Abstract:
Apparatus for forming an ink image with improved image properties on a receiver in response to a digital image includes an ink jet print head for delivering ink to a receiver to form an image. Relative movement is provided between the receiver and the print head and the ink jet print head is actuated in accordance with the digital image so that the print head transfers ink to the receiver to form the ink image corresponding to the digital image. Replaceable receiver treatment device treats the receiver or the ink image to improve selective aspects of image properties.

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” and U.S. patent application Ser. No. 08/961,058, filed Oct. 30, 1997, entitled “Apparatus For Printing Proof Image and Producing Lithographic Plate”. The disclosure of these related applications are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to an ink jet printing apparatus having a replaceable treatment device for ink images. 
     BACKGROUND OF THE INVENTION 
     Ink jet apparatus produces images on a receiver by ejecting ink drops onto the receiver in an imagewise fashion. To improve the quality, physical durability, and stability of the printed image, it is often necessary provide treatment of the receiver or ink spots on the receiver prior to or after the ink drops are placed onto the ink receiver. For instance, U.S. Pat. No. 5,635,969 discloses a print head that conditions the ink receiver by ejecting a treatment fluid to the receiver before printing. The treatment fluid on the receiver helps to immobilize the ink spots printed on the receiver, thereby improving the quality and stability of the print. U.S. Pat. No. 5,633,668 teaches an ink jet printer having a heater for heating the receiver prior to printing to reduce the dry time of the printed ink image. 
     SUMMARY OF THE INVENTION 
     An object of this invention is to provide ink jet printing apparatus which treats the receiver or ink image for enhancing image properties. 
     A further object of this invention is to provide ink jet apparatus that can selectively improve different aspects of the image properties in response to the requirements of specific applications. 
     These objects are achieved by apparatus for forming an ink image with improved image properties on a receiver in response to a digital image, comprising: 
     a) ink jet print head means for delivering ink to a receiver to form an image; 
     b) means for providing relative movement between the receiver and the print head means; 
     c) means for actuating the ink jet print head means in accordance with the digital image so that the print head means transfer ink to the receiver to form the ink image corresponding to the digital image; and 
     d) replaceable receiver treatment means for treating the receiver or the ink image to improve selective aspects of image properties. 
     ADVANTAGES 
     A feature of the present invention is that the ink jet printing apparatus is compatible with different types of receiver treatment devices such as a radiation source, a heat source, an electric fan, or a fluid ejection head such as a spray bar or an ink jet print head. Many different aspects of the image properties can be improved as a result. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic diagram of an ink jet printing apparatus in accordance with the present invention; 
     FIG. 2 is a schematic diagram of the ink jet printing apparatus in another embodiment in accordance with the present invention; and 
     FIG. 3 is a flow chart of the operation of the apparatus of FIG. 1 or FIG. 2 in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is described with relation to an ink jet printing apparatus having a modular unit adapted for improved image properties of the printed image. In the present invention, the term “image properties” includes the properties related to the ink dot formation such as dot size, dot gain, and shapes. The image properties also includes image stability and durability of the ink image. 
     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 heads  31 - 34  for printing black ink (K), cyan ink (C), magenta ink (M), and yellow ink (Y), and a plurality of ink reservoirs  40 - 43  for providing respective colored inks to the print heads  31 - 34 . The ink jet printing apparatus  10  further includes a modular unit  48 , a power supply  60  connected to the modular unit  48 , a receiver transport motor  70 , an ink receiver  80 , and a platen  90 . The power supply is actuated by the control electronics  25  and provides different control signals to the modular unit  48  depending upon which replaceable treatment device is used. A user will input to the computer  20  information as which replaceable treatment device is to be used. The modular unit  48  can receive different replaceable treatment devices, as described below. However, the modular unit  48  will be understood to include structure for receiving different treatment devices so that can be operated by the power supply  60 . The print heads  31 - 34  are fixed to a holder  45  which can be translated by a print head translation motor  71  along the gliding rail  54  in the fast scan direction (as indicated in FIG. 1 by the arrow). The gliding rail is supported by supports  55 . The print heads  31 - 15   34 , the modular unit  48 , and the holder  45  are transported by several mechanisms, shown in FIG.  1 . More specifically, there is shown a belt  56 , a pulley mechanism  57 , and the print head translation motor  71 . The print head translation motor  71  can be a stepping motor, or alternatively can be a DC motor with a servo system. The ink receiver  80  is supported by the platen  90 . The receiver transport motor  70  provides relative movement between the ink receiver  80  and the ink jet print heads  31 - 34  with a roller  65  that moves the ink receiver  80  in a direction (i.e. slow scan) orthogonal to the fast scan direction. It will be appreciated that both the receiver transport motor  70  and the print head translation motor  71  are bidirectional so that the print heads  31 - 34 , the modular unit  48 , and the ink receiver  80  can be transported back to the starting position. 
     As shown in FIG. 1, the treatment device is a UV light source  50  that is installed in the modular unit  48  for physical attachment and electrical connections. The modular unit  48  is fixed to a holder  45  and is translated by the print head translation motor  71 . The UV light source  50  includes a shield  51  and a UV lamp  52 . The UV lamp is shielded in a glass tube that absorbs visible light while permitting the transmittance of UV light. The glass tube also protects the UV lamp from physical damages. A typical compact UV lamp can be 5 inch long, 0.5 inch in diameter, and 70 gram in weight. Such compact UV lamps are available, for example, from Edmund Scientific under the catalogue numbers of C 40 , 759 , C 40 , 760 , and C 40 , 765  etc. The light weight and the compact size of the compact UV light source  50  permit it to be installed together with the print heads  31 - 34  on the holder  45 . 
     Still referring to both FIG. 1, the computer  20  controls the control electronics  25  which in turn controls the power supply  60 , the receiver transport motor  70  and the print head translation motor  71 . The power supply  60  provides an input voltage to the UV light source  50 . The computer  20  also controls the print head control electronics  30  which prepares electrical signals to drive the print heads  31 - 34  according to the data of the digital image. The print heads  31 - 34  can exist in different forms, for example, piezo-electric 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. 
     An input digital image can be applied to, or produced in the computer  20 . The digital image is processed in the computer  20  by image processing algorithms such as tone scale conversion, color mapping, halftoning etc. The computer  20  sends the signals representing the digital image to the print head drive electronics  30  that in turn prepares electrical signals for the print head  31 - 34  according to the digital image data. 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 ink receiver  80  is positioned for a line of image pixels 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 ). The print head drive electronics  30  operates the ink jet print heads  31 - 34  to deliver ink droplets  100  to the receiving surface of the ink receiver  80 . Each printed image can be typically formed by a plurality printing passes. The ink spots  110  on the ink receiver  80  are treated by the UV light source  50  with power being supplied by the power supply  60  also under the control of the control electronics  25 . 
     The ink receiver  80  can be common paper or made of a synthetic material. The receiver can comprise a layer(s) that is porous to the inks, an ink absorbing layer(s), as well as materials with a strong affinity and mordanting effect for the inks. Exemplary receivers are disclosed in U.S. Pat. No. 5,605,750. The printed images can be used for outdoor signages, bill boards, and displays. The present invention also address many other applications in which image durability is required: security printing such as passports or Identification Cards, Compact Disc or Digital Video Disc, pages in a passport, and lithographic printing plates and so on. These applications all require good image durability and stability. 
     The ink colors compatible with the present invention can include yellow, magenta, cyan, black, red, green, blue, and other colors. Several ink densities can also be used for each color. The inks can include dyes or pigments. In addition to the colorants, the ink formula can include stabilizers, surfactants, viscosity modifiers, humectants and other components. The inks in the present invention can also be colorless or not intended for color visual effects, for example, the inks used for producing lithographic printing plates such as the ink compositions as disclosed in U.S. Pat. No. 4,833,486 and EP 488,530A2. The examples of the colored inks used in this invention are found in 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. application Ser. No. 09/034,676, filed Mar. 4, 1998, entitled “Pigmented Inkjet Inks Containing Phosphated Ester Derivatives” to Martin; the disclosures of which are incorporated by reference herein. 
     To be compatible with the UV light source  50  in FIG. 1, the inks stored in the reservoirs  4043  comprise substances curable by UV-irradiation such as photo-initiators and photo-activators. In the present invention, the term cure refers to the processes that harden or solidify the inks in the ink receiver  80 , which can be polymerization, reaction, glass transition, and other similar processes. The curing of the inks on the ink receiver  80  greatly improves the physical durability as well as the image stability (such as water fastness and light fastness) of the printed ink image. UV curable inks are known to a person skilled in the art of ink jet printing. A range of commercial monomers, e.g. having acrylic, vinyl or epoxy functional groups, photo-initiators and photo-activators is available and suitable for use in an ink jet formulation, capable of polymerization by UV light. The reaction may proceed through addition polymerization; all reactants are converted to the final polymeric binder, leaving no by-product or trace of liquid. This reaction can proceed in two processes, either by a free-radical mechanism or by the formation of a cationic species, or combination of both processes. UV curable ink compositions can be found in U.S. Pat. No. 4,303,924, U.S. Pat. No. 5,275,646, and EP Patent Publication No. 407054, EP Patent 488,530 A2, and EP Patent 533,168 A1. 
     FIG. 2 shows another embodiment of the present invention. In the modular unit  48 , the replaceable treatment device is a fluid ejection head  123 . The fluid ejection head  123  head is connected to the power supply  60 . Different treatment fluids can be used for improving different aspects of printing properties. Fluid treatment can be applied to a receiver before an ink image is printed, or to an ink image on the receiver after it is printed. For example, ink spreading is known to affect the ink dot formation and therefore image properties on 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, the image properties on the ink receiver  80  can be improved by transferring a treatment fluid to the ink receiver  80  prior to printing. For an aqueous ink formulation, the treatment fluid is chosen to be hydrophobic. The dot gain and feathering of the ink dots are significantly reduced, therefore improving the image properties for a wide range of receiver types. 
     The fluid ejection head  123  can also eject or deliver a treatment fluid in the form of sprayed fluid drops  125 , for fixing the colorants in the inks to the receivers. The colorant can be fixed to the receiver by mordanting or chemical reaction with the assistance of the treatment fluid. The compositions of the treatment fluid, the inks and the receiver are optimized for the fixing of the colorant in the receiver. Before printing, the fluid ejection head  123  transfers a treatment fluid containing a polymers and binder material to the ink receiver  80 . The ink spots  110  are then placed by print heads  31 - 34  within the fluid treated area  130  on the ink receiver  80  where the treatment fluid is transferred. 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 is often desirable to have the polymers in the treatment fluid to have opposite charge to the colorant 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 operation in accordance with the present invention is exemplified by the flow chart in FIG. 3 for the ink jet printing apparatus  10  in FIG.  1 . The printing operation is started in block  200  in which the computer  20  receives or generates a digital image. The control electronics  25  controls the receiver transport motor  70  to move the ink receiver  80  under the print heads  31 - 34 . In the first printing pass in block  210 , the control electronics  25  sends control signals to the print head  30  according to the input digital image to transfer ink drops  100  to the ink receiver  80 . As the area marked with the ink spots  110  is transported to the UV light source  50 , the control electronics  25  sends control signal to the power supply  60  to activate the UV light source  50  to cure the ink spots  110  on the ink receiver  80  during the first pass, as shown in block  220 . The cured ink spots are indicated by the ink spots  120  on the ink receiver  80 . Since the receiver treatment by the UV light source  50  (as shown in FIG. 1) in block  220  is implemented on-the-fly, no additional time is required for the printing pass. It will be understood that when different replaceable treatment device is used, the computer  20  will adjust the voltage from the power supply  60  to the modular unit  48 . The receiver treatment by the UV light source  50  solidifies the ink spots  110 , which prevents ink coalescence in this printing pass as well as coalescence with the ink spots placed in the subsequent printing passes. Next in block  230 , a question is asked whether the printing is finished or not, if not, the subsequent printing passes will be in the sequence of ink transfer and receiver treatment in each printing pass in blocks  210  and  220 . After all the printing passes are finished, a question is asked in block  240  about whether an additionally final receiver treatment is needed if the answer is no, the printing is finished in block  260 . If the answer is yes, a final receiver treatment is performed by the UV light source  50  (as shown in FIG. 1) in block  250 . The control electronics  25  causes the receiver transport motor  70  to move the ink receiver  80  below the UV light source  50  that is concurrently activated by the control electronics  25 . The last receiver treatment further enhance the curing of all the inks transferred on ink receiver  80 . Because the last receiver treatment is not conducted “on-the-fly” during the ink transfer, the receiver treatment time can be optimized by for example, controlling the receiver transport speed. 
     It will be appreciated that the modular unit  48  in FIGS. 1 and 2 does not have to be mounted on the holder  45  but can be separately moved under the control of the control electronics  25 . It is understood that the modular unit  48  in the present invention is also compatible with other forms of receiver treatment. Other radiation devices can include the application of photons at frequencies other than UV or particles such as IR photons or electron beams. For ejecting treatment fluids, a spray bar can be mounted on the modular unit  48 . For increasing drying efficiency, a fan or fans can be installed inside modular unit  48  for enhanced air circulation. The ink drying rate can also be increased by a heat source such as an IR lamp. It is further appreciated that more than one receiver treatment devices can be installed in the ink jet printing apparatus  10  in accordance with present invention. 
     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 
     48 modular unit 
     50 UV light source 
     51 shield 
     52 UV lamp 
     54 gliding rail 
     55 support 
     56 belt 
     57 pulley mechanism 
     60 power supply 
     65 roller 
     70 receiver transport motor 
     71 print head translation motor 
     80 ink receiver 
     90 platen 
     PARTS LIST (con&#39;t) 
     100 ink droplets 
     110 ink spot 
     120 cured ink spot 
     123 fluid ejection head 
     125 sprayed fluid drops 
     130 fluid treated area 
     200 start printing block 
     210 printing one pass block 
     220 on-the-fly receiver treatment block 
     230 all the printing passes finished? block 
     240 final receiver treatment needed? block 
     250 final receiver treatment block 
     260 end printing