WO1999014043A1

WO1999014043A1 - Laser printing method and substrate

Info

Publication number: WO1999014043A1
Application number: PCT/US1998/018517
Authority: WO
Inventors: Arshavir Gundjian
Original assignee: Nocopi Technologies Inc; Nocopi International Inc
Current assignee: Nocopi Technologies Inc; Nocopi International Inc
Priority date: 1997-09-12
Filing date: 1998-09-04
Publication date: 1999-03-25
Anticipated expiration: 2000-03-12
Also published as: EP1023165A4; EP1023165A1; US6140267A; CA2303068A1; US6013601A; AU9378798A

Abstract

A method and substrate for printing information wherein at least one coating (31) is applied to a substrate (20), the coating (31) having a colorformer leucodye and at least one color activator. The colorformer leucodye and at least one activator react when heated to exhibit a chromic change of at least one of a color change visible in normal light and a fluorescence visible only in ultraviolet light. The at least one coating (31) is heated with at least one laser beam (10) to effect the chromic change at selected points to thereby print information.

Description

LASER PRINTING METHOD AND SUBSTRATE

BACKGROUND OF THE INVENTION

The present invention relates to a multifunctional coating technology that allows one to utilize a laser for printing such that the print can be

designed to be either authenticatably eye visible or only

fluorescently visible or totally invisible. This printing method uses a medium to high power density laser beam as the means for printing on a properly treated

printing substrate.

The search for new methods of printing information and, more particularly, printing variable information goes on continuously. Recently the need to

associate security features to methods of printing has gained a substantial importance, particularly as a result of the increasing concern that the business world is developing towards the monetary damages suffered from counterfeiting and grey marketing activities .

Having the above in mind, this invention

provides a technology which renders direct printing

integrating security features possible using a medium power laser beam typically of a few watts on a wide variety of substrates, provided the latter are coated using the coating scheme prescribed in this disclosure.

The printing method and technology disclosed below becomes even more interesting in view of the possibility, well known in the trade, to control a laser beam direction and intensity in such a way that depending on

the need the printed information may be a fixed and repetitive information or a variable information. Note that laser beams are currently already in use to inscribe

variable information on paper or other substrates using other methods and technologies. For example, in the one

well known case of desktop laser printers that have now become common office printing equipment, a low power laser beam of typically a fraction of a watt power

installed in the printer is directed through appropriate

controls to impart the desired information on to a photo- conductive surface in a way similar to the formation of a photo-image on the drum of a photocopier. The

photoelectric image thus obtained is then transferred through a toner to the paper substrate that is originally

placed in the tray of the laser printer. A second large class and already well known method of marking or information transfer to a substrate utilizing a laser is

that wherein a medium to high power laser beam of several watts to kilowatts power is used. In this case the laser beam is directed to hit the substrate surface, the power

is to be sufficiently high to cause the ablation of more

or less minute quantities of the substrate surface material, thus leaving a visible trace. It is clear that a visible image will be left on the surface when the

laser beam is controlled to hit the surface only at the

spots which cumulatively constitute the desired final

image. Such a control can be obtained either by using a high power laser beam of a few square centimeters cross sectional area that hits a mask where the desired image has been punched through, or with a single or multiple

focussed set of beams of typically a few watts power where the single or multiple beams are controllably deflected in order to scan the surface of the substrate, to trace upon it the desired image, while simultaneously causing an ablation of the surface material by local

melting and/or evaporation, the end result being

obviously the formation of a visible image.

The above two well known laser printing methods

have certain obvious limitations, such as in the first case, the printed surface is constrained to be

essentially that of a printable grade fine paper sheet that can be fed into the printer; in the second case, the

emanation of fumes or printing wastes that have to be continuously exhausted is a major concern. Finally and most importantly, the above laser printing methods do not lend themselves to date to the introduction of any security printing elements to the otherwise ordinary

printing results.

SUMMARY OF THE INVENTION

The present invention is a method and

technology of printing with a laser which can utilize a medium to high power laser beam, such as described above; it includes a coating method and technology that will be applied to the surface of the substrate to be printed.

The use of this method and technology allows the laser beam to produce a fixed or variable image on the substrate without any mechanical action, such as scratching, evaporation or any other form of ablation of

physical material. Furthermore, the disclosed method and

technology not only allows to print on a substrate an eye

invisible image, but it also allows to impart to the printed image one or more security printing features, by making it possible to authenticate the print as having been produced by a legitimate printing party. This method also makes possible to print with the laser a

fluorescent image which becomes visible only when the print is exposed to an ultraviolet light source. Moreover, this method makes it even possible to print with the laser in an entirely invisible way to the eye under regular illumination or exposure to ultraviolet

light. The introduction of many other variations of

security printing features will become clear to anyone knowledgeable in this field given the information

disclosed hereinafter.

These and other features and advantages of the

present invention are achieved in accordance with the

present invention as described hereinafter with reference to the attached drawings and the detailed description of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a partial cutaway view of a substrate according to the present invention for use with the method according to the present invention;

Fig. 2 is a partial cutaway view of a substrate

according to a second embodiment of the invention; Fig. 3 is a partial cutaway view of a substrate according to a third embodiment of the invention;

Fig. 4 is a partial cutaway view of a substrate according to a fourth embodiment of the invention;

Fig. 5 is a partial cutaway view of a substrate

according to a fifth embodiment of the invention;

Fig. 6 is a partial cutaway view of a substrate according to a sixth embodiment of the invention; and

Fig. 7 is a partial cutaway view of a substrate according to a seventh embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The coating system according to the invention comprises coating inks . The coating ink system is chosen according to the preferred method of printing to be

utilized with respect to a given substrate. Typically a flexo printing system can be used in many instances, however, in other cases, an offset printing ink base or even a spraying method may be found to be a more convenient vehicle to coat the substrate with the basic

ingredients that constitute the fundamental components to

be inserted in any of the above-mentioned coating vehicles . The fundamental or critical components used in these coating inks belong to two families of chemicals A and B. The A components are chosen from the family of colorformer leucodyes and the B components are chosen from the family of activators, such as phenolic activator

resins and many others which are well known typically

used in the carbonless paper technology. The coating inks that are utilized in this laser printing scheme may

contain one only of the A or B type components or several

different A components or even both A and B type components together. In this latter case, the printing medium is chosen to be such that at least either one and preferably both A and B components are not soluble in the ink base vehicle.

In general, the coating scheme to be applied on the substrate prepared for the security laser printing process has a multilayer structure as shown in Figure 1. The bottom layer 20 can be paper, cardboard, plastic, mylar, metal, wood, or any material upon which

traditional printing methods are used. Layers 12, 13 and 14 are selected from colorformer components A, activators B and different colors and layer 11 is a protective top coating, as will be described hereinafter. Figure 2 includes a double layer structure on a

base layer 20, where layer 21 is obtained with a coating

ink that contains one particular component B and the

layer 22 is obtained with another essentially colorizing

coating ink that contains generally more than one

colorformer component Aor of which at least one

colorformer is chosen to provide upon activation a

visible distinct color, such as, blue, black, green, red,

etc. and one other component Aβ at least is chosen from

among colorformer leucodyes that we found will fluoresce

when caused to activate by interacting with an activator

B of the layer 21.

An example of Act are the Hilton Davis leucodyes

C 4 which comprises the color former C₃₁H₂₈N₂0₃

6 ' - (dimethylamino) -3 ' -methyl-2 ' - (phenylamino)

spiro (isobenzofuran-1 (3H) , 9 ' - (9H)xanthen) -3-

one

Examples of Aβ are the Hilton Davis leucodyes

CK14 and in general amino phthalides and quinazolines,

which comprises color former C₄₄H_5sN₂0₂

3- (4-dimethylamino)phenyl-3- (di (4-

octyl) henylamino) 1- (3H) -isobenzofuranone.

Examples of B are novalac resins, bisphenols and hydroxybenzoates, specifically the activator 4- hydroxy-4 ' -isopropoxy-diphenyl sulfone .

With the substrate coated with a coating system shown in Fig. 2, when the powerful scribing laser beam 10

hits this surface at a spot, it causes the temperature to

rise. The power density of the laser beam and the exposure time are adjusted in such a way that the local temperature is raised to above 60°C but well below the temperature that would start to cause a permanent physical damage to the coating material, typically 100°C.

It is known that the Aα, Aβ and the B components start to interact in the range of temperatures described above. Thus, if the coating layer 21 contains only the Aα component, the exposed spot will exhibit a chromic change and a visible color will appear. The color depends on the choice of the Aα components and can be blue, black, red or others. On the other hand, when the layer 21 also contains the Aβ component, the presence of Aβ components

and their interaction with B, while contributing somewhat

to the visible color produced, will mainly cause the

substrate to generate a distinct fluorescence at that same spot which can be observed only when a UV light is switched on that spot. It is thus clear that when the laser beam 10 scans the desired full image on the coating in Fig. 2, it will generate on the one hand a clearly visible image of a chosen color without generating any material ablation

wastes, and on the other hand, the printed image will

carry a fluorescent signature that can be used to authenticate this image relative to an image of the same color produced without the utilization of this scheme.

It can be easily seen that the concepts described in the embodiment of Fig. 2 can be implemented in a number of different forms of coating configurations, each one of which will present certain advantages relative to Fig. 2.

The embodiment of Fig. 3 comprises a single layer coating 31 on base 20 obtained with a single coating ink that contains all of the three components Aα, Aβ and B. The advantage of this configuration is clearly

the need for only one printing station. The coating ink

vehicle in this case, however, must imperatively be inert with respect to all of the Aα, Aβ and B components, a good example for such a case is a water base flexo ink

system. Clearly, an offset ink base that does not dissolve the active components A and B can also be used. It may be observed that the coating 31 may tend to snow

scratch marks as a result of rubbing of the printable surface, this can be avoided by the use of a top coat 11

of Fig. 1 described hereinafter.

The embodiment shown in Figure 4 is a three layer coating obtained with the coating inks 41, 42 and 43. The coating ink 41 in this case contains only the Aβ

components. The inks 42 and 43 contain respectively the

Aα and the B components or inversely the B and the Aα components only. The advantage of this configuration is

to render the fluorescent signature of the laser print very evident due to the isolation of the Aβ components at the top layer of the coating structure. The embodiment is applied in three coating ink printing stations. Clearly in this case, the visible color of the print is essentially determined with the combination of the layers 42 and 43.

We shall now describe a number of embodiments that will allow the laser printing of an image that can

be invisible to the eye under normal lighting conditions but which will fluoresce when exposed to a UV light.

The embodiment shown in Figure 5 is a three layer coating system. Layer 51 is obtained with an ink containing the B component while layer 52 contains Aβ components only, and layer 53 is a layer that simply provides a background ordinary color which is made to be in the range of the color that the reaction of B and Aβ

is likely to produce, or even better a much darker color such as blue, red or even black. When the laser beam 10 hits the substrate, the interaction of the B and Aβ components in layers 51 and 52 will produce a fluorescent color that may have a red, orange, yellow or green tint.

It is clear that against the background color of the

layer 53, no visible contrast will be visible in ordinary light. When, on the other hand, the image is exposed to a UV light, the fluorescence of the interacting layers 51

and 52 will stand out and render the image fluorescently visible.

The single layer embodiment of Figure 6 is obtained by mixing all three ink components of Figure 5 together in layer 61. Once more this requires an ink

vehicle, such as a water base flexo ink system where no interaction takes place between the B, Aα and the color

pigments of the layer 53 ink above, until the laser beam

10 raises the temperature of the spot where it hits to above the interaction temperature previously discussed. The advantage of this configuration is that it requires only one ink printing station. Again, because the coating is somewhat vulnerable to accidental mechanical

rubbing or scratching with neighboring surfaces, a top coat 11 of Fig. 1 can be used to avoid this.

This laser image printing method and technology

also allows one to print an image that is invisible to the eye under normal as well as UV illumination conditions .

Typically, an embodiment shown in Figure 7 will provide the possibility to obtain such an invisible print .

The layer 71 in Fig. 7 is a dark colored layer printed with an ordinary ink providing such a color. A typical dark color could simply be black. One condition imposed on this color is that it be transparent to the far infrared wavelength of the laser beams utilized in

the printing process. Since the lasers contemplated for use in the scribing applications herein are either a C0₂ laser with a 10.6μ wavelength or a YAG laser with a 1.06μ wavelength, both in the far infrared, a visibly black ink

which is transparent to the above wavelength is easily obtained. The layer 72 of Fig. 7 will be printed with an ink similar to the ink in the layer 31 in Figure 3, except that this ink would contain only the components Aα

and B.

When the laser beam 10 hits the coating of Figure 7, it will pass through the layer 71 and will

interact with layer 72, thus producing an eye visible color spot on the layer 72. However, since the scanning

laser beam 10 will thus generate this visible image under the screen provided by the dark colored layer 71, the visible image will be hidden to the viewer because of the presence of the masking layer 71. Thus, the printed image is inaccessible to the onlooker and it is revealed when the layer 71 is removed, for example, by simply

scratching, scraping or by other means of mechanical removal .

It is clear that in any one or all of the above discussed embodiments, the chosen basic coating

configuration can be topcoated with a protective top

coating or lamination 11 of Fig. 1 provided that the latter is transparent to visible light and to the specific laser wavelength that is chosen to be utilized for scribing. The coating configurations disclosed herein will clearly achieve the objectives of this invention, which consists of producing a set of coating inks for a

given substrate which can then be printed on with medium

to high power laser beams of typically the C0₂, 10.6μ wavelength or the YAG 1.06μ wavelength.

The inks according to the invention include the fundamental components Aα, Aβ and B inserted in regular

flexographic or offset ink vehicles, as well as in inert vehicles, such as, for example, water in a waterbase flexoink where the components are added in a micronized form.

It is understood that the embodiments described hereinabove are merely illustrative and are not intended to limit the scope of the invention. It is realized that various changes, alterations, rearrangements and

modifications can be made by those skilled in the art without substantially departing from the spirit and scope of the present invention.

Claims

What is claimed is :

1. A method for printing information on a

substrate comprising the steps of: applying at least one coating to a substrate comprising a colorformer leucodye and at least one color activator, wherein the colorformer leucodye and at least

one activator react when heated to exhibit a chromic change of at least one of a color change visible in normal light and a fluorescence visible only in ultraviolet light; and

heating the at least one coating with at least one laser beam to effect the chromic change at selected

points to thereby print information.

2. The method according to claim 1, wherein two layers are applied to the substrate, a first layer comprising the color activator and a second layer thereunder comprising a first colorformer leucodye which

reacts with the activator to produce a color change visible in normal light and a second colorformer leucodye which reacts with the activator to produce a fluorescence

visible only in ultraviolet light.

3. The method according to claim 1, wherein one layer is applied to the substrate comprising the color activator, a first colorformer leucodye which reacts with the activator to produce a color change

visible in normal light and a second colorformer leucodye which reacts with the activator to produce a fluorescence

visible only in ultraviolet light.

4. The method according to claim 1, wherein

three layers are applied to the substrate, a first layer comprising the color activator, a second layer thereover comprising a first colorformer leucodye which reacts with the activator to produce a color change visible in normal

light and a third layer thereover comprising a second

colorformer leucodye which reacts with the activator to produce a fluorescence visible only in ultraviolet light.

5. The method according to claim 1, wherein

three layers are applied to the substrate, a first layer comprising a first colorformer leucodye which reacts with the activator to produce a color change visible in normal light, a second layer thereover comprising the color activator and a third layer thereover comprising a second colorformer leucodye which reacts with the activator to

produce a fluorescence visible only in ultraviolet light.

6. The method according to claim 1, wherein three layers are applied to the substrate, a first layer comprising a background color, a second layer thereover

comprising a colorformer leucodye which reacts with the

activator to produce a color change which is indistinguishable from the background color and a fluorescence visible only in ultraviolet light and a third layer thereover comprising the color activator.

7. The method according to claim 1, wherein one layer is applied to the substrate comprising a background color, a colorformer leucodye which reacts with the activator to produce a color change which is

indistinguishable from the background color and a fluorescence visible only in ultraviolet light and the color activator.

8. The method according to claim 1, wherein

two layers are applied to the substrate, a first layer comprising a background color and a second layer thereunder comprising a colorformer leucodye which reacts with the activator to produce a color change which is

indistinguishable from the background color and the color activator and wherein the first layer is removable

to reveal the information printed on the second layer.

9. The method according to claim 1, wherein the step of heating comprises using a C0₂ 10.6μ wavelength or a YAG 1.06μ wavelength laser.

10. The method according to claim 1, wherein the heating is to a temperature above about 60°C and below about 100^DC.

11. The method according to claim 1, wherein the activator and at least one colorformer leucodye are in a micronized form.

12. A printing substrate comprising: at

least one coating comprising a colorformer leucodye and at least one color activator, wherein the colorformer leucodye and at least one activator react when heated to

exhibit a chromic change of at least one of a color change visible in normal light and a fluorescence visible only in ultraviolet light, whereby heating the at least one coating at selected points effects the chromic change

at those points to thereby print information.

13. The substrate according to claim 12, comprising two layers comprising a first layer comprising

the color activator and a second layer thereunder comprising a first colorformer leucodye which reacts with the activator to produce a color change visible in normal light and a second colorformer leucodye which reacts with the activator to produce a fluorescence

visible only in ultraviolet light.

14. The substrate according to claim 12, comprising one layer comprising the color activator, a

first colorformer leucodye which reacts with the activator to produce a color change visible in normal light and a second colorformer leucodye which reacts with the activator to produce a fluorescence visible only in

ultraviolet light.

15. The substrate according to claim 12, comprising three layers comprising a first layer comprising the color activator, a second layer thereover

comprising a first colorformer leucodye which reacts with the activator to produce a color change visible in normal light and a third layer thereover comprising a second colorformer leucodye which reacts with the activator to

produce a fluorescence visible only in ultraviolet light.

16. The substrate according to claim 12,

comprising three layers comprising a first layer comprising a first colorformer leucodye which reacts with the activator to produce a color change visible in normal light, a second layer thereover comprising the color activator and a third layer thereover comprising a second

colorformer leucodye which reacts with the activator to

produce a fluorescence visible only in ultraviolet light.

17. The substrate according to claim 12,

comprising three layers comprising a first layer comprising a background color, a second layer thereover comprising a colorformer leucodye which reacts with the

18. The substrate according to claim 12, comprising one layer comprising a background color, a colorformer leucodye which reacts with the activator to produce a color change which is indistinguishable from

the background color and a fluorescence visible only in ultraviolet light and the color activator.

19. The substrate according to claim 12, comprising two layers comprising a first layer

comprising a background color and a second layer thereunder comprising a colorformer leucodye which reacts with the activator to produce a color change which is

to reveal the information printed on the second layer.

20. The substrate according to claim 12,

wherein the activator and at least one colorformer leucodye are in a micronized form.

21. The substrate according to claim 12,

wherein the activator and at least one colorformer

leucodye react at a temperature above about 60°C and

below about 100°C.

22. The substrate according to claim 12,

wherein the activator comprises one of a phenolic resin,

a novalac resin, a bisphenol and a hydroxybenzoate .

23. The substrate according to claim 12,

wherein the at least one coating comprises a water base

flexo ink.

24. The substrate according to claim 12,

wherein the at least one coating comprises a flexo ink

system.