GB2040956A - Fibre Reinforced Plastics - Google Patents

Abstract

Cured resin compositions comprise reinforcing fibres and/or filaments of cellulose acetate, e.g. in the form of filamentary tow, staple fibre, or fibre matt. The resins may be the polyester and epoxy compositions used in glass reinforced plastics.

Description

SPECIFICATION Fibre Reinforced Plastics This invention relates to fibre and/or filamentreinforced plastics, the plastics material being for example a cured resin such as a polyester resin accelerated and/or hardened by agents such as various peroxides, cobalt naphthenate etc., or an epoxy resin, and to their production.

Present practice is generally for the use of glass filaments as the reinforcing material (to give "GRP" products) but these have some disadvantages. Thus glass filaments are relatively expensive, are difficult to store and handle, and if not carefully cut to pattern involve substantial waste; furthermore they are difficult to cut and shape with anything except surgically sharp knives. Except in the even more expensive woven form, chopped strand matt is bound by a temporary chemical binder which is only partially effective and which even under ideal conditions can allow disintegration causing the waste listed above and frequently puncturing the operator's skin. Because only the temporary binder and not the glass filaments dissolves in the normal lay-up resins, the inter-fibre (and more importantly the inter-laminar) bond is usually less than ideal.The result of this reluctance to unite is that all matts have to be 'wetted out' by a slow and messy process called stippling, to ensure that no air is trapped and that all the chemical binder is dissolved; the time that has to be given to 'rolling out' voids caused by air-filled blisters is itself an additional cost as well as a source of structural weakness in the cured sheet.

The present invention comprises a cured resin composition incorporating reinforcing fibres and/or filaments of cellulose acetate.

We have found that cellulose acetate fibres and filaments have advantages for use, as at least partial replacement for previously used material, with hardening resins, e.g. polyester and epoxy resins. Because acetate fibres of filaments are finer and closer knit than glass strands, they trap less air, so there may not be the need to stipple or hand-roll out; the matt or other fibrous or filamentary body can be cut to size and simply left to soak up the required amount of resin, and left to cure into hard sheet, rod or other shape. Hand rolling of voids may be necessary to correct errors of operation or defective tools, moulds or materials, but even then can be quicker and easier to do than with conventional glass fibre. The resultant cured material can be more homogeneous than pure glass versions, and can give superior graining for subsequent drilling, machining and screwing etc.

Acetate filaments can be cut with precision with normally sharp knives and/or scissors.

Acetate fibres can be bonded in tow or staple form much more conveniently, and are easier to store and handle without waste, than traditional glass, and detached strands do not puncture the skin.

Acetate-reinforced plastics (ARP) can be laid up in the shape wanted or post-formed. Thus cellulose acetate fibrous or filamentary materials can be laid-up and simply soaked out in the form required, e.g. flat or curved over a male mould to form boxes, ducting, or complete artefacts like fluid tanks, toolboxes, toys or wheel barrows, storage bins or industrial shelving, or any not critically-stressed artefact. They can be laid and drawn into dowel form, both by hand-drawing, and also by high speed extruding machine, or can be spun on a bobbin for use as shafting or light structures. They can also be wrapped round a steel, wood or plastics shaft, and dipped and cured in situ; e.g. a steel chisel knife or screwdriver can be bound with acetate and.

dipped and the resin then cured; the resulting handle is hard and may be locked-on by barbs pre-cast into the shaft. Nuts or bolts may be similarly encapsulated for sub-assembly into other structures. They can equally be lightly wrapped round a cylinder or bobbin e.g. of wood or cardboard (preferably with an intervening layer of release agent e.g. wax) so that continuous tubes can be made by a simple wrap, dip, soak and cure method, and such tubes may be used structurally as a direct, non-corrodable substitute for existing metal or plastics tubes in furniture, building, hydraulic, mechanical and electrical engineering installations. Such tubes may be spun at uniform tension into a circular tube and the tube re-formed with a broaching liner into square or other section before or after soaking.

ARP can be injection -- or vacuum assisted mould formed more easily than GRP which is currently under intense experimentation in the marine trades.

The cellulose fibres or filaments may be wetted-out with a wide range of proportions of accelerated resin e.g. at an acetate/resin w/w ratio of 0.3 or 0.2 to 1,or1 to 1, or 5 or 3.5 to 1 depending on the specification of the finished article.

Furthermore, because of the soak-up features detailed above, preformed solid plugs or rods of cellulose acetate fibre and/or filament may be lightly case- or core-hardened only, giving a differential elasticity across the finished plug.

Cellulose acetate fibres and/or filaments may be used with a giass-strand loaded resin, thereby securing a material of good strength and 'formability', the proportions being adjusted (a) by variation in the length of the glass (e.g. from nearputty powder size up to 30 mm) and (b) by variation in the glass-acetate mix from as low as 5 to as high as 70 wt. % glass. The cellulose acetate may also accept laid-up additions of woven or yarned materials of glass or carbon fibres, in cloth, ribbon or tape form.

The cellulose acetate fibres and filaments may be form bonded by any of the current solvent binders, emulsion binders and/or powder binders.

As indicated above, amongst the embodiments provided by the invention are rods or plugs, of any desired cross-section, of cellulose acetate fibre and/or filament impregnated with hardened resin.

In the production of these products, it is currently found most convenient to first produce a coherent rod or plug of the fibres and/or filaments bonded together at points of contact by a heat-activatable bonding agent. The latter is suitably a liquid plasticiser for the cellulose acetate, for example triacetin. The initial coherent cellulose acetate body can for example be made by condensing a continuous supply of the cellulose acetate fibres and/or filaments (incorporating the bonding agent) into a rod of the required cross-section, applying heat to activate the bonding agent, and subsequently cooling the resultant continuously formed rod which is then cut into convenient individual lengths as it is continuously produced.

The result is a coherent yet porous rod which readily takes up the hardenable resin composition, subsequent curing of the latter providing the final hardened product. The initially formed coherent porous rod may be produced in a wide variety of cross-sections, according to the intended end use of the hardened product. The hardenable resin composition may be applied so as to penetrate only the periphery or only the core of the initially formed coherent porous rod or plug, to provide for case- or core-hardening as mentioned above.

Where matts or webs etc, of the cellulose acetate fibres and/or filaments are employed, it may also be of advantage for these to be prebonded into coherent but porous form by means of a heat-activated bonding agent such as triacetin or other liquid plasticiser.

The hardenable resin compositions which may be used according to the invention are suitably those which have been widely known and used for many years in GRP fabrication. These include the various commercially available polyester resins, which are basically solutions of unsaturated polyesters in styrene and which cure in air at room temperature on admixture with a small proportion (e.g. 1 wt. %) of organic peroxide, cobalt naphthenate etc. accelerator; and various commercially available epoxy compositions, which are supplied as a low molecular weight epoxy condensate component (e.g. epichlorhydrin-diphenylpropane condensate) and a separate hardener component (aliphatic polyamine or acid anhydride) which has to be admixed with the former to give the composition which will cure in air at room temperature.

Conventional fillers and modifiers can be present in the compositions as required.

Cellulose acetate staple fibre, matt and continuous filamentary tow suitable for use in the present invention are commercially available, being materials used in large quantities for the manufacture of, for example, cigarette filters, ink reservoirs, etc.

The following are specific Examples, given by way of illustration only.

Example 1 A 100 cm length of industrial warm air ducting was made using a wooden former a little over 100 cms long and having a circular cross-section of 1 dcms diameter. The former was wrapped with polyethylene sheet as release material, and was then laid up to an average depth of 5 mm and to a density of 0.2 gms/cc by bandaging with a cellulose diacetate matt of filament denier 5 and specific gravity 1.32. The resulting assembly was immersed in a bath of polyester resin (median specific gravity 1.25) containing 1 wt. % max.

organic perioxide catalyst and removed threequarters of the way through the resin gel time; excess resin was removed by light rolling and the polyethylene-wrapped former was subsequently removed.

In a modification, 50 wt. % of the cellulose diacetate fibre in the matt is replaced by grade E glass filament.

Example 2 This Example used a continuous cellulose diacetate matt which was the same as that of Example 1 except that the fibres of the matt were lightly bonded together at points of contact to enhance the cohesive strength of the mats. The bonding was achieved by spraying of the fibres with triacetin, a solvent plasticiser for cellulose diacetate, followed by heating and then cooling of the matt. The matt was advanced continuously longitudinally from the roll with its faces substantially horizontal, the same catalysed polyester composition as in Example 1 was metered onto the upper face of the advancing matt, and the thus treated matt was wound continuously onto a polyethylene-wrapped former of the same dimensions as in Example 1 to form a substantially uniform tubular sleeve.When the resin impregnated matt had been wound tightly to a uniform depth of 7 mm around and over the length of the former, excess resin was removed bu light rolling and the resin allowed to cure, the former thereafter being withdrawn.

In a similar procedure, a former of square (5 cm x 5 cm) cross-section was employed, and after completion of the application of the resinimpregnated matt and removal of excess resin, the relatively sharp exposed longitudinai edges of the wound tube were rounded off by passing an encircling annular former of appropriate size along the length of the tube. The resin was then allowed to cure and the former withdrawn. With a sufficient depth of lay-up, the whole external surface of the wound tube could be rounded in this manner.

Example 3 A plane panel was made by laying bands of continuous filamentary cellulose diacetate tow of 3.5 filament denier over a polyethylene sheet on a flat substrate. The filaments in eacktmndPere non-parallel but aligned generally longitudinally of the band and accordingly the tow was laid up with the bands of one layer transverse to those of adjacent layers. After the formation of each tow layer, the catalysed polyester composition as in Example 1 was applied over its exposed face before formation of the next tow layer. The assembled layers were subsequently lightly rolled out and curing allowed to proceed to completion, forming a strong panel which was separated from the release sheet and trimmed to required size.

Example 4 Cellulose diacetate tow as employed in Example 3 is sprayed with triacetin and fed continuously through a tubular former which gathers it into rod form. As the tow passes through the tubular former, steam is injected laterally into the rod of tow to activate the triacetin binder, and the resulting continuously produced rod is then passed through a cooling chamber where it is cooled to complete the bonding together of the filaments of tow at points of contact. The continuously produced coherent rod is cut into 100 cm lengths. The resulting lengths are immersed in a tray of the catalysed resin composition employed in the preceding Examples, and, three quarters of the way through the resin gel time, the impregnated rods are removed, lightly wiped over to remove excess resin, and then left until curing of the resin is complete. The resulting ARP rods are of high strength and suitable for use as dowelling etc.

Claims (9)

Claims

1. A cured resin composition incorporating reinforcing fibres and/or filaments of cellulose acetate.

2. A cured composition according to claim 1 incorporating reinforcing cellulose acetate filamentary tow.

3. A cured resin composition according to claim 1 or 2 incorporating reinforcing cellulose acetate fibre matt.

4. A cured composition according to any of claims 1 to 3 additionally incorporating reinforcing fibres and/or filaments of glass.

5. A moulded product of a cured composition according to any of claims 1 to 4.

6. A method of making a cured reinforced plastics article which comprises impregnating a body of cellulose acetate fibres and/or filaments with a curable resin composition, and causing or allowing the resin to cure.

7. A method according to claim 6 wherein the fibres and/or filaments of the body are bonded at points of contact before impregnation with the curable resin composition.

8. An article of cured reinforced resin substantially as hereinbefore described in any of Examples 1 to 4.

9. A method of making an article of cured reinforced resin, the method being substantially as hereinbefore described.