JP2005047261A - Ink jet printer and print head - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem of a necessity to repeat frequent wiping and empty delivery which waste expensive ink, as a UV ink jet printer irradiates ultraviolet rays from a light source formed on the print head side to solidify/fix the ink momentarily once it delivers ultraviolet curing type ink, however, if this reflected light enters the print head, the ink adhered to the print head surface gets solidified and fixed and it cannot be removed by wiping thereafter, and as soon as the ultraviolet rays enters the ink in the nozzle which is resting delivery, delivery cannot be resumed. <P>SOLUTION: By adding ultraviolet absorption nature and flipping nature of UV ink to a nozzle panel and a protective plate, the ultraviolet rays which are reflected and advance toward the print head are absorbed. Further, as cation system ink is highly sensitive and increases its viscosity even with an extremely small amount of ultraviolet rays, intermittent delivery nature is improved by fine-vibrating the ink meniscus of the rest nozzle to agitate the ink of which viscosity is increased in the nozzle. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an ink jet printer and a recording head, and more particularly to an ink jet printer and a recording head using ink that is cured by irradiation with ultraviolet rays.

  In recent years, inkjet recording methods have been applied to various printing fields such as special printing such as photography, various printing, marking, and color filters because images can be created more easily, cheaply, and more quickly than screen printing methods. . In particular, in the ink jet recording method, an ink jet printer that discharges and controls fine dots, an ink with improved color reproduction range, durability, and discharge suitability, ink absorptivity, color material coloring, and surface gloss. It is also possible to obtain image quality comparable to silver salt photography by combining with special paper that has been improved dramatically.

  In conventional inkjet printers, a line system that performs image recording by ejecting ink from a line head in which a plurality of ejection openings arranged in the length of the printing width is formed, and recording is performed by moving the recording head in the main scanning direction. There is a serial method in which image recording is performed by ejecting ink from the ejection port of the recording head while the head is moving.

  Inkjet printers can be classified by ink type. In other words, conventional ink jet printers include a water-based ink jet method that discharges water-based ink, a phase change ink jet method that uses a solid wax ink at room temperature, a solvent-based ink jet method that uses an ink mainly composed of a fast-drying organic solvent, Examples include an ultraviolet curable ink jet method using an ultraviolet curable ink that is cured by irradiation. Among them, the ultraviolet curable ink jet method has an advantage that when the discharged ink is irradiated with ultraviolet rays, it is cured instantaneously and adheres to the base, so that no solvent is released and the type of the recording medium is not limited.

By the way, in the ultraviolet curable ink jet printer, the ink adheres to the surface of the nozzle top plate of the recording head in which the ejection port is arranged, and when irradiated with ultraviolet rays, the ink is cured and firmly fixed at that moment. However, the recording head cannot be removed by wiping, and normal ink ejection cannot be performed. Further, when the ink in the nozzles in the discharge pause is irradiated with ultraviolet rays, the ink is cured and the nozzles are clogged, and the discharge cannot be resumed. For this reason, as a preventive measure against this, conventionally, the surface of the nozzle top plate has been subjected to a water repellent treatment that makes it difficult to adhere ink by repelling ink (see, for example, Patent Document 1). Also, frequent printing is interrupted and idle ejection is performed.
In addition to these, a technique for performing a water-repellent treatment on a protective top plate for protecting the nozzle top plate is also disclosed (see, for example, Patent Document 2). Furthermore, a technique for reducing irradiation light on the nozzle top plate by providing a step between the surface of the nozzle top plate and the surface of the protective top plate is also disclosed (for example, see Patent Document 3). In addition, a method for selecting a material used for the water repellent treatment based on the sliding speed is disclosed (for example, see Patent Document 4).
Japanese Patent No. 3188816 Japanese Patent No. 3457458 JP 2002-79666 A JP 2003-266702 A

  However, in particular, in an ink jet printer using an ultraviolet curable ink, when the ultraviolet ray is irradiated, the ink is instantaneously cured and strongly fixed to the base, and thus adheres to the base. Also, if the ink in the nozzles that are not ejected is exposed to ultraviolet rays, it will not be possible to resume ejection in the gift year. In addition, when ultraviolet light is applied to the ink adhered to the surface of the nozzle top plate, the ink is cured, which increases the possibility of causing an ink ejection failure or the like as compared with other types of ink jet printers.

  Accordingly, an object of the present invention is to reduce the amount of ultraviolet light hitting the surface of the nozzle top plate of the recording head, thereby making it difficult for the ink to harden on the surface of the nozzle top plate. An object of the present invention is to provide an ink jet printer that can avoid troubles due to sticking and can prevent ink from being thickly oscillated by slightly vibrating an ink meniscus in a pause nozzle to prevent intermittent ink ejection.

An ink jet printer according to the invention of claim 1
A recording head having a nozzle top plate in which an ejection port for ejecting ink that is cured by being irradiated with ultraviolet rays to a recording medium is disposed;
An ultraviolet irradiation device for irradiating the ink ejected from the recording head onto the recording medium with ultraviolet rays;
With
The critical surface tension of the surface of the nozzle top plate is lower than the surface tension of the ink, and the ultraviolet absorption rate is 80% or more.

According to the first aspect of the invention, since the critical surface tension on the surface of the nozzle top plate is lower than the surface tension of the ink, even if the ink contacts the nozzle top plate, it is repelled by the difference in surface tension. As a result, ink does not remain on the surface of the nozzle top plate, and ink sticking and ejection failure can be prevented. Further, since the material of the surface of the nozzle top plate is selected based on the critical surface tension, it is possible to select more easily than the case of selecting the water-repellent material based on the sliding speed.
Moreover, since the ultraviolet absorptivity at the surface of the nozzle top plate is 80% or more, 80% or more is absorbed when ultraviolet rays are incident. When the ultraviolet ray irradiated from the ultraviolet irradiation device enters the discharge port, it is reflected at least once in most cases. Therefore, the amount of the ultraviolet ray that has reached the discharge port is absorbed by the reflecting surface and hardens the ink. It has fallen to such an extent that it cannot be made. Accordingly, it is possible to prevent ejection failure without fixing the ink on the surface of the nozzle top plate and without curing the ink in the ejection port.

The invention according to claim 2
A recording head having a nozzle top plate on which a discharge port for discharging ink that is cured by being irradiated with ultraviolet rays to a recording medium is disposed, and a protective top plate for protecting the nozzle top plate;
An ultraviolet irradiation device for irradiating the ink ejected from the recording head onto the recording medium with ultraviolet rays;
With
A critical surface tension of the surface of the protective top plate is lower than a surface tension of the ink, and an ultraviolet absorption rate is 80% or more.

  According to the second aspect of the present invention, the same operation and effect as the above-described nozzle top plate can be obtained also in the protective top plate.

The invention described in claim 3 is the ink jet printer according to claim 2,
The critical surface tension of the surface of the nozzle top plate is lower than the surface tension of the ink, and the ultraviolet absorption rate is 80% or more.

  According to the invention of claim 3, since the critical surface tension of the surfaces of the nozzle top plate and the protective top plate is lower than the surface tension of the ink and the ultraviolet absorptance is 80% or more, it is further improved. Ink sticking or ejection failure can be prevented.

The invention according to claim 4 is the ink jet printer according to claim 3,
At least one of the critical surface tensions of the surface of the nozzle top plate and the surface of the protective top plate is 15 mN / m or less.

  Here, since the ink cured by being irradiated with ultraviolet rays (ultraviolet curable ink) is oily, its surface tension is 25 to 35 mN / m. That is, the critical surface tension of the surface must be 25 mN / m or less in order to repel the ultraviolet curable ink, but 15 mN / m or less in order to repel the ultraviolet curable ink more quickly and reliably. Is preferred. That is, as in the fourth aspect of the present invention, if at least one of the critical surface tensions of the surface of the nozzle top plate and the surface of the protective top plate is 15 mN / m or less, the ink in contact with the surface can be quickly and It will be possible to reliably repel.

The invention according to claim 5 is the ink jet printer according to claim 3,
At least one of the surface of the nozzle top plate and the surface of the protective top plate is formed by providing an inorganic ultraviolet absorbent coating layer and a water repellent treatment layer on a substrate.

According to invention of Claim 5, at least one of the surface of a nozzle top plate and the surface of a protection top plate is formed by providing an inorganic ultraviolet absorber coating layer and a water-repellent treatment layer on a board | substrate. Therefore, at least one of the surface of the nozzle top plate and the surface of the protective top plate makes it difficult for ink to adhere to it due to the water-repellent treatment layer, and absorbs ultraviolet rays when it hits the inorganic ultraviolet absorber coating layer. Thus, irregular reflection of ultraviolet rays between the recording head and the recording medium is prevented. As a result, the amount of ultraviolet light hitting the surface of the nozzle top plate can be reduced, and it becomes difficult for the ink to adhere to the surface of the nozzle top plate, and the ink in the discharge pause nozzles does not easily thicken. As a result, it is possible to prevent ink ejection failure based on ink fixation and ink thickening.
In particular, in the present invention, since a coating layer using an inorganic ultraviolet absorber is provided to absorb ultraviolet rays, volatilization and deterioration due to heat are less than those using an organic ultraviolet absorber, and stable for a long period of time. An effect can be obtained.
Further, when the ink is a cation polymerization type ultraviolet curable ink containing a cation polymerizable compound, the cation polymerization type ink has high sensitivity, so that the ink is cured at a low ultraviolet illuminance. Since the amount of ultraviolet rays hitting the surface can be reduced, ink adhesion to the nozzle surface can be effectively prevented even with cationic polymerization inks.

  According to a sixth aspect of the present invention, at least one of the surface of the nozzle top plate and the surface of the protective top plate is provided with a black coloring treatment layer on a substrate, and the inorganic ultraviolet absorbent coating layer and It is characterized by being formed by being provided with a water repellent treatment layer.

  According to the sixth aspect of the present invention, at least one of the surface of the nozzle top plate and the surface of the protective top plate is provided with the black coloring treatment layer on the substrate, and the inorganic ultraviolet absorber coating layer and the water repellency thereon. Since it is formed by being provided with the treatment layer, the ultraviolet absorbing effect can be further enhanced by the black colored layer.

The invention according to claim 7 is the ink jet printer according to any one of claims 4 to 6,
At least one of the nozzle top plate and the protective top plate is made of an aluminum plate or an aluminum die-cast plate.

  According to the seventh aspect of the present invention, since the substrate of the protective top plate is made of an aluminum plate or an aluminum die cast plate, it can be easily processed at the time of manufacture, and the weight of the product can be reduced. In addition, when performing black alumite treatment or black hard alumite treatment suitable as a black colored layer, the film thickness can be kept uniform and black can be colored uniformly, facilitating the formation and management of the black colored layer. can do.

The invention according to claim 8 is the ink jet printer according to claim 3 or 4,
The surface of the nozzle top plate is formed by providing a water-repellent treatment layer on the substrate of the nozzle top plate,
The substrate of the protective top plate is formed of a material having an ultraviolet absorption rate of 80% or more.

  According to the eighth aspect of the present invention, since the surface of the nozzle top plate is formed by providing the water repellent treatment layer on the substrate, the surface of the nozzle top plate is made of ink by the water repellent treatment layer. Is difficult to adhere. On the other hand, since the protective top plate is made of a material having an ultraviolet absorption rate of 80% or more, the ultraviolet rays reflected by the protective top plate before entering the surface of the nozzle top plate are absorbed. Therefore, it is possible to reduce the amount of ultraviolet light hitting the surface of the nozzle top plate, making it difficult for ink to adhere to the surface of the nozzle top plate, and making it difficult for the ink in the idle nozzle to thicken. As a result, it is possible to prevent ink ejection failure based on ink fixation on the surface of the nozzle top plate.

Invention of Claim 9 is an inkjet printer as described in any one of Claims 1-8,
The distance between the surface of the nozzle top plate and the recording medium is 1 mm or more and 4 mm or less.

Here, the shorter the distance between the surface of the nozzle top plate and the recording medium, the shorter the flying distance of the ink ejected from the recording head, thereby preventing the influence of the flying curvature of the ink droplets and improving the sharpness of the image. To do. However, if this distance is less than 1 mm, when foreign matter adheres to the recording head, some troubles are induced when the foreign matter comes into contact with the recording medium or damages the nozzle surface. For this reason, if the distance between the surface of the nozzle top plate and the recording medium is 1 mm or more, it is possible to prevent troubles caused by foreign matter.
On the other hand, if the distance between the surface of the nozzle top plate and the recording medium is longer than 4 mm, not only the sharpness of the image described above is deteriorated, but also the ultraviolet rays reflected on the surface of the recording medium tend to enter the ejection port. . If the distance between the surface of the nozzle top plate and the recording medium is 4 mm or less, the number of times of reflection of ultraviolet rays performed between the recording medium and the surface of the nozzle top plate can be increased, and the ultraviolet rays reach the discharge port. Since it is absorbed many times at the nozzle surface before, the amount of ultraviolet light reaching the discharge port can be reduced as a result.
That is, as in the ninth aspect of the invention, if the distance between the surface of the nozzle top plate and the recording medium is 1 mm or more and 4 mm or less, the amount of ultraviolet light reaching the discharge port can be reduced while preventing a failure due to foreign matter. Can be reduced.

Invention of Claim 10 is an inkjet printer as described in any one of Claims 1-9,
The ultraviolet light source of the ultraviolet irradiation device is any one of a low pressure mercury lamp, a high pressure mercury lamp, a metal halide lamp, a hot cathode tube, a cold cathode tube, and an LED.

  According to the invention of claim 10, any one of a low pressure mercury lamp, a high pressure mercury lamp, a metal halide lamp, a hot cathode tube, a cold cathode tube, and an LED can be used as the ultraviolet light source of the ultraviolet irradiation device. Therefore, it can be set as the structure which acquires an above-described effect concretely.

Invention of Claim 11 is an inkjet printer as described in any one of Claims 1-10,
The recording head includes an ink channel for guiding ink to the ejection port, and a piezoelectric element for ejecting the ink in the ink channel,
The piezoelectric element is characterized in that the ink in the ink flow path is agitated by slightly vibrating the ink meniscus of the discharge port with a voltage waveform that does not cause the ink to be discharged when the ink discharge is stopped.

  Here, since the dot inkjet printer repeats ink ejection and pause according to the image signal, there are nozzles having a long pause period and short nozzles depending on the image. Even if the surface of the nozzle top plate and the surface of the protective top plate have an ultraviolet absorption rate of 80% or more, it is not possible to completely prevent the ink in the pause nozzle from being irradiated with ultraviolet rays. The ink inside thickens a little. Conventionally, the ink is prevented from being cured in the nozzles by periodically ejecting the ink, but the printing speed is slowed by the amount of the idle ejection, and the ink consumption is also increased. It was a cause. However, as in the eleventh aspect of the present invention, the piezoelectric element for ejecting ink slightly vibrates the ink meniscus at the ejection port with a voltage waveform that does not eject ink when ink ejection is stopped, thereby causing ink flow. If the ink in the path is agitated, it is possible to prevent the ink in the nozzles from being hardened when the ejection is stopped, even if the ink is not ejected frequently.

The recording head according to the invention of claim 12 is
A nozzle top plate provided with a discharge port for discharging ink that is cured by irradiation with ultraviolet rays to a recording medium,
The critical surface tension of the surface of the nozzle top plate is lower than the surface tension of the ink, and the ultraviolet absorption rate is 80% or more.

  According to the twelfth aspect of the invention, the same operation and effect as the first aspect of the invention can be obtained.

A recording head according to the invention of claim 13
A nozzle top plate on which a discharge port for discharging ink that is cured by being irradiated with ultraviolet rays to a recording medium is disposed;
A protective top plate for protecting the nozzle top plate;
A critical surface tension of the surface of the protective top plate is lower than a surface tension of the ink, and an ultraviolet absorption rate is 80% or more.

  According to the invention of the thirteenth aspect, the same operation and effect as the invention of the second aspect can be obtained.

According to a fourteenth aspect of the present invention, in the recording head according to the thirteenth aspect,
The critical surface tension of the surface of the nozzle top plate is lower than the surface tension of the ink, and the ultraviolet absorption rate is 80% or more.

  According to the invention of the fourteenth aspect, the same operation and effect as the invention of the third aspect can be obtained.

According to a fifteenth aspect of the present invention, in the recording head according to the fourteenth aspect,
At least one of the critical surface tensions of the surface of the nozzle top plate and the surface of the protective top plate is 15 mN / m or less.

  According to the fifteenth aspect of the invention, the same operation and effect as the fourth aspect of the invention can be obtained.

The invention according to claim 16 is the recording head according to claim 14 or 15, wherein
At least one of the surface of the nozzle top plate and the surface of the protective top plate is formed by providing an inorganic ultraviolet absorbent coating layer and a water repellent treatment layer on a substrate.

  According to the invention of the sixteenth aspect, the same operation and effect as those of the invention of the fifth aspect can be obtained.

According to a seventeenth aspect of the present invention, in the recording head according to the sixteenth aspect,
At least one of the surface of the nozzle top plate and the surface of the protective top plate is provided with a black colored treatment layer on the substrate, and the inorganic ultraviolet absorbent coating layer and the water repellent treatment layer are provided thereon. It is characterized by being formed.

  According to the invention of the seventeenth aspect, the same operation and effect as those of the invention of the sixth aspect can be obtained.

The invention according to claim 18 is the recording head according to any one of claims 15 to 17,
At least one of the nozzle top plate and the protective top plate is made of an aluminum plate or an aluminum die-cast plate.

  According to the eighteenth aspect of the invention, the same operation and effect as the seventh aspect of the invention can be obtained.

The invention according to claim 19 is the recording head according to claim 14 or 15,
The surface of the nozzle top plate is formed by providing a water-repellent treatment layer on the substrate of the nozzle top plate,
The substrate of the protective top plate is formed of a material having an ultraviolet absorption rate of 80% or more.

  According to the nineteenth aspect of the invention, it is possible to obtain the same operation and effect as the eighth aspect of the invention.

The invention according to claim 20 is the recording head according to any one of claims 12 to 19,
The distance between the surface of the nozzle top plate and the recording medium is 1 mm or more and 4 mm or less.

  According to the twentieth aspect, it is possible to obtain the same operation and effect as the ninth aspect.

A twenty-first aspect of the invention is the recording head according to any one of the twelfth to twentieth aspects,
An ink flow path for guiding ink to the ejection port;
A piezoelectric element for discharging the ink in the ink flow path;
The piezoelectric element agitates the ink in the ink flow path by slightly vibrating the ink meniscus of the ejection port with a voltage waveform that does not cause the ink to be ejected when the ink ejection is stopped.

  According to the twenty-first aspect of the invention, it is possible to obtain the same operation and effect as the eleventh aspect of the invention.

According to the first and twelfth aspects of the present invention, even if the ink contacts the surface of the nozzle top plate, the surface tension difference is large, so that the ink is strongly repelled. Accordingly, it becomes difficult for the ink to adhere to and remain on the surface of the nozzle top plate, thereby preventing ejection failure.
In addition, when the ultraviolet ray irradiated from the ultraviolet irradiation device enters the discharge port, in most cases, it is reflected at least once on the surface of the nozzle top plate. It is absorbed to the surface of the ink and is lowered to such an extent that the ink is not cured. Therefore, it is possible to prevent ejection failure without thickening and curing the ink in the ejection port.

According to invention of Claim 2 and 13, also in a protection top plate, the effect | action and effect similar to the nozzle top plate mentioned above can be acquired.
According to the inventions of claims 3 and 14, since the surfaces of both the nozzle top plate and the protective top plate have a critical surface tension lower than the surface tension of the ink and an ultraviolet absorption rate of 80% or more, Ink sticking and ejection failure can be further prevented.

  According to the inventions according to claims 4 and 15, since at least one of the critical surface tensions of the surface of the nozzle top plate and the surface of the protective top plate is 15 mN / m or less, the ink in contact with the nozzle top plate and the protective top plate Can be quickly and reliably repelled.

According to invention of Claim 5 and 16, at least one of the surface of a nozzle top plate and the surface of a protection top plate is formed by providing an inorganic ultraviolet absorber coating layer and a water-repellent treatment layer on a board | substrate. Therefore, at least one of the surface of the nozzle top plate and the surface of the protective top plate is hard to adhere ink by the water-repellent treatment layer, and when the ultraviolet ray hits by the inorganic ultraviolet absorber coating layer, This prevents the ultraviolet rays from being irregularly reflected between the recording head and the recording medium. As a result, the amount of ultraviolet light hitting the surface of the nozzle top plate can be reduced, making it difficult for the ink to adhere to the surface of the nozzle top plate, and making it difficult for the ink in the idle nozzle to thicken. As a result, it is possible to prevent ink ejection failure based on ink fixation and ink thickening.
In particular, in the present invention, since a coating layer using an inorganic ultraviolet absorber is provided to absorb ultraviolet rays, volatilization and deterioration due to heat are less than those using an organic ultraviolet absorber, and stable for a long period of time. An effect can be obtained.
Further, when the ink is a cation polymerization type ultraviolet curable ink containing a cation polymerizable compound, the cation polymerization type ink has high sensitivity, so that the ink is cured at a low ultraviolet illuminance. Since the amount of ultraviolet rays hitting the surface can be reduced, ink adhesion to the nozzle surface can be effectively prevented even with cationic polymerization inks.

  According to invention of Claim 6 and 17, at least one of the surface of a nozzle top plate and the surface of a protection top plate is equipped with a black coloring process layer on a board | substrate, and an inorganic ultraviolet absorber coating layer on it, Since it is formed by being provided with a water repellent treatment layer, the ultraviolet absorption effect can be further enhanced by the black colored layer.

  According to invention of Claim 7 and 18, since the board | substrate of a protection top plate consists of an aluminum plate or an aluminum die-casting board, it is easy to process it at the time of manufacture, and can also attain weight reduction of a product. In addition, when performing black alumite treatment or black hard alumite treatment suitable as a black colored layer, the film thickness can be kept uniform and black can be colored uniformly, facilitating the formation and management of the black colored layer. can do.

  According to the inventions of claims 8 and 19, since the surface of the nozzle top plate is formed by providing the substrate with the water repellent treatment layer, the surface of the nozzle top plate has a water repellent treatment layer. This makes it difficult for ink to adhere. On the other hand, since the protective top plate is made of a material having an ultraviolet absorption rate of 80% or more, the ultraviolet rays reflected by the protective top plate before entering the surface of the nozzle top plate are absorbed. Therefore, it is possible to reduce the amount of ultraviolet light hitting the surface of the nozzle top plate, making it difficult for ink to adhere to the surface of the nozzle top plate, and making it difficult for the ink in the idle nozzle to thicken. As a result, it is possible to prevent ink ejection failure based on ink fixation on the surface of the nozzle top plate.

  According to the ninth and twentieth aspects of the present invention, since the distance between the surface of the nozzle top plate and the recording medium is 1 mm or more and 4 mm or less, it is possible to reduce the amount of ultraviolet light reaching the discharge port while preventing a failure due to foreign matter. Can be reduced.

  According to the invention of claim 10, any one of a low pressure mercury lamp, a high pressure mercury lamp, a metal halide lamp, a hot cathode tube, a cold cathode tube, and an LED can be used as the ultraviolet light source of the ultraviolet irradiation device. Therefore, it can be set as the structure which acquires an above-described effect concretely.

  According to the invention described in claims 11 and 21, since the piezoelectric element for ejecting ink vibrates the ink meniscus at the ejection port and stirs the ink in the ink flow path, The ink inside can be prevented from curing.

[First Embodiment]
Hereinafter, embodiments of an ink jet printer according to the present invention will be described in detail with reference to the drawings. However, the scope of the invention is not limited to the illustrated examples.

FIG. 1 is a perspective view showing an inkjet printer 1 in which an image recording method is a serial method.
As shown in FIG. 1, the inkjet printer 1 includes a printer main body 2 and a support base 3 that supports the printer main body 2 from below. A flat platen 4 that is long in the left-right direction is provided inside the printer body 2, and the platen 4 supports a web-like recording medium 99 (shown in FIG. 5) flatly from below. is there.

  In FIG. 1, a recording medium 99 on which an image is recorded is not shown, but the recording medium 99 is fed from a carry-in port provided on the back surface of the printer main body 2 and disposed inside the printer main body 2. It passes through the inside of the printer main body 2 from the rear to the front while being supported by the platen 4 by a transport mechanism (not shown), and is carried out of the printer main body 2. That is, the recording medium 99 is transported in the transport direction B so as to pass through the inside of the printer main body 2 by the transport mechanism.

  The transport mechanism includes, for example, a transport motor and a transport roller (not shown), and transports the recording medium 99 by rotating the transport roller by driving the transport motor. The conveyance mechanism is configured to intermittently convey the recording medium 99 by repeatedly conveying and stopping the recording medium 99 in accordance with the operation of a carriage 5 described later during image recording.

  Above the platen 4, a guide member 6 extending in the left-right direction inside the printer main body 2 is disposed. A carriage 5 is supported on the guide member 6, and the carriage 5 is guided by the guide member 6 and is movable left and right. A drive mechanism (not shown) moves the carriage 5 along the guide member 6. Hereinafter, the direction in which the carriage 5 moves will be described as the scanning direction A.

  A maintenance unit 7 for maintaining a plurality of recording heads 20 mounted on the carriage 5 is provided on the right side in the scanning direction A of the platen 4. The maintenance unit 7 is disposed within the movement range of the carriage 5 and below the carriage 5.

  On the left side of the platen 4 in the scanning direction A, a plurality of ink tanks 8 for storing ink are disposed. The ink colors used in the inkjet printer 1 are basically yellow (Y), magenta (M), cyan (C), and black (K), and white (W), light yellow (LY), and light. Examples include magenta (LM), light cyan (LC), and light black (LK). One ink tank 8 stores ink of any one of these colors. Basically, different colors of ink are stored for each ink tank 8, but the same color of ink may be stored in two or more ink tanks 8.

Next, “ink” used in the present embodiment will be described.
The ink used in the present embodiment is an ultraviolet curable ink that is cured by irradiation with ultraviolet rays as light, and includes, as main components, a polymerizable compound (including a known polymerizable compound), a photoinitiator, and a coloring material. Is included at least.

  The ultraviolet curable ink is roughly classified into a radical polymerization type ink containing a radical polymerizable compound and a cationic polymerization type ink containing a cationic polymerizable compound as a polymerizable compound. As the ink used in the present embodiment, a hybrid ink in which a radical polymerization ink and a cation polymerization ink are combined may be used as the ink used in the present embodiment. Here, as compared with radical polymerization ink, cationic polymerization ink has higher sensitivity to ultraviolet light and less inhibition of polymerization reaction by oxygen, and therefore can reduce the illuminance necessary for curing the ink. For this reason, in this embodiment, a cationic polymerization type ultraviolet curable ink is used as the ink.

Next, the recording medium 99 used in the ink jet printer 1 will be described.
Examples of the recording medium 99 used in the present embodiment include various papers such as plain paper, recycled paper, and glossy paper that are applied to ordinary inkjet printers, various fabrics, various nonwoven fabrics, vinyl chloride, resin, metal, glass, and the like. What consists of material is applicable. Further, as the form of the recording medium 99, a roll shape, a cut sheet shape, a plate shape, or the like is applicable.
Furthermore, as the recording medium 99 used in the present embodiment, various known papers whose surfaces are coated with a resin, films containing pigments, foamed films, and the like can be applied.

  Hereinafter, the carriage 5 will be described in detail. 2 is a perspective view showing the carriage 5 as viewed in substantially the same direction as FIG. 1, and FIG. 3 is a perspective view showing the carriage 5 as viewed obliquely upward from the lower right in FIG. 2 and 3, the carriage 5 is indicated by a broken line, and the carriage 5 is seen through.

  As shown in FIGS. 2 and 3, eight sub tanks 9 are mounted in a line in the scanning direction A at the rear portion of the carriage 5. In the sub tank 9, ink is supplied from the ink tank 8 for each color and temporarily stored.

  Eight recording heads 20 for ejecting ink are mounted on the front portion of the carriage 5, and these recording heads 20 are divided into two groups 10 and 11 each in four. In each set 10, 11, four recording heads 20 are arranged in a line in the scanning direction A, and one set 10 is arranged on the left side of the other set 11 and on the upstream side in the transport direction B. Each recording head 20 communicates with one sub tank 9 by a supply pipe 12 so that ink is supplied from the sub tank 9 to the recording head 20 for each color. In the present embodiment, since the sub tank 9 is positioned higher than the recording head 20, no negative pressure is generated with respect to the nozzles. For this reason, ink is discharged from the nozzle surface 21 of the recording head 20. I'm drunk. In order to prevent this, in this embodiment, a pump or the like (not shown) is provided, and the pressure is reduced and controlled so that a constant negative pressure is applied to the nozzle.

The outer shape of each recording head 20 is formed in a substantially rectangular parallelepiped shape, and each recording head 20 is arranged such that its longitudinal direction is parallel to the conveyance direction B. Each recording head 20 has a nozzle surface 21 on the lower surface, and is disposed so as to face the recording medium 99 conveyed on the platen 4. A plurality of ejection openings for ejecting ink are arranged in a line in the transport direction B on the nozzle surface 21 of each recording head 20 to form a nozzle array 26. Each recording head 20 includes a piezoelectric element that applies pressure to the internal ink by deformation, a heating element that applies pressure to the internal ink by film boiling the internal ink, and other electrostatic elements that apply pressure to the internal ink. A deformation element or the like is provided for each ejection port, and ink is ejected individually as droplets from each ejection port by the operation of these elements.
In the present embodiment, one color of YMCK is ejected from one recording head 20, and different colors of ink are ejected for each recording head 20 in each set 10, 11.

  As shown in FIG. 4, in the present embodiment, the nozzle surface 21 of the recording head 20 includes a black colored layer 23 and an inorganic ultraviolet absorber coating layer 24 in order from the lower layer on the nozzle top plate 22. The uppermost layer that is the surface layer of the surface 21 is provided with a water repellent treatment layer 25.

The nozzle top plate 22 is a member formed so as to surround the nozzle row 26, and in the present embodiment, is made of an aluminum plate or an aluminum die cast plate.
The black colored layer 23 is a layer that is black-colored on the nozzle top plate 21 so as not to reflect ultraviolet rays. In the present embodiment, the black colored layer 23 is composed of a ceramic layer made of a hard alumite treatment liquid colored black. Yes. The black colored layer 23 is not limited to this, and may be a ceramic layer made of an alumite treatment liquid colored black, for example.

The inorganic ultraviolet absorbent coating layer 24 is a layer coated with an inorganic ultraviolet absorbent. As the inorganic ultraviolet absorber, an inorganic ultraviolet absorber that absorbs ultraviolet rays in the wavelength region near 250 nm, 350 nm, and 450 nm is particularly preferable. Specifically, for example, those coated with a cerium oxide-based inorganic ultraviolet absorber such as Niedral (trade name, manufactured by Taki Chemical Co., Ltd.) can be used.
The water-repellent treatment layer 25 is a layer to which a water-repellent treatment liquid is applied. For example, a fluorine-based water-repellent treatment liquid such as an amorphous fluororesin, FEP (perfluoroethylene-propylene copolymer), or perfluoroalkylsilane is applied. Things.

  In addition, by applying a coating agent in which an inorganic ultraviolet absorbent forming the inorganic ultraviolet absorbent coating layer 24 is mixed to the water repellent treatment liquid forming the water repellent treated layer 25, the inorganic ultraviolet absorbent coating layer 24 and The water repellent treatment layer 25 may be formed as a single layer. With such a configuration, a simple and efficient configuration can be achieved.

  Further, a water repellent treatment liquid for forming the water repellent treatment layer 25, an inorganic ultraviolet absorbent for forming the inorganic ultraviolet absorbent coating layer 24, and a hard alumite treatment liquid or alumite treatment liquid for forming the black colored layer 23. The black coloring layer 23, the inorganic ultraviolet absorber coating layer 24, and the water repellent treatment layer 25 may be formed as a single layer by applying a coating agent mixed with a treatment liquid such as the above. With such a configuration, a simpler and more efficient configuration can be achieved.

  Ultraviolet irradiation devices 30 for irradiating ultraviolet rays are mounted on both left and right ends of the carriage 5. One ultraviolet irradiation device 30 is disposed further to the left of the recording head 20 positioned at the left end, and the other ultraviolet irradiation device 30 is disposed further to the right of the recording head 20 positioned at the right end. Further, one or a plurality of ultraviolet light sources 31 are provided in the recessed portion opened by the ultraviolet irradiation device 30.

  The ultraviolet light source 31 radiates ultraviolet rays radially from the center line along the longitudinal direction thereof, and is at least one of a low pressure mercury lamp, a high pressure mercury lamp, a metal halide lamp, a hot cathode tube, a cold cathode tube, and an LED. One of them applies.

An optical trap 40 is disposed between the ultraviolet irradiation device 30 and the recording head 20 adjacent to the ultraviolet irradiation device 30.
As shown in FIGS. 2 and 3, one optical trap 40 is mounted on the carriage 5 on the left side of the recording head 20 located at the left end, and the other optical trap 40 is located at the right end. It is mounted on the carriage 5 on the further right side.

  These optical traps 40 are long members extending along the conveyance direction B, and the length thereof is at least equal to the length along the conveyance direction B of the ultraviolet irradiation device 30. The optical traps 40 are concave members that open toward the recording medium 99, and are disposed so that, for example, the opened edges are substantially parallel to the recording medium 99.

  The optical trap 40 may have any shape as long as ultraviolet rays can enter the optical trap 40 and the incident ultraviolet rays repeatedly reflect on the inner surface of the optical trap 40.

Next, the operation of the inkjet printer 1 configured as described above will be described.
When the operator sets the recording medium 99 in the ink jet printer 1 and turns on the power of the ink jet printer 1, the ultraviolet light source 31 emits light and irradiates the recording medium 99 with ultraviolet rays.

  With the ultraviolet light source 31 emitting light, the transport mechanism transports the recording medium 99 in the transport direction B. Here, the conveyance mechanism sequentially repeats conveyance and conveyance stop, and conveys the recording medium 99 intermittently.

  The carriage 5 moves forward or backward in the scanning direction A or reciprocates while stopping in the intermittent conveyance. As the carriage 5 moves, the plurality of recording heads 20 also move together with the carriage 5, and these recording heads 20 drop ink droplets from the respective ejection openings on the nozzle surface 21 toward the recording medium 99 during the movement. Ink droplets ejected and then landed on the stopped recording medium 99. Here, the recording heads 20 in the set 10 eject ink when the carriage 5 moves forward in the scanning direction A in FIG. 1, and the recording heads 20 in the set 11 in FIG. When 5 moves backward along the scanning direction A toward the left, ink is ejected. This is to prevent the ejection order from changing in the moving direction of the recording head 20 because the ejection is performed in the order in which the recording heads 20 are arranged.

  As the carriage 5 moves, the two ultraviolet irradiation devices 30 move together with the carriage 5, but when the ultraviolet irradiation device 30 passes over the ink that has landed on the recording medium 99, the ultraviolet light source 31 emits light. The emitted ultraviolet light enters the ink on the recording medium 99. As a result, the ink is cured.

  Here, when the carriage 5 moves forward rightward along the scanning direction A, the ink droplets ejected by the recording heads 20 of the set 10 are transferred from the ultraviolet irradiation device 30 located at the left back in FIG. It is cured by the ultraviolet rays emitted from the ultraviolet light source 31. In this case, the recording direction in which the image is recorded on the recording medium 99 is the direction in which the carriage 5 moves, and the ultraviolet light source 31 of the ultraviolet irradiation device 30 at the left back in FIG. Thus, it is arranged downstream of the recording direction from 20. On the other hand, when the carriage 5 moves backward leftward in the scanning direction A, the ink droplets ejected by the recording heads 20 of the set 11 are the ultraviolet rays of the ultraviolet irradiation device 30 on the right front side in FIG. It is cured by ultraviolet rays emitted from the light source 31. In this case, the recording direction is the direction in which the carriage 5 moves, and the ultraviolet light source 31 of the ultraviolet irradiation device 30 on the right front side in FIG. 1 is arranged downstream of the recording head 20 of the set 11 in the recording direction. Will be.

  As described above, the transport mechanism intermittently transports the recording medium 99 while the plurality of ultraviolet light sources 31 emit light, and the carriage 5 is reciprocated repeatedly, and the recording head 20 appropriately drops ink droplets while the carriage 5 is moving. By discharging, an image is formed on the recording medium 99.

At this time, ultraviolet rays emitted from the ultraviolet light source 31 of the ultraviolet irradiation device 30 may hit the recording medium 99 and be reflected as indicated by arrows U1, U2, and U3 shown in FIG.
Among these, ultraviolet rays emitted at an angle as indicated by an arrow U1 are absorbed by the optical trap 40. Further, ultraviolet rays emitted at an angle as indicated by an arrow U <b> 2 are absorbed by the inorganic ultraviolet absorbent coating layer 24 on the nozzle surface 21 of the recording head 20. In the present invention, since the ultraviolet rays are absorbed by the presence of the inorganic ultraviolet absorbent coating layer 24 and the black colored layer 23, the ultraviolet rays that diffusely reflect between the nozzle surface 21 and the recording medium 99 are eliminated as indicated by the arrow U3. As a result, the amount of ultraviolet rays hitting the nozzle surface 21 can be reduced.

Next, with reference to the table of FIG. 6, the measurement experiment of the light reflectivity when various coating layers are provided on the nozzle surface 21 will be described.
Here, the aluminum die-casting plate as the nozzle top plate 22 is subjected to black-colored alumite treatment as the black coloring layer 23 (denoted as “anodized (black)”), and the aluminum die-casting plate as the nozzle top plate 22 is colored black. The layer 23 is black anodized and coated with an inorganic ultraviolet absorber as the inorganic ultraviolet absorber coating layer 24 (denoted as “anodized (black) + UV”), and an aluminum die casting as the nozzle top plate 22 A black colored hard anodized treatment as a black colored layer 23 on the plate (denoted as “hard anodized (black)”), an aluminum die cast plate as the nozzle top plate 22 and a black colored hard anodized treatment as the black colored layer 23 Applied with an inorganic ultraviolet absorbent as the inorganic ultraviolet absorbent coating layer 24 ("hard Alumite (black) + UV "hereinafter) and those of die-cast aluminum plate only as a nozzle top plate 22 for (denoted as" die casting "), was irradiated with ultraviolet light of 350～360Nm, the reflectance was measured at that time. In addition, the reflectance was measured with two types of reflectance: total reflection measurement and regular reflection measurement. In addition, as a measuring instrument, the Hitachi Ltd. U-3300 Spectrophotometer 150φ integrating sphere type was used.

  As a result, as shown in the table of FIG. 6, in the total reflection measurement, there was not much difference except for the aluminum die-casting plate alone, but in the measurement of the one that cut the regular reflection by adjusting the reflection angle, The reflectance of the sample coated with the inorganic ultraviolet absorber was close to 0, and a great difference was produced from that applied without the inorganic ultraviolet absorber. Thus, it has been found that by providing an inorganic ultraviolet absorbent coating layer on the nozzle surface in the present invention, ultraviolet rays can be absorbed and irregular reflection of ultraviolet rays can be prevented.

As described above, according to the ink jet printer of the present embodiment, since the nozzle surface 21 of the recording head includes the inorganic ultraviolet absorbent coating layer and the water repellent treatment layer on the nozzle top plate 22, The aqueous treatment layer makes it difficult for ink to adhere to the nozzle surface, and when the nozzle surface is exposed to ultraviolet rays, the inorganic ultraviolet absorber coating layer absorbs the ultraviolet rays, and the ultraviolet rays are irregularly reflected between the recording head and the recording medium. Can be prevented. As a result, the amount of ultraviolet light hitting the nozzle surface of the recording head can be reduced, and the ink is difficult to cure on the nozzle surface. As a result, it is possible to prevent ink ejection failure based on ink sticking to the nozzle surface.
In particular, the present embodiment includes a coating layer that uses an inorganic ultraviolet absorber to absorb ultraviolet rays, and therefore has less volatilization and deterioration due to heat compared to those using organic ultraviolet absorbers. A stable effect can be obtained.
Further, when the ink is a cation polymerization type ultraviolet curable ink containing a cation polymerizable compound, the cation polymerization type ink has high sensitivity, and thus the ink is cured at a low ultraviolet illuminance. In addition, by reducing the amount of ultraviolet light hitting the nozzle surface 21 and providing a water-repellent treatment layer, it is possible to effectively prevent ink sticking to the nozzle surface even in the case of cationic polymerization ink and improve intermittent ejection. it can.

  Further, in the present embodiment, the nozzle surface 21 of the recording head includes a black colored treatment layer on the nozzle top plate 22 and an inorganic ultraviolet absorbent coating layer and a water repellent treatment layer thereon. Further, the ultraviolet absorbing effect can be further enhanced by the black colored layer.

  Further, when the inorganic ultraviolet absorbent coating layer and the water repellent treatment layer are formed as one layer, the above-described effects can be obtained with a simple and efficient configuration.

  Furthermore, in this embodiment, since the nozzle top plate is made of an aluminum plate or an aluminum die-cast plate, it is easy to process at the time of manufacture, and the weight of the product can be reduced. In addition, when performing black alumite treatment or black hard alumite treatment suitable as a black colored layer, the film thickness can be kept uniform and black can be colored uniformly, facilitating the formation and management of the black colored layer. can do.

  In the present embodiment, any one of a low-pressure mercury lamp, a high-pressure mercury lamp, a metal halide lamp, a hot cathode tube, a cold cathode tube, and an LED can be used as the ultraviolet light source of the ultraviolet irradiation device. Specifically, the above-described effect can be obtained.

[Second Embodiment]
In the first embodiment, the black colored layer 23 is provided on the nozzle top plate 22 made of an aluminum plate or an aluminum die-cast plate, and the inorganic ultraviolet absorbent coating layer 24 and the water repellent treatment layer are provided thereon. However, in the second embodiment, the nozzle surface is made of a material having an ultraviolet absorption rate of 80% or more. A case will be described in which a water repellent treatment layer is provided on a nozzle top plate. In the following description, the same parts as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

Hereinafter, the carriage 5A provided in the inkjet printer according to the second embodiment will be described with reference to FIGS. FIG. 7 is a perspective view showing the carriage 5A.
As shown in FIG. 7, the carriage 5A includes a pair of ultraviolet irradiation devices 30 disposed at both ends of the carriage 5A, a pair of optical traps 40 disposed inside the pair of ultraviolet irradiation devices 30, and a pair. Four recording heads 50 disposed between the optical traps 40 and four sub tanks 9 corresponding to the recording heads 50 are mounted.

  FIG. 8 is a cross-sectional view illustrating a schematic configuration of the recording head 50, and FIG. 9 is an exploded perspective view illustrating an internal configuration of the recording head 50. As shown in FIGS. 8 and 9, the recording head 50 includes a nozzle top plate 52 having a plurality of ejection ports 51 and a pair of piezoelectric elements 53 and 54 that are superposed for ejecting ink from the ejection ports 51. And are provided. Among the pair of piezoelectric elements 53, 54, one piezoelectric element 53 has a plurality of wall portions 56 erected, and the other piezoelectric element 54 is superimposed on each wall portion 56 of one piezoelectric element 53. A wall portion 57 is provided. The arrows in the figure are the directions of polarization of the piezoelectric elements 53 and 54. By overlapping the pair of piezoelectric elements 53 and 54, each of the wall portions 56 and 57 forms a plurality of pressure chambers 58. A nozzle top plate 52 is fixed to the lower surfaces of the pair of piezoelectric elements 53, 54 so that each discharge port 51 corresponds to each pressure chamber 58. As a result, the plurality of pressure chambers 58 become ink flow paths for guiding the ink to the respective ejection ports 51. An electrode 70 is formed over the entire surface of one surface of the walls 56 and 57 forming the pressure chamber 58.

On the other hand, a supply plate 59 for supplying ink from the sub tank 9 to each pressure chamber 58 is fixed to the opposite surface of the nozzle top plate 52 in the pair of piezoelectric elements 53, 54. An inflow port 60 through which ink flows into each pressure chamber 58 is formed.
A cover plate 61 that closes each pressure chamber 58 is fixed to the wall portion 57 on the upper surface of the other piezoelectric element 54.

  FIG. 10 is a perspective view showing the periphery of the nozzle top plate 52. As shown in FIGS. 8 and 10, a protective top plate 64 that surrounds and protects the nozzle top plate 52 is attached to the nozzle top plate 52 in which the plurality of discharge ports 51 are formed.

The nozzle top plate 52 and the protective top plate 64 are made of a material that absorbs 80% or more of ultraviolet rays having a wavelength of 220 nm to 400 nm. Here, inorganic materials such as aluminum, carbon black, ultrafine titanium oxide, ultrafine zinc oxide, iron oxide (α-Fe ₂ O ₃ , Fe ₃ O ₄ ) cerium oxide are examples of materials having an ultraviolet absorption rate of 80% or more. And organic substances such as benzotriazole compounds, aromatic compounds and polyimide resins. A water repellent treatment layer is provided on the nozzle top plate 52 and the protective top plate 64.

  The water repellent treatment layer must be formed so that the critical surface tension on the surface thereof is lower than the surface tension of the ultraviolet curable ink in order to increase the water repellency to the ultraviolet ink. When the critical surface tension of the surface 52a of the nozzle top plate 52 and the surface 64a of the protective top plate 64 is equal to or greater than the surface tension of the ultraviolet curable ink, the ultraviolet curable ink is used as the surface 52a of the nozzle top plate 52. When contacting the surface 64a of the protective top plate, the surface 52a of the nozzle top plate 52 and the surface 64a of the protective top plate 64 are wet and spread, and when this is irradiated with ultraviolet rays, it is cured and fixed. .

Here, since the surface tension of the solid surface cannot be directly measured, various liquids with known surface tensions are placed on the surface 52a of the nozzle top plate 52 or the surface 64a of the protective top plate 64 as shown in FIG. The angle θ is measured, the contact angle θ and the surface tension are plotted, the surface tension at which the contact angle θ becomes 0 is obtained by extrapolation, and this is regarded as the surface tension of the solid surface (critical surface tension γ _c ) . That is, in order to bounce the ultraviolet curable ink, it is necessary to form the water repellent treatment layer with a material having a critical surface tension γ _c lower than the surface tension of the ultraviolet curable ink. Since a general ultraviolet curable ink has a surface tension of about 25 to 35 mN / m, the critical surface tension γ _c of the surface 52 a of the nozzle top plate 52 and the surface 64 a of the protective top plate 64 is 25 mN / m or less. Preferably there is. Examples of the material having a critical surface tension γ _c of 25 mN / m or less include FEP, Cytop, Teflon (registered trademark) AF, PTFE fine particles, nickel eutectoid plating, and perfluoroalkylsilane.
In order to obtain quick and reliable water repellency, the critical surface tension γ _c of the surface 52a of the nozzle top plate 52 and the surface 64a of the protective top plate 64 is more preferably 15 mN / m or less. Examples of a material having a critical surface tension γ _c of 15 mN / m or less include perfluoroalkylsilane.

The surface 52a of the nozzle top plate 52 and the surface 64a of the protective top plate 64 are frequently wiped by a wiping member (not shown) in order to remove the ultraviolet curable ink adhering thereto. Since wiping involves the mobility of ink droplets on the surfaces 52a and 64a, the mobility of ink droplets on the surfaces 52a and 64a will be described. For example, as shown in FIG. 12, when the ink droplet I starts moving by wiping, the equilibrium contact angle θ of the ink droplet I disappears, and a forward contact angle θ _a and a backward contact angle θ _r appear. The difference between the advancing contact angle θ _a and the receding contact angle θ _r is called the contact angle hysteresis. In contact angle to the surface advancing contact angle theta _a not yet wetted with the ink, the receding contact angle theta _r is already contact angle to wet surfaces in the ink. Since the ink droplet I is very small, gravity is negligible, and the force acting on the ink droplet is only the surface tension. The surface tension of the ink moves the ink droplet I and prevents the ink I from moving. To work. Even if the advancing contact angle θ _a is high, if the receding contact angle θ _r is low, the contact angle hysteresis increases, and the ink droplet I is difficult to move. Since the equilibrium contact angle to the normal measurement close to the advancing contact angle θ _a, and advancing contact angle θ _a is both a low receding contact angle θ _r high, ink stain is hard to fall even if the wiping. Therefore, if the advancing contact angle theta _a and receding contact angle theta _r are both high system can reduce the contact angle hysteresis, it is possible to improve the mobility and the wiping of the ink droplet.

FIG. 13 is a diagram showing the relationship between the advancing contact angle θ _a and the receding contact angle θ _r with respect to the hydrophilic / hydrophobic ratio of the solid surface. As shown in FIG. 13, the advancing contact angle theta _a surface 52a, is insensitive to the presence of hydrophilic regions of 64a, receding contact angle theta _r surface 52a, it is found to be sensitive to the hydrophilic region of 64a . In other words, the advancing contact angle θ _a shows a high contact angle even when a large amount of hydrophilic regions are distributed on the hydrophobic surface. On the other hand, the receding contact angle θ _r rapidly decreases even if the hydrophilic surface is slightly included in the hydrophobic surface. For these reasons, if a material for the water-repellent treatment layer is selected only with a high contact angle, the ink repels well, but it may be difficult to remove the ink even after wiping.

In addition, wiping is repeatedly performed on the water-repellent treatment layer. However, since the water-repellent treatment layer should not be peeled off by wiping, the water-repellent treatment layer is separated from the nozzle top plate 52 and the protective top plate. It is necessary to adhere firmly to 64. For example, when CF ₃ (CF ₃ ) ₇ CH ₂ CH ₂ Si (OCH ₃ ) _3, which is one of the above-mentioned perfluoroalkoxylans, as shown in FIG. Bonding with hydroxyl groups on the surface of the plate 52, the remaining two bonds with moisture in the air to turn into hydroxyl groups, which are condensed by heat treatment to form a tightly packed siloxane network. As a result, the CF ₃ group is oriented on the surface, so that the critical surface tension of the surfaces 52a and 64a is 6 mN / m. Thus hydrophilic component surface 52a, if appear to 64a, it is possible to enhance the high wiping resistance receding contact angle theta _r. In practice, oxygen atoms and carbon atoms in addition to the CF ₃ group also appear on the surfaces 52a and 64a, so the critical surface tension is 10 to 15 mN / m. This water-repellent treatment layer is excellent in durability because it is covalently bonded to the nozzle top plate 52 and the protective top plate 64 through oxygen atoms and is three-dimensionally cross-linked through oxygen atoms. .

Next, the operation of the recording head 50 when ink is ejected and when ejection is stopped will be described.
The piezoelectric elements 53 and 54 of the recording head 50 are expanded and contracted by the applied voltage. When the piezoelectric elements 53 and 54 are deformed and the pressure chamber 58 expands, the ink in the nozzle is drawn into the pressure chamber, and when it contracts, the ink in the nozzle is pushed out.
15A and 15B are explanatory diagrams showing voltage waveforms applied to the piezoelectric elements 53 and 54, a longitudinal section of the pressure chamber 58, and a transverse section of the pressure chamber. FIG. 15A shows when ink is ejected, and FIG. ing. In FIGS. 15A and 15B, (a1) and (b1) are voltage waveforms, (a2) and (b2) are longitudinal sections of pressure chambers, and (a3) and (b3) are pressure chambers. A cross section is shown.

  At the time of ink ejection shown in FIG. 15A, first, when no voltage is applied (t1), the piezoelectric elements 53 and 54 are not deformed, so that the cross section of the pressure chamber is not deformed. The ink in the ejection port 51 is in a state where the meniscus is maintained.

  Thereafter, when a voltage of +10 V is applied to the piezoelectric elements 53 and 54 (t2), the piezoelectric elements 53 and 54 are deformed, the cross section of the pressure chamber is expanded, and the pressure of the ink becomes negative and the inside of the discharge port 51 Ink is sucked into the pressure chamber 58. Here, the time for applying the voltage of +10 V is set to the time (acoustic length AL) for the pressure wave to propagate from end to end of the nozzle.

  When the AL time elapses, a voltage of −10 V is applied to the piezoelectric elements 53 and 54, the piezoelectric elements 53 and 54 are deformed, and the inside of the pressure chamber 58 is reversed from negative pressure to positive pressure. At this timing, the voltage applied to the piezoelectric elements 53 and 54 is removed, and the pressure chamber cross section is subsequently narrowed. When the pressure chamber cross section is in the initial state at the time of the narrowing (t3), ink starts to be pushed out from the ejection port 51, and when the pressure chamber cross section is completely narrowed (t4), ink droplets are formed. Here, the time for applying the voltage of −10 V is set to twice the AL time in order to eliminate the residual pressure when the voltage of +10 V is applied.

  When 2AL time has elapsed, no voltage is applied to the piezoelectric elements 53 and 54, and the piezoelectric elements 53 and 54 and the nozzle cross section return to the basic state (t5). As a result, the ink droplet is ejected away from the ejection port 51. Thereafter, these operations are repeated.

  On the other hand, when the discharge is stopped as shown in FIG. 15B, first, when no voltage is applied (t11), since the piezoelectric elements 53 and 54 are not deformed, the cross section of the pressure chamber is not deformed. The ink in the ejection port 51 is in a state where the meniscus is maintained.

  Thereafter, when a voltage of +10 V is applied to the piezoelectric elements 53 and 54 (t12), the piezoelectric elements 53 and 54 are deformed and the pressure chamber cross section is expanded. The ink in the ejection port 51 is sucked into the pressure chamber 58. Here, the time for applying the voltage of +10 V is set to 2AL.

  When 1 AL time has elapsed (t13), the ink pressure is reversed and becomes positive, and the meniscus is pushed out from the nozzle. When a further 1 AL time elapses (t14), the meniscus is drawn. When the deformation of the pressure chamber 58 is removed at this timing, the meniscus returns to the normal position. Then, until the voltage of +10 V is again applied, the pushed ink returns to the ejection port 51 and maintains the meniscus. Thereafter, these operations are repeated.

  In this way, the piezoelectric elements 53 and 54 for ejecting ink have a voltage waveform that does not eject ink when the ejection of ink is suspended, and cause the ink meniscus in the ejection port 51 to vibrate slightly. The ink in the nozzle can be agitated by repeatedly pushing out and returning the ink. Therefore, the ink in the nozzles can be prevented from curing even when ultraviolet rays are incident on the nozzles during ejection stop.

  The present invention is not limited to the above-described embodiment, and various improvements and design changes may be made without departing from the spirit of the present invention.

For example, in the above embodiment, a serial printer is used as the ink jet printer, but the present invention is not limited to this, and a line printer may be used as the ink jet printer.
Moreover, in the said embodiment, the black coloring layer 23 is provided on the nozzle top plate 22 as a nozzle top plate which consists of an aluminum plate or an aluminum die-casting board, and the inorganic ultraviolet absorber coating layer 24 and water-repellent treatment are provided on it. The water repellent treatment layer is provided on the nozzle surface 21 formed by providing the layer 25 and the nozzle top plate 52 and the protective top plate 64 formed of a material having an ultraviolet absorption rate of 80% or more. The surfaces 52a and 64a formed by the above are illustrated. However, as long as the ultraviolet absorption rate of the surface is 80% or more and the critical surface tension is lower than the surface tension of the ink, any configuration of the nozzle top plate and the protective top plate is possible. It may be a thing. For example, in addition to the above, there are a nozzle top plate and a protective top plate formed of a material having an ultraviolet absorption rate of 80% or more and water repellency.

Moreover, in the said embodiment, although the space | interval of the surface of a nozzle top plate and a protection top plate and the recording medium 99 is not mentioned, it is 1 mm or more and 4 mm or less as this space | interval. Here, the shorter the distance between the surface of the nozzle top plate and the recording medium 99, the shorter the flying distance of the ink droplets ejected from the recording heads 20 and 50, so that the ink can be prevented from being bent, and the sharpness of the image can be prevented. Improves. However, if the distance is less than 1 mm, when foreign matter is fixed on the surfaces of the recording heads 20 and 50, the foreign matter may cause clogging of the recording medium 99 or damage to the surfaces of the nozzle top plate and the protective top plate. . For this reason, if the distance between the surface of the nozzle top plate and the protective top plate and the recording medium 99 is 1 mm or more, it is possible to prevent troubles caused by foreign matter.
On the other hand, when the distance between the surface of the nozzle top plate and the recording medium 99 becomes longer than 4 mm, not only the sharpness of the image described above is deteriorated, but also the ultraviolet rays reflected on the surface of the recording medium 99 are discharged to the ejection port 51. It becomes easy to enter. If the distance between the surface of the nozzle top plate and the protective top plate and the recording medium 99 is 4 mm or less, the number of ultraviolet reflections performed between the recording medium 99 and the nozzle top plate and the protective top plate can be increased. Since the ultraviolet rays are absorbed many times by the surfaces of the nozzle top plate and the protective top plate before reaching the discharge port 51, the amount of ultraviolet light reaching the discharge port 51 can be reduced as a result.

Moreover, in the said embodiment, although the surface of the nozzle top plate and the surface of the protection top plate were illustrated as a part which reflects an ultraviolet-ray, since there is also a part which reflects an ultraviolet-ray other than this, the part which reflects other ultraviolet rays Also, it is preferable that the UV absorption rate is 80% or more, preferably 90% or more. The part that reflects ultraviolet rays includes a direct reflection member that directly reflects ultraviolet rays from the ultraviolet irradiation device 30 and an indirect reflection member that reflects reflected ultraviolet rays again.
The direct reflection member is a member that faces the ultraviolet light source, such as a recording medium, a platen, a maintenance unit, a transport mechanism, various covers, casings, chassis, and the like. On the other hand, the indirect reflection member is a member that faces the ultraviolet light source, such as a recording head, a carriage, an ultraviolet irradiation device, a guide member, an optical trap, an ink tank, various covers, casings, chassis, and the like. If these ultraviolet absorptances are increased, it is possible to reduce the ultraviolet rays incident on the discharge ports by a synergistic effect.

[Example]
Examples will be described below. In this example, the ink jet printer described in the second embodiment is used.
A fluorescent tube having a main peak at a wavelength of 313 nm was used as the ultraviolet light source, and the recording medium immediately below the ultraviolet light source was set so that the illuminance of ultraviolet light in the wavelength range of 220 nm to 400 nm was 8 mW / cm ² . USR40 made by Ushio Electric was used for the measurement of illuminance.

  A cationic polymerization type magenta ink was used as the ultraviolet curable ink. In preparing the ink, first, a magenta pigment dispersion composed of 15 parts by mass of PR-184, 2 parts by mass of a dispersant, and 83 parts by mass of Aron oxetane OXT-221 is prepared. Thereafter, 17 parts by mass of this magenta pigment dispersion, 40 parts by mass of Aron Oxetane OXT-221, 30 parts by mass of Aron Oxetane 221, 30 parts by mass of Celoxide, and 5 parts by mass of UVI 6990 (photoacid generator) were blended. The solution was filtered through a 0.8 μm membrane filter, depressurized and dehydrated while heating to 50 ° C. to obtain a magenta ink. This magenta ink had a viscosity at 25 ° C. of 32.5 mPa / s and a surface tension of 35.2 mN / m.

  As the recording head, an inkjet head that discharges ultraviolet curable ink having a droplet size of 7 pl with a nozzle pitch of 360 dpi using a piezoelectric element was used. This ink jet head includes a heater that can heat the nozzle.

  The nozzle top plate of this recording head has a polyimide resin plate (reflective component including regular reflection component is 15.4% and reflectance not including regular reflection component is 0.9%). Is used. A resist was applied to one surface of the polyimide resin plate to protect it, and a perfluoroalkylsilane solution (NI Material: INT444) having a critical surface tension of 11 mN / m was applied to the other surface. The perfluoroalkylsilane solution was heated to 300 ° C. to form a siloxane network to form a water repellent treatment layer. This water repellent layer had an advancing contact angle of 82 ° and a receding contact angle of 44 °. Then, an ejection port having a diameter of 26 μm was formed on the polyimide resin plate with an excimer laser.

  A protective top plate that surrounds the nozzle top plate and protects the nozzle top plate is manufactured from aluminum that is black anodized, and a water repellent treatment layer is formed on the surface in the same manner as the nozzle top plate. The reflectance of a black anodized aluminum that includes a regular reflection component is 5%, and the reflectance that does not include a regular reflection component is 3.1%.

  In this embodiment, the interval between the nozzle surface of the recording head and the recording medium is 1.5 mm, the interval between the nozzle surface of the recording head and the platen upper surface is 1.7 mm, and the interval between the carriage lower surface and the platen upper surface is 1. The distance between the ultraviolet light source and the upper surface of the platen is set to 20 mm.

  Various ejection tests were performed on the recording medium using the above-described inkjet printer and ultraviolet curable ink. Hereinafter, conditions and results of each discharge test will be described.

"Discharge test 1"
While keeping the distance between the recording head and the recording medium at 1 mm and irradiating the recording medium with ultraviolet rays by an ultraviolet irradiation device, 5 pl ink droplets were continuously ejected from the recording head for 30 minutes at a flight speed of 8 m / sec and an ejection frequency of 12 kHz. .
As a result, even after 30 minutes, no discharge failure such as discharge stop, flight speed reduction, or discharge direction bending occurred.

"Discharge test 2"
While keeping the distance between the recording head and the recording medium at 1 mm and irradiating the recording medium with ultraviolet rays by an ultraviolet irradiation device, 30 minutes, 5 pl of ink droplets from the recording head was applied at a flight speed of 8 m / sec and an ejection frequency of 12 kHz for 1 minute. Discharge and pause were repeated every time (intermittent discharge). When the ejection was stopped, a voltage waveform that did not eject ink was applied to the piezoelectric element to slightly vibrate the ink meniscus in the ejection port.
As a result, even after 30 minutes, no discharge failure such as discharge stop, flight speed reduction, or discharge direction bending occurred.

"Discharge test 3"
While keeping the distance between the recording head and the recording medium at 1 mm and irradiating the recording medium with ultraviolet rays by an ultraviolet irradiation device, 30 minutes, 5 pl of ink droplets from the recording head was applied at a flight speed of 8 m / sec and an ejection frequency of 12 kHz for 1 minute. Discharge and pause were repeated every time (intermittent discharge). Note that the ink meniscus in the discharge port was not vibrated slightly during the discharge stop.
As a result, although normal ejection was performed at the start of ejection, the image density gradually decreased. This is probably because the ink is not vibrated when the ejection is stopped, and the viscosity of the ink is increased by the ultraviolet rays incident into the ejection port, thereby reducing the weight of the ink droplet.
If the recording head is moved to the maintenance unit and ink is ejected idle, the ejection state is recovered, but the ejection operation often has to be interrupted. Also, expensive ink was wasted.

"Discharge test 4"
Keeping the distance between the recording head and the recording medium at 5 mm, and irradiating the recording medium with ultraviolet rays by an ultraviolet irradiation device, 30 minutes, 5 pl ink droplets from the recording head at a flight speed of 8 m / sec and an ejection frequency of 12 kHz for 1 minute Discharge and pause were repeated every time (intermittent discharge). When the ejection was stopped, a voltage waveform that did not eject ink was applied to the piezoelectric element to slightly vibrate the ink meniscus in the ejection port.
As a result, although normal ejection was performed at the start of ejection, the image density gradually decreased. This is probably because the number of reflections of ultraviolet rays is reduced because the distance between the recording head and the recording medium is too wide, and the ultraviolet rays are not sufficiently absorbed.
If the recording head is moved to the maintenance unit and ink is ejected idle, the ejection state is recovered, but the ejection operation often has to be interrupted.

"Discharge test 5"
While keeping the distance between the recording head and the recording medium at 1 mm and irradiating the recording medium with ultraviolet rays by an ultraviolet irradiation device, 5 pl ink droplets were continuously ejected from the recording head for 30 minutes at a flight speed of 8 m / sec and an ejection frequency of 12 kHz. . After 30 minutes, the discharge was stopped for 1 hour. During this time, a voltage waveform that does not eject ink was applied to the piezoelectric element to slightly vibrate the ink meniscus in the ejection port. After 1 hour, it was continuously discharged again under the same conditions for 30 minutes.
As a result, there was no discharge failure such as discharge stop, flight speed reduction, discharge direction bending, and image degradation did not occur.

"Discharge test 6"
While keeping the distance between the recording head and the recording medium at 1 mm and irradiating the recording medium with ultraviolet rays by an ultraviolet irradiation device, 5 pl ink droplets were continuously ejected from the recording head for 30 minutes at a flight speed of 8 m / sec and an ejection frequency of 12 kHz. . After 30 minutes, the discharge was stopped for 1 hour. In this case, immediately before 1 hour elapses, a voltage waveform that does not eject ink is applied to the piezoelectric element to slightly vibrate the ink meniscus in the ejection port, and then the voltage waveform during ink ejection is applied to the piezoelectric element to empty the ink. It is discharged. After 1 hour, it was continuously discharged again under the same conditions for 30 minutes.
As a result, after restarting printing, there was no ejection failure such as ejection stop, flight speed reduction, or ejection direction bending, and image degradation did not occur.

"Discharge test 7"
Using FEP as the water-repellent treatment layer of the nozzle top plate in the recording head, keeping the distance between the recording head and the recording medium at 1 mm and irradiating the recording medium with ultraviolet rays by the ultraviolet irradiation device, 5 pl of ink from the recording head The droplets were continuously discharged for 30 minutes at a flight speed of 8 m / sec and a discharge frequency of 12 kHz.
As a result, since the water repellency of FEP was not sufficient, solid matter adhered to the nozzle surface, and continuous discharge was not possible for 30 minutes. From this, it can be seen that idle ejection and wiping are necessary even during continuous ejection.

"Discharge test 8"
As the nozzle top plate in the ejection test 8, a polyethersulfone resin plate having a reflectance including a regular reflection component of 92% and a reflectance not including a regular reflection component of 74.7% is used. One side of this polyethersulfone resin plate is protected by applying a resist, and the other side is coated with a perfluoroalkylsilane solution having a surface tension of 11 mN / m (manufactured by NI Material Co., Ltd .: INT444). did. The perfluoroalkylsilane solution was heated to 300 ° C. to form a cyclosan network to form a water repellent treatment layer. This water repellent layer had an advancing contact angle of 80 ° and a receding contact angle of 42 °. Then, an outlet having a diameter of 26 μm was formed on the polyethersulfone resin plate with an excimer laser.
Then, while keeping the interval between the recording head and the recording medium at 1 mm, and irradiating the recording medium with ultraviolet rays by the ultraviolet irradiation device, 30 pl of 5 pl ink droplets from the recording head at a flight speed of 8 m / sec and an ejection frequency of 12 kHz, Discharge and pause were repeated every minute (intermittent discharge). When the ejection was stopped, a voltage waveform that did not eject ink was applied to the piezoelectric element to slightly vibrate the ink meniscus in the ejection port.

As a result, although normal ejection was performed at the start of ejection, the image density gradually decreased. This is because the ultraviolet absorption rate of the nozzle surface is less than 80%, the ultraviolet rays cannot be absorbed sufficiently, and even if the ink is slightly vibrated, the ink is thickened by the ultraviolet rays that are incident on the ejection port, and the ink droplets. This seems to be due to the decrease in weight.
If the recording head is moved to the maintenance unit and ink is ejected idle, the ejection state is recovered, but the ejection operation often has to be interrupted.
The results of the above discharge tests 1 to 8 are summarized in Table 1.

1 is a perspective view showing an ink jet printer according to a first embodiment of the present invention. It is the perspective view which showed the carriage with which the inkjet printer of FIG. 1 was equipped. FIG. 3 is a perspective view showing a carriage provided in the ink jet printer of FIG. 1 as viewed in a direction opposite to the perspective direction of FIG. 2. FIG. 3 is a diagram schematically illustrating a state near a nozzle surface of a recording head. It is a figure which shows a mode that the ultraviolet-ray from an ultraviolet irradiation device strikes a recording head. It is a table | surface which shows the measurement result of the measurement experiment of the light reflectivity at the time of providing a various coating layer with respect to a nozzle surface. It is a perspective view showing the carriage 5A with which the inkjet printer of 2nd Embodiment is equipped. FIG. 8 is a cross-sectional view illustrating a schematic configuration of a recording head provided in the ink jet printer of FIG. 7. FIG. 9 is an exploded perspective view illustrating an internal configuration of the recording head in FIG. 8. It is a perspective view showing the nozzle top plate with which the recording head of FIG. 8 is equipped. It is explanatory drawing showing the contact angle of an ink drop. It is explanatory drawing showing the advancing contact angle and renewal contact angle of an ink drop. It is a figure showing the relationship of the advancing contact angle and receding contact angle with respect to hydrophilicity and hydrophobicity. It is explanatory drawing showing an example of the water-repellent processing layer with which the nozzle top plate of FIG. 10 is equipped. It is explanatory drawing showing the voltage waveform applied to a piezoelectric element, the longitudinal cross-section of a pressure chamber, and the cross section of a pressure chamber.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inkjet printer 2 Printer main body 3 Support stand 4 Platen 5, 5A Carriage 6 Guide member 7 Maintenance unit 8 Ink tank 9 Sub tank 20, 50 Recording head 21 Nozzle surface 22, 52 Nozzle top plate 23 Black coloring process layer 24 Inorganic ultraviolet absorber Coating layer 25 Water repellent treatment layer 30 Ultraviolet irradiation device 31 Ultraviolet light source 40 Optical trap 51 Discharge port 53, 54 Piezoelectric element 58 Pressure chamber (ink flow path)
99 Recording medium A Scanning direction B Transport direction

Claims (21)

A recording head having a nozzle top plate in which an ejection port for ejecting ink that is cured by being irradiated with ultraviolet rays to a recording medium is disposed;
An ultraviolet irradiation device for irradiating the ink ejected from the recording head onto the recording medium with ultraviolet rays;
With
An ink jet printer characterized in that a critical surface tension of a surface of the nozzle top plate is lower than a surface tension of the ink, and an ultraviolet absorption rate is 80% or more. A recording head having a nozzle top plate on which a discharge port for discharging ink that is cured by being irradiated with ultraviolet rays to a recording medium is disposed, and a protective top plate for protecting the nozzle top plate;
An ultraviolet irradiation device for irradiating the ink ejected from the recording head onto the recording medium with ultraviolet rays;
With
An ink jet printer characterized in that a critical surface tension of a surface of the protective top plate is lower than a surface tension of the ink, and an ultraviolet absorption rate is 80% or more. The inkjet printer according to claim 2.
An ink jet printer characterized in that a critical surface tension of a surface of the nozzle top plate is lower than a surface tension of the ink, and an ultraviolet absorption rate is 80% or more. The inkjet printer according to claim 3.
At least one of the critical surface tensions of the surface of the nozzle top plate and the surface of the protective top plate is 15 mN / m or less. The inkjet printer according to claim 3 or 4,
At least one of the surface of the nozzle top plate and the surface of the protective top plate is formed by providing an inorganic ultraviolet absorbent coating layer and a water repellent treatment layer on a substrate. . The inkjet printer according to claim 5.
At least one of the surface of the nozzle top plate and the surface of the protective top plate is provided with a black colored treatment layer on the substrate, and the inorganic ultraviolet absorbent coating layer and the water repellent treatment layer are provided thereon. An ink jet printer characterized by being formed. In the ink jet printer according to any one of claims 4 to 6,
An inkjet printer, wherein at least one of the nozzle top plate and the protective top plate is made of an aluminum plate or an aluminum die-cast plate. The inkjet printer according to claim 3 or 4,
The surface of the nozzle top plate is formed by providing a water-repellent treatment layer on the substrate of the nozzle top plate,
An ink jet printer, wherein the substrate of the protective top plate is formed of a material having an ultraviolet absorption rate of 80% or more. In the ink jet printer according to any one of claims 1 to 8,
An ink jet printer, wherein a distance between a surface of the nozzle top plate and the recording medium is 1 mm or more and 4 mm or less. In the ink jet printer according to any one of claims 1 to 9,
An inkjet printer, wherein an ultraviolet light source of the ultraviolet irradiation device is any one of a low pressure mercury lamp, a high pressure mercury lamp, a metal halide lamp, a hot cathode tube, a cold cathode tube, and an LED. In the ink jet printer according to any one of claims 1 to 10,
The recording head includes an ink channel for guiding ink to the ejection port, and a piezoelectric element for ejecting the ink in the ink channel,
The piezoelectric element agitates the ink in the ink flow path by slightly vibrating the ink meniscus of the discharge port with a voltage waveform that does not cause the ink to be discharged when the ink discharge is stopped. . A nozzle top plate provided with a discharge port for discharging ink that is cured by irradiation with ultraviolet rays to a recording medium,
A recording head, wherein a critical surface tension of a surface of the nozzle top plate is lower than a surface tension of the ink, and an ultraviolet absorption rate is 80% or more. A nozzle top plate on which a discharge port for discharging ink that is cured by being irradiated with ultraviolet rays to a recording medium is disposed;
A protective top plate for protecting the nozzle top plate;
A recording head characterized in that a critical surface tension of the surface of the protective top plate is lower than a surface tension of the ink and an ultraviolet absorption rate is 80% or more. The recording head according to claim 13.
A recording head, wherein a critical surface tension of a surface of the nozzle top plate is lower than a surface tension of the ink, and an ultraviolet absorption rate is 80% or more. The recording head according to claim 14, wherein
At least one of the critical surface tensions of the surface of the nozzle top plate and the surface of the protective top plate is 15 mN / m or less. The recording head according to claim 14 or 15,
At least one of the surface of the nozzle top plate and the surface of the protective top plate is formed by providing an inorganic ultraviolet absorbent coating layer and a water repellent treatment layer on a substrate. . The recording head according to claim 16, wherein
At least one of the surface of the nozzle top plate and the surface of the protective top plate is provided with a black colored treatment layer on the substrate, and the inorganic ultraviolet absorbent coating layer and the water repellent treatment layer are provided thereon. A recording head characterized in that the recording head is formed. In the recording head according to any one of claims 15 to 17,
2. A recording head, wherein at least one of the nozzle top plate and the protective top plate is made of an aluminum plate or an aluminum die-cast plate. The recording head according to claim 14 or 15,
The surface of the nozzle top plate is formed by providing a water-repellent treatment layer on the substrate of the nozzle top plate,
The recording head according to claim 1, wherein the substrate of the protective top plate is formed of a material having an ultraviolet absorption rate of 80% or more. In the recording head according to any one of claims 12 to 19,
A recording head, wherein a distance between a surface of the nozzle top plate and the recording medium is 1 mm or more and 4 mm or less. In the recording head according to any one of claims 12 to 20,
An ink flow path for guiding ink to the ejection port;
A piezoelectric element for discharging the ink in the ink flow path;
The piezoelectric element agitates the ink in the ink flow path by slightly vibrating the ink meniscus of the ejection port with a voltage waveform that does not cause the ink to be ejected when the ink ejection is stopped. .

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