GB2038347A - Producing shaped parts - Google Patents

Abstract

A process for producing a fibre- reinforced foamed shaped part, in which the foaming is caused by the reaction of a mixture of a polyhydric alcohol and an isocyanate, in which the reaction mixture additionally comprises from 5 to 30%, by weight of the mixture, of an inert ester whose boiling point is above the reaction temperature of the reaction mixture.

Description

SPECIFICATION Producing shaped parts It is known to produce shaped foamed plastics parts by introducing a mixture of an isocyanate, a polyhydric alcohol and an activator into a moulding tool so that the constituents react and expand to take the form of the mould. The mechanical properties of the shaped products can largely be determined in advance by the choice of the nature and quantity of the constituents. It is generally true that, with increasing density per unit volume, improved strength properties are obtained.

Attempts have been made to improve the strength properties of shaped foam parts having low weight per unit volume by adding fibres or fibre mattings which, following the reaction, are firmly held within the foamed plastics product. However, this technique has not been successful in practice, particularly in the production of large shaped parts, because adequate penetration is possible only over short distances and because adequate wetting is possible only when using very coarsely structured mattings or very short fibres.

However, the use of such fibres and mattings has little or no strengthening effect.

It has been proposed, with a view to improving the flow distances achieved, to use only reactive constituents which react slowly with one another. A procedure of this kind, however, inevitably leads to longer hardening and mould residence times, and is therefore uneconomic.

According to the present invention, in a process of the type described above for producing foamed shaped plastics products, from 5 to 30%, and preferably from 10 to 20%, by weight of an inert ester with a boiling point above the reaction temperature of the reaction mixture is added thereto.

Taking into account the reaction mixtures usually employed, the ester used in the process of this invention should generally have a boiling point of more than 200"C. The use of esters having a sufficiently high boiling point is important because the addition of substances with a low vaporisation point would lead to absorption of the liberated heat and thereby to an undesirable cooling effect during the chemical reaction of the mixture.

The consequence of this would be incomplete hardening. Suitable esters are those of hydrocarbyl mono- or di- carboxylic acids having from 6, more preferably 8, to 25, more preferably 20, carbon atoms with a hydrocarbyl alcohol of up to 12, and preferably from 3 to 10, carbon atoms. Particularly suitable esters are the esters of phthalic or stearic acid with butyl, benzyl or octyl alcohol. Mixtures of such esters can be used.

The ester should not react with the other components.

The flow behaviour of the reaction mixture, which is particularly important as regards good penetration and wetting of the fibres or fibre matting, can be improved, in addition to the improvement caused by the presence of the ester, of an epoxy stearate, in an amount of up to 25%. When both an ester and an epoxy stearate are added to the reaction mixture, a distinct improvement of the flow behaviour can be observed in each case, and flow distances of more than 0.5 m through a compressed fibre matting are readily obtained.

The reaction behaviour of the reaction mixture employed does not change recognisably when the ester and any epoxy stearate are added. Therefore, conventional methods of production of shaped foamed parts, using known metering equipment, can be employed.

A film, e.g. a prefabricated film, may be inserted into the mould in which the process is conducted, the film being forced against the wall of the mould during blowing of the reaction mixture and forming a strong bond with the foam in the process. The mechanical properties of a film-reinforced shaped part are the result of the sandwich bond with the film or films covering the surface and which, if necessary, may also consist of a hard material, and of the position and the mutual anchoring of the fibres arranged in the interior of the foam.

Optimum strength properties are obtained when there is, in the interior of the foam, a non-woven fabric of very fine continuous fibres, the orientation of which is fixed so that they can satisfactorily absorb the stresses subsequently exerted on the product. Strength properties completely independent of orientation are obtained by employing a non-woven fabric of tangled fibres, the fibre structure of which does not allow any preferred orientation to be recognised.

The mould residence times necessary when carrying the process according to the invention into effect are similar to those used in known processes for the production of hard polyurethane foams having satisfactory flow characteristics. For products having a minimum dimension of about 1600 mm, the residence time should be of the order of 4 to 5 minutes.

The process according to the invention permits the embedding of very finely-structured fibre mattings, for example non-woven glass fibre mattings with a weight per unit area of 600 g/m2, an average fibre thickness of 20 lim and a total thickness of the workpiece obtained of less than 3 mm. In general, the fibres used in this invention preferably have a maximum cross-sectional dimension of 200cm, more preferably 1 001lem.

Owing to the high surface area of the very fine fibres which can be used in the invention, a good bond with the foam is obtained. Consequently, when the process according to the invention is conducted, this bond effects a considerably better support of the individual fibres than would be the case with the use of relatively coarse-structured fibres.

By way of example, the process of this invention can be used to produce a shaped product from a commercial integral hard foam system consisting of polyether polyhydric alcohol and liquid crude diphenylmethane diisocyanate, which may be provided with catalysts and blowing agent and which, in this stage, attains flow distances of only a few centimetres through a matting of glass fibres, by the addition of a neutral ester of, for example, phthalic acid with butyl alcohol, whose boiling point is about the reaction temperature of the reaction mixture, optionally in admixture with an epoxy stearate.

The process according to the invention permits the production of workpieces of large size and complicated shape for which particularly high strength properties for a low specific gravity and a thin wall thickness are desired. Typical examples of application consist in the manufacture of suitacase shells or in the manufacture of facings or coverings for the interior spaces of motor vehicles, for example the manufacture of instrument panels.

The process according to the invention allows up to 40% by weight of very fine fibres to be embedded in the foam and the mechanical properties, in particular the impact resistace and bending resistance, of the workpiece obtained can thereby be controlled within side limits. The gross density of parts which are produced by the process according to the invention may be 0.5 for a wall thickness of 3 - 4 mm, in spite of the embedding of the glass fibres.

The following Example of the production of a half shell, for a travelling case, which has a depth of 100 mm, external dimensions of 700 x 500 mm, and a total thickness of 4 mm which includes an external coating of an ABS film with a thickness of 0.8 mm. illustrates the invention.

EXAMPLE In a moulding tool, a preshaped ABS film is placed. The film completely covers the inner surface of one part of the two-parttool.

A blank of non-woven glass fibre fabric consisting of continuous fibres and having a weight per unit area of 450 g/m2 is placed on top of the ABS film. In this state, the non-woven blank is completely uncompressed and unconsolidated and it has a total thickness of about 8 to 10 mm.

Afoamable reaction mixture comprising (in parts by weight): Polyether polyol (OH number > 500) 100 parts Tertiary amine 2 parts Phthalic acid ester 46 parts Fluorohydrocarbon 10 parts Modified diphenylmethanediisocyanate 120 parts is poured, the isocyanate being added last, to initiate foaming, approximately into the centre of the moulding tool, in an amount such that while ensuring complete filling of all the spaces of the mould, the desired foam structure will be obtained. The foam structure is dependent in particular on the specific final pressure which is set up in the moulding tool during the reaction. This pressure can be measured and altered as desired by varying the amount fed in at any particular time.

Immediately after the reaction mixture has been poured in, the mould is closed and the initially very non-woven glass fibre fabric is compressed to a total thickness of about 3 mm. As a consequence of the chemical reaction occurring in the reaction mixture, the foaming process now begins and the foamed plastics material being formed fills all of the remaining empty spaces within the moulding tool, the ABS film being pressed hard against the inner wall of the mould as the final shape is achieved.

After a hardening time of 4 to 5 times, the chemical reaction is substantially complete and the moulding tool is opened. The finished half suitcase shell is removed from the mould and subjected to further processing as desired.

A high boiling epoxy fatty acid ester can be added to the phthalic acid ester, with similar results.

Claims (6)

1. A process for producing a fibre-reinforced foam shaped part, in which the foaming is caused by the reaction of a mixture of a polyhydric alcohol and an isocyanate, in which the reaction mixture additionally comprises from 5 to 30%, by weight of the mixture, of an inert ester whose boiling point is above the reaction temperature of the reaction mixture.

2. A process according to claim 1 in which thereaction mixture comprises from 10 to 20% by weight of the ester.

3. A process according to claim 1 or claim 2 in which the ester has a boiling point of more than 200"C.

4. A process according to any preceding claim in which the ester is of phthalic or stearic acid with butyl, benzyl and/or octyl alcohol.

5. A process according to any preceding claim in which the reaction mixture additionally comprises an epoxy stearate, in an amount of up to 25% by weight, based on the weight of the ester.

6. A process according to claim 1 substantially as described in the Example.