JP2013203066A - Image forming method and printed matter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming method which can form an image of high image quality without cissing and bleeding when a curable composition hits a recording medium surface and which is excellent in processing suitability for an obtained printed matter and to provide a printed matter excellent in processing suitability.SOLUTION: An image forming method includes (A) a base material surface treatment process of surface-treating a nonpolar base material under a nitrogen ambience by an atmospheric pressure plasma, (B) a curable composition layer formation process of forming a curable composition layer by ejecting the curable composition which includes a polymerizable monomer, a polymerization initiator, and a pigment to the surface-treated nonpolar base material surface by an inkjet method, and (C) an image formation process of forming the image through curing by impressing energy to the formed curable composition layer.

Description

  The present invention relates to an image forming method and a printed matter.

As an image recording method for forming an image on a recording medium such as paper based on an image data signal, there are an electrophotographic method, a sublimation type and a melt type thermal transfer method, an ink jet method and the like.
The ink jet method is an inexpensive printing apparatus and does not require a plate at the time of printing, and the ink composition is ejected only on the required image portion to form an image directly on a recording medium. It can be used efficiently, and the running cost is low especially for small lot production. Furthermore, it has low noise and is excellent as an image recording method, and has attracted attention in recent years.
In particular, a curable composition that can be cured by irradiation with radiation such as ultraviolet rays is used as an ink composition for ink jet recording, so that most of the components of the ink composition are cured by irradiation with radiation. Compared to the composition, it has excellent drying properties and is less likely to bleed, so that it has the advantage that images can be formed on various recording media such as non-ink-permeable recording media such as resin films.

So far, various radiation curable ink compositions have been proposed, and they are usually composed of a curable composition containing a colorant, a polymerizable monomer, and a polymerization initiator, and the ink composition is formed on a recording medium. The ink layer formed by ejecting is cured by irradiating ultraviolet rays or the like to form a cured ink image.
At present, high speed, high image quality, and fixability to a recording medium are important issues when ink is ejected onto a non-ink-permeable recording medium such as plastic by the inkjet recording method.
From the viewpoint of improving image quality when forming an image on a non-ink-absorbing recording medium, for example, a printing medium obtained by subjecting an actinic ray curable ink containing a polymerization initiator and a polymerizable monomer to an atmospheric pressure plasma treatment on a film surface An ink jet recording method is disclosed that emits actinic rays and emits actinic rays (see, for example, Patent Document 1). In addition, a method is disclosed in which, when a mark is printed on the surface of a golf ball by an ink jet recording method, surface treatment such as atmospheric pressure plasma irradiation or corona discharge is performed on the surface (see, for example, Patent Document 2).

JP 2003-261799 A Japanese Patent No. 3751996

However, these surface treatments are techniques for roughening the surface of the resin to improve the contact area with the ink composition, thereby achieving close contact with the ink. Depending on the resin material of the substrate used, Various problems such as a decrease in strength, bleeding of the ink composition due to the rough surface of the substrate, and a decrease in workability when forming a printed product after image formation may occur.
The object of the present invention made in consideration of the above problems is to suppress repelling and bleeding when the curable composition lands on the surface of the recording medium, thereby forming a high-quality image and obtaining the printed matter obtained. It is an object of the present invention to provide an image forming method excellent in processing suitability.
A second object of the present invention is to provide a printed material obtained by the image forming method of the present invention, which is excellent in processability, particularly punching processability.

As a result of intensive studies, the present inventors have found that the above problem can be solved by introducing atoms that form an interaction with the curable composition on the surface of the substrate by atmospheric pressure plasma treatment under a nitrogen atmosphere. The present invention has been completed.
That is, the configuration of the present invention is as shown.
<1> (A) Substrate surface treatment step of surface-treating a nonpolar substrate with atmospheric pressure plasma in a nitrogen atmosphere, (B) A polymerizable monomer and a polymerization start on the surface-treated nonpolar substrate surface A curable composition applying step for applying a curable composition containing an agent and a pigment by an inkjet method, and (C) an image forming step for applying energy to the applied curable composition to cure the image. It is a forming method.
<2> The image forming method according to <1>, wherein the nitrogen atmosphere in the substrate surface step is a nitrogen atmosphere having a nitrogen fraction of 90% or more.
<3> The image forming method according to <1> or <2>, wherein the substrate surface treatment step is a step of introducing nitrogen atoms into the nonpolar substrate surface.
<4> The image forming method according to any one of <1> to <3>, wherein the polymerizable monomer is a polymerizable monomer having at least one substituent selected from an amide group and an ether group in the molecule. It is.

<5> The image forming method according to any one of <1> to <4>, wherein the nonpolar substrate is a substrate made of a resin selected from polypropylene and polyethylene.
<6> The <1> to <4>, wherein the nonpolar substrate is a substrate having a surface layer made of a resin selected from polypropylene and polyethylene on the outermost surface on the side where the curable composition layer is formed. The image forming method according to any one of the above.
<7> A printed matter obtained by the method according to any one of <1> to <6>.
<8> Curing containing a pigment, a polymerizable monomer having at least one substituent selected from an amide group and an ether group in the molecule, and a polymerization initiator on the surface of a nonpolar substrate having nitrogen atoms introduced on the surface It is a printed matter having an image formed using the adhesive composition.
<9> The printed material according to <7> or <8>, which is used for molding including punching.

Preferred embodiments of the image forming method of the present invention are as follows.
<A> The image forming method according to any one of <1> to <6>, wherein the atmospheric pressure plasma processing is performed under a condition of 70 kPa to 130 kPa.
<B> Under the condition that the atmospheric pressure plasma treatment includes at least one nitrogen-containing gas selected from the group consisting of organic amine gas, ammonia-containing gas, and nitrogen gas so that the nitrogen fraction is 80%. The image forming method according to any one of <1> to <6>, which is performed.
<C> The image formation according to any one of <1> to <6>, wherein a distance from a gas supply nozzle including plasma in the atmospheric pressure plasma processing to the surface of the nonpolar substrate is 0.01 mm to 100 mm. Is the method.
<D> The image forming method according to any one of <1> to <6>, wherein a plasma processing temperature in the atmospheric pressure plasma processing is −21 ° C. or higher and 100 ° C. or lower.
<E> The atmospheric pressure plasma treatment is performed in this order by a first plasma treatment for plasma treatment in an inert gas atmosphere and a second plasma treatment for plasma treatment in a nitrogen atmosphere. 6. The image forming method according to any one of 6>.
<F> The image forming method according to any one of <1> to <6>, wherein the pigment is a magenta pigment.

According to the present invention, there is provided an image forming method that is free from cissing and blurring when the curable composition lands on the surface of a recording medium, forms a high-quality image, and is excellent in processing suitability of the obtained printed matter. can do.
Further, according to the present invention, it is possible to provide a printed material excellent in processability, particularly punching processability.

1 is an external perspective view showing an example of an ink jet recording apparatus suitably used in the present invention. FIG. 2 is a perspective plan view schematically showing a paper conveyance path of the ink jet recording apparatus shown in FIG. 1. It is a plane perspective view which shows the arrangement configuration of the inkjet head and ultraviolet irradiation part shown in FIG. It is a perspective view which shows the structural example of the light source moving part which moves the ultraviolet irradiation part shown in FIG. It is side surface perspective drawing which shows the structural example of the temporary curing light source unit used as a temporary curing light source of this embodiment. FIG. 6 is a plan perspective view of the temporary curing light source unit of FIG. 5. FIG. 3 is a block diagram illustrating a configuration of an ink supply system of the ink jet recording apparatus. It is a block diagram which shows the structure of an inkjet recording device. (A) is a model diagram showing a state where there is no problem after punching in processing suitability evaluation, and (B) is a model diagram showing a state where cracks due to ink image peeling are observed after punching.

The image forming method and the printed material of the present invention are described in detail below.
The description of the components in the present invention described below may be made based on typical embodiments of the present invention, but the present invention is not limited to such embodiments.

In the notation of groups (atomic groups) in this specification, the notation that does not indicate substitution and non-substitution includes not only those having no substituent but also those having a substituent. For example, the “alkyl group” includes not only an alkyl group having no substituent (unsubstituted alkyl group) but also an alkyl group having a substituent (substituted alkyl group).
In addition, “active light” or “radiation” in the present specification means, for example, an emission line spectrum of a mercury lamp, far ultraviolet rays represented by an excimer laser, extreme ultraviolet rays (EUV light), X-rays, electron beams, and the like. . In the present invention, light means actinic rays or radiation. Unless otherwise specified, “exposure” in this specification is not only exposure with far-ultraviolet rays such as mercury lamps and excimer lasers, X-rays, EUV light, but also drawing with particle beams such as electron beams and ion beams. Are also included in the exposure.

In the present specification, a numerical range represented by using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.
In this specification, the total solid content refers to the total mass of components excluding the solvent from the total composition of the curable composition.

  In this specification, “(meth) acrylate” represents both and / or acrylate and methacrylate, “(meth) acryl” represents both and / or acryl and “(meth) acrylic”. ) "Acryloyl" represents both and / or acryloyl and methacryloyl.

<Image forming method>
In the image forming method of the present invention, (A) a substrate surface treatment step (hereinafter referred to as (A) surface treatment step or (A) step) wherein a nonpolar substrate is surface-treated with atmospheric pressure plasma in a nitrogen atmosphere. And (B) a curable composition application step of applying a curable composition containing a polymerizable monomer, a polymerization initiator, and a pigment to the surface of the non-polar base material that has been surface-treated by an inkjet method [hereinafter, And (B) an ink application process or (B) process] and (C) an image forming process of applying energy to the applied curable composition and curing it (hereinafter referred to as (C) image forming process. Or (C) may be referred to as a step).

Although the operation of the present invention is not clear, it is estimated as follows.
In the image forming method of the present invention, by performing the surface treatment step (A), nitrogen atoms are introduced into the surface of the nonpolar substrate due to the plasma gas containing a large amount of nitrogen, and are thereby applied to the surface. The wettability of the liquid curable composition, that is, the affinity with the liquid curable composition is improved. It is estimated that a high-quality image is formed.
In addition, when surface-treating the base material with atmospheric pressure plasma in a nitrogen atmosphere, the base material is a non-polar base material, so that the surface of the polymer without damaging the polymer structure of the resin constituting the non-polar base material. Nitrogen atoms are introduced in an effective amount. That is, the non-polar base material has a high proportion of C—C bonds in the polymer, the polymer main chain bond is not easily broken even by the atmospheric pressure plasma treatment, and it is effective on the resin layer surface while minimizing damage. Nitrogen can be introduced. On the other hand, when a highly polar resin base material, for example, a base material such as polyethylene terephthalate or polyvinyl chloride, is used, the bonds such as C—O bonds and C—Cl bonds on the surface are cut by plasma due to atmospheric pressure plasma treatment. The polymer structure is damaged, the surface becomes very rough, and the strength of the base material is lowered.

Hereinafter, the image forming method of the present invention will be described in the order of steps.
[(A) Substrate surface treatment process for surface treatment of nonpolar substrate with atmospheric pressure plasma under nitrogen atmosphere]
(Atmospheric pressure plasma treatment)
(A) A surface treatment process is a process of carrying out atmospheric pressure plasma treatment of the nonpolar substrate surface. In the present invention, the atmospheric pressure plasma treatment is preferably treatment using low temperature atmospheric pressure plasma generated under conditions near atmospheric pressure. For example, a non-equilibrium plasma jet, low-temperature plasma by AC pulse discharge, or the like can be used, and it is preferable to use plasma generated under conditions near atmospheric pressure.
In the present invention, “atmospheric pressure” or “near atmospheric pressure” refers to a range in which the atmospheric pressure is 70 kPa or more and 130 kPa or less, and plasma treatment may be performed under these conditions. More preferably, the plasma treatment is performed under a condition of 90 kPa to 110 kPa.
In the present invention, “plasma treatment in a nitrogen atmosphere” means an atmosphere containing a nitrogen-containing gas such as nitrogen gas or organic amine gas, and the nitrogen atom-containing gas has a nitrogen fraction of 80. % Refers to plasma treatment using a gas contained as a plasma gas under conditions of at least%.
In the present specification, the gas in the atmosphere is assumed to be atoms, and the weight% of nitrogen in all atoms is defined as “nitrogen fraction”.
For this reason, the plasma treatment in the air having a nitrogen fraction of around 70% even if nitrogen gas is included is not included in the “nitrogen atmosphere” plasma treatment in the present invention.

Various atmospheric pressure plasma apparatuses can be used for the plasma treatment. For example, a device that can generate low-temperature plasma by performing intermittent discharge while passing an inert gas at a pressure close to atmospheric pressure between electrodes covered with a dielectric is preferable, and any device can be used. Various modification examples can be selected according to the purpose of use.
More specifically, in Japanese Unexamined Patent Application Publication No. 2008-60115, an apparatus used for plasma processing, an atmospheric pressure plasma apparatus described in Japanese Unexamined Patent Application Publication No. 2004-228136, Japanese Unexamined Patent Application Publication No. 2006-21972, Japanese Unexamined Patent Application Publication No. 2007-188690, and Examples thereof include plasma devices described in specifications of International Publications WO2005 / 062338, WO2007 / 024134, and WO2007 / 145513.
The atmospheric pressure plasma apparatus is also available as a commercial product. For example, ATMP-1000 from Arios Co., Ltd., atmospheric pressure plasma apparatus from HEIDEN LABORATORIES, INC. An atmospheric pressure plasma apparatus currently on the market such as a jet apparatus, MyPL100, ILP-1500 of Well Co., Ltd., and RD550 of Sekisui Chemical Co., Ltd. can also be suitably used. Among these, from the viewpoint of avoiding non-uniform concentration (streamer) of plasma and reducing damage to nonpolar substrates, for example, it is described in the specifications of WO / 2005/062338 and WO2007 / 024134. In addition, it is preferable to use a device with a devised electric circuit, such as energizing the discharge part via a pulse control element.

There is no particular limitation on the discharge gas (plasma gas) used when generating the atmospheric pressure plasma, except that it contains a gas containing nitrogen atoms such as nitrogen gas under the condition that the nitrogen fraction is 80% or more. In addition to nitrogen (N ₂ ) gas, selected from ammonia, a nitrogen atom-containing gas selected from gaseous organic amines, and a gas not containing nitrogen atoms such as oxygen, hydrogen, carbon dioxide, helium, and argon Any gas may be contained, and these two or more mixed gases can be appropriately selected and used under the condition that the nitrogen fraction is 80% or more.
Among them, a mixed gas of a rare gas and nitrogen (N ₂₎ gas of He and Ar, etc. which are inert gases, it is preferable to use a mixed gas of an organic amine gas and the nitrogen gas, the nitrogen gas is particularly preferred.
In addition, as long as the nitrogen fraction is 80% or more, a gas, organic amine gas, etc. may be used together with nitrogen gas for ammo, and suitable organic amines that can be used as the organic amine gas are, for example, comparisons. Having a low boiling point structure, R ¹ NH ₂ , R ¹ NHR ² , and H ₂ N—R ³ —NH ₂ , wherein R ¹ and R ² are 1 to 8 carbon atoms, preferably 1 A monovalent hydrocarbon group having ˜4 carbon atoms, and R ³ is a divalent hydrocarbon group having 2 to 8 carbon atoms, preferably 2 to 6 carbon atoms. It is an amine.
Examples of preferred amines include methylamine, dimethylamine, ethylamine, diethylamine, ethylmethylamine, n-propylamine, allylamine, isopropylamine, n-butylamine, n-butylmethylamine, n-amylamine, n-hexylamine, Examples include 2-ethylhexylamine, ethylenediamine, 1,4-butanediamine, 1,6-hexanediamine, cyclohexylamine, n-methylcyclohexylamine, and ethyleneimine. Among them, the nitrogen content is high and plasma is generated. From the viewpoint of easy, dimethylamine is preferable as the combined gas.
The nitrogen atmosphere in the present invention refers to an atmosphere containing a nitrogen atom-containing gas under a condition that the nitrogen fraction is 80% or more, and is preferably a nitrogen atmosphere having a nitrogen fraction of 90% or more, and the nitrogen fraction is 99. % Or more is more preferable. That is, it is an optimal aspect of the present invention to use a nitrogen atom-containing gas as a plasma gas under a condition that the nitrogen fraction is 90% or more. The nitrogen fraction is 90% or more. Nitrogen atoms are more efficiently and sufficiently introduced to the surface of the polar base material, the surface wettability of the curable composition liquid described later is further improved, the bleeding of the image is suppressed, and the cured The adhesion between the image and the substrate is further improved.
The nitrogen fraction in the plasma gas is measured by a known method such as gas chromatography analysis.

From the viewpoint of suppressing damage to the surface of the nonpolar substrate, in the atmospheric pressure plasma treatment, (i) the plasma action site and the discharge site are separated, or (ii) the plasma is localized by devising the discharge circuit. It is effective to suppress the occurrence of concentration (streamer) and generate a uniform plasma. In particular, (ii) the latter method is preferable in that a uniform plasma treatment over a large area can be performed.
(I) The former method is preferably a method in which the plasma generated by the discharge is brought into contact with the surface of the nonpolar substrate by an inert gas stream, and the so-called plasma jet method is particularly preferable. In this case, the path (conducting tube) for transporting the inert gas containing plasma is preferably a dielectric such as glass, porcelain, or organic polymer.
(Ii) As the latter method, more specifically, an electrode energized by a dielectric via a pulse control element described in International Publication No. 2005/062338 and International Publication No. 2007/024134 is applied. Thus, it is preferable to take a method of generating a uniform glow plasma in which streamers are suppressed.
The distance from the supply nozzle of the inert gas containing plasma to the nonpolar substrate surface is preferably 0.01 mm to 100 mm, and more preferably 1 mm to 20 mm.

  The plasma treatment may be performed by a batch method or an in-line method connected to other processes. In the present invention, the plasma treatment needs to be performed in a nitrogen atmosphere. However, even in the case of the transport method using the atom-containing gas having a high nitrogen fraction as described above, the plasma treatment is described in the specification of International Publication No. 2009/096785. Similar to the method, the plasma can be applied to the surface of the non-polar substrate in an in-line method. That is, when supplying a nonpolar base material to the (B) curable composition layer forming step, the surface of the nonpolar base material conveyance line with a nitrogen atom-containing gas and plasma in the region immediately before the (B) step. By providing a blowing nozzle that can be applied to the surface, it becomes possible to continuously carry out the surface treatment step of the surface of the nonpolar substrate, and in the step (A), the nonpolar substrate in which nitrogen atoms are introduced into the surface In the step (B), a curable composition layer is formed.

  In the case of the atmospheric pressure plasma generation method according to the present invention performed in a nitrogen atmosphere, the plasma directly acts on the surface of the nonpolar substrate, whereby nitrogen atoms are efficiently introduced into the surface of the nonpolar substrate, and the curable composition That is, since the wettability of the curable ink composition was improved, an image without bleeding was formed, and the adhesion between the image after curing and the substrate was improved, and the obtained cured image was punched out Even in this case, there is an advantage that cracks due to peeling at the interface of the punching die are suppressed.

The temperature during the plasma treatment can be selected arbitrarily depending on the characteristics of the non-polar substrate to be plasma treated and the amount of nitrogen atoms to be introduced. The smaller one is preferable because softening and deformation of the substrate can be suppressed. By separating the plasma application region for the nonpolar substrate from the plasma generator, the influence on the substrate can be further reduced.
In the above method, by selecting and irradiating the atmospheric low temperature plasma, the supply of thermal energy from the plasma can be reduced, and the temperature rise of the nonpolar substrate can be suppressed. The temperature increase of the nonpolar substrate due to the plasma treatment is preferably 50 ° C. or less, more preferably 40 ° C. or less, and particularly preferably 20 ° C. or less.
The temperature during the plasma treatment is preferably not higher than the temperature that can be withstood by the nonpolar substrate to be plasma-treated, and is generally preferably from −196 ° C. to less than 150 ° C., more preferably from −21 ° C. to 100 ° C. preferable. Particularly preferred is the vicinity of room temperature (25 ° C.) under an ambient temperature atmosphere.

Moreover, as a preferable irradiation condition of the plasma generator at the time of plasma treatment, the voltage is preferably in the range of 110V to 190V, and more preferably 130V to 170V. The current is preferably in the range of 1.1A to 1.9A, more preferably 1.3A to 1.7A. The frequency is preferably in the range of 0.5 kHz to 40 kHz, and more preferably 1 kHz to 30 kHz.
By satisfying these conditions, plasma treatment under a nitrogen atom-containing gas atmosphere can achieve efficient introduction of nitrogen atoms to the substrate surface while suppressing damage to the substrate.

  The nitrogen-containing gas after the plasma treatment may be exhausted without performing special treatment because the plasma has a short life, but it has been treated by providing an inlet near the treatment area. Gas may be recovered.

(Non-polar substrate)
The nonpolar substrate used in the method of the present invention is a substrate having a carbon to hydrogen ratio of 90% or more when surface elemental analysis is performed by ESCA (X-ray photoelectron analysis, manufactured by Shimadzu Corporation) measurement. Preferably, the base material has a carbon to hydrogen ratio of 95% or more. That is, carbon-carbon bonds occupy most of the bonds present on the surface of the substrate, and are included in bonds between carbon atoms and heteroatoms, such as amide bonds, ester bonds, and the like. A base material that does not have a bond such as an O bond or a C—Cl bond, or has a very small ratio is used.
Nonpolar materials constituting the nonpolar substrate include, for example, polyolefins such as polyethylene (PE) and polypropylene (PP), and synthetic rubbers mainly composed of carbon and hydrogen, such as ethylene-propylene-diene rubber (EPDM). Etc.
Relatively high-polarity resin base materials such as polyethylene terephthalate, polyamide, polyvinyl chloride and other C—O bonds, C—N bonds, C—Cl bonds, etc. are broken in the main chain structure by atmospheric pressure plasma treatment. However, application to the present invention is not preferred because there is a concern of surface roughness and strength reduction.
The nonpolar base material may be a base material made of only a nonpolar material such as PE, PP and EPDM, and has a multi-layer structure and is formed from a nonpolar material on the outermost surface, that is, the surface to be plasma-treated. It may have a layer. In the case of having a layer made of a nonpolar material on the outermost surface in a multi-layer structure, a nonpolar material suitable for the present invention can be used if the ratio of carbon to hydrogen is 90% or more when performing surface elemental analysis by ESCA measurement. It becomes a base material.
The thickness of the nonpolar substrate is not limited, but in the case of a substrate made of only a nonpolar material, it is preferably in the range of 10 μm to 500 μm. Moreover, it is preferable that the thickness of the layer which consists of a nonpolar base material in the outermost surface in the case of taking a multilayer structure is similarly the range of 10 micrometers-500 micrometers.

Especially, as a nonpolar base material, what used resin chosen from polyethylene (PE) and polypropylene (PP) from a viewpoint of workability and availability is preferable.
When the nonpolar base material has a multilayer structure, the lower layer may be, for example, paper, woven fabric, non-woven fabric, metal film, etc., as long as the outermost surface is a layer made of a nonpolar material. In the range not affected by the atmospheric pressure plasma treatment from the resin layer, a resin layer made of a polar material can be used as the lower layer of the substrate.

When these nonpolar substrates are subjected to atmospheric pressure plasma treatment under a nitrogen atmosphere, when resin materials such as PP, PE, and EPDM are used, free radicals are generated on the third carbon generated by the polymerization of propylene. In the case of other hydrocarbon elastomers, including synthetic and natural rubber, ionized ammonia or organic amine plasma can bind to free radicals generated at unsaturated sites or other parts, thereby Nitrogen atoms are introduced.
In addition, it was confirmed by the analysis using ESCA (X-ray photoelectron analyzer, Shimadzu Corporation) that the nitrogen atom was introduced into the substrate surface after the step (A). In addition, it is confirmed by observing the surface of the base material with a scanning electron microscope (SEM) that the surface of the base material is free of surface roughness and damage even after nitrogen atoms are introduced into the surface of the base material. it can. When there is damage that causes a decrease in strength or surface roughness, when the surface is observed with an SEM, it is observed that the surface is rougher than before the treatment.

When a nonpolar substrate such as polyethylene (PE) is subjected to an atmospheric pressure plasma treatment, not only a single atmospheric pressure plasma treatment in the nitrogen atmosphere, but also, for example, a nonpolar substrate may be treated pure or in air. A first plasma treatment using oxygen or a plasma gas containing a mixture of oxygen and one or more non-reducing gases such as argon (Ar) and ammonia (NH ₃ ), nitrogen gas, ammonia-containing gas, Two-stage plasma treatment may be performed in which the second plasma treatment is performed in the presence of a nitrogen-containing plasma gas composed of a low-boiling organic amine-containing gas or a mixture thereof (that is, in the nitrogen atmosphere referred to in the present invention). . In addition, since Ar gas has a relatively heavy mass by containing Ar gas in the first plasma treatment, and tends to cause generation of additional free radicals on the surface of the substrate, the second plasma is used. The introduction of nitrogen atoms in the treatment is promoted, which can be said to be a preferred treatment method from the viewpoint of improving the surface treatment effect.
Prior to the plasma treatment step, as a pretreatment, the surface of the nonpolar substrate is degreased with an organic solvent, washed with a detergent solution, then washed with water, dried, etc. Since the surface of the nonpolar base material for the atmospheric pressure plasma treatment is purified and the influence due to impurities can be reduced, it is preferable to perform these pretreatments from the viewpoint of improving the surface treatment efficiency.

In a preferred embodiment of the step (A) of the present invention, the surface of the non-polar substrate made of PP or PE is at a temperature of 50 ° C. or less using a nitrogen atom-containing plasma gas having a nitrogen fraction of 90% or more at 70 kPa or more and 130 kPa. In this mode, the plasma treatment is performed for 10 seconds to 5 minutes under the conditions.
The non-polar base material surface-treated under such conditions is modified to a surface excellent in affinity with a curable composition to be described later by introducing nitrogen atoms on the surface.
In addition, the non-polar base material surface-treated may be wound up, stored, and used for the step (B) as necessary, or may be used for the step (B) immediately after the completion of the step (A). From the viewpoint of making the most of the effect of the treatment, it is preferable to perform the step (B) immediately after the step (A).

[(B) The surface-treated nonpolar substrate surface is cured by discharging a curable composition containing (a) a polymerizable monomer, (b) a polymerization initiator, and (c) a pigment by an inkjet method. Curable composition layer forming step for forming a curable composition layer]
The step (B) is a step of forming a curable composition layer by applying a curable composition to the surface-treated nonpolar substrate surface using an ink jet recording apparatus.
The curable composition according to the present invention is a composition curable by actinic radiation. Here, “active radiation” is radiation that imparts energy capable of decomposing a polymerization initiator contained in the curable composition by the irradiation to generate an initiation species such as a radical, α-rays, γ-rays, X-rays, ultraviolet rays, visible rays, electron beams and the like are included. Of these, ultraviolet rays and electron beams are preferred from the viewpoint of curing sensitivity and device availability, and ultraviolet rays are particularly preferred.
The curable composition according to the present invention is of a radiation curable type and does not contain a volatile solvent in order to cure after applying a liquid curable composition to the surface-treated nonpolar substrate, or Even when a solvent is contained, it is preferable that the amount is extremely small. It is preferable to reduce the content of components that do not contribute to curing in the curable composition as much as possible, and the surface of the cured product resulting from the solvent remaining in the cured product or non-polar substrate This is to reduce the impact on the environment.
Hereinafter, the curable composition used in the image forming method of the present invention will be described in detail.
(Curable composition)
The curable composition used in the present invention is suitably used as a curable ink composition, and contains (a) a polymerizable monomer, (b) a polymerization initiator, and (c) a pigment, if necessary. Other components may be contained.

(A) Polymerizable monomer The polymerizable monomer used in the curable composition of the present invention is not limited as long as it is a monomer having at least one polymerizable group.
The polymerizable group of the polymerizable monomer of the present invention may be a radical polymerizable group or a cationic polymerizable group, but is preferably a radical polymerizable group, and has at least an ethylenically unsaturated bond capable of radical polymerization. An embodiment having one is preferable. That is, as the polymerizable monomer, a compound having at least one ethylenically unsaturated bond capable of radical polymerization in the molecule is a preferred embodiment.

  Examples of polymerizable monomers having an ethylenically unsaturated bond capable of radical polymerization include unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, crotonic acid, isocrotonic acid, maleic acid, unsaturated carboxylic acid esters, and the like. A salt having an ethylenically unsaturated group; acrylonitrile; styrene and the like. Furthermore, macromonomers having a polymerizable group such as various unsaturated polyesters, unsaturated polyethers, unsaturated polyamides, and unsaturated polyurethanes may be used as the polymerizable monomer in the present invention.

  Among these, from the viewpoint of improving wettability and affinity with a surface-treated nonpolar substrate, a polymerizable monomer having at least one functional group selected from an amide group and an ether group in the molecule as the polymerizable monomer Is preferred. Since the polymerizable monomer contains an amide group or an ether group, these functional groups form an interaction with the nitrogen atom introduced on the surface of the nonpolar substrate, so that the curable composition is landed on the surface of the nonpolar substrate. It is believed that the repellency of the liquid curable composition at the time of spraying is suppressed, and blurring due to undesired ink spreading is suppressed by forming an interaction at the time of landing, thereby further improving the effect of the present invention. It is done.

First, the polymerizable monomer having at least one functional group selected from an amide group and an ether group in the molecule used in the present invention will be described.
(A-1) N-vinyl compound A preferred example of the polymerizable monomer according to the present invention is an N-vinyl compound.
As the N-vinyl compound, N-vinyl lactams are preferable, and a compound represented by the following formula (a-1) is more preferable.

  In the formula (a-1), n represents an integer of 1 to 5, from the viewpoint of flexibility after the curable composition is cured, adhesion to a nonpolar substrate, and availability of raw materials. n is preferably an integer of 2 to 4, more preferably n is 2 or 4, and particularly preferably n is 4, that is, N-vinylcaprolactam. N-Vinylcaprolactam is excellent in safety, is generally available and can be obtained at a relatively low cost. By using this polymerizable monomer, the curable composition can be cured with high sensitivity, and the formed cured film is nonpolar. Excellent adhesion to the substrate.

  Content in the case of using the compound represented by the said Formula (a-1) as a polymerizable monomer in the curable composition of this invention is 5 mass%-60 mass with respect to the total solid of a curable composition. % Is preferable, and more preferably 15% by mass to 35% by mass. When the content is 5% by mass or more, the adhesion of the cured film to the nonpolar substrate is improved, and when the content is 60% by mass or less, the storage stability of the curable composition is improved. Excellent.

(A-2) Compound represented by the following formula (a-2) As the polymerizable monomer according to the present invention, a compound represented by the following formula (a-2) is also preferably used.
The polymerizable monomer represented by the following formula (a-2) has a low surface tension, and is presumed to be useful for improving the wettability upon landing of the curable composition and suppressing repelling. Moreover, it has moderate polarity, and the curable composition containing this polymerizable monomer does not easily cause surface curing failure, and a cured product having excellent adhesion can be obtained.

(In the formula (a-2), R ¹ , R ² and R ³ each independently represents a hydrogen atom, a methyl group or an ethyl group, and X ² represents a single bond or a divalent linking group.)
R ¹ is preferably a hydrogen atom or a methyl group, and more preferably a hydrogen atom.
R ² and R ³ are each independently preferably a hydrogen atom or a methyl group, more preferably a hydrogen atom, and still more preferably R ² and R ³ are both hydrogen atoms.
The divalent linking group for X ² is not particularly limited as long as it does not significantly impair the effects of the present invention, but is a divalent hydrocarbon group or a combination of a divalent hydrocarbon group and an ether bond. It is preferably a divalent group, more preferably a divalent hydrocarbon group, a poly (alkyleneoxy) group, or a poly (alkyleneoxy) alkyl group. The number of carbon atoms that the divalent linking group has is preferably 1 to 60, and more preferably 1 to 20.
X ² is preferably a single bond, a divalent hydrocarbon group, or a divalent group in which a hydrocarbon group and an ether bond are combined, and is a divalent hydrocarbon group having 1 to 20 carbon atoms. More preferably, it is more preferably a divalent hydrocarbon group having 1 to 8 carbon atoms, and particularly preferably a methylene group.

  Specific examples of the polymerizable monomer represented by the formula (a-2) are shown below, but the present invention is not limited to these compounds. In the following specific examples, R represents a hydrogen atom or a methyl group.

  Among these, cyclic trimethylolpropane formal (meth) acrylate is preferable, and cyclic trimethylolpropane formal acrylate is particularly preferable. The polymerizable monomer represented by the formula (a-2) is also available as a commercial product, for example, SR531 (trade name: manufactured by SARTOMER), and such a commercial product is also suitable for the present invention. used.

  From the viewpoint of improving the adhesion between the formed cured product and the nonpolar substrate and improving the curability in the curable composition, the content of the polymerizable monomer represented by the formula (a-2) in the curable composition is The total solid content is preferably 1% by mass to 70% by mass, more preferably 3% by mass to 65% by mass, still more preferably 5% by mass to 60% by mass, and most preferably 5% by mass to 50% by mass.

(A-3) Trimethylolpropane triacrylate As a preferable polymerizable monomer in the present invention, trimethylolpropane triacrylate may be mentioned. By containing trimethylolpropane triacrylate as the polymerizable monomer, the curability of the curable composition and the scratch resistance of the formed cured film are improved.

  From the viewpoint of improving curability and scratch resistance, the content of trimethylolpropane triacrylate is preferably 0.1% by mass to 15% by mass with respect to the curable composition, and is 0.2% by mass. 10 mass% is more preferable, and 0.5 mass% to 5 mass% is still more preferable.

(A-4) Other monofunctional polymerizable monomer The curable composition of the present invention preferably contains a polymerizable monomer having the amide group or the ether group, but the amide group or the ether group. You may contain the general purpose monofunctional (meth) acrylate which is a general polymerizable monomer which does not have (hereinafter, may be referred to as other polymerizable monomer).
Examples of other polymerizable monomers include (a-4-1) monofunctional (meth) acrylates having an aromatic hydrocarbon group.
(A-4-1) The monofunctional (meth) acrylate having an aromatic hydrocarbon group preferably has a molecular weight of 500 or less, and more preferably has a molecular weight of 300 or less.
Specific examples of the monofunctional (meth) acrylate having an aromatic hydrocarbon group include, for example, aromatic monofunctional radicals described in paragraphs [0048] to [0063] of JP-A-2009-096985. A polymerizable monomer is mentioned. As a preferable monofunctional (meth) acrylate having an aromatic hydrocarbon group in the present invention, a compound represented by the following formula (a-4) may be mentioned.

(In the formula (a-4), R ¹ represents a hydrogen atom or a methyl group, X ¹ represents a divalent linking group, Ar represents an aromatic hydrocarbon group, and R ⁵ represents a substituent. , U represents an integer of 0 to 5, and when u represents 2 to 5, a plurality of R ⁵ may be the same or different.
In formula (a-4), R ¹ is preferably a hydrogen atom.
X ¹ represents a divalent linking group, and is an ether bond (—O—), an ester bond (—C (O) O— or —OC (O) —), an amide bond (—C (O) NR′— or -NR'C (O)-), a carbonyl group (-C (O)-), an imino group (-NR'-), an optionally substituted alkylene group having 1 to 15 carbon atoms, or A divalent group in which two or more of these are combined is preferable. R ′ represents a hydrogen atom, a linear, branched or cyclic alkyl group having 1 to 20 carbon atoms, or an aryl group having 6 to 20 carbon atoms. Examples of the substituent include a hydroxy group and a halogen atom.
The moiety containing R ¹ and X ¹ (H ₂ C═C (R ¹ ) —C (O) O—X ¹ —) can be bonded at any position on the aromatic hydrocarbon structure. Further, from the viewpoint of improving the affinity with the colorant, the end bonded to the aromatic hydrocarbon group of X ¹ is preferably an oxygen atom, and more preferably an etheric oxygen atom. X ¹ in formula (a-4) is preferably *-(LO) _q- . Here, * shows the coupling | bonding position with the carboxylic ester bond of Formula (a-4), q is an integer of 0-10, L represents a C2-C4 alkylene group. q is preferably an integer of 0 to 4, more preferably an integer of 0 to 2, and even more preferably 1 or 2. (LO) _q is preferably an ethylene oxide chain or a propylene oxide chain.

Ar represents an aromatic hydrocarbon group. Examples of the aromatic hydrocarbon group include monocyclic or polycyclic aromatic hydrocarbon groups having 1 to 4 rings. Specifically, benzene, naphthalene, anthracene, 1H-indene, 9H-fluorene, 1H- Exclude one or more hydrogen atoms from phenalene, phenanthrene, triphenylene, pyrene, naphthacene, tetraphenylene, biphenylene, as-indacene, s-indacene, acenaphthylene, fluoranthene, acephenanthrylene, acanthrylene, chrysene, pleinden, etc. Groups.
Among these, as Ar, a phenyl group or a naphthyl group is preferable, and a phenyl group that is a monocyclic aromatic hydrocarbon group is more preferable.

u ⁵ R ^{5 s} each independently represent a halogen atom, a carboxy group, or a carbon number of 1 to
An acyl group, a hydroxy group, a substituted or unsubstituted amino group, a thiol group, a siloxane group, or a hydrocarbon group or heterocyclic group having a total carbon number of 30 or less which may further have a substituent. preferable. Examples of the substituent include a hydroxy group, an alkyl group having 1 to 10 carbon atoms, and an aryl group having 6 to 12 carbon atoms.
u represents an integer of 0 to 5, and is preferably 0. When u is 0, the aromatic hydrocarbon group Ar is unsubstituted.

  Specific examples of the compound represented by the formula (a-4) that can be used in the present invention include the exemplified compounds [L-1] to [L-9] shown below.

  In the present invention, as described above, the compound represented by the formula (a-4) is preferably a compound in which Ar is a phenyl group, such as 2-phenoxyethyl (meth) acrylate and benzyl (meth) acrylate. More preferred is 2-phenoxyethyl (meth) acrylate, and particularly preferred is 2-phenoxyethyl acrylate.

  From the viewpoint of inkjet dischargeability and flexibility, the content when the compound represented by the formula (a-4) is used as the polymerizable monomer is 1% by mass to 50% by mass with respect to the curable composition. % Is preferable, 3 mass% to 45 mass% is more preferable, and 5 mass% to 40 mass% is still more preferable.

The curable composition which concerns on this invention contains monofunctional (meth) acrylate [(a-4-2)] other than the above-mentioned (a-1)-(a-4-1) polymerizable monomer. Also good.
Examples of other monofunctional polymerizable monomers other than the polymerizable monomers described above (a-4-2) include isoamyl (meth) acrylate, stearyl (meth) acrylate, lauryl (meth) acrylate, and octyl (meth). Acrylate, isooctyl (meth) acrylate, decyl (meth) acrylate, isoamylstil (meth) acrylate, isostearyl (meth) acrylate, 2-ethylhexyl diglycol (meth) acrylate, 2-hydroxybutyl (meth) acrylate, butoxyethyl ( (Meth) acrylate, methoxydiethylene glycol (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, methoxypropylene glycol (meth) acrylate, tetrahydrofurfuryl (meth) acrylate Isobornyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2- (meth) acryloxyethyl succinic acid, 2- (meth) acryloxyethyl-2-hydroxyethyl Phthalic acid, lactone-modified flexible (meth) acrylate, t-butylcyclohexyl (meth) acrylate, 2- (2-ethoxyethoxy) ethyl acrylate, cyclopentenyl acrylate, cyclopentenyloxyethyl acrylate, dicyclopentanyl acrylate, etc. Can be mentioned.

In addition, in this invention, the monofunctional radically polymerizable monomer containing the compound represented by the said formula (a-1) illustrated as a preferable polymerizable monomer, the compound represented by the said formula (a-2), etc. The aspect which is contained in the range used as 50 mass%-90 mass% with respect to the total amount of (a) polymerizable monomer contained in the curable composition of this invention is preferable. In other words, the content of the polyfunctional polymerizable monomer in the polymerizable monomer (a) is preferably in the range of 10% by mass to 50% by mass. In addition, the monofunctional polymerizable monomer in the present specification includes monofunctional polymerizable monomers including a ring structure such as (a-4-1) and (a-4-2) described above. Needless to say.
When the content of the monofunctional polymerizable monomer is within the above range, an image having excellent adhesion between the curable composition and the nonpolar substrate and excellent workability can be obtained.
As for the content rate of a monofunctional polymerizable monomer, it is more preferable that it is 55 mass%-90 mass% with respect to the total amount of (a) polymerizable monomer, and 65 mass%-85 mass% is still more preferable.

(A-5) Polyfunctional (meth) acrylate As a polymerizable monomer which concerns on this invention, you may contain not only the above-mentioned monofunctional polymerizable monomer but a polyfunctional polymerizable monomer as needed.
High curability is obtained when the ink composition contains a polyfunctional (meth) acrylate compound.

  Specific examples of the (a-5) polyfunctional polymerizable monomer that can be used in the present invention include, for example, bis (4-acryloxypolyethoxyphenyl) propane, neopentyl glycol di (meth) acrylate, ethoxylated (2) neo Pentyl glycol di (meth) acrylate (a compound obtained by diacrylate-converting neopentyl glycol ethylene oxide 2 mol adduct), propoxylation (2) neopentyl glycol di (meth) acrylate (neopentyl glycol propylene oxide 2 mol adduct) Acrylated compound), 1,6-hexanediol di (meth) acrylate, 1,9-nonanediol di (meth) acrylate, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethyleneglycol Rudi (meth) acrylate, tetraethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, dipropylene glycol di (meth) acrylate, tripropylene glycol di (meth) acrylate, tetrapropylene glycol di (meth) acrylate, Polypropylene glycol di (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol tetra (meth) acrylate, tetramethylolmethanetetra (meth) acrylate, tetramethylolmethanetri (meth) acrylate , Dimethylol tricyclodecane di (meth) acrylate, modified glycerin tri (meth) acrylate, modified bisphenol Di (meth) acrylate, propylene oxide (PO) adduct di (meth) acrylate of bisphenol A, ethylene oxide (EO) adduct di (meth) acrylate of bisphenol A, dipentaerythritol hexa (meth) acrylate, caprolactone-modified dipenta Examples include erythritol hexa (meth) acrylate. Among these polyfunctional (meth) acrylates, 1,6-hexanediol diacrylate is preferable.

  (A-5) The total content in the case of using a polyfunctional (meth) acrylate is preferably 1% by mass to 30% by mass with respect to the total solid content of the curable composition, from the viewpoint of curability. The content is more preferably 3% by mass to 25% by mass, still more preferably 5% by mass to 20% by mass, and particularly preferably 5% by mass to 15% by mass.

  65 mass%-99 mass% are preferable, and, as for the total content of (a) polymerizable monomer in the curable composition concerning this invention, 70 mass%-90 mass% are more preferable.

(Other polymerizable compounds)
The curable composition according to the present invention further contains other polymerizable compounds not included in the polymerizable monomer (a) for various purposes such as improved curability, as long as the effects of the present invention are not impaired. May be. For example, a polymerizable oligomer having a molecular weight larger than that of the monomer may be used in combination as the polymerizable compound. Suitable examples of the polymerizable oligomer include polyfunctional (meth) acrylate oligomers.
The “oligomer” is a polymer having structural units generally based on a finite number of monomers (generally 5 to 100). The mass average molecular weight of the oligomer is preferably 400 to 10,000, and more preferably 500 to 5,000.
As the oligomer, those having a (meth) acryloyl group as a functional group are preferable.
The number of functional groups contained in the oligomer is preferably from 1 to 15, more preferably from 2 to 6, even more preferably from 2 to 4, and particularly preferably 2 from the viewpoint of the balance between flexibility and curability.

  As the oligomer in the present invention, polyester (meth) acrylate, olefin (ethylene oligomer, propylene oligomer butene oligomer, etc.), vinyl (styrene oligomer, vinyl alcohol oligomer, vinyl pyrrolidone oligomer, (meth) acrylate oligomer, etc.), diene System (butadiene oligomer, chloroprene rubber, pentadiene oligomer, etc.), ring-opening polymerization system (di-, tri-, tetraethylene glycol, polyethylene glycol, polyethylimine, etc.), polyaddition system (oligoester (meth) acrylate, polyamide oligomer) Polyisocyanate oligomers), addition condensation oligomers (phenol resins, amino resins, xylene resins, ketone resins, etc.), amine-modified polyester oligomers, etc. Can. Of these, oligoester (meth) acrylates are preferred, and among them, urethane acrylic and polyester (meth) acrylates are more preferred, and urethane (meth) acrylates are ink compositions with excellent curability and adhesion. Is particularly preferred since The oligomer may be used in combination of a plurality of types in addition to a single type.

  Examples of urethane (meth) acrylates include aliphatic urethane (meth) acrylates and aromatic urethane (meth) acrylates. For details, refer to the oligomer handbook (supervised by Junji Furukawa, Chemical Industry Daily).

Examples of urethane (meth) acrylate oligomers include U-2PPA, U-4HA, U-6HA, U-6LPA, U-15HA, U-324A, UA-122P, UA5201, manufactured by Shin-Nakamura Chemical Co., Ltd. UA-512 etc .; CN964A85, CN964, CN959, CN962, CN963J85, CN965, CN982B88, CN981, CN983, CN996, CN9002, CN9007, CN9010, CN9010, CN7810 EB204, EB230, EB244, EB245, EB270, EB284, EB285, EB810, EB4830, EB4835, EB4858, EB1290, EB210, EB21 , EB4827, EB4830, EB4849, EB6700, EB204, EB8402, EB8804, it includes EB8800-20R like.
As amine-modified polyester oligomers, Daicel-Cytec EB524, EB80, EB81, Sartomer CN550, CN501, CN551, Rahn
A. G. GENOMER 5275 made by the company is mentioned.

  The content when the polymerizable oligomer is used in combination is preferably 1% by mass to 10% by mass, and preferably 2% by mass to 8% by mass with respect to the total mass of the ink composition from the viewpoint of achieving both curability and adhesion. Is more preferable, and 3 mass%-7 mass% is still more preferable.

(B) Polymerization initiator The curable composition of this invention contains a polymerization initiator.
As a polymerization initiator that can be used in the present invention, a known radical polymerization initiator can be used. The radical polymerization initiator that can be used in the present invention may be used alone or in combination of two or more. Moreover, you may use together a radical polymerization initiator and a cationic polymerization initiator.
The polymerization initiator that can be used in the present invention is a compound that absorbs external energy and generates a polymerization initiating species. External energy used for initiating polymerization is roughly divided into heat and actinic radiation, and a thermal polymerization initiator and a photopolymerization initiator are used, respectively. Examples of the active radiation include γ rays, β rays, electron beams, ultraviolet rays, visible rays, and infrared rays.

  The radical polymerization initiator that can be used in the present invention includes (a) aromatic ketones, (b) acylphosphine compounds, (c) aromatic onium salt compounds, (d) organic peroxides, and (e) thio compounds. (F) hexaarylbiimidazole compound, (g) ketoxime ester compound, (h) borate compound, (i) azinium compound, (j) metallocene compound, (k) active ester compound, (l) carbon halogen bond And (m) an alkylamine compound. These radical polymerization initiators may use the above compounds (a) to (m) alone or in combination. The radical polymerization initiator in the present invention is preferably used alone or in combination of two or more.

(B) The polymerization initiator in the present invention is preferably (b-1) a bisacylphosphine compound and (b-2) a monoacylphosphine compound.
As the (b-1) bisacylphosphine compound and the (b-2) monoacylphosphine compound described later, the bisacylphosphine oxide compounds described in paragraphs [0080] to [0098] of JP-A-2009-096985 and Preferred are monoacylphosphine compounds.
As the (b-1) bisacylphosphine compound, those having a partial structure represented by the following formula (b-1-1) in the structure of the compound are preferable.

(In the formula (b-1-1), * represents a bonding position.)
As the (b-1) bisacylphosphine compound, those having a chemical structure represented by the following formula (b-1-2) are particularly preferable.

(In said formula (b-1-2), R < ⁹ >, R < ¹⁰ >, R < ¹¹ > represents the aromatic hydrocarbon group which may have a methyl group or an ethyl group as a substituent.)
As the bisacylphosphine oxide compound represented by the formula (b-1-2), R ^{9 to} R ¹¹ are preferably phenyl groups which may have a methyl group as a substituent, and R ¹¹ Is more preferably a phenyl group, and R ⁹ and R ¹⁰ are more preferably a phenyl group having 1 to 3 methyl groups.
Among them, as the bisacylphosphine oxide compound represented by the formula (b-1-2), bis (2,4,6-trimethylbenzoyl) phenylphosphine oxide (IRGACURE819, trade name: manufactured by BASF Japan Ltd.) is available. preferable.

(B-2) As the monoacylphosphine compound, a compound having a partial structure represented by the following formula (b-2-1) in the structure of the compound is preferable.

(In the formula (b-2-1), * represents a bonding position.)
(B-2) As the monoacylphosphine compound, those having a chemical structure of the formula (b-2-2) are particularly preferable.

In said formula (b-2-3), R < ⁶ >, R <^7> , R < ⁸ > represents the aromatic hydrocarbon group which may have a methyl group or an ethyl group as a substituent. )
As the monoacylphosphine oxide compound represented by the formula (b-2-3), R ^{6 to} R ⁸ are preferably phenyl groups optionally having a methyl group as a substituent, and R ⁷ And R ⁸ is a phenyl group, and R ⁶ is more preferably a phenyl group having 1 to 3 methyl groups.
Among these, as the monoacylphosphine oxide compound represented by the formula (b-2-3), 2,4,6-trimethylbenzoyldiphenylphosphine oxide (Darocur TPO: manufactured by BASF Japan Ltd., Lucirin TPO: BASF Corporation) Product).

  In the step (C) described below, when the curable composition is cured using ultraviolet rays as the active radiation, (c) when a magenta pigment is used as the pigment, the ultraviolet transmittance is lowered and the curability is sufficiently high. It may not be obtained. In such a case, sufficient curability can be obtained by containing the (b-1) bisacylphosphine compound and (b-2) monoacylphosphine compound as the (b) polymerization initiator. The polymerizable compound is particularly useful for a curable composition containing a magenta pigment.

When the total amount of (b) polymerization initiator contained in the curable composition is 100 parts by mass, the total content of (b-1) and (b-2) initiators is 20 parts by mass or more. Preferably, it is more preferably 25 parts by mass or more, and further preferably 30 parts by mass or more.
The (b-2) monoacylphosphine compound has excellent sensitivity and suppresses yellowing of the formed image, so that a curable composition for forming a white or light color image is formed. Is particularly useful.
Therefore, in the case of a curable composition for forming a white or light color image, when (b) the total amount of the polymerization initiator is 100 parts by mass, (b-2) the monoacylphosphine compound is contained by 50 parts by mass or more. It is preferable to contain 60-100 mass parts, and it is more preferable to contain 70-100 mass parts.

(B-3) Thioxanthone compound (b-3) A thioxanthone compound is also preferably exemplified as the (b) polymerization initiator used in the curable composition of the present invention. (B-3) Curability is improved by using an initiator.

(B-3-1) Thioxanthone compound The thioxanthone compound is preferably a compound represented by the following formula (b-3-1).

(In the formula (b-3-1), R ^{1 to} R ⁸ are each independently a hydrogen atom, alkyl group, halogen atom, hydroxy group, cyano group, nitro group, amino group, alkylthio group, alkylamino group ( Mono- and di-substituted), and represents an alkoxy group, an alkoxycarbonyl group, an acyloxy group, an acyl group, a carboxy group, or a sulfo group.)

The alkyl group, alkylthio group, alkylamino group, alkoxy group, alkoxycarbonyl group, acyloxy group, and the alkyl moiety in the acyl group preferably have 1 to 20 carbon atoms, more preferably 1 to 8 carbon atoms. Preferably, it is 1-4.
Two adjacent R ^{1 to} R ⁸ may be connected to each other to form a ring. Examples of the ring structure in the case where these form a ring include a 5- or 6-membered aliphatic ring, an aromatic ring, etc., and may be a heterocyclic ring containing an element other than a carbon atom. The rings may be further combined to form a binuclear ring, for example, a condensed ring. These ring structures may further have a substituent. Examples of the substituent include a halogen atom, a hydroxy group, a cyano group, a nitro group, an amino group, an alkylthio group, an alkylamino group, an alkoxy group, an alkoxycarbonyl group, an acyloxy group, an acyl group, a carboxy group, and a sulfo group. N, O, and S can be mentioned as an example of a hetero atom in case the formed ring structure is a heterocyclic ring.

Examples of the thioxanthone compound include thioxanthone, 2-isopropylthioxanthone, 4-isopropylthioxanthone, 2-chlorothioxanthone, 2-dodecylthioxanthone, 2,4-diethylthioxanthone, 2,4-dimethylthioxanthone, 1-methoxycarbonylthioxanthone, 2-ethoxy. Carbonylthioxanthone, 3- (2-methoxyethoxycarbonyl) thioxanthone, 4-butoxycarbonylthioxanthone, 3-butoxycarbonyl-7-methylthioxanthone, 1-cyano-3-chlorothioxanthone, 1-ethoxycarbonyl-3-chlorothioxanthone, 1 -Ethoxycarbonyl-3-ethoxythioxanthone, 1-ethoxycarbonyl-3-aminothioxanthone, 1-ethoxycarbonyl-3-phenyl Nylsulfurylthioxanthone, 3,4-di [2- (2-methoxyethoxy) ethoxycarbonyl] thioxanthone, 1-ethoxycarbonyl-3- (1-methyl-1-morpholinoethyl) thioxanthone, 2-methyl-6-dimethoxymethyl Thioxanthone, 2-methyl-6- (1,1-dimethoxybenzyl) thioxanthone, 2-morpholinomethylthioxanthone, 2-methyl-6-morpholinomethylthioxanthone, n-allylthioxanthone-3,4-dicarboximide, n-octyl Thioxanthone-3,4-dicarboximide, N- (1,1,3,3-tetramethylbutyl) thioxanthone-3,4-dicarboximide, 1-phenoxythioxanthone, 6-ethoxycarbonyl-2-methoxythioxanthone, 6-et Cycarbonyl-2-methylthioxanthone, thioxanthone-2-polyethylene glycol ester, 2-hydroxy-3- (3,4-dimethyl-9-oxo-9H-thioxanthone-2-yloxy) -N, N, N-trimethyl- An example is 1-propanaminium chloride.
Among these, 2,4-diethylthioxanthone, 2-isopropylthioxanthone, and 4-isopropylthioxanthone are more preferable from the viewpoint of availability and curability.

(B-4) Other polymerization initiator The curable composition of this invention contains (b-4) other polymerization initiators other than said (b-1)-(b-3-2). Also good. As other polymerization initiators, (b-4-1) α-aminoalkylphenone compounds are preferred.
(B-4-1) α-aminoalkylphenone compound The α-aminoalkylphenone compound that can be contained in the curable composition of the present invention is a compound represented by the following formula (b-4-1). preferable.

In the formula (b-4-1), R ¹ , R ² , and R ³ are each independently a hydroxy group, an alkyl group that may have a substituent, or an alkoxy that may have a substituent. Represents an amino group which may have a group or a substituent, and X represents a hydrogen atom, an amino group which may have a substituent, an alkylthio group which may have a substituent, or a substituent. The alkyl group which may have a group is represented. In addition, the substituents in the case where R ¹ , R ² , R ³ , and X are amino groups may be bonded to each other to form a heterocyclic group. Examples of the substituent include an alkyl group having 1 to 10 carbon atoms.

  Moreover, (b-4) As another polymerization initiator, the compound represented by either of following formula (b-4-2) and following formula (b-4-3) is also mentioned preferably.

In the formula (b-4-2), R ⁴ , R ⁵ , R ⁶ , and R ⁷ each represents an alkyl group that may have a substituent, and R ⁴ , R ⁵ , and R ⁶ At least one of R ⁷ may be bonded to each other to form a heterocyclic group. R ^{1, R 2,} and the substituents, ^R 1, ^{R 2} in formula (b-4-1), and are respectively a substituent synonymous.

In the formula (b-4-3), R ⁸ represents an alkyl group which may have a substituent.
R ^{1, R 2,} and the substituents, ^R 1, ^{R 2} in formula (b-4-1), and has the same meaning as the substituent, ^{R 4} and ^{R 5} has the formula (b-4-2 Are the same as R ⁴ and R ⁵ .
There is no restriction | limiting in particular as said heterocyclic group, Although it can select suitably, For example, a morpholino group is preferable.

  The (b-4-1) α-aminoalkylphenone compound is also available as a commercial product, and examples thereof include IRGACURE369 (manufactured by BASF Japan) and IRGACURE907 (manufactured by BASF Japan).

  From the viewpoint of curability, the content of the (b-4-1) α-aminoalkylphenone compound is preferably 0.1% by mass to 15% by mass in the curable composition, and 0.5% by mass. More preferably, it is 10 mass%, More preferably, it is 1 mass%-5 mass%.

  In addition to (b-4) other polymerization initiators other than the above, thiochromanone compounds, aromatic ketones, aromatic onium salt compounds, organic peroxides, thio compounds, hexaarylbiimidazole compounds, ketoximes Examples include ester compounds, borate compounds, azinium compounds, metallocene compounds, active ester compounds, and compounds having a carbon halogen bond. Details of the polymerization initiator are known to those skilled in the art, and are described, for example, in paragraphs [0090] to [0116] of JP-A-2009-185186, and these polymerization initiators are also applicable to the present invention. It is.

In the curable composition of this invention, only 1 type of polymerization initiators may be included and 2 or more types may be used together.
The total content of the polymerization initiator in the curable composition of the present invention is preferably in the range of 0.5% by mass to 20% by mass with respect to the total amount of the curable composition, and is 1% by mass to 10% by mass. More preferably, it is the range.

(C) Pigment For the purpose of forming colored image formation, the curable composition of the present invention contains (c) a pigment depending on the formed image.
By containing the pigment (c) as a colorant, the formed image has excellent light resistance.
The pigment (c) preferably used in the present invention will be described.
The pigment is not particularly limited, and all commercially available organic pigments and inorganic pigments, and those obtained by dyeing resin particles with a dye can be used. Further, commercially available pigment dispersions and surface-treated pigments such as those obtained by dispersing pigments in an insoluble resin or the like using a dispersion medium, or those obtained by grafting a resin on the pigment surface, etc., impair the effects of the present invention. It can be used as long as it is not.
Examples of these pigments include, for example, “Pigment Dictionary” (2000), edited by Seijiro Ito. Herbst, K.M. Hunger “Industrial Organic Pigments”, JP 2002-12607 A, JP 2002-188025 A, JP 2003-26978 A, and JP 2003-342503 A3.

  Specific examples of organic pigments and inorganic pigments that can be used in the present invention include C.I. I. Pigment Yellow 1 (Fast Yellow G etc.), C.I. I. A monoazo pigment such as C.I. Pigment Yellow 74; I. Pigment Yellow 12 (disaji yellow AAA, etc.), C.I. I. Disazo pigments such as C.I. Pigment Yellow 17; I. Non-benzidine type azo pigments such as CI Pigment Yellow 180; I. Azo lake pigments such as C.I. Pigment Yellow 100 (eg Tartrazine Yellow Lake); I. Condensed azo pigments such as CI Pigment Yellow 95 (Condensed Azo Yellow GR, etc.); I. Acidic dye lake pigments such as C.I. Pigment Yellow 115 (such as quinoline yellow lake); I. Basic dye lake pigments such as CI Pigment Yellow 18 (Thioflavin Lake, etc.), anthraquinone pigments such as Flavantron Yellow (Y-24), isoindolinone pigments such as Isoindolinone Yellow 3RLT (Y-110), and quinophthalone yellow Quinophthalone pigments such as (Y-138), isoindoline pigments such as isoindoline yellow (Y-139), C.I. I. Nitroso pigments such as C.I. Pigment Yellow 153 (nickel nitroso yellow, etc.); I. And metal complex salt azomethine pigments such as CI Pigment Yellow 117 (copper azomethine yellow, etc.).

C. As a thing which exhibits red or magenta color, C.I. I. Monoazo pigments such as CI Pigment Red 3 (Toluidine Red, etc.); I. Disazo pigments such as C.I. Pigment Red 38 (Pyrazolone Red B, etc.); I. Pigment Red 53: 1 (Lake Red C, etc.) and C.I. I. Azo lake pigments such as C.I. Pigment Red 57: 1 (Brilliant Carmine 6B); I. Condensed azo pigments such as C.I. Pigment Red 144 (condensed azo red BR, etc.); I. Acidic dye lake pigments such as C.I. Pigment Red 174 (Phloxine B Lake, etc.); I. Basic dye lake pigments such as C.I. Pigment Red 81 (Rhodamine 6G 'Lake, etc.)
. I. Anthraquinone pigments such as C.I. Pigment Red 177 (eg, dianthraquinonyl red); I. Thioindigo pigments such as C.I. Pigment Red 88 (Thioindigo Bordeaux, etc.); I. Perinone pigments such as C.I. Pigment Red 194 (perinone red, etc.); I. Perylene pigments such as C.I. Pigment Red 149 (perylene scarlet, etc.); I. Pigment violet 19 (unsubstituted quinacridone), C.I. I. Quinacridone pigments such as CI Pigment Red 122 (quinacridone magenta, etc.); I. Isoindolinone pigments such as CI Pigment Red 180 (isoindolinone red 2BLT, etc.); I. And alizarin lake pigments such as CI Pigment Red 83 (Mada Lake, etc.).

  As a pigment exhibiting blue or cyan, C.I. I. Disazo pigments such as C.I. Pigment Blue 25 (Dianisidine Blue, etc.); I. Phthalocyanine pigments such as C.I. Pigment Blue 15 (phthalocyanine blue, etc.); I. Acidic dye lake pigments such as C.I. Pigment Blue 24 (Peacock Blue Lake, etc.); I. Basic dye lake pigments such as C.I. Pigment Blue 1 (Viclotia Pure Blue BO Lake, etc.); I. Anthraquinone pigments such as C.I. Pigment Blue 60 (Indantron Blue, etc.); I. And alkali blue pigments such as CI Pigment Blue 18 (Alkali Blue V-5: 1).

As a pigment exhibiting green, C.I. I. Pigment green 7 (phthalocyanine green), C.I. I. Phthalocyanine pigments such as C.I. Pigment Green 36 (phthalocyanine green); I. And azo metal complex pigments such as CI Pigment Green 8 (Nitroso Green).
As a pigment exhibiting an orange color, C.I. I. An isoindoline pigment such as C.I. Pigment Orange 66 (isoindoline orange); I. And anthraquinone pigments such as CI Pigment Orange 51 (dichloropyrantron orange).
Examples of the black pigment include carbon black, titanium black, and aniline black.
Specific examples of the white pigment include basic lead carbonate (2PbCO ₃ Pb (OH) ₂ , so-called silver white), zinc oxide (ZnO, so-called zinc white), titanium oxide (TiO ₂ , so-called titanium white), Strontium titanate (SrTiO ₃ , so-called titanium strontium white) or the like can be used.
Here, titanium oxide has a smaller specific gravity than other white pigments, a large refractive index, and is chemically and physically stable, and thus has a high hiding power and coloring power as a pigment. Excellent durability against other environments. Therefore, it is preferable to use titanium oxide as the white pigment. Of course, other white pigments (white pigments other than the white pigments listed above) may be used as necessary.

When applying a pigment as a colorant to a curable composition, it is preferable to prepare and use a pigment dispersion in advance.
For dispersion of the pigment, for example, a dispersion device such as a ball mill, a sand mill, an attritor, a roll mill, a jet mill, a homogenizer, a paint shaker, a kneader, an agitator, a Henschel mixer, a colloid mill, an ultrasonic homogenizer, a pearl mill, or a wet jet mill is used. Can do.
When dispersing the pigment, a pigment dispersant such as a surfactant or a polymer dispersant may be added.
As the dispersant, a polymer dispersant is preferable. In the present specification, the “polymer dispersant” means a dispersant having a weight average molecular weight of 1,000 or more.
The content of the pigment dispersant is appropriately selected depending on the purpose of use, but is preferably in the range of 10 to 50 parts by mass with respect to 100 parts by mass of the pigment.
In preparing the pigment dispersion, a synergist according to various pigments can be used as a dispersion aid as necessary. The dispersion aid is preferably added in an amount of 1 to 50 parts by mass with respect to 100 parts by mass of the pigment.

As a dispersion medium for various components such as pigments, a solvent may be added, or the polymerizable monomer compound which is a low molecular weight component without a solvent may be used as a dispersion medium.
Since the curable composition of the present invention is an active energy ray-curable liquid, a polymerizable monomer that contributes to curing is used as a dispersion medium, no solvent is used, or solubilization of each component is performed. When used for the purpose, a small amount is preferable. From such a viewpoint, it is preferable to use a polymerizable monomer as the dispersion medium, and in particular, to select a polymerizable monomer having a low viscosity from the viewpoint of improving dispersibility and handling properties of the ink composition.

The average particle size of the pigment used here is excellent in color developability as it is finer, but aggregation is more likely to occur as it is finer. Therefore, considering the balance between color developability and dispersion stability, 0.01 μm to 0. It is preferable that it is 4 micrometers, More preferably, it is the range of 0.02 micrometer-0.2 micrometer. The selection of the colorant, dispersant, and dispersion medium, dispersion conditions, and filtration conditions are set so that the maximum particle diameter is preferably 3 μm or less, more preferably 1 μm or less. By controlling the particle size, it is possible to suppress clogging of the inkjet head nozzle when the curable composition is applied to the inkjet method, and to maintain the storage stability and the curing sensitivity of the curable composition.
The particle size of the colorant can be measured by a known measurement method. Specifically, it can be measured by a centrifugal sedimentation light transmission method, an X-ray transmission method, a laser diffraction / scattering method, and a dynamic light scattering method. In the present invention, a value obtained by measurement using a laser diffraction / scattering method is employed.

(C) The content of the pigment is appropriately selected depending on the color and the purpose of use. It is preferable that it is 1.0 mass%-20 mass%, and it is especially preferable that it is 2.0 mass%-10 mass%.
In forming a white image, the content of the white pigment in the curable composition is preferably 1% by mass to 40% by mass, and more preferably 3% by mass to 30% by mass. More preferably, it is 5 mass%-20 mass%.

(dye)
The curable composition of the present invention may use a dye as a colorant other than the pigment for the purpose of adjusting the hue as long as the effects of the present invention are not impaired.
As the dye, a conventionally known dye can be appropriately selected and used. Specific examples include compounds described in paragraph numbers [0023] to [0089] of JP-A No. 2002-114930 and paragraph numbers [0136] to [0140] of JP-A No. 2008-13646. These can also be applied to the present invention.

(Other ingredients)
In the curable composition of the present invention, if necessary, in addition to the above components, a polymerization inhibitor, a sensitizer, a co-sensitizer, an ultraviolet absorber, an antioxidant, an antifading agent, a conductive salt, Solvents, polymer compounds, basic compounds, surfactants, leveling additives, matting agents, polyester resins for adjusting film properties, polyurethane resins, vinyl resins, acrylic resins, rubber resins, waxes Etc. can be contained. These are described in JP-A-2009-185186 and can also be used in the present invention.

(D) Polymerization inhibitor It is preferable that the curable composition concerning this invention contains a polymerization inhibitor from a viewpoint of improving preservability.
In the image forming method of the present invention, the curable composition is applied onto a substrate by an ink jet recording method, and at the time of discharge, it is preferably discharged at a temperature in the range of 25 to 80 ° C. with a reduced viscosity. In order to prevent clogging of the head, it is preferable to add a polymerization inhibitor.
Examples of the polymerization inhibitor include nitroso polymerization inhibitors, hydroquinone, benzoquinone, p-methoxyphenol, TEMPO, TEMPOL, cuperon Al, hindered amines, etc. Among them, nitroso polymerization inhibitors and hindered amine polymerization inhibitors are preferable. .
Specific examples of the nitroso polymerization inhibitor preferably used in the present invention are shown below, but are not limited thereto.

Examples of commercially available nitroso polymerization inhibitors include FIRSTCURE ST-1 (manufactured by Chem First). Commercially available hindered amine polymerization inhibitors include TINUVIN292, TINUVIN770DF, TINUVIN765, and TINUVIN123, and these are preferably used in the curable composition according to the present invention.
The content of the polymerization inhibitor in the curable composition according to the present invention is preferably 0.01% by mass to 1.5% by mass, more preferably 0.1% by mass to 1.0% by mass, and 0.2%. A mass% to 0.8 mass% is more preferable. When the content is within the above range, an undesirable polymerization reaction during preparation and storage of the curable composition can be suppressed without causing a decrease in sensitivity, and clogging of the inkjet nozzle is effectively prevented.

(Physical properties of curable composition applied to inkjet method)
The curable composition according to the present invention is preferably prepared so that the viscosity at 25 ° C. is 40 mPa · s or less in consideration of dischargeability when applied to the ink jet method. The more preferable viscosity at 25 ° C. is in the range of 5 mPa · s to 40 mPa · s, and further preferably in the range of 7 mPa · s to 30 mPa · s.
The ejection may be performed at room temperature (25 ° C.), or may be performed by heating in an ink jet head or an ink tank, but from the viewpoint of stability, the heating temperature (the curable composition when heated) The liquid temperature of the product is preferably 80 ° C. or lower. The discharge temperature (liquid temperature during discharge) is preferably 25 to 80 ° C., more preferably 25 to 50 ° C., but the viscosity of the curable composition in the temperature range is 3 mPa · s to 15 mPa · s. Preferably, it is 3 mPa · s to 13 mPa · s.
It is preferable that the composition ratio of the curable composition according to the present invention is appropriately adjusted so that the viscosity is in the above range. Setting the viscosity at room temperature to be high is preferable because repelling on a non-polar substrate can be suppressed and undesired bleeding at the time of ink droplet landing can be suppressed, and as a result, the image quality can be improved.
In addition, the viscosity in this specification employs a value obtained using a RE80 viscometer manufactured by Toki Sangyo Co., Ltd., and is a viscosity measured at 25 ° C. unless otherwise specified.
The RE80 type viscometer is a conical rotor / plate type viscometer corresponding to the E type. Measurement was carried out at a rotation speed of 10 rpm using the first rotor. However, for those having a viscosity higher than 60 mPa · s, the measurement was performed by changing the number of revolutions to 5 rpm, 2.5 rpm, 1 rpm, 0.5 rpm, or the like as necessary.
In the image forming method of the present invention, the non-polar substrate surface-treated in the step (a) is used, and the affinity between the curable composition and the substrate surface is improved. Even when the viscosity is lower than the range, repelling and bleeding are suppressed, and the degree of freedom of prescription and heating conditions is increased.

The surface tension at 25 ° C. of the curable composition according to the present invention is preferably 32 mN / m to 40 mN / m. More preferably, it is 35 mN / m-38 mN / m. Within the above range, the gloss is excellent.
Here, the surface tension was measured at 25 ° C. by the Wilhelmy method using a commonly used surface tension meter (for example, Kyowa Interface Science Co., Ltd., surface tension meter CBVP-Z, etc.). Value.

  The curable composition according to the present invention can be applied to a curable ink composition having a desired hue by selecting the type of pigment as a colorant.

[Inkjet recording method]
In the step (B), the colored curable composition is ejected by an ink jet method onto the nonpolar substrate surface-treated in the step (A) to form a curable composition layer.
An ink jet recording method applicable to the image forming method of the present invention will be described.
In the present invention, an inkjet recording method that is particularly preferably used is an inkjet head having a single or a plurality of nozzle rows in which a plurality of nozzles for discharging a curable composition are arranged in a first direction. A scanning step of moving, a relative moving step of moving the recording medium relative to the inkjet head in a second direction not parallel to the first direction, and dividing the nozzle array into a plurality of regions in the second direction. A discharge control step for controlling the ink discharge of the ink jet head for each of the divided nozzle regions, and the ink discharged from the ink jet head by the discharge control step and attached to the recording medium An actinic ray irradiating step for irradiating actinic rays, and the actinic ray irradiating step includes the divided nozzle regions. To be divided into a plurality of regions emission range of the active light correspondingly controls the amount of the divided divided irradiation area by area, which is a step of performing irradiation of the active light, an ink jet recording method.
Hereinafter, it will be described in detail with reference to the drawings.

(Overall configuration of inkjet recording apparatus)
FIG. 1 is an external perspective view showing an example of an ink jet recording apparatus suitably used in the present invention. The ink jet recording apparatus 10 is a printer that forms a color image on the surface-treated nonpolar substrate 12 using an ultraviolet curable ink (UV curable ink).
Hereinafter, the curable composition according to the present invention may be referred to as “curable ink (composition)”, and the “surface-treated nonpolar substrate” may be simply referred to as “recording medium”. That is, hereinafter, in the description of the process of the present invention, the “recording medium” refers to the nonpolar base material surface-treated in the process (A).

  The ink jet recording apparatus 10 includes an apparatus main body 20 and support legs 22 that support the apparatus main body 20. The apparatus main body 20 includes a drop-on-demand type inkjet head 24 that ejects ink toward the recording medium (medium) 12, a platen 26 that supports the recording medium 12, and a guide mechanism as a head moving unit (scanning unit). 28 and a carriage 30 are provided.

  The guide mechanism 28 is disposed above the platen 26 so as to extend along a scanning direction (Y direction) perpendicular to the conveyance direction (X direction) of the recording medium 12 and parallel to the medium support surface of the platen 26. ing. The carriage 30 is supported so as to reciprocate in the Y direction along the guide mechanism 28. An ink jet head 24 is mounted on the carriage 30, and temporary curing light sources (pinning light sources) 32A and 32B for irradiating the ink on the recording medium 12 with ultraviolet rays and main curing light sources (curing light sources) 34A and 34B are provided. It is installed.

  The temporary curing light sources 32A and 32B are light sources that irradiate ultraviolet rays for temporarily curing the ink so that the adjacent droplets do not coalesce after the ink droplets ejected from the inkjet head 24 have landed on the recording medium 12. is there. The main curing light sources 34 </ b> A and 34 </ b> B are light sources that irradiate ultraviolet rays for performing additional exposure after temporary curing and finally completely curing (main curing) the ink. Although details will be described later, one or both of the main curing light sources 34A and 34B are configured to be movable in the X direction so as to be aligned with the inkjet head 24 and the temporary curing light sources 32A and 32B in the Y direction.

  The ink jet head 24, the temporary curing light sources 32 </ b> A and 32 </ b> B, and the main curing light sources 34 </ b> A and 34 </ b> B arranged on the carriage 30 move integrally with the carriage 30 along the guide mechanism 28. The reciprocating direction (Y direction) of the carriage 30 may be referred to as a “main scanning direction”, and the conveyance direction (X direction) of the recording medium 12 may be referred to as a “sub scanning direction”. The Y direction corresponds to the “first direction”, and the X direction corresponds to the “second direction”.

  The nonpolar medium 12 used in the method of the present invention is a nonpolar substrate layer (preferably polypropylene) having at least the outermost surface selected from polyethylene, polypropylene, and the like, and the surface is modified by plasma treatment in the step (A). It is quality. The recording medium only needs to have a layer made of the nonpolar material on the outermost surface, and may be a single-layer resin substrate or a multilayer. In the case of a multilayer, the lower layer is damaged by plasma treatment. It is optional as long as it is not received, and any material such as paper, non-woven fabric, vinyl chloride, synthetic chemical fiber, polyethylene, polyester, and tarpaulin can be used. The recording medium 12 is fed in a roll paper state (see FIG. 1) from the back side of the apparatus, and after printing is wound up by a winding roller (reference numeral 44 in FIG. 1) on the front side of the apparatus. Ink droplets are ejected from the inkjet head 24 to the recording medium 12 conveyed on the platen 26, and the temporary curing light sources 32A and 32B and the main curing light sources 34A and 34B are applied to the ink droplets adhering to the recording medium 12. Ultraviolet rays are irradiated.

  In FIG. 1, an attachment portion 38 for an ink cartridge 36 is provided on the left front surface of the apparatus main body 20. The ink cartridge 36 is a replaceable ink supply source (ink tank) that stores ultraviolet curable ink. The ink cartridge 36 is provided corresponding to each color ink used in the inkjet recording apparatus 10 of this example. Each color-specific ink cartridge 36 is connected to the inkjet head 24 by an ink supply path (not shown) formed independently. When the remaining amount of ink for each color is low, the ink cartridge 36 is replaced.

  Although not shown, a maintenance unit for the inkjet head 24 is provided on the right side of the apparatus main body 20 toward the front. The maintenance unit is provided with a cap for keeping the ink-jet head 24 moisturized during non-printing and a wiping member (blade, web, etc.) for cleaning the nozzle surface (ink ejection surface) of the ink-jet head 24. The cap for capping the nozzle surface of the inkjet head 24 is provided with an ink receiver for receiving ink droplets ejected from the nozzle for maintenance.

(Description of recording medium transport path)
FIG. 2 is an explanatory diagram schematically showing a recording medium conveyance path in the inkjet recording apparatus 10. As shown in FIG. 2, the platen 26 is formed in an inverted bowl shape, and its upper surface serves as a support surface (medium support surface) of the recording medium 12. A pair of nip rollers 40 that are recording medium conveying means for intermittently conveying the recording medium 12 are disposed on the upstream side in the recording medium conveying direction (X direction) in the vicinity of the platen 26. The nip roller 40 moves the recording medium 12 on the platen 26 in the recording medium conveyance direction.
In the present embodiment, a plasma processing apparatus 43 is provided between a feed supply roll 42 that supplies the recording medium 12 and a pair of conveyance nip rollers 40 provided at the entrance of the printing unit. The plasma processing apparatus 43 in the present embodiment employs a plasma jet system in which plasma generated by discharge is conveyed to and contacted the surface of the recording medium 12 by an inert gas stream, and plasma generated in a discharge unit (not shown) Along with a nitrogen atom-containing gas containing nitrogen atoms having a nitrogen fraction of 80% or more, the gas passes through a conducting tube (not shown) and is conveyed to the supply nozzle and applied to the surface of the recording medium 12. In FIG. 2, the plasma irradiation device 43 takes an open system. However, the upstream side and the downstream side are closed by an air curtain or the like according to the conveyance conditions of the recording medium 12 supplied intermittently. An apparatus may be used, and a direct plasma processing apparatus may be applied.

The recording medium 12 sent out from the supply-side roll (feed-out supply roll) 42 constituting the roll-to-roll type medium transport means is provided at the entrance of the printing unit (upstream side of the platen 26 in the recording medium transport direction). The pair of nip rollers 40 are intermittently conveyed in the recording medium conveyance direction. At this time, the recording medium 12 delivered from the delivery supply roll 42 is subjected to plasma processing when passing through a plasma processing apparatus provided on the upstream side of the nip roller 40, and plasma is applied to the printing surface of the recording medium 12 on the side. Nitrogen atoms are introduced by the treatment, and a surface treatment for improving the affinity with the ink is performed.
Here, as the amount of nitrogen atoms introduced into the base material, the nitrogen introduction rate (N / C) with respect to the base material is in the range of 0.16 to 0.3 from the viewpoint of the effect. Preferably, it is in the range of 0.18 to 0.22.
The recording medium 12 subjected to the surface plasma treatment is immediately conveyed to the printing unit by feeding a pair of nip rollers 40.
The recording medium 12 that has reached the printing unit immediately below the ink jet head 24 is printed by the ink jet head 24 and is taken up by the take-up roll 44 after printing. A guide 46 for the recording medium 12 is provided on the downstream side of the printing unit in the recording medium conveyance direction.

  A temperature adjusting unit 50 for adjusting the temperature of the recording medium 12 during printing is provided on the back surface (the surface opposite to the surface supporting the recording medium 12) of the platen 26 at a position facing the inkjet head 24 in the printing unit. Is provided. When the recording medium 12 at the time of printing is adjusted to a predetermined temperature, the physical properties such as the viscosity of the ink droplets that have landed on the recording medium 12 and the surface tension become the desired values, and the desired dot diameter is set. Can be obtained. In addition, as needed, the pre temperature control part 52 may be provided in the upstream of the temperature control part 50, and the after temperature control part 54 may be provided in the downstream of the temperature control part 50.

(Description of inkjet head)
FIG. 3 is a perspective plan view showing an example of an arrangement form of the inkjet head 24, the temporary curing light sources 32A and 32B, and the main curing light sources 34A and 34B arranged on the carriage 30. FIG.

  In FIG. 3, the inkjet head 24 includes yellow (Y), magenta (M), cyan (C), black (K), light cyan (LC), light magenta (LM), clear (transparent) ink (CL ) And white (white) ink (W) for each color ink, nozzle rows 61Y, 61M, 61C, 61K, 61LC, 61LM, 61CL, and 61W are provided for ejecting the respective color inks. Although described, it goes without saying that the number of nozzles is appropriately provided according to the number of hues necessary for printing. In FIG. 3, the nozzle rows are illustrated by dotted lines, and individual illustrations of the nozzles are omitted. In the following description, the nozzle rows 61Y, 61M, 61C, 61K, 61LC, 61LM, 61CL, and 61W may be collectively referred to by the reference numeral 61 to represent the nozzle rows.

  The ink color type (number of colors) and the color combination are not limited to the present embodiment. For example, a form in which the LC and LM nozzle arrays are omitted, a form in which the CL nozzle array is omitted, a form in which a metal ink nozzle array is added, and a form in which a nozzle array for discharging special color ink is added are possible. . Further, the arrangement order of the nozzle rows for each color is not particularly limited. However, a configuration in which an ink having a low curing sensitivity to ultraviolet light among a plurality of ink types is disposed on the side close to the temporary curing light source 32A or 32B is preferable.

  By forming a head module for each color nozzle row 61 and arranging them, it is possible to form an inkjet head 24 capable of color drawing. For example, a head module 24Y having a nozzle row 61Y that discharges yellow ink, a head module 24M having a nozzle row 61M that discharges magenta ink, a head module 24C having a nozzle row 61C that discharges cyan ink, and black ink A head module 24K having a nozzle row 61K for discharging, and head modules 24LC, 24LM, 24CL, 24W having nozzle rows 61LC, 61LM, 61CL, 61W for discharging ink of each color of LC, LM, CL, W, respectively. A mode in which the carriage 30 is arranged at equal intervals so as to be aligned along the reciprocating direction of the carriage 30 (main scanning direction, Y direction) is also possible. The module group (head group) of the head modules 24Y, 24M, 24C, 24K, 24LC, and 24LM for each color may be interpreted as an “inkjet head”, or each module may be interpreted as an “inkjet head”. It is. Alternatively, a configuration in which an ink flow path is formed separately for each color inside one inkjet head 24 and a nozzle array that discharges a plurality of colors of ink with one head is also possible.

  In each nozzle row 61, a plurality of nozzles are arranged in a row (linearly) along the recording medium conveyance direction (sub-scanning direction, X direction) at regular intervals. In the inkjet head 24 of this example, the arrangement pitch (nozzle pitch) of the nozzles constituting each nozzle row 61 is 254 μm (100 dpi), the number of nozzles constituting one nozzle row 61 is 256 nozzles, and the total length of the nozzle row 61 Lw (the total length of the nozzle row) is about 65 mm (254 μm × 255 = 64.8 mm). Further, the discharge frequency is 15 kHz, and three types of discharge droplet amounts of 10 pl, 20 pl, and 30 pl can be distinguished by changing the drive waveform.

  As an ink ejection method of the inkjet head 24, a method (piezo jet method) in which ink droplets are ejected by deformation of a piezoelectric element (piezo actuator) is employed. In addition to a configuration using an electrostatic actuator (electrostatic actuator method) as a discharge energy generating element, a heating element (heating element) such as a heater is used to heat ink to generate bubbles and to eject ink droplets with that pressure. It is also possible to adopt a form (thermal jet system). However, since the ultraviolet curable ink generally has a higher viscosity than the solvent ink, when using the ultraviolet curable ink, it is preferable to adopt a piezo jet method having a relatively large ejection force.

(About drawing mode)
In the inkjet recording apparatus 10 shown in this example, multi-pass drawing control is applied, and the print resolution can be changed by changing the number of print passes. For example, three types of drawing modes, a high production mode, a standard mode, and a high image quality mode, are prepared, and the printing resolution is different in each mode. The drawing mode can be selected according to the printing purpose and application.

In the high production mode, printing is executed with a resolution of 600 dpi (dot per inch: number of dots per 2.54 cm) (main scanning direction) × 400 dpi (sub-scanning direction). In the high production mode, a resolution of 600 dpi is realized by two passes (two scans) in the main scanning direction. In the first scan (outward path of the carriage 30), dots are formed with a resolution of 300 dpi. In the second scan (return pass), dots are formed such that the middle of the dots formed in the first scan (forward pass) is interpolated at 300 dpi, and a resolution of 600 dpi is obtained in the main scan direction.
On the other hand, in the sub-scanning direction, the nozzle pitch is 100 dpi, and dots are formed at a resolution of 100 dpi in the sub-scanning direction by one main scanning (one pass). Therefore, a resolution of 400 dpi is realized by performing interpolation printing by four-pass printing (four scans). The main scanning speed of the carriage 30 in the high production mode is 1270 mm / sec.

In the standard mode, printing is performed at a resolution of 600 dpi × 800 dpi, and a resolution of 600 dpi × 800 dpi is obtained by 2-pass printing in the main scanning direction and 8-pass printing in the sub-scanning direction.
In the high image quality mode, printing is executed with a resolution of 1,200 × 1,200 dpi, and a resolution of 1,200 dpi × 1,200 dpi is obtained with four passes in the main scanning direction and 12 passes in the sub-scanning direction.

[(C) Image forming step of forming an image by applying energy to the applied curable composition layer and curing it]
In the step (C), the curable composition layer (image composed of the ink composition) formed on the nonpolar substrate in the step (B) is cured by applying energy by irradiation with actinic rays or the like. Form. Usually, (B) process and (C) process are continuously performed, for example using the inkjet printing apparatus provided with the ultraviolet irradiation part. Hereinafter, the formation of the curable composition layer by ejection and the image formation by ultraviolet irradiation will be sequentially described.
(Arrangement of UV irradiation part)
As shown in FIG. 3, provisional curing light sources 32 </ b> A and 32 </ b> B are arranged on both the left and right sides of the carriage movement direction (Y direction) of the inkjet head 24. Further, main curing light sources 34 </ b> A and 34 </ b> B are disposed on the downstream side of the inkjet head 24 in the recording medium conveyance direction (X direction). The main curing light sources 34A and 34B are arranged on the outer side (further farther) than the temporary curing light sources 32A and 32B in the Y direction from the inkjet head 24. The main curing light sources 34A and 34B are configured to be movable in the direction opposite to the recording medium conveyance direction (−X direction), and are aligned with the temporary curing light sources 32A and 32B and the inkjet head 24 along the carriage movement direction. The arrangement can be changed.

Color ink droplets ejected from the nozzles for the colored ink composition (color ink) of the inkjet head 24 (nozzles included in the nozzle rows 61Y, 61M, 61C, 61K, 61LC, 61LM) and landed on the recording medium 12 are: Immediately thereafter, the temporary curing light source 32A (or 32B) passing thereover is irradiated with ultraviolet rays for temporary curing.
Ink droplets on the recording medium 12 that have passed through the printing area of the inkjet head 24 as the recording medium 12 is intermittently conveyed are irradiated with ultraviolet rays for main curing by the main curing light sources 34A and 34B. In this way, by temporarily setting the ink droplets in a temporarily cured state, it is possible to take the dot development time (the time for the dots to spread to a predetermined size) while preventing landing interference, Uniformity can be achieved, and the interaction between the droplet and the medium can be promoted to increase the adhesion.

  In the case where the white ink layer formed by white ink is provided as an overcoat layer and / or undercoat layer of the color image layer as shown in the present embodiment, the white ink layer may be another color image layer (curability). Dot resolution as high as the composition layer) is not required.

  The temporary curing light sources 32A and 32B may be turned on at the same time during the printing operation by the inkjet head 24. However, the lifetime of the light source can be increased by turning on only the temporary curing light source on the rear side in the carriage movement in the main scanning direction. You may plan to lengthen. In addition, the main curing light sources 34 </ b> A and 34 </ b> B are turned on simultaneously during the printing operation of the inkjet recording apparatus 10. In the drawing mode with a slow scanning speed, one of the light sources can be turned off, and the light emission start timings of the temporary curing light sources 32A and 32B and the main curing light sources 34A and 34B may be the same or different.

(Explanation of movement of main curing light source)
FIG. 4 is a perspective view illustrating a configuration example of a moving mechanism (light source moving unit) 35 of the main curing light source 34A. A rack and pinion linear movement mechanism is applied to the light source movement unit 35 shown in FIG. That is, the light source moving unit 35 is attached to the shaft 35A fixedly arranged along the recording medium conveyance direction, which is the moving direction of the main curing light source 34A, and the case of the main curing light source 34A, and has a tooth shape along the shaft 35A. A rack 35B having projections and depressions, a drive motor 35D having a pinion gear 35C attached to the rotating shaft, and an optical position sensor 35F for detecting a detection piece 35E formed at the end of the rack. ing.
When the rotation shaft of the drive motor 35D is rotated, the pinion gear 35C rotates, and the rack 35B moves along the shaft 35A due to the meshing of the teeth of the pinion gear 35C and the rack 35B. Move along. When the detection piece 35E provided at the tip of the rack 35B enters the detection range of the position sensor 35F, the rotation of the drive motor 35D is stopped and the main curing light source 34A stops at a predetermined position.

  Note that the main curing light source 34B located on the opposite side of the main curing light source 34A across the inkjet head 24 may be provided with a moving mechanism having the same configuration so as to be movable. Alternatively, a plurality of position sensors 35F may be provided so that the main curing light source 34A is moved to a plurality of positions.

(Description of image forming process)
The ink jet recording apparatus 10 shown in this example includes an order of forming a colored curable composition layer formed with color ink (Y, M, C, K, LC, LM, etc.) and an ultraviolet absorption characteristic of the curable composition ( The ultraviolet irradiation amount is controlled according to the curing characteristics.

  For example, since a white ink composition containing a white pigment contains titanium oxide, zinc oxide, or the like as a pigment, it has a lower ultraviolet transmittance than other color inks or clear inks. When the same amount of ultraviolet light per unit volume as that of clear ink is irradiated, the curing time becomes longer. In order to eliminate the difference in curing characteristics due to the UV transmission characteristics of white ink and color ink of other hues, the amount of UV irradiation per unit time for white ink is larger than that of color inks of other hues UV irradiation is controlled. A specific example of such image formation will be described later.

  Black ink compositions are classified as inks with a long curing time from the viewpoint of ultraviolet ray transmission, but they are used for the formation of color image layers and are temporarily cured immediately after droplet ejection to prevent droplet ejection interference. Since it is necessary to do this, it is classified as color ink.

When exposing the ejected ink composition, in the case of first irradiating pinning light as pinning light, per unit area, that 1mJ ^/ cm ² ~20mJ / cm 2 is irradiated immediately ejected Desirably, ² mJ / cm ² to 8 mJ / cm ² is more preferable.

The pinning light is exposed from one time to a plurality of times by carriage scanning in order to avoid the shape of the droplet from collapsing due to coalescence and interference with other ink immediately after the ink is ejected, or the movement of the droplet. Curing light refers to exposure that completely cures the imaged ink. Curing light is also irradiated a plurality of times by carriage scanning. A plurality of pinning exposure from one, by carrying multiple exposures, exposure of all accumulated reaches from 200 mJ / cm ² to the amount of 1,000~3,000mJ / cm ^2. The tendency of the ink sensitivity is determined by the sensitivity and content of the initiator and sensitizer contained in the ultraviolet curable ink, and the ink is cured by radical polymerization or cationic polymerization.

In this embodiment, the irradiation area of the temporary curing light source is divided according to the divided nozzle area so that appropriate pinning light can be irradiated corresponding to the drawing range of the divided nozzle area forming the curable composition layer, The light quantity (illuminance distribution) of the area is adjusted. Details will be described later.
In addition, although irradiation of pinning light may be performed immediately after ink discharge in an exposure process as described above, it may be performed in a heat drying process, or may be performed in both processes.
When irradiating with pinning light in the drying step, the ink can be dried and then exposed to pinning light to be cured.
The heating temperature is preferably 30 to 150 ° C, more preferably 50 to 120 ° C.

(Detailed description of the image forming process)
In the image forming method applied to the ink jet recording apparatus 10 shown in this example, each nozzle row 61 is divided into a plurality of regions in the recording medium conveyance direction, and the ink composition is ejected using any of the divided regions. A curable composition layer capable of forming a color image is formed. The number of divisions of the nozzle row 61 is the number N of image forming layers. If desired, a transparent layer made of an ink composition not containing a colorant may be formed on the surface of the colored image.

  Further, the recording medium 12 is obtained by the unit obtained by dividing the length of the divided area of the nozzle array 61 in the recording medium conveyance direction by the number of multipasses ((total length Lw of nozzle arrays / number N of image forming layers) / multipass number. The ink layer ejected from the downstream area in the same direction is laminated on the ink layer ejected from the upstream area in the recording medium conveyance direction of the nozzle row 61. It is comprised so that. Here, “the number of multi-passes” is defined as the product of the number of passes in the carriage scanning direction and the number of passes in the recording medium conveyance direction.

  In the present embodiment, the length of the irradiation area of the main curing light sources 34A and 34B in the recording medium conveyance direction is the same as the length of the main curing light sources 34A and 34B in the recording medium conveyance direction. The length of the curing light sources 34A and 34B in the recording medium conveyance direction may be determined so that a predetermined irradiation area can be obtained in consideration of the spread of the irradiation area.

(Configuration example of temporary curing light source unit)
FIG. 5 is a side perspective view showing a configuration example of a temporary curing light source unit used as the temporary curing light sources 32A and 32B of the present embodiment. FIG. 6 is a plan perspective view thereof. The temporary curing light source unit 210 according to the configuration example shown in FIGS. 5 and 6 has a substantially rectangular parallelepiped box shape. The temporary curing light source unit 210 includes a plurality of ultraviolet light emitting diode elements (hereinafter referred to as “UV-LED elements”) 214 in an aluminum housing (enclosure) 212, and the bottom surface of the housing 212. A transmissive light diffusing plate 216 is disposed in the part.

  The wiring board 220 on which the LED element 214 is mounted is housed in a state where the LED mounting surface 221 faces the light diffusion plate 216 (in FIG. 5, the light emitting surface of the UV-LED element 214 faces downward). It is arranged at the top of 212.

  The number of UV-LED elements 214 mounted on the wiring board 220 is not particularly limited, but is preferably as small as possible from the viewpoint of the necessary UV irradiation width and cost. In this example, six UV-LED elements 214 are arranged in a line on the wiring board 220. In order to obtain a UV irradiation width capable of performing UV irradiation at a time with respect to the nozzle row width Lw along the recording medium conveyance direction (X direction) of the inkjet head 24 described in FIG. 3, six UV-LEDs are obtained. The elements 214 are arranged side by side in the recording medium conveyance direction. 5 is the recording medium conveyance direction (X direction), and the recording medium 12 is conveyed from right to left in FIG.

  A metal substrate with enhanced heat dissipation and heat resistance is used as the wiring substrate 220. Although a detailed structure of the metal substrate is not shown, an insulating layer is formed on a metal plate such as aluminum or copper, and a UV-LED element 214 and a wiring circuit for driving the LED (anode wiring, cathode) are formed on the insulating layer. Wiring) and the like are formed. Note that a metal base substrate in which a circuit is formed on a base metal may be used, or a metal core substrate in which a metal plate is embedded inside the substrate may be used.

  Further, the periphery of the LED element 214 on the LED mounting surface 221 of the wiring board 220 is subjected to a UV resisting and high reflectance white resist treatment. By this white resist layer (not shown), ultraviolet rays can be reflected and scattered on the surface of the wiring board 220, and the light generated by the UV-LED elements 214 can be efficiently used for UV irradiation for temporary curing. .

  The light diffusing plate 216 is a milky white plate formed of an optical material that diffuses light emitted from the UV-LED element 214 while transmitting it. For example, the light diffusion plate 216 is a white acrylic plate in which a white pigment (light diffusion material) is dispersed. Not only the white acrylic plate but also an optical member formed by dispersing and diffusing fine particles for light diffusion in a transparent material such as glass can be used. By changing the content of light diffusing substances (white pigments, etc.) and the average particle diameter, light diffusing plates having different transmittances and diffusing characteristics can be obtained.

In addition, as a transmission type light diffusing plate, means for diffusing light is not limited to means for dispersing silica powder in this acrylic resin, and the surface of a substrate made of fused silica is subjected to frost treatment, frosted glass treatment, and ground glass treatment. This can easily be realized.
Such a transmissive light diffusing plate 216 is disposed below the housing 212 so as to face the LED mounting surface 221 of the wiring board 220. In FIG. 5, a lower surface (reference numeral 217) of the light diffusing plate 216 is a light emitting surface facing a recording medium (not shown). When all the UV-LED elements 214 (six in this example) are turned on, the light irradiation width equal to or larger than the nozzle row width Lw of the ink jet head 24 from the light emitting surface 217 of the light diffusion plate 216 onto the recording medium 12 UV light is irradiated.

  In the temporary curing light source unit 210 of this example, an LED array in which six UVLED elements 214 are arranged in the X direction is divided into two regions. That is, the plurality of UV-LED elements 214 arranged in the X direction are divided into two regions, an upstream region 224-1 and a downstream region 224-2 in the recording medium conveyance direction (X direction). Each of the divided regions 224-1 and 224-2 includes three UV-LED elements 214.

  Inside the housing 212, a partition member 226 having a light shielding property is provided as a range restricting member for partitioning the region of the LED element row divided into two, and the UV-LED element 214 of one region is provided. The light does not enter the other region. In general, the UV-LED element has a wide irradiation range and has a property of propagating while spreading. However, as in this example, the irradiation region can be divided by a structure that covers the periphery of the LED element by the partition member 226.

  Further, the light emission amount of the UV-LED element 214 in each of the divided regions 224-1 and 224-2 can be controlled. For example, when the layer is formed with white ink, the three UV-LED elements 214 belonging to the upstream area 224-1 are turned off, and the three UV-LED elements 214 belonging to the downstream area 224-2 are turned on.

  By combining the division of the light emission range by the partition member 226 and the light emission control of the LED elements belonging to the regions 224-1 and 224-2, the ultraviolet irradiation region can be divided. It is possible to individually control the amount of light.

  That is, the configuration example shown in FIG. 5 and FIG. 6 is an upper irradiation type LED light source unit in which the LED element row is arranged on the upper part of the light source box, and the irradiation lighting region of the LED is divided into the divided region of the nozzle row of the inkjet head 24. Correspondingly, the divided lighting control is performed. Control of the light emission amount includes current value control, pulse width modulation control, on / off control, and the like. Any one of a current control unit for controlling a current value, a pulse width modulation control unit for performing pulse width modulation control, an on / off control unit for performing on / off control, or an appropriate combination thereof is used.

  The configuration is not limited to the configuration illustrated in FIG. 5 and FIG. 6, for example, an upstream / downstream side is provided by providing an aluminum plate with a high reflectivity that determines the irradiation area on the lower surface of the housing 212 and shifting the frame of the aluminum plate. It is also possible to change the irradiation area. Or the aspect which changes an irradiation area | region is also possible by replacing | exchanging the frame of the aluminum board of a high reflectance. In this case, since the irradiation range is regulated by an aluminum plate having a high reflectance, this aluminum plate corresponds to a “range regulating member”. In addition, a mode in which a mechanical shutter or a liquid crystal shutter for limiting the light irradiation range is provided to restrict the irradiation region is also possible.

(Ink supply system)
FIG. 7 is a block diagram showing the configuration of the ink supply system of the inkjet recording apparatus 10. As shown in the figure, the ink stored in the ink cartridge 36 is sucked by the supply pump 70 and sent to the inkjet head 24 via the sub tank 72. The sub tank 72 is provided with a pressure adjusting unit 74 for adjusting the pressure of the ink inside. The pressure adjusting unit 74 includes a pressure increasing / decreasing pump 77 communicating with the sub tank 72 via the valve 76, and a pressure gauge 78 provided between the valve 76 and the pressure increasing / decreasing pump 77.

  During normal printing, the pressure increasing / decreasing pump 77 operates in the direction of sucking ink in the sub tank 72, and the internal pressure of the sub tank 72 and the internal pressure of the inkjet head 24 are maintained at negative pressure. On the other hand, at the time of maintenance of the ink jet head 24, the pressure increasing / decreasing pump 77 operates to pressurize the ink in the sub tank 72, and the inside of the sub tank 72 and the inside of the ink jet head 24 are forcibly pressurized. The ink inside is discharged through the nozzle. The ink forcibly discharged from the inkjet head 24 is accommodated in the ink receiver of the cap (not shown) described above.

(Description of control system of inkjet recording apparatus)
FIG. 8 is a block diagram showing the configuration of the inkjet recording apparatus 10. As shown in the figure, the ink jet recording apparatus 10 is provided with a control device 102 as control means. As the control device 102, for example, a computer having a central processing unit (CPU) can be used. The control device 102 functions as a control device that controls the entire inkjet recording apparatus 10 according to a predetermined program, and also functions as a calculation device that performs various calculations. The control device 102 includes a recording medium conveyance control unit 104, a carriage drive control unit 106, a light source control unit 108, an image processing unit 110, and an ejection control unit 112. Each of these units is realized by a hardware circuit or software, or a combination thereof.

  The recording medium conveyance control unit 104 controls the conveyance driving unit 114 for conveying the recording medium 12 (see FIG. 1). The conveyance drive unit 114 includes a drive motor that drives the nip roller 40 shown in FIG. 1 and a drive circuit thereof. The recording medium 12 conveyed on the platen 26 (see FIG. 1) is intermittently fed in the sub-scanning direction in units of swath widths in accordance with the reciprocating scanning (movement of the printing pass) in the main scanning direction by the inkjet head 24.

  The carriage drive control unit 106 shown in FIG. 8 controls the main scanning drive unit 116 for moving the carriage 30 (see FIG. 1) in the main scanning direction. The main scanning drive unit 116 includes a drive motor connected to a moving mechanism of the carriage 30 and a control circuit thereof. The light source control unit 108 is a control unit that controls the light emission of the temporary curing light sources 32A and 32B via the light source drive circuit 118 and the light emission of the main curing light sources 34A and 34B via the light source drive circuit 119. UV lamps such as UV-LED elements (ultraviolet LED elements) and metal halide lamps are applied as the temporary curing light sources 32A and 32B and the main curing light sources 34A and 34B.

  The control device 102 is connected to an input device 120 such as an operation panel and a display device 122. The input device 120 is means for inputting a manual external operation signal to the control device 102. For example, various forms such as a keyboard, a mouse, a touch panel, and operation buttons can be adopted. Various forms such as a liquid crystal display, an organic EL display, and a CRT can be adopted as the display device 122. By operating the input device 120, the operator can select a drawing mode, input printing conditions, and input / edit attached information. Various information such as input contents and search results are stored on the display device 122. It can be confirmed through the display.

  Further, the ink jet recording apparatus 10 is provided with an information storage unit 124 for storing various types of information and an image input interface 126 for taking in image data for printing. As the image input interface, a serial interface or a parallel interface may be applied. In this part, a buffer memory (not shown) for speeding up communication may be mounted.

  Image data input via the image input interface 126 is converted into print data (dot data) by the image processing unit 110. The dot data is generally generated by performing color conversion processing and halftone processing on multi-tone image data. The color conversion process is a process of converting image data expressed in sRGB or the like (for example, 8-bit image data for each RGB color) into color data for each ink color used in the inkjet recording apparatus 10.

  The halftone process is a process for converting the color data of each color generated by the color conversion process into dot data of each color by a process such as an error diffusion method or a threshold matrix. Various known means such as an error diffusion method, a dither method, a threshold matrix method, and a density pattern method can be applied as the halftone processing means. Halftone processing generally converts gradation image data having gradation values of 3 or more into gradation image data having gradation values less than the original gradation value. In the simplest example, it is converted into binary (dot on / off) dot image data, but in halftone processing, it corresponds to the dot size type (for example, three types such as large dot, medium dot, small dot). It is also possible to perform multi-level quantization.

  The binary or multi-valued image data (dot data) obtained in this way controls the driving (ON) / non-driving (OFF) of each nozzle, and in the case of multiple values, controls the droplet amount (dot size). Used as ink ejection data (droplet ejection control data).

  The ejection control unit 112 generates an ejection control signal for the head drive circuit 128 based on the dot data generated by the image processing unit 110. Further, the discharge control unit 112 includes a drive waveform generation unit (not shown). The drive waveform generation unit is a means for generating a drive voltage signal for driving an ejection energy generation element (in this example, a piezo element) corresponding to each nozzle of the inkjet head 24. The waveform data of the drive voltage signal is stored in advance in the information storage unit 124, and waveform data to be used is output as necessary. The signal (drive waveform) output from the drive waveform generation unit is supplied to the head drive circuit 128. Note that the signal output from the drive waveform generation unit may be digital waveform data or an analog voltage signal.

  A common driving voltage signal is applied to each ejection energy generating element of the inkjet head 24 via the head driving circuit 128, and the switching element is connected to the individual electrode of each energy generating element according to the ejection timing of each nozzle. By switching on / off (not shown), ink is ejected from the corresponding nozzle.

  The information storage unit 124 stores programs executed by the CPU of the control device 102, various data necessary for control, and the like. The information storage unit 124 stores resolution setting information according to the drawing mode, the number of passes (the number of scan repetitions), control information for the temporary curing light sources 32A and 32B, and the main curing light sources 34A and 34B.

The encoder 130 is attached to the drive motor of the main scanning drive unit 116 and the drive motor of the transport drive unit 114, and outputs a pulse signal corresponding to the rotation amount and rotation speed of the drive motor. Is sent to the controller 102. Based on the pulse signal output from the encoder 130, the position of the carriage 30 and the position of the recording medium 12 are grasped.

  The sensor 132 is attached to the carriage 30, and the width of the recording medium 12 is grasped based on the sensor signal obtained from the sensor 132.

  The control device 102 controls the operation of the light source moving unit 35 of the main curing light sources 34A and 34B. For example, when the image forming process selection information and the position information of the main curing light sources 34A and 34B are input from the input device 120, the main curing light source 34A (34B) is moved to a position corresponding to the image forming process.

According to the ink jet recording apparatus and the image forming method configured as described above, the pinning exposure area can be divided and controlled in accordance with the divided areas of the nozzle row, so that an appropriate curing process can be realized for each ink layer.
Specifically, the ink composition is preliminarily cured by being irradiated with a low amount of ultraviolet light from the temporary curing light sources 32A and 32B immediately after droplet ejection (landing on the recording medium), after the dot development time has elapsed, and the pile height After the homogenization, the main curing light source 34B (34A) is irradiated with a high amount of ultraviolet light to be in a main curing state. Therefore, it is possible to increase the dot gain by taking the dot development time from the pre-curing to the main curing, and further improve the graininess of the image by taking the time to equalize the pie height. To do. That is, combined with the effect of improving the wettability of the ink composition by the treatment in the step (A), the method of the present invention realizes high-quality image formation.

  In addition, at least one of the main curing light sources 34A and 34B can be configured to be movable in parallel in the recording medium conveyance direction, and can be selectively disposed at a discharge position of ink that has low sensitivity to ultraviolet rays and is slow to cure. Since the irradiation areas of the main curing light sources 34A and 34B are determined in accordance with the ejection range of ink that is low in sensitivity to ultraviolet rays and slow in curing (total length Lw of nozzle row / number of image forming layers (number of divisions) N), Only a low-sensitivity and slow-curing ink is selectively irradiated with a high amount of ultraviolet light, and problems due to a difference in curing time between the inks can be avoided.

In the present invention, the minimum droplet volume of the nozzle that discharges the colored ink composition is preferably 5 pL or more and less than 20 pL.
As described above, the ink composition is required to have a high resolution in order to form a color image. From such a viewpoint, the minimum droplet volume of the nozzle that discharges the colored ink composition is more preferably 6 to 18 pL, and still more preferably 6 to 15 pL.

  In the present invention, since it is preferable to set the discharged ink composition to a constant temperature, an image forming apparatus capable of heat insulation and heating is preferably used from the ink composition supply tank to the inkjet head portion. . The temperature control method is not particularly limited, but for example, it is preferable to provide a plurality of temperature sensors in each piping portion and perform heating control according to the flow rate of the ink composition and the environmental temperature. The temperature sensor can be provided near the ink composition supply tank and the nozzle of the inkjet head. Moreover, it is preferable that the head unit to be heated is thermally shielded or insulated so that the apparatus main body is not affected by the temperature from the outside air. In order to shorten the printer start-up time required for heating or to reduce the loss of heat energy, it is preferable to insulate from other parts and reduce the heat capacity of the entire heating unit.

  A radiation curable ink composition such as the curable composition according to the present invention generally has a higher viscosity than a water-based ink composition usually used as an ink composition for ink jet recording. large. Viscosity fluctuation of the ink composition has a great influence on the change of the droplet size and the change of the droplet discharge speed, and thus causes the image quality deterioration. Therefore, it is preferable to keep the temperature of the ink composition during ejection as constant as possible. Therefore, the temperature control range of the ink composition is preferably ± 5 ° C. of the set temperature, more preferably ± 2 ° C. of the set temperature, and still more preferably ± 1 ° C. of the set temperature.

The curable composition according to the present invention is preferably irradiated with such ultraviolet rays for 0.01 to 2 seconds, more preferably 0.1 to 1.5 seconds, and still more preferably 0.3 to 1 second. Is appropriate.
Irradiation with actinic radiation is performed for a certain time (preferably 0.01 seconds to 0.5 seconds, more preferably 0.01 seconds to 0.3 seconds, still more preferably 0.01 seconds to 0 seconds) after the landing of the ink composition. .15 seconds). As described above, by controlling the time from the landing of the ink composition to the irradiation to an extremely short time, it is possible to prevent the ink composition that has landed on the recording medium from bleeding before being cured. In addition, since the ink composition can be exposed to a porous recording medium before it penetrates to a deep part where the light source does not reach, it is preferable because residual unreacted monomer can be suppressed.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples as long as the gist of the present invention is not exceeded. In the following description, “part” means “part by mass” and “%” means “mass%” unless otherwise specified.

(Preparation of pigment dispersion)
(Preparation Example 1: Preparation of magenta mill base)
-Magenta pigment: CINQUASIA MAGENTA RT-355D
(BASF Japan Co., Ltd.) 30 parts by mass SR9003 [Product name: SARTOMER, propoxylated (2) neopentyl glycol diacrylate (neopentyl glycol propylene oxide 2 mol adduct) compound] 30 parts by mass BYK168 (trade name: dispersant, manufactured by BYK Chemie) 40 parts by mass The above components were stirred to obtain a magenta mill base. The pigment mill base was prepared by dispersing in a disperser motor mill M50 (manufactured by Eiger) using zirconia beads having a diameter of 0.65 mm and dispersing at a peripheral speed of 9 m / s for 8 hours.

(Preparation Example 2: Preparation of yellow mill base)
Yellow pigment: NOVOPERM YELLOW H2G (manufactured by Clariant)
30 parts by mass / SR9003 (trade name: manufactured by SARTOMER) 30 parts by mass / BYK168 brand name: manufactured by BYK Chemie) 40 parts by mass Obtained.

(Preparation Example 3: Preparation of cyan mill base)
・ Cyan pigment: IRGALITE BLUE GLVO (manufactured by BASF Japan)
30 parts by mass / SR9003 (trade name: manufactured by SARTOMER) 30 parts by mass / BYK168 brand name: manufactured by BYK Chemie) 40 parts by mass Obtained.

(Preparation Example 4: Preparation of black mill base)
Black pigment: SPECIAL BLACK 250 (BASF Japan)
30 parts by mass / SR9003 (trade name: manufactured by SARTOMER) 30 parts by mass / BYK168 brand name: manufactured by BYK Chemie) 40 parts by mass The above ingredients were stirred under the same dispersion conditions as the preparation of the magenta mill base, Obtained.

(Preparation of curable composition)
(Preparation of curable composition 1)
<Composition 1>
Magenta mill base (obtained in Preparation Example 1) 13 parts by mass NVC: N-vinylcaprolactam (V-CAP, manufactured by ISP) 23 parts by mass PEA (phenoxyethyl acrylate (SR399S, manufactured by Sartomer))
33.0 parts by mass-FA-512: dicyclopentanyloxyethyl acrylate (manufactured by Hitachi Chemical Co., Ltd.) 5 parts by mass-SR351S: trimethylolpropane triacrylate (manufactured by Sartomer)
5 parts by mass HDDA: 1,6-hexanediol diacrylate (SR238F,
3 parts by mass / CN962: urethane acrylate oligomer (average number of functional groups: 2, manufactured by Sartomer)
3 parts by mass / 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl)
-Butan-1-one (IRGACURE 369, manufactured by BASF Japan Ltd.)
2 parts by mass-bis (2,4,6-trimethylbenzoyl) phenylphosphine oxide (IRGACURE 819, manufactured by BASF Japan) 3 parts by mass-Isopropylthioxanthone (SPEEDCURE ITX,
Lambson) 3 parts by mass: 1: Mixture of 8% by mass of tris (N-nitroso-N-phenylhydroxyamine) aluminum salt and 92% by mass of phenoxyethyl acrylate (polymerization inhibitor, FIRSTCURE ST-1, ChemFirst) Made)
1 part by mass Each component of the composition 1 was stirred and mixed, and filtered through a filter having an opening diameter of 5 μm to obtain a curable composition 1 used as a magenta ink.
(Preparation of curable composition 2)
A curable composition 2 used as a magenta ink was obtained in the same manner except that the polymerization inhibitor (ST-1, FIRSTCURE ST-1, manufactured by ChemFirst) used in the curable composition 1 was not used. .

(Preparation of curable composition 3)
<Composition 2>
Magenta mill base (obtained in Preparation Example 1) 13 parts by mass CTFA (cyclic trimethylolpropane formal acrylate) 30 parts by mass PEA (phenoxyethyl acrylate (SR399S, manufactured by Sartomer))
33.0 parts by mass-FA-512: dicyclopentanyloxyethyl acrylate (manufactured by Hitachi Chemical Co., Ltd.) 5 parts by mass-SR351S: trimethylolpropane triacrylate (manufactured by Sartomer)
5 parts by mass · HDDA: 1,6-hexanediol diacrylate (SR238F, manufactured by Sartomer) 3 parts by mass · CN962: urethane acrylate oligomer (average functional group number 2,
3 parts by mass / Irg 369: 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butan-1-one (IRGACURE 369, manufactured by Sartomer Japan, Inc.)
2 parts by mass Irg819: bis (2,4,6-trimethylbenzoyl) phenyl phosphine oxide (IRGACURE 819, manufactured by BASF Japan)
3 parts by mass. ITX: isopropylthioxanthone (SPEEDCURE ITX,
Lambson) 3 parts by mass. ST-1: Tris (N-nitroso-N-phenylhydroxyamine)
Mixture of 8% by mass of aluminum salt and 92% by mass of phenoxyethyl acrylate (polymerization inhibitor, FIRSTCURE ST-1,
(Chem First Co., Ltd.) 1 part by mass The components of Composition 2 were stirred and mixed, and filtered through a filter having an opening diameter of 5 μm to obtain a curable composition 3 used as a magenta ink.

(Preparation of curable composition 4)
A curable composition 4 used as a yellow ink was obtained in the same manner except that the magenta mill base used in the curable composition 3 was replaced with the yellow mill base obtained in Preparation Example 2.
(Preparation of curable composition 5)
A curable composition 5 used as a cyan ink was obtained in the same manner except that the magenta mill base used in the curable composition 1 was replaced with the cyan mill base obtained in Preparation Example 3.
(Preparation of curable composition 6)
A curable composition 6 used as a black ink was obtained in the same manner except that the magenta mill base used in the curable composition 2 was replaced with the black mill base obtained in Preparation Example 4.

(Preparation of curable composition 7)
<Composition 3>
-Magenta mill base (obtained in Preparation Example 1) 13 parts by mass-PEA (phenoxyethyl acrylate (SR399S, manufactured by Sartomer))
63.0 parts by mass dicyclopentanyloxyethyl acrylate (FA-512:
Hitachi Chemical Co., Ltd.) 5 parts by mass / trimethylolpropane triacrylate (SR351S: manufactured by Sartomer)
5 parts by mass · 1,6-hexanediol diacrylate (SR238F, manufactured by Sartomer) 3 parts by mass · urethane acrylate oligomer (average functional group number 2, CN962:
3 parts by mass / 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl)
-Butan-1-one (IRGACURE 369: manufactured by BASF Japan Ltd.)
2 parts by mass-bis (2,4,6-trimethylbenzoyl) phenylphosphine oxide (IRGACURE 819, manufactured by BASF Japan) 3 parts by mass-Isopropylthioxanthone (SPEEDCURE ITX, manufactured by Lambson)
3 parts by mass of 8% by mass of tris (N-nitroso-N-phenylhydroxyamine) aluminum salt;
Mixture with 92% by mass of phenoxyethyl acrylate (polymerization inhibitor, FIRSTCURE ST-1, manufactured by Chem First)
1 part by mass The components of Composition 3 were stirred and mixed, and filtered through a filter having an opening diameter of 5 μm to obtain a curable composition 7 used as a magenta ink.

[Example 1]
(Surface treatment of nonpolar substrate)
A polypropylene base material (thickness: 200 μm) was irradiated with atmospheric pressure N ₂ plasma for 2 minutes using an S5000 type atmospheric pressure low temperature plasma jet device (discharge gas: nitrogen-containing gas) manufactured by Sakai Semiconductor Co., Ltd. Was modified.
The nitrogen-containing gas contains nitrogen gas as a main component and has a nitrogen fraction of 99.9%. (0.1% is an inevitable impurity)
When the polypropylene base material after the surface treatment was confirmed by ESCA, it was confirmed that nitrogen atoms were introduced on the surface.
Moreover, although the base material was observed, the surface was not damaged by the observation by SEM (magnification: 30,000 times).

<Formation and curing of curable composition layer: inkjet recording>
The ink jet and recording apparatus having the above-described configuration were used.
The inkjet head used was a piezo inkjet head Q-class Sapphire QS-256 / 10 (manufactured by FUJIFILM DIMATIX, 256 nozzles, minimum droplet volume 10 pL, 50 kHz).
Moreover, as a temporary light source (pinning light source), as shown in FIG. 6, a light source in which six light emitting diodes (UV-LED, Nichia Corporation NC4U134, wavelength 385 nm) are arranged is arranged on the left and right sides of the inkjet head. One light source (two in total) was used, and a light source having an illuminance per light source of 780 mW / cm ² was used.
As the main curing light source, the light source provided with 10 light emitting diodes (UV-LED, NC4U134 manufactured by Nichia Corporation, wavelength 385 nm) one on the left and right (2 in total), A light source having an illuminance of 1,500 mW / cm ² was used.
The ink supply system consists of an ink pack, supply piping, deaeration filter SEPAREL EF-G2 (manufactured by DIC Corporation), an ink supply tank immediately before the inkjet head, a deaeration filter, and a piezo-type inkjet head. The pressure was reduced to 0.5 atm.
Using the apparatus configured as described above, the curable composition 1 was ejected and exposed and cured by a plurality of passes using the curable composition 1 (magenta ink) to form a printed material having a cured ink image.

[Examples 2 to 7]
The printed materials of Examples 2 to 5 were formed in the same manner except that the curable composition 1 used for forming the ink image in Example 1 was replaced with the curable compositions 2 to 7, respectively.
Example 8
In the same manner as in Example 1, except that the nitrogen gas used for the atmospheric pressure plasma treatment was changed to a mixed gas of 90% nitrogen gas and 10% oxygen (nitrogen fraction: 90%), the surface-treated polypyropyrene A printed material of Example 8 was formed in the same manner as Example 1 except that a substrate was obtained and used as the substrate.
When the polypropylene base material after the surface treatment was confirmed by ESCA, it was confirmed that nitrogen atoms were introduced on the surface.
Moreover, although the base material was observed, damage was not seen by observation by SEM.
Example 9
In Example 1, except that the atmospheric plasma treatment time was changed from 2 minutes to 30 seconds, a surface-treated polypropylene base material was obtained, and this was used as the base material in the same manner as in Example 1. Thus, a print of Example 9 was formed.
When the polypropylene base material after the surface treatment was confirmed by ESCA, it was confirmed that nitrogen atoms were introduced on the surface.
Moreover, although the base material was observed, damage was not seen by observation by SEM.

[Comparative Example 1]
In Example 1, instead of the polypropylene base material used, a surface treatment was carried out in the same manner as in Example 1, except that polyvinyl chloride as a polar base (indicated in Table 1 as: PVC) was used. A printed material of Comparative Example 1 was formed in the same manner as in Example 1 except that a PVC substrate was obtained and used as the substrate.
When the PVC substrate after the surface treatment was confirmed by ESCA, it was confirmed that nitrogen atoms were introduced on the surface.
Moreover, when the base material was observed, the surface roughness was seen by observation by SEM.

[Comparative Example 2]
In Example 1, instead of the polypropylene base used, instead of polyvinyl chloride, which is a polar base (indicated as PVC in Table 1), the nitrogen gas used for the atmospheric pressure plasma treatment surface treatment was used. Instead, a surface-treated PVC base material was obtained by plasma treatment in air, and a printed material of Comparative Example 2 was formed in the same manner as in Example 1 except that this was used as the base material.
When the PVC substrate after the surface treatment was confirmed by ESCA, it was confirmed that nitrogen atoms were introduced on the surface.
Moreover, when the base material was observed, the surface roughness was seen by observation by SEM.

[Comparative Example 3]
In Example 1, the printed material of Comparative Example 3 was formed in the same manner as in Example 1 except that the used polypropylene substrate was used as a substrate without subjecting it to an atmospheric pressure plasma treatment surface.

The following evaluation was performed on the obtained printed matter.
<Evaluation of processability>
A punch hole having a diameter of 6 mm and a base material is formed in a region where an ink image of the printed material is formed using (Punch No. 9000: trade name, manufactured by Plus Co., Ltd.), and the periphery of the formed punch hole is visually observed. And an optical microscope (BX60 trade name, Olympus Co., Ltd.) and observed at a magnification of 10 times, and evaluated according to the following criteria. The results are shown in the table below.
A: No abnormality is observed around the punch hole by optical microscope observation.
B: No abnormality is recognized around the punch hole by visual observation.
C: Cracks due to peeling of the substrate and the ink image were observed around the punch holes by visual observation.
FIG. 9A shows an aspect in which no crack is observed, and FIG. 9B shows an aspect in which the crack is observed.

[Comparative Example 4]
The polypropylene base material was treated at 2 m / min on both sides of the support at room temperature using a solid state corona treatment machine manufactured by Pillar. Printing was performed in the same manner as in Example 1 except that the surface-treated substrate was used, and a printed material of Comparative Example 4 was formed.

<Evaluation of image quality>
The image on the printed material was observed with an optical microscope (BX60 trade name, Olympus Corporation) at a magnification of 10 times, and the shape of the droplet ejection portion was evaluated according to the following criteria. The ejection was performed so as to form a circular dot having a radius of 1 μm as a design value. The results are shown in the table below.
A: An image according to a design value with a droplet ejection portion having a circular shape and a radius of 1 μm to 1.2 μm.
B: Although the droplet ejection portion is circular, it is an image having a radius of less than 1 μm due to a decrease in adhesion due to repelling.
C: A circular image was not formed due to repelling or bleeding at the droplet ejection portion.

As shown in Table 1, the printed matter obtained by the image forming method of the present invention had high processability and formed a high-quality image regardless of the hue of ink.
On the other hand, Comparative Examples 1 and 2 using a substrate other than the nonpolar substrate are inferior in image quality due to the rough surface of the substrate, and an atmospheric pressure plasma treatment is performed under a nitrogen atmosphere even if the substrate is a nonpolar substrate. In Comparative Example 3 using the base material that did not exist, the adhesion between the ink composition and the base material was low, and both the processability and the image quality were inferior. Further, in Comparative Example 4 using a base material subjected to corona discharge treatment, which is a well-known adhesion improving process, bleeding of the printed portion was confirmed, and punchability was poor. This is because the surface of the base material is roughened in the corona treatment machine, and bleeding occurs, and in the corona treatment, oxygen is mainly introduced (= oxidation reaction), and nitrogen atoms are not efficiently introduced. Therefore, it is considered that the interaction with the ink part is lowered and the punching property is deteriorated.

10 Inkjet recording device 12 Recording medium (nonpolar substrate)
DESCRIPTION OF SYMBOLS 20 Apparatus main body 22 Support leg 24 Inkjet head 26 Platen 28 Guide mechanism 30 Carriage 32A, 32B Temporary curing light source 34A, 34B Main curing light source 35 Moving mechanism (light source moving part)
35A Shaft 35B Rack 35C Pinion gear 35D Drive motor 35E Detection piece 35F Position sensor 36 Ink cartridge 40 Nip roller 42 Supply side roll 44 Winding roll 50 Temperature control part 61, 61C, 61M, 61Y, 61K, 61LC, 61LM, 61CL, 61W Nozzle row 70 supply pump,
72 Subtank 74 Pressure adjusting unit 102 Control device 104 Recording medium conveyance control unit 106 Carriage drive control unit 108 Light source control unit 110 Image processing unit 112 Discharge control unit 114 Conveyance drive unit 116 Main scanning drive unit 120 Input device 124 Information storage unit 128 Head Drive circuit 130 Encoder 132 Sensor

Claims (9)

(A) a substrate surface treatment step of surface-treating a nonpolar substrate with atmospheric pressure plasma in a nitrogen atmosphere;
(B) A curable composition applying step of applying a curable composition containing a polymerizable monomer, a polymerization initiator, and a pigment to the surface of the nonpolar substrate surface-treated by an inkjet method;
(C) an image forming step of applying energy to the applied curable composition and curing it;
An image forming method comprising:   The image forming method according to claim 1, wherein the nitrogen atmosphere in the substrate surface step is a nitrogen atmosphere having a nitrogen fraction of 90% or more.   The image forming method according to claim 1, wherein the substrate surface treatment step is a step of introducing nitrogen atoms into the nonpolar substrate surface.   The image forming method according to claim 1, wherein the polymerizable monomer is a polymerizable monomer having at least one substituent selected from an amide group and an ether group in the molecule.   The image forming method according to claim 1, wherein the nonpolar substrate is a substrate made of a resin selected from polypropylene and polyethylene.   The said nonpolar base material is a base material which has a surface layer which consists of resin chosen from a polypropylene and polyethylene in the outermost surface at the side which forms the said curable composition layer. The image forming method according to item.   A printed matter having an image obtained by the image forming method according to claim 1.   A curable composition containing a pigment, a polymerizable monomer having at least one substituent selected from an amide group and an ether group in the molecule, and a polymerization initiator on the surface of a nonpolar substrate having a nitrogen atom introduced on the surface A print having an image formed using   The printed matter according to claim 7 or 8, which is used in a forming process including a punching process.