GB2048971A

GB2048971A - Plastic Reinforced Mesh

Info

Publication number: GB2048971A
Application number: GB8006223A
Authority: GB
Original assignee: FIBREMESH Ltd
Current assignee: FIBREMESH Ltd
Priority date: 1979-02-24
Filing date: 1980-02-25
Publication date: 1980-12-17

Abstract

A woven mesh (e.g. of glassfibre) is impregnated with plastics resin by spreading the fluid resin, containing catalysts and other desired additives, on a supporting surface, pressing the mesh on to the surface, allowing it to absorb the resin and curing the resin, sufficient resin being applied to impregnate the mesh without closing the mesh openings so that a strong but relatively flexible mesh is formed. The supporting surface may be flat or the mesh may be passed through two pairs of rollers, the first applying accelerated resin and the second applying catalysed resin. The resin- impregnated mesh is suitable for chemically-resistant filters, plaster and cement reinforcement, as a diffuser for fluorescent light or for use in a ventilation panel.

Description

SPECIFICATION Plastic Reinforced Mesh The present invention relates to a method of manufacturing a mesh for use particularly in ventilation panels, coarse filters and plaster and cement reinforcement, to resin-reinforced fibreglass meshes, and to a method of reinforcing plaster or cement.

Ventilation panels usually comprise a perforated screen having openings which allow the passage of air but are sufficiently small to prevent the passage of insects and coarse dirt particles. At present suitable panels and filters are formed from perforated metal or plastics sheets and from woven or welded metal or plastics wires.

Metal screens, however made, are expensive because of the cost of the raw material and/or the cost of treatment to prevent corrosion. Modern plastics material are far more suitable but difficulties have been experienced in forming screens with the required perforation sizes, of the order of 1 mm, combined with other desirable features; for example, screens should preferably be sufficiently rigid to be self-supporting without the need for strong frames, while, at the same time, they should be relatively flexible so that they are not easily broken. Whereas suitable plastics screens can be made, they are again relatively expensive, and an object of the present invention is to provide a method of manufacturing a plastics reinforced mesh which is more convenient and can be carried out more cheaply than the present methods.

A further use of metal screens is in reinforcing cement or providing a base for plaster but the disadvantages of cost and corrosion mentioned above are again encountered and alternative reinforcements have been sought for some time. One potential reinforcing material which has been considered is glass fibre but great difficulty has been experienced in protecting it from attack by the alkalis present in cement and plaster. A further object of the present invention is, therefore, to provide a glass-fibre based reinforcement suitable for use in alkaline materials.

According to the present invention there is provided a method of manufacturing a reinforced, open mesh, comprising applying a layer of fluid resin to a supporting surface to which the resin does not adhere, pressing on to the resin on said surface an open mesh of interwoven mesh elements each comprising a plurality of filaments or fibres, allowing the mesh elements to absorb the resin, the layer being sufficiently thick to impregnate the elements without closing the mesh pores, and curing the resin.

The method of the present invention thus produces, simply and cheaply, an open mesh screen which has a certain degree of rigidity due to the absorbed resin, but which, at the same time, since the resin does not fill the mesh openings, retains some of the pliability of the woven mesh base. Any type of openwork weave may be chosen for the mesh depending on the characteristics, particularly differences in flexing properties in the warp and weft directions of the weave, required for a particular purpose. The thickness of the mesh elements, size of the mesh openings and types of fibre or filament and resin used may also be varied according to the intended purpose of the impregnated mesh. Thus, meshes can be formed which are suitable for use as coarse filters, ventilation panels, plaster, cement and concrete reinforcements, stiffenings for clothing and many other purposes.

The mesh itself may be formed from various materials such as natural fibres or plastics filaments but it has been found that glass fibres are particularly suitable since, in combination with the resin, they provide a mesh which has a useful combination of properties, particularly lightness, strength and rigidity, but which is relatively cheap.

The resin employed is, in most embodiments, a commercial polyester resin since such resins have good general characteristics of strength and chemical, water and abrasion resistance while, at the same time, are also relatively cheap. Glassfibre meshes impregnated with polyester resins are thus suitable for all the purposes specificed above; the properties of the resins can also be modified to a certain extent to meet specific requirements by the addition of, for example, inert fillers, pigments or fire-retardents.

Where the resin-reinforced meshes are to be used under conditions for which a polyester resin is not suitable, alternative resins may be used. For example, it is envisaged that a resin-reinforced fibreglass mesh according to the invention will be useful in screening coarse gravel from sand which accummulates in water stored in reservoirs. Screening occurs after chlorine has been added to the water and thus a resin particularly resistant to chlorine, such as an isophthalic resin, may be required for this purpose.Where a considerable degree of strength or resistance to distortion at high temperatures is required, an epoxy resin, or resins generally known as 'tooling' resins which can be worked on a lathe, may be used; when the mesh is to be subjected, in use, to a considerable amount of abrasion, a furane resin may be chosen, whereas for good, general chemical resistance, for example for filters for use in chemical plants, a bisphenol resin may be chosen.

A polyester resin which is applied to a glassfibre mesh is preferably used in quantities of from 0.4 to 0.8 g/cm3 or glassfibre forming the mesh, calculated in terms of the mesh volume less the pore volume. The fluid resin contains the catalysts necessary for the curing and any other additives commonly added to plastics resin to provide desired properties for a particular use. The curing is carried out by any method suitable for the particular resin, such as hot pressing or air drying at ambient temperatures.

Sufficient resin may be applied to the supporting surface during manufacture of the reinforced mesh to impregnate the entire thickness of the mesh although alternatively, only sufficient resin to impregnate a lower layer of the mesh may be applied to the supporting surface, additional resin being applied to the upper surface of the mesh while it is on the said surface. The method chosen for any particular mesh depends on its intended use since the second method produces a mesh having a substantially flat surface on both sides whereas the first method provides a mesh having one flat surface and one ridged surface, the ridges corresponding to the weaving of the base mesh.The provision of an attractive, ridged surface, together with the possibility of colouring the mesh, either by use of a coloured base mesh or a coloured resin, widens the scope of use of the mesh considerably since it makes it suitable for decorative functions, for example, for use in room dividers and as light shades or diffusers.

The supporting surface used in the method of the present invention may comprise a flat table or, for the production of long rolls of reinforced mesh, may comprise a lower roller of a pair of vertically disposed rollers. In the latter case the said lower roller is preferably arranged to take up resin from a bath of fluid resin and to apply it continuously to the mesh passed between the rollers; the upper roller may apply resin to the mesh simultaneously.In a preferred embodiment of the invention, the mesh is passed between two pairs of juxtaposed, vertically-disposed rollers, the first arranged to apply accelerated resin and the second to apply catalysed resin to the mesh, The present invention further provides a plastics resin reinforced open mesh made by a method as described above and, more particularly, it provides an open mesh of interwoven glass-fibre mesh elements impregnated with plastics resin.

It has been found that such a plastics-resin-reinforced, open, glass-fibre mesh is useful as a cement, concrete or plaster reinforcement since the coating of resin protects the glass from attack by the alkalis present in cement and plaster, as well as strengthening the glass-fibre elements. In particular, the use of a mesh rather than glass-fibre strands for the reinforcement is important since resin impregnated strands tend to be brittle whereas the compression and twisting of the strands to form a mesh reduces the quantity of resin which can be absorbed in certain areas compared with uncompressed strands and allows the mesh to retain a certain degree of flexibility. The use of an open mesh rather than a mesh in which the pores are closed by resin is important for similar reasons.

According to a further aspect of the invention there is therefore provided a method of reinforcing cement, concrete or plaster by incorporating therein a plastics, resin-reinforced open fibre-glass mesh, and a cement, concrete or plaster structure reinforced by such a mesh. Such meshes are particularly important in strengthening a skim coat, of for example plaster or a plastics material, laid over a base which has different drying or heat-expansion properties.

As mentioned above, a plastics-resin-reinforced open mesh is also useful as a ventilation panel and the invention provides a ventilation panel formed from such a mesh. The panel may be provided with a frame adapted to be attached to the edges of an opening across which the panel is to be fitted.

It is envisaged that a ventilation panel according to the invention will be of particular use when incorporated in a screen or board formed from glass-fibre reinforced plastics resin and, accordingly, the invention further includes a soffit board of glass-fibre reinforced plastics resin incorporating at least one ventilation panel as described above..

Several embodiments of the invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic plan view of a first plastics-resin reinforced mesh according to the invention Figure 2 is a diagrammatic plan view of a second plastics-resin reinforced mesh according to the invention; Figure 3 is a diagrammatic elevational view of apparatus for carrying out a-method of manufacturing a plastics-resin reinforced open mesh according to a first embodiment of the invention, and Figure 4 is a diagrammatic elevational view of apparatus for manufacturing a plastics-resin reinforced mesh according to a second embodiment of the invention.

Referring to Figure 1 of the drawings, an open mesh 1 is shown which is woven from strands 2 each containing a plurality of glassfibres, the mesh having opening 3 bounded on each of their four sides by three strands 2 of the glass fibres. The mesh openings occupy approximately 20% of the surface area, and, in the particular mesh under consideration, there are approximately 20 mesh openings per square centimetre and the mesh is approximately 0.4 mm thick, although meshes with a similar weave may be made from glassfibre strands of different thicknesses.

The strands 2 of the mesh 1 are impregnated with a polyester resin 2A applied by the following general method. A flat plate is coated with a suitable wax or alternatively, is made from a material to which the resin to be used does not adhere. The resin is in a suitable carrier liquid, such as styrene, which contains a catalyst and accelerator for the resin. Apart from the addition of the catalyst, commercially available polyester resins are usable directly as supplied by the manufacturer, at a working temperature of about 600 C, although further styrene may be added to increase the fluidity at lower temperatures.

Sufficient fluid resin is applied to the plate to form a thin film containing approximately 1 50 g/m2 of resin of a fluidity at room temperature (500C-700C) such as to allow it to be absorbed into the glassfibre by capillary action. The glassfibre mesh is then pressed in to the resin and left to absorb the fluid, there being sufficient fluid to coat the fibres but not sufficient to fill the pores.

The resin is allowed to cure until it has hardened and the resulting mesh, which is moderately flexible but non-resilient, is peeled off the plate. It is found that the side which was adjacent the plate has an apertured, but substantially flat, resin surface whereas the other side has slight corrugations due to the weaving of the mesh.

A particular application of the mesh 1 is as a diffuser for a fluorescent light. For this purpose the mesh is cut into rectangular panels 15 cm wide by the length of the fluorescent tube and double-sided self adhesive strip is stuck along all four edges on one side of the panel. Immediately before use, the protective strip is peeled off the adhesive to allow the panel to be bent over the tube and stuck to the fitting. Since the mesh 1 has a ridged, decorative surface it may also be useful for loud-speaking fascias or other decorative purposes although it may alternatively be used, for example, as a filter.

A further, important use of the mesh 1 is as a backing or base for plastics mouldings, for example, for vehicle or boat body repairs. In fact it is particularly convenient for the latter use since such repairs are often effected with a fibre-glass-reinforced resin filler and the resin of the reinforced mesh bonds well with the resins commonly used in the filler material. Also, the polyester resin used for the mesh is a thermoplastic resin and the mesh may thus be heat-moulded to the desired shape of the body work and will hold this shape when cold.

Alternative, open glass-fibre meshes which have been found suitable for use in the reinforced meshes of the invention are the following mock-leno type weaves: Mesh 1 2 Strand thickness mm 0.38 0.41 Weight in g/m2 288 366 No. warp threads per cm 11 1 5 No. weft threads per cm 11 11 Referring to Figure 2 of the drawings, a second example of a glass-fibre mesh 1 A is shown. The mesh 1 A is formed with single strands 4 in the warp direction, on either side of each mesh opening 3, and with two twisted strands 5, which lock the weave, in the weft direction, on either side of each mesh opening 3. As is shown in the drawing, the warp threads 4 are considerably wider in the plane of the mesh than the weft threads 5.

It is found that this weave is particularly suitable for cement, concrete or plaster reinforcement since the untwisted warp threads take up a considerable amount of resin during impregnation, as described above, the resin penetrating between, and coating, substantially all the glass fibres to protect them against the alkali in the cement or plaster, in use. The weft threads, on the other hand, being twisted and compressed, are not able to take up such large quantities of resin per weight of glass as the warp threads and the resin coats the outer surfaces of the weft threads, penetrating only a short distance towards their centres, especially at their mutual crossing points.The weft threads thus remain more flexible than the warp threads,- allowing the mesh to be bent and moulded, in use, although they are sufficiently protected by the resin for the mesh to be used as a plaster or cement reinforcement.

In general it is found that a coarser mesh is required for cement reinforcement than for plaster reinforcement and details of two meshes, one suitable for each use are given below.

The breaking stengths given in the following table are each in average often tests made with specimens 35 mm wide by 1 5Q mm in length.

Plaster Cement Reinforcement Reinforcement Mesh Mesh Mesh thickness 0.24 mm 0.55 mm No. of meshes/sq. metre approx. 155,000 approx. 35,000 Wt. of glass/sq. metre 81 g 320 g Wt. of resin/sq. metre 0.15 kg 0.3 kg Breaking strength of warp resin-impregnated 70 kg 251 kg Breaking strength of weft resin-impregnating 65 kg 648 kg The coarser mesh described above may be used in a manner similar to metal meshes for cement reinforcement, the meshes being placed in a mould or layed up over a former and the cement mixture being poured into the mould or plastered over the mesh to fill the pores and coat the mesh to a desired depth.

The coarse mesh described above is particularly useful as a former since it is found that the weft threads, being more flexible than the more impregnated warp threads, bend tq form a smooth curve whereas, if the mesh is bent in a direction perpendicular to the warp threads, the warp threads bend sharply along a straight line of the weave. The mesh may thus be bent around curved surfaces or around sharp-angled corners according to the choice of location and direction of the weave.

The finer mesh described above for use particularly in plaster reinforcement is more flexible in all directions than the coarser weave and can easily be moulded to the contours of a surface to be plastered. It is envisaged that it will be of particular use in covering joins in surfaces to be plastered to strengthen the plaster in the region of the join and help prevent cracking of the hardened plaster due to shrinkage or movement of the supporting surface or framework.

The reinforcement may be tacked or stapled to a surface, particularly a wooden surface, to be plastered but alternatively a joint may be covered as follows: A join between, for example, two sheets of plasterboard is first filled flush with a suitable filler or plaster and allowed to harden. A further coat of the filler or plaster paste is then applied to a sufficient depth to accommodate the thickness of the resin-reinforced glass fibre mesh to be used and a length of the mesh is cut (a knife or scissors are suitable), laid over the join, and pushed into the paste so that the paste is forced through the mesh openings. The paste surface is smoothed over the mesh and allowed to dry before a layer of plaster is applied to the entire surface of the plasterboard sheets.

An even coarser mesh than those described above would be preferably for concrete reinforcement to allow the gravel incorporated in it to pass through the mesh opening.

Any of the above meshes may also be used to strengthen a plastics-resin skin of a type often applied to provide a decorative finish to a wood, metal or cement surface: mesh may be tacked to the surface or, in the last case, may be pressed into the cement surface while it is still wet, care being taken to ensure that part of the mesh remains above the surface. The plastics resin finish may then be applied in the usual manner, and provided the mesh incorporates a resin which bonds well with the resin finish, will be firmly bonded to the surface and reinforced against cracking due to the different shrinkage and thermal expansion properties of the base material and resin finish.

A further use of the coarser mesh described above is as a ventilation panel in a soffit board for a building. Although soffit boards have, until recently, been made from solid, wooden planking, it is now convenient to make them from plastics material, particularly fibre-glass-reinforced plastics resin. With modern methods, such boards may be fitted to a building and adjoining fascia boards leaving very little in the way of ventilation gaps which are essential for ventilating the roof-void to help prevent decay of the timbers.

A plastics soffit board is therefore preferably provided with an opening, approximately 30 cm long by 6 cm wide, every 120 cm of its length, the opening being covered by a screen of the mesh 1 A described above. The mesh may be attached to the edges of the opening by adhesive but the mesh is preferably cut into panels each surrounded by a frame of solid fibre-glass-reinforced resin having adhesive on each side, one side being glued to the mesh and the other to the soffit board.

The method of manufacture of a resin-reinforced glass-fibre mesh described above will now be described in greater detail with reference to Figures 3 and 4 of the drawings.

Referring to Figure 3 of the drawings, a first method of reinforcing a mesh 1 is shown. The prewoven mesh 1 is carried on a first support roller 10 located above a horizontal table 1 1 with its rolling axis 12 horizontal and parallel to one edge 1 3 of the table 1 1. In a first stage of the operation a first portion of the mesh 1 is dependent from the roller 1 0 adjacent the edge 13, as shown by the dotted line 1 B, and the lower, free end of the mesh is taken up on a second support roller 14, located beneath and parallel to the first support roller 10.

A layer of fluid resin 1 5 is applied to the surface of the table 1 1, which is treated so as not to stick to the resin, by a roller (not shown).

A first working roller is next displaced from a rest position (not shown) adjacent and parallel to the edge 13 so as to roll the mesh 1 dependent from the roller 10 on to the resin 1 5 of the table 1 1, further mesh 1 being simultaneously pulled from the roll on the roller 10. It is found necessary to roll the mesh 1 on to the resin in this manner in order to keep the threads of the mesh relatively straight; if the mesh is allowed to unroll under its own weight it tends to sag, the threads are pulled into curves and the mesh may not lie flat on the table to absorb the resin correctly.

The first w#orking roller is returned to its rest position and further fluid resin is applied to the upper surface of the mesh 1 with the aid of a further working roller (not shown). Sufficient resin is applied to the table and to the upper surface of the mesh 1 to impregnate the mesh without closing the mesh openings.

The resin-impregnated mesh, which is still wet, cannot be lifted from the table under its own weight for the reasons given above and the second support roller 1 4 must therefore be displaced from its rest position, shown in the drawing, in the same direction as the working movement of the roller 1 6, to take up the resin-impregnated mesh on to itself.

The roller 14 is then returned to its rest position, a further portion of non-impregnated mesh 1 becoming dependent in the position 1 B, and the impregnation cycle is repeated until all the mesh 1 on the roller 10 has been impregnated and taken up on the roller 14.

The wet, resin-impregnated mesh 1 is finally unwound from the roller 14 and hung in a vertical plane for 2 to 3 hours at room temperature to allow the resin to cure and harden.

Referring to Figure 4 of the drawings, apparatus is shown for impregnating a glass-fibre mesh 1 with resin in a continuous process. In this embodiment of the invention, the mesh 1 is fed from a support roller 10, corresponding to that of Figure 3, over a flat supporting web 17 which prevents the mesh from sagging. The web 17 terminates very close to a pair of vertically-disposed rollers 1 8, arranged with their rolling axes parallel to the axis of the roller 10, and feeds the mesh 1 between the rollers 18.

The lower of the rollers 18 is located in a bath 19 of a fluid polyester resin 20 containing a 6% solution of cobalt naphthelate in styrene as an accelerator. The rollers 18 thus apply accelerated resin 20 to the mesh 1 as it is rolled between them.

From the rollers 18, the mesh is fed to a second pair of vertically disposed rollers 21, closely spaced from, and parallel to, the rollers 18. The lower of the rollers 21 is located in a bath 22 of the same polyester resin as in the bath 19, but containing methyl ethyl ketone peroxide as a catalyst instead of the accelerator. The second rollers 21 thus apply catalysed resin 22 to the mesh 1 as it is passed between them. The two sets of rollers 18, 21 are arranged to apply sufficient polyester resin to the mesh 1 to impregnate it without closing the mesh openings. Also, due to the rolling of the mesh between the second set of rollers 21, the catalyst and accelerator are brought together within the mesh to enable the resin to cure quickly on leaving the rollers 21.

From the rollers 21 the resin-impregnated mesh is fed over a further supporting web 24 and through a drying stage, indicated by a heater 25, in which the curing of the resin is accelerated such that, when the mesh is taken up on its second support roller 14 it is already cured.

The resin applied to the mesh may, of course, contain any other ingredients commonly added to resins, such as fillers, pigments or fire-retardants. It is found, for example, that the addition of 10% by weight of filler or pigment is sufficient to make the resin opaque and also makes the mesh considerably stiffer than the normally translucent mesh.

Although polyester resins are used for the meshes described above, being resistant to water and alkali, other resins, for example thermosetting resins, may be used for meshes intended for other purposes.

The reason for using two resin baths, one containing accelerator, is in order to prolong the pot-life of the resin to allow the process to be carried out continuously with large rolls of mesh.

Claims

1. A method of manufacturing a reinforced, open mesh, comprising applying a layer of fluid resin to a supporting surface to which the resin does not adhere, pressing- on to the resin on said surface an open mesh of interwoven mesh elements each comprising a plurality of filaments or fibres, allowing the mesh elements to absorb the resin, the layer being sufficiently thick to impregnate the elements without closing the mesh pores, and curing the resin.

2. A method as claimed in Claim 1, in which the mesh elements are composed of glass fibres.

3. A method as claimed in Claim 1 or Claim 2, in which the supporting surface is a flat, raised table, the mesh is located in a roll on a horizontal support roller above the table with a mesh portion dependent from the roll adjacent and parallel to an edge of the table, and a working roller is displaced parallel to itself and to the said edge to roll the mesh on to the resin on the table, simultaneously unrolling further mesh from the support roller.

4. A method as claimed in Claim 3, in which a second support roller is rolled in the direction of the first working roller to take up the portion of resin-impregnated mesh and is then returned to a starting position in which an unimpregnated portion of the mesh is dependent adjacent the said edge of the table.

5. A method as claimed in Claim 4, in which the steps of applying resin to the table, rolling a mesh portion on to the resin with the aid of the working roller and rolling the mesh onto the second support roller are repeated until substantially all the mesh carried by the first support roller has been impregnated and rolled on to the second support roller, and the impregnated mesh is unrolled and supported from one end, the resin being cured with the mesh dependent in a vertical plane.

6. A method as claimed in Claim 3, Claim 4 or Claim 5, in which, between the steps of rolling a mesh portion on to the resin on the table and rolling the impregnated mesh on to the second support roller, sufficient resin is applied to the upper surface of the mesh located on the flat table by a second working roller to impregnate an upper portion of the mesh without closing the mesh pores.

7. A method as claimed in Claim 1 or Claim 2, in which the supporting surface comprises a lower roller of each of two pairs of vertically-disposed, juxtaposed rollers, the lower roller of the first pair of rollers to which the mesh is fed being arranged to apply liquid resin containing accelerator to the mesh and the lower roller of the second pair of rollers being arranged to apply liquid resin containing a hardening catalyst to the mesh, the total quantity of resin applied by the two pairs of rollers being sufficient to impregnate the elements without closing the mesh pores.

8. A method as claimed in any of Claims 2 to 7, in which from 0.4 to 0.8 g of a polyester resin are applied per cubic cm of glass fibre in the mesh.

9. A method of manufacturing a reinforced, open mesh substantially as herein described with reference to Figure 3 or Figure 4 of the drawings.

10. A resin-reinforced open mesh made by the method of any preceding claim.

1 1. Apparatus for impregnating an open mesh with a liquid resin, including means for feeding the mesh between a first pair of vertically disposed rollers, the lower roller of which is arranged to take up liquid resin from a bath of accelerator-containing resin and to apply it to-the mesh, and a second pair of vertically disposed rollers arranged to receive mesh partially impregnated with said acceleratorcontaining resin from the first pair of rollers, the lower roller of the second pair of rollers being arranged to take up liquid resin from a bath of catalyst-containing resin and to apply it to the mesh.

12. Apparatus for impregnating an open mesh with a liquid resin substantially as herein described with reference to, and as shown in, Figure 3 or 4 of the accompanying drawings.

13. An open-mesh of interwoven glass-fibre mesh elements impregnated with plastics resin.

14. An open mesh as claimed in Claim 13, in which the plastics resin is a polyester resin.

1 5. An open mesh as claimed in Claim 1 4, containing 0.4 g to o.a g of resin per cubic centimetre of glass fibre.

16. An open mesh of interwoven glass-fibre mesh elements impregnated with plastics resin; substantially as herein described with reference to, and as shown in, Figures 1 and 2 of the accompanying drawings.

17. A cement, concrete or plaster structure incorporating an open plastics-resin-impregnated glass-fibre mesh reinforcement.

1 8. A method of reinforcing cement, concrete or plaster by incorporating therein an open plastics-resin-reinforced fibre-glass mesh.