WO1999065696A1

WO1999065696A1 - Permanent image formation

Info

Publication number: WO1999065696A1
Application number: PCT/AU1999/000445
Authority: WO
Inventors: Jerzy Krasulak
Original assignee: Sony Corporation
Priority date: 1998-06-16
Filing date: 1999-06-09
Publication date: 1999-12-23
Also published as: AUPP413798A0

Abstract

The present invention discloses a method and apparatus for forming a permanent image on a substrate such as an optical disk (2) or compact disk. The disk (2) is covered with an ink having a pigment having a change in visibility due to electromagnetic radiation (3) of a first wavelength and being curable by irradiation at a second wavelength. The first wavelength exposure via a mask (1) determines the resultant image and the second wavelength exposure cures the image. An LCD may be used rather than a mask (1) to determine the image whilst the image information may be stored electronically in a computer to avoid the need for physical storage of the mask (1). A disk (2) having a fixed image is also disclosed.

Description

PERMANENT IMAGE FORMATION

The present invention relates to a method of, an apparatus for, forming a permanent image on a substrate. Although the present invention finds particular application in the formation of images on compact discs (CDs) and disc devices (eg. DVDs or laser discs), the invention is not limited thereto and is also applicable to the creation of images on, or decoration of, packaging - particularly those formed from recycled polycarbonate and/or recycled PET.

BACKGROUND ART

Traditional techniques of introducing images onto substrates, namely printing, transfer an image pattern onto the substrate. In particular, the ink is transferred only to those portions of the substrate where it is intended the image be fixed. These methods require a plate or stencil by which the image pattern is transferred. In the letterpress technique a raised image is used, in the gravure technique an indented image is used, in offset-lithography a difference in ink acceptance on the plate is utilised, whilst in screen printing there is physical obstruction of closed areas of the stencil so that ink only passes in those locations which are unobstructed.

In all the abovementioned prior art techniques, the plate or stencil is produced either photographically or by computer driven laser imaging. Thereafter, time consuming chemical development is required and this requires expensive facilities and adequate equipment. An alternative prior art process is that involved with direct deposits of dots of ink such as those created by inkjet printers which form an image on the substrate or printed surface. Again the ink is transferred only to those areas where the image is desired.

Novelty searches conducted after the priority date have disclosed Japanese Patent Application No 07-286529 (1995) published under No 09-106574 (1997) (Nippon Columbia Co Ltd). The specification describes a compact disc in which a first reflection layer forming a visible image is provided. A second reflection layer is also provided with the first and second reflection layers having different reflection spectra. The reflection layers are sandwiched between a substrate on which information pits are formed and a protective layer. The production of the reflection layer (s) is by means of sputtering through a mask and is therefore analogous to conventional printing. Also the visible image must be formed during the production of the compact disc whereas the present invention is applicable to forming an image on existing stocks of previously manufactured discs and/or printing different images on otherwise identical discs after their manufacture. SUMMARY OF THE INVENTION

The present invention seeks to provide a printing process in which ink is applied to the entire surface of the substrate to carry the image. Therefore the process to be described hereafter fundamentally differs from that of the prior art because in the prior art process only the image areas have ink applied thereto.

In accordance with a first aspect of the present invention there is disclosed an optical disc comprising: a substrate; a layer of ink including a pigment sensitive to electromagnetic radiation of a first wavelength and curable by irradiation with electromagnetic radiation of a second wavelength; said ink layer covering at least a substantial portion of a surface of said substrate for forming a permanent image on said substrate.

In accordance with a second aspect of the present invention there is disclosed a method of forming a permanent image on a substrate, said method comprising the steps of:

(a) covering said substrate with a layer of ink including a pigment sensitive to electromagnetic radiation of a first wavelength and curable by irradiation with electromagnetic radiation of a second wavelength; (b) locating an image mask in a radiation path between said substrate and a source of electromagnetic radiation of said first wavelength;

(c) radiating said ink covered substrate through said mask with said first wavelength radiation to change the visibility of said pigment; and

(d) irradiating said substrate with electromagnetic radiation of said second wavelength to cure said ink and substantially permanently fix said visibility of said pigment.

In accordance with a third aspect of the present invention there is disclosed apparatus for forming a permanent image on a substrate, said apparatus comprising:

(a) means to apply to a substrate a layer of ink including a pigment sensitive to electromagnetic radiation of a first wavelength and curable by irradiation with electromagnetic radiation of a second wavelength;

(b) a source of said first wavelength radiation;

(c) a source of said second wavelength radiation;

(d) an image mask; (e) a first optical path including said source of first wavelength radiation, said image mask and said substrate whereby an ink coated substrate can be irradiated by said first wavelength radiation which is spatially varied by said mask to represent said image; and (f) a second optical path including said source of second wavelength radiation and said substrate and excluding said mask.

BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the present invention will now be described with reference to the drawings in which:

Fig. 1 is a schematic perspective view of a positive image system in accordance with the first embodiment of the present invention,

Fig. 2 is a view similar to Fig. 1 but illustrating a negative image, Fig. 3 is a schematic perspective view of an optical system with a positive image and light amplification,

Fig. 4 is a similar illustration but of a fourth embodiment illustrating an optical system using a diverging lens,

Fig. 5 shows a plurality of laser light sources each of which creates a corresponding beam in the imaging system,

Fig. 6 illustrates a liquid crystal display being utilised as the mask with the image being controlled by electronic inputs to the liquid crystal display, and

Fig. 7 illustrates a computer network able to generate electronic images for the liquid crystal display of Fig. 6.

DETAILED DESCRIPTION

As seen in Fig. 1, the first embodiment of the present invention utilises a positive mask 1 which carries an image A which is prepared by conventional photographic techniques. The mask 1 is positioned in front of a compact disc (CD) 2 onto which the image A is to be created. The surface of the CD 2 to receive the image is coated with a layer of ink (to be described hereafter). This is preferably done by placing several drops of the ink on the upper surface of the CD 2 and spinning the CD 2 in a horizontal plane which results in the ink being spread by centrifugal force into a substantially uniform layer of the CD 2. Laser light 3, being electromagnetic radiation at a first wavelength (preferably in the infrared band about 780nm) is then passed through the mask 1 and falls onto the ink covered surface on the CD 2.

The ink carries a pigment which is transparent prior to irradiation with the laser light, but after irradiation, the irradiated pigment becomes visible thereby creating the image of the letter A. To fix or cure the image, the ink (preferably the entire surface of the CD 2) is then irradiated with electromagnetic radiation at a different wavelength, preferably ultraviolet radiation at approximately 308nm thereby fixing the image permanently. Fig. 2 illustrates the analogous process using a negative mask 11 and different ink. In the embodiment of Fig. 2 the pigment contained by the ink is initially coloured but fades following exposure to the first electromagnetic radiation which is again preferably laser light 3. Thereafter the image is again cured by exposure to ultraviolet light.

It will be appreciated by those skilled in the printing arts that a coloured image can be created utilising the embodiments of Figs. 1 and 2, by sequential application of inks having different coloured^' pigments. Preferably a four step process is utilised using inks with pigments coloured cyan, magenta, yellow and black. Fig. 3 illustrates a still further optical imaging system in which a positive mask 21 is used and laser light 3 is passed therethrough and received by two cascade arranged light amplifiers 25 the output of which is passed through a converging lens 26 before falling on the CD 2.

In the still further embodiment of Fig. 4 an alternative arrangement utilising a positive mask 31 and diverging lens 36 is used to again focus the laser light 3 onto the desired surface of the CD 2.

In a further embodiment illustrated in Fig. 5, a multiplicity of individual lasers Ll-Ln are each connected by means of a corresponding optical fibre 40 to a mask 41 which is used to illuminate a CD 2. The intention of the various embodiments illustrated in Figs. 3-5 is to indicate that various optical systems are able to be put in place in order to deliver the appropriate radiation through the desired mask. Other systems will be apparent to those skilled in the optical and printing arts.

In all of the above described arrangements, the mask 1, 11, 21, 31 and 41 is created by conventional, typically photographic, means. As a consequence, each mask has to be created and stored, particularly if repeat runs of a compact disc are to be ordered. Furthermore, there is a substantial set up time involved in changing masks, ensuring that the mask is correctly installed, and so on. All of these mechanical steps delay production in a CD manufacturing plant where short runs of different CDs are desired to be produced sequentially in the minimum possible time.

In the embodiment illustrated in Fig. 6, the mask 51 takes the form of a liquid crystal display which receives an electrical input via wires 52 from a computer 54. In this arrangement it is the backlight radiation 53 of the liquid crystal display 51 which actually illuminates the ink on the surface of the disc 2. It will be apparent from Fig. 6 that the liquid crystal display 51 creates a negative mask for the positive image produced on the disc 2. Also, as seen in Fig. 6, a lens system 55 is provided between the display 51 and the disc 2 to collimate and focus the backlight radiation 53. Turning now to Fig. 7, one possible form for the computer 54 of Fig. 2 is illustrated in which a network of interconnected PCs 60 enable images to be generated locally or at a distance and output via wires 52 to the mask 51. In addition, a mask printing device 61 utilising a laser or inkjet plotter or similar can be utilised to create masks such as the mask 1, 11, 21, 31 or 41. These masks are printed directly onto glass or similar rigid transparent material. Similarly an image setter output device 62 can be used to create photograph images using conventional processes to produce either positive or negative images. In addition, a CD-R burner device 63 can be used to keep a compact library of permanent images which are able to be re-loaded onto the computer system to be reused at later dates.

The inks used in the present invention had their origin in the attempted production of watermark security devices in plastic cards such as credit cards. The intended application of a watermark to a credit card was rendered commercially redundant by the development of the so called "smart card" . The intention was to print an image and then fade or discolour the image under exposure to laser radiation to a degree sufficient to create a watermark. However, in that proposed arrangement the image of the watermark was created by conventional printing processes, that is to say the ink was only transferred to those portions where it was intended there should be an image. Thereafter the image was faded by illumination of the entire watermark area. That is, the irradiation was uniform over an area and was not spatially arranged to form an image.

The preferred supplier of such inks is Marabuwerke GmbH and Co of Tamm, Germany. The ink chemistry can be based on cationic chemistry or nonacrylate photoinitiator free radical polymerisation with donor or acceptor type monomers, direct photolysis of ground state complexes or acceptor excitation. Preferably a wide gap between narrow band width emission of UV at preferably 308nm and laser excitation at preferably 780nm is used to prevent partial curing of the ink during the image creating exposure. The preferred UV source is a XeCl irradiator with a peak irradiance about 30 times higher than a standard mercury emission spectrum. The preferred laser is an Nd-YAG serialisation laser.

INDUSTRIAL APPLICATION

It will be appreciated by those skilled in the production arts that the embodiment of Figs. 6 and 7 enables images to be rapidly and compactly stored and reused at short notice thereby facilitating sequential productions of short runs of different compact discs.

The foregoing describes only some embodiments of the present invention and modifications obvious to those skilled in the arts can be made thereto without departing from the scope of the present invention. For example, the ink need not be applied using the spinning technique described above, but can be applied by other substantially conventional techniques such as spraying or by using both spraying and spinning.

The term "comprising" as used herein is used in the inclusive sense of "having" or "including" and not in the exclusive sense of "consisting only of" .

Claims

1. An optical disc comprising: a substrate; a layer of ink including a pigment sensitive to electromagnetic radiation of a first wavelength and curable by irradiation with electromagnetic radiation of a second wavelength; said ink layer covering at least a substantial portion of a surface of said substrate for forming a permanent image on said substrate.

2. An optical disc according to claim 1 , in which said first wavelength is in the infrared band, and said second wavelength is in the ultraviolet band.

3. An optical disc according to claim 1 or 2, in which said ink layer comprises a plurality of layers each of which has different coloured pigment.

4. An optical disc according to any one of claims 1-3 in which said ink layer is formed on a protective layer covering said substrate.

5. A method of forming a permanent image on a substrate, said method comprising the steps of:

(a) covering said substrate with a layer of ink including a pigment sensitive to electromagnetic radiation of a first wavelength and curable by irradiation with electromagnetic radiation of a second wavelength;

(b) locating an image mask in a radiation path between said substrate and a source of electromagnetic radiation of said first wavelength;

6. A method as claimed in claim 5 in which steps (a)-(d) are sequentially carried out for each of a plurality of pigments of different colour.

7. A method as claimed in claim 5 or 6 in which said pigment fades on irradiation with said first wavelength radiation.

8. A method as claimed in claim 7 in which said mask is a positive image mask.

9. A method as claimed in claim 5 or 6 in which the colour of said pigment is intensified on irradiation with said first wavelength radiation.

10. A method as claimed in claim 9 in which said mask is a negative image mask.

11. A method as claimed in claim 8 or 10 in which said mask has a fixed image.

12. A method as claimed in claim 8 or 10 in which said mask image is changeable.

13. A method as claimed in claim 12 in which said mask comprises a liquid crystal display and said electromagnetic radiation of said first wavelength is the backlight of said display.

14. A method as claimed in claim 13 in which the image displayed by said liquid crystal display is selected from one of a plurality of electronically stored digital images.

15. A method as claimed in any one of claims 5-14 wherein said first wavelength is approximately 780nm and said second wavelength is approximately 308nm.

16. Apparatus for forming a permanent image on a substrate, said apparatus comprising:

(b) a source of said first wavelength radiation; (c) a source of said second wavelength radiation;

(d) an image mask;

(e) a first optical path including said source of first wavelength radiation, said image mask and said substrate whereby an ink coated substrate can be irradiated by said first wavelength radiation which is spatially varied to represent said image; and (f) a second optical path including said source of second wavelength radiation and said substrate and excluding said mask.

17. Apparatus as claimed in claim 16 wherein said mask has a fixed image.

18. Apparatus as claimed in claim 16 wherein said mask has an image which is changeable.

19. Apparatus as claimed in claim 18 wherein said mask comprises a liquid crystal display.

20. Apparatus as claimed in claim 19 wherein said liquid crystal display has a backlight and said source of first wavelength radiation comprises said backlight.

21. Apparatus as claimed in claim 19 or 20 including computer means connected to said liquid crystal display and including at least one stored mask image able to be displayed by said display.

22. Apparatus as claimed in any one of claims 16-21 wherein said first wavelength radiation source comprises a laser.

23. Apparatus as claimed in claim 16-22 wherein said second wavelength radiation source comprises a source of UV radiation.

24. Apparatus as claimed in claim 23 wherein said UV radiation source is an Xe Cl irradiator.

25. A substrate onto which an image has been formed in accordance with the method of any one of claims 5-15.

26. A substrate having an image formed thereon using the apparatus of any one of claims 16-24.

27. A disc device comprising the substrate of claim 25 or 26.

28. A method of forming a permanent image on a substrate, said method being substantially as herein described with reference to Figs. 1 or 2 or 3 or 4 or 5 or 6 or 6 and 7 of the drawings.

29. Apparatus for forming a permanent image on a substrate, said apparatus being substantially as herein described with reference to Figs. 1 or 2 or 3 or 4 or 5 or 6 or 6 and 7 of the drawings.

30. A substrate having a permanent image formed thereon by the method of claim 29 or the apparatus of claim 30.

31. A substrate as claimed in claim 30 and comprising a compact disc.