GB2562733A

GB2562733A - System and method for antimicrobial coating of polymeric substrates

Info

Publication number: GB2562733A
Application number: GB1708181.1A
Authority: GB
Inventors: Black Stephen
Original assignee: Formology Holdings Ltd
Current assignee: Formology Holdings Ltd
Priority date: 2017-05-22
Filing date: 2017-05-22
Publication date: 2018-11-28
Also published as: GB201708181D0; WO2018215731A1

Abstract

A coating system 10 for applying an antimicrobial coating to a polymeric substrate comprising a sublimation thermal transfer printer having a feed path 20, the feed path including an inlet 22, an outlet 24, a printing zone 26 between the inlet and outlet, and an antimicrobial coating application ribbon 18 locatable in the printing zone of the feed path. The antimicrobial coating application ribbon includes a flexible ribbon body, and one or more vaporisable antimicrobial agents applied on the ribbon body. Upon activation of the sublimation thermal transfer printer it vaporises the vaporisable antimicrobial agent onto the substrate. A method of applying an antimicrobial coating to a polymeric substrate using the coating system is also provided. Also disclosed is an antimicrobial coating application element.

Description

(71) Applicant(s):

Formology Holdings Limited

The Croft, Kidderminster, Worcestershire, DY11 6LX, United Kingdom (72) Inventor(s):

Stephen Black (74) Agent and/or Address for Service:

Albright IP Limited

County House, Bayshill Road, CHELTENHAM, Gloucestershire, GL50 3BA, United Kingdom

(51) INT CL: B41M 5/392 (2006.01)	B41M 5/382 (2006.01)
(56) Documents Cited: CN 103538386 A JP 2008290318 A JPH0995058	JP 2012071447 A US 20070141125 A1

(58) Field of Search:

INTCLA61K, B41F, B41J, B41M, C09D Other: WPI, EPODOC, Patent Fulltext (54) Title of the Invention: System and method for antimicrobial coating of polymeric substrates Abstract Title: Antimicrobial coating of polymeric substrates using sublimation thermal transfer printer (57) A coating system 10 for applying an antimicrobial coating to a polymeric substrate comprising a sublimation thermal transfer printer having a feed path 20, the feed path including an inlet 22, an outlet 24, a printing zone 26 between the inlet and outlet, and an antimicrobial coating application ribbon 18 locatable in the printing zone of the feed path. The antimicrobial coating application ribbon includes a flexible ribbon body, and one or more vaporisable antimicrobial agents applied on the ribbon body. Upon activation of the sublimation thermal transfer printer it vaporises the vaporisable antimicrobial agent onto the substrate. A method of applying an antimicrobial coating to a polymeric substrate using the coating system is also provided. Also disclosed is an antimicrobial coating application element.

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Figure 4

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System and Method for Antimicrobial Coating of Polymeric Substrates

The present invention relates to the application of antimicrobial agents to polymeric substrates, and in particular, the application of antimicrobial agents to polymeric substrates using sublimation thermal transfer printing.

Polymeric materials are ubiquitous in everyday life, and can carry pathogenic bacteria, viruses, and other harmful micro-organisms. Polymeric cards, such as payment cards and security cards, which are handled by large numbers of people in normal use, may be a vector for disease.

Additionally, the introduction of polymeric banknotes into circulation in various jurisdictions worldwide may also be a cause for concern. One recent study (Antimicrob Resist Infect Control 2013 2:22) found that polymeric Romanian Leu banknotes were commonly contaminated with methicillin-resistant Staphylococcus Aureus, E. Coli and vancomycin-resistant Enterococci. Such antibiotic resistant pathogens cause infections which are difficult to treat, and may be of health risk to the immunosuppressed and elderly.

While it is known to provide a surface coating comprising one or more antimicrobial agents to reduce pathogenic contamination of polymeric materials, this does not provide a general solution to the problem. In particular, the polymeric surfaces which present the highest risk of contamination are subject to extensive handling, and thus frictional degradation of the antimicrobial surface coating may be difficult to avoid.

Furthermore, it is desirable to provide cards which can be overprinted with user details, especially in the context of payment cards, identification cards and security cards. This may be achieved by a thermal transfer process. However, overprinting on an antimicrobial coating may chemically deactivate it, or a layer of pigment may be formed above the coating layer, rendering it ineffective.

The present invention seeks to provide solutions to all of the abovementioned problems.

In accordance with a first aspect of the invention, there is provided a coating system for applying an antimicrobial coating to a polymeric substrate, the system comprising: a sublimation thermal transfer printer having a feed path, the feed path including an inlet, an outlet, and a printing zone between the inlet and outlet; an antimicrobial coating application ribbon locatable in the printing zone of the feed path of the sublimation thermal transfer printer; the antimicrobial coating application ribbon including a flexible ribbon body, and one or more vaporisable antimicrobial agents applied on the ribbon body, wherein, upon activation of the sublimation thermal transfer printer, with a substrate at the printing zone, the sublimation thermal transfer printer vaporises the vaporisable antimicrobial agent onto said substrate.

Advantageously, this system can be used to apply an antimicrobial coating to a polymeric substrate with a sublimation thermal transfer method. In this way, the antimicrobial coating may penetrate the surface of the substrate, so that antimicrobial agents will remain present on the surface of the substrate despite frictional wear to the substrate. Furthermore, the system may be used to apply an antimicrobial coating simultaneously to, or otherwise in conjunction with, the overprinting of a pre-prepared substrate.

Preferably the or each vaporisable antimicrobial agent is provided in a single layer on a surface of the antimicrobial coating application ribbon. In this case, the said layer may be located on only one surface of the antimicrobial coating application ribbon, so that heat can be applied through the other surface of the ribbon, preventing direct contact between a heating element and the antimicrobial agents.

The antimicrobial coating application ribbon may beneficially comprise one or more vaporisable dyes. This allows for simultaneous transfer of the dye and the antimicrobial agents in the sublimation thermal transfer printing process.

At least one of the or each vaporisable dye may include the or each antimicrobial agent. This is advantageous, as if a dye of a certain colour is an active antimicrobial agent, the presence of the said antimicrobial agent on the substrate may be determined by visual inspection, ensuring that the substrate is recoated or disposed of before the antimicrobial coating is removed frictionally through use. Additionally, minimizing the number of distinct active agents applied to the substrate is advantageous, as it reduces the risk of user sensitization to active agents present on the substrate.

Preferably the or each vaporisable antimicrobial agent is selected from the group consisting of: 2-phenylphenol, 2,4,4'-trichloro-2'-hydroxydiphenyl ether (triclosan), 2(thiocyanomethylthio)benzothiazole, cyanoacrylates (especially ethyl-2-cyano-3,3'diphenyl acrylate), isothiazolinone and derivatives thereof (especially 2-methyl-4isothiazolin-3-one, 5-chloro-2-methyl-4-isothiazolin-3-one, benzisothiazolin-3-one, 2octyl-4-isothiazlin-3-one, 4,5-dichloro-n-octyl-4-isothiazolin-3-one, and N-butyl-1,2benzisothiazolin-3-one), halogenated phenols (especially 2,4,6-tribromophenol, 2,4,6trichlorophenol, pentachlorophenol, //-chlorocresol), nitrophenols, fatty acids and derivatives thereof (especially octanoic acid, nonanoic acid), triazole fungicides (especially propiconazole, cyproconazole), N-dichlorofluoromethylthio-N',N'-dimethylN-para-tolylsulfamide (tolylfluanid), N-(trihalomethyl-thio)phthalimides (especially N(trichloromethyl-thio)phthalimide), (benzyloxy)methanol, 2-isopropyl-5-methylphenol, phenylpropanoids (especially 2-methoxy-4-(prop-2-en-l-yl)phenol), organic salicylates (especially phenyl salicylate), and rotenoids (especially rotenone).

Each of these compounds or classes of compounds, and structural or functional analogues thereof, may be vaporised and transferred to a polymeric substrate under conditions achievable with sublimation thermal transfer printing.

The inlet of the feed path may be provided as a slot, so that polymeric substrates may be conveniently fed therein by a user.

One or more heating elements may be located in the printing zone. The provision of distinct heating elements within the printing zone, rather than heating the printing zone from without, may be advantageous as it allows topical application of heat and thus localised transfer of antimicrobial agents onto the substrate.

In order to achieve this, the antimicrobial coating application ribbon may preferably be mountable in the printing zone such that the or each heating elements are located proximally to the antimicrobial coating application ribbon, to allow contact between the or each heating elements and the antimicrobial coating application ribbon.

The feed path may further comprise a pre-treatment zone, between the inlet and the printing zone, for surface activation of the polymeric substrate. Surface activation of the polymeric substrate, most preferably by application of heat, is advantageous, because it reduces the energetic barrier to sublimation thermal transfer of antimicrobial agents, and/or dyes, and allows such active chemical species to penetrate the surface of the substrate. This may allow the sublimation thermal transfer to occur at a lower temperature, and may also improve the kinetics of the sublimation thermal transfer, reducing the required duration of heating in the printing zone.

The feed path preferably further comprises a post-treatment zone, between the printing zone and the outlet, for cooling of the substrate. Active cooling of the substrate may improve the quality of application of the antimicrobial coating, by preventing unwanted chemical reactions between constituents of the coating, as well as anomalous coating properties at microirregularities on the substrate surface due to prolonged high-surface activity during cooling.

The antimicrobial coating application ribbon may be mounted on one or more reels, drivable by one or more motors located in the printing zone and engageable with the or each reel. This is advantageous, as it allows fast replacement and compact storage of used antimicrobial coating application ribbon. The reel may also be driven backwards to remove dust from the antimicrobial coating application ribbon, if the sublimation thermal transfer printer is not used regularly.

According to a second aspect of the invention, there is provided a method of applying an antimicrobial coating to a polymeric substrate, comprising the steps of: a) providing a system preferably in accordance with the first aspect of the invention; b) introducing a polymeric substrate to be coated to the feed path of the sublimation thermal transfer printer via the inlet; c) moving the polymeric substrate along the feed path into the printing zone, placing the antimicrobial coating application ribbon in contact with a surface of the polymeric substrate, and applying a pressure between the antimicrobial coating application ribbon and the polymeric substrate; d) heating the antimicrobial coating application ribbon to apply the or each antimicrobial agent onto or into the surface of the polymeric substrate; and e) removing the polymeric substrate from the printing zone, to eject the coated polymeric substrate.

Preferably, the method may further comprise a step prior to step a), wherein the feed path includes a pre-treatment zone, in which the polymeric substrate is pre-heated to increase its surface energy. This may reduce the energetic barrier to the sublimation thermal transfer of antimicrobial agents, among other advantages hereinbefore described.

The polymeric substrate may most preferably be pre-heated at temperature between 60 and 275 degrees Celsius, to prevent chemical degradation or melting of the polymeric substrate, while activating the surface. The polymeric substrate may advantageously be pre-heated for less than 5 seconds, so that the pre-heating step does not significantly increase the application time of the antimicrobial coating.

In step c) the applied pressure is preferably between 150 kPa and 600 kPa, to allowed controlled vaporisation of a variety of antimicrobial agents.

In step d) the ribbon may beneficially be heated topically, to achieve topical application of the antimicrobial coating. This may be particularly important if the or each antimicrobial agent is also a dye, to allow correct printing of a desired design on the substrate by the application of the antimicrobial coating.

In step c) a plurality of antimicrobial coating application ribbons may be placed in contact with a plurality of surfaces of the polymeric substrate, and in this case, in step d) each antimicrobial coating application ribbon may be heated, to apply an antimicrobial coating to the plurality of surfaces of the polymeric substrate. For most combinations of antimicrobial agents and polymers, pressured contact may be insufficient to cause significant transfer of the antimicrobial agent to the polymeric substrate.

In step a) the antimicrobial coating application ribbon includes a plurality of vaporisable antimicrobial agents with different vaporisation points, and in step d) heating of the ribbon is performing via stepwise temperature increments. This may allow the controlled application of a plurality of antimicrobial agents in a particular manner on the substrate; for instance, in broadly defined layers. Furthermore, it may prevent heat-related degradation of antimicrobial agents which are vaporisable at a lower temperature than that required for the applied antimicrobial agent with the highest point of vaporisation.

In step d) the antimicrobial coating application ribbon may be heated to a temperature between 90 and 250 degrees Celsius, to prevent chemical degradation or melting of the polymeric substrate, while allowing transfer of the antimicrobial agents.

The method may preferably comprise a step subsequent to step e), wherein the polymeric substrate is actively cooled in a post-treatment zone of the feed path. As hereinbefore described, active cooling of the substrate may improve the quality of application of the antimicrobial coating.

The polymeric substrate may advantageously be any one of a magnetic strip card, a proximity card, or an integrated circuit card.

According to a third aspect of the invention, there is provided a polymeric substrate with an antimicrobial coating, produced by a method in accordance with the second aspect of the invention.

Preferably, the antimicrobial coating has a depth of at least 5 pm into the surface of the polymeric substrate. This may allow the surface of the polymeric substrate to retain antimicrobial activity despite frictional wear or abrasion to the surface of the polymeric substrate.

In order to ensure sufficient antimicrobial activity to kill pathogens, the concentration of antimicrobial agents in the polymeric substrate may be at least lppm.

According to a fourth aspect of the invention, there is provided an antimicrobial coating application element for sublimation thermal transfer printing on a polymeric substrate, the antimicrobial coating application element comprising a flexible body member, and one or more vaporisable antimicrobial agents applied on the body member.

The invention will now be more particularly described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 shows an exemplary perspective view of one embodiment of a coating system in accordance with the first aspect of the invention;

Figure 2 shows a schematic cross section of the embodiment of a coating system shown in Figure 1;

Figure 3a shows a perspective view of an antimicrobial coating application ribbon, in accordance with the fourth aspect of the invention;

Figure 3b shows a cross-sectional view of the antimicrobial coating application ribbon shown in Figure 3a.

Figure 4 shows a flow-chart for one implementation of the method of applying an antimicrobial coating, in accordance with the second aspect of the invention; and

Figure 5 shows a perspective view of one embodiment of a polymeric substrate with an antimicrobial coating, in accordance with the third aspect of the invention.

Referring to Figures 1 and 2 of the drawings, there is shown a system 10 for applying an antimicrobial coating 12 to a polymeric substrate 14, preferably formed as a card. The system 10 may be used to apply an antimicrobial coating 12 to a card in a commercial or industrial context, and the card may be a payment card, or security card, among other possibilities.

The coating system 10 comprises a sublimation thermal transfer printer 16 and an antimicrobial coating application ribbon 18, the sublimation thermal transfer printer 16 having a feed path 20, the feed path 20 including an inlet 22, an outlet 24 and a printing zone 26 therebetween. The feed path 20 may be non-linear, as shown in Figure 2 of the drawings, but it may also be linear, tortuous, serpentine, or self-intersecting. The sublimation thermal transfer printer may be contained entirely within a housing unit 25, and the feed path 20 may occupy the majority of the volume of the housing unit 25.

The sublimation thermal transfer printer 16 may be a conventional dye sublimation thermal transfer printer, with appropriate modifications as necessary, or a customprepared sublimation thermal transfer printer. The sublimation thermal transfer printer 16 may preferably comprise, in the printing zone 26, a heat source 28, a pressure application element 30, and an actuator 32 for driving one or more rollers 34 and/or the antimicrobial coating application ribbon 18.

The sublimation thermal transfer printer 16 may also preferably comprise a microcontroller 36, a user-interface output module 38 displaying printing indicia, and an input module 40 which allows a user to configure the sublimation thermal transfer printer 16 with respect to the technical specifications of printing operations, including, but not limited to, the durations of stages of the printing process, temperature and pressure applied to the antimicrobial coating application ribbon 18 and/or polymeric substrate 14, the position of the antimicrobial coating application ribbon 18, and the composition and surface properties of the polymeric substrate 14. The sublimation thermal transfer printer 16 may also be activatable via a remote signal over a wireless communications protocol.

As shown in Figure 3 a, the antimicrobial coating application ribbon 18 may advantageously be provided on one or more reels or spools 42, to allows fast replacement and compact storage of used antimicrobial coating application ribbon 18. The reels or spools 42 of the antimicrobial coating ribbon may be mountable on one or more pins or other mounting elements located in the printing zone 26, and most preferably may be drivable by one or more reel-drive motors 44 via the rotation of the said pins or other similar mounting elements.

Referring to Figure 3b, the antimicrobial coating application ribbon 18 preferably includes a backing layer 46, and one or more antimicrobial layers 48, comprising a plurality of antimicrobial agents. Possible compositions of the backing layer 46 and choices of antimicrobial agents are hereinafter provided. The or each antimicrobial layer may contain a single blended mixture of a plurality of antimicrobial agents. Alternatively, if it is desirable to provide distinct areas of different antimicrobial agents on or in the polymeric substrate, the or each antimicrobial layer 48 of the antimicrobial coating application ribbon 18 may be subdivided into a plurality of distinct sections with varying antimicrobial agent compositions. Furthermore, the concentration of any given antimicrobial agent may be distributed in a gradient across the surface of the antimicrobial coating application ribbon 18, by asymmetric distribution of the antimicrobial agent on the antimicrobial coating application ribbon 18.

The inlet 22 preferably defines the entrance of the feed path 20, and the polymeric substrate 14 may be manually or automatically inserted therein. A plurality of motordriven rollers 34 may be provided within, at or without the inlet 22 and throughout the feed path 20, to allow automated transfer of the polymeric substrate 14 along the feed path, although other similar mechanical means for transferring the polymeric substrate 14 along the feed path 20 may be considered. The inlet 22, as well as the outlet 24, may most preferably be formed as a slot on an exterior surface of the sublimation thermal transfer printer 16.

To start the sublimation thermal transfer printing cycle, the polymeric substrate 14 may be manually or automatically inserted into the inlet 22.

Subsequent to the inlet 22, there may preferably be provided a pre-treatment zone 50 in the feed path 20, wherein the polymeric substrate 14 may be heated to achieve surface activation. The pre-treatment zone 50 may simply be defined as a section of the feed path 20 in which pre-treatment occurs, or it may be provided as a dedicated chamber in the sublimation thermal transfer printer 16, which the feed path 20 passes through, whereat the polymeric substrate 14 might be retained for pre-treatment. In any case, there may preferably be a heat source 52 provided in the pre-treatment zone 50, to heat the polymeric substrate 14.

Appropriate heating temperatures and times required to activate the surface of a given polymeric substrate 14 may be highly variable, depending on the composition of the polymeric substrate 14. Surface activation preferably may result in sufficiently high surface energy of the polymeric substrate 14 that vaporised antimicrobial agents, dyes and any other vaporisable additives may substantially penetrate the surface of the substrate during the sublimation thermal transfer printing process. The heating temperature must be below the melting point of the polymeric substrate 14, and any relevant temperature threshold for chemical degradation, to avoid undesirable physical or chemical modification of the surface of the polymeric substrate 14. Preferably, the heating temperature may be between 60 and 275 degrees Celsius, and most preferably, the heating temperature may be between 175 and 250 degrees Celsius. Suitable heating temperatures and times may also vary with the type of heat source 52 used. Only one surface of the polymeric substrate 14 may be activated, or a plurality of the surfaces of the polymeric substrate 14 may be activated.

If and when the polymeric substrate 14 has been surface-activated, it may preferably be transferred along the feed path 20, by the rollers 34 to the printing zone 26. At the printing zone 26, an activated surface of the polymeric substrate 14 may be placed in contact with the antimicrobial coating application ribbon 18.

Before the thermal transfer of the antimicrobial coating 12 to the polymeric substrate 14, a pressure may be imposed between a layer of the polymeric substrate 14, especially an activated layer of the polymeric substrate 14, if surface activation has occurred in pretreatment, and the antimicrobial layer 48 of the antimicrobial coating application ribbon 18, by one or more pressure application elements 30. The pressure application elements 30 may be press elements in engagement with one of, or alternatively both of, the antimicrobial coating application ribbon 18 and polymeric substrate 14, although various other options may be evident to the person skilled in the art. The applied pressure may preferably lie between 150 kPa and 600 kPa, and most preferably between 300 kPa and 400 kPa. The application of pressure reduces the temperature required to vaporise the or each antimicrobial agent, and thus allows a wider range of antimicrobial agents to be used at lower temperatures, which are less likely to cause physical or chemical degradation of the polymeric substrate 14.

Heat may then be applied to the antimicrobial coating application ribbon 18 using the heat source 28, to achieve thermal transfer of the or each antimicrobial agent, by the vaporisation of the or each antimicrobial agent and migration to the polymeric substrate 14. While the heat source 28 may preferably be a heated metallic printing element applicable to the antimicrobial coating ribbon, other heat sources may be considered by the person skilled in the art; for example, infrared flash heating, photonic sintering or laser heating may be used. If laser heating is adopted, the backing layer or the antimicrobial layer may include one or more laser absorbing additives, such as pulverized titanium dioxide or carbon black. In any case, the application of heat may be across the entire contacted surface, or alternatively, it may be topical, to achieve topical transfer of the or each antimicrobial agent. If one or more antimicrobial agents are distributed asymmetrically on the antimicrobial coating application ribbon, for instance so as to form a concentration gradient of the antimicrobial agents across the ribbon, on thermal transfer of the antimicrobial agents to the polymeric substrate, areas which experience the most friction and/or abrasion in normal use of the polymeric substrate may receive greater concentrations of antimicrobial agent, due to the asymmetric distribution of the antimicrobial agents on the antimicrobial coating application ribbon .

The antimicrobial coating application ribbon 18 may be heated to any temperature between 60 and 550 degrees Celsius, to achieve thermal transfer of the or each antimicrobial agent. Preferably, the heating temperature may be between 90 and 250 degrees Celsius, and most preferably between 180 and 230 degrees Celsius. A lower heating temperature is advantageous, as it allows the coating system 10 and method to be applied to a variety of polymeric substrates 14, including those which might experience physical or chemical degradation, or at least surface deterioration, on heating to higher temperatures. Additionally, a lower heating temperature may reduce thermal expansion and contraction of a metallic heating element in use, increasing its lifetime. However, higher heating temperatures may be required to transfer specific antimicrobial agents with high vaporisation points, and may also beneficially reduce the time required for thermal transfer. The preferred heating time may vary between 1 millisecond to 0.1 seconds, depending on the composition of the antimicrobial agents, and the polymeric substrate 14.

After the application of one or more first antimicrobial agents via thermal transfer from the antimicrobial coating application ribbon 18, thermal transfer of further antimicrobial agents, dyes, and other functional coating agents may occur. Thermal transfer of said further agents may be achieved via different application ribbons 18; alternatively, such further agents may be located in the antimicrobial layer 48 of the antimicrobial coating application ribbon 18, but at a different position to the first antimicrobial agents, so that subsequent to the application of the first antimicrobial agents, the antimicrobial coating ribbon may be removed from contact with the polymeric substrate 14, and appropriately repositioned by driving one or more of the reels, so that a new section of the antimicrobial coating ribbon 18 containing the different further agents may be placed in contact with the polymeric substrate 14, so that thermal transfer of the further agents may be achieved. One or more antimicrobially agents may optionally be distributed asymmetrically on the antimicrobial coating application ribbon, so that on application of the coating to the polymeric substrate, areas which experience the most friction and/or abrasion in normal use of the polymeric substrate may contain greater concentrations of antimicrobial agent.

When the sublimation thermal transfer printer 16 is a conventional dye sublimation thermal transfer printer, the antimicrobial coating application ribbon 18 may be interchangeable with a standard colour application ribbon. For instance, in a sublimation thermal transfer printer 16 designed for CYMK four colour printing, the antimicrobial coating application ribbon 18 may be interchangeable with the key ribbon, to provide a

CMY printer with antimicrobial coating application. Alternatively, a four-colour sublimation thermal transfer printer 16 may be used as a RGB printer with antimicrobial coating application functionality. Most preferably, a CYMK four colour printer may be provided with one or more antimicrobial coating application ribbons 18 in addition to standard colour application ribbons.

The coated polymeric substrate 14’ may now be removed from the printing zone 26, and transferred along the feed path 20 to an optional post-treatment zone 54. In the posttreatment zone 54 the polymeric substrate 14’ may be actively cooled, by one or more active cooling elements 56 located in the post-treatment zone 54, such as an air blower or refrigerated gas releaser, in order to improve the quality of application of the antimicrobial coating, by preventing unwanted chemical reactions between constituents of the antimicrobial composition, which may occur due to the high temperature of the newly applied coating. Additionally, in the absence of active cooling, anomalous coating properties may occur at microirregularities on the substrate surface, for example, due to prolonged high-surface activity during cooling. For instance, irregularities in the coating thickness may occur, which may lead to non-optimum frictional wear properties, reducing antimicrobial protection of the polymeric substrate. The cooled polymeric substrate 14’ may then be ejected from the feed path 20 via the outlet 24, for immediate use. The completion of this final step is considered the end of one sublimation thermal transfer printing cycle.

Referring to Figure 4 of the drawings, one possible method 100 of using system 10 to apply an antimicrobial coating 12 to a polymeric substrate 14 is illustrated.

In a step S102 of the method 100, the polymeric substrate 14 is introduced to the feed path 20 via the inlet 22. In a subsequent optional step S104, the substrate 14 is transferred to a pre-treatment zone 50 and heated to increase its surface energy. The polymeric substrate 14 is then transferred to the printing zone 26, in a step S106. In the printing zone, the polymeric substrate 14 is placed in contact with an antimicrobial coating application ribbon 18, in a step S108. In a subsequent step SI 10, the antimicrobial coating application ribbon 18 is heated to apply vaporisable antimicrobial agents to the polymeric substrate 14. In a further optional step SI 12, the polymeric substrate 14 is transferred to a post-treatment zone 54 and actively cooled. In a step SI 14, the polymeric substrate 14’ is removed from the feed path 20 and ejected via the outlet 24.

To avoid having to modify the selection of antimicrobial agents, and the sublimation thermal transfer printer settings, for substrates with different compositions, various modifications to the method hereinbefore presented may be contemplated. For instance, in a first pre-treatment step, a topcoat may be formed on the polymer substrate, in the first pre-treatment zone, the topcoat being formed from a polymer with suitable physical and chemical properties. In a second pre-treatment step, in the first or a second pre-treatment zone, the topcoat may be surface-activated by heating, such that subsequently the antimicrobial coating is applied onto and/or into the topcoat of the polymeric substrate, in the printing zone. Provided that the topcoat is surface-activatable by heating at a temperature below common melting points of plastics materials (for instance, at a temperature between 90 and 120 degrees Celsius), this method may be suitable for the application of an antimicrobial coating to a wide variety of plastic substrates.

In one conceivable modification of this method, in a pre-treatment step, the polymeric substrate may be surface activated by heating, in a pre-treatment zone. Subsequently, in the printing zone, dyes may be applied to the polymeric substrate by sublimation thermal transfer printing, in a first printing zone. In a first, optional, post-treatment step, the polymeric substrate may be cooled, in a first post-treatment zone. In a second posttreatment step, a polymeric topcoat may be applied to the polymeric substrate, in the first or a second post-treatment zone. Optionally, the polymeric topcoat may then be surfaceactivated by heating, in the first, second, or in a third post-treatment zone, or alternatively, in the pre-treatment zone. Subsequently, in the first or a second printing zone, an antimicrobial coating may be applied to the polymeric topcoat by sublimation thermal transfer printing. In an optional post-treatment step, the polymeric topcoat may be cooled in the first or a fourth post-treatment zone. Thus, a polymeric topcoat with an antimicrobial coating may be applied over the polymeric substrate, so that the dye applied to the polymeric substrate is protected from friction and/or abrasion by the polymeric topcoat, and the polymeric substrate has an antimicrobial coating. In a further advantageous modification, an antimicrobial coating may be applied directly to the polymeric substrate as well as to the polymeric topcoat, so that the polymeric substrate retains antimicrobial surface activity even if the polymeric topcoat is substantially degraded by friction and/or abrasion, leading to the exposure of the polymeric substrate.

Thus, as illustrated by the possible embodiments described above, the feed path may have non-linear directionality, especially if it is self-intersecting, with zones thereof having multiple functionalities, or the same functionality but applied multiple times in each sublimation thermal transfer printing cycle. In a simple example, when printing on a polymeric substrate, topcoat application, and printing on the topcoat may be desired, and therefore the feed path may follow the route: pre-treatment zone —> printing zone —> posttreatment zone —> pre-treatment zone —> printing zone —> post-treatment zone, with topcoat application and pre-treatment heating on the second visit of the polymeric substrate to the same pre-treatment zone, and printing onto the polymeric substrate and topcoat in the same printing zone. Any zone on the feed path may advantageously adopt any compatible functionality of any other adjacent zone, while additionally or alternatively, any zone on the feed path with multiple functionalities may be replaced by a plurality of zones, each having one or more of the functionalities of the said zone; a zone which has one functionality, applied in multiple distinct stages of a sublimation thermal transfer printing cycle, may be considered to have a plurality of functionalities, one corresponding to each distinct application of the functionality over the sublimation thermal transfer printing cycle. In particular, if a plurality of printing zones is required, they may be daisy-chained, which advantageously negates the requirement to surfaceactivate the polymeric substrate prior to every printing step.

In any case, the composition used in the polymeric substrate 14 (and any topcoat applied) may be any thermosetting, thermoplastic or other polymer, preferably such that the surface of substrate is activatable at a temperature at or below 275 degrees Celsius and a pressure of below 600 kPa. Advantageously, this results in the antimicrobial coating application method being suitable for the coating of polymeric substrates 14 formed from a wide variety of known commodity, speciality and fine plastics materials.

For example, the composition may include one or more of the following polymers, or one or more polymers selected from the following groups of polymers: polyamides (especially nylon 66), polyacrylates, polypropylene, polyurethane.

As well as such conventional polymers, antimicrobial polymers may also be considered, especially for surface coating (including topcoats) of the polymeric substrate. The composition thus may include one or more of n-alkylated polyethyleneimines (especially quaternary ammonium polyethyleneimine), quaternary phosphonium modified epoxidized natural rubber, poly-(D)glucosamine, guanylated polymethacrylate, lactonemodified poly(N-vinylamine) (especially with γ-butyrolactone), and ammonium ethyl methacrylate homopolymers. Various other such polymers with appropriate technical properties are known, and will be apparent to the person skilled in the art.

Antimicrobial impregnated polymers may also be included in the composition. Active antimicrobial agents, such as silver, gold, copper, arsenic, mercury (and amalgams thereof), 2,4,4'-trichloro-2'-hydroxydiphenyl ether (triclosan), and polyaryl- or polyalkylammonium or phosphonium halides (especially cetrimonium bromide) may be incorporated into various polymers. In particular, polymers formed from (meth)acrylic acid monomers may be particularly appropriate, as such polymers are known to retain silver among other heavy metal antimicrobial agents. However, any such antimicrobial impregnated polymers may be advantageous, due to the provision of sustained release of more potent antimicrobial agents than otherwise could be provided.

The polymeric substrate 14 may be prepared with one or more data storage elements 58. The data storage elements may include, by way of example, a magnetic strip, an RFID tag, or a microchip. Preferably, such data storage elements 58 may be pre-coated with one or more appropriate antimicrobial agents, as sublimation thermal transfer of antimicrobial agents thereon, especially at high temperature, may risk damaging the said data storage elements.

Optionally, the provision of a polymeric substrate with one surface pre-prepared with an antimicrobial agent, and one uncoated surface would allow the sublimation thermal transfer printing of an antimicrobial layer, either directly on the uncoated layer of the polymeric substrate, or on a topcoat applied to the uncoated layer of the polymeric substrate. This may be advantageous, as it would allow the preparation of polymeric substrate with antimicrobial coatings and custom printed designs on a simple sublimation thermal transfer printer, which may only be capable of printing one side of a polymeric substrate during any one printing cycle. In particular, such a polymeric substrate may be used for a hotel guest card, business conference card, or library card, where identifying details of a user may be printed on a polymeric card substrate.

The antimicrobially coated polymeric substrate 14’ may beneficially have an antimicrobial coating which has a depth of at least 5 pm into the surface of the polymeric substrate 14’, although the penetration of the antimicrobial coating into the surface of the polymeric substrate may be highly variable, dependent on the antimicrobial coating composition, the temperature and pressure used in thermal transfer, and the composition of the polymeric substrate. Antimicrobial coating depths of between 0.5 pm and 30 pm may also be considered advantageous; preferably the antimicrobial coating may be sufficiently deep that it is not worn away by friction and/or abrasion during the lifetime of the polymeric substrate, with normal use. However, it will be appreciated that the suitability of any given depth may be dependent on a desired use of the polymeric substrate, and the activity and/or toxicity of the active antimicrobial agent.

The concentration of active antimicrobial agents in the coated polymeric substrate 14’ is preferably no less than 1 ppm, although much higher concentrations of antimicrobial agents may be considered. For instance, for a polymeric substrate card with thickness 1 mm, and coatings of depth 5 pm on either side of the polymeric substrate across the full extent of its surface area, the coatings constitute 1% of the volume of the coated polymeric substrate. Assuming that the concentration of antimicrobial agents in the coating may be approximately 20000 ppm, the concentration of antimicrobial agents in the polymeric substrate will be 200 ppm. If the polymeric substrate is a topcoat applied to a second polymeric substrate, an even higher concentration of antimicrobial agents may be appropriate, such as 3500 ppm or even 5000 ppm. If the card is thinner than 0.1 mm (typical thickness of 80 gsm paper), the coating may conceivably penetrate the entire volume of the card, resulting in extremely high concentrations of antimicrobial agents, such as 20000 ppm to 50000 ppm.

As shown in Figure 5, the coated polymeric substrate 14’ may have a plurality of graphical elements 60 printed thereon in addition to the antimicrobial coating. Most preferably, such graphical elements 60 may be printed with antimicrobial dyes, either through the same or a different sublimation thermal transfer printing cycle. If it is desirable for the graphical elements to be raised with respect to the polymeric substrate, the graphical elements may be embossed on the polymeric substrate subsequent to the application of the antimicrobial coating.

The antimicrobially coated polymeric substrate 14’ may be a magnetic strip card, a proximity card, or an integrated circuit card. Such a card may be applied as an identification card, a payment card, a loyalty card, an insurance card, a public services card or a security card. The antimicrobially coated polymeric substrate may alternatively be a means of exchange, and preferably, a banknote, or a token. The antimicrobially coated polymeric substrate may also be a textile or laminate, especially a textile suitable for use in clothing or furnishing. The antimicrobially coated polymeric substrate may alternatively be a wearable badge.

The backing layer 46 of the antimicrobial agent application ribbon 18 most preferably comprises polyethylene terephthalate film. However, other flexible polymeric materials may also be appropriate, such as polypropylene, polyamides, polyurethanes, polysiloxane elastomer, or polydimethyl siloxane elastomer. The backing layer 46 may also include a thermally resistant coating 62, to prevent physical or chemical deterioration of the backing layer 46 upon heat treatment, which may cause the antimicrobial agent application ribbon 18 to split, deform or stick to a heating element. The thermally resistant coating 62 may include a lubricant, such as silicone or a fatty acid, to prevent the heating element from sticking to the heating element, and may also include a polymeric binder. The or each antimicrobial layer 48 contains one or more antimicrobial agents, and may also contain various other compositions, including a binder, fillers, plasticizers or tackifiers. Such additives should be carefully chosen to avoid inadvertent contamination of the polymeric substrate 14 on thermal transfer of the antimicrobial agents, as well as intercompatibility of the antimicrobial agents.

The or each antimicrobial layer 48 most preferably comprises a plurality of active antimicrobial agents with specific activity against different categories of microorganisms. The active antimicrobial agents may preferably be sufficiently volatile to be vaporisable at a maximum pressure of 600 kPa at 250 degrees Celsius. The active antimicrobial agents may also have low flammability and human/environmental toxicity, and most preferably may be identified as presenting a low risk to human health and/or the environment by a relevant national or international authority, e.g. by the European Chemicals Agency under the Biocidal Products Regulation or Regulation (EC) No 1907/2006 or Directive 98/8/EC, or by the United States Environmental Protection Agency under the Federal Insecticide, Fungicide and Rodenticide Act.

The or each antimicrobial layer 48 may contain antibacterial agents, antiviral agents, antifungal agents, antiprotozoal agents and antiamoebic agents. In particular, the antimicrobial layer 48 may contain one or more of the following active antimicrobial agents, and/or members of one or more of the following groups of active antimicrobial agents, and/or structural or functional analogues thereof, and/or mixtures thereof 2phenylphenol, 2,4,4'-trichloro-2'-hydroxydiphenyl ether (triclosan), 2(thiocyanomethylthio)benzothiazole, cyanoacrylates (especially ethyl-2-cyano-3,3'diphenyl acrylate), isothiazolinone and derivatives thereof (especially 2-methyl-4isothiazolin-3-one, 5-chloro-2-methyl-4-isothiazolin-3-one, benzisothiazolin-3-one, 2octyl-4-isothiazlin-3-one, 4,5-dichloro-n-octyl-4-isothiazolin-3-one, and N-butyl-1,2benzisothiazolin-3-one), halogenated phenols (especially 2,4,6-tribromophenol, 2,4,6trichlorophenol, pentachlorophenol, //-chlorocresol), nitrophenols, fatty acids and derivatives thereof (especially octanoic acid, nonanoic acid), triazole fungicides (especially propiconazole, cyproconazole), N-dichlorofluoromethylthio-N',N'-dimethylN-para-tolylsulfamide (tolylfluanid), N-(trihalomethyl-thio)phthalimides (especially N(trichloromethyl-thio)phthalimide), (benzyloxy)methanol, 2-isopropyl-5-methylphenol, phenylpropanoids (especially 2-methoxy-4-(prop-2-en-l-yl)phenol), organic salicylates (especially phenyl salicylate), and rotenoids (especially rotenone).

The or each antimicrobial layer 48 may additionally or alternatively contain one or more dyes with antimicrobial activity, such as anthraquinone dyes (especially polyfluorinated or perfluorinated anthraquinone dyes), or N-halamine dyes, so that said dyes are applicable to the polymeric substrate in concentrations high enough to have significant antimicrobial activity in the absence of other antimicrobial agents. In this case, during the application of the antimicrobial coating, dyes with antimicrobial activity may be applied to whichever parts of the polymeric substrate require graphical elements 60, and non-dye antimicrobial agents may be applied to the remainder of the surface area of the polymeric substrate for which antimicrobial coating is desired, most preferably the entire surface area of the polymeric substrate, or the entirety of a plurality of surfaces of the polymeric substrate which together constitute 90% or more of the surface area of the polymeric substrate.

It is therefore possible to provide a system and method for applying an antimicrobial coating to a polymeric substrate, using sublimation thermal transfer printing. This method may advantageously result in the possibility of preparation of a polymeric substrate with application of a custom colour printed design and an antimicrobial coating in the same printing cycle. The system and method may be applied to a wide range of polymeric substrate and antimicrobial coating compositions. An antimicrobial coating application ribbon for the system may be compatible with commercially available conventional sublimation thermal transfer printers, to facilitate adoption of the method. The resulting antimicrobially coated polymeric substrate may have an antimicrobial coating with substantial depth in the polymeric substrate, so that the antimicrobial coating is protected from abrasive or frictional deterioration.

The term “polymeric substrate” herein with reference to the present invention may be understood as referring to any substrate formed substantially from a polymeric material on which sublimation thermal transfer printing may be performed, and therefore may be understood to include a topcoat of a polymeric substrate, as well as the polymeric substrate.

The use of the term “coating” herein with reference to the present invention is not limited to the application of a composition on any one surface of a substrate, but also includes the application of the composition into the substrate, such that a sub-surface portion of the substrate is impregnated with the composition.

The use of the term “sublimation” herein with reference to the present invention does not necessarily imply thermodynamic sublimation; as commonly understood in the art, “sublimation” may be achieved by the vaporisation of a solid via a liquid phase, or the vaporisation of a liquid, or one or more components of a gel, directly, as well as the thermodynamic sublimation of a solid.

The words ‘comprises/comprising’ and the words ‘having/including’ when used herein with reference to the present invention are used to specify the presence of stated features, integers, steps or components, but do not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.

The embodiments described above are provided by way of examples only, and various other modifications will be apparent to persons skilled in the field without departing from the scope of the invention as defined herein.

Claims

1. A coating system for applying an antimicrobial coating to a polymeric substrate, the system comprising:

a sublimation thermal transfer printer having a feed path, the feed path including an inlet, an outlet, and a printing zone between the inlet and outlet;

an antimicrobial coating application ribbon locatable in the printing zone of the feed path of the sublimation thermal transfer printer; the antimicrobial coating application ribbon including a flexible ribbon body, and one or more vaporisable antimicrobial agents applied on the ribbon body, wherein, upon activation of the sublimation thermal transfer printer, with a substrate at the printing zone, the sublimation thermal transfer printer vaporises the vaporisable antimicrobial agent onto said substrate.

2. A coating system, as claimed in claim 1, wherein the or each vaporisable antimicrobial agent is provided in a single layer on a surface of the antimicrobial coating application ribbon.

3. A coating system as claimed in claim 2, wherein the said layer is located on only one surface of the antimicrobial coating application ribbon.

4. A coating system as claimed in any one of the preceding claims, wherein the antimicrobial coating application ribbon comprises one or more vaporisable dyes.

5. A coating system as claimed in claim 4, wherein at least one of the or each vaporisable dye includes the or each antimicrobial agent.

6. A coating system, as claimed in any one of preceding claims, wherein the or each vaporisable antimicrobial agent is selected from the group consisting of:

2-phenylphenol, 2,4,4'-trichloro-2'-hydroxydiphenyl ether (triclosan), 2(thiocyanomethylthio)benzothiazole, cyanoacrylates (especially ethyl-2-cyano22

3,3'-diphenyl acrylate), isothiazolinone and derivatives thereof (especially 2methyl-4-isothiazolin-3-one, 5-chloro-2-methyl-4-isothiazolin-3-one, benzisothiazolin-3-one, 2-octyl-4-isothiazlin-3-one, 4,5-dichloro-n-octyl-4isothiazolin-3-one, and N-butyl-l,2-benzisothiazolin-3-one), halogenated phenols (especially 2,4,6-tribromophenol, 2,4,6-trichlorophenol, pentachlorophenol, //-chlorocresol), nitrophenols, fatty acids and derivatives thereof (especially octanoic acid, nonanoic acid), triazole fungicides (especially propiconazole, cyproconazole), N-dichlorofluoromethylthio-N',N'-dimethyl-Npara-tolylsulfamide (tolylfluanid), N-(trihalomethyl-thio)phthalimides (especially N-(trichloromethyl-thio)phthalimide), (benzyloxy)methanol, 2isopropyl-5-methylphenol, phenylpropanoids (especially 2-methoxy-4-(prop-2en-l-yl)phenol), organic salicylates (especially phenyl salicylate), and rotenoids (especially rotenone).

7. A coating system as claimed in any one of the preceding claims, wherein the inlet of the feed path is provided as a slot.

8. A coating system as claimed in any one of the preceding claims, wherein one or more heating elements is located in the printing zone.

9. A coating system as claimed in claim 8, wherein the antimicrobial coating application ribbon is mountable in the printing zone such that the or each heating elements are located proximally to the antimicrobial coating application ribbon, to allow contact between the or each heating elements and the antimicrobial coating application ribbon.

10. A coating system as claimed in any one of the preceding claims, wherein the feed path further comprises a pre-treatment zone, between the inlet and the printing zone, for surface activation of the polymeric substrate.

11. A coating system as claimed in any one of the preceding claims, wherein the feed path further comprises a post-treatment zone, between the printing zone and the outlet, for cooling of the substrate.

12. A coating system as claimed in any one of the preceding claims, wherein the antimicrobial coating application ribbon is mounted on one or more reels, drivable by one or more motors located in the printing zone and engageable with the or each reel.

13. A method of applying an antimicrobial coating to a polymeric substrate, comprising the steps of:

a) providing a system as claimed in any one of the preceding claims;

b) introducing a polymeric substrate to be coated to the feed path of the sublimation thermal transfer printer via the inlet;

c) moving the polymeric substrate along the feed path into the printing zone, placing the antimicrobial coating application ribbon in contact with a surface of the polymeric substrate, and applying a pressure between the antimicrobial coating application ribbon and the polymeric substrate;

d) heating the antimicrobial coating application ribbon to apply the or each antimicrobial agent onto or into the surface of the polymeric substrate; and

e) removing the polymeric substrate from the printing zone, to eject the coated polymeric substrate.

14. A method of applying an antimicrobial coating to a polymeric substrate as claimed in claim 13, further comprising a step prior to step a), wherein the feed path includes a pre-treatment zone, in which the polymeric substrate is pre-heated to increase its surface energy.

15. A method of applying an antimicrobial coating to a polymeric substrate as claimed in claim 13 or 14, wherein the polymeric substrate is pre-heated at temperature between 60 and 275 degrees Celsius.

16. A method of applying an antimicrobial coating to a polymeric substrate as claimed in any one of claims 13 to 15, wherein the polymeric substrate is pre-heated for less than 5 seconds.

17. A method of applying an antimicrobial coating to a polymeric substrate, as claimed in any one of claims 13 to 16, wherein in step c) the applied pressure is between 150 kPa and 600 kPa.

18. A method of applying an antimicrobial coating to a polymeric substrate, as claimed in any one of claims 13 to 17, wherein in step d) the ribbon is heated topically, to achieve topical application of the antimicrobial coating.

19. A method of applying an antimicrobial coating to a polymeric substrate, as claimed in any one of claims 13 to 18, wherein in step c) a plurality of antimicrobial coating application ribbons is placed in contact with a plurality of surfaces of the polymeric substrate, and in step d) each antimicrobial coating application ribbon is heated, to apply an antimicrobial coating to the plurality of surfaces of the polymeric substrate.

20. A method of applying an antimicrobial coating to a polymeric substrate, as claimed in any one of claims 13 to 19, wherein in step a) the antimicrobial coating application ribbon includes a plurality of vaporisable antimicrobial agents with different vaporisation points, and in step d) heating of the ribbon is performing via stepwise temperature increments.

21. A method of applying an antimicrobial coating to a polymeric substrate as claimed in any one of claims 13 to 20, wherein in step d) the antimicrobial coating application ribbon is heated to a temperature between 90 and 250 degrees Celsius.

22. A method of applying an antimicrobial coating to a polymeric substrate as claimed any of claims 13 to 21, further comprising a step subsequent to step e), wherein the polymeric substrate is actively cooled in a post-treatment zone of the feed path.

23. A method of applying an antimicrobial coating to a polymeric substrate as claimed in any one of claims 13 to 22, wherein the polymeric substrate is any one of a magnetic strip card, a proximity card, or an integrated circuit card.

24. A polymeric substrate with an antimicrobial coating, produced by the method of any one of claims 13 to 23.

25. A polymeric substrate with an antimicrobial coating, as claimed in claim 24, wherein the antimicrobial coating has a depth of at least 5 pm into the surface of the polymeric substrate.

26. A polymeric substrate with an antimicrobial coating, as claimed in claim 24 or 25, wherein the concentration of antimicrobial agents in the polymeric substrate is at least lppm.

27. An antimicrobial coating application element for sublimation thermal transfer printing on a polymeric substrate, the antimicrobial coating application element comprising a body member, and one or more vaporisable antimicrobial agents applied on the body member.

Intellectual

Property Office

Application No: GB 1708181.1