JP3035686B2 - Image forming method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in the technical field of a copying apparatus using an electrophotographic process, and particularly relates to an image forming method using a fixing device for fixing toner on a transfer material onto paper. .

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus such as a general electrophotographic copying machine, various fixing methods have been proposed and implemented, but at present, a heat fixing method is the mainstream. Above all, a heat roll fixing system using a pair of rollers is widely adopted because of its good thermal efficiency. The basic configuration is as shown in FIG.
That is, in the drawing, reference numeral 7 denotes a fixing roller, which internally has a heat source such as a halogen heater 7c. Reference numeral 8 denotes a pressure roller whose surface layer is covered with an elastic body 8a such as rubber. The fixing roller 7 and the pressure roller 8 are in pressure contact with each other, and form a pair with an appropriate nip portion. The roller is rotated by receiving driving from a main body by a driving means (not shown). For an unfixed image, the transfer material is
After passing through the nip portion of the pair of rollers after passing through, the toner is fixed to the transfer material by heat and pressure.

However, in the heat roll fixing method, since the transfer material is in direct contact with the surface of the fixing roller, part of the toner on the transfer material adheres to the fixing roller, and the adhered toner is transferred again by rotation of the roller. The occurrence of the so-called offset phenomenon transferred onto the material is inevitable. For the purpose of preventing this phenomenon, a coating of a resin such as a fluororesin having good releasability is generally formed on the surface layer 7a of the fixing roller, but since these materials have high resistance, the surface thereof is transferred. Largely negatively charged due to frictional charging with the material. As a result, when the toner on the transfer material is particularly a positively-charged toner, the toner is electrostatically attracted to the surface of the fixing roller and the offset phenomenon is likely to occur.

In order to prevent the offset phenomenon, a bias voltage having the same polarity as that of the toner is applied to the core 7b of the fixing roller 7 as shown in FIG.
A fixing device having 9) has also been proposed. With such a configuration, there is an effect of clearly preventing the electrostatic offset phenomenon.

[0005]

However, the bias applied voltage required to prevent the occurrence of the electrostatic offset in the above-mentioned conventional device ranges up to about several kV.
Applying a high voltage bias has been a problem for the safety and simplification of the fixing device.

SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming method capable of solving such a problem and effectively and stably preventing the offset phenomenon even with a low voltage bias.

[0007]

According to the present invention, an object of the present invention is to transport an unfixed toner image formed on a transfer material to a nip formed by a fixing roller and a pressure roller. In the image forming method for fixing, the toner is a magnetic black toner containing at least a binder resin, a quaternary ammonium salt-based compound and triiron tetroxide (excluding a magnetic black toner containing nigrosine). The residual magnetization (σ _r ) / saturation magnetization (σ _s ) of the magnetic toner is 0.15 or less, and a DC bias having the same polarity as the toner is applied to a fixing roller in contact with an unfixed toner image on a transfer material. The fixing roller is a fixing roller including a cored bar and a surface layer formed of a resin containing a low-resistance material on the cored bar.

In the present invention, the above object can be achieved by first applying a DC bias having the same polarity as the toner to the fixing roller, whereby the repulsive force between the fixing roller and the toner effectively acts, and This is because, by adding a low-resistance material to the fixing roller, charging and charge-up due to contact and friction with the transfer material or the pressure roller during operation are eliminated, and the characteristics of the fixing roller are not lost.
Further, by containing a quaternary ammonium salt-based compound, the positive charge amount of the toner is properly maintained, adhesion between the toner and the fixing roller due to electrostatic attraction is prevented, and σ _r / σ _{When s} is 0.15 or less, the residual magnetization (σ _r ) of the toner particles is reduced without reducing the content of the magnetic substance in the toner particles. It does not become too much, that is, the toner spikes become longer and the toner scatters or protrudes from the latent image, preventing excess toner from getting on the transfer material. This is because it can prevent.

Hereinafter, a fixing device suitable for the present invention will be described with reference to FIGS. In the drawings, the same parts as those of the conventional apparatus of FIGS. 3 and 4 are denoted by the same reference numerals.

FIG. 1 is a sectional view of a copying apparatus having a fixing device according to the present invention. Reference numeral 1 denotes a photoconductor, and an electrostatic latent image formed on the surface of the photoconductor is transferred onto a transfer material 6 by a transfer charger 2. After the transfer, the transfer material is separated from the photoreceptor 1 by a separation charger 3, conveyed by a conveyance belt 4, and formed by a fixing roller 7 having a heating source and a pressure roller 8 via an entrance guide 5. Into the narrow pressure zone. The toner is fixed at the nip by the action of heat and pressure.

FIG. 2 shows the structure of the fixing device in more detail. The fixing roller 7 has a halogen heater 7c as a heating source at the center, and has a surface layer 7a made of a resin containing a low-resistance material having good releasability and made of an offset prevention layer on the outer layer of the core metal 7b. doing. On the other hand, the pressure roller 8 has an elastic layer 8a provided on a cored bar 8b.

Further, a DC bias having the same polarity as that of the toner (a positive bias is applied in the present invention in order to use a positive toner) is applied to the core metal 7b of the fixing roller 7.

In the present invention, the volume resistivity of the surface layer is suppressed to a low level by dispersing metal powder or metal oxide in the resin of the surface layer of 7a.

[0014] The content of the metal powder or metal oxide in the surface layer of the resin is preferably 0.5 to 20 wt%. At this time, the volume resistivity of the surface layer has dropped to 10 ¹⁰ [Ω · cm] or less. When the content exceeds 20% by weight, the volume resistivity of the surface layer can be kept low, but the releasability and wear resistance of the surface layer are significantly impaired.

Examples of the metal powder include gold, silver, copper, nickel, aluminum, tin, zinc, lead, brass and other alloys. Further, as the metal oxide, S
Examples include nO ₂ , TiO ₂ , TiO _2n-1 (n ≒ 1), antimony oxide, conductive zinc oxide, and mixtures thereof.

As the resin for the surface layer of the fixing roller, a fluorine resin such as polytetrafluoroethylene (PTFE) or Teflon (PFA) is used.

On the other hand, the quaternary ammonium salt compounds usable in the toner of the present invention include quaternary ammonium salts such as tributylbenzylammonium-1-hydroxy-4-naphthosulfonate and tetrabutylammonium tetrafluoroborate. And onium salts such as phosphonium salts, which are analogs thereof, and lake pigments thereof. Among them, the use of the compound represented by the structural formula (A) is preferable because it shows an appropriate charge amount with little dependence on the environment.

[0018]

Embedded image

In the toner of the present invention, these quaternary ammonium salt compounds may be used alone as a positive charge control agent, or may be modified with another positive charge control agent such as nigrosine and a fatty acid metal salt. Triphenylmethane dyes and their lake pigments (phosphorotungstic acid, phosphomolybdic acid, phosphotungsten molybdic acid, tannic acid, lauric acid,
Gallic acid, ferricyanide, ferrocyanide, etc.), metal salts of higher fatty acids, acetylacetone metal complexes, diorganotin oxides such as dibutyltin oxide, dioctyltin oxide, dicyclohexyltin oxide; dibutyltin borate, dioctyltin borate, dicyclohexyltin borate And the like. The quaternary ammonium salt compound can be used in combination with a binder resin 100.
0.1-20 parts by weight when used alone,
Preferably 0.2 to 10 parts by weight, 0.05 in combination
The addition amount is preferably from 16 to 16 parts by weight, preferably from 0.1 to 8 parts by weight, and the total amount of the positive charge control agent added is from 0.1 to 20 parts by weight, preferably from 0.2 to 10 parts by weight.

Σ _r / σ _s of the magnetic toner of the present invention is 0.15.
It is as follows.

When σ _r / σ _s exceeds 0.15, that is, when the residual magnetization (σ _r ) of the toner particles is relatively larger than the saturation magnetization (σ _s ), the toner particles rise from the developing sleeve. The force applied is large and the toner spikes are longer than the width of the fine line latent image because of the longer toner spikes.The toner spatters or protrudes from the latent image, and excess toner is placed on the transfer material. Becomes

When the content of the magnetic substance in the toner particles is reduced and the σ _r of the toner particles is made relatively small with respect to the toner particle size, uneven blotting on the sleeve and the supporting force of the toner particles due to the magnetic force are weakened. Various problems, such as disturbed earing of toner particles, low density, poor image quality, and fog, are likely to occur.

In the present invention, the magnetic properties of the magnetic toner were determined from the results of measurement using VSMP-1-10 (manufactured by Toei Kogyo Co., Ltd.) at room temperature with an external magnetic field of 1 K Oersted.

As the magnetic material contained in the magnetic toner of the present invention, triiron tetroxide is used and can also serve as a colorant.

The ferric oxide has an average particle size of 0.1 to 2 μm,
Preferably about 0.1 to 0.5 μm,
The amount contained in the toner is about 20 to 200 parts by weight, particularly preferably 40 to 1 part by weight, per 100 parts by weight of the binder resin.
50 parts by weight is good.

The magnetic toner used in the present invention comprises:
The quaternary ammonium salt-based compound and the magnetic material are contained in at least a binder made of a binder resin for toner generally used. If necessary, a coloring agent, other additives, etc. may be contained in the resin. May be contained.

As the binder resin, styrene resin, acrylate resin, ester copolymer resin, styrene-acrylate copolymer resin, vinyl chloride resin, vinyl acetate resin, vinylidene chloride resin, phenol resin, epoxy resin Resins, polyester resins and the like commonly used for toners can be mentioned.

For the purpose of improving the releasability at the time of fixing with a hot roll, a wax-like substance such as low-molecular-weight polyethylene, low-molecular-weight polypropylene, microcrystalline wax, carnauba wax, sasol wax, paraffin wax, etc. It is also a preferable embodiment of the present invention to add about 0.5 to 10 parts by weight to the toner.

The colorant that can be used in the toner of the present invention includes any suitable pigment or dye. Toner colorants are well known and include pigments such as carbon black, aniline black, acetylene black, naphthol yellow, hansa yellow, rhodamine lake, alizarin lake, bengara, phthalocyanine blue, and indanthrene blue. These are used in an amount necessary and sufficient to maintain the optical density of the fixed image.
0.1 to 20 parts by weight, preferably 1 to 100 parts by weight
The addition amount of 10 parts by weight is good. A dye is further used for the same purpose. For example, there are azo dyes, anthraquinone dyes, xanthene dyes, methine dyes and the like, and 0.1 to 20 parts by weight, preferably 0.3 to 10 parts by weight, per 100 parts by weight of the binder resin is good. .

In the toner of the present invention, charging stability,
In order to improve developability, fluidity and durability, it is preferable to add silica fine powder.

The silica fine powder used in the present invention is BE
The specific surface area by nitrogen adsorption measured by the T method is 30 m ² / g
Those within the above range (particularly 50 to 400 m ² / g) give good results. It is preferable to use 0.01 to 8 parts by weight, preferably 0.1 to 5 parts by weight of silica fine powder with respect to 100 parts by weight of the toner.

The silica fine powder used in the present invention may be, if necessary, a silicone varnish, various modified silicone varnishes for the purpose of hydrophobization, charge control, etc.
It is also preferable to use a treatment agent such as silicone oil, various modified silicone oils, a silane coupling agent, a silane coupling agent having a functional group, or another organosilicon compound, or a combination treatment with various treatment agents.

As other additives, for example, lubricants such as Teflon, zinc stearate and polyvinylidene fluoride are preferable, and polyvinylidene fluoride is particularly preferable. Or an abrasive such as cerium oxide, silicon carbide, strontium titanate,
Among them, strontium titanate is preferable. Alternatively, for example, a fluidity-imparting agent such as titanium oxide and aluminum oxide, particularly a hydrophobic agent is preferable. A small amount of a caking preventing agent or a conductivity-imparting agent such as carbon black, zinc oxide, antimony oxide, and tin oxide, or white and black fine particles of opposite polarity can also be used as a developability improver.

To prepare the magnetic toner according to the present invention, a binder resin, a pigment as a colorant, or a dye, a magnetic substance, a charge control agent and other additives as necessary are added to a Henschel mixer, a ball mill, or the like. After thoroughly mixing with a mixing machine, a heating roll, a kneader, melting, kneading and kneading using a hot kneading machine such as an extruder to dissolve the resins into each other while mixing the metal compounds, pigments, dyes, The toner according to the present invention can be obtained by dispersing or dissolving the magnetic substance, solidifying it by cooling, pulverizing and classifying.

Further, if necessary, desired additives are sufficiently mixed by a mixer such as a Henschel mixer to obtain the magnetic toner according to the present invention.

[0036]

The present invention will be described below in detail with reference to examples. Parts mean parts by weight. <Production of Developer> (Production Example 1) Styrene-acrylate copolymer resin 100 parts Iron trioxide (average particle size 0.2 μm, σ _r = 5.8 emu / g) 90 parts Low molecular weight polypropylene 4 parts 4 parts of a quaternary ammonium salt compound represented by the above structural formula (A) The above materials were mixed well in a blender.

Thereafter, the mixture was kneaded with a twin-screw kneading extruder set at 110 ° C. The obtained kneaded material is cooled, coarsely pulverized by a cutter mill, and then finely pulverized using a fine pulverizer using a jet stream, and the obtained finely pulverized powder is subjected to a multi-divided classifier utilizing the Coanda effect. 7. Weight average particle size
A black fine powder of 3 μm was obtained.

[0038] 100 parts of the obtained black fine powder is coated with positively charged hydrophobic dry silica (BET specific surface area: 130 m ² / g).
Add 0.6 parts, mix with a Henschel mixer, and add σ _r /
A positively chargeable toner (1) having σ _s = 0.096 was obtained.

(Production Example 2) σ _r / σ was obtained in the same manner as in Production Example 1 except that 3 parts of the quaternary ammonium salt compound represented by the structural formula (A) and 1 part of nigrosine were used as charge control agents. A positively chargeable toner (2) having _s = 0.096 was obtained.

(Production Example 3) As ferric oxide (magnetic material), the average particle size is 0.25 μm, σ
Except for using _r = 10.2 emu / g, a positively chargeable toner (3) having σ _r / σ _s = 0.172 was obtained in the same manner as in Production Example 1.

(Production Example 4) Nigrosine 2 parts as a charge control agent, average particle diameter 0.3 μm as iron trioxide (magnetic substance), σ _r = 18.1 emu
/ G in the same manner as in Production Example 1 except for using σ _r / g
A positively chargeable toner (4) having σ _s = 0.357 was obtained.

(Production Example 5) Production Example 1 except that 2 parts of nigrosine was used as a charge control agent
In the same manner as in the above, a positively chargeable toner (5) having σ _r / σ _s = 0.096 was obtained.

(Production Example 6) As ferric oxide (magnetic substance), the average particle size is 0.3 μm, σ _r
= 18.1 emu / g A positively chargeable toner (6) having σ _r / σ _s = 0.357 was obtained in the same manner as in Production Example 1 except that the toner having an emu / g of 18.1 emu / g was used. <Fixing Roller> Table 1 shows the specifications of the fixing rollers A and B of the present invention and the comparative fixing roller C.

[0044]

[Table 1]

Example 1 An electrophotographic copying machine N comprising a fixing device provided with a fixing roller A using the toner (1) obtained in Production Example 1.
In a modified P4835 (manufactured by Canon Inc.), a fixing test was performed by changing the DC bias value applied to the core metal of the fixing roller, and the occurrence of electrostatic offset was examined. As a result, a favorable offset preventing effect was obtained. . Table 2 shows the results.

Comparative Example 1 Evaluation was performed in the same manner as in Example 1 except that the toner (2) obtained in Production Example 2 was used and a fixing roller A was used. Table 2 shows the results.

Comparative Example 2 Evaluation was performed in the same manner as in Example 1 except that the toner (3) obtained in Production Example 3 was used and a fixing roller A was used. Table 2 shows the results.

Example 2 Evaluation was performed in the same manner as in Example 1 except that the toner (1) obtained in Production Example 1 was used and a fixing roller B was used. As a result, a favorable offset preventing effect was obtained. Table 2 shows the results
Shown in

Comparative Examples 3 to 7 The same evaluation as in Example 1 was performed under various conditions shown in Table 2. Table 2 shows the results.

[0050]

[Table 2]

[0051]

According to the image forming method of the present invention, it has become possible to stably prevent the occurrence of an electrostatic offset which has been conventionally unavoidable. Furthermore, in the present invention, the DC bias applied to the fixing roller can be prevented from generating an electrostatic offset with a lower voltage. As a result, the fixing device is made safe and has a simple configuration.

[Brief description of the drawings]

FIG. 1 is a sectional view of a fixing device according to the present invention.

FIG. 2 is an enlarged view of a main part of the apparatus in FIG. 1;

FIG. 3 is a sectional view of a conventional device.

FIG. 4 is a sectional view of another conventional device. 5 Entrance guide 6 Transfer material 7 (Fixing) roller 8 (Pressure) roller

Continuation of front page (56) References JP-A-3-189673 (JP, A) JP-A-4-3075 (JP, A) JP-A-4-12368 (JP, A) JP-A-2-129654 (JP) , A) JP-A-3-203749 (JP, A) JP-A-60-26953 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 9/00-9/18 G03G 13/20 G03G 15/20

Claims (1)

(57) [Claims] 1. An unfixed toner image formed on a transfer material
The nip formed by the fixing roller and the pressure roller
Transported and fixedYouWherein the toner comprises at least a binder resin and a quaternary ammonium.
Salt compounds andFerric oxideContaining magnetismBlackWith toner
There(However, magnetic black toner containing nigrosine is
except), The residual magnetization of the magnetic toner (σ_r) / Saturation magnetization
(Σ_s)But0.15The following is the fixing roller that comes into contact with the unfixed toner image on the transfer material
To,DC bias of the same polarity as tonerIs applied, and  The fixing roller is, On the mandrel and on the mandrelIncluding low resistance material
Surface layer formed by resin havingFixing row consisting of
, An image forming method comprising: