JP2016224407A - Ultraviolet-curable liquid developer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultraviolet-curable liquid developer that provides high image density, prevents the occurrence of image blur, has sufficient fixability, and is excellent in storage property.SOLUTION: There is provided an ultraviolet-curable liquid developer that contains a cationic polymerizable liquid monomer, a photopolymerization initiator, and toner particles. In the ultraviolet-curable liquid developer, the cationic polymerizable liquid monomer contains a vinyl ether compound; the cationic polymerizable liquid monomer has a molar average SP value of 9.0 or less; the cationic polymerizable liquid monomer has a molar average functional group number of 1.8 or more; the photopolymerization initiator contains a compound represented by the following formula (1); the content of the compound represented by the following formula (1) is 0.01 parts by mass or more and 5.00 parts by mass or less, based on 100 parts by mass of the cationic polymerizable liquid monomer.SELECTED DRAWING: None

Description

  The present invention relates to a liquid developer used in an image forming apparatus using an electrophotographic method such as electrophotographic method, electrostatic recording method, and electrostatic printing.

In the electrophotographic system, the surface of an image carrier such as a photoconductor is uniformly charged (charging process), and an electrostatic latent image is formed on the surface of the image carrier by exposure (exposure process). The electrostatic latent image is developed with a developer made of colored resin particles (development process), the developer image is transferred to a recording medium such as paper or plastic film (transfer process), and the transferred developer image is recorded on the recording medium. It is a method of obtaining a printed matter by fixing (fixing step).
In this case, the developer is a liquid developer in which colored resin particles composed of a material including a colorant such as a pigment and a binder resin are used in a dry state, and liquid development in which the colored resin particles are dispersed in an electrically insulating liquid. It is roughly divided into agents.
In recent years, there is an increasing need for colorization and high-speed printing for image forming apparatuses such as copying machines, facsimiles, and printers that use electrophotography. In color printing, a high-resolution and high-quality image is required. Therefore, a developer capable of forming a high-resolution and high-quality image and corresponding to high-speed printing is required.
A liquid developer is known as an advantageous developer for color image reproducibility. In the liquid developer, since the aggregation of the colored resin particles in the liquid developer is difficult to occur during storage, fine toner particles can be used. Therefore, the liquid developer can easily obtain characteristics excellent in fine line image reproducibility and gradation reproducibility. Development of a high-quality, high-speed digital printing apparatus using an electrophotographic technique using a liquid developer, which takes advantage of these excellent features, is becoming popular. Under such circumstances, development of a liquid developer having better characteristics is demanded.
Conventionally, a liquid developer in which colored resin particles are dispersed in an electrically insulating liquid such as a hydrocarbon organic solvent or silicone oil is known. However, if the electrically insulating liquid remains on a recording medium such as paper or plastic film, the image quality may be significantly deteriorated, and the electrically insulating liquid needs to be removed. For removing the electrically insulating liquid, a method of volatilizing and removing the electrically insulating liquid by applying heat energy is generally used. However, at that time, there is a possibility that organic solvent vapor may be released outside the apparatus, and a great deal of energy is required, which is not necessarily preferable from the viewpoint of environment and energy saving.
As a countermeasure against this, a method of curing an electrically insulating liquid by photopolymerization has been proposed. As the photocurable liquid developer, a monomer or oligomer having a reactive functional group is used as an electrically insulating liquid and a photopolymerization initiator is further dissolved. This photo-curable liquid developer is cured by irradiating light such as ultraviolet rays to react with a reactive functional group, and can cope with high speed. Such a photocurable liquid developer is proposed in Patent Document 1. In Patent Document 1, an acrylate monomer such as urethane acrylate is exemplified as a monomer having a reactive functional group.
Patent Document 2 proposes to use a curable liquid vehicle having a specific viscosity range and a specific resistance value range as the curable electrical insulating liquid. Examples of the curable liquid vehicle include epoxy compounds, vinyl ethers, and cyclic vinyl ethers.

JP 2003-57883 A Japanese Patent No. 3442406

However, since the acrylate monomer has a low volume resistivity and tends to lower the potential of the electrostatic latent image in the development process, it is difficult to obtain a high image density or image blurring (resulting in an image with poor sharpness) occurs. Sometimes happened.
On the other hand, vinyl ether compounds are suitable curable electrical insulating liquids because they have a high volume resistivity and a high reaction rate, but in general, cationically polymerizable photopolymerization initiators and ionic photoacids are generated. It is necessary to use the agent in combination.
However, when the vinyl ether compound and the ionic photoacid generator are mixed, the volume resistivity is greatly reduced as compared with the case of the vinyl ether compound alone.
Therefore, a liquid developer containing a vinyl ether compound and an ionic photoacid generator has problems that it is difficult to obtain a high image density or image blur is likely to occur.
The present invention provides a liquid developer that solves the above problems.
That is, the present invention provides an ultraviolet curable liquid developer that can obtain a high image density, hardly cause image blurring, has sufficient fixability, and has excellent storage stability.

The present invention
An ultraviolet curable liquid developer containing a cationic polymerizable liquid monomer, a photopolymerization initiator, and toner particles,
The cationic polymerizable liquid monomer contains a vinyl ether compound,
The cation polymerizable liquid monomer has a molar average SP value of 9.0 or less,
The cation polymerizable liquid monomer has a molar average functional group number of 1.8 or more,
The photopolymerization initiator contains a compound represented by the following formula (1),
The content of the compound represented by the following formula (1) is 0.01 part by mass or more and 5.00 parts by mass or less with respect to 100 parts by mass of the cationic polymerizable liquid monomer. It is a liquid developer.

［前記式（１）中、Ｒ_１とＲ_２は互いに結合して環構造を形成し、ｘは１以上８以下の整数を表し、ｙは３以上１７以下の整数を表す。］

[In the formula (1), R ₁ and R ₂ are bonded to each other to form a ring structure, x represents an integer of 1 to 8, and y represents an integer of 3 to 17. ]

  According to the present invention, it is possible to provide an ultraviolet curable liquid developer that can obtain a high image density, hardly cause image blurring, has sufficient fixability, and has excellent storage stability.

Hereinafter, the present invention will be described in detail.
The ultraviolet curable liquid developer of the present invention contains a cationic polymerizable liquid monomer, a photopolymerization initiator, and toner particles.
Hereinafter, each component contained in the ultraviolet curable liquid developer of the present invention will be described.

[Photopolymerization initiator]
The photopolymerization initiator used in the present invention contains a compound represented by the following formula (1).

［前記式（１）中、Ｒ_１とＲ_２は互いに結合して環構造を形成し、ｘは１以上８以下の整数を表し、ｙは３以上１７以下の整数を表す。］

[In the formula (1), R ₁ and R ₂ are bonded to each other to form a ring structure, x represents an integer of 1 to 8, and y represents an integer of 3 to 17. ]

The photopolymerization initiator represented by the above formula (1) is photolyzed by ultraviolet irradiation to generate a sulfonic acid that is a strong acid. Moreover, it is also possible to use a photopolymerization sensitizer together and cause the photopolymerization initiator to decompose and generate sulfonic acid by using the photopolymerization sensitizer to absorb ultraviolet rays as a trigger.
By using the photopolymerization initiator represented by the above formula (1), a high resistance liquid developer can be obtained, unlike the case of using an ionic photoacid generator, while enabling good fixability. .
Examples of the ring structure formed by combining R ₁ and R ₂ include 5-membered rings and 6-membered rings. Specific examples of the ring structure formed by combining R ₁ and R ₂ include succinimide structure, phthalimide structure, norbornene dicarboximide structure, naphthalene dicarboximide structure, cyclohexane dicarboximide structure, epoxy Examples thereof include a cyclohexene dicarboximide structure.
The ring structure may have an alkyl group, an alkyloxy group, an alkylthio group, an aryl group, an aryloxy group, or an arylthio group as a substituent. Furthermore, other ring structures such as an alicyclic ring, a heterocyclic ring and an aromatic ring which may have a substituent may be condensed.

The C _x F _y group having a large electron-withdrawing property is a fluorocarbon group, and is a functional group for decomposing a sulfonic acid ester moiety by ultraviolet irradiation, and has 1 to 8 carbon atoms (x is 1 to 8). The number of fluorine atoms is 3 or more and 17 or less (y is 3 or more and 17 or less).
If the number of carbon atoms is 1 or more, the synthesis of strong acid is easy, and if it is 8 or less, the storage stability is excellent. The number of carbon atoms is preferably 1 or more and 4 or less.
If the number of fluorine atoms is 3 or more, it can act as a strong acid, and if it is 17 or less, the synthesis of a strong acid is easy. The number of fluorine atoms is preferably 3 or more and 9 or less.

The C _x F _y group in the above formula (1) includes a linear alkyl group (RF1) in which a hydrogen atom is substituted with a fluorine atom, a branched alkyl group (RF2) in which a hydrogen atom is substituted with a fluorine atom, hydrogen Examples thereof include a cycloalkyl group (RF3) in which an atom is substituted with a fluorine atom, and an aryl group (RF4) in which a hydrogen atom is substituted with a fluorine atom.
Examples of the linear alkyl group (RF1) in which a hydrogen atom is substituted with a fluorine atom include a trifluoromethyl group (x = 1, y = 3), a pentafluoroethyl group (x = 2, y = 5), and hepta. Fluoro n-propyl group (x = 3, y = 7), nonafluoro n-butyl group (x = 4, y = 9), perfluoro n-hexyl group (x = 6, y = 13), and perfluoro n -An octyl group (x = 8, y = 17) etc. are mentioned.
Examples of the branched alkyl group (RF2) in which a hydrogen atom is substituted with a fluorine atom include a perfluoroisopropyl group (x = 3, y = 7) and a perfluoro-tert-butyl group (x = 4, y = 9). ), And a perfluoro-2-ethylhexyl group (x = 8, y = 17).
Examples of the cycloalkyl group (RF3) in which a hydrogen atom is substituted with a fluorine atom include a perfluorocyclobutyl group (x = 4, y = 7), a perfluorocyclopentyl group (x = 5, y = 9), Examples include a fluorocyclohexyl group (x = 6, y = 11) and a perfluoro (1-cyclohexyl) methyl group (x = 7, y = 13).
Examples of the aryl group (RF4) in which a hydrogen atom is substituted with a fluorine atom include a pentafluorophenyl group (x = 6, y = 5) and a 3-trifluoromethyltetrafluorophenyl group (x = 7, y = 7).
Of the C _x F _y groups in the above formula (1), from the viewpoint of availability and decomposability of the sulfonic acid ester moiety, a linear alkyl group (RF1), a branched alkyl group (RF2), and An aryl group (RF4) is preferable, and a linear alkyl group (RF1) and an aryl group (RF4) are more preferable. Particularly preferably, trifluoromethyl group (x = 1, y = 3), pentafluoroethyl group (x = 2, y = 5), heptafluoro n-propyl group (x = 3, y = 7), nonafluoro n- A butyl group (x = 4, y = 9), and a pentafluorophenyl group (x = 6, y = 5).

  It is also a preferred embodiment that the compound represented by the above formula (1) is a compound represented by the following formula (2).

［前記式（２）中、ｘは１以上８以下の整数を表し、ｙは３以上１７以下の整数を表す。Ｒ_３及びＲ_４はそれぞれ独立して、アルキル基、アルキルオキシ基、アルキルチオ基、アリール基、アリールオキシ基、又はアリールチオ基を表し、ｏ及びｐはそれぞれ独立して、０以上３以下の整数を表す。ｏが２以上の場合は複数のＲ_３が互いに結合して環構造を形成してもよく、ｐが２以上の場合は複数のＲ_４が互いに結合して環構造を形成してもよい。また、Ｒ_３とＲ_４が互いに結合して環構造を形成してもよい。］
Ｒ_３及びＲ_４はそれぞれ独立して、炭素数１以上１８以下のアルキル基、炭素数１以上１８以下のアルキルオキシ基、炭素数１以上１８以下のアルキルチオ基、炭素数１以上１４以下のアリール基、炭素数１以上１４以下のアリールオキシ基、又は炭素数１以上１４以下のアリールチオ基を表すことが好ましい。

[In the formula (2), x represents an integer of 1 to 8, and y represents an integer of 3 to 17. R ₃ and R ₄ each independently represents an alkyl group, an alkyloxy group, an alkylthio group, an aryl group, an aryloxy group, or an arylthio group, and o and p each independently represent an integer of 0 or more and 3 or less. Represent. When o is 2 or more, a plurality of R ₃ may be bonded to each other to form a ring structure, and when p is 2 or more, a plurality of R ₄ may be bonded to each other to form a ring structure. R ₃ and R ₄ may be bonded to each other to form a ring structure. ]
R ₃ and R ₄ are each independently an alkyl group having 1 to 18 carbon atoms, an alkyloxy group having 1 to 18 carbon atoms, an alkylthio group having 1 to 18 carbon atoms, and an aryl group having 1 to 14 carbon atoms. It preferably represents a group, an aryloxy group having 1 to 14 carbon atoms, or an arylthio group having 1 to 14 carbon atoms.

  Specific examples [Exemplary compounds A-1 to A-27] of the photopolymerization initiator represented by the above formula (1) are listed below, but the present invention is not limited to these examples.

Among these, (A-23), (A-24), (A-25), (A-26), and (A-27) obtained high fixability in combination with a photopolymerization sensitizer. It is easy and preferable.
The photopolymerization initiator can be used alone or in combination of two or more. Moreover, you may contain photoinitiators other than the compound represented by said Formula (1) to such an extent that the effect of this invention is not inhibited.
In the ultraviolet curable liquid developer of the present invention, the content of the compound represented by the formula (1) is 0.01 parts by mass or more and 5.00 parts by mass or less with respect to 100 parts by mass of the cationic polymerizable liquid monomer. It is. Preferably they are 0.05 mass part or more and 1.00 mass parts or less, More preferably, they are 0.10 mass part or more and 0.50 mass part or less.
When the content of the compound represented by the above formula (1) is less than 0.01 parts by mass, the amount of sulfonic acid generated upon irradiation with ultraviolet rays is insufficient, and the fixability is lowered.
On the other hand, when the content of the compound represented by the above formula (1) exceeds 5.00 parts by mass, the volume resistivity of the ultraviolet curable liquid developer is lowered and the developability is lowered. In addition, sulphonic acid generated by thermal decomposition during storage increases and storage stability decreases.

[Cationically polymerizable liquid monomer]
In the present invention, the cationically polymerizable liquid monomer is selected from liquids having a high volume resistivity and electrical insulation and low viscosity near room temperature.
The cationically polymerizable liquid monomer is preferably selected from liquids that do not dissolve the binder resin contained in the toner particles.
Specifically, it may be selected from a combination of a cationic polymerizable liquid monomer and a binder resin such that the binder resin to be dissolved is 1 part by mass or less with respect to 100 parts by mass of the cationic polymerizable liquid monomer at a temperature of 25 ° C. preferable.
Here, the volume resistivity of the cationic polymerizable liquid monomer is 1 × 10 ⁹ Ω · cm or more and 1 × 1.
It is preferably about 0 ¹⁵ Ω · cm or less, more preferably about 1 × 10 ¹⁰ Ω · cm or more and about 1 × 10 ¹⁵ Ω · cm or less.
When the volume resistivity is less than 1 × 10 ⁹ Ω · cm, the potential of the electrostatic latent image tends to drop, and it tends to be difficult to obtain a high optical density or to cause image blurring.
On the other hand, the viscosity of the cationic polymerizable liquid monomer is preferably about 0.5 mPa · s or more and less than 100 mPa · s at 25 ° C., more preferably about 0.5 mPa · s or more and less than 20 mPa · s.

In the ultraviolet curable liquid developer of the present invention, the cationically polymerizable liquid monomer contains a vinyl ether compound. Moreover, you may contain cationically polymerizable liquid monomers other than a vinyl ether compound to such an extent that the effect of this invention is not inhibited. Preferably, the cationically polymerizable liquid monomer is composed of one or more vinyl ether compounds.
In the present invention, by using a vinyl ether compound, an ultraviolet curable liquid developer having high volume resistivity, low viscosity, and high sensitivity can be obtained.
In addition, the present inventors presume that suitable characteristics are manifested due to a small deviation in electron density in the molecule of the vinyl ether compound.
Here, the vinyl ether compound refers to a compound having a vinyl ether structure (—CH═CH—O—C—).
The vinyl ether structure is preferably represented by R—CH═CH—O—C— (R is hydrogen or alkyl having 1 to 3 carbon atoms, preferably hydrogen or methyl).

As the cationic polymerizable liquid monomer, acrylic monomers and cyclic ether monomers such as epoxide and oxetane are widely used. However, acrylic monomers have an uneven electron density in the molecule and electrostatic interaction acts between the molecules, so that it is difficult to obtain a low-viscosity liquid developer and the volume resistivity tends to be low.
On the other hand, cyclic ether monomers are difficult to obtain a high volume resistivity, and the polymerization reaction rate tends to be much lower than that of vinyl ether compounds, so the amount used is greatly limited when applied to UV curable liquid developers. The

In the present invention, it is also possible to use a mixture of a vinyl ether compound and a small amount of a cyclic ether monomer as long as the volume resistivity and polymerization reaction rate are not significantly reduced.
In the present invention, it is also one of preferred embodiments that the vinyl ether compound is a compound having no hetero atom other than the vinyl ether structure.
Here, the hetero atom means an atom other than a carbon atom and a hydrogen atom.
If it is a compound which does not have a hetero atom other than a vinyl ether structure, the bias | inclination of the electron density in a molecule | numerator will be suppressed and high volume resistivity will be easy to be obtained.
Furthermore, in this invention, it is also one of the preferable aspects that a vinyl ether compound does not have carbon-carbon double bonds other than a vinyl ether structure in a vinyl ether compound. If it is a vinyl ether compound which does not have carbon-carbon double bonds other than a vinyl ether structure, the bias | inclination of an electron density will be suppressed and high electrical resistance will be easy to be obtained.
In the present invention, the vinyl ether compound is preferably represented by the following formula (C).

［式（Ｃ）中、ｎは、一分子中のビニルエーテル構造の数を示し、１以上４以下の整数である。Ｒはｎ価の炭化水素基である。］
上記ｎは、１以上３以下の整数であることが好ましい。
Ｒは、好ましくは、炭素数１以上２０以下の直鎖又は分岐の飽和又は不飽和の脂肪族炭化水素基、炭素数５以上１２以下の飽和又は不飽和の脂環式炭化水素基、及び炭素数６以上１４以下の芳香族炭化水素基から選択される基であり、該脂環式炭化水素基及び該芳香族炭化水素基は、炭素数１以上４以下の飽和又は不飽和の脂肪族炭化水素基を有していてもよい。
上記Ｒは、より好ましくは炭素数４以上１８以下の直鎖又は分岐の飽和脂肪族炭化水素基である。
以下に、ビニルエーテル化合物の具体例〔例示化合物Ｂ−１〜Ｂ−３０〕を挙げるが、本発明はこれらの例に制限されるものではない。

[In the formula (C), n represents the number of vinyl ether structures in one molecule and is an integer of 1 or more and 4 or less. R is an n-valent hydrocarbon group. ]
N is preferably an integer of 1 or more and 3 or less.
R is preferably a linear or branched saturated or unsaturated aliphatic hydrocarbon group having 1 to 20 carbon atoms, a saturated or unsaturated alicyclic hydrocarbon group having 5 to 12 carbon atoms, and carbon. A group selected from an aromatic hydrocarbon group having 6 to 14 carbon atoms, the alicyclic hydrocarbon group and the aromatic hydrocarbon group having a saturated or unsaturated aliphatic carbon group having 1 to 4 carbon atoms You may have a hydrogen group.
R is more preferably a linear or branched saturated aliphatic hydrocarbon group having 4 to 18 carbon atoms.
Specific examples of the vinyl ether compound [Exemplary Compounds B-1 to B-30] are shown below, but the present invention is not limited to these examples.

  Among these, preferred are dicyclopentadiene vinyl ether (B-8), cyclohexanedimethanol divinyl ether (B-17), tricyclodecane vinyl ether (B-10), trimethylolpropane trivinyl ether (B-24), 2-ethyl-1,3-hexanediol divinyl ether (B-25), 2,4-diethyl-1,5-pentanediol divinyl ether (B-26), 2-butyl-2-ethyl-1,3- Examples include propanediol divinyl ether (B-27), neopentyl glycol divinyl ether (B-23), pentaerythritol tetravinyl ether (B-28), 1,2-decanediol divinyl ether (B-30), and the like.

In the present invention, the molar average SP value of the cationically polymerizable liquid monomer is 9.0 or less, preferably 8.8 or less, and more preferably 8.6 or less.
The molar average SP value is about 7.6 or more.
In the present invention, the cationic polymerizable liquid monomer is preferably composed of a cationic polymerizable liquid monomer having an SP value of 9.0 or less, and is preferably composed of a cationic polymerizable liquid monomer having an SP value of 8.9 or less. .
The cationic polymerizable liquid monomer is preferably composed of a cationic polymerizable liquid monomer having an SP value of approximately 7.6 or more.
The SP value is a value introduced by Hildebrand and defined by regular theory, and is indicated by the square root of the cohesive energy density of the solvent (or solute), which is a measure of the solubility of the binary solution.
The SP value in the present invention is a value obtained by calculation from the evaporation energy and molar volume of atoms and atomic groups by Fedors described in coating basics and engineering (page 53, Yuji Harasaki, Processing Technology Research Group).
Further, the cationic polymerizable liquid monomer A having an SP value (Asp) and a molecular weight (Amw) is (Awt) parts by mass, and the cationic polymerizable liquid monomer B having an SP value (Bsp) and a molecular weight (Bmw) is (Bwt) parts by mass. When mixed and used, the molar average SP value of the cationically polymerizable liquid monomer is determined as follows.
Mole average SP value = {(Asp × Awt / Amw) + (Bsp × Bwt / Bmw)} / {(Awt / Amw) + (Bwt / Bmw)}
In the case of using a mixture of three or more kinds of cationic polymerizable liquid monomers, it is obtained in the same manner.
Since the cationic polymerizable UV curable resin is susceptible to curing inhibition by moisture, the UV curable resin is difficult to cure due to an increase in humidity in the curing environment.
However, by setting the molar average SP value to 9.0 or less, it is possible to reduce the water content of the cationic polymerizable liquid monomer and the moisture that permeates into the liquid developer from the interface between the liquid developer and air after transfer. And high fixability can be obtained.
In the present invention, the cationically polymerizable liquid monomer is more preferably composed of a vinyl ether compound having an SP value of 9.0 or less.

In the present invention, the number of mole average functional groups of the cationic polymerizable liquid monomer is 1.8 or more, preferably 2.0 or more, more preferably 2.2 or more.
The number of mole average functional groups is about 6.0 or less.
In the present invention, the cationic polymerizable liquid monomer is preferably composed of a cationic polymerizable liquid monomer having two or more polymerizable functional groups per molecule.
The cationic polymerizable liquid monomer may be a cationic polymerizable liquid monomer having a polymerizable functional group number of about 6.0 or less per molecule.
Here, when one polymerizable functional group is present in one molecule of the cationic polymerizable liquid monomer, the number of polymerizable functional groups per molecule is expressed as “1” (or one function), and n exists. In this case, the number of polymerizable functional groups per molecule is expressed as “n” (or n function).
In the case of a vinyl ether compound, when n vinyl ether structures (—CH═CH—O—C—) exist in one molecule of the vinyl ether compound, it is expressed as n-functional.
In the present invention, the number of polymerizable functional groups per molecule (Af) and the molecular weight (Amw) of the cationic polymerizable liquid monomer A is (Awt) parts by mass, the number of polymerizable functional groups per molecule (Bf), and the molecular weight (Bmw). ) Of the cationic polymerizable liquid monomer B is used by mixing (Bwt) parts by mass, the molar average functional group number of the cationic polymerizable liquid monomer is determined as follows.
Mole average functional group number = {(Af × Awt / Amw) + (Bf × Bwt / Bmw)} / {(Awt / Amw) + (Bwt / Bmw)}
In the case of using a mixture of three or more kinds of cationic polymerizable liquid monomers, it is obtained in the same manner.
In general, the cationic polymerization reaction is a polymerization reaction in which an acid decomposed from a polymerization initiator by irradiation with light reacts with a monomer to produce a cationic active species. As long as this cationic active species exists, the polymerization reaction proceeds one after another. Conceivable. At this time, if water molecules are present in the vicinity of the cationically polymerizable liquid monomer, this cationically active species is trapped, and further polymerization does not proceed.
That is, the chain reaction of one polymerizable functional group of the cationic polymerizable liquid monomer is stopped for each water molecule.
Therefore, by setting the number of mole average functional groups of the cationic polymerizable liquid monomer to 1.8 or more, inhibition of curing due to moisture can be suppressed and high fixability can be obtained.
In the present invention, the cationically polymerizable liquid monomer is more preferably composed of a vinyl ether compound having two or more polymerizable functional groups per molecule.

The ultraviolet curable liquid developer of the present invention may contain a photopolymerization sensitizer as necessary for the purpose of improving the acid generation efficiency of the photopolymerization initiator and increasing the photosensitive wavelength.
The photopolymerization sensitizer is not particularly limited as long as the photopolymerization initiator is sensitized by an electron transfer mechanism or an energy transfer mechanism.
Specifically, aromatic polycondensed compounds such as anthracene, 9,10-dialkoxyanthracene, pyrene and perylene, aromatic ketone compounds such as acetophenone, benzophenone, thioxanthone, and Michlerketone, heterocycles such as phenothiazine and N-aryloxazolidinone A ring compound is mentioned.
Of these, anthracene compounds such as 9,10-diethoxyanthracene, 9,10-dipropoxyanthracene, and 9,10-dibutoxyanthracene, and thioxanthones such as 2,4-diethylthioxanthone and 2-isopropylthioxanthone Preferred examples are compounds.
The photopolymerization sensitizer can be used alone or in combination of two or more.
The content of the photopolymerization sensitizer is appropriately selected according to the purpose, but is preferably 0.1 parts by mass or more and 10.0 parts by mass or less with respect to 1 part by mass of the photopolymerization initiator. Preferably they are 1.0 mass part or more and 5.0 mass parts or less.

The ultraviolet curable liquid developer of the present invention contains a photopolymerization sensitizer as necessary for the purpose of improving the electron transfer efficiency or energy transfer efficiency between the photopolymerization sensitizer and the photopolymerization initiator. May be.
Examples of photopolymerization sensitization agents include 1,4-dihydroxynaphthalene, 1,4-dimethoxynaphthalene, 1,4-diethoxynaphthalene, 4-methoxy-1-naphthol, 4-ethoxy-1-naphthol and the like. And benzene compounds such as naphthalene compounds, 1,4-dihydroxybenzene, 1,4-dimethoxybenzene, 1,4-diethoxybenzene, 1-methoxy-4-phenol, 1-ethoxy-4-phenol, and the like. .
Of these, naphthalene compounds are preferred.
The photopolymerization sensitization aid can be used alone or in combination of two or more.
The content of the photopolymerization sensitizer is appropriately selected according to the purpose, but is preferably 0.1 parts by mass or more and 10.0 parts by mass or less with respect to 1 part by mass of the photopolymerization sensitizer. More preferably, it is 0.5 parts by mass or more and 5.0 parts by mass or less.

[Toner particles]
The ultraviolet curable liquid developer of the present invention contains toner particles.
The toner particles preferably contain a binder resin and a colorant.
<Binder resin>
As the binder resin contained in the toner particles, a known binder resin can be used as long as it has fixability to an adherend such as paper or plastic film and is insoluble in the cationic polymerizable liquid monomer.
Here, the insolubility in the cationically polymerizable liquid monomer means that the binder resin to be dissolved is 1 part by mass or less with respect to 100 parts by mass of the cationically polymerizable liquid monomer at a temperature of 25 ° C.
Specific examples of the binder resin include resins such as epoxy resins, ester resins, (meth) acrylic resins, styrene- (meth) acrylic resins, alkyd resins, polyethylene resins, ethylene- (meth) acrylic resins, and rosin-modified resins. Can be mentioned. Moreover, these can be used alone or in combination of two or more as required.
Although it does not specifically limit as content of binder resin, It is preferable that it is 50-1000 mass parts with respect to 100 mass parts of coloring agents.

<Colorant>
The colorant contained in the toner particles is not particularly limited, and all commercially available organic pigments, organic dyes, inorganic pigments, or pigments are dispersed in an insoluble resin or the like as a dispersion medium. Or those obtained by grafting a resin on the pigment surface can be used.
Examples of the pigment include W.W. Herbst, K.M. Examples include pigments described in Hunger “Industrial Organic Pigments”.
Specific examples of the pigment include, for example, the following ones exhibiting a yellow color.
C. I. Pigment Yellow 1, 2, 3, 4, 5, 6, 7, 10, 11, 12, 13, 14, 15, 16, 17, 23, 62, 65, 73, 74, 83, 93, 94, 95, 97, 109, 110, 111, 120, 127, 128, 129, 147, 151, 154, 155, 168, 174, 175, 176, 180, 181, 185; I. Bat yellow 1, 3, 20
Examples of those exhibiting red or magenta color include the following.
C. I. Pigment Red 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 21, 22, 23, 30, 31, 32, 37, 38, 39, 40, 41, 48: 2, 48: 3, 48: 4, 49, 50, 51, 52, 53, 54, 55, 57: 1, 58, 60, 63, 64, 68, 81: 1, 83, 87, 88, 89, 90, 112, 114, 122, 123, 146, 147, 150, 163, 184, 202, 206, 207, 209, 238, 269; I. Pigment violet 19; C.I. I. Bat red 1, 2, 10, 13, 15, 23, 29, 35.
Examples of the pigment exhibiting blue or cyan include the following.
C. I. Pigment blue 2, 3, 15: 2, 15: 3, 15: 4, 16, 17; I. Bat Blue 6; C.I. I. Acid Blue 45, a copper phthalocyanine pigment in which 1 to 5 phthalimidomethyl groups are substituted on the phthalocyanine skeleton.
Examples of the green pigment include the following.
C. I. Pigment Green 7, 8, 36.
Examples of the orange pigment include the following.
C. I. Pigment Orange 66, 51.
Examples of black pigments include the following.
Carbon black, titanium black, aniline black.
Specific examples of the white pigment include the following.
Basic lead carbonate, zinc oxide, titanium oxide, strontium titanate.
For the dispersion of the pigment in the toner particles, a dispersing means corresponding to the toner particle production method may be used. Examples of the apparatus that can be used as the dispersing means include a ball mill, a sand mill, an attritor, a roll mill, a jet mill, a homogenizer, a paint shaker, a kneader, an agitator, a Henschel mixer, a colloid mill, an ultrasonic homogenizer, a pearl mill, and a wet jet mill. There is.
It is also possible to add a pigment dispersant when dispersing the pigment. Examples of the pigment dispersant include a hydroxyl group-containing carboxylic acid ester, a salt of a long-chain polyaminoamide and a high molecular weight acid ester, a salt of a high molecular weight polycarboxylic acid, a high molecular weight unsaturated acid ester, a high molecular weight copolymer, a modified polyacrylate, a fatty acid An aromatic polyvalent carboxylic acid, naphthalene sulfonic acid formalin condensate, polyoxyethylene alkyl phosphate ester, pigment derivative and the like can be mentioned. It is also preferable to use a commercially available polymer dispersant such as Solsperse series manufactured by Lubrizol.
Moreover, it is also possible to use the synergist according to various pigments as a pigment dispersion aid. These pigment dispersants and pigment dispersion aids are preferably added in an amount of 1 to 50 parts by mass with respect to 100 parts by mass of the pigment.

The ultraviolet curable liquid developer of the present invention may contain a charge control agent as necessary.
As the charge control agent, any known one can be used without particular limitation as long as the volume resistivity of the ultraviolet curable liquid developer is small and the increase in viscosity is small.
Specific examples of the compound include the following.
Oils and fats such as linseed oil and soybean oil; Alkyd resins, halogen polymers, aromatic polycarboxylic acids, acidic group-containing water-soluble dyes, oxidative condensates of aromatic polyamines; zirconium naphthenate, cobalt naphthenate, nickel naphthenate, naphthene Metal soaps such as iron oxide, zinc naphthenate, cobalt octylate, nickel octylate, zinc octylate, cobalt dodecylate, nickel dodecylate, zinc dodecylate, aluminum stearate, cobalt 2-ethylhexanoate; petroleum sulfone Sulfonic acid metal salts such as acid metal salts and metal salts of sulfosuccinic acid esters; phospholipids such as lecithin and hydrogenated lecithin; salicylic acid metal salts such as t-butylsalicylic acid metal complexes; polyvinylpyrrolidone resins, polyamide resins, sulfonic acid-containing resins , Hydroxybenzoic Derivatives and the like.
In the present invention, the content of the charge control agent is preferably 0.01 parts by mass or more and 10 parts by mass or less, and 0.05 parts by mass or more and 5 parts by mass with respect to 100 parts by mass of the toner particles (solid content). The following is more preferable.

<Charge aid>
The toner particles may contain a charge auxiliary agent as necessary. As the charge auxiliary agent, known ones can be used.
Specific compounds include zirconium naphthenate, cobalt naphthenate, nickel naphthenate, iron naphthenate, zinc naphthenate, cobalt octylate, nickel octylate, zinc octylate, cobalt dodecylate, nickel dodecylate, zinc dodecylate. , Metal soaps such as aluminum stearate, aluminum tristearate and cobalt 2-ethylhexanoate; metal sulfonates such as petroleum metal sulfonates and metal salts of sulfosuccinates; phosphorus such as lecithin and hydrogenated lecithin Examples include lipids; salicylic acid metal salts such as t-butylsalicylic acid metal complexes; polyvinylpyrrolidone resins, polyamide resins, sulfonic acid-containing resins, and hydroxybenzoic acid derivatives.

<Cationic polymerization inhibitor>
The ultraviolet curable liquid developer of the present invention may contain a cationic polymerization inhibitor.
Examples of the cationic polymerization inhibitor include alkali metal compounds and / or alkaline earth metal compounds, or amines.
Examples of the amines include alkanolamines, N, N-dimethylalkylamines, N, N-dimethylalkenylamines, N, N-dimethylalkynylamines and the like.
Specifically, triethanolamine, triisopropanolamine, tributanolamine, N-ethyldiethanolamine, propanolamine, n-butylamine, sec-butylamine, 2-aminoethanol, 2-methylaminoethanol, 3-methylamino-1 -Propanol, 3-methylamino-1,2-propanediol, 2-ethylaminoethanol, 4-ethylamino-1-butanol, 4- (n-butylamino) -1-butanol, 2- (t-butylamino) ) Ethanol, N, N-dimethylundecanolamine, N, N-dimethyldodecanolamine, N, N-dimethyltridecanolamine, N, N-dimethyltetradecanolamine, N, N-dimethylpentadecanol Amine, N, N-dimethylnonadecylami N, N-dimethylicosylamine, N, N-dimethyleicosylamine, N, N-dimethylhenicosylamine, N, N-dimethyldocosylamine, N, N-dimethyltricosylamine, N, N- Dimethyltetracosylamine, N, N-dimethylpentacosylamine, N, N-dimethylpentanolamine, N, N-dimethylhexanolamine, N, N-dimethylheptanolamine, N, N-dimethyloctanolamine, N, N-dimethylnonanolamine, N, N-dimethyldecanolamine, N, N-dimethylnonylamine, N, N-dimethyldecylamine, N, N-dimethylundecylamine, N, N-dimethyldodecylamine, N , N-dimethyltridecylamine, N, N-dimethyltetradecylamine, N, N-dimethyl Pentadecyl amine, N, N-dimethyl hexadecylamine, N, N-dimethyl-hepta-decyl amine, N, N-dimethyl octadecyl amine. In addition to these, quaternary ammonium salts and the like can also be used. As the cationic polymerization inhibitor, a secondary amine is particularly preferable.
The content of the cationic polymerization inhibitor is preferably 1 to 5000 ppm on a mass basis in the ultraviolet curable liquid developer.

<Radical polymerization inhibitor>
The ultraviolet curable liquid developer of the present invention may contain a radical polymerization inhibitor.
In order to prevent UV curable liquid developers containing vinyl ether compounds, the photopolymerization initiator may be slightly decomposed during storage over time to form radical compounds and cause polymerization due to the radical compounds. It is good to add to.
Applicable radical polymerization inhibitors include, for example, phenolic hydroxyl group-containing compounds, quinones such as methoquinone (hydroquinone monomethyl ether), hydroquinone, 4-methoxy-1-naphthol, hindered amine antioxidants, 1,1-diphenyl -2-picrylhydrazyl free radical, N-oxyl free radical compounds, nitrogen-containing heterocyclic mercapto compounds, thioether antioxidants, hindered phenol antioxidants, ascorbic acids, zinc sulfate, thiocyanates, Thiourea derivatives, various sugars, phosphate antioxidants, nitrites, sulfites, thiosulfates, hydroxylamine derivatives, aromatic amines, phenylenediamines, imines, sulfonamides, urea derivatives, oximes, dicyandiamide And polyalkyl Polycondensates down polyamine, sulfur-containing compounds such as phenothiazine, complexing agent to tetraazacyclododecane Anne based Len (TAA), and the like hindered amines.
From the viewpoint of preventing thickening of an ultraviolet curable liquid developer by polymerization of a vinyl ether compound, preferred are phenolic hydroxyl group-containing compounds, N-oxyl free radical compounds, 1,1-diphenyl-2-picrylhydrazyl free radicals. , Phenothiazine, quinones and hindered amines, more preferably N-oxyl free radical compounds.
The content of the radical polymerization inhibitor is preferably 1 to 5000 ppm on a mass basis in the ultraviolet curable liquid developer.

<Other additives>
In addition to the above explanation, the ultraviolet curable liquid developer of the present invention may be added to various known additions depending on the purpose of improving the compatibility of the recording medium, storage stability, image storage stability, and other properties, if necessary. An agent may be contained. For example, a surfactant, a lubricant, a filler, an antifoaming agent, an ultraviolet absorber, an antioxidant, a fading preventing agent, an antifungal agent, a rust preventing agent and the like can be appropriately selected and used.

In the present invention, the method for producing the ultraviolet curable liquid developer is not particularly limited, and examples thereof include known methods such as a coacervation method and a wet pulverization method.
Further, as a general production method, a colorant, a binder resin and other additives, and a dispersion medium are mixed and pulverized using a bead mill or the like to obtain a dispersion of toner particles. A production method for obtaining an ultraviolet curable liquid developer by mixing the obtained dispersion of toner particles, a photopolymerization initiator, a cationic polymerizable monomer, and the like can be exemplified.
Details of the coacervation method are described in, for example, JP-A No. 2003-241439, International Publication No. 2007/000974, or International Publication No. 2007/000975.
In the coacervation method, a pigment, a resin, a solvent that dissolves the resin, and a solvent that does not dissolve the resin are mixed, the solvent that dissolves the resin is removed from the mixed solution, and the solution in a dissolved state is obtained. By precipitating the resin, the toner particles embedded with the pigment can be dispersed in a solvent that does not dissolve the resin.
On the other hand, details of the wet pulverization method are described in, for example, International Publication No. 2006/126666 or International Publication No. 2007/108485.
In the wet pulverization method, the toner particles are electrically pulverized by kneading the pigment and the binder resin at a melting point of the binder resin or higher and then dry pulverizing the resulting pulverized material in an electrically insulating medium. Can be dispersed in.
In the present invention, such a known method can be used.
The toner particles preferably have a volume average particle diameter of 0.05 μm or more and 5 μm or less, more preferably 0.05 μm or more and 1 μm or less from the viewpoint of obtaining a high-definition image.
In the present invention, the toner particle concentration in the ultraviolet curable liquid developer is not particularly limited, but may be about 1% by mass to 70% by mass, and may be about 1% by mass to 50% by mass. Preferably, it is more preferably about 2% by mass or more and 40% by mass or less.

<Physical properties of UV curable liquid developer>
The ultraviolet curable liquid developer of the present invention is preferably prepared and used so as to have the same physical property values as those of a normal liquid developer.
That is, the viscosity of the ultraviolet curable liquid developer is set to 0.5 mPa · s or more and 100 mPa · s at 25 ° C. at a toner particle concentration of 2% by mass from the viewpoint of obtaining appropriate electrophoretic mobility of toner particles. The following is preferable. Further, the volume resistivity of the ultraviolet curable liquid developer is preferably 1 × 10 ⁹ Ω · cm or more and 1 × 10 ¹⁵ Ω · cm or less, in terms of not lowering the potential of the electrostatic latent image. × and more preferably at most ^{10 10 Ω} · cm or more 1 × ^{10 13 Ω} · cm.
In the present invention, it is possible to prepare an ultraviolet curable liquid developer satisfying the above physical property values while obtaining high ultraviolet curable properties.

[Image forming apparatus]
The ultraviolet curable liquid developer of the present invention can be suitably used in an electrophotographic general image forming apparatus.
<Light source>
The ultraviolet curable liquid developer of the present invention is irradiated with ultraviolet rays immediately after being transferred to a recording medium, and the image is fixed by being cured.
Here, as a light source for irradiating ultraviolet rays, a mercury lamp, a metal halide lamp, an excimer laser, an ultraviolet laser, a cold cathode tube, a hot cathode tube, a black light, an LED (light emitting diode) and the like can be applied, and a belt shape A metal halide lamp, a cold cathode tube, a hot cathode tube, a mercury lamp or a black light, and an LED are preferred.
It is preferable that the irradiation amount of an ultraviolet-ray is 0.1-1000 mJ / cm < ² >.

The measurement method used in the present invention is shown below.
<Measurement method of volume resistivity>
The volume resistivity of the ultraviolet curable liquid developer is determined by measuring the volume resistivity of the liquid developer using a digital ultrahigh resistance / microammeter R8340A (manufactured by Advantest). The measurement is performed by putting 25 ml of the liquid developer into the liquid sample electrode SME-8330 (manufactured by Hioki Electric Co., Ltd.) and applying a direct current of 1000 V at a room temperature of 25 ° C.

<Composition analysis>
The following method is used to determine the structure of a compound or the like.
Using ECA-400 (400 MHz) manufactured by JEOL Ltd., ¹ H-NMR and ¹³ C-NMR spectra are measured.
Measurement is performed at 25 ° C. in a deuterated solvent containing tetramethylsilane as an internal standard substance. The chemical shift value is shown as a ppm shift value (δ value) with tetramethylsilane as an internal standard substance being zero.

<Measurement Method of SP Value and Mole Average SP Value of Cationic Polymerizable Liquid Monomer, and Number of Polymerizable Functional Groups per Molecule of Cationic Polymerizable Liquid Monomer and Number of Mole Average Functional Groups>
In the present invention, the SP value and molar average SP value of the cationic polymerizable liquid monomer in the ultraviolet curable liquid developer, the number of polymerizable functional groups per molecule of the cationic polymerizable liquid monomer, and the molar average functionality. The radix is determined by the following method.
(1) The ultraviolet curable liquid developer is centrifuged, the toner particles are settled, and the supernatant is extracted.
(2) The supernatant is measured by gel permeation chromatography to determine the molecular weight and content of the inclusion, and fractionated for each molecular weight component.
(3) By performing ¹ H-NMR and ¹³ C-NMR spectrum measurements for each fractionated component, the chemical structure of each component is identified and the contained cationic polymerizable liquid monomer The molecular weight, content, and number of polymerizable functional groups per molecule are determined.
Here, the chemical structure is identified by spectrum measurement of ¹ H-NMR and ¹³ C-NMR, but a known analysis method such as infrared spectroscopy or gas chromatography is used in combination as necessary. It is also possible.
(4) For each cationically polymerizable liquid monomer whose chemical structure has been identified in (3) above, an SP value is calculated by the Fedors method.
(5) From the molecular weight and content of each component calculated in the above (3) and (4), the number of polymerizable functional groups per molecule, and the SP value, the molar average SP value and the molar average functionality are calculated according to the following formula. Find the radix.
Mix (Awt) parts by mass of cationic polymerizable liquid monomer A having SP value (Asp) and molecular weight (Amw) and (Bwt) parts by mass of cationic polymerizable liquid monomer B having SP value (Bsp) and molecular weight (Bmw). When used, the molar average SP value of the cationically polymerizable liquid monomer is determined as follows.
Mole average SP value = {(Asp × Awt / Amw) + (Bsp × Bwt / Bmw)} / {(Awt / Amw) + (Bwt / Bmw)}
Cationic polymerizable liquid monomer A having the number of polymerizable functional groups per molecule (Af) and molecular weight (Amw) (Awt) parts by mass, the number of polymerizable functional groups per molecule (Bf), and cationic polymerization of molecular weight (Bmw) When the functional liquid monomer B is used in a mixture of (Bwt) parts by mass, the number of mole average functional groups of the cationic polymerizable liquid monomer is determined as follows.
Mole average functional group number = {(Af × Awt / Amw) + (Bf × Bwt / Bmw)} / {(Awt / Amw) + (Bwt / Bmw)}
The above is a calculation formula when the cationic polymerizable liquid monomer contains two types of cationic polymerizable liquid monomer A and cationic polymerizable liquid monomer B, but the calculation formula also applies when three or more types are contained. It can be obtained in the same manner by extending to a three-component system or more.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited thereto. In the following description, unless otherwise specified, “part” and “%” mean “part by mass” and “% by mass”, respectively.

<Example 1>
(Production of toner particles)
In a separable flask, 25 parts of Nucrel N1525 (ethylene-methacrylic acid resin, manufactured by Mitsui DuPont Polychemical Co., Ltd.) and 75 parts of cyclohexanedimethanol divinyl ether (Exemplary Compound B-17) were charged, and using a three-one motor, 200 rpm The mixture was heated to 130 ° C. in an oil bath with stirring for 1 hour. After being held at 130 ° C. for 1 hour, it was gradually cooled at a temperature drop rate of 15 ° C. per hour to prepare a binder resin dispersion. The obtained binder resin dispersion was a white paste.
59.40 parts of the binder resin dispersion, Pigment Blue 15: 3 (4.95 parts) as a pigment, 0.20 parts of aluminum tristearate as a charge auxiliary agent, and 35.45 parts of cyclohexanedimethanol divinyl ether, Filled in a planetary bead mill (Classic Line P-6, manufactured by Fritsch) together with zirconia beads having a diameter of 0.5 mm, and pulverized at 200 rpm for 4 hours at room temperature to obtain a toner particle dispersion (solid content 20 mass%). It was.
The toner particles contained in the obtained toner particle dispersion had a volume average particle size of 0.85 μm (measured with a dynamic light scattering (DLS) particle size distribution measuring device, Nanotrack 150 manufactured by Nikkiso Co., Ltd.). .
(Preparation of liquid developer)
10.00 parts of the toner particle dispersion, 0.10 parts of hydrogenated lecithin (Resinol S-10, manufactured by Nikko Chemicals Co., Ltd.) as a charge control agent, and 1.66 cyclohexanedimethanol divinyl ether as a cationic polymerizable liquid monomer Parts, diethylpentanediol divinyl ether (Exemplary Compound B-26) 29.99 parts, pentaerythritol tetravinyl ether (Exemplary Compound B-28) 57.98 parts, Exemplified Compound A-26 (0.29 parts) as a photopolymerization initiator ), 0.49 part of 2,4-diethylthioxanthone (hereinafter referred to as DETX) as a photopolymerization sensitizer, and 1,4-diethoxynaphthalene (hereinafter referred to as DEN) as a photopolymerization sensitizer. ) 0.49 part was mixed to obtain an ultraviolet curable liquid developer.

The obtained ultraviolet curable liquid developer was evaluated as follows, and the results are shown in Tables 1 and 2. Evaluation items and evaluation results are as follows.
(Developability: Evaluation on image density and image blur)
An electrostatic pattern was formed on the electrostatic recording paper with a surface charge of 500 V, and development was performed at a process speed of 20 mm / sec using a liquid developer and a roller developing machine using a metal roller. The distance between the roller and the electrostatic recording paper (development gap) was set to 34 μm. The quality of the obtained image was confirmed visually.
5: A high-density and high-definition image was obtained 4: Slight density unevenness or slight image blurring was observed 3: Although density unevenness and image blurring were sporadic, the image was developed well in general. 2: Severe density unevenness and image blur occurred, and development was insufficient. 1: Development was not possible.

(Fixability)
In an environment of room temperature 25 ° C. and humidity 50%, a liquid developer is dropped onto a polyethylene terephthalate film, and bar coating is performed using a wire bar (No. 6) [supplier: Matsuo Sangyo Co., Ltd.] The cured film was formed by irradiation with an LED (illuminance 1000 mW / cm ² , irradiation distance 15 mm) having an emission wavelength of 385 nm. The irradiation light quantity when the surface was completely cured without tack (adhesiveness) was measured and evaluated according to the following criteria.
10: 100 mJ / cm ²
9: 150 mJ / cm ²
8: 200 mJ / cm ²
7: 300 mJ / cm ²
6: 400 mJ / cm ²
5: 800 mJ / cm ²
4: 1,000 mJ / cm ²
3: 1,500 mJ / cm ²
2: 2,000 mJ / cm ²
1: Not cured If it was 5 or more, it was judged that the effect of the present invention was exhibited in fixability.

(Storability)
An ultraviolet curable liquid developer was sealed in a sealed container at 50 ° C. to evaluate the storage stability. The evaluation criteria are as follows.
In addition, the following viscosity change rate (%) was computed using the following formula.
Viscosity change rate (%) = {(viscosity after storage) − (viscosity before storage)} / (viscosity before storage) × 100
The viscosity was measured as follows using a viscoelasticity measuring device (Physica MCR300 manufactured by Anton Paar). About 2 mL of the sample was filled in a measuring apparatus equipped with a cone plate type measuring jig (75 mm diameter, 1 °) and adjusted to 25 ° C. The viscosity was measured while continuously changing the shear rate from 1000 s ⁻¹ to 10 s ^−1, and the value at 10 s ⁻¹ was taken as the viscosity.
Viscosity change rate after storage for 5 months: ± 5% or less, no change in developability and fixability after storage for 1 month, Viscosity change rate after storage for 4: 1 months: ± 10% or less No significant changes were observed in developability and fixability after storage for 1 month. Viscosity change rate after storage for 3: 1 month was less than ± 100% and deteriorated in developability and fixability after 1 month storage. Although there was a tendency, good developability and fixability were obtained by adjusting development conditions or fixing conditions. Viscosity change rate after storage for 2: 1 month was ± 100% or more, and developability after storage for 1 month The fixing property was greatly deteriorated, and the developing condition or the fixing condition was not adjusted, and good developing property and fixing property could not be obtained.

<Examples 2 to 11, Examples 15 to 17, Comparative Examples 1 to 12>
Example 1 is the same as Example 1 except that the cationic polymerizable liquid monomer, the photopolymerization initiator, the photopolymerization sensitizer, and the photopolymerization sensitization agent are blended so as to have the compositions shown in Tables 1 and 2. Thus, an ultraviolet curable liquid developer was obtained.

<Example 12>
In the same manner as in Example 1 (preparation of toner particles), except that cyclohexanedimethanol divinyl ether (Exemplary Compound B-17) is changed to dodecyl vinyl ether (Exemplary Compound B-3), a toner particle dispersion (solid content 20) is obtained. Mass%).
The toner particles contained in the obtained toner particle dispersion had a volume average particle size of 0.82 μm (measured with a dynamic light scattering method (DLS) particle size distribution measuring device, Nanotrack 150 manufactured by Nikkiso Co., Ltd.). .
(Preparation of liquid developer)
10.00 parts of the toner particle dispersion, 0.10 parts of hydrogenated lecithin (Resinol S-10, manufactured by Nikko Chemicals Co., Ltd.) as a charge control agent, 1.62 parts of dodecyl vinyl ether as a cationic polymerizable liquid monomer, 4.81 parts of cyclopentadiene vinyl ether (Exemplary Compound B-8), 81.76 parts of butylethylpropanediol divinyl ether (Exemplary Compound B-27), Exemplified Compound A-3 (0.96 parts) as a photopolymerization initiator, As a photopolymerization sensitizer, 0.48 part of 2,4-diethylthioxanthone (hereinafter referred to as DETX) and as a photopolymerization sensitization agent, 1,4-diethoxynaphthalene (hereinafter referred to as DEN) 0 .48 parts were mixed to obtain an ultraviolet curable liquid developer.

<Examples 13 and 14>
Example 12 is the same as Example 12 except that the cationic polymerizable liquid monomer, the photopolymerization initiator, the photopolymerization sensitizer, and the photopolymerization sensitizer are blended so as to have the compositions shown in Tables 1 and 2. Thus, an ultraviolet curable liquid developer was obtained.

Evaluation similar to Example 1 was performed using the obtained liquid developer. The evaluation results are shown in Tables 1 and 2.
In Examples 15 to 17 and Comparative Examples 5 to 12, instead of the LED having an emission wavelength of 385 nm, a cured film was formed by irradiating light having a wavelength of 365 nm using a high-pressure mercury lamp having a lamp output of 120 mW / cm ^2. Formed. The irradiation light quantity when the surface was completely cured without tack (adhesiveness) was measured, and the fixing property was evaluated according to the above criteria.

The polymerizable liquid monomer and the polymerization initiator used in the comparative examples are as follows.
<Radically polymerizable monomer (C-1)>
1,6-hexanediol diacrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd., radical polymerizable monomer)
<Photopolymerization initiator (D-1)>
CPI-110P (manufactured by San Apro Co., Ltd., triarylsulfonium salt type photocationic polymerization initiator)
<Photopolymerization initiator (D-2)>
WPI-113 (manufactured by Wako Pure Chemical Industries, Ltd., diphenyliodonium salt type photocationic polymerization initiator)
<Photopolymerization initiator (D-3)>
IRGACURE (registered trademark) 369 (manufactured by BASF Japan Ltd., α-aminoalkylphenone photo radical polymerization initiator)
<Photopolymerization initiator (D-4)>
Lucirin TPO (manufactured by BASF Japan Ltd., acylphosphine oxide photo radical polymerization initiator)

Table 3 shows the SP value of the polymerizable liquid monomer in Table 1 and Table 2 and the number of polymerizable functional groups per molecule.
Moreover, "content (part)" in Table 1 and Table 2 has shown the ratio of each material by the mass part when the sum total of a polymerizable liquid monomer is 100 mass parts.

In Tables 1 and 2, if the fixability satisfies Rank 5 or higher, the developability satisfies Rank 3 or higher, and the storage stability satisfies Rank 3 or higher, sufficient image density is obtained, image blur is small, and sufficient fixability is achieved. And good storage stability.
By comparing Examples 1 to 14 with Comparative Examples 1 to 4, it is understood that developability, fixability and storage stability can be satisfied at a high level by using the ultraviolet curable liquid developer of the present invention. .
Furthermore, when the following conditions are satisfied, it can be seen that the developability, fixability, and storage stability are satisfied at a further excellent level.
The content of the compound represented by the formula (1) is 0.05 parts by mass or more and 1.00 parts by mass or less with respect to 100 parts by mass of the cationic polymerizable liquid monomer.
The cationic polymerizable liquid monomer is composed of a cationic polymerizable liquid monomer having two or more polymerizable functional groups per molecule.
The cationic polymerizable liquid monomer is composed of a cationic polymerizable liquid monomer having an SP value of 9.0 or less.
The photopolymerization initiator is a compound represented by the above formula (2).

From the results of the comparative examples in Table 2, it can be seen that when a large amount of a polymerization initiator that tends to lower the volume resistivity is used in order to obtain sufficient fixability, both developability and fixability cannot be achieved.
On the other hand, it can be seen that Example 17 of the present invention is excellent in developability while obtaining good fixability.
Furthermore, it can be seen that by using a thioxanthone compound or a naphthalene compound as a photopolymerization sensitizer or photopolymerization sensitization agent, excellent fixability can be obtained without impairing developability.

Claims (7)

An ultraviolet curable liquid developer containing a cationic polymerizable liquid monomer, a photopolymerization initiator, and toner particles,
The cationic polymerizable liquid monomer contains a vinyl ether compound,
The cation polymerizable liquid monomer has a molar average SP value of 9.0 or less,
The cation polymerizable liquid monomer has a molar average functional group number of 1.8 or more,
The photopolymerization initiator contains a compound represented by the following formula (1),
The content of the compound represented by the following formula (1) is 0.01 part by mass or more and 5.00 parts by mass or less with respect to 100 parts by mass of the cationic polymerizable liquid monomer. Liquid developer.

[In the formula (1), R ₁ and R ₂ are bonded to each other to form a ring structure, x represents an integer of 1 to 8, and y represents an integer of 3 to 17. ]   The ultraviolet curing according to claim 1, wherein the content of the compound represented by the formula (1) is 0.05 parts by mass or more and 1.00 parts by mass or less with respect to 100 parts by mass of the cationic polymerizable liquid monomer. Type liquid developer.   The ultraviolet curable liquid developer according to claim 1, wherein the cationic polymerizable liquid monomer is composed of a cationic polymerizable liquid monomer having an SP value of 9.0 or less.   The ultraviolet curable liquid developer according to any one of claims 1 to 3, wherein the cationic polymerizable liquid monomer is a cationic polymerizable liquid monomer having two or more polymerizable functional groups per molecule. The ultraviolet curable liquid developer according to any one of claims 1 to 4, wherein the compound represented by the formula (1) is a compound represented by the following formula (2).

[In the formula (2), x represents an integer of 1 to 8, and y represents an integer of 3 to 17. R ₃ and R ₄ each independently represents an alkyl group, an alkyloxy group, an alkylthio group, an aryl group, an aryloxy group, or an arylthio group, and o and p each independently represent an integer of 0 or more and 3 or less. Represent. When o is 2 or more, a plurality of R ₃ may be bonded to each other to form a ring structure, and when p is 2 or more, a plurality of R ₄ may be bonded to each other to form a ring structure. R ₃ and R ₄ may be bonded to each other to form a ring structure. ] The ultraviolet curable liquid developer further contains a photopolymerization sensitizer,
The ultraviolet curable liquid developer according to claim 1, wherein the photopolymerization sensitizer contains a thioxanthone compound or an anthracene compound. The ultraviolet curable liquid developer further contains a photopolymerization sensitization aid,
The ultraviolet curable liquid developer according to claim 6, wherein the photopolymerization sensitization aid contains a naphthalene compound.