Coating film forming method

Abstract

A coating film forming method according to the present invention is a coating film forming method employing an inkjet head, wherein an inkjet ink contains a polymerizable monomer, a blocked isocyanate, and a photopolymerization initiator, and the method includes: a dewatering step for the ink; and a heating step for bringing the temperature of the ink ejected from the inkjet head to 40°C or higher.

Description

Paint film formation method

[0001] The present invention relates to a coating film forming method, and more particularly to a coating film forming method that suppresses the generation of solid matter in the apparatus and the clogging of the head nozzle, and that provides good ejection properties and stable curing properties.

[0002] Conventionally, photolithography and screen printing have been used to form etching resists, solder resists, and markings on printed wiring boards. The use of inkjet printing in the manufacturing method of printed wiring boards, for example, involves using inkjet ink containing a thermosetting agent on a copper-clad laminate for printed wiring boards. It has already been proposed to form solder resist using an inkjet printer (see, for example, Patent Documents 1 to 3).

[0003] The inkjet method can significantly reduce the number of steps and labor compared to photolithography, which requires a photomask, and screen printing methods using resist ink or marking ink, which require a screen. Furthermore, the inkjet method can reduce consumables such as developers, various inks, and cleaning solvents, and can also reduce wastewater, which is expected to contribute to a cleaner environment.

[0004] However, in inks containing the above-mentioned heat curing agent, particularly blocked isocyanate, the blocked isocyanate reacts with water and hydroxy groups contained in the ink to generate solids. As a result, when the ink is ejected from a head using an inkjet method, nozzles are clogged, which can easily cause ejection failures. In particular, in order to improve the ejection performance of curable inks, the ink is usually heated to reduce the ink viscosity before ejection, but heating further accelerates the generation of solids.

[0005] Therefore, a method has been proposed in which the water content is kept low at 500 ppm during the production of ink containing isocyanate groups (see, for example, Patent Document 4). However, the method of keeping the water content at 500 ppm imposes a large production load, is difficult to maintain and store, and leads to increased costs. Furthermore, this method is based on the premise that the ink will be used immediately after production.

[0006] Japanese Patent No. 06069300 Japanese Patent Application Laid-Open No. 2011-043565 Japanese Patent No. 05969208 Japanese Patent Application Laid-Open No. 2014-201593

[0007] The present invention has been made in consideration of the above problems and circumstances. An object of the present invention is to provide a coating film forming method that suppresses the generation of solid matter in the apparatus and the clogging of the head nozzles, and that achieves good ejection properties and stable curing properties. Note that, hereinafter, "inkjet ink" may also be simply referred to as "ink."

[0008] The present inventors have investigated the causes of the above problems in order to solve them. They have found that even when ink containing a blocked isocyanate is used, generation of solid matter in a film forming apparatus can be suppressed by performing a dehydration process on the ink before ejecting the ink. That is, the above problems according to the present invention are solved by the following means.

[0009] 1. A coating film forming method using an inkjet head, wherein the inkjet ink contains a polymerizable monomer, a blocked isocyanate, and a photopolymerization initiator, the coating film forming method comprising: a dehydration step of the inkjet ink; and a heating step of heating the inkjet ink ejected from the inkjet head to a temperature of 40°C or higher.

[0010] 2. The coating film forming method according to Item 1, wherein the heating step is carried out in an ink supply path that supplies the ink-jet ink to the ink-jet head.

[0011] 3. The method for forming a coating film according to Item 1, wherein in the dehydration step, dry gas whose moisture content has been reduced by a drying device is injected into an ink supply path that supplies the inkjet ink to the inkjet head.

[0012] 4. The method for forming a coating film according to Item 3, wherein the dry gas is generated using a membrane filter or activated carbon in the dehydration step.

[0013] 5. The method for forming a coating film according to Item 1, further comprising a step of degassing the ink-jet ink after the dehydration step.

[0014] 6. The method for forming a coating film according to Item 5, wherein the degassing step uses hollow fibers or ultrasonic waves.

[0015] 7. The method for forming a coating film according to Item 2, wherein after the dehydration step, a second heating step is further carried out in addition to the heating step in an ink supply channel that supplies the inkjet ink to the inkjet head.

[0016] The above-described means of the present invention provide a coating film formation method that suppresses the generation of solids and head nozzle clogging in a coating film forming apparatus, even when using an ink containing a blocked isocyanate, and achieves good ejection properties and stable curing. While the mechanism of action or manifestation of the effects of the present invention is unclear, the following is speculated. In inks containing blocked isocyanates, the blocked isocyanates react with water and hydroxy groups contained in the ink to generate solids. In particular, heating such inks accelerates the generation of solids. As a result, the generation of solids in a coating film forming apparatus can lead to ejection defects. The presumed mechanism for solid generation is that the blocked isocyanates react with water and hydroxy groups contained in the ink, hydrolyzing the blocked isocyanate (NCO) moiety and generating amines. Furthermore, the amino groups react with the NCO moieties to form polymers in which the bonding site is urea. It is also speculated that alcohol components generated by hydrolysis of the acrylic monomer react with the NCO moieties to polymerize. Therefore, in the present invention, a dehydration process is performed on the ink containing the blocked isocyanate before it is ejected. This reduces the water content of the ink, suppresses the reaction between the water and hydroxy groups in the ink and the blocked isocyanate, and also suppresses the generation of solids. As a result, the ink has good ejectability and stable curing properties. In particular, even when the temperature of the ink ejected from the inkjet head is heated to 40°C or higher, the ejectability is improved without accelerating the generation of solids.

[0017] FIG. 1 is a diagram illustrating an ink flow path of an inkjet recording device according to the present embodiment; FIG. 2 is a schematic cross-sectional view of an external circulation type degassing module; FIG. 3 is a schematic cross-sectional view showing the internal configuration of a central tube of an external circulation type degassing module; and FIG. 4 is a front view of a desiccant filter, which is another form of dehydration device.

[0018] The coating film forming method of the present invention is a coating film forming method using an inkjet head, wherein the ink contains a polymerizable monomer, a blocked isocyanate, and a photopolymerization initiator, and the method comprises a dehydration step of the inkjet ink, and a heating step of heating the ink ejected from the inkjet head to a temperature of 40° C. or higher. This feature is a technical feature common to or corresponding to each of the following embodiments.

[0019] In an embodiment of the present invention, it is preferable to perform the heating step in the ink supply path that supplies the ink-jet ink to the ink-jet head, since this reduces the viscosity of the ink and improves the ejection properties.

[0020] In addition, in the dehydration step, it is preferable to inject dry gas, the moisture content of which has been reduced by a drying device, into the ink supply path that supplies the inkjet ink to the inkjet head, since this makes it easy to inject the dry gas and ensures that the ink can be dehydrated reliably.

[0021] In the dehydration step, it is preferable to use a membrane filter or activated carbon to generate the dry gas, since this does not change the ink properties and does not affect the ejection properties, and the device can be easily introduced.

[0022] It is preferable to provide a degassing step for the inkjet ink after the dehydration step, since this can remove air bubbles caused by the dehydration treatment, leading to improved ejection properties.

[0023] The degassing step is preferably carried out using hollow fibers or ultrasonic waves, since this improves the coating film performance by preventing the imbalance in curing and film deterioration due to oxygen inhibition, and also improves the ejection property by preventing the formation of bubbles.

[0024] After the dehydration step, it is preferable to perform a second heating step in addition to the heating step in the ink supply path that supplies the ink to the inkjet head, in order to further improve the ejection properties.

[0025] The present invention, its constituent elements, and modes and aspects for carrying out the present invention will be described below. In this application, the symbol "to" is used to mean that the numerical values ​​before and after it are included as the lower and upper limits.

[0026] 1. Overview of the Coating Film Forming Method of the Present Invention The coating film forming method of the present invention is a coating film forming method using an inkjet head, in which an inkjet ink contains a polymerizable monomer, a blocked isocyanate, and a photopolymerization initiator, and the method includes a dehydration step of the inkjet ink, and a heating step of heating the ink ejected from the inkjet head to a temperature of 40°C or higher.

[0027] In the present invention, "(meth)acrylate" means acrylate or methacrylate, "(meth)acryloyl group" means acryloyl group or methacryloyl group, and "(meth)acrylic" means acrylic or methacrylic.

[0028] The ink used in the present invention functions as an insulating film (solder resist) when applied to a substrate and cured with actinic radiation in various fields, such as metal processing, electronic circuits, printed circuit boards, plate making, semiconductors, and color filters. Furthermore, since the ink can be removed with alkali after photocuring, it also functions as an etching resist used when forming an etching pattern on a substrate. In addition to being used as an ink for forming the solder resist pattern described above, the ink can also be used as an adhesive, sealant, or circuit protectant for electronic components. In particular, the ink according to the present invention is preferably an ink for forming a solder resist pattern used on a printed wiring board. When a solder resist pattern (solder resist film) is formed using the ink according to the present invention, its high curability prevents the penetration of oxygen and moisture into the solder resist film. Furthermore, the ink according to the present invention improves the adhesion between the copper foil and the solder resist film interface on a printed wiring board, preventing copper migration and suppressing a decrease in insulation.

[0029] The ink according to the present invention is an ink that can be cured by actinic rays. "Actinic rays (also called "active energy rays")" are rays that can impart energy to the ink to generate reaction initiating species such as active radicals and ions upon irradiation, and include α-rays, γ-rays, X-rays, ultraviolet rays, electron beams, etc. Of these, ultraviolet rays and electron beams are preferred from the viewpoints of curing sensitivity and ease of equipment availability, and ultraviolet rays are more preferred.

[0030] <Dehydration Step and Heating Step> The coating film forming method of the present invention includes a dehydration step of the ink and a heating step of raising the temperature of the ink ejected from the inkjet head to 40°C or higher. The order of the dehydration step and the heating step does not matter, but performing the heating step after the dehydration step is preferable because it is effective in preventing the generation of solids in the ink due to heating. Because the ink according to the present invention contains a blocked isocyanate, the water and hydroxy groups contained in the ink react with the blocked isocyanate to generate solids. In particular, heating of such ink accelerates the generation of solids. Therefore, dehydrating the ink before heating is effective in preventing the formation of solids. It is preferable to perform the heating step multiple times from the viewpoint of ejectability. As described below, the heating step is preferably performed immediately after the dehydration step and after the degassing step and immediately before ejection. The dehydration step and heating step will be described in detail below.

[0031] 2. Coating Film Forming Method The coating film forming method of the present invention preferably includes the following steps (3) to (6) in addition to the dehydration step and heating step described above. The order of the dehydration step and heating step does not matter, but the following description will be given of a preferred embodiment in which the heating step is performed after the dehydration step. As an example of the coating film forming method, a method of forming a resist film will be described. (1) Ink dehydration step (2) Ink heating step (3) Ink degassing step (4) A step of ejecting heated ink from the nozzle of an inkjet head and causing it to land on a printed wiring board with a circuit formed thereon (5) A step of irradiating the landed ink with actinic light rays to provisionally cure the ink (6) A step of heating the ink after provisional curing to fully cure it

[0032] <Step (1)> Step (1) is a step of dehydrating the ink before ejecting the ink from the inkjet head. Dehydration prevents the water and hydroxyl groups contained in the ink from reacting with the blocked isocyanate to produce solids.

[0033] In the dehydration process, it is preferable to inject a dry gas, the moisture content of which has been reduced by a dryer, into the ink supply channel. This injects the dry gas into the ink liquid, resulting in dehydration. Furthermore, a membrane filter or activated carbon can be used as the dryer. Examples of filters using activated carbon include filters with activated carbon, and specifically, the desiccant filter described below is preferred. The desiccant filter is configured by coating the surface of a sheet-like substrate containing a corrugated nonwoven fabric with a dehumidifying agent containing activated carbon, and details of which will be described below.

[0034] The dry gas preferably has a relative humidity of 10% RH or less, more preferably 5% RH or less, and the lower the humidity, the better. Examples of dry gases that can be used include air, nitrogen, helium, and argon. By injecting (supplying) the dry gas into the ink supply channel, the water content of the ink, measured by the Karl Fischer method, is preferably in the range of 0.05 to 0.60% by mass relative to the total mass of the ink. The water content preferably falls within this range from (1) the ink dehydration step to (4) immediately before the ink ejection step.

[0035] (Method for Measuring Water Content) The water content according to the present invention can be measured by a known method such as the Karl Fischer method. The water content measurement method by the Karl Fischer method is a method for quantifying the water content in a substance by utilizing the fact that a Karl Fischer reagent containing iodine, sulfur dioxide, and pyridine reacts specifically with water in the presence of methanol. In particular, the volumetric titration method is a method in which a titration solvent is placed in a titration flask, a sample is dissolved in the titration solvent to extract the water content in the sample, and then the water content is determined by titrating with a Karl Fischer reagent containing iodine, sulfur dioxide, and a base as its main components. Water reacts with iodine and sulfur dioxide in the presence of a base and alcohol. H ２ 0+I ２ +SO ２ +CH ３ OH+3RN → 2RN・HI+RN・HSO ４ CH ３ From the above equation, H ２ 0 and I ２Since this is a 1:1 reaction, the number of milligrams of water (potency) per 1 ml of Karl Fischer reagent is determined in advance using water or a water standard substance. Then, the amount of water (mg) is calculated from the amount of Karl Fischer reagent titer (ml) required to measure the sample. Amount of water (mg) = Karl Fischer reagent titer (ml) × potency (mgH ２ 0 / ml) Karl Fischer reagent is also called KF reagent. Then, the water content relative to the total mass of the ink is calculated from the calculated water content. Water content (%) = (amount of water in ink / total mass of ink) x 100

[0036] One way to control the water content within the range of 0.05 to 0.60% by mass is to control the amount and duration of dry gas supply in the dehydration step. Other ways to control the water content include controlling the octanol / water partition coefficient (ClogP) of the polymerizable monomer contained in the ink, or controlling the hydroxyl value in the ink. Another way to control the water content is to heat the ink.

[0037] The drying gas supply rate is preferably within a range of 0.3 to 1.5 L / min, and the drying gas supply time is preferably continued while the ink is being heated. The ClogP value of the polymerizable monomer is preferably within a range of 2.0 to 7.0. Furthermore, from the viewpoint of ejection stability, it is preferable that the polymerizable monomer having a ClogP value within a range of 2.0 to 7.0 is contained in an amount of 30 mass% or more relative to the total ink. The hydroxy value in the ink is preferably within a range of 0.05 to 60 mgKOH / g. To achieve a hydroxy value in the ink within the above range, it is preferable to control the charge composition of the compound having a hydroxy value contained in the ink or to purify the compound having a hydroxy value. Examples of the compound having a hydroxy value include (meth)acrylate.

[0038] <Step (2)> Step (2) is a step of heating the dehydrated ink. By heating, the ink droplets can be ejected from the inkjet head in a heated state. This can improve ejection stability. The temperature of the ink at the time of ejection is preferably 40°C or higher, with the upper limit being preferably 100°C or lower. In order to further improve ejection stability, the temperature of the ink at the time of ejection is more preferably within the range of 40 to 90°C. In particular, it is preferable to eject the ink at an ink temperature such that the viscosity of the ink is within the range of 7 to 15 mPa·s, more preferably within the range of 8 to 13 mPa·s.

[0039] The ink is preferably heated in a flow path that supplies ink to the inkjet head so that the ink temperature at the time of ejection is 40°C or higher. For example, the heating method can be performed by heating at least one of the ink supply system, such as the ink tank of the head carriage, the supply pipe, and the anterior ink tank immediately before the head, the piping with a filter, and the piezo head, using an ink heater. In particular, in the present invention, it is preferable to perform the heating process multiple times before ejection. Specifically, as described below, in the ink supply system, it is preferable to heat the first sub-tank immediately after dehydration. Furthermore, in addition to heating the first sub-tank, it is also preferable to heat the second sub-tank immediately after degassing and immediately before ejection, in order to improve ejection performance.

[0040] The ink heating unit may be a panel heater, a rubber heater, a ribbon heater, a heated water heater, etc. The specific configuration of the ink heating unit will be described later.

[0041] <Step (3)> Step (3) is a step of degassing the ink to remove air bubbles caused by dehydration. The degassing method preferably uses hollow fibers or ultrasonic waves. A degassing module (degassing device) using hollow fibers or ultrasonic waves will be described later.

[0042] The degassing step preferably adjusts the amount of dissolved oxygen in the ink at the temperature at which the ink is ejected to a range of 0.1 to 10.0 mg / lppm, more preferably 0.1 to 5.0 mg / lppm, and particularly preferably 0.05 to 0.60 mg / lppm.

[0043] (Method for calculating the amount of dissolved oxygen by the fluorescence method) The amount of dissolved oxygen can be measured by known methods such as the fluorescence method. For example, the method for measuring the amount of dissolved oxygen by the fluorescence method mainly uses a phosphor electrode, and is characterized by the fact that when blue excitation light is irradiated onto the phosphor, the phosphor emits red fluorescence. Since the fluorescent energy of the red fluorescence is absorbed by oxygen molecules, the greater the molecular weight of oxygen, the more fluorescent energy is absorbed, and the amount of fluorescent afterglow decreases in inverse proportion to the molecular weight of oxygen. In other words, this is a quantitative method that applies the principle that the greater the amount of oxygen, the less afterglow there is.

[0044] As described above, it is preferable from the viewpoint of injectability to carry out the heating step (2) again after the degassing step and before the injection step described below.

[0045] <Step (4)> In step (4), ink droplets are ejected from an inkjet head and land on a printed wiring board, which is a recording medium, at positions corresponding to the resist film to be formed, thereby forming a pattern. The ejection method from the inkjet head may be either an on-demand method or a continuous method. On-demand inkjet heads may be electro-mechanical conversion types such as single-cavity, double-cavity, bender, piston, shear-mode, and shared-wall types, or electro-thermal conversion types such as thermal inkjet and Bubble Jet (registered trademark) types (Bubble Jet is a registered trademark of Canon Inc.). The amount of ink droplets ejected is preferably within the range of 2 to 20 pL in terms of recording speed and image quality.

[0046] The printed wiring board is not particularly limited, but examples thereof include copper-clad laminates of all grades (FR-4, etc.) made of materials such as paper phenol, paper epoxy, glass cloth epoxy, glass polyimide, glass cloth / non-woven cloth epoxy, glass cloth / paper epoxy, synthetic fiber epoxy, copper-clad laminates for high-frequency circuits made of fluorine, polyethylene, PPO, cyanate ester, etc., as well as polyimide films, PET films, glass substrates, ceramic substrates, wafer plates, stainless steel plates, etc.

[0047] The printed wiring board is preferably subjected to a fine roughening treatment to increase the contact area with the ink and improve adhesion to the ink. When coating ink using an inkjet method, the viscosity of the ink must be low so that it can be ejected from an inkjet head. Therefore, inks containing polymerizable monomers as the main component before coating and cured by actinic radiation after coating are used. Such inks tend to shrink upon curing after coating, resulting in poor adhesion between the ink and the printed wiring board. Therefore, a fine roughening treatment must be performed on the wiring board to increase the contact area with the wiring board. Furthermore, the low viscosity of the ink can cause bleeding on a roughened wiring board. Therefore, a treatment to adjust the contact angle is preferably performed after roughening the wiring board. Therefore, when using the ink of the present invention for the above-mentioned applications, it is preferable to perform a roughening treatment or a treatment to prevent bleeding as a pretreatment for the wiring board.

[0048] Examples of roughening treatment methods include physical polishing, which involves forming irregularities on the surface of the wiring board using a buff, scrub, or the like to form a rough surface. Other roughening treatment methods include chemical polishing treatments such as copper chloride-based, persulfate-based, sulfuric acid / hydrogen peroxide-based, formic acid-based, and organic acid-based. From the viewpoint of adhesion, chemical polishing is preferred as a roughening treatment method, and organic acid-based treatments are more preferred.

[0049] Specific examples of chemical polishing treatments include MacDermid's MultiPrep 200 copper chloride system, MacDermid's Microclean, ME-301, and PR-820 persulfate system, and Shikoku Kasei's GB1000F / 1400, G200, GB3100, and GB4300 sulfuric acid / hydrogen peroxide system, and MacDermid's Metex G-5 and Metex Examples of organic acid-based paints include G-6, ME-501, ME-602, ME-605, ME-709, BTH-2066 from BOARDTEC Corporation, CPE-900, EMR-5000, and EMR-7000 from Mitsubishi Gas Chemical Company, and CZ8100, CZ8101, and CZ8202 from MEC Corporation, and BTH-2083 and BTH-2085 from BOARDTEC Corporation. From the viewpoint of adhesion, sulfuric acid / hydrogen peroxide-based paints and organic acid-based paints are preferred, and organic acid-based paints are more preferred. As a treatment for preventing bleeding, CL8300 series from MEC Corporation and BTH-3066 from BOARDTEC Corporation are preferred.

[0050] The surface roughness of the copper plate roughened by the pretreatment is preferably Ra 0.1 to 1.5 μm, more preferably 0.3 to 1.3 μm, and most preferably 0.4 to 1.1 μm. An Ra of 0.1 μm or more improves adhesion, while an Ra of 1.5 μm or less suppresses bleeding. The thickness of the copper plate roughened by the pretreatment agent is preferably 0.1 to 3.0 μm, more preferably 0.3 to 2.0 μm, and even more preferably 0.5 to 1.5 μm. A roughened thickness of 0.1 μm or more improves adhesion due to the anchor effect, while a roughened thickness of 3.0 μm or less improves adhesion because the copper is not unnecessarily coarsened or densified. Surface roughness can be controlled by adjusting conditions such as the type of pretreatment agent and the treatment temperature and time. Surface roughness can be measured using a laser microscope, white light interference microscope, or the like.

[0051] <Step (5)> In step (5), the ink deposited in step (4) is irradiated with actinic rays to provisionally cure the ink. The actinic rays can be selected from, for example, electron beams, ultraviolet rays, α rays, γ rays, and X-rays, but ultraviolet rays are preferred. The ultraviolet rays can be irradiated using, for example, a water-cooled LED manufactured by Phoseon Technology, under conditions of a wavelength of 300 to 420 nm.

[0052] The ultraviolet irradiation is carried out such that the peak irradiance of ultraviolet light having a wavelength in the range of 300 to 420 nm on the surface of the resist film is preferably 0.5 to 10 W / cm ２ The irradiation of ultraviolet light is more preferably carried out so that the peak irradiance of the ultraviolet light on the surface of the resist film is in the range of 1 to 5 W / cm. ２ From the viewpoint of suppressing the radiation heat from being irradiated onto the ink, the amount of light irradiated onto the resist film is set to be within the range of 1000 mJ / cm. ２ The irradiation with actinic rays is preferably carried out within 0.001 to 300 seconds after the ink has landed, and more preferably within 0.001 to 60 seconds in order to form a highly precise resist film.

[0053] <Step (6)> In step (6), after the temporary curing in step (5), the ink is further heated to fully cure it. The heating method is preferably, for example, placing the ink in an oven or the like set at a temperature in the range of 110 to 180°C for 10 to 60 minutes.

[0054] 3. Film-forming Apparatus A film-forming apparatus used in the film-forming method of the present invention will be described in detail below with reference to the drawings. However, the scope of the present invention is not limited to the illustrated examples. In the following description, components having the same functions and configurations are given the same reference numerals, and their description will be omitted. An example of a film-forming apparatus is an inkjet recording apparatus equipped with an inkjet head. The inkjet recording apparatus preferably has a dehydration device, an ink heating unit, a degassing device, and an inkjet head. The inkjet recording apparatus also preferably has an actinic ray irradiation unit (UV irradiation unit) that irradiates actinic rays onto ink that has landed on the recording medium.

[0055] 1 is a diagram illustrating the ink flow paths in an inkjet recording apparatus. In the inkjet recording apparatus 1, ink is pumped out from an ink tank 51 of an ink supply unit 50 by a supply pump 53 and supplied to each recording head 24a via an ink flow path 24b. The inkjet recording apparatus 1 is also configured to be able to return ink that was not ejected from each recording head 24a to the ink flow path 24b as necessary.

[0056] On the ink flow path 24b, a dehydration device (dehydration means) 300, a first sub-tank 241, a degassing device 280, a liquid feed pump 243, a check valve 244, a second sub-tank 245, etc. are provided. The recording head 24a, the ink flow path 24b, and each component part on the ink flow path 24b are heated and kept warm by an ink heating unit (ink heating means) 270, so that the temperature of the ink is maintained at an appropriate temperature. Specifically, the ink heating unit 270 heats the recording head 24a, the ink flow path 24b, and each component part on the ink flow path 24b so that the ejection temperature of the ink is 40°C or higher.

[0057] <Ink Heating Unit> The ink heating unit 270 is preferably provided in at least one of the components of the recording head 24a and the ink flow path 24b, before the dehydrating device 300, between the dehydrating device 300 and the degassing device 280 (degassing module 242), or between the degassing device 280 and the recording head 24a. The ink heating unit 270 may also be provided in the degassing device 280. From the viewpoint of preventing the formation of solids due to heating, the ink heating unit 270 is preferably provided after the dehydrating device 300, and preferably between the dehydrating device 300 and the degassing device 280. Furthermore, although the ink may be ejected from the recording head 24a immediately after degassing, it is preferable to further provide the ink heating unit 270 between the degassing device 280 and the recording head 24a for more stable ejection in terms of preventing an increase in pressure loss. In the following explanation, we will explain the case where the ink heating unit 270 is installed in the first sub-tank 241 after the dehydration device, the second tank 247 between the dehydration device 300 and the degassing device 280, and the degassing device 280, but this is not limited to this.

[0058] The ink heating unit 270 is composed of a heater and a heat transfer member that transfers heat from the heater. The ink heating unit 270 may also be composed of warm water. The heater may be, for example, an electric heating wire that generates Joule heat when energized. Examples of such heaters include a panel heater, a ribbon heater, and a rubber heater. The heat transfer member is a member with high thermal conductivity, such as a heat conduction plate made of various metals (alloys). The heater or heat transfer member is provided, for example, to cover the piping of the ink flow path 24b or to be in contact with the side walls of the first sub-tank 241 or the second sub-tank 245.

[0059] <Dehydration Device> The dehydration device 300 dehydrates the ink pumped out of the ink tank 51 by the supply pump 53, thereby preventing the formation of solids in the ink when heated in a subsequent process. That is, when the ink of the present invention is heated, the water and hydroxy groups contained in the ink react with the blocked isocyanate to generate solids, but dehydration prevents the generation of such solids. As a result, ink ejection defects are also prevented.

[0060] The dehydration device 300 may be configured to supply the ink with dry gas whose moisture content has been reduced by a dryer. Specific examples of dryers include those using a membrane filter or activated carbon. Examples of dryers using membrane filters include membrane dehumidifiers and general-purpose compressors. Commercially available dehumidifiers can be used, such as the SMC Membrane Dehumidifier IDG5-02B-PS. Examples of dryers using activated carbon include filters with activated carbon, and more specifically, desiccant filters, which will be described later.

[0061] The dry gas that has been dehydrated by such a drying device is then injected into the ink supply channel, whereby the dry gas is injected into the ink liquid and dehydrated. The relative humidity of the dry gas is preferably 10% RH or less. The flow rate of the dry gas supplied to the ink is preferably within the range of 0.3 to 1.0 ml / min, which strikes a balance between bubble formation and bubble destruction at the ink interface. The dry gas supply time is preferably 1 to 12 hours.

[0062] FIG. 4 is a front view of a desiccant filter. The desiccant filter 301 comprises a sheet-like substrate 302 coated with a dehumidifying agent 303. The substrate 302 is made of a corrugated nonwoven fabric and a conductive polymer, which is a conductive material impregnated into the nonwoven fabric. The dehumidifying agent 303 contains activated carbon. A conductor 4, which is a conductive member for supplying power, is connected to the substrate 302 containing the conductive polymer. The conductor 304 is connected to an external power source 305. Note that the conductive member is not limited to the conductor 304, and various known conductive members can be used. The desiccant filter 301 configured as described above is placed inside the dehydration device 300 together with the external power source 305.

[0063] The desiccant filter 301 absorbs the moisture in the ink using the dehumidifying agent 303, and then passes the ink with reduced moisture content. When the amount of moisture absorbed by the dehumidifying agent 303 of the desiccant filter 301 becomes large, it is preferable to perform a regeneration process for the desiccant filter 301.

[0064] In a method for regenerating the desiccant filter 301, power is supplied from an external power source 305 to the conductive polymer in the base 302 via the conductor 304. The supplied power causes the conductive polymer to generate heat, raising the temperature of the base 302. When the temperature of the base 302 reaches a temperature at which moisture can be desorbed, the moisture adsorbed in the dehumidifying agent 303 is desorbed. As a result, the moisture adsorption capacity of the dehumidifying agent 303 is restored, and the dehumidifying agent 303 is restored to a state where it can fully adsorb moisture, i.e., is able to dehumidify.

[0065] The nonwoven fabric is preferably made of, for example, aramid fiber, cellulose fiber, nylon fiber, vinylon fiber, glass fiber, polyester fiber, polyethylene fiber, polypropylene fiber, polyolefin fiber, rayon fiber, etc. Furthermore, the base 302 may be made of a sheet-like member other than nonwoven fabric (for example, woven fabric or resin film) and a conductive material.

[0066] An example of a conductive polymer is polythiophene, which is used in organic electronics. In the present invention, for example, PEDOT:PSS (a composite of poly(3,4-ethylenedioxythiophene) and polystyrene sulfonic acid) can be suitably used as the conductive polymer impregnated into the nonwoven fabric. Poly(3,4-ethylenedioxythiophene) doped with the conductive polymer poly(4-styrenesulfonic acid) can be colloidally dispersed in water, and it is known that the polymer alone can be formed into a film. Furthermore, to improve conductivity, approximately 1 to 3% of a high-boiling point solvent such as dimethyl sulfoxide, N-methyl-2-pyrrolidone, glycerin, or ethylene glycol may be added to the water-dispersed conductive material.

[0067] The dehumidifying agent preferably contains activated carbon. The dehumidifying agent 253 is activated carbon fused with zeolite 4A or an aluminosilicate-carbon composite, as disclosed in Japanese Patent Application Laid-Open No. 2017-222547 or Japanese Patent Application Laid-Open No. 2018-30122. This activated carbon is obtained through the following steps (a) to (d). (a) a step of firing a silica plant in an inert atmosphere at 400°C or higher to produce a silica-carbon composite; (b) a step of preparing a mixture containing the silica-carbon composite, an Al compound, an alkali metal compound or alkaline earth metal compound, and water so as to produce an aluminosilicate having a molar ratio of Si:Al in the range of 1:0.1 to 1.2; (c) a step of subjecting the mixture to a hydrothermal reaction to obtain a porous aluminosilicate-carbon composite; and (d) a step of subjecting the porous aluminosilicate-carbon composite to an inert gas treatment at 600 to 800°C. This activated carbon can desorb moisture at a temperature of about 50 to 100°C.

[0068] The desiccant filter manufacturing method involves first immersing a corrugated nonwoven fabric in an aqueous dispersion of the conductive polymer PEDOT:PSS. The nonwoven fabric is then removed from the solution and left to dry for approximately 10 to 20 hours. This produces a substrate 302 made of nonwoven fabric impregnated with the conductive polymer. Meanwhile, activated carbon is manufactured through steps (a) to (d) as described above.

[0069] The activated carbon produced in this manner is ground in a mortar, mixed with a water-soluble binder, and stirred until evenly dispersed. Water is then added in multiple batches to produce a paste-like activated carbon solution. This activated carbon solution is applied to the surface of the substrate 302, which is made of a nonwoven fabric impregnated with a conductive polymer, to form a layer of dehumidifying agent (activated carbon). The substrate and dehumidifying agent are then dried at room temperature. Conductors are then connected to the substrate. In this manner, a desiccant filter with a high specific surface area is obtained, consisting of a corrugated nonwoven fabric impregnated with a conductive polymer and coated with activated carbon. The substrate 302 is not limited to a corrugated shape and may have various shapes, such as a pleated shape or a flat shape. However, it is preferable that the substrate 302 have a shape that does not impair breathability.

[0070] <First Sub-Tank> The first sub-tank 241 is an ink chamber with a smaller volume than the one or more ink tanks 51 that store ink dehydrated by the dehydration device 300. A first float sensor 241a is provided in the first sub-tank 241. A control unit (not shown) operates the supply pump 53 based on detection data of the liquid level position by the first float sensor 241a, thereby storing a predetermined amount of ink in the first sub-tank 241.

[0071] The first sub-tank 241 is preferably provided with an ink heating section 270. The ink in the first sub-tank 241 is heated by the ink heating section 270, allowing the viscosity of the ink to be adjusted when ejected. The ink heating section 270 preferably heats the ink so that the temperature of the ink when ejected is 40°C or higher, and preferably heats the ink in the first sub-tank 241 to a temperature of 40 to 60°C. The ink heating section 270 is preferably provided in contact with the side wall, bottom wall, etc. of the first sub-tank 241.

[0072] The control unit controls the temperature of the ink heating unit 270. The control unit detects the temperature of the ink heating unit 270 using a thermocouple built into the ink heating unit 270, for example, and performs on / off control using a target temperature that is set appropriately depending on the type of liquid.

[0073] <Degassing device> The degassing device 280 performs a degassing process to remove gases such as air from the ink that has flowed in, and then discharges the degassed ink. The degassing device is preferably configured using a hollow fiber membrane or ultrasonic waves. Below, a degassing device using a hollow fiber membrane and a degassing device using ultrasonic waves will be described. Note that although the degassing device 280 shown in FIG. 1 uses a hollow fiber membrane, it can be changed to a configuration using ultrasonic waves.

[0074] (Degassing Apparatus Using Hollow Fiber Membrane) The degassing apparatus 280 is composed of a degassing module 242, a vacuum pump 249, a vacuum path 250, a pressure sensor 251, an atmosphere release valve 252, etc. The degassing module 242 is an external reflux type degassing module having a hollow fiber membrane therein as a gas permeable membrane that is permeable to gas dissolved in a liquid. The degassing module 242 is also connected to a vacuum pump 249, a vacuum path 250, a pressure sensor 251, and an atmosphere release valve 252. The vacuum pump 249 reduces the air pressure inside the degassing module 242. The vacuum path 250 connects the vacuum pump 249 and the degassing module 242. The pressure sensor 251 measures the air pressure inside the vacuum path 250. The atmosphere release valve 252 is a valve that can switch the inside of the vacuum path 250 between an airtight state and an atmosphere open state.

[0075] The degassing module 242 of the degassing device 280 will be described in detail with reference to FIG. 2 . The example shown in FIG. 2 illustrates an external reflux type degassing module 242. The degassing module 242 is formed, for example, in a cylindrical shape, removes dissolved gases (degasses) from the ink that flows in, and discharges the degassed ink. The degassing module 242 is configured such that, inside an outer shell (chamber) 2421, a central tube 2424 is surrounded by a number of hollow fiber membranes (gas-permeable membranes) 2426. One end of the central tube 2424 is connected to an ink inlet 2422, and the other end is sealed with a plug 2424a. The outer wall of the central tube 2424 is provided with numerous fine holes (holes) 2424b (perforations). Ink that flows in through the ink inlet 2422 flows out through these fine holes 2424b to the surrounding area and then out through an ink outlet 2423. 2, the ink outlet 2423 is provided facing horizontally, and is configured so that ink flows out to the side of the degassing module 242. However, this configuration is not limited thereto, and the ink outlet 2423 may be provided facing any direction, and the ink may be configured to flow out in any direction. Furthermore, it is preferable to provide the ink outlet 2423 at a position corresponding to the upper end of the hollow fiber membrane 2426 as shown in FIG. 2, because this prevents air from pooling in the chamber.

[0076] The hollow fiber membrane 2426 has a structure of many hollow fine fibers with one end closed, and the membrane surface is gas permeable. The other end of the fine fiber structure of the hollow fiber membrane 2426 is connected to a gas outlet 2425 to which a vacuum path 250 is connected. The pressure inside the hollow fiber membrane 2426 is reduced by suction with a vacuum pump 249. In this state, ink comes into contact with the membrane surface of the hollow fiber membrane 2426, and only the dissolved gas in the ink selectively permeates the membrane surface, degassing the ink. The dissolved gas that has passed through the hollow fiber membrane 2426 flows down the vacuum path 250.

[0077] FIG. 3A is a schematic cross-sectional view showing the internal configuration of the central tube of an external reflux-type degassing module. FIG. 3B is a cross-sectional view of the plane taken along line IVB-IVB in FIG. 3A . The degassing module 252 preferably includes a heating unit 2427 (ink heating unit) inside the central tube 2424. The heating unit 2427 is configured, for example, by a stainless steel rod-shaped member having a heating wire and a thermocouple inside. By locating the heating unit 2427 in the center of the degassing module 242, the ink in the degassing module 242 can be uniformly and efficiently heated, allowing the ink to reach the desired temperature in a short time. Furthermore, since the entire ink in the degassing module 242 can be uniformly heated, it is possible to prevent localized unheated ink areas in the corners of the degassing module 242. By uniformly and efficiently heating the ink, the degassing efficiency and ink delivery rate can be improved, and the ink viscosity can be sufficiently reduced, suppressing ink ejection failures.

[0078] The temperature of the heating unit 2427 is controlled by a control unit. The control unit detects the temperature of the heating unit 2427 using, for example, a thermocouple built into the heating unit 2427 and performs on / off control using a target temperature that is set appropriately depending on the type of liquid. The shape and configuration of the heating unit 2427 may be any shape and configuration as long as it can heat the ink in the degassing module 2422 and control the heating temperature. As described above, the shape and configuration of the heating unit 2427 may also be configured so that the heating unit 2427 itself generates heat. The heating unit 2427 may be configured, for example, so that a heating element itself is provided outside the degassing module 2422 and heats the inside of the degassing module 242 by transferring heat from the heating element to the heating unit 2427.

[0079] Furthermore, a second heating unit 2428 (ink heating unit) that heats the liquid inside the degassing module 242 is provided on the outer surface of the degassing module 242. That is, the second heating unit 2428 is formed in a flat shape and is provided so as to cover the outer peripheral surface of the outer shell 2421 of the degassing module 242. For example, a rubber heater or the like is used as this second heating unit 2428. The second heating unit 2428 is provided with a temperature sensor such as a thermistor (not shown), and is controlled to turn on and off by a control unit in the same way as the heating unit 2427. By providing this second heating unit 2428, the ink inside the degassing module can be heated to the target temperature in an even shorter time.

[0080] The vacuum pump 249 shown in Figure 1 is a diaphragm pump that includes a pump chamber and a drive source. The pump chamber includes an expandable diaphragm. The drive source operates the diaphragm so that the volume of the pump chamber expands and contracts. The pump chamber includes an intake port with a check valve that only allows fluid to flow in from the outside, and an exhaust port with a check valve that only allows fluid to flow out from the inside.

[0081] The pressure sensor 251 detects the air pressure in the vacuum path 250 and outputs the result to the control unit. The control unit controls the driving of the vacuum pump 249 based on the detection result from the pressure sensor 251.

[0082] The atmosphere release valve 252 is an electromagnetic valve that can switch the vacuum path 250 between an airtight state and an atmosphere-open state in accordance with an operation command from the control unit.

[0083] The liquid feed pump 243 sends the ink that has flowed out from the ink outlet 2423 of the degassing module 242 to the second sub-tank 245. A check valve 244 is provided between the liquid feed pump 243 and the second sub-tank 245, and prevents the ink that has been sent to the second sub-tank 245 from flowing back.

[0084] The above-described degassing module 242 is an external reflux type hollow fiber membrane degassing module from the viewpoint of preferable degassing efficiency and processing flow rate, but this is not limiting and other types, such as an internal reflux type, may also be used. Furthermore, commercially available products can also be used as external reflux type hollow fiber degassing modules. Examples of commercially available products include SEPAREL EF-002A-P and SEPAREL EF-004P from Dainippon Ink and Chemicals, Inc.

[0085] (Degassing Device Using Ultrasonic Waves) The degassing device may use ultrasonic waves to degas the ink. By using ultrasonic waves to degas the ink, the ink can be degassed without heating, preventing the generation of solids and improving the fluidity of the ink. The method of irradiating the ink with ultrasonic waves is not particularly limited. For example, an ultrasonic vibrator that generates ultrasonic waves is provided in an ink tank used for degassing. Then, the ultrasonic vibrator is driven while ink is contained in the ink tank, thereby irradiating the ink with ultrasonic waves. The ultrasonic vibrator may be provided inside the ink tank used for degassing, and irradiate the ink directly. Alternatively, the ultrasonic vibrator may be provided outside the ink tank used for degassing, and irradiate the ink indirectly through the tank wall or other liquid. When an ultrasonic vibrator is provided inside the ink tank where degassing is performed, ultrasonic wave loss is reduced if the ultrasonic vibrator is immersed entirely or partially in the ink when generating ultrasonic waves. Therefore, ink can be degassed with less energy.

[0086] When ink is irradiated with ultrasonic waves, the ink vibrates, causing the gas dissolved in the ink to gather and precipitate as bubbles, a phenomenon known as cavitation. The bubbles precipitated by cavitation rise to the ink surface and exit the ink, reducing the amount of gas dissolved in the ink.

[0087] Furthermore, ink irradiated with ultrasonic waves has good fluidity even without heating. This is thought to be because the ink vibrates due to ultrasonic irradiation, which breaks down the gelling agent's aggregation and disperses it. In particular, when a crystalline gelling agent is used, the gelling agent may crystallize and form large lumps in the ink when the ink temperature is low, which can reduce the fluidity of the ink. In contrast, in the present invention, the crystalline structure of the gelling agent is broken down by ultrasonic irradiation, allowing the gelling agent to disperse in the ink, which is thought to improve the fluidity of the ink without heating.

[0088] In order to ensure the fluidity of the ink, it is preferable that the viscosity of the ink after being irradiated with ultrasonic waves is in the range of 50 to 300 mPa·s at 30°C.

[0089] The ultrasonic oscillation frequency and irradiation energy can be appropriately set depending on the composition or viscosity of the ink. If the ultrasonic oscillation frequency and irradiation energy are set so that the ultrasonic waves reach the entire ink without attenuation, the entire ink can be sufficiently degassed. The ultrasonic oscillation frequency and irradiation energy can also be set so that the viscosity of the ink after ultrasonic irradiation is in the range of 50 to 300 mPa·s at 30°C. Furthermore, the ultrasonic oscillation frequency and irradiation energy can also be set so that the amount of dissolved oxygen in the ink after degassing is in the range of 0.1 to 10.0 mg / l ppm, for example.

[0090] The oscillation frequency of the ultrasonic waves irradiated onto the ink can be in the range of 5 to 50 kHz, and preferably in the range of 10 to 30 kHz. By setting the oscillation frequency to 5 kHz or higher, sufficient degassing can be achieved, and by setting the oscillation frequency to 50 kHz or lower, aggregation of the coloring material due to vibration is less likely to occur. Furthermore, by setting the oscillation frequency of the ultrasonic waves in the range of 10 to 30 kHz, aggregation of the coloring material is even less likely to occur. This makes it possible to achieve a uniform glossiness of the image and to reduce the occurrence of white streaks in the image.

[0091] The irradiation energy of the ultrasonic waves irradiated to the ink is 1×10 ４ ~1 x 10 ５J, and can be in the range of 2×10 ４ ~8 x 10 ４ It is preferable that the irradiation energy is in the range of 1×10 ４ By setting the irradiation energy at 1×10 or more, degassing can be performed sufficiently. ５ By setting the value to J or less, aggregation of the coloring material due to vibration can be prevented.

[0092] When ultrasonic waves are applied to the ink, the pressure inside the ink tank where degassing is performed may be normal pressure, or may be reduced. By reducing the pressure inside the ink tank where degassing is performed, air bubbles are more likely to escape from the ink. The pressure inside the ink tank where degassing is performed when ultrasonic waves are applied to the ink can be set to, for example, a range of 0 to 1 atmosphere (a range of 0 to 101.3 kPa).

[0093] The temperature of the ink when irradiated with ultrasonic waves is preferably equal to or higher than the ink's freezing point but lower than the ink's gelling temperature. By irradiating the ink with ultrasonic waves at a temperature lower than the ink's gelling temperature, it is possible to prevent the photocurable compound from volatilizing from the ink that has been liquefied (sol) by heating, and to prevent the photocurable compound from deteriorating due to heating. The ink temperature is preferably 10°C or more lower than the ink's gelling temperature, and more preferably 20°C or more lower.

[0094] By irradiating the ink with ultrasonic waves at a temperature below its gelation temperature, ink stored at near room temperature or cooled can be degassed without the need for a heating step. To facilitate the introduction of the ink before degassing into an ink tank where degassing will be performed, the ink before degassing may be heated to impart fluidity. In this case, too, it is preferable to adjust the energy applied to the ink during heating so that the ink temperature does not rise above its gelation temperature. Furthermore, the ink vibrates when irradiated with ultrasonic waves, and the vibration energy may raise the ink temperature. Therefore, it is also preferable to adjust the oscillation frequency and irradiation energy of the ultrasonic waves so that the ink temperature does not rise above its gelation temperature.

[0095] <Second Sub-Tank> The second sub-tank 245 is a small ink chamber that temporarily stores ink that has been degassed by the degassing device 280. The second sub-tank has approximately the same capacity as the first sub-tank 241, although this is not particularly limited. The ink in the second sub-tank 245 is connected to the inlets 240a of each recording head 24a, and ink is supplied to each recording head 24a in an amount corresponding to the amount of ink ejected from the nozzles. The second sub-tank 245 is provided with a second float sensor 245a. Based on data detected by the second float sensor 245a on the liquid level position, the control unit operates the liquid feed pump 243 to store a predetermined amount of ink.

[0096] The second sub-tank 245 is preferably provided with an ink heating section 270, similar to the first sub-tank 241. The ink in the second sub-tank 247 is heated by the ink heating section 270, allowing the viscosity of the ink to be adjusted when ejected. The ink heating section 270 preferably heats the ink so that the temperature of the ink when ejected is 40°C or higher, and preferably heats the ink in the second sub-tank 247 to a temperature of 40 to 60°C. The ink heating section 270 is preferably provided in contact with the side wall, bottom wall, etc. of the second sub-tank 247.

[0097] The control unit controls the temperature of the ink heating unit 270. The control unit detects the temperature of the ink heating unit 270 using a thermocouple built into the ink heating unit 270, for example, and performs on / off control using a target temperature that is set appropriately depending on the type of liquid.

[0098] Ink that is not ejected from the nozzles of the recording head 24a can be returned from the outlet 240b via the recovery path 241b and the valve 241c to the first sub-tank 241. For example, when it is necessary to drain ink from the ink flow path 24b during maintenance of the recording head 24a, the valve 241c can be opened to recover the ink from the recording head 24a without discarding it.

[0099] The control unit controls the operation of each unit of the inkjet recording apparatus 1 and supervises the overall operation. The control unit includes a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), etc. The control unit reads out various processing programs, such as a system program, stored in the ROM and loads them into the RAM, and the programs loaded into the RAM are executed by the CPU. This allows various control processes, such as image formation processing and the above-mentioned temperature control, to be executed.

[0100] In the inkjet recording apparatus having the above-described configuration, the ink in the ink path 24b is heated and kept warm by the ink heating unit 270, and is set so that the ink temperature is 40° C. or higher when ejected from the recording head.

[0101] In the inkjet recording apparatus 1 described above, the ink heating unit 270 is provided in the first sub-tank 241, the second sub-tank 247, and the degassing module 242, but this is not limiting and the ink heating unit 270 may be provided before the dehydration unit 250. The ink heating unit 270 may also be provided by incorporating a heater inside the recording head 24a. In addition, the degassing unit 280 is provided after the first sub-tank 241 and degasses after heating, but this is not limiting and the ink heating unit 270 may be provided before the first sub-tank 241 and degassses before heating.

[0102] The ink ejected from the nozzle is irradiated with actinic rays by an actinic ray irradiation unit. The actinic ray irradiation unit has, for example, a fluorescent tube such as a low-pressure mercury lamp, and causes the fluorescent tube to emit light to irradiate energy rays such as ultraviolet rays. Examples of fluorescent tubes that emit ultraviolet rays include low-pressure mercury lamps and mercury lamps with operating pressures of approximately several hundred Pa to 1 MPa. Examples of such fluorescent tubes include light sources that can be used as germicidal lamps, cold cathode tubes, ultraviolet laser light sources, metal halide lamps, and light-emitting diodes. Among these, light sources that can irradiate ultraviolet rays with higher illuminance and lower power consumption (e.g., light-emitting diodes) are more desirable. Furthermore, the energy rays are not limited to ultraviolet rays, and any energy rays that have the property of curing the ink depending on the properties of the ink may be used, and the light source may be selected depending on the wavelength of the energy rays, etc.

[0103] 4. Ink Composition The ink used in the coating film forming method of the present invention contains a polymerizable monomer, a blocked isocyanate, and a photopolymerization initiator. The polymerizable monomer, the blocked isocyanate, the photopolymerization initiator, etc. will be described below.

[0104] <Polymerizable Monomer> The polymerizable monomer according to the present invention is a monofunctional (meth)acrylate or a polyfunctional (meth)acrylate. A monofunctional (meth)acrylate compound is a compound having one (meth)acrylate group in one molecule. Specific examples of the monofunctional (meth)acrylate compound include glycidyl (meth)acrylate, 3,4-epoxycyclohexyl (meth)acrylate, methylglycidyl (meth)acrylate, 3-methyl-3-(meth)acryloxymethyloxetane, 3-ethyl-3-(meth)acryloxymethyloxetane, 3-methyl-3-(meth)acryloxyethyloxetane, 3-ethyl-3-(meth)acryloxyethyloxetane, 2-phenyl-3-(meth)acryloxymethyl ... oxetane, 2-trifluoromethyl-3-(meth)acryloxymethyloxetane, 4-trifluoromethyl-2-(meth)acryloxymethyloxetane, (meth)acrylic acid, methyl (meth)acrylate, ethyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, iso-butyl (meth)acrylate, t-butyl (meth)acrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate, tricyclo[5.2.1.0 2,6 ] decanyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, isobornyl (meth)acrylate, phenyl (meth)acrylate, glycerol mono(meth)acrylate, tetrahydrofurfuryl (meth)acrylate, (meth)acrylate of an ethylene oxide adduct of lauryl alcohol, succinic acid mono[2-(meth)acryloyloxyethyl], maleic acid mono[2-(meth)acryloyloxyethyl], 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, or 1,4-cyclohexanedimethanol mono(meth)acrylate, n-butyl (meth)acrylate, stearyl (meth)acrylate, lauryl (meth)acrylate, isodecyl (meth)acrylate, tridecyl (meth)acrylate, and 2-(2-ethoxyethoxy)ethyl (meth)acrylate.

[0105] In the present invention, the term "polyfunctional monomer" refers to a compound having two or more functional groups. From the viewpoint of curing by radical polymerization, examples of the functional group include an ethylenically unsaturated bond-containing acryloyl group, methacryloyl group, allyl group, vinyl group, vinyl ester group, etc. However, the functional group is not limited to the above-mentioned groups. From the viewpoint of the physical properties of the coating film, it is preferable that the polymerizable monomer used in the present invention contains a polyfunctional monomer.

[0106] Examples of bifunctional acrylates include triethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate, dipropylene glycol diacrylate (DPGDA), tripropylene glycol diacrylate, polypropylene glycol diacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, 1,9-nonanediol diacrylate, neopentyl glycol diacrylate, bisphenol A PO (propylene oxide) adduct diacrylate, hydroxypivalic acid neopentyl glycol diacrylate, polytetramethylene glycol diacrylate, tricyclodecane dimethanol dimethacrylate, and tricyclodecane dimethanol diacrylate.

[0107] Examples of tri- or higher functional acrylates include trimethylolpropane triacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol hexaacrylate, ditrimethylolpropane tetraacrylate, glycerin propoxy triacrylate, and pentaerythritol ethoxy tetraacrylate.

[0108] Of the above acrylates, phenoxyethyl acrylate, o-phenylphenol acrylate, and 2-hydroxy-3-phenoxypropyl acrylate are preferred from the viewpoint of suppressing cure shrinkage.

[0109] From the viewpoint of rapid curing, neopentyl glycol diacrylate, tricyclodecane dimethanol diacrylate, bisphenol A PO adduct diacrylate, and hydroxypivalic acid neopentyl glycol diacrylate are preferred.

[0110] The acrylate may be a modified product. Examples of the modified acrylate include ethylene oxide-modified acrylates including ethylene oxide-modified trimethylolpropane triacrylate and ethylene oxide-modified pentaerythritol tetraacrylate, propylene oxide-modified acrylates including propylene oxide-modified trimethylolpropane triacrylate and propylene oxide-modified pentaerythritol tetraacrylate, caprolactone-modified acrylates including caprolactone-modified trimethylolpropane triacrylate, and caprolactam-modified acrylates including caprolactam-modified dipentaerythritol hexaacrylate.

[0111] (Polyfunctional (meth)acrylate with ClogP value in the range of 2.0 to 7.0) The ink of the present invention preferably contains a polymerizable monomer with an octanol / water partition coefficient (ClogP) value in the range of 2.0 to 7.0. That is, the ink of the present invention preferably contains a polyfunctional (meth)acrylate with a ClogP value in the range of 2.0 to 7.0. When the ClogP value is in the range of 2.0 to 7.0, amines derived from blocked isocyanates hydrolyzed by moisture in the ink and hydrolysates of (meth)acrylates react with components in the ink to form reaction products. Furthermore, the solubility of the reaction product formed is improved, which can prevent the elution of cured products and foreign matter as solids and improves ejection stability.

[0112] Examples of polyfunctional (meth)acrylate monomers having a ClogP value in the range of 2.0 to 7.0 include EO-modified trimethylolpropane triacrylate (ClogP 4.0), dipropylene glycol diacrylate (ClogP 2.0), 1,10-decanediol dimethacrylate (ClogP 5.75), tricyclodecane dimethanol diacrylate (ClogP 4.69), and tricyclodecane dimethanol dimethacrylate (ClogP 5.12).

[0113] Furthermore, as the polyfunctional (meth)acrylate according to the present invention, the polyfunctional (meth)acrylates shown below can also be used.

[0114]

[0115] From the viewpoint of ejection stability, it is also preferable that the ink contains 30% by mass or more of a polyfunctional (meth)acrylate monomer having a ClogP value in the range of 2.0 to 7.0, based on the total mass of the ink. In particular, it is preferable that the ink of the present invention contains 30% to 50% by mass of a polyfunctional (meth)acrylate monomer having a ClogP value in the range of 2.0 to 7.0, based on the total mass of the ink.

[0116] In the present invention, the "ClogP value" refers to a logP value calculated by calculation. The ClogP value can be calculated by a fragment method, an atomic approach method, or the like. More specifically, the ClogP value can be calculated using the fragment method described in the following document or the following commercially available software package 1 or 2: Document: C. Hansch and A. Leo, "Substitute Constants for Correlation Analysis in Chemistry and Biology" (John Wiley & Sons, New York, 1969) Software package 1: MedChem Software (Release 3.54, August 1991, Medicinal Chemistry Project, Pomona College, Claremont, CA) Software package 2: ChemDraw Ultra ver. 20.0.0.47 (PerkinElmer Informatics) The numerical values ​​of ClogP values ​​described in the present specification and elsewhere are "ClogP values" calculated using software package 2.

[0117] (Bisphenol A Structure) The polyfunctional (meth)acrylate preferably has at least one type of bisphenol A structure. Preferred examples of the polyfunctional (meth)acrylate monomer having a bisphenol A structure include the above-mentioned bisphenol A PO adduct diacrylate, EO-modified bisphenol A diacrylate, and bisphenol A-type epoxy acrylate.

[0118] (Hydroxy Value) The sum of the hydroxy values ​​of the compounds having hydroxy groups contained in the ink of the present invention is preferably in the range of 0.05 to 60 mgKOH / g. When the hydroxy value is within this range, the generation of solids is suppressed even when the ink contains water, resulting in excellent storage stability. Methods for achieving a hydroxy value in the range of 0.05 to 60 mgKOH / g include appropriately selecting the compounds having hydroxy values ​​contained in the ink, controlling the charge composition of the compounds having hydroxy values, and purifying the compounds having hydroxy values. In the present invention, the term "hydroxy value" refers to the amount (mg) of potassium hydroxide (KOH) required to neutralize acetic acid bonded to hydroxy groups when 1 g of the ink of the present invention is acetylated. The hydroxy value can be calculated according to the method described in JIS K0070-1992, or calculated from the charge composition of the compounds having hydroxy groups in 1 g of ink.

[0119] The hydroxy value in the present invention is determined from the charge composition of the compound having a hydroxy group in 1 g of ink using the above calculation method. A specific calculation method is as shown in formula (a) below. Hydroxy value [mg KOH / g] = A [mol] × (number of hydroxy groups in the compound having a hydroxy group) × B [mg / mol] (a) In formula (a) above, "A" represents the number of moles of the compound having a hydroxy group in 1 g of ink. Furthermore, "B" represents the molecular weight of 1 mol of potassium hydroxide (56,000 [mg / mol]). When the ink contains multiple types of compounds having a hydroxy group, the hydroxy value is calculated for each compound having a hydroxy group using formula (a) above. The sum of the obtained hydroxy value values ​​is then regarded as the hydroxy value for 1 g of ink.

[0120] The compound having a hydroxy group is not particularly limited as long as it has a hydroxy group in its structure. Examples of hydroxyalkyl(meth)acrylates include 2-hydroxyethyl(meth)acrylate, 2-hydroxypropyl(meth)acrylate, and 4-hydroxybutyl(meth)acrylate. Examples of hydroxy(meth)acrylates having an alicyclic structure include 1,4-cyclohexanedimethanol mono(meth)acrylate.

[0121] Examples of epoxy (meth)acrylates include aliphatic alcohol-based epoxy (meth)acrylates, aliphatic polyhydric alcohol-based epoxy (meth)acrylates, and phenol-based epoxy (meth)acrylates. Examples of epoxy (meth)acrylates include polyhydric phenol-based epoxy (meth)acrylates, alicyclic carboxylic acid-based epoxy acrylates, and aromatic carboxylic acid-based epoxy (meth)acrylates. Commercially available epoxy (meth)acrylates can be used. Examples of such commercially available products include DENACOL ACRYLATE DA-111, DA-141, DA-212, DA-250, DA-314, DA-721, DA-722, DA-911M, DA-920, and DA-931. All of these commercially available products are manufactured by Nagase ChemteX Corporation. These hydroxyl group-containing compounds can be used alone or in combination of two or more.

[0122] In the ink of the present invention, the content of the polymerizable monomer is preferably in the range of 40 to 90% by mass, and more preferably in the range of 60 to 85% by mass, based on the total mass of the ink. By keeping the content within this range, coating adhesion is improved.

[0123] <Blocked Isocyanate> A blocked isocyanate is a compound having an isocyanate group, in which the isocyanate group is blocked with a blocking agent. Hereinafter, the compound having an isocyanate group will also be referred to as an "isocyanate compound." Heating dissociates the blocking agent from the blocked isocyanate, activating the isocyanate group.

[0124] The ink of the present invention has storage stability because the isocyanate groups are blocked and non-reactive until it is applied to a recording medium. After application, heating the ink at a temperature equal to or higher than the temperature at which the blocking agent dissociates generates isocyanate groups. These groups then react with hydroxyl groups and / or carboxyl groups of the monomers contained in the ink, causing the ink to harden and form a coating film.

[0125] (Isocyanate Compound) From the viewpoint of curability, the isocyanate compound is preferably a polyfunctional isocyanate. The polyfunctional isocyanate is not particularly limited as long as it is a compound having two or more isocyanate groups in the molecule. Specific examples of the polyfunctional isocyanate include aromatic polyisocyanates such as 2,4-tolylene diisocyanate (2,4-TDI), 2,6-tolylene diisocyanate (2,6-TDI), 4,4'-diphenylmethane diisocyanate (4,4'-MDI), 2,4'-diphenylmethane diisocyanate (2,4'-MDI), 1,4-phenylene diisocyanate, xylylene diisocyanate (XDI), tetramethylxylylene diisocyanate (TMXDI), tolidine diisocyanate (TODI), and 1,5-naphthalene diisocyanate (NDI); hexamethylene diisocyanate; aliphatic polyisocyanates such as transcyclohexane-1,4-diisocyanate, isophorone diisocyanate (IPDI), H6XDI (hydrogenated XDI), H12MDI (hydrogenated MDI), and H6TDI (hydrogenated TDI); polyisocyanates such as polymethylene polyphenylene polyisocyanate; and biuret, isocyanurate, and carbodiimide-modified products thereof. The ink of the present invention may use any one of these isocyanates alone, or two or more of them may be used.

[0126] (Blocking Agent) Known blocking agents can be used as the blocking agent. Examples of the blocking agent include alcohols such as ethanol, n-propanol, isopropanol, t-butanol, and isobutanol, phenols such as phenol, chlorophenol, cresol, xylenol, and p-nitrophenol, alkylphenols such as p-t-butylphenol, psec-butylphenol, p-sec-aminophenol, p-octylphenol, and p-nonylphenol, basic nitrogen-containing compounds such as 3-hydroxypyridine, 8-hydroxyquinoline, and 8-hydroxyquinaldine, and active metal ions such as diethyl malonate, ethyl acetoacetate, and acetylacetone. Examples of suitable amines include ethylene compounds, acid amides such as acetamide, acrylamide, and acetanilide, acid imides such as succinimide and maleimide, imidazoles such as 2-ethylimidazole and 2-ethyl-4-methylimidazole, pyrazoles such as pyrazole, 3-methylpyrazole, and 3,5-dimethylpyrazole, lactams such as 2-pyrrolidone and ε-caprolactam, oximes of ketones or aldehydes such as acetoxime, methyl ethyl ketone oxime, cyclohexanone oxime, butanone oxime, and acetaldoxime, ethyleneimine, and bisulfites.

[0127] The blocking agent is preferably at least one compound selected from the group consisting of oxime compounds, pyrazole compounds, and active ethylene compounds, in terms of ink storage stability and thermal dissociation properties. Examples of oxime compounds include formamide oxime, acetaldoxime, acetoxime, methyl ethyl ketone oxime, cyclohexanone oxime, and butanone oxime (MEKO). Examples of pyrazole compounds include pyrazole, 3-methylpyrazole, and 3,5-dimethylpyrazole. Examples of active ethylene compounds include dimethyl malonate, diethyl malonate (DEM), methyl acetoacetate, ethyl acetoacetate, and acetylacetone.

[0128] An example of the polyfunctional isocyanate compound having an isocyanate group protected with a blocking agent is 2-[(3,5-dimethylpyrazolyl)carbonylamino]ethyl methacrylate. An example of the polyfunctional isocyanate compound having an isocyanate group protected with a blocking agent is 2-[(3-butylidene)aminooxycarbonylamino]ethyl methacrylate. An example of the polyfunctional isocyanate compound having an isocyanate group protected with a blocking agent is 2-[(3,5-dimethylpyrazolyl)carbonylamino]ethyl acrylate. An example of the polyfunctional isocyanate compound having an isocyanate group protected with a blocking agent is 2-[(3-butylidene)aminooxycarbonylamino]ethyl acrylate.

[0129] From the viewpoint of ink storage stability and coating film performance, it is preferable that the blocked isocyanate has an aromatic ring. Blocked isocyanates having an aromatic ring are not particularly limited, but examples include aromatic polyisocyanates such as 2,4-tolylene diisocyanate (2,4-TDI), 2,6-tolylene diisocyanate (2,6-TDI), 4,4'-diphenylmethane diisocyanate (4,4'-MDI), 2,4'-diphenylmethane diisocyanate (2,4'-MDI), 1,4-phenylene diisocyanate, xylylene diisocyanate (XDI), tetramethylxylylene diisocyanate (TMXDI), tolidine diisocyanate (TODI), and 1,5-naphthalene diisocyanate (NDI). Furthermore, the blocking agent for the blocked isocyanate may contain an aromatic group, and blocking agents containing a benzene ring and blocking agents containing a heteroaromatic ring are preferred. In particular, it is preferable to contain dimethylpyrazole (DMP) as a blocking agent for the blocked isocyanate containing an aromatic group.

[0130] The blocked isocyanate may contain a polyisocyanate structure. Examples of the polyisocyanate structure include three types: isocyanurate, biuret, and adduct. From the viewpoints of curability and coating film performance, the blocked isocyanate of the present invention is preferably an isocyanurate or biuret type, and particularly preferably an isocyanurate type.

[0131] The content of the blocked isocyanate is preferably in the range of 0.1 to 20 parts by mass, and more preferably in the range of 1 to 10 parts by mass, per 100 parts by mass of the polymerizable monomer. When the content of the blocked isocyanate is 0.1 part by mass or more, sufficient curing by heat is achieved. When the content of the blocked isocyanate is 20 parts by mass or less, the ink has excellent storage stability at high temperatures.

[0132] The blocking agent may be used alone or in combination of two or more kinds. Alternatively, a plurality of blocked isocyanates blocked with a single blocking agent or two or more kinds of blocking agents may be used. Examples of commercially available blocked isocyanates include BI7774, BI7779, BI7950, BI7960, BI7961, BI7981, BI7982, BI7991, and BI7992 (all manufactured by LANXESS Corporation), MFK60X (manufactured by Asahi Kasei Chemicals Corporation), VPLS2253 and BL4265SN (both manufactured by Sumika Bayer Urethane Co., Ltd.), PU5211 and PU5210 (both manufactured by Leeson Polyurethanes), Karenz MOI-BP (2-[(3,5-dimethylpyrazolyl)carbonylamino]ethyl methacrylate), and Karenz MOI-BM (2-(0-[1'-methylpropylideneamino]carboxyamino)ethyl methacrylate) (both manufactured by Showa Denko K.K.).

[0133] <Photopolymerization initiator> When the polymerizable monomer (polyfunctional (meth)acrylate monomer) is a radically polymerizable compound, it is preferable to use a photoradical initiator as the photopolymerization initiator according to the present invention. Furthermore, when the polymerizable monomer is a cationically polymerizable compound, it is preferable to use a photoacid generator as the photopolymerization initiator according to the present invention. The ink of the present invention may contain only one type of photopolymerization initiator, or two or more types of photopolymerization initiators. The photopolymerization initiator may be a combination of both a photoradical initiator and a photoacid generator.

[0134] Photoradical initiators include cleavage-type radical initiators and hydrogen abstraction-type radical initiators. Examples of cleavage-type radical initiators include acetophenone-based initiators, benzoin-based initiators, acylphosphine oxide-based initiators, and benzyl and methylphenyl glyoxyesters.

[0135] Examples of acetophenone-based initiators include diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, benzil dimethyl ketal, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one, 4-(2-hydroxyethoxy)phenyl-(2-hydroxy-2-propyl)ketone, 1-hydroxycyclohexyl-phenyl ketone, 2-methyl-2-morpholino(4-thiomethylphenyl)propan-1-one, and 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone.

[0136] Examples of benzoin-based initiators include benzoin, benzoin methyl ether, and benzoin isopropyl ether. Examples of acylphosphine oxide-based initiators include 2,4,6-trimethylbenzoin diphenylphosphine oxide. Examples of hydrogen abstraction type radical initiators include benzophenone-based initiators, thioxanthone-based initiators, aminobenzophenone-based initiators, and 10-butyl-2-chloroacridone. Furthermore, examples of hydrogen abstraction type radical initiators include 2-ethylanthraquinone, 9,10-phenanthrenequinone, and camphorquinone.

[0137] Examples of benzophenone-based initiators include benzophenone, o-benzoylmethylbenzoate-4-phenylbenzophenone, 4,4'-dichlorobenzophenone, and hydroxybenzophenone. Examples of benzophenone-based initiators include 4-benzoyl-4'-methyl-diphenyl sulfide, acrylated benzophenone, 3,3',4,4'-tetra(t-butylperoxycarbonyl)benzophenone, and 3,3'-dimethyl-4-methoxybenzophenone. Examples of thioxanthone-based initiators include 2-isopropylthioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, and 2,4-dichlorothioxanthone. Examples of aminobenzophenone-based initiators include Michler's ketone and 4,4'-diethylaminobenzophenone. Examples of the photoacid generator include the compounds described in "Organic Materials for Imaging," edited by Organic Electronics Materials Research Group, Bunshin Publishing (1993), pp. 187-192.

[0138] The content of the photopolymerization initiator may be within a range that allows the ink to be sufficiently cured, and may be, for example, within a range of 0.01 to 10% by mass relative to the total mass of the ink of the present invention. Examples of commercially available photopolymerization initiators include Omnirad TPO (manufactured by IGM), Omnirad 819 (manufactured by IGM), and Omnirad 379 (manufactured by IGM). Further, examples of commercially available photopolymerization initiators include Speedgure ITX (manufactured by Sartomer) and Speedcure EPD (manufactured by Sartomer).

[0139] <Polymerization inhibitor> The ink of the present invention preferably further contains a polymerization inhibitor. By containing a polymerization inhibitor, it is possible to reduce the adhesion between multiple curable compounds. The term "polymerization inhibitor" includes all compounds added to suppress polymerization reactions during the preparation of an ink containing a polymerizable monomer or during storage after preparation.

[0140] In the present invention, various known polymerization inhibitors can be used. The polymerization inhibitor preferably contains any one of an N-oxyl-based polymerization inhibitor, a phenol-based polymerization inhibitor containing an o-t-butyl group, or a polymerization inhibitor having two or more aromatic rings.

[0141] Among these, it is more preferable to contain an N-oxyl-based polymerization inhibitor from the viewpoint of adhesion to a printed wiring board. In the ink of the present invention, the content of the polymerization inhibitor is preferably in the range of 0.05 to 0.5% by mass based on the total mass of the ink.

[0142] (N-oxyl-Based Polymerization Inhibitor) Examples of the N-oxyl-based polymerization inhibitor include 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO), 4-hydroxy-2,2,6,6-tetramethyl-piperidine-N-oxyl, 4-oxo-2,2,6,6-tetramethyl-piperidine-N-oxyl, 4-methoxy-2,2,6,6-tetramethyl-piperidine-N-oxyl, 4-acetoxy-2,2,6,6-tetramethyl-piperidine-N-oxyl, and Irgastab (registered trademark) UV10 (manufactured by BASF).

[0143] (Phenol-Based Polymerization Inhibitors) Examples of phenol-based polymerization inhibitors include 2,6-di-tert-butylphenol, 2,4-di-tert-butylphenol, and 2-tert-butyl-4,6-dimethylphenol. Examples of phenol-based polymerization inhibitors include 2,6-di-tert-butyl-4-methylphenol and 2,4,6-tri-tert-butylphenol. Examples of phenol-based polymerization inhibitors include 2,6-di-t-butyl-p-cresol (butylated hydroxytoluene: BHT), 4-methoxyphenol, and 2-methoxy-4-methylphenol.

[0144] (Quinone-Based Polymerization Inhibitor) Examples of quinone-based polymerization inhibitors include hydroquinone, methoxyhydroquinone, benzoquinone, 1,4-naphthoquinone, and p-tert-butylcatechol.

[0145] (Amine-Based Polymerization Inhibitor) Examples of the amine-based polymerization inhibitor include alkylated diphenylamine, N,N'-diphenyl-p-phenylenediamine, and phenothiazine.

[0146] (Other Polymerization Inhibitors) Examples of other polymerization inhibitors include copper dithiocarbamate-based polymerization inhibitors such as copper dimethyldithiocarbamate, copper diethyldithiocarbamate, and copper dibutyldithiocarbamate.

[0147] These may be contained alone or in combination of two or more. Among these, N-oxyl-based and quinone-based polymerization inhibitors are preferred. As the inhibitor, 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) is preferred. As the inhibitor, 2,6-di-t-butyl-p-cresol (butylated hydroxytoluene: BHT) and 2,4-di-tert-butylphenol are preferred. As a polymerization inhibitor having two or more aromatic rings, naphthoquinone and the like are preferred.

[0148] <Other Components> (Surfactant) The ink of the present invention may further contain a surfactant, if necessary. Examples of surfactants include anionic surfactants, nonionic surfactants, cationic surfactants, and silicone-based and fluorine-based surfactants. Examples of the anionic surfactants include dialkyl sulfosuccinates, alkyl naphthalene sulfonates, and fatty acid salts. Examples of the nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene alkyl allyl ethers, acetylene glycols, and polyoxyethylene-polyoxypropylene block copolymers. Examples of the cationic surfactants include alkylamine salts and quaternary ammonium salts.

[0149] (Colorant) The ink of the present invention may further contain a colorant, if necessary. The colorant may be a pigment or a dye, but is preferably a pigment from the viewpoints of good dispersibility in the constituent components of the ink and excellent weather resistance. The pigment is not particularly limited, and examples thereof include organic pigments or inorganic pigments having the following numbers listed in the Color Index.

[0150] The ink of the present invention may contain only one type of colorant, or may contain two or more types of colorants, and may be toned to a desired color. The content of the colorant is preferably within a range of 0.1 to 20% by mass, and more preferably within a range of 0.2 to 10% by mass, based on the total mass of the ink.

[0151] (Pigment) <<Red or Magenta Pigment>> Examples of red or magenta pigments include Pigment Red 3, 5, 19, 22, 31, 38, 43, 48:1, 48:2, 48:3, 48:4, 48:5, 49:1, 53:1, 57:1, 57:2, 58:4, 63:1, 81, 81:1, 81:2, 81:3, 81:4, 88, 104, 108, 112, 122, 123, 144, 146, 149, 166, 168, 169, 170, 177, 178, 179, 184, 185, 208, 216, 226, 257, and Pigment Violet. Pigment Orange 13, 16, 20, 36, or a mixture thereof.

[0152] <Blue or Cyan Pigment> Examples of blue or cyan pigments include pigments selected from Pigment Blue 1, 15, 15:1, 15:2, 15:3, 15:4, 15:6, 16, 17:1, 22, 27, 28, 29, 36, and 60, and mixtures thereof.

[0153] <Green Pigment> Examples of green pigments include pigments selected from Pigment Green 7, 26, 36, and 50, and mixtures thereof.

[0154] <<Yellow Pigment>> Examples of yellow pigments include pigments selected from Pigment Yellow 1, 3, 12, 13, 14, 17, 34, 35, 37, 55, 74, 81, 83, 93, 94, 95, 97, 108, 109, 110, 137, 138, 139, 147, 153, 154, 155, 157, 166, 167, 168, 180, 185, and 193, or mixtures thereof.

[0155] <<Black Pigment>> Examples of black pigments include pigments selected from Pigment Black 7, 28, and 26, and mixtures thereof.

[0156] <<Examples of Commercially Available Pigments>> Examples of commercially available pigments include Black Pigment (manufactured by Mikuni Co., Ltd.), Chromofine Yellow 2080, 5900, 5930, AF-1300, 2700L, Chromofine Orange 3700L, 6730, Chromofine Scarlet 6750, Chromofine Magenta 6880, 6886, 6891N, 6790, 6887, and Chromofine Violet. RE, Chromofine Red 6820, 6830, Chromofine Blue HS-3, 5187, 5108, 5197, 5085N, SR-5020, 5026, 5050, 4920, 4927, 4937, 4824, 4933GN-EP, 4940, 4973, 5205, 5208, 5214, 5221, 5000P, Chromofine Green 2GN, 2GO, 2G-550D, 5310, 5370, 6830, Chromofine Black A-1103, Seika Fast Yellow 10GH, A-3, 2035, 2054, 2200, 2270, 2300, 2400 (B), 2500, 2600, ZAY-260, 2700 (B), 2770, Seika Fast Red 8 040, C405(F), CA120, LR-116, 1531B, 8060R, 1547, ZAW-262, 1537B, GY, 4R-4016, 3820, 3891, ZA-215, Seikafast Carmine 6B1476T-7, 1483LT, 3840, 3870, Seikafast Bordeaux 10B-430, Seikalite Rose R40, Seikalite Violet B800, 7805, Seikafast Maroon 460N, Seikafast Orange 900, 2900, Seikalite Blue C718, A612, Cyanine Blue 4933M, 4933GN-EP, 4940, 4973 (all manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.; "Chromofine" is a registered trademark of the company); KET Yellow 401, 402, 403, 404, 405, 406, 416, 424, KET Orange 501, KET Red 301, 302, 303, 304, 305, 306, 307, 308, 309, 310, 336, 337, 338, 346, KET Blue 101, 102, 103, 104, 105, 106, 111, 118, 124, KET Green 201 (manufactured by DIC);Colortex Yellow 301, 314, 315, 316, P-624, 314, U10GN, U3GN, UNN, UA-414, U263, Finecol Yellow T-13, T-05, Pigment Yellow1705, Colortex Orange 202, Colortex Red101, 103, 115, 116, D3B, P-625, 102, H-1024, 105C, UFN, UCN, UBN, U3BN, URN, UGN, UG276, U456, U457, 105C, USN, Colortex Maroon601, Colortex Brown B610N, Colortex Violet 600, Pigment Red 122, Colortex Blue 516, 517, 518, 519, A818, P-908, 510, Colortex Green 402, 403, Colortex Black 702, U905 (all manufactured by Sanyo Dye Co., Ltd.; "Colortex" and "Finecol" are registered trademarks of the company); Lionol Yellow 1405G, Lionol Blue FG7330, FG7350, FG7400G, FG7405G, ES, ESP-S (all manufactured by Toyo Ink Co., Ltd.; "Lionol" is a registered trademark of the company), Toner Magenta E02, Permanent Rubin F6B, Toner Yellow HG, Permanent Yellow GG-02, Hostaperm Blue B2G (all manufactured by Hoechst Industries); Novoperm P-HG, Hostaperm Pink E, Hostaperm Blue B2G (all manufactured by Clariant; "Novoperm" and "Hostaperm" are registered trademarks of the company); carbon black #2600, #2400, #2350, #2200, #1000, #990, #980, #970, #960, #950, #850, MCF88, #750, #650, MA600, MA7, MA8, MA11, MA100, MA100R, MA77, #52, #50, #47, #45, #45L, #40, #33, #32, #30, #25, #20, #10, #5, #44, and CF9 (all manufactured by Mitsubishi Chemical);

[0157] <<Dispersion of Pigment>> The pigment can be dispersed using, for example, a ball mill, a sand mill, an attritor, a roll mill, an agitator, a Henschel mixer, a colloid mill, an ultrasonic homogenizer, a pearl mill, a wet jet mill, a paint shaker, or the like.

[0158] The pigment is preferably dispersed so that the volume average particle size of the pigment particles is preferably within the range of 0.08 to 0.5 μm. The pigment is also preferably dispersed so that the maximum particle size of the pigment particles is preferably within the range of 0.3 to 10 μm, more preferably within the range of 0.3 to 3 μm. The pigment dispersion is adjusted by selecting the pigment, dispersant, and dispersion medium, dispersing conditions, filtration conditions, etc.

[0159] Dispersant The ink of the present invention may further contain a dispersant to improve the dispersibility of the pigment. Examples of dispersants include carboxylic acid esters having a hydroxy group, salts of long-chain polyaminoamides and high-molecular-weight acid esters, salts of high-molecular-weight polycarboxylic acids, salts of long-chain polyaminoamides and polar acid esters, high-molecular-weight unsaturated acid esters, polymer copolymers, modified polyurethanes, modified polyacrylates, polyether ester-type anionic surfactants, naphthalenesulfonic acid-formalin condensate salts, aromatic sulfonic acid-formalin condensate salts, polyoxyethylene alkyl phosphate esters, polyoxyethylene nonylphenyl ether, and stearylamine acetate. Examples of commercially available dispersants include the Solsperse (registered trademark) series manufactured by Avecia and the PB series manufactured by Ajinomoto Fine-Techno Co., Ltd.

[0160] <<Dispersion Aid>> The ink of the present invention may further contain a dispersion aid, if necessary. The dispersion aid may be selected depending on the pigment. The total content of the dispersant and dispersion aid is preferably within the range of 1 to 50% by mass relative to the total mass of the pigment.

[0161] <<Dispersion Medium>> The ink of the present invention may further contain a dispersion medium for dispersing the pigment, if necessary. The ink of the present invention may contain a solvent as the dispersion medium, but in order to suppress the solvent from remaining in the formed image, it is preferable to use the above-mentioned monomer as the dispersion medium. The above-mentioned monomer may particularly be a monomer having a low viscosity.

[0162] Furthermore, when a solvent is used as a dispersion medium, the solvent is likely to volatilize when the ink is heated, which is a problem from the viewpoint of ejection stability, and the dispersibility of the pigment is likely to decrease. However, by using the above-mentioned polyfunctional (meth)acrylate monomer, the decrease in dispersibility of the pigment can be suppressed.

[0163] (Other Additives) The ink of the present invention may further contain a coupling agent, a solvent, and the like, if necessary.

[0164] Coupling Agent: The ink of the present invention may further contain various coupling agents as needed. The inclusion of a coupling agent can improve adhesion to a printed wiring board. Examples of various coupling agents include silane-based, titanium-based, and aluminum-based coupling agents.

[0165] <<Curing Accelerator>> In the present invention, a curing accelerator may be included as needed. The curing accelerator is not particularly limited as long as it accelerates the thermal curing of the resin component. Examples of the curing accelerator include imidazoles, dicyandiamide derivatives, dicarboxylic acid dihydrazides, triphenylphosphine, and tetraphenylphosphonium tetraphenylborate. Other examples of the curing accelerator include 2-ethyl-4-methylimidazole-tetraphenylborate and 1,8-diazabicyclo[5.4.0]undecene-7-tetraphenylborate.

[0166] <Ion Scavenger> In the present invention, an ion scavenger may be included as needed. The inclusion of an ion scavenger has advantages such as adsorbing ionic impurities and improving the insulating properties of the cured film under hygroscopic conditions. Examples of the ion scavenger include inorganic ion adsorbents such as triazine thiol compounds, bisphenol-based reducing agents, zirconium compounds, and antimony-bismuth-based magnesium aluminum compounds.

[0167] <<Flame Retardant>> In the present invention, a flame retardant may be contained as needed. Examples of flame retardants that can be used include hydrated metals such as aluminum hydroxide and magnesium hydroxide, red phosphorus, ammonium phosphate, ammonium carbonate, zinc borate, zinc stannate, molybdenum compounds, bromine compounds, and chlorine compounds. Examples of flame retardants that can be used include phosphate esters, phosphorus-containing polyols, phosphorus-containing amines, melamine cyanurate, melamine compounds, triazine compounds, guanidine compounds, and silicone polymers.

[0168] <<Solvent>> The ink of the present invention is preferably solvent-free from the viewpoint of rapid curing and ejection stability, but a solvent may be added to adjust the ink viscosity.

[0169] 5. Method for Producing Inkjet Ink The ink according to the present invention can be prepared by mixing the above-described polymerizable monomer, blocked isocyanate, photopolymerization initiator, and any other components. It is preferable to filter the resulting mixture through a predetermined filter. When preparing an ink containing a pigment, it is preferable to prepare a pigment dispersion containing the pigment and polymerizable monomer, and then mix the pigment dispersion with other components. The pigment dispersion may further contain a dispersant.

[0170] The pigment dispersion can be prepared by dispersing a pigment in a polymerizable compound. The pigment can be dispersed using, for example, a ball mill, a sand mill, an attritor, a roll mill, an agitator, a Henschel mixer, a colloid mill, an ultrasonic homogenizer, a pearl mill, a wet jet mill, a paint shaker, or the like. A dispersant may be added at this time.

[0171] 6. Storage Method of Inkjet Ink The ink according to the present invention is preferably stored at a temperature within the range of -15 to 40°C and a humidity of 60% RH or less. Specifically, in order to store the ink within the above temperature and humidity ranges, it is preferable to use the following ink container as a container for storing the ink according to the present invention.

[0172] [Ink Container] The ink according to the present invention has a water vapor transmission rate of 0.05 to 1.50 g / m under conditions of 40° C. and 90% RH. ２ It is preferable that the ink is contained in an ink container that is within the range of 1000 kJ / day / atm. Hereinafter, the ink container will also be simply referred to as the "container."

[0173] The container is a member that is filled with ink and substantially retains the ink. The container according to the present invention may be, but is not limited to, an ink cartridge, a pack, a bottle, a tank, a glass bottle, or a can. Among these, ink cartridges, packs, bottles, and tanks are preferred, with packs being more preferred, because they are widely used and allow for easy control of the water vapor transmission rate to a desired value. Furthermore, the ink of the present invention may be contained in a bottle and then further contained in a pack.

[0174] A pack is a container made of a flexible film, and is preferable because it is lightweight, can be easily placed in a box-shaped container, the volume of the container easily changes according to the amount of ink remaining, and the film can be heat-sealed to form a bag.

[0175] The container of this embodiment can be used in at least the following forms (A) to (C): (A) a form such as an ink cartridge that is separate from the inkjet recording device (film-coating device) and is attached to the recording device to sequentially supply the composition to the recording device; (B) a form such as a tank that is separate from the recording device and transfers only the ink from the container to the recording device when the ink is used; and (C) a form such as a tank that is pre-installed in the recording device and contains the ink.

[0176] The above (A) and (B) can be said to be ink containers from the time the container is shipped until just before ink is supplied (transferred) to the recording device. The above (C) can be said to be ink containers from the time the recording device is shipped until the recording device starts using ink for the first time. Note that the above (A) and (C) can be said to be ink containers that perform printing with the recording device while ink is being supplied to the recording device from a container via a connection such as an ink tube. Also, the above (B) can be said to be an ink container that performs printing with the recording device after ink has been transferred from the container to the recording device. Note that the object to which ink is transferred in (B) can be a tank or the like attached to the recording device.

[0177] Examples of materials constituting the container include polyethylene terephthalate (PET), polypropylene (PP), polyethylene, ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer (EVOH), and polystyrene. The container may also be a film made of these materials. The container may also be made by blending the above materials in an appropriate ratio or by layering multiple types of the above materials. In the case of a film, the container may be obtained by laminating the materials. When multiple types of films are layered, it is not necessary for all of the multiple films to be the above-mentioned films; a portion of the film may be made of another material, such as a metal or a metal compound.

[0178] Furthermore, from the viewpoint of increasing the flexibility of the container, a plasticizer may be contained as a constituent material of the container. Examples of plasticizers include fatty acid esters, epoxy compounds, and polyester compounds. Among these, fatty acid esters are preferred in terms of versatility as plasticizers. Examples of fatty acid esters include phthalate esters, adipic acid esters, trimellitic acid esters, and citrate esters. The fatty acid esters may be used alone or in combination of two or more.

[0179] During storage and transportation, the container may be agitated to release the sedimentation of components contained in the ink. This is because, if the sedimentation of components contained in the ink continues for a long period of time, the sediment may turn into cake, making it difficult to release. Furthermore, when supplying ink from the container to a recording device, it is preferable to agitate the container to release the sedimentation.

[0180] When the container is a container (pack) made of flexible film, durability is particularly required to prevent cracks or tears from occurring during stirring. Durable film materials include, for example, plastic films such as polyethylene terephthalate (PET), polypropylene, polyethylene, ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, and polystyrene. Ethylene-vinyl acetate copolymer is a more preferred film material. Preferred examples of the film include stretched plastic films such as high-density, low-density, or linear low-density polyethylene, polypropylene, ethylene-vinyl alcohol copolymer, and polystyrene. A laminated film made by bonding multiple layers of film may also be used.

[0181] When the container is the above-mentioned pack, if the components contained in the ink settle, the pack may be shaken left and right to agitate the ink and restore the ink. In this case, in order to prevent the pack from cracking or breaking, a plasticizer may be contained as a constituent material of the pack. The plasticizer may be any of those listed above, and fatty acid esters are preferred.

[0182] When the container is the above-mentioned pack, the water vapor transmission rate of the film constituting the pack is 0.05 to 1.50 g / m under conditions of 40°C and 90% RH. ２ The water vapor permeability is preferably in the range of 0.05 to 1.00 g / m. ２ It is more preferable that the range is 0.05 to 0.5 g / m. ２ It is particularly preferable that the water vapor transmission rate is in the range of 0.05 to 1.50 g / m. ２By using a film within the range of 1.50 g / m², it is possible to suppress the increase in the moisture content of the ink filled in the pack even when the pack is stored for a long period of time. ２ To achieve a value of 1.5·day·atm or less, for example, the material constituting the film may be selected appropriately, or a layer composed of at least one of a metal and a metal compound may be provided on the film.

[0183] Among these, from the viewpoint of high versatility, it is preferable to provide a layer composed of at least one of a metal and a metal compound. Examples of metals include Al and Ti. Examples of metal compounds include metal oxides, such as alumina, silica, titania, and zirconia. These are used alone or in combination of two or more. In this specification, metal oxides include silica.

[0184] The thickness of the film constituting the pack is preferably within the range of 50 to 200 μm. The lower limit of the film thickness is more preferably 70 μm or more, and even more preferably 80 μm or more. The upper limit of the film thickness is preferably 150 μm or less, and even more preferably 130 μm or less. The film thickness is the total thickness when the film is a laminated film consisting of multiple layers. A film thickness within the above range is preferable in terms of the durability and flexibility of the film.

[0185] The volume of ink that can be stored in the container is not limited to the following, but is preferably in the range of 100 to 5000 mL. The lower limit of the ink volume is preferably 200 mL or more, and more preferably 500 mL or more. The upper limit of the ink volume is preferably 3000 mL or less, more preferably 2000 mL or less, and even more preferably 1000 mL or less. When the volume is within the above range, the curing property, storage stability, and ejection stability can all be further improved.

[0186] 5. Solder Resist and Printed Wiring Board The above-described ink according to the present invention is preferably used for the solder resist. A method for forming a solder resist pattern involves first patterning the ink according to the present invention by inkjet printing on a conductive oxide film of copper, zinc, or the like formed on a substrate. The ink is then cured with light to form a resist film. The oxide film in the areas not covered by the resist film is then removed with an acid etching solution. Furthermore, the resist film covering the oxide film is removed with an alkali, thereby forming a precise circuit or pattern. In this manner, a printed wiring board having a solder resist is formed.

[0187] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these. In the following examples, unless otherwise specified, operations were carried out at room temperature (25°C). Furthermore, unless otherwise specified, "%" and "parts" mean "% by mass" and "parts by mass", respectively.

[0188] <Preparation of Yellow Pigment Dispersion (Y Dispersion)> Dispersant 1 and Dispersant 2 shown below and a dispersion medium were placed in a stainless steel beaker, heated on a hot plate at 65°C for 1 hour while stirring and dissolving, and then cooled to room temperature. The pigment shown below was then added to the mixture, and the mixture was placed in a glass bottle together with 200 g of zirconia beads having a diameter of 0.5 mm and sealed. The mixture was dispersed using a paint shaker until the desired particle size was reached, and the zirconia beads were then removed. Dispersant 1: EFKA7701 (manufactured by BASF) 5.6 parts by mass Dispersant 2: Solsperse 22000 (manufactured by Lubrizol Japan) 0.4 parts by mass Dispersion medium: dipropylene glycol diacrylate (containing 0.2% UV-10) 80.6 parts by mass Pigment: PY147 (pigment yellow 147) (manufactured by BASF Oracet® Yellow 140) 13.4 parts by mass

[0189] <Preparation of Cyan Pigment Dispersion (Dispersion C)> This was prepared in the same manner as in the preparation of the yellow pigment dispersion, except that the dispersant, dispersion medium, and pigment were changed as shown below. Dispersant: EFKA7701 (manufactured by BASF) 7 parts by mass Dispersion medium: dipropylene glycol diacrylate (containing 0.2% UV-10) 70 parts by mass Pigment: PB15:4 (pigment blue 15:4) (manufactured by Dainichiseika Color & Chemicals Co., Ltd., Chromofine Blue 6332JC) 23 parts by mass

[0190] <Blocked Isocyanate> The following blocked isocyanate was used: Trixene BI7982 (manufactured by LANXESS Corporation, isocyanate compound: HDI Trimer, blocking agent: DMP, trifunctional BI) "HDI Trimer" is C ２４ H ３６ N ６ O ６ and has an isocyanurate structure. "DMP" is dimethylpyrazole and has an aromatic ring structure.

[0191] <Photopolymerizable Monomer> The photopolymerizable monomers shown in Table I below were used.

[0192]

[0193] <Photopolymerization initiator> The following photopolymerization initiators were used: Omnirad 379EG (manufactured by IGM) Omnirad TPO H (manufactured by IGM) Speedcure 2-ITX (2-isopropylthioxanthone, manufactured by Sartomer)

[0194] <Preparation of Inkjet Inks> Inks 1 to 7 were obtained by mixing inks according to the ink compositions shown in Table II below, and filtering the mixtures through a 3 μm Teflon (registered trademark) membrane filter manufactured by Advantec while heating them to 60° C. Note that Inks 1 to 7 all have the same composition, but by carrying out a dehydration process (adjusting the drying gas injection time) described below after ink preparation, Inks 1 to 7 were obtained with different water contents.

[0195]

[0196] <Inkjet Pattern Formation> The ink prepared above was loaded into an inkjet recording device having an inkjet recording head equipped with piezo-type inkjet nozzles. As shown in Figure 1, the ink supply system of the device consisted of a dehydration device, an ink tank (first sub-tank), a degassing device, an ink flow path, a sub-ink tank (second sub-tank) installed immediately before the inkjet recording head, piping with a metal filter, and a piezo head. The dehydration device and degassing device performed dehydration and degassing under the following conditions, and the ink from the ink tank to the head was heated to 55°C. A heater was then installed in the piezo head, and the ink temperature inside the piezo head was heated to 60°C. A Konica Minolta KM1800i-SHC piezo head was used. Using this inkjet recording device, voltage was applied to produce dots with a droplet volume of 3.5 pl. A 70 mm x 70 mm solid pattern and a comb-shaped pattern with 100 μm lines and spaces were printed on a substrate, each with a thickness of 30 μm. 200 mJ / cm with a Phoseon Technology LED lamp (365 nm) for each pass ２ The ink layer was then temporarily cured by irradiating it with light at a temperature of 2000 mJ / cm 2 for 60 minutes in an oven set to 150°C. ２ After irradiation, a print sample was obtained.

[0197] <Ink Dehydration Process> Dry gas was generated using a membrane dehumidifier and a general-purpose compressor. The dehumidifier used was an SMC membrane dehumidifier IDG5-02B-PS. The relative humidity of the generated dry gas was measured and found to be 1.5% RH. Dry gas was injected into the ink in the dehydration device of the ink supply system. The flow rate of the dry gas was set within the range of 0.3 to 1.0 ml / min, which balanced the generation and defoaming of bubbles at the ink interface. The dry gas injection time was varied from 1 to 12 hours to adjust the water content of the ink. After the dehydration process, the water content of the ink before it entered the head was measured. The water content was measured using a Karl Fischer moisture meter (MKV-710, manufactured by Kyoto Electronics Manufacturing Co., Ltd.). The measured water content of the ink is shown in Table II.

[0198] <Ink Degassing Process> An external circulation type hollow fiber degassing module and a vacuum pump were used as the degassing device. After the dehydration process, ink flowing in from the ink tank was allowed to flow outside the hollow fibers through the ink inlet of the degassing module. The vacuum level of the vacuum pump was set to -90 kPa to reduce the pressure inside the hollow fibers, thereby performing degassing and adjusting the amount of dissolved oxygen in the ink. As the external circulation type hollow fiber degassing module, for example, a SEPAREL EF-002A-P manufactured by Dainippon Ink and Chemicals, Inc. was used. After the degassing process, the amount of dissolved oxygen in the ink before it flowed into the head was measured. The amount of dissolved oxygen was measured using a fluorescent dissolved oxygen meter (VisiFarm DO Arc, manufactured by Hamilton).

[0199] <Amount of Solids Generated> After the dehydration and degassing processes, the ink was stored at 40°C and 80% RH for 4 days before flowing into the head. After storing the ink for 1 day at the injection temperature of 55°C, 300 mL of the ink was pressure-filtered using a 5.0 μm PTFE filter (diameter 2.0 mm). The 5.0 μm PTFE filter was then removed and washed with ethanol. The presence or absence of solids was confirmed using an optical microscope and evaluated according to the following criteria. Criteria A and B were deemed acceptable for practical use. (Criteria) A: No solids were present on the entire filter surface. B: Solids were present within 1% or less of the filter area. C: Solids were present within more than 1% and up to 5% of the filter area. D: Solids were present within more than 5% of the filter area.

[0200] <Ink ejection stability (large-volume ejection)> (Number of missing nozzles after ejecting 200 kg of ink) Using the piezo head, continuous ejection (driving) was performed under conditions of a droplet volume of 3.5 pL, a droplet speed of 7.0 m / sec, an ejection frequency of 20 kHz, and a printing rate of 100%. The number of nozzles that were not ejecting after 200 kg of ink had been ejected was counted and evaluated according to the following criteria. The following criteria of "A", "B", and "C" were deemed acceptable for practical use. (Criteria) A: The number of missing nozzles is 0. B: The number of missing nozzles is 1 or more and less than 3. C: The number of missing nozzles is 3 or more and less than 5. D: The number of missing nozzles is 5 or more and less than 10. E: The number of missing nozzles is 10 or more.

[0201] <Ink curability 1 (crosscut resistance, substrate adhesion)> For a solid pattern print sample, grid-shaped cuts were made in the cured film according to the crosscut method of JIS K5600, and adhesive tape was attached and peeled off to observe the peeling state of the cured film. The following criteria "A" and "B" were considered to be acceptable for practical use. (Criteria) A: The residual adhesion rate is 100%. B: The residual adhesion rate is 80% or more and less than 100%. C: The residual adhesion rate is 60% or more and less than 80%. D: The residual adhesion rate is less than 60%.

[0202] <Ink curability 2 (hydrochloric acid resistance)> For a solid pattern print sample, the cured film was immersed in 10% hydrochloric acid for 30 minutes, then washed with water and dried. Then, grid-shaped cuts were made in the cured film according to the cross-cut method of JIS K5600, and adhesive tape was attached and peeled off to observe the peeling state of the cured film. The following criteria, "A" and "B," were determined to be acceptable for practical use. (Criteria) A: The residual adhesion rate is 100%. B: The residual adhesion rate is 80% or more and less than 100%. C: The residual adhesion rate is 60% or more and less than 80%. D: The residual adhesion rate is less than 60%.

[0203]

[0204] As shown by the above results, it is clear that the coating film forming method of the present invention prevents the generation of solid matter, has excellent injection stability after large-volume injection, and has good curing properties compared to the coating film forming method of the comparative example.

[0205] The present invention can be used in a coating film forming method that suppresses the generation of solid matter in the device and the clogging of the head nozzle, and that provides good ejection properties and stable curing properties.

[0206] 1 Inkjet recording apparatus (film forming apparatus) 24a Recording head 24b Ink flow path 50 Ink supply section 51 Ink tank 53 Supply pump 241 First sub-tank 241a First float sensor 242 Degassing module 243 Liquid feed pump 244 Check valve 245 Second sub-tank 245a Second float sensor 249 Vacuum pump 270 Ink heating section (heating means according to the present invention) 280 Degassing device 300 Dehydration device (dehydration means according to the present invention) 2421 Outer shell (chamber) 2424 Central tube 2424b Spherical hole (hole) 2426 Hollow fiber membrane (gas permeable membrane) 2427 Heating section (heating means according to the present invention) 2428 Second heating section (heating means according to the present invention)

Claims

1. A coating film forming method using an inkjet head, the method comprising: a dehydrating step of the inkjet ink containing a polymerizable monomer, a blocked isocyanate, and a photopolymerization initiator; and a heating step of heating the inkjet ink ejected from the inkjet head to a temperature of 40°C or higher.

2. The method for forming a coating film according to claim 1, wherein the heating step is performed in an ink supply path that supplies the ink-jet ink to the ink-jet head.

3. The method for forming a coating film according to claim 1, wherein in the dehydration step, dry gas whose moisture content has been reduced by a drying device is injected into an ink supply path that supplies the inkjet ink to the inkjet head.

4. The method for forming a coating film according to claim 3, wherein in the dehydration step, a membrane filter or activated carbon is used to generate the dry gas.

5. The method for forming a coating film according to claim 1, further comprising a step of degassing the ink-jet ink after the dehydration step.

6. The coating film forming method according to claim 5, wherein the deaeration step uses hollow fibers or ultrasonic waves.

7. The method for forming a coating film according to claim 2, further comprising the step of: after the dehydration step, performing a second heating step in addition to the heating step in an ink supply path that supplies the ink-jet ink to the ink-jet head.

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