JP2614229B2 - Full color image electrophotographic method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Prior Art] In a digital color copying machine (DCC), it is easy to create a four-color image with higher quality than a three-color image by under color removal (UCR). The coexisting images of the full-color painting department and the black text department are going to become the mainstream of office documents.

At this time, the same toner is used as the black toner used for the UCR and the black toner for the black character part separated from the picture part by the editor for saving space and steps.
As the black toner, the current black toner for black-and-white copying is diverted as it is, or the binder used for the currently used three primary color toners is diverted.

However, black toner for black-and-white copying has a reduced glossiness so that the printed characters are easier to read, while three primary color toners have a glossy effect to make the printed picture parts stand out. It is devised as follows. For this reason, when using black toner for black and white copying as the black color of the painting part at the time of UCR, only the black part of the painting part has no gloss and the other part has a glossy painting part,
Also, if a black toner using a binder, which is used for the three primary color toners, is used, the black portion becomes glossy, so that there is a drawback that characters are difficult to read.

(Object of the present invention)

An object of the present invention is to eliminate the above-mentioned disadvantages, suppress the gloss of the black character portion to maintain readability, and maintain the gloss of the black portion of the painting portion equal to that of the other three primary color portions, to achieve a natural color image. The point is to form.

〔Constitution〕

The present invention adopts a configuration as described in the claims to form a high gloss image in the painting part and a high gloss in the painting part while forming the painting part UCR part and the character part black part with one black toner. This is an electrophotographic method for forming an easy-to-read image with reduced gloss.

In the full-color image of the painting section, glossiness (JIS-Z 8
781-1983 In method 3), it is desirable to obtain Gs (60 ° C.) = 10% or more, preferably 15% or more. On the other hand, the character part is
The glossiness is desirably 10% or less, preferably 7% or less.

It is considered that the glossiness of the toner layer indicates that the surface of the toner layer becomes microscopically smooth. The toner particles on the support are fixed to the support by heat, pressure or the like during fixing. At this time, it is considered that a toner layer having a microscopically smooth surface has high gloss, and conversely, a microscopically uneven surface has low gloss.

In general, as a fixing method of a full-color electrophotographic method, a "heat heat roll fixing method", which is advantageous in fixing property and coloring property, is used (because of high thermal efficiency). In this method, the toner particles are melted by heat and pressure and penetrate into the support, and are then discharged, cooled and fixed. It is considered that the gloss of the image differs due to the difference in the viscoelasticity of the toner at the time of fixing.

The present invention focuses on the difference in the viscoelasticity of the toner. The black character portion is glossy and easy to read, and the painting portion is glossy and vividly finished.

That is, in the present invention, the three primary color toners are close to a viscous body that easily gives a glossy feeling, and the black toner is close to an elastic body. The viscoelasticity of the toner depends on the viscoelasticity of the binder which is a main component of the toner.

Referring to FIG. 1, the toner (see 1-a) printed on the base material is subjected to heat and pressure by a heating and pressing roller (see 1-b) in a fixing process, and the binder resin is melted. In this case, when the resin is a viscous material, a smooth film is formed on the printing surface (see 1-c), but when the resin is close to the elastic material, a smooth surface cannot be formed on the printing surface (1).
-D).

Next, when forming a full-color image, the three primary color toners
How to overlap the black toner entering in the UCR is also important.

2 (A) and 2 (B) are cross-sectional views of a black portion of an image, and FIG. 2 (A) shows a base material → black toner → three primary color toner → surface, and FIG. 2 (B) shows a base material → three primary color toner → black toner → surface. In (A), since the surface layer is a three primary color toner, a high glossiness can be obtained at the time of fixing. On the other hand, in (B), since the surface layer is a black toner,
The resulting image has a low glossiness.

As described above, not only the viscoelasticity of the three primary color toners and the black toner but also how they overlap is important for achieving high gloss in the full color image area and low gloss in the character image area.

FIGS. 2 (C) and 2 (D) show the halftone portion, but the glossiness does not decrease because the three primary color toners are buried around the black toner.

A heat heat roll fixing method is used in the fixing process of the present invention, and this heat heat roll fixing method is currently widely used in copiers and the like due to its good thermal efficiency.

Image fixation, during fixing, the base material and the toner layer attached thereto are sandwiched and heated between the heat roller and the pressure roller, and the toner layer is heated and softened by the heat roller and penetrates the base material. At the same time, the toner layer is obtained by making the surface of the toner layer adhere to the surface of the heat roller and smoothing it. Therefore, a heat roller having a rigid body and a smooth surface is used.

The heat roller is made of a metal hollow roller core made of aluminum, stainless steel, copper, etc., and is provided with a heat-resistant release resin layer such as tetrafluoroethylene resin with a thickness of 20 to 100 μm, and the surface is finished smoothly. Use The pressure roller has a relatively thick elastic layer of silicone rubber, fluorine rubber, fluorosilicone rubber, or the like provided on the outer peripheral surface of a metal roller core, and controls the nip width with the heat roller.

In the present invention, the resin for binding the three primary color toners and the black toner may be any resin generally used as a toner resin. However, since the viscoelasticity of the binder resin strongly affects the viscoelasticity of the toner, the selection should be made in consideration of the viscoelasticity of the resin itself.

As the binder resin used in the present invention, for example, polystyrene, poly-P-chlorostyrene, styrene such as polyvinyltoluene and its substituted homopolymer, styrene-
P-chlorostyrene copolymer, styrene-propylene copolymer, styrene-vinyltoluene copolymer, styrene-vinylnaphthalene copolymer, styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene- Butyl acrylate copolymer, styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-butyl methacrylate copolymer, styrene-α-chloromethyl methacrylate copolymer, styrene -Acrylonitrile copolymer, styrene-
Styrene-based copolymers such as vinyl methyl ether copolymer, styrene-vinyl methyl ketone copolymer, styrene-butadiene copolymer, styrene-isobrene copolymer, styrene-acrylonitrile-indene copolymer, polyvinyl chloride, Polyvinyl acetate, polyethylene, polypropylene, silicone resin, polyester, polyurethane, polyamide, epoxy resin, polyvinyl butyral, rosin modified rosin, terpene resin, phenol resin, xylene resin, aliphatic or alicyclic hydrocarbon resin, aromatic petroleum Resin, chlorinated paraffin, paraffin wax or the like is used alone or as a mixture. Among these resins, styrene-based resins, polyesters, epoxy resins, and the like, which are resins excellent in transparency in forming a full-color image, are particularly preferable. As described above, since the viscoelasticity of the resin strongly affects the viscoelasticity of the toner itself, it is considered that it is better to select the resin itself which has the viscoelasticity shown in the claims of the present invention.

By the way, to explain the measurement of the viscoelastic properties, an instrument for measuring the rheological properties is generally called a rheometer. The rheometer used in the present invention is a rheometrics dynamics spectrometer RDS-7700 manufactured by RHEOMETRICS.INC (USA).

The condition was that the frequency was fixed at ω = 100 rad / sec, and the distortion rate was automatic. In this state, the temperature was raised and the temperature dependency was measured. From this result, the tangent loss tan δ when the storage elasticity G ′ (w) = 10 ⁵ dyn / cm ² was measured. The effective fixing time of the hot roll fixing device is usually about 1 × 10 ^{-2 to} 5 × 10 ^-2 seconds, and the rheological properties of the toner were measured at a frequency ω = 100 rad / sec corresponding to this.

Any colorant that can be used as a colorant for the three primary color toners for color electrophotography may be a colorant generally used widely.

Examples of yellow include benzidine yellow (eg, CI Pigment Yellow 12), monoazo dyes (eg, CI Solvent Yellow 16), nitrophenylamine sulfonamide (CI Disperse Yellow 33), and magenta includes quinacridone (eg, CI Pigment Red 12).
2), anthraquinone dyes, diazo dyes (CI Solvent Red 19) and the like. For cyan, copper phthalocyanine (CI Pigment Blue 15), indanthrene blue and the like can be used.

For the black toner, a black colorant that is similarly widely used can be used. For example, carbon black,
Nigrosine dyes can be used.

(Effect of the present invention)

Four colors (three primary colors + black) by the electrophotographic method of the present invention
In an image in which a full-color image part of a full-color image forming system (DCC, full-color printer) and a character part edited separately coexist, the full-color part has a glossy feeling,
Vivid reproduction is possible, and characters can be formed with low gloss and easy-to-read characters, and a high-quality image in which a full-color portion and a black character portion coexist can be formed.

〔Example〕

Binder resin (A) Styrene-n-butyl methacrylate copolymer (St: Ac ratio = 7: 3) Weight average molecular weight (w) → 30,000 Number average molecular weight (n) → 13,000 w / n → 2.3 (B) Styrene-n-butyl methacrylate copolymer (St: Ac ratio = 7: 3) w → 71,000 n → 7,000 w / n → 10.1 (C) Styrene-2-ethylhexyl methacrylate copolymer (St: Ac ratio = 8: 2) w → 180,000 n → 4,200 w / n → 42.9 (D) Polyester resin w → 12,000 n → 3,200 w / n → 3.8 [Example 1] Color toner (a) Yellow toner resin (A) 100 parts by weight CI Pigment Red 125 〃 (b) Magenta Toner Resin (A) 100 parts by weight CI Pigment Red 1225 〃 (c) Cyan Toner Resin (A) 100 parts by weight CI Pigment Blue 155 〃 Black Toner (d) Black Toner Resin (B) 100 parts by weight carbon black 7 〃 above (a) The mixture of the four toners (a) to (d) was heated and kneaded with a three-roll mill, allowed to cool, coarsely pulverized with a cutting mill, and further finely pulverized with an ultrasonic jet mill pulverizer. To obtain four types of toner having a volume average particle size of 11 μm.

5 parts by weight of these four types of toners (three primary colors + black toner) is used as an amorphous redox iron powder carrier (TEFV manufactured by Nippon Iron Powder)
The mixture was stirred with 95 parts by weight to prepare a developer.

For image formation, a digitally written four-color full-color printer was used. In this method, a digital latent image was formed on a photoreceptor by a laser beam, and charging, exposure, development, transfer, charge removal, and cleaning were performed once for each color, and a full-color image was formed in a total of four times. The character portion is edited separately from the full-color portion, and is formed only with black toner.

The fixing heat roller is made by coating the outer peripheral surface of a hollow aluminum core with a 50 μm-thick Teflon resin (polytetrafluoroethylene, manufactured by DuPont) (ψ → 40m /
m), and the pressure roller is a silicone rubber KE-1300RTV (Shin-Etsu Chemical Co., Ltd.) on the outer peripheral surface of the aluminum cored bar.
Was coated at a thickness of 5.0 m / m (ψ → 50 m / m).

The operating conditions were as follows: the linear speed was 90 mm / sec, the nip width (the width at which the fixing heat roller and the pressure roller contacted) was 8.0 mm,
The surface pressure was 8 kg / cm ² . The roller temperature was set such that the surface of the heat roller maintained 150 ° C., and the surface of the heat roller was slightly coated with silicone oil KF-96 (manufactured by Shin-Etsu Chemical Co., Ltd.). Output image is UCR rate 50%
3 patterns of a full-color image portion, a character portion (only black toner), and a UCR rate of 0% (a black toner does not enter the full-color image portion). The glossiness of this image was measured using a gonio-gloss meter (manufactured by Nippon Denshoku) in accordance with JIS Z-8741 Method 2.
It was measured by the 60 ° -60 ° method.

[Comparative Column 1] The same procedure as in Example 1 was carried out except that the toners of the four color toners were all B resins.

[Comparative Example 2] The same operation as in Example 1 was performed except that a toner was prepared using a black toner resin as a C resin.

Comparative Example 3 The same procedure was performed as in Example 1 except that a black toner resin was used as resin A to prepare a toner.

[Comparative Column 4] The same procedure was performed as in Example 1 except that the resin for binding the color toner was D resin.

[Example 2] Binder resin (E) Polyester resin w → 18,000 n → 6,100 w / n → 2.95 (F) Polyester resin w → 43,000 n → 3,100 w / n → 13.9 E resin as color toner, black toner As F
Except using resin, it carried out similarly to Example 1 all.

 The results are shown in Table 1 below.

As is clear from the results of Fig. 1, in Examples 1 and 2, which are the methods of the present invention, in the solid portion of the color portion (solid black portion where four colors overlap (where the highest density is shown)), the use of UCR It has high gloss regardless of the presence or absence, and also has high gloss in a halftone portion (observing a dot area ratio of 50%). In addition, since the character part has low gloss,
The color image has a vivid finish and is a character-like image in which characters are easy to read.

On the other hand, in the comparative example (1), the character portion has a glossy finish and is easy to read, but since the color image is not glossy, an impression of low image density is given, and a poor image lacking in vividness is obtained. turn into.

In Comparative Example (2), the character portion was easy to read and the solid portion of the color image portion was glossy, but the gloss was low in the halftone portion (observed at a dot area ratio of 50%, intermediate density portion). The overall impression is of low quality. Occasionally, an intermediate color such as a flesh color lacks luster, resulting in an unsightly image.

In Comparative Example (3), both the solid portion and the halftone portion of the color image portion have gloss, but the character portion also has gloss and is difficult to read.

In the comparative row (4), the viscoelasticity of the color toner becomes too close to that of the viscous material, so that a hot offset phenomenon occurs,
Image formation failed.

[Brief description of the drawings]

FIG. 1 is a model of the fixing step of the present invention. FIG. 2A shows a case where three primary color toners are superimposed on black toner, and the glossiness is controlled by the three primary color toners. FIG. 2B shows a case where the black toner is superimposed on the three primary color toners, and the gloss is dominated by the black toner. FIG. 2C shows a state of a halftone portion. At this time, the three primary color toners are buried around the black toner, and exhibit the same glossiness as in FIG. 2A. FIG. 2D is a light-colored picture portion, but since the three primary color toners are slightly overcoated, gloss similar to that of FIG. 2A is maintained. 1: Toner, 2: Heating roller 3: Pressure roller, 4: Smooth coating 5: Uneven uneven coating 11: Base material, 12: Black toner 13: Yellow toner, 14: Magenta toner 15: Cyan toner

Claims (2)

(57) [Claims] An electrophotographic method for forming a full color image by superimposing a three primary color toner and a black toner on a substrate, wherein (1) a black toner mainly comprising a binder resin and a black colorant. The rheological characteristics of the toner are such that the relationship between the storage elastic modulus [G ′ (w)] and the tangent loss (tan δ) which is the ratio of the storage elastic modulus to the loss elastic modulus (G ″) satisfies the following equation. An image is formed using a toner, and tan δ at G ′ (w) = 10 ⁵ dyn / cm ² is 1.30 ≦ tan δ <1.60 (2) Next, each mainly comprises a binder resin and three primary colorants. The three primary color toners have a rheological property whose storage elastic modulus [G ′ (w)]
A print is formed using three primary color toners, each of which has a relation of a tangent loss (tan δ), which is a ratio of a storage elastic modulus to a loss elastic modulus (G ″), and satisfies the following formula: G ′ (w) = 10 The tan δ at ⁵ dyn / cm ² is 1.70 ≦ tan δ <3.00. (3) An electrophotographic method for forming a full-color image, characterized by continuously performing a fixing process. 2. The full-color fixing method according to claim 1, wherein in the fixing process, a hot heat roll fixing is performed using a rigid heating roller having a release layer on its surface and an elastic pressing roller. An electrophotographic method for forming an image.