GB2173810A - Process for preparing a moulded article and composition for use in the process - Google Patents

Abstract

A moulded article is prepared by impregnating a body of glass fibres with an aqueous solution of a phenolic resin, raising the temperature of the mixture to gel the resin, then cooling the mixture to retard further polymerisation during handling and storage prior to heating of the mixture in a mould to complete curing.

Description

SPECIFICATION Process for preparing a moulded article and composition for use in the process From one aspect, the present invention relates to a process for preparing a moulded article, the process comprising the steps of preparing a resin composition, mixing the composition with a solid filler and then curing the mixture.

According to the present invention, the process is characterised in that the resin composition mixed with the filler is a liquid at 50"C and contains condensation products of a phenol.

Preferably, the resin composition used in the process consists mainly of condensation products of a phenol or of a mixture of phenols.

In a case where a single solid filler is used, that filler is preferably fibrous and would normally be glass fibre. However, the mixture preferably comprises more than one filler, for example a fibrous filler and at least one particulate, non-fibrous filler. The fillers used may be fillers commonly incorporated in plastics compositions.

A web comprising glass fibres may be impregnated with the liquid resin composition which is then permitted or caused to assume a substantially non-fluent condition prior to application of the mixture to the mould. The mixture can then be handled, stored and cutup without inconvenience, prior to application of the mixture to the mould. In an alternative procedure in accordance with the invention, the liquid resin composition, the filler or fillers and, possibly, a curing agent for the resin composition, are mixed together in a mixer and polymerisation of the condensation products is permitted or caused to proceed until the mixture can be handled without the resin composition draining from the filler. In this alternative also, the mixture can conveniently be stored, transported and cut-up, prior to being applied to a mould.

The temperature of the resin composition is preferably raised, in order to cause the liquid resin composition to assume a substantially non-fluent condition. In the preferred process, the temperature of the resin composition is raised after that composition has been mixed with the filler and the mixture is subsequently cooled, before the mixture is applied to a mould. Raising of the temperature of the mixture promotes polymerisation and cooling retards polymerisation. Thus, the temperature can be raised to achieve quickly a mixture which can be handled without the resin composition draining from the filler and the mixture can then be cooled to retard further polymerisation which would otherwise increase the difficulty of moulding the composition.

According to a second aspect of the invention, there is provided an intimate mixture of a liquid with loose solid fibres, wherein the liquid comprises a phenolic resin. By the description "loose" we mean that the fibres are not rigidly bound to each other. The fibres may be present in a structured body, for example a woven or other textile or the fibres may be dispersed randomly in the liquid.

The liquid component of the mixture may comprise a curing agent for the resin.

The curing agent itself may be resinous and may be capable of undergoing polymerisation with a component or components of the liquid resin composition.

Two or more liquid resin compositions may be mixed with the filler, one or both of these resin compositions containing condensation products of a phenol. Use of this optional feature enables resin compositions of relatively low viscosity to be mixed with the filler and, by suitable choice of the resin compositions, the viscosity of the mixture incorporating the filler to be increased fairly quickly by interaction between the resin compositions. The resin compositions may be mixed with each other before mixing with the filler or during mixing with the filler.

According to a third aspect of the invention, there is provided a moulding composition comprising a curable phenolic resin and a fibrous reinforcement.

The moulding composition is preferably pliable at ambient temperatures. The preferred reinforcement is glass fibre. Other reinforcement or fillers may be present.

In a process in accordance with the first aspect of the invention, the resin composition may include a solvent for the condensation products, which solvent does not itself polymerize in the composition. After mixing of the resin composition with the solid filler, the proportion of solvent present may be reduced, for example by heating the mixture to evaporate the solvent. The resin composition which is mixed with the filler is preferably a liquid at 10 C, so that the liquid can be mixed intimately and conveniently with the filler at ambient temperature.

In an example of a process in accordance with the first aspect of the invention, a resole resin is prepared in a known manner by heating substantially non-aqueous phenol with paraformaldehyde in the presence of an alkaline catalyst. There results an aqueous solution of condensation products of the phenol with formaldehyde. This solution is cooled to ambient temperature, thereby arresting the condensation reaction whilst the condensation products are still liquid. Typically, the proportion of water present in the product will be within the range 10-20%. The proportion of water may be varied, or other solvents may be included, to achieve a required viscosity.

Five parts by weight of the aqueous solution of phenolic condensation products are mixed with one to five parts by weight of glass fibres, with substantially inert particulate fillers and a curing agent for the condensation products. The particulate solids and curing agent may be mixed with the aqueous solution prior to mixing of that solution with the fibres. Mixing of the solution with the fibres may be achieved by impregnating a web of the fibres with the resin composition. Alternatively, glass fibres and the liquid resin composition may both be applied to a common support to form the mixture on the support. In a further alternative procedure, a batch of the mixture is prepared in a mixer.

There may be incorporated in the mixture additives which modify properties of the mixture, for example modify the viscosity of the mixture. It will be understood that an agent capable of promoting curing of the phenolic condensation products may be incorporated in the solution during preparation of the phenolic condensation products, rather than after preparation of those products. Thus, it is not essential that a curing agent be mixed with the solution when or just before that solution is mixed with the fillers.

The mixture comprising the phenolic resin solution and the glass fibres is heated to a temperature within the range 800-120C for a period such that, on cooling to 20"C, the viscosity of the mixture is so high that the phenolic resin does not drain from the fibres under the action of gravity. Whilst the mixture is at the elevated temperature, further condensation of the phenolic resin occurs and water is evaporated. On cooling to 20"C, the condensation reaction is substantially arrested whilst the mixture is still mouldable. The resulting mixture may be stored for several weeks without substantial further condensation occurring. The mixture can be handled, transported and cut-up without difficulty.During storage, transport and handling, the distribution of fibres in the resinous matrix does not change significantly.

Additional fillers incorporated in the mixture may be known fillers used in plastics compositions. In particular, there may be incorporated in the mixture hollow microspheres, for example of silicious material.

Curing agents suitable for incorporation in the mixture include one or more of a novolac resin in powder form, hexamethylene tetramine and an acid catalyst, for example zinc acetate or ammonium chloride.

Pieces of the mixture comprising glass fibres in a substantially solid matrix of the phenolic resin are moulded into an article by applying each piece of the mixture to a mould, subjecting the mixture to pressure in the mould and heating the mixture in the mould. The mixture may be maintained in the mould at an elevated temperature for several minutes. The elevated temperature may be within the range 1 00-200 C.

It will be appreciated that, in a case where the mixture has the form of a web of glass fibres impregnated with the phenolic resin and the mould cavity has a substantially uniform thickness, the moulding operation may involve relatively little flow of the mixture; whereas in a case where the mixture has been prepared in a mixer and the mould cavity does not have a substantially flat shape, the mixture may be required to undergo considerably greater flow during moulding.

There may be used in place of phenol a mixture of phenol with substituted phenols or substituted phenols only. The condensation products may have a high proportion of ortholinks.

The features disclosed in the foregoing description, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method of process for attaining the disclosed result, or a class or group of substances or compositions, as appropriate, may, separately or any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims (10)

1. A process for preparing a moulded article, the process comprising the steps of preparing a resin composition, mixing the composition with a solid filler and then curing the mixture, characterised in that the resin composition mixed with the filler is a liquid at 50"C and contains condensation products of a phenol.

2. A process according to Claim 1 wherein the temperature of the resin composition is raised either before, during or subsequent to mixing of the resin composition with the filler and the temperature of the mixture is subsequently lowered, prior to moulding of the composition.

3. A process according to Claim 1 or Claim 2 wherein, after mixing of the resin composition with the filler, and before moulding of the mixture, the mixture is stored and cut up.

4. A process according to Claim 2 or according to Claim 3 as appendant to Claim 2 wherein the temperature of the mixture is again raised when the mixture is on or in a mould.

5. A process according to any preceding claim wherein said filler is fibrous and mixing of the resin composition with the filler is effected by impregnating a web of the filler with the resin composition, whilst the web is resting on a support.

6. An intimate mixture of a liquid with loose, solid fibres, wherein the liquid comprises a phenolic resin.

7. A pliable body comprising fibres dispersed in a matrix, the body having been prepared by temporarily raising the temperature of a mixture according to Claim 5.

8. A moulding composition comprising a curable phenolic resin and a fibrous reinforce ment.

9. A composition according to Claim 8 which is in the form of a pliable sheet.

10. Any novel feature or combination of features disclosed herein.