Plastic and nonmetallic article shaping or treating: processes – Pore forming in situ – Composite article making
Patent
1991-11-18
1993-12-28
Kuhns, Allan R.
Plastic and nonmetallic article shaping or treating: processes
Pore forming in situ
Composite article making
264 464, 264 466, B29C 6722
Patent
active
052736954
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to the preparation of multihardness polyurethane foam articles by the pouring of differing foam formulations into a mould. In particular the present invention relates to a process for preparing side rolls for seats which comprise a hard polyurethane foam encapsulated within a soft polyurethane foam.
The preparation of multihardness foams comprising inter alia zones of hard foam encapsulated within a soft foam is described in European Patent No. 68820. This patent describes the process of such materials by first introducing a soft foam formulation into a mould and thereafter adding a hard foam formulation into the foaming soft formulation. The hard foam formulation is thus added after the soft foam formulation has had an opportunity to expand.
A problem arises with the technology described in this patent during the manufacture of side rolls for automobile seating. In the side rolls wells of automobile seating moulds there is a tendency for the liquid hard foam formulation to penetrate completely the expanding soft foam formulation particularly at the point of pouring thereby giving rise to areas in the cured foam articles where the hard foam is not encapsulated in the soft. One approach to solving this problem is to partially froth the hard foam formulation as described in European Patent No. 251803.
Another approach to manufacturing multilayer or multihardness seats is described in European Patent No. 251659. This patent describes a process which involves pouring sequentially two or more foam formulations, designed to produce two or more foams of differing hardness, onto a given point in the bottom half of a seat mould and thereafter allowing them to rise and cure. The seat mould is inclined slightly to the horizontal (preferably 5-12 degrees) and the point of pouring is located at or near the top of the inclined bottom surface of the mould. It is a feature of the process described that the formulations are poured sequentially without any waiting time between, hence no foaming of any of the formulations takes place on the time scale on which pouring occurs. Although, according to the patentee, it would be expected that under such conditions, the formulations would mix, this does not however occur and, after curing, a foam seat comprising discrete layers of the various foams is produced. The discrete layers are found to be bonded to one another. It is to be noted that this patent does not disclose what happens when this technology is applied to the side roll wells of automobile seating moulds. From the teaching of the European Patent No. 251659 it would be expected, that two foam layers, e.g. a hard and a soft one, would always be formed, and that there would be no difference between the centre part of the mould and the side roll wells. In addition the patent only describes explicitly the preparation of layered foam cushions with discrete hard side rolls.
It has now been found that by inclining the bottom surface of the mould, such that the bottom of the side rolls well is inclined and by adding the second foam formulation to the first within a specified time after the first has been added then the problem of hard foam penetration can be overcome or at least minimised. It has also has been found that by using the process of the present invention degree of encapsulation of the second foam in the first foam can be controlled.
According to the present invention there is therefore provided a process for preparing a multihardness or multidensity foamed seat, particularly an automobile seat, having side rolls comprising one or more zones of a second polyurethane foam encapsulated in a first polyurethane foam by foaming and curing a first polyurethane foam formulation and a second polyurethane foam formulation in a side roll well of seat mould which comprises the steps of: inclined in a direction parallel to its length, interval corresponding to between 0.01t to 1.5t, preferably 0.05t to 1.5t, most preferably 0.2t to 1.5t, where t is the cream time of the first foam formulation.
The p
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patent: 4714574 (1987-12-01), Tenhagen
patent: 4726086 (1988-02-01), McEvoy
patent: 4762654 (1988-08-01), Fuchigami et al.
patent: 4804506 (1989-02-01), Okamoto et al.
patent: 4975229 (1990-12-01), Kita et al.
Brown Michael J.
Lidy Werner A.
Kuhns Allan R.
The Dow Chemical Company
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