AU775758B2 - A method of manufacturing syntactic foam - Google Patents

Description

AUSTRALIA

Patents Act COMPLETE SPECIFICATION

(ORIGINAL)

Application Number: Lodged: Complete Specification Lodged: Class Int. Class Accepted: Published: Priority: Related Art: Applicants: Address for service in Australia: ROBERTO DE TOFFOL ATHENA AVENUE, ST IVES NSW 2075 PHILLIPS ORMONDE FITZPATRICK 367 Collins Street MELBOURNE VICTORIA 3000 Tel: (03) 9614 1944 Fax: (03) 9614 1867 Attorney Code: PO Complete Specification for the invention entitled: "A METHOD OF MANUFACTURING SYNTACTIC FOAM" Our Ref: IRN 644841 The following statement is a full description of this invention, including the best method of performing it known to applicant: -1formacrm.do A METHOD OF MANUFACTURING SYNTACTIC FOAM Field of the Invention The present invention relates generally to syntactic foams and more particularly to an improved method of manufacturing syntactic foam.

Background of the Invention Syntactic foams are composite materials whose resinous matrix is embedded with preformed particles such as glass or ceramic microspheres.

Syntactic foams distinguish themselves from other foams by the fact that hollow or solid spheres of a predetermined size and packing composition are used to control the density of the foam.

Syntactic foams have been used for purposes which require a low density packing material such as undersea/marine equipment for deep-ocean i" current-metering, anti-submarine warfare, sandwich composites, the :aerospace industry and the automotive industry.

Difficulties have been experienced, however, in producing syntactic foams that have a density which is comparable to conventional foams.

Typical densities of syntactic foams vary between 0.3 and 0.5 g/cm 3 whilst conventional foams typically vary between 0.01 and 0.1 g/cm 3 The density of syntactic foams has generally been restricted by the limited porosity of the foams. Porosity is a measure of the total void volume of the syntactic foam, and constitutes the sum of the void volume of the microspheres and the interstitial void volume. Using current methods of syntactic foam .o manufacture, the void volume provided by the microspheres is greater than the void volume provided by the interstitial spaces. Thus, the density of syntactic foams have been limited by the void volume of the microspheres.

As such, the application of syntactic foams have been limited.

Summary of the Invention An aim of the present invention is to provide a novel method of manufacturing syntactic foam which is ideally suitable for manufacture of low density foams and which is simple and inexpensive.

Accordingly, in a first aspect of the invention, there is provided a method of forming a syntactic foam including the steps of: a) combining a polymer, microspheres and a solvent to form a slurry; N: RJRNV4484le p ecOp4O601 doc b) thereafter removing at least a portion of the solvent through a porous wick; and c) applying conditions which substantially solidify the polymer.

The applicant has found that by manufacturing syntactic foams in accordance with the method of the invention, it is possible to provide adequate coating of the microspheres to form the syntactic foam using a high microsphere mass fraction. This occurs primarily by the solvent reducing the viscosity of the polymer thereby allowing less polymer to be used to coat the microspheres and by causing at least a portion of the solvent to be removed from the composition. The applicant has found that using this method the porosity of the interstitial void volume of the syntactic foams can be greater than the void volume of the microspheres. This enables syntactic foam i densities of less than 0.15 g/cm 3 to be produced. Further, the technique is 5simple and is ideally suited for mass production and easily applicable for manufacturing large items.

In a preferred form, the method further includes the steps of combining the polymer and the microspheres to form a paste, and thereafter adding the solvent to the paste to form the slurry and mixing the slurry to achieve dispersion of the microspheres prior to removal of the solvent. Even more preferred is that a final portion of microspheres necessary to maintain the desired mass fraction is added alternatively with the solvent. This helps to maintain a consistency which allows easy pouring.

In a preferred aspect of the invention, the solvent is removed from the slurry while the slurry is in a mould such that the syntactic foam forms a desired physical conformation upon removal of the solvent. In an especially preferred aspect of the invention, the syntactic foam is made by a method in which the mould is the porous wick for removal of the solvent. The porous wick itself may be made from any material that is capable of soaking up or removing the solvent. The most preferred porous wick is made of plaster.

Alternatively, the porous wick may be made of clay, ceramic, cement, concrete, finely perforated plastic or metallic sheets with absorbent backing, fine metallic mesh/gauze with absorbent backing, rigid porous foams or sponge-like material.

N:1JRN844M1W opfeespeW4OO1.doc An advantage of this arrangement is that the removal of the solvent through the mould walls does not cause any major disturbance of the distribution of the microspheres. As such, the resulting syntactic foam is able to maintain an even density and tactile strength.

To allow for ease of moulding and speed of manufacture, the amount of solvent added is sufficient to form a slip by maintaining a soupy consistency. The mixture can then be quickly poured into the desired mould.

It is a preferred aspect of the present invention that the solvent is a volatile alcohol or ketone. The most preferred alcohols are butyl alcohol, isopropyl alcohol, ethyl alcohol or methyl alcohol. Even more preferred is that the solvent is the ketone acetone. Alternatively, the solvent may be water or a mixture of water and alcohol or water and acetone. In general, a slip made using water requires a lower ratio of solvent to polymer and hardener. The :volume ratio of water to polymer is generally between 9:1 and 6:1. The volume ratio of acetone to polymer is between 40:1 and 9:1. The volume ratio of water to polymer and acetone to polymer varies with the ratio of microspheres to polymer. The greater the ratio of microspheres to polymer, :the greater the volume of solvent required to maintain a consistency necessary to allow pouring of the mixture. Ideally, the volume ratio of solvent to polymer is sufficient to maintain a slip.

The polymer may be dissolved in the solvent, or dispersed throughout the solvent as a suspension. In a preferred aspect of the invention, the polymer is dissolved in the solvent. It is especially preferred that the polymer is dissolved in acetone. Alternatively, the polymer is homogenised or dispersed throughout the solvent as an insoluble suspension.

The polymer used in the method of making the syntactic foam of the present invention may be any resin that is effectively employed in syntactic foam manufacture. The classes of resins used for syntactic foam manufacture may include but is not restricted to amino resins, epoxide resins, phenolic and other tar acid resins, urea and melamine resins, vinyl resins, styrene resins, alkyd resins, acrylic resins, polyethylene resins, polypropylene resins, petroleum polymer resins, polyamide resins, polycarbonate resins, acetal resins, flourohydrocarbon resins, polyester N:VRW6444l'cowniacspc4OOi.doc resins and polyurethane resins. Further, the polymer may be water soluble copolymers such as poly(N-vinylpyrrolidone-vinyl acetate). A particularly preferred resin is a phenolic resin.

Depending on the nature of the polymer, the polymer may include a crosslinking agent or hardener which causes solidification of the polymer material. In cases where the polymer includes a cross-linker to solidify, it is preferred that the weight ratio of hardener to polymer is 1:10. However, it is envisaged that the ratio of hardener to polymer will vary depending on the type of polymer and the degree of crosslinking that is desired. For example, increased amounts of hardener will allow low temperature curing and will speed up gelation. Decreasing the relative amounts of hardener to polymer to a weight ratio as low as 5:100 may be possible, but higher curing temperatures and longer gelation times may be required.

Preferably, the syntactic foam of the present invention is a low density syntactic foam. To reduce the density of the syntactic foam, the microspheres are advantageously hollow gas filled spheres. They are generally made of soda-lime-borosilicate glass, but may also be made from, but not limited to, any one of the following types: carbon, ceramic, phenolic, epoxy or melamine-formaldehyde. For some applications it is envisaged that the microspheres used in the method of the present invention will be thermoplastic. The microspheres may be untreated or precoated. Preferably, the surface of the microspheres is precoated with a coupling agent, such as a silane coupling agent. The microspheres may also be dried prior to use. It is also envisaged that the syntactic foam of the present invention may also comprise a non homogenous mixture of microspheres made of different compounds.

As indicated above, the porosity of the syntactic foam is a combination of the void volume of the microspheres and the interstitial void volume between the microspheres. An advantage of the preferred form of the invention is that the method allows for high interstitial void volume to be produced because adequate coating of the microspheres can occur using low amounts of polymer. The method also does not induce forces in the mix that results in increased packing of the microspheres. As such, it is possible NURtW4841XtWesp4c0601 doc using the method of the invention to lower the density of the syntactic foam by creating a high interstitial void volume. The applicant has found that the density of the syntactic foam produced by the method of the present invention is lowest when the interstitial void volume is greater than the total void volume of the microspheres. Thus, the greater proportion of porosity in the low density syntactic foam of the present invention results from the interstitial voids between the microspheres.

In a preferred aspect of the invention, the microspheres are less than 420 micrometres in diameter. More preferably they are less than 300 micrometres. Even more preferably they are less than 150 micrometers in diameter. To vary the density of the syntactic foam and to obtain tighter packing of the microspheres, the method of making syntactic foam can use microspheres of different sizes. In a preferred aspect of the invention, small microspheres are mixed with large microspheres to produce a closely packed syntactic foam with a high microsphere volume fraction.

The density and mechanical strength of the syntactic foam can be controlled by the weight-ratio of microspheres to polymer. Depending on the structural properties required, the weight ratio of microspheres to polymer is *'...typically between 8:2 and 2:8. It is preferred that the weight ratio of microspheres to polymer is between 8:2 and 1:1. A more preferable weight ratio of microspheres to polymer is between 8:2 and 6:4. Still even more preferred is a weight ratio of microspheres to polymer of between 8:2 and preferred is a weight ratio of microspheres to polymer of between 8:2 and 7:3. However, weight ratios of microspheres to polymer of between 1:1 and 2:8 are also effective in producing a syntactic foam. Lower ratios of microspheres to polymer results in a denser foam with greater mechanical strength. In the case of foams of greater mechanical strength, weight ratios of between 4:6 and 2:8 are preferred. For greater mechanical strength, weight ratios of between 3:7 and 2:8 are preferred. It is likely that the effective ratio of microspheres to polymer will vary with the properties of the polymer and the microspheres employed. Accordingly, polymers with greater wettability may be effective at weight ratios of greater than 8:2.

Preferably, the density of the syntactic foam produced by the method of the present invention is between 0.05 and 0.5 g/cm 3 Even more N:\RNW44l44lInpletese40601 doc preferably, the density of the syntactic foam is between 0.055 g/cm 3 and 0.15 g/cm 3 The polymer and microspheres may be mixed by any method which provides sufficient dispersion of the microspheres through the polymer but does not damage a proportion of the microspheres. The method of mixing the polymer/microsphere mixture with the solvent may be any method which results in dispersion of the microspheres throughout the mixture. It should be noted that the method of mixing the microspheres and polymer need not be the same as the method of mixing the polymer/microsphere mix with the solvent. It is however preferred due to ease of manufacture that the polymer and microspheres are mixed in the same manner as the solvent and polymer/microspheres.

Following removal of the solvent through the porous wick, the *syntactic foam of the present invention may be treated under conditions to cure or solidify the polymer. These may be conditions such as elevated or lowered temperature, stillness, catalytic activity, or any other conditions which allow solidification of the polymer. The conditions will vary with the type of polymer used. The preferred condition is temperature. The temperature used to cure the polymer may be any temperature which does not damage the polymer or the microspheres. The temperature will vary depending on the type of polymer used and the nature of the microspheres or the solvent. Preferably, the temperature will be between 00 and 600C. Even more preferably, the temperature will be between 200 and 350C. Prior to heating, the majority of the solvent is preferably removed through/by the porous wick. Thus, heating should be only sufficient to allow curing of the resin. This will reduce damage to both the resin and the microspheres.

In yet a further aspect, the present invention relates to a syntactic foam when made by any form of the method of the first aspect of the invention discussed above.

The following examples are provided as illustrative of the present invention and are not intended to limit its scope in any way.

N:MRNh44841cwmpelespeO40601 .doc Examples Example 1 Resinox CL1916 phenolic resin was mixed with AH2070S acid hardener in a weight ratio of 100 parts resin to 10 parts hardener and mixed by hand using a bowl and a wooden spatula for a period of 2 minutes. A portion of an equivalent mass of 3M Scotchlite K1 soda-lime-borosilicate glass spheres were added slowly to the mixture to form a smooth viscous paste. Acetone was added to maintain a smooth consistency, and a further portion of the microspheres was added, followed by additional acetone. This process of alternating between addition of microspheres and acetone was continued until a mass of microspheres equivalent to the mass of resin had been added. The total volume of acetone added was twenty millilitres. The mixture was then gently stirred for 8 minutes, and subsequently poured into a plaster mould. The specimen was then placed in an oven at 30.90C for a period of 24 hours. At this stage, the specimen was fully cured.

The resulting syntactic foam has the following properties: Sphere volume fraction 0.310 Resin volume fraction 0.032 Void fraction 0.658 Sphere Mass Fraction 0.50 Resin mass fraction 0.50 Foam Density (g/cm 3 0.077 Tactile Toughness Medium Colour Pearl White Example 2 Resinox CL1916 phenolic resin was mixed with AH2070S acid hardener in a weight ratio of 100 parts resin to 10 parts hardener and mixed by hand using a bowl and a wooden spatula for a period of 3 minutes. 3M Scotchlite K1 soda-lime-borosilicate glass spheres were added slowly to the mixture to form a smooth viscous paste. Acetone was added to maintain a smooth consistency, and a further portion of the microspheres was added, followed by additional acetone. This process of alternating between addition of microspheres and acetone was continued until a mass fraction of spheres to resin of 0.60 to 0.40 was obtained. The mixture was stirred to maintain a smooth paste. The total amount of acetone added was twenty five millilitres.

N:RN 4484lompcltespec40601 doc The mixture was then gently stirred for 12 minutes, and subsequently poured into a plaster mould. The specimen was then placed in an oven at 50 0 C for a period of 24 hours. At this stage, the specimen was fully cured.

The resulting syntactic foam has the following properties: Sphere volume fraction 0.433 Resin volume fraction 0.030 Void fraction 0.537 Sphere Mass Fraction 0.60 Resin mass fraction 0.40 Foam Density (g/cm 0.090 Tactile Toughness Medium Colour Pearl White Under scanning electron microscopic examination, the syntactic foam had few broken spheres and a good microsphere packing structure as can be seen in figure 1.

10 Example 3 Resinox CL1916 phenolic resin was mixed with AH2070S acid hardener in a weight ratio of 100 parts resin to 10 parts hardener and mixed by hand using a bowl and a wooden spatula for a period of 3 minutes. 3M Scotchlite K1 soda-lime-borosilicate glass spheres were added slowly to the 15 mixture to form a smooth viscous paste. Acetone was added to maintain a smooth consistency, and a further portion of the microspheres was added, followed by additional acetone. This process of alternating between addition of microspheres and addition of acetone was continued until a mass fraction of spheres to resin of 0.70 to 0.30 was obtained. The mixture was stirred to maintain a smooth paste. The total amount of acetone added was twenty millilitres. The mixture was then gently stirred for 10 minutes, and subsequently poured into a plaster mould. The specimen was then placed in an oven at 500C for a period of 24 hours. At this stage, the specimen was fully cured.

N:\IRN44841 cxpletespe40601 .doc The resulting syntactic foam has the following properties: Sphere volume fraction 0.411 Resin volume fraction 0.018 Void fraction 0.571 Sphere Mass Fraction 0.70 Resin mass fraction 0.30 Foam Density (g/cm 0.073 Tactile Toughness Soft Colour Pearl White Under scanning electron microscopic examination, the syntactic foam had few broken spheres and a good microsphere packing structure as can be seen in figure 2.

Example 4 Resinox CL1916 phenolic resin was mixed with AH2070S acid hardener in a weight ratio of 100 parts resin to 10 parts hardener and mixed 10 by hand using a bowl and a wooden spatula for a period of 3 minutes. 3M Scotchlite K1 soda-lime-borosilicate glass spheres were added slowly to the mixture to form a smooth viscous paste. Acetone was added to maintain a smooth consistency, and a further portion of the microspheres was added, followed by additional acetone. This process of alternating between addition 15 of microspheres and acetone was continued until a mass fraction of spheres to resin of 0.80 to 0.20 was obtained. The mixture was stirred to maintain a smooth paste. The total amount of acetone added was twenty five millilitres.

I. The mixture was then gently stirred for 10 minutes, and subsequently poured into a plaster mould. The specimen was then placed in an oven at 50 0 C for a period of 24 hours. At this stage, the specimen was fully cured.

The resulting syntactic foam has the following properties: Sphere volume fraction 0. 335 Resin volume fraction 0.035 Void fraction 0.630 Sphere Mass Fraction 0.80 Resin mass fraction 0.20 Foam Density 0.055 Tactile Toughness Soft Colour Pearl White N:MRNW4441komhletespeD4 0601 doc Under scanning electron microscopic examination, the syntactic foam had few broken spheres and a good microsphere packing structure as can be seen in figure 3.

Example Resinox CL1916 phenolic resin was mixed with AH2070S acid hardener in a weight ratio of 100 parts resin to 10 parts hardener and mixed by hand using a bowl and a wooden spatula for a period of 3 minutes. A portion of an equivalent mass of 3M Scotchlite K1 soda-lime-borosilicate glass spheres were added slowly to the mixture to form a smooth viscous paste. Water was added to maintain a smooth consistency, and a further portion of the microspheres was added, followed by additional water. This process of alternating between addition of microspheres and water was i continued until a mass of microspheres equivalent to the mass of resin had 15 been added. The total volume of water added was fifteen millilitres. The mixture was then gently stirred for 15 minutes, and subsequently poured into a plaster mould. The specimen was then placed in an oven at 50 0 C for a period of 24 hours. At this stage, the specimen was fully cured.

~The resulting syntactic foam has the following properties: 5* S

S.

0* Sphere volume fraction 0.472 Resin volume fraction 0.049 Void fraction 0.479 Sphere Mass Fraction 0.50 Resin mass fraction 0.50 Foam Density (g/cm 0.118 Tactile Toughness Medium Colour Pearl White Under scanning electron microscopic examination, the syntactic foam had many broken spheres as indicated in figure 4.

Example 6 Resinox CL1916 phenolic resin was mixed with AH2070S acid hardener in a weight ratio of 100 parts resin to 10 parts hardener and mixed by hand using a bowl and a wooden spatula for a period of 3 minutes. 3M Scotchlite K1 soda-lime-borosilicate glass spheres were added slowly to the N:\RNW44841mpti-lespec40601 Adoc mixture to form a smooth viscous paste. Water was added to maintain a smooth consistency, and a further portion of the microspheres were added, followed by additional water. This process of alternating between addition of microspheres and water was continued until a mass fraction of spheres to resin of 0.60 to 0.40 was obtained. The mixture was stirred to maintain a smooth paste. The total amount of water added was fifteen millilitres. The mixture was then gently stirred for 10 minutes, and subsequently poured into a plaster mould. The specimen was then placed in an oven at 50 0 C for a period of 24 hours. At this stage, the specimen was fully cured.

The resulting syntactic foam has the following properties: Sphere volume fraction 0.507 Resin volume fraction 0.035 Void fraction 0.542 Sphere Mass Fraction 0.60 Resin mass fraction 0.40 Foam Density (g/cm 0.106 Tactile Toughness Medium Colour Pearl White Under scanning electron microscopic examination, the syntactic foam had few broken spheres and a good microsphere packing structure as indicated in Figure Example 7 Synapol 2120 epoxy resin was mixed in Synapol 2120 hardener in a weight ratio of two parts resin to one part hardener and mixed by hand using a bowl and a wooden spatula for a period of three minutes. 3M Scotchlite K1 soda-lime-borosilicate glass spheres were added slowly to the mixture to form a smooth viscous paste. Acetone was added to maintain a smooth consistency, and a further portion of the microspheres was added, followed by additional acetone. This process of alternating between addition of microspheres and addition of acetone was continued until a mass of microspheres equivalent to the mass of resin had been added. The mixture was stirred to maintain a smooth paste. The total amount of acetone added was eighty millilitres. The mixture was then gently stirred for ten minutes, and subsequently poured into a cement mould. The specimen was then left N:u\RN644841onmtpleespc4Ok5O .loc to air dry for a period of twenty-three hours. At this stage, the specimen was fully cured.

The resulting syntactic foam has the following properties: Sphere volume fraction 0.296 Resin volume fraction 0.034 Void fraction 0.670 Sphere Mass Fraction 0.50 Resin mass fraction 0.50 Foam Density (g/cm 0.0738 Tactile Toughness Medium Colour White Example 8 Synapol 2120 epoxy resin was mixed with Synapol 2120 hardener in a weight ratio of two parts resin to one part hardener and mixed by hand using a bowl and a wooden spatula for a period of three minutes. 3M Scotchlite K1 soda-lime-borosilicate glass spheres were added slowly to the mixture to 10 form a smooth viscous paste. Acetone was added to maintain a smooth consistency, and a further portion of microspheres was added, followed by additional acetone. This process of alternating between addition of microspheres and addition of acetone was continued until a mass fraction of microspheres to resin of 0.60 to 0.40 was obtained. The mixture was stirred to maintain a smooth paste. The total amount of acetone added was ninety millimetres. The mixture was then gently stirred for ten minutes, and subsequently poured into a cement mould. The specimen was then left to air dry for a period of twenty-one hours. At this stage the specimen was fully Scured.

20 The resulting syntactic foam has the following properties: Sphere volume fraction 0.346 Resin volume fraction 0.026 Void fraction 0.628 Sphere Mass Fraction 0.60 Resin mass fraction 0.40 Foam Density (g/cm 3 0.072 Tactile Toughness Medium Colour White N :RNW4484Wiconmpepect 0601 doc a a Example 9 Synapol 2120 epoxy resin was mixed with Synapol 2120 hardener in a weight ratio of two parts resin to one part hardener and mixed by hand using a bowl and a wooden spatula for a period of three minutes. 3M Scotchlite K1 soda-lime-borosilicate glass spheres were added slowly to the mixture to form a smooth viscous paste. Acetone was added to maintain a smooth consistency, and a further portion of microspheres was added, followed by additional acetone. This process of alternating between addition of microspheres and addition of acetone was continued until a mass of microspheres equivalent to the mass of resin had been added. The mixture was stirred to maintain a smooth paste. The total amount of acetone added was eighty millilitres. mixture was then gently stirred for ten minutes, and subsequently poured into a plaster mould. The specimen was then left to air dry for a period of twenty-three hours. At this stage, the specimen was fully cured.

The resulting syntactic foam has the following properties: Sphere volume fraction 0.289 Resin volume fraction 0.033 Void fraction 0.678 Sphere Mass Fraction 0.50 Resin mass fraction 0.50 Foam Density (g/cm 0.072 Tactile Toughness Medium Colour White Example Synapol 2120 epoxy resin was mixed with Synapol 2120 hardener in a weight ratio of two parts resin to one part hardener and mixed by hand using a bowl and a wooden spatula for a period of three minutes. 3M Scotchlite K1 soda-lime-borosilicate glass spheres were added slowly to the mixture to form a smooth viscous paste. Acetone was added to maintain a smooth consistency, and a further portion of microspheres was added, followed by additional acetone. This process of alternating between addition of microspheres and addition of acetone was continued until a mass fraction of spheres to resin of 0.60 to 0.40 was obtained. The mixture was stirred to maintain a smooth paste. The total amount of acetone added was N:URNt4484I epecD404l .oc ninety millilitres. The mixture was then gently stirred for ten minutes, and subsequently poured into a plaster mould. The specimen was then left to air dry for a period of twenty-one hours. At this stage, the specimen was fully cured.

The resulting syntactic foam has the following properties: Sphere volume fraction 0.343 Resin volume fraction 0.026 Void fraction 0.631 Sphere Mass Fraction 0.60 Resin mass fraction 0.40 Foam Density (g/cm 3 0.071 Tactile Toughness Soft Colour White Example 11 Synapol 2120 epoxy resin was mixed with Synapol 2120 hardener in a weight ratio of two parts resin to one part hardener and mixed by hand using 10 a bowl and a wooden spatula for a period of three minutes. 3M Scotchlite K1 soda-lime-borosilicate glass spheres were added slowly to the mixture to *form a smooth viscous paste. Acetone was added to maintain a smooth consistency, and a further portion of microspheres was added, followed by additional acetone. This process of alternating between addition of 15 microspheres and addition of acetone was continued until a mass fraction of spheres to resin of 0.70 to 0.30 was obtained. The mixture was stirred to maintain a smooth paste. The total amount of acetone added was fifty millilitres. The mixture was then gently stirred for ten minutes, and subsequently poured into a plaster mould. The specimen was then left to air 20 dry for a period of twenty hours. At this stage, the specimen was fully cured.

The resulting syntactic foam has the following properties: Sphere volume fraction 0.389 Resin volume fraction 0.019 Void fraction 0.592 Sphere Mass Fraction 0.70 Resin mass fraction 0.30 Foam Density (g/cm3) 0.069 Tactile Toughness Soft Colour White N:IRNl444mlcompktespec40601 .doc Accordingly, the present invention discloses methods of producing syntactic foams which are able to produce foam of low density using techniques which are ideally suited for large scale application. It is to be appreciated that variations and/or additions may be made to the parts and processes previously defined without departing from the spirit or ambit of the inventions as defined in the following claims.

o *o

Claims (31)

1. A method of forming a syntactic foam including the steps of: combining a polymer, microspheres and a solvent to form a slurry; thereafter removing a portion of said solvent through a porous wick; and applying conditions which substantially solidify said polymer.

2. The method of claim 1 wherein said polymer and microspheres are combined to form a paste, and thereafter the solvent is combined with said paste to form a slurry.

3. The method of either claim 1 or 2 wherein said microspheres, said polymer and said solvent are combined together in incremental portions.

4. The method of any preceding claim wherein the slurry is inserted in a mould having a desired physical shape, and the solvent is removed from said slurry while the slurry is in a mould to form a syntactic foam with the desired physical shape.

5. The method of claim 4 wherein said mould includes an inner surface in contact with said slurry, and said inner surface forms at least part of the porous wick.

6. The method of any preceding claim wherein said porous wick is 20 selected from plaster, clay, ceramic, cement, concrete, finely perforated plastic sheets with absorbent backing, finely perforated metallic sheets with absorbent backing, fine metallic mesh/gauze with absorbent backing, rigid porous foams or sponge-like material.

7. The method of any preceding claim wherein said solvent is water or a S• 25 volatile alcohol or a ketone.

8. The method of any preceding claim wherein said solvent is selected from water, butyl alcohol, isopropyl alcohol, ethyl alcohol, methyl alcohol, acetone or mixtures thereof.

9. The method of claim 8 wherein said solvent is acetone.

10. The method of any preceding claim wherein said polymer is a resin based compound.

11. The method of claim 10 wherein said resin based compound is selected from amino resins, epoxide resins, phenolic resins, tar acid resins, N: RNA4484I%,,etpW pec4GQW.doc urea resins, melamine resins, vinyl resins, styrene resins, alkyd resins, acrylic resins, polyethylene resins, polypropylene resins, petroleum polymer resins, polyamide resins, polycarbonate resins, acetal resins, fluorohydrocarbon resins, polyester resins and polyurethane resins.

12. The method of claim 10 wherein said polymer is phenolic resin.

13. The method according to claim 10 wherein said polymer is a water soluble polymer.

14. The method according to any one of claims 10 to 13 wherein said polymer further comprises a cross linking agent.

15. The method according to any preceding claim wherein said microspheres are hollow gas filled spheres.

16. The method according to claim 15 wherein said gas filled spheres are selected from carbon, ceramic, phenolic, epoxy, or melamine-formaldehyde, soda-lime-borosilicate glass.

17. The method of claim 16 wherein said gas filled spheres are made of soda-lime-borosilicate glass.

18. The method of any preceding claim wherein the surface of said microspheres is pre-coated with a silane coupling agent.

19. The method of any preceding claim wherein the microspheres are less 20 than 420 micrometers in diameter. The method of any preceding claim wherein the microspheres and polymer are combined in a weight ratio of between 8:2 and 2:8.

21. The method of claim 20 wherein the weight ratio of microspheres to polymer is between 8:2 and 6:4. 25 22. The method of claim 20 wherein the weight ratio of microspheres to polymer is between 8:2 and 7:3.

23. The method of claim 20 wherein the weight ratio of microspheres to polymer is between 1:1 and 2:8.

24. The method of claim 20 wherein the weight ratio of microspheres to polymer is between 4:6 and 2:8. The method of claim 20 wherein the weight ratio of microspheres to polymer is between 3:7 and 2:8. N: MRN44841conmletespec4601 .doc

26. The method of any one of claims 20 to 25 wherein the syntactic foam has total void spaces formed from interstitial voids between the microspheres, and microsphere void spaces within the microspheres, wherein the weight ratio of microspheres to polymer forms a syntactic foam with a total interstitial void space greater than the total microsphere void space.

27. The method of any preceding claim wherein the syntactic foam has a density of between 0.05 and 0.5 grams/cm 3

28. The method of claim 27 wherein the density of the syntactic foam is between 0.055 grams/cm 3 and 0.15 grams/cm 3

29. A syntactic foam when made by a method including the steps of: combining a polymer, microspheres and a solvent to form a slurry; thereafter removing a portion of said solvent through a porous wick; and 15 applying conditions which substantially solidify said polymer.

30. A syntactic foam wherein the syntactic foam has total void spaces formed from interstitial voids between the microspheres, and microsphere void spaces within the microspheres, and wherein the total interstitial void space is greater than the total microsphere void space.

31. A syntactic foam formed by a method including the steps of: combining a polymer, microspheres and a solvent to form a slurry; thereafter removing a portion of said solvent through a porous wick; and 25 applying conditions which substantially solidify said polymer; wherein the syntactic foam has total void spaces formed from interstitial voids between the microspheres, and microsphere void spaces within the microspheres, and wherein the total interstitial void space is greater than the total microsphere void space.

32. A syntactic foam wherein the density of the syntactic foam is between 0.055 grams/cm 3 and 0.15 grams/cm 3

33. A method of forming syntactic foam substantially as herein described with reference to any one of the examples. N:\RN44841conm etespec04060.dloc

34. A syntactic foam substantially as herein described with reference to any one of the examples. DATED: 12 JUNE 2001 ORMVONDE FITZPATRICK Attorneys for ROBERTO DE TOFFOL N:VIRN'C44841 wnpStespeW4060l do