Plastic and nonmetallic article shaping or treating: processes – Pore forming in situ – Composite article making
Patent
1983-02-09
1987-12-22
Anderson, Philip
Plastic and nonmetallic article shaping or treating: processes
Pore forming in situ
Composite article making
264 464, 264 466, 2642711, B29C 6722
Patent
active
047145749
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to the production of foams which contain integrated foam areas having higher or lower hardnesses. Such foams are particularly useful for seats.
Seats, especially car seats have to support the seated person under static and dynamic conditions in a way that the supporting force is compatibly distributed on to the human body. This means, that the main force is taken by the bones without squeezing the veins in the softer areas. In addition to this a seat needs to provide sufficient side stability in case of side acceleration which exists when driving the car in curves.
It is therefore desirable for seats in particular for use in transport, e.g. car seats, to have relatively hard and relatively soft portions. Those skilled in the art of seat construction are familiar with the parts of the seat where it is desired to provide relatively hard portions.
It is well-known that seats may be made from polyurethane foams. Reinforced regions in such polyurethane foams are at present provided in a number of ways. One method is to prepare a foam part of increased hardness and to introduce this separately prepared part into the softer foam part. Another method is to embed steel wire frame inserts into the seat. A third method is for the supporting seat frame, to which the polyurethane foam is attached, to provide additional support in the required areas.
In addition to the above commercially use methods, polyurethane foam seats have been produced on an experimental basis by two methods. In one method a first moulding step is carried out to produce a layer of soft foam between two mould parts.
One of the mould parts is then removed and replaced by another mould part which defines a cavity containing the soft foam layer. A mixture giving a harder polyurethane foam is then injected into the cavity.
Another method which had been tried experimentally is to use two separate machines for producing polyurethane foam which feed simultaneously into the mould. It is then necessary to have a mould design or separating walls which keeps the two different foam mixtures substantially apart but which allows sufficient contact between the two foams to ensure good bonding on curing.
Any kind of insert which needs to be put into the moulds during foam seat production requires processing time, adds material cost and increases repair and scrap rates.
Structural modification of the seat frame is limited and again adds production cost.
The new experimental processes described above require complicated and more costly moulds (two lids) and need double processing time or are either investment intensive or limited in hardness variation.
Furthermore it is required to have some kind of separating walls in the mould which keep the liquid material for a short time in place.
The production of foam articles of different hardness without devices within the mould to separate the harder and softer foams is disclosed in Canadian Patent Specification and German Patent Specification. In the processes described above in these two specifications formulations giving harder and softer foams are poured simultaneously into the mould. The Canadian specification on page emphasises the importance of providing grooves and depressions in the mould so that the different foam formulations are kept separate initially even though they are subsequently allowed to come into contact with each other. In the moulding process specifically described in the German patent specification a mixture producing harder foam is introduced into a recess in a mould corresponding to the side portions of the seat while a mixture producing softer foam is fed into the centre of the mould. The new foam formulations are again kept apart initially. The requirement for the foam formulations to be fed into the moulds in which they are initially separated imposes restrictions on the types of mould which can be used.
Furthermore, it is only possible to produce articles in which the regions of harder and softer foam extend to the surface of the article. It would be desirable t
REFERENCES:
patent: 3229441 (1966-01-01), Heffner
patent: 3366718 (1968-01-01), Komada
patent: 3534129 (1970-10-01), Bartel
patent: 3872199 (1975-03-01), Ottinger
patent: 3929948 (1975-12-01), Welch
patent: 4190697 (1980-02-01), Ahrens
patent: 4246213 (1981-01-01), Takamatsu et al.
Anderson Philip
BP Chemicals Limited
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