GB2454242A

GB2454242A - Plasma coating

Info

Publication number: GB2454242A
Application number: GB0721535A
Authority: GB
Inventors: Stephen Coulson
Original assignee: P2i Ltd
Current assignee: P2i Ltd
Priority date: 2007-11-02
Filing date: 2007-11-02
Publication date: 2009-05-06
Also published as: GB0721535D0

Abstract

A method for maintaining the coefficient of friction of an item, such as a vehicle tyre or shoe, whilst enhancing its oil and/or water repellent properties, comprises forming an oil or water repellent coating or surface modification thereon by ionisation or activation technology, such as plasma processing. Items such as tyres, treated in this way also form part of the invention. For preference, the item is coated by plasma polymerization with 1H,1H,2H,2H-heptadecafluorodecyl acrylate.

Description

Surface Modifying Treatments The present invention relates to methods for treating items so as to maintain or increase the coefficient of friction, whilst imparting oil or water repellent properties thereto, as well as particular items, such as car tyres, which have been treated in this way.

Plasma polyrnerisation in particular is recognised as being a clean, dry technique that generates little waste compared to conventional wet chemical methods. Using this method, plasmas are generally generated from organic molecules, which are subjected to an electrical field. When this is done in the presence of a substrate, the radicals of the compound in the plasma react on the substrate to form a polymer film.

Conventional polymer synthesis tends to produce structures containing repeat units that bear a strong resemblance to the monomer species, whereas a polymer network generated using a plasma can be extremely complex due to extensive monomer fragmentation. The properties of the resultant coating can depend upon the nature of the substrate as well as the nature of the monomer used and conditions under which it is deposited.

W02007/083l24 describes the use of plasma polymerisation in the treatment of a range of fashion accessories including shoes, so as to protect in particular delicate fabrics from oil or water damage and also to make items such as shoes, essentially water-proof.

However, in general, coatings such as Teflon� which make surfaces oil or water repellent generally have a low coefficient of friction and therefore make the item slippery.

This limits the applicability of the coatings in certain circumstances.

However the applicants have found that the plasma deposition process can lead to coatings which, whilst having the desired oil or water repellency, do not increase the "slip" properties of the item. This finding means that the coating process can be applied more widely than hitherto envisaged, and in particular can be applied to items which are required to be oil or water repellent but where reduction in the coefficient of friction is intrinsically undesirable.

According to one aspect, the invention provides a method for maintaining the coefficient of friction of an item whilst enhancing its oil and/or water repellent properties, the method comprising forming an oil or water repellent coating or surface modification thereon by ionisation or activation technology, such as plasma processing.

Thus, for instance, the invention provides the use of a plasma polymerisation deposition process for the deposition of an oil and/or water repellent coating on an item without increasing the coefficient of friction of the item.

The method or use of the invention may in fact, slightly increase the non-slip properties of the item. However, certainly the coefficient of friction is not generally reduced by the treatment although the oil or water repellency (oleophobicity or hydrophobicity) may be significantly enhanced.

Such a process may be particularly favoured in the case for example of shoes, where a whole shoe may be treated in accordance with the invention to make the shoe water-proof, but without increasing the slipperiness of the sole. This is important to facilitate the wearing of the shoe, particularly in the case of fashion shoes, which may have essentially smooth soles, or sports shoes, which are intended to be worn on smooth surfaces such as those found in sports halls and the like.

However, the finding means that another particularly preferred item for treatment in accordance with the invention is vehicle tyres such as car, lorry or tractor tyres. Rubber tyres are, in their natural state, water-proof. The are provided with treads which increase the "grip" of the tyre onto the ground surface. In wet conditions, water enters the treads and is thrown clear as the vehicle moves.

Any treatment which would facilitate this removal will increase the performance of the tyre. This could be particularly important for instance, in racing cars such as Formula 1 racing cars, where the precise performance of the tyre in different conditions can make significant differences to the performance of the car.

Hitherto, the application of coatings such as Teflon� coatings to tyres has not been considered because the penalties in terms of loss of road grip would be too great. However, by using the method of the invention, this facility is possible without any loss of grip.

The ultra low surface energies achievable using ionisation or activation techniques can be less than 15 mNm', for instance less than 12mNm1, for example from 8-lOmNm' (where mNm1 is milli Newtons per metre) In one embodiment, the ionisation or activation technology used is plasma processing. In particular the said surface of the item has an oil or water repellent polymeric coating formed thereon by plasma deposition.

Plasma processing to achieve oil or water repellent properties may be achieved, for example, by exposing the surface to plasma comprising small molecules such as CF4 and a variety of saturated and unsaturated hydrocarbon and fluorocarbon compounds (see, for example, "Plasma Polymerisation", Academic Press Inc. (London) Ltd. 1985) . Longer chain semi and fully fluorinated compounds may also be used to impart non-wetting or non-absorbing properties.

Any monomeric compound or gas which undergoes plasma polymerisation or modification of the surface to form an oil or water-repellent polymeric coating layer or surface modification on the surface of the item may suitably be used. Suitable monomers which may be used include those known in the art to be capable of producing water-repellent polymeric coatings on substrates by plasma polymerisation including, for example, carbonaceous compounds having reactive functional groups, particularly substantially -CF'3 dominated perfluoro compounds (see WO 97/38801), perfluorinated alkenes (Wang et al., Chem Mater 1996, 2212-2214), hydrogen containing unsaturated compounds optionally containing halogen atoms or perhalogenated organic compounds of at least 10 carbon atoms (see WO 98/58117), organic compounds comprising two double bonds (WO 99/64662), saturated organic compounds having an optionally substituted alky chain of at least 5 carbon atoms optionally interposed with a heteroatom (WO 00/05000), optionally substituted alkynes (WO 00/20130), polyether substituted alkenes (US 6,482,531B) and macrocycles containing at least one heteroatom (US 6,329,024B), the contents of all of which are herein incorporated by reference.

In particular, the item such as the tyre, is exposed to plasma comprising a compound of formula (I) R1 R3 (I) R7 where R', R2 and R3 are independently selected from hydrogen, alkyl, haloalkyl or aryl optionally substituted by halo; and R4 is a group -X-R5 where R5 is an alkyl or haloalkyl group and X is a bond; a group of formula -C(O)O--, a group of formula -C(O)O(CH2)Y -where n is an integer of from 1 to 10 and Y is a suiphonamide group; or a group (O)pR6(O)q(CH2)t where R6 is aryl optionally substituted by halo, p is 0 or 1, q is 0 or 1 and t is 0 or an integer of from 1 to 10, provided that where q is 1, t is other than 0, for a sufficient period of time to allow a polymeric layer to form on the surface.

As used therein the term "halo" or "halogen" refers to fluorine, chlorine, bromine and iodine. Particularly preferred halo groups are fluoro. The term "aryl" refers to aromatic cyclic groups such as phenyl or naphthyl, in particular phenyl.

The term "alkyl" refers to straight or branched chains of carbon atoms, suitably of up to 20 carbon atoms in length. The term "alkenyl" refers to straight or branched unsaturated chains suitably having from 2 to 20 carbon atoms. "Haloalkyl" refers to alkyl chains as defined above which include at least Suitable haloalkyl groups for R1, R2, R3 and R5 are fluoroalkyl groups. The alkyl chains may be straight or branched and may include cyclic moieties.

For R5, the alkyl chains suitably comprise 2 or more carbon atoms, suitably from 2-20 carbon atoms and preferably from 4 to 12 carbon atoms.

For R, R2 and R3, alkyl chains are generally preferred to have from 1 to 6 carbon atoms.

Preferably R5 is a haloalkyl, and more preferably a perhaloalkyl group, particularly a perfluoroalkyl group of formula CF2,�1 where m is an integer of 1 or more, suitably from 1-20, and preferably from 4-12 such as 4, 6 or 8.

Suitable alkyl groups for R1, R2 and R3 have from 1 to 6 carbon atoms.

In one embodiment, at least one of R', R2 and R3 is hydrogen. In a particular embodiment R1, R2, R3 are all hydrogen. In yet a further embodiment however R3 is an alkyl group such as methyl or propyl.

Where X is a group -C(O)O(CH2)Y-, n is an integer which provides a suitable spacer group. In particular, n is from 1 to 5, preferably about 2.

Suitable suiphonamide groups for Y include those of formula -N(R6a)S02 where R6 is hydrogen or alkyl such as C14alkyl, in particular methyl or ethyl.

In one embodiment, the compound of formula (I) is a compound of formula (II) CH2=CH-R5 (II) where R5 is as defined above in relation to formula (I) In compounds of formula (II), X in formula (I) is a bond.

However in a preferred embodiment, the compound of formula (I) is an acrylate of formula (III) CH2=CR7C(O)O(CH2)R5 (III) where n and R5 as defined above in relation to formula (I) and R7 is hydrogen, C1.10 alkyl, or C110haloalkyl. In particular R7 is hydrogen or C16alkyl such as methyl. A particular example of a compound of formula (III) is a compound of formula (IV) H(CF) CF3 (IV) where R7 is as defined above, and in particular is hydrogen and x is an integer of from 1 to 9, for instance from 4 to 9, and preferably 7. In that case, the compound of formula (IV) is 1H, lH, 2H, 21-3-heptadecafluorodecylacylate.

Alternatively, a polymeric coating may be formed by exposing the item to plasma comprising one or more organic monomeric compounds, at least one of which comprises two carbon-carbon double bonds for a sufficient period of time to allow a polymeric layer to form on the surface.

Suitably the compound with more than one double bond comprises a compound of formula (V) R8 R1OR11 (V) where R8, R9, R10, R'1, R'2, and R13 are all independently selected from hydrogen, halo, alkyl, haloalkyl or aryl optionally substituted by halo; and Z is a bridging group.

Examples of suitable bridging groups Z for use in the compound of formula (V) are those known in the polymer art. In particular they include optionally substituted alkyl groups which may be interposed with oxygen atoms. Suitable optional substituents for bridging groups Z include perhaloalkyl groups, in particular perfluoroalkyl groups.

In a particularly preferred embodiment, the bridging group Z includes one or more acyloxy or ester groups. In particular, the bridging group of formula Z is a group of sub-formula (VI) o (CR14R15 (VI) where n is an integer of from 1 to 10, suitably from 1 to 3, each R'4 and R'5 is independently selected from hydrogen, alkyl or haloalkyl.

Suitably R8, R9, R°, R11, R'2, and R'3 are haloalkyl such as fluoroalkyl, or hydrogen. In particular they are all hydrogen.

Suitably the compound of formula (V) contains at least one haloalkyl group, preferably a perhaloalkyl group.

Particular examples of compounds of formula (V) include the following: q R14

A

wherein R'4 and R'5 are as defined above, provided that at least one of R'4 or R15 is other than hydrogen. A particular example of such a compound is a compound of formula B.

B C8F17

In a further aspect, the polymeric coating is formed by exposing the item to plasma comprising a compound of comprising a monomeric saturated organic compound, said compound comprising an optionally substituted alkyl chain of at least 5 carbon atoms optionally interposed with a heteroatom for a sufficient period of time to allow a polymeric layer to form on the surface.

The term "saturated" as used herein means that the monomer does not contain multiple bonds (i.e. double or triple bonds) between two carbon atoms which are not part of an aromatic ring. The term "heteroatom" includes oxygen, sulphur, silicon or nitrogen atoms. Where the alkyl chain 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.

Particularly suitable monomeric organic compounds are those of formula (VII) R16 R17 R'8 R19 R2° R21 (VII) where R16, R17 R6' R'9 and R2° are independently selected from hydrogen, halogen, alkyl, haloalkyl or aryl optionally substituted by halo; and R21 is a group X-R22 where R22 is an alkyl or haloalkyl group and X is a bond; a group of formula C(O)0(CH2)Y-where x is an integer of from 1 to 10 and Y is a bond or a suiphonarnide group; or a group -(O)R23(O)(CH2)-where R23 is aryl optionally substituted by halo, p is 0 or 1, s is 0 or 1 and t is 0 or an integer of from 1 to 10, provided that where s is 1, t is other than 0.

Suitable haloalkyl groups for R16, R17, R18, p, and R2° are fluoroalkyl groups. The alkyl chains may be straight or branched and may include cyclic moieties and have, for example from 1 to 6 carbon atoms.

For R22, the alkyl chains suitably comprise 1 or more carbon atoms, suitably from 1-20 carbon atoms and preferably from 6 to 12 carbon atoms.

Preferably P22 is a haloalkyl, and more preferably a perhaloalkyl group, particularly a perfluoroalkyl group of formula C1F2+1 where z is an integer of 1 or more, suitably from 1-20, and preferably from 6-12 such as 8 or 10.

Where X is a group -C(O)O(CH2)Y-, y is an integer which provides a suitable spacer group. In particular, y is from 1 to 5, preferably about 2.

Suitable sulphonamide groups for Y include those of formula -N(R23)S02 where R23 is hydrogen, alkyl or haloalkyl such as C14alkyl, in particular methyl or ethyl.

The monomeric compounds used in the method of the invention preferably comprises a C625 alkane optionally substituted by halogen, in particular a perhaloalkane, and especially a perfluoroalkane.

In yet a further alternative, item is exposed to plasma comprising an optionally substituted alkyne for a sufficient period of time to allow a polymeric layer to form on the surface.

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 Particularly suitable monomeric organic compounds are those of formula (VIII) R2-CC-X1-R25 (VIII) l0 where R24 is hydrogen, alkyl, cycloalkyl, haloalkyl or aryl X1 is a bond or a bridging group; and R25 is an alkyl, cycloalkyl or aryl group optionally substituted by halogen.

Suitable bridging groups X' include groups of formulae -(CH2) s, C02 (CH2), -(CH2) p0 (CH2) q' -(CH2) N (R26) CH2) q' -(CH2)N(R26)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 R26 is hydrogen, alkyl, cycloalkyl or aryl. Particular alkyl groups for R26 include C6 alkyl, in particular, methyl or ethyl.

Where R24 is alkyl or haloalkyl, it is generally preferred to have from 1 to 6 carbon atoms.

Suitable haloalkyl groups for R24 include fluoroalkyl groups.

The alkyl chains may be straight or branched and may include cyclic moieties. Preferably however R24 is hydrogen.

Preferably R25 is a haloalkyl, and more preferably a perhaloalkyl group, particularly a perfluoroalkyl group of formula CrF2r4] 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 (VIII) is a compound of formula (IX) CHC(CH2)-R27 (IX) where s is as defined above and R27 is haloalkyl, in particular a perhaloalkyl such as a C6.12 perfluoro group like C5F13.

in an alternative preferred embodiment, the compound of formula (VIII) is a compound of formula (X) CHC (O)O(CH2)R27 (X) where p is an integer of from 1 to 20, and R27 is as defined above in relation to formula (IX) above, in particular, a group C8F1-,. 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 (XI) CHC(CH2)pO(CH2)qR27, (XI) where p is as defined above, but in particular is 1, q is as defined above but in particular is 1, and R27 is as defined in relation to formula (IX), in particular a group C6F13; or compounds of formula (XII) CHC(CH2)N(R26) (CH2)q R27 (XII) where p is as defined above, but in particular is 1, q is as defined above but in particular is 1, R26 is as defined above an in particular is hydrogen, and R27 is as defined in relation to formula (IX), in particular a group C7F15; or compounds of formula (XIII) CHC(CH2)N(R26)SO2R27 (XIII) where p is as defined above, but in particular is 1,R26 is as defined above an in particular is ethyl, and R27 is as defined in relation to formula (IX), in particular a group C8F17.

In an alternative embodiment, the alkyne monomer used in the process is a compound of formula (XIV) R28CC (CH2) SiR29R30R31 (XIV) where R28 is hydrogen, alkyl, cycloalkyl, haloalkyl or aryl optionally substituted by halo, R29, R3° and R3' are independently selected from alkyl or alkoxy, in particular C16 alkyl or alkoxy.

Preferred groups R28 are hydrogen or alkyl, in particular C16 alkyl.

Preferred groups R29, R3° and R31 are C16 alkoxy in particular ethoxy.

In general, the item to be treated is placed within a plasma chamber together with the material to be deposited in gaseous state, a glow discharge is ignited within the chamber and a suitable voltage is applied, which may be pulsed.

The oil or water repellent polymeric coating or surface modification may be produced under both pulsed and continuous-wave plasma deposition conditions but pulsed plasma is generally preferred.

As used herein, the expression "in a gaseous state" refers to gases or vapours, either alone or in mixture, as well as aerosols.

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 item being treated etc. and will be determined using routine methods and/or the S techniques.

Suitable plasmas for use in the method of the invention include non-equilibrium plasmas such as those generated by radiofrequencies (RF), microwaves or direct current (DC) . They may operate at atmospheric or sub-atmospheric pressures as are known in the art. In particular however, they are generated by radiofrequencies (RF) Various forms of equipment may be used to generate gaseous plasmas. Generally these comprise containers or plasma chambers in which plasmas may be generated. Particular examples of such equipment are described for instance in W02005/089961 and W002/28548, but many other conventional plasma generating apparatus are available.

The gas present within the plasma chamber may comprise a vapour of the monomeric compound alone, but it may be combined with a carrier gas, in particular, an inert gas such as helium or argon, if required. In particular helium is a preferred carrier gas as this can minimise fragmentation of the monomer.

When used as a mixture, the relative amounts of the monomer vapour to carrier gas is suitably determined in accordance with procedures which are conventional in the art. The amount of monomer added will depend to some extent on the nature of the particular monomer being used, the nature of the substrate being treated, the size of the plasma chamber etc. Generally, in the case of conventional chambers, monomer is delivered in an amount of from 50-250mg/mm, for example at a rate of from 100-150mg/mm. It will be appreciated however, that the rate will vary depending on the reactor size chosen and the number of substrates required to be processed at once; this in turn depends on considerations such as the annual through-put required and the capital outlay.

Carrier gas such as helium is suitably administered at a constant rate for example at a rate of from 5-90, for example from 15-30sccm. In some instances, the ratio of monomer to carrier gas will be in the range of from 100:0 to 1:100, for instance in the range of from 10:0 to 1:100, and in particular about 1:0 to 1:10. The precise ratio selected will be so as to ensure that the flow rate required by the process is achieved.

In some cases, a preliminary continuous power plasma may be struck for example for from 15 seconds to 10 minutes, for example from 2-10 minutes within the chamber. This may act as a surface pre-treatment step, ensuring that the monomer attaches itself readily to the surface, so that as polymerisation occurs, the coating "grows" on the surface. The pre-treatment step may be conducted before monomer is introduced into the chamber, in the presence of only an inert gas.

The plasma is then suitably switched to a pulsed plasma to allow polymerisation to proceed, at least when the monomer is present.

In all cases, a glow discharge is suitably ignited by applying a high frequency voltage, for example at 13.56MHz. This is applied using electrodes, which may be internal or external to the chamber, but in the case of larger chambers are generally internal.

Suitably the gas, vapour or gas mixture is supplied at a rate of at least 1 standard cubic centimetre per minute (sccm) and preferably in the range of from 1 to l00sccm.

In the case of the monomer vapour, this is suitably supplied at a rate of from 80-300mg/minute, for example at about 120mg per minute depending upon the nature of the monomer, whilst the pulsed voltage is applied. It may however, be more appropriate for industrial scale use to have a fixed total monomer delivery that will vary with respect to the defined process time and will also depend on the nature of the monomer and the technical effect required.

Gases or vapours may be delivered into the plasma chamber using any conventional method. For example, they may be drawn, injected or pumped into the plasma region. In particular, where a plasma chamber is used, gases or vapours may be drawn into the chamber as a result of a reduction in the pressure within the chamber, caused by use of an evacuating pump, or they may be pumped, sprayed, dripped, electrostatically ionised or injected into the chamber as is common in liquid handling.

Polynierisation is suitably effected using vapours of compounds for example of formula (I), which are maintained at pressures of from 0.1 to 400mtorr, suitably at about 10-l0Omtorr.

The applied fields are suitably of power of from 5 to 500W for example from 20 to 500W, suitably at about 100W peak power, applied as a continuous or pulsed field. Where used, pulses are suitably applied in a sequence which yields very low average powers, for example in a sequence in which the ratio of the time on: time off is in the range of from 1:500 to 1:1500.

Particular examples of such sequence are sequences where power is on for 20-50j.is, for example about 3Ops, and off for from l000ps to 30000jis, in particular about 20000ps. Typical average powers obtained in this way are 0.01W.

The fields are suitably applied from 30 seconds to 90 minutes, preferably from 5 to 60 minutes, depending upon the nature of the compound of formula (I) and the item being treated.

Suitably a plasma chamber used is of sufficient volume to accommodate items such as rubber tyres etc. A particularly suitable apparatus and method for treating items in accordance with the invention is described in W02005/089961, the content of which is hereby incorporated by reference.

In particular, when using high volume chambers of this type, the plasma is created with a voltage as a pulsed field, at an average power of from 0.001 to 500w/rn3, for example at from 0.001 to 100w/rn3 and suitably at from 0.005 to 0.5w/rn3.

These conditions are particularly suitable for depositing good quality uniform coatings, in large chambers, for example in chambers where the plasma zone has a volume of greater than 500cm3, for instance O.1m3 or more, such as from 0.5m3-10m3 and suitably at about 1m3. The layers formed in this way have good mechanical strength.

The dimensions of the chamber will be selected so as to accommodate the particular item being treated. For instance, generally cuboid chambers may be suitable for a wide range of applications, but if necessary, elongate or rectangular chambers may be constructed or indeed cylindrical, or of any other suitable shape.

The chamber may be a sealable container, to allow for batch processes, or it may comprise inlets and outlets for the item, to allow it to be utilised in a continuous process as an in-line system. In particular in the latter case, the pressure conditions necessary for creating a plasma discharge within the chamber are maintained using high volume pumps, as is conventional for example in a device with a "whistling leak".

However it will also be possible to process items at atmospheric pressure, or close to, negating the need for whistling leaks".

Items which have been treated in accordance with the method described above and which are novel form a further aspect of the invention.

Thus in particular, the invention provides a vehicle tyre treated in accordance with the method as described above.

Preferred treatments are as outlined above.

Example 1

Three pairs (A, B and C) of heavy duty walking shoes were placed into a plasma chamber with a processing volume of -300 litres. The chamber was connected to supplies of the required gases and or vapours, via a mass flow controller and/or liquid mass flow meter and a mixing injector or monomer reservoir as appropriate.

The chamber was evacuated to between 3 -10 mtorr base pressure before allowing helium into the chamber at 20 sccm until a pressure of 80 mtorr was reached. A continuous power plasma was then struck for 4 minutes using RE' at 13.56 MHz at 300 W. After this period, 1H,1H,2H,2H-heptadecafluorodecylacylate (CAS # 27905-45-9) of formula H(CF) CF3 was brought into the chamber at a rate of 120 milli grams per minute and the plasma switched to a pulsed plasma at 30 micro seconds on-time and 20 milli seconds off-time at a peak power of 100 W for 40 minutes. On completion of the 40 minutes the plasma power was turned off along with the processing gases and vapours and the chamber evacuated back down to base pressure.

The chamber was then vented to atmospheric pressure and the shoes removed.

These were tested for non-slip properties in wet and dry conditions using standard test methods. In particular, the heel was tested making a 5° and 7° contact angle sliding forward, and the forepart tested separately in the centre of the joint (flexing) position sliding backwards. The tests were carried out on three surfaces (dry clay tile, wet clay tile and wet stainless steel. The results were compared for the same shoes but without treatment. These are summarised in the

following Tables:

Untreated Coefficient of Friction Forepart (centre Heel at 5° Contact Sample and flexing area) angle Mean Condition Dry Wet Wet Dry Wet Wet clay clay Stainless clay clay Stainless tile tile steel tile tile steel A Left 0.82 0.73 0.65 0.80 0.71 0.63 0.72 Right 0.82 0.71 0.61 0.78 0.69 0.61 0.70 B Left 0.72 0.47 0.56 0.77 0.55 0.66 0.62 Right 0.79 0.49 0.36 0.81 0.47 0.57 0.58 C Left 0.79 0.63 0.58 0.86 0.70 0.63 0.70 Right 0.91 0.67 0.48 0.89 0.64 0.64 0.71 Treated Coefficient of Friction Forepart (centre Heel at 5° Contact Sample and flexing area) angle Mean Condition Dry Wet Wet Dry Wet Wet clay clay Stainless clay clay Stainless tile tile steel tile tile steel A Left 0.88 0.77 0.61 0.85 0.74 0.65 0.75 Right 0.83 0.76 0.59 0.80 0.70 0.56 0.71 B Left 0.84 0.51 0.41 0.89 0.57 0.49 0.62 Right 0.83 0.52 0.43 0.92 0.60 0.41 0.62 C Left 0.82 0.70 0.46 0.85 0.70 0.55 0.68 Right 0.90 0.77 0.65 0.87 0.79 0.70 0.78 Untreated Coefficient of Friction Forepart (centre Heel at 7° Contact Sample and flexing area) angle Mean Condition Dry Wet Wet Dry Wet Wet clay clay Stainless clay clay Stainless tile tile steel tile tile steel A Left 0.80 0.68 0.49 0.81 0.70 0.57 0.67 Right 0.82 0.68 0.43 0.77 0.63 0.47 0.63 B Left 0.82 0.34 0.37 0.87 0.36 0.45 0.54 Right 0.80 0.43 0.32 0.90 0.42 0.41 0.55 C Left 0.86 0.66 0.44 0.84 0.64 0.45 0.65 Right 0.88 0.59 0.34 0.81 0.63 0.42 0.61 Treated Coefficient of Friction Forepart (centre Heel at 70 Contact Sample and flexing area) angle Mean Condition Dry Wet Wet Dry Wet Wet clay clay Stainless clay clay Stainless tile tile steel tile tile steel A Left 0.90 0.66 0.40 0.90 0.70 0.57 0.69 Right 0.84 0.63 0.47 0.80 0.65 0.53 0.65 B Left 0.89 0.36 0.33 1.01 0.49 0.46 0.59 Right 0.90 0.34 0.28 0.99 0.48 0.35 0.56 C Left 0.91 0.69 0.36 0.88 0.66 0.44 0.66 Right 1.05 0.40 0.30 1.00 0.38 0.40 0.59 In most cases, the coefficient of friction of the shoes was slightly higher than the untreated shoe, although the increase was generally not very significant. Certainly the overall performance of the treated shoes was no worse than the untreated shoes in this test. However, the treated shoes were significantly more water-proof than the untreated shoes.

Claims

Claims 1. A method for maintaining the coefficient of friction of an item whilst enhancing its oil and/or water repellent properties, the method comprising forming an oil or water repellent coating or surface modification thereon by ionisatiofl or activation technology.
2. A method according to claim 1 wherein the item is a shoe.
3. A method according to claim 1 where the item is a vehicle tyre.
4. A method according to any one of the preceding claims wherein the surface energy of the surface of the item is less than 15 mNm1.
5. A method according to any one of the preceding claims wherein the ionisation or activation technology is plasma processing.
6. A method according to claim 5 wherein the plasma processing uses a plasma which comprises a monomeric compound which undergoes plasma polyrnerisatiorl to form an oil or water repellent polymer, and the item is exposed for a sufficient period of time to allow a uniform polymeric layer to form on the surface thereof.
7. A method according to claim 5 or claim 6 wherein the item is exposed to pulsed plasma within a plasma deposition chamber.
8. A method according to claim 6 or claim 7 wherein the monomeric compound is a compound of formula (I) where R1, R2 and R3 are independently selected from hydrogen, alkyl., haloalkyl or aryl optionally substituted by halo; and R4 is a group -X-R5 where R5 is an alkyl or haloalkyl group and X is a bond; a group of formula -C(O)O-, a group of formula -C(O)O(CH2)Y -where n is an integer of from 1 to 10 and Y is a sulphonamide group; or a group (O)pR6(O)q(CH2)t where R6 is aryl optionally substituted by halo, p is 0 or 1, q is 0 or 1 and t is 0 or an integer of from 1 to 10, provided that where q is 1, t is other than 0.
9. A method according to claim 8 wherein the compound of formula (III) is a compound of formula (IV) H(CF) CF3 (IV) where R7 is where R7 is hydrogen or alkyl, and x is an integer of from 1 to 9.
10. A method according to claim 9 wherein the compound of formula (IV) is 1H,1H,2H,2H-heptadecafluorodecylacylate.
11. A method according to claim 6 or claim 7 wherein the monomeric compound is a compound of formula (V) R8 R1OR11 (V) where R8, R9, R10, R'1, R12, and R'3 are all independently selected from hydrogen, halo, alkyl, haloalkyl or aryl optionally substituted by halo; and Z is a bridging group, or a a compound of formula (VII) R16 R17 R18 j R19 R2° R21 (VII) where R16, R17, R18' R19 and R2° are independently selected from hydrogen, halogen, alkyl, haloalkyl or aryl optionally substituted by halo; and R21 is a group X-R22 where R22 is an alkyl or haloalkyl group and X is a bond; a group of formula -C(O)O(CH2)Y-where x is an integer of from 1 to 10 and Y is a bond or a sulphonamide group; or a group -(O)R23(O)5(CH2)-where R23 is aryl optionally substituted by halo, p is 0 or 1, s is 0 or 1 and t is 0 or an integer of from 1 to 10, provided that where s is 1, t is other than 0, or a compound of formula (VIII) R24-CC-X1-R25 (VIII) where R24 is hydrogen, alkyl, cycloalkyl, haloalkyl or aryl X' is a bond or a bridging group; and R25 is an alkyl, cycloalkyl or aryl group optionally substituted by halogen.
12. A method according to any one of the preceding claims wherein the item is placed in a plasma deposition chamber, a glow discharge is ignited within said chamber, and a voltage

applied as a pulsed field.
13. A method according to claim 12 wherein applied voltage is at a power of from 5 to 500W.
14. A method according to claim 12 or claim 13 wherein the voltage is pulsed in a sequence in which the ratio of the time on: time off is in the range of from 1:500 to 1:1500.
15. A method according to claim 14 wherein the voltage is pulsed in a sequence where power is on for 20-5Ops, and off for from 1000ps to 30000jis.
16. A method according to any one of claims 12 to 15 wherein the voltage is applied as a pulsed field at for a period of from 30 seconds to 90 minutes.
17. A method according to any one of claims 12 to 16, wherein in a preliminary step, a continuous power plasma is applied to the item.
18. A method according to claim 17 wherein the preliminary step is conducted in the presence of an inert gas.
19. A method according to any one of claims 12 to 18 wherein the compound of formula (I) in gaseous form is fed into the plasma at a rate of from 80-300 mg/minute, whilst the pulsed voltage is applied.
20. A method according to any one of claims 12 to 19 wherein the plasma is created with a voltage at an average power of from 0.001 to 500w/rn3.
21. The use of a plasma polymerisation deposition process for the deposition of an oil and/or water repellent coating on an item without increasing the coefficient of friction of the item.
22. A vehicle tyre, treated by a method according to any one of claims 1 to 20.