Ink jet printing using a combination of non-marking and marking inks

Abstract

An ink jet device selectively ejects droplets of non-marking liquid ink into cells of a printing member in a desired latent negative image pattern. Certain cells of the printing member are filled with pigmented ink to create a desired image. An electrical bias is applied for fractionating pigment in the pigmented ink from liquid and transferring an image-wise pigmented ink pattern from the printing member to a receiving member, leaving behind a substantial portion of liquid. The receiver can be an intermediate member whereby the image-wise ink pattern is transferred from the intermediate member to a final receiver, while such receiver is in operative association with said intermediate member.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

In the detailed description of the preferred embodiment of the invention presented below, reference is made to the accompanying drawings, in which:

FIGS. la and lb are views of a portion of a textured imaging member (TIM) and details of the cells thereof, for use in the printing apparatus according to this invention, on a significantly enlarged scale;

FIG. 2 is a schematic illustration of a preferred embodiment of the printing apparatus according to this invention;

FIG. 3 is a side view, in cross-section of a portion of the anilox roller and intermediate member of the printing apparatus according to this invention;

FIG. 4 is a side view, in cross-section of a portion of an alternate embodiment of the anilox roller of the printing apparatus according to this invention;

FIGS. 5 a-5d are respective views, in cross-section, showing the sequential operation of the printing apparatus according to this invention as seen in FIG. 2;

FIG. 6 is a schematic illustration of another preferred embodiment of the printing apparatus according to this invention; and

FIGS. 7 a-7e are respective views, in cross-section, showing the sequential operation of the printing apparatus according to this invention as seen in FIG. 4.

DETAILED DESCRIPTION OF THE INVENTION

According to this invention, an ink jet mechanism is utilized to write an image, using a non-pigmented ink that is jetted into cells of a primary textured imaging member (TIM). The quantity of non-marking ink jetted into each cell varies, according to the negative image density of the image to be produced. Subsequent to the negative image-wise deposition of the non-marking ink, a marking ink of a chosen color is spread across the primary imaging member in such a manner as to fill the partially filled or unfilled cells of the TIM, thereby making a positive inked image. The preferred mode of filling the cells of the TIM with marking ink is to spread the ink using a roller, doctor blade, squeegee, or other known mechanism that is in intimate contact with the TIM, thereby forcing the marking ink into the partially filled or unfilled cells and skiving the ink off the TIM in all other areas.

In similar fashion, this technology can be used to produce digital binary images, i.e. those images where the amount of ink laid down per printed pixel is approximately constant and the density is varied by controlling the number of pixels that are printed. For example, in traditional printing, gray scale is obtained by printing a so-called half-tone pattern. In a typical offset or gravure printing, dots are printed according to a ruled grid, with the higher frequency rulings corresponding to higher quality images. For example, assume that an image is printed on a 150-line rule; that is, a grid in which ink can be deposited periodically with a spatial frequency of 150 dots per inch. The density is controlled, by varying the size of the dot printed on the aforementioned grid. If a white background is desired in a specific area, no ink is deposited at those grid positions corresponding to such specific area. If a solid area is to be developed, the printed dot would cover the entire area within that grid location. Gray scale is achieved by varying the size of the dots laid down on each grid location. For example, assume a 600 dpi printing press printing on a 150-line rule. That means that each grid mark is divided into an array of 4 pixels by 4 pixels. Each pixel can be either inked or left unlinked, thereby allowing 16 levels of gray to be printed. More pixels in an array will allow more gray levels to be printed. In a gravure press, the pixels on the imaging plate or cylinder will be varied to allow the dot size to vary. In a digital press, the number of inked pixels per grid mark determines the number of gray levels.

The present invention provides a solution to several serious limitations in ink jet printing. First, it eliminates ink jet head plugging by eliminating the need to jet inks that can either dry in, or otherwise clog, the heads. Second, in a color engine, it allows the same head to be used for each color as only clear solvent, not colored ink, is jetted. Third, it eliminates the cost and complications associated with formulating new inks for each application. Fourth, it allows the marking ink to be more viscous than inks have to have flow characteristics so as to be jettable. Fifth, inks having larger marking particles, which are easier to produce, but cannot be jetted from an ink jet head because such particles will clog the nozzles, can be used in this process, if desired.

The TIM can include an endless belt, a roller, or other suitable member, such as a plate similar to a gravure plate typically used in the printing industry. However, in contrast to a typical gravure plate, wherein the cells are made to correspond to the image to be printed, in the present invention the cells are approximately uniform in size and distribution across the surface of the TIM. Certain anilox rollers having an electrically conductive member are suitable for use as a TIM. The texture of the TIM is specified so that the ink jet drops are contained in very small wells (cells) that are deep enough to fully contain any ink that is directed toward it. Referring to FIGS. 1a and 1b, a preferred exemplary structure for a TIM is shown (designated by numeral 12) where cells 14 are hexagonally shaped and closely packed. Of course other shapes for the cells 14, such as diamond, rectangular, or oval for example, are suitable for use with this invention. The structural relation of the cells 14 prevents ink deposited in the cells from coalescing, which blurs the image, by preventing the ink in the cells from migrating beyond the cell walls. The cells 14 can also correct satellites and jet errors by collecting ink drops within the cell walls.

To practice this invention, it is important that the TIM 12 include an electrically conducting element. For example, the TIM 12 can have a metal surface. This allows an electrical bias to be established across the inked cells. Suitable TIMs 12 are described in a co-pending application and includes anilox rollers, gravure rollers or plates, or semi-conducting elastomeric members.

It is also important that the marking ink include an electrically insulating solvent, for example, a hydrocarbon such as Isopar L, Isopar G, or Isopar M, sold by Exxon, or various mineral oils, soy oil, or various silicone oils. In addition, the ink should have marking particles that are electrically charged. The particles should preferentially be between 0.1 and 3.0 μm in diameter and include a colorant such as a pigment or dye, although particles without a colorant can be used if desired. The particles can also include a polymer binder that is insoluble in the solvent. Because the ink needs to be electrically insulating, water and certain short chain alcohols such as methanol, ethanol, and isopropanol are not suitable solvents.

Although it is necessary that the particles in the marking ink be charged, the actual sign and magnitude of that charge is not critical as long as the ink remains stable, i.e., does not coagulate at a rate that does not allow it to be used in the printing engine, and is sufficiently high as to allow transfer and fractionation. Typically, the charge can be determined by applying a DC electrostatic field across a pair or parallel electrodes and measuring the charge on the material that is plated onto one electrode. Preferably, the magnitude of the charge per unit volume of ink should be greater than approximately 10⁻⁷ C/cm³.

The non-marking ink may include a solvent similar to that used in the marking ink. Alternatively, the non-marking ink may have a hydrophilic solvent such as water, or short chain alcohols, for example. This will prevent the two inks from mixing and may facilitate fractionation and transfer, providing the size of the cells of the TIM 12 is sufficiently large as to prevent the hydrophobic solvent from displacing the hydrophilic solvent. The electrical resistivity and other physical description of the marking ink are given in co-pending U.S. Patent application Ser. No. ______, and incorporated by way of reference.

In the practice of this of the invention, the non-marking ink is image-wise jetted into cells of the TIM 12, partially or totally filling those cells corresponding to a negative of the image that is to be printed. The marking ink is then spread over the TIM 12 and skived, rolled, or otherwise removed, thereby leaving just enough ink so as to fill each cell. The marking particles, within the marking ink, is then fractionated electrostatically using technology such as described in co-pending U.S. patent application Ser. No. ______ and electrostatically transferred to a receiver. The receiver can be a transfer intermediate member, preferably having a compliant member, such member having a Young's modulus between 1 MPa and 10 MPa and being between 0.1 mm and 10.0 mm thick. The Young's modulus is determined using an Instron Tensile Tester and extrapolating back to zero strain. The applied bias used to effect both transfer and fractionation depends on the resistivity of the opposing electrode. Typically, transfer and fractionation voltages range between approximately 100 volts and 2,000 volts.

In another embodiment of this invention, the marking ink can be jetted into specific cells. While this process has the advantage of limiting the amount of marking ink deposited into undesirable locations on the TIM 12, it may be more susceptible to clogging the ink jet nozzle, thereby being a less robust process. Moreover, the additional jetting process is slow compared to uniformly depositing the marking ink, thereby limiting the speed at which the press can operate.

The receiver can also be the final receiver that is to bear the image, such as paper. In this mode of practicing the invention, the electrical bias can be established using an electrode such as a roller located behind the paper in such a manner as to press the paper against the TIM 12. Alternatively, a bias can be established by other suitable mechanisms such as a corona or a corona in conjunction with a roller. In another alternative mode of practicing this invention, fractionation and transfer can be done simultaneously. Also, TIM 12 can be cleaned after transfer using various devices such as spraying with a solvent that readily evaporates, spraying with compressed air, a combination of the aforementioned mechanisms, or other suitable devices known in the art.

A first preferred embodiment of a printing apparatus 10, according to this invention, is shown in FIG. 2. The TIM 12 is shown as an anilox roller (with hexagonally shaped, closely packed cells 14 as shown in FIG. 1). For the reasons set forth below the anilox roller must have an electrode. As shown in FIG. 3, the anilox roller 12 may be a steel roller 12′ (alternatively may be chrome coated), thus making electrical contact straightforward. That is, the anilox roller 12 is grounded and an intermediate member 22, further described below, in contact therewith, has an applied electrical bias connected thereto, such as voltage source V. Alternatively, the anilox roller, for example designated by the numeral 80 in FIG. 4, may have a structure where a ceramic layer 82 is formed on top of steel (conducting) substrate 84. The ceramic layer 82 is etched (for example with a high powered laser) to form the cells 86. In this case, the ceramic layer 82 is to be relatively thin, i.e., about twice the depth of the etched cell. The steel substrate 84 would then serve as the electrical contact.

Four basic, substantially identical imaging units, designated as 16a-16d, are shown in the embodiment of FIG. 2. More or less imaging units may be used if it is desired to create monochrome prints, two or three spot color prints, or process color prints with four or more color separation images, with or without additional spot color separations. Each of the imaging units 16a-16d includes an ink jet device 18 that selectively jets a non-pigmented ink in an image-wise fashion on to the TIM (anilox roller) 12 thereby creating a negative latent image in the cells 14 on the surface of the respective TIM 12. An inking unit 20 is provided a marking particle in layer, spread on the surface of the TIM 12 to top off all cells 14 that are empty, or partially empty, with a pigmented ink. The image is thereafter fractionated and transferred to an intermediate member 22, which is preferably compliant. A preferred intermediate member 22 has a volume resistivity between 1.0×10⁸ and 1.0×10¹¹ ohm-cm. The intermediate member 22 could be a roller or a web. If the intermediate member is a roller, then the support layer should include an electrically conducting cylinder (aluminum, steel core) and the thickness of the compliant layer would preferably be greater than 1.0 mm and less than 15.0 mm. If the intermediate member is a web, then the support material is preferably a seamless web having a metal layer such as nickel, steel, or such. Alternatively, a thin electrically conducting film can be coated onto a polymer web. Suitable polymers include polyimide, polyester, or polycarbonate for example. As shown in FIGS. 2 and 3, the applied electrical bias (from voltage source V) is applied by conducting rollers 21 engaging the intermediate member web 22 with the anilox rollers 16a-16d. A conditioning unit 24 cleans the cells 14 of the TIM 12 after transfer in order to ready them for receiving the next image. Each imaging unit 16a-16d creates one color separation image, which individual color separation images are combined in register on the intermediate member 22 to form a desired multi-color image. An optional liquid removal unit 26 is shown that acts to remove excess liquid from the imaged intermediate member 22. The liquid depleted image carried by the intermediate member 22 is then transferred to a receiver member R (paper or other media) in a transfer zone 28, and the intermediate member 22 is cleaned by a cleaning unit 30 prior to re-entrance into operative relation with the imaging units 16a-16d.

Activation and timing of operation of the various elements of the printing apparatus 10, according to this invention, are controlled by a logic and control device L. The logic and control device L is preferably a microprocessor-based device, which receives input signals from an operator communication interface, and a plurality of other appropriate sensors (not shown) associated in any well-known manner with the elements of the printing apparatus 10. Based on such signals and suitable programs for the microprocessors, the logic and control device L produces appropriate signals to control the various operating devices and stations within the printing apparatus 10. The production of a program for a number of commercially available microprocessors is a conventional skill well understood in the art, and do not form a part of this invention. The particular details of any such program would, of course, depend upon the architecture of the designated microprocessor.

The method of operation for image formation by the printing apparatus 10 is sequentially shown in FIGS. 5a-5d. FIG. 5a shows non-pigmented liquid 60 from ink jet device 18 filling selective cells 14 of the TIM 12 in an image-wise fashion that is a negative of the image to be created. Cells 14 can be partially filled, or completely filled, depending on the level of gray being implemented. FIG. 5b shows the state of the cells 14 after the TIM 12 passes through the inking unit 20. The inking unit 20 fills empty and partially empty cells with a pigmented ink 62, while the previously fully-filled cells remain filled only with non-pigmented liquid. The TIM 12 is then moved into contact with the intermediate member 22 and an electrical bias is applied to fractionate and preferentially transfer pigmented ink 62 to the intermediate member, leaving mostly liquid 60 behind in the cells 14 after the splitting of the pigmented ink has occurred. The resulting image transferred to the intermediate member 22 in this manner (as shown in FIG. 5c), possibly with some of the pigment-depleted liquid from the TIM cells 14. FIG. 5d shows the state of the TIM after the conditioning unit 24 cleans the cells 14 and removes any remaining liquid 60.

A second preferred embodiment of the printing apparatus 10′, according to this invention, is shown in FIG. 6. The TIM 12′ is shown as an anilox roller (with hexagonally shaped, closely packed cells 14′). Four basic, substantially identical imaging units designated as 40a-40d are shown. More or less imaging units may be used if it is desired to create monochrome prints, two or three spot color prints, or process color prints with four or more color separation images, with or without additional spot color separations. Each of the imaging units 40a-40d includes an inking unit 42 to uniformly apply a pigmented ink 70 to the TIM 12′, filling all of the cells 14′ thereof equally (FIG. 7a). Thereafter, a roller 44 is provided that is suitable for removing a portion of the ink 70, typically about one half of the ink, from the cells 14′ (see FIG. 7b) and returns the ink to the inking unit 42. In order of process, an ink jet unit 46 is provided to then jet a non-pigmented liquid in an image-wise fashion onto the TIM 12′, thereby selectively filling the cells 14′ on the surface of the TIM in an image-wise manner (FIG. 7c). That is, only the cells that correspond to an image to be printed are completely filled. The resultant image is fractionated and transferred to an intermediate member 48, which is preferably compliant. After transfer, a conditioning unit 50 cleans the cells 14′ to ready them for receiving inks for forming the next image. Each imaging unit 40a-40d respectively creates one color separation, which is combined in register on the intermediate member 48 with the other color separations. An optional liquid removal unit 52 is shown that acts to remove excess liquid from the imaged intermediate member 48. The liquid-depleted image is then transferred to a receiver member R′ (paper or other media) in a transfer zone 54, and the intermediate member 48 is thereafter cleaned by a cleaning unit 56 prior to re-entrance into the imaging units 40a-40d. The inked image can be transferred from the intermediate to the final receiver (e.g. paper) by bringing the paper into contact with the intermediate using known transport mechanisms and applying an electrostatic field that urges the charged particles from the intermediate member 48 to the receiver R′ while the final receiver R′ is in contact with the intermediate member 48. Alternatively, the inked image can be transferred from the intermediate member to a final receiver by pressing the intermediate member against the final receiver, preferably with the simultaneous application of heat, i.e., using a pressure or thermal transfer, as is know in the electrophotographic literature. Moreover, a thermal transfer process can be utilized so that the inked image is transferred and fused simultaneously in a process known in the literature as transfusion.

The method of operation for image formation by the printing apparatus 10′ is sequentially shown in FIGS. 7a-7e. FIG. 7a shows the inking unit 42 filling all the cells 14′ of the TIM 12′ uniformly with pigmented ink 70. FIG. 7b shows the half-filled cells, resulting from ink splitting by the roller 44. FIG. 7c shows the cells 14′ filled in an image-wise manner, from the ink jet unit 46, with a non-pigmented compatible liquid 72. The TIM 12′ is then moved into contact with the intermediate member 48 and the liquid is fractionated transferring about half of the filled cells 14′ to the intermediate member 48, and not transferring any ink from the non-image (half-filled) cells. When an electrical bias is applied during this transfer, the pigmented particles are fractionated and preferentially transferred to the intermediate member 48, leaving mostly liquid 72 behind in the cells after the splitting of the ink has occurred. The resulting image transferred in this manner is shown in FIG. 7c, along with the pigment-depleted liquid in the TIM 12′. FIG. 7d shows the state of the TIM 12′ after the conditioning unit 50 cleans the cells and removes most or all of the remaining liquid 72.

The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

PARTS LIST

• 10, 10′ Printing apparatus
• 12, 12′ Textured imaging member (TIM)
• 14, 14′ Cells
• 16 a-16d Imaging units
• 18 Ink jet device
• 20 Inking unit
• 21 Conducting rollers
• 22 Intermediate member
• 24 Conditioning unit
• 26 Removal unit
• 28 Transfer zone
• 30 Cleaning unit
• 40 a-40d Imaging units
• 42 Inking unit
• 44 Roller
• 46 Ink jet unit
• 48 Intermediate member
• 50 Conditioning unit
• 52 Removal unit
• 54 Transfer zone
• 56 Cleaning unit
• 60 Liquid
• 62 Pigmented ink
• 70 Ink
• 72 Liquid
• 80 Anilox roller
• 82 Ceramic layer
• 84 Steel substrate
• 86 Cells
• L Logic and control device
• R, R′ Receiver member
• V Voltage source

Claims

1. A printing apparatus utilizing non-marking ink and marking pigmented ink, said printing apparatus comprising: a printing member including a series of substantially equal sized cells located over the surface of said printing member;an inking unit for filling certain cells of said printing member with pigmented ink;an ink jet device for selectively ejecting droplets of non-marking liquid ink into said cells of said printing member in a desired negative latent image pattern;a receiver operatively associated with said printing member; anda transfer mechanism for fractionating said pigmented ink and transferring such fractionated pigmented ink to said receiver.

2. The printing apparatus of claim 1, wherein said transfer mechanism includes an electrical bias device for facilitating fractionating of said pigmented ink.

3. A printing apparatus according to claim 1, wherein the receiver is paper.

4. A printing apparatus according to claim 1, wherein said transfer mechanism includes an intermediate member.

5. A printing apparatus according to claim 2 comprising: a transport device for transporting a receiver into operative association with said intermediate member;a first transfer mechanism between said intermediate member and said printing member to fractionate said pigmented ink from said non-marking liquid and transfer an image-wise pigmented ink pattern from said printing member to said intermediate member, leaving behind a substantial portion of such liquid; anda second transfer mechanism between said intermediate member and a receiver member to transfer an image-wise pattern from said printing member to such receiver, while such receiver is in operative association with said intermediate member.

6. The printing apparatus of claim 5, wherein said first transfer mechanism includes an electrical bias device for facilitating fractionating of said pigmented ink.

7. The printing apparatus of claim 1, wherein said printing member is a roller with said cells located substantially over the entire circumferential surface of said roller in a closely packed, hexagonal configuration.

8. The printing apparatus of claim 1, wherein said printing member is a roller with said cells located substantially over the entire circumferential surface of said roller in a closely packed configuration.

9. The printing apparatus of claim 8, wherein configuration is selected from the group of configurations including hexagonal, diamond, rectangular, and oval shapes.

10. The printing apparatus of claim 8, wherein said inking unit fills all cells of said printing member.

11. The printing apparatus of claim 10, wherein said certain cells of said printing member filled by said inking member are all cells thereof and further including an ink removing mechanism located downstream, in the process direction, of said inking unit for removing approximately half of said pigmented ink from all cells of said printing member.

12. The printing apparatus of claim 11, wherein said ink removing mechanism also removes ink that is not within a cell.

13. The printing apparatus of claim 12, wherein said ink removing mechanism is a squeegee, a skive, or a roller.

14. The printing apparatus of claim 13, wherein said ink removing mechanism is operatively connected to said inking unit to return removed ink thereto.

15. The printing apparatus of claim 2 further including a cleaning unit in association with said printing member, wherein any liquid remaining in said cells of said printing member is removed prior to reuse.

16. A pigmented ink for use in the printing apparatus according to claim 1 comprising electrostatically charged particles.

17. A printing apparatus according to claim 5, wherein said second transfer mechanism provides for electrostatically transferring said ink pattern from the intermediate member to the final receiver.

18. A printing apparatus according to claim 5, wherein said second transfer mechanism provides for thermally transferring said ink pattern from the intermediate member to the final receiver.

19. A printing apparatus according to claim 5, wherein said second transfer mechanism provides for transferring said ink pattern from the intermediate member to the final receiver by the application of pressure.

20. A printing apparatus according to claim 5, wherein said second transfer mechanism provides for thermally transferring and fusing said ink pattern from the intermediate member to the final receiver.