WO1998013205A1

WO1998013205A1 - Computer activated diazo printing system and method

Info

Publication number: WO1998013205A1
Application number: PCT/US1996/015236
Authority: WO
Inventors: Norman Sweet; Patrick Rich; Richard Folcik
Original assignee: Precision Coatings, Inc.
Priority date: 1996-09-24
Filing date: 1996-09-24
Publication date: 1998-04-02
Also published as: AU7369296A

Abstract

A system (10) of and method for printing diazo images with a computer printer or plotter. The cartridge (14) of the ink jet printer (12) or plotter is filled with an ink (16) or a transfer film ribbon is impregnated therewith which contains a first diazo imaging substance (such as a combination of diazo salts, a coupler, and acid, or an ammonium hydroxide solution, or diazo salts, alone or coupler alone). A substrate (18) coated with a second diazo imaging substance (selected so that it reacts with the first diazo imaging substance to produce a visible image) is provided. The printer or plotter is then used to imprint an image onto the coated substrate. The reaction between the two diazo imaging substances produces a visible, diazo image. The invention is particularly useful to produce intermediate screens and masks in a computerized graphic art production environment, as well as outdoor signage.

Description

COMPUTER ACTIVATED DIAZO PRINTING SYSTEM AND METHOD

Field of the Invention

This invention concerns the field of computerized printing systems, and, more particularly, to such a system employing a diazo imaging process.

Background of the Invention

The diazo imaging process is a standard technique often used to produce large, low cost reproductions, such as blueprints employed in manufacturing and construction industries. The process produces a positive image. Diazo compounds are formed by the reaction of aniline (an aromatic amine) with nitrous acid. Diazo salts, when combined with a coupler (typically, various phenols and coal tar derivatives) in an alkaline environment, will form an azo dye . The a"zo dye is highly colored and can vary in hue, depending upon the particular components involved.

However, the diazo process which produces the azo compound is light sensitive. Hence, exposure of the diazo salt mixture to ultraviolet light prevents the formation of an azo dye. Diazo imaging relies on this ultraviolet light sensitivity. Typically, the diazo salt and coupler are mixed with an acid to prevent the coupling reaction from taking place. Paper or other substrate coated with this sensitized material is exposed to ultraviolet light through a mask consisting of a transparent or translucent drawing or other image which prevents exposure of the coated substrate to the ultraviolet in specific areas. In areas where the light is not blocked, the light decomposes the diazo so that it becomes incapable of compounding into an azo dye. However, in the areas blocked by the mask, a latent image of sensitized diazo material is formed. This latent image is then exposed to ammonia vapor to neutralize the acid, thus permitting the coupling reaction to go forward to form the azo dye. Thus, the latent image on the substrate will form a visible image created by the azo dye.

Because the uncoupled diazonium salts are so sensitive to ultraviolet light, the substrate carrying the latent image thereon must be guarded from accidental exposure thereto. Hence, subsequent handling and development of the latent imaged substrate are necessarily performed under dark room conditions; that is, the only light which is permitted to come into contact with the substrate having the latent image thereon is light completely free of ultraviolet light, referred to as "yellow light". Obviously, this considerably increases the cost and inconvenience of producing images by diazo processes. Furthermore, since the latent image must be exposed to ammonia vapors for development, the diazo process carries the inherent problem of handling the dangerous ammonia vapors; typically, they are either vented out to the roof of the building or are absorbed by a filter. Both of these methods of eliminating ammonia vapors are unsatisfactory to some degree. Once the latent image has been exposed to the ammonia vapors and the coupling reaction occurs, certain resultant azo dyes which create the visible image can also be particularly opaque to ultraviolet light. Because of their high visible image densities and actinic opaqueness, images created by diazo imaging have found particular application in producing high quality, intermediate masks and screens which are used in other imaging processes, such as silk screening. Thus, diazo imaging is often used as part of the process in printing high quality art work, for example. Diazo images are also particularly useful in outdoor signage since they are resistant to degradation from ultraviolet light.

Ink jet printers, which provide a relatively inexpensive way of rendering computer images into high quality, hard copy, have come into very widespread use in recent years. All ink jet printers include a reservoir or cartridge containing the printing ink which is delivered to a nozzle located in the print head of the printer. The ink is under pressure, and is subjected to an AC electric current which causes it to vibrate and break up into tiny ink droplets as it exits the small orifice of the ink nozzle. The ink droplets are subjected to a charge voltage as they leave the nozzle. By varying the applied voltage, the charge carried by the droplets can accordingly be varied. The droplets then pass between two deflector plates which are maintained at a constant potential, thus causing a droplet to deflect toward one of the plates by an amount proportional to the charge carried by the droplet. The charged and deflected droplets then impinge on the moving paper in a pattern which varies as the charge varies. In this way, both printed and graphic images can be created.

Inks suitable for use in ink jet printers typically include a pigment, dye or combination of pigments, a carrier or solvent, and a resin binder to help the printed image adhered to the paper. Other components, such as conductivity agents, humectants, defoamers, surfactants, corrosion inhibitors, plasticizors and viscosity modifying agents may be added to improve and enhance various characteristics of the ink. Ink compositions suitable for use in ink jet printers which are capable of producing a latent image for subsequent development into a visible image are disclosed and described in U.S. Patent No. 5,395,432. This patent discloses various formulations for "invisible inks" which may be used in an ink jet printer to produce a "secure image" invisible to the eye, and which is revealed only after it is subjected to a developing agent, such as heat. However the images produced with the inks disclosed in the '432 patent are not suitable for use as intermediate screens or masks in printing processes because they do not exhibit particularly good image density and opaqueness to ultraviolet light.

What is needed is a system of and method for diazo imaging which eliminates the disadvantages of prior art diazo imaging methods discussed above, and which is particularly useful in producing intermediate printing masks and screens and outdoor signage of high quality.

What is also needed is such a diazo imaging system and method which may be interfaced with various CAD and other computer based design systems in a graphic art production environment.

Summary of. the invention

Disclosed and claimed herein is a system for and method of imprinting a substrate with a diazo image. The system includes a computer activated imager

(such as a printer or plotter) which is provided with a supply of a solution containing a first diazo imaging substance. In the case of an ink jet printer or a plotter, the solution can be disposed in the ink reservoir. In the case of an impact printer, the ribbon can be impregnated with the solution. A substrate having a coating disposed thereon formed of a second diazo imaging substance is imprinted by the imager with a pattern of the solution containing the first diazo compound. This will react with the second diazo compound in the coating to produce a visible diazo image pattern on the substrate.

In a first preferred embodiment, the first diazo substance carried by the ink is a solution of ammonium hydroxide, or any compound capable of developing a diazo image, hereafter referred to as the "developing agent", and the second diazo imaging substance carried by the coating includes a diazo compound, a coupler, and an acid. In other words, the substrate is typical "diazo paper" which carries the diazo compound, coupler, and acid. Due to the presence of the acid, "the diazo compound is prevented from reacting with the coupler. However, as soon as the developing agent is imprinted onto the diazo paper, the action of the developing agent will neutralize the acid, and permit the diazo coupling reaction to go forward, thus producing a visible diazo image on the paper.

In a second and preferred embodiment, the first diazo imaging substance carried by the solution, itself, and the second diazo imaging substance carried by the paper includes a coupler. In this embodiment, the diazo salt is always separated from the coupler until actual imprinting of the substrate. Therefore, no acid needs to be combined with the diazo salts, and no ammonia vapors or solution are needed to enable the coupling reaction, but the coating itself may contain additional compounds to accelerate the coupling reaction. This particular embodiment has the dual advantages of eliminating the hazardous ammonia vapors and the necessity of venting or absorbing them, and eliminating the requirement that printing be carried out under yellow safe lights. Since the paper is not coated with the light sensitive diazo mixture, it requires no special handling, and the process may be carried out under natural light. In a third preferred embodiment, the first diazo imaging substance carried by the solution is the coupler solution, and the second diazo imaging substance carried by the paper is the diazo salt.

In yet another preferred embodiment, the imager may be supplied with a formulation containing a diazo compound, a coupler, and an acid. This can be used to imprint plain paper and produce a latent diazo image. Of course, in this embodiment, the latent diazo image must be subsequently developed by using ammonia vapors in a conventional manner. However, this embodiment has the advantage of using plain, rather than coated paper which is not only considerably cheaper than diazo paper, but is also much easier to handle because it is not light sensitive. Furthermore, no light is required to create the image since only the digital output image from the computer is applied to the paper or film.

In a sixth preferred embodiment, a developed diazo/coupler solution is used in the ink reservoir or carrier so that, when applied to paper or film from an imager, the fully developed solution provides its own image on the substrate. No further development is required.

The method of the present invention contemplates using an ink jet printer (or other computer activated imager) having a reservoir filled with a solution containing a first diazo imaging substance to imprint an image onto a substrate coated with a second diazo imaging substance to form a visible diazo image pattern on the substrate. Again, the first diazo imaging substance, depending on the particular method used, can include: an ammonium hydroxide solution or any compound capable of developing a diazo image,- a mixture of diazo compound; a coupler, and an acid; the diazo compound without any coupler or acid; or simply the coupler, itself. Similarly, the second diazo imaging substance coated on the paper may be any of these components depending on the nature of the first imaging substance. If plain paper is used, the method further contemplates the step of imprinting the plain paper of a solution containing a diazo compound, a coupler, and acid to form a latent image on the plain paper, and subsequently exposing the imaged paper to ammonia vapors to form a visible diazo image thereon.

Brief Description of the Drawings

The following detailed description may best be understood by reference to the following drawings, in which:

Figure 1 is a perspective view of the diazo printing system of the present invention with certain hidden structures therein shown in phantom;

Figure 2 is a cross-sectional view of a coated substrate useful in practicing the present invention;

Figure 3 is a perspective view of a substrate being imprinted according method of the present invention; Figure 4 illustrates a further step in an alternative embodiment of the present invention.

Detailed Description of the Preferred Embodiments

Throughout the following detailed description, like numerals are used to reference identical elements of the present invention shown in multiple figures thereof. Referring now to the drawings, and in particular to figures 1 and 2, there is shown a system 10 for imprinting a substrate 18 with a diazo image. This system 10 includes a conventional ink jet printer 12 which includes an internally disposed reservoir or cartridge 14 for containing a supply of printing ink 16. Of course, the ink jet printer 12 also includes numerous additional elements, such as ink nozzle, charging plates, charge electrode, etc. which are not considered germane to the practice of the present invention and are not depicted in Figure 1. The type of ink jet printer depicted in the drawings is entirely conventional in construction and considered to be well within the knowledge of one skilled in the art.

Ink "jet printer 12 also contains a supply of paper (or other printing substrate) 18 which is disposed in a paper supply tray 17. As can be seen more clearly in Figure 2, the paper 18 is multi- layer and has a base 18a with a coating 18b disposed thereon.

According to the present invention, the ink

16 disposed inside the ink reservoir 14 contains a first diazo imaging substance. Similarly, the coating 18b of paper 18 contains a second diazo imaging substance. The first and second diazo imaging substances are capable of reacting with each other to produce an image 20. Figure 3 depicts the system 10 of the present invention in operation with a sheet of paper 18 emerging from a paper slot 19 and having an image 20 appearing thereon. Image 20 is produced by the reaction between the second diazo imaging substance in coating 18b and the first imaging substance in the printing ink 16 which has been imprinted onto the coated paper 18 by operation of ink jet printer 12.

In the embodiment depicted in Figures 1-3, the first diazo substance may variously include: an ammonium hydroxide solution; a diazo solution (without coupler and without acid) ; or the coupler (without the diazo salts) . in the embodiment where the ink 16 contains ammonium hydroxide solution, coating 18b of paper 18 will include a diazo compound including diazo salts, coupler, and an acid. In other words, paper 18 can be conventional diazo paper. The reaction between the ammonium hydroxide in the ink 16 will cause an image to appear on the diazo paper as the paper 18 emerges from the ink jet printer 12.

In the embodiment where the first diazo imaging substance of ink 16 includes a diazo salt solution, the paper 18 has a coating 18b which includes a coupler. By separating the diazo salt and the coupler in this manner, these two substances cannot react until they are brought together by the act of imprinting the ink onto the paper. Thus, no acid needs to be used to suppress the coupling reaction and, consequently, no ammonia vapors are necessary to neutralize the acid so that the coupling reaction can go forward. Furthermore, this embodiment possesses the advantage that the coupler coated paper is not light sensitive and can be handled in a normal manner. Hence, the printing process can be carried out under normal white light. It is also possible to reverse the first and second diazo imaging substances so that the coupler is supplied in the ink cartridge 14, and the diazo salt solution is disposed on the paper 18. Again, the coupling reaction will not occur until the paper is imprinted with the ink to produce a visible diazo image.

In another embodiment of the diazo printing system and method of the present invention, plain, uncoated paper is employed, and an ink containing a diazo compound, a coupler, and acid is used in the ink jet printer or other imaging device to imprint the plain paper with a latent diazo image 29, as can be seen by examining Figure 4. Figure 4 depicts the additional step of development which must be performed with this embodiment. The latent image 29 is exposed to ammonia vapors 32 to develop into a visible diazo image 30. While this embodiment has the advantage of using plain paper, it does require this additional development step.

Of course, the ink containing the first diazo imaging substance will also normally contain other components and, most particularly a carrier or solvent (such as water, various alcohols, other organic solvents, etc.) which will vary depending upon the particular diazo imaging substance used. Additionally, it may be necessary to include a resin binder to help adherence of the ink to the substrate, as is conventional and well known in the a-rt of formulating inks suitable for use in ink jet printers. Other components may also be present, such as one or more conductivity agents, defoamers, surfactants, corrosion inhibitors, plasticizors, thickeners, drying agents, etc .

Thus7 there has been described herein a diazo printing system and method which employs an ink jet printer including a cartridge filled with an ink having a first diazo imaging substance. The ink is imprinted upon to a substrate which is coated with a second diazo imaging substance to form a visible diazo image thereon.

The resultant image, as is characteristic of images produced by diazo printing, has high optical density and is highly opaque to ultraviolet light. Hence, the system of the present invention is particularly useful for producing intermediate screens and masks on transparent or translucent substrates. Due to the high quality of the diazo image produced, these intermediate masks and screens can be used in such high quality printing processes as silk screening, lithography, photo-lithography, etc. The system is also particularly useful for printing outside signage since the diazo image is particularly resistant to degradation caused by ultraviolet light. The system and method of the present invention have the particular advantage of employing an ink jet printer so that the system is easy to interface with computer based CAD and graphic design systems. Since the ink jet printer, impact printer or plotter is already designed to print computer generated and digitally stored images, it is possible to use the present system to create a visible diazo image directly from a design displayed on or stored in a computer. Thus, the present invention can be used as an integral part of a computerized, integrated production system for printing high quality art works and graphic designs.

The present invention has been described with reference to certain embodiments and exemplifications thereof. Doubtless, one of skill in the art having had the benefit of the teachings of the present invention may design variations of the present inventions other than those described and depicted without departing from the scope of the invention. Thus, it is the claims appended hereto, and all reasonable equivalents thereof, rather than the exact described and depicted embodiments and exemplifications, which define the true scope of the present invention. I claim:

Claims

1. A system for imprinting a substrate with a diazo image comprising: a computer activated imaging device provided with a first diazo imaging substance; and a substrate having a coating formed of a second diazo imaging substance disposed thereon such that an image printed thereon by said imaging device will react with said coating to produce a visible diazo image on said substrate.

2. The system of Claim 1 wherein the first diazo imaging substance comprises an ammonium hydroxide solution and the second diazo imaging substance comprises of a diazo compound, a coupler and an acid.

3. The system of Claim 1 wherein the first diazo imaging substance includes a diazo compound and the second diazo imaging substance includes a coupler.

4. The system of Claim 1 wherein the first diazo imaging substance includes a coupler and the second diazo imaging substance includes a diazo compound .

5. The system of claim 1 wherein the imaging device is an ink jet printer.

6. The system of claim 1 wherein the imaging device is an impact printer.

7. The system of claim 1 wherein the imaging device is a plotter.

8. A system for imprinting a substrate with the diazo image comprising: a computer activated imaging device supplied with a diazo compound, a coupler, and an acid; a substrate for imprinting thereon with said imaging device an image formed by said ink compound; and rnearTs for exposing the imprinted paper to ammonia vapors to develop the image imprinted thereon to produce a visible image.

9. A method of imprinting a substrate with a diazo image comprising steps of : supplying a computer activated imaging device an ink compound including the first diazo imaging substance; and printing an image with said imaging device onto a substrate coated with a second diazo imaging substance to form a visible diazo image on said substrate.

10. The method of Claim 9 wherein the step of supplying said imaging device with an ink compound comprises the further step of supplying said imaging device with an ink compound containing an ammonium hydroxide solution and the step of printing an image onto said substrate further comprises the step of printing an image onto a substrate coated with a second imaging substance containing a diazo compound, a coupler and an acid.

11. The method of Claim 9 wherein the step of supplying said imaging device with an ink compound comprises the further step of supplying said imaging device with an~ink compound containing a diazo compound and the step of printing an image onto said substrate further comprises the step of printing an image onto a substrate coated with a second imaging substance containing a coupler.

12. The method of Claim 9 wherein the step of supplying said imaging device with an ink compound comprises the further step of supplying said imaging device with an ink compound containing a coupler and the step of printing an image onto said substrate further comprises the step of printing an image onto a substrate coated with a second imaging substance containing a diazo compound.