AU739059B2

AU739059B2 - Printing method and ink compositions therefor

Info

Publication number: AU739059B2
Application number: AU51850/98A
Authority: AU
Inventors: Gurjeet Singh Bains; Maxwell Neil Robbie
Original assignee: Metal Sign & Label Pty Ltd
Current assignee: Metal Sign & Label Pty Ltd
Priority date: 1997-12-04
Filing date: 1997-12-04
Publication date: 2001-10-04
Anticipated expiration: 2017-12-04
Also published as: WO1999029789A1; AU5185098A

Description

WO 99/29789 PCT/AU97/00827 1 PRINTING METHOD AND INK COMPOSITIONS THEREFOR This invention relates to a printing method and ink compositions therefor.

This invention has particular but not exclusive application to printing of aluminium and alloy sheet, and for illustrative purposes reference will be made to such application. However, it is to be understood that this invention could be used in other applications, such as printing of microporous surfaces generally.

In the printing of aluminium and aluminium alloy sheet, use is made of the porous adherent oxide layer to absorb a printing medium. In general, the printing medium comprises dye or pigment inks, applied by one of two processes, screen printing or photolithography. In screen printing, the aluminium or other sheet is anodised using conventional anodising process, and prior to pore closure of the anodised surface the required image is printed on the surface by screen printing using paste-borne dyes. The dye component migrates into the porous anodized surface and is fixed therein by immersing the plate in boiling water, with or without fixing salts. If multiple colour printing is required, the screen printing process is repeated for each colour after initial dye set up of the preceding colour has occurred and prior to fixing.

The screen printing process is complicated, particularly for multiple colour work, and requires considerable operator skill. Only one colour can be printed at a time. For each colour, a separate screen must be cut. A common difficulty in WO 99/29789 PCT/AU97/00827 2 screen printing a metal sheet is in maintaining sharp resolution of the image, resolution being reliant on accurate indexing of the screens, accurate cutting of the screens, and the use of fine screens for fine work. Fine screens tend to gum and may become unusable during the print run, requiring preparation of a new screen.

Photolithographic processes offer greater precision.

Anodised plate with open pores is coated with a light sensitive curable polymer composition or photo resist emulsion, usually sensitive to ultraviolet light. The sensitised plate is then exposed through a lithographic film, diazo film, cutting film, plotter film, tracing paper or other mask. The unexposed composition or emulsion is then washed off the plate. The plate is dried and then flooded with dye solution to impregnate the unexposed areas with dye. The exposed resist material is then dissolved off the plate, whereafter the process may be repeated for subsequent colours. Again the image may be fixed or sealed by immersing the plate in boiling water with sealing salts if required.

However, the process requires multiple process steps for multicolour printing. The photo resist materials are expensive and intractable materials to handle, requiring considerable skill in their handling and use. Each colour or separation requires the manufacture of a separate mask, offering multiple possibilities for error. The time required, skill level needed and difficulty in automating the process, and the costs of masks make photolithographic processes suitable for use in metal printing where a premium price may be paid.

WO 99/29789 PCT/AU97/00827 3 Dye compositions for metal printing must have adequate penetration into the open pore of the generally oxidized metal surface to transport the chromophoric material into the oxide later, without excessive migration. As used hereinafter the term migration should be taken to means the diffusion or other transfer of dye from the point of application to an adjacent pixel or portion of the surface. Accordingly it has generally been accepted that metal printing must employ the paste cover or immersion dyeing techniques of screen printing and photographic methods as hereinbefore described.

Both prior art processes are expensive, particularly for small runs, and have multiple opportunities for error in multicolour applications. Both also create environmentally pollution in the form of residues and waste liquors which must be disposed of.

Ink jet printing is a common printing process for home and office use, offering low capital cost and near laser print resolution. The resolution achievable with ink jet printers of common manufacture approaches that of photolithographic processes for printing paper and exceeds that of screen printing processes for all but the thinnest and most intractable masks. However, ink jet printing is not suitable for printing a metal sheet since the dyes are incapable of being absorbed into the microporous metal surface of, for example, an anodized aluminium sheet.

The present invention aims to substantially alleviate at least one of the above disadvantages and to provide a metal printing process and dyes therefor which will be reliable and 4 efficient in use. Other objects and advantages of this invention will hereinafter become apparent.

According to one aspect of the invention there is provided a method for printing an open pore anodized aluminium or aluminium alloy surface, said method comprising ink jet printing of said surface with a non aqueous binder free ink comprising a chromophoric substance and an organic solvent therefor, said solvent having a surface tension less than water and a boiling point range suitable for use in an ink jet printing head, and thereafter allowing said solvent to transport said chromophoric substance into said open pore surface.

It has been surprisingly determined that inks in accordance with the present invention permit ink jet printing of microporous surfaces such as an anodised aluminium sheet. It is speculated that the waterbased inks used in ink jet printing have a surface tension which is too high to permit transport of the dye into the anodised surface of an aluminium sheet. The organic solvents of compositions in accordance o* •oooo with the present invention being of lower surface tension than the most modified water-based ink, achieve penetration in a anodised 20 sheet which would not be expected on the basis of the water like viscosity of the inks.

However, it is envisaged that inks in accordance with the present invention may find application in other direct printing methods.

As used hereinafter, reference to direct printing may be taken to mean 4a any process which deposits ink on the surface of a substrate in the desired printing pattern without masks, screens or resists and includes processes such as plate printing, web offset printing or the like.

However, it is preferred that the printing be by means of ink jet printing.

0: *ee e WO 99/29789 PCT/AU97/00827 The ink Jet printer apparatus may comprise a conventional ink jet printer having a suitable print medium path to accept a metal sheet, or at least be modified to accept a metal sheet.

The ink Jet printer may comprise a single print head whereby multiple passes are required for multicolour applications although it is preferred to use a three or four colour multiple print head machine. Typically the ink jet cartridges are loaded with yellow cyan and magenta inks in the case of three colour apparatus and with an additional black reservoir in the case of four colour printing apparatus.

The substrate is preferably selected from an aluminium or aluminium alloy sheet, preferably uniformly treated by anodizing to a standard suitable for printing although it is envisaged that methods in accordance with the present invention could be used on other surfaces having similar morphological surface characteristics such as oxide surface layer forming metals such as zinc and magnesium, passivated film metal surfaces such as nickel, cermet surfaces and ceramic surfaces.

The aluminium surface may be anodized to a suitable thickness for printing, typically 10 to 25p. Preferably, the surface treatment is provided shortly before printing to enable the ink to penetrate an open surface, the pores of anodised aluminium surfaces tending to close progressively on exposure to the atmosphere and close rapidly upon immersion in boiling water.

However, it is envisaged that proprietary stabilised anodised surfaces may permit the use of long term stored stock when such stock is available.

The inks of the present method may be formed by solution WO 99/29789 PCT/AU97/00827 6 or suspension of chromophoric substances selected from pigments or dyes. Dyes may be selected from inorganic or organic metal complexes and organic dyes. For example, 1:1 or 1:2 metal complex of azo dyes, phthalocyanine dyes, or anthraquinone dyes may be used. Where pigments are used, these are preferably of a particle size of less than 2.0 microns to enable inkjet printing. For colour printing, it is usual to use dyes to produce inks of the CMY or CMYK set, that is, cyan, magenta, yellow and black. Examples of dyes which may be used to create inks of the present invention as the CMY set are the standard dyes Solvent Blue 44, Solvent Yellow 83, and Solvent Red 127.

The organic solvents may be selected from any organic solvents having the specified boiling point characteristics and the ability to solvate the dye or suspend the pigment. For ink jet printing the solvent is preferably selected to be of an appropriate boiling point or boiling range to accommodate the characteristics of available ink jet printing heads, although it is envisaged that the print head may be produced or modified to accommodate the ink. The solvent may be selected to be substantially non aggressive towards print head components currently in use. For example, ink reservoirs are commonly of plastic, requiring selection of a solvent which does not substantially attack the plastic.

Ink jet print heads, being generally adapted to use waterbased inks, are adapted to use inks having a boiling point of about that of water. Such print heads commonly operate at temperatures of from 300 to 350'C to create the vapour bubble which projects the ink jet at the substrate. Accordingly the WO 99/29789 PCT/AU97/00827 7 solvent is preferably selected to be stable against liquid or vapour phase decomposition at the print head operating temperature, and to be capable of forming a jet propelling bubble in operation of the print head. The solvent preferably solvates the dye into an ink composition which is of similar viscosity to the water based inks used in conventional ink jet print heads.

The solvent may comprise a mixture of solvents to achieve the preferred characteristics. Preferably, the solvent mixtures have a relatively narrow boiling range. For example, the solvent mixture may comprise an azeotropic solvent mixture adapted to have a boiling point in the region of 90 to O110 0

C.

Alternatively, the solvent mixture may comprise a mixture of two or more solvents having a preferably narrow boiling range between 90 and In solvent mixtures, there may be used a relatively low boiling solvent of low viscosity and relatively high vapour pressure, and a relatively high boiling solvent of sufficient viscosity to provided the ink with rheological properties suitable for ink jet printing in combination with the selected chromophoric substance and the low boiling solvent. The respective solvents are preferably selected to be of relatively low toxicity. Water miscibility may also be advantageous.

The solvents may be selected from alcohols, ethers, esters, polyol-ethers, aliphatic, branched or cyclic alkanes, alicyclic or aliphatic ketones, aromatic solvents or the like.

Preferably, the ink is dye based and each of the solvents is selected to dissolve the dye at least in combination. The ink 8 may be prepared by dissolution of the dye in the solvent. This may be accompanied by stirring at a temperature of from 40 to 60 0 C for the preferred dyes. The solution may be cooled prior to preferably filtering to a particle size of less than The present applicant has unexpectedly determined that the inks of the present invention permit increased penetration of the dyestuff or pigment into the oxide layer of the metal sheet whilst exhibiting less migration than conventional volatile-solvent based dye. The reasons for this is not clearly understood but may relate to the chromatographic mobility of the dye or pigment in the anodised layer wherein the organic solvents of the present invention function as an eluting solvent, the solvent front extending beyond the dye front. It is speculated that the ink impacts on the surface of anodised aluminium sheet and is rapidly eluted into the thickness of the anodised layer, coo* whereafter the advancing solvent front flashes off. Thus the dye is S: rapidly transported into the surface at a very high effective •o••e concentration in excess of the solubility of the dye, with reduced migration and reduced tendency for bleeding in the sealing process.

20 According to another aspect of the invention there is provided a •coo non-aqueous binder free ink composition for the printing method of any preceding claim, said ink composition comprising a chromophoric *substance and an organic solvent therefor, said solvent having a surface tension less than water and a boiling point range suitable for 8a use in an ink jet printing head, said solvent in use being effective to transport said chromophoric substance into said open pore surface.

In order that this invention may be more readily understood and put into practical effect, reference will now be WO 99/29789 PCT/AU97/00827 9 made to the following example which illustrates a preferred embodiment of the invention.

EXAMPLE 1 An ink composition was prepared comprising 3% by weight of each of standard dyes Solvent Yellow 83 (SANDOZ SAVINYL YELLOW RLSN), Solvent Blue 44 (SANDOZ SAVINYL BLUE GLS) and Solvent Red 127 (SANDOZ SAVINYL PINK 6BLS) were dissolved in a solvent composition comprising 50% by volume of each of 2-propylene glycol 1-methyl ether and methanol. Solvation of the respective dyes in the solvent was achieved by heating the mixtures to 50°C with stirring. The mixtures were allowed to cool before decanting and filtering twice to a final grade of less than 1.6 microns. The resulting filtered solutions were loaded into ink jet cartridges which were installed in an ink jet printing machine.

Anodized aluminium sheet of 0.5mm thickness having a uniformly anodized surface of thickness nominally of 18 to 20 u was fed into the ink jet printing machine, which was operated under the control of a personal computer to print a test pattern on the sheet using ink from the ink cartridge loaded with dye solution in accordance with the present invention.

The printed sheet was removed from the printing machine and immersed in boiling water for ten minutes to fix the dye in the surface of the sheet.

Aluminium sheet printed in accordance with the foregoing embodiment exhibited sharp printing approaching photolithographic resolution and superior to average screen prints, with reduced bleeding and migration.

WO 99/29789 PCT/AU97/00827 It will of course be realised that while the above has been given by way of illustrative example of this invention, all such and other modifications and variations thereto as would be apparent to persons skilled in the art are deemed to fall within the broad scope and ambit of this invention as defined in the claims appended hereto.

Claims

1. A method for printing an open pore anodized aluminium or aluminium alloy surface, said method comprising:- ink jet printing of said surface with a non aqueous binder free ink comprising a chromophoric substance and an organic solvent therefor, said solvent having a surface tension less than water and a boiling point range suitable for use in an ink jet printing head, and thereafter allowing said solvent to transport said chromophoric substance into said open pore surface.

2. A printing method according to claim 1 wherein said ink is selected from cyan, magenta, yellow and/or black coloured inks, each ink being selectively applied to a surface by a multiple print head colour ink jet printing apparatus.

3. A printing method according to claim 2 wherein said cyan, magenta, yellow and/or black coloured inks are stored in respective ink jet cartridges in said printing apparatus.

4. A printing method according to any one of the preceding claims, wherein said ink comprises a dye selected from inorganic or organic metal complexes and organic dyes. A printing method according to claim 4, wherein said dye is an organic dye selected from 1:1 or 1:2 metal complex of azo dyes, phthalocyanine dyes, or anthraquinone dyes.

6. A printing method according to claim 5, wherein at least a CMY dye set is used, and wherein the respective inks are based on the standard dyes Solvent Blue 44, Solvent Yellow 83, and Solvent Red 127. !MEDF SHEETJ -o hEn Si; OGJ PCT/AU97/00827 Received 16 September 1999 12

7. A printing method according to claim 5 wherein at least a CMYK dye set is used, and wherein the respective inks are based on the standard dyes Solvent Blue 44, Solvent Yellow 83, Solvent Red 127 and a Solvent Black.

8. A printing method according to any one of the preceding claims, wherein said ink or inks have a boiling range suitable for use with ink jet printing heads having an operating temperature of from 300 to 350 0 C.

9. A printing method according to claim 8, wherein said ink comprises solvent selected to be stable against liquid or vapour phase decomposition at the print head operating temperature.

10. A printing method according to claim 9, wherein the solvent is selected to provide an ink having a viscosity similar to that of the water based inks used in conventional ink jet printing heads.

11. A printing method according to claim 10, wherein said solvent comprises a mixture of solvents of relatively narrow boiling range.

12. A printing method according to claim 11, wherein said mixture of solvents comprises an azeotropic solvent mixture selected to have a boiling point in the region of 90 to 1 10 0 C.

13. A printing method according to claim 11, wherein said mixture of solvents comprises a mixture of two or more solvents having a narrow boiling range falling in the band between 90 and 110°C.

14. A printing method according to claim 12 or claim 13, wherein said solvent mixture comprises a relatively low boiling solvent of low AMENDED SHEMT IIFFAU 13 viscosity and relatively high vapour pressure, and a relatively high boiling solvent of sufficient viscosity to provide the ink with rheological properties suitable for ink jet printing in combination with the selected chromophoric substance and the low boiling solvent. A printing method according to claim 14, wherein said solvents are selected from alcohols, ethers, esters, polyoleters, aliphatic, branched or cyclic alkanes, alicyclic or aliphatic ketones, or aromatic solvents.

16. A printing method according to claim 15 wherein said solvent mixture comprises 50% by volume of each of 2-propyly glycol 1-methyl ether and methanol.

17. A non-aqueous binder free ink composition for the printing method of any preceding claim, said ink composition comprising chromophoric substance and an organic solvent therefor, said solvent having a surface tension less than water and a boiling point range suitable for use in an ink jet printing head, said solvent in use being effective to transport said chromophoric 20 substance into said open pore surface.

18. An ink composition according to claim 17, wherein said dye is selected from inorganic or organic metal complexes and organic dyes. S9 19. An ink composition according to claim 18, wherein said dye is an organic dye selected from 1:1 or 1:2 metal complex of azo dyes, phthalocyanine dyes, or anthraquinone dyes. 14 An ink composition according to claim 17, wherein said dye is selected from standard dyes Solvent Blue 44, Solvent Yellow 83, Solvent Red 127 and a Solvent Black.

21. An ink composition according to claim 20, wherein said solvent comprises a mixture of solvents of relatively narrow boiling range.

22. An ink composition according to claim 21, wherein said solvents are selected from alcohols, ethers, esters, polyolethers, aliphatic, branched or cyclic alkanes, alicyclic or aliphatic ketones, aromatic solvents or the like.

23. An ink composition according to claim 22, wherein said solvent mixture comprises 50% by volume of each of 2-propyl glycoll- methyl ether and methanol.

24. An ink composition according to any one of claims 17 to 23, prepared by dissolution of the dye in the solvent with stirring at ,eeee a temperature of from 40 to 600C, cooling the solution, and filtering to a particle size of less than S: 25. A printing method according to any one of claims 4 to 16 20 wherein said anodized aluminium or aluminium alloy surface is S* stabilized. coo•

26. A printing method according to any one of claims 4 to 16 wherein said anodized aluminium surface or aluminium alloy surface is freshly anodized.

27. A printing method as claimed in any one of claims 1 to 16, 1 4a or 26 including the further step of immersing the printed surface in water to close open pores in said surface.