JP7593404B2 - Image forming apparatus and inkjet head - Google Patents

Description

This invention relates to an image forming apparatus and an inkjet head.

Conventionally, there are image forming devices that use inkjet heads to eject ink from nozzles to form images, structures, etc. on a medium.

When there is a large temperature difference between the ink temperature and the ambient temperature, heat can be dissipated from the ink in the flow path from the tank that temporarily stores the ink in the image forming device to the nozzle, or the flow path can be heated using a heater, causing the temperature distribution of the ink to become uneven, making it impossible to eject droplets stably.

In relation to this, Patent Document 1 describes a technique for heating ink without heating the heater to a high temperature by spirally winding a flow path around a heater and ensuring a sufficient heating area of the flow path.
Furthermore, Patent Document 2 describes a technology in which, when a flow path is formed by connecting pipes, a pipe that is connected to a heater with high thermal conductivity is routed as far as possible to the nozzle side, thereby lengthening the heating area and bringing the ink temperature closer to the desired level.

JP 2009-233900 A JP 2013-230633 A

However, the technologies in Patent Documents 1 and 2 heat the ink from the walls of the flow path piping, and therefore do not eliminate the unevenness of the temperature distribution of the ink within the piping.

The object of this invention is to provide an image forming apparatus and inkjet head that enable stable droplet ejection in a simple and cost-effective manner.

In order to achieve the above object, the present invention provides an image forming apparatus according to the first aspect of the present invention,
An image forming apparatus that forms an image by ejecting a thixotropic liquid as droplets,
A tank for temporarily storing the liquid;
an inkjet head having a discharge nozzle for discharging the liquid in the tank;
A flow path connecting the tank and the discharge nozzle;
a single homogenizing member, the static mixer being disposed in the flow path and homogenizing the liquid;
having
a heating section having a heater in the flow path for heating the liquid flowing through the flow path;
the homogenizing member is disposed on the discharge nozzle side relative to the heating section,
The homogenizing member and the heating section are thermally connected via a connection portion which is an ink inlet of the inkjet head.

The present invention relates to an image forming apparatus comprising :
The flow of liquid through the flow passage immediately prior to the homogenizing member is laminar.

The present invention relates to an image forming apparatus comprising :
The liquid is a dispersion liquid in which particles are dispersed.

According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects,
A circulation flow path connects the discharge nozzle and the tank.

According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects,
At least a portion of the flow passage section from the homogenizing member to the discharge nozzle is formed of a heat insulating member having a thermal conductivity of 1.0 W/m·K or less.

The present invention relates to an image forming apparatus comprising :
The heat insulating member is at least one of a plastic member, a rubber member, and a glass member.

According to a seventh aspect of the present invention, in the image forming apparatus according to any one of the first to sixth aspects,
The homogenizing member is provided in the flow passage within the inkjet head.

According to an eighth aspect of the present invention, in the image forming apparatus according to any one of the first to sixth aspects,
The homogenizing member is provided in the flow path between the tank and the inkjet head.

The ink jet head according to the invention of claim 9 comprises:
An inkjet head that ejects a thixotropic liquid as droplets to form an image,
a flow path connecting a tank for temporarily storing the liquid and a discharge nozzle;
a single homogenizing member, the static mixer being disposed in the flow path and homogenizing the liquid;
having
a heating section having a heater in the flow path for heating the liquid flowing through the flow path;
the homogenizing member is disposed on the discharge nozzle side relative to the heating section,
The homogenizing member and the heating section are thermally conductively connected via a connection.

According to the present invention, it is possible to provide an image forming apparatus and an inkjet head that enable stable droplet ejection in a simple and low-cost manner.

1 is a diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. 1 is a cross-sectional view of the vicinity of an inlet of an inkjet head according to an embodiment of the present invention. FIG. 13 is a diagram showing a configuration of an image forming apparatus according to a modified example of the embodiment of the present invention. FIG. 11 is a cross-sectional view of the vicinity of an inlet of an ink-jet head according to a modified example of an embodiment of the present invention.

Below, an embodiment of the present invention is explained based on the drawings.

FIG. 1 is a diagram showing the configuration of an image forming apparatus 1. As shown in FIG.
The image forming apparatus 1 includes an inkjet head 10 , an ink tank 20 for temporarily storing ink, and external flow paths 31 and 32 that connect the inkjet head 10 and the ink tank 20 .
The inkjet head 10 includes a connection portion 11 that connects to an external flow path 31, and a connection portion 12 that connects to an external flow path 32. The connection portion 11 is an ink inlet, and the connection portion 12 is an ink outlet.

The ink temporarily stored in the ink tank 20 passes through the external flow path 31 and the connection part 11, reaches the nozzles of the inkjet head 10, and a part of it is ejected. The ink that is not ejected passes through the connection part 12 and the external flow path 32, and returns to the ink tank 20. In this way, the ink circulates between the ink tank 20 and the inkjet head 10, and the external flow path 32 functions as a circulation flow path. The arrows near the external flow paths 31 and 32 in Figure 1 indicate the direction in which the ink flows.
The inkjet head 10 also includes a static mixer 13 between the connection portion 11 and the nozzle for stirring and mixing the ink to homogenize the temperature, viscosity, and the like.

FIG. 2 is a cross-sectional view of the vicinity of the connection portion 11 of the ink-jet head 10. As shown in FIG.
The inkjet head 10 has a nozzle plate 14 on the bottom surface, and a plurality of nozzles are formed in the nozzle plate 14. A flow path 15 from the connection portion 11 to the nozzles is connected to an external flow path 31.
A static mixer 13 is provided in a flow path 15 below a connection part 11 which is an ink inlet, and agitates and mixes the ink that has flowed into the flow path 15 in the inkjet head 10. The agitated and mixed ink reaches the nozzle, and a part of the ink is ejected from the nozzle.

A heater H is provided around the piping of the temperature adjustment section 31a of the external flow path 31, and is capable of heating the ink passing through the temperature adjustment section (heating section) 31a.
When the ink passing through the temperature adjustment section 31a is heated by the heater H, the ink near the walls of the pipe in the temperature adjustment section 31a has a high temperature, and the ink in the center of the pipe has a lower temperature than the ink near the walls of the pipe, resulting in uneven temperature distribution of the ink in the pipe.
In addition, since the flow of ink passing through the portion of the ink flow upstream of the portion where the static mixer 13 of the external flow path 31 and the flow path 15 is disposed is a laminar flow, the non-uniformity of the ink temperature distribution occurring in the piping upstream of the portion where the static mixer 13 of the external flow path 31 and the flow path 15 is disposed is not eliminated. Here, the laminar flow is, for example, one that satisfies the following formula.
Re = Duρ/μ ≦ 2300
Re: Reynolds number
D: Representative diameter of the flow passage (diameter of the circular annulus equivalent to the cross-sectional area) [m]
u: flow velocity [m/sec]
ρ: density of liquid [kg/m3]
μ: Viscosity of liquid [Pa sec]

Furthermore, the ink circulating in the image forming apparatus 1 is a dispersion liquid with particles dispersed therein. The ink, which is a dispersion liquid, exhibits non-Newtonian rheology, and is prone to large non-uniformity in temperature distribution.
Examples of pigment particles that can be used as organic pigments include the following pigments:

Examples of pigments for magenta or red include C.I. Pigment Red 2, C.I. Pigment Red 3, C.I. Pigment Red 5, C.I. Pigment Red 6, C.I. Pigment Red 7, C.I. Pigment Red 15, C.I. Pigment Red 16, C.I. Pigment Red 48:1, C.I. Pigment Red 53:1, C.I. Pigment Red 57:1, C.I. Pigment Red 122, C.I. Pigment Red 123, C.I. Pigment Red 139, C.I. Pigment Red 144, C.I. Pigment Red 149, C.I. Pigment Red 166, C.I. Pigment Red 177, C. Examples of the pigments include C.I. Pigment Red 178, C.I. Pigment Red 202, C.I. Pigment Red 222, C.I. Pigment Violet 19, and the like.

Examples of pigments for orange or yellow include C.I. Pigment Orange 31, C.I. Pigment Orange 43, C.I. Pigment Yellow 12, C.I. Pigment Yellow 13, C.I. Pigment Yellow 14, C.I. Pigment Yellow 15, C.I. Pigment Yellow 15:3, C.I. Pigment Yellow 17, C.I. Pigment Yellow 74, C.I. Pigment Yellow 93, C.I. Pigment Yellow 128, C.I. Pigment Yellow 94, C.I. Pigment Yellow 138, and C.I. Pigment Yellow 155. In particular, C.I. Pigment Yellow 155 is preferred in terms of the balance between color tone and light resistance.

Examples of pigments for green or cyan include C.I. Pigment Blue 15, C.I. Pigment Blue 15:2, C.I. Pigment Blue 15:3, C.I. Pigment Blue 16, C.I. Pigment Blue 60, C.I. Pigment Green 7, etc.

Examples of black pigments include C.I. Pigment Black 1, C.I. Pigment Black 6, and C.I. Pigment Black 7.

Inorganic pigments such as titanium oxide have three crystal forms: anatase, rutile, and brookite, but the most commonly used are broadly classified into anatase and rutile. Although not particularly limited, rutile is preferred because it has a high refractive index and high hiding power. Specific examples include the TR series from Fuji Titanium Kogyo Co., Ltd., the JR series from Teika Corporation, and Typeque from Ishihara Sangyo Co., Ltd.

The insoluble pigment is not particularly limited, but examples thereof include azo, azomethine, methine, diphenylmethane, triphenylmethane, quinacridone, anthraquinone, perylene, indigo, quinophthalone, isoindolinone, isoindoline, azine, oxazine, thiazine, dioxazine, thiazole, phthalocyanine, diketopyrrolopyrrole, etc.

Examples of particulate dyes include insoluble dyes such as sulfur dyes, vat dyes, and disperse dyes.
Examples of vat dyes include threne dyes and indigo dyes.
Disperse dyes include benzene azo types (monoazo and disazo), heterocyclic azo types (thiazole azo, benzothiazole azo, pyridone azo, pyrazolone azo, thiophene azo, etc.), anthraquinone types, and condensation types (quinophthalone, styryl, coumarin, etc.).
Similarly, binder particles contained in the ink can also be considered as particles. Examples of binder particles include latex, resin filler, metal particles, ceramic particles, plastic particles, and glass particles.

In addition, the ink circulating in the image forming device 1 is thixotropic. Therefore, where the ink flow rate is slow near the walls of the piping of the external flow path 31 and the flow path 15, the ink viscosity is higher than in the center of the piping, making it difficult to mix the ink, and this tends to result in large non-uniformity in the temperature distribution of the ink.

The ink, which has a non-uniform temperature distribution, is agitated and mixed by the static mixer 13, thereby reducing the non-uniformity of the temperature distribution.
Furthermore, the member heated by the heater H and the element portion of the static mixer 13 are thermally conductively connected via the connection portion 11. Therefore, the element portion of the static mixer 13 is also heated by the heater H. The ink is stirred and mixed by the heated static mixer 13, thereby further reducing non-uniformity in the ink temperature distribution.
Thus, the static mixer 13 functions as a homogenizing member.

In addition, a heat insulating material having a thermal conductivity of 1.0 W/m·K or less is used for the section of the flow path 15 between the static mixer 13 and the nozzle. Therefore, the static mixer 13 can maintain a state in which non-uniformity in the temperature distribution of the ink is reduced.
The heat insulating member is made of at least one of a plastic member, a rubber member, and a glass member, for example.
Specifically, the plastic member is polyethylene (low density), polyethylene (high density), polycarbonate, polyethylene terephthalate, polypropylene, polystyrene, polyvinyl chloride, polybutylene terephthalate, polyamide, epoxy resin, polyether ether ketone, polyether sulfone, phenol resin, polyacetal, acrylic resin, tetrafluoroethylene resin (PTFE), tetrafluoroethylene-ethylene copolymer (ETFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluorovinyl ether copolymer (PFA), silicone resin, and styrene-acrylonitrile-butadiene (ABS resin), and although not limited to the above, the above can be preferably used.
The rubber member may be silicone rubber, polyurethane rubber, butyl rubber, ethylene-propylene rubber, chloroprene rubber, or natural rubber, and is not limited to the above, but the above may be preferably used.
The glass member may be soda glass, flint glass, or crown glass, and is not limited to the above, but the above may be preferably used.

In addition, the ink that is not ejected from the inkjet head 10 is circulated through the connection part 12, which is the ink outlet, and the external flow path 32, and returned to the ink tank 20, thereby further reducing the unevenness of the ink temperature distribution.

As described above, the image forming apparatus 1 of this embodiment is an image forming apparatus 1 that forms an image by ejecting liquid as droplets, and includes a tank (ink tank 20) for temporarily storing the liquid, an inkjet head 10 having an ejection nozzle that ejects the liquid in the tank (ink tank 20), a flow path (external flow path 31, flow path 15) that connects the tank (ink tank 20) and the ejection nozzle, and a homogenizing member (static mixer 13) that is disposed in the flow path (external flow path 31, flow path 15) and homogenizes the liquid.
Therefore, it is possible to provide an image forming apparatus and an inkjet head that enable stable droplet ejection easily and at low cost.

(Modification)
3 is a diagram showing the configuration of an image forming apparatus 1a according to a modified example of the embodiment of the present invention. In the modified image forming apparatus 1a, a static mixer 13 is provided outside the inkjet head 10.
4 is a cross-sectional view of the vicinity of the inlet of the inkjet head 10 in the image forming apparatus 1a according to a modified example of the embodiment. The following mainly describes the differences from FIG. 2 which shows the vicinity of the inkjet head 10 in the image forming apparatus 1 according to the embodiment.

In the configuration of this modified example, the static mixer 13 is provided outside the inkjet head 10 in a temperature adjustment section 31a of an external flow path 31 in which a heater H is provided. The other configurations and operations are similar to those of the image forming apparatus 1 of the above embodiment.
With the above configuration, even if the static mixer 13 cannot be provided in the inkjet head 10, it is possible to provide an image forming apparatus and an inkjet head that enable stable droplet ejection at low cost and in a simple manner.

The present invention is not limited to the above-described embodiment, but may be modified in various ways.
For example, in the above embodiment and modified examples, the homogenizing member is the static mixer 13, but this is not limited to this. For example, any member that can reduce the non-uniformity of the ink temperature distribution even a little by generating turbulence in the laminar ink flow, such as a lattice filter, may be used.

In addition, in the above embodiment and modified example, the ink is heated by a heater H provided in a part of the external flow path 31, but this is not limited to the above. A cooling device may be provided instead of the heater H to cool the ink. Alternatively, the ink may be cooled by natural heat dissipation without providing the heater H and the cooling device.

In addition, in the above-described modified embodiment, the static mixer 13 is provided in the temperature adjustment section 31a provided in a part of the external flow path 31, but this is not limited to the above. If the temperature adjustment section 31a and the connection section 11 of the inkjet head 10 are separated from each other, the static mixer 13 may be provided between the temperature adjustment section 31a and the connection section 11.

In addition, in the above embodiment and modified example, the heater H is provided outside the inkjet head 10, but this is not limited to the above. The heater H may be provided inside the inkjet head 10.

In addition, the specific details of the configuration shown in the above embodiment may be modified as appropriate without departing from the spirit of the present invention.

This invention can be used in inkjet heads and image forming devices.

1, 1a Image forming apparatus 10 Inkjet head 11, 12 Connection portion 13 Static mixer (homogenizing member)
14 Nozzle plate 15 Flow path 20 Ink tank 31 External flow path (flow path)
31a Temperature control section 32 External flow path (circulation flow path)

Claims (9)

An image forming apparatus that forms an image by ejecting a thixotropic liquid as droplets,
A tank for temporarily storing the liquid;
an inkjet head having a discharge nozzle for discharging the liquid in the tank;
A flow path connecting the tank and the discharge nozzle;
a single homogenizing member, the static mixer being disposed in the flow path and homogenizing the liquid;
having
a heating section having a heater in the flow path for heating the liquid flowing through the flow path;
the homogenizing member is disposed on the discharge nozzle side relative to the heating section,
an image forming apparatus in which the homogenizing member and the heating section are thermally connected via a connection portion which is an ink inlet of the inkjet head; The image forming apparatus according to claim 1, wherein the flow of liquid through the flow path immediately before the homogenizing member is a laminar flow. The image forming apparatus according to claim 1 or 2, wherein the liquid is a dispersion liquid in which particles are dispersed. The image forming apparatus according to claim 1 , further comprising a circulation flow path connecting the ejection nozzle and the tank. 5. The image forming apparatus according to claim 1 , wherein at least a part of a flow passage section from the homogenizing member to the discharge nozzle is formed of a heat insulating member having a thermal conductivity of 1.0 W/m·K or less. 6. The image forming apparatus according to claim 5 , wherein the heat insulating member is at least one of a plastic member, a rubber member, and a glass member. The image forming apparatus according to claim 1 , further comprising: a homogenizing member disposed in the flow passage inside the inkjet head. The image forming apparatus according to claim 1 , further comprising: the homogenizing member disposed in the flow path between the tank and the inkjet head. An inkjet head that ejects a thixotropic liquid as droplets to form an image,
a flow path connecting a tank for temporarily storing the liquid and a discharge nozzle;
a single homogenizing member, the static mixer being disposed in the flow path and homogenizing the liquid;
having
a heating section having a heater in the flow path for heating the liquid flowing through the flow path;
the homogenizing member is disposed on the discharge nozzle side relative to the heating section,
The homogenizing member and the heating section are thermally conductively connected to each other via a connection portion.

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