JP4174516B2 - Inkjet recording method - Google Patents

Description

The present invention relates to an ink jet recording how.

  2. Description of the Related Art Conventionally, as one of recording methods for characters, images, and the like, an ink jet recording method for performing recording by attaching ink ejected from nozzles of a recording head to a recording medium has been performed. In this ink jet recording method, various methods are adopted for improving the printing quality. One of the methods is to use an ink having permeability suitable for recording by preparing the ink. That is, for the purpose of improving the recording density of characters and line drawings and forming sharp images, a technique that uses ink that has a slow penetration speed to the recording medium (recording paper) and a large amount of adhesion to the recording paper surface, and a fixing speed is increased. For this reason, a technique using ink having a high penetration speed with respect to recording paper is known.

  In general, ink having a low permeation rate remains in a large amount on the surface of the recording paper, and is therefore referred to as “overlay ink”. An ink having a high permeation speed is referred to as a “super-penetrating ink”.

  When superpermeable ink having high penetrability is used, the ink droplet 51 dropped on the recording medium has a small amount of ink remaining on the surface of the recording medium 52 as shown in FIG. Immediately after adhering to the medium 52, it penetrates into the recording medium. The permeation speed of the recording paper is high, and depending on the permeability and the material of the recording medium 52, it penetrates deeply to the vicinity of the back surface of the recording medium 52.

On the other hand, when the overlay ink with low permeability is used, components such as the solvent of the ink easily evaporate while remaining on the surface of the recording medium 52 in a convex shape as shown in FIG. . Therefore, the amount of ink droplets 53 dropped on the recording medium 52 permeates in the thickness direction of the recording medium 52 is small.
Japanese Patent Laid-Open No. 06-239013 Japanese Unexamined Patent Publication No. 07-047662 Japanese Patent Laid-Open No. 08-259869 Japanese Patent Laid-Open No. 04-211465

  When using a super-penetrable ink, the ink that has landed on the surface of the recording paper penetrates quickly and is unlikely to mix with other inks on the surface of the recording paper, so there is an advantage that bleeding at the boundary between different colors is difficult to occur. . However, since the ink penetrates deeply into the recording medium and diffuses over a wide range, the pigment component of the pigment or dye is dispersed and light incident on the recording medium is reflected at a deep position from the surface of the recording medium. Therefore, the density of the recorded image is lowered. Further, when viewed in a plan view, the size of the recording dot is excessively increased by spreading around the ink droplet 51, or blurring (feathering) occurs on the outer periphery of the dot, resulting in an unclear outline. There is a problem that it becomes an image.

  When using overlay ink, the amount of ink remaining on the surface is large, so the recording density is high, and when a single dot is viewed, the amount of ink diffusing into the recording medium is much higher than that of superpermeable ink. Therefore, there is an advantage that a sharp image can be recorded. However, since the penetration speed to the recording paper is slow and the time required for the ink remaining on the surface of the recording paper to be fixed becomes long, when other ink droplets adhere to the adjacent positions, Ink flows out. In addition, there is a problem that bleeding occurs at the boundary between different colors, resulting in deterioration of image quality. Also, if the surface of the recording paper is rubbed with another recording paper or a pen, the ink fixed on the surface of the recording paper will be peeled off or the ink will melt when overwritten with a pen such as a line marker. There is also a problem of bleeding, and a problem of poor scratch resistance.

  Conventionally, based on the characteristics of both inks, it has been common to use inks with low penetrability for black and inks with high penetrability for other colors. In other words, black is often used when recording characters and line drawings that require fine lines and dots to be clearly recognized and are easy to see, so the recording density of black ink is high and the contour is high. Has been used for overprinting inks that can be clearly recorded. In addition, when recording color images, characters and fine lines and dots are rarely recorded, and dots of different colors are often recorded adjacent to each other. A super-permeable ink capable of clearly recording the ink was used.

  As described above, recording may be performed using inks having different penetrability between black and other colors depending mainly on the characteristics of the recorded image. However, even in that case, as shown in FIG. 46C, when the black dot 54 of the low penetrability ink and the color dot 55 of the high penetrability ink are adjacent to each other, between the adjacent dots Ink flows out and the recording quality deteriorates. On the black ink side, the ink that remains convex on the surface of the recording medium flows out from the boundary 56 to the color ink, and the density of the boundary 56 on the black ink side decreases by the amount that flows out to the color ink. . As a result, the density of the outline of the black ink dots is reduced, resulting in a whitish and unclear image. Also, in the color ink dots, the black ink is mixed in the boundary portion 56 and the outline becomes unclear. As described above, when inks having different penetrability are adjacent to each other, the problem that the recording quality deteriorates due to bleeding at the boundary portion 56 cannot be avoided.

  By leaving the ink for a long time after discharging the black ink, it is possible to fix the ink to the recording medium to such an extent that bleeding does not occur even if the ink has low permeability. However, it is necessary to provide a long time difference between the black ink discharge and the color ink discharge, and the throughput is lowered. Therefore, it is not suitable for high-speed recording and is not practical.

  Also, a technique for heating a recording medium with a heater provided in a recording apparatus in order to increase the fixing speed is known. For example, a fixing speed can be increased by providing a heater at a position corresponding to the recording position by the recording head from the back side of the recording surface of the recording medium, and evaporating the moisture of the ink droplets adhering to the surface of the recording paper. Are known. However, in this method, when the ink is heated at a high temperature, water vapor is generated when the water in the ink evaporates, and the water vapor adheres to the inside of the recording apparatus to form water droplets, affecting the recording medium. There are problems such as adversely affecting the control circuit and power supply circuit. Therefore, it is conceivable to provide an exhaust means for discharging water vapor to the outside of the apparatus. However, adding a special apparatus increases the cost of the apparatus or increases the power supply capacity of the apparatus, which is not practical. Further, when the recording medium is heated at a high temperature by the heater, it is necessary to sufficiently consider the safety of the user.

  In addition, in order to alleviate the problems related to permeability, it is possible to use specially processed special paper as a recording medium, but considering the cost and convenience of the user, it is better than special special paper. It is desirable to use plain paper.

  As described above, the so-called super-penetrating ink with high penetrability can reduce the blurring at the boundary, but it results in a blurred image with a reduced recording density. In addition, when using so-called overlay ink with low penetrability, it is possible to record a sharp image with a high recording density. However, it takes a long time to fix, and the problem of bleeding between ink droplets and scratch resistance is high. There was a problem that was low. Even when black ink is used and super-permeable ink is used for color images, if black ink dots and other color ink dots are adjacent to each other, bleeding problems due to bleeding between the ink droplets There was a problem that would occur.

  Therefore, the reason why the present inventor completed the present invention is as follows.

  As the conventional ink for ink jet recording, the above-described non-penetrating (overlay) ink is often used. Although this ink has good character quality, it has a problem that fixing is slow. In color recording, a new problem of blurring between the colors has also occurred. In view of this, a method of heating using a heater has been considered in order to improve fixability and prevent blurring between colors. However, the use of the heater also has a problem that a large amount of water contained in the ink is evaporated and a problem of high cost. Therefore, it has been considered to use a super-penetrating ink in order to improve the fixing property of the ink without using a heater. As a result, the fixing property was improved and the blurring at the boundary was reduced. However, when the present inventor analyzed the flow of such a technique, when using a super-penetrating ink, it was found that there was a drawback that the concentration was difficult to be obtained due to the super-penetrating ink. Therefore, as a result of further diligent research, the present inventors have used semi-penetrating ink, and by applying heat to the ink, it is possible to improve the fixing property, reduce the blur at the boundary and improve the density. The present invention was completed by obtaining new knowledge.

The object of the present invention is to solve the above-mentioned problems by simultaneously achieving the three characteristics of improvement of fixing property and improvement of recording density, and reduction of blurring between ink droplets of different colors, and excellent scratch resistance. is to provide an ink jet recording how capable of forming an image.

The inkjet recording method of the present invention comprises a step of discharging black ink having a surfactant content of 0.2 to 0.7% by weight based on the total weight of the ink from a black ink discharge head onto a recording medium; The step of heating the area where the black ink is ejected on the recording medium conveyed to the position downstream of the ink ejection head in the conveying direction of the recording medium, and the content of the surfactant with respect to the total weight of the ink A step of ejecting more than 0.7% by weight of color ink from the color ink ejection head to the recording medium, and a color on the recording medium conveyed to a position downstream of the color ink ejection head in the conveyance direction of the recording medium And a step of heating a region where ink is ejected, wherein the surfactant is ethylene oxide-2,4,7,9-tetramethyl-5-decyne-4,7-diol. .

  According to the present invention, it is possible to achieve an improvement in recording density and a reduction in blurring of ink droplet boundaries by suppressing penetration of permeable ink at a position close to the recording surface inside the recording paper and fixing the ink. . Further, since the ink droplets penetrate into the recording paper, it is possible to form an image with excellent scratch resistance.

  According to the present invention, since the ink does not remain in a convex shape on the surface of the recording medium, bleeding such as bleeding at the boundary between a plurality of ink droplets and white haze can be reduced. Further, since the penetration depth of the ink is suppressed by heating, the light incident on the recording medium is reflected at a shallow position from the surface and looks clear, and the pigment component is not dispersed so much, and the beard-like shape is clear. Occurrence of bleeding (feathering) can also be prevented. Further, when the recording dots are formed by ejecting ink a plurality of times, the permeation time can be shortened and the printing quality can be improved.

  Embodiments of the present invention will be described below with reference to the drawings. First, the technical idea and principle of the present invention will be described in detail.

(1) Permeation control by heater FIG. 1 shows a difference in permeation state of ink droplets depending on the presence or absence of heater 3 when ink droplets 2 having permeability are ejected onto recording paper 1 as a recording medium to form dots. FIG. Here, an example in which plain paper that is generally widely used is used as a recording medium will be described.

  FIG. 1A shows a state in which ink droplets 2 are ejected onto the recording paper 1, and both ink droplets shown on the left and right in FIG. 1A have the same permeability and the same ejection amount. The ink droplets 2 ejected on the recording paper 1 collide with the surface of the recording paper 1, spread to a predetermined size, and adhere to the surface of the recording paper 1. FIG. 1B is a diagram schematically illustrating the state of the ink droplet 2 a attached on the surface of the recording paper 1. The ink droplets 2a adhering to the surface of the recording paper 1 immediately start to penetrate into the recording paper 1. FIG. 1C is a diagram showing a state where the ink droplet 2 has permeated the recording paper 1, 2 b shows a permeation state of the ink droplet 2 when recording is performed without using the heater 3, and 2 c shows the heater 3. The penetration state of the ink droplet 2 is shown when recording is performed. A broken line 2b 'shown around the ink droplet 2c indicates a range in which the ink droplet 2b can penetrate the recording paper 1 when left unheated.

  In the example shown in FIG. 1, the ink droplet 2 is made of ink having such a high permeability that the ink does not remain in a convex shape on the recording paper 1. As shown in FIG. 1C, when recording is performed without using a heater, the ink droplet 2b penetrates to the depth d0 of the recording paper 1 in the thickness direction. However, when the recording paper 1 is heated by the heater 3, water such as a solvent in the ink can be evaporated, and the penetration of the ink droplet 2c can be suppressed to the depth d1 in the thickness direction of the recording paper 1. As shown in FIG. 1C, one of the factors that control the penetration of ink droplets by the heating of the heater 3 is an increase in ink viscosity due to the evaporation of moisture. It is considered that the swelling of the ink is promoted at the surface portion.

  By performing the heating with the heater 3 in this way, it was possible to suppress the penetration of the ink droplets and stop the penetration at the depth d1 in the thickness direction of the recording paper 1.

  The present invention is characterized in that image quality is improved when recording is performed using semipermeable ink. Hereinafter, the detailed mechanism of the phenomenon in the case of using the semi-permeable ink will be described with reference to FIG. 50 (a diagram viewed in the cross-sectional direction of the paper) although it is an inference.

  FIG. 50A shows a state where ink droplets are flying toward the paper. FIG. 50B shows a state where ink droplets have landed on the paper. At this time, the ink has a cylindrical shape with a diameter about twice as large as the ink droplet diameter on the paper. FIG. 50 (c) shows that the ink swells to the paper fibers at a relatively high speed at the surface portion of the paper because the ink has a relatively high permeability. Here, the swelling speed is promoted by the action of heat applied from the back surface of the paper by the heater, and ink evaporation is also promoted. FIG. 50D is a diagram illustrating a state where ink has permeated into the paper. Due to the evaporation of the water, mainly the ink, the next step, the penetration as a capillary phenomenon between the fibers, is less likely to occur. Accordingly, it is difficult for ink to penetrate in the depth direction of the paper. Further, since the permeation is suppressed, the feathering that occurs due to the capillary phenomenon between the fibers becomes difficult to occur. As a result, a large amount of colorant is trapped within 20 μm of the surface of the paper, so that the OD value is high as in the case of the overlay ink.

  In heating, it is desirable to set conditions such as the heating temperature and heating time of the heater 3 so that a large amount of water vapor is not generated.

Next, the composition, permeability, and penetration speed of the ink in this embodiment will be described. An example of ink components used in the present embodiment is shown below.
1. Y (yellow)
C. I. Direct Yellow 86 3 parts Glycerin 5 parts Thiodiglycol 5 parts Urea 5 parts Acetylenol EH (Kawaken Chemical) 1 part Water remainder 2. M (magenta)
C. I. Acid Red 289 3 parts Glycerin 5 parts Thiodiglycol 5 parts Urea 5 parts Acetylenol EH (Kawaken Chemical) 1 part Water remainder 3. C (cyan)
C. I. Direct Blue 199 3 parts Glycerin 5 parts Thiodiglycol 5 parts Urea 5 parts Acetylenol EH (Kawaken Chemical) 1 part Water remainder 4. Bk (black)
C. I. Direct black 3 parts Glycerin 5 parts Thiodiglycol 5 parts Urea 5 parts Acetylenol EH (Kawaken Chemical) 1 part Water Remaining In the above ink, the Bk ink was adjusted to adjust the content of acetylenol in the above composition It was. For CMY inks, the permeability is improved by adding 1% of acetylenol EH.

  Thus, the ink in this example is composed of a dye or pigment, water, glycerin, thiodiglycol, urea, etc. as a solvent, and acetylenol (trade name of Kawaken Fine Chemical Co., Ltd.) which is a nonionic surfactant. It is a mixed one. Acetylenol is obtained by adding ethylene oxide to acetylene glycol. This is ethylene oxide-2,4,7,9-tetramethyl-5-decyne-4,7-diol (ethylene oxide-2,4,7,9-tetramethyl-5-decyne-4,7-diol) It is expressed. Hereinafter, for convenience, the above-described nonionic surfactant is referred to as acetylenol.

When the ink permeability is expressed as an ink amount V per 1 m ^2, V at the time t (unit: ml / m ² = μm) is known to be expressed by the Bristow equation shown below.

V = Vr + Ka (t−tw) ^1/2
However, t> tw
Immediately after the ink droplets are dropped on the surface of the recording paper, the ink droplets are mostly absorbed by the uneven portions on the surface of the recording medium (the surface roughness portion of the recording medium) and hardly penetrate into the recording medium. Absent. The time during that time is tw (wet time: wet time), and the amount of absorption to the uneven portion during that time is Vr. When the elapsed time after the ink droplet is dropped exceeds tw, the penetration amount V increases in proportion to a half power of the excess time (t-tw). The proportionality coefficient at that time is Ka.

FIG. 3 shows the relationship between the ink penetration amount V with respect to the half of the time t (msec) when acetylenol is 0%, 0.2%, 0.35%, 0.7%, and 1%. Shown in (a). Further, the relationship between the time t and the ink penetration amount V is shown in FIG. As is clear from FIGS. 3A and 3B, it can be said that the greater the acetylenol content, the greater the amount of ink permeated with respect to the elapsed time and the higher the permeability. In addition, the experiment which obtained the result shown in FIG. 4 was conducted using a recording paper of 64 g / m ² , a thickness of about 80 μm, and a porosity of about 50%. The time until the inflection point (indicated by the black circle on the left) that appears as the wetting time becomes shorter as the content of acetylenol increases, and the tendency that the permeability increases as the content of acetylenol increases appears in the graph of FIG. Yes. In the case of ink not containing acetylenol (the content ratio is 0%), the permeability is low and the ink has the above-described properties as an overlay ink. Further, when acetylenol is mixed at a content rate of 1%, it has a property of penetrating into the recording paper 1 in a short time, and has a property as the above-mentioned super-penetrating ink.

  The above will be further described with reference to FIGS.

  First, consider the case where heat is not applied. When ink droplets land on the paper, the ink is adsorbed on the fiber of the paper in the first very short time, causing swelling. Thereafter, penetration by capillary action between the fibers begins. Here, since so-called plain paper used in office machines such as copying machines contains a sizing agent to prevent bleeding, it does not start to penetrate, and there is a so-called wetting time tw (wet time). To do. In FIG. 3, the left one of two black circles on the same line is shown as tw. And even if the penetration starts, the wettability of the ink to the paper does not increase due to the above sizing agent. The so-called overlay ink penetrates relatively slowly, and at a certain point, the paper fiber itself swells rapidly. Will start. The time at that time is about 400 to 500 msec for the extra ink. This time is defined as ts (swelling time). In FIG. 3, the right side of two black circles on the same line is shown as ts.

  Here, when a surfactant such as acetylenol is incorporated in the ink, the wettability of the ink with respect to the paper is improved, so that the wetting time is increased and the speed of the swelling (adsorption of the ink to the fibers of the paper) is also increased. Become. Then, the permeation rate of the next step is also increased, and thereafter, with this permeation, the paper fibers rapidly swell. As the amount of acetylenol increases, tw and ts become shorter, and 1% becomes almost zero. From around 0.2 to 0.3% of the acetylenol amount, tw and ts approach each other as the acetylenol amount increases. These relationships are shown in FIG. 48 as the relationship between tw and ts with respect to the amount of acetylenol. As can be understood from FIG. 48, when the acetylenol content is 0.2%, ts is about 200 msec, and in the case of the semipermeable ink having the acetylenol content of 0.2 to 0.7%, 0 is obtained. <Tw <ts ≦ 200 msec. In addition, the above-mentioned penetration rate coefficient Ka shows the inclination of the liquid absorption after ts. In this way, the semi-penetrating ink in which tw and ts are close to each other has a higher liquid absorption speed than the overlay ink, but the liquid absorption speed is relatively slow until ts. It is considered that the swelling speed is promoted by applying heat to the ink and paper during this period, and the permeation speed as a capillary phenomenon is lowered. At this time, if the total amount of ink is reduced, the penetration can be further suppressed, and the color material can be secured near the surface of the paper.

  It should be noted that the necessary amount of heat may be an amount that evaporates to a level that does not allow a substantial amount of ink to permeate during the swelling period.

  FIG. 2 is a graph showing the proportional coefficient Ka of the ink penetration rate with respect to the content of acetylenol. The Ka value was measured using a liquid dynamic permeability test apparatus S (manufactured by Toyo Seiki Seisakusho) by the Bristow method. In this experiment, PB paper from Canon Inc., which is a recording paper that can be used for both copying machines and LBPs (Laser Beam Printers) using an electrophotographic method and printers using an ink jet recording method, was used as the recording paper. . In addition, almost the same results were obtained with PPC paper, which is an electrophotographic recording paper manufactured by Canon Inc.

  As can be seen from FIG. 2, since the proportionality coefficient Ka varies depending on the content of acetylenol, the ink penetration rate is substantially determined by the content of acetylenol.

  Next, FIG. 4 shows the printing results corresponding to the difference in ink permeability when printing is performed in one pass, with and without the heater for heating the recording paper as shown in FIG. The ink permeability was adjusted by adjusting the content of acetylenol.

  In FIG. 4, the vertical axis represents the image density (OD) or the goodness regarding the blur of the different color, the scratch resistance / immediate water resistance in the pigment ink, and the horizontal axis represents the content of acetylenol. Here, the blur on the different color boundary means a state of blur when dots of different colors are recorded adjacent to each other. For example, the occurrence of the blur is less as judged visually by the boundary between the solid black image and the color image. It shows that it is so good. In addition, the scratch resistance means goodness against contact or rubbing with other recording paper on the printed result after recording, and the immediate water resistance means water resistance immediately after recording. is there.

  From FIG. 4, it can be seen that the image density (OD) decreases as the permeability increases regardless of the presence or absence of a heater, and all of the goodness, smear resistance, and immediate water resistance regarding bleeding at different colors are improved. This represents the property itself due to the difference in ink permeability described above. Further, when attention is paid to the recorded image quality according to the presence or absence of the heater, it can be seen that the heater improves both the image density and the goodness regarding the blur of the different color boundary. In particular, when attention is focused on the image density, it can be seen that the difference in image density depending on the presence or absence of the heater increases as the content of acetylenol increases. Moreover, when it sees about the favorableness regarding a discoloration boundary, the content rate of acetylenol is around 0.4%, and it turns out that the big difference has generate | occur | produced with the presence or absence of a heater.

  Although such an effect starts to penetrate into the recording paper as soon as ink with a certain degree of penetrability adheres to the recording paper, the ink penetration inside the paper is suppressed by heating with the heater, and the ink inside the recording paper. However, the ink is fixed in a shallow range from the surface of the recording paper.

  Therefore, according to the present embodiment, a high penetration speed can be obtained in terms of permeability, and in terms of image density, since the ink can be fixed at a position close to the surface inside the recording paper, a high image density can be obtained. Also, since the ink penetrates the inside of the recording paper, the amount of ink remaining on the surface of the recording paper is extremely small, the scratch resistance is excellent, the water resistance immediately after recording is good, and the recorded image is recorded. Even if overwritten with a marker pen or the like, the recorded image is unlikely to deteriorate due to the melting of ink.

  As shown in FIG. 4, the content ratio of acetylenol is about 0.2 to 0.7%, preferably about 0.35% to 0.50% in one pass (one main scanning of the recording head) recording. By adjusting to the extent, an image suitable for recording can be formed in both the recorded image density and the good border blur. In the above range, when emphasizing the improvement of the recorded image density, an ink having a low content of acetylenol is used, and when emphasizing the improvement of the goodness against the boundary blur, an ink having a high content of acetylenol is used. By using it, a desired image can be recorded. For example, black ink for black images that require a high recording density uses an ink having a relatively low acetylenol content within the above range, and color ink that is often mixed and recorded within the above range. It is effective to use an ink having a relatively high content of acetylenol.

  Next, in the embodiment of the present invention, the following table shows the respective components and characteristics of inks having different permeability to the recording medium.

上記の表では、「上乗せ系インク」、「半浸透性インク」、「高浸透性インク」のそれぞれについて、Ｋａ値、アセチレノール含有量（％）、表面張力（ｄｙｎｅ／ｃｍ）を示している。

In the above table, the Ka value, the acetylenol content (%), and the surface tension (dyne / cm) are shown for each of “upper ink”, “semi-permeable ink”, and “highly permeable ink”.

  The Ka values in the above table are measured using the liquid dynamic permeability test apparatus S (manufactured by Toyo Seiki Seisakusho) by the Bristow method as described above. The recording paper used in the experiment was PB paper from Canon Inc., which is a recording paper that can be used for both a copying machine and LBP using an electrophotographic method, and a printer using an inkjet recording method. Similar results were obtained for PPC paper, which is a recording paper for electrophotography manufactured by Canon Inc.

  Here, the ink of the system defined as “semi-permeable ink” is in the range (0.2 to 0.7% by weight) in which good results were obtained in the configuration using the heater according to the above experimental example. An ink containing acetylenol.

  Here, it is known that there is a critical micelle concentration (cmc) of the surfactant in the liquid as a condition when the surfactant is contained in the liquid. Acetylenol contained in the ink described above is a kind of surfactant, and acetylenol also has a critical micelle concentration (cmc) depending on the liquid.

  FIG. 47 is a graph showing the surface tension when the content ratio of acetylenol to water is adjusted, and from this graph, the critical micelle concentration (cmc) of acetylenol to water is about 0.7%. I understand. Corresponding to this and the above table, the “semipermeable ink” described in the embodiment of the present invention contains acetylenol at a rate lower than the critical micelle concentration (cmc) of acetylenol in water. It turns out that it is ink.

  The present invention is characterized by the following techniques. That is, by using the semi-permeable ink shown in Table 1 and performing the recording operation by performing the heating control with the heater, the penetration of the ink droplets can be suppressed to a shallow position from the surface of the recording paper, and as a result, the image density is reduced. While being able to increase, the favorableness with respect to a border of a different color can be improved. In addition, when recording operation is performed by using semi-permeable ink and heating control is performed by a heater, two ink droplets are overlapped with a predetermined time difference to perform recording so that more ink droplets are recorded on the surface of the recording paper. It can be fixed in a state where it penetrates into a shallow position. Furthermore, good results can be obtained with respect to the problem of blurring on the different color boundary, which becomes a problem when recording is performed by ejecting many ink droplets.

  Next, the effect according to the recording method when performing the recording operation by performing the heating control with the heater will be described by taking various recording methods as examples.

(2) Control of ink penetration according to the recording method In the above explanation, by heating the recording paper using a heater, the penetration of the ink into the recording paper is suppressed, and the goodness of the recording density and blurring is improved. The configuration has been described. Here, the effects in the case where recording is performed by ejecting a plurality of ink droplets while being heated using a heater will be described for various recording methods.

(Split printing method)
A recording method for obtaining a predetermined amount of ink by discharging a small amount of ink droplets a plurality of times will be described.

  FIGS. 5A and 5B schematically show a state in which an ink droplet having an ejection amount of about 40 pl is ejected and a state in which the ink droplet collides with and adheres to the surface of the recording paper 1. FIG. 5 (c) and 5 (d) show a state in which two ink droplets 2 'each having an ejection amount of about 20 pl are ejected in succession, and the ink droplets collide with the surface of the recording paper 1. It is a figure which shows typically the state adhering to. Here, the two ink droplets shown in FIG. 5 (c) indicate a state in which the two ink droplets 2 are ejected with a time difference of about 50 msec. Shall. In addition, as described above, the ink is used in which the content of acetylenol is adjusted to about 0.2 to 0.7%, more preferably about 0.35% to 0.5%. In either case, the ink droplets were ejected while the recording paper was heated by the heater 3, and control was performed to suppress penetration of the ink droplets in the thickness direction of the recording paper.

  As shown in FIG. 5D, even when the time interval at which the two ink droplets are ejected is short, the ink droplets that have first adhered to the surface of the recording paper have started to penetrate as indicated by 2c. As can be seen by comparing FIG. 5 (b) and FIG. 5 (d), the surface of the recording paper is obtained when the ink droplet of 40 pl is ejected once and when it is ejected twice with the ejection amount of 20 pl. The heights (h1, h2) of the state where ink droplets collide and adhere to the inks are different. The higher the height immediately after the ink droplets adhere to the recording paper surface, the deeper the penetration depth in the thickness direction of the recording paper. In order to increase the density of the recorded image, it is desirable to reduce the depth of penetration in the thickness direction of the recording paper. Comparing FIG. 5 (b) and FIG. 5 (d), when forming an image with the same amount of ink droplets, the depth of penetration into the recording paper is reduced by recording multiple times. You can see that

  Next, the reason why the relationship between the ink discharge amount and the height of the ink droplets adhering to the surface of the recording paper will be described in detail.

FIG. 6A is a table for explaining the heights of ink droplets after colliding with or adhering to the recording paper with respect to the ink discharge amount Vd (pl). FIG. 6B and FIG. 6C are diagrams for explaining each item in the table of FIG. 6 (b) is shows a state in which the ink droplet 2 is ejected in the discharge amount Vd, the ink droplets (a Vd = 4πr ^3/3) of radius is r in the substantially spherical state. FIG. 6C shows a state immediately after the ink droplet has adhered to the surface of the recording paper, and R represents the radius of the ink droplet immediately after the ink droplet has adhered. The unit of r and R is μm. In addition, when the ejected ink droplet collides with the recording paper, the diameter is about twice as large as in the conventional ink jet recording method, and R = 2r is calculated. Further, the area when the ink droplet immediately after adhering to the recording paper after adhering to the recording paper is regarded as the dot diameter is S (S = πR ² ), and the height is represented by h (h = Vd / S). Is).

In FIG. 6A, AF (area factor) represents the ratio of ink droplets to one dot position when printing is performed at a resolution of 360 dpi (dots per inches). That is, if each pixel to be recorded at 360 dpi has a grid shape with one side of about 70.5 μm, the area is about 4970.25 μm ² . AF represents the ratio of the area of the ink droplet to the area of one pixel as a percentage (AF = S × 100 / 4970.25). As the AF value increases, the distance from the ink droplets of adjacent pixels decreases. When this value exceeds 100, the ink droplets attached to the recording paper reach the adjacent pixel positions. .

  According to the table of FIG. 6A, the height immediately after the ink droplets adhere to the recording paper when ejected at an ejection amount of 40 pl is about 7.1 μm, and when the ejection amount is 20 pl, it is 5.6 μm. . The height immediately after adhering to the recording paper affects the penetration of the ink droplet, and the height of the ink droplet is almost the same as the depth of penetration into the recording paper. Therefore, in the case where 40 pl of ink is recorded by one ejection and in the case where recording is performed twice with 20 pl of ink droplets, the latter has a smaller penetration depth of the ink droplets. As described above, since the recording density can be increased by fixing the ink at a shallow position on the surface of the recording paper, the recording is performed twice with the 20 pl ink droplets rather than the recording by discharging the 40 pl ink droplets. The recording density can be increased by separately recording.

  As described above, in the configuration in which recording is performed by ejecting ink droplets while the recording paper is heated by the heater, the recording density is further increased by performing the recording by dividing the same amount of ink into a plurality of times with a small ejection amount. Can be further enhanced.

(Overlapping printing method)
The effect of the divided printing described above can also be obtained in a configuration in which recording is performed by ejecting ink droplets a plurality of times at the same position, which will be described with reference to FIGS. FIG. 7 shows an example in which a plurality of ink droplets are continuously ejected without leaving a time difference, FIG. 7A shows a state in which two ink droplets are ejected, and FIG. 7B shows two ink droplets. A state in which droplets are attached on the surface of the recording paper 1 is schematically shown.

  When two ink droplets are ejected at a very short time difference, for example, 10 ms, the ink droplets ejected after the ink droplets ejected earlier penetrate into the recording paper 1 before the surface of the recording paper 1 is ejected. To reach. In that case, immediately after the two ink droplets adhere to the surface of the recording paper 1, as shown in FIG. 7B, the two ink droplets adhere to the surface of the recording paper in an overlapping state. Accordingly, the height of the attached ink droplet is also increased, and as a result, the depth of penetration into the recording paper is also increased.

  In contrast, FIG. 8 shows an example in which two ink droplets are recorded at the same position after a sufficient time difference, for example, about 1 second. FIG. 8A shows the state of the ink droplet ejected first. As shown in FIG. 8B, the ejected ink droplet penetrates into the recording paper before the subsequent ink droplet is ejected. In this state, as shown in FIG. 8 (c), when a subsequent ink droplet is ejected, the penetration depth into the recording paper does not become deeper as shown in FIG. 8 (d). The penetration of two ink droplets can be suppressed at a shallow position from the recording paper surface.

  Therefore, when recording a plurality of ink droplets at the same position, by allowing a sufficient time interval for ejecting the plurality of ink droplets, the penetration of the ink droplets can be suppressed at a shallow position from the recording paper surface. The concentration can be increased.

  Such an effect of performing overstrike with a sufficient time difference can also be obtained by a configuration in which no heater is provided. However, if a heater is provided to suppress the penetration of ink droplets in the depth direction of the recording paper, the recording density can be increased even with highly penetrating ink, and the speed at which the ink droplets penetrate into the recording paper is increased. The recording speed can be increased, and a sufficient recording density can be obtained even if the time interval for overstrike is shortened.

(Recording method using small droplets)
Next, it will be described that a further effect can be obtained by ejecting a plurality of ink droplets having a small ejection amount onto a lattice in which the area factor is 100% or more with one ink droplet.

  The divided printing method described above is an example with a certain time difference, but in this example, even if recording is performed by ejecting droplets with small ejection amounts almost simultaneously, it is effective by using a heater. Explain that is obtained.

  FIG. 9A is a diagram illustrating an example in which an ink droplet having an ejection amount of 100 pl is ejected. Reference numeral 101 denotes a lattice of pixels having an area factor of 100% or more with 100 pl ink droplets, and 102 denotes a dot formed with the ink droplets. Reference numerals 103 and 104 denote states immediately after the same amount of ink droplets adheres to the recording paper, as viewed from the cross-sectional direction of the recording paper.

  FIG. 9B is a diagram illustrating an example in which one drop of 100 pl ink is ejected and an example in which four drops of 25 pl ink droplets are ejected. Reference numeral 101 denotes a lattice having the same size as the lattice of FIG. 9A, and 110 denotes a dot formed by a 25 pl ink droplet. Reference numerals 111, 112, and 113 denote states immediately after the same amount of ink droplets adheres to the recording paper.

  According to the table shown in FIG. 6A, the dot diameter w1 (R × 2) when the ejection amount is 100 pl is about 115.2 μm, and the height immediately after adhering to the recording paper is about 9.6 μm. When the discharge amount is 25 pl, the dot diameter w2 is about 72.4 μm and the height is about 6.1 μm.

  In this way, a configuration in which a plurality of ink droplets having a small ejection amount are ejected onto a pixel having an area factor of 100% with one ink droplet so that the area factor is 100% or more is formed on the surface of the recording paper. The height of the ink droplet immediately after adhering can be reduced. In addition, the effect of heating by the heater is added, and the depth of penetration into the recording paper becomes shallow, so that the recording density is increased and the goodness concerning the boundary blur is also improved.

(Method to complete the image by recording multiple times)
Next, a description will be given of a method for recording in a plurality of times when a predetermined recording image is recorded.

  FIG. 10 is a diagram illustrating an example in which recording is performed with the area factor of a predetermined image being 100% by one recording. FIG. 10A shows a state in which heating by the heater 3 is performed and a plurality of ink droplets 2 are ejected onto the recording paper 1. FIG. 10B shows a state immediately after the plurality of ejected ink droplets adhere to the surface of the recording paper. The ink droplets adhere in a state where they rise to the height indicated by h5 as indicated by 2e, and start to penetrate into the recording paper as indicated by arrows in the figure. FIG. 10C shows a state in which the ink 2e shown in FIG. 10B has penetrated into the recording paper. Although the ink penetration is suppressed by the heater, the ink has penetrated to the depth d2 (2f). Ink is fixed.

  FIG. 11 is a diagram for explaining a method of forming a predetermined recording image by recording divided into two times. FIG. 11A is a diagram showing a state in which only ink droplets that are not adjacent to each other among the ink droplets 2 are ejected as compared with FIG. 10A. The ejected ink droplets adhere as shown by a dotted line 2g in FIG. 11A and start to penetrate into the recording paper 1. The height immediately after the ink droplet 2 adheres to the surface of the recording paper is represented by h6. FIG. 11B is a diagram showing a state (2h) in which the ink droplets ejected in FIG. 11A have penetrated into the recording paper, and the penetration is suppressed to the depth d3 by the heater 3. Indicates the state. FIG. 11C is a diagram illustrating a state in which ink droplets that were not ejected in FIG. 11A are ejected after a predetermined time has elapsed since the ink droplets were ejected in FIG. This drawing also shows a state where only ink droplets that are not recorded at positions adjacent to each other are ejected. As shown in FIG. 11A, the ejected ink droplet 2 adheres to the surface of the recording paper 1 as indicated by a dotted line 2g 'and starts to penetrate into the recording paper. The height immediately after the ink droplet adheres to the recording paper 1 is h6 as in FIG.

  FIG. 11D is a diagram showing a state (2h ′) in which the ink droplets 2 ejected in two steps shown in FIGS. 11A and 11C penetrate into the inside of the recording paper 1. The state in which the penetration is suppressed by the heater 3 to the depth d3 is shown. Here, as shown in FIG. 10, the ink permeates between the case where the ink droplets are ejected by one recording and the case where the recording is performed in a plurality of times as shown in FIG. The depth (d2, d3) is different. As shown in FIG. 10, when all of the adjacent ink droplets are ejected in one recording, the adjacent ink droplets overlap each other, and the height of the ink droplets adhering to the recording paper 1 due to the overlapping portion is high. As a result, the ink penetrates to a deep position in the thickness direction of the recording paper. On the other hand, when the ink droplets are configured to be ejected in a plurality of times as shown in FIG. 11, the ink droplets ejected at adjacent positions do not overlap with each other, and the ink droplets are recorded on the recording paper. The height immediately after adhering to the surface can be reduced. As a result, the depth of penetration of the ink into the recording medium can be reduced, and the recording density can be increased.

(3) Recording with Pigment Ink The present invention can be effectively applied not only to dye ink but also to pigment ink. When pigment ink is used, a further effect is obtained by a phenomenon different from that when dye ink is used. Is obtained. Therefore, the effect of heating with a heater in a configuration using pigment ink will be described.

  FIG. 12A is a diagram showing the state of ink penetration after the penetrating pigment ink is ejected onto the recording paper 1 without using a heater, and the state of dots formed on the paper surface. .

  The ink droplets ejected on the recording paper 1 are fixed in a state where they penetrate into the recording paper 1 to a depth d4 as indicated by 131. The pigment in the ink is dispersed in the recording paper 1 and the surface of the recording paper together with the solvent in a wide range as the solvent of the ink permeates into the recording paper 1 and the surface of the recording paper. As a result, the pigment penetrates deep inside the recording paper 1 and the recording density is lowered. Further, on the surface of the recording paper 1, as shown by dots 132, feathering occurs due to its penetrability, and recording is performed in a state where the shape of a single dot itself is deteriorated, and the recording quality is high. It will decline.

  On the other hand, FIG. 12B shows the state of ink penetration after ink droplets of pigment ink are ejected onto the recording paper 1 while the recording paper 1 is heated using a heater, and is formed on the paper surface. It is a figure showing the state of the made dot. In the configuration in which recording is performed by heating the recording paper using a heater, when using a self-dispersing pigment ink that does not contain a dispersant, the moisture of the ink that permeates the paper by heating evaporates and the pigment concentration increases, Difficult to disperse in the ink solvent. As a result, the depth at which the ink penetrates in the thickness direction inside the recording paper can be suppressed to d5, and the recording quality can be improved similarly to the above-described example.

  In FIG. 12B, the ink droplets ejected on the recording paper 1 start to penetrate into the recording paper 1 after adhering to the surface of the recording paper 1. Here, when the heater 3 is heated, the moisture in the paper evaporates to increase the pigment concentration in the ink, making it difficult to disperse in the solvent of the ink. The pigment ink is deep inside the recording paper together with the solvent. It will not penetrate to position 135. Further, when viewed from the surface of the recording paper, the pigment particles permeate into the recording paper together with the solvent, so that the fixing is performed with almost no pigment particles remaining on the surface of the recording paper. As a result, the depth of penetration of ink into the recording paper 1 by the heater can be suppressed to d5, and the recording density is increased. Further, since ink droplets penetrate into the recording paper, a high effect can be obtained in terms of scratch resistance and immediate water resistance.

  Also, with respect to the dots 134 seen on the surface of the recording paper, it is possible to suppress the occurrence of feathering at the edge portions of the dots and to form sharper dots compared to the dots formed with a configuration that does not use a heater. it can. This is presumably because of the ink droplets adhering to the surface of the recording paper 1, the ink located at the edge portion is more easily affected by the heating of the heater and the evaporation of moisture occurs more quickly.

(4) Difference due to time difference when recording a plurality of ink droplets in a stacked manner Next, in a configuration in which a recording medium is heated by using a heater to control ink penetration, a plurality of ink droplets are recorded in a stacked manner. The difference in the effect according to the difference in the time interval for overlapping recording will be described.

  FIG. 13 shows a perspective view of an example of the recording apparatus applied to this example. A recording paper (plain paper) 1 as a recording medium is inserted from the paper supply unit 5 and discharged through the printing unit 6. In this example, inexpensive plain paper that is generally widely used as recording paper is used. The printing unit 6 is provided with a recording head 8 mounted on a carriage 7, and the recording head 8 is configured to be reciprocally movable along a guide rail 9 by driving means (not shown). The recording head 8 includes black discharge portions K1 and K2 that discharge black ink, a cyan discharge portion C that discharges cyan ink, a magenta discharge portion M that discharges magenta ink, and a yellow discharge portion Y that discharges yellow ink. Have. When ink is supplied from an ink tank (not shown), each discharge unit discharges ink of a corresponding color when a drive signal is supplied to the ink discharge means. A ceramic heater 10 is provided over the entire moving range of the carriage 7 at a position facing each discharge portion. In this example, an electrothermal conversion element that applies thermal energy to the ink is provided as ink ejection means, bubbles are generated in the ink by thermal energy, and ink is ejected using the pressure at the time of foaming. The so-called bubble jet method is adopted. The recording head 8 has a resolution of 360 dpi, the nozzle drive frequency is set to 7.2 KHz, and the carriage 7 is configured to reciprocate once in the scanning range in about 1.5 seconds.

(Example when recording interval is short)
The recording result when the time interval between the ink droplets to be recorded is short will be described with an experimental result as an example.

  In this experiment, overlapping recording by the black ejection portions K1 and K2 of the recording apparatus shown in FIG. 13 was performed during the same scanning of the carriage. The recording time interval by the black discharge portions K1 and K2 is a relatively short time interval of about 50 msec. Further, the recording by the color ink discharge portions C, M, and Y was performed at the time of the recording scan following the recording scan by the black discharge portions K1 and K2. 14 and 15 show the relationship between the ink permeability and the recorded image density when the heating temperature by the heater 10 is varied. FIG. 14 is a graph showing experimental results when adjusting the content of acetylenol when the heating voltage to the ceramic heater as the heating means is 28V, 20V, and 0V, respectively. FIG. 15 shows the relationship between the power value (wattage) of the heater as the heating means and the OD value when the content of acetylenol in the ink is 0%, 0.4%, and 1.0%. Yes. Note that the heating temperature by the heater increases as the voltage applied to the heater is increased. When the applied voltage is 0V, heating by the heater is not performed.

  In FIG. 14, the vertical axis represents the OD value (reflection optical density) indicating the recorded image density, and the horizontal axis represents the content of acetylenol. In FIG. 15, the vertical axis represents the OD value (reflection optical density) indicating the recording image density, and the horizontal axis represents the power value (wattage) of the heater as the heating means.

  When the acetylenol content is 0%, the OD value appears high and clear, but as described above, the amount remaining in a convex shape on the surface of the recording medium is large, and ink droplets of different colors are ejected adjacently. If this happens, ink will flow in, and bleeding such as bleeding at the boundary and white haze will likely occur. In order to solve such a problem, it is necessary to leave the ink for a sufficient period of time before ejecting the adjacent ink, thereby reducing the throughput. Further, when the content of acetylenol is increased, the permeability of the ink can be increased, and the ink can be permeated without remaining in a convex shape on the surface of the recording paper, but the OD value is lowered and unclear. It becomes an image. In this example, by setting the content of acetylenol to about 0.4%, a relatively high OD value was obtained, and a good recorded image could be formed even with respect to boundary blurring.

  FIG. 16 is a diagram for explaining how much the difference in OD differs between when a heater is used and when no heater is used. FIG. 16 is a graph based on the results shown in FIG. That is, the difference in concentration when the heating voltage to the heater is 20 V and 0 V (when no heater is used), and the difference between the concentration when the heating voltage to the heater is 28 V and 0 V (when no heater is used) Is shown in a graph corresponding to the content of acetylenol.

  From the results shown in FIGS. 14, 15, and 16, it can be seen that the OD value can be increased by increasing the heating temperature of the heater. Further, it can be seen that even if the ink contains acetylenol and has improved permeability, the density can be increased to almost the same recording image density as that of the ink having low permeability by increasing the heating temperature by the heater.

(Example when recording is performed with a long recording interval)
Next, the recording result when the time interval of the ink droplets to be overlapped is increased will be described with an experimental result as an example.

  In this experiment, the recording apparatus shown in FIG. 13 was used, recording was performed by one of the black ejection portions K1 and K2 during the first recording scan of the carriage 7, and black was detected in the scanning after the carriage 7 reciprocated once in the scanning range. An example in which overprinting is performed by either one of the discharge units K1 and K2 will be described.

  In this experiment, the time interval of the overlap recording performed in two carriage scans is a relatively long time interval of about 1.5 seconds. Further, the recording by the color ink discharge portions C, M, and Y was performed at the second recording scan of the black discharge portion.

  The experimental results are shown in FIGS. FIG. 17 is a graph showing experimental results when adjusting the content of acetylenol when the heating voltage to the ceramic heater as the heating means is 28V, 20V, and 0V, respectively. FIG. 18 shows the relationship between the power value (wattage) of the heater as the heating means and the OD value when the content of acetylenol in the ink is 0%, 0.4%, and 1.0%. Yes. Also in this experimental example, as in the previous experimental example, by setting the content of acetylenol to about 0.4%, a relatively high OD value was obtained, and a good recorded image could be formed even with respect to boundary blurring. .

  FIG. 19 is a diagram for explaining how much the difference in OD differs between when a heater is used and when a heater is not used. FIG. 19 is a graph based on the results shown in FIG. That is, the difference in concentration when the heating voltage to the heater is 20 V and 0 V (when no heater is used), and the difference between the concentration when the heating voltage to the heater is 28 V and 0 V (when no heater is used) Is shown in a graph corresponding to the content of acetylenol.

  Referring to FIG. 19, when the heating voltage to the heater is 28 V, the heater is not used when the acetylenol content is 0.2 to 0.7%, particularly 0.3 to 0.7%. It can be seen that the density difference is large and a high density image can be formed.

  From the results shown in FIG. 17, FIG. 18, and FIG. 19, it can be seen that the OD value can be increased by increasing the heating temperature of the heater. Further, it can be seen that even if the ink contains acetylenol and has improved permeability, the density can be increased to almost the same recording image density as that of the ink having low permeability by increasing the heating temperature by the heater.

  Comparison of the experimental results shown in FIGS. 14 and 15 with the conditions such as the content of acetylenol in the ink, the heating temperature of the heater, and the heater wattage are the same. It can be seen that the result can achieve a higher recording density.

  Further, even when the results of FIG. 16 and FIG. 19 are compared, by setting the time interval for recording a plurality of ink droplets to be stacked to a certain extent, the effect of heating by the heater can be better obtained, and the recording density can be increased. It can be seen that it can be raised.

  In addition, with respect to the ink bleed that occurs at the boundary of the image with other color inks, the use of a relatively highly penetrating ink and the effect of suppressing the penetration of the ink into the recording paper by the heater reduces the occurrence of bleed. Can be suppressed.

  Here, when the occurrence of blurring at the boundary according to the time interval between black ink recording and color ink recording is examined, the time interval between black ink recording and color ink recording is relatively small in the examples shown in FIGS. Because of its long length, it was possible to suppress the occurrence of blurring at the boundary. In the examples shown in FIGS. 17 and 18, the blurring of the boundary between the black ink image and the color ink image is suppressed by the heating effect using the heater. However, since the black ink recording and the color ink recording in the second recording scan are performed in the same scanning, the occurrence of slight bleeding was confirmed as compared with the examples shown in FIGS.

  As described above, it can be seen that in order to increase the image density of the black ink image, it is preferable to increase the recording time interval by the black ejection portions K1 and K2. It can be seen that in order to further suppress the blurring of the boundary between the black ink image and the color ink image, it is preferable to increase the time interval between the black ink recording and the color ink recording.

  From the above, when it is attempted to increase the recording density by overlapping a plurality of ink droplets, it can be said that the recording density can be further increased by setting the time interval for performing the overlapping recording to some extent. Assuming that the set time is a time for the carriage to reciprocate once as described in the experimental example, a configuration in which recording is performed twice by a single black discharge unit can also be employed. Therefore, as in the recording apparatus shown in FIG. 2, in a configuration in which one discharge section corresponding to each ink color is provided, as is generally known, without providing a plurality of black discharge sections that discharge black ink. Is also applicable.

  In addition, a full line type recording apparatus using a recording head having a length corresponding to the entire width direction of the recording paper is generally known. However, in this full line type recording apparatus, the conveyance speed of the recording paper is high. Corresponds to the recording speed. Therefore, in a full-line type recording apparatus in which a plurality of recording heads are juxtaposed along the conveyance direction of the recording paper, the distance between the recording heads is set to a distance corresponding to the time interval in order to adjust the time interval for performing overlapping recording. There is a configuration in which the conveyance speed of the recording paper is set to a speed according to the time interval. Hereinafter, a full line type recording apparatus will be described as an example.

  FIG. 20 is a schematic side view showing the configuration of a full-line type recording apparatus. This recording apparatus employs an ink jet recording system that performs recording by ejecting ink, and a plurality of full multi-type recording heads are juxtaposed in the direction along arrow A in the figure to enable multicolor recording. It is configured. In the configuration shown in this drawing, the recording heads K 1 and K 2 that discharge black ink and the recording heads C, M, and Y corresponding to the respective colors of yellow, magenta, and cyan are provided so as to face the conveyance belt 181. Yes. Each recording head is a full-line type recording head in which ejection openings are arranged in parallel over the entire width of the recording area. Each recording head incorporates an electrothermal transducer (not shown) for each ejection port. When the electrothermal transducer is energized, heat is generated to cause film boiling, bubbles are formed in an ink liquid path (not shown), and ink droplets are ejected by the growth of the bubbles. Each recording head is provided so that a large number of ejection openings are arranged in a row in a direction perpendicular to the paper surface, that is, perpendicular to the conveyance direction of the recording medium. The transport belt 181 for transporting the recording paper is an endless belt, and is held rotatably by the two rollers 182 and 183 in the arrow A direction. Note that a recording sheet, which is a recording medium, is sent to the conveyance belt 181 in synchronization by a pair of registration rollers 184, recorded by ink ejection from the recording head, and discharged onto the stocker 185. The guide 186 is for feeding the recording paper to the transport belt 181.

  In addition, halogen lamp heaters 187a and 187b are provided between the recording heads K1 and K2 and between the recording head K2 and the recording head C as heaters for heating the recording paper. In the configuration shown in FIG. 13, a ceramic heater is used as the heating means. However, the heating means applicable to the present invention is not limited to the heater that heats from the back side of the recording surface of the recording paper. The halogen lamp heater shown in FIG. In particular, in a full-line type recording apparatus, since the recording paper is placed on the conveying belt and conveyed, the apparatus becomes complicated if a heater is provided on the back surface of the recording paper. Therefore, it is preferable to use a heater of the type that heats from the recording surface side as shown in FIG. In this figure, the number of heaters provided between the recording heads K1 and K2 and between the recording heads K2 and C is one, but a plurality of heaters are arranged according to the amount of heat generated by the heaters themselves. May be.

  In the configuration of the apparatus shown in FIG. 20, the distance between the two recording heads K1 and K2 that discharge black ink is set to L0. By determining this distance based on the time during which the recording paper is transported at the transport speed set in the apparatus, the time interval for recording by the recording heads K1 and K2 that eject black ink is determined. In other words, when the time interval from the time when recording is performed by the recording head K1 as described above to the time when the recording is continued by the subsequent recording head K2 is 1.5 seconds, the length that the recording paper is conveyed in 1.5 seconds. The distance L0 may be set to. In the configuration shown in FIG. 20, the distance L1 between the recording head K2 that ejects black ink and the recording head C that ejects cyan ink is set to be substantially the same as the distance L0, and after recording by the recording head K2, A time interval until recording is performed by the subsequent recording head C is set. According to this configuration, since the recording by the subsequent recording head C is performed in a state in which the ink droplets ejected by the recording head K2 have permeated into the recording paper to some extent, the blur of the image boundary due to the different color ink is reduced, which is favorable. A good image can be recorded.

  Hereinafter, a specific recording sequence will be described as an embodiment of the present invention by taking a recording apparatus to which the present invention is applicable as an example.

  FIG. 21 shows a schematic configuration of the color printer unit. This configuration employs a so-called serial system, and performs recording while scanning the recording head in the X direction (main scanning direction) shown in the figure, and the print paper 707 as a recording medium is in the Y direction (sub-direction) shown in the figure. Transported in the scanning direction). In this figure, reference numeral 701 denotes a head cartridge. These are composed of an ink tank filled with four color inks, black (K), cyan (C), magenta (M), and yellow (Y), and a multi-nozzle head 702.

  FIG. 22 shows the state of the multi-nozzles arranged in the multi-nozzle head 702 shown in FIG. 21 from the Z direction. In FIG. 22, reference numeral 801 denotes a multi nozzle arranged on the multi head 702. In the example shown in FIG. 22, the multi-nozzles 801 are arranged in parallel along the Y axis. However, for example, a configuration having a slight inclination with respect to the XY plane may be used. In this case, while the head advances in the traveling direction X, each nozzle performs printing while shifting the timing according to the inclination.

  Referring to FIG. 21 again, the conveying roller 703 rotates in the direction of the arrow in the figure while holding the print paper 707 together with the auxiliary roller 704, and feeds the print paper 707 in the Y direction as needed. The feed roller 705 feeds the print paper and plays a role of suppressing the print paper 707 in the same manner as the rollers 703 and 704. The carriage 706 supports four ink cartridges and moves them together with printing. This is configured to stand by at the home position (h) indicated by the dotted line in the figure when printing is not performed or when multihead recovery work is performed. Prior to the start of printing, when printing is started, the carriage 706 at the home position moves in the X direction shown in FIG. 21 and has a width D on the paper surface by n multi-nozzles 801 on the multi-nozzle head 702. Print. In a general serial recording apparatus, printing on one sheet is completed by repeating such printing in the main scanning direction and conveyance of the printing paper in the sub-scanning direction.

  In FIG. 21, the heater 710 is disposed at a position facing the multi-nozzle head 702. During the printing operation, the printing paper 707 is conveyed between the multi-nozzle head 702 and the heater 710, and the heater 710 heats the printing paper 707 from the opposite side of the printing surface. In addition, the heater 710 is disposed so as to heat the print paper in a range corresponding to the recording area by the main scanning of the multi-nozzle head 702.

  FIG. 23A schematically shows the recording apparatus shown in FIG. FIG. 23B shows recording by the first main scanning. The head cartridge 701 scans in the X direction and uses only the black head cartridge K, and the recording area 290 along the main scanning direction is recorded. Print. FIG. 23C shows the second main scanning recording. After printing in FIG. 23B, the print paper 707 is not transported, and yellow (Y), magenta (M), and cyan (C). Using the head cartridge, printing is performed on the recording area 291 along the main scanning direction.

  The area 290 shown in FIG. 23 (b) and the area 291 shown in FIG. 23 (c) are the same area. In this example, the same area is recorded with black and other colors excluding black. Are recorded by different main scans.

  After the black recording is performed, until the next main scanning is started after the carriage returns, fixing of the black recorded area is performed by the heater 710. The fixing process during this period is the same as described above. Ink penetration is suppressed, and even if a subsequent recording scan with another color is performed, the black image and the other color image do not affect each other. High image quality is achieved.

  FIG. 24A also schematically shows the recording apparatus shown in FIG. FIG. 24B shows recording by the first main scanning. The head cartridge 701 is scanned in the X direction, and only the black head cartridge K is used, and the recording area 301 along the main scanning direction is scanned. Print. FIG. 24C shows recording by the second main scanning. After the first main scan, the print paper 707 is not conveyed, and the head cartridge 701 is scanned in the X direction as in the first main scan, and only the black head cartridge K is used in the main scan direction. Printing is performed on the recording area 302 along the line.

  FIG. 24D shows recording by the third main scanning. After printing in the two main scans shown in FIGS. 24B and 24C, the print paper 707 is not conveyed, and yellow (Y), magenta (M), and cyan (C) head cartridges are used. Then, printing is performed on the recording area 291 along the main scanning direction. In addition to the effect shown in FIG. 24, there is an effect that the density of black can be increased.

(First embodiment)
Examples of the recording method as schematically shown in FIGS. 23 and 24 will be described in more detail. First, the first embodiment will be described. In the drawing, regardless of the color of the ink, the state in which one ink droplet is formed is hatched, and the state in which two ink droplets are superimposed is cross-hatched, and three ink droplets are superimposed. The states formed are shown by vertical and horizontal grid patterns.

  During the first scanning of the carriage 7, black ink is ejected from the black ejection portions K1 and K2 toward the plain paper 1 to form first ink droplets 11a and 11b (see FIG. 25A). After the scanning is completed, the carriage 7 scans in the reverse direction without discharging ink from the recording head 8 and returns to the original position. Subsequently, a second scan of the carriage 7 is performed. At this time, black ink is again ejected from the black ejection portions K1 and K2 toward the plain paper 1, and the black recording dots 14 (FIG. 25) are ejected. (See (b)). After the scanning is completed, the carriage 7 scans in the reverse direction without ejecting ink from the recording head 8 and returns to the original position again. Further, a third scan of the carriage 7 is performed, and color ink (cyan, magenta, yellow) is appropriately ejected from the ejection portions C, M, and Y toward the plain paper 1 to eject a third ink droplet. Then, color recording dots 15 (see FIG. 25C) are formed. After the scanning is completed, the carriage 7 scans in the reverse direction without ejecting ink from the recording head 8 and returns to the original position, thereby completing one line printing. During this time, the ceramic heater 10 always operates and keeps heating the plain paper 1.

  Therefore, when a certain point of the plain paper 1 is taken, as shown in FIG. 26, discharge is first performed by the black discharge portions K1 and K2, and then heated for 1.5 seconds when the carriage 7 reciprocates. . By this heating, the penetration of the first ink droplets 11a and 11b into the plain paper 1 is controlled, and the penetration depth is suppressed as compared with the non-heating case. Then, the black discharge portions K1 and K2 discharge again, and second ink droplets are formed so as to overlap the first ink droplets 11a and 11b. Then, the carriage 7 is heated again for 1.5 seconds during which the carriage 7 reciprocates. Thus, as shown in FIG. 25B, the black recording dots 14 are constituted by the first ink droplets and the second ink droplets. Therefore, color ink is discharged from the discharge portions C, M, and Y, and the color recording dots 15 (configured by the third ink droplets) adjacent to the black recording dots 14 are formed. Thereafter, heating is performed for at least 1.5 seconds during which the carriage 7 reciprocates. Regarding the formation of the color recording dots 15, in order to obtain a desired color, ink is ejected by an arbitrary combination of ejection portions C, M, and Y, and dots are formed by one or a plurality of ink droplets. .

  According to the above operation, the first ink droplets 11a and 11b are heated for 3 seconds and the second ink droplet is heated for 1.5 seconds before the color ink is discharged from the discharge portions C, M, and Y. Thereby, the penetration depth of each ink droplet is suppressed, the ink concentrates in the vicinity of the surface in the thickness direction of the plain paper 1, and the pigment component is not dispersed so much. Since the light incident on the plain paper 1 is reflected at a position relatively close to the surface, the light is clear. Further, since this ink has permeability, the ink does not remain in a convex shape on the surface of the plain paper 1 and does not flow into the adjacent color recording dot 15 side to cause bleeding. By heating and evaporating the moisture in the ink, the viscosity of the ink is raised, bleeding such as bleeding at the boundary is less likely to occur, and by evaporating the solvent in the ink, the solubility of the dye in the solvent is lowered, and the dye is removed. It also has the effect of facilitating adsorption to paper.

  As described above, according to the present embodiment, a non-penetration in which the ink has a behavior unique to the penetrating ink that does not remain convex on the surface of the plain paper 1 as a recording medium and the ink is concentrated at a shallow position from the surface. The same behavior as that of the property ink is also shown. Therefore, it is possible to achieve both of the advantages of both types of ink, that is, clear recording is possible and bleeding can be prevented.

  Note that at the time when the next ink discharge is performed 1.5 seconds after the ink discharge, the penetration of the previously discharged ink droplets into the plain paper 1 may be continued or completed. .

(Second embodiment)
FIG. 27 is an explanatory view showing a second embodiment of the present invention. This is a method in which the second black ink discharge and the color ink discharge are simultaneously performed during the second scanning of the carriage 7.

  That is, when a certain point of the plain paper 1 is taken, discharge is first performed by the black discharge portions K1 and K2, and then heated for 1.5 seconds during which the carriage 7 reciprocates. By this heating, the penetration of the black ink droplets 16a and 16b into the plain paper 1 is controlled, and the penetration depth is suppressed. Therefore, the carriage scan is performed again, the second black ink discharge by the black discharge portions K1 and K2, and the color ink discharge by the discharge portions C, M, and Y are performed, and the black recording dots are formed of black ink droplets. 18 and adjacent color recording dots 19 are formed. Thereafter, the carriage 7 is also heated for 1.5 seconds for reciprocation.

  This embodiment is different from the first embodiment only in that black ink droplets are formed and color recording dots 19 are formed during the second scanning of the carriage. The other steps are the same as in the first embodiment. This is the same as the embodiment. Here, the second black recording and the color recording are performed in the same scan. However, since the black ink penetrates almost into the paper before the color is recorded due to the penetrability of the black ink, the bleeding hardly occurs. Further, it is possible to achieve the same effect as that of the first embodiment in which clear recording of colors is possible and bleed is hardly generated.

(Third embodiment)
FIG. 28 is an explanatory view showing a third embodiment of the present invention. This is a method in which the black ink is not overprinted.

  That is, when a certain point of the plain paper 1 is taken, discharge is first performed by the black discharge portions K1 and K2, and then heated for 1.5 seconds during which the carriage 7 reciprocates. By this heating, the penetration of the black ink droplets 20a and 20b into the plain paper 1 is controlled, and the penetration depth is suppressed. Therefore, the color ink is ejected from the ejection portions C, M, and Y, and the color recording dots 22 adjacent to the black recording dots 21 composed of the black ink droplets 20a and 20b are formed. Thereafter, the carriage 7 is also heated for 1.5 seconds for reciprocation.

  This embodiment is different from the first embodiment only in that the black recording dots 21 are formed by the two black ink droplets 20a and 20b at the first scanning of the carriage, and other steps. Etc. are the same as in the first embodiment. Further, it is possible to achieve the same effect as that of the first embodiment in which clear recording of colors is possible and bleed is hardly generated.

(Fourth embodiment)
FIG. 29 is an explanatory diagram showing a fourth embodiment of the present invention. This uses a recording head (not shown) having a single black discharge portion K3.

  When taking a certain point of the plain paper 1, black ink droplets 23 are first formed by ejection from the black ejection section K3, and then heated for 1.5 seconds when the carriage 7 reciprocates. Then, black ink droplets are ejected again by the black ejection unit K3. Then, the carriage 7 is heated again for 1.5 seconds during which the carriage 7 reciprocates. Thus, one black recording dot 25 is constituted by the black ink droplet. Next, color ink is discharged from the discharge portions C, M, and Y, and the color recording dots 26 adjacent to the black recording dots 25 are formed. Thereafter, the carriage 7 is also heated for 1.5 seconds for reciprocation.

(Fifth embodiment)
FIG. 30 is an explanatory view showing a fifth embodiment of the present invention. In this method, the same recording head (not shown) as in the fourth embodiment is used, and color ink is discharged simultaneously with the second black ink discharge.

  When one point of the plain paper 1 is taken, black ink droplets 27 are first formed by ejection from the black ejection section K3, and then heated for 1.5 seconds when the carriage 7 reciprocates. Therefore, the carriage 7 is scanned again, black ink droplets are formed by the black ejection portion K3, and one black recording dot 29 is formed by the black ink droplets. At the same time, color ink is discharged from the discharge portions C, M, and Y, and the color recording dots 30 are formed. Thereafter, heating is performed for at least 1.5 seconds when the carriage 7 reciprocates.

(Sixth embodiment)
FIG. 31 is an explanatory view showing a sixth embodiment of the present invention. This is a method in which the same recording head (not shown) as in the fourth embodiment is used and black ink droplets are not overprinted.

  When a certain point of the plain paper 1 is taken, ejection by the black ejection portion K3 is performed, and the carriage 7 is heated for 1.5 seconds for reciprocation. Then, color ink is discharged from the discharge portions C, M, and Y, and the color recording dots 32 adjacent to the black recording dots 31 are formed. Thereafter, heating is performed for at least 1.5 seconds when the carriage 7 reciprocates.

(Seventh embodiment)
FIG. 32 is an explanatory view showing a seventh embodiment of the present invention. This is a method using the same recording head (not shown) as in the fourth embodiment. When a certain point of the plain paper 1 is taken, the black discharge portion K is discharged and black recording dots are used. 33 is formed and heated for 1.5 seconds as the carriage 7 reciprocates. Similarly, after the carriage 7 is scanned and color ink droplets (cyan) are formed by the discharge portion C, the carriage 7 is returned to the original position, and the carriage 7 is heated for 1.5 seconds to reciprocate. Subsequently, the carriage 7 is scanned, color ink droplets (magenta) are formed by the ejection unit M, and the carriage 7 is heated for 1.5 seconds to reciprocate. Further, the carriage 7 is scanned, color ink droplets (yellow) are formed by the discharge unit Y, and heated for at least 1.5 seconds when the carriage 7 reciprocates. Thus, the color recording dots 35 are formed by the ink droplets of the respective colors ejected in three times.

(Eighth embodiment)
FIG. 33 is an explanatory view showing an eighth embodiment of the present invention. This is in contrast to the seventh embodiment. When one point of the plain paper 1 is taken, the black discharge portion K3 and the discharge portions C, M, and Y perform the first scanning of the carriage. The black recording dots 36 and the color recording dots 37 are formed simultaneously. These are heated at least for 1.5 seconds during which the carriage 7 reciprocates.

(Ninth embodiment)
FIG. 34 is an explanatory view showing a ninth embodiment of the present invention. This is because, when a recording device (see FIG. 13) provided with two black ink discharge units is used and a certain point of the plain paper 1 is viewed, the black discharge units K1 and K2 and the discharge unit are scanned during the first scan of the carriage. Black recording dots 38 and color recording dots 39 are simultaneously formed by C, M, and Y. These are heated at least for 1.5 seconds during which the carriage 7 reciprocates.

  In the above description, the penetrating black ink is described in detail by controlling the penetration depth by heating after ink droplet ejection. Similarly, the color ink is heated after ink droplet ejection and the penetration depth is controlled, so that the effect of improving the sharpness and preventing bleeding such as boundary bleeding can be obtained.

  In all the embodiments described above, the color ink is a super-penetrating ink and is ejected only once. However, when a semi-permeable ink having an acetylenol content of about 0.4% is also used as the color ink, More effective. Further, the color ink may be overprinted by a plurality of ink ejections. In that case, after ink ejection by the color ejection portions C, M, and Y, the position may be slightly shifted and ink ejection by the color ejection portions C, M, and Y may be performed again. Alternatively, as shown in FIG. 35, an ink jet recording apparatus having a recording head 40 having a plurality of (two in this example) color discharge portions C1, C2, M1, M2, Y1, and Y2 may be used. Good. According to these methods, the color ink can be overprinted by a plurality of ink ejections without increasing the number of times the carriage is scanned. Further, after the process described in the above embodiment, a series of processes for discharging the color ink from the discharge portions C, M, and Y while scanning the carriage 7 again and then returning the carriage 7 to the original position is added. Also good.

  In each of the above embodiments, when ink droplet ejection is performed once to form one recording dot in the main scanning direction (carriage movement direction), about 50 pl of ink is ejected from one nozzle once. Discharge. When ink droplet ejection is performed twice, 20 to 30 pl of ink is ejected by one ejection from one nozzle to form recording dots of about 50 pl. When two black ink ejection heads K1 and K2 are provided and ejection is performed four times for one recording dot, the ink amount of one recording dot is about 100 pl.

  The plurality of ink ejections performed for one recording dot may be performed by overlapping at exactly the same position, or may be performed by slightly shifting the positions in a staggered pattern or an interlaced pattern. In the latter case, for example, in order to obtain a recording dot of 360 × 360 dpi, ink ejection of 720 × 360 dpi is actually performed. The size of ink droplets ejected multiple times may be different (for example, a large ink droplet may be formed on a small ink droplet, or a small ink droplet may be formed on a large ink droplet). . However, even when the size of the ink droplets is changed or the ejection position is slightly shifted, it is desirable that at least some of the ejected ink droplets overlap.

  In each of the above-described embodiments, the discharge heads for the respective colors are arranged side by side in a line in the direction perpendicular to the conveyance direction of the plain paper 1, that is, the main scanning direction. However, the ejection heads for each color may be arranged in a plurality of rows such as two rows or three rows in the vertical direction in the transport direction of the plain paper 1, that is, the sub-scanning direction. For example, a black discharge head may be provided in the first row (first pass) and a color discharge head may be provided in the second row (second pass), and may be configured to be movable independently of each other. In this case, another black discharge head may be provided in the second row (second pass).

  The color discharge head may also be divided and arranged such that C is in the second column, M is in the third column, Y is in the fourth column, and so on. In that case, the ceramic heater may be provided so as to face all the rows, or may be provided only at a position facing any row.

  The above description relates to a serial type recording apparatus in which a carriage on which a recording head is mounted reciprocates at right angles to the conveyance direction of the recording medium. However, the present invention can also be applied to a recording apparatus using a so-called full line type recording head in which a large number of ejection portions (nozzles) are arranged along the entire width of the recording medium.

(Tenth embodiment)
As an example, the tenth embodiment of the present invention shown in FIG. 36 will be described below. The first black discharge head 41, the second black discharge head 42, and the color discharge heads 43a, 43b, and 43c are arranged at intervals. Each of the ejection heads 41, 42, 43a, 43b, and 43c has a large number of nozzles arranged along the entire width of the plain paper 1 as a recording medium. The plain paper 1 is perpendicular to the ejection head (in the direction of the arrow). ) Be transported. Each discharge head is provided with an interval, and a ceramic heater 44 as a heating means is provided at this interval. The time (for example, 1.5 seconds) required for the plain paper to be conveyed by this interval is the time from when an ink droplet is ejected at a certain point until the next ink droplet is ejected. According to the present embodiment, when a certain point of the plain paper 1 as a recording medium is considered, processing substantially similar to that of the fourth embodiment shown in FIG. 29 is performed. In addition, the ceramic heater 44 may be provided so as to be located directly under the discharge heads 41 and 42 (dotted line portion). Further, it is more effective to provide the ceramic heater 45 so as to heat even after the color ink is discharged.

(Eleventh embodiment)
The eleventh embodiment of the present invention shown in FIG. 37 has a configuration in which one black discharge head is omitted from the tenth embodiment. That is, the black ejection head 46 and the color ejection heads 47a, 47b, and 47c are arranged at intervals, and considering a certain point on the plain paper 1 that is a recording medium, the sixth embodiment shown in FIG. Processing substantially similar to the example is performed. The ceramic heater 48 can also be provided so as to be located immediately below the black discharge head 46 (dotted line portion) and after the color discharge heads 47a, 47b, 47c.

  In this way, a full line head is arranged corresponding to the ink discharge point, a space is formed between the full line heads in accordance with a desired time interval of ink discharge and the conveyance speed of plain paper 1, and heating means is provided in the space. May be provided. Accordingly, it is possible to configure a recording apparatus that performs substantially the same processing corresponding to each of the embodiments using the serial type recording head.

  As shown in FIG. 38, the ceramic heater H of each of the above embodiments is preferably covered with a heat insulating material 49. Further, instead of the ceramic heater H, halogen lamp heaters 187a and 187b as shown in FIG. 20 and other various heating means can be used. Note that both the configuration using the ceramic heater and the configuration using the halogen lamp heater can be applied to both the serial type and the full line type.

(Twelfth embodiment)
In the first embodiment and the like, an example in which a black image is recorded by two main scans shown in FIG. In the example shown above, by recording the black image twice, the density of black can be increased, the fixing property of black is improved, and the ink interference between the dots recorded adjacent to each other is suppressed. In this way, the black image may be thinned out in each main scan so as to be completed in two main scans.

  FIG. 39 is a diagram for explaining an example in which recording is performed by thinning an image, and recording is performed so as to be complementary in two main scanning recordings. This figure schematically shows the head 702 and the nozzles 801 arranged in the head. For simplification of explanation, this figure shows a configuration in which eight nozzles are arranged in the head.

  FIG. 39A is a diagram showing a head and a recording position by the head, and dots are formed at intersections of the lattice of FIG. 39A by ink droplets ejected from the head. FIGS. 39B and 39C show examples of dot positions when printing is performed with thinning out. FIG. 39B and FIG. 39C are examples in which dots are thinned out in a checker pattern, and the thinning positions are different from each other. Since the patterns thinned out and recorded in FIGS. 39 (b) and 39 (c) are complementary patterns, recording is completed by thinning out each pattern and recording at the same position. The

  In the drawing, in order to make it easy to understand the dots recorded in each scan, the dot positions to be recorded are shown by circles with hatched lines in FIG. 39 (b), and are not hatched in FIG. 39 (c). Shown in a circle.

  A method of performing thinning recording with such a pattern and recording an image by two main scans is a black recording as in the first embodiment (as shown in FIGS. 25A and 25B). (Main scanning recording), the number of dots recorded by one main scanning can be reduced. Therefore, the amount of ink ejected onto the paper surface can be reduced, the fixing property is further improved, and the interference caused by the ink droplets between adjacent dots can be reduced, thereby achieving high image quality.

  Note that the circles shown in FIG. 39 simply indicate the dot positions and do not represent the size of the dots actually formed on the paper. The pattern to be thinned out is not limited to this.

(Thirteenth embodiment)
Next, a thirteenth embodiment corresponding to the multi-scan recording system will be described. When using a multi-nozzle head with a plurality of nozzles arranged in the inkjet recording method, slight variations in the nozzles that occur in the multi-head manufacturing process affect the ink ejection amount and direction of each nozzle, resulting in a printed image. Density unevenness may occur. In order to reduce such density unevenness, there is a recording method called multi-scan as a method for completing an image by a plurality of main scans.

  A specific example of multi-scan will be described with reference to FIG. In FIG. 40A, the multi-nozzle head 702 is the same as that in FIG. 35 described above, and is configured by eight multi-nozzles 801 for simplification of description. Further, in this drawing, in order to make it easy to understand the state of ink droplets 802 (hereinafter also referred to as “droplets”) ejected from each nozzle 801, a state in which the multi-nozzle head 702 is confirmed from the side is schematically shown. Yes. The applied recording apparatus is the serial type recording apparatus shown in FIG. 21 described above, and a detailed description thereof will be omitted. As shown in FIG. 40, the ink droplets 802 ejected from the head 702 are ideally ejected in a uniform direction with a uniform ejection amount of the ink droplets ejected from each nozzle. If ejection is performed in this manner, dots of a size aligned on the paper surface are landed at normal positions as shown in FIG. 40 (b), and the overall density as shown in FIG. 40 (c). A uniform image without unevenness can be obtained.

  However, in actuality, as described above, each nozzle has a variation, and if it is printed as it is as described above, it is discharged from each nozzle as shown in FIG. Variations in the size and orientation of the ink drop occur. That is, on the paper surface, the ink drop is landed as shown in FIG. According to this figure, there is a blank portion that does not periodically satisfy the area factor of 100% in the head main scanning direction, or conversely, dots overlap more than necessary, or are seen in the center of this figure. Some white streaks have occurred. A collection of dots landed in such a state has a density distribution as shown in FIG. 41C with respect to the nozzle arrangement direction. As a result, these phenomena are regarded as density unevenness as far as the eyes of the human are concerned. Perceived.

  Next, a multi-scan method proposed as a countermeasure against such density unevenness will be described with reference to FIGS.

  According to this method, the multi-nozzle head 702 is scanned three times to complete the print area shown in FIGS. 42 and 43, and the half of the 4-pixel unit area is completed in two passes. In this case, the 8 nozzles of the multi-head are divided into groups of 4 upper nozzles and 4 lower nozzles. The dots that one nozzle prints in one scan are obtained by thinning out prescribed image data by about half according to a predetermined image data arrangement. Then, in the second scan, dots are embedded in the remaining half of the image data to complete printing of the 4-pixel unit area. The printing method as described above is hereinafter referred to as a divided printing method. If such a divided printing method is used, even if the same print head as that shown in FIG. 41 is used, the influence on the print image specific to each nozzle is halved. Therefore, the printed image is as shown in FIGS. 42B and 43B, and the black and white stripes as shown in FIG. 41B are not so noticeable. Therefore, the density unevenness is considerably reduced as compared with the case of FIG. 41 as shown in FIG.

(Fourteenth embodiment)
Next, a fourteenth embodiment of the present invention using an ink jet recording head capable of changing the size of ink droplets will be described.

  2. Description of the Related Art Conventionally, there has been known a technique for achieving gradation recording by making it possible to change the size of ejected ink droplets and ejecting ink droplets of different sizes. As a method, for example, in a method in which thermal energy is applied to ink to generate bubbles and ink is ejected, by providing a plurality of heaters in the nozzle and controlling the driving of the plurality of heaters, There is a technique for ejecting ink droplets of different sizes. According to this technology, it is possible to form a small dot by driving only a predetermined one of a plurality of heaters to eject ink droplets with a small ejection amount, and a large ejection amount by driving all of the plurality of heaters. Large dots can be formed by ejecting ink droplets.

  FIG. 44 shows an example in which an image is formed by two main scanning recordings using a recording head capable of discharging ink having different ink droplet sizes. This figure schematically shows the head 702 and the nozzles 801 arranged in the head. For simplification of explanation, this figure shows a configuration in which eight nozzles are arranged in the head.

  FIG. 44A is a diagram showing a head and a recording position by the head, and dots are formed at intersections of the lattice of FIG. 44A by ink droplets ejected from the head. 44 (b) and 44 (c) show examples of dot arrangements for recording in different main scans. FIG. 44B shows an example in which a dot 360 having a large dot size is recorded at a position where dots are thinned out in a checker pattern, and a dot 361 having a small dot size is recorded at a position not recorded by the dot 360. The dots 360 and 361 are recorded in a pattern that is complementary to each other. Similarly in FIG. 44 (c), the dot 360 indicates a dot having a large dot size, the dot 361 indicates a dot having a small dot size, and each dot has a pattern opposite to that in FIG. 44 (b). The state recorded in the position thinned out by is shown. Accordingly, when attention is paid to the dot 360 having a large dot size, the dots are recorded so as to be complementary by two recording scans (FIGS. 44B and 44C), and the dot 361 having a small dot size is also 2 Recording is performed in a complementary manner by one recording scan.

  If the above-described recording method is applied to the technique of the present invention that suppresses the penetration of ink into the recording paper using the heater, the amount of ink ejected on the recording paper surface by one main scanning can be reduced. It can be suppressed. In addition, since dots with a large dot size and dots with a small dot size are ejected alternately, the area factor of dots recorded in one main scan can be reduced, and the fixing property is further improved, resulting in a problem of density reduction. A solved recorded image can be formed.

  Further, the recording sequence applied to the present invention is not limited to the example shown in FIG. 44, and may be configured to record in a pattern as shown in FIG. 45, for example. FIG. 45 is a diagram for explaining an example in which an image is formed by two main scanning recordings using the recording head capable of ejecting ink droplets having different dot sizes as described above.

  FIG. 45A and FIG. 45B show examples of dot arrangements for recording in different main scans. The example shown in FIG. 45 differs from the example shown in FIG. 44 in the pattern in which dots having a large dot size and dots having a small dot size are arranged. In the example shown in FIG. 45, dots 370 having a large dot size and dots 371 having a small dot size are recorded according to a pattern that is alternately recorded along the arrangement direction of the nozzles 801.

  When the recording sequence as shown in FIG. 45 is also applied to a technique for suppressing ink permeation into the recording paper using the heater of the present invention, the amount of ink ejected on the recording paper surface by one main scanning is reduced. It is possible to form a recorded image that is suppressed, has excellent fixability, and solves the problem of density reduction.

  In the above description, the method of ejecting ink droplets having different dot sizes by driving a plurality of heaters provided in each nozzle is taken as an example. However, the present invention can also be applied to a configuration in which a single ejection unit is provided for each nozzle and the dot size can be changed by controlling a signal for driving the ejection unit.

(15th Example)
Next, as the ink, the concentration of the colorant such as a dye is thinned to 1/3 to 1/6 of that of a normal ink, and the light ink having a dye concentration of 0.3 to 1.2% is used. An example of executing the recording method will be described. According to the present invention, in order to suppress permeation of the permeable ink by the heat of the heater, for example, when a light ink having a density of 1/3 is used, a low duty (100% or less) of a single dot without performing overstrike When printing with, the amount of spreading in the horizontal direction is reduced and the dot diameter is reduced. As a result, as shown in FIG. 49, the OD (optical density) of the highlight portion is lowered, and the graininess is reduced. On the other hand, in printing with high duty (greater than 100% and less than 300%), overprinting of light ink is performed, and combined with the effect of the overstrike interval of about 1 second, the OD is high as shown in FIG. In addition, the OD of the solid portion is high and printing with very high gradation is possible.

  In this embodiment, light ink can be overprinted up to three times by three main scans. This is because the water in the ink evaporates due to the heating of the heater, so that the ink can be sufficiently tolerated even with plain paper. Further, since the ink is semi-permeable, the fixability is good and the OD of the solid portion is high.

  The content of acetylenol, which is a nonionic surfactant in the light ink, is preferably 0.2 to 0.7%, and more preferably 0.3 to 0.5%. In the above embodiment, the overstrike of light inks has been described, but recording may be performed by combining dark ink and light ink.

  Next, further development related to the technical idea of the present invention will be described below.

  For recording using only black ink, the penetration may be adjusted according to the recording speed and image density of the apparatus. If priority is given to the recording speed, use a highly penetrating ink of the semi-penetrating ink according to the present invention so that the fixing time does not show through when the next sheet is discharged. Is preferred. Conversely, if priority is given to image density, it is preferable that the semipermeable ink has a low permeability. As a condition of the heater for obtaining a more preferable effect within the scope of this technical idea, it is preferable that a power of 10 w · sec acts on an image as shown in FIGS. 15 and 18. Further, when the present invention is applied to a color printer, if emphasis is placed on the boundary between different colors, it is preferable that the black ink has high permeability within the range of the semi-permeable ink of the technical idea of the present invention. The color ink may be made more highly penetrating, for example, by setting the acetylenol amount to 1%. However, in order to further improve the image quality, the color ink is also within the scope of the technical idea of the present invention. It is preferable to reduce the property. At this time, when the recording image is divided and recorded by multi-pass, the heater condition is preferable because the power can be reduced, and higher density and higher image quality can be obtained. Of the plurality of embodiments described above, combinations of at least two embodiments are also included in the scope of the present invention.

It is explanatory drawing which shows the technical idea of this invention. FIG. 4 is a relationship diagram between the content ratio of acetylenol in an ink used in the present invention and a coefficient Ka. It is explanatory drawing which shows the penetration speed of the ink used in this invention. FIG. 4 is a relationship diagram between the penetrability (the content of acetylenol) of ink used in the present invention and various printing characteristics. It is explanatory drawing which shows the ink droplet formation state in the division | segmentation printing system of the inkjet recording method of this invention. It is the table | surface and explanatory drawing which show the ink droplet shape in a division | segmentation printing system. It is explanatory drawing which shows the ink droplet formation state in the overlapping printing system of an inkjet recording method. It is explanatory drawing which shows the ink droplet formation state in the suitable overprinting printing system of an inkjet recording method. It is explanatory drawing which shows the ink droplet formation state in the small droplet printing system of an inkjet recording method. It is explanatory drawing which shows the ink droplet formation state in the multiple times printing method of an inkjet recording method. It is explanatory drawing which shows the ink droplet formation state in the suitable multiple times recording printing system of an inkjet recording method. It is explanatory drawing which shows the pigment-containing ink droplet formation state of the inkjet recording method. It is a perspective view of an example of a recording device used in the present invention. FIG. 5 is a relationship diagram between acetylenol content and OD value in a plurality of recordings with a short recording interval. FIG. 6 is a relationship diagram between a power value and an OD value in a plurality of recordings with a short recording interval. FIG. 6 is a relationship diagram between the acetylenol content in a plurality of recordings with a short recording interval and the difference in OD value between heating and heating. FIG. 6 is a relationship diagram between acetylenol content and OD value in a plurality of recordings with a long recording interval. FIG. 6 is a relationship diagram between a power value and an OD value in a plurality of recordings with a long recording interval. FIG. 6 is a relationship diagram between the acetylenol content in a plurality of recordings with a long recording interval and the difference in OD value between heating and heating. It is the schematic which shows the structure of a full line type inkjet recording device. It is the schematic which shows the structure of a serial type inkjet recording device. FIG. 20 is a schematic diagram illustrating a head configuration of the ink jet recording apparatus of FIG. 19. It is explanatory drawing which shows the printing state by the inkjet recording device of FIG. It is explanatory drawing which shows another printing state by the inkjet recording device of FIG. It is explanatory drawing which shows the ink droplet formation state in the 1st Example of the inkjet recording method of this invention. It is explanatory drawing which shows a 1st Example. It is explanatory drawing which shows a 2nd Example. It is explanatory drawing which shows a 3rd Example. It is explanatory drawing which shows a 4th Example. It is explanatory drawing which shows a 5th Example. It is explanatory drawing which shows a 6th Example. It is explanatory drawing which shows a 7th Example. It is explanatory drawing which shows the 8th Example. It is explanatory drawing which shows a 9th Example. It is a perspective view of another example of the recording apparatus used in the present invention. It is explanatory drawing which shows a 10th Example. It is explanatory drawing which shows the 11th Example. It is sectional drawing of the ceramic heater which is a heating means. It is explanatory drawing which shows a 12th Example. It is explanatory drawing which shows a 13th Example. It is explanatory drawing which shows an example of a printing defect state. It is explanatory drawing which shows the suitable division | segmentation printing method. It is explanatory drawing which shows another example of the suitable division | segmentation printing method. It is explanatory drawing which shows the 14th Example. It is explanatory drawing which shows the example of a change of 14th Example. It is explanatory drawing which shows the ink droplet formation state in the conventional inkjet recording method. FIG. 4 is a relationship diagram between the acetylenol content of the ink and the surface tension. It is the figure which showed the relationship of tw and ts with respect to acetylenol content of an ink. It is explanatory drawing which shows a 15th Example. It is explanatory drawing about the mechanism of the phenomenon at the time of using semipermeable ink.

Explanation of symbols

1 Plain paper (recording medium)
2 First ink droplet 3 Heater 5 Paper feed unit 6 Printing unit 7 Carriage 8, 40 Recording head 9 Guide rails 10, 44, 45, 48 Ceramic heater (heating means)
11a, 11b First ink droplets 14, 18, 21, 25, 29, 31, 33, 36, 38 Black recording dots 15, 19, 22, 26, 30, 32, 35, 37, 39 Color recording dots 16a, 16b, 20a, 20b, 23, 27 Black ink droplet 41 First black ejection head 42 Second black ejection head 43a, 43b, 43c, 47a, 47b, 47c Color ejection head 46 Black ejection head 101 Grid 102, 110, 132, 134 Dots 103, 104, 111, 112, 113, 131, 133 Ink droplets 181 Conveying belt 182, 183 Roller 184 Registration roller 185 Stocker 186 Guides 187a, 187b Halogen lamp heaters 290, 291, 301, 302, 303 Recording area 360, 361, 370, 371 dots 70 1 Head cartridge 702 Multi-nozzle head 703 Conveying roller 704 Auxiliary roller 705 Feeding roller 706 Carriage 707 Print paper 710 Heater 801 Multi-nozzle 802 Ink droplets K1, K2, K3 Black discharge portions C, C1, C2 Cyan discharge portions M, M1, M2 Magenta discharge part Y, Y1, Y2 Yellow discharge part H Ceramic heater P Recording head

Claims (6)

A step of discharging black ink having a surfactant content of 0.2 to 0.7% by weight based on the total weight of the ink from a black ink discharge head to a recording medium;
Heating the area where the black ink has been ejected on the recording medium conveyed to a position downstream of the black ink ejection head in the conveying direction of the recording medium;
Discharging a color ink having a surfactant content greater than 0.7% by weight based on the total weight of the ink from a color ink discharge head onto the recording medium;
Heating the area where the color ink is ejected on the recording medium conveyed to a position downstream of the color ink ejection head in the conveying direction of the recording medium,
The inkjet recording method, wherein the surfactant is ethylene oxide-2,4,7,9-tetramethyl-5-decyne-4,7-diol.   The penetration depth of the black ink into the recording medium heated by the heating step is shallower than the penetration depth of the black ink into the recording medium when the heating step is not performed. The ink jet recording method according to claim 1.   2. The ink jet recording method according to claim 1, wherein the content of the surfactant in the black ink is 0.35 to 0.50 wt% with respect to the total weight of the ink.   The inkjet recording method according to claim 1, wherein the black ink is a self-dispersing pigment ink that does not contain a dispersant.   The inkjet recording method according to claim 1, wherein the heating in the heating step is performed at least after the black ink is discharged and before the rapid swelling start time ts is reached. . The quick swelling starting time ts is characterized by an increase in the amount of penetration of the ink ejected on the recording medium is a time required to rapidly jet recording method according to claim 5.

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