GB2366246A

GB2366246A - Method of electrostatically printing onto a substrate by charging the substrate to form a latent image thereon and developing the image thereafter

Info

Publication number: GB2366246A
Application number: GB0021382A
Authority: GB
Inventors: Michael David Gill
Original assignee: MBNA INTERNAT BANK Ltd
Current assignee: MBNA INTERNAT BANK Ltd
Priority date: 2000-09-01
Filing date: 2000-09-01
Publication date: 2002-03-06
Also published as: GB0021382D0

Abstract

Initially, a substrate (e.g. a plastic credit card 12) which is to receive a printed image is electrostatically charged to form an electrostatic latent image thereon. The card is charged by using a matrix of electrodes 2,4 to accelerate ions onto thereon. Print medium (e.g. toner (26,Fig.2)) may then be transferred onto the card by a magnetic roller (22,Fig.2) in dependence upon its electrostatic potential to develop the printed image on the card. The resulting image may be fixed (e.g. by pressure and/or thermal fusing) to produce an indelible image on the card. The system may be included as part of a production line (Fig.4) for encoded cards.

Description

<Desc/Clms Page number 1> DESCRIPTION PRINTER AND MET-HOD OF PRINTING The present invention is concerned with a printer and a method of printing. An important application of the present invention relates to production of encoded cards - credit and debit cards, identity cards, retailers' loyalty cards etc. Such cards will be familiar to the reader. The manufacture of encoded cards is currently a labour intensive and time consuming activity. Rigorous checking and numerous safeguards are required to minimise risk of fraud.

The process of manufacture of encoded cards can be broken down into (1) design, (2) production and (3) personalisation.

Card design is usually carried out by a card bureau using CAD tools. The card manufacturer has access to the designs eg. via an ISDN link or an optical disc interface. The designs can then be transformed into the format required for proofing and printing.

The production process is currently more complicated. The expense involved in preparation for production of cards to a particular design means that it is necessary, for the process to be economic, to produce cards in batches. The process begins with printing. Cards typically have printed images on both faces and to achieve this front and reverse images are printed on separate flat sheets of white plastics - typically PVC. At the printing stage a sheet large enough to produce several cards (eg. seven rows by five columns of cards) is used, individual cards being divided from the sheet at a later stage.

Methods of print transfer currently in use include silk screen, offset lithographic and thermal transfer using foils. Set-up costs for silk screen and lithographic printing are high, making the minimum economic batch number correspondingly high. Thermal transfer is less expensive but is typically used only in conjunction with one of the other printing processes. There are also digital technologies currently in use for plastic card production but these typically use liquid inks and in most cases ink jet technology. Resolution is limited. The one exception to the resolution limitation is the full colour process used in the INDIGO (RTM) machine. This process is however only suitable for small runs as unit production cost is very high.

After printing, the sheets bearing front and reverse images are brought together with a lamination sheet therebetween. Both outer faces of the sheet are covered by a transparent overlay that protects the card surface. Lamination of these five pieces is done by application of heat and pressure. After the cards have been through the lamination process other components are attached - typically a credit or debit card receives a hologram, a magnetic strip and a signature panel, all for the sake of security. Increasingly an electronic chip and associated contacts are also being embedded in the card.

After production comes personalisation. of the card - recording upon it the data which makes the card customer specific. Pre-personalisation cards must be securely stored since in the wrong hands they could be used as instruments of fraud. These cards are stored in a vault from which a quantity of the cards is booked out on

a daily basis. An automated process is then used to encode the magnetic strip with customer details, emboss upon the card information such as the customer card number, "tip" the embossed characters with a colour, if required, and attach an activation label. Personalisation is carried out immediately prior to packaging of the card for despatch ("Fidfilment").

The major concerns with the current methods of card manufacture are the inherent inefficiencies. Batch production imposes the need to hold significant stock of cards prior to personalisation. This is a major logistics exercise. It also results in substantial sums of money being tied up in inventory. Cards are often not available to meet customer requirements. Lead times for card production typically amount to several weeks.

A first object of the present invention is to provide an improved printer and method of printing.

An alternative and more specific object of the present invention is to make possible an improved process of manufacture of encoded cards. It is particularly desired to achieve "Just in Time" manufacture, with all the associated advantages known in industry.

The present inventor has rccognised that the objects of the present invention can be achieved using physical principles known in connection with ionic deposition printing.

Ionic deposition printing is a well known process widely used for printing upon paper. In known ionic deposition printers, a print drum or other body having

an electrically non-conductive exterior is selectively electrically charged to form an electrostatic latent image on the drum. Toner is transferred to the drum, in dependence upon its electrostatic charge, to form a corresponding visible image which is then transferred from the drum to the paper. The toner must then undergo a development process, the nature of which is dependent upon the type of toner being used.

The inventor has recognised that some substrates for print, including card blanks, are capable of receiving the electrostatic latent image themselves, making it possible to print upon such substrates in a particularly advantageous manner.

In accordance with a first aspect of the present invention, there is a printer comprising a charging means for selectively charging a substrate being printed upon such as to form an electrostatic latent image, and a developer for transferring print medium onto the substrate in dependence upon its electrostatic potential to develop the image on the substrate.

Thus the intermediary of a drum for receiving the electrostatic latent image and then receiving the print medium (eg. toner) and transferring this to the substrate (e.g. the plastics card blank) can effectively be dispensed with. The substrate receiving the latent image forms the finished printed article. This allows printer construction and the process of printing to be simplified and improved.

Encoded card blanks are well suited to use as the substrate being printed upon. They can receive the necessary electrostatic charge and have low electrical conductivity.

The physical principles involved in formation of the electrostatic latent image and transfer of the print medium are known in connection with existing ionic deposition printers.

The developer may be constructed such as to provide a transfer surface bearing a layer of print medium in operation, the transfer surface being juxtaposed with the surface of the substrate in operation to enable transfer of print medium to the substrate. Thus print medium can be transferred directly from the transfer surface to the substrate.

A roller, most preferably a magnet roller, can provide the transfer surface. Magnet rollers are used in existing ionic deposition printers.

The print medium most preferably comprises a toner, in which case the printer according to the present invention requires a fuser to fuse the toner and so render the image permanent. Fusers are again known in themselves e.g. for use in other printers (and also in photocopiers) which use toner as a print medium. Toners used in connection with the present invention can be selected for compatibility with the substrate, however, as can the fusing process.

The charging means may utilise a matrix of electrodes for accelerating charged particles in selected regions toward the substrate to form the electrostatic latent image. Again the same physical principles are exploited in print cartridges of existing ionic deposition printers. Positive or negative ions may serve as the charge carriers.

In accordance with a second aspect of the present invention there is a method

of printing comprising selectively electrostatically charging a substrate being printed upon such as to form an electrostatic latent image and transferring print medium onto the substrate in dependence upon its electrostatic potential to develop the image upon the substrate.

Specific embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:- Fig. I illustrates, schematically and from one side, parts of a print cartridge used in a printer embodying the present invention, along with associated control circuitry; Fig. 2 is a diagram of relative potentials of electrodes used in the print cartridge; Fig. 3 illustrates, schematically and from one side, parts of a developer used in a printer embodying the present invention; Fig. 4 illustrates, schematically and in plan, parts of a card production line constructed according to an aspect of the present invention; and Fig. 5 is a process diagram showing steps involved in a method of encoded card production utilising the present invention.

The exemplary printing process to be described can be broken down into three sub-processes thus: 1. an electrostatic latent image is formed upon the substrate; 2. the electrostatic latent image is developed using toners; and 3. the resulting image is fixed to produce a permanent image.

In the present example the latent electrostatic image is formed by selectively charging the substrate using a print cartridge.

The print cartridge comprises a number of crossed electrodes forming a two dimensional matrix whose elements can be individually addressed by control electronics. In Figure I can be seen one of a set of line electrodes 2 and one of a set of finger electrodes 4, the finger electrodes being beneath and separated from the line electrodes.

Beneath the finger electrodes 4, and isolated therefrom by a dielectric layer 6, is a screen electrode 8. The screen and finger electrodes may be formed as tracks on opposite sides of a flexible printed circuit board. Circuitry driving the electrodes is illustrated in a schematic form at 10. Beneath the print cartridge is the substrate 12 itself, in this case a plastics credit card.

Prior to charging the substrate is earthed, e.g. by a set of brushes or any other contact method moved across the substrate surface. This ensures that all residual surface charge is removed from the substrate.

A high frequency AC voltage is applied across the line and finger electrodes so that electron discharge occurs where the line and finger electrodes intersect. The effect is to generate positive and negative ions at the intersections. A biasing potential (in the illustrated embodiment, - 60OV) is applied to the screen electrode 8. A switch 14 controls the level of an additional biasing potential applied to a selected finger electrode 4.

Positive ions are absorbed by both the finger electrode and the screen

electrode due to their negative potential. The latent image is in this embodiment formed by negatively charged particles.

As Figure 2 illustrates, when switch 14 is OFF the finger electrode 4 is at a less negative potential than the screen electrode 8. Negative charges are absorbed by the finger electrode and are not projected through the screen electrode. When switch 14 is ON, however, finger electrode 4 is driven to a greater negative potential by application of a bias voltage Vf from the power supply. The electric field between the finger electrode and the screen electrode is then such that negative charges are accelerated through the screen electrode 8 and onto the substrate 12, which is at ground potential. Of course the switch 14 is typically formed by solid state circuitry. Appropriate switching of the numerous line and finger electrodes allows the electrostatic latent image to be built up in the form of a matrix of pixels.

Looking at the voltages used in the illustrated embodiment, the line/finger driver power supply applies a 2550V p-p voltage to the line electrode of the print cartridge, to cause the print cartridge to generate electrons. When the switch 14 is in the OFF position the voltage being supplied to the finger electrode causes a back bias voltage Vbb(+160 - + 21OV) higher than the screen voltage (-60OV). Asaresultthe negative charges cannot go through the screen electrode. When the switch 14 is in the ON position a finger voltage of -I 80V is applied to the finger electrode. The potential of the finger electrode is thus forced lower than the screen electrode so that negative charges are accelerated towards the credit card which is at ground potential (OV).

Once the latent image is formed on the substrate, it is ready for development. The development process chosen depends very much on the type of toner used. For the present example we shall consider single-component magnetic toners.

Illustrated in Fig. 3 is a development unit 16 which carries out the development by donating toner to the charged substrate. The development unit comprises a generally cylindrical rotating magnet 20 within a sleeve 22. This type of arrangement is known to those skilled in the art as a magnet roller. Toner is supplied to the outer surface of the sleeve 22 from a hopper (not illustrated) and a metering blade 24 is disposed at a selected separation from the sleeve to maintain a uniform thickness of toner on the surface of the magnet roller 20, 22. A common biasing potential is applied to both the magnet roller 20, 22 and the metering blade 24.

In operation, the single component magnetic toner (seen at 26) is magnetically attracted onto the surface of the sleeve 22 such as to form a layer thereupon. The magnet roller 20, 22 traverses the substrate 12, either because the substrate is moved past the roller or vice versa. The toner particles on the sleeve are then electrostatically attracted to the charged parts of the substrate and so transferred thereto so that a visible image is formed on the card.

A monochrome image can be printed using one print station. A ftill colour image can be printed by repeating the process four times to apply toners for red (magenta), blue (aqua), yellow and black. Further stations could be added to suit specific printing requirements. Ultraviolet images could thereby be formed on the

card, or any specific pantone colour.

Once the toner(s) have been transferred to the substrate it is required to make the image permanent, a process referred to by those skilled in the art as "fusing". Fusing processes of two known types are considered most suitable:- i. pressure/thermal fusing, involving a combination of pressure and heat. This is a contact fusing method.

ii. thermal fusing, or flash fusing, which is contactless.

It is envisaged that selection of toner, development and fusing processes will vary according to the application.

Fig. 4 illustrates part of a production line for encoded cards utilising a print station 30 constructed as described above. A card track 32 is preferably formed as a vacuum conveyor and has on its conveyor surface registration features to ensure accurate card positioning. The print station 30 comprises five charging 32/development 34 stations to handle the four colours required for a coloured visual image plus a UV sensitive toner.

The print station can be incorporated in a Just in Time card manufacturing facility and Fig. 5 illustrates the major components of this and their sequence. Plastics card blanks are loaded into the card hopper 50 and fed automatically through the system. Each process is synchronised to ensure smooth flow. The initial print station 52 prints to the reverse of the blanks and the fusing station 54 makes the image permanent. The blank is then inverted at 56 before the second print station 5 8 prints to the blank's other face. It may however be unnecessary to invert the blanks

since the printing process should be capable of printing from below and above. it may also be possible to print front and reverse of the blank simultaneously.

After the card has been printed the lamination station 59 attaches an upper and a lower overlay to the card. This overlay conforms to card provider requirements.

The rest of the production process is familiar to those persons involved in credit card production. The hologram, magnetic strip and signature panel are added at 60, 62 and 64 (normally a manual process although automation is envisaged). The chip is added at 66 then station 68 carries out personalisation prior to fulfilment (packaging) at 70 and despatch.

There is great scope for modification and development of the printer and printing process without departure from the scope of the present invention. As an example, it is envisaged that by matching the melt characteristics of the toner to those of the substrate it will be possible to make the printed image sufficiently robust to allow the protective transparent layer of a conventional encoded card to be dispensed with. Furthermore the printer and print process according to the present invention are suitable for printing not only upon encoded card blanks but on any of a wide range of substrates.

Claims

CLAIMS 1. A printer comprising a charging means for selectively charging a substrate being printed upon such as to form an electrostatic latent image and a developer for transferring print medium onto the substrate in dependence upon its electrostatic potential to develop the image on the substrate.
2. A printer as claimed in claim I wherein the developer is constructed such as to provide a transfer surface bearing a layer of print medium in operation, the transfer surface being juxtaposed with the surface of the substrate in operation to enable transfer of print medium to the substrate.
3. A printer as claimed in claim 2 wherein means are provided for causing the transfer surface to traverse the substrate in operation.
4. A printer as claimed in claim 2 or claim 3 wherein the transfer surface is provided by a roller.
5. A printer as claimed in claim 4 for use with magnetic print medium, the roller being a magnet roller.
6. A printer as claimed in any preceding claim which is for use with print medium comprising toner, the printer further comprising means for fusing the toner upon the substrate.
7. A printer as claimed in any preceding claim wherein the charging means comprises a matrix of electrodes for accelerating charged particles in selected regions toward the substrate such as to form the electrostatic latent image.
8. A printer as claimed in any preceding claim which is adapted to print upon

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an encoded card.
9. A production line for encoded cards comprising a printer as claimed in any preceding claim.
10. A method of printing comprising selectively electrostatically charging a substrate being printed upon to form an electrostatic latent image and transferring print medium onto the substrate in dependence upon its electrostatic potential to develop the image upon the substrate.
11. A method of printing as claimed in claim 10 wherein the print medium comprises toner.
12. A method of printing as claimed in claim I I comprising the ftuther step of fusing the toner.
13. A method of printing as claimed in claim 12 wherein characteristics of the toner and the substrate are chosen such that upon fusing the image becomes indelible.
14. A method of printing as claimed in claim 13 wherein melt characteristics of the toner and the substrate are matched to achieve indelibility.
15. A method of printing as claimed in any of claims 10 to 14 wherein the charging of the substrate is achieved by accelerating charged particles onto selected areas of the substrate.
16. A method of printing as claimed in any of claims 10 to 15 wherein the transfer of print medium to the substrate is achieved by juxtaposing a transfer surface bearing a layer of print medium to the charged substrate.

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17. A method of printing as claimed in claim 16 wherein the transfer surface is caused to traverse the substrate.
18. A method of encoded card manufacture comprising printing upon a card blank by a method of printing as claimed in any of claims 10 to 17.
19. A printer substantially as herein described with reference to, and as illustrated in, accompanying Figs. I to 3.
20. A method of printing substantially as herein described with reference to, and as illustrated in, accompanying Figs. I to 3.
2 1. A method of encoded card manufacture substantially as herein described with reference to, and as illustrated in, the accompanying drawings.