GB1591801A - Production of vermiculite foam - Google Patents

Description

(54) PRODUCTION OF VERMICULITE FOAM (71) We, IMPERIAL CHEMICAL IN DUSTRIES LIMITED, Imperial Chemical House, Millbank, London SW1P 3JF, a British Company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to inorganic foam and in particular to rigid foams of minerals.

Vermiculite is a phyllosilicate mineral having a layer structure. Vermiculite may be swollen by the action of aqueous salts and thereafter the structure broken down i.e. delaminated by mechanical action into extremely thin lamellae. Other phyllosilicate minerals for example hydrobiotites, or chlorite-vermiculites also contain a substantial proportion of vermiculite layers and these also may be swollen in the same or similar manner. These minerals which contain vermiculite layers also give rise to thin lamellae and it is to be understood that they are included in the present invention. It is preferred to use the vermiculite lamellae for the formation of the inorganic foam of this invention.

In our copending application No.

14764/76 (Serial No. 1,585,104) there is described a rigid foam comprising an inorganic cellular structure composed of lamallae of the mineral vermiculite. This foam was made by gasification of an aqueous suspension of small vermiculite lamellae produced by swelling and delaminating the mineral in the presence of water. We have now found that a rigid inorganic foam may be produced more readily from these vermiculite suspensions by the application of electromagnetic energy to the suspension.

According to the present invention a process for the production of a rigid foam of the mineral vermiculite comprises the passage of electro-magnetic energy having a frequency in the range from 104Hz to 1012Hz into aqueous suspension of vermiculite lamellae, supported preferably on a steam-permeable base, whereby bubbles of water vapour generated in the suspension by the absorption of the said energy cause expansion of the suspension to a foam from which further water vapour is removed until a rigid foam is formed.

Throughout this frequency range the electromagnetic energy is preferentially absorbed by the water of the aqueous suspension and therefore rapid heating of the water takes place, leading to a rapid production of water vapour and an expansion of the suspension whilst it is still mobile. Compared with other methods of heating the water in the suspension to make steam available to blow the foam, this method produces a more uniform product. If the electromagnetic heating is continued the foam dries to a solid product which is a rigid foam of vermiculite lamellae produced in a single drying process straight from an aqueous suspension of the vermicu- lite lamellae.If desired, the blowing action of the water vapour produced intemally by the absorption of the applied energy may be aided by the agitation of the suspension before the heating, for example agitation by a mechanical whisk or beater. As soon as a selfsupporting foam has been formed the electromagnetic heating may be stopped and if desired further removal of water vapour may be effected by other methods of heating for example by warm air. Alternatively warm air may be used to pre-heat the vermiculite suspension before the electromagnetic energy is applied.

A large volume of water vapour is produced during the drying of the foam and it is preferable to support the suspension on a steam-permeable base. The base may be a porous material, for example a sintered structure of ceramic or plastic or a woven structure of fibres or wire. The base is preferably a flexible base conveniently in the form of a tray or a belt, for example one which may be moved in and out of the electromagnetic field. The especially preferred materials for the base is a sheet of woven fibres for example textile fibres, suitable fibres including nylon, rayon, cotton, linen, jute, and especially glass or polyester. Paper may be used as permeable lining material in conjuction with a coarse mesh or gauze as a supporting base.

As the mineral suspension is heated, the foam will rise and it may be advantageously allowed to rise under the weight of a sheet of permeable material such as is used for the base or alternatively a sheet of paper or other flimsy porous material which may be stripped away when the foam is dry. If a predetermined depth or thickness of final dry foam is required the foam during drying may be only allowed to rise a predetermined amount. For this purpose a rigid or semirigid permeable membrane may be located above the vermiculite suspension as it is heated to restrict and contain the rise of the foam. A foam product will then be produced sandwiched between permeable sheets which may be removed when the foam is dry or alternatively they may be left in place in order to impart increased strength to the foam product.

The preferred range of frequencies for the applied energy is from 10'Hz to 1010Hi which covers most of the so-called "microwave' and "radio frequency" regions of the electromagnetic spectrum.

Vermiculite is a dielectric material and exhibits very small dielectric losses over the frequency range defined for this invention; whereas water exhibits considerable losses over most of this range and adsorbs much more energy than the vermiculite. The electro-magnetic energy may be applied in any manner known in the art, particularly electrical generators producing high-voltage alternating electro-magnetic fields, gener ators which are conveniently built into a conventional heating device, for example a microwave oven or a dielectric or radio frequency (RF) heater of which there are many patterns currently marketed.

The mineral suspension may conveniently contain from 10% to 70% by wegiht vermiculite solids and the viscosity of the suspensions thus will vary from a free-flowing liquid to a viscous slurry or even a thick paste.

The power required to evaporate the water from the vermiculite suspension depends first upon the mass of water present and second upon the speed of evaporation required. One may wish to vary the latter over a small range, in order to evaporate the water as fast as possible consistent with forming a uniform foam, conveniently from less than a minute to fifteen minutes. The mass of water may vary from a few grams to ca. a kilogram in the laboratory to a plant scale process possibly handling many hundreds of kilograms.

It has been found that the electric power requirements may suitably be from 0.1 kW, to 20 kW for small scale operations, but 100 kW or more might be required for larger scale operations.

By the term rigid inorganic foam we mean a two phase dispersion of gas in solid, the solid phase being an essentially continuous inorganic cellular structure. Small quantities of organic materials may be present in the foam, which may be either deliberately added or inadvertently present, but the organic material is not a fundamental part of the cellular structure although it may usefully modify its properties. On removal of water from an aqueous dispersion of vermiculite lamellae, the lamellae come together to form a coherent film. Accordingly the cell walls of the cellular structure of the present invention derive their mechanical strength largely from the self-adhesion of the flakes when water is removed. Depending on the final equilibrium water content the rigid foam structure may deform or flex under moderate stress but will not normally crumble.

During the process of blowing the foam and subsequent removal of water vapour therefrom the foam will change from being fully mobile to a self-supporting form in which the cellular structure will not collapse even though the heating may be discontinued or interrupted.

The cellular vermiculite is a useful heatresistant and heat insulating material which may be cast as a foam-filling for cavities and voids or which may be used as a coating for the outside of materials, for example wood or s;eeIwork in both cases the foam acting inter alia as a fire-protective layer. An inner sandwich of vermiculite foam as herein provided, optionally bounded by sheets of wood-veneer, paper, asbestos, mica or plastlc, or by vermiculite sheet, forms useful decorative construction panels. If the vermiculite foam is sandwiched between plasterboards or sheets of thermo-setting resin, e.g.

melamine resin, useful fire-resistant and/or sound insulating panels for the building industry may be produced. For some applications the vermiculite foam may require a water-proofing treatment for example a treatment described in our copending UK Patent Application No. 14551/77.

The invention is illustrated by the following examples: Example 1.

A sample of vermiculize ore was swollen in water after treatment with an aqueous solution of n-butyl ammonium chloride. A suspension of vermiculite lamellae was obtained by delamination in a " Greaves" HS mixer and concentrated by evaporation to give a slurry containing between 1S and 25% by weight of solids. (" Greaves " is a Regius tered Trade Mark.) Various examples of this slurry were placed on glass framed traps (7" x 5") with polyester mesh bases previously sprayed with a silicone-release agent and held in a microwave oven approximately half an inch from the base of the oven by glass supports. The oven used was a Rotax* Model MH/1500/50 producing 0.5 to 1.5 kW of power at 2450 MHz. The slurries heated uniformly and a foam began to rise quickly.A restriction was placed above the trays so that only a predetermined depth of foam could be produced against another mesh. The heating was continued for ca. 7 minutes by which time the slurry was converted to a dry rigid foam.

Several vermiculite slurries were heated to form a foam: 1. 17.8% by weight solids without surf actant 2. 23.6% by weight solids without surf actant 3. 22% by weight solids without surf actant but pre-aerated before heating by whisking in a " Kenwood " Chel culi nary mixer.

4. 24% by weight total solids and contain ing a fluorocarbon surfactant (0.25% wt) pre-aerated by whisking in a Ken wood Chef culinary mixer. (" Ken wood" is a Registered Trade Mark.) The results in each case were a solid foam with small bubbles; the strength being imparted by mutually attractive forces operating between the individual vermiculite lamellae.

Some foams were produced with a sheet of vermiculite paper lining the upper and lower layers of polyester mesh. The foam was produced between the sheets of vermiculite paper and the resultant product was a slab of vermiculite foam bounded by smooth non-foamed vermiculite surfaces.

* "Rotax" is a Registered Trade Mark.

Example 2.

Aqueous slurries of vermiculite lamellae in the form of thick pastes were prepared by a method similar to those used in Example 1 and placed on trays having a perforated base.

The trays were held ca. i inch away from the base of a radio-frequency heating oven having a power of 10 kW and working at a frequencv of 80 MHz. Various slurries having solids contents from 10% to 25% by weight were foamed, best results being obtained with slurries having a solids content of from 15% to 20% by weight.

It was found to be necessary to restrict the rise of the foam to prevent crevices forming in its upper surface, for example a sheet of porous paper was found to be very effective.

The paper could be allowed to rest on the foam under its own weight or the paper attached to a rigid upper surface which would act to limit the thickness of the foam produced. Samples of a free-rise foam 9" x 9" x l" having a final density of 0.1 gm/ml were obtained from a slurry having a solid content of 17% and containing 0.2% polypropylene glycol methyl ethers were obtained after 15 minutes heating. Smaller samples of foam from correspondingly smaller volumes of the same slurry were obtained after only 2 minutes heating in the same oven. Some scorching of the samples occurred with these conditions and a lower power RF heater was tried with better results.

Example 3.

A series of pastes of vermiculite lamellae in water prepared as described in Example 1, differing in their concentration of solids, were formed into foams by the method described for slurries 1 and 2 in Example 1. The density of each foam was measured and a correlation observed between the density and the solids content of the paste used. Results are shown in the Table below:

Total solids content Density of foam in % by weight in g/cc 17.5 0.15 33.0 0.40 40.0 0.46 56.0 0.80 60.0 0.94 69.0 1.12

Claims (15)

WHAT WE CLAIM IS:

1. A process for the production of a rigid foam of the mineral vermiculite comprising the passage of electromagnetic energy having a frequency in the range from 104Hz to 10'2her, into an aqueous suspension of vermiculite lamellae, whereby bubbles of water vapour generated in the suspension bv the absorption of said energy cause expansion of the suspension to a foam from which further water vapour is removed until a rigid foam is formed.

2. A process as claimed in claim 1 wherein the expansion of the suspension is aided by agitation of the suspension before the electromagnetic energy is passed therein.

3. A process as claimed in claim 1 or claim 2 wherein the further water vapour is removed by continued application of the electromagnetic energy.

4. A process as claimed in any one of claims 1-3 wherein the electromagnetic energy is passed into the suspension until a self-supporting foam is produced.

5. A process as claimed in claim 4 wherein after a self-supporting foam is produced water is further removed from the foam by another method of heating in order to produce a rigid foam.

6. A process as claimed in any one of claims 1-5 wherein the suspension is preheated with warm air before the electromagnetic energy is passed therein.

7. A process as claimed in any one of claims 1-6 wherein the aqueous suspension of vermiculite lamellae is supported on a steam-permeable base when the electromagnetic energy is applied.

8. A process as claimed in claim 7 wherein the steam-permeable base is a flexible base.

9. A process as claimed in claim 7 wherein the flexible base is a sheet of textile or fibrous material.

10. A process as claimed in any one of daims 1-9 wherein a permeable membrane is provided to contact the upper surface of the foam as it expands.

11. A process as claimed in any one of the preceding claims wherein the frequency of the electromagnetic energy passed into the vermiculite suspension is in the range from 107 to 1010Hz.

12. A process as claimed in claim 11 wherein the energy is applied by means of a microwave or radio-frequency oven or heater.

13. A process as claimed in any one of claims 1-6, 11 or 12 wherein the aqueous suspension is expanded inside a cavity or void by means of electromagnetic energy applied from outside the cavity or void.

14. A process as claimed in claim 1 and substantially as described herein with reference to any one of the foregoing examples.

15. A rigid foam of vermiculite lamellae produced by a process as claimed in any one of the preceding claims.