Surface coatings

Details Surface coatings Surface coatings

2000-02-11

2003-04-22

Barr, Michael (Department: 1762)

Fabric (woven, knitted, or nonwoven textile or cloth, etc.)

Coated or impregnated woven, knit, or nonwoven fabric which...

Coating or impregnation specified as water repellent

C442S043000, C442S059000, C442S063000, C428S102000, C427S490000, C427S492000, C427S513000, C427S569000

Reexamination Certificate

active

06551950

ABSTRACT:

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 fluoropolymer 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., ‘Handbood 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, has previously been subjected to plasma polymerisation (Chem. Mater. Vol. 8, 1, 1996).
U.S. Pat. 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 a monomeric unsaturated organic compound which comprises an optionally substituted hydrocarbon group, wherein the optional substituents are halogen; provided that where the compound is a straight chain perhalogenated alkene, it includes at least 5 carbon atoms; so as to form an oil or water repellent coating on said substrate.
Unsaturated organic compounds are those which contain at least one double bond which is capable of reacting to form a polymeric compound. The compounds used in the method of the invention suitably include at least one optionally substituted hydrocarbon chain. Suitable chains, which may be straight or branched, have from 3 to 20 carbon atoms, more suitably from 6 to 12 carbon atoms
Monomeric compounds used in the method may include the double bond within a chain and so comprise alkenyl compounds. Alternatively, the compounds may comprise an alkyl chain, optionally substituted by halogen, as a substitutent which is attached to an unsaturated moiety either directly or by way of an functional group, such as a ester or sulphonamide group.
As used therein the term “halo” or “halogen” refers to fluorine, chlorine, bromine and iodine. Particularly preferred halo groups are fluoro. The term hydrocarbon includes to alkyl, alkenyl or aryl groups. 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 20 carbon atoms in length. The term “alkenyl” refers to straight or branched unsaturated chains suitably having from 2 to 20 carbon atoms.
Monomeric compounds where the chains comprise unsubstituted alkyl or alkenyl groups are suitable for producing coatings which are water repellent. By substituting at least some of the hydrogen atoms in these chains with at least some halogen atoms, oil repellency may also be conferred by the coating.
Thus in a preferred aspect, the monomeric compounds include haloalkyl moieties or comprise haloalkenyls. Therefore, preferably the plasma used in the method of the invention will comprise a monomeric unsaturated haloalkyl containing organic compound.
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.
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.
Particularly suitable monomeric organic compounds are those of formula (I)
where R
1
, R
2
and R
3
are independently selected from hydrogen, alkyl, haloalkyl or aryl optionally substituted by halo; and R
4
is a group X—R
5
where R
5
is an alkyl or haloalkyl group and X is a bond; a group of formula —C(O)O(CH
2
)
n
Y— where n is an integer of from 1 to 10 and Y is a bond or a sulphonamide group; or a group —(O)
p
R
6
(O)
q
(CH
2
)
t
— where R
6
is aryl optionally substituted by halo, p is 0 or 1, q is 0 or

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