JP3907685B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus using a liquid discharge head having a discharge port for discharging a liquid.

  In this specification, “print” means not only when it forms significant information such as characters and figures, but also when it is manifested so that it can be perceived visually by humans, regardless of significance. Regardless of whether or not, a case where an image, a pattern, a pattern, or the like is widely formed on a print medium or a medium is processed is also included. The “print medium” includes not only paper used in a general printing apparatus but also materials such as cloth, plastic film, metal plate, glass, ceramics, wood, and leather that can accept ink. Further, “ink” (which may be described as “liquid”) should be interpreted broadly in the same way as the definition of “print” above. Any liquid that can be used for forming or processing of print media or ink processing (eg, solidification or insolubilization of colorant in ink applied to print media) Is included.

In recent years, the demand for high gradation color printing has increased due to the spread of digital cameras over the Internet and the like, and along with this, the performance of ink jet printers is being improved. As a means of obtaining high-definition and high-gradation high-quality print images,
(1) Improve the resolution by narrowing the arrangement interval of the ejection ports for ejecting ink.
(2) For a specific color ink, prepare a plurality of print heads that respectively eject a plurality (at least two) of color inks having different ratios of the colorant contained in the color ink, that is, the concentration of the colorant. To improve gradation by selectively overprinting dark ink and light ink
(3) A method is known in which gradation is improved by varying the size of ink droplets ejected from the ejection ports, that is, the amount of ink.

  In a so-called bubble jet (registered trademark) type printer that uses thermal energy as ejection energy for ejecting ink from the ejection port of the print head, generates bubbles in the ink, and uses the foaming pressure at that time, Since the method (3) described above is relatively difficult, the methods (1) and (2) are considered to be particularly effective.

  However, if the method (2) is to be realized, two or more print heads are required for a specific color ink, which increases the cost. Therefore, in the bubble jet (registered trademark) type printer, as shown in (1), the arrangement interval of the ejection ports is narrowed, and the size of each ink droplet ejected from each ejection port is reduced (for example, 10 picoliters or less). ) To improve the resolution is the most desirable and simple method because it hardly increases the manufacturing cost.

  In the case where such small ink droplets are ejected from the ejection port, there is a system in which bubbles that grow due to film boiling as the ink is heated are communicated with the atmosphere via the ejection port, for example. In order to distinguish from the conventional bubble jet (registered trademark) type, which is disclosed in Patent Document 3 and the like, and bubbles that grow by film boiling are not communicated with the atmosphere, they are called so-called bubble through methods. There is a case.

  In the conventional bubble jet (registered trademark) print head that ejects ink droplets without causing bubbles that grow due to film boiling to communicate with the atmosphere, the size of the ink droplets ejected from the ejection port is reduced. The passage cross-sectional area of the ink flow path communicating with the ejection port must be reduced, resulting in a problem that the ejection efficiency is lowered and the ejection speed of ink droplets ejected from the ejection port is lowered. If the discharge speed of ink drops decreases, the discharge direction becomes unstable, and ink thickening occurs as the water vapor evaporates when the print head is paused. May occur, leading to a decrease in reliability.

  In this regard, the bubble-through type print head, in which air bubbles communicate with the atmosphere, can determine the size of ink droplets only by the geometric shape of the ejection port, making it suitable for ejecting small ink droplets, such as temperature High-definition, high-gradation, high-quality print image because it has the advantage that it is less susceptible to the effects of ink droplets and the amount of ink droplets ejected is very stable compared to conventional bubble jet (registered trademark) printheads. Can be obtained relatively easily.

Japanese Patent Laid-Open No. 4-10940 JP-A-4-10941 JP-A-4-10742

  In order to obtain a high-definition and high-gradation high-quality print image, it is preferable to perform printing by ejecting an extremely small amount of ink droplets from one ejection port. In this case, in order to increase the printing speed, it is necessary to eject ink droplets from the ejection ports in a short cycle. In addition, the carriage on which the print head is mounted must be scanned and moved at high speed with respect to the print medium in synchronization with the drive frequency of the print head. From this point of view, it can be said that the bubble-through type is particularly suitable for the ink jet printer.

  When such an ink jet print head is scanned along a print medium at a high speed along with a carriage and ink droplets are continuously ejected from all ejection openings, so-called solid printing is performed on the print medium. The discharge state of the ink droplets is shown in FIG. The scanning movement direction of the print head 1 is a direction perpendicular to the paper surface of FIG. 10, and ejection ports (not shown) are arranged in the left-right direction in the drawing. When the image data is solid, all the ejection energy generation units (not shown) corresponding to the ejection ports are driven at a high driving frequency. For this reason, along with the movement of the ink droplet 3 ejected from the ejection port toward the print medium 2, the viscous air intervening around the ink droplet 3 is also moved by the movement of the ink droplet 3. As a result, the vicinity of the discharge port surface 4 where the discharge port of the print head 1 opens tends to be depressurized more than the surroundings of the print head 1, and the surrounding air flows as an air flow to the depressurized region. It was found that the ink droplets 3 ejected from the ejection ports located at both ends of the outlet in the arrangement direction are attracted to the center side in the arrangement direction and are not ejected to the intended positions with respect to the print medium 2. For this reason, the plurality of ejected droplets at the end are attracted to the center.

  FIG. 11 schematically shows a solid print image formed on the print medium at this time when solid print is performed by scanning movement of the carriage a plurality of times under such a phenomenon. The carriage scans together with the print head from the top to the bottom in the figure. At this time, white stripes 7 are formed between the solid image 5 formed by the previous scanning movement and the solid image 6 formed by the next scanning movement. Will be formed.

  Such inconveniences are particularly noticeable in bubble-through type ink jet printers in which a small interval of ink droplets of 10 picoliters or less can be ejected at a high cycle by a single drive operation with a narrow arrangement interval of ejection openings. This was found by the inventors' investigation.

  FIG. 12 shows the relationship between the ink droplet ejection amount and the edge deflection amount (a half value of the white streak 7) when the ejection port array interval is 21.2 μm (equivalent to 1200 dpi). The reason why such a phenomenon appears is that the ratio of the ink droplet surface area increases due to the relationship between the ink droplet surface area (projected area) with respect to the ink droplet weight, while the size of the ink droplet decreases. This is because the larger the ratio, the more affected.

  In order to prevent such a problem, by increasing the size of the ink droplets ejected from the ejection ports located at both ends in the arrangement direction of the ejection ports, that is, by increasing the inertial mass of the ink droplets, It is also possible to suppress deviations in the ejection trajectory of the ink droplets ejected from the located ejection ports. However, enlarging the ink droplets is an obstacle to forming a high definition and high gradation image. Further, the penetration of ink droplets into the print medium is delayed, and there is a high possibility that the print image will be deteriorated as the print medium swells. Alternatively, it is possible to alleviate the above-described problems by suppressing the driving frequency for the discharge energy generating unit to be low. However, when the drive frequency for the discharge energy generating unit is set low, the printing speed becomes slow, and it becomes impossible to meet the user's need to print out at high speed.

[Object of invention]
An object of the present invention is to discharge ink from discharge ports located at both ends of the arrangement direction even in an ink jet printer that can discharge liquid droplets at a high cycle while scanning in a direction intersecting the print medium conveyance direction. It is an object of the present invention to provide an image forming apparatus in which deviation of ink droplets is suppressed and white stripes are not generated even when a solid print is formed.

An image forming apparatus according to the present invention includes a liquid discharge head that discharges a liquid, a mounting portion of the liquid discharge head, and a conveyance means for the print medium, and the print medium is discharged from the discharge port of the liquid discharge head. image an image forming apparatus for forming on said liquid ejection head includes a plurality of discharge ports you arranged in a predetermined direction, and a plurality of ejection energy generating portion for ejecting liquid from these discharge ports The plurality of discharge ports are located at both ends in the arrangement direction and end discharge port groups composed of a plurality of discharge ports that are involved in image formation, and are positioned in the center in the arrangement direction. is composed of a central discharge port group comprising a plurality of discharge ports involved in the formation of the image, the arrangement interval of the plurality of discharge ports for forming the end portion discharge port group constitutes a pre Symbol central discharge port group wherein more And it is characterized in that it is wider than the array pitch of the outlet.

  In the image forming apparatus according to the present invention, it is preferable that the arrangement interval of the ejection ports constituting the end ejection port group is set 0.1 to 10 μm wider than the arrangement interval of the ejection ports constituting the central ejection port group. . In the case of less than 0.1 μm, the effect of setting the array interval wide becomes extremely small, and it becomes difficult to ensure the positional accuracy in the manufacturing process. On the other hand, if the thickness exceeds 10 μm, the distance between adjacent ejection ports becomes too large, and white streaks occur when a solid image is formed.

  The arrangement direction of the plurality of ejection openings may be the print medium conveyance direction, and the attachment portion may scan and move in a direction intersecting with the arrangement direction of the plurality of ejection openings.

  The diameter of the discharge ports constituting the end discharge port group can be set larger than the diameter of the discharge ports constituting the central discharge port group. In this case, the difference between the arrangement intervals of the discharge ports constituting the end discharge port group and the central discharge port group is discharged from the discharge ports constituting the end discharge port group and the central discharge port group to the print medium. It is effective to correspond to the difference in the dot diameter of each formed droplet. The diameter of the discharge ports constituting the end discharge port group is preferably not more than twice the diameter of the discharge ports constituting the central discharge port group. If it exceeds twice, the density of droplets ejected from the end ejection port group becomes too high, and density unevenness and black streaks occur during the formation of a solid image. A liquid that further has a plurality of liquid passages that respectively guide liquids to the discharge ports, and that communicates with the discharge ports constituting the end portion discharge port group with respect to the width dimension of the liquid passages communicating with the discharge ports constituting the central discharge port group The width dimension of the road can be set wider. In this case, it is preferable that the width dimension of the liquid passage communicating with the discharge ports constituting the end portion discharge port group is not more than twice the width dimension of the liquid passage communicating with the discharge ports constituting the central discharge port group. If it exceeds twice, the width dimension of the liquid passage communicating with the individual discharge ports constituting the central discharge port group becomes extremely narrow, and the discharge frequency in the central discharge port group rapidly decreases, resulting in a decrease in printing speed. .

  It is preferable that the amount of liquid discharged at one time from the discharge port is 10 picoliters or less. If it exceeds 10 picoliters, the inertial mass of the droplet increases, so that the amount of edge deflection as shown in FIG. 12 decreases, and the effect of the present invention is hardly obtained.

  The liquid discharge head may be attached to the attachment portion in a replaceable manner.

  The discharge energy generating unit can be disposed to face the discharge port.

  The discharge energy generating unit may include an electrothermal converter that generates thermal energy for causing film boiling in the liquid and discharging the liquid from the discharge port.

  The liquid discharge head may form an image by scanning and moving the same portion of the print medium a plurality of times.

  The liquid may be a treatment liquid for adjusting the printability of the ink with respect to the ink and / or the print medium.

  The discharge ports constituting the end discharge port group are preferably in a state in which liquid can be discharged during image formation on the print medium.

According to the image forming apparatus of the present invention, the arrangement interval of the plurality of discharge ports constituting the end discharge port group is located in the arrangement direction both end portions of the multiple ejection ports, the arrangement direction central portion of the plurality of outlets Since it is set wider than the arrangement interval of the plurality of discharge ports that are located and constitute the central discharge port group, the position of the droplet that finally reaches the print medium can be corrected to the intended position, Even when solid printing is performed, it is possible to obtain a high-definition and high-gradation high-quality printed image that does not generate white streaks.

  In particular, the effect of the present invention can be obtained more reliably when the arrangement interval of the ejection ports constituting the end ejection port group is set 0.1 to 10 μm wider than the arrangement interval of the ejection ports constituting the central ejection port group. be able to.

  When the diameter of the discharge port constituting the end discharge port group is set larger than the diameter of the discharge port constituting the central discharge port group, in particular, the diameter of the discharge port constituting the end discharge port group is set to the central discharge port. When the diameter is less than twice the diameter of the discharge ports that make up the group, white streaks, etc., occur when solid printing is performed using a print head that does not reach the specified position of the print medium so accurately. Can be prevented. As described above, the difference between the dot diameters of the droplets ejected from the ejection ports constituting the end ejection port group and the central ejection port group and formed on the print medium, respectively, Even when using a print head that does not reach the specified position of the print medium so accurately, white streaks, etc. Can be prevented.

  A plurality of liquid passages that respectively guide the liquid to the discharge ports are further provided, and the width dimension of the liquid passage that communicates with the discharge ports constituting the end portion discharge port group is set to the width of the liquid passage that communicates with the discharge ports constituting the central discharge port group When set wider than the width dimension, the width dimension of the liquid channel communicating with the discharge ports constituting the end discharge port group is particularly twice the width dimension of the liquid channel communicating with the discharge ports constituting the central discharge port group. In the case of the following, even if the amount of droplets ejected from the ejection ports located at both ends in the arrangement direction is set to be large, it is not necessary to reduce the driving frequency for the corresponding ejection energy generation unit, and high-speed driving is maintained. be able to.

  An embodiment in which the image forming apparatus according to the present invention is applied to an inkjet printer will be described in detail with reference to FIGS. 1 to 9, but the present invention is not limited to such an embodiment, and these may be further combined. The present invention can also be applied to other technologies that are included in the concept of the present invention described in the claims of this specification.

  The external appearance of the mechanism part of the ink jet printer according to this embodiment is shown in FIG. 1, the external appearance of the head cartridge used in this ink jet printer is shown in FIG. 2, and the external appearance of the print head is shown in FIG. That is, the chassis 10 of the ink jet printer according to the present embodiment is composed of a plurality of plate-like metal members having a predetermined rigidity, and forms the skeleton of the ink jet printer. For the chassis 10, a medium feeding unit 11 that automatically feeds a sheet-like print medium (not shown) into the ink jet printer, and a print medium that is fed one by one from the medium feeding unit 11 are desired. A medium transport section 13 that guides the print medium from the print position to the medium discharge section 12, a print section that performs a predetermined print operation on the print medium transported to the print position, and a recovery for the print section. A head recovery unit 14 that performs processing is assembled.

  The print unit includes a carriage 16 that is supported so as to be able to scan and move along the carriage shaft 15, and a head cartridge 18 that is detachably mounted on the carriage 16 via a head set lever 17.

  The carriage 16 on which the head cartridge 18 is mounted is engaged with a carriage cover 20 for positioning the print head 19 of the head cartridge 18 at a predetermined mounting position on the carriage 16 and a tank holder 21 of the print head 19. The above-described head set lever 17 is provided to press the print head 19 so as to be positioned at a predetermined mounting position. The head set lever 17 as the attaching / detaching means of the present invention is provided on the upper portion of the carriage 16 so as to be rotatable with respect to a head set lever shaft (not shown), and the engaging portion with the print head 19 is spring-biased. A head set plate (not shown) is provided and is mounted on the carriage 16 while pressing the print head 19 by the spring force of the head set plate.

  One end of a contact flexible print cable (hereinafter referred to as a contact FPC) 22 (not shown) is connected to another engagement portion of the carriage 16 with respect to the print head 19, and a contact (not shown) formed at one end of the contact FPC 22. And the contact part 23 which is an external signal input terminal provided in the print head 19 are in electrical contact so that various information for printing can be exchanged and power can be supplied to the print head 19. It has become.

  An elastic member such as rubber (not shown) is provided between the contact portion of the contact FPC 22 and the carriage 16, and the contact portion of the contact FPC 22 and the print head 19 are set by the elastic force of the elastic member and the pressing force by the headset plate. The contact portion 23 can be reliably contacted. The other end of the contact FPC 22 is connected to a carriage substrate (not shown) mounted on the back surface of the carriage 16.

  The head cartridge 18 in the present embodiment discharges the ink supplied from the ink tank 24 from the discharge port 25 (see FIG. 4) of the print head 19 according to the print information. And a print head 19. The print head 19 of this embodiment employs a so-called cartridge system that is detachably mounted on the carriage 16.

  Further, in this embodiment, in order to enable high-quality color printing with photographic tone, for example, six ink tanks 24 in which black, light cyan, light magenta, cyan, magenta and yellow inks are independent. Can be used. Each ink tank 24 is provided with an elastically deformable detachable lever 26 that can be locked with respect to the head card ridge 18, and by operating the detachable lever 26, as shown in FIG. 19 can be removed. Therefore, the detaching lever 26 functions as a part of the attaching / detaching means of the present invention.

  The print head 19 includes a print element substrate 27, an electrical wiring substrate 28, the tank holder 21 described above, and the like. FIG. 4 shows the fracture structure of the main part of the print head 19 in this embodiment, FIG. 5 shows the arrangement of the discharge ports 25, and FIG. 6 shows the sectional structure taken along the line VI-VI. The print element substrate 27 in this embodiment forms a discharge energy generating unit, a common ink chamber 32, an ink path 34, a discharge port 25, and the like on a silicon substrate having a thickness of 0.5 mm to 1 mm using a film forming technique. It is a thing. In other words, the print element substrate 27 is formed with a long hole ink supply port 29 penetrating therethrough. On both sides of the ink supply port 29, a plurality of (256 in this embodiment) electrothermal transducers 30 arranged in two rows at a predetermined interval along the transport direction of the print medium, that is, the longitudinal direction of the ink supply port 29. Are formed in a state shifted from each other by a half pitch. The distance between the centers of these two rows of electrothermal transducers 30 is 215 μm, and each forms a discharge energy generating portion. In addition to these electrothermal transducers 30, the printed element substrate 27 includes electrode terminals 31 for electrical connection between the electrothermal transducers 30 and the printer main body, electrical wiring (not shown) formed of aluminum, and the like. It is formed by a film forming technique.

  The electrical wiring board 28 connected to the electrode terminal 31 formed on the print element board 27 is for applying an electrical signal for ejecting ink to the print element board 27. It has a corresponding electrical wiring and the above-mentioned contact portion 23 for receiving an electrical signal from the printer main body located at the end of this electrical wiring, and this contact portion 23 is positioned on the back side of the tank holder 21. It is fixed. A drive signal for the electrothermal transducer 30 is given from a drive IC (not shown) via the electrical wiring board 28, and at the same time, drive power is supplied to the electrothermal transducer 30.

  An ink flow path extending from the ink tank 24 to the ink supply port 29 of the print element substrate 27 is formed in the tank holder 21 that detachably holds the ink tank 24.

  On the print element substrate 27, an upper plate member 33 having a plurality of ejection ports 25 respectively facing the electrothermal transducer 30 through a common ink chamber 32 communicating with the ink supply port 29 is formed. That is, an ink path 34 communicating with each ejection port 25 and the common ink chamber 32 is formed between the upper plate member 33 and the print element substrate 27, and a partition wall is formed between the adjacent ink paths 34. 35 is formed. The common ink chamber 32, the ink path 34, the partition wall 35, and the like are formed together with the upper plate member 33 by the photolithography technique in the same manner as the ejection port 25.

  The liquid supplied into each ink path 34 from the ink supply port 29 boils as the electrothermal converter 30 generates heat, when a drive signal is given to the electrothermal converter 30 facing the corresponding ink path 34. , And is discharged from the discharge port 25 by the pressure of the bubbles generated thereby. In this case, bubbles generated in the common ink chamber 32 are brought into an air communication state from the discharge port 25 as they grow.

In the present embodiment, the discharge port 25e that constitutes the end discharge port group of up to 10, counting from the arrangement-direction end of one row, i.e. electrothermal transducer 30e is distance d _1, i.e. 600dpi considerable distance The distance d ₀ of the 236 discharge ports 25c constituting the central discharge port group located on the other central side, that is, the electrothermal transducer 30c is 42.3 μm (600 dpi). Equivalent). Accordingly, the discharge ports 25e of the end portion discharge port group located at both ends in the arrangement direction are displaced in the direction in which the intervals are further expanded by 20 μm, compared to the case where all the discharge ports are arranged at 600 dpi intervals. It will be. Further, the other row is arranged so as to be shifted by a half of the arrangement interval of the discharge ports 25 with respect to the one row. Therefore, the arrangement density of the discharge ports 25 in the two rows is almost 1200 dpi, and the end rows are arranged. The total number of discharge ports 25e constituting the partial discharge port group is 40, and the total number of discharge ports 25c constituting the central discharge port group is 472. In the present embodiment, the interval between these two discharge port arrays (the distance between the centers of the discharge ports 25 in the left and right columns) is set to 21 μm. The electrothermal transducers 30 all have the same dimensions and are squares with sides of 24 μm. The discharge ports 25 all have the same dimensions and are circular with a diameter of 18 μm. A 4.5 picoliter (pl) ink droplet is ejected from each ejection port 25 by a drive pulse of one operation for each electrothermal transducer 30. The ink droplet ejection speed was 10 to 15 m / s.

  In addition to the square as in the present embodiment, the shape of the discharge port 25 may be set to a shape such as a rectangle, a circle, or a star.

The ink jet print head 19 was scanned and moved at high speed along the print medium together with the carriage 16, and ink droplets were continuously ejected from all the ejection ports 25, so-called solid printing was performed on the print medium. In this case, in the conventional print head in which the distances d ₀ and d ₁ described above are all set equal to 42.3 μm (equivalent to 600 dpi), the distance between the white stripes 7 as shown in FIG. 11 reaches about 70 μm. There was found.

  Further, when multi-tone printing such as silver halide photography is performed, the print medium is conveyed in a plurality of times to the scanning area corresponding to the array width of the discharge ports 25 of the print head 19 and the print head 19 is printed. Is used a plurality of times, and a multi-pass method is used in which an image is formed by decimating and driving the ejection ports 25 used when the print head 19 scans and moves. In this case, the connecting portion of the path shown in FIG. 7 is slightly thinner and appears to have unevenness 7 ′. In this embodiment, printing is performed in 4 passes, and PR manufactured by Canon Inc. is used as the print medium. A paper with a trade name of -101 was used. When the interval of the unevenness 7 ′ generated at this time was measured, it was about 40 μm.

When printing by the multi-pass method, the reason why the white streak, that is, the interval of the unevenness 7 'is narrower than that in the case of performing solid printing as described above is the reason why the inventor has examined that when the print duty is low, the amount of skew This is considered to be due to a decrease in the white streak shown in FIG. Therefore, in the case of multi-pass printing can be set smaller the shift amount of spacing d ₁ of the ejection openings 25e which constitutes the end outlet group positioned in the array direction end portions than when performing solid printing .

  FIG. 8 shows the relationship between the print duty and the edge shift amount. 100% corresponds to a solid print in which ink droplets are discharged from all the discharge ports 25 all at once, and the maximum duty of four passes corresponds to 25%. As is apparent from this graph, in the present embodiment, the discharge ports 25e constituting a total of 40 end portion discharge port groups respectively located at both ends in the arrangement direction are the discharge ports constituting the central central discharge port group. The position was shifted in the direction in which the distance further increased by 1 μm with respect to the arrangement distance of 25c. For this reason, the ink droplets ejected from the ejection ports 25e located at both ends in the arrangement direction due to the reduced pressure atmosphere generated at the center side in the arrangement direction of the ejection ports 25 when multi-tone printing is performed. The ink droplets are drawn toward the center in the direction, and finally corrected to substantially the same interval as the interval between the ink droplets discharged from the ejection port 25c located on the center side in the arrangement direction and reaching the print medium. As a result, it is possible to prevent the occurrence of white streaks or the like that has occurred in the conventional scanning movement of the carriage 16 once.

  When performing such multi-tone printing, the interval between the print medium and the discharge port surface 36 where the discharge port 25 of the print head 19 opens is set to 1.6 mm, and the scanning movement speed of the carriage 16 is set to 50 per second. Set to .8 cm. In this case, the drive frequency of the electrothermal transducer 30 of the print head 19 is 24 kHz.

  In the above-described embodiment, the shapes and dimensions of the discharge ports 25 are all set equal. However, the opening area of the discharge ports 25e constituting the end portion discharge port groups at both ends in the arrangement direction constitutes the central discharge port group. It is also effective to set it larger than the opening area of the discharge port 25c.

  FIG. 9 shows a schematic structure of another embodiment in which the liquid discharge head according to the present invention is applied to the above-described print head. Elements having the same functions as those of the previous embodiment are designated by the same reference numerals. The overlapping description will be omitted. In this embodiment, the diameter of the discharge port 25c constituting the central discharge port group is 18 μm, whereas the discharge ports constituting up to ten end discharge port groups counted from both ends in the arrangement direction of one row. The diameter of 25e is set to 19 μm. That is, there is no problem in the case of the print head 19 having a good performance such that the ink droplet accurately reaches a predetermined position of the print medium, but the ink droplet does not reach the predetermined position of the print medium so accurately. In the case of the print head 19, the dot diameter formed on the print medium is increased by the ink droplets discharged from the discharge ports 25 e of the end discharge port groups respectively located at both ends in the arrangement direction. Poor positional accuracy of the formed dots is alleviated, and it is possible to reliably prevent the occurrence of white streaks in solid prints.

  Incidentally, when a coated paper having a bleeding rate of 2.2 is used as the print medium, the ejection amount of ink droplets from the ejection port 25c whose diameter of the central ejection port group located on the center side in the arrangement direction is 18 μm is 4. 5 pl, the dot diameter formed on the print medium is 45 μm, whereas the ejection amount of the ink droplets from the ejection port 25 e whose end ejection port group located at both ends in the arrangement direction is 19 μm is 5 0.5 pl, and the diameter of dots formed on the print medium is set to 48 μm.

As described above, when the ejection amount of the ink droplets ejected from the ejection ports 25e of the end portion ejection port groups located at the both ends in the arrangement direction is increased, the ink supply is performed with respect to the driving of these electrothermal transducers 30e. In such a case, the width of the ink path 34 is increased, that is, the wall thickness of the partition wall 35 that partitions the adjacent ink path 34 is decreased. Can be avoided. Specifically, than the width L ₀ of the ink passage 34 communicating the width L ₁ of the ink passage 34 communicating with the discharge port 25e is positioned in the array direction end portions, a discharge port 25c which is positioned in the array direction central portion Can be set widely.

  The present invention includes means (for example, an electrothermal converter or a laser beam) that generates thermal energy as energy used for ejecting the liquid, and this thermal energy causes a change in the state of the liquid. The ink jet type liquid discharge head, the head cartridge, or the image forming apparatus to be produced has an excellent effect. This is because according to such a method, high density and high definition of the print can be achieved.

  As its typical configuration and principle, for example, those performed using the basic principle disclosed in US Pat. No. 4,723,129 and US Pat. No. 4,740,796 are preferable. This method can be applied to both a so-called on-demand type and a continuous type. In particular, in the case of the on-demand type, it is arranged corresponding to a sheet or a flow path in which liquid is held. Thermal energy is generated by applying at least one drive signal that gives a rapid temperature rise exceeding nucleate boiling corresponding to print information to the electrothermal transducer, thereby causing film boiling on the heat acting surface of the liquid discharge head. As a result, bubbles in the liquid corresponding to the drive signals on a one-to-one basis can be formed, which is effective. Due to the growth and contraction of the bubbles, the liquid is discharged through the discharge port to form at least one droplet. It is more preferable that the drive signal has a pulse shape, since the bubble growth and contraction is performed immediately and appropriately, and thus it is possible to achieve liquid discharge with particularly excellent responsiveness. As this pulse-shaped drive signal, those described in US Pat. No. 4,463,359 and US Pat. No. 4,345,262 are suitable. If the conditions described in US Pat. No. 4,313,124 of the invention relating to the temperature rise rate of the heat acting surface are employed, further excellent printing can be performed.

  In addition, as a configuration of the liquid ejection head, a combination configuration of an ejection port, a liquid path, and an electrothermal transducer as disclosed in each of the above specifications (the electrothermal transducer is arranged along the liquid path) US Pat. No. 4,558,333 which discloses a configuration in which the thermal action part is arranged in a region where the heat acting part bends in addition to the straight liquid flow path or the electrothermal conversion body (right-angle liquid flow path facing the discharge port across the liquid flow path). And configurations using US Pat. No. 4,459,600 are also included in the present invention. In addition, for a plurality of electrothermal transducers, Japanese Patent Application Laid-Open No. Sho 59-123670 that discloses a configuration in which a common slit is used as a discharge portion of the electrothermal transducer, or an aperture that absorbs pressure waves of thermal energy is provided. The effect of the present invention is also effective as a configuration based on Japanese Patent Application Laid-Open No. 59-138461 which discloses a configuration corresponding to the discharge unit. That is, whatever the form of the liquid ejection head is, according to the present invention, printing can be performed reliably and efficiently.

  The present invention can also be effectively applied to a full-line type liquid discharge head having a length corresponding to the maximum width of a print medium that can be printed by the image forming apparatus. As such a liquid discharge head, either a configuration satisfying the length by a combination of a plurality of liquid discharge heads or a configuration as a single liquid discharge head formed integrally may be used.

  Further, even in the serial type as in the above-described embodiment, the liquid discharge head integrally fixed to the carriage that moves by scanning, or the carriage can be replaced with the carriage so that it can be electrically connected to the carriage. Even when using a replaceable chip-in type liquid discharge head that can supply a liquid from the main body of the apparatus or a head cartridge provided with a tank for storing liquid integrally in the liquid discharge head itself The present invention is effective.

  As the configuration of the image forming apparatus of the present invention, it is possible to further stabilize the effect of the present invention by adding a recovery means for making the liquid discharge state from the liquid discharge head appropriate, a preliminary auxiliary means, etc. It is preferable. Specifically, a capping unit for the liquid ejection head, a cleaning unit, a pressurizing or suction unit, an electrothermal converter, a heating element different from this, or a preheating unit for heating using a combination thereof A preliminary discharge means for performing discharge separately from the printing operation can be given.

  Also, regarding the type and number of liquid discharge heads mounted, for example, only one ink corresponding to a single color ink is provided, as well as a plurality of types of inks having different print colors and densities (lightness). A plurality of them may be provided. That is, for example, the print mode of the image forming apparatus is not limited to a print mode of only a mainstream color such as black, but the liquid discharge head may be configured integrally or a plurality of combinations. The present invention is extremely effective for an apparatus having at least one of full-color print modes by color or mixed colors. In this case, it is also effective to discharge a processing liquid (printability improving liquid) for adjusting the printability of ink according to the type of print medium and the print mode from a dedicated or common liquid discharge head to the print medium.

  Further, in the embodiment of the present invention described above, a material that solidifies at room temperature or lower and softens or liquefies at room temperature may be used. Alternatively, in the ink jet system, the liquid itself is within a range of 30 ° C. or higher and 70 ° C. or lower. In general, the temperature is adjusted so that the viscosity of the liquid is controlled so that the viscosity of the liquid is within the stable discharge range. In addition, it is solidified in a standing state and liquefied by heating in order to actively prevent temperature rise due to heat energy by using it as energy for state change from solid state to liquid state, or to prevent liquid evaporation You may use what you do. In any case, it is liquefied by the application of thermal energy according to the print signal and liquefies only by the application of thermal energy, such as the liquid being discharged or the liquid that has already solidified when it reaches the print medium. The present invention can also be applied to the case where a material having a property is used. The liquid in such a case is in a state of being held as a liquid or a solid in a porous sheet recess or through-hole as described in JP-A-54-56847 or JP-A-60-71260. Alternatively, the electrothermal converter may be opposed to the electrothermal converter. In the present invention, the most effective one for each liquid described above is to execute the above-described film boiling method.

  The image forming apparatus according to the present invention can be used as an image output terminal of an information processing device such as a computer, a copying apparatus combined with a reader, a facsimile apparatus having a transmission / reception function, or a textile printing apparatus. The print medium may be a sheet or long paper or fabric, or a plate-like wood or stone, resin, glass, metal, etc. And so on.

1 is a perspective view illustrating a schematic structure of an embodiment in which an image forming apparatus according to the present invention is applied to an inkjet printer. It is a perspective view showing the appearance of one embodiment which applied the head cartridge by the present invention to the ink-jet printer shown in Drawing 1 in an exploded state. FIG. 3 is a perspective view of a print head portion in the head cartridge shown in FIG. 2. FIG. 4 is a cutaway perspective view illustrating a schematic structure of a main part of the print head illustrated in FIG. 3. FIG. 5 is a cutaway plan view showing an arrangement state of discharge ports and electrothermal transducers of the print head shown in FIG. 4. It is VI-VI arrow sectional drawing in FIG. FIG. 12 is a conceptual diagram schematically illustrating a solid image formed in four passes on a print medium according to the ink ejection mode illustrated in FIG. 11. 4 is a graph showing a relationship between a print duty and an edge shift amount of the ink jet printer according to the present invention. It is a fracture | rupture top view showing the arrangement | sequence state of the discharge outlet and electrothermal transducer in other embodiment of the liquid discharge head by this invention. It is a conceptual diagram which represents typically the discharge state of the ink by the conventional inkjet printer. FIG. 11 is a conceptual diagram schematically illustrating a solid image formed in one pass on a print medium according to the ink ejection mode illustrated in FIG. 10. It is a graph showing the relationship between the discharge amount and edge amount of the conventional inkjet printer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Chassis 11 Medium feeding part 12 Medium discharge part 13 Medium conveying part 14 Head recovery part 15 Carriage shaft 16 Carriage 17 Head set lever 18 Head cartridge 19 Print head 20 Carriage cover 21 Tank holder 22 Contact flexible print cable (contact FPC)
DESCRIPTION OF SYMBOLS 23 Contact part 24 Ink tank 25, 25e, 25c Ejection port 26 Removal lever 27 Print element board | substrate 28 Electric wiring board 29 Ink supply port 30, 30e, 30c Electrothermal conversion body 31 Electrode terminal 32 Common ink chamber 33 Upper board member 34 Ink path 35 Partition wall 36 Discharge port face d ₀ , d ₁ Discharge port array interval L ₀ , L ₁ Ink path width

Claims (6)

An image forming apparatus comprising: a liquid discharge head that discharges liquid; a mounting portion of the liquid discharge head; and a transport unit for the print medium, and forming an image on the print medium with the liquid discharged from the discharge port of the liquid discharge head Because
The liquid ejecting head includes a plurality of discharge ports you arranged in a predetermined direction, and a plurality of ejection energy generating portion for ejecting liquid from these discharge ports,
The plurality of discharge ports are located at both ends in the arrangement direction and end discharge port groups composed of a plurality of discharge ports that are involved in image formation, and located in the center in the arrangement direction to form an image. It consists of a central outlet group consisting of a plurality of outlets involved,
Arrangement intervals of the plurality of discharge ports for forming the end portion discharge port group, the image forming, characterized in that it is wider than the plurality of arrangement interval of the discharge ports constituting the front Symbol central discharge port group apparatus.   2. The image according to claim 1, wherein the arrangement direction of the plurality of ejection openings is a conveyance direction of the print medium, and the attachment portion scans and moves in a direction intersecting the arrangement direction of the plurality of ejection openings. Forming equipment.   The diameter of the said discharge port which comprises the said edge part discharge port group is set larger than the diameter of the said discharge port which comprises the said center discharge port group, The Claim 1 or Claim 2 characterized by the above-mentioned. Image forming apparatus.   The difference in the dot diameters of the droplets ejected from the ejection ports constituting the end portion ejection port group and the central ejection port group, respectively, and formed on the print medium is the end ejection port group and the central ejection port. The image forming apparatus according to claim 3, wherein the image forming apparatus corresponds to a difference in an arrangement interval of the discharge ports constituting each group.   5. The image forming apparatus according to claim 1, wherein the amount of liquid ejected from the ejection port at one time is 10 picoliters or less.   The image forming apparatus according to claim 1, wherein the liquid discharge head is attached to the attachment portion in a replaceable manner.

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