Field of the Invention

This invention relates to a method of forming complex or hollow plastics products. The method particularly relates to forming mould components (also known as mould preforms) for injection moulding processes. The invention also relates to forming plastics products by injection moulding through use of the mould component.

Background

In one form, injection moulding involves injecting molten plastics having a relatively high viscosity into a shaped mould. Accordingly, the plastics are injected under high pressure and moulds are formed of steel in order to withstand the high pressures.

Furthermore, forming complex or hollow products requires very complicated moulds.

Specifically, achieving a desired hollow shape requires the hollow-filling portion of the mould to be collapsible for removal from the product after moulding is completed.

The complexity of such steel moulds is limited and, therefore, sacrificial mould preforms are used to form hollows. Mould preforms are separate components to a steel mould and are located within a steel mould so that they are overmoulded during injection moulding. Once a product is moulded, the mould preform is removed by destroying the mould preform, thereby leaving a hollow.

In order to survive the high pressures involved in injection moulding, mould preforms must be strong and must be removable in a post-moulding step.

For many years plastic products with complex shapes, including hollow shapes, have been made via injection moulding using tin-bismuth alloy mould preforms which have a melting point below that of the injection moulded plastics. The post-moulding step involves melting out of the tin-bismuth alloy preforms in a hot oil bath or via induction melting.

However, tin-bismuth alloy mould preforms are expensive due to the high cost of tin-bismuth alloy and because the process of casting preforms and melting the preforms is energy intensive.

Additionally, the tin-bismuth alloy mould preforms are exceptionally heavy when moulding large components and often require the use of heavy lifting robots. In addition the tin-bismuth alloys are corrosive and therefore decrease steel mould-life. The life of the moulds in which the preforms are made is also limited by the corrosive nature of the tin bismuth, requiring frequent replacement of the moulds. The use of tin-bismuth alloy also restricts the design of products that can be made. For example, long thin shapes can be difficult to make, due to bending of the tin-bismuth alloy during the moulding process. In another newer form, injection moulding involves low pressure moulding techniques (such as reaction injection moulding of thermoplastic polymer precursors) which rely on salt (NaCI) preforms for forming hollow and complex shapes. In one form, salt mould preforms are prepared from salt having a specific particle size range. Salt mould preforms are relatively simple to use compared to tin-bismuth alloy mould preforms because removing a salt mould preform from a moulded product involves dissolving the salt mould preform in water. However, salt recovered in this manner has a particle size range outside the size range required for preparing salt preforms. Accordingly, the salt must be treated and refined in a costly recycling process in order to obtain the appropriate particle size range.

In another form, salt mould preforms are prepared from molten salt. This is also energy intensive, but it avoids the need for preparing salt particles in a required size range and the mould preforms can be removed by dissolution in water.

However, salt mould preforms have the disadvantages of being corrosive and creating environmental problems in its manufacture, removal and disposal.

Summary of the Disclosure

It is an object of the present invention to provide an alternative method for forming injection moulded plastics products having complex or hollow shapes.

The alternative method advantageously provides a method for forming injection moulded plastics products having complex or hollow shapes that is simpler than salt and tin- bismuth mould preforms. Advantageously, the alternative method is more cost effective and less corrosive than existing methods. Desirably, the alternative method offers more design flexibility and/or is more environmentally friendly than existing methods.

In a first aspect, there is provided a method of preparing a mould component for an injection moulding process that involves over-moulding the mould component with plastics materials to impart a shape of the mould component on the plastics materials, the method comprising the steps of:

(a) forming a body having the shape from a mixture of a binder material and solid particulates; and

(b) coating the body with a liquid impervious material to form a mould component.

The term "mould component" refers to any part of a mould used in an injection moulding process. According, the term includes mould components used to form complex and hollow shapes in injection moulded plastics products.

Mould components formed in this manner enable production of complex and hollow injection moulded components without the problems associated with tin-bismuth alloy mould preforms and with salt mould preforms. A significant part of avoiding such problems is that mould corrosion is substantially avoided. Specifically, the coating can be formed of material that is non-corrosive, so the operating life of a steel mould will be improved when used with coated mould components.

Additionally, the coating is important where the surface finish of the hollow is important for the performance of the plastics product. In particular, the coating avoids ingress of low viscosity plastics-forming materials, such as polymer precursor materials, into the mould componentwhich would otherwise prevent clean removal of the mould component from the formed plastics moulded product.

The method of forming mould components and coating them is more cost effective than preparing mould preforms of tin-bismuth or salt. Furthermore, the method of preparing mould components and removing them from moulds is more environmentally friendly than the same process for mould preforms of tin-bismuth or salt.

The body of the mould component may be sufficiently porous, prior to application of the coating, to be gas permeable.

The solid particulates may be selected to provide sufficient porosity to enable drying or curing of the binder material in less than 20 minutes or in less than 10 minutes. Preferably the porosity is sufficient to enable drying or curing of the binder material in less than 5 minute, more preferably in less than 2 minutes and even more preferably in less than 1 minute.

The porosity of the mould component is important for enabling the interior of the mould component to be exposed to hot gas, such as hot air, or other forms of energy, to hasten the drying or curing process. For example, the porosity enables hot gas to pass through the mould component. Drying or curing the binder causes the mould component to become self-supporting and substantially rigid. These structural integrity properties are important because deformation of the mould component during the injection moulding process causes product tolerances to be lost. Additionally, the mould component should be strong enough to be transferred into a mould.

Preparing porous mould components therefore contributes to reducing the overall time for preparing mould components. This is advantageous because tin-bismuth mould preforms and salt preforms require significantly longer preparations times. They, therefore, demand investment in a considerable number of additional moulds for preparing mould components in order to ensure that there are sufficient mould components available to run an injection moulding process at its production capacity.

The solid particulates may have a particle size less than 1 mm. The particulates may have a narrow size distribution. Additionally, the particulates may have a size in the range of 100-200 mesh (i.e. <106microns to <75microns).

The particulates may have a top size of less than 250 microns.

Step (a) of the first aspect may involve combining the binder material and solid particulates with a solvent to produce binder-coated particulates.

Step (a) may also involve mixing the binder-coated particulates with solvent to form a binder-coated particulates/solvent mixture prior to forming the binder-coated particulates into the body shape.

The solvent added to the binder-coated particulates may comprise 1 to 40 wt% of the total weight of the binder-coated particles, preferably 1 to 20 wt% and more preferably 1 to 5wt%.

Step (a) may involve placing the mixture in a body mould to shape the binder- coated particulates into the shape of a body.

Placing the mixture in the body mould may involve pneumatically conveying the mixture into the body mould.

The first aspect may comprise a further step intermediate steps (a) and (b) that involves treating the binder-coated particulates in the body mould substantially to remove the additional solvent, thereby solidifying or curing the binder material and forming a rigid body.

The treatment in the intermediate step may involve heating the binder-coated particulates or exposing the binder-coated particulates to an energy source.

The treatment may involve heating the mixture in the mould by passing hot gas, such as hot air, through the mixture and/or heating the heating the body mould to cause heat transfer to the mixture.

The body may be heated to a temperature in the range of 40°C to 180°C.

The body may be removed from the body mould in less than 10 minutes, preferably less than 5 minutes and more preferably less than 2 minutes.

The body may be conditioned to facilitate formation of the coating of liquid impervious material when a coating material is applied to the body.

The body may be conditioned by providing the body at a coating-forming

temperature at which temperature the coating materials is caused to form the coating.

The coating-forming temperature is in the range of 40°C to 250°C. Preferably, the coating-forming temperature is in the range of 80°C to 130°C.

The body may be provided at the coating-forming temperature by heating the body in the body mould. The coating material may be applied to the body to form the mould component by spraying, rolling, dipping, powder coating or electrostatic spraying.

The coating material preferably is selected to be non-reactive with the plastics forming materials injected into the product mould.

The binder material may be a biopolymer. The biopolymer is selected such that it allows later removal of the mould component, such as through disassembly, breaking or through dissolution in a solvent, such as water. The biopolymer forms a structural matrix of the mould component so the particulates may comprise any one or more materials of a range of materials. Accordingly, the mould component can be prepared to be substantially lighter than those made from tin-bismuth alloy, and can be prepared of non-corrosive particulate materials.

The biopolymer may be biodegradable and may be water-soluble.

The method uses a biopolymer or biopolymers selected from the group comprising: collagen, starch, proteins, amino acids, saccharides, peptides, glycoproteins, dextrine, polylactic acid, zein, poly 3-hydroxybutyrate or biological derivatives, extracts, mixtures or compounds such as, but not limited to those of collagen, starch or cellulose. The biopolymer may be derived directly from natural products or may be derived synthetically. One such binder is a mixture of proteins derived from amino acids such as glycerine, alanine, L- glutamic acid, L-aspartic acid and/or small percentages of others, such that the binder is water soluble and easily eliminated from the plastic product after the moulding process.

According to a second aspect, there is provided a method of injection moulding a plastics product, the method comprising the steps of:

(a) preparing a mould component according to the first aspect;

(b) incorporating the mould component into a product mould for an injection

moulding process and injecting plastics-forming materials into the product mould to overmould the mould component, thereby forming a plastics product; and

(c) separating the plastics product from the mould component by removing the mould component.

It will be appreciated, therefore, that the second aspect can be used to form complex and/or hollow injection moulded plastics products. Indeed, it will be appreciated that the second aspect can be used to form composite materials by including suitable additives in the product mould or in the plastics-forming materials supplied to the mould.

In the second aspect, the method of preparing an injection moulded plastics product may be a low-pressure injection moulding method. In step (b) of the second aspect, overmoulding the mould component may involve introducing precursor materials for the formation of a polymer or polymers into the mould to cause in-situ polymerization inside the mould.

This process may result in the production of a polymer, copolymers, terpolymer, dendritic polymers, tetrapolymer, hybrids, polymer blends or other polymer structure or combination of these. There are many chemical reactions that can produce polymers via in situ polymerization (or "in-mould" polymer forming), including, but not limited to, anionic ring opening polymerization, chain shuttling polymerization, resin transfer moulding and vacuum assisted resin transfer moulding. As these reactions generally involve the use of

thermoplastic polymer precursor materials, or dissolved thermoplastic polymers with lower viscosities than the corresponding melted (reacted or undissolved) plastic, these processes are termed "low pressure injection moulding". Thermoset and thermoplastic reactions, where the moulding pressures are less than 100bar, may also be termed "low pressure injection moulding". Additionally, "low pressure injection moulding" includes injection moulding processes where a clamp pressure on a product mould is less than 10% of the clamp pressure for producing the same product by an injection moulding process that involves injecting molten plastics.

Step (c) of the second aspect may involve removing the mould component by contacting the mould component with a solvent to dissolve the binder materials, thereby releasing the solid particulates.

The second aspect may include a further step that comprises recovering and recycling the binder material and the solid particulates to form further mould components.

The solid particulates may be formed of material that is thermally stable at plastics moulding temperatures.

The solid particulate material may comprise inorganic or organic elemental or compounded particulates or mixtures of these. This includes, but is not limited to:

• ceramic particles (including but not limited to ceramic platelets, fibres,

spheres and irregular shaped particles) reground fired ceramic, ceramic beads, ceramic spheres (including but not limited to hollow spheres);

· fly ash (including, but not limited to fly ash spheres);

• glass and glass ceramics(including but not limited to glass beads, platelets, fibres, hollow spheres, and irregular shaped particles);

• metal (including but not limited to metal spheres, platelets, fibres and irregular shaped particles);

· calcium carbonate, graphite, hydroxy apatite, silicon dioxide, aluminium oxide, magnesium oxide, nickel carbide, silicon carbide, zircon, plaster; • rock minerals (including ortho and ring silicates, chain silicates, sheet silicates, framework silicates and non-silicates) and mixtures;

• plastics (including but not limited to thermoset materials including epoxies, polyurethanes, poly vinyl chloride, or thermoplastics such as but not limited to PTFE, polyphenylene sulphide, or copolymers, hybrids or mixtures of thermoplastics, and synthetically produced biopolymers),

• materials derived from plants, animals and other organisms (including but not limited to cellulose and diatomaceous earth).

The biopolymer (or biopolymers) and particulates may combined together in a mould or otherwise shaped, and dried or cured to form a mould component over, under, around or through which is injected plastics forming materials, such as a dissolved polymer material or polymer precursor material(s).

Such formed biopolymer bound particulate mould component imparts shaping or other characteristics to the moulded polymer.

The polymer injection process may include all those processes known to those skilled in the art where polymer is introduced into a mould. This includes, but is not limited to, reaction injection moulding (where polymer precursors are injected into a mould and react in-situ), solvent moulding (where a polymer dissolved in a solvent is introduced into a mould), compression injection moulding (where liquid polymers are injected into an open mould which is then closed), rotomoulding (where a dissolved polymer or polymer precursor materials are introduced into a rotating mould), whether or not assisted by vacuum, heat or other processes.

In addition, the biopolymers may be soluble in a solvent such as water to enable removal of the mould component from the moulded product by dissolution. In one example, these biopolymer mould component can be used as removable mould component for production of hollow plastic products.

Hollow plastic products may be produced by positioning a mould component, or mould components in a product mould and introducing a dissolved polymer material, or polymer precursor material(s) (including but not limited to monomers, oligomers, catalysts, initiators, activators with or without various additives including but not limited to fillers, colorants, heat stabilizers, releasing agents, nanoparticles, reinforcing materials or other materials) around the mould component. The plastics-forming materials may be reacted, cured or formed in the presence of an agent or by a suitable treatment, including but not limited to heat, radiation, or microwave energy. After solidification, evaporation of solvent, reaction and/or curing of the plastics-forming material, the mould component is removed by disintegration, for example by dissolution in water, leaving a hollow plastics product. The final plastics materials produced by low pressure moulding may include, but are not limited to thermoplastics, thermosets, copolymers, terpolymers, tetra polymers, dendritic polymers, hybrids, polymer blends, or mixture of these and polymers that can be produced via chain shuttle polymerization.

This includes, but is not limited to, polyurethanes, styrene, polyols, polyolefins, polypropylene, polyethylene, polyesters, polyarylenoxide, polyarylensulfide, polyetherimide, acetals, polyethylene, polyethylene terephthalate, polyethernapthalate, polymethyl acrylic acid, polyvinyl chloridepolymethylmethacrylate, polyamide-6, polyamide-1 1 , polyamide-12, polyamide-66, polyethyleneteraphlthalate, polybutyleneteraphthalate, polycarbonate, polyetheretherketone, polyetherketone, polythersulfone, polyphenylenesulfide,

polyethylenenaphthalate, polybutylenenaphthalate polyelastomers, polycarbonates, polybutylene terephthalate, polytetrafluoroethylene, polyfluoroethylene. This further includes the above polymers as copolymers, terpolymers, tetrapolymers, dendrimers, blends, hybrids and mixtures.

This also includes precursors of the polymers, including but not limited to monomers, oligomers, activators, catalysts, initiators and additives, whether dissolved in solvents, or combined with activators or initiators, or otherwise, also, for example, further polymers (alone or in combination with the above) such as but not limited to epoxies, thermoset polyurethanes, styrenes and copolymers, and epoxies. The precursors may be dissolved in solvents or otherwise combined, including their copolymers, terpolymers, tetrapolymers, dendrimers, blends and hybrids.

The plastics-forming materials supplied to the product mould, including the above materials and including reactants for forming those materials, may include fillers and reinforcing agents (such as but not limited to glass, talc, wolanstonite, carbon fibre, Kevlar, natural fibres or other materials), and in combination with thermoset or other materials such as but not limited to butadiene, EPDM (ethylene propylene diene M-class rubber), or silicone (whether as a filler or otherwise combined).

The plastics-forming materials supplied to the mould may contain additives such as:

• coloring pigments,

· heat and UV stabilizing agents;

• lubricating agents;

• initiators;

• activators;

• fibres (including but not limited to glass, carbon, metal, ceramic, mineral, plastics, cellulose, or those derived from plants);

• spheres (including but not limited to glass, ceramic, metal, plastics, mica); • platelets (including but not limited to mineral, glass, metal, ceramic, plastics, clay mineral);

• micro and/or nanoparticles, for example, of metal, glass, ceramic;

• other fillers or additives; and

· reinforcing materials.

These fillers or additives may be added to the plastics, precursors, monomers, oligomers, or solvents, or added directly into the product mould or incorporated onto reinforcing materials.

Reinforcing materials may also be coated with suitable coupling agents (such as but not limited to silanes), or may be treated by some other means to enhance bonding

(such as but not limited to corona jet treatment) to enhance the bonding between the plastics and the filler or reinforcing material.

The product mould may be constructed of, but not limited to, metal, ceramic, silicone, plastic, epoxy, polyester, wood, glass, composite, biopolymer bound particulates or a combination of these). The mould may comprise one or more parts and may include moveable or removable parts.

Further variation on the second aspect includes the use of agent or materials to improve the temperature, visual, mechanical or electrical properties, of the moulded plastics product or to improve the biocompatibility or UV stability of the material.

The agents or materials may be incorporated into the polymer by inclusion in, including but not limited to, solvents or precursors or in monomer, oligomer, initiator, or activator materials. Alternatively, the agents or materials may be directly laid or placed into the mould, such as, but not limited to, glass mat, carbon fibre mat, Kevlar mat, natural fibre mat or wrapped around the preform or preforms prior to introduction of the plastics forming materials, such as polymer, precursor, monomer, oligomer, activator, initiator material or polymers dissolved in a solvent.

The applicant has found that the time for preparing a mould component is significantly reduced when the mould component has a higher degree of porosity. This suggests that larger sized particulates will contribute to reducing the drying or setting time of the binder material. More spherical particles are also advantageous.

The applicant has also found that moulding plastics over the larger sized

particulates causes roughness in the surface of the moulded plastics. While this roughness may be acceptable in some applications, it may be considered a defect in other applications, for example where a fluid flows through the moulded plastics product.

Additionally, as many low pressure moulding processes involve injecting plastics- forming materials that have low viscosity, there is a tendency for these materials to infiltrate pores in the preforms. This makes removal of the preform difficult and this infiltration can affect polymerization of the plastics forming materials.

Accordingly, there is a clear preference to use small particulates, and to accept a longer mould component setting times.

Through considerable test work, the applicant has found that larger particulates can be used to form mould components for surface critical moulded products by forming mould components with a liquid impervious coating on the surface. In addition, the coating can be used to reduce or avoid erosion of the preform by the plastics forming materials dissolving the biopolymer particulate binder.

The applicant has arrived at this finding despite concerns that (a) coatings would interfere with tight dimensional tolerances associated with moulding precise plastics products and (b) the coating may bond or react with overmoulded plastics so the coating could be difficult to remove from the moulded plastics product.

The coating material may comprise:

· biopolymers, including collagen, starch, cellulose, proteins, amino acids, saccharides, peptides, glycoproteins, dextrine, polylactic acid, zein, poly 3- hydroxybutyrate or derivatives, mixtures, compounds or extracts such as but not limited to those of proteins, starch, collagen, or cellulose. One such coating is a mixture of proteins derived from amino acids such as glycerine, alanine, L-glutamic acid, L-aspartic acid and/or small percentages of others, such that the coating is water soluble and easily eliminated from the plastics product after the moulding process; and

• inorganic or organic elements or compounds or mixtures of these, including:

=> silicone materials (such as room temperature vulcanizing platinum or tin cured silicones),

=> ceramics and ceramic powders (such as nickel carbide, silicon carbide, zircon flour),

=> metals and metal powders,

=> clay minerals (such as bentonite and kaolin),

=> glass (including powders, fibres, beads, fibres, matts, and spheres),

=> graphite or diamond,

=> silicates (such as sodium silicate and potassium silicate), => carbon fibre,

=> plastic powders and coatings (such as polyphenylene sulfide, PFTE, PVA), and

=> release agents. Forming the coating of the same biopolymer as that used as a binder material significantly simplifies the recycling process by limiting the compounds needed to be separated. In the case of a water soluble gelatin coating on a gelatin bound preform it allows simple mechanical separation of the particulate and the gelatin from the water. Alternatively, the use of silicone allows the thin silicone/binder/particulate layer to be easily separated from the binder and the particulate by simple separation eg sieving, simplifying the separation and recycling of materials.

Through test work, the applicant has recognised the following considerations when selecting a suitable coating material:

(a) The ability to provide a smooth surface on the mould component without adding appreciably to the dimensions of the mould component. This imparts a smooth surface to the final product (or may also, for instance, allow the transfer of various patterned surfaces to the product). This also avoids the need to account for coating thickness when preparing a mould for preparing mould components.

(b) Non-reactivity with a polymer system being moulded. The mould components are over-moulded or come in contact with a polymer or polymer precursor materials (and/or other materials involved in the moulding process including monomers, fillers, activators, catalysts, initiators), and in the case of polymer precursors, monomers, initiators, catalysts or other reactive materials, these materials often contain reactive groups which have a tendency to react with other materials, including water, low molecular weight alcohols, strong acids, strong bases, etc). Reaction with a mould component coating or sealing agent will deleteriously effect the polymerization of the polymer, and conversely, the use of a non-reactive material will maintain the properties of the polymerized material.

(c) The sealing or coating should not contain volatile compounds for

environmental and occupational health and safety reasons.

(d) The sealing or coating material should be able to be removed from the

product once it is over moulded (or in some other way associated with the polymer). The use of a water soluble biopolymer mould component binder, or one that can be disintegrated is some other way, allows the mould component to be washed out or removed from the plastics moulded product. It is therefore desirable that the coating or sealing material applied to the body is either water soluble, or disintegrates when the mould component is dissolved in water or is otherwise disintegrated for example by providing a thin, brittle coating that crumbles away. Likewise it is desirable that the coating or sealing material releases easily from the polymer material, aiding in its removal.

(e) The coating/sealing agent should be convenient to apply. Application by painting, dipping or spraying may allow rapid coating as required of industrial manufacturing systems. Alternatively the coating or sealing material may, for instance, be applied as part of the mould component manufacturing process.

(f) The sealing/coating material should be able to be applied to the body (such as a body bound with a water soluble biopolymer) without causing

disintegration or damage to the body.

(g) Another preferable characteristic is that the coating/sealing material only forms a very thin layer on the outside of the mould component, assisting in the removal of the mould component, such as when a water soluble biopolymer binder is used and subsequently washed out in water. Another preferable characteristic is that the sealing or coating material has a good pot life, minimizing waste and aiding in ease of use.

(h) The setting (or polymerization rate etc) of the sealing or coating material may be controlled such as through the application of heat, or other energy source such as microwave energy or ultraviolet light or radiation source etc.

(i) The sealing or coating material should be able to withstand the temperatures possibly required to pre-heat it prior to over moulding (or otherwise coming in contact) with a polymer/ polymer precursor materials etc, and/or it is able to withstand the temperatures involved in the moulding process.

(j) The sealing or coating material should not crack or peel from the surface of the mould component over time, or due to the application (for instance) of heat or other energy source. (k) The sealing or coating material should not take up water over time or in high humidity conditions.

(I) The sealing or coating material desirably strengthens thin sections of the mould component, and/or protects the mould component from minor accidental damage (for instance, offers some abrasion resistance).

(m) The coating/sealing material should be economical, thus ensuring that the overall cost of the mould component is kept to a minimum.

(n) The coating should be easily separated from the body material once it is

removed from the product, allowing recycling of the body material.

(o) The coating material should be non-hazardous, thereby allowing for easy disposal or recycling (for example such as allows the reuse of the material in another product or application).

It will be appreciated, however, that the method of forming mould components outlined above may be used to form moulds for forming plastics products or products of other materials.

Brief Description of the Drawings

Examples of the aspects outlined above will now be described with reference to the accompanying drawings, in which:

Figure 1 is a schematic cross-section showing shaping of a mixture of particulates and biopolymer into a mould component by loading the mixture into a body mould.

Figure 2 is a schematic cross-section showing placement of the mould component in a product mould and showing plastics-forming materials supplied into the mould.

Figure 3 is a schematic cross-section of a plastics moulded products formed with the use of the mould component.

Detailed Description

Moulding of plastics materials having a complex or hollow shape may be carried out by a series of steps. Referring to an embodiment shown in Figures 1 to 3, these steps involve: preparing a mixture 2 of solid particulates and a suitable binder material, preparing a mould component 10 by placing the mixture 2 in a body mould 4, removing a body from the body mould 4 and covering the body with a coating 8 to form a mould component 10, placing the mould component 10 in a product mould 6 and supplying plastics-forming materials 12 to the product mould 6, and removing the mould component 10 to leave a moulded plastics product 14 with a hollow 16.

According to one embodiment of the process of preparing injection moulded plastics products, dry biopolymer (in the form of hydrolysed collagen, i.e. gelatine such as the product PR1 from Gelita, N.Z) is added to solid particulates (in the form of hollow ceramic spheres such as E-Spheres™ available from Envirospheres Pty Ltd) at a rate of between 1 to 6wt% of the total weight, depending on the density and surface area of the solid particulates.

For example, ceramic particulates, such as silica sand, of bulk density 1.6g/cm ³ may require binder at a rate of 1-2wt%. E-spheres having a bulk density of approximately 0.45 g/cm ³ (relative density of 0.85 g/cm3) may require binder at a rate of 3-6wt%. Less dense particulates may require more biopolymer by weight. A solvent (in the form of water) is added in the amount of 1 to 20 wt% of the total weight of the mixture of gelatine and ceramic spheres.

The mixture is agitated and dried so that the ceramic spheres are coated with the gelatine. This mixture may then be stored for a period of time. Alternatively, the mixture may be prepared by combining gelatine and water and adding this to the ceramic spheres so they are similarly coated and dried.

The ceramic spheres have a size less than 250microns, but solid particulates having a size <100 microns are suitable for many applications.

It will be appreciated, however, that a wide range of solid particulate materials may be used including light weight plastic spheres which may be particularly beneficial for the production of mould components for engine parts, where accidental retention of abrasive particulates may be of concern. More spherical particulates are found to be preferable.

The coated ceramic spheres are mixed with water in the amount of between 1 to 6 wt% of the total weight of the coated spheres (depending on the density and surface area of the particulate) to produce a slightly damp crumbly mixture. This mixture is placed in an air loader that forces a set amount of the mixture into a body mould under the pressure of compressed air so the mixture takes on the shape of a cavity within the body mould that corresponds with the shape of a desired mould component. The size of the ceramic spheres results in the mixture being packed in the body mould as a porous body that is gas permeable. The porosity is important for enabling swift removal of excess water to form a dried, unitary body.

The water is removed by heating the mixture within the body mould by pre-heating the body mould to a temperature of 140°C. Additionally, hot air at 140°C is forced through the pores in the body under pressure of around 210 KPa for a period of 48 seconds and the mixture is removed from the body mould as a formed body. Pre-heating the body mould and passing hot air through the body enables rapid production of bodies and typically each body takes less than one minute to produce. This enables a rapid production cycle and efficient mould utilisation.

The bodies, once manufactured, may be stored prior to use because they are self supporting on removal from the mould.

The next step involves applying a liquid impervious coating to the body to prevent infiltration of plastics-forming materials into the body during an injection moulding process.

One option for coating the body involves applying a coating-forming material to the surface of the body mould prior to the biopolymer/particulate being placed in the body mould. As such a coated mould component is removed from the heated body mould.

Optionally, the body mould is heated at the tme the coating-forming material is applied. The body mould is heated, in this event, to 40°C to 250°C.

The coating provides a suitable impermeable and non-reactive moulding surface for the production of polymer products. It ideally provides a good surface finish to the moulded product. The coating may also protect the mould component from excess humidity and damage.

Another option involves applying a coating-forming material to a heated body because heat from the body causes curing or drying of the coating forming material.

Accordingly, this option involves spraying a heated body with silicone to form a thin layer.

Silicone is predominantly non-reactive and suitable for use with a wide range of low viscosity polymer materials and monomers. Although solid silicone has a number of disadvantages, such as its high cost and limited life in moulding, forming a thin coating layer of silicone on the body allows the removal of complex internal mould components post- moulding. Specifically, the gelatine and ceramic spheres may be washed from the plastics product, leaving only an extremely thin layer of silicone requiring recycling.

A body is preheated to an activation temperature between 60°C to 140°C (or an alternative temperature suitable to the coating material selected). A heat polymerisable 2 or 3 part silicone (such as a solvent-free addition cured silicone) is then applied to the surface of the body by dipping, spraying or other means. On contact the silicone crosslinks forming a thin impervious film (i.e. moulding surface) on the outside of the body to form a mould component. The silicone preferably has low viscosity, long pot life, high release properties and is rapidly activated. In this regard, silcolease 1 1362 (Brenntag Pty Ltd) is preferred as a coating-forming material. While gelatine and other biopolymers are environmentally friendly, when used in the solid they suffer from poor shelf life and readily distort and crack on drying, and are not suitable for moulding processes that require pre-heating of mould components, However when used as a coating gelatine and other biopolymers allow easy removal and full recycling. The biopolymer used must, however, be matched with the polymer moulding system as reactions will vary from biopolymer to biopolymer and from one polymer system to the next.

Coating with gelatine involves preheating the body to 100 to 180°C and a mixture of gelatine and water is sprayed onto the mould or mould component. The water evaporates leaving a thin water-soluble gelatine moulding surface on the outside of mould component.

Alternatively the spray is applied under the influence of hot air, or heat causing the water to evaporate and form a thin film on the surface of the body, thereby forming the mould component. Care must be taken to avoid erosion of the surface of the body by water contained in the spray mixture.

The mould component is complete once the liquid impervious coating is formed and it may now be used in an injection moulding process to produce plastics products.

The mould component manufactured as outlined above is used alone or a larger mould or mould component is assembled from a number of these components. The mould component or components are then preheated to 140°C or otherwise conditioned to meet the requirements of the particular polymer system used. The mould component is then placed in a product mould and is over-moulded with a polymer, polymer mixture (potentially including a variety of additives such as heat stabilizers, reinforcing materials etc) or with a low viscosity monomer or polymer precursor materials that then polymerise in the mould to form a polymer product. For example, the plastics forming materials may comprise Nyrim® 1525 (Brueggemann GmbH).

The polymer product is removed from the mould and the mould component is washed away with water to dissolve the gelatine, leaving a polymer product. The gelatine and ceramic spheres can then be separated from the water and are recycled to form further mould components.

With reference to Nyrim® as an example of an injection moulding process, and in particular a low pressure polymer moulding process in which the said mould components are used, the plastics-forming materials consist of two reactant streams which are ultimately mixed in an intensive mixture. The first of such reactant streams is noted as A-Catalyst and represents a catalysed caprolactam. Typically, a bromide catalyst is added to molten caprolactam in which it reacts and dissolves. Said catalysts comprise from about 5% to 25% by weight of the reaction mixture. The second reactant stream designated as B-Polyol basically comprises a polyol and a bisimide coupler-activator also dissolved in molten caprolactam in stoichiometric portions so as to ensure polymerization. In the uncatalyzed state, i.e., before mixed with reactant stream A, reactant stream B is a stable mixture for an indefinite period of time. Typically, a polyol such as polypropylene glycol is combined with bis-acyllactam to form the prepolymer and from about 10% to 90% by weight of said prepolymer is combined with the molten caprolactam. The acyllactam end groups act as an initiator for the caprolactam polymerization which results in a block copolymer comprised of polyether soft segments and nylon 6 hard segments.

These two reactant streams may be combined together by impingement mixing as they enter the mould. In one embodiment, the product mould has been previously purged with nitrogen to provide an oxygen free (or low oxygen) environment in which the reaction takes place. In this embodiment, the two streams of materials mix and react in the mould, creating a product surrounding the mould component. Once the material has cured or reacted the product is removed from the mould and the preform is dissolved, preferably in water. This may leave a complex hollow product.

Another example involves the use of polymers such as polybutylene terephthalate or polycarbonate dissolved in solvent which are introduced into the mould containing a preform or preforms, and the solvent is evaporated. Once the material has cured or reacted the product is removed from the mould and the preform is removed. A further example involves the in-situ polymerization of polyphenylenesulfide within the mould and the removal of the preforms once the material has reacted.

Another example involves the introduction of polymer pre-cursor materials into a mould containing a preform or performs, the materials reacting (possibly in the presence of heat, radiation, or microwave energy) to form a polymer material. Such polymer precursor materials including precursors for the production of polymers via chain shuttle

polymerizations.

The above described biopolymer particulate material can be used for the production of shaped performs for the production of hollow and complex shaped plastic products. One application of this process is to the production of high temperature automotive components, such as but not limited to air inlet manifolds, turbo chargers, superchargers, powertrain components, engines, motors exhaust components, catalytic converters, fuel cells, battery housings, electric motors, vents and hoses, motor components, and brake components. Also other automotive components such as but not limited to steering components, wheel components, body components, seating components, vehicle panels, cooling components, lighting and mirrors, instrumentation, dash board and interior trim components. The invention can also be used for the production of other products, including but not limited to ballistic shielding, aerospace and aeronautical components, wind turbine blades, bicycles, wheels, solar cell supports, solar hot water heaters, electrical goods, household goods, pumps and pumping equipment, liquid and gas tanks, train components, track components, machinery and equipment.

In the claims which follow and in the preceding description of the invention, 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 invention.