Polypropylene Armchair

Abstract

A unitary moulded chair shell forming the seat, back and arms of a chair, provided with a continuous integral rolled flange forming a channel extending along the under or rear side of at least the front edges of the arm and seal portions of the shell, and having integral webs extending across said channel in the regions where the arms merge with the seat.

Description

This invention relates to shells for chairs of the type comprising a unitary shell forming the seat, arms and back of the chair supported by a frame attached to the underside of the seat portion of the shell.

A major problem in the design of shells for such chairs is the provision of sufficient rigidity, especially in response to loadings due to a user leaning against the back of the chair, and particularly in the case of chairs having arms lounging sideways in the chair.

Earlier chairs of this type usually had shells of fibre reinforced synthetic resin, and local reinforcement of the shell could fairly readily be incorporated during manufacture, for example by local variation of the thickness of the shell; however the material as well as the manufacturing techniques involved were relatively costly. It is desirable to be able to use cheaper materials and moulding processes, in particular injection moulding of unreinforced synthetic resins, for example polypropylene. Unfortunately, practical limitations in injection moulding technique restrict the reinforcement techniques available and it is a practical requirement that the shell be of substantially constant thickness throughout, whilst the absence of fibrous reinforcement reduces the inherent rigidity of the material.

A limited degree of local deformability in certain parts of the chair shell is desirable since it enhances the comfort of a user, but it is necessary to avoid any substantial distortion of the shape of the shell as a whole, and in particular distortions likely to cause fatigue failure of the shell material. Two main expedients are known for this purpose. Firstly, a rolled section or flange can be provided along at least selected parts of the edge of the chair shell. Secondly, if the shell is designed to include integral arms, these help relieve the bending stresses that would otherwise be applied at the junction of the seat and the back. In neither case is any variation in the thickness of the shell required, but even in combination these expedients do not overcome the liability of the shell to certain types of distortion, in particular those caused by the forms of user behavior outlined above. One solution to this problem would be to extend the rolled section of flange to form a completed tubular section around the edge of the chair, but such sections cannot be formed by injection moulding.

Surprisingly, we have found that the problem can be solved, where a continuous roll or flange along the front edges of the seat and arms of the chair is provided, by moulding webs across the channel formed by the roll or flange in the regions where the arms merge into the seat, this modification being found to largely prevent distortion of the shell due to rearward or sideways forces applied by the user to the back of the chair.

Thus, according to the invention, a unitary moulded chair shell forming the seat, arms and back of a chair, provided with a continuous rolled flange forming a channel extending along the under or rear side of the front edges of the arm and seat portions of the shell, also comprises integral webs extending across said channel in the regions where the arms merge with the seat.

The advantage of this construction is that the provision of such webs provides the desired stiffening of the chair shell with the minimum of additional material and without altering the general appearance of the shell, the webs being inconspicuous due to their location, whilst they are readily produced by injection moulding techniques; moreover alteration of the number and exact location of the webs can be carried out without major modification of the mould used. The invention is particularly useful in the moulding of chair shells from thermoplastic materials such as polypropylene or polyethylene, and overcomes the liability to excessive distortion which has hitherto been a serious disadvantage of moulded thermoplastic chair shells.

The invention is described further with reference to the accompanying drawings in which:

FIG. 1 shows a perspective view of a chair shell in accordance with the invention, partially broken away in order to clarify the construction,

FIG. 2 shows an underneath plan of the same shell, and

FIG. 3 shows on an enlarged scale, a part section of the shell on the line III-III in FIG. 2.

Referring to the drawings, only the chair shell 1 comprising a seat portion 2, a back portion 3 and arm portions 4 has been shown, the frame being omitted: this may take a number of forms, and is attached by screws to bosses 5 formed integrally on the lower surface of the seat portion 2. The edges of the shell are turned downwardly and/or rearwardly to form a rolled flange 6 around the periphery of the shell, the extent of this roll along at least the front edges of the arms and seat, and in the example shown also the top edges of the arms, being sufficient to form a channel 7. In each of the regions where the arm portions merge with the seat portion, this channel is spanned by a number of webs 8. In the example shown, five webs are used in each such region, spaced throughout the transitional region of the channel between the arm portion and the seat portion: however, the number and spacing of the webs can be varied experimentally to suit differing designs of shell: it will normally be possible to modify an existing mould in order to add additional webs if necessary. Conveniently, the webs are approximately the same thickness as the main shell.

Claims

I claim:

1. A unitary injection molded chair shell forming a seat, back and arms of a chair, said chair shell being provided with a continuous open angularly disposed flange forming a channel extending along the outside of at least front edges of the arm and the underside of a front edge of said seat, characterized by the provision of a plurality of integral injection molded webs extending across said channel from a location beneath said seat to a location along said arms and across a juncture of said arms and said seat thereby preventing distortion of the chairback and of the chairback relative to the arms due to a user's applying with his back either rearward or combined rearward and sideways forces to the back or both the back and either arm of the chair.

2. The chair shell as defined in claim 1, wherein said plurality of integral injection molded webs are positioned only at the two front points of merger between said arms and said seat.