JP7379982B2 - Image forming method - Google Patents

Description

The present invention relates to an image forming method.

BACKGROUND ART In recent years, an image forming method (inkjet textile printing method) using an inkjet recording device has been used as a method for forming images such as letters, pictures, and designs on fabrics such as woven fabrics and nonwoven fabrics.

An inkjet recording device typically has an inkjet head that includes a pressure chamber and a nozzle for ejecting ink within the pressure chamber. Then, droplets of ink are ejected from a nozzle provided in the inkjet head to form an image on the fabric that is the printing material.

Dye inks containing dyes as coloring materials and pigment inks containing pigments are known as inks used in such inkjet textile printing methods. Among these, it is desirable to use a dispersion ink in which a solid colorant such as a pigment or a disperse dye is dispersed in a solvent, from the viewpoint of being compatible with a plurality of fiber types. However, when dispersion-based ink is ejected from an inkjet head, the ink tends to stagnate near the nozzle, causing the ink to dry and adhere to solids, or solid colorant to aggregate or settle, which can lead to nozzle clogging. There was a problem that it was easy to occur.

On the other hand, an image forming method using an inkjet head having a discharge channel for circulating ink within the inkjet head, specifically, a pressure chamber, a nozzle for discharging ink in the pressure chamber, and a nozzle. An image forming method using an inkjet head having one discharge channel for each inkjet head has been proposed (for example, Patent Documents 1 and 2).

Further, as an inkjet head, an inkjet head having a plurality of discharge channels for each nozzle has also been proposed (for example, Patent Document 3).

Japanese Patent Application Publication No. 2014-51049 JP 2019-14239 Publication Japanese Patent Application Publication No. 2018-202817

The present inventors have discovered that when performing image formation using dispersion ink, by using an inkjet head having a plurality of discharge channels for each nozzle, such as that shown in Patent Document 3, the ink in the vicinity of the nozzle is It has been found that the retention of water can be effectively suppressed. Thereby, drying of the ink and agglomeration and sedimentation of the solid colorant near the nozzle can be suppressed, and nozzle clogging can be made less likely to occur.

However, in an inkjet head that has multiple discharge channels for each nozzle, multiple discharge channels are provided near the ejection opening of the nozzle. There is a problem in that the meniscus (liquid surface) of the ink near the nozzle tends to become unstable and the ejection stability tends to deteriorate compared to the case where an inkjet head without the inkjet head is used.

In particular, since there is a demand for even higher recording speeds, it is desirable to increase the ejection frequency when ejecting ink from an inkjet head. However, when the ejection frequency is increased, the meniscus of ink tends to become more unstable near the nozzle, which tends to further reduce the ejection stability.

The present invention has been made in view of the above circumstances, and provides an image forming method that can suppress nozzle clogging caused by ink stagnation near the nozzles of an inkjet head, and also suppress deterioration in ejection stability. The purpose is to

The present invention relates to the following image forming method.
The image forming method of the present invention includes an ink chamber, a nozzle for discharging ink supplied from the ink chamber, and a plurality of nozzles provided for each nozzle, and a plurality of nozzles for discharging ink supplied from the ink chamber to an ejection port of the nozzle. An image forming method using an image forming apparatus comprising: an inkjet head having a discharge channel for taking out a portion of the ink; and an ink circulation section that returns the ink taken in by the discharge channel to the ink chamber and circulates the ink. The method includes a step of ejecting ink from a nozzle of the inkjet head, the ink including a solid colorant and a solvent,
The viscosity of the ink at 25° C. is 6 to 20 cp.

According to the present invention, it is possible to provide an image forming method that can improve ejection stability while suppressing nozzle clogging caused by ink retention near the nozzle.

FIG. 1 is a schematic diagram showing the configuration of an image forming apparatus used in the image forming method of the present invention. FIG. 2 is a perspective view of an inkjet head in the image forming apparatus of FIG. 1. FIG. 3 is an exploded perspective view of the inkjet head. FIG. 4 is a cross-sectional view of the inkjet head. FIG. 5 is an exploded perspective view of the head chip. FIG. 6 is a bottom view of the pressure chamber substrate. FIG. 7 is a partial cross-sectional view of the head chip along the Y direction. FIG. 8 is a partial cross-sectional view of the head chip along the X direction. FIG. 9 is an explanatory diagram showing an example of an ink circulation section.

As mentioned above, in an image forming method using an inkjet head that has multiple discharge channels for each nozzle, the ink meniscus tends to become unstable near the nozzle discharge opening, resulting in ejection failure when ejecting at a high ejection frequency. tends to occur.

In contrast, the present inventors have proposed that when forming an image using an inkjet head such as the one described above, the viscosity of the ink should be appropriately increased, specifically, the viscosity of the ink at 25° C. should be 6 to 20 cp. We have found that it is effective to adjust within the range of . As a result, the meniscus of ink near the nozzle ejection opening can be stabilized, so even if ejection is performed at a high ejection frequency (while suppressing nozzle clogging due to ink stagnation), there is no reduction in ejection stability. Can be suppressed.

That is, the image forming method of the present invention is an image forming method using an inkjet head having a plurality of discharge channels for each nozzle, and uses ink having a suitably high viscosity. First, the configurations of the image forming apparatus and ink used in the image forming method of the present invention will be explained.

1. Image Forming Apparatus FIG. 1 is a schematic diagram showing the configuration of an image forming apparatus 200 used in the image forming method of the present invention.

As shown in FIG. 1, the image forming apparatus 200 includes a transport device 210, an inkjet head 100, an ink supply device 220 (having an ink circulation section 8), and a main tank 230.

The conveying device 210 is a device for conveying the fabric (print material) 240 to the inkjet head 100. The conveyance device 210 includes, for example, a belt conveyor 211 and a rotatable feed roller 212. The belt conveyor 211 includes rotatable pulleys 213a and 213b, and an endless belt 214 stretched around these pulleys 213a and 213b. The feed roller 212 is disposed at a position facing the pulley 213a on the upstream side in the transport direction X of the fabric 240 so as to sandwich the belt 214 and the fabric 240 and feed the fabric 240 onto the belt 214.

The inkjet head 100 is arranged so as to be able to scan, for example, in a direction transverse to the transport direction X of the fabric 240 on which an image is to be formed. Inkjet head 100 has a plurality of nozzles for ejecting ink droplets onto fabric 240, which is a printing medium. The inkjet head 1 is configured, for example, so that a plurality of types of ink of different colors are supplied to corresponding nozzles. The configuration of the inkjet head 100 will be described later.

The ink supply device 220 is arranged integrally with the inkjet head 100. The ink supply devices 220 are arranged for each type of ink. For example, when using four color inks of Y (yellow), M (magenta), C (cyan), and K (black), four ink supply devices 220 are arranged in the inkjet head 100. The ink supply device 220 has an ink circulation section 8 that takes out ink from inside the inkjet head 100, reintroduces it into the inkjet head 100, and circulates the ink (see FIG. 9).

Ink in the main tank 230 is supplied to the ink supply device 220 via a flow path 251 and a valve 254 connected to the main tank 230. Further, the ink supply device 220 communicates with a common ink chamber 51 (ink chamber) described below of the inkjet head 100 via a flow path 252, and supplies ink of each color to a first ink port described below that communicates with the common ink chamber 51. 53 so that it can be supplied.

The inkjet head 100 is also connected to the main tank 230 by a bypass flow path 253 branching from the flow path 251 . A valve 254 that can switch and set the ink flow path in one or both of the flow path 251 and the bypass flow path 253 is disposed at a branch point between the flow path 251 and the bypass flow path 253. The flow path 251, the flow path 252, and the bypass flow path 253 are all flexible tubes, for example. Valve 254 is, for example, a three-way valve.

The main tank 230 is a tank for storing ink to be supplied to the inkjet head 100. The main tank 230 is arranged separately from the inkjet head 100. Main tank 230 includes, for example, a stirring device (not shown). The main tank 230 can be appropriately determined depending on the image forming performance, size, etc. of the image forming apparatus 200. For example, when the image forming speed of the image forming apparatus 200 is 1 to 3 m ² /min, the capacity of the main tank 230 is, for example, 1 L.

(Inkjet head 100)
2 is a perspective view of the inkjet head 100 in the image forming apparatus 200 of FIG. 1, and FIG. 3 is an exploded perspective view of the inkjet head 100. FIG. 4 is a cross-sectional view of the inkjet head 100. Note that the cover member 9 is omitted in FIGS. 3 and 4.

As shown in FIG. 3, the inkjet head 100 of this embodiment includes a head chip 1, a wiring board 2, a flexible board 3, a drive circuit board 4, a manifold 5, a housing 6, and a cap receiving plate. 7 and a cover member 9 (see FIG. 2). Hereinafter, the stacking direction of these members will be referred to as the Z direction, the direction parallel to the direction in which a discharge flow path 121 (described later) is extended in a plane perpendicular to the Z direction will be referred to as the Y direction, and the direction perpendicular thereto will be referred to as the X direction. .

The head chip 1 includes a nozzle substrate 11, a flow path spacer substrate 12, and a pressure chamber substrate 13. The configuration of the head chip 1 will be explained in detail later.

The wiring board 2 has an opening 22 approximately in the center. A manifold 5 is arranged on one surface of the wiring board 2 so as to correspond to the opening 22, and a head chip 1 is arranged on the other surface so as to correspond to the opening 22. That is, the wiring board 2 allows the manifold 5 and the head chip 1 to communicate with each other through the opening 22 . Specifically, when the head chip 1 is attached to the wiring board 2, the opening 22 exposes the inlet of a pressure chamber 131 (described later) and the outlet of the second common discharge channel 135 of the head chip 1. It looks like this. The lower end of the manifold 5 is fixed to the outer edge of the wiring board 2 .

The flexible substrate 3 electrically connects the drive circuit board 4 and the electrode portion of the wiring board 2. Thereby, a signal from the drive circuit board 4 can be applied to the drive electrode provided on the partition wall 136 in the head chip 1 via the flexible substrate 3.

The manifold 5 is arranged on the head chip 1 via the wiring board 2, and communicates with the pressure chamber 131 of the head chip 1 via the wiring board 2 (see FIG. 4). The manifold 5 has a hollow main body portion 52 forming a common ink chamber 51 (ink chamber), first to fourth ink ports 53 to 56 forming an ink flow path, and a discharge liquid chamber 57.

The common ink chamber 51 has a filter F therein for removing foreign matter from the ink. Thereby, the common ink chamber 51 is divided into a first liquid chamber 51a and a second liquid chamber 51b. The common ink chamber 51 stores ink introduced into the pressure chamber 131.

The first ink port 53 communicates with the first liquid chamber 51a and is used to introduce ink into the common ink chamber 51. That is, the first ink port 53 functions as an inlet for introducing ink into the inkjet head 100. A first joint 81a is inserted into the tip of the first ink port 53.

The second ink port 54 communicates with the first liquid chamber 51a, and is used to remove air bubbles within the first liquid chamber 51a. A second joint 81b is inserted into the tip of the second ink port 54.

The third ink port 55 communicates with the second liquid chamber 51b and is used to remove air bubbles within the second liquid chamber 51b. Furthermore, a third joint 82a is fitted onto the tip of the third ink port 55.

The fourth ink port 56 communicates with a discharge liquid chamber 57 that communicates with the second common discharge channel 135 of the head chip 1 . Ink discharged from the head chip 1 through the fourth ink port 56 is discharged to the outside of the inkjet head 100 through the fourth ink port 56. That is, the fourth ink port 56 functions as an outlet that discharges ink to the outside of the inkjet head 100.

The discharge liquid chamber 57 is arranged between a second common discharge channel 135 (described later) and a fourth ink port 56 of the head chip 1, and connects these. Thereby, the ink discharged from the second common discharge flow path 135 can be introduced into the fourth ink port 56.

The casing 6 is formed to be able to house the head chip 1, the wiring board 2, the flexible board 3, the manifold 5, etc. (see FIG. 3). The bottom surface of the housing 6 is open. Furthermore, mounting holes 68 are formed at both ends of the housing 6 in the X direction, respectively, for attaching the housing 6 to the printer main body.

The cap receiving plate 7 has a nozzle opening 71 approximately in the center. The cap receiving plate 7 is attached so as to cover the bottom opening of the housing 6 while exposing the nozzle substrate 11 through the nozzle opening 71.

The cover member 9 is attached to the housing 6 (see FIG. 2).

(About head chip 1)
FIG. 5 is an exploded perspective view of the head chip 1. FIG. 6 is a bottom view of the pressure chamber substrate. FIG. 7 is a partial cross-sectional view of the head chip 1 taken along the Y direction (a partial cross-sectional view of the head chip 1 taken along the line AA in FIG. 6). FIG. 8 is a partial cross-sectional view of the head chip 1 taken along the X direction (a partial cross-sectional view of the head chip 1 taken along the line BB in FIG. 6).

As shown in FIG. 5, the head chip 1 includes a nozzle substrate 11, a flow path spacer substrate 12, and a pressure chamber substrate 13.

The nozzle substrate 11 has a plurality of nozzles 111. The nozzle 111 penetrates from one surface to the other surface of the nozzle substrate 11 and communicates with a pressure chamber 131 formed from the flow path spacer substrate 12 to the pressure chamber substrate 13. The nozzle 111 then discharges the ink supplied from the common ink chamber 51 via the pressure chamber 131 from the discharge port.

The flow path spacer substrate 12 has a plurality of pressure chamber communication holes 120 and a plurality of discharge flow paths 121 (see FIG. 7).

The pressure chamber communication hole 120 is a through hole for forming the pressure chamber 131, and is provided at a position corresponding to the nozzle 111 of the nozzle substrate 11. The pressure chamber communication hole 120 is connected to the pressure chamber communication hole 130 of the pressure chamber substrate 13 to form a pressure chamber 131.

The discharge flow path 121 is a flow path that constitutes a circulation flow path 87 described later in the ink circulation section 8, and a plurality of discharge flow paths 121 are provided for each nozzle 111. The discharge flow path 121 may communicate with the pressure chamber 131 or between the pressure chamber 131 and the discharge port of the nozzle 111. In this embodiment, the discharge flow path 121 communicates with the pressure chamber 131. That is, the discharge flow path 121 has one end connected to the pressure chamber communication hole 120 and the other end connected to the first common discharge flow path 134 . Thereby, the discharge channel 121 can take out a part of the ink supplied to the ejection port of the nozzle 111 from the common ink chamber 51 (via the pressure chamber 131) and allow it to flow into the first common discharge channel 134. can. The number of discharge channels 121 provided for each nozzle 111 is not particularly limited as long as it is two or more, but is two in this embodiment.

In this embodiment, the discharge channel 121 includes a first discharge channel 122 and a second discharge channel 123 (see FIG. 7).

The first discharge channel 122 extends along the Y direction. The second discharge flow path 123 extends along the Z direction. The connecting portion between the first discharge flow path 121 and the second discharge flow path 123 is a bent portion 121a that changes the direction in which the ink flows. As a result, the pressure waves are more likely to hit the channel walls of the individual ink discharge channels 121, so the pressure waves are efficiently absorbed within the discharge channel 121, and the pressure waves are less likely to leak into the first common discharge channel 134, etc. .

The pressure chamber substrate 13 has a plurality of pressure chamber communication holes 131a, an air chamber 132, a first common discharge channel 134, and a second common discharge channel 135 (see FIGS. 5 to 7).

The pressure chamber communication hole 131a is a through hole that forms the pressure chamber 131, and is provided at a position corresponding to the pressure chamber communication hole 121 of the flow path spacer substrate 12. Then, by stacking the pressure chamber substrate 13 and the flow path spacer substrate 12, the pressure chamber communication hole 131a and the pressure chamber communication hole 121 are connected to form a pressure chamber 131. The pressure chamber 131 applies ejection pressure to the ink ejected from the nozzle 111 by changing its volume.

The air chamber 132 is separated from the pressure chamber 131 by a partition wall serving as a pressure generating means. Unlike the pressure chamber 131, the air chamber 132 is not communicated with the common ink chamber 51, so that ink does not flow into the air chamber 132. Furthermore, the air chamber 132 is not communicated with the nozzle 111 (see FIGS. 5 and 8).

A partition wall (not shown) is arranged between the air chamber 132 and the pressure chamber 131, and functions as a pressure generating means. The partition wall is provided with a drive electrode (not shown), and when a voltage is applied to the drive electrode, the partition wall portion between adjacent pressure chambers 131 repeats a shear mode type displacement, so that the pressure chambers 131 Pressure is applied to the ink inside.

The first common discharge flow path 134 constitutes a circulation flow path 87 (see FIG. 9, which will be described later), and extends in the X direction (see FIGS. 5 and 8). The first common discharge passage 134 communicates with the discharge passage 121 communicating with one of the two adjacent nozzles 111 and the discharge passage 121 communicating with the other (see FIG. 7).

The second common discharge channel 135 is provided along the Z direction at the end of the pressure chamber substrate 13 in the X direction (see FIGS. 5 and 8). Further, one end of the second common discharge channel 135 communicates with the first common discharge channel 134, and the other end communicates with the discharge liquid chamber 57. Thereby, the second common discharge channel 135 can discharge the ink that has flowed from the first common discharge channel 134 to the outside of the head chip 1 toward the discharge liquid chamber 57. Further, the second common discharge flow path 135 is provided to have a larger volume than the pressure chamber 131. Thereby, ink discharge efficiency can be improved.

In the inkjet head 100 configured in this way, the common ink chambers 51 of the manifold 5 communicate with each other, and the pressure chambers 131 (pressure chamber communication holes 131a and pressure chambers 131 provided from the pressure chamber substrate 13 to the flow path spacer substrate 12) The chamber communication hole 121) and the nozzle 111 of the nozzle substrate 11 constitute an ink supply flow path to the ejection port.

Further, the discharge passage 121 of the passage spacer substrate 12 and the first common discharge passage 134 and the second common discharge passage 135 of the pressure chamber substrate 13 are connected to each other from the common ink chamber 51 via the pressure chamber 131. An ink circulation unit 8 that takes out (branches) a part of the ink supplied to the ejection opening of the nozzle 111, once discharges it to the outside of the inkjet head 100, and then returns it to the common ink chamber 51 for circulation. (circulation flow path 87).

FIG. 9 is an explanatory diagram showing an example of the ink circulation section 8. As shown in FIG.

The ink circulation unit 8 is a mechanism that generates a circulation flow of ink from the pressure chamber 131 to the discharge channel 121 in the inkjet head 100. The ink circulation unit 8 includes a supply sub-tank 81 , a circulation sub-tank 82 , channels 252 , 85 , and 86 communicating therebetween, and a filter unit 90 disposed on the channel 85 .

The supply sub-tank 81 is filled with ink to be supplied to the common ink chamber 51 of the inkjet head 100, and is connected to the first ink port 53 of the inkjet head 100 via a flow path 252. Note that the supply sub-tank 81 is connected to the main tank 230 via a flow path 251 and a pump 89, so that ink can be supplied from the main tank 230.

The circulation sub-tank 82 is filled with ink discharged from the discharge liquid chamber 57 (see FIG. 4) of the inkjet head 100, and is connected to the fourth ink port 56 of the inkjet head 100 via a flow path 85. There is. Further, the filter unit 90 is disposed on the flow path 85 and is capable of removing foreign matter in the ink discharged from the discharge liquid chamber 57.

The supply sub-tank 81 and the circulation sub-tank 82 are provided at different positions in the Z direction (gravitational direction) with respect to the nozzle surface (hereinafter also referred to as "position reference surface") of the head chip 1. As a result, a pressure P1 due to a water head difference between the position reference plane and the supply sub-tank 81 and a pressure P2 due to a water head difference between the position reference plane and the circulation sub-tank 82 are generated.

The supply sub-tank 81 and the circulation sub-tank 82 are connected via a flow path 86. The pressure applied by the pump 88 allows the ink to be returned from the circulation sub-tank 82 to the supply sub-tank 81.

That is, the supply sub-tank 81, the flow path 252, the flow path in the inkjet head 100 (common ink chamber 51, pressure chamber 131, discharge flow path 121, first common discharge flow path 134, second common discharge flow path 135, discharge The liquid chamber 57 ), the flow path 85 , the circulation sub-tank 82 , and the flow path 86 constitute the circulation flow path 87 of the ink circulation section 8 .

Furthermore, the pressures P1 and P2 can be adjusted by appropriately changing the ink filling amount in each sub-tank and the position of each sub-tank in the Z direction (direction of gravity). The ink within the inkjet head 100 can be circulated at an appropriate circulation flow rate due to the pressure difference between the pressure P1 and the pressure P2. This makes it possible to remove air bubbles and foreign matter generated within the head chip 1 with the filter unit 90, while suppressing clogging of the nozzle 111 and defective injection.

(Operation of inkjet head 100)
Ink is introduced into the first liquid chamber 51a of the common ink chamber 51 from the first ink port 53. The introduced ink passes through the filter F, the second liquid chamber 51b, and is introduced into the inlet of the pressure chamber 131.

When a voltage is applied to the drive electrode provided on the partition wall of the ink introduced into the pressure chamber 131, the partition wall is displaced and pressure is applied to the ink inside the pressure chamber 131. Due to the generation of such pressure, the ink within the pressure chamber 131 is ejected from the tip (ejection port) of the nozzle 111 toward the fabric 240.

A part of the ink supplied from the common ink chamber 51 to the discharge port of the nozzle 111 via the pressure chamber 131 is taken out from the two discharge channels 121 branching from the pressure chamber 131, and is taken out from the ink circulation section. 8 (see FIG. 9). Specifically, the ink taken out from the two discharge passages 121 is collected in the first common discharge passage 134, and the ink is collected in the first common discharge passage 134, the second common discharge passage 135, the discharge liquid chamber 57, and the fourth ink port 56. The liquid is discharged to the outside of the inkjet head 100 through the inkjet head 100 . Thereafter, the ink is returned to the supply sub-tank 81 installed outside the inkjet head 100 via the filter unit 90 located in the middle of the flow path 85, and is introduced from the first ink port 53 through the flow path 251 again. The common ink chamber 51 is reached (see FIG. 9). The ink returned to the common ink chamber 51 is then supplied to the pressure chamber 131 again.

Such circulation of ink within the inkjet head 100 is performed by driving the pump 88 not only when ink is ejected but also when ink is not ejected. As a result, the ink is less likely to stay near the ejection opening of the nozzle 111, making it difficult for the ink to dry or for solid colorant to precipitate or aggregate near the ejection opening of the nozzle 111, thereby suppressing nozzle clogging.

On the other hand, in the inkjet head 100 that has a plurality of discharge channels 121 per nozzle 111, there is an inkjet head that does not have a discharge channel 121, or an inkjet head that has only one discharge channel 121 per nozzle 111. The pressure near the ejection port of the nozzle 111 is more likely to become unstable due to the influence of the discharge flow path 121 than in an inkjet head. As a result, when ink is ejected at a high ejection frequency, the meniscus of ink at the ejection opening of the nozzle 111 tends to become unstable more easily than in the past, resulting in a problem that ejection failure is more likely to occur. Such instability of the meniscus of the ink was more pronounced as the viscosity of the ink was lower.

In contrast, the present inventors have found that when forming an image using the image forming apparatus 200 having the inkjet head 100 having a plurality of discharge channels 121 per nozzle 111 as described above, first, the ink is It has been found that it is effective to increase the viscosity appropriately, specifically, to adjust the viscosity of the ink at 25°C within the range of 6 to 20 cP. As a result, it is possible to stabilize the ink meniscus near the ejection opening of the nozzle 111, thereby suppressing nozzle clogging caused by ink stagnation and reducing the drop in ejection stability when ejecting at a high ejection frequency. Can be suppressed. The composition of the ink will be explained in detail later.

Furthermore, by adjusting the impedance between the discharge channel 121 and the nozzle 111 or between the plurality of discharge channels 121, the meniscus of ink near the ejection opening of the nozzle 111 can be further stabilized.

That is, when the impedance Z of the discharge flow path 121 expressed by the following formula (1) is Za, and the impedance Z of the nozzle 111 expressed by the following formula (1) is Zb, 5≦ΣZa/Zb≦7 is satisfied. It is preferable to do so. However, ΣZa indicates the sum of the impedances Za of the plurality of discharge channels 121 connected to each nozzle 111.
Formula (1): Z=(R ² +2πfM ² ) ^1/2

In equation (1), Z indicates the impedance of the discharge flow path 121 or the nozzle 111, and f indicates the discharge frequency.

R in equation (1) represents the viscous resistance of the ink flowing in the discharge channel 121 or the nozzle 111, which is expressed by the following equation (2). M represents the inertance of ink flowing in the discharge channel 121 or the nozzle 111, which is expressed by the following equation (3).
Formula (2): R=8ηL(h+w ² )/(hw) ³
Formula (3): M=ρL/hw

In equations (2) and (3), η is the viscosity (Pa·s) of the ink. ρ is the density of the ink (kg/m ³ ).
L is the length (μm) of the discharge channel 12 or the nozzle 111, assuming that the discharge channel 121 or the nozzle 111 is a rectangular parallelepiped channel.
h is the height (μm) of the discharge channel 12 or the nozzle 111, assuming that the discharge channel 121 or the nozzle 111 is a rectangular parallelepiped channel.
w is the width (μm) of the discharge channel 12 or the nozzle 111, assuming that the discharge channel 121 or the nozzle 111 is a rectangular parallelepiped channel.

When the impedance ratio ΣZa/Zb is 5 or more, the flow path resistance of the discharge channel 121 is appropriately high, so that it is easy to prevent ink from flowing too much into the discharge channel 121 and no longer flowing into the nozzle 111. On the other hand, when the impedance ratio ΣZa/Zb is 7 or less, the flow resistance in the discharge channel 121 is not too high, so that it is possible to prevent ink from flowing into the discharge channel 121 at all.

In this embodiment, the discharge channel 121 is a combination of the first discharge channel 122 and the second discharge channel 123, so the impedance of the discharge channel 121 is the same as that of the first discharge channel 122. It can be determined as the sum of the impedance and the impedance of the second discharge flow path 123.

In FIG. 7, for example, the length L (L ₁ to L ₄ in FIG. 7) of the first discharge channel 122 means the length in the ink flow direction (Y direction). When the first discharge channel 122 is a rectangular parallelepiped channel with a length L, the height h of the first discharge channel 122 in the cross section perpendicular to the ink flow direction (cross section parallel to the XZ plane) is The width w means the length in the X direction.

The length L of the second discharge channel 123 means the length in the ink flow direction (Z direction). When the second discharge channel 123 is a rectangular parallelepiped channel with a length L, the height h of the second discharge channel 123 in the cross section perpendicular to the ink flow direction (cross section parallel to the XY plane) is The width w means the length in the X direction.

Similarly, the length L of the nozzle 111 means the length in the ink flow direction (Z direction). When the nozzle 111 is a rectangular parallelepiped channel with a length L, the height h of the nozzle 111 means the length in the Y direction, and the width w means the length in the X direction.

Further, it is preferable that the impedances of the plurality of discharge channels 121 (two discharge channels 121 in this embodiment) connected to one nozzle 111 are different. In this way, if the impedances between the plurality of discharge channels 121 are different, the flow of ink near the ejection opening of the nozzle 111 is likely to be moderately disturbed, and a stirring effect is likely to be obtained. The retention of ink can be further suppressed.

Specifically, the ratio (Zmax/Zmin) between the impedance Zmax of the discharge passage 121 with the maximum impedance among the plurality of discharge passages 121 and the impedance Zmin of the discharge passage 121 with the minimum impedance is 2. -7 is preferable. When Zmax/Zmin is 2 or more, a difference tends to occur in the discharge flow, and the effect of stirring the ink near the ejection opening of the nozzle 111 tends to be effectively enhanced. When Zmax/Zmin is 7 or less, there is no fear that ink cannot be taken out to some of the discharge channels 121.

The impedance and impedance ratio (ΣZa/Zb) of the discharge channel 121 depend on the physical properties of the ink, but for example, the length L (the length in the ink flow direction) of the discharge channel 121 and the nozzle 111 and the cross-sectional area of the channel (Height h and width w) can be adjusted.

Next, the structure of the ink (inkjet ink) used in the image forming method of the present invention will be explained.

2. Ink Ink includes a solid colorant, a hydrophobic polymer, and water. The viscosity of the ink at 25° C. is adjusted to a range of 6 to 20 cp.

If the viscosity of the ink is 6 cp or more, even if the inkjet head 100 having a plurality of discharge channels 122 per nozzle 111 is used to eject at a high ejection frequency, the ink will not flow near the ejection opening of the nozzle 111. Since the meniscus is less likely to become unstable, deterioration in injection stability can be suppressed. When the viscosity of the ink is 20 cp or less, the viscosity of the ink is not too high, so nozzle clogging can be suppressed. From the same viewpoint, the viscosity of the ink is more preferably 7 to 15 cp.

The viscosity of the ink can be measured at 25° C. using an E-type viscometer. The rotation speed may be set depending on the viscosity, and may be, for example, 10 rpm or 20 rpm.

The viscosity of the ink can be adjusted by adjusting the ink composition, such as the content of solid colorant, the content of hydrophobic polymer, and the composition of solvent. From the viewpoint of increasing the viscosity of the ink appropriately, the content of solid colorants should be kept above a certain level, and water-soluble organic solvents such as polyhydric alcohols containing trihydric or higher alcohols such as glycerin should be used. It is preferable that the content is above a certain level, or that the content of the hydrophobic polymer is above a certain level, and it is more preferable to combine two or more of these.

As mentioned above, inkjet inks include solid colorants, hydrophobic polymers, and water.

2-1. Solid Colorant The solid colorant is not particularly limited and may be, for example, a solid dye or pigment.

(pigment)
The pigment is not particularly limited, but may be, for example, an organic pigment or an inorganic pigment listed in the color index below.

Examples of red or magenta pigments include Pigment Red 3, 5, 19, 22, 31, 38, 43, 48:1, 48:2, 48:3, 48:4, 48:5, 49:1, 53 :1, 57:1, 57:2, 58:4, 63:1, 81, 81:1, 81:2, 81:3, 81:4, 88, 104, 108, 112, 122, 123, 144 , 146, 149, 166, 168, 169, 170, 177, 178, 179, 184, 185, 208, 216, 226, 257, Pigment Violet 3, 19, 23, 29, 30, 37, 50, 88, Pigment Includes Orange 13, 16, 20, and 36.

Examples of blue or cyan pigments include Pigment Blue 1, 15, 15:1, 15:2, 15:3, 15:4, 15:6, 16, 17-1, 22, 27, 28, 29, 36 , 60 are included.

Examples of green pigments include Pigment Green 7, 26, 36, 50. Examples of yellow pigments include Pigment Yellow 1, 3, 12, 13, 14, 17, 34, 35, 37, 55, 74, 81, 83, 93, 94, 95, 97, 108, 109, 110, 137 , 138, 139, 153, 154, 155, 157, 166, 167, 168, 180, 185, 193.

Examples of black pigments include Pigment Black 7, 28, 26.

Examples of commercially available pigments include Chromofine Yellow 2080, 5900, 5930, AF-1300, 2700L, Chromofine Orange 3700L, 6730, Chromofine Scarlet 6750, Chromofine Magenta 6880, 6886, 6891N, 6790, 6887, Chromofine Fine Violet RE, Chromofine Red 6820, 6830, Chromofine Blue HS-3, 5187, 5108, 5197, 5085N, SR-5020, 5026, 5050, 4920, 4927, 4937, 4824, 4933GN-EP, 4940, 4973, 5205, 5208, 5214, 5221, 5000P, Chromofine Green 2GN, 2GO, 2G-550D, 5310, 5370, 6830, Chromofine Black A-1103, Seika Fast Yellow 10GH, A-3, 2035, 2054, 2200, 2270 , 2300, 2400 (B), 2500, 2600, ZAY-260, 2700 (B), 2770, Seika Fast Red 8040, C405 (F), CA120, LR-116, 1531B, 8060R, 1547, ZAW-262, 1537B , GY, 4R-4016, 3820, 3891, ZA-215, Seika Fast Carmine 6B1476T-7, 1483LT, 3840, 3870, Seika Fast Bordeaux 10B-430, Seika Light Rose R40, Seika Light Violet B800, 7805, Seika Fast Maroon 460N, Seika Fast Orange 900, 2900, Seika Light Blue C718, A612, Cyanine Blue 4933M, 4933GN-EP, 4940, 4973 (manufactured by Dainichiseika Chemical Industries); KET Yellow 401, 402, 403, 404, 405, 406, 416 , 424, KET Orange 501, KET Red 301, 302, 303, 304, 305, 306, 307, 308, 309, 310, 336, 337, 338, 346, KET Blue 101, 102, 103, 104, 105, 106 , 111, 118, 124, KET GREEN 201 (manufactured by COLORTEX YELLOW 301, 314, 315, 316, P -624, 314, U10GN, U3GN, UNN, UNN, UNN, UA -414, U263, U263, U263, FineCOL YE LLOW T- 13, T-05, Pigment Yellow1705, Colortex Orange 202, Colortex Red101, 103, 115, 116, D3B, P-625, 102, H-1024, 105C, UFN, UCN, UBN, U3BN, URN , UGN, UG276, U456, U457, 105C, USN, Colortex Maroon601, Colortex BrownB610N, Colortex Violet600, Pigment Red 122, ColortexBlue516, 517, 518, 519, A818, P-908, 510, Colortex Green402, 403, Colortex Black 702, U905 (Sanyo Color Lionol Yellow1405G, Lionol Blue FG7330, FG7350, FG7400G, FG7405G, ES, ESP-S (Toyo Ink), Toner Magenta E02, Permanent RubinF6B, Toner Yellow HG, Permanent Yellow GG-02, Hostapeam BlueB2G (Hoechst Industries) Novoperm P-HG, Hostaperm Pink E, Hostaperm Blue B2G (manufactured by Clariant); Carbon black #2600, #2400, #2350, #2200, #1000, #990, #980, #970, #960, # 950, #850, MCF88, #750, #650, MA600, MA7, MA8, MA11, MA100, MA100R, MA77, #52, #50, #47, #45, #45L, #40, #33, #32 , #30, #25, #20, #10, #5, #44, and CF9 (manufactured by Mitsubishi Chemical).

(dye)
The dye is not particularly limited as long as it is a solid dye, and may be, for example, a disperse dye.

Examples of disperse dyes include
C. I. Disperse Yellow: 3, 4, 5, 7, 9, 13, 23, 24, 30, 33, 34, 42, 44, 49, 50, 51, 54, 56, 58, 60, 63, 64, 66, 68 , 71, 74, 76, 79, 82, 83, 85, 86, 88, 90, 91, 93, 98, 99, 100, 104, 108, 114, 116, 118, 119, 122, 124, 126, 135 , 140, 141, 149, 160, 162, 163, 164, 165, 179, 180, 182, 183, 184, 186, 192, 198, 199, 202, 204, 210, 211, 215, 216, 218, 224 , 227, 231, 232;
C. I. Disperse Orange: 1, 3, 5, 7, 11, 13, 17, 20, 21, 25, 29, 30, 31, 32, 33, 37, 38, 42, 43, 44, 45, 46, 47, 48 , 49, 50, 53, 54, 55, 56, 57, 58, 59, 61, 66, 71, 73, 76, 78, 80, 89, 90, 91, 93, 96, 97, 119, 127, 130 , 139, 142;
C. I. Disperse Red: 1, 4, 5, 7, 11, 12, 13, 15, 17, 27, 43, 44, 50, 52, 53, 54, 55, 56, 58, 59, 60, 65, 72, 73 , 74, 75, 76, 78, 81, 82, 86, 88, 90, 91, 92, 93, 96, 103, 105, 106, 107, 108, 110, 111, 113, 117, 118, 121, 122 , 126, 127, 128, 131, 132, 134, 135, 137, 143, 145, 146, 151, 152, 153, 154, 157, 159, 164, 167, 169, 177, 179, 181, 183, 184 , 185, 188, 189, 190, 191, 192, 200, 201, 202, 203, 205, 206, 207, 210, 221, 224, 225, 227, 229, 239, 240, 257, 258, 277, 278 , 279, 281, 288, 298, 302, 303, 310, 311, 312, 320, 324, 328, 337, 343;
C. I. Disperse Violet: 1, 4, 8, 23, 26, 27, 28, 31, 33, 35, 36, 38, 40, 43, 46, 48, 50, 51, 52, 56, 57, 59, 61, 63 , 69, 77;
C. I. Disperse Green9;
C. I. Disperse Brown: 1, 2, 4, 9, 13, 19;
C. I. Disperse Blue: 3, 7, 9, 14, 16, 19, 20, 26, 27, 35, 43, 44, 54, 55, 56, 58, 60, 62, 64, 71, 72, 73, 75, 77 , 79, 79:1, 79:2, 81, 82, 83, 87, 91, 93, 94, 95, 96, 102, 106, 108, 112, 113, 115, 118, 120, 122, 125, 128 , 130, 139, 141, 142, 143, 146, 148, 149, 153, 154, 158, 165, 167, 171, 173, 174, 176, 181, 183, 185, 186, 187, 189, 197, 198 , 200, 201, 205, 207, 211, 214, 224, 225, 257, 259, 267, 268, 270, 281, 284, 285, 287, 288, 291, 291:1, 293, 295, 297, 301 , 315, 330, 333, 373;
C. I. Disperse Black1, 3, 10, 24
is included.

Among these, pigments are preferred because they have good dispersibility in the constituent components of the ink and are excellent in weather resistance.

The content of the solid colorant is not particularly limited, but from the viewpoint of making it easy to adjust the viscosity of the ink within the above range and forming a high-density image, it should be 4 to 15% by mass based on the ink. is preferred. When the content of the solid colorant is 4% by mass or more, not only can the viscosity of the ink be appropriately increased, but also it is easy to form a high-density image. When the content of the solid colorant is 15% by mass or less, the viscosity of the ink does not become too high, so nozzle clogging is less likely to occur. From the same viewpoint, the content of the solid colorant is more preferably 5 to 15% by mass, and even more preferably 6.5 to 12% by mass, based on the ink.

2-2. Hydrophobic polymer The hydrophobic polymer is a water-dispersible polymer, and can be a polymer dispersant, a water-dispersible resin (binder resin), or the like.

(polymer dispersant)
The type of polymeric dispersant is not particularly limited, but examples include styrene, styrene derivatives, vinylnaphthalene derivatives, acrylic acid, acrylic acid derivatives, maleic acid, maleic acid derivatives, itaconic acid, itaconic acid derivatives, fumaric acid. , block copolymers and random copolymers made of two or more types of monomers selected from fumaric acid derivatives, salts thereof, polyoxyalkylenes, polyoxyalkylene alkyl ethers, and the like.

When the polymer dispersant has an acidic group such as a carboxyl group, the acidic group is preferably neutralized with a neutralizing base. Examples of neutralizing bases include organic bases such as ammonia, monoethanolamine, diethanolamine, triethanolamine, morpholine, and the like.

(Water dispersible resin)
Examples of water-dispersible resins include urethane resins, butadiene resins, acrylic resins, polystyrene, and the like. Examples of butadiene-based resins include styrene-butadiene copolymers and acrylonitrile-butadiene copolymers. Examples of acrylic resins include acrylic ester copolymers, styrene-acrylic copolymers, silicone-acrylic copolymers, and acrylic-modified fluororesins. Among these, urethane resins and styrene-acrylic copolymers are preferred.

Examples of styrene-acrylic copolymers include styrene-(meth)acrylic acid copolymers and styrene-(meth)acrylic acid-(meth)acrylic acid ester copolymers. Examples of (meth)acrylates include benzyl (meth)acrylate, cyclohexyl (meth)acrylate, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, hexyl (meth)acrylate, ) acrylate, octyl (meth)acrylate, lauryl (meth)acrylate, 2-ethylhexyl (meth)acrylate, 2-ethylhexylcarbitol (meth)acrylate, phenol EO modified (meth)acrylate, isobornyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentanyl (meth)acrylate, and dicyclopentenyloxyethyl (meth)acrylate.

Urethane resin is a polymer obtained by reacting polyol and polyisocyanate. Examples of polyols include polypropylene glycol, polyethylene glycol, polytetramethylene glycol, poly(ethylene adipate), poly(diethylene adipate), poly(propylene adipate), poly(tetramethylene adipate), poly(hexamethylene adipate), poly -ε-caprolactone, poly(hexamethylene carbonate), and silicone polyols. Examples of isocyanates include tolylene diisocyanate, 4,4-diphenylmethane diisocyanate, xylylene diisocyanate, naphthalene diisocyanate, hexamethylene diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated 4,4-diphenylmethane diisocyanate, isophorone diisocyanate, tetramethylxylylene diisocyanate. Contains diisocyanate.

The Tg of the water-dispersible resin is not particularly limited, but may be, for example, -30 to 100°C, preferably -10 to 50°C, more preferably 20 to 40°C.

The acid value of the water-dispersible resin is not particularly limited, but from the viewpoint of improving dispersion stability, it is preferably 44 mgKOH/g or more, and more preferably 60 mgKOH/g or more. The upper limit of the acid value may be, for example, 110 mgKOH/g. The acid value can be measured according to JIS K 0070.

The average particle diameter of the water-dispersible resin is not particularly limited, but from the viewpoint of making the nozzle of an inkjet head less likely to clog, it is preferably 300 nm or less, more preferably 130 nm or less. The average particle size of the water-dispersible resin can be measured by laser diffraction scattering particle size distribution measurement.

The content of the hydrophobic polymer is appropriately set depending on its type. For example, when the hydrophobic polymer is a polymer dispersant, the content of the polymer dispersant is preferably 4% by mass or less, preferably 0.8 to 2% by mass, based on the ink. When the polymer dispersant is 0.8% by mass or more, it is easy to sufficiently improve the dispersibility of solid colorants such as pigments, and when it is 4% by mass or less, it is easy to suppress excessive increase in viscosity.

If the hydrophobic polymer is a water-dispersible resin (binder resin), the content of the water-dispersible resin (binder resin) should be adjusted according to the amount of water-dispersible resin (binder resin) in order to easily adjust the viscosity of the ink within the above range. The amount is preferably 1 to 15% by mass. When the content of the water-dispersible resin is 1% by mass or more, it is easy to increase the viscosity of the ink appropriately, which not only improves the injection stability but also improves the adhesion of the resulting image to the fabric and the scratch resistance. It's also easy to raise. When the content of the water-dispersible resin is 15% by mass or less, the viscosity of the ink does not become too high and nozzle clogging is less likely to occur. From the same viewpoint, the content of the water-dispersible resin is more preferably 2 to 10% by mass based on the ink.

When the hydrophobic polymer contains both a polymeric dispersant and a water-dispersible resin, the total amount of the hydrophobic polymer is 1 to 20% by mass relative to the ink, from the viewpoint of making it easier to adjust the viscosity of the ink to the above range. %, preferably 2 to 15% by mass.

2-3. Water-soluble organic solvent Water-soluble organic solvents are not particularly limited as long as they are compatible with water, but examples thereof include polyhydric alcohols (e.g., ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, , dipropylene glycol, tripropylene glycol, dihydric alcohols such as polypropylene glycol, trihydric or higher alcohols such as glycerin, trimethylolpropane, hexanetriol); polyhydric alcohol ethers (e.g. ethylene glycol monomethyl ether, Ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monophenyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol dimethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether); Monohydric alcohols ( For example, methanol, ethanol, propanol, pentanol, hexanol, cyclohexanol, benzyl alcohol); Amines (for example, ethanolamine, N-ethyldiethanolamine, morpholine, N-ethylmorpholine, ethylenediamine, diethylenediamine, triethylenetetramine); Amides (e.g., formamide, N,N-dimethylformamide, N,N-dimethylacetamide); Heterocycles (e.g., 2-pyrrolidone, N-methyl-2-pyrrolidone, N-cyclohexyl-2-pyrrolidone, 2- oxazolidones, 1,3-dimethyl-2-imidazolidine), sulfoxides (eg, dimethyl sulfoxide); and sulfones (eg, sulfolane).

Among these, from the viewpoint of easily increasing the viscosity of the ink, it is preferable that the water-soluble organic solvent contains polyhydric alcohols. From the viewpoint of easily increasing the viscosity of the ink, the polyhydric alcohol preferably contains trihydric or higher alcohols, and more preferably contains glycerin.

It is preferable that the content of polyhydric alcohols is appropriately large. Specifically, the content of polyhydric alcohol is preferably 25 to 50% by mass based on the ink. When the content of the polyhydric alcohol is above a certain level, the viscosity of the ink tends to increase, and when it is below a certain level, it is easy to prevent nozzle clogging due to the viscosity of the ink becoming too high. From the same viewpoint, the content of the polyhydric alcohol is more preferably 30 to 45% by mass based on the ink.

2-3. Other Components The inkjet ink may further contain other components as necessary. Examples of other components include solvents, surfactants, preservatives, fungicides, rust preventives, pH adjusters, and the like.

(surfactant)
The water-based inkjet ink may further contain a surfactant to control its surface tension.

Examples of surfactants include anionic, cationic, amphoteric, and nonionic surfactants. Examples of anionic surfactants include fatty acid salts, alkyl sulfates, alkyl sulfates, alkylbenzene sulfonates, alkylnaphthalene sulfonates, dialkyl sulfosuccinates, alkyl phosphate ester salts, alkylnaphthalene sulfonic acid formalin condensation Contains polyoxyethylene alkyl sulfate salts. Examples of cationic surfactants include amine salts, tetraalkyl quaternary ammonium salts, trialkyl quaternary ammonium salts, alkylpyridinium salts, and alkylquinolinium salts. Examples of nonionic surfactants include polyoxyethylene alkyl ether, polyoxyethylene alkylphenyl ether, polyoxyethylene fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene alkylamine, and ethylene oxide adduct of polypropylene glycol. , acetylene glycol, and ethylene oxide adducts of acetylene glycol.

(preservative, antifungal agent)
Examples of preservatives or antifungal agents include aromatic halogen compounds (e.g., Preventol CMK), methylene dithiocyanate, halogen-containing nitrogen-sulfur compounds, 1,2-benzisothiazolin-3-one (e.g., PROXELGXL), and the like. It will be done.

(pH adjuster)
Examples of pH adjusters include urea, sodium hydroxide, and the like.

Next, the image forming method of the present invention will be explained with reference to FIG.

3. Image Forming Method The image forming method of the present invention is to form an image on the fabric 140 by ejecting the above ink from the inkjet head 1 of the image forming apparatus 100 shown in FIG.

Specifically, the image forming method of the present invention includes 1) a step of ejecting ink from the inkjet head 1 to apply ink droplets onto the fabric 140 (ink application step); and 2) applying the ink to the fabric 140. The method includes a step of drying the ink (drying step).

Regarding the step 1) (ink application step) In the ink application step, at least the above-mentioned ink is ejected from the inkjet head 100 of the image forming apparatus 200 in FIG. 1 to apply the ink onto the fabric 140.

The fiber material composing the fabric 240 is not particularly limited, but may include natural fibers such as cotton (cellulose fiber), silk, and wool, chemical fibers such as nylon, rayon, polyurethane, polyester, and acrylic resin, or a combination of these. It can be a woven fabric, a knitted fabric, a non-woven fabric, etc. of composite fibers.

The ejection frequency of the inkjet head 100 is preferably 20 to 50 kHz from the viewpoint of enabling high-speed printing.

In the present invention, as described above, ink is ejected from the inkjet head 100 of the image forming apparatus 200 shown in FIG. In the inkjet head 100, in order to constantly circulate and circulate ink in the circulation channel 87 of the ink circulation section 8, that is, the discharge channel 121 provided in plurality for each nozzle 111, It is possible to suppress ink stagnation and nozzle clogging caused by it. Further, the above-mentioned ink whose viscosity is appropriately increased is used. This prevents a decrease in ejection stability due to instability of the ink meniscus near the ejection opening of the nozzle 111, which is likely to occur when using the inkjet head 100 having a plurality of discharge channels 121 provided for each nozzle 111. It can be suppressed.

The surface of the fabric 240 to which the ink is applied may be heated. Thereby, the drying speed after applying the ink can be increased, and bleeding of the image can be easily suppressed. The surface temperature of the fabric 240 when the ink is applied is preferably 35 to 70°C.

The heating method is not particularly limited, but heating can be performed from the surface of the fabric 240 opposite to the surface to which ink is applied. The heating means is not particularly limited and may be any of an infrared heater, heating wire, UV lamp, gas, hot air dryer, etc. Among these, heating using a heating wire or an infrared heater is preferable from the viewpoint of safety and energy efficiency.

Regarding the step 2) (drying step) In the drying step, the ink applied to the fabric 240 is dried to remove moisture and solvent components in the ink.

The drying method is not particularly limited, and may be a method using a heater, a hot air dryer, a heated roller, or the like. Among these, it is preferable to heat and dry both sides of the fabric 140 using a hot air dryer and a heater.

When drying is performed using a heating means such as a heater, the heating means may be placed on the downstream side of the inkjet head 100 in the conveyance direction of the fabric 240, or the heating means may be placed on the downstream side of the inkjet head 100 in the conveyance direction of the fabric 240. The fabric 240 may be placed on the upstream side of the inkjet head 100 to dry the ink using heat stored in the fabric 240 before the ink is ejected by the inkjet head 1. They may be placed on both downstream sides for drying.

The drying temperature is not particularly limited, but may be, for example, 160° C. or lower. The drying time may be, for example, about 0.5 to 30 minutes, depending on the drying temperature.

Furthermore, the image forming method of the present invention may further include steps other than those described above, depending on the type of inkjet ink. For example, before step 1), 3) a step of applying a pretreatment agent to the fabric 140 (pretreatment step) may be performed, or after step 2), 4) fabric 140 on which an image is formed A step (fixing step) of drying the image and fixing the image onto the fabric 140 may be further performed.

Regarding the step 3) (pretreatment step) In the image forming method according to the present invention, from the viewpoint of preventing ink bleeding and improving fixing properties, water, polyvalent metal ions, polymer The fabric 240 may be imaged on a fabric 240 that has been pretreated with a pretreatment agent that includes.

The pre-treatment may be performed by off-line processing in which an image is formed on the fabric 240 to which the pre-treatment agent has been applied, or may be performed by in-line processing in which the pre-treatment is performed continuously with image formation.

The method for applying the pretreatment agent is not particularly limited, and may be an inkjet method or a coating method using a coater or the like.

Regarding the step 4) (fixing step) In the fixing step, the ink dried on the fabric 140 is heated and fixed on the fabric 140. Thereby, the solid colorant is fixed on the fabric 140 and the original hue of the ink is expressed.

Examples of the fixing method include heat treatment using a normal pressure steam method, a high pressure steam method, a thermofix method, and the like. The temperature during the heat treatment is preferably 120 to 200°C, more preferably 140 to 180°C.

Further, after the above step 4), 5) a step of removing dyes and pretreatment agents that could not be dyed onto the fabric 240 (washing step) and 6) a step of drying the washed fabric 240 (drying step). You can go further.

Regarding the step 5) (washing step) In the washing step, the solid colorant and pretreatment agent that could not be dyed onto the fabric 240 after the fixing step are removed. The solid colorant that could not be fixed onto the fabric 240 can be removed using a conventionally known cleaning method. For example, cellulose fibers are generally washed with water and hot water, treated with a soaping bath containing a nonionic detergent, and then washed with hot water and then water. By removing undyed solid colorants, washing fastness, water fastness, and sweat fastness tend to improve.

Regarding the step 6) (drying step) The drying step is performed after the washing step, and the washed fabric 240 is dried. The drying method is not particularly limited, but may be a method of squeezing the washed fabric 240, drying it, or drying it using a dryer (heat roll, iron, etc.).

Note that as an inkjet head used in the image forming method of the present invention, an example is shown in which the discharge channel 121 is connected to the pressure chamber 131 in the inkjet head 100 shown in FIGS. It may be connected midway between the chamber 131 and the discharge port of the nozzle 111.

Further, although FIG. 9 shows an example in which the filter unit 90 is arranged in the flow path 85, the present invention is not limited thereto. The filter unit 90 may be placed, for example, in any of the circulation channels 87 of the ink circulation section 8.

Further, in FIG. 9, a method of controlling the circulation of ink by the difference in water head has been described as an example of the ink circulation section 8, but it can be modified as appropriate as long as the structure can generate a circulating flow of ink.

Further, in the inkjet head 100 of FIGS. 2 to 7, an example is shown in which the ejection method is a piezo method, but the ejection method is not limited to this, and a thermal method may be used.

Further, the printing method of the image forming apparatus 200 in FIG. 1 is not particularly limited, and may be a single pass method or a scan method. A single pass method is preferable in that it is effective for high-speed printing. As the single-pass type image forming apparatus, it is preferable to use a line head type inkjet head.

EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples, but the present invention is not limited thereto.

1. Components of ink (1) Solid colorant Pigment Black7
Disperse Blue60
Cab-o-jet 400 (self-dispersing pigment, manufactured by CABOT, black aqueous pigment dispersion)

(2) Hydrophobic polymer (polymer dispersant)
J819 (Jonkryl 819 manufactured by BASF Japan, Tg: 57°C, acid value 75mgKOH/g, ammonia neutralization)

(Water dispersible resin)
WBR-2000U (Taisei Fine Chemical Co., Ltd. Acrit, polyurethane resin particles, Tg: 45°C)
J7600 (Joncryl 7600 manufactured by BASF Japan, Tg: 35°C, acrylic resin particles, average particle size: 90 nm)
J390 (Joncryl 390 manufactured by BASF Japan, styrene-acrylic acid copolymer, Tg: -5°C, acid value: 54mgKOH/g, average particle size: 0.09μm)

(3) Solvent Glycerin Propylene glycol Diethylene glycol

(4) Surfactant KF351A (manufactured by Shin-Etsu Silicone Co., Ltd., polyoxyethylene modified silicone)

(5) Preservative Proxel GXL (1,2-benzisothiazolin-3-one)

2. Preparation of ink <Preparation of inks 1 to 14>
Inks 1 to 13 were prepared by mixing each component to have the composition shown in Table 1 or 2.

<Evaluation>
The viscosity of the obtained inks 1 to 14 was measured by the following method.

(viscosity)
The viscosity of the ink was measured using an E-type viscometer V-25 (manufactured by Toki Sangyo Co., Ltd.) at 25°C and 20 rpm (inks 1 to 4, 7, 8, and 10 to 14) or 10 rpm (inks 5, 6, 9, and 10).

The compositions and physical properties of Inks 1 to 10 are shown in Table 1, and the compositions and physical properties of Inks 11 to 14 are shown in Table 2.

3. Image forming method and evaluation <Comparative Examples 1 and 2, Examples 5 to 16>
(Image forming device)
First, an image forming apparatus 200 shown in FIGS. 1 to 9 was prepared. The configuration of image forming apparatus 200 is as follows.
-Position of filter unit 90: placed in the flow path 85 outside the inkjet head 100 (see FIG. 9)
- Number of discharge channels 121 connected to the nozzle 111: 2 (the cross-sectional areas of the two discharge channels 121 are the same, the lengths are different, impedance ratio Zmax/Zmin between the discharge channels 121: 3)
・Printing method of inkjet head 100: Scan method

(fabric)
T/C broad (35% cotton, 65% polyester) was prepared as a fabric.

(image formation)
Then, the inks shown in Table 3 or 4 were ejected from the nozzle 11 of the inkjet head 1 of the image forming apparatus 100 to form an image on the fabric. Specifically, image formation was performed using the following procedure.

1) Ink application step The obtained ink was set in the image forming apparatus 100. Then, a solid image was formed on the fabric using the obtained ink at 540 dpi in main scanning and 720 dpi in sub-scanning. Note that dpi represents the number of ink droplets (dots) per 2.54 cm. The discharge frequency was 22.4kHz.

2) Drying process The fabric to which the ink was applied was dried at 160° C. for 3 minutes using a belt conveyance dryer.

<Examples 1 and 2>
Image formation was performed in the same manner as in Example 5, except that the width w and height h (cross-sectional area) of the discharge channel of the inkjet head were changed and the impedance ratio (ΣZa/Zb) was changed as shown in Table 3. Ta.

<Example 3>
Image formation was performed in the same manner as in Example 5, except that the width w and height h (cross-sectional area) of the discharge channel of the inkjet head were changed to make the impedance of the two discharge channels the same.

<Example 4>
Image formation was performed in the same manner as in Example 5 except that the filter unit 90 was not provided on the flow path 85 of the ink circulation section 8.

<Comparative Examples 3 and 4>
Image formation was performed in the same manner as in Example 5, except that the number of discharge channels communicating with one nozzle was changed as shown in Table 3.

<Evaluation>
The injection stability during image formation of Examples 1 to 16 and Comparative Examples 1 to 4, the presence or absence of nozzle clogging, and the resulting image quality were evaluated by the following methods.

(injection stability)
After continuous ejection (ejection frequency: 22.4 kHz) for 10 minutes, defects such as ejection defects and bends were checked using an injection inspection machine. Then, the injection stability was evaluated based on the following criteria.
5: There is no problem even after long-term continuous use. 4: No injection defects occur. 3: Slight bending occurs, but there is no problem. 2: Injection defects occur during printing during injection. 1: Injection defects occur immediately. occurs or normal injection is not possible.If the score is 3 or higher, it is considered to be good.

(nozzle clogging)
Maintenance of the nozzle surface was performed during image formation using a print tester, and the state of missing nozzles after the maintenance was confirmed using a nozzle check chart. Then, nozzle clogging was evaluated based on the following criteria.
5: No clogging occurs even after long-term continuous use 4: No clogging occurs 3: Even if clogging occurs, it can be recovered by maintenance 2: Many cloggings occur that cannot be recovered by maintenance 1: Normal injection is not possible 3 or more I judged it to be good.

(image quality)
After confirming the presence or absence of white streaks in the obtained 100% solid image, the density L ^* was measured using a colorimeter. Then, evaluation was made based on the following criteria.
5: No defects, very high concentration (L ^* is 23 or less)
4: No defects and high concentration (L ^* is more than 23 and less than 25)
3: No defects and sufficient concentration (L ^* is more than 25 and less than 30)
2: Missing spots are found here and there or the density is insufficient (L ^* is over 30)
1: Many defects occurred and printing could not be performed normally. A score of 3 or higher was judged to be good.

Note that since the colors of ink 11 were different, the image quality was evaluated based on the presence or absence of white streaks. Specifically, 5 is when there are no white stripes at all, 4 is when there are some white stripes but they are hardly noticeable, 3 is when there are white stripes but there is no practical problem, and 3 is when there are white stripes and it cannot be used for practical purposes. was set to 2.

The evaluation results of Comparative Examples 1 to 4 and Examples 1 to 6 are shown in Table 3, and the evaluation results of Examples 7 to 16 are shown in Table 4.

As shown in Tables 3 and 4, in Examples 1 to 14, in which an image forming apparatus having an inkjet head having a plurality of discharge channels for each nozzle was used, and ink having a viscosity above a certain level was used, all of the nozzles It can be seen that good injection stability is exhibited without clogging. It can also be seen that the image quality is also good.

On the other hand, it can be seen that in Comparative Example 1, in which an ink with an ink viscosity of less than 6 cP was used, the ejection stability was lower than that in Example 4. On the other hand, it can be seen that in Comparative Example 2 using an ink with an ink viscosity exceeding 20 cP, the injection stability and nozzle clogging were remarkable compared to Example 4. In addition, in Comparative Example 3 using an inkjet head with only one discharge channel and Comparative Example 4 using an inkjet head without a discharge channel, the ejection stability is low and the obtained image quality is also poor. I understand that.

According to the present invention, it is possible to provide an image forming method that can suppress nozzle clogging caused by ink retention near the nozzles of an inkjet head, and also suppress deterioration in ejection stability.

1 Head chip 8 Ink circulation unit 11 Nozzle board 12 Channel spacer board 13 Pressure chamber board 51 Common ink chamber 81 Supply sub-tank 82 Circulation sub-tank 84 Circulation channel 85, 86 Channel 87 Circulation channel 88, 89 Pump 90 Filter Unit 121 Discharge channel 131 Pressure chamber 134 First common discharge channel 135 Second common discharge channel 100 Inkjet head 200 Image forming device 210 Conveyance device 211 Belt conveyor 212 Feed rollers 213a, 213b Pulley 214 Belt 220 Ink supply device 230 Main Tank 240 Fabric 251, 252 Channel 253 Bypass Channel 254 Valve

Claims (14)

an ink chamber, a nozzle for discharging ink supplied from the ink chamber, and a plurality of discharge channels provided for each nozzle and for taking out a portion of the ink supplied from the ink chamber to the discharge port of the nozzle; an inkjet head having
An image forming method using an image forming apparatus comprising: an ink circulation section that returns ink taken in by the discharge flow path to the ink chamber and circulates the ink;
comprising a step of ejecting ink from a nozzle of the inkjet head,
The ejection frequency of the ink is 20kHz or more,
The ink includes a solid colorant and a solvent,
The viscosity of the ink at 25° C. is 6 to 20 cp.
Image forming method. In the step, ink is ejected to form an image on the fabric.
The image forming method according to claim 1. The content of the solid colorant is 4 to 15% by mass based on the ink,
The image forming method according to claim 1 or 2. The solvent further includes a water-soluble organic solvent.
The image forming method according to any one of claims 1 to 3. The water-soluble organic solvent contains polyhydric alcohols,
The image forming method according to claim 4. The polyhydric alcohols include trihydric or higher alcohols,
The image forming method according to claim 5. The content of the polyhydric alcohol is 25% by mass or more based on the ink.
The image forming method according to claim 5 or 6. The ink further includes a hydrophobic polymer.
The image forming method according to any one of claims 1 to 7. The hydrophobic polymer includes the polymer dispersant and the water-dispersible resin,
The total amount of the hydrophobic polymer is 1 to 20% by mass based on the ink,
The image forming method according to claim 8 . The hydrophobic polymer includes a water-dispersible resin selected from the group consisting of urethane resin, butadiene resin, and acrylic resin.
The image forming method according to claim 8 or 9 . When the impedance Z of the discharge flow path expressed by the following formula (1) is Za, and the impedance Z of the nozzle expressed by the following formula (1) is Zb, 5≦ΣZa/Zb≦7 is satisfied.
The image forming method according to any one of claims 1 to 10 .
Formula (1): Z=(R ² +2πfM ² ) ^1/2
(In formula (1),
Z is the impedance of the discharge channel or the nozzle,
f is the ejection frequency (Hz),
R is the viscous resistance of the ink flowing in the discharge channel or the nozzle, expressed by the following formula (2),
M is the inertance of the ink flowing in the discharge flow path or the nozzle, expressed by the following formula (3))
Formula (2): R=8ηL(h+w ² )/(hw) ³
Formula (3): M=ρL/hw
(In formulas (2) and (3),
η is the fluid viscosity (Pa·s) of the ink,
ρ is the density of the ink (kg/m ³ ),
L is the length (μm) of the discharge channel or the nozzle, assuming that the discharge channel or the nozzle is a rectangular parallelepiped channel,
h is the height (μm) of the discharge channel or the nozzle, assuming that the discharge channel or the nozzle is a rectangular parallelepiped channel;
w is the width (μm) of the discharge channel or the nozzle, assuming that the discharge channel or the nozzle is a rectangular parallelepiped channel) The impedances of the at least two discharge channels provided for each nozzle are different from each other,
The image forming method according to claim 11 . The ink circulation section includes a circulation flow path that returns the ink taken in by the discharge flow path to the ink chamber and circulates the ink, and a filter unit disposed in the circulation flow path.
The image forming method according to any one of claims 1 to 12 . The ejection frequency of the ink is 20 to 50 kHz,
The image forming method according to any one of claims 1 to 13 .

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