Improvements in methods of manufacturing building products from moulding compositions.

This invention relates to moulding compositions and especially dough moulding compositions containing phenolic resins.

Over the years considerable development of synthetic resin moulding materials has resulted in their use for all kinds of building products for both internal and external applications.

Polyester resins, for example, have proven to be readily acceptable for;use as constituents in moulding compositions partly because of their cost and ease of processing vis-a-vis that of phenolic resins.

However, for any materials used as building products, there are stringent fire performances to be met, and polyester resins, which normally burn quite readily, must have fire retardants admixed thereto. Such retardants whilst reducing the fire hazard add disproportionately to the overall cost of an article manufacture from a polyester resin based composition.

One such polyester based moulding composition is disclosed in British Patent No. 1156205.

While polyester resins themselves were cheaper and easier to process than phenolics it was not always a practical consideration to develop phenolic resin moulding materials for construction materials.

One such preparation is the consideration of phenolic based moulding materials for artificial stone building products, for example, cladding panels and roofing slates, because of the self extinguishing property of phenolic resins when compared to combustible polyester resins.

Phenolic resin moulding materials have found acceptance for some applications, parthcularly foamed phenolic resins, and several process routes for moulding products therefrom have been proposed. It has been found, however, that most of the proposed systems use too much resin or give a finished product which does not meet the property requirements of natural building components, for example, slates, or even the properties of the artificial slate such as that described in British Patent No. 1156205 and marketed under the Registered Trade Mark "Petarch".

A further disadvantage of phenolic moulding materials developed hitherto has been the inherent lack of durability of the building products made therefrom. For example cladding panels and roofing tiles suffered from U.V. attach resulting in loss of flexural strength. In addition inclement weather conditions resulted in delamination and break-up of the tiles.

This lack of durability of phenolic based products has been due in part, it is believed, to the inability to produce finished products with little or no void content. Voids in moulded products appear to contribute to the formation of cracks in inclement weather conditions.

However with the cost of polyester resins rising: <ul id="ul0001" list-style="none"><li>(a) because of the rise in world demand;</li><li>(b) because of short supply thereof; and</li><li>(c) because of the rise in standards set by governmental huthorities in respect of fire performance and durability, etc., of building products containing polyester resins, it has now become an attractive proposition to consider alternative materials.</li></ul>

In addition to the drawbacks listed above proposed acid catalysed systems create process hazards which in an industrial environment are also quite unacceptable and necessitate costly extraction plant which adds to the overall unit cost'.

The "Petrarch" material, referred to hereinbefore, when made into slate sized components has a 24 hours water absorption of 0.07% to 0.43% and a flexural strength of 40 MN/m² dry and 29 _MN/m² after immersion in water for 24 hours.

Attempts have been made to provide slates made from phenolic resin moulding compositions which will match the properties of natural slate and also the artificial slates referred to above while presenting a more economical product in terms of cost and ease of manufacture. However single resin compositions have all suffered from disadvantage.

The present invention provides a dough moulding composition, particularly for manufacturing building products, and comprising an inorganic mineral filler mineral or plastics fibres and a resin mixture consisting of a resole resin in liquid form and a novolak resin.

Preferably the composition comprises from 55% to 90% by weight of the mineral filler and from 10% to 30% by weight of the resin mixture.

The resin mixture may comprise from 30% to 70% by weight of each resin and preferably from 40% to 60% by weight of each resin. In one embodiment, approximately equal parts of each resin were used.

Conveniently the composition comprises from 15% to 25% by weight of the mixture of the resole and novolak resins.

Preferably the dough moulding composition comprises 17% by weight of the resins made up 9% by weight liquid resole resin and 8% by weight powdered novolak resin.

Conveniently the composition contains an amino-silane coupling agent to facilitate the wetting out and the bond strength of the resin with the other constituents of the composition.

Preferably the mineral filler is slate powder.

Preferably the fibres are glass fibres and the composition may comprise from 0.5% to 15% by weight of glass fibres.

Preferably the glass fibre content is 2.5% by weight of the composition.

Conveniently the glass fibres are chopped glass rovings and the length of the chopped rovings may be 1 to 50 mm and preferably 6 to 25 mm.

Conveniently the composition may comprise up to 5% by weight of pigment and preferably 1% by weight.

Preferably the dough moulding composition is suitable for pressing under heat to form a building material, the composition comprising 9% by weight of liquid resole resin, 8% by weight of a dry powdered novolak resin, 2.5% by weight of glass fibres of 25 mm length, 1% by weight of pigment and 79.5% of slate powder.

Conveniently in the composition as set out in the last preceding paragraph the novolak resin contains approximately 2% by weight of the novolak resin, of an amino-silane coupling agent.

The invention also provides a method of manufacturing a building product of a composition as described above, the method comprising the steps of mixing together the novolak resin and the inorganic mineral filler, wetting out by addition to the mixture of the resole resin, adding to the mixture the mineral or plastics fibres and forming the mixed composition into the building product. Preferably pigment is added after the wetting out.

The dough like consistency of the mix allows ready formation of artificial slates therefrom by pressing the mixture at a mould pressure of 0.34 to 4.27 MN/m², preferably 1.4 MN/m² and at a platen temperature of-110° to 190°C preferably 150°C for 1 to 30 minutes, preferably for 2 to 4 minutes.

The invention also provides a slate-like building product formed-under heat and pressure from a composition as described above and/or by the method described above. The product preferably has a water absorption after 24 hours of less than 1% by weight and is particularly suitable as a roofing tile.

There now follows by way of example of the invention a detailed description of a composition according to the invention.

. The following constituents were mixed together in a standard two blade Winkworth mixer:- <ul id="ul0002" list-style="none"><li>(a) 8% by weight solid novolak resin powder which contained approximately 2% by weight of the novolak resin, of an amino-silane coupling agent.</li><li>(b) 9% by weight liquid resole resin;</li><li>(c) 2.5% by weight chopped glass rovings of 25 mm length, the roving being MSS1618 available from Fibreglass Limited;</li><li>(d) 1% of black pigment, viz Bayer 320; and,</li><li>(e) 79.5% by weight of inorganic mineral filler, i.e. slate powder, viz Delabole slate grade S12, a material with a wide distribution of particles sizes.</li></ul>

The novolak resin powder and slate powder were first mixed together. The liquid resole resin was added to wet out the mixture and finally the glass roving ahd pigment added.

The resultant dough like mixture was then extruded and subdivided into preforms of controlled weight for loading into the mould cavities of a platen press where it was pressed at a pressure of ₁.₄ MN/m for 3 minutes at a platen temperature of 156°C to give a 30 cm sq product of approximately 3 to 4 mm thick.

Venting of the mould during pressing was effected for ten seconds at one minute intervals to release condensation vapours.

The resulting properties of the product were:- <ul id="ul0003" list-style="none"><li>(i) Dry flexural strength:- 44.3 MN/m²</li><li>(ii) Wet flexural strength after 24 hours water absorption:- 45._{7 MN/m}²</li><li>(iii) 24 hours water absorption:- 0.06% by weight (when tested according to British Standard 680 leart 2, 1971) .</li></ul>

Normally of course one would expect a lower flexural strength after water absorption. However, such is the quality of the product that water absorption is very low and figures for flexural strength of 42 to 48 MN/m² are readily obtained.

It has been found that an artificial slate made by the process disclosed, and from the composition set out in the example, has a greatly reduced void content when compared to products made from phenolic based resin compositions processed by other routes.

Indeed it has been found that the void content is as low as that to be found in natural materials and the artificial slate material of the aforementioned British Patent No. 1156205.

It is this lack of voids which it is believed contributes particularly to the strength of the material and the apparent durability thereof.

Although slate powder is utilised in the composition any inorganic mineral filler may be included depending upon the characteristics of the product to be manufactured.

Whereas the mixing of the constituents of the dough moulding composition was said to be in one particular succession of addition of the constituents it is to be realised that the mixing may take place in any suitable order.

The composition described may be used to form many building products and is particularly suitable for making a product such as that described in our co-pending Application'No. 7917940 dated 23rd May, 1979 and entitled "An Improved Roofing Tile".