WO2005084939A2

WO2005084939A2 - A panel

Info

Publication number: WO2005084939A2
Application number: PCT/ZA2005/000046
Authority: WO
Inventors: Michael Windsor Symons
Original assignee: Tower Technology Holdings (Pty) Ltd
Priority date: 2004-03-04
Filing date: 2005-03-04
Publication date: 2005-09-15
Also published as: WO2005084939A3; ZA200610539B

Abstract

A panel and a method of manufacture thereof which panel has an upper sheet member with a plurality of downwardly depending keying formations, a lower sheet member with a plurality of upwardly depending keying formations and a settable core material in a liquid or particulate form which is located between the upper and lower sheet members and which is meshed with the keying formations.

Description

A PANEL

BACKGROUND OF THE INVENTION

[0001] This invention relates to a panel and to a method of making the panel.

[0002] Panels are used in a multitude of industries which require good performance of the panels in fire and high strength in all its aspects, such as lapshear, internal bond, tensile strength, stiffness or modulus of rapture and flexural strength. In addition resistance to abrasion and wear can be important. Dimensional stability, waterproofness and resistance to weather are also required attributes.

SUMMARY OF THE INVENTION

[0003] This invention aims to provide an alternative panel for use in industry.

[0004] The invention provides a panel which includes an upper sheet member which has a plurality of downwardly depending keying formations, a lower sheet member which has a plurality of upwardly depending keying formations and a settable core material in a liquid or particulate form which is located between the upper and lower sheet members and which is meshed with the keying formations.

[0005] The upper and lower sheet members may be made from metal, each of which has a plurality of apertures.

[0006] Each keying formation may include a burr formation.

[0007] The core material preferably includes a resin and an appropriate catalyst. The core material may include a filler. [0008] In one form of the invention the core material includes a thermoplastics material. The thermoplastics material preferably includes any one or a combination of polyethylene, polystyrene and an extender. The core material may include an elastomer and a coupling agent.

[0009] In another form of the invention the core material includes any one or a combination of vermiculite, perlite and cellulosic fibres. The core material may include a hydraulic binder.

[0010] The invention also provides a method of forming a panel of the aforementioned kind which includes the steps of: A) Perforating an upper metal sheet member and a lower metal sheet member; B) Locating a settable core material in liquid or particulate form between the upper and lower sheet members; and C) Causing burr formations on the upper and lower members to mesh with the core material.

[0011] The method may include the step of applying pressure to the sheet members and the core material. Preferably the pressure is in the range of 10 kg/cm² and 70 kg/cm².

[0012] The method may include the step of applying heat to the sheet members and the core material. Preferably the heat is in the range of 130° C to 220° C.

[0013] The method may include the step of hydrating the core material. BRIEF DESCRIPTION OF THE DRAWINGS

[0O14] The invention is further described by way of examples with reference to the accompanying drawings in which:

Figure 1 is a partial, cross sectional side view of a panel according to the invention; and

Figures 2 and 3 are schematic representations of alternative methods of manufacturing the panel of Figure 1.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0015] Figure 1 shows a panel 10 which has a perforated upper sheet 12, a perforated lower sheet 14 and a settable core material 16 in liquid or particulate form which is located between the sheets 12, 14.

[0016] Although the sheets 12, 14 can be made from any appropriate material they are in this example made from metal. Each of the sheets 12, 14 has a plurality of apertures 18 formed therein. Each aperture 18 has a burr formation 20 which extends away from the sheet 12, 14. The burr 20 on the upper sheet 12 extends downwardly and the burr 20 on the lower sheet 14 extends upwardly.

[0017] Figures 2 and 3 illustrate alternative methods of construction of the panel 10. The difference between the processes of Figures 2 and 3 is in the composition and form of the materials 16A, 16B.

[0018] In both processes the liquid material 16 is located between the sheets 12, 14 and is meshed with the burr 20 on the sheets12, 14 to form an intermediate panel product 22 made from the sheets 12, 14 and the material 16. The product 22 is subjected to pressure 24 and heat 26 and once the material 16 has set the sheets 12, 14 and the material 16 are cohesively keyed or locked to each other to form the panel 10. The burr 20 on the upper and lower sheets 12, 14 thus act as keying formations which are trapped in the material 16.

[0019] If the material 16 contains a hydraulic binder 28 which is shown Figure 3 the material 16 is optionally hydrated in a step 30 by impregnating water into the material 16 by, for example, vacuum pressure impregnation in a pressure cylinder. In certain applications the product 22 is subjected to the pressure 24 and heat 26 simultaneous, after or before the hydration 30.

[0020] The first optional core feedstock or material 16A is shown in Figure 2 and is in a liquid form. The feedstock 16A is made from a thermoplastics material 32 which comprises any one or combination of polyethylene 34, polystyrene 36 and an extender 38 in powder form.

[0021] The polyethylene 34 can be for example a linear low density polyethylene for a panel 10 with toughness and flexibility or a high density polyethylene for a panel 10 with high rigidity.

[0022] The polyethylene 34 can either be virgin polyethylene or, more preferably in terms of cost, be recycled or post industrial grade polyethylene, reduced to a relatively small particle size. When the polyethylene 34 comes from a waste stream, it is acceptable for the waste stream and thus the polyethylene 34 in the thermoplastics material 32 to contain a quantity of other polymers from the waste stream, such as, polyethylene teraphthalate from bottles, polypropylene, polycarbonates, and polyesters. These additional waste polymers act as extenders 38, as they generally have melting points higher than the temperatures used in step 26.

[0023] The polyethylene 34 melts and commences to flow in the temperature range of from 120°C to 130°C inclusive.

[0024] The polyethylene 34 must be in powder form. Preferably, the polyethylene particles have a particle size of 1 ,0mm in diameter or less, more preferably 0.5mm in diameter or less, most preferably 150 microns in diameter or less.

[0025] The polystyrene 36 is preferably expanded and milled polystyrene foam or polystyrene packaging from a waste stream.

[0026] The polystyrene 36 is a clear glass-like material manufactured by the free radical polymerisation of phenylethene using benzoyl peroxide as an initiator. It has excellent thermal and electrical insulation properties and, in the method of the invention after having melted, it sets on cooling to a very hard inflexible, glass-like solid which is extremely resistant to water, having a water absorption after 24 hours of immersion of less than 0.06% by weight.

[0027] The polystyrene 36 melts and commences to flow in the temperature range of from 10O°C to 120°C inclusive.

[0028] The polystyrene 36 must be in powder form. Preferably, the polystyrene particles have a particle size of 1 ,0mm in diameter or less, more preferably 0.5mm in diameter or less, most preferably 150 microns in diameter or less. [0029] The polyethylene 34 and polystyrene 36 are blended at a ratio of 5 to 100 parts by weight of polyethylene 34 in powder form and 0 to 95 parts by weight of the polystyrene 36 in powder form. A preferred feedstock 16A comprises 40 to 100 parts by weight of the polyethylene 34 in powder form and 0 to 60 parts by weight of polystyrene 36 in powder form.

[0030] Depending upon the end use to which the panel 10 is to be put, the relative quantities of polyethylene 34 and polystyrene 36 may be varied to give the panel 10 the desired properties.

[0031] An additional extender 38 can be added to the thermoplastics material 32.

[0032] The extender 38 can comprise reinforcing inorganic particles or fibres such as glass fibre, either milled or up to 12mm in length, but preferably of the order of 6mm in length for ease of processing; platelet minerals such as mica, preferably with a particle size in the range of 8 to 100 mesh, more preferably about 40 mesh, or phlogopite; or rod-like particles such as wollastonite.

[0033] The extender 38 can also comprise lightweight inorganic volume extenders such as hollow glass balloons, generally sourced from ground coal firing, which are siliceous, with a low bulk density in the range of from 200g/l to 300g/l and with a particle size in the range of from 50 to 300 microns; or milled expanded perlite such as Dycalite™ 411 or 471 by Chemserve Perlite South Africa, which has a similar bulk density to hollow glass micro balloons, or undensified silica fume with a bulk density in the range of 200g/l to 300g/l. [0034] The extender 38 can additionally comprise reinforcing organic particles or fibres such as lignocellulosic fibres, e.g. typha reed fibres, kenaf, flax, sisal and wood; or synthetic fibres such as polyester fibres capable of withstanding pressing temperatures in excess of 180°C.

[0035] The extender 38 can further comprise lightweight organic volume extenders such as particles of cork or leather with bulk densities in the range of from 150 to 250g/l inclusive.

[0036] The extender 38 can even be a blend of two or more of the above examples.

[0037] The purpose of adding an extender 38 to the thermoplastics material 32 is to control the density of the material 16 once set with a minimum reduction in stiffness, and to minimise the coefficient of linear expansion in order to achieve acceptable dimensional stability.

[0038] The extender 38 is most preferably an inorganic extender selected from those set out above.

[0039] When the thermoplastics material 32 includes an extender 38, the extender 38 is preferably present in an amount of from 90 to 5 parts by weight, more preferably 40 to 15 parts by weight, to 50 parts by weight of the combination of polyethylene 34 and polystyrene 36.

[0040] An unsaturated polyester resin 40 which is in liquid form is mixed with the thermoplastics material 32. An example of a suitable polyester resin 40 is a high reactivity resin for hot pressed dough moulding compound applications (DMC), which resin is an orthophthalic, unsaturated polyester resin designed for use in the manufacture of glass and aggregate filled dough moulding compounds. It may be used in conjunction with low profile/low shrink additives for zero or low shrink hot press moulded products. Typical properties of this resin 40 are a viscosity at 25°C of 1470 mPa.s, a volatile content of 35.5%, and a curing characteristic at 126°C using one part per hundred of a Triganox™ 29B50 catalyst 42 of a five minute gel time.

[0041] Another suitable resin 40 is a chemical and water resistant isophthalic, neo- pentyl glycol unsaturated polyester resin used for high performance laminates. An example of this resin is NCS™ 993 by NCS Resins South Africa, which has a viscosity at 25°C of 540 to 800 mPa.s, an acid value of 10 to 16 mgKOH/g, a volatile content of 39 to 43%, which can be cured with a latent catalyst 42 such as Triganox™ 29B50 which is a benzoyl peroxide.

[0042] The combination of polyethylene 34 and polystyrene 36 and the resin 40 are preferably used in amounts of from 90 to 40 parts by weight of the combination of polyethylene 34 and polystyrene 38 to 10 to 60 parts by weight of the resin 40.

[0043] A catalyst 42 for the unsaturated polyester resin 40 is preferably used in an amount of from 0.5% to 2.5% to 100% of the resin 40 on a weight basis.

[0044] The resin 40 can optionally be mixed with up to 50% by weight of the polyester resin of a styrene monomer for viscosity modification.

[0045] In order to propagate the adhesion between the polyethylene 34 and the polystyrene 36, i.e. to induce the formation of a physical co-polymer between the two and in order to impose upon the panel 10 improved toughness, and shock resistance when polystyrene 36 is used in relatively large proportions, the feedstock 16A can include a thermoplastic elastomer 44, also known as a thermoplastic rubber or block co- polymer.

[0046] The elastomer 44 is used in an amount of from 2.5% to 35.0% based on 100% by weight of the polystyrene 36 present and the elastomer 44 is dissolved in a styrene monomer to produce a saturated solution. This saturated solution is then preferably blended with the resin 40 and its catalyst 42 before this is added to the thermoplastics material 32.

[0047] Examples of suitable elastomers 44 are those having styrene end blocks and an elastomeric mid-block such as for example butadiene, isoprene, ethylene and the like, i.e. those that have two different polymers in each molecule. Thus for example, suitable elastomers 44 include a styrene/butadiene/styrene polymer, a styrene/isoprene polymer, and an acrylonitrile/butadiene/styrene polymer. The preferred elastomers 44 are the styrene/butadiene polymers. Specific examples of suitable elastomers 44 are the Kraton™ grades by Shell Chemicals. The Kraton™ "D" series are unsaturated and suitable for interior application and are comprised of styrene/isoprene/styrene block copolymers which are linear, and styrene/butadiene radial copolymers. The Kraton™ "G" series are fully hydrogenated grades for exterior applications and include styrene- ethylene/butylene-styrene block co-polymers which are linear and styrene- ethylene/propylene di-block polymers. The Kraton™ "G" range of thermoplastic elastomers possess excellent resistance to oxygen, ozone and UV light degradation.

[0048] In addition, the propagation of adhesion between the, polyethylene 34, polystyrene 36, any inorganic extender 38 present and the resin 40 can be further induced by the use of a silane coupling agent 46. [0049] A filler material 48 can be added to the thermoplastics material 32 in the form of inorganic or organic fillers.

[0050] The second optional core feedstock or material 16B is shown in Figure 3 and can be either in a liquid or particulate form. The feedstock 16B comprises a blend of a mixture 52 and a dry powder thermosetting resin 54. The mixture 52 is a combination of one or more particles of exfoliated vermiculite 56 of a diameter of less then 0.5mm, particles of expanded perlite 58 of a diameter of less then 250 micron and cellulosic fibres 60 in the range of 1mm to 8mm in length the highest possible aspect ratio such as pulp, MDF fibre, recycled paper or similar which does not swell when water wetted.

[0051] The vermiculite 56 belongs to the group of hydrated lamina industrial minerals, which are all aluminium-iron magnesium silicates, high in silica, and which propagate bonding in a cement matrix. They resemble a muscavite (mica) in appearance. When subjected to heat the vermiculite 56 exfoliates due to the inter lamina generation of steam. The pH is typically in the region of 9, specific gravity 2,5, melting point 1315°C, sintering temperature 1260°C and bulk densities are between 50 and 120g/litre. The exfoliated vermiculite 56 is non corrosive, non combustible and non abrasive. A typical particle size suitable for this invention is the grade FNX™ by Micronised Products of South Africa, with a screen analysis - 20 to 40% retained on a 2000 micron screen, 90 to 95% retained on a 710 micron screen, or alternatively the grade SFX™ where 50 to 75% is retained on a 1000 micron screen, 20 to 35% retained

on a 710 micron screen and 0 to 10% retained on a 355 micron screen. Because the exfoliated vermiculite 56 is compressible, densities of the final feedstock 16B may be reduced downward to as low as 850kg/m³. Typical applications of panels 10 with a core of this specification would be interior building boards for walls or ceilings, bound either with calcium sulphate hemihydrates or ordinary Portland cement.

[0052] The perlite 58 is a natural glass. It is an amorphous mineral consisting of fused sodium potassium aluminium silicate. It occurs naturally as a silicacious volcanic rock. The distinguishing feature that sets the perlite 58 apart from other volcanic glasses is that when heated rapidly to above 870°C, it expands to from four to twenty times its original volume as the chemically combined water vaporises. This creates countless tiny bubbles in the heat softened glassy particles. Typical chemical analysis of perlite indicates that silicon oxide percentage exceeds 70%, aluminium oxide exceeds 11% and metallic oxides make up virtually the rest of the composition. Specific gravity is 2,3, softening point 870°C to 1093°C and fusion point 1260°C to 1345°C. The preferred particle size is from 200 to 2000 micron. An example is Genulite™ Grade M 75 S by Chemserve Perlite (Pty) Ltd of South Africa.

[0053] The cellulosic fibres 60 is in the form of finely divided lignocellulosic fibres which are unifibres or bundles of a small number of unifibres of a lignocellulosic material. In other words, the lignocellulosic material is broken down into single fibres or bundles of a small number of fibres, rather than being in chip or particle form. The fibres have a length of from 0,5mm to 12mm inclusive, preferably from 1mm to 6mm inclusive.

[0054] The resin 54 is preferably a novolac phenol formaldehyde resin, which is used with a suitable catalyst 62. A novolac phenol formaldehyde resin is a resin in which the molar ratio of phenol to formaldehyde exceeds parity. [0055] An example of a suitable catalyst 62 for use with such a resin 54 is hexamethylene tetramine. An example of a suitable novolac phenol formaldehyde resin 54 and catalyst 62 combination is a two stage resin with a hexamethylene tetramine contents of between 6 and 14%, with a hot plate gel time at 150°C of between 40 and 120 seconds, with a flow in mm at 125°C of between 30 and 75mm, and with a particle size sieve analysis percentage retained on a 200 mesh screen of a maximum of 2%. Examples are the PRP resins of South Africa, code Varcum™ 7608 which may be used

as modifier for a slow curing phenolic system such as Varcum™ 3337. A more rapid

curing system i.e. gel in 20-40 S, at 150°C, is preferred i.e. PRP Code 7608.

[0056] The resin 54 is preferably used in an amount of 2% to 20% inclusive of the resin 54 by mass of the binder 28, i.e. in a mass ratio of the resin 54 to the binder 28 of from 2:100 to 20:100.

[0057] The binder 28 is preferably chosen from the group comprising Portland Cement, high alumina cement, gypsum cement, calcium sulphate hemihydrate either in the alpha or beta form, magnesium oxychloride, magnesium oxysulphate, a calcium sulphoaluminate cement, an alkali silicate, such as sodium silicate, and a ground granulated blast furnace slag or a combination of any two or more thereof.

[0058] The binder 28 is preferably used in an amount of 50% to 2000% inclusive of the binder 28 by mass of the feedstock 16B, i.e. a mass ratio of the binder 28 to the feedstock of from 1:2 to 7:1 , preferably in a mass ratio of 10:1 to 5:1 for finished products with high densities, and preferably in a mass ratio of 5:1 to 1:1 for finished products with low densities. [0059] The feedstock 16B is in a particulate form except if water 66 is added to the feedstock 16B which contains a binder 28 before the feedstock 16A is located between the sheets 12, 14. Water 66 in amounts sufficient for the hydration of the binder 28 is added to the feedstock 16B so that the binder 28 sets once the feedstock 16B is located between the sheets 12, 14 to form the panel 10.

[0060] Another optional additive is a suitable amount of a filler material 64 selected from inorganic or mineral fibres such as rock wool, mineral wool, glass fibres and ceramic fibres; inorganic particles such as silica fume and fly ash; and synthetic fibres such as acrylic fibres, polyester fibres, acrylonitrile fibres, and the like.

[0061] These fillers 64, when in particulate form, must have a surface area of 100m² per kilogram or greater, and when in fibrous form, must be unifibres or bundles of a small number of unifibres. ,

[0062] A preferred filler 64 is silica fume. Silica fume has the capacity to react with free calcium hydroxide, forming calcium silicate hydrate. It accelerates the setting of the hydraulic binder. As a result of its very small particle size of 20 000m²/kg, it minimises porosity in the panel 10, improves strength, minimises retardation by the soluble substances in the lignocellulosic fibres, contributes to the cohesion of the cohesive product and minimises particle separation as a function of its low bulk density. The silica fume, such as CSF-90™ by Anglo Alpha Cement of South Africa, may be added in an amount of up to 15% by mass on the mass of the binder 28.

[0063] The material 16A or 16B is thoroughly mixed and laid up uniformly between the sheets 12, 14. The sheets 12, 14 with the material 16 there between are subjected to pressure from 10kg/cm² of up to 70kg/cm² and is exposed to heat at temperatures between 130 and 220°C more preferably between 145 and 185°C to form the panel 10.

[0064] When strength required is such that the sheets 12, 14 must be situate as far as possible from the neutral axis the material 16 can be pressed onto a single sheet of perforated metal at a time, then two such unilamina components are adhesively secured to a light weight core with the perforated metal on the outer surfaces of the resulting panel.

Claims

1. A panel which includes an upper sheet member which has a plurality of downwardly depending keying formations, a lower sheet member which has a plurality of upwardly depending keying formations and a settable core material in a liquid or particulate form which is located between the upper and lower sheet members and which is meshed with the keying formations.

2. A panel according to claim 1 wherein the upper and lower sheet members are made from metal, each of which has a plurality of apertures.

3. A panel according to claim 1 or 2 wherein each keying formation includes a burr formation.

4. A panel according to claim 1 , 2 or 3 wherein the core material includes a resin.

5. A panel according to any one of claims 1 to 4 wherein the core material includes a catalyst.

6. A panel according to any one of claims 1 to 5 wherein the core material includes a filler.

7. A panel according to any one of claims 1 to 6 wherein the core material includes a thermoplastics material.

8. A panel according to claim 7 wherein the thermoplastics material includes any one or a combination of polyethylene, polystyrene and an extender.

9. A panel according to claim 7 or 8 wherein the core material includes an elastomer.

10. A panel according to claim 7, 8 or 9 wherein the core material includes a coupling agent.

11. A panel according to any one of claims 1 to 6 wherein the core material includes any one or a combination of vermiculite, perlite and cellulosic fibres.

12. A panel according to claim 11 wherein the core material includes a hydraulic binder.

13. A method of forming a panel according to any one of claims 1 to 12 which includes the steps of:

A) Perforating an upper metal sheet member and a lower metal sheet member; B) Locating a settable core material in a liquid or particulate form between the upper and lower sheet members; and C) Causing burr formations on the upper and lower members to mesh with the core material.

14. A method according to claim 13 which includes the step of applying pressure to the sheet members and the core material.

15. A method according to claim 14 wherein the pressure is in the range of 10 kg/cm² and 70 kg/cm².

16. A method according to claim 13, 14 or 15 which includes the step of applying heat to the sheet members and the core material.

17. A method according to claim 16 wherein the heat is in the range of 130° C to 220° C.

8. A method according to any one of claims 13 to 17 which includes the step of hyd rating the core material.