2 FIELD OP THE INVENTION

3 The present invention relates generally to printing

4 apparatus and more particularly to ink-jet printing 5 apparatus. 6 BACKGROUND OF THE INVENTION

*- 7 Ink-jet and bubble-jet printers are known in the art.

8 In such printers, droplets of hot wax-based ink or ink in a

9 water-based solvent are ejected in image forming

10 configuration from a print-head onto a sheet of paper or

11 other substrate. The substrate may be heated so as to fix

12 the image on the substrate by evaporation of the water

13 solvent or melting of the waxy ink. However, the images

14 formed by such printers are often blurred somewhat, as a

15 result of the "wicking" of the ink into the paper, due to

16 flow of the water-based solvent or melted waxy ink.

17 Attempts to correct this problem by increasing the

18 viscosity of the ink have not been particularly successful,

19 since the ink-jet process does not work well with viscous 20 ink.

21 SUMMARY OF THE INVENTION

22 It is the object of the present invention to provide

23 ink-jet printing apparatus which produces a sharp and

24 unblurred image on a substrate such as paper using

25 conventional water-based or waxy ink. It is a further

26 object of the present invention to provide multi-color ink-

27 jet printing apparatus in which very precise registration

28 of the color images is obtained. The present invention

29 accomplishes these objects by interposing an intermediate

30 member between the ink-jet head and the substrate, such

31 that the functions of image-formation and image-transfer

32 are separated into two distinct stages.

33 In the first stage, the ink-jet printing head is ^ψ - 34 operated in the conventional manner to form the desired ψ 35 image, but instead of the image being formed directly on

36 the substrate, it is formed on the surface of the

37 intermediate member. In the second stage, the image is

38 transferred from the surface of the intermediate member to

the desired final substrate. Interposing the intermediate member affords the possibility of using conventional water- based, non-viscous inks for the initial image formation, and then evaporating a desired amount of the water solvent while the image is still on the intermediate member, prior to final transfer to the substrate. Heating the water-based and waxy inks allows for good transfer without excessive heating of the substrate, reducing power requirements of the system. Interposing the intermediate member also affords the possibility of applying resins or binders onto the image prior to final transfer, thereby enhancing the fixing of the ink image and its adhesion to the substrate. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be better understood and appreciated from the following detailed description taken in conjunction with the accompanying drawings in which: Fig. 1 is a schematic representation of ink-jet printing apparatus in accordance with an embodiment of the invention. Fig. 2 is a schematic representation of ink-jet printing apparatus in accordance with another embodiment of the invention. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Reference is now made to Fig. 1 which provides a schematic representation of ink-jet printing apparatus in accordance with an embodiment of the present invention. Included in the apparatus of Fig. 1 is an electronic imaging control assembly 8 which comprises a microprocessor and other standard user operated hardware and software as are known in the art. Control assembly 8 is connected to an ink-jet assembly 10 which includes an ink-jet printing head, liquid ink and other ink-jet apparatus as are known in the art. Slightly spaced from ink-jet assembly 10 is a drum 12 having a surface 14 which may be rigid but which preferably is comprised of a resilient polymeric material. Surface 14 is preferably coated with a non-sticking layer, such as silicone, silicone rubber or teflon which is

abhesive to the ink. When the apparatus is in operation, drum 12 rotates in the direction of arrow 13, and control assembly 8 is operative to provide appropriate control commands to ink- jet assembly 10 so as to cause ink-jet assembly 10 to eject droplets of ink in the direction of surface 14 such that the drops of ink adhere to surface 14 in a desired image configuration. In accordance with a preferred embodiment of the invention, surface 14 may be heated by means of an internal heater 16, or by means of a blower (not shown) . Heater 16 is operative to evaporate a substantial portion of the liquid carrier of the ink in solvent based inks, so as to prevent "wicking" of the image when it is transferred to the final substrate, as described below. After the ink image has been deposited on surface 14, drum 12 continues to rotate and the surface bearing the ink image is brought into contact with a final substrate 18, such as a web or a sheet of paper, which is fed into a nip 19 between drum 12 and an impression roller 20. If surface 14 is slightly resilient, impression roller 20 is preferably rigid. However, if surface 14 is solid, impression roller 20 should have a slightly resilient surface. It will be appreciated that as a result of the application of pressure at nip 19 between the two surfaces, the ink image is transferred to final substrate 18 from the non-stick surface 14 as the substrate is fed through the nip. The inventor has discovered that the specific configuration of ink-jet printing apparatus described above produces an image on the final substrate superior to that produced by the conventional ink-jet apparatus known in the art. Because the ink image is first produced on surface 14 of drum 12 and only then transferred to the final substrate, the ink-jet apparatus of the present invention effectively prevents "wicking" of the solvent based liquid ink when the image is transferred to the final substrate. Heating of surface 14 causes a substantial portion of the liquid solvent to be evaporated prior to final transfer.

such that a very clean, concentrated image is transferred. As a consequence, it is also unnecessary to heat the final substrate so as to fix and dry the image after transfer thereto. It will also be appreciated that the apparatus of the present invention affords not only single color printing of images but also multi-color printing of images. For multi- color image printing, ink-jet assembly 10 includes several ink-jet sub-assemblies, one for each of the process colors as is known in the art, and each such sub-assembly is connected to control assembly 8. As drum 12 rotates, each of the sub-assemblies is operative to deposit an image of a single color on surface 14. The use of drum 12 as an intermediate member facilitates a much more precise registration of the colored images than direct printing on paper, thereby providing a significantly sharper color image on the final substrate. Reference is now made to Fig. 2 which shows ink-jet printing apparatus in accordance with another embodiment of the present invention. The apparatus of Fig. 2 is similar to that of Fig. 1 except that upstream of ink-jet assembly 10 there is provided a squeegee roller 24 which engages surface 14 of drum 12. In a space 26, between squeegee roller 24 and drum 12, is a quantity of a binder resin, preferably a polymeric binder with or without solvent. The binder resin in space 26 is replenished by a dispenser assembly 28. Squeegee roller 24 rotates in the direction opposite that of drum 12, as shown by arrow 25, and is operative to cause a controlled thin layer of the binder resin to be coated on surface 14 prior to the deposition of the ink image thereon by ink-jet assembly 10. The binder resin acts to improve the fixing of the ink image when the image is transferred to the final substrate. In a preferred embodiment of the invention, the polymer binder is chosen to be reactive either with the ink dye and/or with the final substrate so as to improve the adhesion of the image to the substrate and to protect the image. In an alternative embodiment, squeegee roller 24 may be replaced

by a squeegee blade or other coating apparatus. A large number of materials are useful as polymer binders in the present invention, the choice being made on the basis of the characteristics of the ink, the substrate and the transfer member. Examples of suitable materials are marketed by Monsanto under the trade name Scripset. It will be appreciated that the present invention is not limited by the embodiments described above in conjunction with the drawings. Rather, the invention is limited only by the claims which follow: