Patterned composite product

Abstract

The present invention relates to methods for forming a composite product having a patterned surface. A substrate including a porous structure (136), a sheet-form material (134) and a patterned sheet (131) are pressed together to form the composite product. In preferred examples, the patterned sheet is permeable to curable material in the sheet-form material.

Claims

1. A composite product comprising a substrate having a substantially open-celled structure and a skin of cured plastics material, wherein the composite product further comprises a patterned sheet bonded by and at least to the surface of the skin and wherein the patterned sheet is substantially embedded in the skin.

2. The composite of claim 1, wherein the patterned sheet is bonded at least partially within the surface of the skin.

3. The composite of claim 1, wherein the patterned sheet is bonded within the surface of the skin.

4. The composite of claim 1, wherein the patterned sheet is formed from material of fabric.

5. The composite of claim 1, wherein the patterned sheet comprises a non-woven material.

6. The composite of claim 1, wherein the patterned sheet comprises a glass veil.

7. The composite of claim 1, wherein the patterned sheet has a weight of less than 200 g/m.sup.2.

8. The composite of claim 1, wherein the patterned sheet is printed.

9. The composite of claim 8, wherein the patterned sheet is a screen-printed patterned sheet, an offset printed pattern sheet or and inkjet printed pattern sheet.

10. The composite of claim 1, wherein the patterned sheet provides a surface texture to the composite.

11. The composite of claim 1, wherein the skin of cured plastic material includes a thermosetting material.

12. The composite of claim 1, wherein the skin of cured plastic material includes reinforcing fibers.

13. The composite of claim 1, wherein the skin of cured plastic material comprises sheet molding compound (SMC) or a phenolic material.

14. The composite of claim 1, wherein the skin of cured plastic material includes an impregnated fiber composite material.

15. The composite of claim 1, wherein the substrate comprises an open-celled foam.

16. The composite of claim 15, wherein the open-celled foam is frangible.

17. The composite of claim 15, wherein the open-celled foam is a phenolic open-celled foam.

18. A household item formed from a composite comprising a substrate having a substantially open-celled structure and a skin of cured plastics material, wherein the composite product further comprises a patterned sheet bonded by and at least to the surface of the skin and wherein the patterned sheet is substantially embedded in the skin.

19. A vehicle fitting formed from a composite comprising a substrate having a substantially open-celled structure and a skin of cured plastics material, wherein the composite product further comprises a patterned sheet bonded by and at least to the surface of the skin and wherein the patterned sheet is substantially embedded in the skin.

Description

(1) Preferred features of the present invention will now be described, purely by way of example, with reference to the accompanying drawings, in which:

(2) FIG. 1a to c show an example of a method of forming a composite product.

(3) In a method described in UK Patent Application No. 0719343.6, the skins are bonded directly to a foam core during a moulding step. A layer of sheet-form SMC is provided on the mould surface, a foam core is placed on the layer of SMC, and pressure is applied to mould the components together. During the moulding step, the core and SMC layer are moulded to the desired shape, and the SMC material becomes bonded to the core.

(4) FIGS. 1a to c show an example of a method of forming a composite product. Here, a panel is being formed.

(5) FIG. 2 shows the patterned composite product formed using the method shown in FIGS. 1a to c.

(6) A lower mould 130 is provided which has a moulding surface having the required contours for forming the desired surface profile for the panel to be formed.

(7) The lower mould is located at an assembly station and the elements of the panel to be formed are loaded onto the mould 130.

(8) The moulding surface may first be cleaned using any suitable cleaning materials. The components to be moulded are then loaded onto the mould 130.

(9) Immediately onto the moulding surface of the mould 130 is placed a printed sheet, here a glass veil 131. The veil 131 has a pattern 132 printed onto its surface. In this example, the veil 131 is sized so as to fit to the mould surface with little overlap, but the veil may be oversized, in which case trimming may be required after moulding.

(10) Onto the veil 131 is placed a sheet of SMC 134. Again, in this example, the size of the sheet of SMC 134 is so that it is similar to that of the moulding surface, but the SMC sheet may be oversized in which case some finishing may be required after moulding.

(11) A frame 138 is then placed onto the SMC 134 and a foam block 136 is inserted into the frame 138.

(12) A perspective view of the assembled components is shown in FIG. 1b. In FIG. 1b, the thicknesses of the various components are not shown to scale, for clarity.

(13) The mould 130 supporting the components is then placed onto a heated lower press platen in a press. In this example, the temperature of the lower platen is chosen so that the mould temperature during moulding is about 140 degrees C.

(14) An upper platen is then lowered towards the lower platen in the press and pressure applied to effect the moulding operation and form the moulded composite product 140.

(15) FIG. 1c shows schematically a cross sectional view of the resulting moulded composite product 140. For clarity, the relative thicknesses of the various components are not shown to scale. It is seen from FIG. 12c that a composite skin 139 has been formed on a surface of the product. The composite skin 139 comprises the cured SMC layer and also the veil 131 material. Inspection indicates that the resin of the SMC appears to have penetrated fully through the veil material to give a smooth glossy outer surface while the filler material in the SMC (for example the glass fibres) have been captured beneath the veil.

(16) As shown in FIG. 2, the printed image 132 on the veil 131 can be seen clearly from the surface of the skin 139. The image originally provided on the veil 131 surface is seen to be essentially undistorted during the moulding operation. This is considered to be because there is little lateral flow of material across the mould face during the moulding step.

(17) A boundary layer 141 is also seen between the composite skin 139 and the compressed foam core 136′. In this layer 141, the resin of the SMC appears to have penetrated the foam, for example by passing into the open cell structure of the foam core 136. This is seen to give good bonding between the composite skin 139 and the core 136′.

(18) The composite product shown being formed in FIGS. 1a to c may be for example a precursor for a panel or door.

(19) The finished panel or door may be formed by attaching two similar precursors together to give a double skinned panel or door. It will be seen that alternatively the panel or door might be made in a single moulding step.

(20) For example, a layered product could be provided for moulding which comprised, on a lower moulding surface, a first veil, an SMC layer, a foam core (with any frame or other components required), a second SMC layer and second veil. An upper mould surface would be pressed onto the second veil and pressure applied to mould a full panel or door in one piece.

(21) Without wishing to be bound by any particular theory, the veil can be provided as a barrier between the filler material and the product surface to improve the surface finish of the composite product in certain arrangements. It is also thought that the presence of a veil can reduce flow of the matrix material in the plane of the mould, thus improving the appearance and other features of the moulded product in some arrangements.

(22) In the present example, the SMC includes glass fibres. The veil comprises a glass veil sheet.

(23) It is to be noted that in some of the preferred examples, there is no requirement for the surface of the mould to be treated before the application of the components for moulding, for example the SMC, and veil if required. In particular, in some examples, there will be no requirement for the application of a dye to the mould, liquid resin, and/or other surface treatments. In many examples, any such components required may be included in the SMC material.

(24) In other arrangements, the mould may be coated with a powder coating which then forms a coating on the product. This feature may be present in relation to any of the aspects of the invention. As an example, a powder coating can be applied electrostatically to the mould surface. Where the mould surface is heated, the powder coating melts or softens almost as soon as it is applied to the surface. For example the powder may include a polyester. The SMC or other matrix material (with or without integral reinforcing material) is then applied over the melted or softened powder coating. The melted or softened powder coating is then “sticky” on the surface of the mould and is thought to reduce movement of the matrix material during the moulding operation, which can in some cases give improved surface finish. In this example, the coating remains on the surface of the product, and provides a surface which is scratch and/or impact resistant. The powder coating can be coloured and thus provide a coloured coating to the product. The powder coating may be transparent or translucent and may have the appearance of a varnish on the surface of the product.

(25) It will be understood that a very wide range of different composite products could be formed using methods as described herein. The application of the present invention is not restricted to the formation of, for example, doors

(26) It will be understood that a very wide range of different composite products could be formed using methods as described herein. The application of the present invention is not restricted to the formation of, for example, doors.

(27) As discussed above, the image on the panel may be part of a larger image, and the composite products including the image elements may be joined or mounted together to form the larger image.

(28) For example, the image elements may be printed onto one or more sheets of the veil material. The sheets may be cut where appropriate.

(29) Data relating to the image elements required may be input into the printer and/or the printer software may be adapted to calculate the image element data in response to a command and information relating to the full image and the number and configuration of the elements required.

(30) Preferably the printer used is a digital printer allowing for fast changing of images on the printing line.

(31) It is envisaged that bespoke images can be printed for particular composite products. For example, a door made to order may have a particular door number printed onto the patterned veil, the door number being visible on the finished door.

(32) It will be appreciated that a wide number of images, text, patterns can be applied to composite products in this way.

(33) Example of Preparation of SMC

(34) The SMC comprises a curable matrix and reinforcement.

(35) To prepare the SMC, the matrix is prepared by mixing, for example a polyester resin with minerals and additives, for example including calcium carbonate and titanium dioxide together with appropriate pigments.

(36) The matrix in the form of the resin paste is then applied to a bottom film carrier. Glass fibres as the reinforcement are then applied to the upper surface of the resin paste on the film carrier. A further layer of the resin paste is applied to sandwich the fibres between the layers of matrix. A top film is applied to the upper layer of the matrix. The resulting layered composition is subsequently compressed using a series of rollers to form a sheet of the sheet moulding compound between the film carriers. The material is rolled onto rollers and kept for at least 3 days at a regulated temperature of for example 23 to 27 degrees C. The resulting SMC can be compression moulded with heat. The shelf life of the SMC before use is usually a few weeks.

(37) Foam

(38) In some examples of the invention, the substrate comprises a foam having frangible cell walls. Preferably this term includes a foam for which under compression the foam crumbles by brittle fracture of the cell walls e.g. involving a clean fracture of the cell walls. Such a foam can retain a clear and substantially dimensionally accurate imprint in the crushed zone of an object through which the compressive force is applied. In general, it is preferred that the yield strength of the foam, which in this case means the minimum force required to cause the fracture of the cell walls and for the foam to crumble, is in the range of about 100 to 140 KPa (15 to 20 lbs/sq.in) more preferably at least 200 KPa (30 lbs/sq.in), since this provides useful impact resistance. In general, for a given foam composition, the greater the density, the greater the yield strength.

(39) By using a substantially rigid plastics foam with frangible cell walls, mouldings with depressed zones of moulding detail can be readily formed by applying a layer to the foam core with sufficient pressure to cause the cell walls of the foam in the areas behind the depressed zones of the skin to be fractured whereby the foam is caused to conform to the contours of the skin in those zones by controlled localised crushing. Thus, air gaps between the skin and the substrate can be avoided and it is not necessary to pre-form the substrate in the form of complicated shapes. This is particularly advantageous since the presence of such air gaps in prior art products has in some cases contributed to their inability to resist changes in temperature.

(40) For such a method, it is advantageous to use an open cell foam having frangible walls as pressing into a conventional foamed core such as of polystyrene is in some cases not successfully achieved because the resilience of the foam may cause distortion of the skins when the pressure is released.

(41) In some examples of the invention, plastics foam are preferred which are substantially open-cell and rigid. However, the foam is advantageously selected to be of a high density relative to the foamed polystyrene conventionally used, e.g. a density of 75 kg/m.sup.3 or above, since this gives a better feel to the panel and makes it sound and handle more like a conventional wooden panel. However, foams having lower densities may also be selected. Where a higher density is desirable, the foam may contain a filler, more preferably a finely divided inert and preferably inorganic solid. The filler may be selected such that it contributes to the panels ability to resist changes in temperature. In a particularly preferred embodiment, the filler is capable of absorbing moisture, e.g. as water of crystallisation.

(42) While particular reference is made in the examples to open celled frangible foams, any suitable foam may be used. In some examples of the invention, foams which are substantially open cell are preferred; for example, a polyurethane foam, but in some examples the foam might not be open celled. Preferably in such example, the structure of the substrate is such that gases can be released from the mould. Where the foam is open celled, a foam that has an open-cell configuration at production is particularly suitable. A foam that also has frangible cell walls is particularly preferred where the panel or other product to be formed has depressed areas, such as to provide a moulding effect. However, as described herein, the moulding of the substrate can be provided by other methods, for example machining.

(43) Any foam can be used some aspects of the invention. In many examples, rigid foam materials are preferred. For example a rigid foam could be used to form a panel having a substantially flat (unmoulded) surface which may or may not include surface pattern as described herein.

(44) Alternatively, or in addition, the surface of the foam may be contoured. The contours could for example be formed on the surface of a foam block, for example by machining or any other suitable method. In such cases, the foam need not for example be a frangible or compressible foam.

(45) Where a foam having frangible cell walls is used, the cell wall will fracture as pressure is placed on the foam by the application of the depressed areas of the mould. This localised increase in pressure will increase the pressure inside the cell, which will cause the gases to travel through the foam, and the cell to collapse thereby accommodating the depressed area of the skin.

(46) One suitable foam is a rigid filled phenolic foam. One particularly suitable foam is that produced by effecting a curing reaction between:

(47) (a) a liquid phenolic resole having a reactivity number (as defined below) of at least 1 and

(48) (b) a strong acid hardener for the resole,

(49) in the presence of:

(50) (c) a finely divided inert and insoluble particulate solid which is present in an amount of at least 5% by weight of the liquid resole and is substantially uniformly dispersed through the mixture containing resole and hardener; the temperature of the mixture containing resole and hardener due to applied heat not exceeding 85 C and the said temperature and the concentration of the acid hardener being such that compounds generated as by-products of the curing reaction are volatilised within the mixture before the mixture sets whereby a foamed phenolic resin product is produced.

(51) By a phenolic resole is meant a solution in a suitable solvent of the acid-curable prepolymer composition obtained by condensing, usually in the presence of an alkaline catalyst such as sodium hydroxide, at least one phenolic compound with at least one aldehyde, in well-known manner. Examples of phenols that may be employed are phenol itself and substituted, usually alkyl substituted, derivatives thereof provided that the three positions on the phenolic benzene ring o- and p- to the phenolic hydroxyl group are unsubstituted. Mixtures of such phenols may also be used. Mixtures of one or more than one of such phenols with substituted phenols in which one of the ortho or para positions has been substituted may also be employed where an improvement in the flow characteristics of the resole is required but the cured products will be less highly cross-linked. However, in general, the phenol will be comprised mainly or entirely of phenol itself, for economic reasons.

(52) The aldehyde will generally be formaldehyde although the use of higher molecular weight aldehydes is not excluded.

(53) The phenol/aldehyde condensation product component of the resole is suitably formed by reaction of the phenol with at least 1 mole of formaldehyde per mole of the phenol, the formaldehyde being generally provided as a solution in water, e.g. as formalin. It is preferred to use a molar ratio of formaldehyde to phenol of at least 1.25 to 1 but ratios above 2.5 to 1 are preferably avoided. The most preferred range is 1.4 to 2.0 to 1.

(54) The mixture may also contain a compound having two active H atoms (dihydric compound) that will react with the phenol/aldehyde reaction product of the resole during the curing step to reduce the density of cross-linking. Preferred dihydric compounds are diols, especially alkylene diols or diols in which the chain of atoms between the OH groups contains not only methylene and/or alkyl-substituted methylene groups but also one or more hetero atoms, especially oxygen atoms, e.g. ethylene glycol, propylene glycol, propane-1,3-diol, butane-1,4-diol and neopentyl glycol. Particularly preferred diols are poly-, especially di-, (alkylene ether) diols e.g. diethylene glycol and, especially, dipropylene glycol. Preferably the dihydric compound is present in an amount of from 0 to 35% by weight, more preferably 0 to 25% by weight, based on the weight of phenol/aldehyde condensation product. Most preferably, the dihydric compound, when used, is present in an amount of from 5 to 15% by weight based on the weight of phenol/aldehyde condensation product. When such resoles containing dihydric compounds are employed in the present process, products having a particularly good combination of physical properties, especially strength, can be obtained.

(55) Suitably, the dihydric compound is added to the formed resole and preferably has 2-6 atoms between OH groups.

(56) The resole may comprise a solution of the phenol/aldehyde reaction product in water or in any other suitable solvent or in a solvent mixture, which may or may not include water. Where water is used as the sole solvent, it is preferred to be present in an amount of from 15 to 35% by weight of the resole, preferably 20 to 30%. Of course the water content may be substantially less if it is used in conjunction with a cosolvent. e.g. an alcohol or one of the above-mentioned dihydric compounds where one is used.

(57) As indicated above, the liquid resole (i.e. the solution of phenol/aldehyde product optionally containing dihydric compound) must have a reactivity number of at least 1. The reactivity number is 10/x where x is the time in minutes required to harden the resole using 10% by weight of the resole of a 66-67% aqueous solution of p-toluene sulfonic acid at 60 degreesC. The test involves mixing about 5 ml of the resole with the stated amount of the p-toluene sulfonic acid solution in a test tube, immersing the test tube in a water bath heated to 60 degrees C. and measuring the time required for the mixture to become hard to the touch. The resole should have a reactivity number of at least 1 for useful foamed products to be produced and preferably the resole has a reactivity number of at least 5, most preferably at least 10.

(58) The pH of the resole, which is generally alkaline, is preferably adjusted to about 7, if necessary, for use in the process, suitably by the addition of a weak organic acid such as lactic acid.

(59) Examples of strong acid hardeners are inorganic acids such as hydrochloric acid, sulphuric acid and phosphoric acid, and strong organic acids such as aromatic sulphonic acids, e.g. toluene sulphonic acids, and trichloroacetic acid. Weak acids such as acetic acid and propionic acid are generally not suitable.

(60) The preferred hardeners for the process of the invention are the aromatic sulfonic acids, especially toluene sulfonic acids.

(61) The acid may be used as a solution in a suitable solvent such as water.

(62) When the mixture of resole, hardener and solid is to be poured, e.g. into a mould and in slush moulding applications, the amount of inert solid that can be added to the resole and hardener is determined by the viscosity of the mixture of resole and hardener in the absence of the solid. For these applications, it is preferred that the hardener is provided in a form, e.g. solution, such that when mixed with the resole in the required amount yields a liquid having an apparent viscosity not exceeding about 50 poises at the temperature at which the mixture is to be used, and the preferred range is 5-20 poises. Below 5 Poises, the amount of solvent present tends to present difficulties during the curing reaction.

(63) The curing reaction is exothermic and will therefore of itself cause the temperature of the mixture containing resole and acid hardener to be raised. The temperature of the mixture may also be raised by applied heat but the temperature to which said mixture may then be raised (that is, excluding the effect of any exotherm) must not exceed 85 degrees C.

(64) If the temperature of the mixture exceeds 85 degrees C. before addition of the hardener, it is difficult or impossible thereafter to properly disperse the hardener through the mixture because of incipient curing. On the other hand, it is difficult, if not impossible, to uniformly heat the mixture above 85 degrees C. after addition of the hardener.

(65) Increasing the temperature towards 85 degrees C. tends to lead to coarseness and non-uniformity of the texture of the foam but this can be offset at least to some extent at moderate temperatures by reducing the concentration of hardener. However at temperatures much above 75 degrees C. even the minimum amount of hardener required to cause the composition to set is generally too much to avoid these disadvantages. Thus, temperatures above 75 degrees C. are preferably avoided and preferred temperatures for most applications are from ambient temperature to about 75 degrees C. The preferred temperature range appears to depend to some extent on the nature of the solid (c). For most solids it is from 25 to 65 degrees C. but for some solids, in particular wood flour and grain flour, the preferred range is 25 to 75 degrees C. The most preferred temperature range is 30 to 50 degrees C. Temperatures below ambient, e.g. down to 10 degrees C. can be used, if desired, but no advantage is gained thereby. In general, at temperatures up to 75 degrees C., increase in temperature leads to decrease in the density of the foam and vice versa.

(66) The amount of hardener present also affects the nature of the product as well as the rate of hardening. Thus, increasing the amount of hardener not only has the effect of reducing the time required to harden the composition but above a certain level dependant on the temperature and nature of the resole it also tends to produce a less uniform cell structure. It also tends to increase the density of the foam because of the increase in the rate of hardening. In fact, if too high a concentration of hardener is used, the rate of hardening may be so rapid that no foaming occurs at all and under some conditions the reaction can become explosive because of the build up of gas inside a hardened shell of resin. The appropriate amount of hardener will depend primarily on the temperature of the mixture of resole and hardener prior to the commencement of the exothermic curing reaction and the reactivity number of the resole and will vary inversely with the chosen temperature and the reactivity number. The preferred range of hardener concentration is the equivalent of 2 to 20 parts by weight of p-toluene sulfonic acid per 100 parts by weight of phenol/aldehyde reaction product in the resole assuming that the resole has a substantially neutral reaction, i.e. a pH of about 7. By equivalent to p-toluene sulfonic acid, we mean the amount of chosen hardener required to give substantially the same setting time as the stated amount of p-toluene sulfonic acid. The most suitable amount for any given temperature and combination of resole and finely divided solid is readily determinable by simple experiment. Where the preferred temperature range is 25-75 degrees C. and the resole has a reactivity number of at least 10, the best results are generally obtained with the use of hardener in amounts equivalent to 3 to 10 parts of p-toluene sulfonic acid per 100 parts by weight of the phenol/aldehyde reaction product. For use with temperatures below 25 degrees C. or resoles having a reactivity number below 10, it may be necessary to use more hardener.

(67) It may be necessary to make some adjustment of the hardener composition in accordance with the nature, especially shape and size, of the mould and this can be established by experiment.

(68) By suitable control of the temperature and of the hardener concentration, the time lapse between adding the hardener to the resole and the composition becoming hard (referred to herein as the setting time) can be varied at will from a few seconds to up to an hour or even more, without substantially affecting the density and cell structure of the product.

(69) Another factor that controls the amount of hardener required can be the nature of the inert solid. Very few are exactly neutral and if the solid has an alkaline reaction, even if only very slight, more hardener may be required because of the tendency of the filler to neutralize it. It is therefore to be understood that the preferred values for hardener concentration given above do not take into account any such effect of the solid. Any adjustment required because of the nature of the solid will depend on the amount of solid used and can be determined by simple experiment.

(70) The exothermic curing reaction of the resole and acid hardener leads to the formation of by-products, particularly aldehyde and water, which are at least partially volatilised.

(71) The curing reaction is effected in the presence of a finely divided inert and insoluble particulate solid which is substantially uniformly dispersed throughout the mixture of resole and hardener. By an inert solid we mean that in the quantity it is used it does not prevent the curing reaction.

(72) It is believed that the finely divided particulate solid provides nuclei for the gas bubbles formed by the volatilisation of the small molecules, primarily CH.sub.2O and/or H.sub.2O, present in the resole and/or generated by the curing action, and provides sites at which bubble formation is promoted, thereby assisting uniformity of pore size. The presence of the finely divided solid may also promote stabilization of the individual bubbles and reduce the tendency of bubbles to agglomerate and eventually cause likelihood of bubble collapse prior to cure. The phenomenon may be similar to that of froth flotation employed in the concentration of low grade ores in metallurgy. In any event, the presence of the solid is essential to the formation of the product. To achieve the desired effect, the solid should be present in an amount of not less than 5% by weight based on the weight of the resole.

(73) Any finely divided particulate solid that is insoluble in the reaction mixture is suitable, provided it is inert. The fillers may be organic or inorganic (including metallic), and crystalline or amorphous. Even fibrous solids have been found to be effective, although not preferred. Examples include 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, mineral fibres such as finely chopped glass fibre and finely divided asbestos, chopped fibres, finely chopped natural or synthetic fibres, ground plastics and resins whether in the form of powder or fibres, e.g. reclaimed waste plastics and resins, pigments such as powdered paint and carbon black, and starches.

(74) Solids having more than a slightly alkaline reaction, e.g. silicates and carbonates of alkali metals, are preferably avoided because of their tendency to react with the acid hardener. Solids such as talc, however, which have a very mild alkaline reaction, in some cases because of contamination with more strongly alkaline materials such as magnesite, are acceptable.

(75) Some materials, especially fibrous materials such as wood flour, can be absorbent and it may therefore be necessary to use generally larger amounts of these materials than non-fibrous materials, to achieve valuable foamed products.

(76) The solids preferably have a particle size in the range 0.5 to 800 microns. If the particle size is too great, the cell structure of the foam tends to become undesirably coarse. On the other hand, at very small particle sizes, the foams obtained tend to be rather dense. The preferred range is 1 to 100 microns, most preferably 2 to 40 microns. Uniformity of cell structure appears to be encouraged by uniformity of particle size. Mixtures of solids may be used if desired.

(77) If desired, solids such as finely divided metal powders may be included which contribute to the volume of gas or vapour generated during the process. If used alone, however, it be understood that the residues they leave after the gas by decomposition or chemical reaction satisfy the requirements of the inert and insoluble finely divided particulate solid required by the process of the invention.

(78) Preferably, the finely divided solid has a density that is not greatly different from that of the resole, so as to reduce the possibility of the finely divided solid tending to accumulate towards the bottom of the mixture after mixing.

(79) One preferred class of solids is the hydraulic cements, e.g. gypsum and plaster, but not Portland cement because of its alkalinity. These solids will tend to react with water present in the reaction mixture to produce a hardened skeletal structure within the cured resin product. Moreover, the reaction with the water is also exothermic and assists in the foaming and curing reaction. Foamed products obtained using these materials have particularly valuable physical properties. Moreover, when exposed to flame even for long periods of time they tend to char to a brick-like consistency that is still strong and capable of supporting loads. The products also have excellent thermal insulation and energy absorption properties. The preferred amount of inert particulate solid is from 20 to 200 parts by weight per 100 parts by weight of resole.

(80) Another class of solids that is preferred because its use yields products having properties similar to those obtained using hydraulic cements comprises talc and fly ash. The preferred amounts of these solids are also 20 to 200 parts by weight per 100 parts by weight of resole.

(81) For the above classes of solid, the most preferred range is 50 to 150 parts per 100 parts of resole.

(82) Thixotropic foam-forming mixtures can be obtained if a very finely divided solid such as Aerosil (finely divided silica) is included.

(83) If a finely divided metal powder is included, electrically conducting properties can be obtained. The metal powder is preferably used in amounts of from 50 to 250 parts per 100 parts by weight of resole.

(84) In general, the maximum amount of solid that can be employed is controlled only by the physical problem of incorporating it into the mixture and handling the mixture. In general it is desired that the mixture is pourable but even at quite high solids concentrations, when the mixture is like a dough or paste and cannot be poured, foamed products with valuable properties can be obtained.

(85) In general, it is preferred to use the fibrous solids only in conjunction with a non-fibrous solid since otherwise the foam texture tends to be poorer.

(86) Other additives may be included in the foam-forming mixture; e.g. surfactants, such as anionic materials e.g. sodium salts of long chain alkyl benzene sulfonic acids, non-ionic materials such as those based on poly(ethylene oxide) or copolymers thereof, and cationic materials such as long chain quaternary ammonium compounds or those based on polyacrylamides; viscosity modifiers such as alkyl cellulose especially methyl cellulose, and colorants such as dyes or pigments. Plasticisers for phenolic resins may also be included provided the curing and foaming reactions are not suppressed thereby, and polyfunctional compounds other than the dihydric compounds referred to above may be included which take part in the cross-linking reaction which occurs in curing; e.g. di- or poly-amines, di- or poly-isocyanates, di- or poly-carboxylic acids and aminoalcohols.

(87) Polymerisable unsaturated compounds may also be included possibly together with free-radical polymerisation initiators that are activated during the curing action e.g. acrylic monomers, so-called urethane acrylates, styrene, maleic acid and derivatives thereof, and mixtures thereof.

(88) Other resins may be included e.g. as prepolymers which are cured during the foaming and curing reaction or as powders, emulsions or dispersions. Examples are polyacetals such as polyvinyl acetals, vinyl polymers, olefin polymers, polyesters, acrylic polymers and styrene polymers, polyurethanes and prepolymers thereof and polyester prepolymers, as well as melamine resins, phenolic novolaks, etc.

(89) Conventional blowing agents may also be included to enhance the foaming reaction, e.g. low boiling organic compounds or compounds which decompose or react to produce gases.

(90) The foam-forming compositions may also contain dehydrators, if desired.

(91) A preferred method of forming the foam-forming composition comprises first mixing the resole and inert filler to obtain a substantially uniform dispersion of the filler in the resole, and thereafter adding the hardener. Uniform distribution of both the filler and the hardener throughout the composition is essential for the production of uniformly textured foam products and therefore thorough mixing is required.

(92) If it is desired that the composition is at elevated temperature prior to commencement of the exothermic reaction, this can be achieved by heating the resole or first mixing the resole and the solid and then heating the mixture. Preferably the solid is added to the resole just before the addition of the hardener. Alternatively, the mixture of resole, solid and hardener may be prepared and the whole mixture then heated, e.g. by short wave irradiation, preferably after it has been charged to a mould. A conventional radiant heat oven may also be used, if desired, but it is difficult to achieve uniform heating of the mixture by this means.

(93) Preferably, the foam has a density in the range 75 to 500 kg/m.sup.3, more preferably 100 to 400 kg/m.sup.3 and most preferably 100 to 250 kg/m.sup.3. Foam cell size is also important because up to a limit the larger the size of the cell for a given density, the thicker will be the walls and hence the greater the physical strength of the foam. However if the cell size is too large, the strength begins to suffer. Preferably, the cell size is in the range of 1 to 3 mm.

(94) It will be understood that the present invention has been described above purely by way of example, and modification of detail can be made within the scope of the invention.

(95) In particular, the examples above have been described in relation to the manufacture of panels, in particular the manufacture of doors. However, it should be appreciated that the invention has very wide application including other products. Indeed it is envisaged that an extremely wide range of products could be made in accordance with methods of the present invention. Many moulded products could be made using the methods of the present invention, even where those products may currently be manufactured using different materials (for example wood, metal, porcelain) at present. In addition to building products, it is envisaged that for example, the invention could find application to vehicle parts and fittings, casings for electrical equipment and many household items of which furniture, picture frames, chairs, tables, lamp bases, vases, bowls are only a few examples.

(96) The methods described may, for example, be used to produce products for sports, or other leisure activities. For example, methods described might be used for forming rackets, bats, or other products, for example skis. Products made by the methods may find application for example in the aerospace, aircraft or other vehicle fields. For example, the methods described could be used to form panels for use in aircraft skins and/or as internal panels in the aircraft. The products might find application as blades, for example for wind turbines.

(97) Each feature disclosed in the description, and (where appropriate) the claims and drawings may be provided independently or in any appropriate combination.