Hydrodegradable moulding materials

Amusement devices: games – Aerial projectile game; game element or accessory therefor... – Target

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Details

106212, 106216, 106284, 10628404, F41J 916, C08L 300, C08L 9500, C02K 326

Patent

active

054603838

DESCRIPTION:

BRIEF SUMMARY
This invention relates to a hydro-degradable moulding materials, to articles made of such materials and to a method of making such articles.
A commercial and utilitarian demand exists for articles made from materials which, whilst physically adequate for their immediate purpose, should disintegrate on disposal so as not to remain in the environment as visually offensive litter or become a source of hazard to humans or animals.
The applicants have recognised that one example of an article which should ideally be capable of disintegration under environmental influence is the projected target used for shot gun shooting and generally known as a clay pigeon. These clay pigeons must be strong enough to withstand the considerable stresses of projection from the spring launching devices used for the purpose and must also be hard and somewhat brittle in order to achieve a spectacular break when a hit is scored. As a result the fragments that are distributed over a wide area around the shooting site are sharp edged and being durable, remain as offensive and hazardous litter.
It is among the objects of the present invention to provide a clay pigeon which (or the fragments of which resulting from a "hit"), will degrade as a result of their exposure to the outdoor ground contact environment. Other items which can benefit by being perfectly stable in dry storage but progressively disintegratable when scattered on the earth or buried are articles utilised in military training exercises such as dummy land mines.
The inventor has been discovered that compositions made from resinous materials that are intrinsically brittle can be made surprisingly sensitive to exposure to moisture by incorporating swellable particulate materials within the resin as fillers. The diffusion of moisture into the surface of moulded articles made from mixtures of intrinsically brittle resins with swellable particulates stresses the surface layer of resin beyond the point of mechanical failure and the surface resin becomes permeated by a network of fine cracks. These reticulated cracks permit the further penetration of moisture causing particle swelling at a deeper level within the moulded mass and thus create a progressive failure situation which results in the moulded articles progressively disintegrating into a fine sludge of particles. In the case where the filler particles are carbohydrate or proteinaceous material the presence of fungal or bacterial action associated with moisture greatly accelerates the disintegration because the organic particles are converted by the action of enzymes derived from the micro-organisms into sugary or aminoacid substances of low molecular weight which attract water osmotically and contribute substantially to the swelling action.
According to one aspect of the present invention, there is provided an article intended to remain stable under dry conditions but to undergo fragmentation under moist conditions, the article being made from a brittle resinous or synthetic resin material incorporating moisture-swellable particles as a filler.
In accordance with a preferred embodiment, there is provided a clay pigeon, as herein defined, formed by moulding a composition comprising molten pitch and a particulate filler comprising moisture-swellable particles.
The composition preferably also includes a mineral filler or fillers which, whilst not contributing to the fragmentation under moist conditions, may be necessary to adjust the density of the composition so as to achieve the optimum weight for the finished article to ensure that its performance as a projectile is satisfactory.
According to a further aspect of the invention, there is provided a hydro-degradable moulding material comprising a brittle resinous or synthetic resin material incorporating a moisture-swellable particulate filler.
According to a yet further aspect of the invention, there is provided a method of making an article intended to remain stable under dry conditions but to undergo fragmentation under moist conditions, comprising mixing, with a fluid r

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