Plastic and nonmetallic article shaping or treating: processes – Pore forming in situ – Composite article making
Reexamination Certificate
2000-11-27
2003-01-21
Kuhns, Allan R. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Pore forming in situ
Composite article making
C264S046400
Reexamination Certificate
active
06508963
ABSTRACT:
FIELD OF THE INVENTION
BRIEF DESCRIPTION OF THE INVENTION
This invention concerns the manufacture of polyurethane foam cushions with covers especially for automobile vehicle seats but which can also be used for other automobile interior components, for example: headrests, armrests, dashboards, door panels, roofs, etc.
BACKGROUND OF THE INVENTION
Two main techniques are used for the manufacture of such cushions.
According to a first technique, the foam padding is manufactured by expansion of foam in a mould shaped to the form of the cushion to be obtained. Then the cover is assembled on the padding by bonding or by mechanical attachment for the so-called traditional padding methods.
According to the second technique, also called “in-situ manufacture”, a mould shaped to the form of the cushion to be obtained is used in which the prepared cover is placed, utilisation face against the surface of the mould. The cover can be held in place in the mould by various means, especially by suction through the surface of the mould. Then the polyurethane foam is moulded, on the back of the cover, in the mould where it is expanded in a manner known per se, after having closed the mould, to take the form of the mould.
In common practice, the cover consists of a compound textile (textile and foam back) that is, with, on its face located on the cushion internal side, a sublayer consisting of a more or less thin covering, generally cellular (the foam back), which can favour the adhesion with the foam by penetration of the foam into the sublayer of the cover.
However, in this case, the polyurethane foam may have a tendency to traverse the material of the cover, which is of course not acceptable for obvious aesthetic and comfort reasons. To avoid this problem, it is known to use for the cover a composite material, generally designed as “complex”, integrating either an impervious film protecting the fabric or the decorative covering, or a sufficiently thick layer of cellular flexible material to prevent the polyurethane foam of the padding from completely passing through the cover, this process being known as the “permeable in-situ process”.
If a cellular layer is used alone, this layer must be sufficiently thick, for example around 4 to 7 mm, dense and with air permeability as low as possible. However, this air permeability is difficult to achieve in a satisfactory and reproducible manner. Moreover, the parts obtained have foam overdensifications, that is zones where the foam is more compact, under the textile cover. They can also have penetrations of foam into the cellular sublayer detrimental to comfort and to feel. These overdensification and penetration phenomena are also the consequence of the negative pressure applied through the wall of the mould, passed on through the cover, which creates heat losses and a suction effect of the polyurethane foam within the thickness of the material of the cover.
If an impervious film is used, the hygrothermic comfort of the resulting cushion is very poor due to the air and water vapour impermeability at cushion surface. It has already been proposed to solve this problem by making the films used permeable to vapour and to air after moulding either by mechanical means such as needles perforating the film or by at least partial destruction of the film during or after the foaming of the polyurethane, for example by heat. A notable disadvantage is that the destruction of the film is difficult to control, the synchronisation between the polyurethane curing reaction and the effect of the destruction of the film being especially tricky: either the destruction of the film occurs too early during the foaming and leads to a risk of the polyurethane penetrating the cover or, on the contrary, the destruction of the film occurs only on completion of the moulding and, in this case, the adhesion between the foam and the cover is liable to be significantly degraded. In addition, the relatively high temperatures required, for example more than 120° C. to act on meltable films, is not suitable to all textiles and there is a risk that they will be degraded.
It has also been proposed, in document DE-A-3 728 923, to apply to the back of the cover, previously positioned in the mould, a layer intended to ensure impermeability during the subsequent expansion of the polyurethane foam. After the curing and the hardening of the foam and extraction of the cushion from the mould, the impermeable film applied to the back of the cover is made permeable to air by heat or water vapour which have the effect of destroying the said layer. The impervious layer is applied by spraying onto the back of the cover either a product consisting of or including sugar, gelatine, starch or modified gelatine, or a product with vinyl properties, for example polyvinyl alcohol, associated with acetic or boric acid salts. In both cases, the product is sprayed on in a liquid state then dried, for example by heating at 60°
0
C. for gelatine, to obtain a solid impervious film adhering to the back of the cover. The impermeability of the film must be ensured until the end of the expansion of the polyurethane in the mould when it is degraded by heat or vapour on completion of curing to obtain the final permeability sought. Adhesion is obtained between the deposited film and the polyurethane foam thanks to the reaction between the material of the said film and the isocyanate contained in the polyurethane.
A disadvantage of this process is that the film obtained, with a thickness as stated from 50 to 400 micrometers is not very flexible and tends to break. The process must therefore be performed after the cover has been placed and held in the mould. Moreover, after the heat or vapour treatment, the adhesion between the polyurethane foam and the cover may be degraded as the impermeability of the film during the expansion of the foam prevents the bond between the foam and the cover. Furthermore, the later destruction of the film, at least partial, tends to eliminate the bonds existing between the film and the cover.
The aim of this invention is to avoid these disadvantages and to propose a process for the manufacture of a cushion, or any other similar part, including polyurethane foam padding which ensures perfect adhesion between the foam and the cover and very good hygrothermic comfort by a permeability to water vapour. The invention aims also at proposing a process simple to perform without the need for specific treatment after moulding.
With these targets in mind, the subject of the invention is a process for manufacturing a polyurethane foam cushion covered with a cover where the cover is placed in a mould shaped to the form of the cushion to be obtained, the cover having a front face forming the exterior decorative layer which is placed against the inside wall of the mould and a rough back face, located towards the inside of the mould, then the polyurethane is injected in the mould and forms the said foam by expanding, characterised in that, before the polyurethane is injected, a film of a thermoplastic material containing agents reacting with the isocyanate, said film being initially permeable to water vapour, is placed on the rough back face of the cover, the said film having a plastification capability under the effect of the chemical reactions occurring between the material of the film and the isocyanate contained in the polyurethane and a sufficiently low predetermined thickness so that the polyurethane foam can, during its expansion and under the effect of the pressure generated by the said expansion, pass through the said film and anchor onto the back face of the cover.
The process according to the invention is based on the use of a thermoplastic film, placed in contact with the cover before moulding, injection or spraying of the polyurethane, which has intrinsic water vapour permeability properties but which however is sufficiently impermeable to air and liquids to prevent it from being traversed directly by the polyurethane at the start of moulding which therefore avoids all direct contact between the p
Jaillet Laurent
Le Pimpec Yves
Rancon Hervé
Connolly Bove & Lodge & Hutz LLP
Faurecia Sieges d'Automobile S.A.
Kuhns Allan R.
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