GB2504764A

GB2504764A - Antimicrobial ink, coating solutions, method and product

Info

Publication number: GB2504764A
Application number: GB1214277.4A
Authority: GB
Inventors: Martin Jones
Original assignee: W O JONES PRINTERS Ltd
Current assignee: W O JONES PRINTERS Ltd
Priority date: 2012-08-09
Filing date: 2012-08-09
Publication date: 2014-02-12
Also published as: GB201214277D0

Abstract

An antimicrobial paper or paperboard is provided by adding colloidal silver and/or copper and/or zinc to the ink, aqueous fountain solution (9) or overprint varnish used in offset lithographic printing. Preferably antimicrobial metal in the ink has a mean particle size of 0.6-500nm. Preferably an outer coating is formed from overprint varnish or aqueous fountain solution applied from a coating unit (CU) in the printing press downstream of the colour units (C1 to Cn). The product is useful in hospital environments in which there is a risk of transfer of pathogens between paper and users' hands.

Description

Antimicrobial ink, coating solutions. method and product The present invention relates to a method of forming an antimicrobial coating on a substrate surface, to an antimicrobial ink, overprint varnish or fountain solution for use in printing, and to a printed paper or printed board substrate provided with an antimicrobial coating.

It has been demonstrated that bacterial pathogens suwive on conventional office paper and can be transferred to users' hands (see Hübner et ai, Am J Nursing 2011 Dcc; 111(12): 30-4; quiz 35-6 "Survival qf bacterial pathogens on paper and bacterial retrieval from paper to handc: preiimina;y results").

M Patel, "Developments in Antibacterial Paper" Industry Insight, 2009 (pub: Pira International Ltd), downloaded from www.smitherspira.com, discloses antibacterial papers containing silver compounds introduced during the papermaking process (p col 2). However this adds to the cost of production and much of the silver content below the surface of the paper does not come into contact with surface bacteria and is arguably wasted.

The above Patel reference also discloses papers coated with antibacterial zinc oxide nanoparticles, p 12 col 2). However in many printing processes a coating of overprint varnish is applied to the paper and there is a danger that oils and other deposits from users' skin could harbour bacteria which are protected from the antibacterial coating by the layer of overprint varnish between the skin deposits and the antibacterial coating. The same disadvantage arises following printing, since the deposited ink can also separate surface bacteria from the underlying antibacterial coating.

It has been proposed to add a chemical antibacterial agent to overprint varnish but there are concerns that chemical or physical interaction with the overprint varnish could compromise the print quality and possibly the effectiveness of the antibacterial agent.

The former concern applies particularly to offset lithographic printing, in which the chemical and physical properties of the inks and other liquids used in the printing and coating processes must be closely controlled in order to achieve high quality print.

Metallic inks contain copper-zinc alloy particles (to produce a gold colour) or aluminum particles (to produce a silver colour) which typically have a particle size of 3 to 7 micromctres. Particles of this size have little if any antimicrobial effect. A smaller particle size would impair the reflectance to visible light.

Conversely the metallic particles in colloidal solutions, which typically have a mean particle size by volume, as measured by light scattering, in the range 0.6 to 500 nm, remain in suspension as a result of Brownian motion of the surrounding water molecules.

It has now been found that colloidal solutions of antimicrobial metals, particularly silver and copper, do not impair the print quality and retain their biological activity in overprint varnish and in the aqueous fountain solutions and inks used in eg offset lithographic printing.

Accordingly, in one aspect the invention provides a method of forming an antimicrobial coating on a substrate surface, the method comprising the steps of applying at least one ink to the substrate surface in a printing machine to form a printed substrate surface, and applying an overprint varnish containing a colloidal solution of antimicrobial metal or an aqueous coating containing a colloidal solution of antimicrobial metal to said printed substrate surface, said overprint varnish or aqueous coating containing sufficient antimicrobial metal to inhibit the growth of microorganisms on said substrate surface.

Preferably said overprint varnish or fountain solution is applied from a roller of said printing machine.

In another aspect the invention provides a method of forming an antimicrobial coating on a substrate surface, the method comprising the steps of printing on the substrate surface with an ink containing antimicrobial metal, thc antimicrobial metal having a mean particle size by volume in the range 0.6 to 500 mm The mean particle size can be measured (eg prior to formulation of the ink) by light scattering, Preferably the overprint varnish, aqueous fountain solution or ink contains nanoparticlcs of the antimicrobial metal. Nanoparticles arc defined in ISO/TS 27687:2008 as particles having all three dimensions in the range 100 nm to 1 nm.

The particle size can be measured by light scattering methods. Such particles are considered to be highly effective antimicrobial agents by virtue of their high surface area.

Preferably said printing machine is an offset lithographic printing machine.

In another aspect the invention provides an overprint varnish or fountain solution for application to a substrate surface from a roller of a printing machine to form a solid coating on said surface, the overprint varnish or fountain solution comprising a colloidal solution of antimicrobial metal for inhibiting the growth of microorganisms on said solid coating.

In another aspect the invention provides an ink containing antimicrobial metal for inhibiting the growth of microorganisms in a printed region formed by the ink on a substrate surface, the antimicrobial met& having a mean partide size by volume in the range 0.6 to 500 nm. Other substrates besides paper or paperboard can also be used -The invention also provides a printed paper or board substrate having an antimicrobial metal in the print or in a coating overlying the print, the antimicrobial metal having a mean particle size by volume in the range 0.6 to 500 nm.

Preferably said antimicrobial metal comprises colloidal silver, colloidal copper, or both. Colloidal silver mixed with colloidal copper is considered to be particularly advantageous because the combination has a synergistic antimicrobial effect against certain bacteria, eg Staphylococcus aureus.

Prcfcrably said antimicrobial agcnt comprises coHoida sflvcr and colloidal zinc, colloidal copper and colloidal zinc, or colloidal silver, colloidal copper and colloidal zinc.

Preferably said antimicrobial metal is an antibacterial or bactericidal metal (eg silver or copper or a combination thereof as noted above). Printed materials such as manuals or leaflets protected by such metals are suited for use in hospitals for

example.

In preferred embodiments said antimicrobial metal is effective agaillst one or both of meticil lin-resistant Staphylococcus aureus and clilostridluin difJlciie.

Suitable antimicrobial metal compositions can be prepared by electrochemical methods cg as disclosed in GB2449893A (Aguacure Ltd). This company, based in Bangor, UK, supplies a commercial product containing antimicrobial silver and copper also under the name AG1JACURE.

Preferred embodiments of the invention are described below with reference to Figurcs I to 3 of thc accompanying drawings, whercin: Figure 1 is a diagrammatic side elevation of an offset lithographic printing machine suitable for carrying out methods in accordance with the invention; Figure 2 is a diagrammatic side elevation showing a colour unit C. of the machine of Figure 1 in more detail, and Figure 3 is a diagrammatic side elevation showing a variant CU' of the coating unit CiJofFigurel.

Referring to Figure 1, a conventional sheet fed offset lithographic printing machine is shown, comprising a paper delivery arrangement I which, in combination with a paper transport arrangement in the form of roller-driven endless belts 2, feeds sheets of paper or paperboard through successive lithographic colour units Cl to Cn. The colour units each print a different colour, the final image (on the sheets delivered from colour unit Cn) being a composite of the coloured images produced by the colour units.

Each colour unit has a delivery cylinder (not shown) which feeds sheets into the nip between an impression cylinder 5 and a blanket cylinder 6. The blanket cylinder 6, which has a synthetic rubber surface, transfers to the sheet an image formed thereon by a thin layer of ink. This image is formed by a printing plate clamped around a plate cylinder 7.

Referring to the detailed illustration in Figure 2, the printing plate on plate cylinder 7 is continuously moistened by a damping system comprising a fountain roller 10 (which rotates in an aqueous fountain solution 9a in a trough 8), fabric-covered feed roller 11 which alternately contacts the fountain roller and a metal distributing roller 12, and two plate-damping rollers 13 which arc bridged by the distributing roller and transfer moisture from the distributing roller to the printing plate.

The fountain solution 9a (also known as a damping solution) has a controlled pH typically in the range 4.8 to 55 It also has a lowered surface tension (typically two thirds that of water) which is achieved by the addition of 5% isopropanol. Other damping systems can be employed instead of the roller-based system described above, but in all cases the surface tension and pH of the fountain solution must be controlled.

The damped plate cylinder 7 is inked by an inking system comprising a duct roller 17 which rotates in a bath of oil-based lithographic ink, the transfer of the ink to the duct roller being controlled by a duct blade 19 which applies a film of ink between its trailing cdgc and the adjacent cylindrical surface of the duct blade. Excess ink is caughtbyadriptray l8andreturnedtotheinkbath.

A feed roller 16 transfers ink from duct roller 17 to at least one distributor roller 15, either continuously (in which case it is in continuous contact with both the duct roller and distributor roller) or intermittently (in which case it alternates between the two). The distributor roller 15 (or a chain of such rollers) contacts two inking toilets 14 in bridging fashion.

The ink forming the image on the printing plate is confined to the oleophilic region of the plate and the moisture on the printing plate is confined to the oleophobic region of the plate.

Lithographic inks are based on vehicles which are composed of low molecular weight resins and/or drying oils and non-polar hydrocarbon solvents. The inks typically dry by a combination of physical and chemical processes. Thc %rmcr include absorption of the hydrocarbon solvent into the paper or paperboard substrate and the latter include oxidation of the resins to form peroxides (typically catalysed by added manganese or cobalt salts) and subsequent free-radical polymerisation of the resins to form solids.

It will be apparent fixm the above discussion that both the physical and the chemical properties of the fountain solution and the lithographic ink are important for satisfactory printing.

These requirements also apply to a lesser extent to the coating applied from coating unit CU (Figure 1). This transfers a coating from an aqueous fountain solution 9 via a chain of rollers to the printed sheets fed between the nip of a delivery cylinder and a roller carrying a film of coating solution. Thus the coating unit CU is analogous to the damping system 8, 10, 11, 12 and 13 described above.

The coated printed sheets are fed from the coating unit to a further conventional transport system 3 and are deposited in a paper pile 4 as shown in Figure 1.

Another possible coating unit CU' is illustrated in Figure 3 and can be substituted for coating unit CU. It is analogous to the inking system described above and comprises a duct blade 19b whose trailing edge bears against a duct roller 17b.

Overprint varnish (a non-polar material) is contained in the bath between the duct roller 17b and the duct blade 19b. It is transfened to a synthetic rubber-coated roller 16 and thence to a metal distributor roller 15b which is in simultaneous contact with two synthetic rubber coated rollers 14b. These contact a metal roller 20 and form a uniform coating of overprint varnish thereon, which is transferred to printed sheets carried into the nip of this roller and a delivery roller Sb.

To summarise, the sheets of paper or paperboard receive a coating of non-aqueous (Ic, non-polar) ink and an aqueous (Ic, polar) fountain solution in the colour units Cl to Cn, and the printed sheets arc then coated either with an aqueous (ic, polar) coating from a fountain solution in coating unit CU, or with a non-aqueous (ie, non-polar) coating, namely overprint varnish in coating unit CU'. The physical and chemical properties of the ink and fountain solution applied during printing, and to a lesser extent those of the fountain solution or the overprint vamish applied subsequently, must be controlled in order to ensure reliable high quality printing.

In accordance with a first preferred embodiment of the invention, a colloidal solution of an antimicrobial metal (eg silver and/or copper) is added to the fountain solution 9 which is applied after printing. The resulting printed paper or paperboard includes an outer coating with antimicrobial properties.

In accordance with a second preferred embodiment of the invention, a colloidal solution of an antimicrobial metal (eg silver and/or copper) is added to the bath of

S

overprint varnish in coating unit CU'. Again, the resulting printed coated paper or paperboard includes an outer coating with antimicrobial properties.

In accordance with a third embodiment, a colloidal solution of an antimicrobial metal (eg silver andlor copper) is added to the fountain solution 9 used in printing.

The resulting printed paper or paperboard includes a coating with antimicrobial properties. This coating will cover the unprinted areas which are typically handled by users and will inhibit microorganisms at least on those areas.

In accordance with a fourth embodiment, a colloidal solution of an antimicrobial metal (eg silver and/or copper) is added to the ink in one or more of the colour units Cl to Cn. The resulting printed paper or paperboard includes a coating with antimicrobial properties. This coating will cover the corresponding printed areas and will inhibit microorganisms at least on those areas. This embodiment can be 1 5 combined with the third embodiment.

The third or fourth embodiment (or their combination) can be combined with the second or third embodiment.

Surprisingly, it has been found that such colloidal solutions of antimicrobial metals do not impair the quality of the printed sheets. Furthermore, the resulting printed sheets have antimicrobial properties.

This is demonstrated in the following Example.

Example 1

All-purpose printing paper (SOg/m2) was treated with an ethane sealer in a printing unit of a sheet-fed ofEet lithographic printing machine. The ethane sealer was conventional but was supplemented with l2wt% AGUACTJRE® solution, obtained from Aguacure Ltd, Bangor, UK. AGUACURE is believed to contain about 5000 ppb (parts per billion) colloidal silver and about 3000 ppb colloidal copper. The resulting coating contained a low conccntration of silver and coppcr nanoparticics.

Samples were cut fixm the coated paper and sterilised, and the resulting sterilised swatches of coated papcr were innoculatcd with a test supcnsion containing Escherlchia coil. The swatches were dried and left at room tcmpcraturc for 24 hours. The swatches were then treated by standard methods with saline solution to extract any bacteria and the resulting saline solution samples plated on agar plates to detect surviving bacteria. No colonies of bacteria were detected, indicating that the coating was bactericidal against E.coil.

Claims

Claims 1. A method of forming an antimicrobial coating on a substrate surface, the method comprising the steps of applying at least one ink to the substrate surface in a printing machine to form a printed substrate surface, and applying an overprint vamish containing a colloidal solution of antimicrobial metal or an aqueous coating comprising a colloidal solution of antimicrobial metal to said printed substrate surface, said overprint varnish or aqueous coating containing sufficient antimicrobial metal to inhibit the growth of microorganisms on said substrate surface.
2. A method according to claim 1 wherein said overprint varnish or aqueous coating is applied from a roller of said printing machine.
3. A method of forming an antimicrobial coating on a substrate surface, the method comprising the steps of printing on the substrate surface with an ink containing antimicrobial metal, the antimicrobial metal having a mean particle size by volume in the range 0.6 to 500 nm.
4. A method according to any preceding claim wherein said printing machine is an offset lithographic printing machine.
5. A method according to any preceding claim wherein said antimicrobial metal comprises colloidal silver, colloidal copper, or both.
6. A method according to claim 5 wherein said antimicrobial agent comprises colloidal silver and colloidal zinc, colloidal copper and colloidal zinc, or colloidal silver, colloidal copper and colloidal zinc.
7. A method according to any preceding claim wherein said antimicrobial metal is an antibacterial or bactericidal metal.
8. A method according to claim 7 wherein said antimicrobial metal is effective against one or both of meticillin-resistant Staph ylococcits' aurelLs and Chiostridiwn dUjicile.
9. A method according to any preceding daim wherein said substrate is paper or paperboard.
10. An overprint varnish or fountain solution for application to a substrate surface from a roller of a printing machine to form a solid coating on said surface, the overprint varnish or fountain solution comprising a colloidal solution of antimicrobial metal for inhibiting the growth of microorganisms on said solid coating.
11. An overprint varnish or fountain solution as claimed in claim 10 wherein said antimicrobial metal is an antibacterial or bactericidal metal.
12. An overprint varnish or fountain solution as claimed in claim 11 wherein said antimicrobial metal is effective against one or both of meticillin-resistant Staphylococcus' aureus and Chlostridium dfJicile.
13. An overprint varnish or fountain solution as claimed in claim 12 wherein said antimicrobial metal is as defined in any of claims S to 8.
14. An ink containing antimicrobial metal for inhibiting the growth of microorganisms in a printed region formed by the ink on a substrate surface, the antimicrobial metal having a mean particle size by volume in the range 0.6 to 500 nm.
15. An ink as claimed in claim 14 wherein said antimicrobial metal is an antibacterial agent or bactericidal agent.
16. An ink as claimed in claim 15 wherein said antimicrobial metal is effective against one or both of meticillin-resistant Staphylococcus aureus and Chlostridium d9iciIe.
17. An ink as claimed in claim 14 wherein said antimicrobial metal is as defined in any of claims 5 to 8.
18. A printed paper or board substrate having an antimicrobial metal in thc print or in a coating overlying the print the antimicrobial metal having a mean particle size byvolumeintherangeO.6to500nm.
19. A printed paper or board substrate as claimed in claim 18 wherein said antimicrobial agent is an antibacterial agent or bactericidal agent.
20. A printed paper or board substrate as claimed in claim 19 wherein said antimicrobial agent is effective against one or both of meticillin-resistant Staphylococcus aureus and ChIost rid/urn diffidle.
21.A printed paper or board substrate as claimed in claim 18 wherein said antimicrobial agent is as defined in any of claims 5 to 8.
22. A method as claimed in any of claims 1 to 9, substantially as described hereinabove with reference to Figures 1 and 2, optionally as modified in accordance with Figure 3 of the accompanying drawings.
23. A fountain solution substantially as described hereinabove with reference toExample 1.AMENDMENTS TO THE CLAIMS HAVE BEEN FILED AS FOLLOWS1. A method of forming an antimicrobial coating on a substrate surface, the method comprising the steps of applying at least one ink to the substrate surface in a printing machine to form a printed substrate surface, and applying an overprint varnish containing a colloidal solution of antimicrobial mctal or an aqueous coating comprising a colloidal solution of antimicrobial metal to said printed substrate surface, said overprint varnish or aqueous coating containing sufficient antimicrobial metal to inhibit thc growth of microorganisms on said substrate surface, wherein said antimicrobial metal comprises colloidal silver and colloidal copper, colloidal silver and colloidal zinc, colloidal copper and colloidal zinc, or colloidal silver, colloidal copper and colloidal zinc.2. A method according to claim 1 wherein said overprint vamish or aqueous coating is applied r 15 from a roller of said printing machine. r3. A method of forming an antimicrobial coating on a substrate surface, the method 0) comprising the steps of printing on the substrate surface with an ink containing antimicrobial 0 metal, wherein said antimicrobial metal comprises colloidal silver and colloidal copper, colloidal silver and colloidal zinc, colloidal copper and colloidal zinc, or colloidal silver, colloidal copper and colloidal zinc, the antimicrobial metal having a mean particle size by volume in the range 0.6 to 500 nm.4. A method according to any preceding claim wherein said printing machine is an offset lithographic printing machine.5. A method according to any preceding claim wherein said antimicrobial metal is effective against one or both of meticillin-resistant Staphylococcus aureus and Chlostridiu;n difficile.6. A method according to any preceding claim wherein said substrate is paper or paperboard.7. An overprint varnish or fountain solution for application to a substrate surface from a roller ofa printing machine to form a solid coating on said surface, the overprint varnish or fountain solution comprising a colloidal solution of antimicrobial metal for inhibiting the growth of microorganisms on said solid coating, wherein said antimicrobial metal comprises colloidal silver and colloidal copper, colloidal silver and colloidal zinc, colloidal copper and colloidal zinc, or colloidal silver, colloidal copper and colloidal zinc.8. An overprint varnish or fountain solution as claimed in claim 7 wherein said antimicrobial metal is effective against one or both of mcticillin-rcsistant Staphylococcus aureus and Chlostriclium difJicile.9. An ink containing antimicrobial metal for inhibiting the growth of microorganisms in a printed region formed by the ink on a substrate surface, wherein said antimicrobial metal comprises colloidal silver and colloidal copper, colloidal silver and colloidal zinc, colloidal copper and colloidal zinc, or colloidal silver, colloidal copper and colloidal zinc, the r antimicrobial metal having a mean particle size by volume in the range 0.6 to 500 nm. r0') 10. An ink as claimed in claim 9 wherein said antimicrobial metal is effective against one or 0 both of meticil lin-resistant Staphylococcus aureus and Chlostridiuin difJicile.11. A printed paper or board substrate having an antimicrobial metal in the print or in a coating overlying the print, wherein said antimicrobial metal comprises colloidal silver and colloidal copper, colloidal silver and colloidal zinc, colloidal copper and colloidal zinc, or colloidal silver, colloidal copper and colloidal zinc, the antimicrobial metal having a mean particle size by volume in the range 0.6 to 500 nm.12. A printed paper or board substrate as claimed in claim 11 wherein said antimicrobial agent is effective against one or both of meticillin-resistant Staphylococcus aureus and Chlostridium difflcile.13. A method as claimed in any of claims I to 6, substantially as described hereinabove with reference to Figures 1 and 2, optionally as modified in accordance with Figure 3 of the accompanying drawings.14. A fountain solution substantially as described hereinabove with reference to Exampc I. r r a)