GB2306909A

GB2306909A - Moulded articles from a polyurethane matrix and fillers

Info

Publication number: GB2306909A
Application number: GB9522992A
Authority: GB
Inventors: Geoffrey Charles Habin; John Dixon Habin
Original assignee: PANEL HOLDINGS Ltd
Current assignee: PANEL HOLDINGS Ltd
Priority date: 1995-11-09
Filing date: 1995-11-09
Publication date: 1997-05-14
Anticipated expiration: 2015-11-09
Also published as: GB2306909B; GB9522992D0; ZA967218B

Abstract

Moulded articles, comprising a polyurethane matrix incorporating a vegetable filler and a mineral filler, methods for their production and their use in a variety of applications notably as substitutes for conventional building materials are disclosed.

Description

MOULDED ARTICLES. THEIR PRODUCTION AND USE This invention relates to moulded articles, to a method for their production and to their use in a variety of applications, notably as substitutes for conventional building materials.

Considerable time and skill are required to construct buildings from conventional materials such as bricks and blocks. Also, these materials are expensive, not least because their manufacture requires high temperature firing in the case of clay bricks or prolonged curing in the case of concrete blocks, which favour centralised large scale production and this in turn raises transportation costs particularly to inaccessible and often rural construction sites.

Timber is of course an even more traditional construction material especially for residential buildings, and still finds wide use in rural locations in developing countries. However, even if construction-grade timber is available locally it is of relatively low strength, presents a fire hazard and is subject to attack by insects, fungus and weather.

Further its large-scale utilisation may be environmentally undesirable.

A need therefore exists for a strong, weather proof, fireproof and inexpensive building material which is capable of being manufactured simply at or near the construction site with minimal skill and equipment and erected quickly and easily to fulfil a variety of functions.

The present invention is based on the observation that a particular combination of filler materials incorporated into a conventional polyurethane matrix not only satisfies these requirements but also provides a material that can fulfil a wide variety of other uses.

In accordance with the invention therefore in its widest aspect there is provided a moulded article comprising a polyurethane matrix incorporating (i) a vegetable filler and (ii) a mineral filler.

The moulded article is suitably in the form of a panel adapted for use in the building/construction industry and as such may be manufactured in a size and shape appropriate to form a floor or ceiling panel on the one hand or the whole facade of a single storey dwelling house on the other hand. These and other uses for the moulded articles of the invention are described in detail below.

The polyurethane matrix is suitably derived from known polyurethane precursors, that is to say diisocyanates and polyols. Aromatic polynuclear diisocyanates are preferred in view of their low cost, rapid curing at room temperature and because they confer sufficient rigidity, stability and fire retardant properties to the finished panel.

Diphenylmethane diisocyanates (MDI) are especially suitable in view of their ready commercial availability. The polyol is suitably one derived from a natural product, for example a natural drying or non-drying oil and amongst those, polyester polyols such as castor oil are especially preferred. Such polyols are readily commercially available.

The polyurethane component of the moulded articles of the invention forms a matrix, or continuous phase, which incorporates at least one vegetable filler and at least one mineral filler. The mineral filler is generally selected to provide the moulded article with a degree of inherent rigidity and strength consistent with the use to which the article is intended to be put but may also serve any one or more of a number of other functions. For example, the mineral filler may confer colour or texture on the panel and contribute to a brick or stone-like appearance. It also adds bulk, and minimises costs, and may resist fungal, acid, weather, and fire damage.

Examples of suitable mineral fillers are sand, glass fibres, crushed aggregate, chalk, fly ash and crushed slag. The particle size of the mineral filler will affect the strength of the final panel and preferably should be less than 10 mm and more preferably less than 5 mm.

The vegetable filler is generally selected to provide the moulded article with a density lower than that which would have been attained in its absence.

Again, the vegetable filler may also serve any one or more of a number of other functions, for example to increase bulk, to produce a more economic panel, or to enhance the sound or thermal insulation properties of the final panel. It may also render the article less brittle and allow it to be easily drilled or similarly fashioned after it has been cast.

Examples of suitable vegetable fillers are sawdust, woodchips, paper, rubber, grass, wheat stalks, ground bark, crushed mielies, straw, vegetable husks, jute, hemp and similar fibrous material.

Clearly, the vegetable filler and mineral filler will be selected so as to be mutually compatible, and of course more than one vegetable filler and/or more than one mineral filler may be used simultaneously as required or desired.

Additionally, non-mineral, non-vegetable fillers such as expanded polystyrene or soil may be incorporated to produce or enhance chosen properties in the finished article.

In many instances, where it is desired to manufacture moulded panels for construction or building purposes at a remote site, the choice of fillers may be largely dictated by locally available vegetable and mineral materials. For example, sand or fine aggregate or finely crushed coarse aggregate may be used in such circumstances in combination with timber products such as sawdust or wood chips or with chopped straw, depending upon the function which the moulded article has to serve.

The total amount of fillers and the proportions of the two types of fillers will depend largely upon the desired physical properties of the moulded article. For example, when the moulded article is a building panel, strength considerations will generally take priority, but for other purposes density may be the overriding consideration. Preferably, the mineral filler should form between 5 to 85 percent by weight of the moulded article. The vegetable filler should preferably form between 5 to 85 percent by weight of the moulded article. Together the fillers should constitute from 20 to 90 percent by weight of the moulded article and more preferably from 60 to 90 percent by weight.

The quantities of polyurethane precursors will generally be selected so that both react completely during formation of the polyurethane matrix. However, a slight stoichiometric excess of one or other ingredient may be permitted without detriment to the quality of the moulded article.

The moulded articles of the invention may be produced by simply mixing the polyurethane precursors, that is to say the diisocyanate, if desired in a capped or blocked form, and the polyol, together with any auxiliary ingredients such as catalysts, colorants, fire retardants, fungicides or mould release agents, with the vegetable and mineral fillers and any auxiliary ingredients associated with the fillers, and dispensing the mixture into a mould. The mould should then be closed and the polyurethane allowed to cure fully under the pressure developed in the mould. The moulded article may then be released from the mould and either used immediately or allowed to stand for any necessary post-cure stabilisation.

The moulded articles of the invention are quickly and simply prepared using relatively inexpensive and readily available materials without the need for complex machinery or highly skilled personnel. The preferred building panels may therefore be manufactured at or close to the site of utilisation, using locally available fillers, thus minimising transport costs.

Such panels are strong, light, inexpensive, acid-, water- and fire-retardant and can be produced in any desired size and shape and in a number of surface finishes to achieve a chosen external appearance and coloured during or after manufacture as appropriate. They can be used to produce complete walls in a single unit for the construction of low cost housing; with or without moulded brick shaped/effect indentations, windows or doors blanks, and interlocking means for joining them to other panels. Large particle fillers such as coarse sand are favoured for external or load bearing walls because they produce strong panels with a granular, brick-like texture, whilst chalk or other smaller particle mineral fillers produce a smoother panel which may be preferred for internal walls.

The articles are quickly and easily joined together using a moulded interlocking means or using separate joining elements or moulded into a single desired shape for example to provide plant pots, paving slabs, fence posts, drainage channels etc.

EXAMPLE 4.1 kg of Suprasec 5005n (a blend of diphenylmethane diisocyanate isomers), 3.7 kg of first pressing castor oil, and 384 g of sodium silicate are mixed for one minute, 7 g of 25% ammonia (to neutralise the tannin in the sawdust) is added and mixing is continued. 53.5 kg of dry river sand (whose particle size is from 0.1 mm to 5 mm) and 5.5 kg of sawdust (whose particle size if from 0.1 mm to 5 mm) are added with mixing for a further 2 minutes. The mixture is poured into a 50 mm x 1 m x 1 m closed mould compressed with a one and a half ton roller and cured for one and a half hours.The resulting panels are able to withstand forces of 40 kN, they weigh between 65 to 70 kg, resist water penetration for at least 24 hours at a spray rate of 40 to 50 mm water per hour (which corresponds to a mean annual rainfall of over 1 m at mean wind speeds of 30 m/s), and resist fire penetration for at least 51 minutes of continuous flaming.

They can be joined together by interlocking means which may be further secured by adhesives and/or overlaying the joints with metal plates. For use in mining shafts and ventilation tunnels, the panels abut against one another in an overlapping arrangement, they are secured to a wooden frame which is wedged into the shaft.

In another embodiment the panels may be adapted çor use as cladding.

In another embodiment the panels may adapted for use as roofing material.

In another embodiment the panels may be adapted for use as decorative features, as alternatives to stone/bronze etc.

In another embodiment the panels may be adapted for use as fire resistant means for protecting "vulnerable areas".

In another embodiment the panels may be adapted for the construction of channels for drainage or ventilation.

In another embodiment the panels may be adapted for use as beams, posts, slabs, paving or kerb stones, or as receptacles such as plant pots.

Claims

CLAIMS:

1. A moulded article comprising a polyurethane matrix incorporating (i) a vegetable filler and (ii) a mineral filler.

2. A moulded article as claimed in claim 1, wherein the polyurethane is derived from a polynuclear aromatic diisocyanate.

3. A moulded article as claimed in claim 1 or claim 2, wherein the polyurethane is derived from diphenylmethane-diisocyanate.

4. A moulded article as claimed in any one of claims 1 to 3, wherein the polyurethane matrix is derived from a naturally derived polyol.

5. A moulded article as claimed in claim 4, wherein the polyol is castor oil.

6. A moulded article as claimed in any preceding claim wherein the vegetable filler is selected from sawdust, wood chips, ground bark, wheat stalks,paper, rubber, straw, vegetable husks, jute, hemp, grass and crushed mielies.

7. A moulded article as claimed in any preceding claim wherein the mineral filler is selected from sand, fly ash, chalk, glass fibres, crushed slag and crushed aggregate.

8. A moulded article as claimed in any preceding claim, wherein the mineral filler forms 5 to 85 % by weight of the article.

9. A moulded article as claimed in any preceding claim wherein the vegetable filler forms 5 to 85 W by weight of the article.

10 A moulded article as claimed in any preceding claim wherein the total fillers forms 20 to 90 % by weight of the article.

11. A moulded article as claimed in any preceding claim which is in the form of a building panel.

12. A method for preparing a moulded article of any preceding claim, comprising mixing the polyurethane precursors together with the fillers, dispensing the mixture into a mould, allowing the polyurethane to cure and removing the article from the mould.

13. Use of an article according to any preceding claim for the construction of buildings.

14. Use of a panel according to any preceding claim for cladding.

15. use of a panel according to any preceding claim for lining, tunnels, ventilation shafts or drainage channels.