AU651285B2 - Cellulosic bodies - Google Patents

Description

6- 5 1 8

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

Applicant(s): RICHARD LAURANCE LEWELLIN Actual Inventor(s): Richard Laurance Lewellin Address for Service: PATENT ATTORNEY SERVICES 26 Ellingworth Parade Box Hill Victoria 3128 Australia

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Title: CELLULOSIC BODIES Associated Provisional Applications: PL5239, PL6630, PL9873 The following statement is a full description of this invention, including the best method of performing it known to me/us:- CELLULOSIC BODIES This invention relates to cellulosic bodies, such as bodies in the form of panels and sheets, and including extruded and moulded shapes.

One well known sheet product using substantial amounts of cellulose based material is corrugated cardboard which consists of a planar front sheet of paper or cardboard, a corrugated core also made of paper or cardboard and a planar back face sheet of the same material. This corrugated sheet material is used extensively in packaging. The central corrugated core is generally formed of a paper or cardboard sheet material which is heated and/or wetted, e.g.

by being exposed to steam, after which the sheet is passed between two intermeshing corrugating rollers. To form the final layered product, webs from continuous rolls of sheet paper or cardboard are brought into contact with the corrugated sheet emerging from the meshing corrugated rollers so as to form the front and back faces of the product. The formation of this corrugated sheet product involves substantial energy both in formation of the sheet which is eventually to form the corrugated core of the final product, as well as in the 20 corrugating process itself.

Other cellulosic bodies include cladding or lagging for pipes, protective sheaths for saplings or trees, building and structural panels used for various purposes, including structural elements, ceiling tiles, door infills; and other moulded and extruded shaped products.

It is an object of the present invention to provide a process for effectively forming a body of a cellulosic material.

It is a preferred object of the present invention to provide a process for forming a novel sheet material which can be used as a 30 substitute for corrugated cardboard sheets.

It is also a preferred object of the present invention to provide a novel body of cellulosic material in sheet form which can be a substitute for corrugated cardboard material.

It is a further preferred object of the present invention to provide a process for forming a panel which can be used as a substitute for known panel constructions.

It is also a preferred object of the present invention to provide a novel panel which can be a substitute for known panels.

It is a further preferred object to provide a process for forming a novel extruded body, and to provide such an extruded body.

According to the present invention there is provided a process for forming a body of cellulosic material, the process comprising: mixing a particulate cellulosic feed material with a binder, the feed material including rice hulls and/or particles obtained by comminuting rice hulls, the binder comprising an RF curable composition; forming the mixture of the particulate feed material and binder into the generally desired shape of the body; and curing or setting the binder so as to form an adherent body having substantially the required shape, the step of curing the binder comprising application to the formed shape vr an RF field of a suitable frequency and intensity and for a suitable period of time to cause dielectric heating within the mixture so as to cure the binder to form the adherent body.

The particles of feed material may be predominantly greater than 2mm in their maximum dimension.

Alternatively, the mixture formed into the generally desired shape may include at least at the surface of the shape a proportion of comminuted rice hulls so as to form a relatively smooth surface of the body after curing of the binder.

The RF field may be applied through metal bodies between which the mixture is located, and the metal bodies may also be heated so as to heat at least surface areas of the shape by conduction in addition 25 to RF dielectric heating of the mixture.

In one possible embodiment, the body is in the form of a panel, the step of forming the mixture of the particulate feed material and -:binder into the generally desired shape comprising locating the mixture between two parallel planar faces having the desirep e e S 30 separation corresponding to the thickness of the panel to be formed, .The panel may be composed of at least two layers, including a base layer and a core layer composed of the mixture of particulate feed material and binder, the layers being bound together in the final eeee formed panel. The base layer may comprise a prefabricated base sheet 35 on which the core layer is formed, whereby after curing of the binder in the core layer, the panel comprises an outer surface composed of the prefabricated base sheet and a core layer composed of a bound adherent mass of particulate feed material. Alternatively, the base layer may be composed of a substantial proportion of rice hulls with a binder mixed therein, and the core layer comp~rises particulate feed material of substantiall~y larger particle size, whereby after curing of the binder, the comr~inuted rice hulls in the base layer form a relatively smooth outer face beneath which there is the core layer comp~osed of bound particulate feed material of coarser texture.

The panel may further include an upper layer at the opposite face of the panel to the base layer, the core layer being sandwiched between the base layer and the, upper layer and being bound thereto.

At least one of the layers may include an embedded reinforcing means compuosed of a material to increase the tensile strength of the panel. For example, the reinforcing means may comp~rise a proportion of cellulose fibres. Alternatively, the reinforcing means may comprise metallic or non-metallic wire, fibres, mesh, rods and/or bars provided internally or externally of the bound mixture.

The mixture may include a foaming agent and the forming step of the process includes foaming the mixture to adopt the generally desired shape.

mtalIn one possible embodimtent, the RF field is applied through mtalbodies between which the mixture is located, at least one of the metal bodies remaining attached to and thereby forminc, a surface 6 :0pai t of the adherent body after curing of the binder.

Instead of moulding the body, it is possible to extrude the mixture through a die having the generally desired shape, the curing step including at least partially curing the binder resident in the die so that the emerging body has a stable shape.

The present invention also provides an adherent body of cellulosic material when made by the process of the present invention.

S 30 Possible and preferred features of the present invention will now be described with particular reference to the accoumpanying 'drawings. However it is to be understood that the features illustrated in and described with reference to the drawings are not to be construed as limiting on the scope of the invention. In the drawings: Fig. 1 shows a sample number of rice hulls suitable for use in production of a body according to the present invention, Fig. 2 shows a magnified view of some rice hulls showing the general shape and configuration of these particles as they are derived from processes which have been used in the recovery of the rice grains for food stuffs, Fig. 3 shows a section through a layered product comp~rising a base layer, intermediate cellulosic particulate layer and upper sheet layer, Fig. 4 shows schematically apparatus for carrying out the invention in making a panel, and Fig. 5 shows at a magnified scale a section -through a panel according to the invention made of plywood face sheets and a core layer of uncosininuted rice hulls.

The cellulosic material used in the present invention comprises particles of dry vegetable matter derived from rice. The particles of the plant comprise the husks or hulls which surround the cereal plant grain and which are separated during threshing or other operations in recovery of the grains for animal or human consumption. Rice husks or hulls are presently discarded or burnt as a waste by-product. It has been found that for some fields of use rice hulls are suitable for use as the cellulosic feed material without substantial further processing, particularly without further physical processing to treat the rice hulls.

As shown in Fig. 1, the hulls 10 are generally about 5 to in length and about 1 to 3nsi width. The hulls 10 as shown in Fig. 2 have a generally concave shape 11 along their length and/or cavities 12 and these shapes are particularly useful for forming quiescent air pockets and thus providing effective thermal insulating properties.

The concave shapes are also believed to assist acoustic insulation *~~..properties.

30 As illustrated in Fig. 3 the body 15 of cellulosic material is in the form of a panel or sheet 16. The sheet 16 is comp~osed of a base layer 17, a core layer 18 of the particulate material, and optionally also an upper face layer 19. In a further possible embodiment (not illustrated), the body or panel may be composed substantially entirely of the particulate material, without the provision of the base layer 17 and/or upper face layer 19.

In Fig. 3, the sheet 16 comprises a base layer 17 in the form of a continuous planar sheet and an upper face layer 19. The layers 17 and 19 may be made of any suitable material.

Although for most applications it is expected that rice hulls which have not been further treated will be useful, for some applications the initial feed material composed of rice hulls, may be comm~inuted prior to mixing with the binder and curing or setting of the binder. For example, rice hulls may be ground or pulverised, e.g. in a hamer mill, to form a rm.wh smaller average particle size, e.g. generally in the form of powder. Use of such cormminuted particle material will produce a denser feed maiterial which may be useful for substituting for cardboard or high density board for producing a smoother surface. In particular, it is possible to produce a sheet or panel having at least one face composed of or including a substantial proportion of ground or pulverised rice hulls (or other suitable cellulosic material) so that the outer face of the layer of the particulate material, after setting of the resin, can be relatively smooth. This can provide a surface suitable for bonding of laminates, for painting or as a final exterior surface. Also the commrinuted cellulose material would be suitable for making relatively thin sheets while keeping the outer faces of the sheets relatively smooth, thus enabling the sheets to be used as a substitute for conventional cardboard. Comrminuted hulls could be also used for **.making the corrugated core used as the intermediate laver in corrugated cardboard sheets.

It has also been found that a desirable property of rice hulls is that they are water resistant. This means that any treatment of the rice hulls in forming or using the sheet material product and which involves adding water based compositions does not result in significant absorption into the rice hulls of the water. In turn, this means that the additive compositions can remain at the surface of the rice hulls where they are effective. This refers to additives such as the fire retardants, compoxsitions resisting biological attack, and binders. Furthermore, the low absorption by the rice hulls means that the energy required for drying of the particulate material necessary after addition of the aqueous compositions can be minimised because the water is predominantly or essentially surface water.

A fire retardant composition which can be added to the particles may be any suitable fire retardant such as a borax or boracic acid based fire retardant, or a synthetic fire retardant corrposition. Preferably the fire retardant is added in an aqueous solution or suspension and may be added simultaneously with other additives.

The composition resisting biological attack of the cellulosic particles may comprise for example an agent resisting or deterring attack by vermin, or other pests such as insects. In addition, the coan~osition resisting biological attack may resist micro-organism attack iuch as fungal or mo~uld development. The cosprosition resisting biological attack is also desirably applied in an aqueous solution or suspension so that it may be applied at the same time as -the fire retardant.

The cellulosic particles forming the core layer 18 of the panel :16 may be adhered to the base 1.7 and/or the upper layer 19 by any iuitable means.* For example in a first possible embodiment the cellulosic particles of the core layer 18 and/or the base layer 17, and/or the upper layer 19 may have an adhesive composition applied thereto during the manufacture of the panel. The adhesive material for example may be an aqueous adhesive material which may for example be sprayed onto the cellulosic particles forming the core layer 18 or :onto the base or upper layer 17, 19 prior to or at the time of bringing the cellulosic particles into contact with the base or upper too. layer.

In a mrodification or variation of the process, the cellulosic particles and/or the particles of adhesive material may be electrostatically charged so that the adhesive material is attracted to and more uniformly contacts the cellulosic particles which are then introduced onto the surface of the base and/or upper layer 17, ago 19.

30 In a further possible embodiment, the sheet material forming the base and/or upper layer 17, 19 may be electrostatically charged and passed over a supply of the cellulosic particles, e.g. an open topped bin, the cellulosic particles in the supply if desired being charged at the opposite polarity. With this arrangement, the particles can be electrostatically attracted onto the surface of the sheet material so as to substantially uniformly coat the surface. If desired or necessary, adhesive mate-ial may then be sprayed onto the surface of the sheet material having the cellulosic materials on the surface thereof.

The thickness of the layer of cellulose particles will depend upon the required uses of the final product. In the case of rice hulls having a length of 5 to l0rr and about 1 to 3rM width, the thickness of the layer of cellulosic particles may be of any desired value from about ixum upwards.

The base layer 17 may be a sheet such as plywood or the like, the core layer 18 is of particulat.e cellulose material mixed with a binder and cured or set to form an adherent intermediate layer, and, if desired, the upper layer 19 may also be a sheet composed of plywood or other suitable material bonded to the core layer 18 of the particulate material. Fig. 5 shows a magnified section through such a panel. Such panels may be used in building structures, e.g. where other known panels are used. For example, panels could be used where chipboard is presently used, or where thermal and/or building panels are used.

The product according to the present invention caiy be formed in *a factory in the form of panels in standard sizes. The density and 20 thickness of the product can be adjusted to provide the required structural properties anxd, if desired, the required thermal and/or acoustic insulation properties.

The density and thickness of the cellulosic particle layer body may be selectively controlled as desired. For examplde, the particles 25 may be or mixed with a resin binder using known mixing techniques, such as spraying, and the particles are then deposited onto the base layer 17 under quiescent conditions so that the particles rest upon each other and the body is built up to the required thickness. If desired, a greater density can be achieved by compressing the body of 30 particles as they are formed or subsequent to formation of the body and prior to or at the timne of activating or curing the binder. For example, pressure may be applied to the upper surface of the body of particles before or during the activation and curing of the binder so as to determine the density of the final cellulosic particle layer.

The binder may be any suitable binder composition such as a curable resin composition. Preferably the binder is able to be applied in an aqueous solution or suspension although other solvents may be used if desired or applicable. one suitable class of binders comprises RF curable resins which can be applied and then cured by application of an RF field of suitable frequency and intensity and for a suitable period of time. PVA resin binders may be particularly suitable.

Another binder which has been found suitable is a urea formaldehyde resin composition. Such resin compositions can be in liquid form, particularly as an aqueous solution, and can be mixed with the particulate material at the time of or prior to location of the particulate material in position prior to curing of the resin.

The amount of resin can be varied according to the properties of the resin and the desired final properties of the body. For examp~le, it has been found that an aqueous urea. formaldehyde resin coposition can be mixed with untreated rice hulls in proportion of about 40C0 grams of the liquid resin composition per kilogram of rice 'hulls. A catalyst, such as a suitable weakly acidic catalyst of known type, can be mixed at the same time with the resin composition. The application of heat then causes the resin to cure and to bind the particulate material into an adherent body.

The application of heat, as mentioned above, may be achieved by application of an RF field of suitable frequency and intensity. It has been found that application of an RF field at a frequency of 13.5 MHz is suitable to cure urea formaldehyde resins. Generally frequencies in the range 4 to 30 Mz will be usable. For larger area panels a lower frequency may be preferred and for thicker panels a 25 higher frequency may be preferred. The frequency can be adjustable so as to optimise the frequency for the mass, area, thickness, and materials of the panel which is being made. The period of time for which the RF field is applied is also dependent on the parameters of the apparatus and the product, but ties of 10 to 30 seconds can be 30 suitable to effect curing of the binder.

Otkor thermosetting resins or binders may be suitable. RE' heating is particularly suitable for thicker panels or sheets where the thermal insulating properties would retard heating by conduction. However, direct conductive heating of the metal bodies between which the body is being formed can improve surface texture of the panel, particularly if the surface layer is being formed of comtminuted feed material.- In the example apparatus in Fig. 4, a base sheet 17 e.g. of plywood was placed on a bottom metal plate 21, a rice hulls layer 28 wetted with the resin composition was then formed on the base sheet 17, a further sheet 19 of plywood was then located on top of the rice hulls layer 18, and finally a top metal plate 22 was located over the top plywood sheet 19. Insulating members 24, 25 formed end walls of the volume between the plates 21, 22. Pressure was applied between the two metal plates 21, 22 to produce the required thickness and density of the rice hulls layer 18. Untreated not comminuted) rice hulls result in a sponge like consistency, although increasing the pressure applied produces a thinner and denser layer. comrminuted rice hulls would produce a considerably denser particle layer 18. RF energy was applied from generator 26 through capacitor 27 between the two metal plates 21, 22, the frequency being about. 13.5 MHz and the field was applied for 30 seconds to a 30mmx thick panel. About 3.5 KW of energy was applied. The power flux applied depends on the thickness, mass, area and other parameters of the body being cured.

The 1RF energy produces heat by a dielectric heating process which in *turn causes the resin to cure and to bind the rice hulls into an 20 adherent self supporting layer.

In variations of this process, instead of plywood or other prefabricated top and bottom sheets 17, 19, pulverised or other comminuted material can be first applied to form a base layer 17, followed by untreated hulls forming an intermediate layer 18 and 25 finally a top layer 19 of commuinuted material can be applied. This produces a relatively simooth surfaced panel composed entirely of rice *hulls.

If desired a metal sheet or other metal body 28 (Fig. 3) may be provided at one or both faces of the body being formed, the body 28 30 remaining attached to the final body by binding thereto so as to form outside surface part of the body 16. The body 28 may be composed of aluminium foil so that the panel 16 can be used as a building panel, e.g. for insulation within wall and ceiling spaces, such panels sometimes being sufficiently robust to comply with building regulations for a new building having such panels to be deemed to have reached "lock-up stage". The metal body 28 can be used as one of the metal plates 21, 22 or as a "sacrificial" part of one of the metal plates 21, 22 through which the RF field is applied.

Alternatively, the body 28 may be adhered to the panel 16 after its formation.

The application of RF energy to produce dielectric heating is believed necessary or at least highly desirable for thicker sheets or panels, but for relatively thin sheets and/or for producing a different surface texture or binding effects heat may be applied by direct conventional heating processes, e.g. by electrically heating the top and bottom plates 21, 22 applied to the layer of cellulosic material.

A further step that may be included in the process is the incorpol..tion of a foaming agent in the materials forming the body, e.g. in the mixture of cellulosic feed material and binder. Th( step of forming the mixture of cellulosic material and binder into the final desired shape can include activating the foaming agent so that the mixture expands to fill a cavity of the desired shape, e.g. the space between the metal plates 21, 22 and end walls 24, 25. This can produce a light weight thermal and/or acoustic insulation panel, ceiling tile, or other desired product.

A further step that can be incorporated in the process is to mix a proportion of fibres into the cellulose material so as to increase the tensile .'trength of the final product. Preferably cellulose fibres are included, e.g. derived from wood either by processing of new wood or recycling of previously processed wood derivative products paper). The greater length of cellulose 25 fibres, especially when mixed with comminuted rice hulls, will provide increased tensile strength. The use of wood derived cellulose fibres will not alter significantly the dielectric properties of the material between the metal plates 21, 22 through which the RF electric field is applied and will therefore not interfere with the curing process.

"'0.Alternatively, or in addition, there can be i.-orporated in the bound body of cellulosic particles and/or externally secured in or to the body, reinforcing filaments or mesh such as fibres made of glass or carbon or other non-metallic materials, metal or non-metallic wires, mesh or rods or bars. Such reinforcing means 30 can be incorporated for example within the core layer 18 as shown in Fig. 4 to increase the tensile strength of the final panel.

The product which includes reinforcing cellulose f ibres or other reinforcing filaments or mesh will have a greater tensile strerTqih than one made solely from rice hulls and the invention covers sheets and panels and other bodies having such reinforcing means incorporated therein.

Although forming of bodies in a mo~uld e.g. between plates, as a batch process has been described in detail, it is also possible to form bodies according to the invention by other processes. An extrusion process can be used. For examtple, the mixture of rice hulls and binder can be forced, e.g. by an auger, through a die and, while passing through the die, the binder is cured at least at the surfaces to form a substantially self supporting, or at least stable shaped, body emerging from the die. The die may be defined by spaced die plates and the RF field may be applied between the plates to effect curing in the die. Further curing after emergence of the body from the die can be effected if needed.

The rate of feed of the mixture into the die can be matched to the rate of curing in the die so that the process can be continuous with the body emerging from the die being substantially completely 20 cured. Alternatively, the feed rate can be faster than the curing rate provided that the emerging body is sufficiently stable in shape to enable additional curing to be affected. As a further alternative, the mixture can be fed at an intermittent rate to the the mixture resident in the die being cured, and subsequently a S 25 further plug of mixture being forced into the die to eject the cured body and to enable curing of the further plug.

The die may taper slightly towards its exit end to provide desired resistance to passage of the mixture, thereby enabling compression of the mixture being forced into the die and thus 30 enabling zontrol of the density of the body being formed.

An extruded body can be semicircular to be usable for example to form from two such bodies cylindrical pipe lagging, tree trunk protection, etc.

It is to be understood that various alterations, modifications and/or additions may be made to the features of the possible and pref erred embodTient of the invention as herein described without departing from the invention as defined in the claims.

Claims (19)

1. A process for forming a body of cellulosic material, the process comprising: mixing a particulate f *losic feed material with a binder, the fed material includi rice hulls and/or particles obtained by comminuting rice hulls, the binder comprising an RF curable composition; forming the mixture of the particulate feed material and binder into the generally desired shape of the body; and curing or setting the binder so as to form an adherent body having substantially the required shape, the step of curing the binder comprising application to the formed shape of an RF field of a suitable frequency and intensity and for a suitable period of time to cause dielectric heating within the mixture so as to cure the binder to form the adherent body.

2. A process as claimed in Claim 1 wherein the particles of feed material are predominantly greater than 2mm in their maximum dimension.

3. A process as claimed in Claim 1 wherein the mixture formed into the generally desired shape includes at least at the surface of the shape a proportion of comminuted rice hulls so as to form a relatively smooth surface of the body after curing of the binder.

4. A process as claimed in Claim 1, 2 or 3 wherein the RF field is applied through metal bodies between which the mixture is located, the metal bodies being heated so as to heat at least surface areas of 25 the shape by conduction in addition to RF dielectric heating of the mixture. A process as claimed in any one of the preceding claims wherein the body is in the form of a panel, the step of forming the mixture of the particulate feed material and binder into the generally desired shape comprising locating the mixture between two parallel planar faces having the desired separation corresponding to the thickness of the panel to be formed.

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6. A process as claimed in Claim 5 wherein the panel is composed of at least two layers, including a base layer and a core layer 35 composed of the mixture of particulate feed material and binder, the :oo. layers being bound together in the final formed panel.

7. A process as claimed in Claim 6 wherein the base layer comprises a prefabricated base sheet on which the core layer is formed, whereby after curing of the binder in the core layer, the panel comprises an outer surface composed of the prefabricated base sheet and a core layer composed of a bound adherent mass of particulate feed material.

8. A process as claimed in Claim 6 wherein the base layer is S composed of a substantial proportion of rice hulls with a binder mixed therein, and the core layer comprises particulate feed material of substantially larger particle size, whereby after curing of the binder, the comminuted rice hulls in the base layer form a relatively smnooth outer face beneath which there is the core layer composed of bound particulate feed material of coarser texture.

9. A process as claimed in any one of Claims 6 to 8 wherein the panel further includes an upper layer at the opposite face of the panel to the base layer, the core layer being sandwiched between the base layer and the upper layer and being bound thereto.

10. A process as claimed in any one of Claims 5 to 9 wherein at least one of the layers includes an embedded reinforcing means composed of a material to increase the tensile strength of the panel.

11. A process as claimed in Claim 10 wherein the reinforcing means comprises a proportion of cellulose fibres.

12. A process as claimed in Claim 11 wherein the reinforcing means comprises metallic or non-metallic filaments, fibres, wire, mesh, rods and/or bars.

13. A process as claimed in Claim 3 or 8 or any claim appended to SClaim 3 or 8 wherein the comminuted rice hulls have the consistency of a powder. S14. A process as claimed in any one of the preceding claims wherein the mixture includes a foaming agent and the forming step of the process includes foaming the mixture to adopt the generally desired shape.

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15. A process as claimed in any one of the preceding claims wherein the RF field is applied through metal bodies between which the mixture is located, at least one of the metal bodies remaining attached to and thereby forming a surface part of the adherent body after curing of the binder.

16. A process as claimed in any one of Claims 1 to 4 wherein the mixture is extruded through a die having the generally desired shape, the curing step including at least partially curing the binder resident in the die so that the emerging body has a stable shape.

17. A process as claimed in any one of the preceding claims wherein the binder comprises a urea formaldehyde resin.

18. A process for forming a body of cellulosic feed material substantially as herein before described with particular reference to the accompanying drawings.

19. A body of cellulosic material when made by a process is claimed in any one of the preceding claims. Dated this 4th day of October 1993 PATENT ATTORNEY SERVICES Attorneys for RICHARD LAURANCE LEWELLIN *0* o• oo ABSTRACT A process for forming a panel (16) or other body (13) of cellulosic material including rice hulls and/or comminuted rice hulls. A mixture of the particulate feed material and a binder is formed into the generally desired shape and the binder is cured by application of an RF field to cause dielectric heating within the mixture so as to cure the binder to form the adherent body. The panel (16) is composed of a base layer a core layer composed of the mixture of particulate feed material and binder and an upper layer An embedded reinforcing means can increase the tensile strength of the panel. The mixture can include a foaming agent. The RF field can be applied through metal bodies (21,22) between which the mixture is located, at least one of the metal bodies remaining attached to and thereby forming a surface part (28) of the adherent body (15) after curing of the binder. As an alternative to mo~lding, the mixture can be extruded through a die, the binder resident in the die being cured so that the emerging body has a stable shape. L