JP7786064B2 - Actinic radiation curable ink, image forming method, and output - Google Patents

Description

The present invention relates to an actinic radiation curable ink, an image forming method, and an output product.
More specifically, the present invention relates to actinic radiation curable inks and the like that have high antibacterial and antiviral properties.

Actinic radiation-curable inks are widely used as inks capable of forming images with high abrasion resistance and adhesion, even on non-absorbent media. Furthermore, with the recent spread of infectious diseases, there has been a growing demand in the commercial and industrial printing sector for printed materials with antibacterial and antiviral properties. As one means of providing printed materials with antibacterial and antiviral properties, actinic radiation-curable inks are also required to have antibacterial and antiviral properties.

As a technology related to actinic radiation-curable inks with antibacterial and antiviral properties, Patent Document 1 describes that an antibacterial composition comprising a silver-based antibacterial agent and a polymerizable compound can be used as a UV inkjet ink.

However, the silver-based antibacterial agent used in the invention described in Patent Document 1, as well as other commonly used antibacterial substances such as ionic compounds of copper, zinc, etc., and photocatalysts such as titanium oxide, have the drawback of not being sufficiently effective in low-moisture, low-humidity environments. Furthermore, even if these antibacterial substances are incorporated into actinic radiation-curable ink, there is also the problem that the antibacterial and antiviral effects are only exerted in the area where the actinic radiation-curable ink is applied.

As mentioned above, there is room for improvement in conventional technology, and there is a demand for actinic radiation-curable inks with stronger antibacterial and antiviral properties.

International Publication No. 2019/172041

The present invention was made in consideration of the above problems and circumstances, and its objective is to provide an actinic radiation-curable ink with high antibacterial and antiviral properties, as well as an image forming method and output using the same.

In order to solve the above problems, the present inventors investigated the causes of the above problems and found that by incorporating a photosensitizer capable of generating singlet oxygen, it is possible to provide an actinic radiation-curable ink or the like that has high antibacterial and antiviral properties, and thus arrived at the present invention.
That is, the above-mentioned problems of the present invention are solved by the following means.

An actinic radiation curable ink containing at least a polymerizable compound and a photosensitizer,
the photosensitizer has singlet oxygen generating ability,
The actinic radiation-curable ink, wherein the photosensitizer has a structure represented by the following general formula (1) :
[In the above general formula (1), M represents a metal atom of Group 14. _Q1 and Q2 _each independently represent a monovalent axial ligand. Note that the above general formula (1) may not have either Q1 or Q2. _{A1 to} A4 _each independently _represent an atomic group forming an aromatic ring which may have a substituent.]

2. Contains a photopolymerization initiator, and
2. The actinic radiation curable ink according to claim 1, wherein the maximum absorption maximum wavelength of the photosensitizer in a monomolecular state is on the longer wavelength side than the absorption end of the absorption spectrum of the photopolymerization initiator.

3. The polymerizable compound is an actinic radiation-polymerizable compound, and
2. The actinic radiation-curable ink according to claim 1, wherein the maximum absorption maximum wavelength of the photosensitizer in a monomolecular state is on the longer wavelength side than the absorption end of the absorption spectrum of the actinic radiation-polymerizable compound.

4. The actinic radiation-curable ink according to any one of items 1 to 3, wherein the maximum absorption maximum wavelength of the photosensitizer in a monomolecular state is within the range of 360 to 800 nm.

5. The actinic radiation-curable ink according to any one of items 1 to 4, further comprising a colorant.

6. The actinic radiation-curable ink according to any one of items 1 to 5 , characterized in that it exhibits a color derived from the monomolecular absorption spectrum of the photosensitizer.

7. An image forming method using actinic radiation curable ink, comprising:
7. An image forming method, wherein the actinic radiation curable ink is the actinic radiation curable ink according to any one of items 1 to 6 .

8. The image forming method according to item 7, wherein the difference between the maximum absorption maximum wavelength of the photosensitizer in a monomolecular state and the maximum maximum wavelength of the actinic ray irradiated to cure the actinic ray-curable ink is 100 nm or more.

9. The image forming method according to item 7 or 8 , wherein the actinic radiation curable ink is applied independently of the image area.

10. The image forming method according to any one of items 7 to 9 , further comprising transferring a foil onto the area where the actinic radiation curable ink has been applied, thereby forming a decorative image.

11. The image forming method according to any one of items 7 to 10 , wherein the actinic radiation curable ink is applied onto the recording medium by an inkjet system.

1 2. An output formed using actinic radiation curable ink,
7. An output product, wherein the actinic radiation curable ink is the actinic radiation curable ink according to any one of items 1 to 6 .

The above-mentioned means of the present invention make it possible to provide actinic radiation-curable ink with high antibacterial and antiviral properties, as well as an image forming method and output using the same.

The mechanism by which the effects of this invention are manifested or the mechanism of action are not clear, but are speculated as follows.

The actinic radiation-curable ink of the present invention contains a photosensitizer capable of generating singlet oxygen, and generates singlet oxygen when exposed to indoor light. Singlet oxygen is known to have high antibacterial and antiviral properties even in low-humidity environments.

In addition, because singlet oxygen is a gas, it diffuses after it is generated, providing antibacterial and antiviral effects not only to the area where the actinic radiation-curable ink is applied, but also to the surrounding area.

It is believed that these mechanisms of expression or action can provide actinic radiation-curable inks and other products with high antibacterial and antiviral properties.

The antibacterial and antiviral effects of singlet oxygen generated by photosensitizers have been demonstrated by technology developed by the research institute at the University of Regensburg in Germany and TriOptoTec GmbH, and by a water-based varnish (Lock3) commercialized by Varcotec of Germany based on this technology (see, for example, https://www.sinsei-corp.co.jp/information/lock3.html).

Schematic diagram showing energy transfer between photosensitizer and oxygen Diagram showing changes in absorption spectrum due to differences in the molecular aggregation state of photosensitizers Schematic diagram 1 of an inkjet image forming apparatus Schematic diagram 2 of an inkjet image forming apparatus 1 is a diagram showing each step of forming a decorative image; FIG. 10 is a diagram illustrating a compression method for forming a decorative image. Schematic diagram 1 of a decorative image forming apparatus Schematic diagram 2 of a decorative image forming apparatus

The actinic radiation-curable ink of the present invention (hereinafter, the "actinic radiation-curable ink" may also be simply referred to as "ink") is an actinic radiation-curable ink containing at least a polymerizable compound and a photosensitizer, and is characterized in that the photosensitizer has the ability to generate singlet oxygen.
This feature is a technical feature common to or corresponding to the following embodiments.

In an embodiment of the actinic radiation-curable ink of the present invention, it is preferable that the ink contains a photopolymerization initiator, and that the maximum absorption wavelength of the photosensitizer in a monomolecular state is longer than the absorption end of the absorption spectrum of the photopolymerization initiator. This allows the ink to be cured using actinic radiation that does not overlap with the absorption wavelength range of the photopolymerization initiator, and prevents the photosensitizer from losing its singlet oxygen-generating ability.

In an embodiment of the actinic radiation-curable ink of the present invention, it is preferable that the polymerizable compound is an actinic radiation-polymerizable compound, and that the maximum absorption maximum wavelength of the photosensitizer in a monomolecular state is on the longer wavelength side than the absorption end of the absorption spectrum of the actinic radiation-polymerizable compound. This allows the ink to be cured using actinic radiation that does not overlap with the absorption wavelength range of the actinic radiation-polymerizable compound, and prevents the photosensitizer from losing its singlet oxygen-generating ability.

In an embodiment of the actinic radiation-curable ink of the present invention, the maximum absorption wavelength of the photosensitizer in a monomolecular state is preferably within the range of 360 to 800 nm. This makes it possible to avoid the photosensitizer's ability to generate singlet oxygen being deactivated when the ink is cured using ultraviolet light.

In one embodiment of the actinic radiation-curable ink of the present invention, a colorant may further be contained. This allows the color of the ink to be adjusted as desired.

In an embodiment of the actinic radiation-curable ink of the present invention, the photosensitizer preferably has a structure represented by the above general formula (1). This makes it easier for the photosensitizer to be contained in the ink in a monomolecular state with high singlet oxygen generation ability.

In an embodiment of the actinic radiation-curable ink of the present invention, it is preferable that the ink exhibits a color derived from the monomolecular absorption spectrum of the photosensitizer. This makes it possible to visually confirm whether the photosensitizer contained in the ink fixed on a recording medium has singlet oxygen generating ability.

The image forming method of the present invention is an image forming method using actinic radiation-curable ink, characterized in that the actinic radiation-curable ink is the actinic radiation-curable ink of the present invention.

In an embodiment of the image forming method of the present invention, it is preferable that the difference between the maximum absorption wavelength of the photosensitizer in a monomolecular state and the maximum wavelength of the actinic radiation irradiated when curing the actinic radiation-curable ink is 100 nm or more. This prevents the singlet oxygen generating ability from being lost due to absorption of the actinic radiation irradiated when the ink is cured.

In one embodiment of the image forming method of the present invention, it is preferable to apply the actinic radiation-curable ink independently of the image area. This allows the ink to be applied independently of the image pattern, making it possible, for example, to provide antibacterial and antiviral effects over the entire surface of the printed object.

In one embodiment of the image forming method of the present invention, a decorative image is preferably formed by transferring foil onto the area where the actinic radiation-curable ink has been applied. This makes it possible to obtain a decorative image and output product that have been imparted with antibacterial and antiviral properties.

In one embodiment of the image forming method of the present invention, the actinic radiation-curable ink is preferably applied to a recording medium by an inkjet method. This makes it possible to form images with antibacterial and antiviral properties on demand.

The output product of the present invention is an output product formed using actinic radiation-curable ink, characterized in that the actinic radiation-curable ink is the actinic radiation-curable ink of the present invention.

The present invention, its components, and modes and aspects for implementing the invention are described in detail below. Note that in this application, the symbol "to" is used to mean that the numerical values before and after it are included as both the lower limit and upper limit.

(1) Actinic Radiation-Curable Ink The actinic radiation-curable ink of the present invention is an actinic radiation-curable ink containing at least a polymerizable compound and a photosensitizer, and is characterized in that the photosensitizer has the ability to generate singlet oxygen.

(1.1) Photosensitizer The photosensitizer according to the present invention is characterized by having the ability to generate singlet oxygen.

The content of the photosensitizer is preferably in the range of 0.001 to 1% by mass, and more preferably in the range of 0.01 to 0.1% by mass, relative to the total mass of the ink.

(Singlet oxygen generating ability)
"Singlet oxygen generating ability" refers to the property of being able to generate singlet oxygen by exciting triplet-state oxygen molecules present in the air, etc., to a singlet state. In other words, the photosensitizer according to the present invention needs to be contained in the ink in a state that allows it to generate singlet oxygen.

In the case of the photosensitizer according to the present invention, the photosensitizer PS (T ₁ ) reaches a triplet excited state through photoexcitation and intersystem crossing, and then excites nearby triplet oxygen O ₂ ( ³ Σ _g ) through energy transfer to generate singlet oxygen O ₂ ( ¹ Δ _g ) (see FIG. 1 ).

By using a photosensitizer PS whose excitation energy in the triplet excited state _T1 is equivalent to the energy required to excite triplet oxygen _O2 ( ^3Σg ), energy transfer from the photosensitizer PS _{( T1} ) to ^triplet oxygen _O2 ( _3Σg ) is facilitated, and ^singlet oxygen _O2 ( _1Δg ) can be efficiently generated.

General antibacterial substances such as ionic compounds of silver, copper, zinc, etc., and photocatalysts such as titanium oxide, are not sufficiently effective in low-humidity environments, but singlet oxygen is known to have sufficient antibacterial and antiviral effects even in low-humidity environments. Therefore, by using the ink of the present invention, it is possible to produce printed objects with high antibacterial and antiviral properties, even in low-humidity environments where bacteria and viruses are likely to be a problem.

In addition, because singlet oxygen is a gas, it diffuses after generation, providing antibacterial and antiviral effects not only in the area where the ink is applied, but also in the surrounding area. Furthermore, the diffusion distance of singlet oxygen (the distance it diffuses before reverting to triplet oxygen and losing its antibacterial and antiviral effects) depends on humidity; the lower the humidity, the greater the diffusion distance. Therefore, the ink of the present invention is particularly effective in low-humidity environments.

The diffusion distance of singlet oxygen can be calculated by the following formula.
Formula X ² = 2Dt
X: Diffusion distance [m]
D: Diffusion coefficient [m ² /sec]
t: Life [seconds]

Using the above formula, the diffusion distance X of singlet oxygen at a humidity of 50% can be calculated to be approximately 1.57 mm. Here, the diffusion coefficient D and lifetime t are based on reported values of 2×10 ⁻⁵ m ² /sec at a humidity of 50% and 62×10 ⁻³ seconds at a humidity of 50%.

From the above calculation results, singlet oxygen can diffuse up to a range of approximately 1.57 mm in an environment with 50% humidity, so if the ink of the present invention is present on a printed object with a dot spacing of 3 mm, the generated singlet oxygen will diffuse over roughly the entire surface of the printed object.

If the dot spacing is 3 mm, adjusting the dot size to, for example, 30 μm makes it possible to apply ink that exhibits coloration derived from a photosensitizer so that it is invisible. Therefore, by applying the ink of the present invention to the entire surface of a recording medium with an invisible dot size and dot spacing, it is possible to impart antibacterial and antiviral effects to the entire surface of the printed material without degrading image quality.

(Confirmation of singlet oxygen generating ability)
Whether or not the photosensitizer in the ink is in a state capable of generating singlet oxygen can be determined by detecting phosphorescence derived from singlet oxygen.

In this case, the ink is first applied to a recording medium and then subjected to a photo-curing process to fix the ink to the recording medium. When the recording medium on which the ink has been fixed is irradiated with monochromatic light corresponding to the maximum absorption wavelength of the photosensitizer in a single molecular state, if phosphorescence having a maximum emission wavelength attributable to singlet oxygen around 1270 nm is observed, it can be determined that the photosensitizer in the ink is in a state capable of generating singlet oxygen. Phosphorescence can be measured using, for example, a spectrofluorometer (EP-8700 manufactured by JASCO Corporation).

(Molecular aggregation state of photosensitizer)
The molecular aggregation state of the photosensitizer in the ink is not particularly limited as long as it is in a state that allows singlet oxygen to be generated. For example, it may be in a monomolecular state or an aggregated state. However, since the photosensitizer can generate singlet oxygen more efficiently in a monomolecular state, it is preferable that the ink of the present invention contains the photosensitizer in a monomolecular state.

Whether or not the contained photosensitizer is in a monomolecular state can be determined by whether or not an absorption peak of the photosensitizer in a monomolecular state is present in the absorption spectrum of the ink. For example, in the case of a photosensitizer that has an absorption peak with a maximum absorption maximum at 680 nm in a monomolecular state, if an absorption peak at 680 nm is present in the absorption spectrum of the ink, it can be determined that the contained photosensitizer is in a monomolecular state. In the case of pigment-containing ink, this can be determined without being affected by the pigment by measuring the absorption spectrum of the ink after separating and removing the solid component made of the pigment using a centrifuge.

This determination is possible because the absorption spectrum of the compound used as the photosensitizer differs between its single-molecule state and its aggregated state. Figure 2 shows an example of the absorption spectrum of a phthalocyanine compound, which has an absorption peak with a maximum absorption maximum at 680 nm in its single-molecule state. Thus, while the absorption spectrum in the single-molecule state (Figure 2(a)) has an absorption peak at 680 nm, the absorption spectrum in the aggregated state (Figure 2(b)) broadens the absorption wavelength range due to factors such as intermolecular interactions, and the absorption peak shifts to the longer or shorter wavelengths depending on the molecular orientation. Because these differences in the absorption spectrum of the photosensitizer also affect the absorption spectrum of the ink, whether the contained photosensitizer is in a single-molecule state can be determined by whether the absorption peak of the photosensitizer in its single-molecule state is present in the absorption spectrum of the ink.

Furthermore, if the ink does not contain pigment, this determination method can be performed not only from the absorption spectrum of the liquid ink, but also from the absorption spectrum of the cured ink present on the printed object.

(Ink indicator properties)
The ink of the present invention preferably exhibits a color derived from the monomolecular absorption spectrum of the photosensitizer as an indicator of the photosensitizer's ability to generate singlet oxygen, which makes it possible to visually confirm whether the photosensitizer contained in the ink fixed on a recording medium has singlet oxygen generating ability, without detecting phosphorescence derived from singlet oxygen as described above.

In inks that exhibit indicator properties like this, if the photosensitizer has the ability to generate singlet oxygen, the ink must exhibit a color derived from the monomolecular absorption spectrum of the photosensitizer, and therefore the photosensitizer must be contained in a monomolecular state.

Ink that exhibits indicator properties has the property that when the molecular structure or molecular aggregation state of the photosensitizer changes due to deterioration over time, etc., and it no longer exhibits the color derived from the monomolecular absorption spectrum, it also loses its ability to generate singlet oxygen.

For example, if an ink exhibiting indicator properties contains a photosensitizer that exhibits a blue color due to the monomolecular absorption spectrum, when the ink no longer exhibits the blue color, it can be determined that the ink has lost its singlet oxygen generating ability and the associated antibacterial effect.

(Absorption wavelength range of photosensitizer taking into account actinic rays)
Since the ink of the present invention is actinic radiation-curable, it must be designed on the assumption that actinic radiation will be irradiated during image formation. The photosensitizer can generate singlet oxygen to a certain extent continuously, even though it will deteriorate over time due to light absorption, provided that the light intensity is comparable to that of indoor light. However, if the absorption wavelength range of the photosensitizer largely overlaps with the wavelength range of the actinic radiation irradiated during image formation, the photosensitizer may rapidly deteriorate upon irradiation with actinic radiation, and its singlet oxygen generating ability may be lost. Therefore, for the ink of the present invention, it is preferable to select a photosensitizer taking into account the wavelength range of the actinic radiation irradiated during image formation.

The wavelength of the actinic light irradiated during image formation is set to match the absorption wavelength of the photopolymerization initiator or actinic light-polymerizable compound contained in the ink. Therefore, if the ink contains a photopolymerization initiator, it is preferable that the maximum absorption maximum wavelength of the photosensitizer in a monomolecular state be longer than the absorption end of the absorption spectrum of the photopolymerization initiator. Alternatively, if the ink contains an actinic light-polymerizable compound, it is preferable that the maximum absorption maximum wavelength of the photosensitizer in a monomolecular state be longer than the absorption end of the absorption spectrum of the actinic light-polymerizable compound. This allows the ink to be cured using actinic light that does not overlap with the absorption wavelength range of the photosensitizer, avoiding inactivation of the photosensitizer's singlet oxygen-generating ability.

In the present invention, the "absorption end of the absorption spectrum" refers to the point on the longest wavelength side of the absorption intensity curve on the side where the light absorption intensity decreases from the maximum absorbance point at the light absorption peak (also called the "light absorption band") in the spectrum obtained by absorbance measurement with a UV-visible spectrophotometer, reaches a value equivalent to the baseline (a baseline obtained by correcting using an absorption spectrum measured excluding the object being measured).

Furthermore, assuming that commonly used ultraviolet light is used as actinic light, the maximum absorption wavelength of the photosensitizer in a monomolecular state is preferably within the range of 360 to 800 nm, and more preferably within the range of 500 to 800 nm. This prevents the photosensitizer's singlet oxygen generating ability from being deactivated when the ink is cured using ultraviolet light.

(Compounds that can be used as photosensitizers)
The compound that can be used as the photosensitizer according to the present invention is not particularly limited as long as it can be contained in the ink in a state that allows it to generate singlet oxygen. For example, conventionally known compounds that can be used as photosensitizers capable of generating singlet oxygen include phthalocyanine compounds, naphthalocyanine compounds, phenalene compounds, and rose bengal compounds.

Among these compounds, phthalocyanine compounds are preferred, and those having a structure represented by the following general formula (1) are particularly preferred because they have high singlet oxygen generating ability and are easily contained in ink in a monomolecular state.

[In the above general formula (1), M represents a metal atom of Group 14. _Q1 and _Q2 each independently represent a monovalent axial ligand. Note that the above general formula (1) may not have either _Q1 or _Q2 . _A1 to _A4 each independently represent an atomic group forming an aromatic ring which may have a substituent.]

The central metal atom M is a Group 14 metal atom, which allows it to take on multiple axial ligands above and below the conjugated plane. In the present invention, Group 14 metal atoms also include Si, and specific examples include Si, Ge, Sn, and Pb. Among these, silicon atoms, Si, are preferred.

In the compound having the structure represented by general formula (1), the axial ligands (Q ₁ , Q ₂ ) suppress the π-π stacking interaction of the conjugated plane, making it difficult for aggregation of photosensitizers to occur, and therefore, it is easy for the compound to assume a monomolecular state.

In the present invention, "axial ligand" refers to a ligand that is coordinated from above and below the plane that constitutes the phthalocyanine ring.

Examples of the substituent that the atomic groups A ₁ to A ₄ may have include electron-withdrawing groups such as a chlorine atom, a methyl chloride halide group (-CClX ₂ ) (where X is a halogen atom), a fluoromethyl group (-CH ₂ F), a trifluoromethyl group (-CF ₃ ), and a nitro group (-NO ₂ ), as well as alkyl and alkoxy groups. In particular, alkyl or alkoxy groups having 4 to 18 carbon atoms are preferred from the viewpoint of solubility in the polymerizable compound. Furthermore, the alkyl or alkoxy group may further have a substituent.

Furthermore, the solubility of the photosensitizer in the polymerizable compound can be improved by adopting a molecular structure that allows the introduction of a soluble group into the aromatic rings (A ₁ to A ₄ ) or the axial ligands (Q ₁ , Q ₂ ). In particular, introducing a soluble group into the axial ligands (Q ₁ , Q ₂ ) is preferable because it enhances the effect of suppressing the π-π stacking interaction of the conjugated planes of the molecules due to steric hindrance.

Among compounds having a structure represented by general formula (1), compounds having a structure represented by the following general formula (1F) or (1G) are more preferred.

[In general formula (1F) and general formula (1G), M, _Q1 , and _Q2 have the same meanings as M, _Q1 , and _Q2 in general formula (1), respectively. _R1 to _R4 each independently represent a hydrogen atom or a substituent.]

Examples of the substituents R ₁ to R ₄ include electron-withdrawing groups such as a chlorine atom, a methyl chloride halide group (-CClX ₂ ) (where X is a halogen atom), a fluoromethyl group (-CH ₂ F), a trifluoromethyl group (-CF ₃ ), and a nitro group (-NO ₂ ), as well as alkyl and alkoxy groups. In particular, alkyl or alkoxy groups having 4 to 18 carbon atoms are preferred from the viewpoint of solubility in the polymerizable compound. The alkyl or alkoxy group may further have a substituent.

Preferred specific examples of compounds having a structure represented by general formula (1F) or general formula (1G) are exemplified in Table I. In addition, * in _Q1 and _Q2 represents the bonding site with M.

Next, we will explain compounds that do not have the structure represented by general formula (1) but can be used as photosensitizers according to the present invention, such as compounds that have the structure represented by general formula (H).

[In general formula (H), M' represents a metal atom other than that of Group 14 or two hydrogen atoms (2H). _{Q 1} ' represents a monovalent or divalent axial ligand. _{R 1} to R ₄ each independently represent a hydrogen atom or a substituent.]

Examples of the substituents R ₁ to R ₄ include electron-withdrawing groups such as a chlorine atom, a methyl chloride halide group (-CClX ₂ ) (where X is a halogen atom), a fluoromethyl group (-CH ₂ F), a trifluoromethyl group (-CF ₃ ), and a nitro group (-NO ₂ ), as well as alkyl and alkoxy groups. In particular, alkyl or alkoxy groups having 4 to 18 carbon atoms are preferred from the viewpoint of solubility in the polymerizable compound. The alkyl or alkoxy group may further have a substituent.

Preferred examples of compounds having the structure represented by formula (H) are shown in Table II. In addition, * in Q ₁ ' represents the bonding site with M.

Next, examples of compounds other than those listed above that can be used as photosensitizers according to the present invention are listed below. However, compounds that can be used as photosensitizers according to the present invention are not limited to these.

(1.2) Polymerizable Compound The ink of the present invention is characterized by containing a polymerizable compound.

The content of the polymerizable compound is preferably within the range of 1 to 97% by mass, and more preferably within the range of 30 to 90% by mass, relative to the total mass of the ink.

The polymerizable compound is not particularly limited as long as it can be used in actinic radiation-curable inks. Any compound that initiates a polymerization reaction upon irradiation with actinic radiation in the presence or absence of a photopolymerization initiator and cures through polymerization and crosslinking can be used. The polymerizable compound may be a monomer, polymerizable oligomer, prepolymer, or a mixture thereof.

Among polymerizable compounds, those that can initiate a polymerization reaction and sufficiently cure upon irradiation with actinic rays (e.g., electron beams) even in the absence of a photopolymerization initiator are referred to as "actinic radiation-polymerizable compounds" in the present invention.

Examples of polymerizable compounds include cationically polymerizable compounds, radically polymerizable compounds, and mixtures thereof. In particular, radically polymerizable compounds are preferred from the standpoints of polymerization rate, degree of polymerization, etc.

The term "radical polymerizable compound" refers to a compound having an ethylenically unsaturated double bond in the molecule. The radical polymerizable compound may be either a monofunctional or polyfunctional compound. An example of a radical polymerizable compound is (meth)acrylate, which is an unsaturated carboxylic acid ester compound. In the present invention, "(meth)acrylate" refers to acrylate or methacrylate, "(meth)acryloyl group" refers to acryloyl group or methacryloyl group, and "(meth)acrylic" refers to acrylic or methacrylic.

Examples of monofunctional (meth)acrylates include isoamyl (meth)acrylate, stearyl (meth)acrylate, lauryl (meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, isomylstyryl (meth)acrylate, isostearyl (meth)acrylate, 2-ethylhexyl-diglycol (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 2-(meth)acryloyloxyethyl hexahydrophthalate, butoxyethyl (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, methoxydiethylene glycol (meth)acrylate, methoxypoly Examples include ethylene glycol (meth)acrylate, methoxypropylene glycol (meth)acrylate, phenoxyethyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, isobornyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, 2-(meth)acryloyloxyethyl succinate, 2-(meth)acryloyloxyethyl phthalate, 2-(meth)acryloyloxyethyl-2-hydroxyethyl phthalate, and t-butylcyclohexyl (meth)acrylate.

Examples of polyfunctional (meth)acrylates include triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, dimethylol-tricyclodecane di(meth)acrylate, bisphenol A PO adduct di(meth)acrylate, hydroxypivalic acid neopentyl glycol di(meth)acrylate, polytetramethylene glycol di(meth)acrylate, Examples of the acrylates include difunctional (meth)acrylates such as trimethylolpropane tri(meth)acrylate, polyethylene glycol diacrylate, and tripropylene glycol diacrylate; trifunctional (meth)acrylates such as trimethylolpropane tri(meth)acrylate and pentaerythritol tri(meth)acrylate; tri- or higher functional (meth)acrylates such as pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, glycerin propoxy tri(meth)acrylate, and pentaerythritol ethoxy tetra(meth)acrylate; oligomers having (meth)acryloyl groups, including polyester acrylate oligomers, and modified products thereof. Examples of the modified products include ethylene oxide-modified (EO-modified) acrylates in which ethylene oxide groups have been inserted, and propylene oxide-modified (PO-modified) acrylates in which propylene oxide has been inserted.

The term "cationically polymerizable compound" refers to a compound having a cationically polymerizable group in the molecule. Examples of cationically polymerizable compounds include epoxy compounds, vinyl ether compounds, and oxetane compounds.

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

Examples of the vinyl ether compound include monovinyl ether compounds such as ethyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, octadecyl vinyl ether, cyclohexyl vinyl ether, hydroxybutyl vinyl ether, 2-ethylhexyl vinyl ether, cyclohexanedimethanol monovinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, isopropenyl ether-o-propylene carbonate, dodecyl vinyl ether, diethylene glycol monovinyl ether, and octadecyl vinyl ether, as well as di- or trivinyl ether compounds such as ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, propylene glycol divinyl ether, dipropylene glycol divinyl ether, butanediol divinyl ether, hexanediol divinyl ether, cyclohexanedimethanol divinyl ether, and trimethylolpropane trivinyl ether.

Examples of the above oxetane compounds include 3-hydroxymethyl-3-methyloxetane, 3-hydroxymethyl-3-ethyloxetane, 3-hydroxymethyl-3-propyloxetane, 3-hydroxymethyl-3-n-butyloxetane, 3-hydroxymethyl-3-phenyloxetane, 3-hydroxymethyl-3-benzyloxetane, 3-hydroxyethyl-3-methyloxetane, 3-hydroxyethyl-3-ethyloxetane, 3-hydroxyethyl-3-propyloxetane, 3-hydroxyethyl Examples include 1-ethyl-3-phenyloxetane, 3-hydroxypropyl-3-methyloxetane, 3-hydroxypropyl-3-ethyloxetane, 3-hydroxypropyl-3-propyloxetane, 3-hydroxypropyl-3-phenyloxetane, 3-hydroxybutyl-3-methyloxetane, 1,4-bis{[(3-ethyl-3-oxetanyl)methoxy]methyl}benzene, 3-ethyl-3-(2-ethylhexyloxymethyl)oxetane, and di[1-ethyl(3-oxetanyl)]methyl ether.

(1.3) Photopolymerization Initiator The ink of the present invention preferably further contains a photopolymerization initiator, if necessary.

The content of the photopolymerization initiator can be set arbitrarily as long as the ink is sufficiently cured by irradiation with actinic rays and the ink's inkjet ejection stability is not reduced. For example, the content of the photopolymerization initiator is preferably in the range of 0.1 to 20% by mass, and more preferably in the range of 1.0 to 12% by mass, relative to the total mass of the ink.

The photopolymerization initiator may be any that can initiate polymerization of the polymerizable compound. For example, if the ink contains a radically polymerizable compound, the photopolymerization initiator should be a radical photopolymerization initiator, and if the ink contains a cationic polymerizable compound, the photopolymerization initiator should be a cationic photopolymerization initiator.

One type of photopolymerization initiator may be used alone, or two or more types may be used in combination. Furthermore, both a radical photopolymerization initiator and a cationic photopolymerization initiator may be used in combination.

Radical photopolymerization initiators include intramolecular bond cleavage types and intramolecular hydrogen abstraction types.

Examples of intramolecular bond cleavage type radical photopolymerization initiators include acetophenone-based initiators such as diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, benzyl dimethyl ketal, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one, 4-(2-hydroxyethoxy)phenyl-(2-hydroxy-2-propyl)ketone, 1-hydroxycyclohexyl-phenyl ketone, 2-methyl-2-morpholino(4-methylthiophenyl)propan-1-one, and 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone; benzoin-based initiators such as benzoin, benzoin methyl ether, and benzoin isopropyl ether; acylphosphine oxide-based initiators; and benzyl and methylphenyl glyoxyesters.

Among these, acylphosphine oxide polymerization initiators are preferred, as they further improve the curing properties of the polymerizable compound, particularly in the curing process using UV-LED light.

Acylphosphine oxide polymerization initiators are not particularly limited, and examples include 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, and bis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide.

Commercially available examples of such acylphosphine oxide polymerization initiators include IRGACURE® 819 (bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide), IRGACURE® 1800 (a mixture of bis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide and 1-hydroxycyclohexylphenyl ketone in a mass ratio of 25:75), and IRGACURE® TPO (2,4,6-trimethylbenzoyldiphenylphosphine oxide).

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

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

(1.4) Colorant The ink of the present invention may further contain a colorant, if necessary. This allows the ink to be used as a colored ink with high antibacterial and antiviral properties.

The colorant content is preferably in the range of 0.1 to 20% by mass, and more preferably in the range of 0.4 to 10% by mass, relative to the total mass of the ink. A pigment or dye content of 0.1% by mass or more provides good color development, while a content of 20% by mass or less provides appropriate ink viscosity.

In the present invention, the term "colorant" refers to a component that is added primarily for the purpose of coloring, separately from a component capable of generating singlet oxygen, such as the photosensitizer described above.

The colorant is not particularly limited and examples include pigments and dyes. From the viewpoint of obtaining dispersion stability and weather resistance of the ink, it is preferable that the colorant be a pigment. From the viewpoint of not reducing the sensitivity of the curing reaction due to irradiation with actinic rays, it is preferable to select a compound that does not function as a polymerization inhibitor.

The pigment is not particularly limited and examples include known organic pigments and inorganic pigments, as well as dyed resin particles, commercially available pigment dispersions, and surface-treated pigments (for example, pigments dispersed in an insoluble resin as a dispersant, or pigments with a resin grafted onto the surface). Examples of the pigments include those described in "Dictionary of Pigments" edited by Seijiro Ito (published in 2000), "Industrial Organic Pigments" by W. Herbst and K. Hunger, and JP-A Nos. 2002-12607, 2002-188025, 2003-26978, and 2003-342503.

Examples of red or magenta pigments include Pigment Red 3, 5, 19, 22, 31, 38, 43, 48:1, 48:2, 48:3, 48:4, 48:5, 49:1, 53:1, 57:1, 57:2, 58:4, 63:1, 81, 81:1, 81:2, 81:3, 81:4, 88, 104, 108, 112, 122, 123, 144, 146, 149, 166, 168, 169, 170, 177, 178, 179, 184, 185, 208, 216, 226, 257, Pigment Violet 3, 19, 23, 29, 30, 37, 50, 88, Pigment Examples include pigments selected from Orange 13, 16, 20, and 36, or mixtures thereof.

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

Examples of green pigments include pigments selected from Pigment Green 7, 26, 36, and 50, or mixtures thereof.

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

Examples of black pigments include pigments selected from Pigment Black 7, 26, and 28, or mixtures thereof.

Examples of white pigments include titanium oxide or hollow particles.

Examples of commercially available pigments include Chromofine Yellow 2080, 5900, 5930, AF-1300, 2700L, Chromofine Orange 3700L, 6730, Chromofine Scarlet 6750, Chromofine Magenta 6880, 6886, 6891N, 6790, 6887, Chromofine Violet RE, Chromofine Red 6820, 6830, Chromofine Blue HS-3, 5187, 5108, 5197, 5085N, SR-5020, 5026, 5050, 4920, 4927, 4937, 4824, 4933GN-EP, 4940, 4973, 5205, 5208, 5214, 5221, 5000P, Chromofine Green 2GN, 2GO, 2G-550D, 5310, 5370, 6830, Chromofine Black A-1103, Seika Fast Yellow 10GH, A-3, 2035, 2054, 2200, 2270, 2300, 2400 (B), 2500, 2600, ZAY-260, 2700 (B), 2770, Seikafast Red 8040, C405(F), CA120, LR-116, 1531B, 8060R, 1547, ZAW-262, 1537B, GY, 4R-4016, 3820, 3891, ZA-215, Seikafast Carmine 6B1476T-7, 1483LT, 3840, 3870, Seikafast Bordeaux 10B-430, Seikalite Rose R40, Seikalite Violet B800, 7805, Seikafast Maroon 460N, Seikafast Orange 900, 2900, Seikalite Blue C718, A612, Cyanine Blue 4933M, 4933GN-EP, 4940, 4973 (all manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.); KET Yellow 401, 402, 403, 404, 405, 406, 416, 424, KET Orange 501, KET Red 301, 302, 303, 304, 305, 306, 307, 308, 309, 310, 336, 337, 338, 346, KET Blue 101, 102, 103, 104, 105, 106, 111, 118, 124, KET Green 201 (all manufactured by Dainippon Ink &Chemicals); Colortex Yellow 301, 314, 315, 316, P-624, 314, U10GN, U3GN, UNN, UA-414, U263, Finecol Yellow T-13, T-05, Pigment Yellow1705, Colortex Orange 202, Colortex Red101, 103, 115, 116, D3B, P-625, 102, H-1024, 105C, UFN, UCN, UBN, U3BN, URN, UGN, UG276, U456, U457, 105C, USN, Colortex Maroon601, Colortex Brown B610N, Colortex Violet 600, Pigment Red 122, Colortex Blue 516, 517, 518, 519, A818, P-908, 510, Colortex Green 402, 403, Colortex Black 702, U905 (all manufactured by Sanyo Pigment Co., Ltd.); Lionol Yellow 1405G, Lionol Blue FG7330, FG7350, FG7400G, FG7405G, ES, ESP-S (all manufactured by Toyo Ink Co., Ltd.), Toner Magenta E02, Permanent Rubin F6B, Toner Yellow HG, Permanent Yellow GG-02, Hostaperm Blue B2G (all manufactured by Hoechst Industrie); Novoperm P-HG, Hostaperm Pink E, Hostaperm Blue B2G (all manufactured by Clariant); carbon black #2600, #2400, #2350, #2200, #1000, #990, #980, #970, #960, #950, #850, MCF88, #750, #650, MA600, MA7, MA8, MA11, MA100, MA100R, MA77, #52, #50, #47, #45, #45L, #40, #33, #32, #30, #25, #20, #10, #5, #44, and CF9 (all manufactured by Mitsubishi Chemical).

There are no particular restrictions on the average particle size of the pigment, but since the finer the particle size, the better the color development, it is preferably in the range of 0.01 to 0.4 μm, and more preferably in the range of 0.02 to 0.2 μm. The maximum particle size of the pigment is preferably around 3 μm, and more preferably around 1 μm. The particle size of the pigment can be adjusted by selecting the type of pigment, dispersant, dispersion medium, dispersion conditions, and filtration conditions. Controlling the particle size of the pigment can prevent clogging of the head nozzles and maintain the storage stability, transparency, and curing sensitivity of the ink.

The particle size of pigments can be measured using known methods. Specifically, it can be measured using centrifugal sedimentation light transmission, X-ray transmission, laser diffraction scattering, and dynamic light scattering.

Note that one type of colorant may be used alone, or two or more types may be used in combination.

(1.5) Gelling Agent The ink of the present invention preferably further contains a gelling agent, if necessary.

The gelling agent content is 0.5 to 10% by mass, preferably 1 to 7% by mass, relative to the total mass of the ink. A content of 0.5% by mass or more allows the ink droplets to be sufficiently gelled (temperature-dependent sol-gel phase transition). Furthermore, a content of 10% by mass or less allows the gelling agent to be sufficiently dissolved in the ink, preventing a decrease in the inkjet ejection stability of the ink.

The gelling agent has the function of imparting sol-gel phase transition properties to the ink, as described below. Such a gelling agent must at least [1] dissolve in a polymerizable compound, etc., at a temperature higher than the sol-gel phase transition temperature, and [2] crystallize at a temperature below the sol-gel phase transition temperature.

While the type of gelling agent is not particularly limited, it is preferred that, when crystallized in the ink, the gelling agent forms a three-dimensional space surrounded by platelet crystals, encapsulating the polymerizable compound within the space. This structure, in which the polymerizable compound is encapsulated within the three-dimensional space surrounded by platelet crystals, is sometimes referred to as a "house of cards structure." When a house of cards structure is formed, the polymerizable compound is retained within the structure, pinning the ink droplets. This means that ink droplets are less likely to spread after landing on the recording medium, enabling the formation of images with fine patterns. For ink droplets to form a house of cards structure after landing on the recording medium, it is preferable that the polymerizable compound dissolved in the ink and the gelling agent are compatible. Furthermore, when forming images using an inkjet system, good compatibility between the polymerizable compound and the gelling agent is important in the ink's sol state (at high temperatures), from the perspective of stably ejecting ink droplets from an inkjet recording device.

Examples of such gelling agents include:
Aliphatic ketone compounds;
aliphatic ester compounds;
Petroleum-based waxes such as paraffin wax, microcrystalline wax, and petrolactam;
vegetable waxes such as candelilla wax, carnauba wax, rice wax, Japan wax, jojoba oil, jojoba solid wax, and jojoba esters;
Animal waxes such as beeswax, lanolin, and spermaceti;
Mineral waxes such as montan wax and hydrogenated wax;
hydrogenated castor oil or hydrogenated castor oil derivatives;
modified waxes such as montan wax derivatives, paraffin wax derivatives, microcrystalline wax derivatives, and polyethylene wax derivatives;
Higher fatty acids such as behenic acid, arachidic acid, stearic acid, palmitic acid, myristic acid, lauric acid, oleic acid, and erucic acid;
higher alcohols such as stearyl alcohol and behenyl alcohol;
hydroxystearic acids such as 12-hydroxystearic acid;
12-hydroxystearic acid derivatives;
fatty acid amides such as lauric acid amide, stearic acid amide, behenic acid amide, oleic acid amide, erucic acid amide, ricinoleic acid amide, and 12-hydroxystearic acid amide (for example, the Nikkaamide series manufactured by Nippon Kasei Chemical Co., Ltd., the ITOWAX series manufactured by Ito Oil Mills, and the FATTYAMID series manufactured by Kao Corporation);
N-substituted fatty acid amides such as N-stearyl stearic acid amide and N-oleyl palmitic acid amide;
Special fatty acid amides such as N,N'-ethylene bisstearylamide, N,N'-ethylene bis-12-hydroxystearylamide, and N,N'-xylylene bisstearylamide;
higher amines such as dodecylamine, tetradecylamine, and octadecylamine;
fatty acid ester compounds such as stearyl stearic acid, oleyl palmitic acid, glycerin fatty acid esters, sorbitan fatty acid esters, propylene glycol fatty acid esters, ethylene glycol fatty acid esters, and polyoxyethylene fatty acid esters (e.g., the EMALLEX series manufactured by Nippon Emulsion Co., Ltd., the Rikemal series manufactured by Riken Vitamin Co., Ltd., and the Poem series manufactured by Riken Vitamin Co., Ltd.);
Sucrose fatty acid esters such as sucrose stearic acid and sucrose palmitic acid (e.g., Ryoto Sugar Ester series, manufactured by Mitsubishi Chemical Foods Corporation);
Synthetic waxes such as polyethylene wax and α-olefin maleic anhydride copolymer wax (e.g., UNILIN series manufactured by Baker-Petrolite);
Dimer acid;
Dimer diol (PRIPOR series manufactured by CRODA, etc.);
fatty acid inulins such as stearate inulin;
Fatty acid dextrins such as dextrin palmitate and dextrin myristate (e.g., Leopearl series manufactured by Chiba Flour Milling Co., Ltd.);
Glyceryl Behenate Eicosanedioate;
Eicosanepolyglyceryl behenate (Nomcoat series manufactured by Nisshin Oillio Co., Ltd., etc.);
Amide compounds such as N-lauroyl-L-glutamic acid dibutylamide and N-(2-ethylhexanoyl)-L-glutamic acid dibutylamide (available from Ajinomoto Fine-Techno);
Dibenzylidene sorbitols such as 1,3:2,4-bis-O-benzylidene-D-glucitol (Gelol D available from New Japan Chemical Co., Ltd.);
Low molecular weight oil gelling agents described in JP-A-2005-126507, JP-A-2005-255821, and JP-A-2010-111790;
etc. are included.

The gelling agent molecule preferably contains a linear alkyl structure with 12 or more carbon atoms. A linear alkyl structure with 12 or more carbon atoms refers to a structure consisting of a linear alkyl group, with the linear portion containing 12 or more carbon atoms. When the gelling agent molecule contains a linear alkyl structure with 12 or more carbon atoms, the aforementioned house-of-cards structure is more likely to form.

Specific examples of gelling agents having such a structure include aliphatic ketone compounds, aliphatic ester compounds, higher fatty acids, higher alcohols, fatty acid amides, etc., all of which have a linear alkyl group with 12 or more carbon atoms.

Among these, from the viewpoint of increasing the hydrophobicity of the adhesive layer made of the cured ink, it is preferable that the gelling agent be an aliphatic ketone represented by the following general formula (2), or a fatty acid or aliphatic ester represented by the following general formula (3).

R ₁ -CO-R ₂ ...General formula (2)
In general formula (2), _R1 and _R2 each independently represent a linear or branched hydrocarbon group having 1 to 24 carbon atoms, provided that at least one of _R1 and _R2 contains a linear alkyl structure having 12 or more carbon atoms.

_R1 and _R2 are each independently more preferably a linear hydrocarbon group having 1 to 24 carbon atoms, and even more preferably a linear hydrocarbon group having 8 to 22 carbon atoms. Preferably, both _R1 and _R2 contain a linear alkyl structure having 12 or more carbon atoms.

In the aliphatic ketone represented by the general formula (2) above, the linear alkyl structure preferably has 12 or more carbon atoms and 24 or less. When the linear alkyl structure has 12 or more carbon atoms, the crystallinity of the gelling agent is likely to be increased. Furthermore, in the house-of-card structure described above, it becomes easier to sufficiently encapsulate the polymerizable compound, making it easier to form a dense image. On the other hand, when the linear alkyl structure has 24 or less carbon atoms, the melting point of the gelling agent does not become excessively high, and the gelling agent dissolves sufficiently in the ink.

Examples of aliphatic ketones represented by the above general formula (2) include dilignoceryl ketone (C24-C24), dibehenyl ketone (C22-C22, melting point 88°C), distearyl ketone (C18-C18, melting point 84°C), dieicosyl ketone (C20-C20), dipalmityl ketone (C16-C16, melting point 80°C), dimyristyl ketone (C14-C14), dilauryl ketone (C12-C12, melting point 68°C), lauric acid ketone (C12-C12, melting point 68°C), and lauric acid ketone (C12-C12, melting point 68°C). These include myristyl myristyl ketone (C12-C14), lauryl palmityl ketone (C12-C16), myristyl palmityl ketone (C14-C16), myristyl stearyl ketone (C14-C18), myristyl behenyl ketone (C14-C22), palmityl stearyl ketone (C16-C18), palmityl behenyl ketone (C16-C22), stearyl behenyl ketone (C18-C22), etc.

Commercially available examples of the compound represented by general formula (2) include 18-Pentatriacontanon (manufactured by Alfa Aeser), Hentriacontan-16-on (manufactured by Alfa Aeser), and Kaowax T1 (manufactured by Kao Corporation).

The ink of the present invention may contain only one type of aliphatic ketone represented by the above general formula (2), or may contain two or more types.

R ₃ -COO-R ₄ ...General formula (3)
[In general formula (3), _R3 represents a linear or branched hydrocarbon group having 1 to 24 carbon atoms. _R4 represents a hydrogen atom or a linear or branched hydrocarbon group having 1 to 24 carbon atoms. However, at least one of _R3 and _R4 contains a linear alkyl structure having 12 or more carbon atoms.]

_R3 and _R4 are each independently more preferably a linear hydrocarbon group having 1 to 24 carbon atoms, and even more preferably a linear hydrocarbon group having 8 to 22 carbon atoms. Preferably, both _R3 and _R4 contain a linear alkyl structure having 12 or more carbon atoms.

In general formula (3), the linear alkyl structure preferably has 12 to 24 carbon atoms. When the linear alkyl structure has 12 or more carbon atoms, the crystallinity of the gelling agent is likely to be increased. Furthermore, in the house-of-card structure described above, it becomes easier to sufficiently encapsulate the polymerizable compound, making it easier to form images in a dense pattern. On the other hand, when the linear alkyl structure has 24 or fewer carbon atoms, the melting point of the gelling agent does not become excessively high, and the gelling agent dissolves sufficiently in the ink.

Examples of fatty acids or aliphatic esters represented by general formula (3) include behenic acid, behenyl behenate (C21-C22, melting point 70°C), icosanoic acid icosyl (C19-C20), stearyl stearate (C17-C18, melting point 60°C), palmityl stearate (C17-C16), lauryl stearate (C17-C12), cetyl palmitate (C15-C16, melting point 54°C), stearyl palmitate (C15-C18), myristyl myristate (C13-C14, melting point 43°C), and cetyl myristate. These include myricyl oleate (C13-C16, melting point 50°C), octyldodecyl myristate (C13-C20), stearyl oleate (C17-C18), stearyl erucate (C21-C18), stearyl linoleate (C17-C18), behenyl oleate (C18-C22), myricyl cerate (C25-C16), stearyl montanate (C27-C18), behenyl montanate (C27-C22), arachidyl linoleate (C17-C20), palmityl triacontanoate (C29-C16), etc.

Commercially available examples of aliphatic esters represented by general formula (3) include Unistar M-2222SL (manufactured by NOF Corporation), Exepar SS (manufactured by Kao Corporation, melting point 60°C), EMALEX CC-18 (manufactured by Nippon Emulsion Co., Ltd.), Amreps PC (manufactured by Kokyu Alcohol Kogyo Co., Ltd.), Exepar MY-M (manufactured by Kao Corporation), Sperm Acetate (manufactured by NOF Corporation), and EMALEX CC-10 (manufactured by Nippon Emulsion Co., Ltd.). These commercially available products are often mixtures of two or more types, so they may be separated and purified as necessary.

The ink of the present invention may contain only one type of fatty acid or aliphatic ester compound represented by the above general formula (2), or may contain two or more types.

(1.6) Non-polymerizable resin The ink of the present invention may further contain a non-polymerizable resin, if necessary. In particular, it is preferable for an ink that contains a gelling agent and has sol-gel phase transition properties to further contain a non-polymerizable resin.

In the present invention, "non-polymerizable resin" refers to a resin that does not have groups that crosslink or polymerize when irradiated with actinic rays (photopolymerizable groups).

Examples of non-polymerizable resins include polyester resins and ketone resins, which have at least one polar functional group in their molecules. When ink contains such polyester resins or ketone resins, the polar functional groups make it easier for the gelling agent to precipitate on the droplet surface after the ink lands on a recording medium. Meanwhile, the relatively weakly polar moieties (ester moieties and ketone moieties) of the polyester resin or ketone resin have affinity for the gelling agent. This means that the gelling agent is more easily mixed uniformly into the ink in a sol state. Furthermore, the polar functional groups of the polyester resin or ketone resin bond with functional groups on the recording medium surface, enhancing adhesion between the cured ink and the recording medium.

The polar functional group possessed by the polyester resin or ketone resin is preferably a group selected from an -OH group, a -COOH group, an _-NH2 group, an _-NO2 group, and a -CN group. When the polyester resin or ketone resin has these polar functional groups, the gelling agent is more likely to precipitate on the surface of the ink after it has landed on the recording medium. In particular, it is preferable that the polyester resin or ketone resin has both an -OH group and a -COOH group. When the polyester resin or ketone resin has these groups, adhesion is likely to be improved regardless of the type of functional group present on the surface of the recording medium.

While there are no particular restrictions on the amount of polar functional groups contained in the polyester resin or ketone resin, it is preferable that the polyester resin or ketone resin have an acid value or base value in the range of 10 to 350 mgKOH/g. The acid value or base value of the polyester resin or ketone resin is more preferably 10 to 65 mgKOH/g. If the acid value or base value of the polyester resin or ketone resin is 10 mgKOH/g, the adhesion between the cured ink and the recording medium will not be sufficiently enhanced, and the ink will not undergo a sufficient sol-gel phase transition. On the other hand, if the acid value or base value of the polyester resin or ketone resin exceeds 350 mgKOH/g, it will be difficult to introduce polar functional groups into the polyester resin or ketone resin. Furthermore, if the amount of polar functional groups is excessive, the compatibility of the gelling agent in the ink sol state may be reduced. The acid value and base value are measured in accordance with the neutralization value test method described in JIS K2501.

The number-average molecular weight of the polyester resin or ketone resin having a polar functional group is preferably 1,000 to 5,000, and more preferably 1,200 to 3,000. If the number-average molecular weight of the polyester resin or ketone resin is less than 1,000, the compatibility with the gelling agent will be increased, making it difficult for the gelling agent to precipitate. On the other hand, if the number-average molecular weight of the polyester resin or ketone resin is greater than 5,000, the viscosity of the ink will increase, reducing the ejection stability of the ink from the inkjet recording device when forming images using the inkjet method. The number-average molecular weight is a value measured using gel permeation chromatography (GPC) in polystyrene equivalent terms.

Specific examples of polyester resins containing hydroxyl groups include special ester resins manufactured by EVONIK INDUSTRIES (TEGOAddBond series (LTH, LTW, 1270, 2440, 3350UV), all of which have an average molecular weight of 1500-3000, an acid value of 15-65 mgKOH/g, and a base value of 10-50 mgKOH/g).

Specific examples of ketone resins having hydroxy groups include ketone resin manufactured by Degussa (TEGO VARIPLUS SK (average molecular weight 1000-2000, acid value approximately 0 mg KOH/g, base value approximately 300 mg KOH/g)).

Specific examples of ketone resins having urethane groups include ketone resin (TEGO VARIPLUS PZZ-1201) manufactured by Degussa.

The amount of polyester resin or ketone resin having a polar functional group contained in the ink is preferably in the range of 1.0 to 15.0% by mass, more preferably 3.0 to 10.0% by mass, relative to the total mass of the ink. When two or more types of polyester resin or ketone resin having a polar functional group are contained, it is preferable that the total amount of these is within the above range. If the amount of polyester resin or ketone resin having a polar functional group is less than 1.0% by mass, the gelling agent may not precipitate (crystallize) sufficiently in the ink after it has landed. On the other hand, if the amount of polyester resin or ketone resin having a polar functional group exceeds 15.0% by mass, not only will the viscosity of the ink in the sol state increase, but the solubility of the gelling agent in the ink in the sol state will decrease.

The method for preparing the polyester resin having a polar functional group is not particularly limited. For example, the polyester resin can be obtained by preparing the polyester resin from a polyhydric alcohol, a polycarboxylic acid, a cyclic lactone, or the like having a polar functional group. Specifically, the polyester resin having a polar functional group can be prepared by carrying out the following reaction.
(i) Direct esterification reaction of difunctional or higher polyhydric alcohols and difunctional or higher polycarboxylic acids. (ii) Transesterification reaction of difunctional or higher polyesters and difunctional or higher polyhydric alcohols. (iii) Esterification reaction of difunctional or higher polyhydric alcohols and acid anhydrides. (iv) Direct esterification reaction of hydroxycarboxylic acids having one or more hydroxy groups and one or more carboxy groups per molecule. (v) Ring-opening polymerization of cyclic lactones having polar functional groups bonded to the ring.

The acid value and base value of polyester resins are adjusted by the number of functional groups in the raw materials, such as polyhydric alcohols, polycarboxylic acids, hydroxycarboxylic acids, and polar group-containing cyclic lactones.

Ketone resins with polar functional groups can also be prepared by reacting an aromatic ketone compound such as acetophenone with a compound with a polar functional group. For example, a ketone resin with -OH groups can be prepared by reacting an aromatic ketone compound such as acetophenone with an aldehyde compound such as formaldehyde, and then hydrogenating the resulting ketone resin.

The acid value and base value of the ketone resin are adjusted by the amount of compound reacted with the ketone compound, the type of compound, etc.

(1.7) Photopolymerization Initiator Auxiliary Agent The ink of the present invention may further contain a photopolymerization initiator auxiliary agent, if necessary.

The photopolymerization initiator aid may be a tertiary amine compound, with aromatic tertiary amine compounds being preferred. Examples of aromatic tertiary amine compounds include N,N-dimethylaniline, N,N-diethylaniline, N,N-dimethyl-p-toluidine, N,N-dimethylamino-p-benzoic acid ethyl ester, N,N-dimethylamino-p-benzoic acid isoamyl ethyl ester, N,N-dihydroxyethylaniline, triethylamine, and N,N-dimethylhexylamine. Of these, N,N-dimethylamino-p-benzoic acid ethyl ester or N,N-dimethylamino-p-benzoic acid isoamyl ethyl ester is preferred.

(1.8) Polymerization Inhibitor The ink of the present invention may further contain a polymerization inhibitor, if necessary.

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

(1.9) Other Components The ink of the present invention may further contain other components as needed. These other components may be various additives, other resins, etc.

Examples of additives include dispersing aids, surfactants, leveling additives, matting agents, ultraviolet absorbers, infrared absorbers, antibacterial agents, and basic compounds to improve the storage stability of the ink.

Examples of basic compounds include basic alkali metal compounds, basic alkaline earth metal compounds, and basic organic compounds such as amines.

Examples of other resins include resins used to adjust the physical properties of the cured ink, such as polyester resins, polyurethane resins, vinyl resins, acrylic resins, rubber resins, and waxes.

(1.10) Sol-Gel Phase Transition Property of Ink The ink of the present invention preferably has sol-gel phase transition property. In the present invention, "sol-gel phase transition property" refers to the property of reversibly changing between a sol state with fluidity and a gel state with no fluidity, and is in a sol state at high temperatures and a gel state at low temperatures above the sol-gel phase transition temperature.

By allowing the ink to transition between sol and gel phases, when forming images using the inkjet method, the ink is put into a sol state during ejection, improving ejection stability, and after landing, it is put into a gel state, preventing liquid segregation.

The sol-gel phase transition temperature is preferably in the range of 40 to 70°C, and more preferably in the range of 50 to 65°C. When the ejection temperature from the inkjet device is around 80°C, if the ink's sol-gel phase transition temperature is 70°C or lower, it will easily change to a sol state during ejection, resulting in good ejection stability. Furthermore, if the sol-gel phase transition temperature is 40°C or higher, the temperature of the recording medium, which is preferably set at least 30°C lower than the ink's sol-gel phase transition temperature, can be set at 10°C or higher, eliminating the need to complicate the image formation process.

In addition, from the perspective of improving the ejection stability of ink droplets from an inkjet device, it is preferable that the viscosity of the ink at high temperatures (sol state) be below a certain level. Specifically, it is preferable that the viscosity of the ink at 80°C be 3 to 20 mPa·s. On the other hand, from the perspective of forming images with fine patterns, it is preferable that the viscosity of the ink after landing on the recording medium (gel state) be above a certain level. Specifically, it is preferable that the viscosity of the ink at 25°C be 1000 mPa·s or higher.

The ink's viscosity at 80°C, viscosity at 25°C, and sol-gel phase transition temperature can be determined by measuring the temperature change in the ink's dynamic viscoelasticity using a rheometer. Specifically, the ink is heated to 100°C and cooled to 20°C at a shear rate of 11.7 (/s) and a cooling rate of 0.1°C/s, and a viscosity temperature change curve is obtained. The viscosity at 80°C and 25°C can then be determined by reading the viscosities at 80°C and 25°C, respectively, on the viscosity temperature change curve. The sol-gel phase transition temperature can be determined as the temperature at which the viscosity reaches 200 mPa·s on the viscosity temperature change curve.

The rheometer used can be a stress-controlled rheometer, Physica MCR series, manufactured by Anton Paar. The cone plate diameter can be 75 mm, and the cone angle can be 1.0°.

(1.11) Method for Preparing Ink The ink of the present invention can be prepared by mixing the above-mentioned photosensitizer, polymerizable compound, photopolymerization initiator, colorant, etc., while heating using a known method.

(2) Image Forming Method The image forming method of the present invention is characterized by using the actinic radiation-curable ink of the present invention. Specifically, the ink of the present invention described above is applied to a recording medium, and the ink is cured by irradiating with actinic radiation to form an image. This makes it possible to form an image that has been imparted with antibacterial and antiviral properties.

The image forming method will be described in detail below. Note that "applying ink independently of the image area" and "forming a decorative image," which are embodiments of the image forming method of the present invention, will be described later.

(2.1) Recording Medium There are no particular limitations on the recording medium that can be used and it can be appropriately selected depending on the application. For example, it can be various plastic substrates, metal substrates, glass substrates, stone substrates, cloth substrates, natural pulp substrates, fleece substrates made of a mixture of natural pulp and synthetic fibers, Japanese paper substrates, etc.

The recording medium may be a discrete sheet, a long sheet wound into a roll, or a molded body made of various resins.

When using ink with sol-gel phase transition properties, it is preferable to set the temperature of the recording medium at least 30°C lower than the sol-gel phase transition temperature of the ink. In this case, the temperature of the recording medium is preferably 30 to 70°C lower, and more preferably 30 to 50°C lower, than the sol-gel phase transition temperature of the ink. This allows ink droplets that land on the recording medium to quickly gel, forming an image in the desired pattern. Here, the temperature of the recording medium refers to the surface temperature of the recording medium on which the ink lands; the entire recording medium does not have to be at the above temperature. The surface temperature of the recording medium is measured using an infrared radiation thermometer, etc.

The temperature of the recording medium is adjusted by heating or cooling the recording medium using known methods. There are no particular restrictions on the heating or cooling method, and it can be done using various heaters, chillers, Peltier elements, etc.

(2.2) Application of Ink The method of applying ink is not particularly limited, and ink can be applied by an inkjet method or an offset method. The inkjet method is preferred when forming an image on demand, and the offset method is preferred when forming the same image in large quantities.

In the case of inkjet printing, the amount of ink ejected from each nozzle of the inkjet recording head depends on the image resolution, but is preferably 0.5 to 10 pl, and more preferably 0.5 to 2.5 pl to form high-resolution images.

When using ink with sol-gel phase transition properties in an inkjet system, in order to improve the ejection stability of ink droplets, it is preferable to set the temperature of the ink inside the inkjet recording head at a temperature 10 to 30°C higher than the sol-gel phase transition temperature of the ink. If the ink temperature inside the inkjet recording head is 10°C above the sol-gel phase transition temperature, the ink is less likely to gel inside the inkjet recording head or on the nozzle surface, resulting in good ejection stability of ink droplets. On the other hand, if the ink temperature inside the inkjet recording head is 30°C above the sol-gel phase transition temperature, the ink does not become too hot, preventing deterioration of the ink components.

(2.3) Irradiation with actinic rays After the ink is applied onto the recording medium, it is irradiated with actinic rays to crosslink or polymerize the polymerizable compound contained in the ink and harden it, thereby fixing the ink on the recording medium.

The actinic rays used for irradiation are not particularly limited and are selected appropriately depending on the type of photopolymerization initiator or actinic radiation-polymerizable compound contained in the ink, taking into account its absorption wavelength range. Examples include electron beams, ultraviolet rays, alpha rays, gamma rays, and X-rays, but ultraviolet rays are preferred, and ultraviolet rays from an LED light source are particularly preferred. An example of an LED device capable of irradiating ultraviolet rays is a 395 nm water-cooled LED manufactured by Phoseon Technology.

Metal halide lamps are commonly used as ultraviolet light sources, but when LEDs are used as the light source, the radiant heat from the light source can be reduced. This means that the radiant heat reduces the viscosity of the ink, preventing changes in the shape of the image, etc.

From the viewpoint of suppressing radiation heat irradiation and sufficiently curing the ink, the peak irradiance of the actinic rays on the ink surface is preferably within a range of 0.5 to 10 W/ ^cm2 , and more preferably within a range of 1 to 5 W/ ^cm2 .

The energy of the irradiated actinic rays is preferably within the range of 200 to 1000 mJ/ ^cm2 . When the energy is 200 mJ/ ^cm2 or more, the polymerizable compound can be sufficiently polymerized and crosslinked, and when the energy is 1000 mJ/ ^cm2 or less, a decrease in pinning ability due to a decrease in ink viscosity caused by the heat of the irradiated actinic rays is less likely to occur. From the above viewpoints, the energy of the irradiated actinic rays is more preferably within the range of 300 to 800 mJ/ ^cm2 , and even more preferably within the range of 350 to 500 mJ/ ^cm2 .

Furthermore, the photosensitizer contained in the ink of the present invention may lose its singlet oxygen generating ability due to absorption of actinic rays irradiated during curing of the ink. To prevent this, the difference between the maximum absorption wavelength of the photosensitizer in a monomolecular state and the maximum maximum wavelength of the actinic rays irradiated onto the ink is preferably 100 nm or more, and more preferably 200 nm or more.

(2.4) Inkjet Image Forming Apparatus An image forming apparatus (also referred to as an "inkjet image forming apparatus") that can be used in an inkjet image forming method will be described.

Inkjet image forming devices are generally divided into on-demand and continuous types depending on the ink ejection method. Inkjet image forming devices that can be used in the image forming method of the present invention may be of either type. Examples of on-demand inkjet image forming devices include electro-mechanical conversion types, including single-cavity, double-cavity, bender, piston, shear-mode, and shared-wall types, as well as electro-thermal conversion types, including thermal inkjet and bubble-jet (Bubble Jet is a registered trademark of Canon Inc.) types.

Inkjet image forming devices are further divided into scan type and line type (also called "single pass type") devices depending on the head scanning method. Inkjet image forming devices that can be used in the image forming method of the present invention may be of either type, but from the perspective of high-speed image formation, a line type device is preferred.

The following describes a line-type inkjet image forming apparatus using Figure 3.

Figure 3 is a schematic diagram showing an exemplary configuration of a line-type inkjet image forming apparatus 100. The inkjet image forming apparatus 100 shown in Figure 3 has an ink ejection unit 104 and an actinic light irradiation unit 103.

The ink ejection unit 104 has an inkjet recording means 113 and a temperature control means 119.

The inkjet recording means 113 has a head carriage 116 that houses multiple inkjet recording heads 114, an ink flow path 117 connected to the head carriage 116, and an ink tank 118 that stores ink supplied through the ink flow path 117.

The ink tank 118 is connected to the head carriage 116 via an ink flow path 117. The ink flow path 117 is a path that supplies ink in the ink tank 118 to the head carriage 116.

The head carriage 116 is fixedly positioned so as to cover the entire width of the recording medium 1, and houses multiple inkjet recording heads 114. In the example shown in Figure 3, each head carriage 116 houses an inkjet recording head 114 for each of the colors yellow (Y), magenta (M), cyan (C), and black (K).

A plurality of inkjet recording heads 114 are arranged in the transport direction of the recording medium 1, and the number of inkjet recording heads 114 arranged in the transport direction of the recording medium 1 is determined by the nozzle density of the inkjet recording heads 114 and the resolution of the print image. For example, when forming an image with a resolution of 1440 dpi using inkjet recording heads 114 with a droplet volume of 2 pl and a nozzle density of 360 dpi, four inkjet recording heads 114 are arranged with a staggered arrangement in the transport direction of the recording medium 1. Also, when forming an image with a resolution of 720 x 720 dpi using inkjet recording heads 114 with a droplet volume of 6 pl and a nozzle density of 360 dpi, two inkjet recording heads 114 are arranged with a staggered arrangement. dpi represents the number of ink droplets (dots) per 2.54 cm.

The ink tank 118, ink flow path 117, head carriage 116, and inkjet recording head 114 may be provided with temperature adjustment means (not shown), which can control the temperature inside these so that the ink is in a sol state, for example.

The temperature control means 119 is arranged to cover the entire width of the recording medium 1. As shown in Figure 3, if the ink ejection unit 104 and the actinic ray irradiation unit 103 are continuous, the temperature control means 119 may be arranged continuously from the ink ejection unit 104 to the actinic ray irradiation unit 103.

The temperature control means 119 includes a temperature detection unit (not shown) for detecting the surface temperature of the recording medium 1, and a temperature adjustment unit (not shown) such as a heater or chiller. In the inkjet image forming apparatus 100 shown in Figure 3, the temperature control means 119 is located on the underside of the recording medium 1, but the temperature control means 119 can be located at any position depending on the thickness, shape, etc. of the recording medium 1.

The actinic ray irradiation unit 103 has an actinic ray irradiation section 131. The actinic ray irradiation section 131 is installed so as to cover the entire width of the recording medium 1. The actinic ray irradiation unit 103 irradiates the ink applied to the recording medium with the actinic rays described above, causing the ink to harden.

(3) Applying Ink Independently of Image Area In one embodiment of the image forming method of the present invention, the ink of the present invention can be applied independently of the image area.

"Image area" refers to the area where an image (visible letters, figures, patterns, etc. formed on a recording medium by the cured ink or foil transferred onto it) is formed, or the area where an image has been formed. Also, "non-image area" refers to the area that is not an image area.

"Applying ink independently of the image area" means applying ink to the recording medium in invisible dot sizes and dot spacing, regardless of whether it is an image area or a non-image area, for the purpose of imparting antibacterial and antiviral properties to the output.

As mentioned above, the singlet oxygen generated by the photosensitizer contained in the ink of the present invention is in the form of a gas, and therefore diffuses into the surroundings after generation. For example, at 50% humidity, the diffusion distance is approximately 1.57 mm. Therefore, for example, by applying the ink of the present invention to the entire surface of a recording medium, independently of the image area, with a dot size of 30 μm and a dot spacing of 3 mm, it is possible to impart antibacterial and antiviral effects to the entire surface of the printed material without degrading image quality.

It is preferable that the ink applied in this way independently of the image area is not visible, so it is preferably an ink that does not contain a colorant (hereinafter also referred to as "clear ink").

From the perspective of balancing antibacterial and antiviral effects with maintaining image quality, the coverage rate of ink applied independently of the image area is preferably within the range of 0.001 to 0.5%, and more preferably within the range of 0.01 to 0.3%. As mentioned above, when ink is applied to the entire surface of a recording medium with a dot size of 30 μm and dot spacing of 3 mm, the coverage rate of ink applied independently of the image area is approximately 0.01%. Note that "coverage rate" refers to the percentage of the area to which ink is applied relative to the total area of the recording medium or printed object.

When the ink of the present invention is applied independently of the image area in this way, it is preferable that the ink used to form the image area is also the ink of the present invention, but it does not necessarily have to be the ink of the present invention and may be another ink.

The process of applying ink independently of the image area can be carried out simultaneously with the process of applying ink to form the image area, but it can also be carried out separately before or after the process of applying ink to form the image area. Furthermore, the timing of curing the ink applied independently of the image area and the timing of curing the ink to form the image area may be simultaneous or different. In other words, after one ink application process, the ink is cured by irradiation with actinic light, and then the other ink application process is carried out, and the ink is cured again by irradiation with actinic light; thus, each ink application process can be carried out separately.

When using the inkjet method, if the process of applying ink that does not contain a colorant independently of the image area and the process of applying ink that forms the image area are carried out simultaneously, the respective processes can be carried out simultaneously by adding a head carriage 116 for the ink that does not contain a colorant (N), as shown in Figure 4, for example.

In the offset method, when the process of applying ink that does not contain colorant independently of the image area and the process of applying ink that forms the image area are carried out simultaneously, each process can be carried out simultaneously by applying each ink using a different plate.

(4) Formation of Decorative Image In one embodiment of the image forming method of the present invention, a decorative image (also referred to as a "foil image") can be formed by transferring foil onto an area where the ink of the present invention has been applied. This makes it possible to obtain a decorative image that has been imparted with antibacterial and antiviral properties.

In this invention, a "decorative image" refers to an image formed by adhering a foil such as a metal foil in a desired shape to a recording medium.

When forming decorative images, foil is transferred onto the ink applied to the recording medium before it is cured, and then the ink is irradiated with actinic light to cure it.

In image formation methods for forming decorative images, it is preferable to use ink that has sol-gel phase transition properties. This makes it difficult for ink droplets to wet and spread after landing on the recording medium, making it possible to form decorative images that include fine patterns. Furthermore, because ink droplets are less likely to penetrate into the unevenness of the recording medium after landing, the thickness of the uncured image (an image made of ink before curing) tends to be uniform, making it less likely for defects to occur in the resulting decorative image.

Below, an example of each step in forming a decorative image will be explained using Figure 5.

First, as shown in Figure 5(a), ink is ejected in a pattern onto a recording medium 1 to form an uncured image 2.

The average thickness of the uncured image 2 is preferably approximately 0.1 to 1000 μm, and more preferably approximately 1 to 300 μm. If the thickness of the uncured image is 1 μm or more, the adhesive strength between the foil layer 5 of the transfer foil 3 and the uncured image 2 tends to be sufficiently high. The average thickness can be measured by observing the cross section of the uncured image 2 with an SEM.

Next, as shown in Figure 5(b), a transfer foil 3 including a support material 4 and a foil layer 5 is pressed onto the uncured image 2 with the foil layer 5 facing downwards.

The transfer foil 3 may be a single sheet or a long sheet wound into a roll. The transfer foil 3 includes at least a support material 4 and a foil layer 5. For example, a release layer or a colored layer may be formed between the support material 4 and the foil layer 5. If a colored layer is formed, it is also transferred onto the uncured image 2 along with the foil layer 5. An adhesive layer may also be formed on the transfer surface of the transfer foil 3.

The foil layer 5 is a layer used to impart metallic or glossy characters or designs, or transparent watermark characters or designs, to the recording medium, which are difficult to achieve through conventional printing. The foil layer 5 can be, for example, a metal foil, a metal-deposited film, a hologram film, a pearlescent film, an iridescent film, a black/white film, a color film, or a clear film. The foil layer 5 can also be a layer made of a composite material of a plastic film and metal to improve strength. The foil layer 5 can also be a layer in which a regular pattern has been imparted to a metal film using known processing methods such as water-washed seelite processing, etching, or laser processing. The thickness of the foil layer 5 is selected appropriately depending on the type, but is typically around 10 to 100 nm.

The support material 4 is not particularly limited as long as it is a material capable of supporting the foil layer 5, and may be, for example, a film or sheet made of a flexible resin, or a paper sheet. Examples of resins that may be used to make up the support material 4 include well-known resins such as polyethylene terephthalate (PET) resin, polyethylene naphthalate (PEN) resin, polypropylene (PP) resin, polyethersulfone resin, and polyimide resin. The support material 4 may have a single-layer structure or a multi-layer structure.

As mentioned above, a release layer (not shown) may be formed on the transfer foil 3. The release layer is a layer that ensures the foil layer 5 can be easily peeled from the support material 4. The release layer may be, for example, a layer made of a thermosetting resin that uses melamine or isocyanate as a curing agent, or a layer containing a known wax such as a fluorine-based or silicon-based monomer or polymer.

As mentioned above, an adhesive layer (not shown) may also be formed on the transfer foil 3. The adhesive layer may be a layer that develops adhesiveness to the uncured image when heated. The adhesive layer may be, for example, a layer made of a heat-sensitive adhesive known as a hot-melt type. Examples of heat-sensitive adhesives include adhesives containing acrylic resin, vinyl chloride-vinyl acetate copolymer, epoxy resin, and ethylene-vinyl alcohol copolymer.

The force (bonding force) used to bond the uncured image 2 and the transfer foil 3 together is preferably 100 to 800 kPa, more preferably 200 to 600 kPa, in terms of nip surface pressure. The bonding time is preferably 0.1 to 30 seconds, more preferably 0.5 to 10 seconds.

The crimping method is not particularly limited, and crimping can be performed using the methods shown in Figures 6(a) to 6(c), for example.

In the pressure-bonding method shown in Figure 6(a), the recording medium 6 on which the uncured image is formed and the transfer foil 3 are pressed against a flat or desired shaped plate 41 to bond them together.

The pressing method shown in Figure 6(b) involves passing the recording medium 6 on which the uncured image has been formed and the transfer foil 3 between a pair of transfer rollers 42a and 42b to press them together.

The pressing method shown in Figure 6(c) is a method in which the recording medium 6 on which the uncured image is formed and the transfer foil 3 are pressed together by applying pressure with a transfer roller 43.

Here, the recording medium 6 on which the uncured image has been formed and the transfer foil 3 may be pressed together while being heated. Heating can be performed, for example, by heating the transfer roller or plate. The heating temperature is preferably 30 to 90°C, and more preferably 40 to 60°C. Heating makes it easier to peel the foil layer 5 from the transfer foil 3, allowing the foil layer 5 to be transferred in a short period of time. However, if the heating temperature is excessively high, the ink that makes up the uncured image 2 may soften, causing the pattern to collapse. Therefore, it is preferable to keep the heating temperature within the above range.

Next, as shown in Figure 5(c), the transfer foil 3 is removed. At this time, the foil layer 7 that was pressed onto the uncured image 2 remains on the uncured image 2. Meanwhile, the foil layer 5 that was not pressed onto the uncured image 2 is removed together with the support material 4. In other words, the foil layer 7 remains on the recording medium 1 in the pattern of the uncured image 2, and this becomes the decorative image.

Finally, as shown in Figure 5(d), the uncured image 2 is irradiated with actinic rays from the actinic ray irradiation unit 131 to cure the ink and fix the foil layer 7 onto the recording medium 1.

At this time, actinic rays may be irradiated from above the foil layer 7, or, if the recording medium 1 is transparent to actinic rays, actinic rays may be irradiated from below the recording medium 1.

Figure 7 shows an example of an image forming device (decorative image forming device) that can be used to form decorative images.

The decorative image forming apparatus 200 shown in Figure 7 has an adhesive ink ejection unit 101, a foil transfer unit 102, and an actinic ray irradiation unit 103.

The adhesive ink ejection unit 101 is an ejection unit for adhesive ink used to adhere foil to a recording medium. The adhesive ink ejection unit 101 shown in Figure 7 has an inkjet recording means 113 and a temperature control means 119. The details of each component are the same as those shown in Figure 3.

The foil transfer unit 102 has a pair of transfer rollers 42a and 42b that sandwich the recording medium 1, a foil delivery spool 121 that supplies the transfer foil 3 between the pair of transfer rollers 42a and 42b, and a take-up spool 122 that collects the transfer foil 3 after the foil layer has been transferred.

In the foil transfer unit 102, the uncured image formed by the adhesive ink ejection unit 101 and the transfer surface of the transfer foil are pressed together by a pair of transfer rollers 42a and 42b. This transfers the foil layer of the transfer foil onto the uncured image, forming a decorative image. Meanwhile, the transfer foil 3 after pressing is collected by the take-up spool 122.

The actinic ray irradiation unit 103 has an actinic ray irradiation section 131. The actinic ray irradiation section 131 is installed so as to cover the entire width of the recording medium 1. In the actinic ray irradiation unit 103, the actinic ray irradiation section 131 irradiates the uncured image with actinic rays, curing the ink and fixing the foil layer on the recording medium.

The image forming method of the present invention can also be used, for example, with the decorative image forming apparatus shown in Figure 8, to form a decorative image and then apply ink from above. This makes it possible to form an image composed of a combination of foil and colorant-containing ink, or a decorative image to which ink is applied independently of the image area. In this case, the irradiation of actinic light to fix the foil layer and the irradiation of actinic light to cure the colorant-containing ink, etc., can be performed together, or separately.

It is also possible to apply a colorant-containing ink or an ink that is separate from the image area, then irradiate it with actinic rays to harden it, and then apply another ink to form a decorative image.

(5) Output Product The output product of the present invention is characterized by being formed using the actinic radiation curable ink of the present invention.

In the present invention, the term "output" refers to an image (including a decorative image) formed on a recording medium. By using the actinic radiation-curable ink of the present invention, it is possible to form an output with high antibacterial and antiviral properties.

The present invention will be explained in more detail below using examples, but the present invention is not limited to these. In the examples, the terms "parts" and "%" are used, but unless otherwise specified, they represent "parts by mass" or "% by mass."

1. Preparation of Colorant Dispersions A cyan pigment dispersion and a black pigment dispersion were prepared as colorant dispersions according to the following procedure.

(Cyan pigment dispersion)
A cyan pigment "Lionol Blue FG-7400-G" (manufactured by Toyocolor Co., Ltd.) (20 parts by mass), a dispersant "BYKJET-9151" (manufactured by BYK Corporation, "BYKJET" is a registered trademark of the company) (6.5 parts by mass), (polyethylene glycol #400 diacrylate) (73.2 parts by mass), a photopolymerization inhibitor "IrgastabUV10" (manufactured by BASF Corporation, "Irgastab" is a registered trademark of the company) (0.3 parts by mass), and 0.3 mm zirconia beads "YTZ ball" (manufactured by Nikkato Corporation) were placed in a 100 mL plastic container and dispersed for 3 hours using a paint shaker. The zirconia beads were then removed to prepare a cyan pigment dispersion.

(Black pigment dispersion)
A black pigment dispersion was prepared in the same manner as the cyan pigment dispersion, except that the cyan pigment was changed to a black pigment, "Pigment Black 7" (carbon black, manufactured by Mitsubishi Chemical Corporation).

2. Ink Preparation Inks No. 1 to 17 were prepared according to the following procedure. The maximum absorption maximum wavelength of each photosensitizer in the monomolecular state is shown in Table III. The maximum absorption maximum wavelength in the monomolecular state was determined from the absorption spectrum of a solution in which the photosensitizer was dissolved in THF (tetrahydrofuran). However, in the case of photosensitizer B-1 only, the maximum absorption maximum wavelength was determined from the absorption spectrum of a solution in which the photosensitizer was dissolved in THF:methanol = 1:1. The solution concentration was adjusted so that the absorbance at the maximum absorption maximum wavelength in the absorption spectrum of the solution was 1.0 Abs. The absorption spectra were measured using a UV-Vis-Infrared Spectrophotometer V-750 (manufactured by JASCO Corporation).

(Ink No. 1)
Polyethylene glycol #400 diacrylate (25.0 parts by mass), 4EO-modified pentaerythritol tetraacrylate (20.0 parts by mass), 3PO-modified trimethylolpropane triacrylate (15.0 parts by mass), phenoxyethyl acrylate (40 parts by mass), photopolymerization initiator "IRGACURE 819" (manufactured by BASF Corporation, "IRGACURE" is a registered trademark of the company) (5.0 parts by mass), photosensitizer F-13 (0.08 parts by mass), and photopolymerization inhibitor "Irgastab UV10" (0.1 parts by mass) were added to a mixture, stirred at 105°C for 45 minutes, and then filtered through a 3 μm membrane filter (Teflon (registered trademark) manufactured by ADVANTEC Corporation), to prepare Ink No. 1.

The absorption spectrum of the photopolymerization initiator "IRGACURE819" has an absorption end point of 450 nm.

(Ink No. 2)
Ink No. 2 was prepared in the same manner as Ink No. 1, except that the photosensitizer was changed to F-13 (0.008 parts by mass).

(Ink No. 3)
Ink No. 3 was prepared in the same manner as Ink No. 1, except that the photosensitizer was changed to F-13 (0.8 parts by mass).

(Ink No. 4)
Ink No. 4 was prepared in the same manner as Ink No. 1, except that the photosensitizer was changed to E-1 (0.08 parts by mass).

(Ink No. 5)
Ink No. 5 was prepared in the same manner as Ink No. 1, except that the photosensitizer was changed to F-7 (0.08 parts by mass).

(Ink No. 6)
Ink No. 6 was prepared in the same manner as Ink No. 1, except that the photosensitizer was changed to F-10 (0.08 parts by mass).

(Ink No. 7)
Ink No. 7 was prepared in the same manner as Ink No. 1, except that the photosensitizer was changed to H-5 (0.08 parts by mass).

(Ink No. 8)
Ink No. 8 was prepared in the same manner as Ink No. 1, except that the photosensitizer was changed to H-2 (0.08 parts by mass).

(Ink No. 9)
Ink No. 9 was prepared in the same manner as Ink No. 1, except that the photosensitizer was changed to G-6 (0.08 parts by mass).

(Ink No. 10)
Ink No. 10 was prepared in the same manner as Ink No. 1, except that the photosensitizer was changed to F-10 (0.08 parts by mass) and a cyan pigment dispersion (10 parts by mass, equivalent to 2 parts by mass of pigment) was added.

(Ink No. 11)
Ink No. 11 was prepared in the same manner as Ink No. 1, except that the photosensitizer was changed to B-1 (0.08 parts by mass) and a cyan pigment dispersion (10 parts by mass, equivalent to 2 parts by mass of pigment) was added.

(Ink No. 12)
Ink No. 12 was prepared in the same manner as Ink No. 1, except that the photosensitizer was changed to F-13 (0.16 parts by mass) and a black pigment dispersion (10 parts by mass, equivalent to 2 parts by mass of pigment) was added.

(Ink No. 13)
Ink No. 13 was prepared in the same manner as Ink No. 1, except that the photosensitizer was changed to F-13 (0.16 parts by mass) and a cyan pigment dispersion (10 parts by mass, equivalent to 2 parts by mass of pigment) was added.

(Ink No. 14)
Ink No. 14 was prepared in the same manner as Ink No. 1, except that the photosensitizer was changed to I-2 (0.08 parts by mass).

(Ink No. 15)
Ink No. 15 was prepared in the same manner as Ink No. 1, except that the photosensitizer was changed to F-10 (0.08 parts by mass), and a cyan pigment dispersion (10 parts by mass, 2 parts by mass in terms of pigment) and behenyl behenate (8 parts by mass) were added as a gelling agent.

(Ink No. 16)
Ink No. 16 was prepared in the same manner as Ink No. 1, except that no photosensitizer was added.

(Ink No. 17)
Ink No. 17 was prepared in the same manner as Ink No. 1, except that no photosensitizer was added and a cyan pigment dispersion (10 parts by mass, 2 parts by mass in terms of pigment) was added.

3. Confirmation of the Molecular Aggregation State of the Photosensitizer in the Ink The absorption spectra of the above inks No. 1 to 15 were measured using a V-750 UV-Vis-Infrared Spectrophotometer (manufactured by JASCO Corporation). For inks No. 10 to 13 and 15, the absorption spectra were measured after separating and removing the solid pigment components from each ink using a centrifuge. When the measured absorption spectra were confirmed, an absorption peak was found in each of the absorption spectra of the inks that coincided with the maximum absorption maximum wavelength of the photosensitizer contained in each ink in a monomolecular state (see Table III). These results confirmed that the photosensitizer contained in inks No. 1 to 15 was in a monomolecular state.

4. Image Formation Images were formed using the above inks by the following image forming methods No. 1 to 3, and output products were obtained.

(Image forming method No. 1)
A piezoelectric ink jet recording head filled with the ink shown in Table III was installed in an ink jet recording apparatus (KM512MHX, manufactured by Konica Minolta).

Using this device, ink was applied to printing coated paper (OK Topcoat, basis weight 128 g/m ² , manufactured by Oji Paper Co., Ltd.) at a resolution of 720×720 dpi with a printing rate of 100% to form a 5 cm square solid image area.

Thereafter, the photoresist was cured by irradiating it with actinic rays having a maximum wavelength of 395 nm at a cumulative dose of 350 mJ/cm ² to obtain an output product.

(Image forming method No. 2)
A piezoelectric inkjet recording head 1 filled with ink No. 13 (cyan ink) and a piezoelectric inkjet recording head 2 filled with ink No. 1 (clear ink) were installed in series in an inkjet recording apparatus (KM512MHX, manufactured by Konica Minolta).

Using piezoelectric inkjet recording head 1 of the device, ink No. 13 (cyan ink) was applied to coated printing paper (OK top coat, basis weight 128 g/ ^m , manufactured by Oji Paper Co., Ltd.) at a resolution of 720 x 720 dpi at a print rate of 100% to form a 5 cm square solid image. Simultaneously, using piezoelectric inkjet recording head 2, ink No. 1 (clear ink) was applied to the entire surface of the coated printing paper at a print rate of 0.1%.

Thereafter, the photoresist was cured by irradiating it with actinic rays having a maximum wavelength of 395 nm at a cumulative dose of 350 mJ/cm ² to obtain an output product.

In the image formed using Image Forming Method No. 2, the areas where solid image areas were formed are "image areas," and the areas where no solid image areas were formed and only Ink No. 1 (clear ink) was applied at a printing rate of 0.1% are "non-image areas."

(Image forming method No. 3)
A piezoelectric inkjet recording head filled with Ink No. 15 (gelling agent-containing cyan ink) was installed in an inkjet recording apparatus (KM512MHX, manufactured by Konica Minolta).

Using this device, while maintaining the head temperature (discharge temperature) at 80°C, ink No. 15 (gelling agent-containing cyan ink) was applied to coated printing paper (OK top coat, basis weight 128 g/m, manufactured by ^Oji Paper Co., Ltd.) heated to 50°C under conditions of a resolution of 720 x 720 dpi, at a printing rate of 100% to form a 5 cm square solid image area.

Thereafter, the photoresist was cured by irradiating it with actinic rays having a maximum wavelength of 395 nm at a cumulative dose of 350 mJ/cm ² to obtain an output product.

5. Evaluation of singlet oxygen generating ability by phosphorescence detection Images were formed by applying Ink Nos. 1 to 17 and Image forming methods Nos. 1 to 3 in the combinations shown in Table III to printouts, and the presence or absence of singlet oxygen generating ability of the photosensitizer was evaluated by detecting phosphorescence derived from singlet oxygen.

The image or non-image area shown in Table III was used as the evaluation area, and the printout was cut into a 5 cm square to create an image sample.

The phosphorescence spectrum of the ink on the image sample was measured under the following conditions.
Measurement system: EP-8700 (manufactured by JASCO Corporation)
Measurement mode: Fluorescence (monochromatic light monitor ratio calculation method)
Measurement interval 5nm
Measurement wavelength range: 1200 to 1350 nm
Data capture interval: 2 nm

The excitation wavelength during measurement was set to the maximum absorption wavelength in the single molecule state of the photosensitizer contained in the ink used to form each image sample (see Table III).

For inks No. 1 to 15, the phosphorescence spectra obtained confirmed an emission peak near 1270 nm, the emission peak of singlet oxygen, and phosphorescence derived from singlet oxygen was detected.

These results confirm that the photosensitizer contained in the ink of the present invention is a sensitizer for oxygen and has the ability to generate singlet oxygen.

6. Evaluation of Singlet Oxygen Generating Ability by Rubrene Fade Test Images were formed by applying Ink Nos. 1 to 17 and Image Forming Methods Nos. 1 to 3 in the combinations shown in Table III to output products, and the singlet oxygen generating abilities of the photosensitizers were relatively evaluated by the rubrene fading test.

The image or non-image area shown in Table III was used as the evaluation area, and the printout was cut into a 5 cm square to create an image sample.

A 5 mm square piece of filter paper was soaked in 0.1% rubrene-alcohol solution. The dye concentration of the filter paper was then measured.

The image sample was placed in a transparent petri dish, and the filter paper was placed on top and sealed. This was left at room temperature under a 1000 (lx) fluorescent light for 24 hours.

The filter paper was removed from the dish and the dye concentration was measured again. The dye concentration remaining rate was calculated from the dye concentration before and after leaving it, and the rubrene fading effect was evaluated according to the following criteria.

◎ Dye concentration remaining rate less than 10% ○ Dye concentration remaining rate 10% or more but less than 30% △ Dye concentration remaining rate 30% or more but less than 90% × Dye concentration remaining rate 90% or more

The results of this evaluation are shown in Table III. Because the rubrene fading effect is thought to be due to singlet oxygen, it was possible to relatively evaluate the singlet oxygen generating ability of the photosensitizer contained in the ink of the present invention.

Furthermore, these results confirmed that the photosensitizer contained in the ink of the present invention can generate singlet oxygen from oxygen in the air even under weak light such as indoor illumination. In Table III, the "present invention" in the Remarks column for Examples 4, 7, 8, 11, and 15 should be read as "Reference Example."

7. Evaluation of Indicator Properties for Singlet Oxygen Generating Ability Ink No. 1, which was confirmed to have singlet oxygen generating ability, was evaluated for its indicator properties for singlet oxygen generating ability according to the following procedure.

A 5 cm square solid image area was cut out from the printout on which an image was formed using Ink No. 1 and Image Forming Method No. 1 to serve as an image sample.

Ink No. 1 applied to the image sample exhibited a blue color due to the monomolecular absorption spectrum of the photosensitizer F-13 it contains. Furthermore, as mentioned above, Ink No. 1 has an emission peak near 1270 nm, confirming its ability to generate singlet oxygen.

The ink No. 1 applied to the image sample was irradiated with light using a xenon lamp under the condition of 1 sun (100 mW/cm ² ) for 8 hours and 30 days.

After 8 hours of light exposure, Ink No. 1 applied to the image sample exhibited the same blue color as before light exposure. The phosphorescence spectrum of Ink No. 1 after 8 hours of light exposure was measured under the same conditions as above, and it was found to have an emission peak near 1270 nm, confirming that it possessed the same singlet oxygen generating ability as before light exposure.

After 30 days of light exposure, Ink No. 1 applied to the image sample did not fade to a blue color, unlike before light exposure. The phosphorescence spectrum of Ink No. 1 after 30 days of light exposure was measured under the same conditions as above, and it was found that there was no emission peak near 1270 nm, confirming that the singlet oxygen generating ability had been lost by 30 days of light exposure.

These results confirm that the ink of the present invention exhibits coloration derived from the monomolecular absorption spectrum of the photosensitizer, and can be used as an indicator of singlet oxygen generation ability.

8. Evaluation of antibacterial and antiviral properties by film adhesion method Ink No. 1, which was confirmed to have singlet oxygen generating ability, was evaluated for antibacterial and antiviral properties by the following procedure.

A 5 cm square solid image area was cut out from the printout on which an image was formed using Ink No. 1 and Image Forming Method No. 1 to serve as an image sample.

An antibacterial test was conducted on the image sample using the film adhesion method in accordance with JIS Z 2801:2010 (Antibacterial processed products - Antibacterial test method/antibacterial effect) using the following procedure.

5 g of meat extract, 10 g of peptone, and 5 g of sodium chloride were dissolved in 1 L of distilled water to prepare a normal bouillon solution. This normal bouillon solution was further diluted 500 times. Escherichia coli (ISO3301) was added and suspended in this diluted solution to a bacterial concentration of 1.0 x ¹⁰ cells/mL to prepare a test bacterial solution.

0.5 mL of test bacteria solution (equivalent to 0.5×10 ⁶ bacteria) was dropped onto the image sample, and a covering film (polyethylene film) was attached to the sample, followed by leaving the sample at 35° C. for 24 hours.

Bacteria adhering to the image sample and coating film were washed away into a sterile petri dish using 9.5 mL of SCDLP medium (manufactured by Nippon Pharmaceuticals). The viable bacterial count in 1 mL of this washed-out liquid was measured using the agar plate dilution method using standard agar medium for measuring bacterial counts (manufactured by Nissui). The sterilization rate calculated from the measured viable bacterial count was 99.99%.

Based on the film adhesion method standards, which define good antibacterial properties as a reduction in the number of viable bacteria to less than one thousandth (i.e., a sterilization rate of 99.9% or more), Ink No. 1 was confirmed to have high antibacterial properties.

Furthermore, as is commonly known, singlet oxygen has antiviral as well as antibacterial properties, so Ink No. 1 is thought to have strong antiviral properties as well.

Furthermore, it is assumed that other inks that have been confirmed to have the same singlet oxygen generating ability as Ink No. 1 also have the same antibacterial and antiviral properties as Ink No. 1.

1 Recording medium 2 Uncured image 3 Transfer foil 4 Support material 5 Foil layer 6 Recording medium on which an uncured image has been formed 7 Pressed foil layer 41 Plate 42a, 42b Pair of transfer rollers 43 Transfer roller 100 Inkjet image forming apparatus 101 Adhesive ink ejection unit 102 Foil transfer unit 103 Actinic ray irradiation unit 104 Ink ejection unit 113 Inkjet recording means 114 Inkjet recording head 116 Head carriage 117 Ink flow path 118 Ink tank 119 Temperature control means 121 Foil delivery spool 122 Take-up spool 131 Actinic ray irradiation unit 200 Decorative image forming apparatus

Claims (12)

An actinic radiation curable ink containing at least a polymerizable compound and a photosensitizer,
the photosensitizer has singlet oxygen generating ability,
The actinic radiation-curable ink, wherein the photosensitizer has a structure represented by the following general formula (1) :
[In the above general formula (1), M represents a metal atom of Group 14. _Q1 and Q2 _each independently represent a monovalent axial ligand. Note that the above general formula (1) may not have either Q1 or Q2. _{A1 to} A4 _each independently _represent an atomic group forming an aromatic ring which may have a substituent.] Contains a photopolymerization initiator, and
2. The actinic radiation curable ink according to claim 1, wherein the maximum absorption maximum wavelength of the photosensitizer in a monomolecular state is on the longer wavelength side than the absorption end of the absorption spectrum of the photopolymerization initiator. the polymerizable compound is an actinic radiation-polymerizable compound, and
2. The actinic radiation-curable ink according to claim 1, wherein the maximum absorption maximum wavelength of the photosensitizer in a monomolecular state is on the longer wavelength side than the absorption end of the absorption spectrum of the actinic radiation-polymerizable compound. 4. The actinic radiation-curable ink according to claim 1, wherein the photosensitizer in a monomolecular state has a maximum absorption maximum wavelength within a range of 360 to 800 nm. The actinic radiation-curable ink according to any one of claims 1 to 4, further comprising a colorant. The actinic radiation-curable ink according to any one of claims 1 to 5 , which exhibits a color derived from the monomolecular absorption spectrum of the photosensitizer. An image forming method using actinic radiation curable ink, comprising:
An image forming method, wherein the actinic radiation curable ink is the actinic radiation curable ink according to any one of claims 1 to 6 . 8. The image forming method according to claim 7, wherein a difference between the maximum absorption maximum wavelength of the photosensitizer in a monomolecular state and the maximum maximum wavelength of the actinic ray irradiated to cure the actinic ray-curable ink is 100 nm or more. 9. The image forming method according to claim 7 , wherein the actinic radiation curable ink is applied independently of the image area. 10. The image forming method according to claim 7 , further comprising transferring a foil onto the area where the actinic radiation curable ink has been applied, thereby forming a decorative image. The image forming method according to any one of claims 7 to 10 , wherein the actinic radiation curable ink is applied onto the recording medium by an inkjet method. An output formed using actinic radiation curable ink,
An output product, wherein the actinic radiation curable ink is the actinic radiation curable ink according to any one of claims 1 to 6 .