JPH0625875B2 - Liquid developer for electrostatic photography - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a liquid developer for electrostatic photography, and more particularly to a wet electrophotographic developer in which a toner fixed by ultraviolet irradiation is dispersed in a carrier liquid.

[Prior art]

The developing means for visualizing the electrostatic latent image is roughly classified into a dry method and a wet method. Although both methods have advantages and disadvantages, the wet development method (liquid developer) is advantageous for obtaining an image with good resolution and gradation. However, when the conventional liquid developer is used, it takes a long time to fix the toner, and therefore, defects are found at a low copying speed.

In addition, conventional liquid developers do not always have sufficient toner fixing power. Therefore, when such liquid developers are used for color electrophotography, the four primary colors and black toner are not uniformly superposed and the faithful color is reproduced. There is also a tendency that reproduction is difficult.

〔Purpose〕

A first object of the present invention is to provide a liquid developer for electrostatic photography which has improved fixing performance of wet toner. A second object of the present invention is to provide a liquid developer capable of high-speed color copying as well as monochromatic copying. A third object of the present invention is to provide a liquid developer capable of performing non-contact fixing and obtaining clear image quality.

〔Constitution〕

The liquid developer for electrostatic photography according to the present invention is characterized in that an ultraviolet-fixing toner containing the following (a) and (b) as main components is dispersed in an aliphatic hydrocarbon solution.

(A) Colorant, (b) [However, R is hydrogen or a methyl group, A is -COOC _n H _{2n + 1} or-
OCOC _n H _{2n + 1} (n is an integer of 6 to 20). ] The composition containing the monomer or its polymer represented by these, and a polyfunctional acrylate (methacrylate) monomer or its polymer; or these copolymers.

Hereinafter, the present invention will be described in more detail. Prior to that, the reaction principle under ultraviolet irradiation is referred to "Coloring Material" 48, 1975, and the "light" related to the present invention from the currently reported photosensitive group is referred to. The polymerizable unsaturated group "will be described.

The photopolymerizable unsaturated group is an unsaturated group which is polymerized by addition polymerization by light directly or by the action of a photopolymerization initiator, and generally has the following structure.

When X and X ′ are electron-withdrawing groups, adjacent double bonds are activated and the polymerization rate increases. Since the ethylenically unsaturated group of the non-conjugated vinyl monomer has absorption at 180 to 200 nm, it means that the energy of 142 Kcal / mol was given when the ultraviolet ray of this wavelength was absorbed. Since this energy is sufficient to break even the σ bond, various radicals may be generated.

However, the wavelength of light absorbed by these unsaturated groups is usually in the short wavelength ultraviolet region, and, for example, a high pressure mercury lamp or a xenon lamp used as a light source has a weak emission intensity in the short wavelength ultraviolet region. Therefore, polymerization by direct excitation is inefficient, and free radicals (R
The polymerization is initiated using a photopolymerization initiator that generates
In this case, the photopolymerization process is considered to proceed according to the following elementary reaction.

When such a photopolymerizable unsaturated group is used as a photosensitive group, the photo-curing rate of the oligomer depends on the polymerization rate of the unsaturated group. When the thin film is irradiated with light, the polymerization rate R is represented by the following equation.

(K _t = k _td + k _te ) where I ₀ is the incident light intensity, Q is the quantum yield of initiator radical formation, ε is the extinction coefficient of the initiator, l is the film thickness, and f is the initiator. Efficiency, [I] is the initiator concentration.

Therefore, the factors that govern the photo-curing rate of the oligomer are (i) the reactivity of the initiator radical with the monomer and the large rate constant k _{p of} growth, and (ii) the initiation of the radiant energy of the light source at a large wavelength. The extinction coefficient of the agent is high, the quantum yield is high, and (iii) the unsaturated group concentration in the oligomer is high.

Generally, the reactivity between the initiator radical and the monomer is such that the stabilization energy (ΔErs) obtained by delocalizing the unpaired electron to the monomer through the conjugated system in the transition state of the reaction is large. Grows in. The same applies to the reactivity between the growing radical and the monomer.

Due to the application of this principle, in the present invention, the acrylate represented by the above general formula is used as the binder component of the ultraviolet fixing toner (hereinafter, may be referred to as "component A" for convenience).
In addition, a UV-curable polyfunctional acrylate or methacrylate (hereinafter, may be referred to as “component B” for convenience) is adopted.

In the wet toner, the component A is present in the form of a monomer or an oligomer. Preferably component A is present in the form of an oligomer with component B.

On the other hand, the component B is also present as a monomer or an oligomer in the wet toner. Ingredient A and ingredient B
Copolymers (oligomers) with are also useful.

Incidentally, the component A has a property of being solvated with a carrier liquid (aliphatic hydrocarbon solvent) regardless of whether it is a monomer or an oligomer. Further, the component B has a property of being solvated with the above solvent if it is a monomer, but not solvated in the form of an oligomer.

Incidentally, the ratio of the component B to the component A is appropriately 0.01 to 1: 1 (weight).

Specific examples of the component A include lauryl methacrylate, lauryl acrylate, stearyl methacrylate, stearyl acrylate, 2-ethylhexyl methacrylate, 2-ethylhexyl acrylate, dodecyl methacrylate, dodecyl acrylate, hexyl methacrylate, hexyl acrylate, octyl methacrylate, octyl methacrylate, cetyl methacrylate. ,
Examples thereof include cetyl acrylate, vinyl laurate, vinyl stearate and the like.

Specific examples of the component B include ethylene glycol diacrylate, ethylene glycol dimethacrylate, diethylene glycol diacrylate, diethylene glycol methacrylate, triethylene glycol triacrylate, triethylene glycol trimethacrylate, butanediol diacrylate, butanediol dimethacrylate, 1,6 -Hexanediol diacrylate, 1,6-hexanediol dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, tetramethylolmethane triacrylate, tetramethylolmethane trimethacrylate, tetramethylolmethane tetraacrylate, tetramethylolmethane tetramethacrylate , Dipropylene Recall diacrylate, dipropylene glycol dimethacrylate, trimethylol hexane triacrylate, trimethylol hexane trimethacrylate, pentaerythritto tetraacrylate, pentaerythritto tetramethacrylate, 1,3-butylene glycol diacrylate, 1,3-butylene glycol diacrylate Methacrylate, trimethylolethane triacrylate, trimethylolethane methacrylate and the like can be mentioned.

Examples of the colorant include dyes or pigments such as carbon black, oil blue, alkali blue, phthalocyanine blue, phthalocyanine green, spirit black, aniline black, oil violet, benzidine yellow, methyl orange, brilliant carmine, farestred, and crystal violet. can give.

A photopolymerization initiator is preferably added to the toner.

The photopolymerization initiator (photosensitizer) is a substance that is easily decomposed by ultraviolet rays to generate radicals, and is added to the binder component (the component A and the component B) in advance to perform development. This is followed by irradiation with ultraviolet rays to initiate polymerization by radicals from the photosensitizer.

Such photosensitizers include, in addition to carbonyl compounds such as diacetyl, benzyl, benzophenone, benzaldehyde, and cyclohexanone, azobisisobutyronitrile, azomethane, tetramethylthiuram disulfide, dibenzothiazolyl disulfide, tetra- Examples thereof include carbon chloride, organic peroxides, uranyl nitrate and eosin, erythrosine, neutral red, Victoria blue and the like.

Examples of the aliphatic hydrocarbon that is a solvent (carrier liquid) include kerosene, ligroin, n-hexane, n-heptane, n-octane, i-octane, and i-dodecane (commercially available products manufactured by Exxon Corporation. Isopar H, G, L,
K; naphtha No. 6; sorbetso 100, etc.), carbon tetrachloride, perfluoroethylene, etc.

In the liquid developer according to the present invention, as described above, the binder of the toner is mainly composed of the component A and the component B, but the most preferable example is (a) a copolymer of the component A and the component B. Combination of (oligomer) and monomer component A, (b) Copolymer of component A and component B (oligomer)
And a combination of the monomer component B.

Such an oligomer can be obtained by heat-polymerizing monomer A and monomer B in an aliphatic hydrocarbon solvent in the presence of a polymerization initiator such as benzoyl peroxide or azobisisobutyronitrile.

To prepare the liquid developer of the present invention, generally 0.5 to 5 parts by weight of the binder component (component A, component B) per 1 part by weight of the colorant.
1 part by weight, and this is sufficiently dispersed in the presence of 10 to 20 parts by weight of an aliphatic hydrocarbon solvent with a disperser such as an attritor, a ball mill, or a keddy mill to give a concentrated toner, which is then added with a similar solvent. It may be diluted 5 to 10 times. In this case, the copolymer dispersion obtained as described above can be used as it is as the above-mentioned copolymer (oligomer) and solvent.

The liquid developer thus obtained is subjected to development by a conventional means, and subsequently, is irradiated (fixed) with ultraviolet rays to form a toner image on a transfer target such as paper.

As described above, since the binder component in the toner of the present invention is an ultraviolet curable one, it is exposed to ultraviolet rays (300 to 400
(nm) easily fixes the toner.

The ultraviolet irradiation device is composed of a lamp, a reflector, a lamp housing, a power supply unit and the like.

By developing and fixing (ultraviolet irradiation) with the ultraviolet curable wet toner as in the present invention, high-speed copying of about 70 sheets per minute or more in A-4 size is possible. However, if an ultraviolet absorber is contained in this toner, the fixing can be performed more efficiently, and higher speed copying can be performed. The addition of the ultraviolet absorber is advantageous because it also functions as an anti-fading agent and provides an image with good light resistance.

Specific examples of such an ultraviolet absorber include p-dimethylaminobenzaldehyde p-dimethylaminobenzoic acid p-dimethylaminoacetophenone N-methyl N, β-chloroethylaminobenzaldehyde 4,4′bis (diethylamino) benzophenone p- Chlorobenzophenone p, p'-dichlorobenzophenone Irgakiure 651 (Ciba Geigy) Irgakiure 184 (〃) Daroquiure 1116 (Merck) Daroquiure 1173 (〃) 4-benzoyl diphenyl ether 4-benzoyl-4'-methyl Diphenyl ether 4-benzoyl-4'-ethyldiphenyl ether 4-benzoyl-4'-methoxydiphenyl ether 4-benzoyl-4'-chlorodiphenyl ether 4-p-toluoyl-4'-methyldiphenyl ether -Benzoyl-3 ', 4'-dimethyldiphenyl ether 4-benzoyldiphenyl sulfide 4-benzoyl-4'-methyldiphenyl sulfide 4-p-toluoyl-4'-methyldiphenyl sulfide benzophenone benzoylbenzoic acid Methyl ester Benzoin ethyl ether Benzoin isopropyl ether Benzoin isobutyl ether Benzyl xanthone 2-Methylthioxanthone 2-Isopropylthioxanthone 2-Chlorothioxanthone Counterkyur DBS (manufactured by Wart Brekinsott) Counterkyur PDO (〃) Kayakiure MBP (Nippon Kayaku) KAYAKI YOUR RTX (〃) KAYAKI YOUR DITX (〃) KAYAKI YOUR DMBI (〃) NITSUSOKIA EMA (manufactured by Nippon Oil & Chemicals) PAIKIURE 55 Sandle 1000 (made by Sand) Acetokiure 1NPP (made by Acetochemical) Trigonal 12 (made by Akzo Chemie) DEAP (made by AUPJYON).

The content of the ultraviolet absorber is 20% by weight or less, preferably 0.1 to 5% by weight, based on the toner. The method of adding the ultraviolet absorber may be dispersion in a polymer solvent, adsorption to a pigment, or addition of the ultraviolet absorber into a colorant, a resin, and a solvent at the time of preparation of a concentrated toner, and dispersion.

Next, examples will be shown. All parts here are parts by weight.

Example 1 Carbon black (Mitsubishi Kasei Co., Ltd., Mitsubishi # 44) 300
Part Ethylene glycol dimethacrylate (monomer)
350 parts 2-ethylhexyl methacrylate (monomer)
50 parts Isopar G
300 parts was dispersed with a three-roll mill to make a concentrated type wet toner for electrostatic photography, and 200 g of this toner was added to Isopar G200 g.
To prepare a liquid developer.

Next, a plain paper copier manufactured by Ricoh Company (Recopy DT-120
1) after copying to fine paper with the above liquid developer using
The toner was cured with two 60 W / cm high pressure mercury lamps (manufactured by Nippon Battery Co., Ltd.) at a conveyor speed of 3.0 m / min to obtain a copy.

Example 2 Carbon black (made by Columbia Carbon Co., Raven
1225)
200 parts Diethylene glycol diacrylate / styrene copolymer (polymerization cell ratio 5/5) 350 parts Lauryl methacrylate (monomer)
100 copies Isopar G
350 parts of the toner was dispersed by a ball mill to prepare a concentrated type wet toner for electrostatic photography, and 200 g of this toner was dispersed in 1000 g of Isopar G to prepare a liquid developer.

Subsequently, using the above liquid developer, a copy was obtained in the same manner as in Example 1 (however, conveyor speed 3.0 m / min).

Example 3 Phthalocyanine green (manufactured by Dainichiseika Co., Ltd.)
300 parts Trimethylolpropane triacrylate (monomer)
100 parts Hexyl acrylate / maleic acid copolymer (polymerization molar ratio 8/2) 300 parts Benzophenone [UV absorber]
0.5 part Isopar H
300 parts of the toner was dispersed by a ball mill to prepare a concentrated type wet toner for electrostatic photography, and 500 g of this toner was dispersed in 1000 g of Isopar H to prepare a liquid developer.

Then, a plain paper copier made by Ricoh Company (Recopy DT / 1800
1) after copying to fine paper with the above liquid developer using R)
The toner was cured with two 60 W / cm high-pressure mercury lamps (manufactured by Nippon Battery Co., Ltd.) at a conveyor speed of 3.5 m / min to obtain a copy.

Example 4 300 parts of carbon black (Raven 1225) Tetramethylolpropane tetraacrylate (monomer)
150 parts octyl methacrylate
150 parts 2- (2'-hydroxy-5'-methylphenyl) benzotriazole [UV absorber]
2nd part Isopar H
300 parts were dispersed by a ball mill to prepare a concentrated liquid developer for electrostatic photography.

Then, after developing by the roller developing method using the above liquid developer and transferring the toner image to the high-quality paper, two 160 W / cm high pressure mercury lamps (manufactured by Nippon Battery Co., Ltd.) and a conveyor speed of 5.0 m are used.
The toner layer was cured at a speed of 1 / min to obtain a copy.

Examples 5 to 9 The mixtures shown in Table 1 were dispersed by a ball mill to prepare concentrated liquid developers for electrostatic photography. Subsequently, using these developers, a copy was obtained in the same manner as in Example 4. The curing speed of the toner layer at that time was 0.3 m / min in Example 5 and 2.
6 m / min, Example 7 was 4.3 m / min, Example 8 was 4.0 m / min, and Example 9 was 5.5 m / min.

[Effect] As described above, the present invention provides a wet toner having excellent fixability by ultraviolet irradiation. The use of the liquid developer for electrostatic photography of the present invention brings about the following effects.

(i) Since fixing is instantaneously completed, the fixing speed is high, and in addition, there is almost no generation of harmful vapor or odor.

(ii) Since the non-image portion is not overheated during fixing, a plastic film or the like can be used as the image supporting member other than paper.

(iii) A clear image peculiar to the wet type developer is obtained, but this image is more clear because fixing is performed in a non-contact manner.

(iv) The toner once fixed is not affected by the irradiation of ultraviolet rays again, which is suitable for obtaining a color copy.

Claims (2)

[Claims] 1. A liquid developer for electrostatic photography, characterized in that an ultraviolet fixing toner containing the following (a) and (b) as main components is dispersed in an aliphatic hydrocarbon solvent. (A) Colorant. (B) [Wherein R is hydrogen or a methyl group, and A is -COOC _n H _{2n + 1}
Alternatively, it is —OCOC _n H _{2n + 1} (n is an integer of 6 to 20). ] The composition containing the monomer or its polymer represented by these, and a polyfunctional acrylate (methacrylate) monomer or its polymer; or these copolymers. 2. The liquid developer according to claim 1, wherein the toner contains an ultraviolet absorber.