Ink jet recording method and apparatus used in the same method

Abstract: An ink jet recording method for effecting polychromatic recording by the use of inks of two or more colors includes the process of repeating one-­ line printing by color in conformity with the number of colors used at least on the same line, and forming one line of a polychromatic recorded portion.

Description: BACKGROUND OF THE INVENTION Field of the Invention This invention relates to an ink jet recording method and an apparatus used in said method, and in particular to a recording method suitable for forming good polychromatic images on plain paper or the like by the use of inks of two or more colors, and an apparatus used in said method. Related Background Art Polychromatic recording by an ink jet recording apparatus i.e., formation of an image composed of two or more colors, has been accomplished by the use of an ink jet recording apparatus of the construction as shown, for example, in Figures 3A and 3B of the accompanying drawings and by causing a carriage 2 carrying the four-color recording head 1 of said apparatus to scan along sliding shafts 3, causing ink of each color to be discharged from the recording head during one scan in conformity with recording information, as shown, for example, in Figure 4 of the accompanying drawings, and thereby expressing a single color or a mixed color portion of two colors (Figures 4(b) of the accompanying drawings). Howeber, with the above-described recording method, it is possible to form good images on a recording medium of high water absorving property such as coated paper, but much time is required for the drying of recording liquid in the case of plain paper or OHP (overhead project) paper which is low in water absorbing property and therefore, "blot" of colors arises between picture elements expressing different colors, and this has sometimes resulted in remarkable deterioration of the quality of images formed. That is, if as shown in Figure 4(c) of the accompanying drawings, inks of different colors are caused to adhere to a recording medium in a lump by one scan to thereby form one line of polychromatic record portion (record portion comprising picture elements expressing two or more different colors) mixing of inks occurs in the portion wherein ink dots overlap one another until the ink dots dry and are fixated. Such mixing of the inks, if it occurs in the boundary portion between picture elements expressing different colors (e.g. picture elements Y and M), causes the "blot or blur" of colors in the recorded image. To suppress such "blot", the diameter of the ink dots may be made small to thereby prevent the contact between adjacent dots, but this will give rise to a limit in the density of the entire recorded image, which in turn will be inconvenient for obtaining images of good contrast. On the other hand, even in a printing method wherein as shown in Figure 5 of the accompanying drawings, the amount of ink per picture element is made equal between the case of a mixed color portion (a portion to which inks of two or more colors are caused to adhere in one picture element) and the case of a single-colored portion (a portion to which only an ink of a single color is caused to adhere in one picture element), the occurrence of the "blot" as shown in Figure 5(c) cannot be prevented on a recording medium of poor water absorbing property. An example of the afore described prior art arrangement is to be covered in US Patent No. 4,528,576. SUMMARY OF THE INVENTION According to the present invention a method of discharging ink from a recording head which is adapted to discharge at least two colours of ink in one line of print is characterised in that only one colour is printed during each scan of the head. How the invention may be carried out will now be described by way of example only and with reference to the accompanying drawings in which: BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a dot construction diagram showing an embodiment of the recording method of the present invention. Figure 2 is a dot construction diagram showing another embodiment of the recording method of the present invention. Figures 3A and 3B are schematic views showing the essential portions of an ink jet recording apparatus applied to the recording method of the present invention. Figures 4(a) - (c) and 5(a) - (c) are dot construction diagrams showing a recording method according to the prior art. Figure 6 is a graph for explaining a relationship between the addition signal and a gamma selection signal. Figure 7 is a view showing a relationship between an addition signal and a correction coefficient. DESCRIPTION OF THE PREFERRED EMBODIMENTS The ink jet recording method of the present invention can be carried out by an ink jet recording apparatus of the construction as shown, for example, in Figures 3A and 3B. That is, this apparatus has a construction in which a recording head 1 in which recording head units corresponding to four colors, i.e., yellow (Y), magenta (M), cyan (C) and black (BK), are compounded is carried on a head carriage 2, and the carriage 2 is scanned along sliding shafts 3 by a carriage driving motor not shown, whereby a polychromatic recorded image can be formed on recording paper (a recording medium) 4. Figure 3B shows the essential portions of the recording head 1 shown in Figure 3A, and each head unit has a plurality of discharge ports 7 through which flying droplets of ink 8 are discharged toward the recording paper 4. The kinds of ink (the number of colors) and the number of recording heads for respective colors are not limited to four, but may be suitably changed as desired. An embodiment of the recording method of the present invention is shown in Figure 1. According to this method, the same amount of ink of one color adheres to each picture element constituting one line of a polychromatic record portion. Thus, an amount of ink twice as great as the ink adhering to a picture element to which only ink of one color adheres to a picture element to which inks of two colors adhere. In this method, printing by only the black (BK) head is first effected in conformity with recording information during the first scan of the recording head, and only BK dots are printed on the recording medium. Subsequently, during the second scan, printing by only the cyan (C) head is effected in conformity with the recording information, and C dots are printed on the recording medium. Further, during the third scan, the magenta (M) head is scanned and during the fourth scan, the yellow (Y) head is scanned, whereby M dots and Y dots are printed in the named order in conformity with the recording information. The intervals between the above-described printing scans by color are set to such a degree that mixing of the inks in the boundary portion between the dots of the color printed earlier and the dots of the color printed later hardly occurs. As a result, for example, in the boundary between the cyan and the black printed by the first scan and the second scan, respectively, C dots adjacent to the BK dots printed earlier are printed in a state in which the drying and fixation of the BK dots have progressed to a certain degree, whereby it is difficult for undried inks to mix together and therefore it is difficult for the "blot" as previously described to occur in the boundary area between the picture element C expressing cyan and the picture element BK expressing black. One scan in the printing scan by color may be effected by the reciprocal scanning of the recording head on the recording medium or by only the forward scanning or the backward scanning in the reciprocal scanning of the recording head. Also, the case where printing of four colors is effected in one line is shown in Figure 1, but depending on the recording information, there is a case where a print of only two or three colors is included in one line and therefore, in such a case, the number of scans required for one line may be adjusted to two or three, and if printing is effected while the number of scans is adjusted by a judgment being formed each time, the throughput can also be made quick. Further, the order of colors printed is not restricted to the above-described example, but it is desirable to suitably choose the order in which efficient drying and fixation of the dots printed earlier can progress between the printing scans by color. In the method shown in Figure 1, for example, in the case of a mixed color portion by two colors or a picture element portion expressing one color by inks of two colors, such as the picture element B, the amount of ink in one picture element is twice that in a single color portion or a picture element portion expressing one color by an ink of one color, such as the picture element Y, and when use is made of a recording medium which is so poor in water absorbing property that a longer time is required for drying and fixation, the intervals between the printing scans by color must be made longer. So, when such a recording medium is used, the mixed color portion of two colors is formed by a 1/2-thinned pattern as shown in Figure 2, that is, printing is effected with the amounts of inks of two colors adhering to the recording medium being rendered into 1/2 each, whereby the amounts of adhering inks can be made equal between the mixed color portion and the single color portion and thus, the extension of the intervals between the printing scans by color can be avoided. When a mixed color portion of three colors is to be formed, the amounts of inks of the three colors adhering to the recording medium may likewise be rendered into 1/3 each. According to the present invention, a polychromatic recorded portion is formed by the repetition of the printing scans by color effected at suitable intervals and therefore, the occurrence of "blot" in the boundary area between picture elements expressing different colors is prevented and polychromatic images of good quality can be easily formed even on a recording medium such as plain paper which is low in water absorbing property and requires a relatively long time for drying and fixation of recorded images. Moreover, the present invention can be achieved by very simple and low-cost means which is a change in the control program of the ink jet recording apparatus such as a change in the carriage scanning method and discharge timing. Also, when one line has been printed in full colors, recording paper becomes swollen due to the great amount of ink and "swelling" often occurs and thus, it has been necessary to secure a certain degree of distance between the recording medium and the recording head, whereas in the printing scan by color according to the present invention, the amount of ink printed during one scan is small and the ink printed is dried each time printing is effected and therefore, it is difficult for the swelling of the recording paper to occur and the distance between the recording medium and the recording head can be set to a small value. Therefore, good images having very little printing twist can be obtained. The present invention may be used particularly for the back print mode which is the back print forming mode in which the above-noted problem arises and in which a mirror image is formed on the back of back printing paper (paper having an ink absorbing layer provided on the back of the resin surface thereof) and a positive image is seen from the resin surface side, and may also be used only in the photographic mode in which the quality of image need be made good. In addition, the present invention is particularly effective in the dark original mode in which an original high in its density which can be discriminated by an operation or automatically is read by a copying machine and is recorded by ink jet, and the present invention is more effective in a mode in which the amount of information is controlled by error the diffusing method and then the present invention is carried out. The above-described embodiment is most preferable as an embodiment in which the present invention is also used in the other heads than the black head, but the present invention is sufficiently effective even if only the control of the amount of information of the black head is adopted as a countermeasure for black streaks. The present invention brings about an excellent effect particularly in a recording head or a recording apparatus of the buble jet type among the ink jet recording systems. As regards the typical construction and principle of such system, it is preferable to use the basic principles disclosed, for example, in U.S. Patent No. 4,723,129 and U.S. Patent No. 4,740,796. This system is applicable to both of the so-called on-demand type and the so-called continuous type, and particularly in the case of the on-demand type, at least one driving signal corresponding to recording information and providing a rapid temperature rise exceeding the nuclear boiling is applied to an electro-thermal converting member disposed correspondingly to a sheet or a liquid path in which liquid (ink) is retained, whereby heat-energy is generated in the electro-thermal converting member and film boiling is generated on the heat acting surface of the recording head with a result that a bubble in the liquid (ink) corresponding to said driving signal at one to one can be formed, and this is effective. The liquid (ink) is discharged by the growth and contraction of this bubble through a discharge opening and at least one droplet is formed thereby. If this driving signal is pulse-shaped, the growth and contraction of the bubble take place appropriately on the spot and therefore, liquid (ink) discharge particularly excellent in responsiveness can be accomplished, and this is more preferable. This pulse-shaped driving signal may suitably be one as described in U.S. Patent No. 4,463,359 or U.S. Patent No. 4,345,262. If the conditions described in U.S. Patent No. 4,313,124 regarding the rate of temperature rise of said heat-acting surface are adopted, more excellent recording can be accomplished. As the construction of the recording head, besides the combination of a discharge port, a liquid path and an electro-thermal converting member as disclosed in the aforementioned U.S. Patents (a rectilinear liquid flow path or a perpendicular liquid flow path), the constructions using U.S. Patent No. 4,558,333 and U.S. Patent No. 4,459,600 which disclose constructions in which the heat-acting portion is disposed in a bent area are also covered by the present invention. In addition, the present invention is also effective if use is made of the construction based on Japanese Laid-Open Patent Application No. 59-123670 which discloses a construction in which a slit common to a plurality of electro-thermal converting members is used as the discharge portion of the electro-thermal converting members, or Japanese Laid-Open Patent Application No. 59-138461 which discloses a construction in which an opening for absorbing the pressure wave of heat energy is made to correspond to a discharge portion. Further, the full line type recording head having a length corresponding to the maximum width of a recording medium on which recording can be effected by a recording apparatus may be of a construction which satisfies that length by a combination of a plurality of recording heads as disclosed in the aforementioned Laid-Open Patent Applications or a construction as a single recording head formed as a unit, and the present invention can display the above-noted effect more effectively. In addition, the present invention is also effective for a case where use is made of an interchangeable chip type recording head which is mounted on an apparatus body, whereby electrical connection with the apparatus body and supply of ink from the apparatus body become possible, or a cartridge type recording head which is integrally provided in a recording head itself. Also, it can make the effect of the present invention more stable to add to the present invention recovery means, preliminary auxiliary means, etc. for the recording head which are provided as the construction of the recording apparatus, and this is preferable. More specifically, it is also effective for accomplishing stable recording to provide capping means, cleaning means, pressurizing or suction means, and preliminary heating means comprising an electro-thermal converting member or a heating element discrete therefrom or a combination thereof for the recording head, and carry out the preliminary discharge mode in which discharge discrete from recording is effected. Further, the recording mode of the recording apparatus is not limited to the recording mode of only the main color such as black, but may also be a mode provided by a recording head constructed as a unit or a combination of a plurality of recording heads, and the present invention is also very effective for an apparatus provided with at least one of a plurality of different colors or full colors by mixed colors. In the case of plain paper, the amount of blur becomes great and therefore, in a recording mode using plain paper, it is preferable to adopt a control mode prescribed in advance so as to carry out the present invention. In any case, in the present invention, the sum of image data is calculated and only when the value thereof exceeds a data value for which the amount of blur is great, that data amount is subtracted (preferably on the basis of the correction means of the apparatus body predetermined on the basis of a subtraction formula as indicated by a gamma curve as shown in Figs. 6 and 7 is used as the data for actually effecting recording and therefore, recording of good quality free of black streaks, white streaks, density irregularity and color irregularity can be accomplished.

Claims: A method of discharging ink from a recording head (1,2) which is adapted to discharge at least two colours of ink (Y,M,C,K) in one line of print characterised in that only one colour is printed during each scan of the head. A method as claimed in claim 1, in which scanning is achieved by means of a reciprocating print carriage and head. A method as claimed in claim 1, in which scanning is achieved by means of a full line recording head. A method as claimed in any previous claim, in which the darkest of the plurality of colours is recorded first. A method as claimed in any one of claims 1 to 3, in which black is recorded first. A method as claimed in any one of claims 1, 2, 4 or 5, in which recording takes place during both the outward and the return movement of the reciprocable printing head (1,2). A method according to any one of claims 1, 2, 4 or 5, in which recording takes place only during the outward movement of the recording head/carriage. A method as claimed in any one of claims 1, 2, 4 or 5, in which recording only takes place during the return movement of the recording head/carriage (1,2). A method as claimed in any previous claim, in which back printing is effected. A method as claimed in any previous claim, in which a composite colour for any given picture element is achieved by first partially printing in a first colour and then partially printing in a second colour in the same pixel, there being no overlap between the first and second colours in a given pixel. A method as claimed in any previous claim, in which recording is effected by means of an electrothermal converting element adapted to generate thermal energy in order to effect film boiling of the ink.

Inventors: WATANABE KENJIRO, WATANABE, KENJIRO
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1989
Main classification: B41J2
IPC codes: B41J2, B41J19