JPH07114222A - Electrophotographic liquid developer - Google Patents

Abstract

PURPOSE:To provide a red color electrophotographic liquid developer with which high quality picture images can be stably obtd. for a long time without requiring a charge controlling agent, and to provide a liquid developer with high picture image density, high gradation reproducibility, drying property and transparency, and excellent color reproducibility and secondary fixing property. CONSTITUTION:Basic dyes expressed by general formula are used as a coloring agent of this electrophotographic liquid developer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic liquid developer, and more specifically, electrostatically attaching toner particles to an electrostatic latent image formed on an electrophotographic photoreceptor or electrostatic recording body. The present invention relates to a liquid developer for electrophotography, which is used in a process of attaching and visualizing.

[0002]

2. Description of the Related Art A method for obtaining an image by an electrophotographic method or an electrostatic recording method is an electrostatic latent image which is positively or negatively charged on an electrophotographic photosensitive member, electrostatic recording paper or the like by a conventional method. To form
Toner particles in the liquid developer which are positively or negatively charged may be attached to the toner particles to form a visible image. In this case, the electrostatic latent image is visualized with a dry developer, but
A liquid developing method is preferable as a method for obtaining a high-quality image having high resolution. As a liquid developer for electrophotography, it is well known that a liquid obtained by uniformly dispersing a toner having an inorganic or organic pigment coated with a binder resin in a carrier liquid having a high insulating property and a low dielectric constant (Japanese Patent Application Laid-Open No. 2004-242242) 50-151528, 53-109633, 55-144252, etc.). Such a liquid developer is produced by a method in which a mixture of a pigment, a binder resin, and a carrier liquid is pulverized and dispersed by a pulverizing / mixing machine such as a ball mill, but in this method, the toner is not dispersed to primary particles. In addition to being easily caked, the obtained image has poor transparency and color reproducibility. Further, the chargeability of the surface of the toner particles is generally low if there is no charge control agent such as metal soap, so that in the absence of the charge control agent, the transfer rate is lowered or an image defect often occurs.

It has been studied to color latex with a dye to prepare a toner for a liquid developer (JP-A-45-45).
No. 25878, No. 56-10619, etc.), the toner has a low coloring density and may cause background fog if the remaining dye is not sufficiently removed. Therefore, a wax and a pigment are dispersed in a heated carrier liquid, the liquid is rapidly cooled to attach the wax to the surface of the pigment, and the wax-treated pigment is dispersed in a carrier liquid together with a binder resin to obtain a developer. (JP-A-57-34720, 57-1937)
No. 3, etc.), a wax and a pigment are kneaded, and this is spray-granulated with a spray dryer to obtain a wax-treated pigment.
It has been proposed to disperse this together with a binder resin in a carrier liquid to form a developer (Japanese Patent Laid-Open No. 57-201245). However, both are unsatisfactory in that they are not well compatible with the wax and the pigment and that the chargeability of the toner particles changes over time, which deteriorates the image.

In order to solve the above-mentioned problems, the present inventors have used a specific carbazole derivative as a coloring agent and flushing it with a resin or wax having a softening temperature of 50 to 120 ° C. to obtain toner particles. In the absence of the charge control agent, good chargeability was exhibited, storage stability and fixability were high, and color reproducibility by an overhead projector (hereinafter abbreviated as OHP) was also satisfactory (Japanese Patent Laid-Open No. 62-62). 38478). This result is presumed to be because the above-mentioned colorant is dispersed in a state close to the primary particles. Therefore, if a proper colorant is used, a highly transparent liquid developer that can be used for OHP and the like can be obtained. Is expected. In addition, since the colorant particles of the liquid developer are close to the primary particles, it is presumed that the storability and fixing property of the toner are superior to those of the conventional product. However, only the sepia color is obtained with the colorant according to the prior application of the present inventors, and a colorant having a color tone suitable for a color toner has not been obtained. Further, the liquid developer of the prior application cannot be said to be sufficiently satisfactory because the color density is rather low.

With the development of color copying, technical development of a color liquid developer for electrostatic photography has been promoted, and particularly yellow and magenta colors having few pigments having good weather resistance are active. That is, carbon black for black color and phthalocyanine pigment for cyan color can be used as a colorant for most color liquid developers, but in the fields of yellow color and magenta color, a colorant comparable to the above can be found. Absent. From the above points, the present applicant at least uses an azo pigment (Japanese Patent Application No. 4-24598) having a specific structure as a colorant for a yellow liquid developer, at least as a colorant for a magenta liquid developer. A colorant (Japanese Patent Application No. 3-32960) containing both a water-insoluble azo pigment and a quinacridone pigment, which are partially solid-dissolved with each other, has been proposed. Such a charge control agent is required. Further, with the seriousness of environmental problems, discharge of waste liquid containing metal has become a problem in the field of liquid developer for electrostatic photography.

By the way, as a magenta liquid developer colorant, an azo lake pigment such as Carmine 6B is recommended because of its vivid color tone and transparency. However, when the pigment is used as a liquid developer colorant. It is known that the background fog is likely to occur. Therefore, Japanese Patent Laid-Open No. 64-2065,
JP-A-1-94353, JP-A-1-116565
In Japanese Patent Laid-Open Publication No. 9-242242, it has been proposed to prevent background fog by using various naphthol-based pigments as magenta colorants. However, when the pigment is used as a colorant, a desired color tone cannot be obtained, and it is often difficult to use it in combination with a liquid developer of another color, and it cannot be said to be a satisfactory colorant. Also,
As disclosed in JP-A-56-75660, a suitable magenta colorant can be obtained by using a rhodamine-based pigment and a quinacridone-based pigment together. However, the colorant provides a desired color tone. It is not satisfactory because it is difficult to adjust the mixing ratio of both pigments, and the rhodamine-based pigment has low light resistance.

[0007]

SUMMARY OF THE INVENTION The present invention solves the above problems found in a liquid developer for electrophotography, and does not change the chargeability of the toner particle surface even when a large number of copies are continuously made. , The chargeability of the toner particle surface does not change even after storing the concentrated toner or the developer for a long time, and the high chargeability can be stably maintained in the absence of the charge control agent, so that the high quality is stable. The first object is to provide a liquid developer for red electrophotography capable of obtaining the above image. In addition, a red image having a high image density, excellent gradation reproducibility, drying property, transparency, and the like, which produces a copy image with high color reproducibility when OHP is used, and has a high secondary fixing property. The second object is to provide a liquid electrophotographic liquid developer.

[0008]

The present inventors have completed the present invention as a result of intensive studies to solve the above problems. That is, according to the present invention, a compound represented by the following general formula (1) is used as a colorant in an electrophotographic liquid developer containing a highly insulating liquid, a binder resin and a colorant as main components. A liquid developer for electrophotography is provided.

[Chemical 1]

Further, according to the present invention, there is provided the electrophotographic liquid developer, wherein the colorant is subjected to a flushing treatment with a resin or wax having a softening temperature of 50 to 120 ° C. Further, according to the present invention, there is provided the liquid developer for electrophotography, wherein the colorant is laked. The compounds of the general formula (1), which characterize the present invention, are slightly different in hue depending on their structures as shown in Table 1 described later, but all of them are red colorants that give a clear hue and are stable. It has a positive charge. Therefore, the colorant easily combines with the electrostatic latent image having a negative charge in the absence of the charge control agent to give a toner image.
At this time, the counter anion A ⁻ adheres to the background along with the excess developer. As described above, A is a colorless or light-colored anion, and any anion that does not adversely affect the charging characteristics of the colorant can be used, but Cl ⁻ ,
Br ⁻ , NO ₂ ⁻ , HSO ₄ ⁻ , H ₂ BO ₃ ⁻ , H ₂ PO ₄ ⁻ , C
H ₃ COO ⁻ , oxalate ion and the like are preferable.

Specific examples of the compound represented by the general formula (1) are shown in Table 1, but the present invention is not limited to these specific examples. Further, all of the compounds in Table 1 are water-soluble basic dyes which are stable with respect to heat and with time, and are excellent compounds as charge control agents.

[Table 1]

As an example of producing the compound represented by the general formula (1), the outline of the method for synthesizing the compounds (a) to (c) in Table 1 is as follows. [Synthesis Method of Compound (a)] 250 parts by weight of water was placed in a four-necked flask equipped with a thermometer, a condenser and a stirrer,
Heat to 50 ° C on a hot water bath. To this warm water, 100 parts by weight of the following compound (f) manufactured by Tokyo Kasei Co., Ltd. and 15 parts by weight of hydrochloric acid were added, and the mixture was reacted for 4 hours at 50 ° C. with good stirring, and then No. 10 manufactured by Toyo Roshi Kaisha, Ltd. The precipitate in the flask was separated using 2 filter paper and dried under reduced pressure to obtain 25 parts by weight of the compound (a).

[Chemical 2]

[Synthesis Method of Compound (b)] Compound (a)
Using the same reactor as in the synthesis of, 100 parts by weight of water and 50 parts by weight of ethanol were taken and heated to 30 ° C. in a hot water bath. To this solution, 120 parts by weight of the following compound (g) commercially available from Tokyo Kasei Co., Ltd. and 30 parts by weight of hydrochloric acid were added, and the mixture was reacted at 30 ° C. for 4 hours, and the resulting precipitate was synthesized to synthesize compound (a). Compound (b) becomes 1 when treated in the same manner as
8 parts by weight were obtained.

[Chemical 3] [Synthesis method of compound (c)] The amount of ethanol used is 150
In addition to 50 parts by weight of water, the following compound (h) 10 commercially available from Tokyo Kasei Co., Ltd.
The synthesis reaction was carried out in the same manner as in the synthesis of compound (b) except that 0 part by weight was used as the raw material and the addition amount of hydrochloric acid was 20 parts by weight, and 16 parts by weight of compound (c) was obtained.

[Chemical 4]

The compound of the general formula (1) can provide more stable and high quality electrophotographic characteristics by flushing treatment or rake formation. The flushing treatment is a treatment method in which a pigment or the like is extremely well dispersed in a resin or a wax, and is recommended as a method for well dispersing a dye or pigment in the resin or the wax using a water-containing paste of the pigment or a dye aqueous solution as a raw material. . This method has very good dispersibility because water, solvent and the like can be removed while kneading with a kneader, but the contaminants may be removed by a reduced pressure method. In the present invention, the colorant or its water-containing paste is put in a kneader called a flasher together with a resin (including wax) or a resin solution and mixed well. In this process, water in the colorant is replaced with the resin solution. When the kneaded product is taken out from the kneader, the aqueous phase is removed, the kneaded product is dried to remove the solvent, and then crushed to a desired particle size. In the present application, the powder of the kneaded product pulverized in this manner is referred to as a "flushing-treated colorant".

In the present invention, in order to produce the "flushing-treated colorant", the resin (including wax) having a softening temperature of 50 to 120 ° C. is 0.1 to 4.0 times the weight of the colorant,
It is preferably used in an amount of 0.5 to 2.0 times by weight. The resins (including wax) used here are polyolefins such as polyethylene and polypropylene, polyvinyl chloride, paraffin wax, beeswax, natural wax, and the like. The softening temperature, the trade names and the softening temperatures of resins (including wax) manufactured by manufacturers other than those listed in Table 2 are shown in Tables 3 and 4, and Table 5 shows the resins other than those shown in Tables 2 to 4. Indicates the product name. The softening temperature of waxes used in the flushing process is 50 to 98 for paraffin wax.
℃, about 60 ℃ for dense wax, about 51 ℃ for natural wax.

[0015]

[Table 2] Manufacturer name Product name Softening temperature (° C) BASF OA wax 93-96 Petrolite BARECO 500 86 〃 〃 655 102 〃 〃 1000 113 〃 E 730 93 〃 E 2018 105 117 〃 E 2020 〃 E 2020 E 117 C 90.5 〃 〃 C-36 90.5 〃 〃 C-400 104.5 〃 〃 C-7500 97.8 Hoechst PE 520 118-123 〃 PED 121 113-118 〃 136 107-112 〃 153 115-120 〃 521 103 to 108 〃 522 100 to 105 〃 534 98 to 105 Allied Chemical AC-Polyethylene 6 & 6A 102 〃 〃 615 105 Sanyo Kasei Sun Wax 131-P 108 〃 〃 151-P 107 〃 〃 161- 11 undefined undefined 165-P 107 undefined undefined 171-P 105

[0016]

[Table 3] Manufacturer name Product name Softening temperature (° C) Eastman Chemical N-10 111 〃 N-11 108 〃 N-12 113 〃 N-14 106 〃 N-34 103 〃 N-45 118 〃 C-10 104 〃 C-13 110 〃 C-15 102 〃 C-16 106 〃 E-10 106 〃 E-11 106 〃 E-12 112 〃 E-14 104 〃 E-15 100 Mitsui Petrochemical 110P 100 〃 220P 220 〃 113 〃 320MP 114 〃 210MP 120 〃 4202E 108 〃 4053E 111

[0017]

[Table 4] Maker name Product name Softening temperature (° C) Union Carbide DYN I 102 〃 F 〃 F 〃 H 102 〃 〃 J 102 〃 〃 K 102 AT 5 3 MU R SON 805 116 L 5 liters R ION 805 116 L 5 liters R ION 805 116 L 5 70 R 5 103 〃 〃 10 96 〃 〃 12 84 〃 〃 14 80 〃 〃 16 95 〃 〃 20 20 86 〃 〃 22 84 〃 25 96

[0018]

[Table 5- (1)] Manufacturer's name Resin type Product name Sanyo Kasei Polyethylene Sun Wax E200 〃 〃 〃 E250P Chubu Polyethylene 〃 2000 〃 〃 2,500 〃 〃 〃 〃 〃 4 〃 4100 〃 4 〃 4 100 〃 4 〃 〃 7000 Sanyo Kasei polypropylene Viscole 500P 〃 〃 〃 660P Electrochemical vinyl chloride resin Denkavinyl SS-100 〃 〃 〃 〃 〃 DSS-130 〃 〃 〃 〃 〃 -70 〃 〃 〃 SS-Y 〃 〃 〃 SH-250 〃 〃 〃 SH-170 〃 〃 〃 M-70 〃 〃 〃 〃 〃 〃 〃 〃 〃 〃

[0019]

[Table 5- (2)] Manufacturer name Resin type Product name Electrochemical vinyl chloride resin Denka vinyl VP-30 〃 〃 〃 SE-130 〃 〃 ME-120 〃 〃 〃 ME-180 〃 〃 MHE-100 〃 〃 〃 PA-100 〃 〃 〃 P-80

The lake formation of the colorant carried out in the present invention is a general lake formation carried out to render the compound represented by the general formula (1) water-insoluble. Since the compound of 1) is a basic dye, a known method used for lake formation of a basic dye may be applied. That is, it is preferable to lake with a heteropolyacid such as phosphotungstic acid or phosphomolybdic acid, and instead of the heteropolyacid, a water-soluble salt of molybdic acid or tungstic acid and a water-soluble salt of phosphoric acid may be used in combination. The lake is manufactured by dissolving the compound of the general formula (1) in water weakly acidified with acetic acid or the like, adding an aqueous solution of the heteropolyacid or the like to this solution to form a precipitate, and separating the solution from the mother liquor under reduced pressure. A conventional method of drying by a method or the like may be used.

The binder resin used in the liquid developer of the present invention is an alkyd resin, a rosin-modified phenol-formaldehyde resin, a polyhydric alcohol ester of hydrogenated rosin, a poly (meth) acrylic acid ester resin, a styrene resin, For example, chlorinated rubber. Particularly preferable as the binder resin for a liquid developer of the present invention is a copolymer resin containing an unsaturated ester represented by the following general formula (2) as a main component, and containing the unsaturated ester of the general formula (2): The monomers to be copolymerized are acrylic acid, methacrylic acid, vinyl pyridine,
Examples thereof include unsaturated esters represented by the following general formula (3), acrylic acid or methacrylic acid derivatives represented by the following general formula (4), and ethylene glycol dimethacrylate.

[Chemical 5] (In the formula, R_FourIs a hydrogen atom or a methyl group, R_FiveIs -CO-
OC_nH_{2n + 1}Or -O-CO-C_nH_{2n + 1}Represents R_Five
N represents an integer of 6 to 20)

[0022]

[Chemical 6] (In the formula, R₆Is a hydrogen atom or a methyl group, R₇Is -CO-
OC_mH_{2m + 1}Or -O-CO-C_mH_{2m + 1}Represents R₇
M represents an integer of 1 to 5)

[Chemical 7] (In the formula, R₈Is a hydrogen atom or a methyl group, R₉Is dimethyl
Represents an amino group, a diethylamino group or a hydroxyl group)

As described above in detail, the optimum resin as the binder resin used in the developer of the present invention is a copolymer containing an unsaturated ester represented by the general formula (2) as a main component. However, the content ratio of the compound of the general formula (2) in the copolymer is 30 to 95% by weight, preferably 40 to 60% by weight.
It is good to Further, the copolymer in this case may be a block copolymer or a graft copolymer. In the developer of the present invention, it is desirable to use the binder resin in an amount of 1 to 20 times, preferably 1 to 7 times the weight of the colorant. The binder resin is the above-mentioned binder resin or the following natural resin. Alternatively, a resin added with a natural resin-modified resin is used. The natural resin or the natural resin-modified resin, which is added as needed, is added in an amount of 10 to 70%, preferably 20 to 50% of the total weight of the binder resin. Natural resins such as ester gum and softened rosin; heat modified with natural resins such as natural resin-modified maleic acid resin, natural resin-modified phenol resin, natural resin-modified polyester resin, natural resin-modified pentaerythritol resin, natural resin-modified epoxy resin Curable resin or thermoplastic resin.

The liquid developer of the present invention has an electric resistance of 10 ¹⁰
An aliphatic hydrocarbon or an aliphatic halogenated hydrocarbon having a high insulating property and a low dielectric constant of Ω · cm or more and a dielectric constant of 3 or less is added as a carrier liquid. Specific examples of the carrier liquid include paraffinic or isoparaffinic hydrocarbons (Esso Co. Isopar H, Isopar G, Isopar L, Isopar K, Naphtha No. 6, Solvesso 100, etc.), ligroin, n-.
Hexane, n-heptane, isooctane, n-octane, carbon tetrachloride, trichlorotrifluoroethane, cyclohexane and the like, which may be used alone or in combination. The liquid developer of the present invention may be added with a charge control agent such as metal soap and a charge enhancer such as metal oxide fine particles, if necessary. As described above, since the compound of the general formula (1) used in the liquid developer of the present invention is also excellent as a charge control agent, generally, a conventional charge control agent or charge enhancer is not required. However, the above-mentioned additives rarely act negatively, and when the compound of the general formula (1) is used in combination with known dyes and pigments, the above-mentioned additives may show some positive effects.

[0025]

EXAMPLES Next, the present invention will be described more specifically by way of examples, but the present invention is not limited to these examples. The following parts and% are based on weight. Further, LMA shown below is lauryl methacrylate,
GMA is an abbreviation for glycidyl methacrylate and MAA is an abbreviation for methacrylic acid.

Example 1 25 parts of LMA-GMA-MAA copolymer and 20 parts of the compound (C) shown in Table 1 were mixed with hydrocarbon solvent Isopar H manufactured by Esso Co.
80 parts, and this was dispersed and mixed for 40 hours in a ball mill whose internal temperature was kept at 25 ° C. to prepare a concentrated toner. The compound (c) used as a raw material here was prepared using the compound (h) commercially available from Tokyo Kasei Co., Ltd. as a raw material as described above.

Concentrated toner 10 produced as described above
0 g was diluted with 1 liter of Isopar H to obtain a liquid developer, and this developer was used as an electrophotographic copying machine CT-50 manufactured by Ricoh.
It was set at 85 and a copy image was prepared on plain paper and OHP film. Then, for the image obtained on the plain paper, the image density is measured with a Macbeth densitometer, and the OH
The color reproducibility of the P image was visually evaluated. Further, the secondary fixing property was examined using a drawing tester, and this result was visually judged. The above test shows that when using the developer immediately after production, when the concentrated toner is stored for 3 months and then produced and used immediately, the developer is supplied while replenishing the consumed concentrated toner and solvent. The results were shown in Table 6 for three kinds of cases of using for one month and then using.

Example 2 Polyethylene wax (Sun wax 1 listed in Table 2)
31-P) 10% toluene solution 100 parts and the compound (c) 10% aqueous solution 100 parts described in Table 1 were put into a flasher and kneaded at 150 ° C. for 4 hours with good stirring to separate water and toluene. Then, the kneaded product was dried under reduced pressure to sufficiently remove residual water and toluene, and then the cooled kneaded product was pulverized with a funnel plex to 2 to 10 mm to obtain a flushing pigment. To 25 parts of this pigment, LMA-G
Add 20 parts of MA-MAA copolymer and 80 parts of Eyeper H and disperse for 45 hours with a ball mill keeping the internal temperature at 25 ° C.
A concentrated toner was prepared by mixing. Using the concentrated toner prepared as described above, a liquid developer was prepared in the same manner as in Example 1 and then the same test as in Example 1 was conducted. The results are shown in Table 6.

Example 3 A mixture of 10 parts of compound (c), 2 parts of acetic acid and 300 parts of ion-exchanged water was stirred at 80 ° C. for 30 minutes to obtain a uniform acidic aqueous solution of compound (c). To this solution, an aqueous solution containing 10 parts of sodium dihydrogen phosphate, 10 parts of sodium tungstate, 15 parts of sodium molybdate and 100 parts of ion-exchanged water was added, and the mixture was stirred at 80 ° C. for 2 hours to lake the compound (c). did. After the completion of the reaction, the liquid was cooled and the precipitate was separated from the mother liquor by filtration and dried in a vacuum dryer to obtain a fine powder lake. In 17 parts of this rake, LMA-GMA-
Add 15 parts of MAA copolymer and 80 parts of Isopar H,
A ball mill whose internal temperature was kept at 25 ° C. was used for dispersion and mixing for 50 hours to prepare a concentrated toner. Using the concentrated toner prepared as described above, a liquid developer was prepared in the same manner as in Example 1 and then the same test as in Example 1 was conducted. The results are shown in Table 6.

Comparative Example 1

[Chemical 8] A liquid developer was prepared in the same manner as in Example 1 except that the compound (e) represented by the above structural formula was used in place of the compound (c), and the same test as in Example 1 was performed using this liquid developer. The results obtained are shown in Table 6.

[0031]

[Table 6]

The results in Table 6 show that both the OHP color reproducibility and the secondary fixability of the example are significantly superior to those of the comparative example. In addition, the image density of the embodiment is higher than that of the comparative example from the first use, and when the concentrated toner after storage for 3 months or the developer after use for 1 month is used, the image density of the embodiment and the comparison example is It is observed that the image density difference is significantly increased over that at the first use. Summarizing these results, when the colorant was used as it was, the developer of the example was significantly superior to that of the comparative example, and the developer of the example was superior even by the flushing treatment and rake formation of the colorant. Recognized in another experiment. It is presumed that the superiority of the colorants of the examples is that the charging characteristics hardly change even when left standing or in use, and such stability of the charging characteristics is due to the stability of the conventional charge control agents such as metal soap. Can not be obtained by adding. In addition, the developer performance deteriorates due to long-term storage of the developer and continuous use for many times.However, by flushing the colorant or making it into a lake, long-term storage and continuous use for many times are possible. Almost no deterioration is observed, and the developer of the present invention is superior to the conventional product in this respect as well.

[0033]

INDUSTRIAL APPLICABILITY The liquid developer for electrophotography of the present invention uses the basic dye having a specific structure having a stable charge represented by the general formula (1) as a colorant, and thus has stability over time and color reproduction. And a primary fixing property are higher than those of conventional products. The developer does not require a charge control agent as can be seen from the charge characteristics of the colorant, and also has a high image density. It is possible to form a high transfer image. In the electrophotographic liquid developer according to claim 2, the above-mentioned various characteristics are further improved because the colorant is subjected to the flushing treatment.
In particular, it is a liquid developer for electrophotography, which has greatly improved stability over time. The liquid developer for electrophotography according to claim 3 is a liquid developer for electrophotography in which the above-mentioned various properties are further improved because the basic dye of the colorant is laked, but the stability with time is greatly improved.

Front page continuation (72) Inventor Kazuhiko Umemura 1-3-6 Nakamagome, Ota-ku, Tokyo Within Ricoh Co., Ltd.

Claims (3)

[Claims] 1. A liquid developer for electrophotography comprising a highly insulating liquid, a binder resin and a colorant as main components, wherein a compound represented by the following general formula (1) is used as a colorant. Liquid developer for electrophotography. [Chemical 1] 2. The liquid developer for electrophotography according to claim 1, wherein the colorant is flushed with a resin or wax having a softening temperature of 50 to 120 ° C. 3. The liquid developer for electrophotography according to claim 1, wherein the colorant is laked.