Patent Application
20200243309
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.
It is known to deposit layers of cured polymer onto a web substrate using vacuum deposition. However, known processes of vacuum condensation and curing of polymer precursors have a number of drawbacks/risks, associated with impurities in the commercial grades of raw materials used, particularly for the substrate, or inherent in the process itself.
The risks associated with impurities, 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:
Various radiation sources have been used to cure polymer precursors once condensed on a substrate, for example ultraviolet, visible or infra-red or, particularly, electron beam radiation. Atmospheric plasmas are also used, generally for secondary curing (i.e. as an adjunct to electron beam, to complete the cure). 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 a monomer vapour through a glow discharge electrode to create a glow discharge conjugated monomer plasma and then direct it towards a substrate using a driving voltage in the glow discharge which is positive with respect to the local conditions at the substrate. The monomer containing these free radicals then condenses on the substrate, where the free radicals initiate curing. However, such systems may not be suitable for running at high line speeds.
It is also known to treat or process web substrates prior to the application of further materials to aid in adhesion. This may be achieved by exposing the surface of the web substrate to radiation such as plasma. While such steps may be beneficial, they generally increase the amount of space required to implement the process due to the additional pieces of apparatus that are required to perform the steps.
According to a first aspect of the present invention there is provided apparatus comprising:
The ion flux described herein may comprise cations and in some cases other positively charged or non-charged particles and species, but the positively charged ions are the primary curing or processing initiator. The present inventors have discovered that an ion flux having an energy level between 3.6 eV and 250 eV can unexpectedly perform useful processing and curing operations.
The ion flux may be biased or extracted from the plasma with a driving voltage that is positive relative to the substrate and/or support. The driving voltage may be provided on the opposite side of the plasma with respect to the substrate and/or support. In some embodiments the ions may be attracted towards the drum by a negative voltage, which repels electrons within the plasma.
The substrate of embodiments of the invention may comprise a web of film of material such as a plastics material.
The apparatus may further comprise a delivery device arranged to deliver radiation curable material to the substrate.
The energy level 3.6 eV is that needed to break a carbon-carbon single bond in saturated precursor materials, such as parylene, in order to induce polymerisation.
The lower energy limit may be at least 6.5 eV. The energy level 6.5 eV is that needed to break a carbon-carbon double bond in precursor materials, such as acrylates, in order to induce polymerisation.
The upper energy limit may be no greater than 100 eV. This may reduce ion impact on the substrate and/or layer of condensed radiation curable material.
Although it is known that an electron flux extracted from a low pressure gas plasma and having an energy level between 6.5 eV and 300 eV can be used for curing a radiation curable material, the present inventors discovered that an ion flux having an energy range between 3.6 eV and 250 eV can be used to cure a radiation curable material. This was unexpected due to the prior art teaching that an ion flux having an energy level within the claimed range would not cure a condensed film having a minimum thickness of 0.01 μm and moving at a rate of at least 50 m/min because of the relatively poor penetration characteristics ions exhibit in comparison with electrons and the limited exposure time for the thickness of film. This suggests that although the surface adjacent to the ion flux could be fully cured, the surface adjacent to the substrate would be uncured or partially cured, giving rise to a weak surface layer which would have poor adhesion to the substrate.
Moreover, the relatively high momentum of ions has been known to cause damage to surfaces of substrates such as webbing and/or a film of radiation curable material. Indeed, taking information from the Handbook of Sputter Deposition Technology (p50, ISBN 9780815512806), it is known that the damage threshold for a film of radiation curable material can be as low as 30 eV. As such, the prior art teaches away from using an ion flux having an energy level above 30 eV, and anything below this level would be viewed as being particularly unsuitable due to the perceived penetration problem referred to above.
An advantage to using an ion flux having an energy level between 3.6 eV and 250 eV for the curing, rather than an electron flux having an energy level between 6.5 eV and 300 eV, is that any overspray of radiation curable material or re-evaporate thereof will also be cured due to species generated at earthed surfaces inside the process chamber.
In some embodiments the apparatus may be arranged to deliver one or more further gases along with the primary gas used to create the plasma, the further gas(es) being arranged to perform one or more additional functions such as removing unwanted species from the web, or including certain species in the developing polymer film on the web substrate. The use of an ion flux as the primary curing initiator has a further advantage over the use of an electron flux in that the ion flux may contain ionised species from both the primary plasma gas and the further plasma gas, meaning that, even with the plasma spaced from the web substrate, the further gas can act upon the web or polymer film though migration of its ions. In one example, hydrogen could be used to passivate the surface. In an other example, nitrogen could be introduced as the further gas in order to introduce a reactive bonding species aimed at increasing or changing the cross-linking within the film.
In embodiments of the invention the plasma gas and one or more additional gases may be delivered to the plasma defining region by one or more gas delivery conduits.
The delivery device may be arranged to deliver vaporised or atomised radiation curable material such that it condenses on the substrate.
The delivery device may deliver the radiation curable material to the substrate concurrently or sequentially with respect to the delivery of the ion flux.
The radiation curable material may comprise a saturated or unsaturated radiation curable material. In some embodiments the unsaturated radiation curable material comprises acrylate.
The support may be arranged to move the substrate at a line speed of at least 50 meters per minute.
The delivery device may be arranged to deliver the condensed radiation curable material to provide a thickness in the range 0.001 μm to 50 μm and preferably in the range of 0.01 μm to 1 μm.
The apparatus may be arranged to provide a unit energy dose, which may be an average unit energy dose, which is no greater than 15 J/cm2, preferably no greater than 13 J/cm2, more preferably no greater than 0.1 J/cm2 and even more preferably no greater than 0.04 J/cm2. Generally speaking, a lower unit energy dose may enable a faster line speed for the web substrate.
The apparatus may further comprise a magnet array arranged to spatially define the plasma.
The support may comprise a rotatable drum.
The magnet array may be arranged to define a magnetic field configured to influence the generated plasma to form:
The first and second surface regions may be circumferentially spaced from one another by at least about 20 mm. In other embodiments of this aspect or other aspects of the invention, the first and second surface regions may be rotationally spaced from one another by an angle of at least about 22.5°, at least about 45°, at least about 90°, or at least about 135°.
The magnet array may comprise a first magnet assembly arranged to define the first race track portion and a second magnet assembly arranged to define the second race track portion. Each magnet assembly may comprise one or more magnets.
The magnet array may comprise a first magnet assembly arranged to define a race track comprising the first and second race track portions.
The magnet array may be arranged to define one or more further race track portions, each race track portion being adjacent to the surface of the drum and circumferentially spaced from each other race track portion by at least 20 mm.
In some embodiments the apparatus may comprise a delivery device arranged to deliver the radiation curable material to the substrate between race tracks.
In some embodiments the apparatus may comprise a delivery device may be arranged to deliver the radiation curable material to the substrate between race track portions.
The magnet array may be disposed within the drum.
The drum may define an electrode arranged to generate the plasma.
In accordance with a second aspect of the present invention, there is provided a process comprising the steps of:
The process may include the step of condensing a radiation curable material on the substrate and curing the radiation curable material with the ion flux extracted from the plasma.
The substrate may be moving at a rate or instantaneous velocity of at least 50 m/min and preferably at least 5 m/s and more preferably at least 10 m/s.
The condensed radiation curable material may have a thickness in the range 0.001 μm to 50 μm and preferably in the range of 0.01 μm to 1 μm.
The apparatus may be arranged to provide a unit energy dose, which may be an average unit energy dose, which is no greater than 15 J/cm2, preferably no greater than 13 J/cm2, more preferably no greater than 0.1 J/cm2 and even more preferably no greater than 0.04 J/cm2. Generally speaking, a lower unit energy dose may enable a faster line speed for the web substrate.
The step of generating a plasma may comprise exciting a gas to form a gas plasma.
The ion flux may be extracted from the plasma with a driving voltage that is positive relative to the substrate and/or support. The driving voltage may be provided on the opposite side of the plasma with respect to the substrate and/or support. In some embodiments the ions may be attracted towards the drum by a negative voltage.
The plasma may be spatially defined by a magnet array. The moving substrate may be transported by a rotating drum.
A magnetic field may be provided that is configured to influence the generated plasma to form:
wherein the first and second surface regions are circumferentially spaced from one another.
The first and second surface regions may be circumferentially spaced from one another by at least 20 mm.
A first magnet assembly may define the first race track portion and a second magnet assembly may define the second race track portion. Each magnet assembly may comprise one or more magnets.
A first magnet assembly may define a race track comprising the first and second race track portions.
One or more further race track portions may be defined, each race track portion being adjacent to the surface of the drum and circumferentially spaced from each other race track portion by at least 20 mm.
The magnet array may be disposed within the drum.
The drum may define an electrode arranged to generate the plasma.
In accordance with a third aspect of the present invention, there is provided an apparatus comprising:
wherein the first and second surface regions are circumferentially spaced from one another.
Thus, the apparatus according to this aspect and embodiments of the first aspect generates distinct race track portions at spaced locations around the drum surface, such that the race track portions can be used for different purposes; for example, the first race track portion can be used to treat a first side of the moving substrate, while the second race track portion can be used to treat the opposite side of the substrate.
The first and second surface regions may be circumferentially spaced from one another by at least 20 mm.
The magnet array may comprise a first magnet assembly arranged to define the first race track portion and a second magnet assembly arranged to define the second race track portion. Each magnet assembly may comprise one or more magnets.
The magnet array may comprise a first magnet assembly arranged to define a race track comprising the first and second race track portions.
The magnet array may be arranged to define one or more further race track portions, each race track portion being adjacent to the surface of the drum and circumferentially spaced from each other race track portion by at least 20 mm.
The magnet array may be disposed within the drum.
The drum may define an electrode arranged to generate the plasma.
The apparatus may further comprise:
The apparatus may further comprise a delivery device arranged to deliver radiation curable material to the substrate. The delivery device may deliver the radiation curable material to the substrate concurrently or sequentially with respect to the delivery of the ion flux.
The apparatus may be arranged to provide a unit energy dose, which may be an average unit energy dose, which is no greater than 15 J/cm2, preferably no greater than 13 J/cm2, more preferably no greater than 0.1 J/cm2 and even more preferably no greater than 0.04 J/cm2. Generally speaking, a lower the unit energy dose results in a faster line speed for the web substrate.
In some embodiments the apparatus may comprise a delivery device arranged to deliver the radiation curable material to the substrate between race tracks.
In some embodiments the apparatus may comprise a delivery device arranged to deliver the radiation curable material to the substrate between race track portions.
The radiation curable material may comprise a saturated or unsaturated radiation curable material. In some embodiments the unsaturated radiation curable material comprises acrylate.
Embodiments of the invention may 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.
Embodiments of the invention may increase robustness over prior art and allow for longer running times due to the greatly reduced ‘fouling’ and build up of deposits on process components other than the substrate being coated. The lower power density utilised reduces the wear and heat damage on the substrate.
Embodiments of the invention may enable multiple processing and/or curing steps to be provided with apparatus that is more compact than prior art arrangements.
The electrons generated on adjacent earthed surfaces have the beneficial effect of curing any re-evaporated monomer or monomer that has not landed on the substrate as it arrives on these surfaces preventing the detrimental effects of monomer migration.
The adhesion of the various layers of the product may be sufficient to prevent delamination during any subsequent conversion or use.
Permeability 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 substrate when the described process is used to deposit combinations of inorganic and organic layers (such as aluminium or aluminium oxide and polymerised radiation curable material) on to the same web substrate.
The polymerised radiation curable material may form a coating on the substrate that provides abrasion protection to any underlying functional layers during conversion or use.
By way of example only, certain embodiments of the invention will now be described by reference to the accompanying drawings, in which:
The apparatus in
An alternative embodiment of the invention is illustrated in
As shown in
In other embodiments, any suitable ion flux source may be provided, and different means may be employed to direct the ion flux towards the substrate. For example, as will be described in more detail below with reference to
The drum 10 has an interior space 26, which may be water cooled. The drum 10 is rotatably mounted on a stationary yoke 22 disposed within the interior space 26. The stationary yoke 22 supports a magnet array 21. The magnet array 21 is arranged to produce closed loop magnetic flux lines that interact with the ion flux 6′ to define relatively narrow ‘race track’ of high density ion flux having portions 6″a, 6″b that are located in close proximity to the web 2. The inventors have discovered that the position of the magnet relative to the outer surface of the drum 10 affects the configuration, in including the separation, of the discrete race track portions. Generally speaking, the discrete race track portions are relative close together when the magnet is relatively close to the drum surface, and relative widely spaced when the magnet is located away from the drum surface, closer to the central axis of the drum.
In the illustrated embodiment, the web 2 shields the cathode roller 10 from the ion flux 6′; this is advantageous because it inhibits oxidisation and fouling of the cathode 10. In such embodiments, the radiation source 6 should be powered by an AC supply, preferably operating within the radio frequency (RF) range; for example, 40-320 kHz. In some embodiments the voltage source may be an AC source having any suitable frequency, such as 50 Hz.
In the embodiment of
The embodiment of
The embodiment of
The embodiment of
The embodiment of
The race track portions of embodiments of the invention such as those described with reference to
Embodiments of the invention having a magnet array 21 disposed within the drum cavity 26 advantageously enable a magnetically enhanced plasma to be defined with a small mechanical footprint, due to the magnets being contained inside the drum 10. This lends itself to retrofitting such a drum in existing plasma processing devices. In some embodiments, separate processing functions can be achieved with a magnet array consisting of a single magnet assembly that is conveniently housed within the drum 10. In some embodiments, such as those described with reference to
Embodiments of the invention having a magnet array 21 disposed within the drum cavity 26 can use any suitable means of plasma curing i.e. these embodiments are not limited to using an ion flux having an energy level between 3.6 eV and 250 eV for curing and/or processing.
Embodiments of the invention may include a magnet array arranged to form one or more race tracks having any suitable configuration.
Thus, embodiments of the invention provide a low energy ion flux that can be used for curing or processing steps. An advantage to using an ion flux having an energy level between 3.6 eV and 250 eV for the curing, rather than an electron flux having an energy level between 6.5 eV and 300 eV, is that any overspray of radiation curable material or re-evaporate thereof will also be cured due to species generated at earthed surfaces inside the process chamber.
The functional element of the radiation curable precursor is any saturated or unsaturated material capable of being vaporised or atomised and sprayed onto the substrate, and also capable of being polymerised by the ion flux. Precursors can be organic or inorganic and include unsaturated organic materials, silicon-based materials, halogen-based materials, organo-metallic composites etc, with acrylates such as tripropylene glycol diacrylate or isobornyl acrylate being preferred. Most polymerisable materials described in the art can be used in the process. 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, antibacterial properties, hydrophillia, hydrophobia, electrical conductivity etc.
The thickness of the precursor film or the cured polymer coating can be any suitable value. For example, in some embodiments the value may be at least 0.001 μm. In some embodiments, the value is in the range 0.001 μm-50 μm, and preferably 0.01 μm to 1 μm, 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 may be around 0.02 μm, as below this there is insufficient protection. The upper limit may be subjective, as above about 1 μm, the benefit of mechanical protection will begin to be outweighed by the risk of delamination.
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 including cellulose diacetate, also known as cellulose acetate, may also be used. Thermoset polymer films, such as polyimides may also be used. Fibrous, non-woven or woven substrates (such as paper or textiles) may also be used. The invention is not limited by this list of web substrates.
The process of embodiments of the invention may be a “high speed process”, meaning that the web substrate is moving at a speed of at least 50 m/min. It is preferred that the web is moving at a speed of at least 5 m/s, and more preferably that that the web is moving at a speed of at least 7 m/s. In some embodiments of the invention, the web may form part of a reel to reel process.
Embodiments of the invention may use any easily ionisable inert gases to generate the plasma; for example argon, helium and neon, or other non-reactive gases or reactive gases including nitrogen or oxygen. Combinations of gases could be used to tailor the gas to specific applications. The gas used to generate the plasma is distinct from the radiation curable monomer. This may provide a more controllable and practicable method compared to generating a plasma using the monomer itself, due to the quantities involved. For example, the ‘high’ flow rates, such as 25 ml per minute, used in embodiments of the invention would cause considerable vacuum problems if ionised in a plasma.
One or more further gases may be added to the primary gas used to create the plasma, the further gas(es) being arranged to perform one or more additional functions such as removing unwanted species from the web, or including certain species in the developing polymer film on the web substrate. The use of an ion flux as the primary curing initiator has a further advantage over the use of an electron flux in that the ion flux may contain ionised species from both the primary plasma gas and the further plasma gas, meaning that, even with the plasma spaced from the web substrate, the further gas can act upon the web or polymer film though migration of its ions. In one example, hydrogen could be used to passivate the surface. In an other example, nitrogen could be introduced as the further gas in order to introduce a reactive bonding species aimed at increasing or changing the cross-linking within the film.
The moving substrate is exposed to the ion flux for a period of time inversely proportional to the web speed. This period of time shall be referred to as the ‘dwell time’ and this can be influenced by the web speed and the length of web being exposed to the flux, which shall be referred to as the ‘dwell length’. It is preferred that the dwell length be as short as is reasonably practicable. A unit power dose measured in W/cm2 experienced by the web can be calculated by dividing the operating power of the plasma generator by the cross sectional area of the ion flux. The unit power dose can be used with the dwell time to establish a unit energy dose on the web, measured in J/cm2. With a known flow rate of radiation curable precursor and width of delivery the energy dose per unit precursor can be attained.
The plasma generator used in embodiments of the present invention may be connected to a an AC or a DC power supply. Depending on the power supply used, it is possible to create and control an ion flux having the stated energy ranges, such as an energy level that is no greater than 250 eV or an energy level that is no greater than 100 eV. For example, the voltage applied to the plasma generator may define the maximum energy level and as such applying 250V results in an ion flux having a maximum energy level of 250 eV.
In embodiments of the invention it is preferred that the unit energy dose, described above, is no greater than 15 J/cm2, more preferably no greater than 13 J/cm2, and in some embodiments the unit power may be no greater than 0.1 J/cm2. It is preferred that the dwell length, as described above is between 5-50 cm and even more preferred to be 10 cm. A short flux may undesirably limit the line speed of the web, whereas a long flux length may lead to undesirably high power consumption and impracticability of space. It is preferred that the dwell time be as low as possible whilst still giving full cure to ensure a high process efficiency.
The substrate can optionally be pre-coated or post-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 non-transparent 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. oxide of aluminium or oxide of silicon) 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, which however may be transparent or non-transparent. However, the invention is not limited to these specified coatings.
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, i.e. with no voids or defects, and have good surface smoothness to maximise the barrier of the second or subsequent 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.
Materials manufactured by the invention are suitable for use in multiple different applications including: packaging applications; abrasion-resistant material or intermediate (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).
Some more specific examples of embodiments of the invention will now be set out.
A planar magnetron such as that shown in
A roller magnetron similar to
In this example, a simulated small roller magnetron similar
In this example, a roller magnetron similar to
In a further experiment following the above example 4, the substrate line speed was reduced in stages to observe the level the substrate could endure before thermal degradation. Carbonisation of the web was observed at a web speed of ˜0.25 m/min. At ˜0.5 m/min some film distortion was noted, above 1 m/min no damage was observed on the substrate. The roller surface was connected to an RF power source running at a frequency of 40 kHz sustaining 0.3 kW with a voltage ˜200V. At the point of observed thermal degradation, when run at approximately 0.25 m/min line speed, giving a 24 second dwell time in the plasma, the energy dose to the substrate was 14.4 J/cm2.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1301839.5 | Feb 2013 | GB | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 14764622 | Jul 2015 | US |
| Child | 16838304 | US |
