GB2096194A - Non-woven electrically conductive sheet material - Google Patents

Abstract

A protective cover, e.g. for gramophone records, which comprises non-woven sheet material having incorporated therein particulate, electrically conductive matter. The protective cover may be prepared by carding a web of textile fibres, depositing a layer of these fibres on a moving foraminous carrier in the form of a fleece by means of an airstream, saturating the fleece with a latex bonding agent, heating the impregnated fleece to gel and cure the bonding agent. The conductive matter may be in the form of a very finely divided carbon or metal powder aqueous dispersion and applied to the non-woven bonded fabric by impregnating it with the dispersion and a polymeric bonding agent or it may be applied to the fleece of fibres at the same time as the bonding agent. The non-woven sheet material is then calendered to provide a smooth surfaced compacted material which is formed into a protective cover.

Description

SPECIFICATION Non-woven electrically conductive sheet material The present invention relates to non-woven electrically conductive sheet material.

Static electricity charges on a gramophone record are a sound quality problem causing dust and dirt to be attracted to, and retained on, the record surface, creating "popping" noises when the stylus first touches the record (with possible damage to loudspeakers); crackling or frying noises during playing; excessive stylus pressure (the static charge attracts the cartridge body to the record); mistacking due to the dust accumulation impeding the stylus movement; and extra stylus and record wear because of the abrasive action of the dust.

Numerous means of reducing this nuisance are available, e.g. record sprays, conductive turntable mats, ionisation devices or discharging brushes and all are useful in reducing the electrostatic charge and its effect.

But for example when a discharging brush has been used to collect the debris together there is difficulty in actually removing it from the record due to static attraction.

The amount of static charge on the record may vary across the surface and according to the humidity of the surrounding atmosphere (a dry, low humidity atmosphere, as in centrally heated houses, tending to encourage, more static than a damp, high humidity atmosphere, for the simple reason that the moisture in the atmcsphere is more electrically conductive and so more likely to conduct the static charge away and down to ground, whereas a dry atmosphere is electrically insulating).

It has been shown that a 30,000 volt charge can be measured on a record just after being lifted from the turntable. So, although a lot of care may be used when a record is on a turntable, perhaps even placing it on a conductive turntable mat to neutralise the underside and using a spray or discharging brush to discharge the upper surface, the chances are that as soon as the record is lifted from the turntable it is immediately recharged to attract the duct. (This can be checked by just using the record to attract torn scraps of paper.) For protection records are usually stored in fairly heavy covers after first slipping them into a light inner sleeve of paper or plastic, usually polythene. With a paper sleeve tiny paper fibres will be attracted to the record surface and often the paper sleeves are lined with plastic to prevent this.However the plastic lining or sleeve is a very good insulator, and so encourages the record surface to retain any charge and even increases it by the friction of removing the record.

So we have developed a new record sleeve made from non-woven electrically conductive sheet material which removes the hazard of the high static charge and the chance of dirt or dust being attacted to the record surface during storage. The sheet material may be used to protect other audio and/or visual storage systems for example computer software storage systems (floppy discs, magnetic discs, or cassettes), video discs or cassettes.

According to the present invention therefore a protective cover is provided made from nonwoven sheet material having incorporated therein particulate electrically conductive matter.

The non-woven sheet material can be any suitable fibrous bonded fabric (e.g. it should be of a thickness suitable for making into a record sleeve and it should be able to absorb a dispersion of the electrically conductive matter) and the incorporation of the particulate matter renders it electrically conductive.

The fibres of the non woven sheet material may be chosen from natural, synthetic or artificial fibres or mixtures of these. Synthetic fibres for example polyester or polyamide are particularly suitable where strength requirements are of importance.

The bonding agents used to join the fibres together can be for example natural or synthetic polymer lattices e.g. polyacrylates or nitrile rubbers or synthetic fibres themselves e.g.

polypropylene or polyamide which can, under the action of heat and pressure, be used to effect bonding of webs of fibrous materials.

The particulate conductive matter may be, for example, a conductive carbon or metal in the form of a very fine particle size powder e.g. a powder where the majority of the particles are less than 75 microns in size.

The fibrous fabric can be manufactured for example by any of the well-known techniques such as the dry laid, wet laid or spun-bonded methods. A particularly suitable method is by carding a web of textile fibres, depositing a layer of these fibres on a moving foraminous carrier in the form of a fleece by means of an airstream, saturating the fleece with a latex bonding agent and then heating the impregnated fleece to gel and cure the bonding agent.

The conductive matter may be, for example, in the form of a very finely divided powder in aqueous dispersion and applied to the non-woven bonded fabric by impregnating it with the dispersion and a polymeric bonding agent, or it may be applied to the fleece of fibres at the same time as the bonding agent.

Preferably, the dispersion of particulate conductive matter is applied to a previously formed fibre bonded fabric together with, as a fixing agent, a thermosetting resin and/or a synthetic polymeric latex binder in order to fix the conductive matter to the fabric. Such a fixing agent may be'four example a polyacrylic resin, butadiene acrylonitrile or butadiene styrene rubbers or polyvinyl chloride. The fixing agent and the bonding agent may be chemically the same or different.

The non-woven sheet material loaded with the particulate matter is finally given a calendering treatment to provide a smooth surfaced compacted material which can be made up into d protective cover such as for example a record sleeve.

The conductive properties of the material are related to the quantity and type of conductive matter applied to it, the proportion of conductive matter to fixing agent, the thickness of the sheet material and the denier of the fibres used.

As the fibres coated with the conductive matter serve as electrical conductors the quantity and thickness of the fibres is important. For good surface and volume conductivity uniform distribution of the conductive matter on the surface and throughout the material is important.

For use as an anti-static record sleeve it is important that the sheet material should have a high conductivity e.g. having a resistance of less than 108 ohms and suitably a thickness less than 2 millimetre and to achieve this it is better to reduce the thickness of the sheet material by calendering than to reduce the quantity of fibres.

Sheet material having satisfactory conductive properties is obtained using a conductive carbon to fixing agent ratio of 1 to 1.

To discharge static from a record satisfactorily it is necessary to touch every point of the surface, and we have now produced a record sleeve made from a conductive material so that both sides of the record are in close contact with it while stored.

Its effectiveness may be maximised by sliding the record carefully from its conductive sleeve directly on to the turntable mat, which of course may also be conductive. Static cleaning may then be applied to the playing surface if desired, and when playing is completed the record returned to the sleeve with the minimum possible loss of contact with the mat.

This commonsense care will minimise the collection of dust and debris on the record surface, prolonging the life of the record (which may be irreplaceable) and the stylus, whilst at the same time reducing the interference that careless storage creates.

The invention is illustrated by the following Example.

EXAMPLE A fibre-bonded fabric was made from a fleece of polyester fibres of 1.7 decitex and 38 mm staple and weighting 28.0 g.s.m. by bonding the fibres together by impregnating the sleeve in a bath containing a styrene-butadiene-acrylonitrile synthetic rubber latex. After being dried and cured at 1 300C for 2 minutes the bonded fabric weighed 43 g.s.m. This bonded fabric was impregnated with a mixture containing 50% of a conductive carbon the majority of the particles being less than 75 microns in size (Dispersed Black 671 3 - Anchor Chemicals) and 25% of a styrenebutadiene acrylonitrile rubber (Revinex 5044) and 25% of a melamine-formaldehyde resin (Glazamine M'). The impregnated fabric was dried over hot cylinders at 1 300C for 2 minutes. This carbon loaded product weighed 67 g.s.m. and contained 12 g.s.m. of conductive carbon.

The product was finally calendered at 4000F (204cm) to produce a smooth surfaced, thin flexible sheet material of 0.1 5 mm gauge, which has a surface resistance of 0.5 x 104 ohms per square and a volume resistance of 300 ohms per square.

Note The term "ohms per square surface resistance" means the electrical resistance in ohms as measured between two electrodes each 1 inch (2.54 cm) square and loaded with an 8 Ib (3.6 kilos) weight and placed on the same side of the sheet material one inch (2.54 cm) apart.

The term "ohms per square volume resistance" means the electrical resistance in ohms as measured between two electrodes as described above and loaded as above, placed opposite each other, one on each surface of the sheet material.

Claims (25)

1. A protective cover, which comprises nonwoven sheet material having incorporated therein particulate, electrically conductive matter.

2. A protective cover as claimed in claim 1, wherein the non-woven sheet material is a fibrous bonded fabric.

3. A protective cover as claimed in claim 2, wherein the fibrous bonded fabric comprises fibres chosen from natural, synthetic or artificial fibres or mixtures thereof.

4. A protective cover as claimed in claim 3, wherein the synthetic fibres are polyester or polyamide fibres.

5. A protective cover as claimed in any of claims 2 to 4, wherein the fibrous bonded fabric comprises fibres joined together using, as a bonding agent, a natural or synthetic polymer latex or synthetic fibres.

6. A protective cover as claimed in claim 5, wherein the polymer latex is a polyacrylate or a nitrile rubber.

7. A protective cover as claimed in claim 5, wherein the synthetic fibres used as the bonding agent are polypropylene or polyamide fibres.

8. A protective cover as claimed in any of claims 1 to 7, wherein the particulate, electrically conductive matter is a conductive carbon or metal.

9. A protective cover as claimed in claim 8, wherein the conductive carbon or metal is in the form of a powder where the majority of the particles are less than 75 microns in size.

10. A protective cover as claimed in claim 1 and substantially as hereinbefore described with reference to the Example.

11. A method of manufacturing a protective cover, which comprises carding a web of textile fibres, depositing a layer of the fibres on a moving foraminous carrier in the form of a fleece by means of an airstream, saturating the fleece with a latex bonding agent, heating the impregnated fleece to gel and cure the bonding agent, applying an aqueous dispersion of particulate, electrically conductive matter to the bonded fabric, the particular electrically conductive matter being in the form of a very finely divided powder, calendering the resulting non-woven sheet material to provide a smooth surfaced, compacted material, and forming this material into a protective cover.

12. A method as claimed in claim 1 wherein the aqueous dispersion of particulate, electrically conductive matter is applied together with, as a fixing agent, a thermosetting and/or a synthetic polymeric latex binder to fix the conductive matter to the bonded fabric.

13. A method as claimed in claim 12, wherein the fixing agent is a polyacrylic resin, butadiene acrylonitrile or butadiene styrene rubber or polyvinyl chloride.

14. A method as claimed in any of claims 11 to 13, wherein the fibres are chosen from natural, synthetic or artificial fibres or mixtures thereof.

15. A method as claimed in claim 14, wherein the synthetic fibres are polyester or polyamide fibres.

16. A method as claimed in any of claims 11 to 15, wherein the bonding agent is a polyacrylate or a nitrile rubber.

17. A method as claimed in any of claims 11 to 16, wherein the particulate, electrically conductive matter is a conductive carbon or metal.

18. A method as claimed in claim 17, wherein the conductive carbon or metal is in the form of a powder where the majority of the particles are less than 75 microns in size.

1 9. A method of manufacturing a protective cover, which comprises carding a web of textile fibres, depositing a layer of the fibres on a moving foraminous carrier in the form of a fleece by means of an airstream, saturating the fleece with a latex bonding agent and, at the same time, applying an aqueous dispersion of particulate, electrically conductive matter to the fleece of fibres, heating the impregnated fleece to gel and cure the bonding agent, calendering the resuiting non-woven sheet material to provide a smoother surface compacted material, and forming this material into a protective cover.

20. A method as claimed in claim 19, wherein the fibres are chosen from natural, synthetic or artificial fibres or mixtures thereof.

21. A method as claimed in claim 20, wherein the synthetic fibres are polyester or polyamide fibres.

22. A method as claimed in any of claims 1 9 to 21, wherein the bonding agent is a polyacrylate or a nitrile rubber.

23. A method as claimed in any of claims 1 9 to 22, wherein the particulate, electrically conductive matter is a conductive carbon or metal.

24. A method as claimed in claim 23, wherein the conductive carbon or metal is in the form of a powder where the majority of the particles are less than 75 microns in size.

25. A method of manufacturing a protective cover substantially as hereinbefore described with reference to the Example.