PT2275598E - Surface coatings - Google Patents

Abstract

A method of coating a surface with an oil and water repellent polymer layer, which method comprises exposing said surface to a continuous wave plasma comprising the compound of formula (I) €ƒ€ƒ€ƒ€ƒ€ƒ€ƒ€ƒ€ƒ CH 2 = CR 7 C(O)O(CH 2 ) n R 5 €ƒ€ƒ€ƒ€ƒ€ƒ(I) where n is an integer of from 1 to 10, R 7 hydrogen or C 1-6 alkyl and R 5 is a C 6-20 perhaloalkyl group.

Description

DESCRIPTION " Surface Coatings " The present invention relates to coating surfaces, in particular to the manufacture of oil and water impermeable surfaces, as well as the coated articles obtained therefrom.

Oil and water impermeable treatments for a wide variety of surfaces are in common use. For example, it may be desirable to communicate such properties to solid surfaces, such as metal, glass, ceramics, paper, polymers etc., in order to improve their preservation properties, or to prevent or prevent dirt.

A particular substrate, which requires such coatings, consists of fabrics, in particular for applications in outdoor clothing, sportswear and leisure clothing and in military applications. Their treatments generally require the incorporation of a fluoropolymer into or more particularly attached above the surface of the garment fabric. The degree of oil or water tightness is a function of the number and length of fluorocarbon groups or parts that may be placed within the space available. The higher the concentration of these parts, the greater the waterproofing of the finish.

In addition, however, the polymeric compounds must be capable of forming durable bonds with the substrate. The treatments of oil and water impermeable textiles are generally based on fluoropolymers which are applied to the fabric in the form of an aqueous emulsion. The fabric remains breathable and air permeable since the treatment simply coats the fibers with a very thin, liquid impermeable film. In order to render these finishes durable, they are sometimes applied in conjunction with crosslink resins which attach the fluoropolymer treatment to the fibers. While good durability levels for washing and dry cleaning can be achieved in this way, the crosslink resins can seriously spoil the cellulosic fibers and reduce the mechanical strength of the material. Chemical methods for the manufacture of oil- and water-impermeable textiles are shown for example in WO 97/13024 and British patent No. 2,110,903 or in the book by M. Lewin et al., &Quot; Handbook of Fiber Science and Technology " Marcel and Decker Inc., New York (1984) Vol 2, Part B Chapter 2.

Plasma deposition techniques have been widely used for the deposition of polymer coatings on a range of surfaces. This technique is recognized as being a clean, dry technique which creates little waste compared to conventional wet chemical methods. Using this method, the plasmas are generated from small organic molecules, which are subjected to an ionizing electric field in a low pressure environment. When this is done in the presence of a substrate, excited ions, radicals and molecules of the compound in the plasma polymerize in the gas phase and react with an increasing polymer film on the substrate. Conventional synthesis of the polymer tends to produce structures containing repeating units which show a strong resemblance to the monomer species, given that the polymer network generated using a plasma can be extremely complex. The success or otherwise of plasma polymerization depends on a number of factors, including the nature of the organic compound. Reactive oxygen containing compounds such as maleic anhydride, has previously been subjected to plasma polymerization (Chem. Mater. Vol. 8, 1. 1996). U.S. Patent No. 5,328,576 describes the treatment of paper fabrics or surfaces to impart liquid sealing properties to them by subjecting the surfaces to pretreatment with an oxygen plasma followed by plasma methane polymerization.

However, plasma polymerization of the desirable oil and water impermeable fluorocarbons has proved more difficult to achieve. Cyclic fluorocarbons have been reported to undergo plasma polymerization more readily than their acyclic counterparts (H. Yasuda et al., J. Polym. Sci, Polym. Chem. Ed., 1977, 15, 2411). Plasma polymerization of trifluoromethyl substituted perfluorocyclohexane monomers has been reported (A. M. Hynes et al., Macromolecules, 1996, 29, 18-21).

A process in which the textiles are subjected to a plasma discharge in the presence of an inert gas and subsequently exposed to a fluorine-containing acrylic monomer is described in SU-1158-634. A similar process for the deposition of a fluoroalkyl acrylate coating on a solid substrate is described in European patent application no. Japanese Patent Application No. 2,816,773 describes plasma polymerization of compounds including fluoro-substituted acrylates. In that process, a mixture of acrylate compounds with fluoro-substituted and an inert gas is subjected to an incandescent discharge. US 5 041 304 describes plasma polymerization of partially fluorinated alkenes and alkanes and cycloalkanes perfluorinated at atmospheric pressure by incandescent discharge of a gas mixture containing an inert gas. The mentioned compounds include, for example, fluoropropylene, difluoropropylene, etc., difluorobutene, trifluorobutene, etc., but preferred are perfluorinated compounds such as hexafluoropropylene and octafluorocyclobutane.

Applicants have discovered an improved method of producing halo-polymer coatings which are impermeable to water and / or oil on the surfaces.

According to the present invention there is provided a surface coating method with an oil-impermeable polymer layer and water, wherein the method comprises exposing said surface to a pulsed plasma field comprising the compound of formula (I) CH 2 = CHC (O) O (CH 2) n R 5 (I)

Where the average power of the field is less than 1W, n is an integer from 1 to 10 and R5 is a per-haloC6-20 alkyl group.

As used herein the term " halo " or " halogen " refers to fluoro, chloro, bromo and iodo. In particular, preferred halo groups are fluoro. Preferably, R5 is a perfluoroalkyl group of the formula CmF2m + i, where m is an integer from 6 to 12, such as 8 or 10. The term the hydrocarbon includes the alkyl, alkenyl or aryl groups. The term " aryl " refers to aromatic cyclic groups, such as phenyl or naphthyl, in particular phenyl. &Quot; alkyl " refers to the straight or branched chains of carbon atoms, suitably up to 20 carbon atoms in length. The term " alkenyl " refers to unsaturated straight or branched chains having suitably 2 to 20 carbon atoms.

Monomeric compounds in which the chains comprise unsubstituted alkyl or alkenyl groups are suitable for the production of coatings which are impermeable to water. By substituting at least some of the hydrogen atoms in these chains for at least a few halogen atoms, the waterproofing to the oil may also be provided by the coating.

Plasmas suitable for use in the method of the invention include unbalanced plasmas such as those created by radio frequency (Rf), microwave or DC (direct current) frequencies. They may operate at atmospheric or sub-atmospheric pressures as is well known in the art. The plasma may comprise only the monomeric compound, in the absence of other gases or mixed for example with an inert gas. Plasmas consisting solely of the monomeric compound can be achieved as shown below by first discharging the reactor vessel to the extent 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.

All compounds of formula (I) are known compounds or they may be prepared from known compounds using conventional methods. The coated surface according to the invention may be any solid substrate, such as fabrics, metal, glass, ceramics, paper or polymers. In particular, the surface comprises a woven substrate such as a cellulosic fabric to which oil and / or water waterproofing is to be applied. Alternatively, the fabric may be a synthetic fabric such as a nylon / acrylic fabric. The tissue may not be treated or may have undergone previous treatments. For example, it has been found that the treatment according to the invention can increase water impermeability and impart a good oil-impermeable finish to a fabric which already has a silicone finish which is only impermeable to water.

The exact conditions in which the plasma polymerization takes place in an efficient manner will vary depending upon such factors as the nature of the polymer, the substrate, etc., and will be determined using routine methods and / or techniques illustrated below. In general, the polymerization is conveniently carried out using vapors of compounds of formula (I) at pressures of from 0.01 to 10 mbar, suitably about 0.2 mbar.

An incandescent discharge is then triggered by the application of a high frequency voltage, for example 13.56 MHz.

Suitable conditions include continuous fields. The pulsations are applied in a sequence which produces very low average powers, for example of less than 10 W and preferably less than 1 W. Examples such frequencies are those in which the current is switched on for off for 1 000 s to 20 000 s.

The fields are conveniently applied for a period sufficient to give the desired coating. In general, this will be from 30 seconds to 20 minutes, preferably from 2 to 15 minutes, depending on the nature of the compound of formula (I) and the substrate, etc. Plasma polymerization of the compounds of formula (I), particularly at low average potencies, has been found to result in the deposition of highly fluorinated coatings exhibiting super water impermeability. In addition, a high level of structural retention of the compound of formula (I) occurs in the coating layer, which can be attributed to the direct polymerization of the alkene monomer, by means of its highly sensitive double bond.

Because the compound of formula (I) includes a perfluoroalkylated tip or portion, the process of the invention may have oil and water impermeability surface properties.

Thus, the invention further provides a substrate with water and / or oil impermeability which comprises a substrate comprising a coating of a haloalkyl polymer which has been applied by the method described above. In particular, the substrates are woven but may be solid materials such as biomedical devices. The invention will now be particularly described by way of example, with reference to the accompanying schematic drawings, in which: Fig. 1 shows a diagram of the apparatus used to effect plasma deposition; Fig. 2 is a graph showing the characteristics of a 1H, 1H, 2H-perfluoro-1-decene continuous wave plasma polymerization; Fig. 3 is a graph showing the pulsed plasma polymerization characteristics of 1H, 1H, 2H-perfluoro-1-dodecene at 50 W Pp, Ton = 20 s e0 = 10000 s for 5 minutes; and Fig. 4 is a graph showing the characteristics of a continuous (a) and (b) pulsed plasma polymerization of 1H, 1H, 2H, 2H-heptadecafluorodecyl acrylate.

Comparative Example 1

Alkene 1 H, 1H, 2H-perfluoro-1-dodecene (C 10 F 12 Cl CH 2) (Fluorochem F 06003, 97% purity) plasma polymerization was placed into the further purified monomer tube (1) (Fig. 1) using freezing and thawing cycles. A series of plasma polymerization experiments were performed in an induction-connected (5) cylindrical plasma reactor vessel 4 cm 3 by volume, base pressure of 7 × 1 3 mbar, and with a flow rate of greater than 2 × 1 3 cm 3 min -1. The reactor vessel (2) was connected by means of a " viton " (3) to a gas inlet (4) and a needle valve (5) to the monomer tube (1).

A pressure gauge thermocouple (6) was connected by a Young tap (7) to the reactor vessel (2). Another Young tap 8 has been connected to the air supply and a third 9 leads to a two-stage Edwards rotary pump E2M2 (not shown) by means of a cold liquid nitrogen siphon (10). All connections were fat free.

An LC junction 11 and a power meter 12 were used to connect the output of a 13.56 MHz radio frequency generator 13 which was connected to a power supply 14 to the coils of copper (15) surrounding the reactor vessel (2). This arrangement ensured that the steady-wave ratio (SWR) of the energy transmitted to the partially ionised gas in the reactor vessel (2) could be minimized. For pulsed plasma deposition, a pulsed signal generator (16) was used to trigger the radio frequency energy supply, and a cathode ray oscilloscope (17) was used to control the pulse width and amplitude. The mean energy < P > supplied to the system during pulsation is given by the following formula: < P > = P cw {T on / (Ton Ί "Toff)} where Ton / (Ton + Toff) is defined as the service cycle and Pcw is the average energy of the continuous wave. In order to carry out the polymerization / deposition reactions the reactor vessel (2) was cleaned by immersing it overnight in a chlorinated bleach bath, then wiping with detergent and finally rinsing with isopropyl alcohol followed by oven drying. The reactor vessel (2) was then incorporated into the assembly as shown in Fig. 1 and further cleaned with a 50 W air plasma for 30 minutes. The reactor vessel 2 was then air-vented and the substrate to be coated 19, in this case a glass slide, was placed in the center of the chamber defined by the reactor vessel 2 in a glass plate 18. The chamber was then evacuated to the base pressure (7.2 x lH 3 mbar).

Perfluoroalkene vapor was then introduced into the reaction chamber at a constant pressure of ~ 0.2 mbar and allowed to bleed the plasma reactor, followed by ignition of the incandescent discharge. Typically a settling time of 2-15 minutes has been found to be sufficient to give complete coverage to the substrate. Thereafter, the radio frequency generator was shut down and the perfluoroalkene vapor was allowed to continue to pass over the substrate for a further 5 minutes before evacuating the reactor back to the base pressure, and finally ventilating it at atmospheric pressure.

Polymer deposited plasma coatings were characterized immediately after deposition by X-ray Photoelectron Spectroscopy (XPS). Full coverage by the plasma polymer was confirmed by the absence of any Si signals in the XPS (2p) as it passes through the underlying glass substrate.

A control experiment where the fluoroalkene vapor was allowed to pass over the substrate for 15 minutes and then pumped to the base pressure allowed to show the presence of a large Si signal in XPS (2p) originating from the substrate. Therefore coatings obtained during plasma polymerization are not only due to the absorption of the fluoroalkene monomer on the substrate.

The experiments were performed with average powers of the order of 0.3 to 50 W. The XPS spectrum results of a plasma polymer deposition with a 0.3 W continuous wave on a glass slide for 13 minutes are shown in Fig . 2.

It can be seen that CF2 and CF3 are the main environments in the C (ls) envelope in XPS: CF2 (291.2 eV) 61% CF3 (293.3 eV) 12%

The remaining carbon environments comprised partially fluorinated carbon centers and a small amount of hydrocarbon (CxHy). The experimental and theoretically predicted values (taken from the monomer) are given in Table 1.

The difference between the theoretical and experimental percentages of the CF2 group and the CF3 group can be attributed to the small amount of perfluoroalkene monomer fragmentation.

Fig. 3 shows the XPS spectrum of C (ls) for a 5 minute pulsed plasma polymerization experiment where: - Pcw = 50 W Ton = 20 S

Toff = 10,000 s < P > = 0.1 w The chemical composition of the deposited coating for a pulsed plasma deposition is given in Table 2 below.

It can be seen that the CF2 region is better resolved and has a higher intensity which means less perfluoroalkyl tip fragmentation compared to continuous wave plasma polymerization.

Surface energy measurements were performed on slides produced in this manner using dynamic contact angle analysis. The results showed that the surface energy was of the order of 5-6 mJnm -1.

Lisbon, 2015-01-22

Claims (6)

A method for coating a surface with a polymer layer, wherein the method comprises exposing said surface to a continuous wave plasma field, comprising a compound of the formula (I), CH 2 = CHC (O) Wherein the average power of the field is less than 1 W, n is an integer from 1 to 10 and R 5 is a perhalo C 20 -alkyl group. A method according to claim 1, wherein R 5 is a perfluoroalkyl group of the formula Cm F 2m + i, where m is an integer from 6 to 12. A method as claimed in claim 1 or claim 2, wherein the surface is a surface of a fabric, metal, glass, ceramic, paper, or polymer substrate. A method according to claim 3, wherein the substrate is a tissue. A method according to any preceding claim, wherein the incandescent discharge is ignited in an atmosphere containing the compound at a gas pressure of from 0.01 to 10 mbar by a high frequency voltage. A method according to any preceding claim, wherein the plasma polymerization is carried out for 2 to 15 minutes. Lisbon, 2015-01-22