JP2021102692A - Ink set and inkjet method - Google Patents

Abstract

To provide an ink set including color ink and clear ink and capable of improving adhesion to a recording medium, and an inkjet method.SOLUTION: An ink set of radiation curable inkjet ink including a polymerizable compound includes color ink and clear ink. The weighted average of SP values of the polymerizable compound using the mass ratio of each content of the polymerizable compound included in the clear ink as a weight is 9.0-10.0; the weighted average of SP values of the polymerizable compound using the mass ratio of each content of the polymerizable compound included in the color ink as a weight is 9.5-10.0; and the color ink includes a monofunctional monomer of 90 mass% or more to the total amount of the polymerizable compound included in the color ink.SELECTED DRAWING: None

Description

The present invention relates to an ink set and an inkjet method.

The inkjet method is a relatively simple device that can record high-definition images, and is rapidly developing in various fields. Among them, various studies have been made on radiation-curable inkjet inks such as UV (Ultra Violet) inks, which are capable of high-speed printing and are compatible with various non-absorbent recording media. For example, Patent Document 1 discloses a radiation-curable inkjet ink composition using a monofunctional monomer having an SP value of 8.5 or less and a monofunctional monomer having an SP value of 10.3 or more.

Japanese Unexamined Patent Publication No. 2013-79383

However, after printing an image with color UV ink, clear UV ink may be printed on the image to protect the image, and when the color ink and clear ink are overlapped, the adhesion to the recording medium becomes poor. There was a problem that it was easy to decrease. Specifically, in such a case, even if the SP value of the color ink is set as in Patent Document 1, when the clear ink is applied on the color ink, the print coating film as a whole has adhesion to the recording medium. May decrease. That is, it is necessary to consider the adhesion to the recording medium not only for the SP value of the color ink that is in direct contact with the recording medium but also for the clear ink that is not in direct contact with the recording medium.

The ink set is an ink set of a radiation-curable inkjet ink containing a polymerizable compound, and the ink set contains a clear ink and a color ink, and each content of the polymerizable compound contained in the clear ink. The weighted average of the SP values of the polymerizable compound is 9.0 to 10.0, and the weight is the mass ratio of each content of the polymerizable compound contained in the color ink. The weighted average of the SP values of the polymerizable compound is 9.5 to 10.0, and the color ink contains 90 masses of monofunctional monomer with respect to the total amount of the polymerizable compound contained in the color ink. Including% or more.

The inkjet method is an inkjet method using the above-mentioned ink set, and is a first coating step of ejecting the color ink from an inkjet head and applying the color ink to the recording medium, and the color ink applied to the recording medium. The first curing step of irradiating the radiation, the second coating step of ejecting the clear ink from the inkjet head and applying the clear ink to at least a part of the area where the color ink is applied on the recording medium, and the recording medium. It has a second curing step of irradiating the applied clear ink with radiation.

The schematic perspective view which shows the structure of the inkjet printer which concerns on embodiment.

1. 1. Ink set The ink set according to the present embodiment includes a color ink and a clear ink, which are radiation-curable inkjet inks containing a polymerizable compound. The ink set may contain a plurality of types of color inks having different coloring materials. The inkjet method of the present embodiment is used for forming an image, a color, a character, a pattern, or the like on a recording medium by the inkjet method using the ink set. By including a plurality of color inks in which the ink sets exhibit different color tones, it becomes easy to obtain a desired color tone in the image to be formed or the like. The use of the ink set of this embodiment is not limited to the above, and may be used for 3D modeling, for example. In the following description, the coating film formed from the clear ink is also referred to as a clear ink coating film, and the coating film formed from the color ink is also referred to as a color ink coating film.

Here, the radiation-curable inkjet ink is an inkjet ink that is cured by being irradiated with radiation. Examples of radiation include ultraviolet rays, electron beams, infrared rays, visible rays, and X-rays. Among these, it is preferable to use ultraviolet rays as radiation because the radiation source is easily available and widely used, and the material suitable for curing is easily available and widely used for the peak wavelength of radiation.

1.1. Clear ink The clear ink according to the present embodiment contains a photopolymerization initiator and a polymerizable compound containing a monofunctional monomer, and weights the mass ratio of each content of each polymerizable compound. The weighted average of the SP values is 9.0 to 10.0.

Further, the clear ink is not used for coloring the recording medium, but is used for protecting the coating film formed from the color ink, adjusting the glossiness of the printed matter, and the like. Therefore, the content of the color material contained in the clear ink is preferably 0.2% by mass or less, more preferably 0.1% by mass or less, based on the total amount of the clear ink. It is more preferable not to include it. Hereinafter, the components contained in the clear ink of the present embodiment will be described.

1.1.1. Polymerizable Compounds The polymerizable compound includes a monofunctional monomer having one polymerizable functional group, a polyfunctional monomer having a plurality of polymerizable functional groups, and an oligomer having one or more polymerizable functional groups. These polymerizable compounds may be used alone or in combination of two or more.

The polymerizable functional group contained in the polymerizable compound of the present embodiment is not particularly limited as long as the polymerization reaction can be carried out by radiation, and known polymerizable functional groups can be adopted. In particular, the polymerizable functional group is preferably a polymerizable functional group having an unsaturated double bond between carbons, more preferably a methacryloyl group, and even more preferably an acryloyl group from the viewpoint of polymerization reactivity. is there.

In addition, in this specification, (meth) acryloyl means at least one of acryloyl and corresponding methacryloyl, and (meth) acrylate means at least one of acrylate and corresponding methacrylate, and ( Meta) Acryloyl means at least one of acrylic and its corresponding methacryl.

In the clear ink of the present embodiment, the weighted average of the SP values of each polymerizable compound, weighted by the mass ratio of each content of each polymerizable compound, is 9.0 to 10.0. According to this, it is possible to improve the adhesion to the recording medium when the coating film of the clear ink is overlaid on the coating film of the underlying color ink. According to the study by the present inventors, even when the color ink has a polymerizable compound having a high SP value and a polymerizable compound having a low SP value, a coating film of clear ink is applied on the coating film of the color ink. It has been found that the adhesiveness of the coating film as a whole may decrease when the coating films are stacked. As a result of further studies on this, in order to improve the adhesion to recording media made of various materials, each polymerizable compound is weighted by the mass ratio of each content of each polymerizable compound contained in the clear ink. It has been found that the weighted average of the SP values of the compounds needs to be within a certain numerical range.

The calculation method of the weighted average of the SP value will be described. The weighted average value of the SP values is SP _All , the SP value of each polymerizable compound is SP _N , and the mass ratio of the content of the polymerizable compound is X _N (mass%). N is a numerical value that applies in order from 1 depending on the type of the polymerizable compound contained in the clear ink. Specifically, when three kinds of polymerizable compounds are used, SP ₁ , SP ₂ , and SP ₃ are set. The weighted average SP _All of the SP values is the sum of the products of _{SP N} calculated by each polymerizable compound and the content X _N. Therefore, the following equation (1) holds.
SP _All = ΣSP _N x X _N ... (1)

Further, the weighted average of the glass transition temperature of each homopolymer in the polymerizable compound, which is weighted by the mass ratio of each content of the polymerizable compound contained in the clear ink of the present embodiment, is preferably 48 ° C. or higher. , 60 ° C. or higher, more preferably 75 ° C. or higher. When the weighted average of the glass transition temperature is 48 ° C. or higher, the scratch resistance of the clear ink coating film in a room temperature environment of about 25 ° C. is improved, and the clear ink coating film is applied on the color ink coating film. When the above is formed, the coating film of the color ink can be suitably protected. The upper limit of the weighted average of the glass transition temperature is not particularly limited, but is preferably 140 ° C. or lower, more preferably 120 ° C. or lower, and even more preferably 110 ° C. or lower.

The method of calculating the weighted average of the glass transition temperature will be described. The weighted average value of the glass transition temperature is Tg _All (° C.), the glass transition temperature of each homopolymer of the polymerizable compound is Tg _N (° C.), and the mass of the content of the polymerizable compound corresponding to each homopolymer. Let the ratio be X _N (mass%). N is a numerical value that applies in order from 1 depending on the type of the polymerizable compound contained in the clear ink. Specifically, when three kinds of polymerizable compounds are used, Tg ₁ , Tg ₂ , and Tg ₃ are set. The weighted average Tg _All of the glass transition temperature is the sum of the products of _{the glass transition temperature Tg N} of the homopolymer corresponding to each polymerizable compound and the content ratio X _{N of each polymerizable compound.} Therefore, the following equation (2) holds.
Tg _All = ΣTg _N x X _N ... (2)

_{The weighted average SP All} of the above SP values and the weighted average Tg _All of the glass transition temperature can be adjusted by the SP value and the glass transition temperature of each polymerizable compound used for the clear ink, and the mass ratio of each polymerizable compound. It is possible. The SP value of the polymerizable compound and the glass transition temperature of each homopolymer can be obtained from the safety data sheet (SDS) of the corresponding polymerizable compound, catalog information, and the like.

1.1.1.1. Monofunctional Monomer The monofunctional monomer of the present embodiment is not particularly limited, and examples thereof include a monofunctional (meth) acrylate having an alicyclic group, a nitrogen-containing monofunctional monomer, and an aromatic group-containing monofunctional monomer. Further, other monofunctional monomers may be contained if necessary. The other monofunctional monomer is not particularly limited, but conventionally known polymerizable functional groups, particularly monofunctional monomers having a polymerizable functional group having an unsaturated double bond between carbons can be used.

The content of the monofunctional monomer is preferably 90% by mass or more, more preferably 97% by mass or more, based on the total amount of the polymerizable compounds contained in the clear ink. According to this, the adhesion of the clear ink coating film to the underlying color ink coating film and the recording medium is further improved. The upper limit of the content of the monofunctional monomer is not particularly limited, but is preferably 99% by mass or less, more preferably 98% by mass or less, based on the total amount of the polymerizable compounds contained in the clear ink. According to this, the curability of the ink and the scratch resistance of the coating film are further improved. In the following description, the adhesion of the recording medium or other ink to the coating film may be simply referred to as adhesion.

The content of the monofunctional monomer contained in the clear ink is preferably 70% by mass or more, more preferably 75% by mass or more, still more preferably 80% by mass or more, based on the total amount of the clear ink. is there. According to this, the stretchability of the coating film is further improved. The upper limit of the content of the monofunctional monomer is preferably 95% by mass or less, more preferably 92% by mass or less, and further preferably 90% by mass or less with respect to the total amount of the clear ink. According to this, the curability of the clear ink and the scratch resistance of the coating film are further improved.

The monofunctional monomer contained in the clear ink in the present embodiment preferably contains an alicyclic monofunctional (meth) acrylate. The alicyclic monofunctional (meth) acrylate refers to a polymerizable monomer having a saturated or unsaturated carbon ring having no aromaticity. Since such a monomer has an alicyclic group, it tends to be bulky as a whole, easily satisfying the conditions of the polymerizable monomer A described later, and the glossiness of the obtained clear ink coating film is improved. Further, since the glass transition temperature of the homopolymer formed from such a monomer tends to be relatively high, the coating film of the obtained clear ink is excellent in scratch resistance.

The content of the alicyclic monofunctional (meth) acrylate contained in the clear ink is preferably 55% by mass or more and 95% by mass or less, more preferably 65% by mass or less, based on the total amount of the polymerizable compounds contained in the clear ink. It is by mass% or more and 90% by mass or less, and even more preferably 75% by mass or more and 85% by mass or less. According to this, the scratch resistance and glossiness of the coating film of the clear ink are improved.

The content of the alicyclic monofunctional (meth) acrylate contained in the clear ink is preferably 50% by mass or more and 90% by mass or less, and more preferably 60% by mass or more and 85% by mass with respect to the total amount of the clear ink. It is more preferably 70% by mass or more and 80% by mass or less. According to this, the scratch resistance and glossiness of the coating film of the clear ink are improved.

Hereinafter, the monofunctional monomer will be exemplified, but the monofunctional monomer in the present embodiment is not limited to the following.

1.1.1.1.1. Monofunctional (meth) acrylate having a crosslinked condensed ring structure The crosslinked condensed ring structure in a monofunctional (meth) acrylate having a crosslinked condensed ring structure is such that two or more cyclic structures share a one-to-one side and share a side. A structure in which two or more atoms of the same cyclic structure or different cyclic structures that are not adjacent to each other are linked. Examples of the monofunctional (meth) acrylate having a crosslinked condensed ring structure include dicyclopentenyl (meth) acrylate, dicyclopentenyloxyethyl (meth) acrylate, and dicyclopentanyl (meth) acrylate. Further, as another crosslinked condensed ring structure, the structures of the following general formulas (a) and (b) can be mentioned. The monofunctional (meth) acrylate having a crosslinked condensed ring structure is included in the alicyclic monofunctional (meth) acrylate described above.

Among these, it is more preferable to include dicyclopentenyl acrylate (DCPA). According to this, the scratch resistance, stretchability, and adhesion are further improved in the clear ink coating film. Furthermore, the glossiness of the clear ink coating film is further improved.

The content of the monofunctional (meth) acrylate having a crosslinked condensed ring structure contained in the clear ink is preferably 25% by mass or more and 65% by mass or less, based on the total amount of the polymerizable compounds contained in the clear ink. It is preferably 30% by mass or more and 63% by mass or less, and even more preferably 35% by mass or more and 60% by mass or less. According to this, the scratch resistance, adhesion and glossiness of the clear ink coating film are improved.

The content of the monofunctional (meth) acrylate having a crosslinked condensed ring structure contained in the clear ink is preferably 20% by mass or more and 60% by mass or less, and more preferably 25% by mass or more, based on the total amount of the clear ink. It is 55% by mass or less, and even more preferably 30% by mass or more and 50% by mass or less. According to this, the scratch resistance, adhesion and glossiness of the clear ink coating film are improved.

1.1.1.1.2. Saturated aliphatic group-containing monofunctional (meth) acrylate The saturated aliphatic group-containing monofunctional (meth) acrylate is not particularly limited, and is, for example, isobornyl (meth) acrylate, tertbutylcyclohexanol (meth) acrylate, 2-(. Acrylate group-containing (meth) acrylates such as meta) acrylic acid-1,4-dioxaspiro [4,5] deci-2-ylmethyl; isoamyl (meth) acrylates, stearyl (meth) acrylates, lauryl (meth) acrylates, Octyl (meth) acrylate, decyl (meth) acrylate, isodecil (meth) acrylate, isomyristyl (meth) acrylate, isostearyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, butoxyethyl (meth) acrylate, tetrahydrofur Linear or branched aliphatic group-containing (meth) acrylates such as frill (meth) acrylate, 2-hydroxyethyl (meth) acrylate, and 2-hydroxypropyl (meth) acrylate; Can be mentioned. In this embodiment, the saturated aliphatic group-containing monofunctional (meth) acrylate is not a compound having a crosslinked condensed ring structure.

Among these, isobornyl (meth) acrylate, tertbutylcyclohexanol (meth) acrylate, 2- (meth) acrylic acid-1,4-dioxaspiro [4,5] deci, which are alicyclic monofunctional (meth) acrylates. It preferably contains -2-ylmethyl, and more preferably contains isobornyl acrylate (IBXA) and tert-butylcyclohexanol acrylate (TBCHA). According to this, the scratch resistance and glossiness of the clear ink coating film and the adhesion of the recording medium and the color ink to the coating film are improved.

The content of the saturated aliphatic group-containing monofunctional (meth) acrylate contained in the clear ink is preferably 15 to 85% by mass, more preferably 20 to 85% by mass, based on the total amount of the polymerizable compounds contained in the clear ink. It is 80% by mass, more preferably 25 to 75% by mass. According to this, the scratch resistance and glossiness of the clear ink coating film and the adhesion of the recording medium and the color ink to the coating film are improved.

The content of the saturated aliphatic group-containing monofunctional (meth) acrylate contained in the clear ink is preferably 15 to 80% by mass, more preferably 17 to 75% by mass, based on the total amount of the clear ink. More preferably, it is 20 to 70% by mass. According to this, the scratch resistance and glossiness of the clear ink coating film and the adhesion of the recording medium and the color ink to the coating film are improved.

1.1.1.1.3. Nitrogen-containing monofunctional monomer The nitrogen-containing monofunctional monomer is not particularly limited, but is, for example, a nitrogen-containing monofunctional monomer such as N-vinylcaprolactam, N-vinylformamide, N-vinylcarbazole, N-vinylacetamide, and N-vinylpyrrolidone. Nitrogen-containing monofunctional acrylate monomers such as vinyl monomer and acryloylmorpholine, (meth) acrylamide, N-hydroxymethyl (meth) acrylamide, diacetone acrylamide, N, N-dimethyl (meth) acrylamide, dimethylaminoethyl acrylate benzyl chloride 4 Examples thereof include nitrogen-containing monofunctional acrylamide monomers such as (meth) acrylamide such as grade salts.

Among these, it is preferable to contain either a nitrogen-containing monofunctional vinyl monomer or a nitrogen-containing monofunctional acrylate monomer, and a nitrogen-containing complex such as N-vinylcaprolactam, N-vinylcarbazole, N-vinylpyrrolidone, or acryloylmorpholine. It is more preferable to contain a monomer having a ring structure, and further preferably to contain acryloylmorpholine.

By using such a nitrogen-containing monofunctional monomer, the scratch resistance of the clear ink coating film is improved. Further, the nitrogen-containing monofunctional acrylate monomer having a nitrogen-containing heterocyclic structure such as acryloylmorpholin improves the stretchability and the adhesion of the recording medium and the color ink to the coating film in the clear ink coating film.

The content of the nitrogen-containing monofunctional monomer contained in the clear ink is preferably 2% by mass or more and 15% by mass or less, and more preferably 3% by mass or more and 13% by mass, based on the total amount of the polymerizable compounds contained in the clear ink. It is mass% or less, and more preferably 4 mass% or more and 12 mass% or less. According to this, the scratch resistance and the adhesion are improved in the coating film of the clear ink.

The content of the nitrogen-containing monofunctional monomer contained in the clear ink is preferably 2% by mass or more and 15% by mass or less, and more preferably 3% by mass or more and 12% by mass or less, based on the total amount of the clear ink. More preferably, it is 4% by mass or more and 11% by mass or less. According to this, the scratch resistance and the adhesion are improved in the coating film of the clear ink.

1.1.1.1.1.4. Aromatic group-containing monofunctional monomer The aromatic group-containing monofunctional monomer is not particularly limited, and is, for example, phenoxyethyl (meth) acrylate, benzyl (meth) acrylate, alkoxylated 2-phenoxyethyl (meth) acrylate, nonyl ethoxylated. Phenyl (meth) acrylates, alkoxylated nonylphenyl (meth) acrylates, p-cumylphenol EO modified (meth) acrylates, and 2-hydroxy-3-phenoxypropyl (meth) acrylates can be mentioned.

Among these, phenoxyethyl (meth) acrylate and benzyl (meth) acrylate are preferable, phenoxyethyl (meth) acrylate is more preferable, and phenoxyethyl acrylate (PEA) is further preferable. According to this, the solubility of the photopolymerization initiator is further improved, and the curability of the clear ink is improved. In particular, it is suitable when an acylphosphine oxide-based photopolymerization initiator or a thioxanthone-based photopolymerization initiator is used as the photopolymerization initiator described later.

The content of the aromatic group-containing monofunctional monomer contained in the clear ink is preferably 2% by mass or more and 15% by mass or less, more preferably 3% by mass, based on the total amount of the polymerizable compounds contained in the clear ink. It is 13% by mass or less, and more preferably 4% by mass or more and 12% by mass or less. According to this, the solubility of the photopolymerization initiator is further improved, and the curability of the clear ink is improved.

The content of the aromatic group-containing monofunctional monomer contained in the clear ink is preferably 2% by mass or more and 15% by mass or less, and more preferably 3% by mass or more and 12% by mass or less, based on the total amount of the clear ink. Yes, and even more preferably 4% by mass or more and 11% by mass or less. According to this, the solubility of the photopolymerization initiator is further improved, and the curability of the clear ink is improved.

11.1.1.1.5. Other monofunctional monomers Examples of other monofunctional monomers other than the above include unsaturated carboxylic acids such as (meth) acrylic acid, itaconic acid, crotonic acid, isocrotonic acid, and maleic acid, and salts of the unsaturated carboxylic acid. , Esters of unsaturated carboxylic acids, urethanes, amides and anhydrides, acryliconitrile, styrene, various unsaturated polyesters, unsaturated polyethers, unsaturated polyamides, unsaturated urethanes.

1.1.1.2. Polyfunctional Monomer The polymerizable compound contained in the clear ink may contain a polyfunctional monomer. Examples of the polyfunctional monomer include vinyl ether group-containing (meth) acrylate and polyfunctional (meth) acrylate.

The content of the polyfunctional monomer contained in the clear ink is preferably 0.01% by mass or more and 10.00% by mass or less, and more preferably 1.00% by mass or more, based on the total amount of the polymerizable compound. It is 00% by mass or less. When the content of the polyfunctional monomer is 0.01% by mass or more, the curability of the clear ink and the scratch resistance of the coating film are improved. Further, when the content of the polyfunctional monomer is 10.00% by mass or less, the stretchability and adhesion of the coating film of the clear ink are improved.

Specific examples of the polyfunctional monomer will be described below, but the polyfunctional monomer in the present embodiment is not limited to the following.

1.1.1.2.1. Vinyl ether group-containing (meth) acrylate The vinyl ether group-containing (meth) acrylate is not particularly limited, and examples thereof include compounds represented by the following general formula (c). By including such a vinyl ether group-containing (meth) acrylate, the viscosity of the clear ink is lowered and the ejection stability is improved. In addition, the curability of the clear ink is improved, and the recording speed on the recording medium can be increased as the curability is improved.
CH ₂ = CR ^1- COOR ^2- O-CH = CH-R ³ ... (c)
(In the formula, R ¹ is a hydrogen atom or a methyl group, R ² is a divalent organic residue having 2 to 20 carbon atoms, and R ³ is a hydrogen atom or a monovalent organic residue having 1 to 11 carbon atoms. It is a group.)

In the above general formula (c), the ^{divalent organic residue having 2 to 20 carbon atoms represented by R 2} is substituted in a linear, branched or cyclic form having 2 to 20 carbon atoms. May be an alkylene group, an optionally substituted alkylene group having 2 to 20 carbon atoms, optionally having an oxygen atom due to an ether bond and / or an ester bond in the structure, optionally substituted 2 having 6 to 11 carbon atoms. Valuable aromatic groups can be mentioned.

Among these, an alkylene group having 2 to 6 carbon atoms such as an ethylene group, an n-propylene group, an isopropylene group and a butylene group, an oxyethylene group, an oxyn-propylene group, an oxyisopropylene group, an oxybutylene group and the like. An alkylene group having 2 to 9 carbon atoms having an oxygen atom due to an ether bond in the structure of is preferable. Further, from the viewpoint of lowering the viscosity of the clear ink and improving the curability of the clear ink, R ² has an ether bond in the structure of an oxyethylene group, an oxyn-propylene group, an oxyisopropylene group, an oxybutylene group and the like. It is more preferable to have a glycol ether chain, which is an alkylene group having 2 to 9 carbon atoms having an oxygen atom according to the above.

In the general formula (c), the ^{monovalent organic residue having 1 to 11 carbon atoms represented by R 3} may be a linear, branched or cyclic monovalent organic residue having 1 to 10 carbon atoms, even if it is substituted. A good alkyl group, an optionally substituted aromatic group having 6 to 11 carbon atoms, is preferred. Among these, an aromatic group having 6 to 8 carbon atoms such as an alkyl group having 1 to 2 carbon atoms, which is a methyl group or an ethyl group, a phenyl group and a benzyl group is more preferable.

When each of the above organic residues is a optionally substituted group, the substituent is divided into a carbon atom-containing group and a carbon atom-free group. First, when the substituent is a group containing a carbon atom, the carbon atom is counted in the number of carbon atoms of the organic residue. The group containing a carbon atom is not limited to the following, and examples thereof include a carboxyl group and an alkoxy group. The group containing no carbon atom is not limited to the following, and examples thereof include a hydroxyl group and a halo group.

Specific examples of the compound of the general formula (c) are not particularly limited, but for example, 2-vinyloxyethyl (meth) acrylate, 3-vinyloxypropyl (meth) acrylate, 1-methyl-2 (meth) acrylate. − Vinyloxyethyl, 2-vinyloxypropyl (meth) acrylate, 4-vinyloxybutyl (meth) acrylate, 1-methyl-3-vinyloxypropyl (meth) acrylate, 1-vinyloxymethylpropyl (meth) acrylate, 2-Methyl-3-vinyloxypropyl (meth) acrylate, 1,1-dimethyl-2-vinyloxyethyl (meth) acrylate, 3-vinyloxybutyl (meth) acrylate, 1-methyl-2-methyl-2-methyl (meth) acrylate Vinyloxypropyl, 2-vinyloxybutyl (meth) acrylate, 4-vinyloxycyclohexyl (meth) acrylate, 6-vinyloxyhexyl (meth) acrylate, 4-vinyloxymethylcyclohexylmethyl (meth) acrylate, (meth) ) 3-Vinyloxymethylcyclohexylmethyl acrylate, 2-vinyloxymethylcyclohexylmethyl (meth) acrylate, p-vinyloxymethylphenylmethyl (meth) acrylate, m-vinyloxymethylphenylmethyl (meth) acrylate, O-vinyloxymethylphenylmethyl (meth) acrylate, 2- (2-vinyloxyethoxy) ethyl (meth) acrylate, 2- (vinyloxyisopropoxy) ethyl (meth) acrylate, 2 (meth) acrylate -(Vinyloxyethoxy) propyl, (meth) acrylate 2- (vinyloxyethoxy) isopropyl, (meth) acrylate 2- (vinyloxyisopropoxy) propyl, (meth) acrylate 2- (vinyloxyisopropoxy) Isopropyl, 2- (vinyloxyethoxyethoxy) ethyl (meth) acrylate, 2- (vinyloxyethoxyisopropoxy) ethyl (meth) acrylate, 2- (vinyloxyisopropoxyethoxy) ethyl (meth) acrylate, ( 2- (Vinyloxyisopropoxyisopropoxy) ethyl (meth) acrylate, 2- (vinyloxyethoxyethoxy) propyl (meth) acrylate, 2- (vinyloxyethoxyisopropoxy) propyl (meth) acrylate, (meth) 2- (Vinyloxyisopropoxyethoxy) propyl acrylate, 2- (vinyloxyisopropoxyisopropoxy) propyl (meth) acrylate, 2- (vinyloxyethoxyethoxy) (meth) acrylate Isopropyl, 2- (vinyloxyethoxyisopropoxy) isopropyl (meth) acrylate, 2- (vinyloxyisopropoxyethoxy) isopropyl (meth) acrylate, 2- (vinyloxyisopropoxyisopropoxy) isopropyl (meth) acrylate , (Meta) acrylate 2- (vinyloxyethoxyethoxyethoxy) ethyl, (meth) acrylate 2- (vinyloxyethoxyethoxyethoxy) ethyl, (meth) acrylate 2- (isopropenoxyethoxy) ethyl, ( 2- (Isopropenoxyethoxyethoxy) ethyl (meth) acrylate, 2- (isopropenoxyethoxyethoxyethoxy) ethyl (meth) acrylate, 2- (isopropenoxyethoxyethoxyethoxy) ethyl (meth) acrylate, Polyethylene glycol monovinyl ether (meth) acrylate and polypropylene glycol monovinyl ether (meth) acrylate can be mentioned. Among these specific examples, 2- (2-vinyloxyethoxy) ethyl acrylate is particularly preferable from the viewpoint of easily balancing the curability and viscosity of the clear ink. In this embodiment, 2- (2-vinyloxyethoxy) ethyl acrylate may be referred to as VEEA.

The content of the vinyl ether group-containing (meth) acrylate contained in the clear ink is preferably 0.1% by mass or more and 10.0% by mass or less, more preferably, with respect to the total amount of the polymerizable compounds contained in the clear ink. Is 1.0% by mass or more and 3.0% by mass or less. According to this, the viscosity of the clear ink is reduced, and the ejection stability of the clear ink from the inkjet head is improved. In addition, the curability of the clear ink is also improved.

The content of the vinyl ether group-containing (meth) acrylate contained in the clear ink is preferably 0.1% by mass or more and 10.0% by mass or less, and more preferably 1.0% by mass, based on the total amount of the clear ink. It is 3.0% by mass or less. According to this, the viscosity of the clear ink is reduced, and the ejection stability from the inkjet head is improved.

1.1.1.2.2.2. Polyfunctional (meth) acrylate The polyfunctional (meth) acrylate is not particularly limited, and is, for example, dipropylene glycol diacrylate (DPGDA), diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, or tetraethylene glycol. Di (meth) acrylate, polyethylene glycol di (meth) acrylate, dipropylene glycol dimethacrylate, 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-tricyclodecandi (meth) acrylate, EO (ethylene) of bisphenol A Oxide) adduct Di (meth) acrylate, PO (propylene oxide) adduct di (meth) acrylate of bisphenol A, neopentyl glycol di (meth) acrylate of hydroxypivalate, polytetramethylene glycol di (meth) acrylate, etc. Bifunctional (meth) acrylate; trimethylolpropantri (meth) acrylate, EO-modified trimethylolpropanthry (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) Acrylate, Ditrimethylol Propanetetra (meth) Acrylate, Glycerin Propoxytri (Meta) Acrylate, Caprolactone Modified Trimethylol Propantri (Meta) Acrylate, Pentaerythritol ethoxytetra (Meta) Acrylate, and Caprolactam Modified Dipentaerythritol Hexa (Meta) Acrylate Examples thereof include polyfunctional (meth) acrylates having three or more functionalities such as.

The content of the polyfunctional (meth) acrylate contained in the clear ink is preferably 0.1% by mass or more and 10.0% by mass or less, more preferably 0.1% by mass or more, based on the total amount of the polymerizable compounds contained in the clear ink. It is 1.0% by mass or more and 3.0% by mass or less. When the content of the polyfunctional (meth) acrylate is 0.1% by mass or more, the scratch resistance of the clear ink coating film is improved. When the content of the polyfunctional (meth) acrylate is 10.0% by mass or less, the stretchability and adhesion of the clear ink coating film are improved.

The content of the polyfunctional (meth) acrylate contained in the clear ink is preferably 0.1% by mass or more and 10.0% by mass or less, more preferably 1.0% by mass, based on the total amount of the clear ink. % Or more and 3.0% by mass or less. When the content of the polyfunctional (meth) acrylate with respect to the total amount of the clear ink is 0.1% by mass or more, the scratch resistance of the coating film of the clear ink is improved. When the content of the polyfunctional (meth) acrylate with respect to the total amount of the clear ink is 10.0% by mass or less, the stretchability and adhesion of the coating film of the clear ink are improved.

1.1.1.3. Polymerizable monomer A
The polymerizable compound contained in the clear ink according to the present embodiment may contain a polymerizable monomer A having the following characteristics. According to this, when a clear ink coating film is formed on the color ink coating film, the glossiness of the entire coating film is improved. The polymerizable monomer A may be the monofunctional monomer described above or a polyfunctional monomer.

The heavy synthetic monomer A has the characteristics of bulkiness of the molecular structure described below. The volume defined by the Van-der-Wals radius of the polymerizable monomer A is 0.26 cubic nm or more, preferably 0.27 cubic nm or more, and more preferably 0.28 cubic nm or more. The upper limit of the volume defined by the Van-der-Wals radius of the polymerizable monomer A is not particularly limited, but is preferably 0.60 cubic nm or less, and more preferably 0.55 cubic nm or less. Even more preferably, it is 0.50 cubic nm or less.

The area of the polysynthetic monomer A in the height direction with respect to the long side defined by the Van-der-Wals radius is 0.25 square nm or more, preferably 0.27 square nm or more, and more preferably 0. It is 29 square nm or more. Further, the upper limit of the area of the polymerizable monomer A in the height direction with respect to the long side defined by the Van-der-Wals radius is not particularly limited, but is preferably 0.50 square nm or less, and more preferably 0. It is 45 square nm or less, and even more preferably 0.40 square nm or less. Since the molecular structure of the polymerizable monomer A has the above-mentioned bulkiness characteristic, the glossiness of the coating film of the clear ink can be improved.

Here, the area in the height direction with respect to the volume and the long side, which is defined by the Van-der-Wals radius, is the area in the height direction with respect to the volume and the long side in the molecular structure having the lowest energy among the structural isomers of the molecule. Obtained as the area. For the identification of the three-dimensional shape defined by the Van-der-Wals radius of the molecule and the calculation of the volume and the area in the height direction with respect to the long side based on the three-dimensional shape, known software such as thermodynamic physical property estimation software can be adopted. Is.

The volume defined by the Van-der-Wals radius is a molecule in a state of floating in a vacuum approximated from a chemical formula, and the volume of the molecule formed by the Van-der-Wals radius of each atom constituting the molecule. The three-dimensional shape, that is, the volume of the cavity. The long side defined by the Van-der-Wals radius is the longest side in the three-dimensional shape. The long side is obtained by modeling the structure in which the molecule is most stable and calculating the distance between the farthest terminal skeleton atoms among the terminal skeleton atoms such as carbon, oxygen, and nitrogen. Further, the area in the height direction with respect to the long side is a value obtained by dividing the volume by the long side, and is an index of the area in the plane orthogonal to the long side.

The polysynthetic monomer A is not particularly limited, and for example, dicyclopentenyl acrylate (DCPA), isobornyl acrylate (IBXA), isobornyl methacrylate, 3,3,5-trimethylcyclohexyl acrylate (TMCHA), and the like. Monofunctional monomers such as tertbutylcyclohexanol acrylate (TBCHA), isononyl acrylate (INAA), lauryl acrylate (LA), 2-hydroxy-3phenoxypropyl acrylate, and polyfunctional monomers such as dipropylene glycol diacrylate (DPGDA) Can be mentioned.

The content of the polymerizable monomer A contained in the clear ink is preferably 80% by mass or more, more preferably 83% by mass or more, still more preferably 83% by mass, based on the total amount of the polymerizable compounds contained in the clear ink. It is 85% by mass or more. According to this, the glossiness of the coating film of the clear ink can be further improved. The upper limit of the content of the polymerizable monomer A is not particularly limited, but is preferably 95% by mass or less, more preferably 92% by mass or less, based on the total amount of the polymerizable compounds contained in the clear ink. Even more preferably, it is 90% by mass or less. According to this, it is possible to suppress the odor of the coating film of the cured clear ink while improving the curability of the clear ink.

The content of the polymerizable monomer A contained in the clear ink is 70% by mass or more, preferably 73% by mass or more, and more preferably 78% by mass or more, based on the total amount of the clear ink. According to this, the glossiness of the coating film of the clear ink can be further improved. The upper limit of the content of the polymerizable monomer A is not particularly limited, but is preferably 90% by mass or less, more preferably 87% by mass or less, based on the total amount of the polymerizable compounds contained in the clear ink. Even more preferably, it is 85% by mass or less. According to this, it is possible to suppress the odor of the coating film of the cured clear ink while improving the curability of the clear ink.

1.1.2. Photopolymerization Initiator The photopolymerization initiator has a function of producing an active species by irradiation with radiation and advancing the polymerization reaction of the polymerizable compound by the active species. The active species resulting from the photopolymerization initiator are, specifically, radicals, acids, bases and the like. The photopolymerization initiator is not particularly limited as long as it has the above functions, but for example, an acylphosphine oxide-based photopolymerization initiator, an alkylphenone-based photopolymerization initiator, a titanosen-based photopolymerization initiator, and a thioxanthone-based light. Known photopolymerization initiators such as polymerization initiators can be mentioned. Among these, acylphosphine oxide-based photopolymerization initiators and thioxanthone-based photopolymerization initiators are preferable. By using such a photopolymerization initiator, the curability of the clear ink, particularly the curability of the UV-LED (ultraviolet light emitting diode) in the light curing process, is improved. One type of photopolymerization initiator may be used alone, or two or more types may be used in combination. In particular, an acylphosphine oxide-based photopolymerization initiator and a thioxanthone-based photopolymerization initiator may be used in combination. Is preferable.

The acylphosphine oxide-based photopolymerization initiator is not particularly limited, and for example, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis (2,4,6-trimethylbenzoyl) -phenylphosphin oxide, bis- (2,6-dimethoxybenzoyl) -2,4,4-trimethylpentylphosphine oxide and the like can be mentioned.

Commercially available products of such an acylphosphine oxide-based photopolymerization initiator include, for example, IRGACURE (registered trademark) 819 (bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide) and IRGACURE manufactured by BASF. 1800 (a mixture of bis- (2,6-dimethoxybenzoyl) -2,4,4-trimethylpentylphosphine oxide and 1-hydroxy-cyclohexyl-phenylketone in a mass ratio of 25:75), IRGACURE TPO (2, 4,6-trimethylbenzoyldiphenylphosphine oxide) and the like.

The content of the photopolymerization initiator contained in the clear ink is preferably 3% by mass or more and 12% by mass or less, more preferably 5% by mass or more and 11% by mass or less, and further, with respect to the total amount of the clear ink. More preferably, it is 7% by mass or more and 10% by mass or less. According to this, the curability of the clear ink is improved, and the solubility of the photopolymerization initiator is ensured.

1.1.3. Other Additives The clear ink may further contain other additives such as polymerization inhibitors, slip agents, photosensitizers and the like, if desired.

11.3.1. Polymerization inhibitor The polymerization inhibitor has a function of suppressing the unintended progress of the polymerization reaction of the polymerizable compound during storage and improving the storage stability of the clear ink. One type of polymerization inhibitor may be used alone, or two or more types may be used in combination.

The polymerization inhibitor is not particularly limited, but is, for example, 4-methoxyphenol (MEHQ), 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl, hydroquinone, cresol, t-butylcatechol, 3 , 5-Di-t-butyl-4-hydroxytoluene, 2,2'-methylenebis (4-methyl-6-t-butylphenol), 2,2'-methylenebis (4-ethyl-6-butylphenol), and 4 , 4'-thiobis (3-methyl-6-t-butylphenol), hindered amine compounds and the like.

The content of the polymerization inhibitor contained in the clear ink is preferably 0.05% by mass or more and 1.00% by mass or less, and more preferably 0.05% by mass or more and 0.50 by mass, based on the total amount of the clear ink. It is mass% or less.

11.3.2. Slip agent The slip agent has a function of improving the wettability of the clear ink with respect to the recording medium and improving the adhesion. One type of slip agent may be used alone, or two or more types may be used in combination.

As the slip agent, a silicone-based surfactant is preferable, and a polyester-modified silicone or a polyether-modified silicone is more preferable. As these slip agents, commercially available products can be adopted, for example, polyester-modified silicones such as BYK®-347, -348, BYK-UV3500, -3510, -3530, BYK-Adaptives & Instruments, Inc. Examples include polyether-modified silicones such as 3570.

The content of the slip agent contained in the clear ink is preferably 0.01% by mass or more and 2.00% by mass or less, and more preferably 0.05% by mass or more and 1.00% by mass with respect to the total amount of the clear ink. % Or less.

11.3.3. Photosensitizer The photosensitizer has a function of absorbing radiation to be in an excited state and promoting the generation of active species from the photopolymerization initiator. One type of photosensitizer may be used alone, or two or more types may be used in combination.

Photosensitizers include aliphatic amines, aromatic group-containing amines, piperidine, reaction products of epoxy resins and amines, amine compounds such as triethanolamine triacrylate, and ureas such as allylthiourea and o-tolylthiourea. Compounds, sulfur compounds such as sodium diethyldithiophosphate, soluble salts of aromatic sulfinic acid, nitrile compounds such as N, N-diethyl-p-aminobenzonitrile, tri-n-butylphosphine, sodium diethyldithiophosphide Phosphorus compounds such as Michler ketone, N-nitrisohydroxylamine derivatives, oxazolidine compounds, tetrahydro-1,3-oxazine compounds, nitrogen compounds such as formaldehyde or condensates of acetaldehyde and diamine, chlorine compounds such as carbon tetrachloride and hexachloroethane. And so on.

When a photosensitizer is used for the clear ink, the content is preferably 0.1% by mass or more and 3.0% by mass or less with respect to the total amount of the clear ink.

1.2. Color Ink The color ink according to the present embodiment contains a polymerizable compound, a photopolymerization initiator, and a coloring material. The color ink is used for coloring a recording medium or forming an image or the like on a recording medium. Hereinafter, the components contained in the color ink of the present embodiment will be described.

1.2.1. Polymerizable Compounds The polymerizable compound includes a monofunctional monomer having one polymerizable functional group, a polyfunctional monomer having a plurality of polymerizable functional groups, and an oligomer having one or more polymerizable functional groups. Each of these polymerizable compounds may be used alone or in combination of two or more.

In the color ink of the present embodiment, the weighted average of the SP values of each polymerizable compound, weighted by the mass ratio of each content of each polymerizable compound, is 9.5 to 10.0. When the weighted average of the SP values is within the above range, the adhesion to recording media made of various materials can be improved. The weighted average of the SP value of the polymerizable compound contained in the color ink is calculated in the same manner as the weighted average of the SP value of the polymerizable compound of the clear ink described above.

1.2.1.1. Monofunctional Monomer The polymerizable compound contained in the color ink contains a monofunctional monomer. The monofunctional monomer is not particularly limited, but for example, a monofunctional (meth) acrylate having a crosslinked condensed ring structure, a saturated aliphatic group-containing monofunctional (meth) acrylate, a nitrogen-containing monofunctional monomer, and an aromatic group-containing monofunctional monomer. Can be mentioned. Further, if necessary, other monofunctional monomers may be used in place of or in addition to the above monofunctional monomers. The polymerizable functional group contained in the monofunctional monomer is not particularly limited, but a known polymerizable functional group, particularly a polymerizable functional group having an unsaturated double bond between carbons, can be applied.

The content of the monofunctional monomer contained in the color ink is 90% by mass or more, preferably 95% by mass or more, based on the total amount of the polymerizable compounds contained in the color ink. According to this, the coating film of the color ink becomes flexible, and the adhesion and the stretchability can be improved. The upper limit of the content of the monofunctional monomer is not particularly limited, but is preferably 99% by mass or less, more preferably 98% by mass or less, and further, with respect to the total amount of the polymerizable compound contained in the color ink. More preferably, it is 97% by mass or less. According to this, the curability of the color ink is improved.

The content of the monofunctional monomer contained in the color ink is preferably 80% by mass or more, more preferably 85% by mass or more, based on the total amount of the color ink. According to this, the stretchability of the coating film of the color ink is improved. The upper limit of the content of the monofunctional monomer is preferably 95% by mass or less, more preferably 92% by mass or less, and even more preferably 90% by mass or less, based on the total amount of the color ink. .. According to this, the curability of the color ink is improved.

As monofunctional (meth) acrylates having a crosslinked condensed ring structure, saturated aliphatic group-containing monofunctional monomers, nitrogen-containing monofunctional monomers, aromatic group-containing monofunctional monomers, and other monofunctional monomers contained in color inks. Can be used in the same manner as clear ink. The monofunctional monomer contained in the color ink may include those corresponding to the above-mentioned polymerizable monomer A.

The content of the monofunctional (meth) acrylate having a crosslinked condensed ring structure contained in the color ink is preferably 3% by mass or more and 50% by mass or less, more preferably 5% by mass, based on the total amount of the polymerizable compound. It is 40% by mass or less, and more preferably 10% by mass or more and 30% by mass or less. According to this, the adhesion of the coating film of the color ink is improved.

The content of the monofunctional (meth) acrylate having a crosslinked condensed ring structure contained in the color ink is preferably 3% by mass or more and 50% by mass or less, and more preferably 5% by mass or more, based on the total amount of the color ink. It is 40% by mass or less, and even more preferably 7% by mass or more and 30% by mass or less. According to this, the adhesion of the coating film of the color ink is improved.

The content of the saturated aliphatic group-containing monofunctional (meth) acrylate contained in the color ink is preferably 15% by mass or more and 45% by mass or less, and more preferably 15% by mass or more, based on the total amount of the polymerizable compound. It is 40% by mass or less, and even more preferably 20% by mass or more and 35% by mass or less. According to this, the adhesion of the coating film of the color ink is improved.

The content of the saturated aliphatic group-containing monofunctional (meth) acrylate contained in the color ink is preferably 5% by mass or more and 40% by mass or less, and more preferably 10% by mass or more and 45% by mass, based on the total amount of the color ink. It is 5% by mass or less, and more preferably 15% by mass or more and 30% by mass or less. According to this, the adhesion of the coating film of the color ink is improved.

The content of the nitrogen-containing monofunctional monomer contained in the color ink is preferably 3% by mass or more and 17% by mass or less, and more preferably 5% by mass or more and 15% by mass, based on the total amount of the polymerizable compounds contained in the color ink. It is 8% by mass or less, and more preferably 8% by mass or more and 12% by mass or less. According to this, the adhesion of the coating film of the color ink is improved.

The content of the nitrogen-containing monofunctional monomer contained in the color ink is preferably 3% by mass or more and 17% by mass or less, and more preferably 5% by mass or more and 15% by mass or less, based on the total amount of the color ink. Even more preferably, it is 8% by mass or more and 12% by mass or less. According to this, the adhesion of the coating film of the color ink is improved.

The content of the aromatic group-containing monofunctional monomer contained in the color ink is preferably 1% by mass or more and 70% by mass or less, more preferably 5% by mass, based on the total amount of the polymerizable compounds contained in the color ink. It is 60% by mass or less, and more preferably 10% by mass or more and 50% by mass or less. According to this, the solubility of the photopolymerization initiator is further improved, and the curability of the color ink is improved.

The content of the aromatic group-containing monofunctional monomer contained in the color ink is preferably 1% by mass or more and 60% by mass or less, and more preferably 5% by mass or more and 50% by mass or less, based on the total amount of the color ink. Yes, and even more preferably 10% by mass or more and 40% by mass. According to this, the solubility of the photopolymerization initiator is further improved, and the curability of the color ink is improved.

1.2.1.2. Polyfunctional Monomer The polymerizable compound contained in the color ink preferably contains a polyfunctional monomer. Examples of the polyfunctional monomer include vinyl ether group-containing (meth) acrylate and polyfunctional (meth) acrylate. The polyfunctional monomer is not limited to the above. As the polyfunctional monomer, the same one as the clear ink can be adopted. The polyfunctional monomer contained in the color ink may include the one corresponding to the above-mentioned polymerizable monomer A.

The content of the polyfunctional monomer contained in the color ink is preferably 0.01% by mass or more and 10.00% by mass or less, more preferably 1.00% by mass, based on the total amount of the polymerizable compounds contained in the color ink. It is 5.00% by mass or more and 5.00% by mass or less. When the content of the polyfunctional monomer is 0.01% by mass or more, the scratch resistance of the coating film of the color ink is improved. Further, when the content of the polyfunctional monomer is 10.00% by mass or less, the stretchability and adhesion of the coating film are improved.

The content of the polyfunctional monomer contained in the color ink is preferably 0.01% by mass or more and 10.00% by mass or less, and more preferably 1.00% by mass or more and 5.00 with respect to the total amount of the color ink. It is mass% or less. When the content of the polyfunctional monomer is 0.01% by mass or more, the scratch resistance of the coating film of the color ink is improved. Further, when the content of the polyfunctional monomer is 10.00% by mass or less, the stretchability and adhesion of the coating film of the color ink are improved.

The content of the vinyl ether group-containing (meth) acrylate contained in the color ink is preferably 1% by mass or more and 10% by mass or less, more preferably 2% by mass, based on the total amount of the polymerizable compounds contained in the color ink. It is 5% by mass or less. According to this, the viscosity of the color ink is reduced, and the ejection stability of the color ink from the inkjet head is improved.

The content of the vinyl ether group-containing (meth) acrylate contained in the color ink is preferably 1% by mass or more and 10% by mass or less, more preferably 2% by mass, based on the total amount of the polymerizable compounds contained in the color ink. It is 5% by mass or less. According to this, the viscosity of the color ink is reduced, and the ejection stability of the color ink from the inkjet head is improved.

The content of the polyfunctional (meth) acrylate contained in the color ink is preferably 1% by mass or more and 10% by mass or less, and more preferably 2% by mass or more, based on the total amount of the polymerizable compounds contained in the color ink. It is 5% by mass or less. When the content of the polyfunctional (meth) acrylate is 1% by mass or more, the scratch resistance of the coating film of the color ink is improved. Further, when the content of the polyfunctional (meth) acrylate is 10% by mass or less, the stretchability and adhesion of the coating film of the color ink are improved.

The content of the polyfunctional (meth) acrylate contained in the color ink is preferably 1% by mass or more and 10% by mass or less, and more preferably 2% by mass or more and 5% by mass or less, based on the total amount of the color ink. .. When the content of the polyfunctional (meth) acrylate is 1% by mass or more, the scratch resistance of the coating film of the color ink is improved. Further, when the content of the polyfunctional (meth) acrylate is 10% by mass or less, the stretchability and adhesion of the coating film of the color ink are improved.

1.2.2. Photopolymerization Initiator As the photopolymerization initiator contained in the color ink, the same photopolymerization initiator as the clear ink can be adopted. The content of the photopolymerization initiator contained in the color ink is preferably 3% by mass or more and 12% by mass or less, more preferably 5% by mass or more and 10% by mass or less, and further, with respect to the total amount of the color ink. More preferably, it is 7% by mass or more and 10% by mass or less. According to this, the curability of the color ink is improved, and the solubility of the photopolymerization initiator is ensured.

1.2.3. Coloring material The coloring material has a function of coloring the coating film formed by the color ink. By coloring the coating film of the color ink, it is possible to color the recording medium and form a color image or the like on the recording medium. Examples of the coloring material contained in the color ink include pigments and dyes.

1.2.3.1. By using a pigment as the pigment coloring material, the light resistance of the coloring material in the coating film of the color ink can be improved. As the pigment, either an inorganic pigment or an organic pigment can be adopted. One type of pigment may be used alone, or two or more types may be used in combination.

As the pigment, either a known organic pigment or an inorganic pigment can be adopted. Examples of organic pigments include azo pigments such as azo lake pigments, insoluble azo pigments, condensed azo pigments, and chelate azo pigments, phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, and isoindolinone pigments. , Isoindrin pigments, quinophthalone pigments, polycyclic pigments such as diketopyrrolopyrrole pigments, dye lake pigments such as basic dye type lakes and acidic dye type lakes, nitro pigments, nitroso pigments, aniline blacks, daylight fluorescent pigments, etc. Can be mentioned. Examples of the inorganic pigment include metal oxide pigments such as titanium dioxide, zinc oxide and chromium oxide, and carbon black. Further, a bright pigment such as a pearl pigment or a metallic pigment may be used.

Examples of the black pigment include C.I. I. (Color Index Generic Name) Pigment Black 1, 7, 11 can be mentioned. Among these, C.I. I. It is preferable to use carbon black, which is Pigment Black 7.

Specific examples of carbon black include No. 1 of Mitsubishi Chemical Corporation. 2300, No. 900, MCF88, No. 33, No. 40, No. 45, No. 52, MA7, MA8, MA100, No. 2200B, etc., Columbia Carbon, Inc., Raven® 5750, 5250, 5000, 3500, 1255, 700, etc., CABOT, Inc., Rega1® 400R, 330R, 660R, Mogul® L, Monarch ( Registered Trademarks) 700, 800, 880, 900, 1000, 1100, 1300, 1400, etc. Degussa's Color Black FW1, FW2, FW2V, FW18, FW200, S150, S160, S170, Printex® 35, U , V, 140U, Special Black 6, 5, 4A, 4.

Examples of the white pigment include C.I. I. Pigment White 6, 18 and 21 can be mentioned.

Examples of the yellow pigment include C.I. I. Pigment Yellow 1,2,3,4,5,6,7,10,11,12,13,14,16,17,24,34,35,37,53,55,65,73,74,75, 81, 83, 93, 94, 95, 97, 98, 99, 108, 109, 110, 113, 114, 117, 120, 124, 128, 129, 133, 138, 139, 147, 151, 153, 154 155,167,172,180 can be mentioned.

Examples of magenta color pigments include C.I. I. Pigment Red 1,2,3,4,5,6,7,8,9,10,11,12,14,15,16,17,18,19,21,22,23,30,31,32, 37, 38, 40, 41, 42, 48 (Ca), 48 (Mn), 57 (Ca), 57: 1,88,112,114,122,123,144,146,149,150,166,168 , 170, 171, 175, 176, 177, 178, 179, 184, 185, 187, 202, 209, 219, 224, 245, or C.I. I. Pigment Violet 19, 23, 32, 33, 36, 38, 43, 50.

Examples of the cyan pigment include C.I. I. Pigment Blue 1,2,3,15,15: 1,15: 2,15: 3,15:34,15: 4,16,18,22,25,60,65,66, C.I. I. Bat blue 4,60 can be mentioned.

Examples of pigments for colors other than the above include C.I. I. Pigment Green 7, 10, C.I. I. Pigment Brown 3, 5, 25, 26, C.I. I. Pigment Orange 1,2,5,7,13,14,15,16,24,34,36,38,40,43,63.

One type of the above pigment may be used alone, or two or more types may be used in combination. When a pigment is used, a dispersant described later may be used in combination. The average particle size of the pigment is preferably 300 nm or less, more preferably 50 nm or more and 200 nm or less. When the average particle size of the pigment is within the above range, the color ink of the radiation-curable inkjet ink is improved in ejection stability and dispersion stability, and the image quality of the image formed on the recording medium is excellent. Can be. The average particle size referred to here refers to a volume-based particle size distribution (50%) measured by a dynamic light scattering method.

The content of the pigment contained in the color ink is more than 0.2% by mass and 20% by mass or less, preferably 1% by mass or more and 20% by mass or less, and more preferably 1% by mass with respect to the total amount of the color ink. % Or more and 15% by mass or less, and even more preferably 1% by mass or more and 10% by mass or less.

1.2.3.2. A dye may be used as the dye coloring material. The dye is not particularly limited, but an acid dye, a direct dye, a reactive dye, and a basic dye can be used. One type of dye may be used alone, or two or more types may be used in combination.

The dye is not particularly limited, but for example, C.I. I. Acid Yellow 17, 23, 42, 44, 79, 142, C.I. I. Acid Red 52,80,82,249,254,289, C.I. I. Acid Blue 9,45,249, C.I. I. Acid Black 1,2,24,94, C.I. I. Hood Black 1, 2, C.I. I. Direct Yellow 1,12,24,33,50,55,58,86,132,142,144,173, C.I. I. Direct Red 1,4,9,80,81,225,227, C.I. I. Direct Blue 1,2,15,71,86,87,98,165,199,202, C.I. I. Direct Black 19, 38, 51, 71, 154, 168, 171, 195, C.I. I. Reactive Red 14, 32, 55, 79, 249, C.I. I. Reactive Black 3, 4, 35 can be mentioned.

When a dye is used for the color ink, the content of the dye is more than 0.2% by mass and 20.0% by mass or less, preferably 1.0% by mass or more and 20.0% by mass, based on the total amount of the color ink. It is more preferably 1.0% by mass or more and 15.0% by mass or less, and even more preferably 1.0% by mass or more and 10.0% by mass or less.

1.2.4. Other Additives The clear ink may further contain other additives such as dispersants, polymerization inhibitors, slip agents and photosensitizers, if desired.

1.2.4.1. Dispersant The dispersant has a function of imparting dispersibility to a coloring material such as a pigment in a color ink. By using the dispersant, pigments and the like are stably dispersed in the color ink, and the sedimentation resistance during storage and the ejection stability from the inkjet head are improved.

The dispersant is not particularly limited, and examples thereof include known dispersants commonly used for preparing a pigment dispersion such as a polymer dispersant. Specific examples of the dispersant include polyoxyalkylene polyalkylene polyamines, vinyl polymers and copolymers, acrylic polymers and copolymers, polyesters, polyamides, polyimides, polyurethanes, amino polymers, silicon-containing polymers, sulfur-containing polymers, and fluorine-containing polymers. Examples thereof include those containing one or more types of polymers and epoxy resins as main components. One type of dispersant may be used alone, or two or more types may be used in combination.

Commercially available products may be used as the polymer dispersant, for example, Ajinomoto Fine-Techno's Ajispar (registered trademark) series, Lubrizol's Solsperse (registered trademark) series such as Solspace36000, BYK Adaptives & Instruments' Disperbic series, etc. Kusumoto Kaseisha's Disparon (registered trademark) series can be mentioned.

1.2.4.2. Polymerization inhibitor As the polymerization inhibitor, the same one as that of clear ink can be adopted. One type of polymerization inhibitor may be used alone, or two or more types may be used in combination. The content of the polymerization inhibitor contained in the color ink is preferably 0.05% by mass or more and 1.00% by mass or less, and more preferably 0.05% by mass or more and 0.50 by mass, based on the total amount of the color ink. It is mass% or less.

1.2.4.3. Slip agent A slip agent similar to that of clear ink can be used. One type of slip agent may be used alone, or two or more types may be used in combination. The content of the slip agent contained in the color ink is preferably 0.01% by mass or more and 2.00% by mass or less, and more preferably 0.05% by mass or more and 1.00% by mass with respect to the total amount of the color ink. % Or less.

1.2.4.4. Photosensitizer As the photosensitizer, the same one as that of clear ink can be adopted. One type of photosensitizer may be used alone, or two or more types may be used in combination. When the photosensitizer is used for the color ink, the content is preferably 0.01% by mass or more and 5.00% by mass or less with respect to the total amount of the color ink.

1.3. Method for preparing clear ink and color ink In the preparation of clear ink and color ink, each of the above-mentioned components is mixed, and sufficient stirring is performed so that each component is uniformly mixed. In the present embodiment, at least one of ultrasonic treatment and heating treatment is applied to a mixture of a photopolymerization initiator and at least a part of the polymerizable compound in the preparation process. As a result, in the prepared color ink and clear ink, dissolved oxygen is reduced, and ejection stability and storage stability can be improved. Here, in the following description, color ink and clear ink may be collectively referred to as ink.

The mixture may contain at least a photopolymerization initiator and a part of the polymerizable compound, may further contain other components, or may contain all the components of the ink.

1.4. Physical Characteristics of Ink The viscosity of the ink at 20 ° C. is preferably 22 mPa · s (millipascal seconds) or more and 28 mPa · s or less, more preferably 22 mPa · s or more and 26 mPa · s or less, and even more preferably 22 mPa · s. It is s or more and 24 mPa · s or less. According to this, an appropriate amount of ink is ejected from the inkjet head, and it is possible to suppress flight bending and scattering of ink droplets. To measure the viscosity of the ink, use a viscoelasticity tester MCR-300 manufactured by Pysica to raise the Shear Rate from 10 to 1000 in an environment of 20 ° C. to increase the viscosity when the Shear Rate is 200. It can be measured by reading.

The surface tension of the ink at 20 ° C. is preferably 20 mN / m or more and 40 mN / m or less. According to this, it becomes difficult for the ink to get wet with the nozzle surface of the liquid-repellent inkjet head. Therefore, the ink is ejected normally and in an appropriate amount from the inkjet head, and the flying bending and scattering of the ink droplets can be suppressed. The surface tension of the ink is measured by checking the surface tension when the platinum plate is wetted with the ink in an environment of 20 ° C. using an automatic surface tension meter CBVP-Z manufactured by Kyowa Interface Science Co., Ltd. It is possible.

2.1. Inkjet recording device Next, a serial type inkjet printer will be illustrated as an inkjet recording device used in the inkjet method of the present embodiment described later. FIG. 1 is a schematic perspective view showing a configuration of an inkjet printer according to an embodiment.

The inkjet printer 1 of this embodiment is a so-called serial type printer. A serial printer is a printer in which an inkjet head is mounted on a carriage that moves in a predetermined direction, and printing is performed while the inkjet head moves as the carriage moves. Hereinafter, the inkjet printer 1 is also simply referred to as a printer 1.

As shown in FIG. 1, the printer 1 includes an inkjet head 3, a carriage 4, a main scanning mechanism 5, a platen roller 6, a light source 11, a control unit (not shown) that controls the operation of the entire printer 1. The carriage 4 is equipped with an inkjet head 3 and a light source 11, and ink cartridges 7a, 7b, 7c, 7d, and 7e as containers containing ink supplied to the inkjet head 3 can be attached and detached.

The main scanning mechanism 5 has a timing belt 8 connected to the carriage 4, a motor 9 for driving the timing belt 8, and a guide shaft 10. The guide shaft 10 is installed as a support member of the carriage 4 in the main scanning direction, which is the scanning direction of the carriage 4. The carriage 4 is driven by a motor 9 via a timing belt 8 and can reciprocate along the guide shaft 10. As a result, the main scanning mechanism 5 reciprocates the carriage 4 in the main scanning direction.

The platen roller 6 conveys the recording medium 2 to which the ink is applied in the sub-scanning direction orthogonal to the main scanning direction. Therefore, the recording medium 2 is conveyed in the sub-scanning direction that substantially coincides with the length direction of the recording medium 2. The carriage 4 can reciprocate in the main scanning direction which substantially coincides with the width direction of the recording medium 2. Therefore, the inkjet head 3 and the light source 11 can scan relative to the recording medium 2 in the main scanning direction and the sub-scanning direction.

The ink cartridges 7a, 7b, 7c, 7d, and 7e are five independent ink cartridges. The ink cartridges 7a, 7b, 7c, 7d, and 7e contain the above-mentioned color ink and clear ink. For example, the ink cartridges 7a, 7b, 7c, 7d, and 7e can be used as an ink set by individually accommodating color inks having colors such as black, cyan, magenta, and yellow, and clear inks. .. In FIG. 1, the number of ink cartridges is set to 5, but the number is not limited to this. The bottoms of the ink cartridges 7a, 7b, 7c, 7d, and 7e are provided with supply ports (not shown) for supplying the contained ink to the inkjet head 3.

For the members of the ink cartridges 7a to 7e, a forming material that is unlikely to cause evaporation or deterioration of the ink component or deterioration of the member due to the ink component is used. In the present embodiment, an ink cartridge has been exemplified as an ink container, but the present invention is not limited to this, and an ink pack, an ink bottle, or the like may be used as the ink container in addition to the ink cartridge.

An inkjet head 3 and a light source 11 are arranged on the side of the carriage 4 facing the recording medium 2. The inkjet head 3 has a nozzle surface (not shown) on the surface facing the recording medium 2. A polymer film containing a fluorine compound and a silicone compound, an eutectoid plating film containing nickel and a fluorine compound, and the like may be formed as a liquid repellent film on the nozzle surface. Further, although not shown, nozzle rows composed of a plurality of ejection nozzles are individually arranged on the nozzle surface corresponding to each ink. Each ink is supplied to the inkjet head 3 from the ink cartridges 7a, 7b, 7c, 7d, and 7e, respectively, and is ejected as droplets from the ejection nozzle by an actuator (not shown) in the inkjet head 3. The ejected ink droplets land on the recording medium 2 and are applied.

In the present embodiment, the printer 1 includes one inkjet head 3 for ejecting color ink and clear ink, but the printer 1 is not limited to this. The printer 1 may individually include an inkjet head that ejects color ink and an inkjet head that ejects clear ink.

In the inkjet head 3, a piezoelectric element is used as an actuator as a driving means, but the present invention is not limited to this. As the driving means, for example, an electromechanical conversion element that displaces a diaphragm as an actuator by electrostatic adsorption, or an electrothermal conversion element that ejects ink as droplets by bubbles generated by heating may be used.

The light source 11 is arranged side by side with the inkjet head 3 in the main scanning direction. The light source 11 is a radiation irradiation device, and includes, for example, a light emitting element (not shown) such as a UV-LED (ultraviolet light emitting diode). The radiation emitted from the light source 11 is not limited to ultraviolet rays, and may be infrared rays, electron beams, visible rays, X-rays, or the like. Here, as the light source 11, a lamp or the like may be used instead of a light emitting element such as an LED (light emitting diode) or LD (semiconductor laser), but a light emitting element may be used from the viewpoint of miniaturization and cost reduction. preferable.

When the ink droplets applied to the recording medium 2 are irradiated with light from the light source 11, the photopolymerization reaction of the polymerizable compound in the ink proceeds, and the ink droplets are cured to form the ink. The coating film is formed. As a result, the recording medium 2 is colored, images, colors, characters, patterns and the like are formed on the recording medium 2, and a clear ink coating film is formed.

Here, the light source 11 is not limited to being arranged side by side with respect to the inkjet head 3 in the main scanning direction. The light source 11 is opposite to the direction in which the recording medium 2 is conveyed to the inkjet head 3. It may be offset in the sub-scanning direction. The light source 11 is not limited to being arranged on the carriage 4, and may be separate from the carriage 4.

In the present embodiment, the on-carriage type printer 1 is exemplified as the inkjet recording device, but the present invention is not limited to this. The inkjet recording device may be, for example, an off-carriage type such as a large format printer in which the ink container is not mounted on the carriage. Further, the inkjet recording apparatus used in the present embodiment is not limited to a serial printer, and a line in which the inkjet head is formed as wide as the width of the recording medium 2 or more and the inkjet head prints without moving. It may be a head printer.

2.2. Recording medium The recording medium 2 is appropriately selected depending on the intended use of the printed matter produced from the ink and the recording medium. The material for forming the recording medium 2 is not particularly limited, but for example, polyvinyl chloride (PVC), polyethylene terephthalate, polypropylene, polyethylene, polycarbonate, cellulose diacetate, cellulose triacetate, cellulose propionate, cellulose butyrate, cellulose acetate butyrate, Examples thereof include plastics such as cellulose nitrate, polystyrene and polyvinyl acetal, and those whose surfaces are processed, glass, paper, metal, wood and the like. The ink set of the present embodiment can be suitably used for these recording media because the adhesion of polypropylene and polyethylene terephthalate to the recording medium is particularly improved.

The form of the recording medium 2 is not particularly limited, and examples thereof include a film, a sheet, a board, and a cloth. Since the ink set of the present embodiment has improved stretchability and scratch resistance, the ink coating film is less likely to be cracked or peeled off due to cutting or bending when the printed matter is post-processed for signage use. There is. In addition to this, the glossiness of the clear ink coating film is improved, so that the ink set of the present embodiment can be suitably used for signage applications.

3. 3. Inkjet method In the inkjet method according to the present embodiment, the ink set is used to eject color ink from the ink jet head 3 to apply it to the recording medium 2, and to apply the color ink to the recording medium 2. On the other hand, a first curing step of irradiating radiation, a second coating step of ejecting clear ink from the inkjet head 3 and applying the clear ink to a region containing the irradiated color ink in the recording medium 2, and a clear ink. Includes a leveling step of allowing the recording medium 2 coated with the ink to stand still, and a second curing step of irradiating the clear ink coated on the recording medium 2 with radiation. Hereinafter, each step included in the inkjet method of the present embodiment will be described with reference to FIG.

3.1. First coating step In the first coating step, color ink is ejected from the inkjet head 3 and coated on the recording medium 2. Specifically, the piezoelectric element is driven to eject the color ink filled in the pressure generating chamber of the inkjet head 3 from the ejection nozzle. Such a coating method is also called an inkjet method. At this time, a multipath may be used in which the reciprocating movement of the carriage 4 in the main scanning direction is repeated a plurality of times with respect to a predetermined position of the recording medium 2. That is, the transport of the recording medium 2 in the sub-scanning direction is stopped for a certain period of time to eject the color ink in multipath, and then the recording medium 2 is transported for a short distance and then the multipath is performed again.

By applying the color ink to the recording medium 2 while moving the inkjet head 3 relatively, a liquid layer of the color ink, which is a base for a desired image or the like, is formed on the recording medium 2.

3.2. First Curing Step In the first curing step, the liquid layer of the color ink applied to the recording medium 2 is irradiated with radiation from the light source 11 to cure the color ink on the recording medium 2, and the coating film of the color ink is formed. Form. Specifically, radiation is emitted from the light source 11 toward the recording medium 2 while moving the carriage 4 in the main scanning direction with respect to a predetermined position of the recording medium 2. The movement of the carriage 4 in the main scanning direction may be performed once or repeated. Further, the irradiation region of the radiation to the recording medium 2 may include a region coated with the color ink. By irradiation with radiation, the liquid layer of the color ink on the recording medium 2 is cured to form a coating film of the color ink. The first coating step and the first curing step may or may not be repeated for a specific position on the recording medium 2.

3.3. Second coating step In the second coating step, clear ink is ejected from the inkjet head 3 and coated on the recording medium 2. At this time, the region to which the clear ink is applied may include the region on the recording medium 2 on which the coating film of the color ink is formed. That is, the clear ink does not have to be applied to the region where the color ink coating film is not formed, or is included on substantially the entire surface of the recording medium 2 including the region where the color ink coating film is not formed. It may be applied in a solid form. As with the color ink in the first coating step, the second coating step may be multi-passed or may be single-passed without multi-passing. As a result, a liquid layer of clear ink is formed at least on the coating film of color ink.

3.4. Leveling Step The inkjet method preferably includes a leveling step of allowing the recording medium 2 coated with the clear ink to stand for a predetermined time between the second coating step and the second curing step described later. By providing the leveling step, the liquid layer of the clear ink is flattened on the coating film of the color ink. Therefore, after the liquid layer of the clear ink is flattened, a coating film of the clear ink is formed from the liquid layer in the second curing step described later. As a result, the smoothness of the clear ink coating film is increased, and the glossiness of the clear ink coating film is further improved.

The term "standing" as used herein means that the recording medium 2 coated with the clear ink in the second coating step is not irradiated with radiation in the second curing step. Therefore, in the leveling step, the recording medium 2 may be conveyed in the sub-scanning direction.

The standing time in the leveling step is preferably 1 second or more and 120 seconds or less, more preferably 2 seconds or more and 100 seconds or less, and even more preferably 4 seconds or more and 80 seconds or less. According to this, since the liquid layer of the clear ink is sufficiently flattened on the coating film of the color ink, the glossiness of the coating film of the clear ink is further improved.

When the leveling step is provided, the light source 11 is not driven in the pass for ejecting the clear ink from the inkjet head 3, and the light source 11 is driven without driving the inkjet head 3 after the pass for ejecting the clear ink. May be provided, and then the sub-scanning may be performed. Further, by arranging the light source 11 at a position shifted in the sub-scanning direction with respect to the inkjet head 3, sub-scanning is performed after the pass for applying the clear ink from the inkjet head 3, and the portion coated with the clear ink is subjected to sub-scanning. A path for irradiating radiation with the light source 11 may be provided. As a result, the coating film can be cured by the light source 11 after the inkjet composition is sufficiently leveled, so that the glossiness of the coating film is improved.

The leveling step can be omitted if the glossiness of the clear ink coating film is ensured. From the viewpoint of further improving the glossiness, it is preferable to provide a leveling step.

3.5. Second Curing Step In the second curing step, the liquid layer of the clear ink applied to the recording medium 2 is irradiated with radiation from the light source 11 to cure the clear ink, and a coating film of the clear ink is formed. Specifically, radiation is emitted from the light source 11 toward the recording medium 2 while moving the carriage 4 in the main scanning direction with respect to a predetermined position on the recording medium 2 including the coating film of the color ink. The movement of the carriage 4 in the main scanning direction may be performed once or repeated. Further, the irradiation region of the radiation to the recording medium 2 may include a region coated with clear ink. By irradiation with radiation, the liquid layer of clear ink on the recording medium 2 is cured to form a coating film of clear ink. The second coating step to the second curing step may or may not be repeated for a specific position on the recording medium 2.

4. Examples and Comparative Examples Hereinafter, the effects of the present invention will be described in more detail with reference to Examples and Comparative Examples. The present invention is not limited to the following examples.

4.1. Preparation of Clear Ink and Color Ink Tables 1 and 2 show the composition of each clear ink and each color ink, the type of polymerizable compound used, the compound name, the non-polymerizable monomer A, and the SP value of each polymerizable compound. It shows the glass transition temperature (Tg) of the homopolymer of each polymerizable compound, the parameters defined by the Van-der-Wals radius, and the content regarding the type of the polymerizable compound. In addition, in the composition column of Table 1 and Table 2, the unit of the numerical value is mass%, and it means that the column of -notation is not included. In addition, abbreviations are used for the names of the components in Tables 1 and 2. The abbreviation will be described later.

4.1.1. Preparation of Clear Ink According to the composition of clear ink 1 to clear ink 10 shown in Table 1, a polymerizable compound, a photopolymerization initiator, a polymerization inhibitor, and a slip agent are measured in a stainless steel mixture tank. It was. Then, using a mechanical stirrer, the mixture was stirred in an environment of about 20 ° C. for 1 hour to completely dissolve the solid content such as the photopolymerization initiator in the polymerizable compound. Then, filtration was carried out with a membrane filter having a pore size of 5 μm to prepare clear inks 1 to 10.

4.1.2. Preparation of color ink According to the composition of color ink 1 and color ink 4 shown in Table 2, some of the pigments, dispersants, and polymerizable compounds that are color materials are weighed and placed in a tank for bead mill dispersion. It was. Next, ceramic beads having a diameter of 1 mm were placed in the tank and dispersed by a bead mill to prepare a pigment dispersion liquid in which the pigment was dispersed in the polymerizable compound.

In addition to the pigment dispersion, the remaining polymerizable compounds, photopolymerization initiators, polymerization inhibitors, and slip agents other than the components blended in the pigment dispersion were weighed into a stainless steel mixture tank. .. Then, the mixture was stirred using a mechanical stirrer to completely dissolve the solid content such as the polymerizable compound in the polymerizable compound. Then, the pigment dispersion liquid was weighed in and stirred for another 1 hour in an environment of about 20 ° C. Then, filtration was carried out with a membrane filter having a pore size of 5 μm to prepare color ink 1 and color ink 4, respectively.

Details of the abbreviations used in Tables 1 and 2 are as follows.

Monofunctional monomer DCPA: Dicyclopentenyl acrylate. Hitachi Kaseisha IBXA: Isobornyl acrylate. Osaka Organic Chemical Industry Co., Ltd. TBCHA: tert-butylcyclohexanol acrylate. Product name SR217, Sartmer INAA: Isononyl acrylate. Osaka Organic Chemical Industry Co., Ltd. PEA: Phenoxyethyl acrylate. Product name Viscoat # 192, Osaka Organic Chemical Industry Co., Ltd. ACMO: Acroylmorpholin. KJ Chemicals Co., Ltd. Among the above-mentioned monofunctional monomers, those corresponding to the polymerizable monomer A are DCPA, IBXA, TBCHA, and INAA.

Polyfunctional monomer VEEA: 2- (2-vinyloxyethoxy) ethyl acrylate. Nippon Shokubai Co., Ltd. DPGDA: Dipropylene glycol diacrylate. Sartmer Co., Ltd. Of the above polyfunctional monomers, DPGDA corresponds to the polymerizable monomer A.

Photopolymerization initiator, IRGACURE 819: Trade name. Bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide. BASF / IRGACURE TPO: Product name. 2,4,6-trimethylbenzoyldiphenylphosphine oxide. BASF

Polymerization inhibitor ・ MEHQ: 4-methoxyphenol. Kanto Chemical Co., Inc.

Slip agent-BYK-UV3500: Polyester-modified polydimethylsiloxane having an acroyl group. BYK Adsives & Instruments

Pigment as a coloring material ・ PB 15: 3: C.I. I. Pigment Blue 15: 3

Dispersant-Solspace36000: Trade name. Polymer dispersant. Lubrizol

Further, in Tables 1 and 2, among the parameters defined by the Van-der-Wals radius, the numerical value of the volume is calculated by using the software COSMOtherm of MOLSIS, and the molecule is in a state of being floated in a vacuum. It is the volume of the cavity of the molecule formed by the Van-der-Wals radius of each atom constituting the molecule. Among the above parameters, the numerical value of the length of the long side is the longest side of the cavity used for calculating the volume. Among the above parameters, the area in the height direction is a numerical value obtained by dividing the volume by the length of the long side.

4.2. Ink sets and recorded matter Table 3 shows the contents of the ink sets of Examples 1 to 7 and Comparative Examples 1 to 6 and the evaluation results of the printed matter prepared using each ink set. Hereinafter, Examples 1 to 7 may be collectively referred to as Examples, and Comparative Examples 1 to 6 may be collectively referred to as Comparative Examples.

Here, the ink set of Comparative Example 1 uses clear ink 8. In the clear ink 8, the weighted average of the SP values of each polymerizable compound, which is weighted by the mass ratio of each content of each polymerizable compound, is 8.8, which is less than 9.0.

The ink set of Comparative Example 2 uses clear ink 9. In the clear ink 9, the weighted average of the SP values of each polymerizable compound, which is weighted by the mass ratio of each content of each polymerizable compound, is 8.3, which is less than 9.0 and less than 8.5. ..

The ink set of Comparative Example 3 uses clear ink 10. In the clear ink 10, the weighted average of the SP values of each polymerizable compound, which is weighted by the mass ratio of each content of each polymerizable compound, is 10.2, which is more than 10.0.

The ink set of Comparative Example 4 uses color ink 2. In the color ink 2, the weighted average of the SP values of each polymerizable compound, which is weighted by the mass ratio of each content of each polymerizable compound, is 8.9, which is less than 9.5.

The ink set of Comparative Example 5 uses color ink 3. In the color ink 3, the weighted average of the SP values of each polymerizable compound, which is weighted by the mass ratio of each content of each polymerizable compound, is 10.4, which is more than 10.0.

The ink set of Comparative Example 6 uses color ink 4. In the color ink 4, the content of the monofunctional monomer with respect to the total amount of the polymerizable compound contained in the color ink 4 is 88% by mass, which is less than 90% by mass.

4.3. Evaluation Each ink set of Examples and Comparative Examples was evaluated as described below, and the evaluation results are shown in Table 3.

4.3.1. Evaluation of PP Adhesion of Color Inks Each color ink was applied on a polypropylene (PP) board (manufactured by Coroplast) to a thickness of 10 μm with a bar coater. Then, using a metal halide lamp (manufactured by Eye Graphics Co., Ltd.), the coating film was formed by curing with an energy of ^{400 mJ / cm 2.} The obtained coating film was evaluated in a cross-cut test according to JIS K5600-5-6.

More specifically, with a cutter, the blade of the cutting tool was applied so as to be perpendicular to the coating film, and squares with a distance of 1 mm between the cuts were inserted to form a grid of 10 × 10 squares. A transparent adhesive tape (width 25 mm) having a length of about 75 mm was attached to the lattice, and the tape was sufficiently rubbed with a finger so that the coating film could be seen through. Next, within 5 minutes after the tape was applied, the tape was surely peeled off from the coating film at an angle close to 60 ° in 0.5 to 1.0 seconds, and the state of the lattice was visually observed. The evaluation criteria are as follows.
(Evaluation criteria)
A: No peeling was observed on the lattice.
B: Peeling of the coating film was observed in less than 5% of the lattice.
C: Peeling of the coating film was observed in 5% or more and less than 50% of the lattice.
D: Peeling of the coating film was observed in 50% or more of the lattice.

4.3.3. Evaluation of PET adhesion of color ink Same as PP adhesion evaluation of color ink except that polyethylene terephthalate (PET) film (manufactured by Toray Industries, Inc.) was used instead of polypropylene board (manufactured by Coroplast) as a recording medium. The adhesion to the polyethylene terephthalate film was evaluated.
(Evaluation criteria)
A: No peeling was observed on the lattice.
B: Peeling of the coating film was observed in less than 5% of the lattice.
C: Peeling of the coating film was observed in 5% or more and less than 50% of the lattice.
D: Peeling of the coating film was observed in 50% or more of the lattice.

4.3.3.3. Evaluation of PP Adhesion of Clear Ink The adhesion of clear ink to polypropylene board was evaluated in the same manner as the evaluation of PP adhesion of color ink, except that clear ink was used as the ink.
(Evaluation criteria)
A: No peeling was observed on the lattice.
B: Peeling of the coating film was observed in less than 5% of the lattice.
C: Peeling of the coating film was observed in 5% or more and less than 50% of the lattice.
D: Peeling of the coating film was observed in 50% or more of the lattice.

4.3.4. Evaluation of PET Adhesion of Clear Ink Adhesion to polyethylene terephthalate film was evaluated in the same manner as PET adhesion evaluation of color ink except that clear ink was used as the ink.
(Evaluation criteria)
A: No peeling was observed on the lattice.
B: Peeling of the coating film was observed in less than 5% of the lattice.
C: Peeling of the coating film was observed in 5% or more and less than 50% of the lattice.
D: Peeling of the coating film was observed in 50% or more of the lattice.

4.3.5. Evaluation of PP Adhesion of Superposed Coating Film of Color Ink and Clear Ink Using a bar coater, color ink was applied onto a polypropylene board (manufactured by Coroplast) to a thickness of 10 μm. Then, using a metal halide lamp (manufactured by Eye Graphics Co., Ltd.), the coating film was formed by curing with an energy of ^{400 mJ / cm 2.} Then, the clear ink was applied on the coating film of the color ink with a bar coater so as to have a thickness of 10 μm. Next, using the metal halide lamp, radiation was irradiated with an energy of ^{400 mJ / cm 2 to form a clear ink coating film.} Then, the adhesion to the polypropylene board was evaluated in the same manner as the PP adhesion evaluation of the color ink.
(Evaluation criteria)
A: No peeling was observed on the lattice.
B: Peeling of the coating film was observed in less than 5% of the lattice.
C: Peeling of the coating film was observed in 5% or more and less than 50% of the lattice.
D: Peeling of the coating film was observed in 50% or more of the lattice.

4.3.6. Evaluation of PET adhesion of the layered coating film of color ink and clear ink As a recording medium, polyethylene terephthalate film (manufactured by Toray Co., Ltd.) was used instead of polypropylene board (manufactured by Coroplast Co., Ltd.). The adhesion to the polyethylene terephthalate film was evaluated in the same manner as the evaluation of the PP adhesion of the layered coating film of the clear ink.
(Evaluation criteria)
A: No peeling was observed on the lattice.
B: Peeling of the coating film was observed in less than 5% of the lattice.
C: Peeling of the coating film was observed in 5% or more and less than 50% of the lattice.
D: Peeling of the coating film was observed in 50% or more of the lattice.

4.3.7. Evaluation of scratch resistance of the coating film Using a bar coater, a color ink was applied onto a recording medium so as to have a thickness of 10 μm. As the recording medium, the trade name JT5829 manufactured by MACtac was used as the vinyl chloride film. Next, a metal halide lamp manufactured by Eye Graphics Co., Ltd. was used ^{to irradiate radiation with an energy of 400 mJ / cm 2} to form a coating film of color ink. Then, the clear ink was applied on the coating film of the color ink with a bar coater so as to have a thickness of 10 μm. Next, using the metal halide lamp, radiation was irradiated with an energy of ^{400 mJ / cm 2 to form a clear ink coating film.}

A microscratch test of JIS R3255 was performed on the above coating film as an index of scratch resistance. Specifically, Nanotech's ultra-thin scratch tester CSR-5000 is used to scratch the coating film by changing the load applied to the stylus, and the stylus penetrates the coating film to reach the PVC film, which is the recording medium. The above-mentioned load was measured. Here, the load applied to the stylus when the stylus reaches the vinyl chloride film is also referred to as a load capacity. The measurement conditions were a stylus diameter of 15 μm, an amplitude of 100 μm, and a scratching speed of 10 μm per second. The scratch resistance of the measured load capacity was evaluated according to the following evaluation criteria. The larger the load capacity, the better the scratch resistance.
(Evaluation criteria)
A: The load capacity is 30 mN / cm ² or more.
B: The load capacity is 25 mN / cm ² or more and less than 30 mN / cm ^2.
C: The load capacity is 20 mN / cm ² or more and less than 25 mN / cm ^2.
D: The load capacity is less than ^{20 mN / cm 2.}

4.3.8. Evaluation of Glossiness of Coating Film Using a bar coater, color ink was applied onto a recording medium so as to have a thickness of 10 μm. As the recording medium, Mitsubishi Gas Chemical Company's Upiron (registered trademark) NF2000 was used as the polycarbonate. Next, using a UV-LED ^{, radiation was irradiated with an energy of 400 mJ / cm 2} to form a coating film of color ink. Then, the clear ink was applied on the coating film of the color ink with a bar coater so as to have a thickness of 10 μm. Here, after applying the clear ink, it was allowed to stand for 1 minute as a leveling step. Next, using the above UV-LED, radiation was irradiated with an energy of ^{400 mJ / cm 2 to form a clear ink coating film.} When the coating film of the clear ink was visually observed under a fluorescent lamp, the distance between the fluorescent lamp in which the reflection of the fluorescent lamp could be confirmed and the coating film of the clear ink was measured. The glossiness of the above distance was evaluated according to the following evaluation criteria.
(Evaluation criteria)
A: The reflection of the fluorescent lamp can be confirmed even if the distance is 50 cm or more.
B: The reflection of the fluorescent lamp can be confirmed at a distance of 30 cm or more and less than 50 cm.
C: The reflection of the fluorescent lamp can be confirmed at a distance of 10 cm or more and less than 30 cm.
D: The reflection of the fluorescent lamp can be confirmed or the reflection cannot be confirmed at a distance of less than 10 cm.

4.4. Summary of Evaluation Results As shown in Table 3, the weighted average of the SP values of each polymerizable compound, weighted by the mass ratio of each content of each polymerizable compound in the clear ink, is 9.5 to 10.0. In Examples 1 to 7, the A evaluation was such that the adhesion of the overlapping coating film of the color ink and the clear ink was excellently equivalent. Among them, in the clear ink, in the examples other than Example 6 in which the content of the monofunctional monomer was 90% by mass or more with respect to the total amount of the polymerizable compound, the adhesion of the clear ink was B or more, which was good. there were. From this, it was shown that the ink set of the example was excellent in adhesion to the recording medium.

Further, in terms of the scratch resistance of the coating film, Examples 1, 5, 6 and 7 were evaluated as A, which corresponded well. The glossiness of the coating film was evaluated as A, which corresponds well to Examples 2 and 3, and was evaluated as B or higher in Examples other than the other Examples 7, which was good. As a result, it was shown that the ink set of the example tends to improve the scratch resistance and the glossiness.

On the other hand, in Comparative Examples 1, 2 and 3, the weighted average of the SP values of each polymerizable compound, which is weighted by the mass ratio of each content of each polymerizable compound in the clear ink in the ink set, is 9.5 to 10. It was out of the range of .0 and the adhesion was C or less, which corresponds to impossibility. In Comparative Examples 4 and 5, the weighted average of the SP values of each polymerizable compound, which is weighted by the mass ratio of each content of each polymerizable compound in the color ink in the ink set, deviates from 9.5 to 10.0. The adhesion was C or less, which corresponds to impossibility. In Comparative Example 6, the amount of monofunctional monomer in the color ink in the ink set was less than 90% by mass with respect to the total amount of the polymerizable compound, and the adhesion was C or less, which corresponds to impossibility. That is, it was found that it is difficult to improve the adhesion with the ink set of the comparative example.

1 ... Inkjet printer, 2 ... Recording medium, 3 ... Inkjet head, 4 ... Carriage, 5 ... Main scanning mechanism, 6 ... Platen roller, 7a, 7b, 7c, 7d, 7e ... Ink cartridge, 8 ... Timing belt, 9 ... Motor, 10 ... guide shaft, 11 ... light source.

Claims (7)

An ink set of radiation-curable inkjet ink containing a polymerizable compound.
The ink set includes clear ink and color ink.
The weighted average of the SP values of the polymerizable compounds, weighted by the mass ratio of each content of the polymerizable compound contained in the clear ink, is 9.0 to 10.0.
The weighted average of the SP values of the polymerizable compounds, weighted by the mass ratio of each content of the polymerizable compound contained in the color ink, is 9.5 to 10.0.
The color ink is an ink set containing 90% by mass or more of a monofunctional monomer with respect to the total amount of the polymerizable compound contained in the color ink. The ink set according to claim 1, wherein the clear ink contains 90% by mass or more of a monofunctional monomer with respect to the total amount of the polymerizable compound contained in the clear ink. The polymerizable compound contained in the clear ink has a volume defined by a Van-der-Wals radius of 0.26 cubic nm or more and an area in the height direction with respect to a long side of 0.25 square nm or more. The ink set according to claim 1 or 2, wherein the sex monomer A is contained in an amount of 80% by mass or more based on the total amount of the clear ink. The ink set according to any one of claims 1 to 3, wherein the polymerizable monomer A contains an alicyclic monofunctional (meth) acrylate. Claimed from claim 1, wherein the weighted average of the glass transition temperature of each homopolymer in the polymerizable compound is 48 ° C. or higher, weighted by the mass ratio of each content of the polymerizable compound contained in the clear ink. Item 6. The ink set according to any one of Item 4. An inkjet method using the ink set according to any one of claims 1 to 5.
The first coating step of ejecting the color ink from the inkjet head and coating it on the recording medium, and
The first curing step of irradiating the color ink applied to the recording medium with radiation, and
A second coating step of ejecting the clear ink from the inkjet head and applying the clear ink to at least a part of the area where the color ink is applied on the recording medium.
An inkjet method comprising a second curing step of irradiating the clear ink applied to the recording medium with radiation. The inkjet method according to claim 6, further comprising a leveling step of allowing the recording medium coated with the clear ink to stand between the second coating step and the second curing step.

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