WO2000020130A1

WO2000020130A1 - Surface coatings

Info

Publication number: WO2000020130A1
Application number: PCT/GB1999/003224
Authority: WO
Inventors: Colin Robert Willis; Stuart Anson Brewer; Jas Pal Singh Badyal; Stephen Richard Coulson
Original assignee: The Secretary Of State For Defence
Priority date: 1998-10-01
Filing date: 1999-09-29
Publication date: 2000-04-13
Also published as: GB2365437A; AU6106899A; GB9821267D0; EP1128912A1; GB0106703D0

Abstract

A method of coating a surface with a polymer layer, which method comprises exposing said surface to a plasma comprising an optionally substituted alkyne so as to form an oil or water repellent coating on said substrate. Suitable compounds for use in the methods are compounds of formula (I) R4-C C-X-R5 where R4 is hydrogen, alkyl, cycloalkyl, haloalkyl or aryl optionally substituted by halo; X is a bond or a bridging group; and R5 is an alkyl, cycloalkyl or aryl group optionally substituted by halogen. The method is particularly useful in the production of oil and/or water repellent fabrics.

Description

iqurface Coatings

The present invention relates to the coating of surfaces, in particular to the production of oil- and water- repellent surfaces, as well as to coated articles obtained thereby.

Oil- and water- repellent treatments for a wide variety of surfaces are in widespread use. For example, it may be desirable to impart such properties to solid surfaces, such as metal, glass, ceramics, paper, polymers etc. in order to improve preservation properties, or to prevent or inhibit soiling.

A particular substrate which requires such coatings are fabrics, in particular for outdoor clothing applications, sportswear, leisurewear and in military applications. Their treatments generally require the incorporation of a fluoropoly er into or more particularly, fixed onto the surface of the clothing fabric. The degree of oil and water repellency is a function of the number and length of fluorocarbon groups or moieties that can be fitted into the available space. The greater the concentration of such moieties, the greater the repellency of the finish.

In addition however, the polymeric compounds must be able to form durable bonds with the substrate. Oil- and water- repellent textile treatments are generally based on fluoropolymers that are applied to fabric in the form of an aqueous emulsion. The fabric remains breathable and permeable to air since the treatment simply coats the fibres with a very thin, liquid-repellent film. In order to make these finishes durable, they are sometimes co-applied with cross -linking resins that bind the fluoropolymer treatment to fibres. Whilst good levels of durability towards laundering and dry-cleaning can be achieved in this way, the cross-linking resins can seriously damage cellulosic fibres and reduce the mechanical strength of the material .

Chemical methods for producing oil- and water-repellent textiles are disclosed for example in WO 97/13024 and British patent No 1,102,903 or M. Lewin et al . , 'Handbook of Fibre Science and Technology' Marcel and Dekker Inc., New York, (1984) Vol 2, Part B Chapter 2.

Plasma deposition techniques have been quite widely used for the deposition of polymeric coatings onto a range of surfaces. This technique is recognised as being a clean, dry technique that generates little waste compared to conventional wet chemical methods. Using this method, plasmas are generated from small organic molecules, which are subjected to an ionising electrical field under low pressure conditions . When this is done in the presence of a substrate, the ions, radicals and excited molecules of the compound in the plasma polymerise in the gas phase and react with a growing polymer film on the substrate. Conventional polymer synthesis tends to produce structures containing repeat units which bear a strong resemblance to the monomer species, whereas a polymer network generated using a plasma can be extremely complex.

The success or otherwise of plasma polymerisation depends upon a number of factors, including the nature of the organic compound. Reactive oxygen containing compounds such as maleic anhydride, have previously been subjected to plasma polymerisation (Chem. Mater. Vol. 8, 1, 1996). US Patent No 5,328,576 describes the treatment of fabric or paper surfaces to impart liquid repellent properties by subjecting the surfaces to a pre-treatment with an oxygen plasma, followed by plasma polymerisation of methane.

However, plasma polymerisation of the desirable oil and water repellent fluorocarbons have proved more difficult to achieve. It has been reported that cyclic fluorocarbons undergo plasma polymerisation more readily than their acyclic counterparts (H. Yasuda et al . , J. Polym. Sci.,

Polym. Chem. Ed. 1977, 15, 2411) . The plasma polymerization of trifluoromethyl-substituted perfluorocyclohexane monomers has been reported (A. M. Hynes et al . , Macromolecules, 1996, 29, 18-21) .

A process in which textiles are subjected to plasma discharge in the presence of an inert gas and subsequently exposed to an F-containing acrylic monomer is described in SU-1158-634. A similar process for the deposition of a fluroalkyl acrylate resists on a solid substrate is described in European Patent Application No. 0049884.

Japanese application no. 816773 describes the plasma polymerisation of compounds including fluorosubstituted acrylates . In that process, a mixture of the fluorosubstituted acrylate compounds and an inert gas are subjected to a glow discharge.

The applicants have found an improved method of producing polymer and particular halopolymer coatings which are water and/or oil repellent on surfaces.

According to the present invention there is provided a method of coating a surface with a polymer layer, which method comprises exposing said surface to a plasma comprising an optionally substituted alkyne so as to form an oil or water repellent coating on said substrate.

Suitably the alkyne compounds used in the method of the invention comprise chains of carbon atoms, including one or more carbon-carbon triple bonds. The chains may be optionally interposed with a heteroatom and may carry substituents including rings and other functional groups. Suitable chains, which may be straight or branched, have from 2 to 50 carbon atoms, more suitably from 6 to 18 carbon atoms. They may be present either in the monomer used as a starting material, or may be created in the monomer on application of the plasma, for example by the ring opening of an optionally substituted cycloalkyl group.

As used herein, the term "heteroatom" includes oxygen, sulphur, silicon or nitrogen atoms. Where a chain of carbon atoms is interposed by a nitrogen atom, it will be substituted so as to form a secondary or tertiary amine .

Similarly, silicons will be substituted appropriately, for example with two alkoxy groups.

Other terms used herein include "halo" or "halogen" which refer to fluorine, chlorine, bromine and iodine.

Particularly preferred halo groups are fluoro. The term "aryl" refers to aromatic cyclic groups such as phenyl or napthyl , in particular phenyl. The term "alkyl" refers to straight or branched chains of carbon atoms, suitably of up to 50 carbon atoms in length. Derivatives of alkyl groups, such as would be understood by "alkoxy" include such groups. The term "heterocyclyl" includes aromatic and non aromatic rings or ring systems, suitably containing up to 12 atoms, up to three of which may be heteroatoms .

Suitable optional substituents for the alkynes used in the process of the invention include halo, cyano, nitro, oxo, epoxide, optionally substituted cycloalkyl, optionally substituted aryl, optionally substituted aralkyl, optionally substituted heterocyclyl, C(0)_nR\ OR¹, S(0)_mR\ NR²R³,

S(0)_mNR²R³ or -NR²S(0)_mR¹ where R¹, R² and R³ are independently selected from hydrogen or alkyl, aralkyl, cycloalkyl, aryl or heterocyclyl, any of which may be optionally substituted, or R² and R³ together form an optionally substituted ring which optionally contains further heteroatoms such as sulphur, oxygen and nitrogen, n is 1 or 2 , m is 0 , 1 or 2.

Suitable optional substituents for aryl, aralkyl and cycloalkyl and heterocyclyl groups R¹, R² and R³ include halo, perhaloalkyl, mercapto, hydroxy, alkoxy, oxo, heteroaryloxy, alkenyloxy, alkynyloxy, alkoxyalkoxy, aryloxy (where the aryl group may be substituted by halo, nitro, or hydroxy) , cyano, nitro, amino, mono- or di-alkyl amino, alkylamido or oximino.

Suitable alkynyl chains, which may be straight or branched, have from 2 to 50 carbon atoms, more suitably from 6 to 20 carbon atoms, and preferably from 8 to 15 carbon atoms.

Monomeric compounds where the chains comprise unsubstituted alkynyl groups are suitable for producing coatings which are water repellent. By substituting at least some of the hydrogen atoms in these compounds with at least some fluorine atoms, oil repellency may also be conferred by the coating .

Thus in a preferred aspect, the monomeric compounds include haloalkyl moieties and in particular fluoroalkyl moieties. Therefore, preferably the plasma used in the method of the invention will comprise a monomeric unsaturated haloalkynyl containing organic compound.

Particularly suitable monomeric organic compounds are those of formula (I)

R-C≡C-X-R⁵ (I)

where R⁴ is hydrogen, alkyl, cycloalkyl, haloalkyl or aryl optionally substituted by halo; X is a bond or a bridging group; and R⁵ is an alkyl, cycloalkyl or aryl group optionally substituted by halogen.

Suitable bridging groups X include groups of formulae -(CH₂)_S-, -C0₂(CH₂)_p-, -(CH₂)_pO(CH₂)_q-, - (CH₂) _pN (R⁶) CH₂) _q- , - (CH₂)_PN(R⁶) S0₂- , where s is 0 or an integer of from 1 to 20, p and q are independently selected from integers of from 1 to 20; and R⁶ is hydrogen, alkyl, cycloalkyl or aryl. Particular alkyl groups for R⁶ include C_x_₆ alkyl, in particular, methyl or ethyl.

Where R⁴ is alkyl or haloalkyl, it is generally preferred to have from 1 to 6 carbon atoms.

Suitable haloalkyl groups for R⁴ include fluoroalkyl groups. The alkyl chains may be straight or branched and may include cyclic moieties. Preferably however R⁴ is hydrogen.

Preferably R⁵ is a haloalkyl, and more preferably a perhaloalkyl group, particularly a perfluoroalkyl group of formula C_rF_2r+1 where r is an integer of 1 or more, suitably from 1-20, and preferably from 6-12 such as 8 or 10.

In a preferred embodiment, the compound of formula (I) is a compound of formula (II)

CH≡C(CH₂)_S-R⁷ (II)

where s is as defined above and R⁷ is haloalkyl, in particular a perhaloalkyl such as a C_6-12 perfluoro group like C₆F₁₃.

In an alternative preferred embodiment, the compound of formula (I) is a compound of formula (III)

CH≡C(0)0(CH₂ 2)'_DpR¹⁷ (III

where p is an integer of from 1 to 20, and R⁷ is as defined above in relation to formula (II) above, in particular, a group C_βF₁₇. Preferably in this case, p is an integer of from 1 to 6 , most preferably about 2.

Other examples of compounds of formula (I) are compounds of formula (IV) CH≡C(CH₂)_pO(CH₂)_qR⁷, (IV) where p is as defined above, but in particular is 1, q is as defined above but in particular is 1, and R⁷ is as defined in relation to formula (II) , in particular a group C₆F₁₃; or compounds of formula (V)

CH≡C(CH₂)_pN(R⁶) (CH₂)_q R¹ (V) where p is as defined above, but in particular is 1, q is as defined above but in particular is 1, R⁶ is as defined above an in particular is hydrogen, and R⁷ is as defined in relation to formula (II) , in particular a group C₇F₁₅;

or compounds of formula (VI)

CHsC(CH₂)_pN(R⁶)S0₂R⁷ (VI)

where p is as defined above, but in particular is 1,R⁶ is as defined above an in particular is ethyl, and R⁷ is as defined in relation to formula (II) , in particular a group C_βF₁₇.

In an alternative embodiment, the alkyne monomer used in the process of the invention is a compound of formula (VII)

R⁸C≡C(CH₂)„SiR⁹R¹⁰R^u (VII) where R⁸ is hydrogen, alkyl, cycloalkyl, haloalkyl or aryl optionally substituted by halo, R⁹, R¹⁰ and R¹¹ are independently selected from alkyl or alkoxy, in particular C_1-6 alkyl or alkoxy.

Preferred groups R^β are hydrogen or alkyl, in particular C_1-6 alkyl .

Preferred groups R⁹, R¹⁰ and R¹² are C_1-6 alkoxy in particular e hoxy .

Using these compounds, coatings with water hydrophobicity oleophobicity can be achieved. Compounds of formula (I), (II), (III), (IV), (V), (VI) and (VII) are either known compounds or they can be prepared from known compounds using conventional methods.

Suitable plasmas for use in the method of the invention include non-equilibrium plasmas such as those generated by alternating current (AC) (e.g. radiofrequencies (Rf) , microwaves) or direct current (DC) . They may operate at atmospheric or sub-atmospheric pressures as are known in the art .

The plasma may comprise the monomeric compound alone, in the absence of other gases or in mixture with for example an inert gas. Plasmas consisting of monomeric compound alone may be achieved as illustrated hereinafter, by first evacuating the reactor vessel as far as possible, and then purging the reactor vessel with the organic compound for a period sufficient to ensure that the vessel is substantially free of other gases .

The surface coated in accordance with the invention may be of any solid substrate, such as fabric, metal, glass, ceramics, paper or polymers. In particular, the surface comprises a fabric substrate such as a cellulosic fabric, to which oil- and/or water-repellency is to be applied. Alternatively, the fabric may be a synthetic fabric such as an acrylic/nylon fabric.

The fabric may be untreated or it may have been subjected to earlier treatments. For example, it has been found that treatment in accordance with the invention can enhance the water repellency and confer a good oil-repellent finish onto fabric which already has a silicone finish which is water repellent only.

Precise conditions under which the plasma polymerization takes place in an effective manner will vary depending upon factors such as the nature of the polymer, the substrate etc. and will be determined using routine methods and/or the techniques illustrated hereinafter. In general however, polymerisation is suitably effected using vapours of compounds of formula (I) at pressures of from 0.01 to 10 mbar, suitably at about 0.2mbar.

A glow discharge is then ignited by applying a high frequency voltage, for example at 13.56MHz.

The applied fields are suitably of average power of up to 50W. Suitable pulsed fields are those which are applied in a sequence which yields very low average powers, for example of less than 10W and preferably of less than 1W. Examples of such sequences are those in which the power is on for 20μs and off for from lOOOOμs to 20000μs.

The fields are suitably applied for a period sufficient to give the desired coating. In general, this will be from 30 seconds to 3 hours, preferably from 2 to 30 minutes, depending upon the nature of the monomer compound used and the substrate etc.

Plasma polymerisation in accordance with the invention particularly at low average powers has been found to result in the deposition of highly fluorinated coatings which exhibit very high levels of hydrophobicity. In a preferred embodiment, the pulses are applied at a variable rate, with relatively long pulses applied, for example of from 1 to 10 sees on initially, reducing down to short pulses for example of from lOOμs to lμs on and lOμs to lOOOμs off, later in the process. It is believed that such a regime leads to improved coatings because the initial long pulse leads to greater fragmentation of the monomer, leading to a more disorganised and therefore strongly bonding layer directly adjacent the substrate. Shorter late pulses means that the upper layers deposited retain a more organised structure and so contain a greater number of long chains, which are responsible for the oil and water repellency on the surface.

Suitably the compound of formula (I) includes a perfluoroalkylated tail or moiety, in which case, the coating obtained by the process of the invention may have oleophobic as well as hydrophobic surface properties.

Thus the invention further provides a hydrophobic or oleophobic substrate which comprises a substrate comprising a coating of a alkyl polymer and particularly a haloalkyl polymer which has been applied by the method described above. In particular, the substrates are fabrics but they may be solid materials such as biomedical devices.

In a further aspect the invention provides the use of an optionally substituted alkyne or optionally substituted cycloalkyne having at least 5 carbon in the production of water and/or oil repellent coatings by pulsed plasma deposition methods. The invention will now be particularly described by way of example with reference to the accompanying diagrammatic drawings in which:

Figure 1 shows a diagram of the apparatus used to effect plasma deposition.

Example 1

Plasma Polymerisation of Alkyne A fluorinated alkyne is placed into a monomer tube (I) (Fig. 1) and, if necessary, further purified using freeze-thaw cycles. Plasma polymerisation experiments can then be carried out in an inductively coupled cylindrical plasma reactor vessel (2) of 5cm diameter, 470cm³ volume, base pressure of 7xl0^"3mbar, and with a leak rate of better than 2xl0^"3 cm³min^_1. The reactor vessel (2) is connected by way of a "viton" 0-ring (3), a gas inlet (4) and a needle valve (5) to the monomer tube (1) .

A thermocouple pressure gauge (6) is connected by way of a Young's tap (7) to the reactor vessel (2) . A further Young's tap (8) connected with an air supply and a third (9) lead to an E2M2 two stage Edwards rotary pump (not shown) by

way of a liquid nitrogen cold trap (10) . All connections are grease free.

An L-C matching unit (11) and a power meter (12) is used to couple the output of a 13.56 Mhz R.F. generator (13), which is connected to a power supply (14) , to copper coils (15) surrounding the reactor vessel (2) . This arrangement ensures that the standing wave ratio (SWR) of 'the transmitted power to partially ionised gas in the reactor vessel (2) can be minimised. For pulsed plasma deposition, a pulsed signal generator (16) can be used to trigger the R.F power supply, and a cathode ray oscilloscope (17) is used to monitor the pulse width and amplitude. The average power <P> delivered to the system during pulsing is given by the following formula:

< P> = P_cw{T_on/ (T_on + T_oM ) }

where T_on/ (_Ton + T_o££) is defined as the duty cycle and P_cw is the average continuous wave power.

In order to carry out polymerization/deposition reactions the reactor vessel (2) was cleaned by soaking overnight in a chloros bleach bath, then scrubbing with detergent and finally rinsing with isopropyl alcohol followed by oven drying. The reactor vessel (2) is then incorporated into the assembly as shown in Figure 1 and further cleaned with a 50W air plasma for 30 minutes. Next the reactor (2) vessel is vented to air and the substrate to be coated (19) is placed in the centre of the chamber defined by the reactor vessel (2) on a glass plate (18). The chamber_is then evacuated back down to base pressure (7.2 x 10^"3mbar) .

Monomeric vapour is then introduced into the reaction chamber at a constant pressure of ~0.2mbar and allowed to purge the plasma reactor, followed by ignition of the glow discharge. Typically 2-15 minutes deposition time can be used, and should be sufficient to give complete coverage of the substrate. After this, the R.F generator is switched off and the vapour allowed to continue to pass over the substrate for a further 5 minutes before evacuating the reactor back down to base pressure, and finally venting up to atmospheric pressure. The deposited plasma polymer coatings can be characterised immediately after deposition by X-ray photoelectron spectroscopy (XPS) . Complete plasma polymer coverage is confirmed by the absence of any Si (2p) XPS signals showing through from the underlying glass substrate.

A control experiment, where the vapour is allowed to pass over the substrate for 15 minutes and then pumped down to base pressure can be carried out. If the results of the control show the presence of a large Si (2p) XPS signal from the substrate, it can be concluded that the coatings obtained during plasma polymerisation are not just due to absorption of the monomer onto the substrate.

The experiments are preferably carried out with average powers in the range of from 0.01 to 50W, for example from 0.3 to 50W.

Example 2

Oil and Water Repellency Test

Once a substrate such as cotton, has been subjected to deposition conditions as described in Example 1, they may then be for wettability using "3M Test Methods" (3M oil repellency Test 1, 3M Test Methods Oct.l, 1988) . As a Water repellency test, the 3M water repellency Test II, water/alcohol drop test, 3M Test 1, 3M Test Methods, October 1, 1988 is suitable. These tests are designed to detect a fluorochemical finish on all types of fabrics by measuring:

(a) aqueous stain resistance using mixtures of water and isopropyl alcohol . (b) the fabric's resistance to wetting by a selected series of hydrocarbon liquids of different surface tensions .

These tests are not intended to give an absolute measure of the fabric's resistance to staining by watery or oily materials, since other factors such as fabric construction, fibre type, dyes, other finishing agents, etc., also influence stain resistance. These tests can, however, be used to compare various finishes. The water repellency tests comprises placing 3 drops of a standard test liquid consisting of specified proportions of water and isopropyl alcohol by volume onto the plasma polymerised surface. The surface is considered to repel this liquid if after 10 seconds, 2 of the 3 drops do not wet the fabric. From this, the water repellency rating is taken as being the test liquid with the greater proportion of isopropyl alcohol which passes the test. In the case of the oil repellency test, 3 drops of hydrocarbon liquid are placed on the coated surface. If after 30 seconds no penetration or wetting of the fabric at the liquid-fabric interface occurs around 2 of the 3 drops is evident, then the test is passed.

The oil repellency rating is taken to be the highest- numbered test liquid which does not wet the fabric surface (where the increasing number corresponds to decreasing hydrocarbon chain and surface tension) .

Claims

.Claims

1. A method of coating a surface with a polymer layer, which method comprises exposing said surface to a plasma comprising an optionally substituted alkyne containing monomer so as to form an oil or water repellent coating on said substrate.

2. A method according to claim 1 wherein the optionally substituted alkyne containing monomer comprises chain of carbon atoms which include one or more carbon-carbon triple bonds and may be optionally interposed with a heteroatom.

3. A method according to claim 1 or claim 2 wherein the alkyne is optionally substituted by halo, cyano, nitro, oxo, epoxide, optionally substituted cycloalkyl, optionally substituted aryl, optionally substituted aralkyl, optionally substituted heterocyclyl, C(0)_nR\ OR¹, S(0)_mR^x, NR²R^J,

S(0)_mNR²R³or -NR²S(0)_mR¹ where R¹, R² and R³ are independently selected from hydrogen or alkyl, aralkyl, cycloalkyl, aryl or heterocyclyl, any of which may be optionally substituted, or R² and R³ together form an optionally substituted ring which optionally contains further heteroatoms such as sulphur, oxygen and nitrogen, n is an integer of 1 or 2, m is 0 or 1 or 2.

4. A method according to any one of the preceding claims wherein the optional substitutents comprise halogen.

5. A method according to any one of the preceding claims wherein the alkyne containing monomer is a compound of formula (I) R - C≡C-X-R^b ( I )

where R⁴ is hydrogen, alkyl, cycloalkyl, haloalkyl or aryl optionally substituted by halo;

X is a bond or a bridging group; and

R⁵ is an alkyl, cycloalkyl or aryl group optionally substituted by halogen.

6. A method according to claim 5 wherein the bridging group X comprises a group of formula

-(CH₂)_B-, -C0₂(CH₂)_p-, -(CH₂)_p0(CH₂)_q-, - (CH₂) _pN (R⁶) CH₂) _q- , - (CH₂) _pN(R⁶) S0₂- , where s is 0 or an integer of from 1 to 20, p and q are independently selected from integers of from 1 to 20; and R^c is hydrogen, alkyl, cycloalkyl or aryl.

7. A method according to claim 5 or claim 6 wherein R⁴ is hydrogen .

8. A method according to claim 7 wherein the compound of formula (I) is a compound of formula (II)

CHsC(CH₂)₃-R⁷ (II)

where s is as defined in claim 6 and R⁷ is haloalkyl.

9. A method according to claim 7 wherein the compound of formula (I) is a compound of formula (III)

CH≡C(0)0(CH₂)_pR⁷ (III)

where p is an integer of from 1 to 20, and R⁷ is as defined in claim 8.

10. A method according to claim 7 wherein the compound of formula (I) is a compound of formula (IV)

CH≡C(CH₂)_p0(CH₂)_qR⁷, (IV) where p and q are as defined in claim 6, and R⁷ is as defined in claim 8.

11. A method according to claim 7 wherein the compound of formula (I) is a compound of formula (V)

CH≡C(CH₂)_pN(R⁶) (CH₂)_q R⁴ (V) where p and q are as defined in claim 6, R⁶ is as defined in claim 6 and R⁷ is as defined in claim 8.

12. A method according to claim 7 wherein the compound of formula (I) is a compound of formula (VI)

CHsC(CH₂)_pN(R⁶)S0₂R⁷ (VI) where p is as defined in claim 6 and and R⁷ is as defined in claim 8.

13. A method according to any one of claims 1 to 4 wherein the alkyne containing monomer is a compound of formula (VII)

R^βC≡C(CH₂)_n SiR'R^R¹¹ (VII) where R⁸ is hydrogen, alkyl, cycloalkyl, haloalkyl or aryl optionally substituted by halo, R⁹, R¹⁰ and R¹¹ are independently selected from alkyl or alkoxy.

14. A method according to any one of the preceding claims wherein the surface is a surface of a fabric, metal, glass, ceramics, paper or polymer substrate.

15. A method according to claim 14 wherein the substrate is a fabric.

16. A method according to any one of the preceding claims wherein the plasma is generated by an alternating current voltage.

17. A method according to claim 16 wherein the alternating current voltage is produced by radio frequencies or microwaves .

18. A method according to any one of claims 1 to 15 wherein the plasma is produced by direct current voltage.

19. A method according to any one of the preceding claims wherein the gas pressure of the organic compound is from 0.01 to 10 mbar.

20. A method according to anyone of claims 1 to 18 wherein the plasma is operated at atmospheric pressure.

21. A method according to any one of the preceding claims wherein a glow discharge is ignited by applying a high frequency voltage.

22. A method according to claim 21 wherein the voltage is applied as a continuous field.

23. A method according to claim 21 wherein the voltage is applied as a pulsed field.

24. A method according to claim 23 wherein pulses are applied in a sequence which yields low average power.

26. A method according to any one of the preceding claims wherein the plasma polymerisation takes place for from 2 to 15 minutes.

27. A hydrophobic or oleophobic substrate which comprises a substrate comprising a coating of a polymer which has been applied by the method according to any one of claims 1 to 26.

28. A hydrophobic or oleophobic substrate according to claim 27 wherein the polymer is a haloalkyl polymer.

29. A substrate according to claim 27 or claim 28 which is a fabric.

30. An item of clothing which comprises a fabric according to claim 29.