JP2005096222A - Inkjet recording device and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet recording device and method that prevent a degradation of image quality due to the influence of air streams occurring during discharge when ink droplets are discharged by high frequency vibration and realizes high quality image recording. <P>SOLUTION: The inkjet recording device 100 records an image on a recording medium 1 by discharging ink droplets from nozzles while making a recording head 5 having a plurality of nozzles relatively mainly scan in a direction different from the direction of arrangement of the nozzles. The recording device has a means to thin out image data to be recorded in a main scanning direction and a driving control means for controlling the driving of the recording head 5 to ensure that the image data to be recorded is recorded by a plurality of main scans on the basis of the image data thinned out in one main scanning of the recording head 5. The quantity of ink droplets discharged from the nozzles is 0.7 pl or higher and 1.5 pl or lower. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an ink jet recording apparatus and an ink jet recording method for recording an image on a recording medium by ejecting ink droplets from nozzles of a recording head.

  In an ink jet recording apparatus, it is important for ensuring uniformity of an image that ink droplets ejected from a nozzle of a recording head land on a target position of a recording medium.

Patent Document 1 proposes an ink jet recording apparatus that improves the landing accuracy by setting the ink droplet amount, the interval between the recording medium and the nozzle of the recording head, and the ejection speed of the ink droplets within a predetermined range. Yes. However, in such an ink jet recording apparatus, there is no description about a driving frequency or a method of ejecting ink droplets.
JP 2000-255057 A

  In recent years, as a trend of inkjet recording apparatuses, in order to record higher quality images, nozzle density and ink droplet size have been reduced. At the same time, a higher recording speed is also demanded. For this purpose, the drive frequency is increased and the number of nozzles is increased.

  While the present inventor has been studying such high image quality and high recording speed, when an image is recorded on a recording medium by ejecting ink droplets by high-frequency driving, the ink droplets continuously flow. Since it becomes closer to the (group), the influence of the air flow generated with the ejected ink droplets becomes large. In particular, when the amount of ink droplets is reduced to about 1 pl (picoliter), the influence of the air flow It has been found that there is a problem that the landing position of the ink droplets ejected from the nozzles is shifted and the image quality is deteriorated.

  That is, when an ink droplet composed of a small droplet of about 1 pl is ejected from one nozzle by high frequency driving, the speed drop due to the air resistance of the first droplet with respect to the second and subsequent droplets is large, and the second droplet is first. And the air flow generated by the ink droplets collides with the recording medium and flows in the direction of driving the adjacent ink droplets outward in the main scanning direction (direction in which the dot interval is widened). For example, when 10 droplets are ejected in succession along the main scanning direction from one nozzle, except for the 1st and 10th droplets, the ink droplets on both sides are affected by the airflow, but the 1st and 10th droplets on both ends Since the eyes are affected by the airflow only from one side, the dots are shifted in the direction in which the dot interval is widened, and unevenness of the image occurs. Since it does not deviate as a whole, it depends on the image data, so that correction by shifting the discharge timing is extremely difficult.

  Accordingly, an object of the present invention is to provide an ink jet recording apparatus and an ink jet which can prevent image quality deterioration due to the influence of an air flow generated at the time of ejection when ink droplets are ejected by high frequency driving and realize high image quality image recording. It is to provide a recording method.

  Other problems of the present invention will become apparent from the following description.

  The above problems are solved by the following inventions.

  According to the first aspect of the present invention, a recording head having a plurality of nozzles is ejected ink droplets from the nozzles while performing main scanning relative to the recording medium in a direction different from the arrangement direction of the nozzles. An ink jet recording apparatus for recording an image on the recording medium, wherein the image data to be recorded in the main scanning direction is thinned by the thinning means in one main scanning of the recording head. An ink droplet ejected from the nozzle, and a drive control means for controlling the drive of the recording head so that the image data to be recorded is recorded in a plurality of main scans based on the image data. Is an ink jet recording apparatus having a droplet amount of 0.7 pl to 1.5 pl.

According to a second aspect of the present invention, when the drive frequency in a state where the image data is thinned out by the thinning means is Y (kHz) and the droplet amount of the ink droplet is X (pl), the following relational expression is obtained. 2. The ink jet recording apparatus according to claim 1, wherein:
Y ≦ −40X ² + 115X−45

  A third aspect of the present invention is the ink jet recording apparatus according to the second aspect, wherein the drive frequency Y (kHz) in a state where the image data is thinned out by the thinning means is 10 ≦ Y.

  The invention according to claim 4 has a thinning mode for recording an image based on the image data thinned out by the thinning means and a non-thinning mode for recording an image based on image data not thinned out by the image data. 4. The ink jet recording apparatus according to claim 1, further comprising selection means for selecting the thinning mode and the non-thinning mode.

According to a fifth aspect of the present invention, when the driving frequency in the non-thinning mode is Z (kHz) and the droplet amount of the ink droplet is X (pl), the following relational expression is satisfied. 4. An ink jet recording apparatus according to item 4.
Z ≧ −60X ² + 165X−70

  The invention according to claim 6 is the ink jet recording apparatus according to claim 4 or 5, wherein the thinning mode and the non-thinning mode have the same moving speed of the recording head in the main scanning direction.

  A seventh aspect of the present invention is the ink jet recording apparatus according to any one of the first to sixth aspects, wherein the recording head is an on-demand type recording head.

  In the invention according to claim 8, by ejecting ink droplets from the nozzles while scanning a recording head having a plurality of nozzles relative to the recording medium in a direction different from the arrangement direction of the nozzles, An ink jet recording method for recording an image on the recording medium, wherein, in one main scan of the recording head, image data to be recorded is thinned out in the main scan direction, and ink droplets ejected from the nozzles An ink jet recording method for recording the image data to be recorded in a plurality of main scans based on the thinned image data with a droplet amount of 0.7 pl to 1.5 pl It is.

The invention according to claim 9 satisfies the following relational expression, where Y (kHz) is the driving frequency in the state where the image data is thinned out, and X (pl) is the droplet amount of the ink droplets. 9. The ink jet recording method according to claim 8, wherein
Y ≦ −40X ² + 115X−45

  A tenth aspect of the present invention is the ink jet recording method according to the ninth aspect, wherein the drive frequency Y (kHz) in a state where the image data is thinned is 10 ≦ Y.

  The invention according to claim 11 is the ink jet recording method according to claim 8, 9 or 10, characterized in that the recording head is an on-demand type recording head.

  According to the present invention, it is possible to provide an ink jet recording apparatus and an ink jet recording method capable of preventing deterioration in image quality due to the influence of an air flow generated during ejection when ink droplets are ejected by high frequency driving.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  First, a schematic configuration of an ink jet recording apparatus that can be used in the present invention will be described.

  FIG. 1 is a schematic configuration diagram illustrating an example of an ink jet recording apparatus. In the figure, 100 is an ink jet recording apparatus, 1 is a roll-shaped recording medium, and 2a is a recording medium conveying roller for conveying the recording medium 1 in the direction of the arrow X. The transport roller 2a is configured to be drivable by the drive mechanism 3.

  As shown in the figure, the drive mechanism 3 includes a conveyance motor 30, a drive pulley 32 connected to the conveyance motor 30 via a drive shaft 31, and a driven force that transmits the driving force of the drive pulley 32 via a belt 33. The driven pulley 34 and the conveying roller 2 a are connected by the rotation shaft 4. Reference numeral 2b denotes a driven roller that presses the recording medium 1 against the conveying roller 2a.

  In the figure, reference numeral 5 denotes a recording head for recording on the recording medium 1. A preferred recording head used in the present invention includes a single recording head having a plurality of nozzles that discharge monochromatic ink, a plurality of recording heads that are formed by arranging a plurality of nozzles that discharge Y, M, C, and K inks, For the same color ink, there are exemplified a plurality of recording heads in which a plurality of nozzles for discharging dark and light inks having different concentrations of colorants such as dyes and pigments are arranged.

  In the case of a recording head having a plurality of ink discharge ports for discharging the single color ink described above, the recording head 5 can be configured with only one head. In the present embodiment, an example using a single recording head having a plurality of nozzles that discharge K ink will be described.

  The recording head 5 is arranged along the sub-scanning direction, which is the conveyance direction of the recording medium 1, with, for example, 256 nozzles opened at a surface facing the recording medium 1 at intervals of 70 μm (360 dpi). By applying a drive waveform to the recording head 5, each nozzle is configured to be driven independently by deformation of the piezoelectric element.

  In the recording head 5, the method for ejecting ink from each nozzle as ink droplets is not limited to that using a piezoelectric element, but the ink is discharged from each nozzle, such as an electric field type recording head or a bubble burst type recording head. There is no particular limitation as long as it can be ejected as ink droplets.

  The recording head 5 is mounted on a carriage 6, and the carriage 6 is configured to be able to scan in the main scanning direction orthogonal to the sub-scanning direction that is the conveyance direction of the recording medium 1 by the driving force of the driving motor 7. Yes. Specifically, the bottom surface of the carriage 6 is fixed to a scanning belt 8, and the scanning belt 8 is stretched over a driving pulley 9 and a driven pulley 10, and the driving pulley 9 is connected to a driving shaft 11 of a driving motor 7. Yes. Therefore, when the drive motor 7 is driven, the scanning belt 8 moves and the carriage 6 can move in the main scanning direction.

  In order to detect the amount of movement of the carriage, a linear encoder (not shown) is provided along the main scanning direction, and a linear encoder signal is read by a sensor provided on the carriage 6 according to the movement of the carriage 6. doing.

  Reference numeral 12 denotes a scanning guide for restricting the movement of the carriage 6 in the main scanning direction, and normally two restriction rods are used.

  In order to perform recording using the inkjet recording apparatus 100 having the above configuration, the carriage 6 is scanned in the main scanning direction while being regulated by the scanning guide 12. At this time, since the recording head 5 moves while ejecting ink from the nozzles toward the recording medium 1, recording in the main scanning direction can be performed on the recording medium 1. When one main scanning recording by the recording head 5 is finished, the recording medium 1 made of a long sheet wound in a roll shape is conveyed by a predetermined amount in the X direction which is the sub-scanning direction by the recording medium conveying roller 2a, and thereafter Then, the carriage 6 is again scanned in the main scanning direction to perform recording in the main scanning direction by the recording head 5. A predetermined image is obtained by repeating the above operation.

  Here, the recording head 5 is moved in the main scanning direction and the recording medium 1 is moved in the sub-scanning direction. However, in the ink jet recording apparatus, the recording head 5 is different from the nozzle arrangement direction. What is necessary is just to scan relatively with respect to the recording medium 1 to a direction, and is not restricted to the example of illustration.

  In the present invention, in one main scan of the recording head 5, the image data to be recorded is thinned out in the main scan direction, so that the image data to be recorded is a plurality of times based on the thinned image data. The drive of the recording head 5 is controlled so that recording is performed separately in the main scanning. However, the ink droplets ejected from the nozzles of the recording head 5 during the image recording have a droplet amount of 0.7 pl (picoliter) or more and 1.5 pl or less.

  The thinning of image data is generally performed by thinning prescribed image data according to a predetermined image data array. There are various thinning patterns of image data, but any thinning pattern may be used in the present invention.

  For example, FIG. 2A shows an example in which the image data recorded in the main scanning direction from one nozzle is thinned out to 1 on / 3 off. Circles in the figure indicate dots formed by ink droplets, and the same oblique line pattern is dots recorded at the same time. This is because recording is performed every three pixels in the main scanning direction by the recording head 5, and then one of the remaining three pixels is complementarily recorded by the next main scanning, and the remaining remaining is complementarily by the next main scanning. By recording one of the two pixels and further recording the remaining one pixel complementarily by the next main scanning, all the pixels are filled.

  Further, FIG. 2B shows an example in which image data recorded in the main scanning direction from one nozzle is thinned out to 1/2 to 1 on / 1 off. After recording every other pixel in the main scanning direction by the recording head 5, all the pixels are filled by recording the remaining one pixel complementarily by the next main scanning.

  FIG. 2C shows a case of recording without thinning out for comparison, and recording is performed so that one main scanning line is completely filled by one main scanning.

  Note that the driving frequency by thinning out such image data depends on the moving speed of the recording head 5 and the dot interval printed in one main scan with a solid image, or on the frequency of the driving signal for ejection. Can be confirmed.

  Further, when the remaining pixels are complementarily filled in the second and subsequent main scans, the main scan is repeated in a state where the conveyance of the recording medium 1 is stopped, so that the same nozzle is used for the first main scan. Alternatively, the recording medium 1 may be transported by a small amount in the nozzle scanning pitch unit in the sub-scanning direction, and may be performed by another nozzle.

  In the example shown in FIG. 2, attention is paid to one main scanning line recorded by one nozzle of the recording head 5, but the recording head 5 performs the number of nozzles in the nozzle arrangement direction (sub-scanning direction) by one main scanning. Minute dots can be recorded. Accordingly, when executing the thinning pattern as exemplified in FIGS. 2A and 2B, only thinning in the main scanning direction may be performed, and an image may be recorded without thinning in the sub scanning direction. However, the image may be recorded by thinning in the sub-scanning direction as well as thinning in the main scanning direction.

  An example of the latter is shown in FIG. This is a pattern in which image data is thinned out so that a vertical (sub-scanning direction) and a horizontal (main scanning direction) form a staggered pattern for each pixel. That is, this is an example in which the thinning pattern shown in FIG. 2B is also applied in the sub-scanning direction. Here, pixels are filled in a staggered pattern for each pixel vertically and horizontally by the first main scanning (this is indicated by white circles), and pixels are obtained by the first main scanning by the second main scanning. An image of a predetermined area is recorded by filling the remaining pixels of the inverted staggered pattern that are not filled (indicated by hatching). Also in this case, the nozzle for the second main scan may be the same as the nozzle for the first main scan, or may be a different nozzle.

  It is preferable to perform thinning in the sub-scanning direction in this way because the influence of the airflow due to ink droplets can be further reduced.

  Further, the thinning pattern is not limited to the regular thinning pattern described above, but may be thinned so as to be an irregular thinning pattern in the main scanning direction or in the main scanning direction and the sub-scanning direction. Good. However, regular thinning is preferable because the influence of airflow can be reduced on average.

  By thinning and recording the image data as described above, it is possible to record a high-quality image by preventing the landing deviation of the ink droplets. The inventor presumes the reason as follows. .

  By thinning and recording the image data to be recorded in the main scanning direction, the distance between the ink droplets in the main scanning direction at the time of one main scanning ejection increases, so that the recording medium 1 and the recording head 5 The ink droplet density in the space between the nozzles is reduced, and the influence of the airflow generated with the ejection of the ink droplets is reduced.

  In addition, since the driving frequency is substantially reduced by thinning and recording in the main scanning direction without changing the main scanning speed of the recording head 5, in the space between the recording medium 1 and the nozzles of the recording head 5. The ink droplet density per unit time is reduced, and the influence of the airflow generated along with the ejection of the ink droplets is reduced.

In the present invention, it is preferable that the following relational expression is satisfied, where Y (kHz) is the driving frequency when the image data is thinned out by the thinning means, and X (pl) is the amount of ink droplets.
Y ≦ −40X ² + 115X−45

  When Y and X satisfy the above relational expression, it is possible to effectively reduce the influence of airflow caused by ink droplets.

  However, the amount of ink droplets is a droplet amount of 0.7 pl to 1.5 pl as described above. If it is smaller than 0.7 pl, the ink droplets are too small, so that landing deviation increases even if the image data is thinned out.

  On the other hand, when the value exceeds 1.5 pl, the dot shape on the recording medium becomes large and the image quality becomes conspicuous, and the resolution and gradation are also deteriorated, thereby degrading the image quality. Furthermore, when the droplet amount exceeds 1.5 pl, the total amount of ink droplets (liquid amount per unit area) ejected to a recording medium necessary to obtain the same image density increases. This is because it is empirically known that the dot diameter on the recording medium is not proportional to the volume of the ink droplet but is approximately proportional to the diameter of the ink droplet. Therefore, when the recording is performed by increasing the resolution with an ink droplet having a small droplet amount of 1.5 pl or less as in the present invention, the droplet amount per unit area required to obtain an image having the same density is reduced. .

  As a result, the range for selecting the recording medium becomes wider. That is, it is possible to use a recording medium with little paper dust that contaminates the nozzle surface of the recording head, or a recording medium with low rigidity and curl. Further, since the total amount of ink droplets ejected onto the recording medium is small, the number of accidents where the recording medium floats by absorbing ink and contacts the nozzle surface of the recording head is reduced. From this point of view, the present invention is particularly effective for plain paper.

  The lower limit of the drive frequency Y (kHz) in a state where the image data is thinned out by the thinning means is preferably 10 ≦ Y. Thus, by setting the lower limit of the drive frequency Y in a state where the image data is thinned out to 10 kHz, it is possible to suppress a decrease in recording speed.

  The inkjet recording apparatus according to the present invention includes a thinning mode for recording an image by thinning out the image data as described above, and a normal mode (non-thinning mode) for recording an image without thinning out the image data. It is preferable to selectively switch between the thinning mode and the normal mode by a selection switch switching operation by an operator or the like. Select the thinning mode if you want to record high-quality images with priority on image quality and without ink droplet landing deviation, and do not perform thinning if you want to prioritize recording time over image quality The user-friendliness can be improved by selecting the mode.

In the case of such an ink jet recording apparatus, when the drive frequency in the normal mode in which image data is not thinned is Z (kHz) and the ink droplet amount is X (pl), the following relational expression is satisfied. It is preferable.
Z ≧ −60X ² + 165X−70

When Z and X satisfy the above relational expression, the recording speed can be increased. In this case, the landing deviation of ink droplets during image recording increases, but the image quality improvement effect obtained by switching to the thinning mode that prioritizes image quality becomes significant. In this thinning mode, as described above, the drive frequency Y (kHz) when the image data is thinned out by the thinning means and the droplet amount X (pl) of the ink droplets are Y ≦ −40X ² + 115X−45. By satisfying the relational expression, it becomes a high image quality mode.

Further, in the ink jet recording apparatus having the thinning mode and the normal mode, it is preferable that the moving speed of the recording head 5 in the main scanning direction is the same in both modes. When the moving speed of the recording head 5 in the main scanning direction is the same, it is easy to thin out the image data so as to satisfy the relational expression Y ≦ −40X ² + 115X−45 even when the thinning mode is switched. Since there is no need to change the moving speed, the drive system of the recording head 5 does not need to be particularly complicated.

  The recording head in the ink jet recording apparatus includes an on-demand type and a continuous type. In the present invention, the recording head 5 is preferably an on-demand type recording head. On-demand is more susceptible to airflow because the speed of ink droplets is slower than the continuous type. This is because the continuous type is controlled by charging ink droplets, so that landing deviation can be easily corrected, and the on-demand type can exhibit the effects of the present invention more remarkably.

  In the present invention, the recording head 5 is not limited to one in which the nozzle rows are arranged in a single row along the sub-scanning direction, and the nozzle rows arranged in the sub-scanning direction are arranged in two rows in the main scanning direction. The recording head may be used. In this case, when the interval between the nozzle rows is close to 10 mm or less, the effect of the present invention is great because the influence of the air flow becomes large. As the two nozzle rows, there can be a case where each nozzle row has the same color or a different color.

  If the initial velocity of the ink droplets ejected from the nozzles of the recording head 5 is 10 m / s or less, the image quality is greatly deteriorated due to the landing deviation of the ink droplets, and the effect of the present invention is remarkably obtained. This is preferable.

  Furthermore, in the present invention, the interval (gap interval) between the recording head 5 and the recording medium 1 during image recording is preferably 1.3 mm or less. A narrower interval is preferable because the speed of ink droplets during flight is less likely to decrease, and is less susceptible to airflow.

  While moving the on-demand type recording head in the main scanning direction, changing the ejection interval (driving frequency when the image data is thinned out) and the amount of ink droplets on the stationary recording medium The interval between dots on the recording medium in the main scanning direction at the time of ejection was examined over time. Since the regular dot interval can be obtained from the moving speed and the driving frequency of the recording head, the deviation from the steady state was examined. The results are shown in Table 1.

Recording head moving speed: 105 cm / sec
Gap interval: 1.3mm
Initial velocity of ink droplet: 6m / sec
Judgment criteria are as follows.

○: The dot interval is 1.25 times or less of the steady state Δ: The dot interval exceeds 1.25 times of the steady state and less than 1.75 times ×: The dot interval is 1.75 times or more of the steady state

  As is apparent from Table 1, it can be seen that the ink droplet landing deviation is reduced by thinning out the image data in the range of 0.7 pl to 1.5 pl.

In particular, when the relationship between the driving frequency Y (kHz) in the thinned-out state and the droplet amount X (pl) of the ink droplet is a relationship of Y ≦ −40X ² + 115X−45, the occurrence of landing deviation is almost complete. And favorable results were obtained.

  Note that, under the condition that the amount of ink droplets was 0.5 pl, each drive frequency stalled on the way and did not reach the recording medium.

  In addition, by making the ink droplets small droplets of 1.5 pl or less, the dot shape on the recording medium is also reduced, image quality is reduced, resolution or gradation is increased, and image quality can be improved. Further, by making the ink droplets into small droplets, the total amount of ink droplets (liquid amount per unit area) ejected to the recording medium necessary to obtain the same image density can be reduced. However, when the amount of ink droplets is 2 pl or 4 pl exceeding 1.5 pl, this effect is insufficient.

Schematic configuration diagram showing an example of an ink jet recording apparatus (A) (b) is explanatory drawing which shows the example of a thinning pattern, (c) is explanatory drawing which shows the example which does not thin out Explanatory drawing which shows the other example of a thinning pattern

Explanation of symbols

DESCRIPTION OF SYMBOLS 100: Inkjet recording device 1: Recording medium 2a: Conveyance roller 2b: Driven roller 3: Drive mechanism 30: Conveyance motor 31: Drive shaft 32: Drive pulley 33: Belt 34: Driven pulley 4: Rotating shaft 5: Recording head

Claims (11)

An image is recorded on the recording medium by ejecting ink droplets from the nozzle while causing a recording head having a plurality of nozzles to perform main scanning relatively to the recording medium in a direction different from the nozzle arrangement direction. An ink jet recording apparatus,
Means for thinning out image data to be recorded in the main scanning direction in one main scanning of the recording head;
Drive control means for controlling the drive of the recording head so as to record the image data to be recorded in a plurality of main scans based on the image data thinned out by the thinning means;
An ink jet recording apparatus, wherein the ink droplets ejected from the nozzle have a droplet amount of 0.7 pl to 1.5 pl. The following relational expression is satisfied, where Y (kHz) is a driving frequency in a state where image data is thinned out by the thinning means, and X (pl) is a droplet amount of the ink droplets. The inkjet recording apparatus according to 1.
Y ≦ −40X ² + 115X−45   3. The ink jet recording apparatus according to claim 2, wherein the driving frequency Y (kHz) in a state where image data is thinned out by the thinning means is 10 ≦ Y.   A thinning mode for recording an image based on the image data thinned out by the thinning means; and a non-thinning mode for recording an image based on image data that does not thin out the image data. 4. The ink jet recording apparatus according to claim 1, further comprising selection means for selecting a thinning mode. 5. The ink jet recording apparatus according to claim 4, wherein the following relational expression is satisfied when the driving frequency in the non-thinning mode is Z (kHz) and the droplet amount of the ink droplet is X (pl).
Z ≧ −60X ² + 165X−70   6. The ink jet recording apparatus according to claim 4, wherein the thinning mode and the non-thinning mode have the same moving speed in the main scanning direction of the recording head.   The inkjet recording apparatus according to claim 1, wherein the recording head is an on-demand type recording head. An image is recorded on the recording medium by ejecting ink droplets from the nozzle while scanning a recording head having a plurality of nozzles relative to the recording medium in a direction different from the arrangement direction of the nozzles. An ink jet recording method comprising:
In one main scan of the recording head, image data to be recorded in the direction of the main scan is thinned out,
Based on the thinned image data, the image data to be recorded is divided into a plurality of main scans and the amount of ink droplets ejected from the nozzle is 0.7 pl or more and 1.5 pl or less. An ink jet recording method comprising: The following relational expression is satisfied, where Y (kHz) is a driving frequency in a state where the image data is thinned out, and X (pl) is a droplet amount of the ink droplets. Inkjet recording method.
Y ≦ −40X ² + 115X−45   10. The inkjet recording method according to claim 9, wherein the drive frequency Y (kHz) in a state where the image data is thinned satisfies 10 ≦ Y.   The ink jet recording method according to claim 8, wherein the recording head is an on-demand type recording head.

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