GB2479154A

GB2479154A - Electron flux coated substrate

Info

Publication number: GB2479154A
Application number: GB1005365A
Authority: GB
Inventors: John Topping; David Anthony
Original assignee: Camvac Ltd
Current assignee: Camvac Ltd
Priority date: 2010-03-30
Filing date: 2010-03-30
Publication date: 2011-10-05
Also published as: GB201005365D0

Abstract

A process for coating a substrate (2) comprising condensing a radiation curable organic material (5') containing a saturated covalent bond on a substrate and curing it using an electron flux (6') with energy between 1.6eV and 300eV, whereby the electron flux (6') is extracted from a low pressure gas plasma (6) and directed from the low pressure gas plasma towards the substrate. An example of a radiation curable organic material is Parylene (RTM) C (di-chloro-di-p-xylene).

Description

Radiation-Cured Coatings

Technical Field

Films having enhanced barrier properties for oxygen or other gases or odours or water vapour are produced by depositing alternate layers of cured polymer and metal or compounds onto a web substrate using processes such as vacuum deposition. These films are useful for packaging of oxygen or moisture sensitive foodstuffs, encapsulation of gas or moisture sensitive components, and a variety of other functional applications requiring barrier properties. Films are also manufactured having an enhanced holographic effect, isotropic light scattering or colour shift by depositing alternate layers of a transparent or translucent cured polymer and a metal onto a web substrate.

It is known to deposit layers of cured polymer onto a web substrate using vacuum deposition and radiation curing. However, the existing processes of vacuum condensation and curing of unsaturated polymer precursors have a number of drawbacks/risks, associated with impurities in the commercial grades of raw materials used, particularly for the substrate, or with the toxicity of the precursors, or inherent in the process itself The risks associated with impurities in the substrate, such as the inhibition of polymerisation of the condensate by oxygen adsorbed in the substrate and associated adhesion problems, or uneven wetting due to contaminants or low molecular weight species on the substrate surface, can often be alleviated by plasma treatment of the substrate before coating e.g. with a gas plasma. However, other problems inherent in the process are more difficult to overcome. For example: a) It is known that the condensate can re-evaporate before reaching the curing zone.

This vapour can then potentially contaminate the pumps, or become entrained with the moving web, re-condensing on the surface of the cured coating as an uncured, and therefore weak surface layer (giving poor adhesion of any subsequent coatings applied to the material).

b) It is known that as the curing of the condensate only takes place within the zone of irradiation, at high line speeds (essential for an economically viable process), 100% polymerisation is difficult to achieve, particularly at the surface adjacent to the substrate and thus furthest from the radiation source. Increasing the radiation flux to increase curing can result in over-curing and embrittlement of the top surface of the coating closest to the radiation source, whilst still leaving the bottom surface under-cured and with poor adhesion. It is difficult therefore to achieve the homogeneity of curing through the thickness of the coating desirable for good mechanical strength, adhesion or barrier.

c) It is known that if the precursor vapour or atomised monomer is passed through the radiation flux prior to delivery on the substrate, it can partially polymerise, giving rise to a non-homogeneous and mechanically weak coating with poor adhesion. This phenomenon is known in the art as "snowing".

d) It is known that if the coating is cured using a charged radiation flux, such as a high energy electron beam, the resultant coated web can "block" (i.e. stick to itself) when it is wound up into a roll, and then later tear when it is unwound. The risk of damage on unwinding is further accentuated by poor homogeneity through the coating.

e) It is known that the surfaces of cured films produced by the processes already known in the art have to be further treated (e.g. with a plasma) before they can be further coated.

Various radiation sources have been used to cure unsaturated polymer precursors once condensed on a substrate, for example ultraviolet, visible or infra-red or, particularly, electron beam radiation. However, the electron beams currently used in the art for primary curing have very high energy levels (generally >300eV), as this is considered necessary to achieve sufficient polymerisation. Atmospheric plasmas are also used, generally for secondary curing (i.e. as an adjunct to electron beam, to complete the cure). Again, these have high energy levels, and high ionisation fractions, and the prior art teaches that this high level of ionisation is essential for polymerisation.

It is also known to pass an unsaturated monomer vapour or atomised unsaturated monomer through a low pressure glow discharge containing a high level of free radicals, and then direct it towards the substrate using a driving voltage in the glow discharge which is positive with respect to the local conditions at the substrate. This generates free radicals in the monomer, which then initiate curing of the monomer on the substrate.

It is also known to pass an unsaturated monomer vapour or atomised unsaturated monomer through a low pressure gas plasma generated using a microwave or radio frequency (RF) source. However, such higher frequency sources can be subject to intermittent breakdown (e.g. arcing), which can both damage the coating and give rise to short lengths of web in which the coating is only partially cured. This is particularly a problem where the web speed needs to be high (e.g. for cost reasons), and the dwell time in the reaction zone consequently short.

A problem with some unsaturated precursors used in the art is that they have relatively high levels of toxicity, and if the curing process is not continuous or complete, free monomer can be present in the coatings, making them unsuitable for direct food contact, or for use in ethical applications.

It is also known to produce barrier coatings on materials or articles via evaporation and thermal decompositionlpolymerisation of precursors containing saturated covalent bonds.

For example, coatings of poly(para-xylylene) or its derivatives (commonly known as Parylenes) can be produced by evaporating dipara-xylylene and inducing the polymerising reaction to Parylene-C at temperatures of ca 600°C. However, this process can give rise to problems when carried out on web materials, and particularly plastic web materials, which generally have melting points or transition temperatures well below 600°C. The requirement for a secondary thermal curing step can also limit coating speed.

Disclosure of the Invention

According to a first aspect of the present invention, there is provided a process for coating a substrate comprising condensing a radiation curable organic material containing a saturated covalent bond on a substrate and curing it using an electron flux with energy between 1.6eV and 300eV, whereby the electron flux is derived from a low pressure gas plasma.

Despite the fact that the claimed electron flux has significantly lower energy levels (<300eV) than electron beams, atmospheric plasmas etc, it has been found that effective curing can be achieved. The lower energy level is that needed to break the saturated covalent bond in the precursor material, in order to induce polymerisation. This lower energy level will vary according to the nature of the covalent bond. For example, bonds such as 0-0 can be broken using an energy of ca 1.6eV, whereas a C-C bond will require an energy of ca 3.5eV to break it. Preferably, the electron flux energy range is between the lower energy level defined above and 100eV.

Due to the electron flux being extracted from the low pressure gas plasma, and directed away from the plasma towards the substrate, substantially only the electron flux is used to cure the radiation curable material. The electron flux isolated from the plasma can penetrate deeper into the radiation curable material than would be possible if the ionised gas defining the plasma was itself used for curing, using the same voltages. Due to the fact that the extracted electron flux can penetrate deeper into the radiation curable material, it can provide better curing through interactions with the radiation curable material as it penetrates it. This provides a useful synergy with the radiation curable material delivery system used in embodiments of the present invention and can enable an increased delivery rate of the radiation curable material. Furthermore, any arcing that occurs at or adjacent the plasma source will generally not damage the cured material because the web supporting the radiation curable material can be spaced from the plasma source due to the fact that an extracted, directional, beam of electron flux is used to cure the radiation curable material.

Furthermore, the dose of the extracted electron flux applied to the substrate can be greater than that needed to cure the radiation curable material, without damaging the radiation curable material due to the fact that substantially only electrons are used to cure the polymer (electrons having a lower mass and thus lower momentum than, say, argon particles).

The electron flux may be directed at the substrate either simultaneously or sequentially with delivery of the precursor material. In the former case, curing is preferably initiated spatially and temporally concurrently with delivery of the precursor material to the substrate, which avoids the need for the electron flux to penetrate the condensed precursor material in order to cure it.

The electron flux may be derived from a low pressure gas plasma generated using a magnetron.

The low pressure gas plasma may be magnetically enhanced by, for example, incorporating crossed magnetic and electric fields to form a magnetron. A cathode is provided in the form of a sputter cathode or polarised reaction plate. A negative polarity on the cathode and the relative positive polarity of the surroundings or substrate (possibly positive or earthed), drive the required electron flux. Alternatively, a high frequency AC discharge signal may be applied to the cathode, and the physical nature of the self bias and the very low time period of the AC source produces the appropriate polarity at the cathode.

All of the radiation curable material may pass through the flux prior to condensing on the surface of the substrate.

The substrate may comprise a web which is composed of a plastics film; or is composed of polyester or a polyolefin or a polyamide or polyethylene terephthalate or polyethylene naphthalate or a mixture of polyethylene terephthalate and polyethylene naphthalate; or is obtained from a renewable resource; or comprises a fibrous material, paper or textile or polylactic acid or a cellulose derivative.

The substrate may comprise a plastics film which is pre-coated with an inorganic barrier material; or a metal; or a conductive organic or inorganic material; or aluminium or aluminium oxide or an oxide of silicon; or a conductive organic or inorganic material; or copper.

The saturated covalent bond in the precursor material may be C-C, 0-0, N-N, S-S, Si-Si, C-N or any other combination of these elements.

The precursor material may be cyclic. The precursor material may be dipara-xylylene or a derivative thereof The method according to embodiments of the present invention can obviate the need to perform the secondary thermal curing step identified above because electrons impinging upon the condensing dimer vapour with energies in excess of 3.5eV can cause the rearrangement induced by the secondary thermal curing step, which can increase the ease and speed of the process.

The cured polymer coating may contain a mixture of dielectric domains so as to provide a scattering enhanced iridescent appearance.

The coated substrate may be subsequently coated with a further layer of an inorganic barrier material or with a plurality of alternate layers of inorganic barrier and polymer materials.

The substrate may comprise an aluminium or aluminium oxide coated plastic film and may be coated with radiation cured material and recoated with a further layer of aluminium or aluminium oxide to produce an enhanced barrier to oxygen, other gases, water vapour, odour or taint.

The adhesion of the various layers may be sufficient to prevent delamination during any subsequent conversion or use; or the permeability of the product to oxygen, other non-condensable gases or water vapour may be at least one order of magnitude lower than the inherent permeability of the web; or the polymerised radiation curable material may form a coating in the substrate that provides abrasion protection to any underlying functional layers during conversion or use.

Embodiments of the invention serve to reduce the risk of re-evaporation and "snowing" and produce a more homogenously cured coating. The tendency to "blocking" is reduced, and the substrate surface does not need further treatment before recoating. The process of the invention can therefore be run at higher line speeds, thereby reducing unit production costs.

According to a second aspect of the present invention there is provided a coated substrate produced by the process of the first aspect.

The cured polymer coating may contain a mixture of dielectric domains giving it a scattering enhanced iridescent appearance. This iridescent appearance may be further enhanced and a colour shift affect achieved if the coating has a thickness of approximately one quarter of the wavelength of the incident light and/or it is deposited on a substrate which has been coated with a reflective metal layer and/or it is further coated with a semi-transparent layer of metal or other high refractive index material.

The adhesion of the various layers of the product may be sufficient to prevent delamination during any subsequent conversion or use.

The permeability of the product to oxygen, other non-condensable gases or water vapour may be at least one order of magnitude lower than the inherent permeability of the web The polymerised radiation curable material may form a coating in the substrate that provides abrasion protection to any underlying functional layers during conversion or use.

Description of the Drawings

Figure 1 is a schematic drawing of apparatus for carrying a process according to a first embodiment of the invention; Figure 2 is a schematic drawing of apparatus for carrying out a process according to a second embodiment of the invention; Figure 3 is a schematic drawing that illustrates the radiation and vapour flows in Figure 1; Figure 4 is a schematic drawing that illustrates a plasma source for use in Figures 1 to 3; Figures 5a and 5b are schematic drawings that illustrate a precursor source for use in Figure ito 3; Figure 6 is a schematic drawing that illustrates an alternative precursor source for use in Figures i to 3; Figure 7 is a schematic drawing that illustrates another alternative precursor source for use in Figures ito 3, and io Figure 8 is a schematic drawing showing configuration for sequential delivery and cure.

Embodiments of the Invention iS As a general overview, embodiments of the present invention relate to in-vacuo coating of web substrates with organic compounds containing saturated covalent bonds, with concurrent or consecutive curing of said compounds with an electron flux derived from a low pressure gas plasma, and processes and equipment for this. By coating with a layer of cured polymer, or one or more alternate layers of cured polymer and metal or compounds, the barrier properties for oxygen or other gases or odours or water vapour are enhanced.

These films are useful for packaging of oxygen or moisture sensitive foodstuffs, packaging of oxygen or moisture sensitive articles or components for use in ethical applications, encapsulation of gas or moisture sensitive articles or components (including those for ethical applications), and a variety of other applications.

The apparatus in Figure i is housed in a vacuum chamber i. A web 2 to be treated is fed over idle rollers 3, 7 between web unwind and rewind stations (not shown). The web is fed past a deposition station 4 defined by an enclosure 38 in which is housed a device 5 that generates a directional beam 5' of a radiation curable material, and a low pressure gas plasma source 6 that generates a directional electron flux 6'. The flux 6' may comprise electrons and other negatively charged or non-charged particles and species 6' but the electron flux is the primary curing agent. As will be known to a person skilled in the art, a low pressure gas plasma defines a localised electron flux that forms part of the plasma.

The apparatus according to embodiments of the present invention isolates at least some of the electron flux from the plasma and directs the electron flux away from the plasma and towards the web 2. The ionisation fraction might typically be 10 to 10'. The beam of radiation curable material, such as a polymer precursor vapour or atomised liquid, is directed at the web 2 as it passes below device 5, and the plasma source 6 simultaneously directs the electron flux 6' at the web 2 to be incident on the web generally concurrently with the beam 5'. The beam 5' and flux 6' overlap so that the overlap region is exposed to the electron radiation during delivery, thereby to initiate curing as the vapour is delivered to the web 2. The enclosure 38 serves to support a differential pressure between the inside of the enclosure and the vacuum chamber 1 so as to control escape of the precursor vapour and process gases outside of the enclosure. The apparatus can optionally have surface treatment stations 8 and 9 to enhance the properties of the web prior to and after the deposition station 4.

An alternative embodiment of the invention is illustrated in Figure 2 in which the linear feed of the web 2 between rollers 3, 7 is supplemented by a rotating drum feed 10. The rotating drum 10 allows additional treatment processes to take place, e.g., further depositing stations 11, 12 for coating metallic or non-metallic compounds before and after the deposition station 4, and treatment stations 13, 14 to enhance the properties of the film before and after the optional depositing stations 11 and 12.

Figure 3 shows the pattern of the precursor beam 5' and electron flux 6', and how these beams overlap in space and are incident concurrently on the web 2 SO that a coating is progressively deposited and cured as the web passes the deposition station 4.

Figure 4 shows a low pressure gas plasma source 6 suitable for use in the embodiments described herein. The plasma is generated between an anode element 15, which may or may not be water cooled, and a reaction plate 16. An outer core 17 is insulated from a cathodic inner core 18 by an insulating layer 19. Spatial separation between the anode and cathode is supplied by insulators 20. Magnets of a magnetron are arranged with an outer set 21 in opposite polarity to a centre set 22 on a yoke plate 25 to which they are magnetically attached to create a magnetic field to trap the ionised gas. A plasma gas is supplied to the plasma area from a gas inlet pipe 23. The magnets 21, 22 operate as a magnetron to enhance ionisation of the plasma in the glow discharge in the region of the reaction plate 16. A driving voltage is applied to the cathode 18 which is negative relative to the web 2 so as to direct the electron flux 6' towards the web 2. Despite the fact that such plasmas have significantly lower energy levels (<300eV) than other types of plasmas, S it has been found that effective curing can be achieved. In embodiments of the invention, the applied beam of electron flux 6' can be relatively wide in comparison with narrow electron beams known in the art because its cross sectional area is dependent upon the size of the plasma zone. Providing a relatively wide electron flux 6' can be advantageous because if the plasma source, for example, arcs, the energy of the electron flux 6' momentarily decreases. If the electron flux 6' is narrow the momentary decrease could adversely affect the curing process. However, a wide electron flux 6' reduced the likelihood of the curing process being adversely affected by such an occurrence.

Figures 5a and Sb show a device S suitable for use in the embodiments described herein to generate a beam of vapour precursor. The radiation curable material is fed into the device via a delivery pipe 28. This delivers the radiation curable material into a heated chamber 34, which is heated by a cartridge heater 33 up to its operating temperature. The radiation curable material then effuses out of the outlet hole 29 whereupon it will arrive at the web substrate 2 to be cured by the electron flux 6'. This type of delivery system works in synergy with the directed beam of electron flux 6 because the dose and delivery can be matched to one another.

Figure 6 shows an alternative device S to that of Figures Sa, Sb, which is suitable for use in the embodiment of Figure 2. The components are similar except that the heated chamber 34 extends substantially parallel to the axis of the drum 10 above its surface, and an outlet slot 3S is formed along the length of the chamber 34 to direct a beam of precursor vapour at the web on the surface.

As shown in Figure 6, the device S directs a vapour beam 5' radially of the drum 10 towards the web 2, and a source of radiation flux 6 is located one each side of the source 5 to direct a flux 6' towards the web 2 and to each overlap with the beam 5' at either side, thereby ensuring that all of the vapour is irradiated during delivery to the web.

Figure 7 shows yet another alternative device to deliver a precursor vapour to the web 2.

The radiation curable material is fed into the device via a delivery pipe 28. This delivers the radiation curable material into a T-shaped' heated chamber 34, which is heated by three cartridge heaters 33 up to its operating temperature. The radiation curable material then effuses out of the holes 29 along the crosspiece 34' of the T-shape', which extends substantially parallel to the axis of the feed drum 10. Figure 7 shows a low pressure plasma source 6 located over the delivery pipe 28 to deliver an electron flux 6' to the web on feed drum 10. The source 6 is similar to that of Figure 4 but has modified diode system with an enlarged reaction plate 16 to produce a lower density electron flux, the flux being indicated by the lines 6'.

Figure 8 shows an embodiment of the invention in which the deposition device 5 has been repositioned away from the electron flux source 6. In Figures 1 to 7, the deposition and curing occurs concurrently in space and time onto the web 2, whereas in this embodiment, the web 2 first passes the deposition beam 5 and transports the uncured deposited material to the electron flux 6' to be cured. Although the devices 5' and 6 are still active concurrently in time, they are acting sequentially upon the web 2, and so the respective beams 5' and 6' are not concurrent spatially.

As shown in Figures 1 and 2, the device 5 may be relocated relative to the radiation source 6 so that it is downstream rather than upstream of the radiation 6 in the movement of the web. However, the precursor beam 5' would still be angled to overlap the electron flux 6' in a similar manner shown in Figure 3.

A low pressure gas plasma is the preferred source 6 of the irradiation flux, and as such, the pressure of this process will determine not only the mean free path of any molecule within the plasma zone, but also the electron energy dependent upon the electric field used.

Reference Handbook of Plasma Processing Technology pages 38-43 (ISBNO-8155-1220-1).

The devices 5 delivering the beam 5' should be positioned so that the mean free path is greater than or comparable to the distance the vapour must travel from the device 5 before it condenses on the substrate to be coated.

The delivery of the precursor beam to the substrate should also allow for a high degree of irradiation. This irradiation is generally maximised directly in front of the reaction plate 16 that causes the plasma to be excited. Often magnetic fields are introduced that concentrate the irradiation within what is termed, the race track'. In such systems the area of highest irradiation flux is directly opposite these race track' zones. Therefore, the vapour should preferably be directed into these zones.

By following these design rules, it is possible to design the geometry of a system so that the radiation and vapour fluxes are matched for the desired amount of curing.

In embodiments of the invention, the delivery of the vapour is typically 50mm from the surface to be coated, and is placed adjacent to the source of the radiation flux so that when angled, the distance the vapour has to travel to interact with the maximum radiation zone is approximately 75mm. This distance is comparable to the mean free path at the process pressure of Sx 1 0-3mbar. However, the invention is not limited by these parameters and if higher process pressures were used this would still allow for a portion of the vapour to be incident upon the substrate in the maximum irradiation zone and to be cured.

In a preferred embodiment of the invention, the electron flux is provided by a detuned magnetron such as shown in Fig 4.

The precursor can comprise any organic material containing a saturated covalent bond capable of being vaporised or atomised and sprayed onto the substrate, and also capable of being polymerised by electron radiation with energy between 1.6eV and 300eV. In the context of this specification, the precursor can also contain aromatic linkages (which are non-frmnctional in the curing step). Precursors can be organic compounds containing saturated covalent bonds between two divalent, trivalent or tetravalent elements. The elements in the saturated covalent bond can be the same (including, but not limited to C-C, Si-Si, 0-0, N-N, S-S etc) or different (including, but not limited to C-N, C-Si, C-O, C-N, C-S etc). Cyclic organic compounds containing a saturated covalent bond are preferred, with dipara-xylylene and its derivatives being especially preferred (in the context of this specification, the aromatic links in dipara-xylylene are non-frmnctional in the curing step).

The vaporised or atomised material may optionally include other radiation curable or non-curable components to provide functionality such as adhesion promotion, dimensional stability, mechanical properties, colour, electrical conductivity etc. Any web substrate which can be handled by the equipment can be used in the invention.

Substrates can include a wide variety of commercially available thermoplastic films (including polyesters such as polyethylene terephthalate (PET) or polyethylene naphthalate (PEN) or blends or coextrusions thereof), polyamides (including nylon 6 and nylon 6.6), polyolefines (including polypropylene and high and low density polyethylene) and other thermoplastic films known in the art. Non-thermoplastic films, including biodegradable films and films derived from renewable resources, such as polylactic acid or cellulose-based materials may also be used. Thermoset polymer films, such as polyimides may also be used. Fibrous or woven substrates (such as paper or textiles) may also be used. The invention is not limited by this list of web substrates. The substrate can optionally be pre-coated, vacuum deposited or printed with a wide variety of metals, metallic or non-metallic compounds and other materials, in order to achieve desired properties or effects. For barrier applications, for example, substrates such as polyester films coated with a metal such as aluminium are especially preferred. For transparent barrier applications, substrates such as polyester films coated with a transparent metallic or non-metallic oxide, nitride or other compound (e.g. aluminium oxide or silicon oxide) are especially preferred. For electrical or electronic applications, the web substrate may be optionally pre-coated with a metal such as copper or another conductive inorganic or organic material. However, the invention is not limited to these specified coatings.

It is known that an optically variable colour shift coating can be produced by depositing a reflective coating, such as a metal or a high refractive index material, on a web substrate, and then applying over it a further coating of a transparent or translucent material, having an optical thickness from 1/4 to 1/2 the wavelength of visible light (380nm-760nm). The colour shift effect can be further enhanced by depositing on top of said transparent material a further semi-transparent layer of metal or high refractive index material. The transparent or translucent layer can be a radiation-cured organic polymer deposited and cured using a sequential delivery and curing process. It has now been found that if this transparent or translucent layer is produced using the process of the invention, the coating contains a mixture of dielectric domains, giving it a holographic-like iridescent appearance, and the intensity of colour and the degree of the colour shift in any continuously optically variable device are enhanced.

The thickness of the cured polymer coating can be in the range 0.001 tm -50pm, and preferable 0.1tm to 50jim, the preferred thickness largely being decided on the basis of the function of the polymer layer in the intended application, and cost constraints, rather than constraints arising from the process. For example, for barrier packaging applications, the function of the polymer layer is to protect the barrier coating (i.e. the aluminium or aluminium oxide) against physical damage or abrasion. In this case, the lower limit of thickness of the polymer layer is around 20tm, as below this there is insufficient protection. The upper limit may be subjective, as above about 1 tm, the benefit of mechanical protection will begin to be outweighed by the risk of delamination. For very high barrier applications, a plurality of barrier layers, separated by polymer layers, is used, as this extends the diffusion pathway for gas or vapour between the permeable defects in each barrier layer. In this case, since the polymer layer is functioning as a separating layer between two metal or ceramic layers, and has little or no inherent barrier of its own, it should preferably be as thin as practicable conducive with the requirements that it should be continuous (with no voids or defects) and have good surface smoothness (to maximise barrier of the second barrier layer). For optically variable devices, the function of the polymer layer is to generate light interference, and thus produce a "colour shift". For such applications, a coating thickness of approximately a quarter to half of the wavelength of the incident light is preferred but the invention is not limited by this thickness.

Various examples of polymer coating processes according to the invention are now described in more detail.

Example 1

In this example, a liquid delivery system was used to deliver olive oil into a heated delivery device. The delivery device in this example included a machined volume inside a graphite block, having an exit slot with internal ducts to pass vapours from a delivery zone to the exit slot without any direct line of sight. A vapour stream exiting the slot can be directed toward a substrate in opposition to a 4 inch sputtering magnetron. With the graphite block heated to 25 0°C and the sputter cathode of the magnetron running in mid frequency (MF) mode at 400W and 430 volts, 40kHz at a chamber pressure of 3.6x10-2mbar Ar., a volume of lml of olive oil was introduced into the delivery zone of the heated block; the olive oil was vaporised and directed onto the substrate in the space exposed to the electron flux from the sputtering magnetron. This resulted in a solid transparent continuous film on the substrate having good adhesion qualities. It should be noted that a suitable DC power supply could be used rather than the described AC supply.

Example 2

In this example, Parylene C (the chemical name for which is Di-chloro-di-p-xylyene and the chemical abstract number 28804-46-8) was vaporised at 150 °C and directed toward a substrate exposed to the electron flux from a 4 inch circular magnetron running at 50 Watts 350 volts at 2x 10-1 mbar. The resulting coatings were continuous and transparent and were well adhered to the substrate. The coated substrate samples had reduced oxygen (OTR) and moisture (MVTR) transmission rates compared with the substrate with no coating deposited. The delivery system, or evaporator, was an aluminium structure having external dimensions lOOx8Ox23mm with a single louvered exit along one of the 100mm wide sides that directed any effusing parylene diamer towards the curing zone on the web. The exit slot had similar geometry to that used in the first example.

Materials manufactured by the invention are suitable for use in multiple different applications, including, but not limited to: packaging of oxygen or moisture sensitive foodstuffs, packaging of oxygen or moisture sensitive ethical compounds (such as drugs or fluids), packaging of oxygen or moisture sensitive materials or devices for ethical applications (such as sutures); webs for use on or in the body (such as bandages, dressings etc); abrasion resistant materials or intermediates (in which the polymer coating prevents abrasion damage to any underlying functional layers during conversion or use); security or anti-counterfeit applications, including continuously optically variable devices; decorative applications, including continuously optically variable devices; functional industrial applications; and electrical or electronic applications (inclusive of static electricity dissipation).

Claims

Claims 1. A process for coating a substrate comprising condensing a radiation curable organic material containing a saturated covalent bond on a substrate and curing it using an electron flux with energy between 1.6eV and 300eV, whereby the electron flux is extracted from a low pressure gas plasma and directed from the low pressure gas plasma towards the substrate.
2. A process as claimed in any of the preceding claims in which the saturated covalent bond in the precursor material is one or more of C-C, 0-0, N-N, S-S, Si-Si and C-N.
3. A process as claimed in any of the preceding claims in which the precursor material is cyclic.
4. A process as claimed in claim 3 in which the precursor material is dipara-xylylene or a derivative thereof.
5. A process as claimed in any of the preceding claims in which the electron flux is directed at the substrate substantially simultaneously with delivery of the material to said substrate, so that curing is initiated spatially and temporally substantially concurrently with the delivery of the material to the substrate.
6. A process as claimed in any of claims 1 to 4 in which the electron flux is directed at the substrate substantially sequentially with condensation of the material on said substrate.
7. A process as claimed in any of the preceding claims in which the electron flux is derived from a low pressure gas plasma with an electron driving voltage that is negative relative to the substrate.
8. A process as claimed in any of the preceding claims in which the low pressure gas plasma is magnetically enhanced.
9. A process as claimed in any of the preceding claims in which the low pressure gas plasma is generated using a magnetron.
10. A process as claimed in claim 5 in which substantially all of the radiation curable material passes through the flux prior to condensing on the surface of the substrate.
11. A process as claimed in any of the preceding claims in which the substrate comprises a web which is composed of a plastics film; or is composed of polyester or a polyolefin or a polyamide or polyethylene terephthalate or polyethylene naphthalate or a mixture of polyethylene terephthalate and polyethylene naphthalate; or is obtained from a renewable resource; or comprises a fibrous material, paper or textile or polylactic acid or a cellulose derivative.
12. A process as claimed in any of the preceding claims in which the substrate comprises a plastics film which is pre-coated with an inorganic barrier material; or a metal; or a conductive organic or inorganic material; or aluminium or aluminium oxide or an oxide of silicon; or a conductive organic or inorganic material; or copper.