Abstract:
Apparatus for forming a colorant image with improved image structure on a receiver in response to a digital image, including ink jet print heads responsive to the digital image for transferring colorant to the receiver; a passive fluid delivering structure for delivering treatment fluid to the receiver, the treatment fluid being selected to improve image structure; and relative movement is provided between the receiver and the ink jet print heads so that colorant is transferred to the receiver to provide the colorant image corresponding to the digital image on the receiver which has improved image structure.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     Reference is made to commonly assigned U.S. patent application Ser. No. 08/934,370, filed Sep. 19, 1997 entitled “Ink Jet Printing with Radiation Treatment” to Wen. The disclosure of this related application is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to methods and apparatus for providing a high quality colorant images on a receiver. 
     BACKGROUND OF THE INVENTION 
     To enhance the quality of the images printed by an ink jet printer, it is often desirable to treat the surface of the ink receiver with a fluid prior to ink jet printing. For example, U.S. Pat. No. 5,635,969 discloses a print head that pre-conditions the ink receiver with a treatment fluid that immobilizes the ink spots printed on the receiver. This technique, however, requires electrically driving the print head to deliver the treatment fluid to the ink receiver. The technique consumes power and its reliability can also be affected by the failure of the fluid chambers and nozzles in the print head. 
     SUMMARY OF THE INVENTION 
     An object of this invention is to provide a printing apparatus including capability of treating the receiver for enhanced image structure. 
     A further object of this invention is to provide receiver treatment without requiring the use of power during the treatment. 
     An additional object of the present invention is to provide receiver treatment that is reliable. 
     These objects are achieved by apparatus for forming a colorant image with improved image structure on a receiver in response to a digital image, comprising: 
     a) print head means responsive to the digital image for transferring colorant to the receiver; 
     b) passive fluid delivering means for delivering treatment fluid to the receiver, the treatment fluid being selected to improve image structure; and 
     c) means for providing relative movement between the receiver and the print head means so that colorant is transferred to the receiver to provide the colorant image corresponding to the digital image on the receiver which has improved image structure. 
     ADVANTAGES 
     An advantage of this invention is that the power is reduced for producing an image on a receiver. 
     Another advantage of this invention is that the reliability of the receiver treatment is improved. 
     A further advantage of this invention is that different treatment fluids can be selected which are compatible with improving different aspects of image structure. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic front view of the ink jet printing apparatus in the present invention diagramatically showing the control electronics; 
     FIG. 2 is a partial top view of the ink jet printing apparatus of FIG. 1; and 
     FIG. 3 is a partial side view of the ink jet printing apparatus of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is described with relation to a digital printing apparatus including the treatment the receiver for enhanced image structure. 
     Referring to FIG. 1, an ink jet printing apparatus  10  is shown to comprise a computer  20 , control electronics  25 , print head drive electronics  30 , ink jet print head  31 - 34  respectively for printing black ink (K), cyan ink (C), magenta ink (M), and yellow ink (Y), a plurality of ink reservoirs  40 - 43  for providing the color inks to the print heads  31 - 34 . Throughout the specification and claims, the term “colorant” will be understood to include inks such as pigmented or dye based materials. The ink jet printing apparatus  10  further includes a receiver transport motor  70  and a roller  65  for transporting an ink receiver  80  across a platen  90  past the ink jet print heads  31 - 34 . The print heads  31 - 34  are fixed to a holder  45 . The print heads  31 - 34  and the holder  45  are translated by a belt  56 , a pulley mechanism  57 , and a print head translating motor  71  along the gliding rail  54  in the fast scan direction (as indicated in FIG.  1 ). The gliding rail is supported by supports  55 . The print heads  31 - 34  can take various forms known in the art, for example, piezoelectric or thermal ink jet print head. An example of such a print head is shown in commonly assigned U.S. Pat. No. 5,598,196. The inks stored in the reservoirs  40 - 43  are supplied to the print heads  31 - 34 , respectively. The receiver  80  is supported by the platen  90 . 
     A digital image is applied to the computer  20 . Alternatively, the computer  20  can produce this digital image itself. The digital image is processed in the computer  20  by image processing algorithms such as tone scale conversion, color mapping and halftoning well known in the art. The computer  20  sends electrical signal according to the image data to the print head drive electronics  30  which controls the print heads  31 - 34  in a conventional manner. During each printing pass, the computer  20  controls the control electronics  25  to operate the receiver transport motor  70  and the print head translating motor  71 . Under the control of the computer, the receiver is positioned for a line of pixels of colorant to be formed and then the print head translating motor  71  moves the ink jet print heads  31 - 34  in a fast scan direction (shown in FIG. 1) and the print head drive electronics  30  operates the ink jet print heads  31 - 34  so that colorant provided from the reservoirs  40 - 43  is caused to be delivered as droplets to the receiving surface of the receiver  80 . More particularly, the print heads  31 - 34  transfer ink drops  100  to the receiver  80  during each printing pass, which forms ink spots  110  on the receiver  80 . After each printing pass, the receiver  80  is transported by the receiver transport motor  70  under the control of the control electronics  25  in the slow scan direction (FIG.  2 ). Each printed image  210  is typically formed by a plurality of printing passes. 
     FIG.  2  and FIG. 3 show, respectively, partial top and side views of the ink jet printing apparatus  10  in the present invention. The receiver  80  is placed on a platen  90 . The receiver  80  is transported by the receiver transport motor  70  with roller  65  under the control of control electronics  25 . A fluid dispensing roller  120  containing treatment fluid is in contact with the receiver  80  prior to printing by print heads  31 - 34 . The fluid dispensing roller  120  comprises a roller core and a support  140 . The fluid dispensing roller  120  is a passive delivering device that does not require power for transferring the treatment fluid. The fluid dispensing roller  120  can be rotated by the friction force from contact with the receiver  80 . Or, alternatively, the fluid dispensing roller  120  can be moved by roller transport mechanism  150  to and off from contact with the ink receiver  80 . 
     The fluid dispensing roller  120  can exist in different forms. In one embodiment, the fluid dispensing roller  120  includes a layer of porous open-celled material wrapped around the roller core  130 . The porous material absorbs the treatment fluid and releases the treatment fluid the receiver  80  when it is in contact with the receiver  80 . One example of the porous materials is silicon rubber. The fluid dispensing roller  120  can also include a multiple-layered structure. A layer of porous material containing the treatment fluid is wrapped around the roller core  130 . An additional outer layer is provided on the outer surface of the layer of porous materials for controlling the fluid release rate. Roller structures are described in U.S. Pat. Nos. 5,232,499 and 5,482,552. These disclosures are hereby incorporated in the present invention. 
     Different treatment fluids can be used for improving different aspects of printing properties. The purpose of the treatment fluid is to improve the image structure of the ink image on the receiver. This image structure includes the properties related to the ink dot formation such as dot size, dot gain, and shapes. The image structure also includes image stability and durability of the ink image. For example, ink spreading is known to affect the ink dot formation and therefore image structure on ink receiver such as a plain paper. The dot formation of ink spot  110  can be improved by using more expensive glossy paper that includes special coating layer on the top of the receiver. In accordance with the present invention, to improve the image structure on plain paper and other receivers, a treatment fluid is uniformly transferred to the receiver  80  prior to printing. For an aqueous ink formulation, a relatively hydrophobic fluid is used in the fluid dispensing roller  120 . The dot gain and feathering of the ink dots are significantly reduced. This embodiment of the present invention improves the printing image structure for a wide range of receiver types. For a desired image structure, the receiver cost can be reduced. 
     In accordance with the present invention, the image structure can also be improved by fixing the colorant in the inks to the receivers. The fixing of the colorant involves mordanting or reacting the colorants to the receiver with the assistance of the treatment fluid. The composition and the treatment fluid, the ink and the receiver are designed for optimizing the fixing of the colorant in the receiver. Before printing, the fluid dispensing roller  120  transfers a treatment fluid containing a polymers and binder material to the receiver  120 . The ink spots  110  are then placed by print heads  31 - 34  within the area  200  of the receiver  80  where the treatment fluid is transferred (FIG.  2 ). The binder material in the treatment fluid helps to bind (and fix) the colorant (dyes or pigment) in the ink to the receiver substrate. It can be desirable to select the polymers in the treatment fluid to have opposite charge to the dyes or pigment in the ink. The treatment fluid and ink formulations and receiver compositions are exemplified in U.S. Pat. No. 5,640,187 and European Patent EP 776,950 A2, which are incorporated by reference herein. Another example of reactive ink jets is disclosed in U.S. Pat. No. 4,694,302, which is also incorporated by reference. 
     The inks in accordance with in the present invention can include dyes or pigments. The ink colors typically will be yellow, magenta, cyan, black, red, green, blue, and other colors. Several ink densities can also be used for each color. The examples of the inks are found is U.S. Pat. No. 5,611,847, as well as the following commonly assigned U.S. Pat. Nos. 5,679,139; 5,679,141; 5,679,142; 5,698,018; and U.S. patent application Ser. No. 08/764,379; the disclosures of which are incorporated by reference herein. Colorants such as the Ciba Geigy Unisperse Rubine 4BA-PA, Unisperse Yellow RT-PA, and Unisperse Blue GT-PA can also be used in the inks of the present invention. 
     Although the above examples show that a receiver is treated before an image is formed on the receiver, it is understood that the present invention is also compatible with treatment of a receiver after an image if formed on the receiver. 
     An important feature of the present invention is that it does not require powering the fluid dispensing roller during the receiver treatment. In addition, the treatment fluid transfer to the receiver  80  does not require active motion such as thermal and mechanical ejection of treatment fluid drops in the prior art. It is therefore is not subject to the electrical and mechanical failure mechanisms that exist in the prior art techniques. 
     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  ink jet printing apparatus 
       20  computer 
       25  control electronics 
       30  print head drive electronics 
       31  ink jet print head 
       32  ink jet print head 
       33  ink jet print head 
       34  ink jet print head 
       40  ink reservoir 
       41  ink reservoir 
       42  ink reservoir 
       43  ink reservoir 
       45  holder 
       56  belt 
       65  roller 
       70  receiver transport motor 
       71  print head translating motor 
       80  ink receiver 
       90  platen 
       100  ink drop 
       110  inkspot 
       120  fluid dispensing roller 
       130  roller core 
       140  roller support 
       150  roller transport mechanism 
       200  treated area 
       210  printed image