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"Composite Material"

Field of the Invention

[0001] The present invention relates to a composite material. More particularly, the composite material of the present invention is intended for use in the construction of apparatus and structures that will benefit from the properties of strength and resistance to weathering, rotting and insects not provided through other softwood materials of the prior art.

Background Art

[0002] Timber and timber materials are presently used extensively throughout a large range of industries. These uses range from structural materials for construction to frameworks for buildings. Throughout the world there are extensive plantations of softwood timbers. These plantations provide fast growing timbers that can be used in a variety of applications, including pine ceiling beams and medium density fibreboard. The high growth rate of softwood trees makes them very economical in comparison to other hardwood timbers.

[0003] However, softwood timbers have many physical disadvantages, which include susceptibility to weathering and rotting, and a vulnerability to insects, which can each be crippling to building framework. Additionally, softwood timbers have limited structural strength and are soft and compressive. The physical disadvantages of softwood timbers are very evident in, for example, the transport industry where the weathering and rotting of softwood transport pallets can lead to safety concerns during transport.

[0004] In an attempt to overcome the problems of weathering, rotting and insect infestation a number of chemical treatments have been applied to timber products. However, these chemical treatments generally present a high risk due to their toxicity and carcinogenic properties. As such, many chemical treatments have been banned or at least actively discouraged from use. An example of such a treatment is copper chromium arsenic (CCA), which was once among one of the most widely used pine timber treatments. CCA is currently banned, or its domestic use restricted in many countries due to the potential for heavy metal contamination of the environment.

[0005] In the building industry, treated pine is used to construct outdoor structures such as pergolas and gazebos. There exists a great controversy regarding the impact of the chemical treatment of such structures due to the high level of human contact therewith. A further alternative is the use of hardwood timbers for such applications. However, hardwood timbers are expensive and are of increasingly limited supply.

[0006] A still further alternative is to coat softwood materials in strips of composite reinforcement, such as is shown in US Patent Application Publication 2002/0095905, and this can be used in many applications. Such materials are known to have advantages of high strength, design flexibility, dimensional stability and corrosion resistance whilst being relatively lightweight.

[0007] The increase of the strength however, has an impact to on the flexibility or the compressive properties of the material. There are many applications in which this is undesirable. Such an example is the composition of rail sleepers, where the use of timber is preferred to almost any other material, as it has relatively high strength, yet a low modulus of elasticity (Young's Modulus), which enables shock absorption. Sleepers constructed of concrete may be stronger than timber, but the high modulus of elasticity this material possesses transfers vibration back up through the train and down the train line, which is highly undesirable, particularly in high speed rail systems.

[0008] The composite material of the present invention has as one object thereof to overcome substantially the abovementioned problems associated with the prior art, or to at least provide a useful alternative thereto. j

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[0009] The preceding discussion of the background art is intended to facilitate an understanding of the present invention only. It should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was part of the common general knowledge in Australia or elsewhere as at the priority date of the application.

[0010] Throughout the specification and claims, unless the context requires otherwise, the word "comprise" or variations such as "comprises'' or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Disclosure of the Invention

[001 1 ] In accordance with the present invention there is provided a composite material comprising: at least two core members; a layer of fibre reinforced thermosetting polyester resin enclosing at least in part the two or more core members; and an outer gel coat layer provided so as to substantially enclose the two or more core members.

[0012] Preferably, the core members are constructed of compressed cellulose fibres, wood fibres or foam cores. Still preferably, the foam cores are selected from the group of polyurethane; polyethylene; polyethylene terephthalate; polypropylene and close cell expanded polyvinylchloride. Still further preferably, the foam cores further comprises a filler component selected from the group of glass fibres, wood fibres and rubbers.

[0013] In one form of the present invention the core members are each first individually coated with a modified polyurethane coating and enclosed in a resin blend prior to being enclosed in the fibre reinforced thermosetting polyester resin. Preferably, the modified polyurethane coating is a two part, hydrocarbon based mixture.

[0014] Preferably, the core members with their coating of modified polyurethane and resin blend are arranged so as to be adjacent to one another. Still preferably, the core members with their coating of modified polyurethane and, resin blend are arranged so as to abut one another.

[0015] Still preferably, the modified polyurethane and modified resin blend coats will penetrate to at least some extent, and bind the core members.

[0016] In a further embodiment of the present invention the layer of fibre reinforced thermosetting polyester resin enclosing the core members further comprises a base resin, a monomer, an initiator, a promoter, modifying additives and reinforcing fibres.

[0017] Preferably, the base resin is selected ^' from a group containing orthophthalic, isophthalic, dicyclopentadiene, chiorendic or bisphenol-A resins. Most preferably, the base resin is an orthophthalic resin.

[0018] Preferably, the monomer is selected from a group containing styrene, methyl methacrylates, vinyl toluene, a-methyl styrene, paramethyi styrene and diallylphthalate. , Most preferably, the monomer is a styrene.

[0019] Preferably, the initiator is selected from a group containing ketone peroxides, acetylacetone peroxides, benzoyl peroxides and cumine hydroperoxide. Still preferably a ketone peroxide is used. Most preferably, the initiator is methyl ethyl ketone peroxide.

[0020] Preferably, the promoter is selected from a group containing cobalt napthenate, cobalt octoate, dimethylaniline, diethylamide and dimethylacetamide. Still preferably, the promoter is either cobalt octoate or dimethylaniline. r

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[0021] Preferably, the modifying additives may include thixotropes, fillers pigments, fire retardants, suppressants and UV inhibitors.

[0022] Preferably, the reinforcing fibres may be in the form of a woven fabric or a woven roving. Still preferably, lime aluminium borosilicate (E-type) glass fibres are used.

[0023] In a still further embodiment of the present invention the outer gel coat layer further consists of a base resin and modifying additives.

[0024] Preferably, the base resin is selected from a group containing polyester or Vinyl ester resins. Most preferably, the base resin is polyester.

[0025] Preferably, the modifying additives include thixotropic agents, fillers, UV inhibitors and pigments.

[0026] In accordance with the present invention there is provided a method of manufacturing a composite material comprising the steps of:

(i) High pressure compressing of fibres to form core members;

(ii) Arranging two or more core members as required;

(iii) Enclosing the core members of step (ii) in a layer of fibre reinforced thermosetting polyester resin; and

(iv) Applying an outer gel coat layer to the product of step (iii).

[0027] Preferably, the core members are constructed of compressed cellulose fibres, wood fibres or foam cores. Still preferably, the foam cores are selected from a group containing polyurethane; polyethylene; polyethylene terephthalate; polypropylene and close cell expanded polyvinylchloride.. Still further preferably,

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- 6 - the foam cores further comprise a filler component selected from a group containing glass fibres, wood fibres and rubbers.

[0028] In one form of the present invention the core members are treated with the additional step of being: initially coated with a modified polyurethane coating and enclosed in a resin blend prior to being enclosed in the fibre reinforced thermosetting polyester resin.

[0029] Preferably, the core members with their coating of modified polyurethane and resin blend are arranged so as to be adjacent to one another. Still preferably, the core members with their coating of modified polyurethane and resin blend are . arranged so as to abut one another.

[0030] Still preferably, the modified polyurethane and modified resin blend coats will penetrate to at least some extent, and bind the core members.

[0031 ] In a further embodiment of the present invention the layer of fibre reinforced thermosetting polyester resin enclosing the core members further comprises a base resin, a monomer, an initiator, a promoter, modifying additives and reinforcing fibres.

[0032] Preferably, the base resin is selected from a group containing orthophthalic, isophthalic, dicyclopentadiene, chlorendic or bisphenol-A resins. Most preferably, the base resin is an orthophthalic resin.

[0033] Prefereably, the monomer is selected from a group containing styrene, methyl methacrylates, vinyl toluene, a-methyl styrene, paramethyl styrene and diallylphthalate. Most preferably, the monomer is a styrene.

[0034] Preferably, the initiator is selected from a group containing ketone peroxides, acetylacetone peroxides, benzoyl peroxides and cumine r

- 7 - hydroperoxide. Still preferably a ketone peroxide is used. Most preferably, the initiator is methyl ethyl ketone peroxide.

[0035] Preferably, the promoter is selected from a group containing cobalt napthenate, cobalt octoate, dimethylaniline, diethylamide and dimethylacetamide. Still preferably, the promoter is either cobalt octoate or dimethylaniline.

[0036] Preferably, the modifying additives may include thixotropes, fillers pigments, fire retardants, suppressants and UV inhibitors.

[0037] Preferably, the reinforcing fibres may be in the form of a woven fabric or a woven roving. Still preferably, lime aluminium borosilicate (E-type) glass fibres are used.

[0038] In a still further embodiment of the present invention the outer gel coat layer further consists of a base resin and modifying additives.

[0039] Preferably, the base resin is selected from a group containing polyester or vinyl ester resins. Most preferably, the base resin is polyester.

[0040] Preferably, the modifying additives include thixotropic agents, fillers, UV inhibitors and pigments.

Brief Description of the Drawings

[0041] The present invention will ^, now be described, by way of example only, with reference to two embodiments thereof and the accompanying drawings, in which:

Figure 1 is a perspective view of a composite material in accordance with the present invention;

Figure 2 is a cross-sectional view of the composite material of Figure 1 , showing the core members and the enclosing resins; and r

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Figure 3 is an exploded perspective view of the composite material of Figure 1 , showing the core members and the enclosing resins.

Best Mode(s) for Carrying Out the Invention

[0042] In Figures 1 to 3 there is shown a composite material 10 in accordance with the present invention. The composite material 10 comprises two core members 12, each separately enclosed in a resin blend 14, arranged so as to lay adjacent to one another before being enclosed in a layer of fibre reinforced thermosetting polyester resin 16. The layer of fibre reinforced thermosetting polyester resin 16 is then coated in an outer gel coat layer 18.

[0043] The core members 12 are constructed of compressed softwood fibres formed under heat and pressure. The core members 12 determine the length and overall dimensions of the final product formed thereby.

[0044] Each of the core members 12 are initially coated in a modified polyurethane coating (not shown) followed by the resin blend 14. The poiyurethane coating is a two part, hydrocarbon based mixture. Typically, a raw polyurethane sealer, without additional thickeners is used, this has a lower viscosity in order to aid the penetration into the core material.

[0045] A further coat of a blend of polyester resin, with approximately 20-24% vinyl ester resin and 0.07-1 % additional cobalt can be applied over the polyurethane resin coat. The The additional cobalt further enhances the coating bonding characteristics.

[0046] The two treated core members are then arranged to abut one another, along the longitudinal axes, as is best seen in Figure 3. The two core members 12 are then enclosed in a layer of fibre reinforced thermosetting polyester resin 16. x

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[0047] The layer of fibre reinforced thermosetting polyester resin 16 is comprised of a base resin, a monomer, an initiator, a promoter, modifying additives and reinforcing fibres.

[0048] The base resin is selected , from a group containing orthophthalic, isophthalic, dicyclopentadiene, chlorendic or bisphenol-A resins. The monomer is selected from a group containing styrene, methyl methacrylates, vinyl toluene, a- methyl styrene, paramethyl styrene and diallylphthalate. The initiator is selected from a group containing ketone peroxides, acetylacetone peroxides, benzoyl peroxides and cumine hydroperoxide. The promoter is selected from a group containing cobalt napthenate, cobalt octoate, dimethylaniline, diethylamide and dimethylacetamide. The reinforcing fibres may be in the form of a woven fabric or a woven roving.

[0049] Alternatively, a phenolic base resin can be used to increase the high temperature resistance of the composite material 10.

[0050] Further modifying additives that can be included in the composition of the layer of fibre reinforced thermosetting polyester resin 16 which include thixotropic agents, fillers, pigments, fire retardants, suppressants and UV inhibitors. Typically, the thixotropic agent is silica fume. Typically, the pigments are oxides. The typical fire retardant is aluminium trihydrate, which further acts as a filler and increases ultraviolet protection and hardness. Additionally, aluminium oxide -is added as a filler which also improves hardness and scratch resistance.

[0051] However, the composition of the fibre reinforced thermosetting polyester resin 16 may be varied depending on the intended use of the final composite material 10 and the desired physical attributes. The amount of glass fibre and the type of weave and direction of the glass fibre will vary the strength of the product and also the impact resistance.

[0052] Chop strand matt can be used to increase impact resistance of the final composite material 10. However, the chop strand matt is required to be provided j

- 10 - in combination with unidirectional glass fibres to allow the resin to flow. A quad core uni-directional weave mat can also increase impact resistance and consists of 3 or 4 layers of glass fibres. The first layer being uni-directional weave, followed by 2 layers of uni-directional weave positioned 45 degrees relative to each other, with a final chop strand matt woven in on the outer layer.

[0053] The fibre reinforced thermosetting polyester resin 16 is applied to the treated core members 12 by first wrapping the core members 2 in the reinforcing fibres. This is then followed by either one of two different moulding methods.

[0054] Firstly, the wrapped core members 12 are then placed into a mould constructed from aluminium extrusion which has been coated in various release agents and Teflon to provide a non-stick surface. Nylon end caps are used to close each end of the mould. The mould is then injected with the base resin, the monomer, the initiator, the promoter and modifying additives and allowed to cure with a gel time of up to 20 minutes in the liquid state during which time the glass fibres must be wet out before the resin turns to a solid state. The mould is then left to stand for approximately 2 hours for the composite material 10 to fully cure. Once cured, the products are extracted using a hydraulic press.

[0055] Alternatively, the core members can be placed into a two part mould constructed of aluminium or nylon, which is again coated in release agents and Teflon. The base resin, the monomer, the Initiator, the promoter and modifying additives are poured into the mould with the core members. The top of the mould is then closed, which will press all of the components within the mould tight. The mould covers can be mechanically clamped, vacuumed closed or hydraulically closed. The mould further comprises air release points to evacuate any air trapped within the mould.

[0056] Once the product is extracted from the mould it is abraded in order to prepare the surface for the outer gel coat 8. The outer gel coat 8 forms a tough UV stabilised, coloured coating which completely seals the inner core members. i

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It is formed from a polyester base resin and modifying additives such as thixotropic agents, fillers, UV inhibitors and pigments. It is typically applied to the composite material by a spray applicator and allowed to dry before being handled. A vinyl ester resin layer (not shown) can be applied prior to the application of the outer gel coat 18. The vinyl ester resin layer acts as a water and chemical resistant layer which further acts to increase the bonding to the outer gel coat 18. The vinyl ester resin layer is further modified by the addition of between 14% and 25% styrene monomer and approximately 1% additional cobalt.

[0057] It is envisaged that apparatus and structures may be formed from . the composite material 10. Such apparatus and structures are expected to exhibit the beneficial properties of strength and resistance to weathering, rotting and insects not provided through other softwood materials of the prior art. One example of an apparatus that can be formed from the composite material 10 of the present, invention is a pallet for the transport and storage of goods. Each structural member forming such a pallet, traditionally formed of a soft wood, may be replaced by a member formed of the composite material 10.

Examples

[0058] Aspects of the present invention will now be illustrated with reference to a series of experimental examples. The description of the examples should not be understood to be limiting the generality of the preceding description of the invention. For the purposes of comparison, the experimental examples include reference to compositions outside the scope of the present invention. The inclusion of such compositions does not derogate from the preceding discussion.

[0059] Samples of the composite material of the present invention underwent testing with a Poplar timber selected as the core material. Bending and shear tests were conducted in the Structural Laboratory of the Department of Civil and Resource Engineering, University of Western Australia. Beam testing was carried out with an Amsler Test Machine with a calibrated two tonne load cell. Shear testing was carried out in a Baldwin Test Machine with an internal calibrated load cell. Displacements were recorded using a calibrated Linear Variable Differential Transformer (LVDT).

[0060] Beam tests utilised a single point load at mid-span. Failure loads have been converted to stress assuming that the fibre reinforcement is equivalent in modulus and strength to the enclosed timber. Values in the table below are based upon Ζχχ = 1/6bh ² ; M PL/4 Ιχ* = 1/12bh ³ ; σ = M/Z _xx and δ = PL ³ /48Elxx

Table 1 : Results of Bending and Shear Test

[0061] As demonstrated in Table 1, the modulus of the sample far exceeded the typical bending capability of natural soft or hard woods. Poplar alone typically exhibits a maximum stress of 22-28 Mpa and a modulus of 7000 Mpa.

[0062] Most importantly, as demonstrated by the moment results above, the tested material is able to deform excessively without achieving significant structural damage. By way of comparison, the tested material was able to deform in excess of 5 times that of a radiate pine sample. Without being bound by theory, it is believed that the resin casing upholds the structural integrity of the wood cores by not allowing the splintering of the wood.

[0063] Beam shear tests were conducted with a single point load producing a shear span equal to the beam depth. A pine wood sample was also tested for x

- 13 - comparative purposes. Tests were conducted for both vertical and horizontal grain directions. Shear stress was calculated by τ = P/2A.

Table 2: Shear Stress Results

[0064] As appreciated by those skilled in the art, Poplar is relatively soft wood, with an average air dry density of about 350 - 500 kg/m ³ as compared to pine products which have a density of about 500 - 700 kg/m ³ . As shown in Table 2, the calculated shear stress withstood by the product once treated in accordance with the present invention was significantly higher than that exhibited by a pine product.

[0065] Modifications and variations such as would be apparent to the skilled addressee are considered to fall within the scope of the present invention.