Patent Description:
A printer disclosed in <CIT> includes a supply tank and a recovery tank each connected to an ejection head and transfers ink from the supply tank to the recovery tank through the ejection head by reducing the pressure inside the recovery tank to be lower than that inside the supply tank. Further, the printer includes a circulation pump for feeding the ink from the recovery tank to the supply tank. With this configuration, generated is a circulation path of ink in which ink reaching the recovery tank from the supply tank through the ejection head is returned to the supply tank.

Furthermore, the printer includes a solenoid valve between the recovery tank and the supply tank. This solenoid valve shuts off the recovery tank and the supply tank from each other when energized and causes the recovery tank and the supply tank to communicate with each other when de-energized. With this configuration, the pressure difference between the recovery tank and the supply tank is cancelled when the circulation pump is stopped due to a power failure or the like and the flow of the ink from the supply tank to the recovery tank can be stopped. It is thereby possible to prevent the ink from overflowing from the recovery tank to any other portion. A further prior art document is <CIT>.

In the above-described printer, with the communication between the recovery tank and the supply tank, a negative pressure inside the recovery tank increases. For this reason, the negative pressure inside the recovery tank becomes insufficient with respect to a water head pressure between the recovery tank and the ejection head, and the ink sometimes leaks from the ejection head.

The present invention is intended to solve the above problem, and it is an object of the present invention to provide a technology to make it possible to prevent leakage of ink from an ejection head when the pressure difference is cancelled between a supply tank for supplying ink to the ejection head and a recovery tank for recovering the ink from the ejection head.

A printer according to the invention, comprises: an ejection head which ejects ink from a nozzle; a recovery tank which stores ink recovered from the ejection head; a buffer part which communicates with the recovery tank; a supply tank which stores ink to be supplied to the ejection head; a first pressure applying part configured to apply a first pressure into the supply tank; a second pressure applying part configured to apply a second pressure which is a negative pressure lower than the first pressure into the recovery tank and the buffer part; a circulation pump which performs a liquid feed operation of feeding ink from the recovery tank to the supply tank, with supplied electric power; a bypass solenoid valve provided between the supply tank and the recovery tank, shutting off the supply tank and the recovery tank from each other when energized and causing the supply tank and the recovery tank to communicate with each other when de-energizes; and a power supply part configured to supply electric power to the circulation pump and the bypass solenoid valve, wherein the recovery tank is disposed above the ejection head, and the buffer part communicates with the recovery tank and the supply tank when the bypass solenoid valve is de-energized and causes a third pressure which is a negative pressure higher than the second pressure and lower than the first pressure to be generated in the recovery tank and the supply tank, to thereby prevent leakage of ink from the nozzle with the third pressure resisting a water head pressure between the recovery tank and the supply tank, and the nozzle of the ejection head.

A printing method according to the invention, comprises: supplying ink to an ejection head ejecting the ink from a nozzle to thereby perform printing, from a supply tank connected to the ejection head, and recovering the ink from the ejection head to a recovery tank connected to the ejection head by applying a first pressure into the supply tank and applying a second pressure which is a negative pressure lower than the first pressure into the recovery tank and a buffer part communicating with the recovery tank, feeding the ink from the recovery tank to the supply tank by supplying electric power to a circulation pump provided between the recovery tank and the supply tank, and causing a third pressure which is a negative pressure higher than the second pressure and lower than the first pressure to be generated in the recovery tank and the supply tank when the supply of the electric power to the circulation pump is stopped, by causing the recovery tank and the supply tank to communicate with each other and causing the buffer part to communicate with the recovery tank and the supply tank, to thereby prevent leakage of the ink from the nozzle with the third pressure resisting a water head pressure between the recovery tank and the supply tank, and the nozzle of the ejection head.

In the present invention (the printer and the printing method) having such a configuration, the buffer part communicating with the recovery tank is provided. Then, in the state where the recovery tank and the supply tank are shut off from each other, the first pressure is applied into the supply tank and the second pressure which is a negative pressure lower than the first pressure is applied into the recovery tank and the buffer part. In such a configuration, when the supply tank and the recovery tank communicate with each other, the difference between the first pressure inside the supply tank and the second pressure inside the recovery tank and the buffer part is cancelled, and the pressure inside the recovery tank increases. Since the buffer part is provided separately from the recovery tank, however, the increase range of the pressure inside the recovery tank is suppressed, as compared with the case where no buffer part is provided. Specifically, the third pressure which is a negative pressure higher than the second pressure and lower than the first pressure is generated in the recovery tank and the supply tank, and leakage of the ink from the nozzle can be prevented, with this third pressure resisting the water head pressure between the recovery tank and the supply tank, and the nozzle of the ejection head. Thus, it becomes possible to prevent leakage of the ink from the ejection head when the pressure difference is cancelled between the supply tank supplying the ink to the ejection head and the recovery tank recovering the ink from the ejection head.

A printing system according to the invention, comprises: the above printer; and a drying apparatus which dries ink ejected onto a printing medium by the printer. Also in such a printing system, it becomes possible to prevent leakage of ink from the ejection head when the pressure difference is cancelled between the supply tank supplying ink to the ejection head and the recovery tank recovering the ink from the ejection head.

Thus, according to the present invention, it becomes possible to prevent leakage of ink from the ejection head when the pressure difference is cancelled between the supply tank supplying ink to the ejection head and the recovery tank recovering the ink from the ejection head.

The above and further objects and novel features of the invention will more fully appear from the following detailed description when the same is read in connection with the accompanying drawing. It is to be expressly understood, however, that the drawing is for purpose of illustration only and is not intended as a definition of the limits of the invention.

<FIG> is an elevational view schematically showing one example of a printing system in accordance with the present invention. In <FIG> and the following figures, a horizontal direction X and a vertical direction Z are shown as appropriate. As shown in <FIG>, a printing system <NUM> includes a printer <NUM> and a drying apparatus <NUM> which are arranged in the horizontal direction X. The printing system <NUM> transfers a long strip-like printing medium M from a feed roll <NUM> to a wind-up roll <NUM> in a roll-to-roll manner. Further, the material of the printing medium M is a film such as OPP (oriented polypropylene), PET (polyethylene terephthalate), or the like. The material of the printing medium M, however, is not limited to the film but may be paper or the like. Such a printing medium M has flexibility. Furthermore, hereinafter, among both surfaces of the printing medium M, the surface on which an image is printed is referred to as a front surface M1 and the other surface opposite to the front surface M1 is referred to as a back surface M2 as appropriate.

The printer <NUM> ejects water-based ink by an inkjet method onto the front surface M1 of the printing medium M transferred from the feed roll <NUM> to the wind-up roll <NUM>, to thereby print an image on the front surface M1 of the printing medium M. Detailed configuration of the printer <NUM> will be described later. The printing medium M on which the image is thus printed is transferred from the printer <NUM> to the drying apparatus <NUM> in the horizontal direction X.

The drying apparatus <NUM> includes a drying furnace <NUM> and dries the printing medium M unloaded from the printer <NUM> in the course of the transfer from the feed roll <NUM> to the wind-up roll <NUM>. Inside the drying furnace <NUM>, provided are two upper-stage blower units 61u arranged in the horizontal direction X, two middle-stage blower units <NUM> arranged in the horizontal direction X below these upper-stage blower units 61u, and two lower-stage blower units <NUM> arranged in the horizontal direction X below these middle-stage blower units <NUM>.

The printing medium M unloaded from an unloading port <NUM> of the printer <NUM> goes through the two upper-stage blower units 61u in the horizontal direction X and then are folded back toward the two middle-stage blower units <NUM> by a pair of rollers <NUM>. Subsequently, the printing medium M goes through the two middle-stage blower units <NUM> in the horizontal direction X and then are folded back toward the two lower-stage blower units <NUM> by a pair of air turn bars <NUM>. Further, the printing medium M goes through the two lower-stage blower units <NUM> in the horizontal direction X and then are unloaded to the outside of the drying apparatus <NUM>.

The upper-stage blower unit 61u has two blower chambers <NUM> which are so disposed as to sandwich the printing medium M going in the horizontal direction X from the vertical direction Z. Each of the blower chambers <NUM> has a plurality of nozzles <NUM> arranged in the horizontal direction X and injects warm air (gas at <NUM> or more) from each of the nozzles <NUM> to the printing medium M. Thus, the printing medium M is dried by the warm air injected from the nozzles <NUM> of these blower chambers <NUM> while passing through between the two blower chambers <NUM> provided on the upper and lower sides. Further, each of the middle-stage blower unit <NUM> and the lower-stage blower unit <NUM> has two blower chambers <NUM> sandwiching the printing medium M from the vertical direction Z, like the upper-stage blower unit 61u.

Specific configuration of the upper-stage blower unit 61u is not limited to this exemplary one. For example, a plurality of rollers <NUM> arranged in the horizontal direction X may be provided, instead of the lower-side blower chamber <NUM> among the upper-side and lower-side blower chambers <NUM>. In such a configuration, the warm air can be injected onto the front surface M1 of the printing medium M from the upper-side blower chamber <NUM> while the plurality of rollers support the back surface M2 of the printing medium M from below.

<FIG> is an elevational view schematically showing the printer included in the printing system of <FIG>. In <FIG>, one side X1 of the horizontal direction X and the other side X2 thereof are shown as appropriate. The one side X1 refers to a side toward the drying apparatus <NUM> from the printer <NUM> and the other side X2 refers to the opposite side of the one side X1. The printer <NUM> includes a cabinet <NUM>, a color printing part <NUM> disposed inside the cabinet <NUM>, a white printing part <NUM> disposed above the color printing part <NUM> inside the cabinet <NUM>, and a transfer part <NUM> for transferring the printing medium M by using the plurality of rollers disposed inside the cabinet <NUM>.

The color printing part <NUM> has a plurality of (six) ejection heads <NUM> arranged in a traveling direction of the printing medium M (direction toward the one side X1 from the other side X2) above the printing medium M transferred by the transfer part <NUM>. The plurality of ejection heads <NUM> have nozzles facing, from above, the front surface M1 of the printing medium M going through therebelow, and eject color inks of different colors by an inkjet method from the nozzles. Herein, the color ink refers to ink other than white, including ink of cyan, magenta, yellow, black, or the like. Thus, the plurality of ejection heads <NUM> of the color printing part <NUM> eject color inks, from above, onto the front surface M1 of the printing medium M going through therebelow, to thereby print a color image on the printing medium M1 of the printing medium M.

Further, the white printing part <NUM> has a single ejection head <NUM> disposed above the printing medium M transferred by the transfer part <NUM>. The ejection head <NUM> has a nozzle facing, from above, the front surface M1 of the printing medium M going through therebelow, and ejects white ink by an inkjet method from the nozzle. Thus, the ejection head <NUM> of the white printing part <NUM> ejects white ink, from above, onto the front surface M1 of the printing medium M going through therebelow, to thereby print a white image on the printing medium M1 of the printing medium M.

A loading port <NUM> is opened in a sidewall of the cabinet <NUM> on the other side X2, and the unloading port <NUM> is opened in a sidewall of the cabinet <NUM> on the one side X1. Then, the transfer part <NUM> transfers the printing medium M from the loading port <NUM> to the unloading port <NUM> through the color printing part <NUM> and the white printing part <NUM> described above.

The transfer part <NUM> has a loading part <NUM> provided below the color printing part <NUM>, an upward transfer part <NUM> provided on the one side X1 of the color printing part <NUM>, an upper transfer part <NUM> provided above the color printing part <NUM>, and a downward transfer part <NUM> provided on the other side X2 of the color printing part <NUM>. The loading part <NUM> transfers the printing medium M loaded from the loading port <NUM> toward the one side X1 by rollers <NUM>, the upward transfer part <NUM> transfers the printing medium M transferred by the loading part <NUM>, upward by rollers <NUM>, the upper transfer part <NUM> transfers the printing medium M transferred by the upward transfer part <NUM> toward the other side X2 by rollers <NUM>, and the downward transfer part <NUM> transfers the printing medium M transferred by the upper transfer part <NUM>, downward by rollers <NUM>.

Further, the transfer part <NUM> has a color transfer part <NUM> for supporting, from below, the printing medium M facing the color printing part <NUM>, and the printing medium M which has passed through the downward transfer part <NUM> enters the color transfer part <NUM>. The color transfer part <NUM> has a plurality of rollers <NUM> arranged from the other side X2 to the one side X1, and each of the rollers <NUM> comes into contact with the back surface M2 of the printing medium M from below. Thus, the front surface M1 of the medium M which is supported by the color transfer part <NUM> faces upward, and each of the ejection heads <NUM> of the color printing part <NUM> ejects color ink while facing this front surface M1 from above.

Furthermore, the transfer part <NUM> has rollers <NUM>, <NUM>, and <NUM> arranged between the color transfer part <NUM> and the downward transfer part <NUM> in the traveling direction of the printing medium M. The roller <NUM> is a driving roller to drive the printing medium M. Each of the rollers <NUM> and <NUM> is a driven roller which follows the printing medium M to rotate.

Further, the transfer part <NUM> has an inversion transfer part <NUM> which inverts the printing medium M transferred from the color transfer part <NUM> to the one side X1 upside down twice. This inversion transfer part <NUM> has a plurality of rollers <NUM> to <NUM> including a driving roller <NUM>, and these rollers <NUM> to <NUM> invert the printing medium M upside down twice while coming into contact with the back surface M2 of the printing medium M. Specifically, the inversion transfer part <NUM> transfers the printing medium M transferred from the color transfer part <NUM> downward by the rollers <NUM> and <NUM>, and changes the traveling direction of the printing medium M to the other side X2 by the roller <NUM> to transfer the printing medium M, to thereby invert the front surface M1 and the back surface M2 of the printing medium M upside down. Subsequently, the inversion transfer part <NUM> transfers the printing medium M from the one side X1 toward the other side X2 by the plurality of rollers <NUM>, and next transfers the printing medium M upward by the rollers <NUM> to <NUM>. Further, the inversion transfer part <NUM> changes the traveling direction of the printing medium M to the one side X1 by the roller <NUM>, to thereby invert the front surface M1 and the back surface M2 of the printing medium M upside down again, and transfers the printing medium M from the other side X2 toward the one side X1 by the roller <NUM>.

Furthermore, the transfer part <NUM> has a white transfer part <NUM> to support, from below, the printing medium M facing the white printing part <NUM>, and the printing medium M inverted upside down twice by the inversion transfer part <NUM> enters the white transfer part <NUM>. This white transfer part <NUM> has a roller <NUM> which comes into contact with the back surface M2 of the printing medium M from below. Thus, the front surface M1 of the printing medium M supported by the white transfer part <NUM> faces upward, and the ejection head <NUM> of the white printing part <NUM> ejects white ink while facing the front surface M1 from above.

Further, the transfer part <NUM> has an unloading part <NUM> provided above the upper transfer part <NUM>. The unloading part <NUM> has a plurality of rollers <NUM> arranged from the other side X2 to the one side X1 in the horizontal direction X. The unloading part <NUM> transfers the printing medium M transferred by the white transfer part <NUM> toward the one side X1 by the plurality of rollers <NUM>, to thereby unload the printing medium M from the unloading port <NUM> of the cabinet <NUM> to the drying apparatus <NUM>.

As described above, the color printing part <NUM> and the white printing part <NUM> of the printer <NUM> have the ejection heads <NUM> and <NUM>, respectively. Subsequently, an ink supply mechanism which supplies ink to these ejection heads <NUM> and <NUM> will be described. The basic configuration of the ink supply mechanism is common to the ejection heads <NUM> and <NUM>. Then, description will be made, centering on the ejection head <NUM> for ejecting white ink. Hereinafter, each of the ejection heads <NUM> and <NUM> will be referred to as an ejection head H as appropriate.

<FIG> and <FIG> are views each schematically showing a configuration of the ejection head and the ink supply mechanism which supplies ink to the ejection head, and <FIG> shows a state during power transmission and <FIG> shows a state during a power failure. As shown in these figures, the ejection head H has a housing Ha, and a plurality of nozzles N are arranged and opened in the bottom of the housing Ha. Inside the housing Ha, a plurality of cavities Hb communicating with the plurality of nozzles N, respectively, and an ink supply chamber He communicating with the plurality of cavities Hb are provided, and the ink supplied from the ink supply chamber He is stored in the cavities Hb. Then, a piezoelectric element provided in each of the cavities Hb extrudes the ink from the cavity Hb and the ink is thereby ejected from the nozzle N which communicates with the cavity Hb. Further, the specific method of ejecting the ink is not limited to the above method using the piezoelectric element but may be a thermal method in which the ink is heated. Furthermore, in an upper portion of the ejection head H, an ink inflow port Hd and an ink outflow port He are opened, and the ink flows into the ink supply chamber He from the ink supply mechanism <NUM> through the ink inflow port Hd and flows out from the ink supply chamber He through the ink outflow port He to the ink supply mechanism <NUM>.

The ink supply mechanism <NUM> includes a supply tank <NUM> connected to the ink inflow port Hd through a pipe <NUM> and a recovery tank <NUM> connected to the ink outflow port He through a pipe <NUM>, and the ink is stored in each of the supply tank <NUM> and the recovery tank <NUM>. Each of the supply tank <NUM> and the recovery tank <NUM> is disposed above the ejection head H. The ink supply mechanism <NUM> includes a circulation pump <NUM> which is arranged to a pipe <NUM> connecting the recovery tank <NUM> and the supply tank <NUM> to feed the ink from the recovery tank <NUM> to the supply tank <NUM> and a degassing filter <NUM> arranged to the pipe <NUM> at a location between the circulation pump <NUM> and the supply tank <NUM>, and the degassing filter <NUM> removes gas from the ink flowing out from the circulation pump <NUM> before flowing into the supply tank <NUM>.

This ink supply mechanism <NUM> has a power supply circuit <NUM> which supplies electric power to the constituent elements of the apparatus. Then, the circulation pump <NUM> feeds the ink from the recovery tank <NUM> to the supply tank <NUM> by using the electric power supplied from the power supply circuit <NUM> (liquid feed operation). The circulation pump <NUM> thereby performs an ink circulation operation of circulating the ink in a circulation path C that leads from the recovery tank <NUM> through the supply tank <NUM> to the ink supply chamber He of the ejection head H and then returns to the recovery tank <NUM>.

Further, the ink supply mechanism <NUM> includes a main tank <NUM> capable of storing a large amount of ink and a main pump <NUM> which is arranged to a pipe <NUM> connecting the main tank <NUM> and recovery tank <NUM> to feed the ink from the main tank <NUM> to the recovery tank <NUM>. Then, when the amount of ink circulating in the circulation path C is reduced by the ejection of the ink from the nozzles N, the main pump <NUM> supplements the ink to the recovery tank <NUM> from the main tank <NUM> by using the electric power supplied from the power supply circuit <NUM>.

Furthermore, the ink supply mechanism <NUM> includes a supply-side pressure applying part <NUM> (hereinafter, referred to as a "pressure applying part <NUM>" as appropriate) which applies a positive pressure P1 to the supply tank <NUM>. The pressure applying part <NUM> includes a pressure tank <NUM>, a pump <NUM> applying the positive pressure P1 to the inside of the pressure tank <NUM> by supplying gas (air) to the pressure tank <NUM>, and a flexible tube <NUM> having one end connected to the pressure tank <NUM>. Then, in the pressure applying part <NUM>, the pump <NUM> supplies gas to the pressure tank <NUM> by using the electric power supplied from the power supply circuit <NUM>. The positive pressure P1 generated thus inside the pressure tank <NUM> by the pump <NUM> is given to the supply tank <NUM> through the tube <NUM> and further through the pipe <NUM>.

On the other hand, inside the supply tank <NUM>, gas (air) is accumulated above a liquid surface of the ink. In other words, inside the supply tank <NUM>, the ink is stored below a gas-liquid interface and gas exists above the gas-liquid interface. Therefore, the positive pressure P1 is applied to the gas-liquid interface inside the supply tank <NUM> by the pressure applying part <NUM>.

Further, the pressure applying part <NUM> includes a solenoid valve <NUM> provided between the other end of the tube <NUM> and one end of the pipe <NUM>. This solenoid valve <NUM> is a valve of normally closed type. Therefore, during the power transmission shown in <FIG>, the solenoid valve <NUM> forms a communication state in which an atmosphere in the pressure tank <NUM> communicates with an atmosphere in the supply tank <NUM> by using the electric power supplied from the power supply circuit <NUM> and the positive pressure P1 inside the pressure tank <NUM> is thereby given to the inside of the supply tank <NUM> through the tube <NUM>, the solenoid valve <NUM> and pipe <NUM>. On the other hand, during the power failure shown in <FIG>, since the power supply from the power supply circuit <NUM> to the solenoid valve <NUM> is lost, the solenoid valve <NUM> forms a shut-off state in which an atmosphere in the pressure tank <NUM> is shut off from an atmosphere in the supply tank <NUM> and the application of the positive pressure P1 from the pressure tank <NUM> to the supply tank <NUM> is shut off.

Furthermore, the pressure applying part <NUM> has a check filter <NUM> between the pipe <NUM> and the solenoid valve <NUM>. This check filter <NUM> inhibits passage of the ink from the supply tank <NUM> toward the pressure tank <NUM> while permitting passage of gas from the supply tank <NUM> toward the pressure tank <NUM>. Thus, the check filter <NUM> prevents inflow of the ink from the supply tank <NUM> into the tube <NUM>.

Further, the ink supply mechanism <NUM> includes a recovery-side pressure applying part <NUM> (hereinafter, referred to as a "pressure applying part <NUM>" as appropriate) which applies a negative pressure to the recovery tank <NUM>. The pressure applying part <NUM> includes a pressure tank <NUM>, a pump <NUM> decompressing the inside of the pressure tank <NUM> by sucking gas (air) from the pressure tank <NUM>, and a flexible tube <NUM> having one end connected to the pressure tank <NUM>. Then, in the pressure applying part <NUM>, the pump <NUM> exhausts gas from the inside of the pressure tank <NUM> by using the electric power supplied from the power supply circuit <NUM>. The negative pressure P2 generated thus inside the pressure tank <NUM> by the pump <NUM> is given to the recovery tank <NUM> through the tube <NUM> and further through a pipe <NUM>.

On the other hand, inside the recovery tank <NUM>, gas (air) is accumulated above a liquid surface of the ink. In other words, inside the recovery tank <NUM>, the ink is stored below a gas-liquid interface and gas exists above the gas-liquid interface. Therefore, the negative pressure P2 is applied to the gas-liquid interface inside the recovery tank <NUM> by the pressure applying part <NUM>.

Furthermore, the pressure applying part <NUM> includes a solenoid valve <NUM> provided between the other end of the tube <NUM> and one end of the pipe <NUM>. This solenoid valve <NUM> is a valve of normally closed type. Therefore, during the power transmission shown in <FIG>, the solenoid valve <NUM> forms a communication state in which an atmosphere in the pressure tank <NUM> communicates with an atmosphere in the recovery tank <NUM> by using the electric power supplied from the power supply circuit <NUM> and the negative pressure P2 inside the pressure tank <NUM> is thereby given to the inside of the recovery tank <NUM> through the tube <NUM>, the solenoid valve <NUM> and the pipe <NUM>. On the other hand, during the power failure shown in <FIG>, since the power supply from the power supply circuit <NUM> to the solenoid valve <NUM> is lost, the solenoid valve <NUM> forms a shut-off state in which an atmosphere in the pressure tank <NUM> is shut off from an atmosphere in the recovery tank <NUM> and the application of the negative pressure P2 from the pressure tank <NUM> to the recovery tank <NUM> is shut off.

Further, the pressure applying part <NUM> has a check filter <NUM> between the pipe <NUM> and the solenoid valve <NUM>. This check filter <NUM> inhibits passage of the ink from the recovery tank <NUM> toward the pressure tank <NUM> while permitting passage of gas from the recovery tank <NUM> toward the pressure tank <NUM>. Thus, the check filter <NUM> prevents inflow of the ink from the recovery tank <NUM> into the tube <NUM>.

Further, the ink supply mechanism <NUM> has a buffer tank <NUM> communicating with the recovery tank <NUM> through a pipe <NUM>. This buffer tank <NUM> communicates with above the gas-liquid interface of the recovery tank <NUM> (in other words, a layer of gas). In other words, the gas moves to and from between the buffer tank <NUM> and the recovery tank <NUM>. On the other hand, the ink does not move to and from between the buffer tank <NUM> and the recovery tank <NUM> and there is no ink inside the buffer tank <NUM>. During both the power transmission (<FIG>) and the power failure (<FIG>), an atmosphere in the buffer tank <NUM> and an atmosphere in the recovery tank <NUM> communicate with each other and the pressure inside the buffer tank <NUM> and that inside the recovery tank <NUM> are always equal to each other.

Specifically, during the power transmission shown in <FIG>, the solenoid valve <NUM> forms the communication state in which an atmosphere in the pressure tank <NUM> communicates with an atmosphere in the buffer tank <NUM> by using the electric power supplied from the power supply circuit <NUM> and the negative pressure P2 inside the pressure tank <NUM> is thereby given to the inside of the buffer tank <NUM> through the tube <NUM>, the solenoid valve <NUM>, pipe <NUM> and pipe <NUM>. On the other hand, during the power failure shown in <FIG>, since the power supply from the power supply circuit <NUM> to the solenoid valve <NUM> is lost, the solenoid valve <NUM> forms the shut-off state in which an atmosphere in the pressure tank <NUM> is shut off from an atmosphere in the buffer tank <NUM> and the application of the negative pressure P2 from the pressure tank <NUM> to the buffer tank <NUM> is shut off.

During the power transmission shown in <FIG>, the pressure P2 inside the recovery tank <NUM> and the buffer tank <NUM> is lower than the pressure P1 inside the supply tank <NUM>, and the ink thereby moves from the supply tank <NUM> to the recovery tank <NUM> through the circulation path C. If this state continues, the liquid surface of the supply tank <NUM> becomes lower and the liquid surface of the recovery tank <NUM> becomes higher, and a meniscus required for the nozzle N of the ejection head H does not occur. Then, the circulation pump <NUM> circulates the ink from the recovery tank <NUM> to the supply tank <NUM>, to thereby keep the respective liquid surfaces of the supply tank <NUM> and the recovery tank <NUM> at a constant level.

Further, the ink supply mechanism <NUM> includes a solenoid valve <NUM> provided to a pipe <NUM> connect the recovery tank <NUM> and the supply tank <NUM> to communicate an atmosphere in the recovery tank <NUM> with an atmosphere in the supply tank <NUM>, and in other words, the solenoid valve <NUM> is provided in parallel with the circulation pump <NUM> between the recovery tank <NUM> and the supply tank <NUM>. This solenoid valve <NUM> is a valve of normally open type. Therefore, during the power transmission shown in <FIG>, the solenoid valve <NUM> is opened by using the electric power supplied from the power supply circuit <NUM> and the communication state between an atmosphere in the recovery tank <NUM> and an atmosphere in the supply tank <NUM> through the solenoid valve <NUM> is shut off. On the other hand, during the power failure shown in <FIG>, since the power supply from the power supply circuit <NUM> to the solenoid valve <NUM> is lost, the solenoid valve <NUM> is closed and an atmosphere in the recovery tank <NUM> and an atmosphere in the supply tank <NUM> communicate with each other through the solenoid valve <NUM>. Thereby, an upper-side (that is, layer of gas) above the gas-liquid interface in the recovery tank <NUM> and an upper-side (that is, layer of gas) above the gas-liquid interface in the supply tank <NUM> communicate with each other.

Thus, during the power failure (<FIG>), when the solenoid valve <NUM> causes the recovery tank <NUM> and the supply tank <NUM> to communicate with each other, the pressure inside the recovery tank <NUM> and that inside the supply tank <NUM> each become a predetermined negative pressure P3. This negative pressure P3 is a negative pressure higher than the negative pressure P2 and lower than the positive pressure P1. During the power transmission (<FIG>), the negative pressure P2 is applied into the buffer tank <NUM> in advance, and during the power failure (<FIG>), the buffer tank <NUM> communicates with the recovery tank <NUM> and the supply tank <NUM>. With such a function of the buffer tank <NUM>, inside the recovery tank <NUM> and the supply tank <NUM>, the negative pressure P3 is maintained to a certain extent during the power failure. On the other hand, as described above, the supply tank <NUM> and the recovery tank <NUM> are each disposed above the ejection head H. Therefore, between the gas-liquid interface of each of the recovery tank <NUM> and the supply tank <NUM> and the nozzle N of the ejection head H, a water head pressure in accordance with the level difference among these occurs. Then, the capacity which is large enough to generate the negative pressure P3 which can keep the ink against the water head pressure is provided in the buffer tank <NUM>.

The ink supply mechanism <NUM> in accordance with the present embodiment described above circulates the ink in the circulation path C that leads from the recovery tank <NUM> through the supply tank <NUM> to the ejection head H and then returns to the recovery tank <NUM> by feeding the ink from the recovery tank <NUM> to the supply tank <NUM> by the circulation pump <NUM>. Further, the solenoid valve <NUM> is provided between the supply tank <NUM> and the recovery tank <NUM> and shut off an atmosphere in the supply tank <NUM> from an atmosphere in the recovery tank <NUM> when energized (<FIG>). Therefore, the solenoid valve <NUM> does not inhibit generation of the pressure difference (= P2 - P1) between the supply tank <NUM> and the recovery tank <NUM>. On the other hand, this solenoid valve <NUM> causes an atmosphere in the supply tank <NUM> and an atmosphere in the recovery tank <NUM> to communicate each other when de-energized (<FIG>). Therefore, when the circulation pump <NUM> is stopped due to the power failure, it is possible to quickly cancel the pressure difference between the supply tank <NUM> and the recovery tank <NUM> and suppress the inflow of the ink from the supply tank <NUM> to the recovery tank <NUM> through the ink supply chamber Hc of the ejection head H.

Particularly, the buffer tank <NUM> (buffer part) whose atmosphere communicates with an atmosphere in the recovery tank <NUM> is provided. Then, in the state where an atmosphere in the recovery tank <NUM> and an atmosphere in the supply tank <NUM> are shut off from each other, the positive pressure P1 (first pressure) is applied into the supply tank <NUM> and the negative pressure P2 (second pressure) which is a pressure lower than the positive pressure P1 is applied into the recovery tank <NUM> and the buffer tank <NUM>. In such a configuration, when an atmosphere in the supply tank <NUM> and an atmosphere in the recovery tank <NUM> communicate with each other, the difference between the positive pressure P1 inside the supply tank <NUM> and the negative pressure P2 inside the recovery tank <NUM> is cancelled and the pressure inside the recovery tank <NUM> increases. Since the buffer tank <NUM> is provided separately from the recovery tank <NUM>, however, the increase range of the pressure inside the recovery tank <NUM> is suppressed, as compared with the case where no buffer tank <NUM> is provided. Specifically, the negative pressure P3 (third pressure) which is a pressure higher than the negative pressure P2 and lower than the positive pressure P1 occurs in the recovery tank <NUM> and the supply tank <NUM>, and leakage of the ink from the nozzle N can be prevented, with the negative pressure P3 resisting the water head pressure between the recovery tank <NUM> and the supply tank <NUM>, and the nozzle N of the ejection head H. It becomes possible to prevent leakage of the ink from the ejection head H when the pressure difference is cancelled between the supply tank <NUM> supplying the ink to the ejection head H and the recovery tank <NUM> recovering the ink from the ejection head H.

Further, the pressure applying part <NUM> (first pressure applying part) has the solenoid valve <NUM> (first solenoid valve) and the pressure tank <NUM> (first pressure tank) whose atmosphere can communicate with an atmosphere in the supply tank <NUM> through the solenoid valve <NUM> and applies the positive pressure P1 generated in the pressure tank <NUM> to the supply tank <NUM> through the solenoid valve <NUM>. Then, the solenoid valve <NUM> causes an atmosphere in the supply tank <NUM> and an atmosphere in the pressure tank <NUM> to communicate with each other when energized and shuts off an atmosphere in the supply tank <NUM> and an atmosphere in the pressure tank <NUM> from each other when de-energized. Furthermore, the pressure applying part <NUM> (second pressure applying part) has the solenoid valve <NUM> (second solenoid valve) and the pressure tank <NUM> (second pressure tank) whose atmosphere can communicate with an atmosphere in the recovery tank <NUM> (and buffer tank <NUM>) through the solenoid valve <NUM> and applies the negative pressure P2 generated in the pressure tank <NUM> to the recovery tank <NUM> and the buffer tank <NUM> through the solenoid valve <NUM>. Then, the solenoid valve <NUM> causes an atmosphere in the recovery tank <NUM> and the buffer tank <NUM>, and an atmosphere in the pressure tank <NUM> to communicate with each other when energized and shuts off an atmosphere in the recovery tank <NUM> and the buffer tank <NUM>, and an atmosphere in the pressure tank <NUM> from each other during de-energized. In such a configuration, with the communication between an atmosphere in the supply tank <NUM> and an atmosphere in the recovery tank <NUM> during the power failure, an atmosphere in the pressure tank <NUM> and the pressure tank <NUM> are cut off from an atmosphere in the supply tank <NUM>, the recovery tank <NUM>, and the buffer tank <NUM>. Therefore, it is possible to reliably generate the negative pressure P3 required to prevent the leakage of the ink from the ejection head H in each of the supply tank <NUM>, the recovery tank <NUM>, and the buffer tank <NUM>.

Further, during the power transmission shown in <FIG>, the positive pressure P1 is applied to the supply tank <NUM>. Thus, in the configuration where the positive pressure P1 is generated in the supply tank <NUM>, there is a tendency that the above-described problem of the leakage of the ink becomes noticeable. Therefore, as described above, the configuration in which the buffer tank <NUM> is provided is particularly preferable.

Furthermore, in the ink supply mechanism <NUM> with respect to the ejection head H for ejecting white ink, by applying the positive pressure P1 to the supply tank <NUM>, the following advantage rises. Specifically, white ink is used for printing of a so-called solid image forming a background or the like in most cases. In a case of printing such a solid image, when the amount of white ink ejected from the ejection head H is short, an image failure in which areas with no white ink deposited appear in streaks can occur. In order to prevent this, by applying the positive pressure P1 into the supply tank <NUM>, sufficient amount of white ink can be ejected from the ejection head H and it is thereby possible to print a preferable solid image.

In the above-described embodiment, the printing system <NUM> corresponds to one example of a "printing system" of the present invention, the printer <NUM> corresponds to one example of a "printer" of the present invention, the drying apparatus <NUM> corresponds to one example of a "drying apparatus" of the present invention, the supply tank <NUM> corresponds to one example of a "supply tank" of the present invention, the recovery tank <NUM> corresponds to one example of a "recovery tank" of the present invention, the circulation pump <NUM> corresponds to one example of a "circulation pump" of the present invention, the power supply circuit <NUM> corresponds to one example of a "power supply part" of the present invention, the pressure applying part <NUM> corresponds to one example of a "first pressure applying part" of the present invention, the pressure tank <NUM> corresponds to one example of a "first pressure tank" of the present invention, the solenoid valve <NUM> corresponds to one example of a "first solenoid valve" of the present invention, the pressure applying part <NUM> corresponds to one example of a "second pressure applying part" of the present invention, the pressure tank <NUM> corresponds to one example of a "second pressure tank" of the present invention, the solenoid valve <NUM> corresponds to one example of a "second solenoid valve" of the present invention, the buffer tank <NUM> corresponds to one example of a "buffer part" of the present invention, the solenoid valve <NUM> corresponds to one example of a "bypass solenoid valve" of the present invention, the ejection head H corresponds to one example of an "ejection head" of the present invention, the nozzle N corresponds to one example of a "nozzle" of the present invention, the positive pressure P1 corresponds to one example of a "first pressure" of the present invention, the negative pressure P2 corresponds to one example of a "second pressure" of the present invention, and the negative pressure P3 corresponds to one example of a "third pressure" of the present invention.

The pressure applied from the pressure tank <NUM> of the pressure applying part <NUM> to the supply tank <NUM> does not need to be a positive pressure but may be a negative pressure. In the ink supply mechanism <NUM> for supplying the ink to the ejection head H which ejects color ink, particularly, a negative pressure (first pressure) higher than the negative pressure P2 may be applied to the supply tank <NUM> during the power transmission.

Further, as the "buffer part" to which the negative pressure P2 is applied in advance during the power transmission, a redundant pipe may be provided, instead of the above-described buffer tank <NUM>.

Furthermore, the solenoid valve <NUM>, the solenoid valve <NUM>, and the solenoid valve <NUM> described above do not need to be each formed as a single valve but may be collectively formed as a multi-way valve.

The present invention can be applied to general printing technology.

As described above, the printer may be configured so that the first pressure applying part has a first solenoid valve and a first pressure tank which is connected to the supply tank through the first solenoid valve and applies the first pressure generated in the first pressure tank to the supply tank through the first solenoid valve, the first solenoid valve causes the supply tank and the first pressure tank to communicate with each other when energized and shuts off the supply tank and the first pressure tank from each other when de-energized, the second pressure applying part has a second solenoid valve and a second pressure tank which is connected to the recovery tank through the second solenoid valve and applies the second pressure generated in the second pressure tank to the recovery tank through the second solenoid valve, and the second solenoid valve causes the recovery tank and the second pressure tank to communicate with each other when energized and shuts off the recovery tank and the second pressure tank from each other when de-energized. In such a configuration, with the communication between the supply tank and the recovery tank, the first and second pressure tanks are shut off from the supply tank, the recovery tank, and the buffer part. Therefore, it is possible to reliably generate the third pressure required to prevent the leakage of the ink from the ejection head in each of the supply tank, the recovery tank, and the buffer part.

The printer may be configured so that the first pressure is a positive pressure. In the configuration where a positive pressure is generated in the supply tank, there is a tendency that the above-described problem of the leakage of the ink becomes noticeable. Therefore, it is particularly preferable that the present invention should be applied to such a configuration.

The printer may be configured so that the ink is white ink. White ink is used for printing of a so-called solid image forming a background or the like in most cases. In a case of printing such a solid image, when the amount of white ink ejected from the ejection head is short, an image failure in which areas with no white ink deposited appear in streaks can occur. In order to prevent this, by applying a positive pressure into the supply tank, sufficient amount of white ink can be ejected from the ejection head, and it is thereby possible to print a preferable solid image.

Claim 1:
A printer (<NUM>), comprising:
an ejection head (<NUM>) which is configured to eject ink from a nozzle;
a recovery tank (<NUM>) which is configured to store ink recovered from the ejection head (<NUM>);
a buffer part (<NUM>) which communicates with the recovery tank (<NUM>);
a supply tank (<NUM>) which is configured to store ink to be supplied to the ejection head (<NUM>);
a first pressure applying part (<NUM>) configured to apply a first pressure (P1) into the supply tank (<NUM>);
a second pressure applying part (<NUM>) configured to apply a second pressure (P2) which is a negative pressure lower than the first pressure (P1) into the recovery tank (<NUM>) and the buffer part (<NUM>);
a circulation pump (<NUM>) which is configured to perform a liquid feed operation of feeding ink from the recovery tank (<NUM>) to the supply tank (<NUM>), with supplied electric power;
a bypass solenoid valve (<NUM>) provided between the supply tank (<NUM>) and the recovery tank (<NUM>), which is configured to shut off the supply tank (<NUM>) and the recovery tank (<NUM>) from each other when energized and causing the supply tank (<NUM>) and the recovery tank (<NUM>) to communicate with each other when de-energizes; and
a power supply part (<NUM>) configured to supply electric power to the circulation pump (<NUM>) and the bypass solenoid valve (<NUM>),
wherein the recovery tank (<NUM>) is disposed above the ejection head (<NUM>), and
the buffer part (<NUM>) communicates with the recovery tank (<NUM>) and the supply tank (<NUM>) when the bypass solenoid valve (<NUM>) is de-energized and causes a third pressure (P3) which is a negative pressure higher than the second pressure (P2) and lower than the first pressure (P1) to be generated in the recovery tank (<NUM>) and the supply tank (<NUM>), to thereby prevent leakage of ink from the nozzle with the third pressure (P3) resisting a water head pressure between the recovery tank (<NUM>) and the supply tank (<NUM>), and the nozzle of the ejection head (<NUM>).