WO2002051639A2

WO2002051639A2 - Digital printing device and method

Info

Publication number: WO2002051639A2
Application number: PCT/IL2001/001208
Authority: WO
Inventors: Shay Kaplan
Original assignee: Mizur Technology, Ltd.
Priority date: 2000-12-27
Filing date: 2001-12-27
Publication date: 2002-07-04
Also published as: AU2002217402A1; WO2002051639A3

Abstract

A digital printing apparatus comprises a substrate (10) having a surface modified with a plurality of pixels. Each pixel includes a) a cavity (14) having an upper opening which extends below the surface of the substrate; b) a flexible membrane (11) bonded to the substrate surface and covering the plurality of pixels; c) means (20) for maintaining portions of the membrane in a first depressed position over each of the plurality of pixels; and means (36) for selectively elevating the depressed portions of the membrane from the first depressed position to a second elevated position in a selected number of the plurality of pixels.

Description

DIGITAL PRINTING DEVICE AND METHOD

Field Of the Invention

The present invention relates to an apparatus and method for the deposition of ink or a conductive material onto a printable substrate, i.e. printing. More particularly, the present invention provides an apparatus and method for the digitally-controlled deposition of liquid ink or a conductive material onto a printable substrate such as paper or a printed circuit board.

Background Of The Invention

Of the various methods known for the putting of type to page, digital printing is useful for the way it allows each document or a small group of documents to be different from the other and thus 'personalized'. Another advantage of digital printing in printing machines is that it saves the cost of manufacturing etched print plates, which are both costly to manufacture, set up and to store.

However, digital printing is not typically thought of when one desires large quantities of printing to be done, nor is it particularly suitable for providing textured printing such as the type known as gravure printing. The most widely used of the currently known technologies are based on ink jet printing, which is rather slow and thus commercially useful only for low quantity print jobs, or photoelectric technologies that deposit special inks comprising light sensitive materials on the ink holding surface and then change the attraction of the inks to the exposed material vs. the unexposed material. The latter of these systems is faster than ink jet printers but still slower than traditional, liquid ink-based typesetting printing machines and require special, more expensive inks.

As mentioned hereinabove, traditional liquid ink-based typesetting printing machines requires the manufacture of etched printing plates. These are expensive to manufacture, set up, store and are essentially unrecyclable. Summary Of The Invention

Thus, there is a need for a method and apparatus for printing which combines many of the advantages of traditional liquid-ink based printing, i.e. speed and print quality, with the flexibility and economy of digital printing. The present invention achieves these goals by providing a new mechano-digital printing plate useful for delivering liquid ink or a conductive material to a print surface, whether paper or PCB substrate, in the manner of printing, while providing the ease of customization provided by digital printing. The plate may be either a rigid or flexible substrate having a surface covered by mechano-digital pixels.

In an exemplary embodiment of the present invention, each pixel in the plate includes a heating element, conductors for the heating element, a small amount of liquid and a flexible membrane covering. It should be understood that the exemplary embodiments disclosed herein may be used for many "print" processes wherein a substance, usually liquid, is deposited on a print surface, such as paper, or a PCB. Thus, although the exemplary embodiments are referred to as useful with ink, in fact, the exemplary embodiments could be used in the process of making printed circuit boards by deposition of conductive material onto a PCB substrate in the desired pattern, or for any other pattern deposition process.

During manufacturing of one exemplary embodiment, a partial vacuum is formed in the space below the membrane, which causes the membrane to be pulled downward below the level of the undistended portions of the surface. When printing, the whole plate is covered with liquid printing ink. Since all the areas of the membrane covering the pixels are depressed due to the partial vacuum, each depressed area comprises a reservoir to hold a quantity or pool of ink or conducting polymer, which is available for deposition on a print surface unless removed from the membrane prior to printing. The removal of unwanted ink is accomplished by wiping it off by passing the plate under a "squeegee" blade that removes the excess ink from the areas where printing is not desired, or by passing the squeegee blade over the plate. Thus excess ink is removed from all portions of the membrane outer surface which are not depressed due to reversal of the partial vacuum in the pixel. Ink is reserved in those pixels needed to form the image (hereinafter the "off-pixels") which will ultimately be created by deposition onto a print surface. The ink is reserved only in the off-pixels by causing the ink carried by the membrane covering the remaining undepressed pixels (hereinafter "on-pixels") to be wiped away along with the rest of the excess ink covering the surface of the membrane. In an exemplary embodiment of the present invention, reversal of the partial vacuum is accomplished by applying a pressure to the underside of the depressed membrane areas covering the on-pixels just before the squeegee blade passes. This is done by applying an electric current to the selected on-pixels. The electric current is directed through the heating element disposed in the bottom of each pixel. The liquid covering the energized heating element evaporates and the pressure exerted by the vapor counteracts the partial pressure pushing against or inflating the membrane out so that its outer surface opposite the membrane/plate interface surface is at least flush with the undepressed portions of the membrane outer surface. When the squeegee passes over the membrane and each line of on-pixels, the ink is removed from all surfaces of the membrane which are not below the plane of the undepressed membrane portions, and ink is left only in the off-pixels in which current didn't flow. Current is then switched off and the liquid cools down. By the time the line of off- pixels is in a position to transfer the ink to a print surface or transfer surface, the membrane surface has ink only in the unheated off-pixels.

In an alternative exemplary embodiment of the present invention, the pixel space can be separated into more than one fluid chambers, each having it's own heating element. In this case, it is possible to only heat part of the liquid to evaporation by passing current through only selected heating elements. Thus, the partially displaced membranes are not pushed above the surface but only to a certain level below it that can be predetermined by the number of heaters activated, thus, changing the amount of ink in that pixel that will be left after the squeegee operation, and leaving different amounts of ink for transfer. In this case, depending on the materials used and the heat losses as will be further elaborated upon hereinbelow, the partially activated pixels may optionally have current flowing through them until the ink transfer. In pixels that do need not to carry ink, sufficient heat will be applied by the heaters before the squeegee operation so sufficient liquid is evaporated and the on-pixel membrane coverings are pushed towards the squeegee. In all cases, it is an alternative possibility that each line of heating elements parallel to the squeegee may have one common conductor connecting all pixels and each pixel will have one or more computer-operable or otherwise controllable conductors that will determine the off or on status of the pixel.

Similarly, it is an alternative embodiment that the entire space between the heating element and the pixel membrane covering is substantially filled with controllably heat- expandable liquid. In the course of manufacturing a plate having such an arrangement, the liquid may be filled into the pixel cavity while hot; sealed in by the membrane coverings; and then allowed to cool, thereby contracting and creating a lower pressure on the pixel cavity side of the membrane covering. Heating of the expandable liquid would bring the pressure on both sides of the membrane covering into equilibrium and cause the membrane covering of the on-pixel to be in an at least flush position with the undistended portions of the membrane, exposed to the sweep of the squeegee blade.

It is a further alternative embodiment of the present invention that, rather than causing the cupping of a flat, flexible membrane by creating a partial vacuum in the pixel cavity, the membrane is manufactured with preformed dimples or cups, i.e. the resting state of the membrane is dimpled and activation of a pixel causes pressure to be applied against the membrane thereby "de-dimpling" the membrane at that spot. The pre-formed dimples are positioned on the membrane such that each one protrudes down into the pixel cavity when the membrane is adhered to the substrate of the printing plate. On the upper surface thereof, each dimple has an opening flush with the plane of the outer surface of the membrane, when viewed as a whole. Each dimple provides a potential reservoir for liquid ink which can be allowed to remain filled or may be emptied by the novel control mechanism of the present invention, described hereinbelow.

Brief Description Of The Drawings

FIG. 1 is a cross-sectional view of a pixel in a printing plate, wherein the membrane is depressed in the area covering the pixel opening and the membrane is covered in its entirety by a layer of printing ink, constructed in accordance with an exemplary embodiment of the present invention;

FIG. 1a is a cross-sectional view of a pixel in a printing plate, wherein the membrane is depressed in the area covering the pixel opening and only that area of the membrane is left containing a bead of ink after an inflation and wiping cycle, in accordance with the exemplary embodiment of the present invention shown in FIG. 1 ;

FIG. 2 is a cross-sectional view of the pixel shown in FIG. 1 hereinabove, wherein the membrane is pushed out, constructed in accordance with an exemplary embodiment of the present invention;

FIG. 3 is a cross-sectional view of an alternative embodiment of a pixel in a printing plate, wherein the space below the membrane is separated into two chambers, each having it's own heating element, constructed in accordance with the present invention;

FIG. 4 is a cross-sectional view of the pixel illustrated in FIG. 3 hereinabove, wherein only part of the liquid is evaporated, in accordance with an alternative embodiment of the present invention;

FIG. 5 is a cross-sectional view of the pixel illustrated in FIGs. 3 and 4 hereinabove, wherein a substantial quantity of liquid is evaporated, in accordance with an alternative embodiment of the present invention;

FIG. 6 is a top plan view, in partial cross-section of a plurality of pixels in a printing plate, in accordance with an exemplary embodiment of the present invention;

FIG. 7 is a cross-sectional view of an alternative embodiment of a pixel constructed substantially in accordance with that shown in FIGs. 1 and 1a, having a centrally located membrane covering area treated for increased ink affinity; and FIG. 8 is a perspective view of the present invention adapted into a drum for use on a drum-printing machine in accordance with another exemplary embodiment of the present invention.

Detailed Description Of Exemplary Embodiment

The present invention consists of a digital mechanical printing plate 10 particularly useful for printing and covered substantially over one whole surface thereof by membrane 11. Each pixel 12 in plate 10 comprises a pixel cavity 14 which includes therein a heating element 16, conductors 18 for the heating element 16, a determined amount of fluid 20 (which may be caused to evaporate or otherwise sufficiently expand during a heating process, causing a desired pressure inside the pixel cavity 14) and an area of membrane 11 termed flexible membrane covering 22.

A suitable area size for the pixel opening 23 and thence the flexible membrane covering 22 of the exemplary embodiment may range from about 4 μ²to about 90,000 μ². The thickness of the membrane covering 22 can range correspondingly from about 1 to 50 μ. The flexibility range of the membrane 22 should be sufficient to permit a deflection to a depth at the center of the covered pixel area of from about 1 to 50 μ. Typically, the depth of deflection is from 1 to 10 μ for use in standard printing, and from 10 to about 50 μ, i.e. the rest of the range, is used for heavy ink deposition of the kind found in gravure printing. In the alternative described hereinbelow, wherein a membrane having pre-formed dimples is used, then the depth is not one of deflection, but the dimples still are provided with a resting depth of 1 to 50 μ.

The membrane 11 can be manufactured from a thin single layer or laminate of metal, or from a flexible organic material for example polyimide derivatives, bis- benzocyclobutane (BCB), neoprene, silicon rubber, polyxylylenes, such as parylene, mylar, a polyimide such as KAPTON^tm, a product marketed by Dupont Chemicals, or a latex derivative. The choice between the aforementioned options is made keeping in mind the correlation between the desired performance of the present embodiment of the invention and the chosen material's properties. A suitable fluid 20 might be a liquid, a gas, or a mixture thereof selected based on the following characteristics: boiling point, specific heat of vaporization, energy, surface energy and influence of the liquid on the membrane material.

Examples of an appropriate liquid are water, alcohol or a fluorinated organic solvent such as fluorinert™, also a product marketed by Dupont Chemicals. Additionally, the fluid 20 should be selected so as not to be corrosive or otherwise chemically reactive with the membrane 11.

The inks which may be used with the present invention are the standard liquid ink used in and known by practitioners of the art of printing.

The printing plate 10 can be manufactured from a rigid plate if a flat print plate is desired, or on a flexible substrate to fit on cylinder drums.

Referring now to FIGs. 1- 4, during manufacturing, a partial vacuum is formed in the pixel cavity space 14 below membrane covering 22, which causes membrane covering 22 to be pulled down below the level of the surface of membrane 11 when the pressure forces on both sides of membrane 11 are in equilibrium. In an alternative exemplary embodiment, the effect of having membrane covering 22 pulled down as being its resting position can be achieved by filling cavity 14 to the top with a relatively easily expandable fluid 20 first having been heated, or fully expanded, and then sealing membrane 11 onto substrate 24. Then, as fluid 20 cools, it contracts, causing a lower pressure on the undersurface of membrane covering 22 than on its upper surface and the result that the membrane covering 22 is pulled down below the top of pixel cavity 14.

The steps of a printing process are [1] the whole membrane 11 is covered with ink 26 with depressed membrane coverings 22 being filled with liquid ink; and [2] a squeegee blade is moved parallel to the printing plate 10 in order to clear the ink 26 from all the areas which we don't want to print. In an intermediate step, just before the squeegee blade passes a particular line of pixels, an electric current is directed through the heating elements 16 of those pixels 12 in the line from which no printing is desired. The electric current causes the heating elements 16 of those activated pixels to heat up and evaporate (or expand) fluid 20. The pressure caused by expanding vapor 28 pushes upward against membrane 22. When the squeegee (not shown) passes over the activated line of pixels 12, the ink 26 is removed from all the flat and raised areas, i.e., the upwardly distended or inflated membranes 30, and ink is left only in those pixels 12 to which no current was directed, or off-pixels. The fluid 20 cools down, and when the line of pixels is in a position to transfer the ink 26, the surface of membrane 11 is left having transferable ink 26 only in the unheated or off- pixels.

Referring now to FIG. 8, in another exemplary embodiment of the present invention, the system is adapted for use on an imaging drum 42 for incorporation into a drum printing machine. In this embodiment, the substrate 24 is sufficiently flexible to be wrapped around a drum 42 comprising a stationary axle 32 integrated with a fiberoptic coupler 34, an optoelectronic convertor 36, an optical fiber rotating link 38. In this embodiment, electrical impulses of digital data are passed via a digital data conductor 40 to the fiberoptic coupler 34 located on the axle 32, which in turn converts the electric impulses into light signals. Said light signals are thence passed via the optical fiber rotating link 38 to the optoelectronic convertor 36. The optoelectronic convertor 36 converts the light signals back into electric impulses, which are then directed to each of the pixel 12 on the substrate 24, which is wrapped around the outer surface of the rotating drum. Said electric impulses generated by the optoelectronic convertor 36 can then selectively and controllably activate heating elements of each of the individual pixels 12.

Still referring to FIG. 8, please note that each square within the gridded section represents a group of pixels 12 which are actually nano pixels in size, and therefore undistinguishable by the naked eye.

Referring specifically now to FIG. 3 and to FIG. 4, in an alternative embodiment of the present invention, the space 32 below the membrane covering 22 is separated into two or more fluid chambers 34, 36 each having it's own heating elements 38, 40. In this embodiment, if only part of liquid 42 is evaporated by passing current through only some of heating elements 40, membrane coverings 22 are not pushed above the surface but only to a certain level below it that can be programmed or controlled according to the number of heaters activated, and therefore, the pressure buildup in the cavity. This results in a change in the amount of ink 26 that will be left in the pixel after the squeegee operation, and will leave a less than full amount of ink 26 for transfer. In this case, depending on the materials used and the heat losses, among other factors, the partially filled pixels may have to have current flowing through them until ink 26 is transferred. This is so since the height of the bead of remaining ink may not be too low for the top of the bead to protrude above the plane of the membrane's surface. This can potentially affect the transfer of the ink to a print or transfer surface.

Referring now to FIG. 5, in pixels that need not carry ink, on-pixels, all heaters 38, 40 will be activated before the squeegee operation so all liquid 42, 44 is evaporated and membrane covering 22 is pushed upwards.

Referring now to FIG. 6, each line of heating elements parallel to the squeegee, has one common conductor 18 connecting all pixels, and each pixel has one or more programmable conductors 48 that determines the status of the pixel.

Referring to FIG. 1a, a thick light-sensitive polymer is then applied in a coating 60 to this structure. This coating 60 is then patterned to create the pixel cavities 14. Pixel cavities 14 are filled with fluid 20, using a micro-dispenser, and the whole structure is bonded to a sheet of flexible membrane sheet 11, either in partial vacuum or by using a flexible pressure sheet that causes the membranes to be bonded in the depressed position.

The embodiment aforementioned in which the space below the membrane is separated into two or more chambers can be manufactured in the same way, except for the chambers, which are multiple and the polymer partitions 62 between them that optionally are not as high as the side walls and are formed using an additional wall definition step.

In an alternative embodiment of the present invention, the membrane is manufactured with pre-formed dimples which have openings on one side of the membrane surface and protrude outwardly from the opposing surface. The dimples are sized and positioned to correspond with the pixel cavity positions and so as not to extend too deeply into the pixel cavities, a depth of roughly from 1 to about 50μ. In this embodiment, the evaporable or expandable liquid would be heated to either press directly against the dimple or to form a gas pressure to push against it thereby pushing it upward at least flush with or above the surface of the membrane.

With reference to FIG. 7, in a further alternative embodiment, a desired area of the center of each membrane covering 22 (or dimple) is subjected to a treatment, such as abrading, coating with, covering with or having attached thereto a substance, whereby the ink is more attracted to the thus treated central area 70 of the covering or dimple than to the untreated portions thereof. In this manner, the ink bead 72 of a partially-filled pixel, will effectively stand-up to a fuller height so as to be transferable to a print or transfer surface when the membrane is in a fully depressed position, or at rest in the case of a membrane having pre-formed dimples.

One method for manufacturing the printing plate of the present invention, consists of the following steps: a polymer substrate 50, with a conductive metal 52 on it, such as used in the PCB industry, is patterned to form the conductors 18 in one direction. On it, a layer of light sensitive polymer 54 is coated. Via holes 56 are opened for each pixel common conductor by a layer-forming means such as a photolithography process.

Thin low conductive metal/alloy 58 is deposited on the structure. Conductors 48 are then formed perpendicular to the first layer of conductors 18, together with the shape of the heating elements 16, again by layer-forming means such as a photolithography process. In the following masking process, the thick metal/alloy 48 is removed from the heating element 16 only, leaving the heating elements 16, which are made out from a thin, relatively poorly-conductive material.

Claims

What is claimed is:

1. A digital printing apparatus comprising a substrate having a surface modified with a plurality of pixels, each pixel including a cavity having an upper opening and extending below the surface of said substrate, said surface and plurality of pixels being covered by a deformable membrane bonded thereon, and said pixels further comprising means for selectively elevating that portion of said membrane covering said pixel opening from a first depressed position to a second elevated position.

2. A digital printing apparatus according to claim 1 , further comprising means for maintaining said membrane in a first depressed position over each of said plurality of pixel openings.

3. A digital printing apparatus according to claim 1 , said means for selectively elevating said membrane covering further comprising a quantity of an expandable fluid in said cavity and means for expanding said expandable fluid.

4. A digital printing apparatus according to claim 1 , said means for selectively elevating said membrane covering comprising a quantity of evaporable liquid in said cavity and means for vaporizing at least a portion of said evaporable liquid.

5. A digital printing apparatus according to claim 2, said means for maintaining said membrane in said first depressed position comprising providing at least a partial vacuum in said cavity.

6: A digital printing apparatus according to claim 2, wherein said means for selectively maintaining said membrane in a first depressed position over each of said plurality of pixel openings comprises covering said substrate surface and said plurality of pixels with a membrane having dimples pre-formed therein and arranged on said membrane in spatial orientations corresponding to those of said pixel openings, said membrane being positioned such that a single one of said dimples extend downwardly into each of said pixel openings.

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7. A digital printing apparatus in accordance with claim 1 , wherein said cavity is subdivided into at least two fluid chambers.

8. A digital printing apparatus according to claim 7, wherein each one of said at least two fluid chambers is independently provided with means for selectively elevating said membrane covering means .

9. A digital printing apparatus according to claim 1 , wherein said substrate is adapted for use on a drum printing machine.

10. A digital printing apparatus according to claim 9, wherein said substrate is an integral part of a drum in said drum printing machine.

11. A digital printing apparatus according to claim 1 , wherein the area of said pixel opening is between 4 μ²and 90,000 μ².

12. A digital printing apparatus according to claim 1 , wherein the maximum depth of depression of the surface of said membrane at said first depressed position is between 1 and 50 μ.

13. A digital printing apparatus according to claim 1 , wherein said membrane is manufactured from a metal film.

14. A digital printing apparatus according to claim 1 , wherein said membrane is manufactured from a polyimide derivative.

15. A digital printing apparatus according to claim 1 , wherein said membrane is manufactured from bis-benzocyclobutane or a derivative thereof.

16. A digital printing apparatus according to claim 1 , wherein said membrane is manufactured from a latex derivative.

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17. A digital printing apparatus according to claim 1 , wherein said membrane is manufactured from a neoprene derivative.

18. A digital printing apparatus according to claim 1 , wherein said membrane is manufactured from silicon rubber derivative.

19. A digital printing apparatus according to claim 1 , wherein said membrane is manufactured from a polyxylylene.

20. A digital printing apparatus according to claim 19, wherein said polyxylylene is parylene.

21. A digital printing apparatus according to claim 1 , wherein said membrane is manufactured from mylar.

22. A digital printing apparatus according to claim 3, wherein said fluid is a hydrous solvent.

23. A digital printing apparatus according to claim 3, wherein said fluid is water.

24. A digital printing apparatus according to claim 3, wherein said fluid is an organic solvent.

25. A digital printing apparatus according to claim 3, wherein said fluid is a fluorinated organic solvent.

26. A digital printing apparatus according to claim 3, wherein said fluid is an alcohol solvent.

27. A digital printing apparatus according to claim 4, wherein said liquid is a hydrous solvent.

28. A digital printing apparatus according to claim 4, wherein said liquid is water.

29. A digital printing apparatus according to claim 4, wherein said liquid is an organic solvent.

30. A digital printing apparatus according to claim 4, wherein said liquid is a fluorinated organic solvent.

31. A digital printing apparatus according to claim 4, wherein said liquid is an alcohol solvent.

32. A membrane for use with a digital printing apparatus, said membrane having on at least one surface thereof affinity spots corresponding in position to pixels on a printing plate, said affinity spots having being treated to permanently have a greater affinity to liquid ink than the surrounding membrane surface, whereby beads of ink placed on said affinity spots spread less than on adjacent portions of said membrane surface.

33. A pixel for use in printing, comprising : a) a cavity extending below the surface of a substrate; b) a quantity of expandable fluid; c) means for expanding said liquid; and d) a flexible membrane covering the opening of said cavity, said flexible membrane being maintained in a depressed position unless a determined portion of said fluid is expanded.

34. A pixel for use in printing, comprising : a) a cavity extending below the surface of a substrate; b) a quantity of expandable fluid in said cavity; c) means for controllably expanding said fluid; and d) a flexible membrane covering said cavity, said flexible membrane being movable between a depressed position to an undepressed position when said fluid is energized from a non-expanded condition to an expanded condition.

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5. A method of printing comprising the steps of: a) applying ink to a digital printing plate comprising a plurality of pixels covered by a deformable membrane bonded thereon, said membrane being depressed wherever said membrane covers a pixel, said pixels further comprising means for selectively elevating that portion of said membrane covering said pixel to an elevated position; b) selectively activating at least one of membrane covering elevating means; c) wiping excess ink from said membrane; and d) transferring ink from the depressed portions of membrane covering pixels the membrane covering elevating means of which were not activated in step

(b) to a transfer surface or print surface.

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