JP6750217B2 - Inkjet recording method - Google Patents

Description

The present invention relates to an inkjet recording method.

The inkjet recording method is used in various printing fields because it can easily and inexpensively form an image. As one of the inkjet inks, an ink containing a photopolymerizable compound that is cured by being irradiated with an actinic ray (hereinafter, also simply referred to as “actinic ray curable ink”) is known. Actinic radiation curable inks have recently been attracting attention because they can form images with high adhesion even on recording media with low water absorption.

Further, in recent years, an actinic ray curable ink (hereinafter, also simply referred to as “gel ink”) containing a gelling agent and having a sol-gel phase transition depending on temperature has been developed. Gel ink is in a sol state when heated and can be ejected from the nozzle of an inkjet head, but when ejected onto a recording medium after ejection, it cools and gels, resulting in high pinning properties after impact. Have. By irradiating the gel ink pinned on the surface of the recording medium with a gliding light beam, the gel ink is cured on the surface of the recording medium to form an image.

For example, in Patent Document 1, a gel ink in which the glossiness of an image-formed region on a recording medium and an image-unformed region of the recording medium are closely matched, although its specific mechanism of action is unknown. Is listed.

The inkjet recording method is an image forming method capable of forming an image on various types of recording media. However, even if the ink is ejected under the same conditions, the behavior of the ink after landing differs depending on the recording medium, and thus the image quality of the image formed may differ depending on the recording medium. There is known an inkjet recording method in which the amount of ink ejected from nozzles is changed according to the recording medium in order to form an image of high image quality regardless of the recording medium.

For example, Patent Document 2 describes an inkjet recording method in which the amount of ink discharged per unit area is changed between plain paper and a transparent film. According to the method of Patent Document 2, on plain paper having a high ink absorption rate, the amount of ink ejected per unit area can be increased to prevent the generation of unclear edges, color mixture and wrinkles due to ink seepage, and ink absorption. It is said that a transparent film having a low rate can reduce the discharge amount of ink per unit area to suppress the occurrence of uneven density due to the solidification of unfixed ink.

Patent Document 3 describes an ink jet recording method in which the ejection amount of ink is changed according to the air permeability of a recording medium to adjust the difference in ink bleeding due to the difference in the paper quality of plain paper. According to Japanese Patent Application Laid-Open No. 2004-242242, by reducing the ink ejection amount in a recording medium having low air permeability, it is possible to suppress the occurrence of bleeding during image formation regardless of the type of plain paper.

JP, 2009-132919, A JP-A-7-276615 JP, 2008-23842, A

Patent Document 1 describes that when an image is formed with gel ink, a difference in gloss between an image-formed area and an image-unformed area is small. However, according to the study by the present inventor, the difference in gloss when the image is formed using the gel ink is different depending on the recording medium.

Patent Document 2 describes a method of changing the ink ejection amount between plain paper and a transparent film, and Patent Document 3 describes a method of changing the ink ejection amount depending on the type of plain paper. Has been done. However, these documents are methods of forming an image by absorbing ink in a recording medium, and the same effect cannot be expected in gel ink in which the ink is cured on the surface of the recording medium. Further, the inkjet method can form an image on various recording media other than plain paper or a transparent film, and even a recording medium other than plain paper or a transparent film targeted by these documents can be formed regardless of the recording medium. There is a demand for a method that can reduce variations in the image quality of the image.

The present invention has been made in view of the above problems, and an object thereof, when forming an image by an inkjet method using a gel ink, does not form an area and an image formed area regardless of a recording medium. An object of the present invention is to provide an inkjet recording method that can reduce the difference in gloss from an area, and an image forming apparatus that can perform such an inkjet recording method.

The above object of the present invention is achieved by the following means.
[1] The maximum amount of ink that can be landed on the unit area of the recording medium is referred to by referring to a table that associates the type of the recording medium to be printed and the maximum amount of ink that can land on the unit area of the recording medium. A setting step and a photopolymerizable compound and a gelling agent are contained so that an amount of the inkjet ink that does not exceed the maximum amount set in the setting step is landed on the recording medium, and a sol-gel phase transition occurs depending on the temperature. A step of ejecting a droplet of an inkjet ink from a nozzle of an inkjet head and landing it on a recording medium; and a step of irradiating the inkjet ink that has landed on the recording medium with actinic rays to cure the inkjet ink. An inkjet recording method having the following.
[2] The type of the recording medium is classified based on one or more criteria selected from the coating amount of resin contained in the recording medium, the air permeability of the recording medium, and the Beck smoothness of the recording medium. The method according to [1].
[3] The maximum amount is 20 g/m ² when the resin coating amount of the recording medium is 20 g/m ² or more, and the resin coating amount of the recording medium is 10 g/m ² or more. When the amount is less than 20 g/m ² , the maximum amount is 15 g/m ² , and when the coating amount of the resin layer is 0 g/m ² or more and less than 10 g/m ² , the maximum amount is 10 g/m ^2. The method according to [1] or [2].
[4] The maximum amount is 20 g/m ² when the air permeability of the recording medium is 100 seconds or more, and the maximum amount is 10 g/m ² when the air permeability of the recording medium is less than 100 seconds. The method according to [1] or [2], which is m ² .
[5] The maximum amount is 20 g/m ² when the air permeability of the recording medium is 100 seconds or more and the Beck smoothness of the recording medium is 200 seconds or more. The maximum amount is 15 g/m ² when the air permeability is 100 seconds or more and the Beck smoothness of the recording medium is 1 second or more and less than 200 seconds. [4] Method.
[6] An inkjet head having a nozzle surface, which contains a photopolymerizable compound and a gelling agent, and is provided with an ejection port of a nozzle capable of ejecting a droplet of an inkjet ink which undergoes a sol-gel phase transition depending on temperature. A transport unit that transports the recording medium so that the recording medium facing the inkjet head moves directly below the ejection port of the nozzle, an irradiation unit that irradiates the upper surface of the transport unit with an active ray from a light source, and recording. A storage unit that stores a table that correlates the type of medium and the maximum amount of ink that can land on a unit area of the recording medium, and controls the inkjet head, the transport unit, the irradiation unit, and the storage unit. And a control unit for setting the maximum amount of ink that can land on a unit area of a recording medium to be recorded by referring to the table stored in the storage unit, and controlling the transport unit. Controlling the recording medium to be conveyed, controlling the inkjet head to eject the inkjet ink so that the maximum amount of ink landed on a unit area of the recording medium does not exceed the set maximum amount, Forming equipment.

According to the present invention, when forming an image by an inkjet method using a gel ink, an inkjet recording method capable of reducing a difference in gloss between an image-formed area and an image-not-formed area regardless of a recording medium, And an image forming apparatus capable of carrying out such an ink jet recording method is provided.

FIG. 1 is a conceptual diagram showing an image forming apparatus for inkjet according to an embodiment of the present invention.

As a result of earnest research, the present inventor has found that gel ink has strong pinning property and does not decrease in thickness due to wetting and spreading after landing on a recording medium. Therefore, in the method described in Patent Document 1 or Patent Document 2, gel ink is used. It has been found that, when an image is formed, the difference in gloss between the image-formed area and the image-not-formed area is unlikely to be sufficiently small. That is, since the pinned gel ink has a large thickness, it covers the irregularities on the surface of the recording medium and flattens the plane of the recording medium. The region where the gel ink has landed and the surface has become flatter is more likely to reflect light and has a higher gloss than the region where the ink has not landed. Therefore, when a large amount of gel ink is applied and cured on a recording medium with large irregularities, the area where the image is formed (the area where the ink is applied) becomes flatter and the gloss becomes higher, but the image is not formed. It is considered that the gloss difference of the formed image becomes large because the glossiness of the region (the region where the ink has not landed) remains low.

The unevenness of the surface of the recording medium becomes large when the thickness of the resin layer coating the surface is small (the amount of resin is small) or when the amount of fibers constituting the recording medium is small. Therefore, in a recording medium having a small amount of resin or a recording medium having a small amount of fibers, it is considered that the difference in gloss can be reduced by reducing the amount of ink landed on the recording medium.

In addition, the recording medium having a small amount of resin or the recording medium having a small amount of fiber easily absorbs a component having a low viscosity (for example, a part of the photopolymerizable compound) from the ink into the recording medium, so that the landed ink Is likely to be insufficiently cured, and odor and blocking are likely to occur. Therefore, it is expected that generation of the odor and blocking can be suppressed by reducing the amount of landed ink on these recording media.

Further, in the recording medium having a small amount of resin or the recording medium having a small amount of fibers, the gel ink that has landed tends to wet and spread more easily than other recording media, and thus it is difficult to reproduce fine lines. Therefore, it is expected that the fineness of the image to be formed can be increased by reducing the amount of ink landed on these recording media.

According to the present invention, in particular, when an image is formed on various types of recording media by one image forming apparatus by an ink jet recording method, it is possible to adjust the ejection amount of ink to various types of recording media. As a result, the effect of reducing the gloss difference, the effect of suppressing the generation of odor, the effect of suppressing the occurrence of blocking, or the effect of increasing the fineness of the image can be easily obtained.

The recording medium targeted by the present invention may be any medium capable of forming an image by an inkjet method, and examples thereof include coated papers including art papers, coated papers, lightweight coated papers, lightly coated papers and cast papers, and Consists of absorbent media including uncoated paper, polyester, polyvinyl chloride, polyethylene, polyurethane, polypropylene, acrylics, polycarbonate, polystyrene, acrylonitrile-butadiene-styrene copolymer, plastics including polyethylene terephthalate and polybutadiene terephthalate. A non-absorbent recording medium (plastic base material) and a non-absorbent inorganic recording medium such as metals and glass can be used. Among these, the absorptive medium more suitably exerts the effect of suppressing the generation of the odor and blocking. Further, the coated paper more suitably exerts the effect of reducing the gloss difference, the effect of suppressing the generation of odor and blocking, and the effect of increasing the fineness of the image.

The inkjet ink targeted by the present invention is an inkjet ink that contains a photopolymerizable compound and a gelling agent and undergoes a sol-gel phase transition depending on temperature (hereinafter, also simply referred to as “ink of the present invention”).

Hereinafter, the present invention will be described with reference to exemplary embodiments, but the present invention is not limited to the following embodiments.

1. Inkjet recording method According to an embodiment of the present invention, a step of setting a maximum amount of ink that can land on a unit area of a recording medium, a step of landing a droplet of ink of an amount that does not exceed the maximum amount on the recording medium, and The present invention relates to an inkjet recording method having a step of curing ink.

1-1. Step of setting the maximum amount of ink that can land on the unit area of the recording medium In this step, the maximum amount of ink droplets that can land on the unit area of the recording medium to be printed is set.

The types of recording media are classified based on arbitrarily defined criteria such as the amount of change in gloss when an image is formed with gel ink, the amount of odor, the degree of blocking, or the ease with which the gel ink can spread. be able to. The amount of change in gloss, the amount of odor, the degree of blocking, or the ease of wetting and spreading of the gel ink correlates with the coating amount of the resin of the recording medium and the amount of fibers constituting the recording medium. Therefore, for example, the type of the recording medium may be classified into any number of stages based on the coating amount of the resin included in the recording medium. At this time, the type of recording medium may be classified into art paper, coated paper, lightweight coated paper, and slightly coated paper (and non-coated paper) that are commonly used. The amount of fibers constituting the recording medium correlates with the air permeability and smoothness of the recording medium. Therefore, the type of the recording medium may be classified into any number of stages based on the air permeability and the smoothness of the recording medium. The classification of these recording media is preferably set in advance.

The air permeability is an index showing the resistance of the recording medium to the passage of air. The air permeability is related to the density, texture, water absorbability, printability, etc. of the recording medium and can be used as one measure showing the porous structure of the recording medium.

The smoothness is an index showing the flatness and smoothness of the surface of the recording medium, and the larger the value, the smoother the recording medium. Smooth soil is greatly affected by surface properties (skin, texture), gloss, ink acceptability, and bulk. The Beck method and the Oken method are generally known as methods for measuring the smoothness, and both measure the smoothness of paper using air. In the present invention, a value measured by either the Beck method or the Oken method may be used as the smoothness.

The air permeability of the recording medium may be, for example, the air permeability determined by the Gurley method according to JIS P8117. The Beck's smoothness of the recording medium can be the smoothness obtained according to JIS P 8119, for example.

According to the knowledge newly obtained by the present inventors, in order to obtain the effect of reducing the gloss difference, the effect of suppressing the generation of odor, the effect of suppressing the occurrence of blocking, or the effect of increasing the fineness of the image, When an image is formed on a recording medium having a resin coating amount of 20 g/m ² or more (for example, art paper and coated paper), the maximum amount is 20 g/m ² , preferably 18 g/m ² , When the image is formed on a recording medium having a resin coating amount of 10 g/m ² or more and less than 20 g/m ² (for example, light-weight coated paper and lightly coated paper), more preferably 16 g/m ² , The maximum amount is set to 15 g/m ² , preferably 13 g/m ^2, and an image is formed on a recording medium (for example, uncoated paper) having a resin coating amount of 0 g/m ² or more and less than 10 g/m ^2. In that case, the maximum amount may be 10 g/m ² .

Further, in order to obtain the effect of reducing the gloss difference, the effect of suppressing the generation of odor, the effect of suppressing the occurrence of blocking, or the effect of increasing the fineness of the image, a recording medium having an air permeability of 100 seconds or more. When forming an image on the recording medium, the maximum amount is set to 20 g/m ² , more preferably 16 g/m ^2, and when forming an image on a recording medium having an air permeability of less than 100 seconds, the maximum amount is set to 20 g/m ^2. It may be 10 g/m ² . At this time, when an image is further formed on a recording medium having an air permeability of 100 seconds or more and a Beck's smoothness of 200 seconds or more, the maximum amount is set to 20 g/m ^2, and more preferably When the image is formed on a recording medium having an air permeability of 16 g/m ² , an air permeability of 100 seconds or more, and a Bekk smoothness of 1 second or more and less than 200 seconds, the maximum amount is 15 g/m ^2. Good.

From the viewpoint of expanding the color gamut of the formed image, when the image is formed on a recording medium (for example, art paper or coated paper) having a resin coating amount of 20 g/m ² or more, The minimum amount is preferably 15 g/m ^2, and an image is formed on a recording medium (for example, lightweight coated paper or lightly coated paper) having a resin coating amount of 10 g/m ² or more and less than 20 g/m ^2. In that case, it is preferable that the minimum amount is 10 g/m ² .

Similarly, from the viewpoint of expanding the color gamut of an image to be formed, when the image is formed on a recording medium having an air permeability of 100 seconds or more, the maximum amount is preferably set to 20 g/m ² . Further, when an image is formed on a recording medium having an air permeability of 100 seconds or more and a Beck's smoothness of 200 seconds or more, the maximum amount is set to 15 g/m ² and the air permeability is 100. When an image is formed on a recording medium having a Beck's smoothness of 1 second or more and less than 200 seconds, the maximum amount is preferably 10 g/m ² .

1-2. Step of landing ink droplets on a recording medium In this step, an amount of ink droplets of the present invention that does not exceed the maximum amount of ink droplets that can land on the recording medium determined in the above step (and optionally an amount of a minimum value or more) The droplets of the ink of the present invention are ejected from the nozzles of the inkjet head so that the ink lands on the recording medium and land on the recording medium. At this time, the ink of the present invention is ejected so that the amount of ink landed on the unit area of the recording medium does not exceed the set maximum amount.

The inkjet head may be either an on-demand type or a continuous type inkjet head. Examples of on-demand inkjet heads include electro-mechanical conversion methods including single cavity type, double cavity type, bender type, piston type, shear mode type and shared wall type, as well as thermal inkjet type and bubble jet ( The bubble jet includes an electric-heat conversion method including a type (registered trademark of Canon Inc.) type.

The adjustment of the amount of the ink of the present invention landing on the recording medium may be performed by changing the amount of the ink ejected from the nozzles or by changing the number of the nozzles ejecting the ink. Alternatively, these may be combined. The amount of ink ejected from the nozzle can be changed, for example, by changing the vibration width of the piezoelectric element in the electromechanical conversion type inkjet head. The number of nozzles from which ink is ejected can be changed without ejecting ink from some of the plurality of nozzles of the inkjet head. In this way, the volume or number of ink droplets ejected from the inkjet head may be changed to set the amount of the ink of the present invention landing on the recording medium to a desired value.

1-3. Step of Curing Ink In this step, the ink of the present invention that has landed is irradiated with actinic rays to cure the ink. From the viewpoint of enhancing the curability of the ink of the present invention, the actinic ray is preferably irradiated within 0.001 seconds or more and 1.0 seconds or less after the ink has landed, and from the viewpoint of forming a higher definition image, It is more preferable that the irradiation is performed for 0.001 seconds or more and 0.5 seconds or less.

Examples of actinic rays that can be applied to the ink in the present embodiment include electron rays, ultraviolet rays, α rays, γ rays, and X rays. Among these, it is preferable to irradiate with ultraviolet rays from the viewpoint of easy handling and little influence on the human body. The light source is preferably a light emitting diode (LED) from the viewpoint of suppressing the occurrence of defective curing of the ink of the present invention due to the radiant heat of the light source melting. Examples of LED light sources that can be irradiated with actinic radiation to cure the ink of the present invention include 395 nm, water-cooled LEDs, from Phoseon Technology.

1-4. Other Steps The present embodiment may further include a step of characterizing the type of recording medium before the step of setting the maximum amount of ink. The specifying may be performed based on the information of the recording medium included in the print information that the image forming apparatus receives from an external device or the like, or in the image forming apparatus including the measuring unit upstream from the inkjet head, the measuring unit May be performed based on the information obtained by measuring the recording medium. The measuring unit may be, for example, a member capable of measuring the coating amount of the resin included in the recording medium, the air permeability of the recording medium, and optionally the Beck smoothness of the recording medium. The type of the recording medium is specified, for example, based on the information of the recording medium or the information obtained by the measurement, into a classification corresponding to the content of the information.

1-5. Ink of the Present Invention The ink of the present invention is an inkjet ink that contains a gelling agent and undergoes a sol-gel phase transition depending on temperature. More specifically, the ink of the present invention contains a photopolymerizable compound and a gelling agent, and becomes a sol or liquefaction when heated, but gels when cooled, if it is a known ink Good. The ink of the present invention may further contain a photopolymerization initiator, a coloring material and other components.

1-5-1. Gelling Agent The content of the gelling agent is preferably 1.0% by mass or more and 10.0% by mass or less based on the total mass of the ink. By setting the content of the gelling agent to 1.0% by mass or more, the pinning property of the ink can be sufficiently enhanced and a higher-definition image can be formed. By setting the content of the gelling agent to 10.0% by mass or less, it becomes difficult for the gelling agent to deposit on the surface of the formed image, and the gloss of the image can be brought closer to the gloss of the image by another ink, In addition, it is possible to further enhance the ink ejection property from the inkjet head. From the above viewpoint, the content of the gelling agent in the ink of the present invention is preferably 1.0% by mass or more and 5.0% by mass or less, and 2.5% by mass or more and 5.0% by mass or less. It is more preferable that the amount is 2.5 mass% or more and 4.0 mass% or less.

From the following viewpoints, the gelling agent is preferably crystallized in the ink at a temperature not higher than the gelation temperature of the ink. When the gelling agent is crystallized in the ink, a structure may be formed in which the photopolymerizable compound is included in the three-dimensional space formed by the plate-like crystallized gelling agent. , Hereinafter referred to as "card house structure"). When the card house structure is formed, since the liquid photopolymerizable compound is held in the space, the ink droplets are more difficult to spread and wet, and the pinning property of the ink is further enhanced. When the pinning property of the ink is increased, it becomes difficult for the ink droplets landed on the recording medium to coalesce with each other, and a higher-definition image can be formed.

In order to form a card house structure, it is preferable that the photopolymerizable compound dissolved in the ink and the gelling agent are compatible with each other. On the other hand, when the photopolymerizable compound dissolved in the ink and the gelling agent are phase-separated, it may be difficult to form a card house structure.

Examples of gelling agents suitable for forming a card house structure by crystallization include ketone wax, ester wax, petroleum wax, plant wax, animal wax, mineral wax, hydrogenated castor oil, modified wax, higher fatty acid. , Higher alcohols, hydroxystearic acid, fatty acid amides including N-substituted fatty acid amides and special fatty acid amides, higher amines, esters of sucrose fatty acids, synthetic waxes, dibenzylidene sorbitol, dimer acids and dimer diols.

Examples of the above ketone waxes include dilignoceryl ketone, dibehenyl ketone, distearyl ketone, dieicosyl ketone, dipalmityl ketone, dilauryl ketone, dimyristyl ketone, myristyl palmityl ketone and palmityl stearyl ketone. Be done.

Examples of the above-mentioned ester waxes include behenyl behenate, icosyl icosate, stearyl stearate, palmityl stearate, cetyl palmitate, myristyl myristate, cetyl myristate, myricel stearate, stearyl stearate, oleyl palmitate, glycerin fatty acid. Esters, sorbitan fatty acid esters, propylene glycol fatty acid esters, ethylene glycol fatty acid esters and polyoxyethylene fatty acid esters are included.

Examples of commercial products of the above ester waxes include the EMALEX series manufactured by Nippon Emulsion Co., Ltd. (“EMALEX” is a registered trademark of the same company), and the Riken Vitamin Co., Ltd. All include the company's registered trademark).

Examples of the above petroleum waxes include petroleum waxes including paraffin wax, microcrystalline wax and petrolactam.

Examples of the vegetable waxes include candelilla wax, carnauba wax, rice wax, wax, jojoba oil, jojoba solid wax and jojoba ester.

Examples of the above-mentioned animal waxes include beeswax, lanolin and whale wax.

Examples of the mineral wax include montan wax and hydrogenated wax.

Examples of the modified wax include montan wax derivatives, paraffin wax derivatives, microcrystalline wax derivatives, 12-hydroxystearic acid derivatives and polyethylene wax derivatives.

Examples of the higher fatty acids include behenic acid, arachidic acid, stearic acid, palmitic acid, myristic acid, lauric acid, oleic acid, and erucic acid.

Examples of the higher alcohols include stearyl alcohol and behenyl alcohol.

Examples of the hydroxystearic acid include 12-hydroxystearic acid.

Examples of the fatty acid amide include lauric acid amide, stearic acid amide, behenic acid amide, oleic acid amide, erucic acid amide, ricinoleic acid amide and 12-hydroxystearic acid amide.

Examples of commercially available fatty acid amides include Nikka Kasei Co., Ltd., Nikka Amide series ("Nikka Amide" is a registered trademark of the company), Ito Oil Co., ITOWAX series, and Kao Corporation's FATTYAMID series. ..

Examples of the N-substituted fatty acid amide include N-stearyl stearic acid amide and N-oleyl palmitic acid amide.

Examples of the special fatty acid amide include N,N'-ethylenebisstearylamide, N,N'-ethylenebis-12-hydroxystearylamide and N,N'-xylylenebisstearylamide.

Examples of the higher amines include dodecylamine, tetradecylamine and octadecylamine.

Examples of the ester of sucrose fatty acid include sucrose stearic acid and sucrose palmitic acid.

Examples of commercially available esters of sucrose fatty acid include Ryoto Sugar Ester Series (“Ryoto” is a registered trademark of the same company) manufactured by Mitsubishi Chemical Foods.

Examples of the synthetic wax include polyethylene wax and α-olefin maleic anhydride copolymer wax.

Examples of commercially available synthetic waxes include UNILIN series manufactured by Baker-Petrolite (“UNILIN” is a registered trademark of the same).

Examples of the dibenzylidene sorbitol include 1,3:2,4-bis-O-benzylidene-D-glucitol.

Examples of commercially available products of dibenzylidene sorbitol include Gelol D manufactured by Shin Nippon Rika Co., Ltd. (“Gelol” is a registered trademark of the same company).

Examples of commercially available dimer diols include PRIPOR series manufactured by CRODA (“PRIPOR” is a registered trademark of the same).

Among these gelling agents, a ketone wax, an ester wax, a higher fatty acid, a higher alcohol and a fatty acid amide are preferable from the viewpoint of further improving the pinning property, and from the above viewpoint, a ketone represented by the following general formula (G1). Wax and ester wax represented by the following general formula (G2) are more preferable. The ketone wax represented by the following general formula (G1) and the ester wax represented by the following general formula (G2) may be contained in the ink of the present invention in only one kind, or in two or more kinds. May be. In addition, either one of the ketone wax represented by the following general formula (G1) and the ester wax represented by the following general formula (G2) may be contained in the ink of the present invention, or both. May be included.

General formula (G1): R1-CO-R2
In the general formula (G1), each of R1 and R2 is a linear or branched hydrocarbon group having 9 to 25 carbon atoms.

General formula (G2): R3-COO-R4
In General Formula (G2), R3 and R4 are each a linear or branched hydrocarbon group having 9 to 25 carbon atoms.

The ketone wax represented by the general formula (G1) or the ester wax represented by the general formula (G2) has a linear or branched hydrocarbon group having 9 or more carbon atoms, and therefore gels. The crystallinity of the agent is further increased, and more sufficient space is created in the card house structure. Therefore, the photopolymerizable compound is easily included in the space, and the pinning property of the ink is further enhanced. In addition, since the linear or branched hydrocarbon group has 25 or less carbon atoms, the melting point of the gelling agent does not excessively increase, and therefore it is not necessary to excessively heat the ink when ejecting the ink. .. From the above viewpoint, R1 and R2 are particularly preferably a linear hydrocarbon group having 11 or more and less than 23 carbon atoms.

Further, from the viewpoint of increasing the gelling temperature of the ink to cause the ink to gel more rapidly after landing, either R1 or R2, or R3 or R4 is saturated and has 11 or more carbon atoms. It is preferably a hydrocarbon group of less than 23. From the above viewpoint, it is more preferable that both R1 and R2, or both R3 and R4 are saturated hydrocarbon groups having 11 or more and less than 23 carbon atoms.

Examples of the ketone wax represented by the above general formula (G1) include dilignoceryl ketone (carbon number: 23-24), dibehenyl ketone (carbon number: 21-22), distearyl ketone (carbon number: 17). -18), dieicosyl ketone (carbon number: 19-20), dipalmityl ketone (carbon number: 15-16), dimyristyl ketone (carbon number: 13-14), dilauryl ketone (carbon number: 11) -12), lauryl myristyl ketone (carbon number: 11-14), lauryl palmityl ketone (11-16), myristyl palmityl ketone (13-16), myristyl stearyl ketone (13-18), myristyl behenyl ketone (13) -22), palmityl stearyl ketone (15-18), valmityl behenyl ketone (15-22) and stearyl behenyl ketone (17-22). The number of carbon atoms in the parentheses represents the number of carbon atoms of each of the two hydrocarbon groups divided by the carbonyl group.

Examples of commercially available ketone waxes represented by the general formula (G1) include 18-Pentatriaconton and Hentriacontan-16-on manufactured by Alfa Aeser, and Kaowax T1 manufactured by Kao Corporation.

Examples of the fatty acid or ester wax represented by the general formula (G2) include behenyl behenate (carbon number: 21-22), icosyl icosanoate (carbon number: 19-20), stearyl stearate (carbon number: 17). -18), palmityl stearate (carbon number: 17-16), lauryl stearate (carbon number: 17-12), cetyl palmitate (carbon number: 15-16), stearyl palmitate (carbon number: 15-18) ), myristyl myristate (carbon number: 13-14), cetyl myristate (carbon number: 13-16), octyldodecyl myristate (carbon number: 13-20), stearyl oleate (carbon number: 17-18). , Stearyl erucate (carbon number: 21-18), stearyl linoleate (carbon number: 17-18), behenyl oleate (carbon number: 18-22) and arachidyl linoleate (carbon number: 17-20) are included. Be done. The number of carbon atoms in the parentheses represents the number of carbon atoms of each of the two hydrocarbon groups divided by the ester group.

Examples of commercially available ester waxes represented by the general formula (G2) include NOF CORPORATION, Unistar M-2222SL and Sperm Aceti (“Unistar” is a registered trademark of the same company), Kao Corporation, Exepearl SS and Exepearl MY-M ("Exepar" is a registered trademark of the same company), Nippon Emulsion Co., Ltd., EMALEX CC-18 and EMALEX CC-10 ("EMALEX" is a registered trademark of the same company), and High-grade Alcohol Industry Co., Ltd., Amreps PC ("Amreps" is a registered trademark of the same company). Since many of these commercially available products are a mixture of two or more kinds, they may be separated and purified as necessary to be contained in the ink.

1-5-2. Photopolymerizable Compounds Examples of photopolymerizable compounds include radically polymerizable compounds and cationically polymerizable compounds. The photopolymerizable compound has a function of cross-linking or polymerizing by being irradiated with the actinic ray to cure the ink. The photopolymerizable compound may be a monomer, a polymerizable oligomer, a prepolymer or a mixture thereof. The photopolymerizable compound may be contained in the ink of the present invention in only one kind or in two or more kinds.

The content of the photopolymerizable compound can be, for example, 1% by mass or more and 97% by mass or less based on the total mass of the ink of the present invention.

The radically polymerizable compound is preferably an unsaturated carboxylic acid ester compound, more preferably (meth)acrylate. In the present invention, "(meth)acrylate" means acrylate or methacrylate, "(meth)acryloyl group" means acryloyl group or methacryloyl group, and "(meth)acryl" means acryl. It also means methacryl.

Examples of (meth)acrylates include isoamyl (meth)acrylate, stearyl (meth)acrylate, lauryl (meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, isomystil (meth)acrylate, isostearyl (meth). Acrylate, 2-ethylhexyl-diglycol (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 2-(meth)acryloyloxyethyl hexahydrophthalic acid, butoxyethyl (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, Methoxydiethylene glycol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, methoxypropylene glycol (meth)acrylate, phenoxyethyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, isobornyl (meth)acrylate, 2-hydroxyethyl (meth) ) Acrylate, 2-hydroxypropyl(meth)acrylate, 2-hydroxy-3-phenoxypropyl(meth)acrylate, 2-(meth)acryloyloxyethylsuccinic acid, 2-(meth)acryloyloxyethylphthalic acid, 2 -(Meth)acryloyloxyethyl-2-hydroxyethyl-phthalic acid and monofunctional acrylates including t-butylcyclohexyl (meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, Polyethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1 , 9-nonanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, dimethylol-tricyclodecane di(meth)acrylate, di(meth)acrylate having a bisphenol A structure, hydroxypivalic acid neopentyl glycol di( (Meth)acrylate, polytetramethylene glycol di(meth)acrylate, bifunctional (meth)acrylates including polyethylene glycol diacrylate and tripropylene glycol diacrylate, and trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate ) Ax relay Tri- or higher-functionality including pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, glycerin propoxytri(meth)acrylate and pentaerythritol ethoxytetra(meth)acrylate. (Meth)acrylates, oligomers having a (meth)acryloyl group including polyester acrylate oligomers, and modified products thereof are included. Examples of the modified product include ethylene oxide-modified (EO-modified) acrylate having an ethylene oxide group inserted therein and propylene oxide-modified (PO-modified) acrylate having propylene oxide inserted therein.

Examples of the cationically polymerizable compound include epoxy compounds, vinyl ether compounds and oxetane compounds.

1-5-3. Photopolymerization initiator The photopolymerization initiator, when the photopolymerizable compound is a compound having a radically polymerizable functional group, includes a photoradical initiator, the photopolymerizable compound has a cationically polymerizable functional group. When it is a compound having, it includes a photoacid generator. The photopolymerization initiator may be contained in the ink of the present invention in only one kind or in two or more kinds. The photopolymerization initiator may be a combination of both a photo radical initiator and a photo acid generator.

The photo radical initiator includes a cleavage type radical initiator and a hydrogen abstraction type radical initiator.

Examples of the cleavable radical initiator include an acetophenone-based initiator, a benzoin-based initiator, an acylphosphine oxide-based initiator, benzyl and methylphenylglyoxyester.

Examples of the hydrogen abstraction type radical initiator include a benzophenone-based initiator, a thioxanthone-based initiator, an aminobenzophenone-based initiator, 10-butyl-2-chloroacridone, 2-ethylanthraquinone, 9,10-. Includes phenanthrenequinone and camphorquinone.

Examples of the photo-acid generator include compounds described in "Organic Materials for Imaging", edited by Organic Electronics Materials Research Group, Bushin Publishing Co., Ltd. (1993), pp. 187-192.

The content of the photopolymerization initiator may be in the range in which the ink can be sufficiently cured, and can be, for example, 0.01% by mass or more and 10% by mass or less based on the total mass of the ink of the present invention.

1-5-4. Color Materials Color materials include dyes and pigments. From the viewpoint of obtaining an image having good weather resistance, the coloring material is preferably a pigment. The pigment can be selected from, for example, a yellow pigment, a red or magenta pigment, a blue or cyan pigment and a black pigment depending on the color of the image to be formed.

1-5-5. Other Components The ink of the present invention may further contain other components including a dispersant, a photosensitizer, a polymerization inhibitor, and a surfactant within the range where the effects of the present invention can be obtained. These components may be contained in the ink of the present invention in only one kind or in two or more kinds.

1-5-6. Physical Properties From the viewpoint of further improving the ejection property from the inkjet head, the viscosity of the ink of the present invention at 80° C. is preferably 3 mPa·s or more and 20 mPa·s or less. Further, from the viewpoint of sufficiently gelling the ink when landed and cooled to room temperature, the viscosity of the ink of the present invention at 25° C. is preferably 1000 mPa·s or more.

The gelation temperature of the ink of the present invention is preferably 40° C. or higher and lower than 100° C. When the gelation temperature of the ink is 40° C. or higher, the ink rapidly gels after landing on the recording medium, so that the pinning property becomes higher. When the gelling temperature of the ink is less than 100° C., the ink gelled by heating can be ejected from the inkjet head, and thus the ink can be ejected more stably. From the viewpoint of enabling the ink to be ejected at a lower temperature and reducing the load on the image forming apparatus, the gelation temperature of the ink of the present invention is more preferably 40°C or higher and lower than 70°C.

The viscosity at 80° C., the viscosity at 25° C. and the gelling temperature of the ink of the present invention can be determined by measuring the temperature change of the dynamic viscoelasticity of the ink with a rheometer. In the present invention, these viscosity and gelation temperature are values obtained by the following method. The ink of the present invention was heated to 100° C., and the shear rate was 11.7 while measuring the viscosity by a stress control rheometer Physica MCR301 (cone plate diameter: 75 mm, cone angle: 1.0°), manufactured by Anton Paar. (1/s), the ink is cooled to 20° C. under the condition of the temperature decreasing rate of 0.1° C./s to obtain a temperature change curve of viscosity. The viscosity at 80° C. and the viscosity at 25° C. can be determined by reading the viscosities at 80° C. and 25° C. on the temperature change curves of viscosity. The gelation temperature can be determined as the temperature at which the viscosity becomes 200 mPa·s on the temperature change curve of viscosity.

From the viewpoint of further improving the ejection property from the inkjet head, the average particle diameter of the pigment particles when the ink of the present invention contains a pigment is 0.08 μm or more and 0.5 μm or less, and the maximum particle diameter is 0.3 μm or more. It is preferably 10 μm or less. The average particle diameter of the pigment particles in the present invention means a value determined by a dynamic light scattering method using Datasizer Nano ZSP, manufactured by Malvern. Since the ink containing the coloring material has a high density and light is not transmitted by this measuring device, the ink is diluted 200 times before the measurement. The measurement temperature is room temperature (25° C.).

2. Image forming apparatus Another embodiment of the present invention relates to an image forming apparatus for inkjet, which is capable of implementing the above method. FIG. 1 is a side view showing the concept of an inkjet image forming apparatus 100 according to this embodiment.

As shown in FIG. 1, the image forming apparatus 100 includes an inkjet head 110, a conveyance unit 120, an irradiation unit 130, a control unit 140, and a storage unit 150. The image forming apparatus 100 may further include a data input unit 160. The image forming apparatus 100 may further include a measuring section 170 that measures the type of the recording medium, on the upstream side of the inkjet head 110 in the recording medium conveyance direction. In addition, in FIG. 1, the arrow indicates the conveyance direction of the recording medium.

2-1. Inkjet head 110
The inkjet head 110 has a nozzle surface 113 provided with the ejection ports of the nozzles 111 on the surface facing the transport unit 120 when forming an image, and with respect to the recording medium 200 transported by the transport unit 120. To eject ink. From the viewpoint of making the ink of the present invention into a sol to improve the ejection property, the inkjet head 110 may have a temperature adjusting means for adjusting the temperature of the ink to adjust the viscosity of the ink to be low. Examples of the temperature adjusting means include a panel heater, a ribbon heater, and heating means using warm water.

The inkjet head 110 may be a scan type inkjet head whose width in the direction orthogonal to the recording medium conveyance direction is smaller than that of the recording medium 200, and a line whose width in the direction orthogonal to the recording medium conveyance direction is larger than that of the recording medium 200. Type inkjet head may be used.

The nozzle 111 has a discharge port on the nozzle surface 113. The number of nozzles 111 may be the number of inks used for image formation (for example, four) or more. When the inkjet head 110 has a plurality of nozzles 111, the plurality of nozzles 111 are arranged side by side in the transport direction of the recording medium at substantially equal intervals from the viewpoint of simplifying the configuration of the apparatus and facilitating control. Preferably.

The inkjet head 110 is configured to be able to change the amount of ink ejected and landed on the recording medium. For example, the inkjet head 110 is configured to be controlled by the control unit 140 so that the vibration width of the piezoelectric element can be changed and ink can be prevented from being ejected from some nozzles.

2-2. Transport unit 120
The transport unit 120 transports the recording medium 200 so that the recording medium 200 facing the inkjet head 110 moves immediately below the inkjet head 110 in the vertical direction when forming an image. For example, the transport unit 120 includes a drive roller 121, a driven roller 122, and a transport belt 123.

The drive roller 121 and the driven roller 122 are arranged in a state where they are spaced apart from each other in the recording medium conveyance direction and extend in a direction orthogonal to the recording medium conveyance direction. The drive roller 121 is rotated by a drive source (not shown).

The transport belt 123 is a belt for transporting the recording medium 200 placed on the transport belt 123, and is stretched over the drive roller 121 and the driven roller 122. The transport belt 123 can be, for example, an endless belt formed wider than the recording medium 200. At this time, when the drive source rotates the drive roller 121, the transport belt 123 rotates around the drive roller 121, and the recording medium 200 on the transport belt 123 is transported. A plurality of suction holes (not shown) may be formed on the belt surface of the transport belt 123 from the viewpoint of holding the recording medium 200 by suction and making it more difficult to detach the recording medium.

2-3. Irradiation unit 130
The irradiation unit 130 has a light source, and irradiates the upper surface of the transport unit 120 with an actinic ray from the light source. As a result, the droplets of the inkjet ink that have landed on the recording medium 200 being conveyed can be irradiated with actinic rays to cure the droplets. The irradiation unit 130 can be arranged on the downstream side of the inkjet head 110 and directly above the transport unit 120. The light source is preferably a light emitting diode (LED) from the viewpoint of suppressing the occurrence of defective curing of the ink due to the melting of the inkjet ink by the radiant heat of the light source. Examples of LED light sources that can be irradiated with actinic radiation to cure the inkjet ink include 395 nm, water-cooled LEDs, from Phoseon Technology.

2-6. Control unit 140
The control unit 140 controls the operation of the image forming apparatus 100 during image formation.

2-5. Storage unit 150
The storage unit 150 includes various types of tables including a control program executed by the control unit 140, a type of recording medium, and a table that associates the maximum amount (and optionally the minimum amount) of ink that can land on the unit area of the recording medium. Store information so that it can be referenced.

2-7. Data input section 160
The data input unit 160 transmits/receives various types of information such as the type of recording medium to be printed and data including an image to be printed to/from an external device.

2-8. Measuring unit 170
The measuring unit 170 measures the type of recording medium on which an image is formed and transmits the obtained information to the control unit 140. The measuring unit 170 may be, for example, a known device that can measure the coating amount of the resin included in the recording medium, the air permeability of the recording medium, or the Beck smoothness of the recording medium.

2-9. Other Configurations In addition to the above-described configuration, the image forming apparatus 100 includes an ink tank (not shown) for storing inkjet ink before ejection, and an ink flow path that allows the ink to communicate with the inkjet head 110. (Not shown) may be included.

2-10. The image forming control unit 140 using the image forming apparatus 100 stores the type of recording medium stored in the storage unit 150, the maximum amount (and optionally the minimum amount) of ink that can land on the unit area of the recording medium. , The maximum amount of ink that can land on the unit area of the specified type of recording medium, and optionally the minimum amount are set.

In addition, the control unit 140 controls the transport unit 120 to transport the recording medium 200 and controls the inkjet head 110 so that the image included in the print information is formed on the recording medium 200. The ink droplets of the present invention are ejected from the nozzle 111. At this time, the control unit 140 adjusts the ejection amount of the ink of the present invention so that the maximum amount of ink landed on the unit area of the recording medium 200 does not exceed the set maximum amount. The recording medium may be conveyed after the maximum amount of the ink is set, or before the setting.
Further, the control unit 140 controls the irradiation unit 130 to irradiate the ink of the present invention landed on the recording medium 200 with an actinic ray to cure the ink. At this time, the control unit 140 controls the inkjet head 110 to eject ink and land an amount of ink that does not exceed the maximum amount on the downstream side of the recording medium 200 to form an image on the downstream side at the same time. You may start.

Also, the control unit 140 determines the type of recording medium to be printed from the print information received by the data input unit 160 or the recording medium information measured by the measuring unit 170 before setting the maximum amount of ink that can be landed. May be specified.

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

1. Preparation of ink 1-1. Preparation of Pigment Dispersion The following types and amounts of dispersants and dispersion media were placed in a stainless beaker, and heated and stirred for 1 hour while heating on a hot plate at 65° C. to dissolve, and after cooling to room temperature, a pigment was added. , 200 g of zirconia beads having a diameter of 0.5 mm were placed in a glass bottle and sealed. After that, dispersion treatment was carried out with a paint shaker until the desired particle size was obtained, and then the zirconia beads were removed to prepare a yellow pigment dispersion, a magenta pigment dispersion, a cyan pigment dispersion and a black pigment dispersion, respectively.

(Material of yellow pigment dispersion)
Dispersant 1: EFKA7701 (manufactured by BASF) 5.6 parts by mass Dispersant 2: Solsperse 22000 (manufactured by Nippon Lubrizol) 0.4 parts by mass Dispersion medium: tripropylene glycol diacrylate (containing 0.2% UV-10) 80.6 parts by mass Pigment: PY185 (manufactured by BASF, Pariotor Yellow D1155) 13.4 parts by mass

(Material of magenta pigment dispersion)
Dispersant: JET-9151 (manufactured by BYK) 11 parts by mass Dispersion medium: Tripropylene glycol diacrylate (containing 0.2% UV-10) 69 parts by mass Pigment: PV19/PR202 (manufactured by BASF, D4500J) 20 parts by mass

(Cyan pigment dispersion material)
Dispersant: JET-9151 (manufactured by BYK) 7 parts by mass Dispersion medium: Tripropylene glycol diacrylate (containing 0.2% UV-10) 70 parts by mass Pigment: PB15:4 (manufactured by Dainichiseika, Chromofine Blue 6332JC) ) 23 parts by mass

(Material of black pigment dispersion)
Dispersant: JET-9151 (manufactured by BYK) 7 parts by mass Dispersion medium: tripropylene glycol diacrylate (containing 0.2% UV-10) 70 parts by mass Pigment: PB7 (manufactured by Mitsubishi Chemical Corporation, MA-7) 23 parts by mass Department

1-2. Preparation of Ink The following components were mixed with the pigment dispersion according to the ink composition shown in Tables 1 and 2 below, and the mixture was heated to 80° C. and stirred. While heating the obtained solution, it was filtered through a Teflon (registered trademark) 3 μm membrane filter manufactured by ADVATEC to prepare yellow ink, magenta ink, cyan ink and black ink constituting ink set 1 and ink set 2, respectively. ..

(Ink material)
Pigment dispersion Y: Yellow pigment dispersion prepared above Pigment dispersion M: Magenta pigment dispersion prepared above Pigment dispersion C: Cyan pigment dispersion prepared above Pigment dispersion Bk: Black pigment dispersion prepared above Gelation Agent 1: Ketone wax represented by general formula (G1) (Kao wax T1 manufactured by Kao Corporation)
Gelling agent 2: Ester wax represented by General Formula (G2) (Unistar M-2222SL manufactured by NOF CORPORATION)
Gelling agent 3: ester wax represented by the general formula (G2) (NOF Corporation, behenyl stearate)
Photopolymerizable compound 1: Tripropylene glycol diacrylate Photopolymerizable compound 2: Polyethylene glycol #600 diacrylate Photopolymerizable compound 3: 6EO-modified trimethylolpropane triacrylate Photopolymerizable compound 4: 3PO-modified trimethylolpropane triacrylate Light Polymerizable compound 5: Polyester acrylate oligomer having an average number of functional groups of 8 (manufactured by ETERNAL CHEMICAL, ETERCURE 6361-100)
Photopolymerizable compound 6: Polyester acrylate oligomer having an average number of functional groups of 2 (CN2270 manufactured by Sartomer Co.)
Photopolymerizable compound 7: amine-modified acrylate oligomer (CN371, manufactured by Sartomer)
Photopolymerization initiator 1: Acylphosphine oxide-based radical polymerization initiator (IRGACURE TPO manufactured by BASF Ltd. (“IRGACURE” is a registered trademark of the same company))
Photopolymerization initiator 2: Acyl phosphine oxide-based radical polymerization initiator (IRGACURE 819, manufactured by BASF Ltd. (“IRGACURE” is a registered trademark of the same company))
Photosensitizer 1: 2-isopropylthioxanthone (ITX)
Photosensitizer 2: Polymeric thioxanthone (Lambson, SPEEDCURE 7010-L)
Polymerization inhibitor: manufactured by BASF, IRGASTAB UV10 (“IRGASTAB” is a registered trademark of the same company)
Surfactant: TSF-4452 manufactured by Momentive Performance Materials Japan Co., Ltd.

2. Image Forming Ink set 1 was loaded in a drum type ink jet recording apparatus having an ink jet recording head equipped with piezo type ink jet nozzles. The ink supply system used had an ink tank, an ink flow path, a sub-ink tank immediately before the inkjet recording head, a pipe with a metal filter, and a piezo head. Heat the ink from the ink tank to the head to 90°C. A heater was also incorporated in the piezo head to heat the ink temperature in the recording head to 90°C. The piezo head used has a nozzle diameter of 22 μm, a head with a nozzle resolution of 600 dpi is arranged, and a nozzle array of 1200 dpi is formed.

Using this ink jet recording apparatus, images were continuously formed while adsorbing the recording media shown in Tables 3 and 4 onto the drums and transporting them. A voltage is applied in order of yellow ink, magenta ink, cyan ink, and black ink so that the droplet amount becomes two size dots of 3.5 pl and 9.0 pl, and recording is performed on the recording medium at 1200×1200 dpi. A plurality of total ink amounts ejected onto the medium are set, and with the respective total ink amounts, solid images of Blue, Green, Red and 3C, 5 points of MS Mincho type, and 7 points of the positive character of "excellent" and A negative (white letters) and a natural image were printed. A blue solid image was formed by ejecting magenta ink and cyan ink in this order. A green solid image was formed by ejecting yellow ink and cyan ink in this order. The red solid image was formed by ejecting yellow ink and magenta ink in this order. The above characters were formed by ejecting black ink. The natural image was formed by ejecting all four color inks. The temperature of the drum was controlled so that the surface temperature of the base material in front of the head was 46° C. (dpi represents the number of dots per 2.54 cm).

Within 1 second after printing, an LED lamp (395 nm, 8 W/cm ² , from Phoseon Technology) was irradiated to cure the ink layer. The distance from the tube surface of the LED lamp to the recording medium was 50 mm (irradiation width in the transport direction was 100 mm). The transport speed of the recording medium was 800 mm/sec.

Image formation was similarly performed for the ink set 2.

The recording media used for image formation are shown in Tables 3 and 4. The “basis weight” shown in Tables 3 and 4 is a value announced by each manufacturer. In addition, "air permeability" described in Table 4 is a value measured by using a Oken type smoothness/air permeability tester manufactured by Kumagai Riki Kogyo Co., Ltd., and "Beck smoothness" is It is a value measured using a Beck smoothness tester manufactured by Kumagai Riki Kogyo Co., Ltd.

The “name” described in Tables 3 and 4 is the name of each recording medium in Tables 6 to 11, and the recording medium described as “A class paper” in “Name” in Table 4 is A recording medium having an air permeability of 100 seconds or more and a Beck smoothness of 200 seconds or more, and a recording medium described as "B class paper" has an air permeability of 100 seconds or more and a Beck smoothness. Is 1 second or more and less than 200 seconds, and the recording medium described as “C class paper” is a recording medium having an air permeability of less than 100 seconds.

3. Evaluation The images prepared above were evaluated according to the following criteria.

3-1. Odor Regarding each of the images created above, a panel of 6 people (subjects) performed an odor sensory evaluation according to the rating shown in Table 5. The average of the odor intensity of the 6 persons who scored was rounded off to the first decimal place, and based on that value, evaluation was made according to the following criteria.

◯: 3.0 points or less on average Δ: 3.1 to 3.9 points on average ×: 4.0 points or more on average

3-2. Gloss The gloss of each solid image and natural image created above was visually compared with the gloss of the surface of the recording medium that was not printed.

◯: There is almost no difference in gloss between the printed part and non-printed part, and there is no discomfort. Δ: There is a part where a difference in gloss between the printed part and non-printed part is felt. ×: There is a large difference in gloss between the printed part and non-printed part. Can not stand

3-3. Curability According to the method described in "JIS standard K5701-1 6.2.3 Friction resistance test", a recording medium cut into an appropriate size is placed on each solid image created above. , A load was applied and the pieces were rubbed together. Then, the degree of decrease in image density was visually observed and evaluated according to the following criteria.

⊚: No change in image is observed even after rubbing 100 times or more. ◯: After rubbing 100 times or more, a slight mark is left on the surface, but there is no decrease in density, which is in a practically acceptable range. Δ: Stage after rubbing 100 times The decrease in image density is observed, but it is in a practically acceptable range. x: The image density is clearly decreased by rubbing less than 50 times, and the quality is not practical.

3-4. Character Quality Each of the character images prepared above was visually observed and evaluated according to the following criteria.

◎: Negative and positive of 5 point characters can be reproduced without collapse of details ○: Possibility of 5 points of character is starting to show some damage but details are legible △: 5 points of character Although the details are crushed in the positive, it is readable enough and the 7-point character can be reproduced without being crushed. ×: The details are crushed in the negative and positive of the 7-point character.

Tables 6 to 11 show the types of recording media, basis weight, air permeability and Beck's smoothness, and the evaluation results for each ejected ink. Tables 6 to 11 show the evaluation results of the images created using Ink set 1, but the same results were obtained for the images created using Ink set 2.

As is clear from Tables 6 to 8, when an image is formed on a recording medium (art paper or coated paper) having a resin coating amount of 20 g/m ² or more, the ink landed on the unit area of the recording medium. When the image is formed on a recording medium (lightweight coated paper or lightly coated paper) having a maximum coating amount of 20 g/m ² and a resin coating amount of 10 g/m ² or more and less than 20 g/m ² , the recording medium When forming an image on a recording medium (non-coated paper) in which the maximum amount of ink landed on the unit area is 15 g/m ² and the resin coating amount is 0 g/m ² or more and less than 10 g/m ² When the maximum amount of ink landed on the unit area of the recording medium was 10 g/m ² , all of the odor, gloss, curability and character quality were evaluated highly.

As is clear from Tables 9 to 11, when an image is formed on a recording medium (A class paper and B class paper) having an air permeability of 100 seconds or more, the maximum amount of ink landed on the unit area of the recording medium is When forming an image on a recording medium (C class paper) having a large amount of 20 g/m ² and an air permeability of less than 100 seconds, the maximum amount of ink landed on the unit area of the recording medium is 10 g/m ² . Then, the odor, gloss, curability and character quality were all highly evaluated.

Further, when an image is formed on a recording medium (Class A paper) having an air permeability of 100 seconds or more and a Beck's smoothness of 200 seconds or more, the ink landed on the unit area of the recording medium. When the image is formed on a recording medium (B class paper) having a maximum amount of 20 g/m ² and an air permeability of 100 seconds or more and a Beck's smoothness of 1 second or more and less than 200 seconds, When the maximum amount of ink landed on the unit area of the recording medium was 10 g/m ² , all of the odor, gloss, curability and character quality were evaluated highly.

According to the inkjet recording method of the present invention, it is possible to form an image with gel ink having a small difference in gloss between an image-formed area and an image-free area, regardless of the type of recording medium. Therefore, the present invention is expected to broaden the range of application of gel ink by the inkjet method and contribute to the progress and spread of the technology in the same field.

100 Image forming apparatus 110 Inkjet head 111 Nozzle 113 Nozzle surface 120 Conveying section 121 Drive roller 122 Driven roller 123 Conveying belt 130 Irradiating section 140 Control section 150 Storage section 160 Data input section 170 Measuring section 200 Recording medium

Claims (3)

Based on one or more criteria selected from the coating amount of resin of the recording medium, the air permeability of the recording medium, and the smoothness of the recording medium, the maximum amount of ink that can land on the unit area of the recording medium is as follows ( I) to (III) at least one of the steps,
A droplet of an inkjet ink that contains a photopolymerizable compound and a gelling agent and undergoes a sol-gel phase transition depending on temperature so that an amount of the inkjet ink that does not exceed the maximum amount set in the setting step will land on the recording medium. Is discharged from a nozzle of the inkjet head to land on the recording medium,
And a step of irradiating the inkjet ink landed on the recording medium with actinic rays to cure the inkjet ink.
(I)
When the coating amount of the resin contained in the recording medium is 20 g/m ² or more, the maximum amount is 20 g/m ² ,
When the coating amount of the resin included in the recording medium is 10 g/m ² or more and less than 20 g/m ² , the maximum amount is 15 g/m ² ,
When the coating amount of the resin layer is 0 g/m ² or more and less than 10 g/m ² , the maximum amount is 10 g/m ² .
(II)
When the air permeability of the recording medium is 100 seconds or more, the maximum amount is 20 g/m ² ,
The maximum amount of time the air permeability of the recording medium is less than 100 seconds to 10 g / m ²
(III)
When the air permeability of the recording medium is 100 seconds or more and the Beck smoothness of the recording medium is 200 seconds or more, the maximum amount is 20 g/m ² ,
Wherein A is the air permeability of the recording medium is more than 100 seconds, and, when Bekk smoothness of the recording medium is less than 200 seconds or more for 1 second, the maximum amount is set to 15 g / m ² The method according to claim 1, wherein the types of the recording medium are classified based on the criterion. An inkjet head having a nozzle surface, which contains a photopolymerizable compound and a gelling agent, and is provided with a discharge port of a nozzle capable of discharging a droplet of an inkjet ink that undergoes a sol-gel phase transition depending on temperature,
A transport unit that transports the recording medium so that the recording medium facing the inkjet head moves directly below the ejection port of the nozzle of the inkjet in the vertical direction,
An irradiation unit that irradiates the upper surface of the transfer unit with an actinic ray from a light source,
A control unit that controls the inkjet head, the transport unit, the irradiation unit, and the storage unit;
Equipped with
The control unit determines the unit area of the recording medium to be recorded based on one or more criteria selected from the coating amount of the resin of the recording medium, the air permeability of the recording medium, and the smoothness of the recording medium. The maximum amount of ink that can land is set to at least one of the following (I) to (III) , the transport unit is controlled to transport the recording medium, and the inkjet head is controlled to control the unit area of the recording medium. An image forming apparatus, wherein the inkjet ink is ejected so that the maximum amount of ink landed on the ink does not exceed the set maximum amount.
(I)
When the coating amount of the resin contained in the recording medium is 20 g/m ² or more, the maximum amount is 20 g/m ² ,
When the coating amount of the resin included in the recording medium is 10 g/m ² or more and less than 20 g/m ² , the maximum amount is 15 g/m ² ,
When the coating amount of the resin layer is 0 g/m ² or more and less than 10 g/m ² , the maximum amount is 10 g/m ² .
(II)
When the air permeability of the recording medium is 100 seconds or more, the maximum amount is 20 g/m ² ,
The maximum amount of time the air permeability of the recording medium is less than 100 seconds to 10 g / m ²
(III)
When the air permeability of the recording medium is 100 seconds or more and the Beck smoothness of the recording medium is 200 seconds or more, the maximum amount is 20 g/m ² ,
Wherein A is the air permeability of the recording medium is more than 100 seconds, and, when Bekk smoothness of the recording medium is less than 200 seconds or more for 1 second, the maximum amount is set to 15 g / m ²

Images