claims, further comprising the step of applying a silane coating to the panel.

12. A coloured, autoclaved fibre-cement panel produced by the method set out in any one of claims 1 to 11.

13. A coloured, autoclaved fibre-cement panel, the panel formed from a cementitious slurry comprising a cementitious matrix, fibres and a pigment, wherein the pigment is distributed throughout the cementitious slurry by means of a pigment-bearing slurry, such that the autoclaved fibre-cement panel is coloured in the mass by the pigment.

14. A panel according to claim 13, wherein the pigment-bearing slurry comprises 0.1% to 30% carbon black by weight of the pigment-bearing slurry, the balance of the pigment-bearing slurry comprising water.

15. A panel according to claim 13 or claim 14, wherein the pigment-bearing slurry comprises particles suspended in the slurry, the particles having a maximum size of less than 0.1mm.

16. A panel according to any one of claims 13 to 15, wherein the autoclaved panel comprises 0.1 to 3% carbon black by weight of the panel.

12145308_1 (GHMatter) P112870.AU.1

17. A panel according to any one of claims 13 to 16, wherein the autoclaved panel is surface finished.

18. A panel according to any one of claims 13 to 17, wherein the panel comprises 7% to 9% cellulose fibres by weight of the panel.

19. A panel according to any one of claims 13 to 18, wherein the panel comprises 33-36% cement, 50-55% silica, and 2-4% aluminium trihydrate by weight of the panel.

20. A panel according to any one of claims 13 to 19, wherein the panel has a modulus of rupture of at least 18MPa, as determined according to AS2908.2.

21. A coloured, autoclaved fibre-cement panel, the panel formed from a cementitious slurry comprising a cementitious matrix, reinforcing fibres and pigment, wherein the pigment is present in the panel in an amount equivalent to 0.1 to 3%, by weight of the panel.

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