Method for producing cured polymeric skins

Abstract

A method of forming a masonry-effect polymeric skin comprises the steps of: providing a frame 2 having a plurality of openings shaped to receive a masonry tile 4, each opening including an elastomeric

Description

Field of the invention This invention relates to the production of masonry-effect polymeric skin materials. In particular, the invention relates to methods for the production of masonry-effect polymeric skin materials for use, for example, in building and as architectural components for example in roofing materials such as roofing tiles, or for brick wall effect materials. Background to the Invention Panels and other elements used in building have traditionally been made of natural materials. For example, structures formed from masonry have traditionally been constructed from masonry blocks which are generally laid in and bound together by mortar, in some cases with steel reinforcement. Such structures are generally highly durable, resistant to weathering, have good weight-bearing properties, and are also visually appealing, making masonry a widely-used construction material. However, masonry does have the disadvantages that masonry blocks are heavy, time-consuming to install, and can be extremely costly. Particularly in the case of stone blocks, such as granite or marble, only a small portion of the expensive stone is visible in use, making the use of entire blocks of such stone types unnecessary and economically prohibitive. Furthermore, traditional masonry construction techniques do not have the architectural flexibility that is found with more modern construction techniques, such as steel or concrete frame buildings. For instance, masonry construction techniques are generally unsuited to the construction of very tall buildings due to the weight of the masonry blocks. There has been interest in developing techniques to overcome the disadvantages of traditional masonry techniques, whilst maintaining the visual appeal and durability of traditional masonry in the completed structures. Generally, these techniques involve some kind of masonry cladding or siding. The terms “cladding” or “siding” are used to refer to a non-structural layer of masonry that is added to a pre-existing structure, such as a wall or building, usually to imitate the appearance of a traditional masonry structure. The masonry layer is generally substantially thinner than traditional masonry building blocks, being required only for visual and non-structural purposes. Thus, siding materials often take the form of a tile or slip having the surface dimensions of a brick or stone block on the visible surface but are typically between 10 to 50 mm in depth. For example, brick siding is generally applied by using individual brick slips and applying them to structures (such as building facades) by being embedded in a layer of mortar coating the surface of the structure or otherwise stuck to a surface of the building, occasionally with the use of guide rails (such as a plastic or metal frame) to maintain even spacing between the brick slips. Mortar is then pointed around and between the brick slips to provide a brickwork pattern. The use of siding materials, whilst having some advantages over traditional masonry construction techniques, nonetheless has the disadvantage that the installation of large numbers of separate tiles remains comparatively time consuming, particularly where the materials still require pointing. There is now a trend for building elements and other products which would traditionally have used natural products to be made from “non-natural” or synthetic products, for example plastics materials. Such modem materials have many chemical, physical and cost advantages compared with traditional materials. Resin skin panels of the kind comprising a polymeric cured skin, for example, a sheet moulding compound (SMC) can be employed in the building industries because of the wide range of useful properties achievable. Increasingly surface effects have been added to the skin material to form, for example, simulated surfaces such as a simulated stone surface, ora brick wall. In a known method of forming panels, the panels comprise a pair of outer skins and an internal foam core. The skin or skins and the foam core are formed separately and may then be bonded together, usually by means of an adhesive. In known systems, the skins may be formed by compression moulding of a SMC. The SMC includes a thermosetting resin, for example a polyester resin, together with reinforcing fibres, for example glass fibres. The SMC is folded to form a block of charge and placed into a preheated moulding cavity. The mould is closed and pressure is applied to press the moulding compound so that it spreads to all parts of the mould. Heat and pressure is applied until the moulded material has cured. There are disadvantages associated with forming the SMC skins using such a method. For example, the SMC needs to be folded to form a block in the mould cavity. Thus, high pressure is required to affect the moulding; pressures of 1000 to 1200 tonnes per m2 are not unknown. Another disadvantage associated with known methods of forming cured skins is that the skin damages the mould whilst curing so that it cannot be reused. Specifically, the skin stretches the mould during curing, or if a surface decoration is present, this may scratch the mould and causes damage to it- both of these disadvantages prevent the mould being reused. To try and alleviate these problems, other methods have been sought. In another known method of forming polymeric skin panels, a sheet of sheet moulding compound is applied to cover a template. Masonry tiles are placed directly on top of the sheet of sheet moulding compound and a layer of particulate sand is arranged on top. The layers are then pressed together such that the masonry tiles and sand are embedded into the sheet moulding compound. However, there are disadvantages associated with forming polymeric skin panels using such a method. For example, as the masonry tiles often do not have exactly the same depth, this method can cause uneven surface finishes. Additionally, taller masonry tiles are put under a greater amount of pressure, thus subjecting the tiles to greater strain which can cause cracking of the tiles. Another disadvantage is that thinner masonry tiles are typically more brittle and therefore can also be at risk ofcracking under the large pressures required by typical methods. There remains a need in the art for an alternative process for the production of a polymeric cured skin, which seeks to alleviate or reduce one or more of the issues discussed above. Summary of the Invention According to the present invention, there is provided a method of forming a masonry-effect polymeric skin, the method comprising: i) providing a frame comprising a plurality of openings shaped to receive a masonry tile, each opening comprising an elastomeric material which acts as a cushion within the opening; ii) providing a layer comprising a sheet-form material having reinforcing fibres, the sheet-form material comprising a curable material; and iii) providing a masonry tile; the method comprising the step of applying the layer of sheet-form material onto the frame, applying the masonry tile onto the layer of sheet-form material within an area of the openings, and applying pressure to press the masonry tile and the sheet-form material to form the masonry-effect polymeric skin. Also provided in accordance with the present invention is a masonry-effect polymeric skin formed by the process disclosed herein. Such masonry-effect polymeric skins comprise a skin of sheet-form material having reinforcing fibres, the sheet-form material comprising a masonry tile bonded to a surface of the skin of sheet-form material, and wherein at least a part of the sheet-form material has flowed into grooves or around protrusions on the surface of the masonry tile, or into spaces in the coarse structure of the masonry tile. The masonry surface effect can provide a desirable aesthetic finish to the product and / or provide durability to the product. The methods of the present invention may be advantageous in a number of respects. For instance, it has surprisingly been found that the use of an elastomeric material within the frame openings controls the depth to which the masonry tiles are embedded into the sheet form material. This in turn allows for masonry tiles with different thicknesses to be used within the same apparatus. Accordingly, where multiple masonry tiles are used in a single product, a masonry-effect polymeric skin that has a uniform surface height of masonry tiles can advantageously be produced. This provides a more efficient process as it removes the requirement of assuring that the masonry tiles are of the same thickness. The process also removes the need for any additional steps of levelling the polymeric skin after it has been made, such as by sanding. Therefore, the process of the present invention takes less time. Additionally, the combination of a frame and elastomeric material advantageously allows for controlling the depth of the masonry tile and grout lines between the adjacent masonry tiles to provide a variety of different patterns. As used herein, the term “masonry tile” is intended to refer to a tile formed, at least in part, from concrete, clay, natural stone, artificial stone, ceramic, glass, ora combination thereof. For example, the masonry tile may be formed from brick, marble, granite, limestone, travertine, sandstone, slate, cast stone, porcelain, earthenware, glass, or other similar materials, or a combination thereof. Where the masonry tile is formed from a porous material such as clay, porcelain or earthenware, it may be at least partially glazed. For example, the visible surface may be glazed, with the surface that contacts the sheet-form material remaining unglazed. As will be appreciated by persons of skill in the art, an unglazed surface provides a better key for attachment to the sheet-form material and is therefore preferable to form a strong bond. The masonry tile may extend over substantially all or only a part of the sheet-form material and / or the frame area. Preferably, a plurality of masonry tiles is provided which collectively extend over substantially all or only a part of the sheet-form material and / or the frame area. In this way, the plurality of masonry tiles may be rigidly bonded onto the surface of the sheet-form material in any desired arrangement. For example, the plurality of masonry tiles may be arranged so as to imitate the arrangement of masonry building blocks found in traditional masonry construction techniques, such as the traditional brickwork bonds (e.g. Flemish bond, stretcher bond, English bond, header bond, herringbone bond and basket bond). The depth of the masonry tile is preferably less than 50 mm, more preferably less than 30 mm, and still more preferably less than 20 mm. Generally, a depth of at least 5 mm is preferred for reasons of durability, although with smaller masonry tiles the depth may be less than 5 mm, for example from 2 to 5 mm, e.g., 3 mm or 4 mm. Suitably, the masonry tile has a depth in the range of from 3 to 50 mm, more preferably from 3 to 30 mm, for example from 5 to 30 mm, or 5 to 20 mm. Generally, the surface area of the masonry tile will not be greater than about 500 mm by 500 mm. However, the exact size of the masonry tile depends on the type of material used to form the masonry tile and the desired visual effect of the polymeric skin product. For instance, where the polymeric skin product is intended to look like a brick wall, the masonry tiles advantageously have a surface area of from about 190 mm to about 250 mm by about 55 to about 75 mm to simulate the dimensions of a major side face of a standard building brick. Alternatively, the masonry tile may have a surface area of from about 95 to about 125 mm by about 55 to about 75 mm to simulate the dimensions of an end face of a standard building brick. For example, the masonry tile could be cut from a standard building block, such as a standard building brick. Alternatively, the masonry tile could be a brick slip of the type known in the art. In some embodiments, the masonry tile may be sized to fill the dimensions of the frame openings. In the United Kingdom a standard size building brick generally has a major side face of about 65 mm by about 215 mm and an end face of about 65 mm by about 102.5 mm. In the United States a standard size building brick generally has a major side face of about 57 mm by about 203 mm and an end face of about 57 mm by about 102.5 mm. Where the polymeric skin product is intended to look like a stone wall, a larger masonry tile size may be appropriate. The surface of the masonry tile that contacts the sheet-form material may be provided with surface indentations or protrusions to form a key to ensure a strong bond is formed between the sheet-form material and the masonry tile. For example, a series of parallel or crossed grooves may be provided. In some cases, however, the masonry material may have a sufficiently coarse structure that the provision of surface indentations or protrusions is unnecessary for a strong bond to be formed between the sheet-form material and the masonry tile. In accordance with the present invention, the sheet-form material having reinforcing fibres comprises a curable polymer material. Preferably, the sheet-form curable material comprises a thermosetting polymer resin matrix. For example, the thermosetting polymer resin matrix may be selected from polyester resins, vinyl ester resins, epoxy resins, phenolic resins, bismaleimide resins or polyimide resins. The layer of sheet-form curable material may comprise SMC (sheet moulding compound). The SMC preferably may include a thermosetting resin, preferably a polymer matrix as defined above, and reinforcing fibres. For example, the SMC may include a thermosetting resin, for example a polyester resin, together with reinforcing fibres, for example glass fibres. The thermosetting polymer may further comprise additives, for example minerals, inert fillers, pigments, stabilizers, inhibitors, release agents, catalysts, thickeners, hydrating additives and / or suitable materials. There are benefits in using SMC. For example, SMC has a low density, but favourable mechanical properties compared with other sheet-form materials, and also exhibits good thermal properties. Of particular importance for some applications, for example building applications, resistance to fire is good. SMC also shows good chemical resistance. The sheet-form material may also include melamine, which is useful as a fire retardant. The sheet-form material may further include additives selected from hardeners, accelerators, fillers, pigments, stabilizers, inhibitors, release agents, catalysts, thickeners, hydrating additives and / or any other components as required. With regard to the use of phenolic resins, the prior art (see for example US3,005,798, US3,663,503 and US4,369,259) teaches that in order to produce a phenolic resin with limited or reduced colour change, both a colour-stabilising agent and an acid catalyst must be present. Clearly, the requirement of both reactants will increase the costs of producing lighter coloured resins. Furthermore, as shown in some of the above-mentioned documents, the colour stabilising agent may be required to be added at a specific point in the reaction process (i.e. whilst the phenol resin is still in water-soluble form) in order to achieve the colour-stabilising effect throughout the resin formed. This creates a more complex reaction process, which will inevitably affect time efficiency and therefore, once again, cost efficiency of producing such resins. In addition, many of the methods available for producing lighter coloured phenolic resins require the presence of strong acids or bases to catalyse the reaction process. It is known that the use of such chemicals causes corrosion of equipment which will therefore need to be replaced more frequently. Therefore, in preferred embodiments, the sheet-form curable material comprises a phenolic resin sheet comprising: - uncured phenolic resin, such as a phenol-formaldehyde resin; - filler; - a catalyst in an amount of less than 2wt.% relative to the content of phenolic resin; and wherein the filler is present in a ratio of filler to uncured phenolic resin in an amount of 2.5:1 and greater, and further wherein the filler comprises a transition metal hydroxide and / or aluminium hydroxide in a ratio of metal hydroxide to uncured phenolic resin in an amount of 1:1.5 to 3:1. The phenolic compositions described herein are particularly concerned with phenolformaldehyde resins. It has been surprisingly found that the addition of a metal hydroxide compound within the filler allows forthe amount of catalyst present to be significantly reduced, and even possibly avoided altogether. Without wishing to be bound by any particular theory, it is believed that the addition of the metal hydroxide compound allows forthe uncured phenolic material to reach an equivalent of B-stage curing without the need for a catalyst to be present in any significant quantity, or even at all. As would be fully understood by persons of skill in the art, the B-stage refers to a partially cured state which allows for increased processability of such phenolic resins, for example, allowing them to be formed into sheets which may then be applied to a frame. The stability is such that the formed sheets can be formed into rolls for storage and later use. Such materials can then be fully cured by the application of heat and pressure. As discussed above, a problem with the use of traditional catalysts is the discolouration of the cured resin produced, and therefore the ability to produce polymeric skins of different colour finishes and patterns. By use of the material disclosed herein, it is possible to reduce or even alleviate such issues as the amount of catalyst can be used, and in some embodiments avoided altogether. Preferably, the amount of catalyst that is present may be less than 1 wt.% relative to the content of the phenolic resin, more preferably less than 0.5 wt.% relative to the content of the phenolic resin, such as less than 0.2 wt.%. In some embodiments, the uncured material may be substantially free of catalyst. By substantially free, it is meant that the amount of any catalyst present is negligible in terms of the overall effect that it has on uncured material, and its ability to reach a B-stage equivalent of curing. For the avoidance of any doubt, the term catalyst is intended to refer to additives which are known to catalyse the curing of such phenolic resins, and are known to aid B-stage curing. Traditionally, such catalysts fall into two main categories, namely acidic and basic. Examples of acidic catalysts include, but are not limited to, one or more of hydrochloric acid, sulphuric acid and oxalic acid. Examples of basic catalysts include, but are not limited to, one or more of ammonia, sodium hydroxide, potassium hydroxide, lithium hydroxide, rubidium hydroxide, caesium hydroxide, barium hydroxide, calcium hydroxide and ethylamine. It will also be appreciated that by reducing the presence of the catalyst material, or even avoiding its presence altogether, it is possible to avoid discolouration issues without the need to add colour-stabilising agents, for example, glyoxal, thiones, phosphinic acid salts or phosphonic acid salts. In accordance with the uncured materials described herein (including sheet-form materials in general), the filler may be present in an amount of 3:1 and greater, and preferably in an amount of 3.5:1 and greater. It will be appreciated that the amount of filler which is added is dependent, in some instances on the intended use of the polymeric skin being prepared. It will also be appreciated that there is a significant economic advantage in being able to increase the amount of filler whilst still being able to meet the stringent requirements for such polymeric skins, such as strength, modulus, fire resistance, weathering resistance etc. Accordingly, the amount of filler present may also be in an amount of 5:1 and greater where applicable. The fillers used may be organic or inorganic materials. For some embodiments, it is preferable for the filler to be an inorganic material. Suitable fillers for use in the sheet-form curable materials include particulate solids which are insoluble in the thermosetting material, such as filler selected from one or more of clays, clay minerals, talc, vermiculite, metal oxides, refractories, solid or hollow glass microspheres, fly ash, coal dust, wood flour, grain flour, nut shell flour, silica, ground plastics and resins in the form of powder, powdered reclaimed waste plastics, powdered resins, pigments, and starches. In preferred embodiments of the materials described herein, the fillers do not substantially comprise silicates and / or carbonates of alkali metals. This is due to the fact that solids having more than a slightly alkaline reaction, for example silicates and carbonates of alkali metals, are preferably avoided because of their tendency to react with acid hardeners. However, solids such as talc, which have a very mild alkaline reaction, in some cases because of contamination with more strongly alkaline materials such as magnesite, are acceptable for use as fillers. In accordance with the uncured materials described herein (which includes in general the sheet-form materials described herein), the amount of filler may be present in an amount of 20:1 and less, such as in an amount of 10:1 and less. In general, the fillers used in the sheet-form materials described herein may be any particulate solid which is insoluble in the resin mixture. As will be appreciated, it is preferable that the filler is inert to the rest of the uncured material. As discussed above, the use of the transition metal and / or aluminium hydroxide compound allows for the amount of catalyst used to be reduced, or even avoided altogether. A significant benefit of this is that issues known in the art associated with discolouration can be avoided, thus allowing for the use of pigments which previously would not have been suitable, especially for commercial uses where finishes are of great importance. It will also be understood that suitable colours may include white, yellow, pink, red, orange, green, blue, grey or purple. The reduction in catalyst and therefore the associated discolouration means that lighter colours may now be produced, for example, white, yellow, pink, red, orange, as well as light green, blue, grey and purple. The ability to produce finishes having such light colours greatly improves the commercial applications of such materials. Preferably, the transition metal or aluminium hydroxides are selected from compounds of formula M(OH)3, wherein M is a metal. Suitable metals (M) may be selected from one or more of scandium, vanadium, chromium, manganese, iron, cobalt and aluminium. In a preferred embodiment, the metal hydroxide is aluminium hydroxide. In the materials described herein, the transition metal and / or aluminium hydroxide may be present in a ratio of metal hydroxide to uncured phenolic resin in an amount of 1:1.6 to 2.5:1, such as a ratio of metal hydroxide to uncured phenolic resin in an amount of 1:2 to 2:1. In addition to the transition metal and / or aluminium hydroxide in the compositions described herein, the uncured phenolic material may further comprise ethylenediaminetetraacetic acid (EDTA). However, it is not in any way essential to the present invention. Phenolic resin materials such as described herein have significant advantages over more traditional materials such as SMC. It has been found that the phenolic resin material disclosed herein generally has the following advantages over SMC: • Better temperature performance and thermal shock resilience o The phenolic materials of the present invention can be used to form brake pads, foundry moulds, aerospace heat shields etc. • Excellent resistance to chemicals, corrosives / solvents, oil and water / salt water (including acid rain) o The phenolic materials of the present invention can be used to make laboratory countertops • Improved fire, smoke and toxicity performance o The phenolic materials of the present invention can be used in mass transport and defence applications • Improved anti-microbial properties • Harder, stronger, excellent dimensional stability • Electrical resistance • Good thermal insulation • Superior workability • Low temperature processing The sheet-form materials described herein may further comprise a viscosity controlling agent. Suitable viscosity controlling agents may be selected from one or more of butanol, chloroform, ethanol, water, acetonitrile, hexane, and isopropyl alcohol. In a preferred embodiment, the viscosity controlling agent is water. It will be appreciated that the amount of viscosity controlling agent used is dependent on the intended use of the uncured material. It is considered that the controlling of the viscosity is within the knowledge of the person of skill in the art. The sheet-form materials may be produced by mixing of the components as described above so as to form a generally homogeneous distribution of the components throughout the material. Any known method may be used to produce the general homogeneous distribution, such as high-shear mixing. The length of time required to produce a generally homogeneous distribution of the components is dependent on, amongst other things, the amount of each component added, the viscosity of the components and the method of mixing used. In general, a substantially homogeneous distribution of the components can be formed within 5 minutes to 2 days, preferably within 10 minutes to 1 day, more preferably within 15 minutes to 10 hours. The sheet-form material of the present invention comprises reinforcement fibres. The fibres may include one or more materials. For example, the fibres may include one or more of carbon fibres, glass fibres, aramid fibres and / or mixtures thereof. Preferably, the reinforcement fibres comprise or consist of glass fibres. Alternatively, the fibres may be selected from one or more of mineral fibres (such as finely chopped glass fibre and finely divided asbestos), chopped fibres, finely chopped natural or synthetic fibres, and ground plastics and resins in the form of fibres. The fibres may be added to the uncured material in a ratio of resin to fibre of 6:1 to 1:3, such as a ratio of from 4:1 to 1:1. The reinforcing fibres may be short fibres, for example having lengths of 5.0 cm or less, or may be longer fibres. The fibres may be loose, for example, the fibres may be arranged in a uni- or multi-directional manner. The fibres may be part of a network, for example woven or knitted together in any appropriate manner. The arrangement of the fibres may be random or regular, and may comprise a fabric, mat, felt or woven or other arrangement. Fibres may provide a continuous filament winding. Optionally, more than one layer of fibres may be provided. The sheet-form material may extend over substantially all or only a part of the frame area. Preferably, the sheet-form material extends over substantially all of the frame area. The thickness of the sheet-form curable material may range from 0.3 mm to 50 mm, such as 0.5 to 10 mm, for example 1 mm to 5 mm. The thickness of the sheet-form material used depends on the type and weight of the masonry tile that is used. Generally, an increased thickness of sheet-form material is preferred when heavier masonry tiles are used. The thickness of the sheet-form material may be obtained by using a single layer of sheet-form material having the required thickness, or by assembling a plurality of layers of sheet-form material until the required thickness is obtained. In addition, a mosaic of pieces of sheet-form material may optionally be used to extend over the frame or a part thereof. Preferably at least some part of the sheet-form curable material flows into a surface of the masonry tile during pressing. Preferably, the material is keyed into the masonry tile. In this way, a strong bond between the matrix and the masonry tile can be obtained. Alternatively, or in addition, adhesive material may be applied between the sheet-form material and the masonry tile to aid bonding. The frame of the present invention defines a pattern to be formed by the masonry tiles. Such a frame may be used to help position the masonry tiles when forming a skin. In the present invention, the frame is used to shape the final skin. The frame of the present invention may be made from a material selected form steel, aluminium, wood or any other suitable material. The frame comprises a plurality of openings shaped to receive a masonry tile. Each opening comprises an elastomeric material which acts as a cushion within the opening. The elastomeric material is positioned such that during the step of application of pressure to press the masonry tile and the sheet-from material together the masonry tile and sheetform material are pressed into the elastomeric material. The elastomeric material is compressible to allow the extent to which the masonry tile(s) are embedded in the sheetform material to be controlled. As such, a variety of masonry tiles with different depths can be used with the same frame and elastomeric material. This method further ensures that where a plurality of masonry tiles is used, the surface of the plurality masonry tiles opposite the surface in contact with the sheet-form material forms a consistent height in the final polymeric skin product. This means that the masonryeffect polymeric skin has a uniform surface across the masonry tiles, whilst also allowing for indentations to be formed that simulate or are configured to contain grouting material for grout lines between adjacent masonry tiles. The frame may be used to control the profile of the sheet-form material between adjacent masonry tiles. For the avoidance of doubt, the frame may be used to control the depth of the skin in the area between the masonry tiles. This allows the position, shape and / or depth of the grout or render between the masonry tiles to be selected. In certain countries, it is known for the grout or render to be lower than the upper surface of the masonry (i.e. the grout or render is sunken compared to the masonry). In other countries, it is preferred for the grout or render to be at a height similar to that of the upper surface of the masonry. The present invention allows for either design to be easily achieved by modulating the height of the frame between the openings. It will also be appreciated that the use of a frame enables the present invention to be used to produce a range of different styles in situ without needing complicated mould systems or multiple processes. The openings of the frame may form a regular repeating pattern to allow a plurality of masonry tiles to be positioned regularly, to form a pattern such as that formed by a brick wall. Alternatively, the openings of the frame may form an irregular repeating pattern, to form a pattern such as that formed by a stone wall or mosaic. Preferably, the plurality of openings substantially covers the area of the frame. In preferred embodiments, the elastomeric material is heat resistant. This allows for the frame to be reused and thus reduces the costs of performing the process. Furthermore, it is preferable that the elastomeric material is impervious to the sheet-form material to allow for easy removal of the polymeric skin. Alternatively, a protective layer is provided between the elastomeric material and the sheet-form curable to prevent the sheet-form material from curing or sticking to the elastomeric materials. Suitable materials for the elastomeric materials may include a variety of rubbers. Preferably, the elastomeric material may be selected from nitrile rubbers, butyl rubbers, chloroprene rubbers, epichlorohydrin rubbers, ethylene propylene rubbers, fluorocarbon rubbers and silicone rubbers, or mixtures thereof. The use of a frame may also result in a set of channels in the back surface of the cured skin. Such channels may be particularly beneficial with respect to allowing the flow of air behind the skin once installed. The method of the present invention also includes a step of applying pressure to press the masonry tile and the sheet-form material to form the masonry-effect polymeric skin The step may include heating the sheet-form curable material. Alternatively, the method may include an additional separate heating step. When heated the sheet-form curable material cures to form the skin. In some embodiments the curing step comprises heating the sheetform curable material to a temperature greater than 100 °C, preferably to a temperature greater than 120 °C. Heating may improve the flow of the sheet-form curable material. Preferably, the heating may be provided at least in part by heating the frame. The frame is first heated and then in turns heats the sheet-form curable material when the two layers come into contact. Preferably, the heating is provided at least in part by heating the elastomeric material, such as by means of a heated matt or other heating element. Preferably the method includes applying heat to the masonry tile and the sheet-form material. Preferably, the sheet form material may be reduced in viscosity and / or at least partially liquified on the application of heat and / or pressure. In this way, some flow of the material can be achieved. In preferred embodiments, the material at least partly flows into the masonry tile during the application of pressure. The step of applying pressure to press the masonry tile and the sheet-form curable material together to form the polymeric skin may be achieved by using pressing plates or by using heated weighted plates. Accordingly, multiple polymeric skins according to the present invention may be formed on an assembly line, where the layers of components are provided on a heated base and then the application of pressure is achieved using a weighted lid. The weighted lid is simply removed when the sheet-form material has cured into a polymeric skin. Alternatively, the system may be heated using microwaves, induction heating or a heating tunnel, or any other suitable heating method. Such a system allows for multiple masonry-effect polymeric skins to be produced at once rather than needing to rely on one or more presses and the significant costs associated with such apparatus. The pressing plates or heated weight plates may be preferably made from metal, for example aluminium. Preferably the pressure applied is in the range of from 1 to 20 kg cm-3, more preferably 2 to 15 kgcm-3, and more preferably 5 to 10 kg cm-3. The temperature required during the pressing step is dependent on the type of sheet form material used, and the type of any adhesive (if any) which may be used, and can readily be determined by persons of skill in the art by routine experimentation. However, where the sheet form material comprises or consists of SMC, a temperature in the range of from 100 to 200 °C is appropriate, for example 120 to 160 °C. The heating may be achieved using microwaves, infrared, induction heating of the plates ora heating tunnel. Preferably the pressure and temperature and cycle time are chosen so that the sheet-form material cures during the pressing operation. Preferably the sheet form material is cured directly onto the masonry tile during the pressing operation. In a preferred embodiment, the masonry tile is preheated prior to the pressing step. Preheating the masonry tile reduces the necessary duration of the pressing step, enabling a fasterturnover of products. Any conventional means of preheating the masonry tile could be used, for example, using hot air or infrared irradiation. Pressing of the sheet-form material and masonry tile is preferably performed for a period of from 30 seconds to 20 minutes, for example 1 minute to 10 minutes. In some embodiments, the frame further comprises one or more voids into which the sheetform material can flow during the application of pressure, so as to form one or more protrusions. Preferably the depth of the one or more voids is selected in order to control the depth of the flow of the sheet-form material and therefore the extent of the protrusions. These protrusions may be used to space the final polymeric skin from the surface to which the polymeric skin panel is attached, to allow air flow when the polymeric skin is installed In preferred embodiments, a rendering or grouting substance is provided in the spaces between adjacent masonry tiles. The rendering or grouting may be provided by using a particulate material. Suitable particulate materials include sand, gypsum, graphite, calcium carbonate, hydrated organic salts, ceramic materials, ground glass, ground stone, clay materials, metal oxides, powdered paints, and mixtures thereof. Pigments may be added to the particulate material in order to control colour. The presence of a particulate material is particularly preferable as it facilitates the displacement of gas and / or vapour from the pressing region. This is important as the process of curing resins, such as those present in sheet-form material, produces gas which otherwise might become trapped in the cured sheet-form material and compromise desirable properties such as strength and may also contribute to undesirable warping of the skin. This also allows for a reduction in the pressure required to shape the skin and press the masonry tiles. In some embodiments, the particulate material is placed on the sheet-form material prior to the step of applying pressure to press the masonry tile and the sheet-form material together. Simultaneously with pressing the masonry tile and the sheet-form curable material together to form the polymeric skin product, the particulate material may be pressed into the sheet-form curable material between the masonry tiles to simulate the appearance of bricks bonded together by mortar, or a tiled wall or floor. Alternatively, the particulate material may be pressed into the sheet-form curable material in a separate step, especially during curing of the sheet-form material. Preferably, the sheet-form material is heated during the step of pressing the particulate material into the sheet-form material. This provides the particular advantage of being to produce siding materials where the masonry tile and grouting can be formed in situ, and at the same time during the pressing step. Such a process significantly reduces the duration for formation of siding panels, and indeed the duration of construction projects. In addition, as noted above, by using a particulate material, air and gas produced during the pressing step can pass through interstitial spaces between particles so that the risk of air and gasses leading to deformities in the skin are reduced. In some embodiments, more traditional materials are used for rendering or grouting. The rendering or grouting materials may comprise sand, cement or monocouche, or mixtures thereof. Alternatively, or in addition, the rendering or grouting materials may comprise binders, for example, Portland cement, lime and / or gypsum. These materials are used to fill the gaps between the masonry tiles, to at least partially fill the indentations formed by the sheet-form material and the frame. This still allows for the grouting and tiling to be produced in situ, i.e., not at the construction site, thus reducing the time required at a construction site, whilst achieving a highly attractive finish. Even where it is desired to grout or render between masonry tiles after pressing, it has been found beneficial to have at least some grout or render material formed in situ. The reason for this is that the in situ material provides a suitable surface for application of the grout or render and the formation of a strong bond. The method of the invention may further comprise providing interconnecting means to enable a series of polymeric skin panels according to the invention to be interconnected, e.g. to cover a wall or floor. In one preferred embodiment, the interconnecting means is a tongue and groove arrangement. For instance, the tongue and groove arrangement may be provided by profiling or machining the polymeric skin. In another embodiment, the method of the invention may comprise providing a fixing means on the surface of the composite material panels which is opposite the masonry tile, wherein said fixing means are adapted to enable the composite product panel to be attached to a wall, frame or other surface. A variety of suitable fixing means are known in the art, and include metal clips. In another aspect of the present invention, a masonry-effect polymeric skin formed according to the process described herein is provided. The masonry-effect polymeric skin comprises a skin of sheet-form material having reinforcing fibres, the sheet-form material comprising a masonry tile bonded to a surface of the skin of sheet-form material, and wherein at least a part of the sheet-form material has flowed into grooves or around protrusions on the surface of the masonry tile, or into spaces in the coarse structure of the masonry tile. The masonry tile may extend over substantially all or only a part of the sheet-form material and / or frame area. Preferably, a plurality of masonry tiles is provided which collectively extend over substantially all or only a part of the sheet-form material and / or the frame area. Similarly, the sheet-form material may extend over substantially all or only a part of the frame area. Preferably, the sheet-form material extends over substantially all of the frame area. Preferably, the sheet-form material may be bonded to the masonry tile by way of a key. In this way, a strong bond between the matrix and the masonry tile can be obtained. More specifically, the sheet-form material may extend into grooves or around protrusions on the surface of the masonry tile, or into spaces in the coarse structure of the masonry tile thus forming a strong bond between the sheet-form material and the masonry tile. Alternatively, or in addition, a layer of an adhesive material may be provided between the sheet-form material and the masonry tile. The plurality of masonry tiles may be spaced apart and a rendering or grouting provided in the spaces between adjacent masonry tiles to simulate the appearance of bricks bonded together by mortar, or a tiled wall or floor. The grouting or rendering may be provided by a particulate material cured into the polymeric skin or a traditional grouting material pointed between the masonry tiles. The masonry-effect polymeric skins may comprise one or more masonry tiles present on a surface of the skin as well as at least a portion of a particulate material. Preferably, the masonry tiles are in a pattern, and the particulate material is between the masonry tiles forming grouting lines between adjacent masonry tiles. In a preferred embodiment, the cured polymeric skin comprises masonry tiles which are brick-slips in the pattern of a traditional brick wall, and the grouting material forms a grout for the bricks. The polymeric skin may comprise an interconnecting means to enable a series of composite product panels to be interconnect. Such a connecting means may include a tongue and groove arrangement. The polymeric skin may further comprise protrusions, which in use, space the masonryeffect polymeric skin from a wall, frame or other surface to which it is attached. The protrusions can also act as a point for fixing the skin Alternatively or in addition, the polymeric skin may comprise fixing means on the surface of the cured skin which is opposite the masonry tile, wherein said fixing means are adapted to enable the masonry-effect polymeric skinto be attached to a wall, frame or other surface. The polymeric skin may comprise a fixing frame or fixing frame members such as stiles, rails, and / or mullions. The frame members may be of wood, metal (for example, aluminium) or plastics (such as uPVC) ora combination of these, e.g. metal-reinforced plastics. The plastics material may contain filler, if desired, to improve hardness and / or rigidity. Brief Description of the Drawings Figure 1 shows an exploded cross-sectional view of the components of the masonry-effect polymeric skin prior to being pressed together. Figure 2 shows a schematic cross-sectional view of the components of the masonry-effect polymeric skin during the step of applying pressure. Figure 3 shows a schematic cross-sectional view of an embodiment of a polymeric skin of the present invention. Figure 4 shows a schematic cross-sectional view of the components of the masonry-effect polymeric skin during the step of applying pressure, where the masonry tiles have different thicknesses. Description of the Inventions As shown in Figure 1, on a lower part of a press, a frame (2), wherein the frame comprises a plurality of openings shaped to receive a masonry tile (4). In particular, the frame comprises raised portions which, in the final product, will result in mimicking of grouting between masonry tiles in traditional brick walls. Each opening of the frame comprises an elastomeric material (6) which acts as a cushion, made from silicon rubber. A sheet of SMC material (8) was applied to the surface of the frame (2), and the sheet was extended so that it covered the whole area of the frame. Masonry tiles (4) were subsequently positioned directly on top of the sheet of SMC (8), such that the masonry tiles (4) were positioned in each opening of the frame (2) between the raised portions of the frame. As seen in Figure 2, an upper part of the press (10) was then placed onto the layers, and a downward pressure of around 10 kgcm2 was applied, such that the masonry tiles (4) were embedded into the sheet of SMC material (8). Once formed, the produced skin was removed from the frame (2). As shown in Figure 3, grouting material (12) was then positioned between adjacent masonry tiles to form grout lines between the masonry. Additionally, channels (14) had been formed by the frame on the back surface of the polymeric skin, to allow for air flow behind the panel. Figure 4 shows an embodiment of the present invention where the masonry tiles (4) have different heights. As shown, advantageously during the step of applying pressure, the elastomeric material (6) acts as a cushion and is compressed such that the masonry tiles provide a surface of constant height. In Figure 4, masonry tile A is thinner than masonry tile B, which is respectively thinner than masonry tile C. Accordingly, the elastomeric material (6) in the opening with masonry tile A is compressed to a lesser amount than the elastomeric material (6) provided in the frame (2) opening containing masonry tiles B or C. Also, the elastomeric material in the opening containing masonry tile C was compressed to a greater extent. In this manner, the present invention can advantageously control the depths which the masonry tiles are pressed to produce a masonry effect polymeric skin where the polymeric skin has a surface with a constant height across the masonry tiles. It will be appreciated that the present invention has been described by way of example. Each feature disclosed in the description, and (where appropriate) the claims and drawings may be provided independently or in any appropriate combination. Thus it will be appreciated that the various methods described herein could be combined as appropriate to form a particular product.

Claims

1. A method of forming a masonry-effect polymeric skin, the method comprising: (i) providing a frame comprising a plurality of openings shaped to receive a masonry tile, each opening comprising an elastomeric material which acts as a cushion within the opening; (ii) providing a layer comprising a sheet-form material having reinforcing fibres, the sheet-form material comprising a curable material; and (iii) providing a masonry tile;the method comprising the step of applying the layer of sheet-form material onto the frame, applying the masonry tile onto the layer of sheet-form material within an area of the openings, and applying pressure to press the masonry tile and the sheet-form material to form the masonry-effect polymeric skin.

2. A method according to Claim 1, wherein the masonry tile is formed, at least in part from concrete, clay, natural stone, artificial stone, ceramic, glass, or a combination thereof.

3. A method according to Claim 2, wherein the masonry tile is formed, at least in part from brick, marble, granite, limestone, travertine, sandstone, slate, cast stone, porcelain, earthenware, glass, ora combination thereof.

4. A method according to any one of the preceding claims, wherein the masonry tile is partially glazed.

5. A method according to any one of the preceding claims, wherein the masonry tile has a depth in the range of from 3 to 30 mm.

6. A method according to any one of the preceding claims wherein the masonry tile has dimensions of from 190 to 250 mm by 55 to 75 mm.

7. A method according to any one of Claims 1 to 5, wherein the masonry tile has dimensions of from 95 to 125 mm by 55 to 75 mm.

8. A method according to any one of the preceding claims, wherein the masonry tile is provided with surface indentations or protrusions on the surface that contacts the sheet-form material.

9. A method according to any one of the preceding claims, wherein the sheet-form material comprises a thermosetting polymer resin matrix.

10. A method according to Claim 9, wherein the thermosetting polymer resin matrix is selected from polyester resins, vinyl ester resins, epoxy resins, phenolic resins, bismaleimide resins or polyimide resins.

11. A method according to Claim 10, wherein the sheet-form curable material comprises a phenolic resin sheet comprising:uncured phenolic resin, such as a phenol-formaldehyde resin;filler;a catalyst in an amount of less than 2wt.% relative to the content of phenolic resin; andwherein the filler is present in a ratio of filler to uncured phenolic resin in an amount of 2.5:1 and greater, and further wherein the filler comprises a transition metal hydroxide and / or aluminium hydroxide in a ratio of metal hydroxide to uncured phenolic resin in an amount of 1:1.5 to 3:1.

12. A method according to Claim 10, wherein the sheet-form material comprises sheet moulding compound (SMC).

13. A method according to any one of Claims 1 to 12, wherein the reinforcing fibres comprise or consist of carbon fibres, glass fibres or aramid fibres, and mixtures thereof.

14. A method according to any one of the preceding claims, wherein the sheet-form material extends over substantially all of the frame comprising a plurality ofopenings shaped to receive a masonry tile.

15. A method according to any one of the preceding claims, wherein the sheet-form material has a thickness in the range of from 0.5 mm to 10 mm.

16. A method according to any one of the preceding claims, wherein the elastomeric material is heat resistant.

17. A method according to any one of the preceding claims, wherein the elastomeric material is selected from nitrile rubbers, butyl rubbers, chloroprene rubbers, epichlorohydrin rubbers, ethylene propylene rubbers, fluorocarbon rubbers and silicone rubbers.

18. A method according to any one of the preceding claims, wherein a rendering or grouting substance is provided in the spaces between adjacent masonry tiles.

19. A method according to Claim 18, wherein the rendering or grouting materials comprise sand, cement or monocouche, or mixtures thereof.

20. A method according to Claim 18 or Claim 19, wherein the rendering or grouting materials comprise binders, for example, Portland cement, lime and / or gypsum.

21. A method according to any one of the preceding claims, further comprising providing interconnecting means to enable a series of composite product panels according to the invention to be interconnected.

22. A method according to Claim 21, wherein the interconnecting means is a tongue and groove arrangement.

23. A method according to any one of the preceding claims, wherein the pressure applied during the step of applying pressure to press the masonry tile and the sheetform material is in the range of from 1 to 20 kg cnr2.

24. A method according to any one of the preceding claims, further comprising heating the masonry-effect polymeric skin to a temperature of from 100 to 200 °C after and / or during the step of applying pressure to press the masonry tile and the sheetform material.

25. A method according to Claim 24, wherein the heating is provided at least in part by heating the frame.

26. A method according to Claim 24 or Claim 25, wherein the heating is provided at least in part by heating the elastomeric material.

27. A method according to any one of the preceding claims, further comprising preheating the masonry tile prior to the pressing step.

28. A method according to any one of the preceding claims wherein the frame further comprises one or more voids into which the sheet-form material can flow during the application of pressure, so as to form one or more protrusions.

29. A method according to Claim 28, wherein the depth of the one or more voids is selected in order to control the depth of the flow of the sheet-form material and therefore the extent of the protrusions.

30. A method according to any one of the preceding claims, wherein the openings of the frame define a regular repeating pattern, such as formed by a brick wall.

31. The method of any one of Claims 1 to 29, wherein the openings of the frame define an irregular repeating pattern such as formed by a stone wall or mosaic.

32. The method of any one of Claims 30 to 31, wherein the plurality of openings substantially cover the frame.

33. A masonry-effect polymeric skin formed according to the process of any one of Claims 1 to 32, the product comprising a skin of sheet-form material havingreinforcing fibres, the sheet-form material comprising a masonry tile bonded to a surface of the skin of sheet-form material, and wherein at least a part of the sheetform material has flowed into grooves or around protrusions on the surface of the masonry tile, or into spaces in the coarse structure of the masonry tile.

34. A masonry-effect polymeric skin according to Claim 33, further comprising interconnecting means to enable a series of composite product panels to be interconnected.

35. A masonry-effect polymeric skin according to Claim 34, wherein the interconnecting means is a tongue and groove arrangement.

36. A masonry-effect polymeric skin according to any one of Claims 33 to 35, further comprising protrusions, which in use, space the masonry-effect polymeric skin from a wall, frame or other surface to which it is to be attached.

37. A masonry-effect polymeric skin according to any one of Claims 33 to 35, further comprising fixing means on the surface of the cured skin which is opposite the masonry tile, wherein said fixing means are adapted to enable the masonry-effect polymeric skin to be attached to a wall, frame or other surface.

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