JP7600653B2 - Precoat agent and image forming method using the same - Google Patents

Description

The present invention relates to a precoat agent and an image forming method using the precoat agent.

The inkjet method can easily and inexpensively produce images, and is therefore used in a variety of printing fields, including various types of printing, marking, fine line formation, and special printing such as color filters. The inkjet method allows for digital printing without using plates, making it particularly suitable for applications in which a variety of images are produced in small quantities.

Inkjet image formation methods are used in various printing fields because they can form images easily and inexpensively. One type of inkjet ink is known to contain an actinic radiation polymerizable compound and a polymerization initiator that hardens when irradiated with actinic radiation (hereinafter simply referred to as "actinic radiation curable ink"). When droplets of actinic radiation curable ink are deposited on the surface of a recording medium and the deposited droplets are irradiated with actinic radiation, the ink hardens and a cured film is formed on the surface of the recording medium. By forming this cured film, a desired image can be formed.

On the other hand, in the above image forming method, when actinic radiation curable ink is applied to the surface of a recording medium that absorbs ink, such as paper, some of the ink that is ejected from the inkjet head and lands on the recording medium penetrates into the recording medium, making it difficult to control the ink dot diameter to a specified size and making it difficult to obtain an image with good image quality.

As a method for solving the above problems, an image formation method is being considered in which a precoat layer is formed on the surface of a recording medium, and an actinic radiation curable ink is applied onto the precoat layer to form an image.

For example, Patent Document 1 describes an image forming method in which a precoat agent applied to the surface of an intermediate transfer body is transferred to the surface of a recording medium, ink is applied to the surface of the transferred precoat agent, and actinic radiation is applied to cure the precoat agent and ink simultaneously. Patent Document 1 claims that by applying a precoat agent to the surface of the recording medium before applying ink, it is possible to provide an image forming method that can easily and quickly produce high image quality.

JP 2012-192607 A

According to the inventor's research, by using the pretreatment liquid and ink, which are actinic radiation curable compositions, described in Patent Document 1, it was possible to simultaneously cure the pretreatment liquid applied to the surface of the recording medium and the ink applied to the surface of the pretreatment liquid by irradiation with actinic radiation. However, with the pretreatment liquid of Patent Document 1, the ink would sometimes seep into the interior of the recording medium and seep out while being applied. Also, it was sometimes impossible to control the dot diameter of the ink applied to the surface of the pretreatment liquid to a predetermined size.

The present invention has been made in consideration of the above points, and has as its first object to provide a precoat agent that can control the ink dot diameter and form an image in which the precoat agent is less likely to seep out. It also has as its second object to provide an image forming method that uses the precoat agent.

The precoat agent of the present invention, which is used to solve the above problems, is a precoat agent that is applied to the surface of a recording medium before the actinic ray-curable ink is applied in an image forming method using the actinic ray-curable ink, and the precoat agent contains an actinic ray-polymerizable compound, and glucose or glucan, or a derivative thereof.

The image forming method of the present invention for solving the above problem includes a step of applying the above precoat agent to the surface of a recording medium, a step of applying an actinic ray curable ink to the surface of the recording medium to which the precoat agent has been applied, and a step of irradiating the surface to which the precoat agent and the actinic ray curable ink have been applied with actinic rays to simultaneously cure the precoat agent and the actinic ray curable ink.

According to the present invention, it is possible to provide a precoat agent that can control the ink dot diameter and form an image in which the precoat agent is less likely to seep out. It is also possible to provide an image forming method that uses the precoat agent.

FIG. 1 is a schematic diagram showing the configuration of an image forming apparatus for carrying out an image forming method according to one embodiment of the present invention.

One embodiment of the present invention is described in detail below.

1. Precoat Agent A precoat agent according to one embodiment of the present invention is applied to the surface of a recording medium that absorbs ink, such as paper (hereinafter, simply referred to as an "absorbent recording medium"), before ink is applied to the surface, and serves to inhibit the ink from penetrating into the absorbent recording medium and to control the wetting and spreading of the ink.

The precoat agent contains an actinic radiation polymerizable compound, and glucose or glucan or a derivative thereof. The precoat agent may also contain a polymerization initiator, water (e.g., ion-exchanged water), an adjuster for adjusting the surface tension and viscosity, and a polymerization inhibitor.

1-1. Actinic ray polymerizable compound An actinic ray polymerizable compound is a compound that is polymerized and crosslinked by irradiation with actinic rays and hardens. Examples of actinic rays include electron beams, ultraviolet rays, α rays, γ rays, and X-rays. Among the actinic rays, ultraviolet rays or electron beams are preferred, and ultraviolet rays are more preferred. Examples of the actinic ray polymerizable compound include radical polymerizable compounds, cation polymerizable compounds, or mixtures thereof. The actinic ray polymerizable compound may be any of a monomer, a polymerizable oligomer, a prepolymer, and a mixture thereof.

When a glucan derivative having an ethylene oxide group (described later) is used as the glucan derivative, it is preferable that the actinic radiation polymerizable compound is a compound having an ethylene oxide group or a propylene oxide group, from the viewpoint of increasing the affinity with the glucan derivative and more effectively suppressing the penetration of the actinic radiation polymerizable compound into the interior of the recording medium.

The radical polymerizable compound is a compound having an ethylenically unsaturated double bond group in the molecule. The radical polymerizable compound may be a monofunctional or polyfunctional compound. Examples of the radical polymerizable compound include vinyl monomers such as (meth)acrylate, styrene, and allyl ether, which are unsaturated carboxylic acid ester compounds. 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.

Examples of monofunctional (meth)acrylates include isoamyl (meth)acrylate, stearyl (meth)acrylate, lauryl (meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, isomylstyryl (meth)acrylate, isostearyl (meth)acrylate, 2-ethylhexyl-diglycol (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 2-(meth)acryloyloxyethylhexahydrophthalic acid, butoxyethyl (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, methoxydiethylene glycol (meth)acrylate, methoxypolyethylene These include ethylene 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)acryloyloxyethyl succinate, 2-(meth)acryloyloxyethyl phthalate, 2-(meth)acryloyloxyethyl-2-hydroxyethyl-phthalate, and t-butylcyclohexyl (meth)acrylate.

Examples of polyfunctional (meth)acrylates include 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, neopentyl ethylene glycol di(meth)acrylate, dimethylol-tricyclodecane di(meth)acrylate, PO adduct di(meth)acrylate of bisphenol A, hydroxypivalic acid neopentyl glycol di(meth)acrylate, polytetramethylene glycol di(meth)acrylate, polyethylene glycol Examples of the acrylates include difunctional (meth)acrylates such as cole di(meth)acrylate, dipropylene glycol di(meth)acrylate, and tripropylene glycol di(meth)acrylate; trifunctional (meth)acrylates such as polyethylene glycol tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, and pentaerythritol tri(meth)acrylate; tri- or higher functional (meth)acrylates such as pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, glycerin propoxy tri(meth)acrylate, and pentaerythritol ethoxy tetra(meth)acrylate; oligomers having a (meth)acryloyl group, including polyester acrylate oligomers, and modified products thereof. Examples of the modified products include ethylene oxide-modified (EO-modified) (meth)acrylates in which ethylene oxide groups have been inserted, and propylene oxide-modified (PO-modified) (meth)acrylates in which propylene oxide has been inserted. The polyfunctional (meth)acrylates may be used alone or in combination of two or more types.

For the reasons mentioned above, it is preferable that the (meth)acrylate is a compound having an ethylene oxide group or a propylene oxide group.

A cationic polymerizable compound is a compound that has a cationic polymerizable group in the molecule. Examples of cationic polymerizable compounds include monofunctional and polyfunctional epoxy compounds, monofunctional and polyfunctional vinyl ether compounds, monofunctional and polyfunctional oxetane compounds, etc.

Examples of monofunctional epoxy compounds include vinylcyclohexene monoepoxide.

Examples of polyfunctional epoxy compounds include 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate, bis(3,4-epoxycyclohexylmethyl)adipate, ε-caprolactone-modified 3,4-epoxycyclohexylmethyl 3',4'-epoxycyclohexanecarboxylate, alicyclic epoxy resins such as 1-methyl-4-(2-methyloxiranyl)-7-oxabicyclo[4,1,0]heptane, 2-(3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy)cyclohexanone-meta-dioxane and bis(2,3-epoxycyclopentyl)ether, diglycidyl ether of 1,4-butanediol, diglycidyl ether of 1,6-hexanediol, triglycidyl ether of glycerin ... These include aliphatic epoxy compounds including triglycidyl ether of dimethylolpropane, diglycidyl ether of polyethylene glycol, diglycidyl ether of propylene glycol, polyglycidyl ether of polyether polyol obtained by adding one or more alkylene oxides (such as ethylene oxide and propylene oxide) to aliphatic polyhydric alcohols such as ethylene glycol, propylene glycol, and glycerin, as well as aromatic epoxy compounds including di- or polyglycidyl ether of bisphenol A or its alkylene oxide adduct, di- or polyglycidyl ether of hydrogenated bisphenol A or its alkylene oxide adduct, and novolac type epoxy resin.

Examples of monofunctional vinyl ether compounds include ethyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, octadecyl vinyl ether, cyclohexyl vinyl ether, hydroxybutyl vinyl ether, 2-ethylhexyl vinyl ether, cyclohexanedimethanol monovinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, isopropenyl ether-o-propylene carbonate, dodecyl vinyl ether, diethylene glycol monovinyl ether, and octadecyl vinyl ether.

Examples of polyfunctional vinyl ether compounds include di- or trivinyl ether compounds including ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, propylene glycol divinyl ether, dipropylene glycol divinyl ether, butanediol divinyl ether, hexanediol divinyl ether, cyclohexanedimethanol divinyl ether, and trimethylolpropane trivinyl ether.

Examples of monofunctional oxetane compounds include 3-hydroxymethyl-3-methyloxetane, 3-hydroxymethyl-3-ethyloxetane, 3-hydroxymethyl-3-propyloxetane, 3-hydroxymethyl-3-normal butyloxetane, 3-hydroxymethyl-3-phenyloxetane, 3-hydroxymethyl-3-benzyloxetane, 3-hydroxyethyl-3-methyloxetane, 3-hydroxyethyl-3-ethyloxetane, 3-hydroxyethyl-3-propyloxetane, 3-hydroxyethyl-3-phenyloxetane, 3-hydroxypropyl-3-methyloxetane, 3-hydroxypropyl-3-ethyloxetane, 3-hydroxypropyl-3-propyloxetane, 3-hydroxypropyl-3-phenyloxetane, 3-hydroxybutyl-3-methyloxetane, and 3-ethyl-3-(2-ethylhexyloxymethyl)oxetane.

Examples of polyfunctional oxetane compounds include 1,4 bis{[(3-ethyl-3-oxetanyl)methoxy]methyl}benzene and di[1-ethyl(3-oxetanyl)]methyl ether.

Among the actinic radiation polymerizable compounds, it is particularly preferable that the radical polymerizable compound has a Hansen solubility parameter (HSP value) of more than 17, more preferably a radical polymerizable compound with an HSP value of 17.5 to 20.5, and even more preferably a radical polymerizable compound with an HSP value of 19 to 20.5. By having the HSP value of the radical polymerizable compound exceeding 17, even if the precoat agent contains water (e.g., ion-exchanged water), the difference in SP value between water and the actinic radiation polymerizable compound is not too large, so that water and the actinic radiation polymerizable compound are easily compatible with each other. As a result, water is easily retained in the precoat agent, so that even if the precoat agent is applied to the surface of the recording medium, water can be prevented from penetrating into the inside of the recording medium and seeping out. In addition, by having an HSP value of more than 17, it is easily compatible with highly polar compounds such as glucose or glucan or derivatives thereof. As a result, the hydrophilicity of the precoat agent is increased, and it becomes difficult to be compatible with actinic radiation curable ink, so that it is easy to control the dot diameter of the ink applied to the surface of the precoat agent. In addition, by having an HSP value of 20.5 or less, the hydrophilicity of the precoat agent is not excessively high, which can prevent the precoat film applied to the surface of the recording medium from expanding or softening due to moisture absorption.

Of the above-mentioned radical polymerizable compounds, polypropylene glycol diacrylate with an HSP value of 17.6, neopentyl-ethylene glycol diacrylate with an HSP value of 17.7, polyethylene glycol triacrylate with an HSP value of 19.0, and polyethylene glycol diacrylate with an HSP value of 19.5 are preferred, and polyethylene glycol triacrylate with an HSP value of 19.0 and polyethylene glycol diacrylate with an HSP value of 19.5 are more preferred.

In addition, the content of the active radiation polymerizable compound contained in the precoat agent is preferably 65.8% by mass or more and 99.3% by mass or less, and more preferably 80.6% by mass or more and 98.4% by mass or less, based on the total mass of the precoat agent.

1-2. Glucose or glucan or derivatives thereof The precoating agent according to one embodiment of the present invention contains glucose or glucan or derivatives thereof. Glucose is a monosaccharide having six carbon atoms and is also a structural unit of polysaccharides. Glucan is a polymer in which glucose is bonded via glycosidic bonds. The polymer has a chain structure or a cyclic structure.

Examples of glucose or its derivatives include D-glucose, D-mannose, D-galactose, 2-deoxy-D-glucose, n-octyl-β-D-glucoside, penta-O-ethyl-β-D-glucopyranose, penta-O-acetyl-β-D-glucopyranose, penta-O-benzyl-β-D-glucopyranose, etc. Among the above glucose or its derivatives, D-glucose, penta-O-ethyl-β-D-glucopyranose, penta-O-acetyl-β-D-glucopyranose, and penta-O-benzyl-β-D-glucopyranose are preferred, and D-glucose and penta-O-acetyl-β-D-glucopyranose are more preferred.

Examples of glucans or derivatives thereof include maltose, sucrose, maltotriose, dextran, cellobiose, α-D-cellobiose octaacetate, trimethyl-β-cyclodextrin, triacetyl-β-cyclodextrin, cellulose derivatives, starch, amylose, amylopectin, etc. Among the above glucans, linear glucans or derivatives thereof such as maltose, maltotriose, α-D-cellobiose octaacetate, and linear cellulose derivatives are preferred, with linear cellulose derivatives being more preferred.

Examples of the above cellulose derivatives include cellulose, methyl cellulose, ethyl cellulose, acetyl cellulose (cellulose acetate), carboxymethyl cellulose, and other cellulose derivatives in which some or all of the hydrogen atoms of the hydroxyl groups have been replaced with alkyl groups, acetyl groups, or carboxymethyl groups, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxybutyl cellulose, hydroxypropyl methyl cellulose, hydroxybutyl methyl cellulose, and cationized hydroxyethyl cellulose, and other cellulose derivatives in which some or all of the hydrogen atoms of the hydroxyl groups have been replaced with hydroxyalkyl groups (hereinafter also referred to as hydroxyalkyl cellulose).

The cellulose derivative is preferably a hydroxyalkyl cellulose. The hydroxyalkyl group of the hydroxyalkyl cellulose preferably has 1 to 9 carbon atoms, more preferably 1 to 4 carbon atoms. The OH portion of the hydroxyalkyl group may be at the terminal of the alkyl group or at a position other than the terminal.

Among the above hydroxyalkyl celluloses, hydroxymethyl cellulose, hydroxyethyl cellulose, and hydroxypropyl cellulose are preferred, hydroxymethyl cellulose and hydroxyethyl cellulose are more preferred, and hydroxyethyl cellulose is even more preferred.

By including the above-mentioned actinic radiation polymerizable compound and the above-mentioned glucose or glucan or derivatives thereof in the precoat agent, an image can be obtained without the precoat agent seeping out even when the precoat agent is applied to the surface of an absorbent recording medium (e.g., plain paper). This is believed to be because (1) the intermolecular force acts between the polar functional group (e.g., hydroxyl group) contained in the glucose or glucan or derivatives thereof and the hydroxyl group of cellulose contained in the recording medium (e.g., plain paper), suppressing the penetration of the glucose or glucan or derivatives thereof into the inside of the recording medium. (2) The polar functional group (e.g., hydroxyl group) of the glucose or glucan or derivatives thereof has a high affinity with the polar functional group (e.g., carbonyl group) of the actinic radiation polymerizable compound, so that the actinic radiation polymerizable compound tends to remain inside the precoat agent together with the glucose or glucan or derivatives thereof, suppressing the penetration into the recording medium. (3) The precoat agent is cured by irradiation with actinic radiation while its penetration into the recording medium is suppressed, so it is believed to be less likely to seep out of the recording medium after the image is formed.

By applying a precoat agent containing the above-mentioned actinic radiation polymerizable compound and the above-mentioned glucose or glucan or a derivative thereof to the surface of an absorbent recording medium (e.g., plain paper), droplets of actinic radiation curable ink can be made to wet and spread to a substantially uniform size on the surface of the precoat agent, forming a clear line image without unevenness and improving image quality. This is thought to be because the polar functional group (e.g., hydroxyl group) of glucose or glucan or a derivative thereof has a high affinity with the polar functional group (e.g., carbonyl group) of the actinic radiation polymerizable compound contained in the actinic radiation curable ink, so that the actinic radiation curable ink is more likely to remain on the surface of the precoat agent than to penetrate into the interior of the recording medium, and therefore an amount of actinic radiation curable ink sufficient to wet and spread on the surface of the precoat agent can be secured.

Among the above-mentioned glucose or glucan or derivatives thereof, the use of hydroxyethyl cellulose, which is a cellulose derivative, can provide images with good image quality and can further suppress bleeding from the recording medium after image formation. This is because hydroxyethyl cellulose is cellulose to which ethylene oxide has been added, and therefore has a high affinity with actinic radiation polymerizable compounds having ethylene oxide groups or propylene oxide groups. This makes it easier for the actinic radiation polymerizable compounds to remain inside the precoat agent together with glucose or glucan or derivatives thereof, suppressing penetration into the recording medium.

The content of glucose or glucan or a derivative thereof contained in the precoat agent is preferably 3% by mass or less, more preferably 0.5% by mass or more and 3% by mass or less, and even more preferably 0.5% by mass or more and 2% by mass or less, based on the total mass of the precoat agent. If the content is 0.5% by mass or more, it is possible to prevent the precoat agent from penetrating into the interior of the recording medium and seeping out, as described above. If the content is 3% by mass or less, glucose or glucan or a derivative thereof is sufficiently dissolved in the actinic radiation polymerizable compound described above, and is therefore uniformly present in the precoat agent applied to the surface of the recording medium. This allows the actinic radiation curable ink, which has a high affinity with the precoat agent, to be uniformly wetted and spread.

1-3. Polymerization initiator The precoat agent according to one embodiment of the present invention may contain a polymerization initiator. The polymerization initiator may be any that can initiate polymerization of the above-mentioned actinic ray-polymerizable compound by irradiation with actinic rays. For example, when the precoat agent contains a radical polymerizable compound, the polymerization initiator may be a photoradical initiator, and when the actinic ray-curable ink contains a cationically polymerizable compound, the polymerization initiator may be a photocationic initiator (photoacid generator).

Radical polymerization initiators include intramolecular bond cleavage type radical polymerization initiators and intramolecular hydrogen abstraction type radical polymerization initiators.

Examples of intramolecular bond cleavage type radical polymerization initiators include acetophenone-based initiators including diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, benzyl 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-methylthiophenyl)propan-1-one, and 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone, benzoins including benzoin, benzoin methyl ether, and benzoin isopropyl ether, acylphosphine oxide-based initiators including 2,4,6-trimethylbenzoin diphenylphosphine oxide, and benzyl and methylphenyl glyoxyesters.

Examples of intramolecular hydrogen abstraction type radical polymerization initiators include benzophenone-based initiators including benzophenone, o-benzoylmethylbenzoate, 4-phenylbenzophenone, 4,4'-dichlorobenzophenone, hydroxybenzophenone, 4-benzoyl-4'-methyl-diphenyl sulfide, acrylated benzophenone, 3,3',4,4'-tetra(t-butylperoxycarbonyl)benzophenone, and 3,3'-dimethyl-4-methoxybenzophenone; thioxanthone-based initiators including 2-isopropylthioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, and 2,4-dichlorothioxanthone; aminobenzophenone-based initiators including Michler's ketone and 4,4'-diethylaminobenzophenone; 10-butyl-2-chloroacridone, 2-ethylanthraquinone, 9,10-phenanthrenequinone, and camphorquinone.

Examples of the cationic polymerization initiator include photoacid generators, such as B(C 6 F 5 ) ₄ ⁻ , PF ₆ ⁻ , AsF ₆ ⁻ , SbF ₆ ⁻ , and CF ₃ SO _{3 −} salts of aromatic onium compounds including diazonium, ammonium, _iodonium , sulfonium, and phosphonium, sulfonates that generate sulfonic acid, halides that photogenerate hydrogen halide, and iron ^- allene complexes.

The content of the polymerization initiator can be set arbitrarily as long as the precoat agent is sufficiently cured by irradiation with actinic radiation (e.g., ultraviolet light) and does not reduce the applicability to the surface of the recording medium. For example, the content of the polymerization initiator is preferably 0.1% by mass or more and 20% by mass or less, and more preferably 1% by mass or more and 12% by mass or less, based on the total mass of the precoat agent.

1-4. Water The precoat agent according to an embodiment of the present invention may contain water. The water contained in the precoat agent is not particularly limited, and may be ion-exchanged water, distilled water, or pure water. The water content is preferably 10% by mass or less, more preferably 0% by mass or more and 10% by mass or less, and even more preferably 0% by mass or more and 5% by mass or less, based on the total mass of the precoat agent. By setting the water content to 10% by mass or less, based on the total mass of the precoat agent, the precoat agent has sufficient curability, and therefore it is possible to prevent the precoat agent remaining after curing from being absorbed into the recording medium and seeping out.

The precoat agent according to an embodiment of the present invention may contain an adjuster for adjusting the surface tension and viscosity. Examples of the adjuster include surfactants.

Examples of surfactants include anionic surfactants including dialkyl sulfosuccinates, alkyl naphthalene sulfonates, and fatty acid salts, nonionic surfactants including polyoxyethylene alkyl ethers, polyoxyethylene alkyl allyl ethers, acetylene glycols, and polyoxyethylene-polyoxypropylene block copolymers, cationic surfactants including alkylamine salts and quaternary ammonium salts, silicone-based surfactants, and fluorine-based surfactants.

The content of the regulator is preferably 0.005% by mass or more and 1% by mass or less relative to the total mass of the precoat agent, and more preferably 0.01% by mass or more and 0.2% by mass or less relative to the total mass of the precoat agent.

1-6. Polymerization Inhibitor The precoat agent according to an embodiment of the present invention may contain a polymerization inhibitor.

Examples of polymerization inhibitors include (alkyl)phenols, hydroquinone, catechol, resorcinol, p-methoxyphenol, t-butylcatechol, t-butylhydroquinone, pyrogallol, 1,1-picrylhydrazyl, phenothiazine, p-benzoquinone, nitrosobenzene, 2,5-di-t-butyl-p-benzoquinone, dithiobenzoyl disulfide, picric acid, cupferron, aluminum N-nitrosophenylhydroxylamine, tri-p-nitrophenylmethyl, N-(3-oxyanilino-1,3-dimethylbutylidene)aniline oxide, dibutylcresol, cyclohexanone oxime cresol, guaiacol, o-isopropylphenol, butylaldoxime, methyl ethyl ketoxime, and cyclohexanone oxime.

The content of the polymerization inhibitor can be 0.05% by mass or more and 0.2% by mass or less based on the total mass of the precoat agent.

1-7. Physical properties of the precoat agent The viscosity of the precoat agent according to one embodiment of the present invention is preferably 1 mPa·s or more and 100 mPa·s or less, and preferably 5 mPa·s or more and 30 mPa·s or less at 20°C. If the viscosity of the precoat agent is 1000 cPs or more, when the actinic radiation curable ink (described later) is applied to the surface of the precoat agent, the precoat agent can be prevented from following the wetting and spreading of the actinic radiation curable ink. This allows the ink droplets to have an appropriate size, improving the hiding rate and preventing image unevenness, thereby allowing a high-definition image to be obtained. The viscosity of the precoat agent at 20°C can be measured using a stress-controlled rheometer (Physica MCR301 (diameter of cone plate: 75 mm, cone angle: 1.0°) manufactured by Anton Paar).

The amount of the precoat agent applied is preferably 1 g/m2 or ^more and 50 g/m2 ^or less, and more preferably 2 g/m2 or ^more and 30 g/m2 or ^less , relative to the recording medium. By applying the precoat agent in an amount of 1 g/m2 ^{or more} , the actinic ray curable ink can be made to wet and spread more sufficiently, so that a clear line image without unevenness can be formed. In addition, by applying the precoat agent in an amount of 50 g/m2 or ^less , the precoat agent can be quickly cured when irradiated with actinic rays, so that the precoat agent can be prevented from penetrating into the recording medium.

The structure of glucose or glucan or a derivative thereof contained in the precoating agent can be confirmed by extracting glucose or glucan or a derivative thereof with an aqueous solvent, dissolving the extracted glucose or the like in heavy water (D ₂ O), and performing ¹ H-NMR and ¹³ C-NMR measurements with an FT-NMR device. Alternatively, the structure can be confirmed by alkylating (e.g., ethylating) the hydroxyl groups of the extracted glucose or glucan or a derivative thereof, and then measuring the number of alkylated hydroxyl groups, the number of hydrogen atoms at the 1st position of glucose or the 6th position of glucose, and mass spectrometry.

2. Actinic ray curable ink The actinic ray curable ink according to one embodiment of the present invention is an ink that contains an actinic ray polymerizable compound, and is cured by polymerization and crosslinking of the actinic ray polymerizable compound upon irradiation with actinic rays. The actinic ray curable ink may also contain, as necessary, a polymerization initiator, a gelling agent, a polymerization inhibitor, a coloring material such as a dye or pigment, a dispersant for dispersing the pigment, a fixing resin for fixing the pigment to the substrate, a surfactant, a pH adjuster, a moisturizing agent, an ultraviolet absorbing agent, and the like. Only one type of other component may be contained in the composition, or two or more types may be contained.

2-1. Actinic ray polymerizable compound The actinic ray polymerizable compound may include an actinic ray polymerizable compound that can be contained in the above-mentioned precoat agent. In the present invention, the actinic ray polymerizable compound contained in the actinic ray curable ink is preferably the same type of compound as the actinic ray polymerizable compound contained in the precoat agent.

In addition, the content of the actinic radiation polymerizable compound is preferably 1% by mass or more and 97% by mass or less, and more preferably 30% by mass or more and 90% by mass or less, based on the total mass of the actinic radiation curable ink.

The actinic radiation curable ink according to an embodiment of the present invention preferably contains a polymerization initiator. The polymerization initiator may be the same as the polymerization initiator that can be contained in the precoat agent described above, and may be selected depending on the type of actinic radiation polymerizable compound.

The content of the polymerization initiator can be set arbitrarily within a range in which the actinic ray curable ink is sufficiently cured by irradiation with actinic rays (e.g., ultraviolet light) and the ejection properties of the actinic ray curable ink are not reduced. For example, the content of the polymerization initiator is preferably 0.1% by mass or more and 20% by mass or less, and more preferably 1% by mass or more and 12% by mass or less, based on the total mass of the actinic ray curable ink.

The actinic ray curable ink according to an embodiment of the present invention preferably contains a gelling agent. The gelling agent is an organic substance that is solid at room temperature but becomes liquid when heated, thereby causing the actinic ray curable ink to undergo a sol-gel phase transition in response to a change in temperature.

The gelling agent preferably crystallizes in the ink at a temperature equal to or lower than the gelling temperature of the ink. Here, the gelling temperature refers to the temperature at which the ink undergoes a phase transition from sol to gel and the viscosity of the ink changes suddenly when the ink, which has been solated or liquefied by heating, is cooled. Specifically, the ink that has been solated or liquefied is cooled while the viscosity is measured using, for example, a rheometer MCR300 (manufactured by Anton Paar), and the temperature at which the viscosity increases suddenly can be regarded as the gelling temperature of the ink.

When the gelling agent crystallizes in the ink, a structure may be formed in which the actinic radiation polymerizable compound is encapsulated in a three-dimensional space formed by the gelling agent and wax crystallized into plate-like shapes (such a structure will be referred to as a "house of cards structure" below). When a house of cards structure is formed, the liquid actinic radiation polymerizable compound is held within the space, making it harder for the ink to spread when dots are formed, and the pinning ability of the ink is enhanced. When the pinning ability of the ink is enhanced, it is possible to suppress excessive spreading of dots formed when the ink is adhered to the surface of a recording medium or precoat agent.

Examples of gelling agents include aliphatic ketone waxes such as dipentadecyl ketone, diheptadecyl ketone, dilignoceryl ketone, dibehenyl ketone, distearyl ketone, dieicosyl ketone, dipalmityl ketone, dimyristyl ketone, lauryl myristyl ketone, lauryl palmityl ketone, myristyl palmityl ketone, myristyl stearyl ketone, myristyl behenyl ketone, palmityl stearyl ketone, palmityl behenyl ketone and stearyl behenyl ketone; cetyl palmitate, stearyl stearate, behenyl behenate, icosyl icosanoate, behenyl stearate, palmityl stearate, lauryl stearate, stearyl palmitate, myristyl myristate, cetyl myristate, octyldodecyl myristate, oleic acid ... aliphatic ester waxes such as stearyl oleate, stearyl erucate, stearyl linoleate, behenyl oleate, and arachidyl linoleate; amide compounds such as N-lauroyl-L-glutamic acid dibutylamide, and N-(2-ethylhexanoyl)-L-glutamic acid dibutylamide; dibenzylidene sorbitols such as 1,3:2,4-bis-O-benzylidene-D-glucitol; petroleum waxes such as paraffin wax, microcrystalline wax, and petrolatum; vegetable waxes such as candelilla wax, carnauba wax, rice wax, wood wax, jojoba oil, jojoba solid wax, and jojoba ester; animal waxes such as beeswax, lanolin, and spermaceti; mineral waxes such as montan wax and hydrogenated wax; hardened castor oil wax, hardened castor oil wax, and hardened castor oil wax. derivatives of cane oil or hydrogenated castor oil; modified waxes such as montan wax derivatives, paraffin wax derivatives, microcrystalline wax derivatives, and polyethylene wax derivatives; higher fatty acids such as behenic acid, arachidic acid, stearic acid, palmitic acid, myristic acid, lauric acid, oleic acid, and erucic acid; higher alcohols such as stearyl alcohol and behenyl alcohol; hydroxystearic acids such as 12-hydroxystearic acid; 12-hydroxystearic acid derivatives; fatty acid amides such as lauric acid amide, stearic acid amide, behenic acid amide, oleic acid amide, erucic acid amide, ricinoleic acid amide, and 12-hydroxystearic acid amide; N-substituted fatty acid amides such as N-stearyl stearic acid amide and N-oleyl palmitic acid amide. amides; special fatty acid amides such as N,N'-ethylene bisstearylamide, N,N'-ethylene bis-12-hydroxystearylamide, and N,N'-xylylene bisstearylamide; higher amines such as dodecylamine, tetradecylamine, and octadecylamine; fatty acid ester compounds such as stearyl stearic acid, oleyl palmitic acid, glycerin fatty acid ester, sorbitan fatty acid ester, propylene glycol fatty acid ester, ethylene glycol fatty acid ester, and polyoxyethylene fatty acid ester; sucrose fatty acid esters such as sucrose stearic acid and sucrose palmitic acid; synthetic waxes such as polyethylene wax and α-olefin maleic anhydride copolymer wax; polymerizable waxes; dimer acids; dimer diols, etc. These waxes may be used alone or in combination of two or more types.

Of these, from the viewpoint of further enhancing the pinning properties of the ink, aliphatic ketone waxes, aliphatic ester waxes, higher fatty acids, higher alcohols and fatty acid amides are preferred, and aliphatic ketone waxes or aliphatic ester waxes in which the carbon chains on both sides of the keto group or ester group each have a carbon number of 9 or more and 25 or less are more preferred.

The content of the gelling agent is preferably 0.5% by mass or more and less than 10% by mass of the total mass of the actinic ray curable ink, more preferably 1% by mass or more and less than 10% by mass of the total mass of the actinic ray curable ink, and even more preferably 2% by mass or more and less than 7% by mass of the total mass of the actinic ray curable ink.

The actinic radiation curable ink may contain a polymerization inhibitor. The polymerization inhibitor may be the same compound as the polymerization inhibitor that can be contained in the precoat agent.

The content of the polymerization inhibitor can be 0.05% by mass or more and 0.2% by mass or less based on the total mass of the actinic radiation curable ink.

2-5. Coloring material The actinic ray curable ink may contain a coloring material. Coloring materials include pigments and dyes. From the viewpoint of further increasing the dispersion stability of the actinic ray curable ink and forming an image with high weather resistance, it is preferable that the coloring material is a pigment. Examples of pigments include organic pigments and inorganic pigments. Examples of dyes include various oil-soluble dyes.

The pigments can be selected from, for example, red or magenta pigments, yellow pigments, green pigments, blue or cyan pigments, and black pigments listed in the Color Index, depending on the color of the image to be formed.

The content of the pigment or dye is preferably 0.1% by mass or more and 20% by mass or less, and more preferably 0.4% by mass or more and 10% by mass or less, based on the total mass of the actinic ray curable ink. If the content of the pigment or dye is 0.1% by mass or more, based on the total mass of the actinic ray curable ink, the color development of the resulting image will be sufficient. If the content of the pigment or dye is 20% by mass or less, based on the total mass of the ink, the viscosity of the ink will not increase too much.

2-6. Dispersant The pigment may be dispersed with a dispersant. The dispersant may be any dispersant capable of dispersing the pigment sufficiently. Examples of dispersants include hydroxyl group-containing carboxylic acid esters, 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, naphthalene sulfonic acid formalin condensate salts, aromatic sulfonic acid formalin condensate salts, polyoxyethylene alkyl phosphate esters, polyoxyethylene nonylphenyl ether, and stearylamine acetate.

The content of the dispersant is preferably 10% by mass or more and 200% by mass or less, and more preferably 20% by mass or more and 100% by mass or less, based on the total mass of the pigment. When the content of the dispersant is 10% by mass or more based on the total mass of the pigment, the dispersion stability of the pigment is improved, and when the content of the dispersant is 200% by mass or less based on the total mass of the pigment, the ejection of the ink from the inkjet head becomes more stable.

2-7 Fixing Resin The actinic radiation curable ink may contain a fixing resin in order to further improve the abrasion resistance and blocking resistance of the coating film.

Examples of fixing resins include (meth)acrylic resins, epoxy resins, polysiloxane resins, maleic acid resins, vinyl resins, polyamide resins, nitrocellulose, cellulose acetate, ethyl cellulose, ethylene-vinyl acetate copolymers, urethane resins, polyester resins, and alkyd resins.

The content of the fixing resin can be, for example, 1% by mass or more and 10% by mass or less relative to the total mass of the actinic radiation polymerizable compound.

2-8. Surfactant The actinic ray curable ink may contain a surfactant.

Surfactants can adjust the surface tension of the ink, thereby adjusting the wettability of the ink to the substrate after application, and can also suppress the coalescence of adjacent droplets.

Examples of surfactants include silicone-based surfactants, acetylene glycol-based surfactants, and fluorine-based surfactants having perfluoroalkenyl groups.

The surfactant content is preferably 0.001% by mass or more and 10% by mass or less, and more preferably 0.001% by mass or more and 1% by mass or less, relative to the total mass of the actinic radiation curable ink.

2-9. Other Components In addition to the components described above, the actinic ray curable ink may contain, as necessary, a viscosity adjuster, a resistivity adjuster, a film-forming agent, an ultraviolet absorber, an antioxidant, a discoloration inhibitor, an anti-mold agent, an anti-rust agent, and the like.

2-10. Physical Properties of Actinic Ray Curable Ink From the viewpoint of further improving the ejection properties from an inkjet head, when the actinic ray curable ink does not contain a gelling agent, the viscosity of the actinic ray curable ink at 40° C. is preferably 3 mPa·s or more and 20 mPa·s or less. When the actinic ray curable ink contains a gelling agent, the viscosity of the actinic ray curable ink at 80° C. is preferably 3 mPa·s or more and 20 mPa·s or less. When the viscosity at 80° C. is 3 mPa·s or more and 20 mPa·s or less, the actinic ray curable ink is less likely to gel when ejected from an inkjet head, and therefore the actinic ray curable ink can be ejected more stably. Furthermore, when the actinic ray curable ink contains a gelling agent, from the viewpoint of sufficiently gelling the ink when it lands and is cooled to room temperature, the viscosity of the actinic ray curable ink at 25° C. is preferably 1000 mPa·s or more. If the viscosity at 25° C. is 1000 mPa·s or more, the ink droplets applied to the surface of the recording medium to which the precoat agent has been applied are less likely to spread and are less likely to coalesce with each other.

The viscosities of actinic radiation curable ink at 40°C and 80°C are determined by heating the actinic radiation curable ink to 100°C, measuring the viscosity with a stress-controlled rheometer "Physica MCR301" (manufactured by Anton Paar), and then cooling the ink to 40°C under conditions of a shear rate of 11.7 (1/s) and a cooling rate of 0.1°C/s. The viscosity at 40°C and 80°C is then read from the viscosity temperature change curve obtained.

2-11. Method for preparing actinic ray curable ink The actinic ray curable ink can be prepared by mixing the actinic ray polymerizable compound, polymerization initiator, polymerization inhibitor, colorant, and any other components under heating. At this time, it is preferable to filter the obtained mixture through a predetermined filter. When preparing an ink containing a pigment, it is preferable to prepare a pigment dispersion containing the pigment and the actinic ray polymerizable compound, and then mix the pigment dispersion with other components. The pigment dispersion may further contain a dispersant.

The pigment dispersion can be prepared by dispersing a pigment in an actinic radiation 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.

2-12. Recording medium The recording medium according to an embodiment of the present invention is not particularly limited as long as the precoat agent can be applied to the surface thereof, and absorbent, non-absorbent and low-absorbent recording media can be used. The present invention exerts a remarkable effect when an absorbent recording medium is used.

Examples of the above-mentioned recording media include plain paper ranging from thin to thick paper, high-quality paper, art paper, coated printing paper, etc. Examples of the above-mentioned absorbent recording media include plain paper ranging from thin to thick paper, high-quality paper, art paper, coated paper, etc.

Examples of the non-absorbent and low-absorbent recording media include films. The films include known plastic films. Examples of the plastic films include biodegradable films such as polyester (PET) film, polyethylene (PE) film, polypropylene (PP) film, nylon (NY) film, polystyrene (PS) film, ethylene-vinyl acetate copolymer (EVA) film, polyvinyl chloride (PVC) film, polyvinyl alcohol (PVA) film, polyacrylic acid (PAA) film, polycarbonate film, polyacrylonitrile film, and polylactic acid film.

The shapes and colors of the absorbent, non-absorbent and low-absorbent recording media are not particularly limited and can be selected appropriately depending on the final image to be formed.

3. Image Forming Method The image forming method according to one embodiment of the present invention includes the steps of (1) applying the above-mentioned precoat agent to the surface of a recording medium, (2) applying actinic ray curable ink to the surface of the recording medium to which the precoat agent has been applied, and (3) irradiating the surface to which the precoat agent and actinic ray curable ink have been applied with actinic rays to simultaneously cure the precoat agent and the actinic ray curable ink. Each step will be described below.

3-1. Step of Applying a Precoat Agent The step of applying a precoat agent is a step of applying the precoat agent to the surface of a recording medium to form a liquid precoat layer.

The precoat agent can be applied to the surface of the recording medium using known liquid application methods such as spray application, spiral application using a nozzle or slit, dipping application, roll coater application, gravure application, flexo application, and application by the inkjet method. Since the precoat agent has a high viscosity, it is preferable to apply it to the entire surface of the recording medium using the roll coater application method among the above liquid application methods.

By applying a precoat agent containing glucose or glucan or a derivative thereof to the surface of the recording medium (e.g., plain paper) before applying the actinic radiation curable ink to the surface of the recording medium, it is possible to form a clear line image without unevenness. This is thought to be because the polar functional group (e.g., hydroxyl group) of glucose or glucan or a derivative thereof has a high affinity with the polar functional group (e.g., carbonyl group) of the actinic radiation polymerizable compound contained in the actinic radiation curable ink, so that the actinic radiation curable ink is more likely to remain on the surface of the precoat agent than to penetrate into the interior of the recording medium, and therefore it is possible to ensure an amount of actinic radiation curable ink that can sufficiently wet and spread on the surface of the precoat agent.

In addition, since a precoat agent is applied to the surface of the recording medium, even if actinic radiation-curable ink is applied to the surface of the precoat agent, the ink can be prevented from penetrating into the recording medium. In addition, since the ink is cured by irradiation with actinic radiation together with the precoat agent, it is also prevented from seeping out of the recording medium after image formation.

In addition, when the precoat agent is applied to the recording medium using the inkjet method, a clear line image without unevenness can be formed in the areas where the precoat agent is applied. Furthermore, the texture of the recording medium in areas where the precoat agent is not applied can be maintained. In addition, since the precoat agent is used only where it is needed, costs can be reduced.

3-2. Step of applying actinic ray curable ink The step of applying actinic ray curable ink is a step of applying actinic ray curable ink to the surface of the precoat agent applied to the surface of the recording medium to form an image.

The method of applying the actinic ray curable ink to the surface of the precoat agent is not particularly limited, and known methods such as spray coating, immersion, screen printing, gravure printing, offset printing, and inkjet methods can be used. In this embodiment, in the process of applying the actinic ray curable ink to the surface of the precoat agent to form an image, it is preferable to use an inkjet method in which the actinic ray curable ink is ejected from an inkjet head and applied to the surface of the precoat agent.

The inkjet head used in the inkjet method may be either an on-demand type or a continuous type inkjet head. Examples of on-demand type inkjet heads include electro-mechanical conversion types including single cavity type, double cavity type, bender type, piston type, shear mode type and shared wall type, as well as electro-thermal conversion types including thermal inkjet type and bubble jet type ("Bubble Jet" is a registered trademark of Canon Inc.).

The inkjet head may be either a scanning type or a line type inkjet head.

At this time, in order to improve the ejection properties of the droplets of actinic ray curable ink, it is preferable to heat the actinic ray curable ink in the inkjet head to 40 to 120°C and eject the heated actinic ray curable ink.

When the actinic ray curable ink contains a gelling agent, it is preferable to set the temperature of the actinic ray curable ink in the inkjet head to a temperature 10°C or more and less than 40°C higher than the gelling temperature of the actinic ray curable ink. By setting the temperature of the actinic ray curable ink in the inkjet head to a gelling temperature + 10°C or more, the actinic ray curable ink does not gel inside the inkjet head or on the nozzle surface, and the actinic ray curable ink can be ejected well. Furthermore, by setting the temperature of the actinic ray curable ink in the inkjet head to a temperature less than the gelling temperature of the actinic ray curable ink + 40°C, the thermal load of the inkjet head can be reduced. In particular, since inkjet heads using piezoelectric elements are prone to performance degradation due to thermal load, it is particularly preferable to set the temperature of the actinic ray curable ink within the above range.

When the actinic ray curable ink contains a gelling agent, the gelling agent crystallizes and pins the actinic ray curable ink applied to the surface of the recording medium. This makes it possible to prevent the dots formed by applying the actinic ray curable ink from spreading excessively.

At this time, in order to improve the pinning properties of the actinic radiation curable ink, the surface temperature of the recording medium may be set to be close to or below the gelling temperature of the gelling agent.

3-3. Step of curing the precoat agent and the actinic ray curable ink The step of curing the precoat agent and the actinic ray curable ink is a step of irradiating the surface onto which the precoat agent and the actinic ray curable ink have been applied with actinic rays, thereby curing the precoat agent and the actinic ray curable ink simultaneously.

In the process of curing the precoat agent and the actinic ray curable ink, the precoat agent applied to the surface of the absorbent recording medium and the actinic ray curable ink applied to the surface of the precoat agent are irradiated with actinic rays (e.g., ultraviolet rays), and both the precoat agent and the actinic ray curable ink are completely cured at the same time. Since the process from applying the precoat agent to the surface of the absorbent recording medium to the process of curing the precoat agent and the actinic ray curable ink is performed continuously, an image can be formed in a short time. In addition, since the precoat agent is cured by irradiating it with actinic rays, it is possible to suppress bleeding from the recording medium after image formation. Note that the wavelength of the actinic rays irradiated in this process is preferably 350 nm or more and 450 nm or less, and more preferably 380 nm or more and less than 430 nm.

4. Image Forming Apparatus Fig. 1 is a schematic diagram showing an exemplary configuration of an inkjet image forming apparatus 100 according to an embodiment of the present invention.

The image forming apparatus 100 according to one embodiment of the present invention includes a recording medium 110, a precoat agent application section 120 that applies a precoat agent to the surface of the recording medium 110, an ink application section 130 that applies an actinic ray curable ink to the surface to which the precoat agent has been applied, and an actinic ray irradiation section 140 that irradiates the surface to which the precoat agent and the actinic ray curable ink have been applied with actinic rays.

In FIG. 1, from the upstream side along the substrate transport direction (the direction of the arrow in the figure), a precoat agent application section 120, an ink application section 130, and an actinic radiation irradiation section 140 are arranged in this order.

The precoat agent application unit 120 may be configured to apply the precoat agent to an area larger than the area on the recording medium 110 where the droplets of the actinic radiation curable ink land. For example, the precoat agent application unit 120 may include a dispenser 122 that supplies the precoat agent to the application roller 121, and the application roller 121 that applies the supplied precoat agent in the form of a film. The precoat agent application unit 120 may use a method using a bar coater or an inkjet method.

In this embodiment, the ink application unit 130 is an ink application unit that forms an image by an inkjet method, and has inkjet heads 132Y, 132M, 132C, and 132K for ejecting actinic radiation curable compositions (inkjet inks) of the respective colors Y (yellow), M (magenta), C (cyan), and K (black) from nozzles 131 and applying them onto the precoat layer formed on the surface of the recording medium 110. The inkjet heads 132Y, 132M, 132C, and 132K apply the actinic radiation curable inks of the respective colors to positions on the precoat layer formed on the surface of the recording medium 110 according to the image to be formed, thereby forming an image.

The active ray irradiation unit 140 is disposed downstream of the ink application unit 130 in the transport direction of the recording medium 110, and irradiates active rays (ultraviolet rays) toward the surface of the recording medium 110 on which the precoat agent and active ray curable ink are applied. In this way, the active ray irradiation unit 140 irradiates the precoat agent and active ray curable ink applied to the surface of the recording medium 110 with active rays, curing the precoat agent and active ray curable ink. This makes it possible to prevent the precoat agent from seeping out of the recording medium 110.

In the above explanation, an image is formed on the surface of the precoat agent applied to the surface of the recording medium by the inkjet method, but the method of forming the image is not particularly limited, and known methods such as spray coating, immersion method, screen printing, gravure printing, and offset printing can be used.

The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these.

1. Preparation of actinic ray curable ink Actinic ray curable ink was prepared by the following procedure.

(Preparation of Pigment Dispersion)
20 parts by mass of a cyan pigment (Lionol Blue FG-7400-G, manufactured by Toyo Color Co., Ltd.), 6.5 parts by mass of a dispersant "BYKJET-9151" (manufactured by BYK Corporation, "BYKJET" is a registered trademark of the company), 73.2 parts by mass of an actinic radiation polymerizable compound "polyethylene glycol #400 diacrylate", 0.3 parts by mass of a polymerization inhibitor "Irgastab UV10" (manufactured by BASF Corporation, "Irgastab" is a registered trademark of the company), and zirconia beads "YTZ ball" (0.3 mm, manufactured by Nikkato Corporation) were placed in a 100 mL poly container and dispersed for 3 hours with a paint shaker, and the zirconia beads were removed to obtain a pigment dispersion.

(Preparation of actinic ray curable ink 1)
A stainless steel beaker was charged with 5 parts by weight of a gelling agent "Lunac BA" (behenic acid, manufactured by Kao Corporation, "Lunac" is a registered trademark of the company), 10 parts by weight of the above-mentioned pigment dispersion, 38.9 parts by weight of polyethylene glycol #400 diacrylate, 25 parts by weight of 4EO-modified pentaerythritol tetraacrylate, 15 parts by weight of 3PO-modified trimethylolpropane triacrylate, 6 parts by weight of a polymerization initiator, and 0.1 parts by weight of a polymerization inhibitor, and the mixture was stirred at 105°C for 45 minutes, and then filtered through a 3 μm Teflon (registered trademark) membrane filter manufactured by Advantec Corporation, to obtain actinic ray-curable ink 1. The types of polymerization initiator and polymerization inhibitor used were the same as those used in the preparation of the pigment dispersion.

(Preparation of actinic ray curable ink 2)
10 parts by mass of the above-mentioned pigment dispersion, 43.9 parts by mass of polyethylene glycol #400 diacrylate, 25 parts by mass of 4EO-modified pentaerythritol tetraacrylate, 15 parts by mass of 3PO-modified trimethylolpropane triacrylate, 6 parts by mass of polymerization initiator, and 0.1 parts by mass of polymerization inhibitor were placed in a stainless steel beaker, stirred at 105° C. for 45 minutes, and then filtered through a 3 μm Teflon (registered trademark) membrane filter manufactured by Advantec Corporation to obtain actinic ray-curable ink 2. The types of polymerization initiator and polymerization inhibitor used were the same as those used in the preparation of the pigment dispersion.

2. Preparation of Precoat Agent A precoat agent was prepared by the following procedure.

(Preparation of Precoat Agent 1)
96.4 parts by mass of an actinic radiation polymerizable compound "polyethylene glycol #600 diacrylate", 0.5 parts by mass of glucose (manufactured by Tokyo Chemical Industry Co., Ltd.), 3 parts by mass of a polymerization initiator, and 0.1 parts by mass of a polymerization inhibitor were mixed and stirred at 90° C. for 20 minutes to obtain a precoat agent 1. The types of the polymerization initiator and polymerization inhibitor used were the same as those used in the preparation of the pigment dispersion liquid.

(Preparation of Precoat Agents 2 to 13, 29, and 31)
Precoating agents 2 to 13, 29, and 31 were obtained in the same manner as precoating agent 1, except that glucose, glucan, or a derivative thereof shown in Table 1 was used.

(Preparation of Precoat Agents 17 to 22, 26, and 27)
Precoat agents 17 to 22, 26, and 27 were obtained in the same manner as precoat agent 1, except that the glucose or glucan or derivative thereof shown in Table 1 was used and the content was changed from 0.5 parts by mass to the content shown in Table 1.

(Preparation of Precoat Agent 14)
94.4 parts by weight of polyethylene glycol #600 diacrylate, 0.5 parts by weight of glucose, 2 parts by weight of ion-exchanged water, 3 parts by weight of a polymerization initiator, and 0.1 parts by weight of a polymerization inhibitor were mixed and stirred at 90°C for 20 minutes to obtain a precoat agent 14.

(Preparation of Precoat Agents 15 and 16)
Precoating agents 15 and 16 were obtained in the same manner as precoating agent 14, except that glucose, glucan, or a derivative thereof shown in Table 1 was used.

(Preparation of Precoat Agents 23 to 25, 28, and 30)
Precoat agents 23 to 25, 28, and 30 were obtained in the same manner as precoat agent 14, except that the glucose or glucan or derivative thereof shown in Table 1 was used and the water content was changed from 2 parts by mass to the content shown in Table 1.

(Preparation of precoat agent 32)
97.1 parts by mass of polyethylene glycol #600 diacrylate, 3 parts by mass of a polymerization initiator, and 0.1 parts by mass of a polymerization inhibitor were mixed and stirred at 90° C. for 20 minutes to obtain a precoat agent 32. The types of the polymerization initiator and polymerization inhibitor used were the same as those used in the preparation of the pigment dispersion liquid.

(Preparation of Precoat Agent 33)
96.4 parts by mass of polyethylene glycol #600 diacrylate, 0.5 parts by mass of polyvinyl alcohol (manufactured by Tokyo Chemical Industry Co., Ltd.), 3 parts by mass of a polymerization initiator, and 0.1 parts by mass of a polymerization inhibitor were mixed and stirred at 90° C. for 20 minutes to obtain a precoat agent 33. The types of the polymerization initiator and polymerization inhibitor used were the same as those used in the preparation of the pigment dispersion liquid.

Table 1 shows the content (unit: parts by mass) of each component in precoat agents 1 to 33.

The abbreviations for glucose or glucan or their derivatives shown in Table 1 are as follows:

A-1: Glucose A-2: Maltose A-3: Maltotriose A-4: Penta-O-ethyl-β-D-glucopyranose A-5: Penta-O-acetyl-β-D-glucopyranose A-6: Penta-O-benzyl-β-D-glucopyranose A-7: α-D-cellobiose octaacetate A-8: Trimethyl-β-cyclodextrin A-9: Triacetyl-β-cyclodextrin A-10: Cellulose A-11: Hydroxymethylcellulose A-12: Hydroxyethylcellulose A-13: Acetylcellulose (cellulose acetate)
A-14: Cationic hydroxyethyl cellulose A-15: Hydroxypropyl cellulose

The abbreviations for the water-soluble synthetic resins shown in Table 1 are as follows.
PVA: Polyvinyl alcohol

A-1 to 3, 5, 7 to 9, and PVA are manufactured by Tokyo Chemical Industry Co., Ltd., A-10, 12, and 13 are manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., A-14 is manufactured by Kao Corporation, and A-15 is manufactured by Sigma-Aldrich. A-4, 6, and 11 were synthesized by known methods.

3. Evaluation Images were formed using recording media to which precoat agents 1 to 33 had been applied, and image quality and bleeding were evaluated.

3-1. Image quality evaluation (evaluation method)
Precoat agents 1 to 33 were applied to a recording medium (OK topcoat paper, 157 g/ ^m2 per square meter, manufactured by Oji Paper Co., Ltd.) using wire bar #2, and then the above-mentioned actinic ray curable ink was ejected from an inkjet head HA1024 (manufactured by Konica Minolta, Inc.) to print a thin line of 1 dot width. Next, an LED lamp was used as an actinic ray irradiation light source, and actinic rays (ultraviolet rays) having an energy of 250 mJ were irradiated to cure the thin line.

(Evaluation Criteria)
⊚: When observed from a distance of 5 cm, no unevenness or misalignment is observed in the thin line. ◯: When observed from a distance of 10 cm, no unevenness or misalignment is observed in the thin line. △: When observed from a distance of 15 cm, no unevenness or misalignment is observed in a part of the thin line. ×: When observed from a distance of 15 cm, unevenness or misalignment is observed in the thin line.

3-2. Bleeding evaluation (evaluation method)
After measuring the initial weight (M0) of the above-mentioned recording medium of 5 cm x 5 cm, precoat agents 1 to 33 were applied to the above-mentioned recording medium using wire bar #2. Next, the above-mentioned actinic radiation curable ink was ejected from inkjet head HA1024 type to form a solid image, and the solid image was cured by irradiating it with actinic radiation (ultraviolet rays) having an energy of 250 mJ using an LED lamp. The weight (M1) of the recording medium having the solid image after curing was measured, and the amount of the precoat agent and the actinic radiation curable ink applied was calculated.

Next, the recording medium with the cured solid image was immersed in 10 ml of distilled water at 25°C for 24 hours, and the ratio of monomers contained in the distilled water was measured by liquid chromatography (manufactured by Hitachi High-Technologies Corporation), and the amount of precoat agent and actinic radiation curable ink that had dissolved (M2) was calculated. In the same manner, a solid image was cured by applying only actinic radiation curable ink to the recording medium. The recording medium with the cured solid image was immersed in 10 ml of distilled water at 25°C for 24 hours, and the amount of dissolved actinic radiation curable ink (M3) was measured and calculated by liquid chromatography (manufactured by Hitachi High-Technologies Corporation).

The amount of monomer eluted was calculated using the formula (1) Monomer elution amount = (M2-M3)/(M1-M0) x 100 (%).

(Evaluation Criteria)
⊚: The amount of eluted monomer is 0% or more and less than 1%. ◯: The amount of eluted monomer is 1% or more and less than 3%. Δ: The amount of eluted monomer is 3% or more and less than 5%. ×: The amount of eluted monomer is 5% or more.

The above evaluation results are shown in Table 2.

As shown in Table 2, it was found that by including the above-mentioned actinic radiation polymerizable compound and the above-mentioned glucose or glucan or derivatives thereof in the precoat agent, an image without exudation of the precoat agent can be obtained even when the precoat agent is applied to the surface of an absorbent recording medium (e.g., plain paper). First, it is believed that this is because the intermolecular force acts between the polar functional group (e.g., hydroxyl group) contained in the glucose or glucan or derivatives thereof and the hydroxyl group of cellulose contained in the recording medium (e.g., plain paper), thereby suppressing the penetration of the glucose or glucan or derivatives thereof into the inside of the recording medium. Second, since the polar functional group (e.g., hydroxyl group) of the glucose or glucan or derivatives thereof has a high affinity with the polar functional group (e.g., carbonyl group) of the actinic radiation polymerizable compound, the actinic radiation polymerizable compound tends to remain inside the precoat agent together with the glucose or glucan or derivatives thereof, and therefore the penetration into the recording medium is suppressed. Third, it is believed that the precoat agent is cured by irradiating it with actinic radiation while its penetration into the recording medium is suppressed, so that it is less likely to exude from the recording medium after the image is formed.

As shown in Table 2, it was found that by including the actinic radiation-polymerizable compound and the glucose or glucan or derivatives thereof in the precoat agent, a clear line image without unevenness can be formed, and image quality can be improved. This is thought to be because the polar functional group (e.g., hydroxyl group) of glucose or glucan or derivatives thereof has a high affinity with the polar functional group (e.g., carbonyl group) of the actinic radiation-polymerizable compound contained in the actinic radiation-curable ink, so that the actinic radiation-curable ink is more likely to remain on the surface of the precoat agent than to penetrate into the interior of the recording medium, and therefore an amount of actinic radiation-curable ink sufficient to wet and spread on the surface of the precoat agent can be secured.

By using the precoat agent of the present invention, the ink can be uniformly wetted and spread, and the precoat agent can be prevented from seeping out during image formation. Therefore, the present invention is expected to broaden the scope of application of image formation methods using actinic radiation-curable inks, and contribute to the advancement and dissemination of technology in this field.

REFERENCE SIGNS LIST 100 Image forming apparatus 110 Recording medium 120 Precoat agent application section 121 Application roller 122 Dispenser 130 Ink application section 131 Nozzle 132 Inkjet head 140 Actinic ray irradiation section

Claims (11)

In an image forming method using actinic ray curable ink, a precoat agent is applied to a surface of a recording medium before the actinic ray curable ink is applied, the precoat agent comprising:
the precoat agent contains an actinic radiation polymerizable compound, and glucose or glucan or a derivative thereof;
The glucose or glucan or derivative thereof is at least one compound selected from the group consisting of D-glucose, D-mannose, D-galactose, 2-deoxy-D-glucose, n-octyl-β-D-glucoside, penta-O-ethyl-β-D-glucopyranose, penta-O-acetyl-β-D-glucopyranose, penta-O-benzyl-β-D-glucopyranose, maltose, sucrose, maltotriose, dextran, cellobiose, α-D-cellobiose octaacetate, trimethyl-β-cyclodextrin, triacetyl-β-cyclodextrin, cellulose, cellulose in which some or all of the hydrogen atoms of the hydroxyl groups are substituted with alkyl groups, acetyl groups, or carboxymethyl, hydroxyalkylcellulose in which the hydroxyalkyl group has 1 to 9 carbon atoms, cationized hydroxyethylcellulose, starch, amylose, and amylopectin, which are precoating agents. The precoat agent according to claim 1, wherein the glucan or its derivative is a polymer bound via a glycosidic bond. The precoat agent according to claim 1 or 2, wherein the glucose or glucan or derivative thereof has a structure in which some or all of the hydrogen atoms of the hydroxyl groups of the glucose or glucan or derivative thereof are substituted with acetyl groups. The precoat agent according to claim 2, wherein the polymer is a cellulose derivative. The precoat agent according to claim 4 , wherein the cellulose derivative is a hydroxyalkyl cellulose. The precoat agent according to claim 5, wherein the number of carbon atoms in the hydroxyalkyl group of the hydroxyalkyl cellulose is 1 to 4. The precoating agent according to any one of claims 1 to 6, wherein the content of the glucose or glucan or a derivative thereof is 3% by mass or less based on the total mass of the precoating agent. Contains water,
The precoat agent according to any one of claims 1 to 7, wherein the water content is 10 mass % or less based on the total mass of the precoat agent. A step of applying the precoat agent according to any one of claims 1 to 8 to a surface of a recording medium;
applying an actinic ray curable ink to the surface of the recording medium on which the precoat agent has been applied;
a step of irradiating the surface onto which the precoat agent and the actinic ray curable ink have been applied with actinic ray to simultaneously cure the precoat agent and the actinic ray curable ink;
The image forming method according to claim 1, The image forming method according to claim 9, wherein the actinic radiation curable ink contains a gelling agent. The image forming method according to claim 9 or claim 10, wherein the recording medium is an absorbent recording medium.