WO1992013809A1

WO1992013809A1 - Moulding of artificial stone

Info

Publication number: WO1992013809A1
Application number: PCT/GB1992/000175
Authority: WO
Inventors: Brian Milton Smith; Christopher Cyril Smith
Original assignee: Recon Developments Ltd
Current assignee: Recon Developments Ltd
Priority date: 1991-01-30
Filing date: 1992-01-30
Publication date: 1992-08-20
Anticipated expiration: 1993-07-30
Also published as: AU1196892A; GB9318046D0; GB2270921B; GB2270921A; GB9102025D0

Abstract

The moulding is produced by blending highly filled thixotropic prepolymer formulations of polyol and polyisocyanate, respectively, the formulations being anhydrous and non-porous mineral-filled, allowing the blend to gel, and then curing the gelled material in a smooth-surfaced mould. Veining (such as a marble) may result from the addition of a pigment concentrate to the gel prior to introducing to the mould.

Description

Moulding of Artificial Stone

This invention relates to the moulding of artificial stone.

There are many forms of artificial stone, and it is convenient for most purposes to mould the substance directly into the shape required. However, the end result can often be something that looks artificial, and the more artificial-looking is the product, the less acceptable it is.

One requires both a good quality mould and a substance which will solidify into convincing-looking stone. There should not be any tendency to tarnish, and if possible the mould should enable release of surfaces on the moulded structure parallel to the direction of release rather than at a slight angle.

High quality moulds in metal are extremely expensive, and not practical for short runs. However, if one moves to less expensive materials the result is usually an inferior finish and often breaking of the mould as the release is carried out.

It is the aim of this invention to alleviate these problems.

According to one aspect of the present invention there is provided a method of producing a moulded body simulating a mineral stone material, which comprises providing a first thixotropic prepolymer formulation comprising 0.5 to 1.5 parts by weight of a viscous polyol prepolymer containing a least 0.5 parts by weight of a paniculate mineral filler which is substantially non-porous and anhydrous; providing a second thixotropic prepolymer formulation comprising 0.5 to 1.5 parts by weight of a reactive viscous polyisocyanate containing at least 0.5 parts by weight of a paniculate mineral filler which is substantially non-porous and anhydrous, and which may be the same as the first-mentioned filler, or different thereto, blending said first and second thixotropic formulations together and allowing them to gel, introducing the gelled blend into a mould, allowing the blend to cure in said mould, and demoulding the resulting cured blend once the cure is substantially complete. The respective mould parts may, for example, each comprise a formed sheet of plastics, such as polystyrene, which can enable a moulded body to be produced with an extremely smooth surface, but also with considerable sharpness of detail. Articles of smooth artificial stone such as marble and onyx substitutes can be made from it with convincing reality with a surface complementary to that of the mould. However, after several uses of such moulds, the interior surface of the mould inevitably begins to deteriorate, but it need not then be discarded; it can be used to mould further articles in artificial stone whose finish is not expected or required to be so smooth or shiny. The mould may then complete its useful life after about a dozen uses but its materials and its process of manufacture are cheap enough to make this economic.

The resulting moulded body may be highly resistant to thermal shock and may be suitable for the moulding of aesthetic features in the home/hotels such as fire surrounds, lamp bases etc., in a range of luxury effects emulating e.g. marble and onyx.

The properties of the product also allow it to be used to manufacture a full range of bathroom and sanitary ware. The afore-mentioned properties of the invention are superior to other cross-linked synthetic polymeric substances currently available for the stated purposes. Apart from aesthetics, the resulting body also has superior hardness, strength and can well exceed the ultimate hot and cold water cycle requirements.

The polyol prepolymer is generally an alkylene oxide adduct of a polyol (that is, a polyether polyol) or of a polyamine, which polyols typically have 4 to 8 carbon atoms (e.g. 1, 4-butane diol). It is typically a white liquid having a viscosity of 5000 to 15000 (preferably 10000 to 14000) centipoise at 25°C and a specific gravity of 1.5 to 1.6 (such as 1.53 to 1.57), also at 25°C. The polyol formulation generally contains catalyst for the urethane-forming reaction with the polyisocyanate. Such catalysts may be based on mercury, tin, bismuth or vanadium, optionally in combination with one or more tertiary amine. The catalyst may be present in an amount of 0.05 to 5%, based on the weight of polyol. An example of such a material is commercially available under the name Hyperlast 7853289. The polyol formulation may contain a water-binding or desicating agent (that is, a material which absorbs unwanted water); an example of such a material is a molecular sieve, such as that available commercially under the name Sylosiv.

The filler may comprise stone dust, marble, chalk or lime, or granules of materials such as slate, alumina or pulverised fly ash. It is the filler powder that determines the type of stone that is simulated. For an onyx effect, for example, white alumina powder Al₂O₃ is suitable.

For a granite-like effect, there are proprietary granite fillers of various colours. Slate dust is also usable. A marbled effect can be obtained using pulverised fly ash, such as the material commercially available under the name Thermalite.

The polyisocyanate prepolymer is typically di (4-isocyanatophenyl) methane (MDI), an MDI prepolymer, or the like, the polyisocyanate may be the partial reaction product of a polyol and a polyisocyanate. The polyisocyanate is typically a white liquid having a viscosity of 5000 to 15000 centipoise at 25°C and a specific gravity of 1.7 to 1.8 (such as about 1.73 to 1.75) also at 25°C. The polyisocyanate typically has a functionality of 2.0 to 2.7, such as 2.1 to 2.3. An example of such a material is commercially available under the name Hyperlast 7855052.

The filler for the polyisocyanate may be substantially as described with reference to the polyol; it is preferred that a filler of the same nature should be used in the two prepolymer formulations.

The resulting moulding is preferably substantially foam-free (for which purpose, water is rigorously excluded from the blend).

It is preferred that the blend of the two thixotropic formulations be mixed with a pigment, which is mixed in such a way that the polymer curing takes place more rapidly than diffusion of the pigment into the polymer. By this means a veining effect, simulating that of natural marble, may be attained. The pigment may be solid or in the form of a paste or the like. The pigment may be mixed with the whole batch of blended prepolymers. However, in a preferred embodiment, part of the batch may be separated off to be blended with the pigment to form a masterbatch; this masterbatch is then gently mixed with the remainder of the batch of blended prepolymers.

The following example is given by way of illustration only. Example

1. Stone filler was mixed with polyol (equal parts by weight) in a suitably sized container using an electric mixer, until an acceptable thixotropic dispersion was achieved.

2. The MDI was separately mixed with stonefiller (equal parts by weight), and then mixed with the first blend.

3. TiO₂ pigment was then blended, followed by a catalyst sufficiently to achieve an homogeneous mixture,- which was allowed to gel.

4. A small amount of the mixture was withdrawn into a small container and an amount of colourant, sufficient to achieve the required colour/shade density was mixed in (by hand). The mixture was added to the mass and mixed gently sufficiently to retain veining striations, then the whole was poured into the mould. The veining mixture may also be added to the mass whilst pouring to the mould to achieve varying styles of veining.

The final product, after curing and demoulding, had the following properties: Shore Hardness 88°D

Heat Dist. Temp. 70°C

Izod Impact Str. 2.4 Kj/m²

Flexural Modules 3700 Mn/m²

Flexural Str. 65 Mn/m²

Density 1650 kg/m³

Claims

CLAIMS:

1. A method of producing a moulded body simulating a mineral stone material, which comprises providing a first thixotropic prepolymer formulation comprising 0.5 to 1.5 parts by weight of a viscous polyol prepolymer containing a least 0.5 parts by weight of a paniculate mineral filler which is substantially non-porous and anhydrous; providing a second thixotropic prepolymer formulation comprising 0.5 to 1.5 parts by weight of a reactive viscous polyisocyanate containing at least 0.5 parts by weight of a paniculate mineral filler which is substantially non-porous and anhydrous, and which may be the same as the first-mentioned filler, or different thereto, blending said first and second thixotropic formulations together and allowing them to gel, introducing the gelled blend into a mould, allowing the blend to cure in said mould, and demoulding the resulting cured blend once the cure is substantially complete.

2. A method according to claim 1, wherein said mould comprises one or more mould parts of formed plastics sheet.

3. A method according to claim 1 or 2, wherein at least one said formulation contains a water-binding agent.

4. A method according to any of claims 1 to 3, wherein said thixotropic formulations are mixed with a pigment so as to produce a veined effect.

5. A method according to claim 4, wherein said mixing is carried out in such a way that polymer curing takes place more rapidly than diffusion of the pigment into the resulting polymer.

6. A method according to claim 4 or 5, wherein said pigment is mixed with a separated part of the blended formulations prior to mixing with the remainder of said blend.