GB2254854A - Decreasing the static electrification of nylon - Google Patents

Abstract

A continuous method of modifying the surface static electrification of a nylon filament which comprises exposing the moving filament to a plasma generated in an atmosphere of a gas which is a halogen compound of either hydrogen, carbon or sulphur or a mixture of such halogen compound with another gas, such plasma gas modifying the surface of the filament to such an extent that the normally positive static charge on the surface of the filament is converted into a static charge which has a mean value which is either negative or zero. The plasma gas is derived from carbon tetrafluoride, carbon tetrachloride, hexafluoropropene, hexafluorobenzene or sulphur hexafluoride. It may be used in combination with argon, nitrogen or air. The plasma gas is excited by a microwave generator.

Description

NYLON FILAMENT HAVING AN IMPROVED SURFACE STATIC ELECTRIFICATION The present invention relates to a method for improving the surface static electrification of a nylon monofilament or multifilament, ie decreasing the tendency of nylon filaments to accumulate static electricity on the surface of a nylon filament, by means of a sub atmospheric plasma treatment. It also relates to a nylon filament having improved static electrification made by such a method.

The presence of a high positive charge on the surfaces of nylon filaments is a considerable nuisance. In particular, static charging is responsible for the rapid soiling of clothing made from nylon filaments, while charge exchange between carpets made from nylon filaments and shoes can cause unpleasant shocks to persons walking on the carpet. It is thus evident that the elimination of static electrification on a nylon filament would be of considerable commercial importance.

Therefore, it is very important to develop a convenient and efficient method for the improvement of the antistatic performance of, or for the decrease of the accumulation of static electricity on, the surface of a nylon filament. Various attempts have already been made to achieve this. For example, the nylon polymer from which the filament is produced may be compounded with a sufficient amount of an electroconductive particulate material such as a metal powder or carbon black before the polymer is melt spun or extruded into a filament. The surface resistivity of a nylon filament can also be decreased by providing the filament with a very thin electroconductive film of metal by such methods as sputtering or vapour deposition.Static electricity on the surface of a nylon filament can also be decreased by increasing the hydrophilicity of the surface by the use of a surface active agent as an antistatic agent which may be either incorporated into the body of the filament by the admixture of the resin with the nylon polymer prior to formation of the filament or by applying a coating on to the surface of the filament. Alternatively, the introduction of hydrophilic groups or structure to the surface of a filament is also effective in decreasing the static electricity, as is obtained by a chemical treatment, eg acid etching, flame treatment, surface grafting by means of actinic rays, by which we mean radiation capable of producing chemical change such as electron beams, ultraviolet light or ionizing radiation.

These methods are all designed to reduce static hazards by providing a means of dissipating charge in contrast to the invention which is concerned with altering the generation of static charge. Though these known methods are effective to some extent they are usually are insufficiently effective in improving antistatic performance, or cause adverse effects on the characteristics of the bulk shaped article; involve extremely high costs; can only be used with relatively short lengths of filament and may be negated by subsequent processing.

British Patent Application 2111064A describes a method for improving the antistatic performance of a synthetic resin, which may be a polyamide, shaped article which comprises treating the article by the steps of (a) forming a cross-linked layer in at least the surface stratum of the shaped article; and (b) exposing the surface of the thus obtained article to a low temperature plasma generated in an atmosphere containing a gaseous silicon compound of the formula R H Si X4 a b in which a 6 4-a-b R, or a combination of any two R's, is an organic radical, X is halogen or alkoxy, a is 0,1,2,or 3 and b is 0 or (except when a is 3) 1, or a hydrolysis - condensation product thereof, to such an extent that a plasma - polymerised surface film of the silicon compound having a thickness of at least 5 nm (nanometres) is formed in stratification on the cross-linked layer.

In Japanese Patent No 59-216980 there is described a process for treating the filaments, including filaments of nylon 6, with an organic silicon compound of the general formula Si-X (where X is a halogen) within a low temperature plasma.

East German Patent No 122692 describes a process and apparatus for modifying the surfaces of fibres and textile fabrics by treatment with a plasma. No details of the plasma are provided. Furthermore though there is an isolated reference to improvement in antistatic properties, the main object of the invention is to improve physical properties such as tear strength, resistance to abrasion, shrinking and resistance to pilling and dimensional stability.

Though the Examples provided in British Patent Application 2111064A and Japanese Patent No 59-216980 show that a considerable improvement in antistatic performance may be achieved there is no indication that the normally positive static charge on an article made from a polyamide is converted into a negative or zero charge which is a feature of the present invention.

An article in Polymer Material Science Engineering 1990, 62, pages 348 to 352 by E M Charlson et al describes the deposition of layers of plasma polymers on the surface of nylon or brass in order to achieve an alteration in triboelectric performance as would be expected. The plasma polymers were generated from methane, acetylene, trimethylsilane, tetramethyl disiloxane and tetrafluorethylene.

According to the present invention we provide a continuous method of modifying the surface static electrification of a nylon monofilament or multifilament which comprises exposing the filament while it is moving at a minimum speed of 100 metres/minute to a plasma generated in an atmosphere of a gas which is a halogen compound of either hydrogen, carbon or sulphur or a mixture of such halogen compound with another gas, such plasma gas modifying the surface of the filament to such an extent that the normally positive static charge on the surface of the filament is converted into a static charge which has a mean value which is either negative or zero.

Examples of suitable halogen compounds which can be used are carbon tetrafluoride (CF4), carbon tetrachloride (CCl4), hexafluoropropene (HFP), hexafluorobenzene (HFB), sulphur hexafluoride (SF6). If desired the selected compound may be used in combination with another gas for example an inert gas such as argon, or a gas such as nitrogen or air.

Modification of the nylon surface may take place by either one of two processes; grafting of species on to the nylon chain by use of non-polymer forming gases, or formation of a film on the nylon surface by a polymer created within the plasma (plasma polymerisation). Grafting may take place by direct replacement of species present on the nylon chain by a halogen (eg fluorine for hydrogen) or by a more complex free radical created within the plasma (eg CF3 for hydrogen). The grafting process leads to a complex nylon surface containing a variety of grafted species attached at various sites on the nylon. Film formation occurs for most organic compounds and other compounds which may form polymers in the presence of other organic molecules.

It is well known that the magnitude and sign of the charge developed on a given material after contact with a second material depends on the choice and nature of the second material.

There have been many attempts to construct a so called "triboelectric series" for insulators. In such a series or list, materials appearing higher charge positive when contacted with materials appearing lower, and vice versa, with the magnitude of the charge being greater the greater the separation in the list.

Nylon invariably appears at or near the top of such lists and consequently normally charges positive (see for example Electrostatics, JA Cross. Publ. Adam Hilger Bristol 1987., p 28 et seq for a useful summary).

However, it is also well known that measurements of contact electrification may be strongly affected by surface contamination and are often subject to considerable scatter. In our measurements, therefore, we have chosen to use as the contacting material a highly reproducible and readily cleanable material viz gold. Moreover in our experience the sign and magnitude of the charging of materials against gold is a good indication of the charging of the same materials against standard shoe sole materials. Thus, herein, the terms positive and negative static charge refer to the sign of the charge after the specimen filament is brought into contact with, and then separated from, gold. The particular test method used is described below.

Though the method of the invention is generally described herein with reference to a premade monofilament or multifilament, it should be appreciated that the method of the invention can be carried out during the manufacture of the filament, more particularly the surface of the spinning threadline of filament can be modified by the method of the invention before the filament is wound up.

According to another aspect of the invention, therefore, we provide a method of producing a continuous filament having a static charge which has a mean value which is either negative or zero comprising melt spinning a filament, cooling the filament, exposing the filament to a plasma generated in an atmosphere of a gas which is a halogen compound of either hydrogen, carbon or sulphur or a mixture of such halogen compound with another gas and winding up the filament.

Two embodiments of the method of the invention will now be described in more detail with reference to the accompanying schematic drawings designated Figures 1 and 2.

Referring to Fig 1 an untreated nylon monofilament or multifilament is progressively unwound from a bobbin 1 at a speed in excess of 100 m/min and passes along a 12 inch long glass capillary 2 having an internal diameter of 0.4 mm and into a chamber 3 connected to a vacuum pump (not shown) by means of which chamber 3 is evacuated. An indication of the pressure within chamber 3 is provided by a pressure gauge (not shown). The filament then passes through another 12 inch long glass capillary 4 having an internal diameter of 0.4 mm and into chamber 5 connected to a vacuum pump (not shown) by means of which chamber 5 is evacuated. The action of the pumps attached to chambers 3 and 5 serve to prevent ingress of air into the system. The filament then passes into and through a glass tube 6 which passes through a cavity 7 and into chamber 9.At chamber 9 a plasma gas at a pressure in excess of atmospheric is introduced into the system and enters glass tube 6 because of the pumping action on chamber 5. While the filament passes through the glass tube 6 within the confines of the cavity 7 the plasma gas is excited by means of a microwave generator 8 and this reacts with the surface of the filament. The electrons and ions within the plasma bombard the surface. The electron bombardment heats the surface of the filament whereas the heavier ions have a more complex interaction which can include implantation, recoil mixing, bond breaking, sputtering, chemical reaction and heating. After passing through the chamber 9 the treated filament passes through a 12 inch long glass capillary 10 having an internal diameter of 0.4 mm and into chamber 11 which is continuously evacuated by a pump (not shown).The action of the pump attached to chamber 11 serves to prevent ingress of air into the system.

After leaving chamber 11, the treated filament passes through another 12 inch long glass capillary having an internal diameter of 0.4 mm before being finally wound up at 12. A winding control device 13 is provided.

According to another aspect of the invention, therefore, we provide a method of modifying the surface static electrification of a nylon monofilament or multifilament which comprises passing the filament at a speed in excess of 100 metres/minute into and through a first chamber which is evacuated continuously, into and through a second chamber which is evacuated continuously, into and through a tube containing a gaseous compound of a halogen compound of either hydrogen, carbon or sulphur which is excited by a microwave generator, into and through a third chamber into which said gaseous compound is introduced into the system, into and through a fourth chamber which is evacuated continuously and winding up the treated filament.

Referring to Fig 2, an untreated nylon monofilament or multifilament is progressively unwound from a bobbin 1 and passes through a glass capillary 2 into a cylindrical first chamber 3.

Chamber 3 is continuously supplied through conduit 4 with a background gas, typically argon, at a pressure in excess of atmospheric pressure. The presence of this background gas at elevated pressure serves to reduce the ingress of air into the system through capillary 2. The moving filament then passes through an orifice 5 and into cylindrical second chamber 6.

Chamber 6 is continuously supplied through conduit 7 with a mixture of the background gas, typically argon, and a reactive plasma gas which is a halogen compound of either hydrogen, carbon or sulphur. On leaving chamber 6, the filament passes through a silica glass tube 8 which itself passes through a cylindrical third chamber 9. The silica glass tube is a suitable low loss dielectric material which allows the electromagnetic field to penetrate throughout. The microwave generator is connected to a surface wave launching device which encloses a portion of the silica tube. The electric component of the electromagnetic field generated by this device, when applied to the gas, accelerates the electrons within it and these, through collisions, ionise some of the gas to form the plasma. Once the gas in the plasma has been ionised, surface waves will begin to propagate along the interface between the tube and the plasma and will sustain the latter. The silica tube which carries the treated filament then exits into a cylindrical fourth chamber 11 which is evacuated through conduit 12 by means of a suitable vacuum pump (not shown). Chamber 11 is also provided with a suitable pressure gauge (not shown) attached to conduit 13. The treated filament then passes through a glass capillary after which it is wound up on a bobbin 15 provided with a suitable winding control 16.

According to yet another aspect of the invention we provide a method of modifying the surface static electrification of a nylon monofilament or multifilament which comprises passing the filament at a speed in excess of 100 metres/minute into and through a first chamber containing a non reactive gas at a pressure in excess of atmospheric pressure, through a second chamber containing a gaseous mixture of a halogen compound of either hydrogen, carbon or sulphur and a non-reactive gas, through a third, reaction, chamber in which the gaseous atmosphere is excited by means of microwaves and finally into and out of a fourth chamber which is being progressively evacuated by means of a vacuum pump.

The test method adopted to measure electrostatic charge on treated nylon filaments will now be described. The test is based on the empirical observation that contact charge transfer to a given point on a nylon surface can be reproduced if the charge from any previous contact is removed by exposure to ionised air. The mechanism of charge removal is not known but we think this does not compromise the usefulness of the test.

Referring to figure 3 of the drawings, the nylon filament 1 is pulled over the gold plated peg 2 by a motor (not shown) which winds the filament onto the drum 3 via a brass pulley 4. Filament tension is maintained by a 1 gram weight 5.

Peg 2 is connected to an electrometer (not shown) which measures the charge transfer from peg 2 to the nylon filament. 6 is a region of ionised air generated by a radioactive source, while 7 is a screen to help keep ions away from 2. Drum 3 is rotated and measurements started when the part of the filament initially at X reaches 2. Charge transfers to ten successive sections of about 2 cm long are then recorded and a mean value taken and a standard deviation calculated.

The invention will now be described with reference to the following Examples.

EXAMPLES.

The control fibres used in the Examples were 1300f68 drawn nylon 6.6 multifilament yarns to which no surface finish had been applied. The filaments were subjected to a plasma treatment under a variety of conditions including gas composition, microwave power, pressure and speed as indicated in the following tables.

In Examples 1 to 3 (the results of which are set out in the accompanying table) treatment of multifilament was carried out in the apparatus shown in Fig 2.

In Examples 4 to 8 (the results of which are set out in the accompanying table) the treatment of monofilament was carried out in the apparatus shown in Fig 1.

In Examples 9 to 11 (the results of which are set out in the accompanying table) the treatment of monofilament was carried out in the apparatus shown in Fig 1 but using a plasma which did not contain a halogen. The results show that the static charge has remained positive and similar to the control (the results of which are set out in the accompanying table as Example 12).

TABLE No Gases Ratio Pressure Power Speed Mean Standard Torr Watts m/min Charge Deviation pC 1 Ar:CF3Cl 4:1 2 50 100 -52 15 2 Ar:CF3Br 4:1 2 50 100 -62 16 3 Ar:SF6 6:1 2 50 100 -199 66 4 Ar:C6F6 17:1 5 30 100 -4.5 2.6 5 Ar:C F 30:1 3 25 250 -2.3 2.1 6 Ar:CF4 5:1 0.5 50 130 -6.2 5.1 7 Ar:CF, 1:1 8 50 500 -4.3 3.3 8 CF4 0.5 50 130 -3.3 2.1 9 Ar:HMDSO 1:18 5 50 250 28 4.2 10 Ar:HMDSO 1:20 5 25 250 20 6.1 11 Ar 5 25 250 25.2 5.2 12 No Treatment - - - 21 5.5 HMDSO = Hexamethyldisiloxane

Claims (4)

1. CLAIMS 1. A continuous method of modifying the surface static electrification of a nylon monofilament or multifilament which comprises exposing the filament while it is moving at a minimum speed of 100 metres/minute to a plasma generated in an atmosphere of a gas which is a halogen compound of either hydrogen, carbon or sulphur or a mixture of such halogen compound with another gas, such plasma gas modifying the surface of the filament to such an extent that the normally positive static charge on the surface of the filament is converted into a static charge which has a mean value which is either negative or zero.
2. 2. A method of producing a continuous filament having a static charge which has a mean value which is either negative or zero comprising melt spinning a filament, cooling the filament, exposing.the filament to a plasma generated in an atmosphere of a gas which is a halogen compound of either hydrogen, carbon or sulphur or a mixture of such halogen compound with another gas and winding up the filament.
3. 3. A method of modifying the surface static electrification of a nylon monofilament or multifilament which comprises passing the filament at a speed in excess of 100 metres/minute into and through a first chamber which is evacuated continuously, into and through a second chamber which is evacuated continuously, into and through a tube containing a gaseous compound of a halogen compound of either hydrogen, carbon or sulphur which is excited by a microwave generator, into and through a third chamber into which said gaseous compound is introduced into the system, into and through a fourth chamber which is evacuated continuously and winding up the treated filament.
4. 4. A method of modifying the surface static electrification of a nylon monofilament or multifilament which comprises passing the filament at a speed in excess of 100 metres/minute into and through a first chamber containing a non reactive gas at a pressure in excess of atmospheric pressure, through a second chamber containing a gaseous mixture of a halogen compound of either hydrogen, carbon or sulphur and a non-reactive gas, through a third, reaction, chamber in which the gaseous atmosphere is excited by means of microwaves and finally into and out of a fourth chamber which is being progressively evacuated by means of a vacuum pump.