JP6171312B2 - Inkjet recording apparatus and inkjet recording method - Google Patents

Description

  The present invention relates to an ink jet recording apparatus and an ink jet recording method using the same.

  Conventionally, as a recording apparatus for forming an image on a recording medium such as paper based on an image data signal, apparatuses using various methods are used. Among these, an apparatus using an ink jet method is an inexpensive apparatus, and ink is ejected only to a required image portion to form an image directly on a recording medium. Therefore, the ink can be used efficiently and the running cost is low. cheap. Further, the ink jet method is excellent as a recording apparatus because of low noise.

  In recent years, an ink jet recording apparatus equipped with an ultraviolet curable ink in which a monomer is photopolymerized (cured) by being irradiated with ultraviolet rays forms an image having excellent water resistance and abrasion resistance on a recording surface of a recording medium. Therefore, it is used for manufacturing color filters, printing on printed boards, plastic cards, vinyl sheets, large signs, and plastic parts, and printing barcodes and dates.

  Examples of the ink used for inkjet recording include a solvent-based aqueous ink and a solvent-free ultraviolet curable ink (UV ink). Among these, solvent-free UV curable ink has a significantly higher viscosity than solvent-based water-based inks, so viscosity fluctuations due to temperature fluctuations during ejection are large, and this viscosity fluctuation causes changes in droplet size and droplet ejection. It has a great influence on the change in speed, which in turn causes image quality degradation. Therefore, a technique is disclosed in which when ultraviolet curable ink is ejected, the ink is heated to lower the viscosity and then ejected.

  For example, in Patent Document 1, since UV ink has a higher viscosity than ordinary ink at normal temperature, it is heated in the recording head and set to a target set temperature (set temperature necessary for the ink to be ejected viscosity). The ink viscosity is 7,000 to 500 mPa · s at 5 ° C. and the ink viscosity is 20 to 3 mPa · s at 80 ° C. Thus, a UV ink that is changed by heating temperature control is disclosed (paragraphs 0034, 0041, and 0042 of Patent Document 1).

JP 2003-200559 A

  However, the UV ink disclosed in Patent Document 1 has a problem that the head member is deteriorated by heating. Further, since the UV ink has a very high viscosity, there arises a problem that the discharge stability is poor when it is discharged without heating.

  Accordingly, an object of the present invention is to provide an ink jet recording apparatus that is excellent in durability of a head and ejection stability of an ultraviolet curable ink.

  In order to solve the above-mentioned problems, the inventors of the present invention have made extensive studies and obtained the following knowledge. First, an ultraviolet curable ink having a very low viscosity (hereinafter, ultraviolet curable ink is also simply referred to as “ink”) was prepared, and a method for discharging the ink without heating was examined. However, according to the method, it has been found that the temperature of the ink is likely to fluctuate due to a change in the environmental temperature, and the ink ejection stability cannot be improved. Furthermore, it has been found that due to the composition of the ultraviolet curable ink having a very low viscosity, the head member deteriorates, the durability of the head deteriorates, and curing wrinkles easily occur. Therefore, the inventors of the present application tried to heat an ultraviolet curable ink having a relatively low viscosity and a predetermined range of viscosity at a predetermined range of temperatures at a relatively low temperature. As a result, it has been found that deterioration of the head member can be prevented. In addition to this, it has been found that the temperature fluctuation at the time of ejection can be reduced, the viscosity fluctuation can be suppressed, and the ejection stability of the ultraviolet curable ink is also improved.

  In addition, based on the idea that the ink ejection stability can be further improved by providing a deaeration mechanism to sufficiently deaerate the ink, the deaeration efficiency of the ink changes depending on the temperature and viscosity of the ink. I found out. Therefore, the inventors of the present application have repeatedly investigated the relationship between the deaeration efficiency of ink, the temperature, and the viscosity. As a result, the deaeration efficiency is extremely high by setting the temperature and viscosity of the ultraviolet curable ink within the above-described predetermined ranges. It has been found that the ink ejection stability can be improved.

  Based on the above findings, the inventors of the present invention conducted further diligent studies. As a result, the temperature of the ultraviolet curable ink having a viscosity at 28 ° C. of 8 mPa · s or more is 28 to 40 ° C. In a state of deaerated ink having a viscosity at a temperature of 15 mPa · s or less, an ink jet recording apparatus that discharges from a head toward a recording medium and cures the ink attached to the recording surface by ultraviolet irradiation from a light source, The present inventors have found that the above problems can be solved and have completed the present invention.

That is, the present invention is as follows.
[1]
A head for ejecting and adhering ultraviolet curable ink toward a recording medium;
An ink path for supplying the ultraviolet curable ink from an ink container to the head;
The ultraviolet curable ink having a viscosity at 28 ° C. of 8 mPa · s or more is heated, the temperature of the ejected ink is set to 28 to 40 ° C., and the viscosity of the ink at the temperature is 15 mPa · s or less. And a heating mechanism
A degassing mechanism for degassing the ultraviolet curable ink and supplying the degassed ink to the head;
A light source for curing the ink by irradiating the ultraviolet curable ink attached to the recording medium with ultraviolet rays;
An inkjet recording apparatus comprising:
[2]
The inkjet recording apparatus according to [1], wherein the deaeration mechanism is provided in the ink path.
[3]
The inkjet recording apparatus according to [1] or [2], wherein at least a part of the ink path is an ink circulation path for circulating the ultraviolet curable ink.
[4]
The inflow amount of the ultraviolet curable ink per unit time supplied from the ink circulation path to the head is at least twice the maximum ink ejection amount per unit time for ejecting the ultraviolet curable ink from the head. The inkjet recording apparatus according to [3].
[5]
The inkjet recording apparatus according to any one of [1] to [4], wherein an amount of dissolved oxygen of the ultraviolet curable ink supplied to the head is 20 ppm or less.
[6]
The heating mechanism and the deaeration mechanism are provided in the ink circulation path,
The inkjet according to any one of [3] to [5], wherein the deaeration mechanism is provided in a direction in which ink circulates, downstream of the heating mechanism and upstream of the head. Recording device.
[7]
The inkjet recording apparatus according to any one of [1] to [6], wherein the ultraviolet curable ink includes a thioxanthone photopolymerization initiator.
[8]
The inkjet recording apparatus according to any one of [1] to [7], wherein an epoxy resin is used in at least a part of a portion of the head that contacts the ultraviolet curable ink.
[9]
The ink jet recording apparatus according to any one of [1] to [8], wherein the light source is a light emitting diode, and the light emitting diode emits ultraviolet light having an irradiation peak intensity of 800 mW / cm ² or more.
[10]
An inkjet recording method for performing recording using the inkjet recording apparatus according to any one of [1] to [9].

It is a block diagram which shows an example of a structure of the inkjet recording device of this invention. FIG. 2 is a schematic cross-sectional view illustrating an example of the periphery of a head unit, a transport unit, and an irradiation unit in a line printer that is an example of the inkjet recording apparatus of the present invention. It is a schematic front view which shows an example of the ink supply apparatus with which the inkjet recording device of this invention is provided.

  Hereinafter, embodiments for carrying out the present invention will be described in detail. In addition, this invention is not restrict | limited to the following embodiment, A various deformation | transformation can be implemented within the range of the summary. Moreover, in each drawing used for the following description, the scale is appropriately changed for each component in order to make each component (member) recognizable on the drawing. The present embodiment is not limited only to the ratio of the number, shape, and size of the components and the relative positional relationship of the components described in these drawings.

  In this specification, “recorded material” refers to a material in which ink is recorded on a recording medium to form a cured product. In addition, the hardened | cured material in this specification means the hardened | cured substance containing a cured film and a coating film.

  Further, in the present specification, “ejection stability” refers to a property of ejecting a stable ink droplet from the nozzle without any missing nozzle. In this specification, “head durability” refers to deterioration including deterioration such as swelling when a member of a head (specifically, an adhesive among the head members) constituting the recording apparatus comes into contact with ink. A property that is difficult to occur.

  In this specification, “curing” means that when an ink containing a polymerizable compound is irradiated with light, the polymerizable compound is polymerized and the ink is solidified. “Curable” refers to the property of curing in response to light and is also referred to as photopolymerization. “Curing wrinkle” is a result of an increase in the polymerization volume shrinkage rate caused by the uncured ink existing inside the coating film to be cured flowing irregularly before being cured. It means wrinkles generated on the film surface.

  In the present specification, “storage stability” refers to the property that the viscosity before and after storage is difficult to change when the ink is stored. “Abrasion resistance” refers to the property that when the cured product is rubbed, the cured product is difficult to peel off and scratch.

  In the present specification, “(meth) acrylate” means at least one of acrylate and methacrylate corresponding thereto, and “(meth) acryl” means at least one of acrylic and methacryl corresponding thereto. “(Meth) acryloyl” means at least one of acryloyl and methacryloyl corresponding thereto.

[Inkjet recording apparatus]
One embodiment of the present invention relates to an inkjet recording apparatus, that is, an inkjet printer. The ink jet recording apparatus (hereinafter also simply referred to as “recording apparatus”) uses an ultraviolet curable ink (hereinafter also simply referred to as “ink”) having predetermined physical properties. At least an ink path, a heating mechanism, a deaeration mechanism, and a light source.

  The recording apparatus of the present embodiment can record inks of various colors on a recording medium (form an image). For example, four color inks of CMYK (cyan, magenta, yellow, black) are used. For example, an image may be formed, or a base image may be formed using white ink to impart excellent concealability to the recording medium.

  Line printers and serial printers can be cited as the types of printers in this embodiment, and any of them can be used. These are different printer systems.

  A line printer, which is a line-type ink jet recording apparatus, includes a line head having a length equal to or greater than the length corresponding to the width of a recording medium as a head. From the line head to the recording medium, the line head and the recording medium move relative to each other in the scanning direction intersecting the width direction, that is, onto the recording medium scanned relative to the line head. Is discharged. In the line printer, the head is fixed without moving (almost) and recording is performed in one pass (single pass). Line printers are more advantageous than serial printers because of their high recording speed.

  Here, the above-mentioned “line head having a length corresponding to the width of the recording medium” is not limited to the case where the width of the recording medium and the length (width) of the line head completely match each other. May be different. For example, the length (width) of the line head may correspond to the width (recording width) of the recording medium on which ink is to be ejected (image should be recorded). This is the case.

  On the other hand, a serial printer, which is a serial ink jet recording apparatus, performs main scanning (pass) in which ink is ejected while the head moves in the main scanning direction intersecting the sub-scanning direction of the recording medium, and usually two or more passes. (Multi-pass) is used for recording.

  Hereinafter, a line printer which is an example of a printer according to the present embodiment will be described in detail with reference to the drawings. FIG. 1 is a block diagram illustrating an example of the configuration of an inkjet recording apparatus (printer 1) according to the present embodiment. FIG. 2 is a schematic cross-sectional view illustrating an example of the periphery of the head unit, the transport unit, and the irradiation unit in the line printer of the present embodiment.

[1. Configuration of recording apparatus]
The printer 1 is a recording device that forms an image on a recording medium, and is communicably connected to a computer 130 that is an external device.

  A printer driver is installed in the computer 130 which is an external device. The printer driver is a program for displaying a user interface on a display device (not shown) and converting image data output from an application program into print data (image formation data). This printer driver is recorded on a “computer-readable recording medium” such as a flexible disk FD or a CD-ROM. Alternatively, the printer driver can be downloaded to the computer 130 via the Internet. In addition, this program is comprised from the code | cord | chord for implement | achieving various functions.

  Then, the computer 130 outputs print data corresponding to the image to the printer 1 in order to cause the printer 1 to form an image.

  The printer 1 includes an ink supply unit 10, a transport unit 20, a head unit 30, an irradiation unit 40, a detector group 110, a memory 123, an interface (I / F) 121, and a controller 120. The printer 1 that has received the print data from the computer 130 controls each unit by the controller 120 and records an image on a recording medium in accordance with the print data. The situation in the printer 1 is monitored by the detector group 110, and the detector group 110 outputs the detection result to the controller 120. The controller 120 controls each unit based on the detection result output from the detector group 110. The controller 120 stores print data input via the interface 121 in the memory 123 and includes a CPU 122 and a unit control circuit 124. The memory 123 also stores control information for controlling each unit.

The ink supply unit 10 adjusts the ink supply amount. The ink supply unit 10 includes a device that adjusts an ink supply amount (hereinafter referred to as “ink supply device”) between an ink container such as an ink tank or an ink cartridge and a head.
The ink supply unit (ink supply device) 10 will be described in detail later.

  The transport unit 20 transports the recording medium S in the transport direction. As shown in FIG. 2, for example, the transport unit 20 includes a transport motor (not shown) that rotates a transport roller including an upstream roller 25 </ b> A and a downstream roller 25 </ b> B, and a transport drum 26 is driven. The recording medium S is transported along the peripheral surfaces of the transport roller and transport drum 26 to a recordable region (region facing the head) as the transport roller rotates.

The head unit 30 ejects ink toward the recording medium S. The head unit 30 forms dots on the recording medium S by discharging each ink onto the recording medium S being conveyed, thereby forming an image. The printer 1 of this embodiment is a line printer, and each head of the head unit 30 can form dots corresponding to the width of the recording medium at a time. Specifically, as shown in FIG. 2, each head including a black ink head K, a cyan ink head C, a magenta ink head M, and a yellow ink head Y in order from the upstream side in the transport direction around the transport drum 26. (Hereinafter, the respective heads are collectively referred to as “heads”.) Are arranged to face the transport drum 26. The black ink head K is a discharge portion for ultraviolet curable black ink. The cyan ink head C is an ultraviolet curable cyan ink ejection unit. The magenta ink head M is an ejection unit for ultraviolet curable magenta ink. The yellow ink head Y is a discharge portion for ultraviolet curable yellow ink. Each of these heads discharges the ultraviolet curable ink toward the recording medium S. The ejected ink adheres to the recording surface of the recording medium S. In this way, each head is controlled from the upstream side, and dots are formed at necessary positions in one line corresponding to the width of the recording medium S, so that the recording medium S is scanned once in the transport direction. An image can be formed.
The head (inkjet head) will be described in detail later. In addition, although the term “paper” is used here for convenience, the recording medium described later can be used as the recording medium in the present embodiment.

  The irradiation unit 40 irradiates ultraviolet rays toward the dots of the ultraviolet curable ink landed on the recording medium S. The dots formed on the recording medium S are cured by being irradiated with ultraviolet rays from the irradiation unit 40. The irradiation unit 40 in this embodiment has a light source that irradiates the ink attached to the recording medium S with ultraviolet rays. Specifically, as shown in FIG. 2, the irradiation unit 40 includes pre-curing irradiation units 42a, 42b, 42c, and 42d as light sources on the downstream side in the transport direction of each head, and further downstream in the transport direction. Includes a main curing irradiation section 44 as a light source. Such a recording apparatus can be configured as shown in FIG. 11 of Japanese Patent Application Laid-Open No. 2010-269471, for example.

  Here, in this specification, “temporary curing” means temporary pinning of ink, and more specifically, curing before main curing in order to prevent bleeding between dots and control of the dot diameter. It means that Generally, the polymerization degree of the polymerizable compound in the temporary curing is lower than the polymerization degree of the polymerizable compound by the main curing performed after the temporary curing. Further, “main curing” refers to curing the dots formed on the recording medium to a curing state necessary for using the recorded material. In the present specification, the term “curing” means main curing unless otherwise specified.

  In addition, since it is only necessary that the main curing irradiation unit 44 is irradiated with ultraviolet rays and the ink is finally cured, the preliminary curing irradiation units 42a, 42b, 42c, and 42d are not irradiated with ultraviolet rays from some or all of them. The curing process may be terminated by irradiating with ultraviolet rays from the main curing irradiation unit 44. As described above, the curing step may perform only the main curing without performing the temporary curing.

  The detector group 110 includes a rotary encoder (not shown), a paper detection sensor (not shown), and the like. The rotary encoder detects the rotation amount of the upstream roller 25A and the downstream roller 25B described above. The transport amount of the recording medium S can be detected based on the detection result of the rotary encoder. The paper detection sensor detects the position of the tip of the recording medium S being fed.

  The controller 120 is a control unit (control unit) for controlling the printer. The controller 120 includes an interface unit 121, a CPU 122, a memory 123, and a unit control circuit 124. The interface unit 121 transmits and receives data between the computer 130 that is an external device and the printer 1. The CPU 122 is an arithmetic processing device for controlling the entire printer 1. The memory 123 is for securing an area for storing the program of the CPU 122, a work area, and the like, and includes storage elements such as a RAM and an EEPROM. The CPU 122 controls each unit via the unit control circuit 124 in accordance with a program stored in the memory 123.

[2. Configuration of the head of the recording device)
As described above, the head unit 30 included in the inkjet recording apparatus (printer 1) includes a head (inkjet head) that performs recording by discharging ultraviolet curable ink toward a recording medium.

  The head includes a cavity that discharges the stored ink from the nozzle, a discharge driving unit that is provided for each of the cavities and applies a driving force for discharging the ink, and a head that is provided for each of the cavities. A nozzle for discharging ink to the outside. A plurality of cavities, and ejection drive units and nozzles provided for each cavity may be provided in one head independently of each other. The ejection drive unit is formed using an electromechanical conversion element such as a piezoelectric element that changes the volume of the cavity by mechanical deformation, or an electrothermal conversion element that generates and discharges bubbles in ink by generating heat. be able to. The ink jet recording apparatus may be provided with one head or a plurality of heads for each color ink. When a plurality of heads are provided, a line head is formed by arranging a plurality of heads in the width direction of the recording medium. In this case, the above-mentioned recorded width can be increased. In the case where recording is performed using a plurality of colors of ink, the ink jet recording apparatus includes a head for each ink.

  Here, the head included in the serial printer or the line printer that is the printer of the present embodiment is preferably a head that uses an epoxy resin in at least a part of the inside or the surface of the head that comes into contact with the ink. The epoxy resin can be used, for example, as an adhesive that bonds the members of the head when the head is manufactured. By setting the head using such an epoxy resin adhesive, it is possible to maintain a strong adhesive force between the head members even when the temperature of the head is changed. The above-mentioned “in contact with ink” includes direct contact with ink or indirect contact by permeation of ink components. At this time, since the ultraviolet curable ink in the present embodiment can prevent the epoxy resin adhesive from swelling, it is difficult to cause deterioration including alteration, and therefore has excellent head durability. In this way, the ultraviolet curable ink can be suitably discharged from the head using an epoxy resin adhesive.

  Examples of the epoxy resin adhesive include, but are not limited to, a conventionally known adhesive in which a main agent including a compound having an epoxy group is cured by a curing agent. Examples of the compound having an epoxy group contained in the main agent include, but are not limited to, bisphenol type epoxy such as bisphenol A type and bisphenol F type, novolak type epoxy such as phenol novolac type and cresol novolak type, and epoxy polyol. Type epoxy, urethane-modified epoxy, chelate-modified epoxy, and rubber-modified epoxy. Examples of the curing agent include, but are not limited to, amines such as amines and polyamines, amides such as acid anhydrides, amides and polyamides, imidazoles, and polymercaptan. Among these, a combination of bisphenol type epoxy as the main agent and amines as the curing agent is preferable because of excellent adhesive strength. Since the mixing ratio of the main agent and the curing agent (main agent: curing agent) is excellent in the curability of the adhesive, it is preferably 10: 1 to 1:10 in terms of mass. The head can be configured, for example, as shown in FIG. 3 of JP-A-2009-279830.

[3. Configuration of ink supply device among recording devices]
In the ink jet recording apparatus of the present embodiment, the ink supply unit 10 includes a device (ink supply device) that adjusts the ink supply amount. The ink supply device is provided, for example, between an ink container such as an ink tank or an ink cartridge and a head. The ink path provided in the ink supply device supplies ink to the head. More specifically, the ink path connects an ink container and a head and supplies ink from the ink container to the head.

  Here, it is preferable that an ink circulation path is provided in at least a part of the ink path, whereby the amount of ink flowing into the head can be adjusted. More specifically, the ink supply device first adjusts the inflow amount of ink supplied from the ink circulation path to the head. Secondly, the ink supply device discharges at least a part of the flow rate from the head (the discharge amount is the discharge amount), and returns the remaining flow rate (ink outflow amount) from the head to the ink circulation path. Can be. Therefore, for example, if the amount of ink inflow per unit time supplied to the head is greater than or equal to the amount of ink ejected from the head (ink ejection amount per unit time), the ink flows out of the head and returns to the ink circulation path. Ink circulates. If the ink inflow amount per unit time is twice or more the ink discharge amount, the ink outflow amount is one or more times the ink discharge amount.

  Hereinafter, the ink supply device will be described with reference to the drawings. FIG. 3 is a schematic front view showing an example of the ink supply device 10 provided in the ink jet recording apparatus of the present embodiment.

  The ink supply device 10 is located between the ink cartridge 50 and the head 60 in the ink jet recording apparatus. The ink supply device 10 includes an ink cartridge 50, an ink path 51 (preferably, an ink path 51 including an ink circulation path 80), a sub tank 70, a heating mechanism 90, a deaeration mechanism 100, a head 60, Is provided. The head 60 also belongs to the head unit 30 described above.

  The ink cartridge 50 contains ultraviolet curable ink. The holder 52 is for mounting the ink cartridge 50. The ink path 51 is a flow path through which ink passes from the ink cartridge 50 to the head 60, preferably including the ink circulation path 80. In other words, it is preferable that at least a part of the ink path 51 that supplies ink from the ink cartridge 50 that is an ink container to the head 60 is the ink circulation path 80 that circulates the ink. In the ink path 51, a pipe between the ink cartridge 50 and the sub tank 70 is provided with a holder 52, a valve 53, a supply pump 54, and a filter 55.

  The valve 53 is configured to open when the ink cartridge 50 containing ink is attached to the holder 52. The supply pump 54 pushes ink from the ink cartridge 50 to the ink path 51 when the valve 53 is opened. The ink path 51 supplies the ink pushed out from the ink cartridge 50 by the supply pump 54 to the sub tank 70 through the filter 55 that filters foreign matter in the ink. The pressurizing pump 56 pressurizes the sub tank 70 and supplies ink from the sub tank 70 to the ink circulation path 80.

  In the sub tank 70, the liquid amount sensor 71 detects the amount of ink in the sub tank 70. If the amount of liquid becomes equal to or higher than a predetermined first liquid amount, the ink is supplied to the ink circulation path 80, and the liquid amount is predetermined. The ink is received from the ink cartridge 50 when the amount is less than the second liquid amount.

  The ink circulation path 80 communicates with the sub tank 70 and the head 60, and ink is supplied from the sub tank 70 to supply the ink to the head 60. The ink circulation path 80 can keep the temperature of the ink heated by the heating mechanism 90 to be described later constant, or can prevent sedimentation of components contained in the ink by constantly flowing the ink. The ink circulation path 80 is a pipe having a filter 81, a circulation pump 82, and a head filter 83. The ink supplied from the sub tank 70 circulates in the ink circulation path 80 by the circulation pump 82. By circulating the ink in this way, the deaeration efficiency becomes higher, and the temperature of the ink supplied to the head 60 when the ink is heated is easily stabilized. The filter 81 is provided downstream of the circulation pump 82 in the ink circulation path 80, and filters foreign matter in the ink. A part of the ink circulation path 80 is provided in the head 60, and at least a part of the circulated ink is ejected from the head 60 through a head filter 83 that filters foreign matter in the ink.

  In FIG. 3, the heating mechanism 90 and the deaeration mechanism 100 are provided in the ink circulation path 80, and more specifically, are located in the middle of the ink circulation path 80, that is, between the sub tank 70 and the head 60, respectively.

  The heating mechanism 90 heats the ultraviolet curable ink whose viscosity at 28 ° C. is 8 mPa · s or more. By this heating mechanism, the temperature of the discharged ultraviolet curable ink (hereinafter also referred to as “discharge temperature”) is set to 28 to 40 ° C., and the viscosity of the ultraviolet curable ink at the temperature is set to 15 mPa · s or less. can do. In FIG. 3, the heating mechanism 90 is provided at a position other than at least the position connected to the head 60 in the ink circulation path 80. Here, the “position where the ink circulation path 80 is connected to the head 60” corresponds to a coupling portion of the ink circulation path 80 outside the head 60 in FIG. The heating mechanism 90 heats the ink in the ink circulation path 80 by the temperature adjustment module 94 while circulating the hot water in the hot water tank 91 between the temperature adjustment module 94 and the hot water tank 91 by the hot water circulation pump 92. is there. The heater 93 of the hot water tank 91 adjusts the temperature of the circulating ink to a target temperature.

  The deaeration mechanism 100 degass the ultraviolet curable ink. The degassed ultraviolet curable ink is supplied to the head 60. In FIG. 3, the deaeration mechanism 100 is a direction in which ink circulates, is downstream of the heating mechanism 90 (more specifically, the temperature adjustment module 94 of the ink circulation path 80), and the head 60. It is provided more upstream. Since the deaeration mechanism 100 is positioned downstream of the heating mechanism 90, the ink is deaerated at a high temperature, and thereby the deaeration efficiency can be further increased. The deaeration module 102 includes a deaeration chamber (not shown) into which ink flows and a decompression chamber (not shown) in contact with the deaeration chamber through a separation membrane that does not allow liquid such as ink to pass through. The negative pressure pump 101 depressurizes the decompression chamber. When the decompression chamber is depressurized, the amount of dissolved air in the ink circulation path 80 is reduced and bubbles are removed. In this way, the degassing mechanism 100 degass the ink in the ink circulation path 80.

  Here, the amount of dissolved oxygen in the ultraviolet curable ink supplied to the head 60 is preferably 20 ppm or less. By performing the treatment with the deaeration mechanism 100 located in front of the head 60 so that the dissolved oxygen amount is 20 ppm or less, it is possible to obtain an ink having excellent ejection stability and curability. Thereby, the ink can be suitably used for an ink jet recording apparatus.

Moreover, 1-20 ppm is preferable, as for the said dissolved oxygen amount, 3-20 ppm is more preferable, and 5-15 ppm is further more preferable. In particular, when the amount of dissolved oxygen is 1 ppm or more, the polymerization of the polymerizable compound can be sufficiently inhibited, so that excellent storage stability can be effectively maintained.
In addition, although the dissolved oxygen amount in this specification can be measured by a conventionally well-known method, the value obtained by the measuring method implemented in the below-mentioned Example shall be employ | adopted for convenience.

  Returning to FIG. 3, the description will be continued. The head 60 discharges ink toward the recording medium. The head 60 includes a nozzle (not shown) for discharging ink, a nozzle plate having a nozzle surface on which the nozzle is formed, a cavity (not shown) communicating with the nozzle and containing ink, and a reverse flow of ink. A reservoir (not shown) for preventing, a discharge driving unit (not shown) for applying ejection driving force to the ink contained in the cavity to form ink droplets suitable for ejection and ejecting them from the nozzles; Is provided. In FIG. 3, for example, the cavity is a pressure generating chamber, and the ejection driving unit is a piezoelectric element. The cap 61 protects the nozzles of the head 60 in order to prevent the ink adhering to the vicinity of the nozzles from drying when the recording apparatus is not used.

  In FIG. 3, four heads 60 are provided in parallel in the ink circulation path 80. Thus, it is preferable that there are a plurality of heads 60 to which ink is supplied from the ink circulation path 80, and ink is ejected from the plurality of heads 60. In this case, as will be described later, since there is one ink circulation path 80 for the plurality of heads 60, the ink circulation path 80 and the temperature control module 94 are made common to supply ink to the four heads 60. Can be made uniform, and the cost of the recording apparatus can be reduced.

[4. Operation of the recording device)
First, the ink is initially filled by the operation of the ink supply device 10. When the ink cartridge 50 containing the ink is mounted in the holder 52, the valve 53 is opened, and the ink is supplied to the sub tank 70 by the supply pump 54 through the filter 55 that filters out foreign matter of the ink. . When the liquid level sensor 71 detects that the ink level in the sub tank 70 has become equal to or higher than the predetermined first level, the supply pump 54 is stopped and the valve 53 is closed. The sub tank 70 is pressurized by the pressurizing pump 56, and ink is supplied from the sub tank 70 to the ink circulation path 80. Here, before the ink circulation path 80 is completely filled with ink, if the liquid amount in the sub tank 70 falls below a predetermined second liquid amount (that is, an amount smaller than the predetermined first liquid amount), The pressurizing pump 56 is stopped and the sub tank 70 is returned to normal pressure. Then, in the same manner as described above, ink is supplied again from the ink cartridge 50 to the sub tank 70, and ink is supplied again from the sub tank 70 to the ink circulation path 80. By repeating such an operation, when the ink circulation path 80 is completely filled with ink, the pressurizing pump 56 is stopped, the sub tank 70 is returned to the atmospheric pressure, and the amount of liquid in the sub tank 70 is a predetermined first liquid. Ink is supplied again from the ink cartridge 50 to the sub-tank 70 so that the amount exceeds the amount. In this way, the initial ink filling is completed.

  When the initial ink filling is completed, the ink is circulated through the ink circulation path 80 by the circulation pump 82 by the operation of the ink supply device 10. The warming mechanism 90 in which the heater 93 is turned on in advance circulates the warm water in the warm water tank 91 between the temperature control module 94 and the warm water tank 91 by the warm water circulation pump 92. Then, the temperature control module 94 heats the ink circulating in the ink circulation path 80. A filter 81 provided downstream of the circulation pump 82 in the ink circulation path 80 filters ink foreign matter. The deaeration module 102 in the deaeration mechanism 100 includes a deaeration chamber (not shown) through which ink flows, and a decompression chamber in contact with the deaeration chamber through a separation membrane that does not pass a liquid such as ink through a gas such as air. (Not shown). When the decompression chamber is depressurized by the negative pressure pump 101, bubbles and dissolved air contained in the ink in the deaeration chamber escape to the decompression chamber through the separation membrane, so that the amount of dissolved air in the ink circulation path 80 decreases. Bubbles are removed. Since four degassing modules 102 are provided in parallel, the degassing efficiency is increased, and the ink can be degassed while circulating the ink. By providing the deaeration mechanism 100 on the downstream side of the temperature control module 94, deaeration can be performed at a position where the ink temperature is highest in the ink circulation path 80. Therefore, the deaeration efficiency of the ink is very high, and the deaeration module 102 is located downstream of the circulation pump 82, so that the ink can be deaerated at a position where the pressure of the ink is high, and the deaeration efficiency is remarkably increased. can do.

  Here, in the ink circulation path 80, four heads 60 are provided in parallel. In the ink circulation path 80 in the head 60, a reservoir (not shown) is provided on the downstream side of the head filter 83 that filters out foreign matters of ink. The ink that has flowed into the head and passed through the reservoir flows out of the head 60 again, and the ink that has flowed out of each head 60 joins at the coupling portion of the ink circulation path 80 and returns to the sub tank 70. The reservoirs are connected to 600 pressure generation chambers (not shown) per head, and each pressure generation chamber is driven individually by a piezoelectric element (not shown) provided for each chamber. Thus, the volume of the pressure generating chamber can be changed. Further, a nozzle (not shown) is provided for each pressure generating chamber, and ink can be ejected from the nozzle to the outside. Since the ink supply device is common to the four heads, the temperature of the ink supplied to the four heads 60 can be made uniform by making the ink circulation path 80 and the temperature control module 94 common, and the recording device can be Cost can also be reduced. The ink returned to the sub tank 70 is circulated again to the ink circulation path 80. When assembling the head 60 by bonding the members constituting the reservoir, the above-described epoxy resin adhesive is used. In FIG. 3, the ink circulation path 80 passes through the head 60, but the ink circulation path passes outside the head without passing through the head and passes outside the head. Ink may be supplied to a reservoir in the head. In this case, the ink circulates up to the ink circulation path that passes outside the head. However, also in this case, ink flowing into the ink circulation path is ink flowing into the head, and ink flowing out from the ink circulation path is ink flowing out from the head.

  Subsequently, preparation before the start of printing is performed by the operation of the ink supply device 10. Ink circulation is performed for 15 minutes to stabilize the ink temperature in the ink circulation path 80. The ink temperature is detected as a nozzle temperature by a temperature sensor (not shown) provided in the vicinity of the nozzle, and is adjusted to the target temperature before and during printing by controlling the heater 93 of the hot water tank 91. ing.

  When preparation for printing is completed, printing is started by an ejection operation. By the ejection operation, piezoelectric elements (piezo elements) are individually driven, and ultraviolet curable ink is ejected from the nozzles of the head 60 toward the recording medium S. The ejected ink lands on the recording medium S and adheres to the recording surface.

Subsequently, the ink adhered by the curing operation is cured. A light source such as a light emitting diode is used for the curing operation, and the ink is cured by irradiating the ink adhering to the recording surface from the light source.
The above-described ejection operation and curing operation will be described in detail in the later-described ejection process and curing process, respectively.

  Further, during the ejection (during printing), the ink supply operation by the ink supply device 10 is performed continuously or intermittently, and the ink is supplied to the head 60. As described above, it is preferable that the ink inflow amount per unit time in the ink circulation path 80 is larger than the ejection amount per unit time for ejecting ink from the head during printing. In this case, the deaeration efficiency becomes higher. In order to achieve such a relationship between the ink inflow amount per unit time and the discharge amount, it is preferable that the ink inflow amount per unit time be larger than the maximum ink discharge amount per unit time described above. Further, as described above, the ink inflow amount per unit time is preferably larger than the maximum ink discharge amount per unit time, and more preferably twice or more the maximum ink discharge amount per unit time. The ink inflow per unit time flowing from the ink circulation path 80 to the head 60 is A (mL / min), and all the nozzles of all the heads 60 are driven at the maximum driving frequency at the time of printing and discharged during printing. The maximum ink discharge amount B (mL / min) per unit time, which is the discharge amount when ink is discharged with the maximum amount of ink per drive to be obtained, when the head 60 is discharging with the maximum ink discharge amount The amount of ink outflow per unit time flowing out from the head 60 to the ink circulation path 80 is C (mL / min). At this time, it is set to satisfy the following mathematical formula (A).

    A ≧ 2B = 2 (AC) (A)

  The ink inflow amount is set so as to satisfy the above formula (A) and the ink circulates, whereby the ink temperature and the dissolved oxygen amount (degassing degree) can be further stabilized. In addition, by performing such printing preparation, it is possible to stabilize the ink temperature and the degree of deaeration already before the start of printing. The maximum discharge amount of the head can be the above-described maximum ink discharge amount. However, the actual discharge amount during printing can change depending on the discharge state, such as whether or not each nozzle is driven according to the image to be recorded, and the actual ink outflow amount can also change according to this change. . The setting information regarding the ink inflow amount is determined in advance based on the maximum ink discharge amount of the ink jet recording apparatus and stored in the memory 123 and the like. The controller 120 controls the ink inflow amount based on the information. Is called. The maximum ink discharge amount may be grasped by performing discharge under the above-described conditions. When the maximum ink discharge amount per head 60 is D (mL / min), “B = 4D”. During printing, the amount of liquid in the sub tank 70 is gradually consumed as ink is ejected. Therefore, the ink is always supplied to the sub tank 70 by the supply pump 54 during printing so that the liquid amount in the sub tank 70 is always equal to or larger than the predetermined first liquid amount. Although not provided with the ink supply device 10 shown in FIG. 3, in order to stabilize the ink temperature during printing, the temperature adjustment module is provided at an arbitrary position in the ink path 51 between the supply pump 54 and the sub tank 70. May be further provided.

  As described above, according to this embodiment, the durability of the head and the discharge stability of the ultraviolet curable ink are excellent, and the solubility, curability and curling wrinkle suppression of the photopolymerization initiator contained in the ultraviolet curable ink are further reduced. In addition, an excellent ink jet recording apparatus can be provided. In particular, the present embodiment is characterized by the temperature range and viscosity range of ink during heating. Further, the recording apparatus is provided with a circulation path and a deaeration mechanism, and the amount of dissolved oxygen in the ink is lowered by the deaeration mechanism, so that the ejection stability is excellent. At that time, the deaeration efficiency (the amount of dissolved oxygen) varies depending on the viscosity and temperature of the ink. Therefore, the deaeration efficiency can be increased by setting the temperature and viscosity of the ink within a predetermined range.

[5. Modification of recording apparatus]
The heating mechanism 90 and the deaeration mechanism 100 are respectively located in the middle of the ink circulation path 80 in FIG. However, the heating mechanism 90 and the deaeration mechanism 100 are not limited to the middle of the ink circulation path 80, but are independent of each other from the ink container (ink cartridge 50) to the front of the nozzle (not shown) of the head 60. It can be provided in the position. That is, as long as the temperature and viscosity of the ejected ink are within the above-described predetermined range, the ink may be provided at any position as described above, and may be provided between the ink cartridge 50 and the sub tank 70. In particular, it is preferable to provide the deaeration mechanism 100 on the downstream side of the heating mechanism 90 because of excellent deaeration efficiency. Alternatively, since the deaeration efficiency is excellent and the temperature of the ink when the ink is heated is easily stabilized, the heating mechanism 90 and the deaeration mechanism 100 are independent of each other as shown in FIG. It is preferable to provide in the circulation path 80.

  In any device configuration, the positional relationship between the heating mechanism 90 and the deaeration mechanism 100 is such that the deaeration mechanism is located downstream of the heating mechanism when viewed in the direction of ink flow (ink circulation direction) as shown in FIG. Instead of being located, a heating mechanism may be provided downstream of the deaeration mechanism. However, as will be described later in the embodiments, it is possible to sufficiently deaerate when the deaeration mechanism is located downstream of the heating mechanism, and the discharge stability is further improved.

Further, as described above, the recording apparatus of the present embodiment may be an on-carriage type or off-carriage type serial printer instead of the line printer.
Further, the present invention is not limited to the form in which a part of the ink circulation path 80 passes through the head 60 as shown in FIG. 3, and the ink path 51 extending from the ink circulation path 80 may be a modified form having an end point in the head 60. Good. Specifically, the ink circulation path 80 has a branch in front of each head 60 (in FIG. 3, it corresponds to a black spot portion above the head 60) (in FIG. 3, it is said). The black spot corresponds to a branch point.) One of the branches extends to the head 60 via the ink path 51 and ends there. In other words, the ink flowing from the ink circulation path 80 to the head 60 no longer circulates and is ejected from the nozzles of the head 60 or stays in the ink path 51. The other of the branches flows through the ink circulation path 80 and reaches a similar branch provided before the next head 60 (the path after branching is the same as described above. The description is omitted.) Then, in the branch provided in front of the head 60 located at the most downstream side of the ink circulation path 80, when ink flows not to the head 60 side but to the ink circulation path 80 side, the ink eventually returns to the sub tank 70. . Thereafter, the ink flows again from the sub tank 70 through the ink circulation path 80.
Also in the above modification, the amount of ink flowing into the branch (branch point) is defined as the ink inflow amount, the amount of ink returned to the sub tank 70 from the branch point is defined as the ink outflow amount, and from the branch point to the head 60. The amount of ink supplied is defined as the ink discharge amount. In addition, even in the case of the modified embodiment, the upstream side from the head 60 means the upstream side from the branch point.

[Inkjet recording method]
One embodiment of the present invention relates to an inkjet recording method (hereinafter also simply referred to as “recording method”). The recording method uses the ink jet recording apparatus of the above embodiment and performs ink jet recording using an ultraviolet curable ink having a viscosity at 28 ° C. of 8 mPa · s or more when applied to the recording method. It is. The recording method includes a discharge step of discharging ultraviolet curable ink heated to 28 to 40 ° C. and having a viscosity of 15 mPa · s or less and degassed from a head toward a recording medium, and discharged and recorded. And a curing step for curing the ink that has landed (attached) to the medium. In this way, a cured product of ink is formed by the ink cured on the recording medium.

[1. Viscosity of UV curable ink at 28 ° C]
The ultraviolet curable ink used in the recording method has a viscosity of 8 mPa · s or higher, preferably 8 to 25 mPa · s, more preferably 8 to 20 mPa · s at 28 ° C. By using the ultraviolet curable ink having such a viscosity, generation of cured wrinkles in the obtained cured product can be effectively prevented. The principle of occurrence of hardening wrinkles is estimated as follows, but the scope of the present invention is not limited by the following estimation. Curing wrinkle is the ink film, after the surface of the coating has hardened first, when the inside of the coating is cured later than the surface of the coating, It is presumed that the ink is generated due to irregular flow of the ink inside the coating film until it is cured. In addition, the ultraviolet curable ink having a low viscosity has a polymerization shrinkage rate due to curing (the difference between the volume of the ink and the volume of the ink (cured product) after curing with respect to the volume of the ink before curing having a predetermined mass). Therefore, it is estimated that the occurrence of hardening wrinkles is remarkable. In addition, the ultraviolet curable ink containing a monofunctional (meth) acrylate, which will be described later, and in particular the vinyl ether group-containing (meth) acrylate represented by the general formula (I), tends to cause curing wrinkles. It is presumed that the UV curable ink containing the vinyl ether group-containing (meth) acrylate represented by the general formula (I) and having a low viscosity has a remarkable occurrence of curing wrinkles. Even when the ultraviolet curable ink used in the inkjet recording method of the present embodiment contains these, by setting the viscosity within the above range, generation of cured wrinkles can be effectively prevented. In addition, the value measured by the method performed in the below-mentioned Example can be employ | adopted for the viscosity in this specification.
Among them, in the present embodiment, the viscosity of the ink can be measured using an E-type viscometer. When using an E-type viscometer, it is within the common sense that it is measured in accordance with the instruction manual of the viscometer. Therefore, the type and rotation speed of the rotor are determined according to the instruction manual. It is needless to say that the viscosity of the ink is set so that it can be measured normally. In this embodiment, the viscosity of the ink is measured according to the instruction manual. It is self-evident to set it to something that can be measured normally.

[2. (Recording medium)
Examples of the recording medium include a non-ink-absorbing or low-absorbing recording medium. Among the recording media, the non-ink-absorbing recording media include, for example, on a substrate such as a plastic film or paper that is not surface-treated for inkjet recording (that is, has no ink absorbing layer formed). And those coated with plastic and those with a plastic film adhered thereto. Examples of the plastic herein include polyvinyl chloride (vinyl chloride), polyethylene terephthalate (PET), polycarbonate (PC), polystyrene (PS), polyurethane (PU), polyethylene (PE), polypropylene (PP), and the like. Examples of the recording medium with low ink absorption include printing paper such as art paper, coated paper, and matte paper.

[3. (Discharge process)
The ejection process in the present embodiment is a process in which ultraviolet curable ink (hereinafter simply referred to as “ink”) is ejected from a head toward a recording medium. And the temperature of the ultraviolet curable ink discharged is 28-40 degreeC, and the viscosity of the ultraviolet curable ink in the said temperature is 15 mPa * s or less.

  The temperature of 28 to 40 ° C. is relatively low as the temperature raised by heating. Thus, when the temperature of the ejected ink (hereinafter, also simply referred to as “ejection temperature”) is relatively low, the head member can be prevented from deteriorating, and the durability of the head is excellent. Further, since there is almost no variation in temperature, an advantageous effect that ink ejection stability is good can be obtained.

  Here, the “temperature of the UV curable ink to be ejected” in the present specification means that the ink is ejected continuously from the head for 60 minutes, and the temperature of the nozzle is measured every 5 minutes during that time. It shall be expressed by the average value of.

  Hereinafter, the discharge temperature will be described more specifically. When the temperature is 28 ° C. or higher, the dissolved oxygen amount is increased due to the temperature (the degree of deaeration is decreased), and thus the discharge stability is excellent. In addition to this, the ultraviolet curable ink that can be discharged at a temperature lower than 28 ° C. has a very low viscosity, but the problem due to this low viscosity, that is, the head member deteriorates and the durability of the head deteriorates, and There arises a problem that hardening wrinkles are likely to occur. On the other hand, the ink in this embodiment can avoid the problem. The above problem is particularly noticeable when the printer method is a line printer and when the light source is a light emitting diode (LED). Therefore, when a line printer or LED is used in this embodiment, a particularly great effect is brought about.

  In addition, UV curable ink having an ink viscosity of 15 mPa · s or less when the heating temperature exceeds 40 ° C. can prevent the occurrence of curing wrinkles, but is caused by the heating temperature being too high. The problem that durability deteriorates arises. On the other hand, the ink in this embodiment can avoid the problem.

  Further, when the viscosity of the ink at the above discharge temperature is 15 mPa · s or less, the amount of dissolved oxygen becomes high (the degree of deaeration becomes low), so that the ink discharge stability is excellent even when the viscosity is high. An advantageous effect is obtained. The ejection stability may be deteriorated when the viscosity of the ink is high. However, when the viscosity is 15 mPa · s or less, such a problem does not occur and the ejection stability is excellent.

  Moreover, in order to make said effect still larger and to avoid said problem more reliably, said discharge temperature is preferably 34 to 40 ° C. The upper limit of the viscosity of the ink at a predetermined discharge temperature is preferably 12 mPa · s or less. The lower limit of the viscosity is preferably 5 mPa · s or more, more preferably 6 mPa · s or more, further preferably 7 mPa · s or more, and even more preferably 8 mPa · s or more. When the lower limit of the viscosity of the ink at a predetermined discharge temperature is the above value, the durability of the head due to the ink composition becomes better, and the occurrence of curing wrinkles due to the ink composition is effectively prevented. And instability of discharge due to high viscosity can be prevented. The fact that discharge instability caused by high viscosity can be prevented means that the discharge stability is further improved.

  Further, as described above, since the ultraviolet curable ink has a higher viscosity than the water-based ink used in a normal inkjet ink, the viscosity fluctuation due to the temperature fluctuation during ejection is large. Such a variation in the viscosity of the ink has a great influence on the change in the droplet size and the change in the droplet ejection speed, and can cause image quality degradation. Therefore, it is preferable to keep the temperature of the ejected ink (ejection temperature) as constant as possible. The ink in the present embodiment has a relatively low discharge temperature, and the discharge temperature can be kept substantially constant by adjusting the temperature by heating. Therefore, the ink in the present embodiment is excellent in image quality.

  Here, an example of an ink design method for setting the viscosity of the ink within a desired range will be described.

  The mixed viscosity of the whole polymerizable compound contained in the ink can be estimated from the viscosity of each polymerizable compound used and the mass ratio of each polymerizable compound to the ink.

  It is assumed that the ink contains N kinds of polymerizable compounds A, B,. The viscosity of the polymerizable compound A is VA, and the mass ratio of the polymerizable compound A to the total amount of the polymerizable compound in the ink is MA. The viscosity of the polymerizable compound B is VB, and the mass ratio of the polymerizable compound B to the total amount of the polymerizable compound in the ink is MB. Similarly, the viscosity of the Nth polymerizable compound N is VN, and the mass ratio of the polymerizable compound N to the total amount of the polymerizable compound in the ink is MN. If it shows in confirmation, numerical formula "MA + MB + ... (middle omission) ... + MN = 1" is formed. Further, the mixed viscosity of the entire polymerizable compound contained in the ink is defined as VX. Then, it is assumed that the following formula (1) is satisfied.

    MA × LogVA + MB × LogVB + (not shown) ... + MN × LogVN = LogVX (1)

  For example, when two kinds of polymerizable compounds are contained in the ink, the mass ratio of the polymerizable compounds after MB is set to zero. The number of types of polymerizable compounds can be any number of one or more.

  Next, an example of a procedure (steps 1 to 7) for setting the ink viscosity to a desired range will be described.

First, information on the viscosity at a predetermined temperature of each polymerizable compound to be used is obtained (step 1). Examples of the obtaining method include obtaining from a manufacturer catalog or measuring the viscosity of each polymerizable compound at a predetermined temperature. Since the viscosity of a single polymerizable compound may vary depending on the manufacturer even if it is the same polymerizable compound, it is preferable to employ viscosity information from the manufacturer of the polymerizable compound to be used.
Subsequently, the target viscosity is set in VX, and the composition ratio (mass ratio) of each polymerizable compound is determined based on the above formula (1) so that VX becomes the target viscosity (step 2). The target viscosity is the viscosity of the ink to be finally obtained, and is set to a certain viscosity within the range of 8 to 15 mPa · s. The predetermined temperature is a certain temperature in the range of 28 to 40 ° C.

Subsequently, the polymerizable compound is actually mixed to prepare a composition of the polymerizable compound (hereinafter referred to as “polymerizable composition”), and the viscosity at a predetermined temperature is measured (step 3).
Subsequently, when the viscosity of the polymerizable composition is approximately close to the above target viscosity (in this step 4, it is only necessary that the target viscosity is ± 5 mPa · s), the polymerizable composition and photopolymerization are performed. An ink containing a component other than the polymerizable compound such as an initiator and a pigment (hereinafter referred to as “component other than the polymerizable compound”) is prepared, and the viscosity of the ink is measured (step 4). In Step 4, when there is a component other than the polymerizable compound that is mixed with the ink in the form of a pigment dispersion such as a pigment, for example, the polymerizable compound previously contained in the pigment dispersion is also contained in the ink. Therefore, it is necessary to adjust the ink at a mass ratio obtained by subtracting the mass ratio of the polymerizable compound that is brought into the ink as a pigment dispersion from the composition ratio of each polymerizable compound determined in Step 2. .

  Subsequently, the difference between the measured viscosity of the ink and the measured viscosity of the polymerizable composition is calculated, and this is defined as VY (step 5). Here, normally, “VY> 0”. VY depends on the content conditions such as the type and content of components other than the polymerizable compound, but in the examples described later, VY was 3 to 5 mPa · s.

  Subsequently, “target viscosity of step 2−VY” is defined for VX, and the composition ratio of each polymerizable compound is set so that VX becomes “target viscosity of step 2−VY” defined above from the above formula (1). Is determined again (step 6).

  Subsequently, each polymerizable compound having a composition ratio determined in Step 6 is mixed with components other than the polymerizable compound to prepare an ink, and the viscosity at a predetermined temperature is measured (Step 7). If the measured viscosity is the target viscosity, the ink adjusted in step 7 is obtained as an ink having the target viscosity.

  On the other hand, when the measured viscosity of the composition of the prepared polymerizable compound is not within the range of “target viscosity ± 5 mPa · s” in Step 3, the following fine adjustment is performed and the process is performed again from Step 3. First, when the measured viscosity is too high, the content of the polymerizable compound having a viscosity as a simple substance higher than the target viscosity is reduced, and the content of the polymerizable compound having a viscosity as a simple substance lower than the target viscosity is increased. Make fine adjustments. On the other hand, when the measured viscosity is too low, the content of the polymerizable compound whose viscosity as a simple substance is lower than the target viscosity is reduced, and the content of the polymerizable compound whose viscosity as a simple substance is higher than the target viscosity is increased. Make fine adjustments. If the measured viscosity of the prepared ink does not reach the target viscosity in step 7, the same adjustment as the above fine adjustment is performed, and the process is performed again from step 7.

[4. Ink supply process]
The recording method of the present embodiment may perform recording using an ink jet recording apparatus in which at least part of an ink path for supplying ink from an ink container to a head is an ink circulation path for circulating ink. . In other words, the recording method includes an ink supply step that includes an ink circulation path that circulates ink in at least a part of an ink path that supplies ink to the head of the inkjet recording apparatus, and circulates ink in the ink circulation path. Further, it may be included. The ink flowing out from the head circulates in at least a part of the ink path, so that the temperature of the ink in the ink circulation path is easily stabilized, and thus the discharge amount is easily stabilized.

  In the ink supply step, the inflow amount (ink inflow amount) of the ultraviolet curable ink supplied from the ink circulation path to the head may be adjusted, and the ink having the ink inflow amount may be supplied to the head. The ink supply process may be performed during the above-described ejection process. In the ink supply step, it is preferable that the ink inflow amount is larger than the discharge amount for ejecting ink from the head during recording (during printing) because the ink flows out and the ink circulates. Further, the ink inflow amount is more preferably larger than the maximum value of the amount of ink discharged from the head (maximum ink discharge amount described later), and more preferably twice or more the maximum ink discharge amount. It is even more preferable that the maximum ink discharge amount is 2.5 times or more. When the ink inflow amount is within the above range, the discharge amount is easily stabilized. On the other hand, the upper limit of the ink inflow amount is not particularly limited, but may be four times or less the maximum ink discharge amount. The amount of ink ejected from the head, that is, the ink inflow amount and the maximum ink ejection amount are both volume-based amounts.

  The ink supply process can be performed, for example, by providing a device for adjusting an ink supply amount (hereinafter also simply referred to as “ink supply device”) in an ink jet recording apparatus described later. The ink supply device will be described later.

[5. Curing process]
The curing step included in the recording method of the present embodiment cures the ultraviolet curable ink adhering to the recording medium when irradiated with ultraviolet rays (light) from a light source. In this step, the photopolymerization initiator contained in the ink is decomposed by irradiation with ultraviolet rays to generate starting species such as radicals, acids, and bases, and the polymerization reaction of the photopolymerizable compound depends on the function of the starting species. Promoted. Alternatively, in this step, the polymerization reaction of the photopolymerizable compound is initiated by irradiation with ultraviolet rays. At this time, if the sensitizing dye is present together with the photopolymerization initiator in the ink, the sensitizing dye in the system absorbs ultraviolet rays to be in an excited state, and promotes decomposition of the photopolymerization initiator by contacting with the photopolymerization initiator. And a more sensitive curing reaction can be achieved.

  As the light source (ultraviolet light source), a mercury lamp, a gas / solid laser or the like is mainly used, and as the light source used for curing the ultraviolet curable ink, a mercury lamp and a metal halide lamp are widely known. On the other hand, there is a strong demand for mercury-free from the viewpoint of environmental protection, and replacement with a GaN-based semiconductor ultraviolet light-emitting device is very useful industrially and environmentally. Further, LEDs (light-emitting diodes) such as ultraviolet light-emitting diodes (UV-LEDs) and ultraviolet laser diodes (UV-LDs) are small, have a long lifetime, high efficiency, and low cost, and are expected as light sources for ultraviolet-curable inks. ing.

  As described above, the ultraviolet curable ink in the present embodiment can be suitably used regardless of whether the light source is an LED or a metal halide lamp, but an LED is particularly preferable.

  The light emission peak wavelength of the light source (ultraviolet light source) is preferably in the range of 360 to 420 nm, and more preferably in the range of 380 to 410 nm. When the emission peak wavelength is within the above range, it is preferable because the UV-LED is easily available and inexpensive.

The light source having an emission peak wavelength in the range (preferably LED) peak intensity (illumination peak intensity) of ultraviolet light emitted from, preferably 800 mW / cm ² or more, more preferably 1,000 mW / cm ² That's it. When the irradiation peak intensity is within the above range, the curability is further improved and the generation of curing wrinkles can be more effectively prevented. The upper limit of the irradiation peak intensity is not particularly limited, but is preferably 3,000 mW / cm ² or less. The principle of occurrence of curing wrinkles is presumed as described above. However, if the irradiation peak intensity is within the above range, the coating surface can be cured at the same time as the coating surface, and ultraviolet rays are effective in generating curing wrinkles. It is estimated that this can be prevented. When the viscosity at 28 ° C. of the ultraviolet curable ink in the present embodiment is 8 mPa · s or more, generation of curing wrinkles can be more effectively prevented. In particular, when the ultraviolet curable ink contains a vinyl ether group-containing (meth) acrylic acid ester represented by the general formula (1) described later, and the irradiation peak intensity is within the above range, the curability is further improved, and The generation of cured wrinkles can be more effectively prevented.

  In addition, the irradiation peak intensity | strength in this specification employ | adopts the value measured using the ultraviolet-ray intensity meter UM-10 and the light-receiving part UM-400 (all are Konica Minolta Sensing, Inc. (KONICA MINOLTA SENSING, INC. Product)). . However, this does not mean that the measurement method of the irradiation peak intensity is limited, and a conventionally known measurement method can be used.

Further, the light source having an emission peak wavelength in the above range, preferably 600 mJ / cm ² or less, more preferably a curable UV-curable ink irradiation energy of 200~500mJ / cm ^2, the recording method of the present embodiment Use it. In this case, it is easy to increase the output of the LED, and low-cost printing and a high printing speed can be realized. Here, said irradiation energy is total irradiation energy which totaled each irradiation energy, when irradiation is performed in multiple times.

  The irradiation energy in this specification is calculated by multiplying the time from the start of irradiation to the end of irradiation by the irradiation peak intensity. Moreover, when irradiation is performed over multiple times, said irradiation energy is represented by the irradiation energy amount which totaled multiple times of irradiation. There may be one or a plurality of emission peak wavelengths within the preferable wavelength range. Even in the case where there are a plurality, the total irradiation energy amount of the ultraviolet light having the emission peak wavelength in the above range is set as the irradiation energy.

  Such an ink can be obtained by including at least one of a photopolymerization initiator that decomposes upon irradiation with ultraviolet rays in the wavelength range and a polymerizable compound that starts polymerization upon irradiation with ultraviolet rays in the wavelength range.

Further, the discharge amount (attachment amount and driving amount) per unit area at the time of discharge onto the recording medium is preferably 5 to 16 mg / inch ^{2 in} order to prevent wasteful use of the ink.

Further, the ink discharge amount per unit area varies depending on the recording resolution and the amount of ink applied per recording unit area (pixel) defined by the recording resolution, but the recording resolution (printing resolution) is set to “sub-scanning direction”. In this case, 300 dpi × 300 dpi to 1,500 dpi × 1,500 dpi is preferable. Then, it is preferable to adjust the nozzle density and the discharge amount of the head according to the recording resolution.
The lower limit value of the ink discharge amount per pixel is preferably 2 ng / pixel, and more preferably 3 ng / pixel. On the other hand, the upper limit value of the discharge amount is preferably 200 ng / pixel, more preferably 160 ng / pixel, further preferably 50 ng / pixel, and still more preferably 20 ng / pixel. The nozzle density (distance between nozzles in the nozzle row) is preferably 180 to 720 dpi, and more preferably 300 to 720 dpi.

  As described above, according to this embodiment, the durability of the head and the discharge stability of the ultraviolet curable ink are excellent, and the solubility, curability and curling wrinkle suppression of the photopolymerization initiator contained in the ultraviolet curable ink are further reduced. In addition, an ink jet recording method used in an ink jet recording apparatus can be provided.

[UV curable ink]
Further, one embodiment of the present invention relates to an ultraviolet curable ink that can be used in the ink jet recording apparatus and the ink jet recording method of the above embodiment. As described above, the ultraviolet curable ink is characterized in that the viscosity at 28 ° C., the discharge temperature, and the viscosity at the temperature are in a predetermined range. The ink for setting the viscosity in a predetermined range can be designed by the ink design method as described above.

  Hereinafter, additives (components) included in the ultraviolet curable ink of the present embodiment or which may be included as desired will be described.

[1. Polymerizable compound)
The polymerizable compound contained in the ink of the present embodiment can be polymerized at the time of light irradiation alone or by the action of a photopolymerization initiator described later to cure the printed ink. As other polymerizable compounds, conventionally known various monomers and oligomers such as monofunctional, bifunctional, and trifunctional or more polyfunctional can be used. Examples of the monomer include unsaturated carboxylic acids such as (meth) acrylic acid, itaconic acid, crotonic acid, isocrotonic acid and maleic acid, salts or esters thereof, urethane, amide and anhydride thereof, acrylonitrile, styrene, various types Unsaturated polyesters, unsaturated polyethers, unsaturated polyamides, and unsaturated urethanes. Examples of the oligomer include oligomers formed from the above monomers such as linear acrylic oligomers, epoxy (meth) acrylate, oxetane (meth) acrylate, aliphatic urethane (meth) acrylate, and aromatic urethane (meth). Acrylate and polyester (meth) acrylate are mentioned.

Among these, an ester of (meth) acrylic acid, that is, (meth) acrylate is preferable. Among the (meth) acrylates, at least one of the vinyl ether group-containing (meth) acrylic acid esters represented by the general formula (I) and other monofunctional (meth) acrylates is preferable. ) Acrylic acid esters are more preferred, and the vinyl ether group-containing (meth) acrylic acid esters and other monofunctional (meth) acrylates are more preferred.
Hereinafter, the polymerizable compound will be described in detail with a focus on these (meth) acrylates.

(1-1. (Meth) acrylic acid ester containing vinyl ether group)
The ink of the present embodiment preferably contains a vinyl ether group-containing (meth) acrylic acid ester represented by the following general formula (I).
_{^{CH 2 = CR 1 -COOR 2 -O}} -CH = CH-R 3 ··· (I)
Wherein R ¹ is a hydrogen atom or a methyl group, R ² is a divalent organic residue having 2 to 20 carbon atoms, and R ³ is a hydrogen atom or a monovalent organic residue having 1 to 11 carbon atoms. Group.)

  When the ink contains the vinyl ether group-containing (meth) acrylic acid esters, the ink can be reduced in viscosity, the ink curability can be improved, and curing wrinkles can be generated. It can be effectively prevented. In addition, it is better to use a compound having both a vinyl ether group and a (meth) acryl group in one molecule than to use a compound having a vinyl ether group and a compound having a (meth) acryl group separately. It is preferable for improving curability.

In the above general formula (I), the divalent organic residue having 2 to 20 carbon atoms represented by R ² is a linear, branched or cyclic substituted having 2 to 20 carbon atoms. May be an alkylene group, an optionally substituted alkylene group having an oxygen atom by an ether bond and / or an ester bond in the structure, and an optionally substituted divalent alkylene group having 6 to 11 carbon atoms. Aromatic groups are preferred. Among these, C2-C6 alkylene groups such as ethylene group, n-propylene group, isopropylene group, and butylene group, oxyethylene group, oxy n-propylene group, oxyisopropylene group, and oxybutylene group An alkylene group having 2 to 9 carbon atoms having an oxygen atom due to an ether bond in the structure is preferably used.

In the general formula (I), the monovalent organic residue having 1 to 11 carbon atoms represented by R ³ is a linear, branched or cyclic substituted group having 1 to 10 carbon atoms. Suitable alkyl groups and optionally substituted aromatic groups having 6 to 11 carbon atoms are preferred. Among these, C6-C2 aromatic groups, such as a C1-C2 alkyl group which is a methyl group or an ethyl group, a phenyl group, and a benzyl group, are used suitably.

  When each of the organic residues is an optionally substituted group, the substituent is divided into a group containing a carbon atom and a group not containing a carbon atom. First, when the substituent is a group containing a carbon atom, the carbon atom is counted in the carbon number of the organic residue. Examples of the group containing a carbon atom include, but are not limited to, a carboxyl group and an alkoxy group. Next, examples of the group not containing a carbon atom include, but are not limited to, a hydroxyl group and a halo group.

  Examples of the vinyl ether group-containing (meth) acrylic acid esters include, but are not limited to, for example, 2-vinyloxyethyl (meth) acrylate, 3-vinyloxypropyl (meth) acrylate, and 1-methyl (meth) acrylate. 2-vinyloxyethyl, 2-vinyloxypropyl (meth) acrylate, 4-vinyloxybutyl (meth) acrylate, 1-methyl-3-vinyloxypropyl (meth) acrylate, 1-vinyloxymethyl (meth) acrylate Propyl, 2-methyl-3-vinyloxypropyl (meth) acrylate, 1,1-dimethyl-2-vinyloxyethyl (meth) acrylate, 3-vinyloxybutyl (meth) acrylate, 1-methyl- (meth) acrylate 2-vinyloxypropyl, 2-vinyloxybutyl (meth) acrylate, (meth) a 4-vinyloxycyclohexyl silylate, 6-vinyloxyhexyl (meth) acrylate, 4-vinyloxymethylcyclohexylmethyl (meth) acrylate, 3-vinyloxymethylcyclohexylmethyl (meth) acrylate, (meth) acrylic acid 2-vinyloxymethylcyclohexylmethyl, p-vinyloxymethylphenylmethyl (meth) acrylate, m-vinyloxymethylphenylmethyl (meth) acrylate, o-vinyloxymethylphenylmethyl (meth) acrylate, (meth) 2- (vinyloxyethoxy) ethyl acrylate, 2- (vinyloxyisopropoxy) ethyl (meth) acrylate, 2- (vinyloxyethoxy) propyl (meth) acrylate, 2- (vinyloxy) (meth) acrylate Ethoxy) isopropyl, (meth) acrylic acid 2- Vinyloxyisopropoxy) propyl, 2- (vinyloxyisopropoxy) isopropyl (meth) acrylate, 2- (vinyloxyethoxyethoxy) ethyl (meth) acrylate, 2- (vinyloxyethoxyisopropoxy) (meth) acrylate ) Ethyl, 2- (vinyloxyisopropoxyethoxy) ethyl (meth) acrylate, 2- (vinyloxyisopropoxyisopropoxy) ethyl (meth) acrylate, 2- (vinyloxyethoxyethoxy) propyl (meth) acrylate 2- (vinyloxyethoxyisopropoxy) propyl (meth) acrylate, 2- (vinyloxyisopropoxyethoxy) propyl (meth) acrylate, 2- (vinyloxyisopropoxyisopropoxy) propyl (meth) acrylate, (Meth) acrylic acid 2- (vinylo) Xylethoxyethoxy) isopropyl, (meth) acrylic acid 2- (vinyloxyethoxyisopropoxy) isopropyl, (meth) acrylic acid 2- (vinyloxyisopropoxyethoxy) isopropyl, (meth) acrylic acid 2- (vinyloxyisopropoxy) Isopropoxy) isopropyl, (meth) acrylic acid 2- (vinyloxyethoxyethoxyethoxyethoxy) ethyl, (meth) acrylic acid 2- (vinyloxyethoxyethoxyethoxyethoxy) ethyl, (meth) acrylic acid 2- (isopropenoxyethoxy) ) Ethyl, (meth) acrylic acid 2- (isopropenoxyethoxyethoxyethoxy) ethyl, (meth) acrylic acid 2- (isopropenoxyethoxyethoxyethoxy) ethyl, (meth) acrylic acid 2- (isopropenoxyethoxyethoxyethoxy) D ) Ethyl, and (meth) Polyethylene glycol monovinyl ether acrylate, and (meth) acrylic acid polypropylene glycol monovinyl ether.

  Among these, since the viscosity of the ink can be further lowered, the flash point is high, and the curability of the ink is excellent, 2- (vinyloxyethoxy) ethyl (meth) acrylate, that is, 2- (vinyloxy) acrylate At least one of ethoxy) ethyl and 2- (vinyloxyethoxy) ethyl methacrylate is preferable, and 2- (vinyloxyethoxy) ethyl acrylate is more preferable. In particular, since 2- (vinyloxyethoxy) ethyl acrylate and 2- (vinyloxyethoxy) ethyl methacrylate have a simple structure and a small molecular weight, the viscosity of the ink can be significantly reduced. Examples of 2- (vinyloxyethoxy) ethyl (meth) acrylate include 2- (2-vinyloxyethoxy) ethyl (meth) acrylate and 2- (1-vinyloxyethoxy) ethyl (meth) acrylate. Examples of 2- (vinyloxyethoxy) ethyl acrylate include 2- (2-vinyloxyethoxy) ethyl acrylate and 2- (1-vinyloxyethoxy) ethyl acrylate. Incidentally, 2- (vinyloxyethoxy) ethyl acrylate is superior in terms of curability compared to 2- (vinyloxyethoxy) ethyl methacrylate.

  A vinyl ether group containing (meth) acrylic acid ester may be used individually by 1 type, and may be used in combination of 2 or more type.

  The vinyl ether group-containing (meth) acrylic acid esters, in particular, the content of 2- (vinyloxyethoxy) ethyl (meth) acrylate is 10 to 70% by mass relative to the total mass (100% by mass) of the ink. Preferably, 10-60 mass% is more preferable, and 20-50 mass% is further more preferable. When the content is not less than the above lower limit, the viscosity of the ink can be lowered and the curability of the ink can be further improved. On the other hand, when the content is not more than the above upper limit value, the storage stability of the ink can be maintained in a good state, and the generation of curing wrinkles can be more effectively prevented.

  The method for producing the vinyl ether group-containing (meth) acrylic acid esters is not limited to the following, but is a method of esterifying (meth) acrylic acid and a hydroxyl group-containing vinyl ether (Production Method B), (meth) acrylic acid halide. And esterification of (meth) acrylic anhydride and hydroxyl group-containing vinyl ether (production method D), esterification of (meth) acrylic acid ester and hydroxyl group-containing vinyl ether Method of exchange (Production method E), Method of esterifying (meth) acrylic acid and halogen-containing vinyl ether (Method of production F), Method of esterifying alkali (earth) metal salt of (meth) acrylic acid and halogen-containing vinyl ether (Production G), hydroxyl group-containing (meth) acrylic acid ester and carboxylic acid vinyl ester How to vinyl exchange and Le (Procedure H), hydroxyl group-containing (meth) How to ether exchange and acrylic acid ester and an alkyl vinyl ether (Process I).

  Among these, since the desired effect can be further exhibited in this embodiment, the production method E is preferable.

(1-2. Monofunctional (meth) acrylate)
The ink of this embodiment preferably contains a monofunctional (meth) acrylate. Here, when the ink of this embodiment contains the above-described vinyl ether group-containing (meth) acrylic acid esters (however, only those that are monofunctional (meth) acrylates), the vinyl ether group-containing (meth) acrylic acid. Esters are also included in the monofunctional (meth) acrylate, but the explanation of the vinyl ether group-containing (meth) acrylic esters is omitted. Below, monofunctional (meth) acrylates other than the above-mentioned vinyl ether group containing (meth) acrylic acid esters are demonstrated. When the ink contains the monofunctional (meth) acrylate, the viscosity of the ink can be reduced, and the solubility of the photopolymerization initiator and other additives and the curability of the ink are both excellent. . Furthermore, due to the excellent solubility of the photopolymerization initiator and other additives, the ink ejection stability is excellent, and the toughness, heat resistance, and chemical resistance of the coating film are also improved. Increases nature.

  Examples of the monofunctional (meth) acrylate include phenoxyethyl (meth) acrylate, isoamyl (meth) acrylate, stearyl (meth) acrylate, lauryl (meth) acrylate, octyl (meth) acrylate, decyl (meth) acrylate, Myristyl (meth) acrylate, isostearyl (meth) acrylate, 2-ethylhexyl-diglycol (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 2-methoxyethyl (meth) acrylate , Butoxyethyl (meth) acrylate, ethoxydiethylene glycol (meth) acrylate, methoxydiethylene glycol (meth) acrylate, methoxypolyethylene glycol (meth) acrylate Rate, methoxypropylene glycol (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, isobornyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl (Meth) acrylate, lactone-modified flexible (meth) acrylate, t-butylcyclohexyl (meth) acrylate, dicyclopentanyl (meth) acrylate, dicyclopentenyloxyethyl (meth) acrylate, benzyl (meth) acrylate, ethoxy Nonylphenyl (meth) acrylate, alkoxylated nonylphenyl (meth) acrylate, and p-cumylphenol EO-modified (meth) acrylate.

  Among these, monofunctional (meth) acrylates having an aromatic ring skeleton in the molecule are preferable because they are more excellent in curability, storage stability, and solubility of the photopolymerization initiator. Examples of monofunctional (meth) acrylates having an aromatic ring skeleton include, but are not limited to, phenoxyethyl (meth) acrylate, benzyl (meth) acrylate, 2-hydroxyphenoxypropyl (meth) acrylate, and phenoxydiethylene glycol (meth) ) Acrylate is preferred. Among these, since the viscosity of the ink can be reduced and the curability, abrasion resistance, adhesion, and solubility of the photopolymerization initiator can be excellent, phenoxyethyl ( At least one of meth) acrylate and benzyl (meth) acrylate is preferable, and phenoxyethyl (meth) acrylate is more preferable.

  Monofunctional (meth) acrylates other than the vinyl ether group-containing (meth) acrylic acid esters may be used alone or in combination of two or more.

  The content of the monofunctional (meth) acrylate other than the vinyl ether group-containing (meth) acrylic acid esters is preferably 10 to 65% by mass, and 20 to 50% by mass with respect to the total mass (100% by mass) of the ink. More preferably, 10-40 mass% is further more preferable. When the content is not less than the above lower limit value, the solubility of the photopolymerization initiator is further improved in addition to the curability. On the other hand, when the content is not more than the above upper limit value, in addition to curability, adhesion is further improved.

  In addition, when the vinyl ether group-containing (meth) acrylic acid esters (but limited to those containing monofunctional (meth) acrylates) are included, the total content of the monofunctional (meth) acrylates containing these is the ink 30-90 mass% is preferable with respect to the total mass (100 mass%), and 40-70 mass% is more preferable. When the content is within the above range, the ink viscosity, specifically, the ink viscosity at 28 ° C. and the ink viscosity at the discharge temperature can be easily set in the desired range described above.

(1-3. Polymeric compounds other than the above)
The ink of the present embodiment may further contain a polymerizable compound other than the above (hereinafter referred to as “other polymerizable compound”). Examples of other polymerizable compounds include the monomers and oligomers described above, and among these, (meth) acrylates having 2 or more functional groups are preferable.

  Examples of the bifunctional (meth) acrylate include diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, and dipropylene glycol di (meth). ) Acrylate, tripropylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, 1,4-butanediol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, 1,9-nonanediol Di (meth) acrylate, neopentyl glycol di (meth) acrylate, dimethylol-tricyclodecane di (meth) acrylate, bisphenol A EO (ethylene oxide) adduct di (meth) ) Acrylate, PO-bisphenol A (propylene oxide) adduct di (meth) acrylate, hydroxypivalic acid neopentyl glycol di (meth) acrylate, and polytetramethylene glycol di (meth) acrylate.

  Examples of the trifunctional or higher polyfunctional (meth) acrylate include trimethylolpropane tri (meth) acrylate, EO-modified trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, and pentaerythritol tetra (meth) acrylate. Dipentaerythritol hexa (meth) acrylate, ditrimethylolpropane tetra (meth) acrylate, glycerin propoxytri (meth) acrylate, cowprolactone-modified trimethylolpropane tri (meth) acrylate, pentaerythritol ethoxytetra (meth) acrylate, and Examples include caprolactam-modified dipentaerythritol hexa (meth) acrylate.

  Other polymerizable compounds may be used alone or in combination of two or more.

  When the other polymerizable compound is contained in the ink, the content thereof is preferably 10 to 50% by mass with respect to the total mass (100% by mass) of the ink. In particular, when the ink contains a bifunctional (meth) acrylate, the content of the bifunctional (meth) acrylate is preferably 5 to 45% by mass with respect to the total mass (100% by mass) of the ink, and 10 to 30 The mass% is more preferable. When the content is within the above range, the ink curability and the rub resistance of the cured product are excellent, and the ink viscosity can be easily designed to a desired viscosity. In addition, a monofunctional (meth) acrylate having a relatively low viscosity of the polymerizable compound, particularly the above-mentioned vinyl ether group-containing (meth) acrylic acid ester having a low viscosity, and other polymerizable compounds having a relatively high viscosity, Are preferably combined. This makes it easy to design the ink viscosity to a desired viscosity.

  Although it is possible to omit the addition of a photopolymerization initiator by using a photopolymerizable compound as the polymerizable compound, the use of a photopolymerization initiator can easily adjust the start of polymerization. Can be preferred.

[2. Photopolymerization initiator)
The ink of this embodiment may contain a photopolymerization initiator. The photopolymerization initiator is used to form a print by curing the ink present on the surface of the recording medium by photopolymerization by ultraviolet irradiation. By using ultraviolet light (UV) among light, it is excellent in safety and the cost of the light source lamp can be suppressed. There is no limitation as long as it generates active species such as radicals and cations by the energy of ultraviolet rays and initiates the polymerization of the polymerizable compound, but a photoradical polymerization initiator or a photocationic polymerization initiator should be used. Among them, it is preferable to use a photo radical polymerization initiator.

  Examples of the photo radical polymerization initiator include aromatic ketones, acyl phosphine oxide compounds, aromatic onium salt compounds, organic peroxides, thio compounds (thioxanthone compounds, thiophenyl group-containing compounds, etc.), hexaarylbiphenyls, and the like. Examples include imidazole compounds, ketoxime ester compounds, borate compounds, azinium compounds, metallocene compounds, active ester compounds, compounds having a carbon halogen bond, and alkylamine compounds.

  Among these, a thioxanthone compound (thioxanthone photopolymerization initiator) is preferable because the curability of the ink can be further improved. A thioxanthone compound and an acyl phosphine oxide compound (acyl phosphine oxide photopolymerization initiator) are preferable. Is more preferable.

  Specific examples of the photo radical polymerization initiator include acetophenone, acetophenone benzyl ketal, 1-hydroxycyclohexyl phenyl ketone, 2,2-dimethoxy-2-phenylacetophenone, xanthone, fluorenone, benzaldehyde, fluorene, anthraquinone, triphenylamine, carbazole 3-methylacetophenone, 4-chlorobenzophenone, 4,4′-dimethoxybenzophenone, 4,4′-diaminobenzophenone, Michler's ketone, benzoin propyl ether, benzoin ethyl ether, benzyldimethyl ketal, 1- (4-isopropylphenyl)- 2-hydroxy-2-methylpropan-1-one, 2-hydroxy-2-methyl-1-phenylpropan-1-one, thioxanthone, diethyl Oxanthone, 2-isopropylthioxanthone, 2-chlorothioxanthone, 2-methyl-1- [4- (methylthio) phenyl] -2-morpholino-propan-1-one, bis (2,4,6-trimethylbenzoyl) -phenyl Phosphine oxide, 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide, 2,4-diethylthioxanthone, and bis- (2,6-dimethoxybenzoyl) -2,4,4-trimethylpentylphosphine oxide Can be mentioned.

  Examples of commercially available photo radical polymerization initiators include IRGACURE 651 (2,2-dimethoxy-1,2-diphenylethane-1-one), IRGACURE 184 (1-hydroxy-cyclohexyl-phenyl-ketone), DAROCUR 1173. (2-hydroxy-2-methyl-1-phenyl-propan-1-one), IRGACURE 2959 (1- [4- (2-hydroxyethoxy) -phenyl] -2-hydroxy-2-methyl-1-propane- 1-one), IRGACURE 127 (2-hydroxy-1- {4- [4- (2-hydroxy-2-methyl-propionyl) -benzyl] phenyl] -2-methyl-propan-1-one}, IRGACURE 907 (2-Methyl-1- (4-methylthiophenyl) -2-morphol Linopropan-1-one), IRGACURE 369 (2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone-1), IRGACURE 379 (2- (dimethylamino) -2-[(4- Methylphenyl) methyl] -1- [4- (4-morpholinyl) phenyl] -1-butanone), DAROCUR TPO (2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide), IRGACURE 819 (bis (2, 4,6-trimethylbenzoyl) -phenylphosphine oxide), IRGACURE 784 (bis (η5-2,4-cyclopentadien-1-yl) -bis (2,6-difluoro-3- (1H-pyrrole-1-) Yl) -phenyl) titanium), IRGACURE OXE 01 (1.2-octanedione, 1- [4- (phenylthio)-, 2- (O-benzoyloxime)]), IRGACURE OXE 02 (ethanone, 1- [9-ethyl-6- (2-methylbenzoyl) -9H-carbazol-3-yl]-, 1- (O-acetyloxime)), IRGACURE 754 (oxyphenylacetic acid, 2- [2-oxo-2-phenylacetoxyethoxy] ethyl ester and oxyphenylacetic acid, 2- (Mixture of (2-hydroxyethoxy) ethyl ester) (above, trade name manufactured by BASF), KAYACURE DETX-S (2,4-diethylthioxanthone) (trade name, manufactured by Nippon Kayaku Co., Ltd.) ), Speedcure TPO (2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide), Spe dcure DETX (2,4-diethylthioxanthen-9-one) (above, trade name manufactured by Lambson), Lucirin TPO, LR8883, LR8970 (above, trade name manufactured by BASF), Ubekrill P36 (trade name, manufactured by UCB) Quantacure ITX (isopropylthioxanthone) (manufactured by Biddle Sawyer Corporation).

A photoinitiator may be used individually by 1 type and may be used in combination of 2 or more type.
The content of the photopolymerization initiator can improve the ultraviolet curing rate and have excellent curability, and in order to avoid undissolved photopolymerization initiator and coloring derived from the photopolymerization initiator, It is preferably 20% by mass or less with respect to the total mass (100% by mass) of the ink.

  In particular, when the photopolymerization initiator includes a thioxanthone compound, the content is preferably 0.5 to 4% by mass with respect to the total mass (100% by mass) of the ink because the curability becomes better. 1-3 mass% is more preferable. Further, the dissolved oxygen content of the ink containing the thioxanthone compound is preferably 20 ppm or less, and more preferably 1 to 20 ppm, because the discharge stability can be maintained satisfactorily.

  In addition to the above, when the photopolymerization initiator includes an acylphosphine compound, the content is more preferably 5 to 15% by mass with respect to the total mass (100% by mass) of the ink, More preferably, it is 13 mass%. When the content is not less than the above lower limit, the curability is further improved. More specifically, the curability is further improved because a sufficient curing speed can be obtained particularly when curing with an LED (preferable emission peak wavelength: 360 nm to 420 nm). On the other hand, when the content is not more than the above upper limit value, the solubility of the photopolymerization initiator is further improved.

[3. Color material)
The ink of this embodiment may include a color material. As the color material, at least one of a pigment and a dye can be used.

(3-1. Pigment)
By using a pigment as the color material, the light resistance of the ink can be improved. As the pigment, both inorganic pigments and organic pigments can be used.

  As the inorganic pigment, carbon black (CI pigment black 7) such as furnace black, lamp black, acetylene black and channel black, iron oxide, and titanium oxide can be used.

  Organic pigments include insoluble azo pigments, condensed azo pigments, azo lakes and chelate azo pigments, phthalocyanine pigments, perylene and perinone pigments, anthraquinone pigments, quinacridone pigments, dioxane pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, etc. Polycyclic pigments, dye chelates (eg basic dye chelates, acid dye chelates, etc.), dye rakes (basic dye rakes, acid dye rakes), nitro pigments, nitroso pigments, aniline black, daylight A fluorescent pigment is mentioned.

  Examples of pigments used in white ink include C.I. I. Pigment white 6, 18, and 21.

  Examples of pigments used in yellow ink include C.I. I. Pigment Yellow 1, 2, 3, 4, 5, 6, 7, 10, 11, 12, 13, 14, 16, 17, 24, 34, 35, 37, 53, 55, 65, 73, 74, 75, 81, 83, 93, 94, 95, 97, 98, 99, 108, 109, 110, 113, 114, 117, 120, 124, 128, 129, 133, 138, 139, 147, 151, 153, 154, 167, 172, 180.

  Examples of pigments used in magenta ink include C.I. I. Pigment Red 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 17, 18, 19, 21, 22, 23, 30, 31, 32, 37, 38, 40, 41, 42, 48 (Ca), 48 (Mn), 57 (Ca), 57: 1, 88, 112, 114, 122, 123, 144, 146, 149, 150, 166, 168 170, 171, 175, 176, 177, 178, 179, 184, 185, 187, 202, 209, 219, 224, 245, or C.I. I. Pigment violet 19, 23, 32, 33, 36, 38, 43, 50.

  Examples of pigments used for cyan ink include C.I. I. Pigment Blue 1, 2, 3, 15, 15: 1, 15: 2, 15: 3, 15:34, 15: 4, 16, 18, 22, 25, 60, 65, 66, C.I. I. Bat Blue 4, 60.

  Examples of pigments other than magenta, cyan, and yellow include C.I. I. Pigment green 7,10, C.I. I. Pigment brown 3, 5, 25, 26, C.I. I. Pigment orange 1, 2, 5, 7, 13, 14, 15, 16, 24, 34, 36, 38, 40, 43, 63.

  The said pigment may be used individually by 1 type, and may use 2 or more types together.

  When using said pigment, the average particle diameter has preferable 300 nm or less, and 50-200 nm is more preferable. When the average particle diameter is in the above range, the ink can be more excellent in reliability such as ejection stability and dispersion stability, and an image with excellent image quality can be formed. Here, the average particle diameter in the present specification is measured by a dynamic light scattering method.

(3-2. Dye)
A dye can be used as the coloring material. The dye is not particularly limited, and acid dyes, direct dyes, reactive dyes, and basic dyes can be used. Examples of the dye include C.I. I. Acid Yellow 17, 23, 42, 44, 79, 142, C.I. I. Acid Red 52, 80, 82, 249, 254, 289, C.I. I. Acid Blue 9, 45, 249, C.I. I. Acid Black 1, 2, 24, 94, C.I. I. Food Black 1, 2, C.I. I. Direct Yellow 1,12,24,33,50,55,58,86,132,142,144,173, C.I. I. Direct Red 1,4,9,80,81,225,227, C.I. I. Direct Blue 1, 2, 15, 71, 86, 87, 98, 165, 199, 202, C.I. I. Directed Black 19, 38, 51, 71, 154, 168, 171, 195, C.I. I. Reactive Red 14, 32, 55, 79, 249, C.I. I. Reactive black 3, 4, and 35 are mentioned.

  The said dye may be used individually by 1 type, and may use 2 or more types together.

  The content of the color material is preferably 1 to 20% by mass with respect to the total mass (100% by mass) of the ink because excellent concealability and color reproducibility can be obtained.

[4. (Dispersant)
When the ink of this embodiment includes a pigment, a dispersant may be included in order to improve pigment dispersibility. Although it does not specifically limit as a dispersing agent, For example, the dispersing agent currently used for preparing pigment dispersion liquids, such as a polymer dispersing agent, is mentioned. Specific examples include polyoxyalkylene polyalkylene polyamines, vinyl polymers and copolymers, acrylic polymers and copolymers, polyesters, polyamides, polyimides, polyurethanes, amino polymers, silicon-containing polymers, sulfur-containing polymers, fluorine-containing polymers, and epoxies. The thing which has 1 or more types of resin as a main component is mentioned. Commercially available polymer dispersants include Ajinomoto Fine Techno Co., Ltd. Ajisper series (trade name), Solsperse series available from Avecia Co. (Solsperse 32000, 36000, etc. [above, trade name]) , BYK Chemie's Disperbic series (trade name) and Enomoto Kasei's Disparon series (trade name).

  A dispersing agent may be used individually by 1 type, and may be used in combination of 2 or more type. The content of the dispersant is not particularly limited, and a preferable amount may be added as appropriate.

[5. (Polymerization inhibitor)
The ink of this embodiment may contain a polymerization inhibitor. When the ink contains a polymerization inhibitor, the polymerization reaction of the polymerizable compound before curing can be prevented.

  Although it does not restrict | limit especially as a polymerization inhibitor, For example, a phenol type polymerization inhibitor is mentioned. Examples of the phenol-based polymerization inhibitor include, but are not limited to, for example, p-methoxyphenol, cresol, t-butylcatechol, di-t-butylparacresol, hydroquinone monomethyl ether, α-naphthol, 3,5-di- t-butyl-4-hydroxytoluene, 2,6-di-t-butyl-4-methylphenol, 2,2'-methylene-bis (4-methyl-6-t-butylphenol), 2,2'-methylene -Bis (4-ethyl-6-butylphenol) and 4,4'-thio-bis (3-methyl-6-tert-butylphenol).

  Examples of commercially available phenolic polymerization inhibitors include p-methoxyphenol (trade name, p-methoxyphenol, manufactured by Tokyo Chemical Industry Co., Ltd.), non-flex MBP (Seiko Chemical Co., Ltd. ( Seiko Chemical Co., Ltd., trade name, 2,2′-methylene-bis (4-methyl-6-tert-butylphenol)), BHT Swanox (trade name, 2,6-di-t, manufactured by Seiko Chemical Co., Ltd.) -Butyl-4-methylphenol).

  A polymerization inhibitor may be used individually by 1 type, and may be used in combination of 2 or more type. The content of the polymerization inhibitor is not particularly limited, and a preferable amount may be added as appropriate.

[6. Surfactant]
The ink of this embodiment may contain a surfactant. The surfactant is not particularly limited. For example, polyester-modified silicone or polyether-modified silicone can be used as the silicone-based surfactant, and polyether-modified polydimethylsiloxane or polyester-modified polydimethylsiloxane can be used. Particularly preferred. Examples of commercially available slip agents include BYK-347, BYK-348, BYK-UV3500, 3510, 3530, and 3570 (manufactured by BYK).

  Surfactant may be used individually by 1 type and may be used in combination of 2 or more type. The content of the surfactant is not particularly limited, and a preferable amount may be added as appropriate.

[7. Other additives]
The ink of this embodiment may contain additives (components) other than the additives listed above. Such components are not particularly limited, and may include, for example, conventionally known fluorescent whitening agents, polymerization accelerators, penetration accelerators, wetting agents (humectants), and other additives. Examples of the other additives include conventionally known fixing agents, antifungal agents, preservatives, antioxidants, ultraviolet absorbers, chelating agents, pH adjusting agents, and thickeners.

  As described above, according to the present embodiment, the durability and durability of the head and the discharge stability of the ultraviolet curable ink are excellent, and the curability and the photopolymerization start used in the ink jet recording apparatus are also excellent in suppressing curing wrinkles. An ultraviolet curable ink excellent in the solubility of the agent can be provided.

  Hereinafter, the present embodiment will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

[Materials used]
The materials used in the examples and comparative examples are as shown below.
(Polymerizable compound)
・ 2-MTA (2-methoxyethyl acrylate, trade name, OSAKA ORGANIC CHEMICAL INDUSTRY LTD., Monofunctional (meth) acrylate)
・ 4-HBA (4-hydroxybutyl acrylate, trade name, manufactured by Osaka Organic Chemical Industry Co., Ltd., monofunctional (meth) acrylate)
VEEA (2- (2-vinyloxyethoxy) ethyl acrylate, trade name of Nippon Shokubai Co., Ltd., monofunctional (meth) acrylate, hereinafter referred to as “VEEA”)
New Frontier PHE (phenoxyethyl acrylate, trade name, monofunctional (meth) acrylate, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., hereinafter referred to as “PEA”)
V # 160 (benzyl acrylate, trade name of Osaka Organic Chemical Industry, monofunctional (meth) acrylate, hereinafter referred to as “BZA”)
IBXA (Isobornyl acrylate, trade name of Osaka Organic Chemical Industry Co., Ltd., hereinafter referred to as “IBX”)
A-DPH (tripropylene glycol diacrylate, bifunctional (meth) acrylate, trade name of SHIN-NAKAMURA CHEMICAL CO., LTD., Hereinafter referred to as “TPGDA”)
SR295 (pentaerythritol tetraacrylate, tetrafunctional (meth) acrylate, trade name of Sartomer Company Inc.)
(Photopolymerization initiator)
・ Lucirin TPO (trade name, manufactured by BASF, hereinafter referred to as “TPO”)
Speedcure DETX (trade name, manufactured by Lambson, hereinafter referred to as “DETX”)
Quantacure ITX (trade name manufactured by Biddle Sawyer Corporation, hereinafter referred to as “ITX”)
IRGACURE 369 (trade name manufactured by BASF, hereinafter referred to as “369”)
(Polymerization inhibitor)
P-methoxyphenol (trade name, p-methoxyphenol manufactured by Tokyo Chemical Industry Co., Ltd., hereinafter referred to as “MEHQ”)
[Surfactant]
BYK-UV3500 (polyether-modified polydimethylsiloxane, manufactured by BYK, hereinafter referred to as “BYK3500”)
[Color material]
Cyanine Blue KRO (CI Pigment Blue 15: 3 (phthalocyanine pigment), SANYO COLOR WORKS, Ltd. trade name, pigment particle size of 80 nm, hereinafter referred to as “Blue 15: 3”. )
[Dispersant]
Solsperse 32000 (trade name, manufactured by Avecia, hereinafter referred to as “SOL32000”)

[Preparation of UV curable inks A to O]
Each material shown in the following Table 1 was added so as to have the content (unit: mass%) shown in Table 1, and this was stirred with a high-speed water-cooled stirrer, whereby ultraviolet curable inks A to O were obtained. Got.

[Measurement / Evaluation Items]
[Ink viscosity rank at 1.28 ° C.]
Using a DVM-E rotational viscometer (manufactured by Tokyo Keiki Co., Ltd.), the viscosity at 28 ° C. of each ink prepared above was measured.
As the rotor, a DVM-E type cone having a cone angle of 1 ° 34 ′ and a cone radius of 2.4 cm was used. The rotation speed was 10 rpm.
The evaluation criteria are as follows. The evaluation results are shown in Table 1 below.
A: It was less than 8 mPa · s.
B: 8 mPa · s or more and 10 mPa · s or less.
C: It was 12 mPa * s or less exceeding 10 mPa * s.
D: It was 15 mPa * s or less exceeding 12 mPa * s.
E: It exceeded 15 mPa * s.

[2. Evaluation of solubility of photopolymerization initiator)
Each ink prepared above was stirred at room temperature for 30 minutes. After stirring, the presence or absence of undissolved photopolymerization initiator was visually observed.
The evaluation criteria are as follows. The evaluation results are shown in Table 1 below. In Table 1, this evaluation column is abbreviated as “initiator solubility”.
A: The undissolved residue of the photoinitiator was not seen.
B: The undissolved residue of the photoinitiator was seen.

[3. (Evaluation of ink curability)
Each of the above inks was applied to Lumirror # 125-E20 (trade name, PET film, manufactured by Toray Industries, Inc.) using a bar coater manufactured by TESTER SANGYO CO., LTD. The applied film thickness was 10 μm after curing. Next, from a LED having a peak at a wavelength of 395 nm (Firefly [trade name], manufactured by Phoseon), ultraviolet light having an irradiation peak intensity of 1,000 mW / cm ² was irradiated to the applied ink for a predetermined time, and cured ink. A coating film was obtained. After the irradiation, the surface of the ink coating film was rubbed 20 times with a Johnson & Johnson cotton swab under a load of 100 g, and the irradiation energy required until no scratch marks were observed was measured while changing the predetermined time.
The evaluation criteria are as follows. The evaluation results are shown in Table 1 below.
A: 300 mJ / cm ² or less.
B: It was 400 mJ / cm ² or less exceeding 300 mJ / cm ² .
C: It exceeded 400 mJ / cm < ² >.

[4. (Hardening wrinkle evaluation)
The head shown in FIG. 2 and each of the temporary curing light sources 42a to 42d are not used, and an LED having an irradiation peak intensity of 1,000 mW / cm ² having a peak wavelength of 395 nm is disposed in the main curing light source. The ink was applied to the film with a bar coater in the same manner as in "Evaluation of properties", and the film was transported to the main curing light source and irradiated toward the ink. The irradiation time was adjusted so that the irradiation energy was irradiated until it was cured by the same test method as in the curability test. However, the film thickness after ink curing was 12 μm.
And the surface of the cured film was observed visually. The evaluation criteria are as follows. The evaluation results are shown in Table 1 below.
A: Wrinkles were not generated at all.
B: Wrinkles were generated in some areas of the cured film.
C: Wrinkles were generated on the entire surface of the cured film.

The ultraviolet curable inks A, B, C, D, E, F, G, K, L, M, N, and O correspond to inks that can be used as examples, and the low viscosity ultraviolet curable inks H, I and J correspond to the inks used in the comparative examples.
Hereinafter, a recording method in each example and each comparative example will be described.

[Examples 1 to 18, Comparative Examples 2, 5, 6, 10, 13, 14]
The ink supply device shown in FIG. 3 is provided, and four heads 60 having a length substantially corresponding to the width (recording width) on which an image of a recording medium is to be recorded shown in FIG. 2 are arranged in the width direction. A line printer equipped with a line head was used. The nozzle density of the head was 600 dpi. The dissolved oxygen amount of the ink in the ink cartridge was 20 ppm. The measurement of the dissolved oxygen amount was performed by the method described later.

  The heater provided in the ink circulation device measures the temperature of the nozzle plate with a thermocouple provided on the nozzle plate of the head, and the temperature (discharge temperature) of the discharged ink is shown in Tables 2 and 3 below. The heating temperature of the heater is adjusted for each of the examples and comparative examples so that the temperature becomes the same, and the temperature is measured every 5 minutes during 60 minutes of continuous discharge from the head, and the average temperature becomes each temperature of the examples and comparative examples. The average temperature was determined as the ink discharge temperature.

  The ink supply device has a diameter of an ink supply pipe for supplying ink to a sub tank and a diameter of an ink pipe of an ink circulation path connecting the sub tank and the head, both 6 mm, the total length of the ink circulation path is 1 m, and the capacity of the sub tank is 100 mL. It was. The maximum ink discharge amount D per head was 10 mL / min, and since four heads were provided, the maximum ink discharge amount B of the ink supply device was 40 mL / min. The ink inflow amount A was set to 80 mL / min, and the ink was circulated with the ink inflow amount. Ink was ejected from the four heads at the maximum ink ejection amount for 60 minutes. The ink outflow amount C was 40 mL / min.

  Each ink was filled in the head Y of the recording apparatus shown in FIG. The other heads shown in FIG. 2 were not used.

[Examples 19 to 21, Comparative Example 17]
Recording was performed in the same manner as in Example 1 except that the ink inflow amount A was changed and “ink inflow amount A / maximum ink discharge amount B” was changed to the values described in Tables 2 and 3 below. .

[Example 22]
In FIG. 3, recording is performed in the same manner as in the first embodiment, except that the positions of the heating mechanism 90 and the deaeration mechanism 100 are interchanged (the heating mechanism 90 is located downstream of the deaeration mechanism 100). It was.

[Examples 23 to 25]
Recording was performed in the same manner as in Example 1 except that the irradiation peak intensity in the evaluation of curing wrinkles was changed from 1,000 mW / cm ² to 500 mW / cm ² .

[Comparative Examples 1, 4, 7-9, 11, 12]
Recording was performed in the same manner as in Example 1 except that the heater was turned off and the temperature was not adjusted. At this time, the nozzle temperature (“discharge temperature” in Tables 2 and 3 below) was 25 ° C.

[Comparative Example 3]
Evaluation was performed in the same manner as in Example 2 except that the pump of the deaeration mechanism 100 was stopped and deaeration was not performed.
[Comparative Examples 15 and 16]
Except that the ink inflow amount A was changed and “ink inflow amount A / maximum ink discharge amount B” was set to the values described in Tables 2 and 3 below, and the temperature was not adjusted by turning off the heater. Recording was performed in the same manner as in Example 1 above. At this time, the nozzle temperature (“discharge temperature” in Tables 2 and 3 below) was 25 ° C.

[Comparative Example 18]
Other than the point where the heater was not turned off and the temperature was not adjusted, and the positions of the heating mechanism 90 and the deaeration mechanism 100 in FIG. 3 were interchanged (the heating mechanism 90 was placed downstream of the deaeration mechanism 100). Were recorded in the same manner as in Example 1 above. At this time, the nozzle temperature (“discharge temperature” in Tables 2 and 3 below) was 25 ° C.

[Measurement / Evaluation Items]
[1. (Ink viscosity rank during ejection)
Except that the measurement temperature was set to the ejection temperature in Tables 2 and 3, the viscosity at the time of ejection of each ink was measured in the same manner as the ink viscosity rank at 28 ° C. described above.
The evaluation criteria are the same as the ink viscosity rank at 28 ° C. described above. The evaluation results are shown in Table 2 and Table 3 below.

[2. Measurement of dissolved oxygen amount)
Each ink prepared above was collected from the head of the line printer. And the dissolved oxygen amount of each said ink was measured using gas chromatography Agilent 6890 (made by Agilent Technologies). Helium (He) gas was used as the carrier gas. In addition, the deaeration degree was measured by measuring the amount of dissolved oxygen. The measurement results are shown in Tables 2 and 3 below.

[3. (Discharge stability evaluation)
Evaluation was performed by the number of non-ejection nozzles when all nozzles of one head were ejected for 5 minutes.
The evaluation criteria are as follows. The evaluation results are shown in Table 2 and Table 3 below.
A: The number of non-ejection nozzles was 2 or less.
B: There were 3 to 5 non-ejection nozzles.
C: There were 6 to 8 non-ejection nozzles.
X: There were 9 or more non-ejection nozzles.

[4. Head durability evaluation)
The durability of the head was evaluated by measuring and calculating the swelling rate of the adhesive.
About 0.2 g of an epoxy resin adhesive (a mixture of EPIKOTE 828 which is an epoxy resin manufactured by shell and VERSAMID 125 which is a curing agent manufactured by COGNIS) is cured to about 0.2 g. The weight was measured. Thereafter, the adhesive piece was dipped in each ink placed in a screw tube, capped, and left for 6 months. The temperature during standing was the discharge temperature of each ink described in Table 2 and Table 3 below. After leaving, the adhesive piece was taken out and the ink was washed thoroughly, and the weight was measured. And the swelling rate was computed from the following numerical formula.

Weight change rate (%) = {(weight after charging−weight before charging) / weight before charging} × 100
The evaluation criteria are as follows. The evaluation results are shown in Table 2 and Table 3 below.
A: It was less than 50%.
B: It was 50% or more.

[5. (Hardening wrinkle evaluation)
The head of FIG. 2 and each of the temporary curing light sources 42a to 42d are not used, and an LED having an irradiation peak intensity of 1000 mW / cm ² having a peak wavelength at 395 nm is disposed in the main curing light source, and the above-described ink curability evaluation is performed. In the same manner as described above, the ink was applied to the film with a bar coater, and the film was conveyed to the main curing light source and irradiated toward the ink. The irradiation time was adjusted so that the irradiation energy was irradiated until it was cured by the same test method as in the curability test. However, the film thickness after ink curing was 12 μm.
And the surface of the cured film was observed visually. The evaluation criteria are as follows. The evaluation results are shown in Table 2 and Table 3 below.
A: Wrinkles were not generated at all.
B: Wrinkles were generated in some areas of the cured film.
C: Wrinkles were generated on the entire surface of the cured film.

  Based on the above results, a head for discharging and adhering ultraviolet curable ink toward the recording medium, an ink path for supplying the ink to the head, and heating the ink having a viscosity at 28 ° C. of 8 mPa · s or more. Then, the temperature of the ejected ink is set to 28 to 40 ° C. and the viscosity of the ink at the temperature is set to 15 mPa · s or less, and the ink is degassed and degassed. An ink jet recording apparatus (each embodiment) that includes a deaeration mechanism that supplies to the head and a light source that cures the ink by irradiating the ink attached to the recording medium with ultraviolet rays is a recording apparatus that does not (each comparison) Compared to Example), it is excellent in ejection stability and head durability, and also in the solubility of the photopolymerization initiator contained in the ink, the curability of the ink, and the suppression of curing wrinkles. It was. Here, there was no difference in curability and curing wrinkles due to the heating temperature. Hereinafter, although consideration will be made based on the above results, the content of the consideration does not limit the scope of the present invention.

  First, when the viscosity of the ink at the time of ejection is 8 to 12 mPa · s, that is, when the evaluation result of the viscosity is “B” or “C”, the recording by the recording apparatus equipped with the ink is ejection stability. Became even better. In addition, when the said viscosity exceeds 15 mPa * s, ie, when the evaluation result of the said viscosity is "E", it is estimated that discharge stability deteriorated because of high viscosity. In addition, when the ink discharge temperature is higher than 40 ° C. or the ink viscosity at the time of discharge is less than 8 mPa · s, the tendency to be inferior in the head durability is observed in the ink in a high temperature state or a low viscosity state. This is presumably because the head tends to erode.

  Subsequently, each example and comparative example will be considered. From the comparison between each Example and Comparative Examples 7 to 10, when the viscosity was 8 mPa · s or more at 28 ° C., the durability of the head and the suppression of curing wrinkles were excellent. Specifically, Example 9 was an example having a viscosity of 8 mPa · s at 28 ° C., and was excellent in head durability. On the other hand, Comparative Examples 7 to 10 using any one of the inks H, I, and J having an ink viscosity rank of A at 28 ° C. were inferior in curing wrinkle evaluation.

  Further, from the comparison between Examples 1 and 2 and Comparative Example 1 and the comparison between Examples 9 and 10 and Comparative Example 4, when the discharge temperature was 28 ° C. or higher, the ink discharge stability was excellent. Further, from the comparison between Examples 3 and 4 and Comparative Example 2, the comparison between Example 11 and Comparative Example 6, and the comparison between Example 17 and Comparative Example 14, when the discharge temperature is 40 ° C. or less, the head The durability was excellent. Comparative Example 3 is an example in which the ink was not degassed because the pressure was not reduced using the degassing mechanism. From the comparison between Example 2 and Comparative Example 3, (preferably up to 20 ppm or less of dissolved oxygen). The degassed ink was excellent in ejection stability. Also, the comparison between Example 11 and Comparative Example 5, the comparison between Examples 13 and 14 and Comparative Example 11, the comparison between Examples 15 and 16 and Comparative Example 12, and the comparison between Example 17 and Comparative Example 13 Accordingly, when the ink viscosity at a discharge temperature of 28 to 40 ° C. is 15 mPa · s or less, the ink discharge stability was excellent. Further, from the comparison between Example 1 and Comparative Example 1, the comparison between Example 13 and Comparative Example 11, the comparison between Example 15 and Comparative Example 12, and the comparison between Example 17 and Comparative Example 13, thioxanthone The ink containing the photopolymerization initiator was superior in curability than the ink containing no photopolymerization initiator, but the ejection stability when the dissolved oxygen content of the ink was high was noticeably deteriorated.

  Further, from each comparison between Examples 2 and 19, Examples 8 and 20, and Examples 11 and 21, “ink inflow amount / maximum ink discharge amount”, that is, the greater the circulation speed (the greater the circulation amount). The degree of deaeration increased (the amount of dissolved oxygen decreased), and the ink ejection stability was excellent. Further, from the comparison between Comparative Examples 4, 15, and 16, when the ink discharge temperature was low, the discharge stability did not change even when “ink inflow amount / maximum ink discharge amount” was changed.

  Moreover, even if it arrange | positioned the heating mechanism downstream from the deaeration mechanism from the comparative example 18, when discharge temperature was low, it was inferior to discharge stability. Further, from Example 22, when the heating mechanism was disposed downstream of the deaeration mechanism, the amount of dissolved oxygen was slightly increased (the discharge stability tended to be slightly inferior).

Further, considering Examples 23 to 25 from the viewpoint of the light source, when an LED whose irradiation peak intensity was changed from 1,000 mW / cm ² to 500 mW / cm ² was used, there was an inferior curing wrinkle evaluation. Specifically, Example 2 and Example 23 are different from each other in that the irradiation peak intensity is different, but it is estimated that the generation of curing wrinkles can be effectively prevented as the irradiation peak intensity increases. . Further, Example 11 and Example 24 are also different from each other in that the irradiation peak intensity is different. However, since the ink having higher viscosity than those in Examples 2 and 23 is used, the irradiation peak is different. Regardless of the strength, it is presumed that generation of hardening wrinkles can be prevented. Further, Example 7 and Example 25 are also different from each other in that the irradiation peak intensity is different, but the ink containing the vinyl ether group-containing (meth) acrylic acid ester represented by the general formula (I) has an irradiation peak. When the strength is large, it is presumed that generation of hardening wrinkles can be prevented.

Although not shown as an example, curing was performed using a metal halide lamp having an irradiation peak intensity of 1,000 mW / cm ² instead of the LED as the light source. As a result, among the examples and comparative examples, in the case where the evaluation result of cured wrinkles was B or C, the cured wrinkle evaluation was improved to one rank superior, and the curability result was further improved. I understood. However, the film was deformed by the heat generated by the metal halide lamp, and the installation space was required because it was a larger light source than the LED. In other words, it has been found that the use of LEDs is preferable in terms of low heat generation, space saving, and a low-cost recording apparatus, and it is more preferable in terms of curing wrinkles to increase the irradiation peak intensity of the LEDs.

Further, although not shown as an example, recording was performed in the same manner as in Example 1 except that instead of a line printer, a serial printer having an LED with a peak intensity of 500 mW / cm ² mounted on the side of the carriage was used as a light source. Went. The serial printer used is the ink jet printer described in FIG. 2 of JP2010-167777A. The nozzle density of the head is 300 dpi, the recording resolution is 600 dpi × 600 dpi, but the recording resolution per pass is 300 dpi × 300 dpi, and dots are formed in the same recording area of the recording medium in four passes (main scanning direction 2 Pass × sub-scanning direction 2 pass). As a result, the cured wrinkle evaluation result was A, but since it was a serial printer, it was found that the recording speed was low. That is, according to the recording apparatus of the present invention, even when high-speed printing is performed by a line printer, it is possible to effectively prevent the occurrence of curing wrinkles by using LEDs and increasing the irradiation peak intensity. It was found that it was possible to make a good record.

  DESCRIPTION OF SYMBOLS 1 ... Printer, 10 ... Ink supply unit (ink supply apparatus), 20 ... Conveyance unit, 25A ... Upstream roller, 25B ... Downstream roller, 26 ... Conveyance drum, 30 ... Head unit, 40 ... Irradiation unit, 42a, 42b , 42c, 42d ... provisional curing irradiation unit, 44 ... main curing irradiation unit, 50 ... ink cartridge, 51 ... ink path, 52 ... holder, 53 ... valve, 54 ... supply pump, 55 ... filter, 56 ... pressurization Pump, 60 ... head, 61 ... cap, 70 ... sub tank, 71 ... liquid sensor, 80 ... ink circulation path, 81 ... filter, 82 ... circulation pump, 83 ... head filter, 90 ... warming mechanism, 91 ... warm water tank 92 ... Warm water circulation pump, 93 ... Heater, 94 ... Temperature control module, 100 ... Deaeration mechanism, 101 ... Negative pressure pump, DESCRIPTION OF SYMBOLS 02 ... Deaeration module, 110 ... Detector group, 120 ... Controller, 121 ... Interface part, 122 ... CPU, 123 ... Memory, 124 ... Unit control circuit, 130 ... Computer, K ... Black ink head, C ... Cyan ink head , M ... magenta ink head, Y ... yellow ink head, S ... recording medium.

Claims (13)

A head for ejecting and adhering ultraviolet curable ink toward a recording medium;
An ink path for supplying the ultraviolet curable ink from an ink container to the head;
The ultraviolet curable ink having a viscosity at 28 ° C. of 8 mPa · s or more is heated, the temperature of the ejected ink is set to 28 to 40 ° C., and the viscosity of the ink at the temperature is 15 mPa · s or less. And a heating mechanism
A degassing mechanism for degassing the ultraviolet curable ink and supplying the degassed ink to the head;
A light source for irradiating the ultraviolet curable ink attached to the recording medium with ultraviolet rays to cure the ink, and
A subtank having a liquid level in contact with the atmosphere and the ultraviolet curable ink in the ink path;
At least a part of the ink path is an ink circulation path for circulating the ultraviolet curable ink,
In the ink circulation path, the sub tank, the heating mechanism, the deaeration mechanism, and the head are arranged in the direction in which the ink circulates, the heating mechanism on the downstream side of the sub tank, and the downstream of the heating mechanism. The degassing mechanism on the side, and the head on the downstream side of the degassing mechanism,
The ink jet recording apparatus, wherein the dissolved oxygen amount of the ultraviolet curable ink supplied to the head after degassing is 3 to 20 ppm. The inkjet recording apparatus according to claim 1, further comprising a plurality of heads as the heads to which ink is supplied from the ink circulation path . The inflow amount of the ultraviolet curable ink per unit time supplied from the ink circulation path to the head is 1.5 times the maximum ink discharge amount per unit time for discharging the ultraviolet curable ink from the head. or more, an ink jet recording apparatus according to claim 1 or 2. The inflow amount of the ultraviolet curable ink per unit time supplied from the ink circulation path to the head is at least twice the maximum ink ejection amount per unit time for ejecting the ultraviolet curable ink from the head. The inkjet recording device according to claim 1, wherein   The ink jet recording apparatus according to claim 1, wherein an amount of dissolved oxygen of the ultraviolet curable ink supplied to the head is 5 to 20 ppm. The ink jet recording apparatus according to claim 1, wherein the ultraviolet curable ink contains an acyl phosphine oxide compound as a photopolymerization initiator.   The ink jet recording apparatus according to claim 1, wherein the ultraviolet curable ink contains a thioxanthone photopolymerization initiator.   The inkjet recording apparatus according to claim 1, wherein an epoxy resin is used for at least a part of a portion of the head that comes into contact with the ultraviolet curable ink. The ink jet recording apparatus according to claim 1, wherein the light source is a light emitting diode, and the light emitting diode emits ultraviolet light having an irradiation peak intensity of 800 mW / cm ² or more . The said ultraviolet curable ink contains 30-90 mass% of monofunctional (meth) acrylate with respect to the total mass of an ink, and the bifunctional or more (meth) acrylate is any one of Claims 1-9. 2. An ink jet recording apparatus according to 1.   The inkjet recording apparatus according to claim 1, wherein the ultraviolet curable ink is not a water-based ink.   The inkjet recording method which records using the inkjet recording device of any one of Claims 1-11. A step of ejecting and adhering ultraviolet curable ink from a head toward a recording medium; and
Supplying the ultraviolet curable ink from an ink container to the head via an ink path;
The ultraviolet curable ink having a viscosity at 28 ° C. of 8 mPa · s or more is heated by a heating mechanism so that the temperature of the ejected ink is 28 to 40 ° C., and the viscosity of the ink at the temperature is A heating step of 15 mPa · s or less;
A degassing step of degassing the ultraviolet curable ink with a degassing mechanism and supplying the degassed ink to the head;
Irradiating the ultraviolet curable ink attached to the recording medium with ultraviolet rays from a light source to cure the ink, and
A subtank having a liquid level in contact with the atmosphere and the ultraviolet curable ink in the ink path;
At least a part of the ink path is an ink circulation path for circulating the ultraviolet curable ink,
In the ink circulation path, the sub tank, the heating mechanism, the deaeration mechanism, and the head are arranged in the direction in which the ink circulates, the heating mechanism on the downstream side of the sub tank, and the downstream of the heating mechanism. The degassing mechanism on the side, and the head on the downstream side of the degassing mechanism,
The ink jet recording method, wherein a dissolved oxygen amount of the ultraviolet curable ink supplied to the head after degassing is 3 to 20 ppm.

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