JP2010186059A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus that is able to make the image qualities on both sides of a sheet identical, in full-color image formation. <P>SOLUTION: The image forming apparatus includes a first transfer means transferring toner images from four first image carriers carrying toner images of four colors respectively to a second image carrier; and a second transfer means transferring the toner images from the second image carrier to a third image carrier or a recording medium, and the apparatus also includes a fixing device that holds a plurality of toner images which are formed by using the first image carriers, on the third image carrier by the first transfer means and the second transfer means, and transfers the toner images on both sides of a recording medium, and then simultaneously fixes the toner images on both sides of the recording medium. Each station of the first image carriers has a plurality of developing colors. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus for an electrostatic copying process, such as a copying machine, a color copying machine, a facsimile machine, and a printer.

  Conventionally, some image forming apparatuses of this type are configured to form images on both sides of a recording medium (hereinafter referred to as paper). In a conventional image forming apparatus capable of double-sided recording, an image on one side (developed image) formed on an image carrier is transferred and fixed on a sheet, the sheet is reversed by a reversing path, and fed again. In general, a method of transferring and fixing an image on the other side (a visible image) to the back side of the paper is used.

  In the case of double-sided recording by this method, there are many problems in ensuring the reliability of paper conveyance by switching the paper conveyance direction or by paper curling by fixing a single-sided image.

  In order to improve this point, the one described in Patent Document 1 includes two sets of image carriers and intermediate transfer belts for the purpose of forming respective images on the first and second surfaces of the sheet. This configuration is excellent in productivity (imaging speed), but enlarging the apparatus and increasing the cost are inevitable.

  Further, the one described in Patent Document 2 has a configuration of one set of image carrier and two sets of intermediate transfer belts, and four colors are formed when the first surface is formed and when the second surface is formed. The order of the toner on the paper is completely reversed, and in full color, the hues that require careful attention differ.

However, in the conventional image forming apparatus that fixes the unfixed toner images transferred on both sides of the paper at once, there is a problem that the image quality after fixing may differ between the front and back sides of the paper.
In recent years, the demand for full-color image forming apparatuses has been increasing, and even in a full-color image forming apparatus that requires a large amount of heat for fixing, the image quality after fixing is the same on both sides of the paper when performing double-sided recording. It is required to be.

  For example, as shown in FIG. 7, when a double-sided full-color image is formed, four colors (yellow (Y), magenta (M), cyan (C), black (K )) If the order of toner image formation (hereinafter referred to as color order) is different, the following problems occur.

  In the transfer process, the toner on the top of the paper is difficult to transfer, so that the toner of multiple colors overlaps (for example, the part where M and C on the second side overlap) Since it is the uppermost part, the toner amount of M toner decreases after transfer.

  On the other hand, in the portion where M and C overlap on the first surface, the C toner is the uppermost portion, so the toner amount of C toner decreases after transfer.

  As a result, the final image after fixing is that the first side of the paper where the first side and the second side overlap M and C, the first side is blue with less C, and the second side is M. Becomes a little blue, and the first surface and the second surface have different colors.

  The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide an image forming apparatus capable of making the image quality of both sides of a sheet in particular full color the same.

  According to the first aspect of the present invention, four first image carriers that respectively carry four color toner images, a second image carrier comprising a first intermediate transfer belt, and a third image comprising a second intermediate transfer belt. An image carrier, a first transfer means for transferring the toner image from the first image carrier to the second image carrier, and a second for transferring the toner image from the second image carrier to the third image carrier or the recording medium. A plurality of toner images formed using the first image carrier and held on the third image carrier by the first transfer means and the second transfer means, and the toner images on both sides of the recording medium. An image forming apparatus including a fixing device that simultaneously fixes the toner image to both sides of a recording medium after transferring the toner image, wherein each station of the first image carrier has a plurality of development colors. Image forming apparatus.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, when images are formed on both sides of the recording medium, the toner color is changed to the toner on the first side at each station of the first image carrier. By switching between when creating an image and when creating a toner image on the second surface, the color order of the toner on the first surface and the color order of the toner on the second surface on the recording medium are made the same. It was characterized by that.

  According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, at least one of the second image carrier and the third image carrier comprises an endless belt made of polyimide. It was characterized.

The invention according to claim 4 is the image forming apparatus according to claim 1 or 2, wherein at least one of the second image carrier and the third image carrier has a volume resistance of 10 ⁶ to 10 ¹³ (Ω). -Cm).

  According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects, the toner used has a volume average particle diameter of 3 to 8 μm and a volume average particle diameter ( The ratio (Dv / Dn) of Dv) to the number average particle diameter (Dn) is in the range of 1.00 to 1.40.

  According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects, the toner used has a shape factor SF-1 in the range of 100 to 180, and has a shape. The coefficient SF-2 is in the range of 100 to 190.

  According to a seventh aspect of the present invention, in the image forming apparatus according to any one of the first to sixth aspects, the toner used is a polyester prepolymer having at least a functional group containing a nitrogen atom, It is a toner obtained by crosslinking and / or stretching reaction of a toner material liquid in which polyester, a colorant, and a release agent are dispersed in an organic solvent in an aqueous medium.

  According to an eighth aspect of the present invention, in the image forming apparatus according to any one of the first to seventh aspects, the toner used has a substantially spherical shape.

  According to a ninth aspect of the present invention, in the image forming apparatus according to the eighth aspect, the shape of the toner is defined by a major axis r1, a minor axis r2, and a thickness r3 (provided that r1 ≧ r2 ≧ r3). The ratio of the major axis r1 to the minor axis r2 (r2 / r1) is in the range of 0.5 to 1.0, and the ratio of the thickness r3 to the minor axis r2 (r3 / r2) is 0.7 to 1. .. in the range of .0.

  In particular, it is possible to provide an image forming apparatus capable of making the image quality of both sides of a full color sheet the same.

1 is an overall configuration diagram of an image forming apparatus of the present invention. 1 is a configuration diagram (Example 1) of a developing device of the present invention. FIG. FIG. 6 is a configuration diagram of a developing device according to the present invention (Example 2). It is a toner color order on the paper (both sides) of the present invention. FIG. 6 is a diagram schematically illustrating the shape of a toner in order to explain the shape factor SF-1 and the shape factor SF-2. It is a figure which shows typically the toner shape of this invention. This is the order of toner colors on conventional paper (both sides).

FIG. 1 shows an outline of the main unit.
FIG. 1 shows an electrophotographic apparatus according to an embodiment of the present invention. A first intermediate transfer belt 10 as a second image carrier that is wound around rollers 11, 12, and 13 is disposed substantially at the center of the main body. The first intermediate transfer belt 10 is rotated in a counterclockwise direction in the figure by a driving roller 11 connected to a driving means (not shown). The first intermediate transfer belt 10 is provided with four image forming portions (first image carriers) a, b, c, and d along the downstream running side, and each image forming portion is a first intermediate transfer belt. The photosensitive drum 5 is disposed so as to be in contact with 10.

  Around the photosensitive drum 5, a static eliminating device L, a cleaning device 6, a charging device 7, and a developing device 8 are arranged, and the photosensitive drum 5 is rotationally driven in a direction indicated by an arrow by a driving unit (not shown).

  An exposure device 9 is provided below each image forming unit a, b, c, d, and laser light emitted from the exposure device 9 is applied to the photosensitive drum 5 at a writing position between the charging device 7 and the developing device 8. Irradiated. The image forming units a, b, c, and d have the same peripheral component configuration, but the color of the color material (toner) handled by the developing device 8 can be a plurality of colors.

  A specific configuration of the developing device is shown in FIGS. The developing device may have one of the configurations shown in FIGS.

  In FIG. 2, a four-color developing device is configured as an integral rotatable frame 81, and four colors (yellow (Y), magenta (M), cyan (C), and black (K)) are provided. Any selected toner color can be imaged. Here, all the four stations (a, b, c, d) can have the same configuration.

  In FIG. 3, the two developing devices are integrated into a two-color developing device 82, and the two-color developing device 82 rotates around the fulcrum 86 by the rotation of the contact / separation cam 85 so that two colors (magenta (M), Black (K)) can be selected for the selected toner color.

Here, station a is magenta (M), black (K)
Station b is cyan (C), yellow (Y)
Station c is yellow (Y), cyan (C) (same as station b)
Station d is black (K), magenta (M) (same as station a)
A combination of (Here two sets of identically configured stations are possible)

  A process of forming a toner image (full color) on both sides of a sheet using the above developing device will be described.

  First, an image of the first surface is formed. At this time, magenta (M), cyan (C), yellow (Y), and black (K) toners were used for the four image forming units (first image carriers) a, b, c, and d, respectively. First, the magenta (M) toner formed at the station a is arranged on the back side of the first intermediate transfer belt 10 and is applied to the first intermediate transfer belt by the transfer roller 20 applied with the opposite polarity to the toner. 10 is transferred. Next, the cyan (C) toner formed at the station b is transferred onto the first intermediate transfer belt 10 by the transfer roller 20 disposed on the back side of the first intermediate transfer belt 10 and applied with a reverse polarity to the toner. Similarly, at the stations c and d, the toner is transferred onto the first intermediate transfer belt 10 in the order of yellow (Y) and black (K) toners. (At this time, the order of toner on the first intermediate transfer belt 10 is magenta (M) → cyan (C) → yellow (Y) → black (K) from the belt surface).

  Next, the four color toner images on the first intermediate transfer belt 10 are placed on the second intermediate transfer belt 100 by a transfer roller 120 disposed on the back side of the second intermediate transfer belt 100 and applied with a polarity opposite to that of the toner. (At this time, the order of toner on the second intermediate transfer belt 100 is black (K) → yellow (Y) → cyan (C) → magenta (M) from the belt surface). The first intermediate transfer belt 10 and the second intermediate transfer belt 100 are in contact with the transfer roller 120, the roller 113, and the roller 11 that supports the first intermediate transfer belt 10 to form a predetermined transfer nip.

  Next, an image of the second surface is formed. At this time, black (K), yellow (Y), cyan (C), and magenta (M) toners were used for the four image forming portions (first image carriers) a, b, c, and d, respectively. Image formation is possible. First, the black (K) toner formed at the station a is arranged on the back side of the first intermediate transfer belt 10 and is applied to the first intermediate transfer belt by the transfer roller 20 applied with the opposite polarity to the toner. 10 is transferred. Next, the yellow (Y) toner formed at the station b is transferred onto the first intermediate transfer belt 10 by the transfer roller 20 disposed on the back side of the first intermediate transfer belt 10 and applied with a reverse polarity to the toner. Similarly, at the stations c and d, the toner is transferred onto the first intermediate transfer belt 10 in the order of cyan (C) and magenta (M) toners. (At this time, the order of toner on the first intermediate transfer belt 10 is black (K) → yellow (Y) → cyan (C) → magenta (M) from the belt surface).

  The full-color image on the first surface on the second intermediate transfer belt 100 and the full-color image on the second surface on the first intermediate transfer belt 10 are moved to the paper in synchronization with each other. P is fed from the sheet feeding unit 2 via the registration roller 28 (pair). Thereafter, when the sheet P reaches between the first intermediate transfer belt 10 and the second intermediate transfer belt 100, the toner image on the second surface carried on the first intermediate transfer belt 10 is transferred to one surface by the transfer roller 120. Transcribed. At this time, the toner image on the first surface previously transferred to the second intermediate transfer belt 100 is superimposed on the other surface of the sheet. When the paper P is further conveyed upward, the toner image on the first surface carried on the second intermediate transfer belt 100 is transferred to the other surface of the paper P by the charger CH.

FIG. 4 shows how the toner is transferred to the paper P according to this embodiment.
Unlike FIG. 7, which describes the prior art, it can be easily seen that the order of toner (color order) on the first and second sides of the paper is the same.

  As described above, the sheet P having the toner images transferred on both sides thereof is sent to the fixing means 40, and the toner images on both sides of the sheet P are simultaneously fixed, and are discharged by the discharge roller 32 (pair) through the guide 31. It is discharged to the paper stack unit 30.

  Here, the toner used in this image forming apparatus is a small diameter, narrow particle size distribution and spheroidization (sphericalization) with a polymerized toner in order to cope with recent rapid colorization and accompanying high image quality. ) Is becoming mainstream.

  The distribution of toner with a small diameter and a narrow particle diameter is advantageous for high-resolution development, and the spheroidization (true sphere) is advantageous for transfer efficiency, and thereby the image quality such as the sharpness of the toner image is remarkably improved.

  However, reducing the particle size of the toner increases the specific surface area and increases the adhesion force of the toner per unit weight to the surface of the image carrier, which makes it difficult to clean the surface of the image carrier. Further, the reduction in the toner particle size deteriorates the fluidity of the toner and requires a larger amount of additive, which may cause chipping and abrasion of the cleaning blade, local streak scratches on the surface of the image carrier, and the like. It is known to be.

  In addition, when the sphericity of the toner is increased, the above-described blade counter contact method generally used in the related art increases the amount of toner passing through the blade, so that it is necessary to increase the contact pressure more than before. Increasing the pressure reduces the margin against edge chipping due to the local shearing force of the blade.

Next, the toner suitably used in the image forming apparatus of the present invention will be described.
In order to reproduce minute dots of 600 dpi or more, the toner preferably has a volume average particle diameter of 3 to 8 μm. The ratio (Dv / Dn) of the volume average particle diameter (Dv) to the number average particle diameter (Dn) is 1. It is preferable that it exists in the range of 00-1.40. The closer (Dv / Dn) is to 1.00, the sharper the particle size distribution. With such a toner having a small particle size and a narrow particle size distribution, the toner charge amount distribution is uniform, a high-quality image with little background fogging can be obtained, and the electrostatic transfer method has a high transfer rate. can do.

  The shape factor SF-1 of the toner is preferably in the range of 100 to 180, and the shape factor SF-2 is preferably in the range of 100 to 190.

FIG. 5 is a diagram schematically showing the shape of the toner in order to explain the shape factor SF-1 and the shape factor SF-2. The shape factor SF-1 indicates the ratio of the roundness of the toner shape and is represented by the following formula (1). This is a value obtained by dividing the square of the maximum length MXLNG of the shape formed by projecting toner on a two-dimensional plane by the figure area AREA and multiplying by 100π / 4.
SF-1 = {(MXLNG) 2 / AREA} × (100π / 4) Expression (1)
When the value of SF-1 is 100, the shape of the toner becomes a true sphere, and becomes larger as the value of SF-1 increases.

  The shape factor SF-2 indicates the ratio of the unevenness of the toner shape, and is represented by the following formula (2). A value obtained by dividing the square of the perimeter PERI of the figure formed by projecting the toner on the two-dimensional plane by the figure area AREA and multiplying by 100π / 4.

SF-2 = {(PERI) 2 / AREA} × (100π / 4) Expression (2)
When the value of SF-2 is 100, unevenness does not exist on the toner surface, and as the value of SF-2 increases, the unevenness of the toner surface becomes more prominent.

  Specifically, the shape factor is measured by taking a photograph of the toner with a scanning electron microscope (S-800: manufactured by Hitachi, Ltd.), introducing it into an image analyzer (LUSEX 3: manufactured by Nireco) and analyzing it. Calculated.

  When the shape of the toner is close to a spherical shape, the contact state between the toner and the toner or the toner and the photoconductor becomes a point contact, so that the adsorbing force between the toners becomes weak and the fluidity increases, and the toner and the photoconductor The attraction force becomes weaker and the transfer rate becomes higher. If either of the shape factors SF-1 and SF-2 exceeds 180, the transfer rate is lowered, which is not preferable.

  The toner suitably used in the image forming apparatus of the present invention includes a toner material liquid in which at least a polyester prepolymer having a functional group containing a nitrogen atom, a polyester, a colorant, and a release agent are dispersed in an organic solvent. A toner obtained by crosslinking and / or elongation reaction in an aqueous solvent. Hereinafter, the constituent material and the manufacturing method of the toner will be described.

(polyester)
The polyester is obtained by a polycondensation reaction between a polyhydric alcohol compound and a polycarboxylic acid compound.

  Examples of the polyhydric alcohol compound (PO) include dihydric alcohol (DIO) and trihydric or higher polyhydric alcohol (TO). (DIO) alone or a mixture of (DIO) and a small amount of (TO) preferable. Examples of the dihydric alcohol (DIO) include alkylene glycol (ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,6-hexanediol, etc.); alkylene ether glycol (diethylene glycol) , Triethylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene ether glycol, etc.); alicyclic diols (1,4-cyclohexanedimethanol, hydrogenated bisphenol A, etc.); bisphenols (bisphenol A, bisphenol) F, bisphenol S, etc.); alkylene oxide (ethylene oxide, propylene oxide, butylene oxide, etc.) adduct of the above alicyclic diol; Alkylene oxide bisphenol (ethylene oxide, propylene oxide, butylene oxide, etc.), etc. adducts. Among them, preferred are alkylene glycols having 2 to 12 carbon atoms and alkylene oxide adducts of bisphenols, and particularly preferred are alkylene oxide adducts of bisphenols and alkylene glycols having 2 to 12 carbon atoms. It is a combined use. The trihydric or higher polyhydric alcohol (TO) includes 3 to 8 or higher polyhydric aliphatic alcohols (glycerin, trimethylolethane, trimethylolpropane, pentaerythritol, sorbitol, etc.); trihydric or higher phenols (Trisphenol PA, phenol novolak, cresol novolak, etc.); and alkylene oxide adducts of the above trivalent or higher polyphenols.

  Examples of the polyvalent carboxylic acid (PC) include divalent carboxylic acid (DIC) and trivalent or higher polyvalent carboxylic acid (TC). (DIC) alone and (DIC) with a small amount of (TC) Mixtures are preferred. Divalent carboxylic acids (DIC) include alkylene dicarboxylic acids (succinic acid, adipic acid, sebacic acid, etc.); alkenylene dicarboxylic acids (maleic acid, fumaric acid, etc.); aromatic dicarboxylic acids (phthalic acid, isophthalic acid, terephthalic acid) And naphthalenedicarboxylic acid). Of these, preferred are alkenylene dicarboxylic acids having 4 to 20 carbon atoms and aromatic dicarboxylic acids having 8 to 20 carbon atoms. Examples of the trivalent or higher polyvalent carboxylic acid (TC) include aromatic polycarboxylic acids having 9 to 20 carbon atoms (such as trimellitic acid and pyromellitic acid). In addition, as polyhydric carboxylic acid (PC), you may make it react with polyhydric alcohol (PO) using the above-mentioned acid anhydride or lower alkyl ester (Methyl ester, ethyl ester, isopropyl ester, etc.).

  The ratio of the polyhydric alcohol (PO) to the polycarboxylic acid (PC) is usually 2/1 to 1/1, preferably as the equivalent ratio [OH] / [COOH] of the hydroxyl group [OH] and the carboxyl group [COOH]. Is 1.5 / 1 to 1/1, more preferably 1.3 / 1 to 1.02 / 1.

  The polycondensation reaction between a polyhydric alcohol (PO) and a polycarboxylic acid (PC) is carried out in the presence of a known esterification catalyst such as tetrabutoxytitanate or dibutyltin oxide, and heated to 150 to 280 ° C. while reducing the pressure as necessary. The produced water is distilled off to obtain a polyester having a hydroxyl group. The hydroxyl value of the polyester is preferably 5 or more, and the acid value of the polyester is usually 1 to 30, preferably 5 to 20. By giving an acid value, it tends to be negatively charged, and furthermore, when fixing to a recording paper, the affinity between the recording paper and the toner is good and the low-temperature fixability is improved. However, when the acid value exceeds 30, there is a tendency to deteriorate with respect to the stability of charging, particularly environmental fluctuation.

  The weight average molecular weight is 10,000 to 400,000, preferably 20,000 to 200,000. A weight average molecular weight of less than 10,000 is not preferable because offset resistance deteriorates. On the other hand, if it exceeds 400,000, the low-temperature fixability is deteriorated.

  In addition to the unmodified polyester obtained by the above polycondensation reaction, the polyester preferably contains a urea-modified polyester. The urea-modified polyester is obtained by reacting a terminal carboxyl group or hydroxyl group of the polyester obtained by the above polycondensation reaction with a polyvalent isocyanate compound (PIC) to obtain a polyester prepolymer (A) having an isocyanate group. It is obtained by cross-linking and / or extending the molecular chain by the reaction of the amine with amines.

  Examples of the polyvalent isocyanate compound (PIC) include aliphatic polyisocyanates (tetramethylene diisocyanate, hexamethylene diisocyanate, 2,6-diisocyanatomethylcaproate, etc.); alicyclic polyisocyanates (isophorone diisocyanate, cyclohexylmethane diisocyanate, etc.) Aromatic diisocyanates (tolylene diisocyanate, diphenylmethane diisocyanate, etc.); araliphatic diisocyanates (α, α, α ′, α′-tetramethylxylylene diisocyanate, etc.); isocyanates; Those blocked with caprolactam or the like; and combinations of two or more of these.

  The ratio of the polyvalent isocyanate compound (PIC) is usually 5/1 to 1/1, preferably as an equivalent ratio [NCO] / [OH] of the isocyanate group [NCO] and the hydroxyl group [OH] of the polyester having a hydroxyl group. 4/1 to 1.2 / 1, more preferably 2.5 / 1 to 1.5 / 1. When [NCO] / [OH] exceeds 5, low-temperature fixability deteriorates. When the molar ratio of [NCO] is less than 1, when a urea-modified polyester is used, the urea content in the ester is lowered and hot offset resistance is deteriorated.

  The content of the polyvalent isocyanate compound (PIC) component in the polyester prepolymer (A) having an isocyanate group is usually 0.5 to 40 wt%, preferably 1 to 30 wt%, more preferably 2 to 20 wt%. . If it is less than 0.5 wt%, the hot offset resistance deteriorates, and it is disadvantageous in terms of both heat-resistant storage stability and low-temperature fixability. On the other hand, if it exceeds 40 wt%, the low-temperature fixability deteriorates.

  The number of isocyanate groups contained per molecule in the polyester prepolymer (A) having an isocyanate group is usually 1 or more, preferably 1.5 to 3 on average, more preferably 1.8 to 2 on average. Five. If it is less than 1 per molecule, the molecular weight of the urea-modified polyester will be low, and the hot offset resistance will deteriorate.

  Next, as amines (B) to be reacted with the polyester prepolymer (A), a divalent amine compound (B1), a trivalent or higher polyvalent amine compound (B2), an amino alcohol (B3), an amino mercaptan (B4) ), Amino acid (B5), and amino acid block of B1 to B5 (B6).

  Examples of the divalent amine compound (B1) include aromatic diamines (phenylenediamine, diethyltoluenediamine, 4,4′-diaminodiphenylmethane, etc.); alicyclic diamines (4,4′-diamino-3,3′-dimethyldicyclohexyl). Methane, diamine cyclohexane, isophorone diamine, etc.); and aliphatic diamines (ethylene diamine, tetramethylene diamine, hexamethylene diamine, etc.) and the like. Examples of the trivalent or higher polyvalent amine compound (B2) include diethylenetriamine and triethylenetetramine. Examples of amino alcohol (B3) include ethanolamine and hydroxyethylaniline. Examples of amino mercaptan (B4) include aminoethyl mercaptan and aminopropyl mercaptan. Examples of the amino acid (B5) include aminopropionic acid and aminocaproic acid. Examples of the compound (B6) obtained by blocking the amino group of B1 to B5 include ketimine compounds and oxazolidine compounds obtained from the amines of B1 to B5 and ketones (acetone, methyl ethyl ketone, methyl isobutyl ketone, etc.). Among these amines (B), preferred are B1 and a mixture of B1 and a small amount of B2.

  The ratio of amines (B) is equivalent to the equivalent ratio [NCO] / [NHx] of isocyanate groups [NCO] in the polyester prepolymer (A) having isocyanate groups and amino groups [NHx] in amines (B). Is usually 1/2 to 2/1, preferably 1.5 / 1 to 1 / 1.5, more preferably 1.2 / 1 to 1 / 1.2. When [NCO] / [NHx] is more than 2 or less than 1/2, the molecular weight of the urea-modified polyester is lowered, and the hot offset resistance is deteriorated.

  The urea-modified polyester may contain a urethane bond together with a urea bond. The molar ratio of the urea bond content to the urethane bond content is usually 100/0 to 10/90, preferably 80/20 to 20/80, and more preferably 60/40 to 30/70. When the molar ratio of the urea bond is less than 10%, the hot offset resistance is deteriorated.

  The urea-modified polyester is produced by a one-shot method or the like. Polyhydric alcohol (PO) and polyvalent carboxylic acid (PC) are heated to 150-280 ° C. in the presence of a known esterification catalyst such as tetrabutoxytitanate, dibutyltin oxide, etc., and water generated while reducing the pressure as necessary. Distill off to obtain a polyester having a hydroxyl group. Subsequently, at 40-140 degreeC, this is made to react with polyvalent isocyanate (PIC), and the polyester prepolymer (A) which has an isocyanate group is obtained. Further, this (A) is reacted with amines (B) at 0 to 140 ° C. to obtain a urea-modified polyester.

  When reacting (PIC) and when reacting (A) and (B), a solvent may be used if necessary. Usable solvents include aromatic solvents (toluene, xylene, etc.); ketones (acetone, methyl ethyl ketone, methyl isobutyl ketone, etc.); esters (ethyl acetate, etc.); amides (dimethylformamide, dimethylacetamide, etc.) and ethers And those inert to isocyanates (PIC), such as tetrahydrofuran (such as tetrahydrofuran).

  In addition, in the crosslinking and / or extension reaction between the polyester prepolymer (A) and the amines (B), a reaction terminator can be used as necessary to adjust the molecular weight of the resulting urea-modified polyester. Examples of the reaction terminator include monoamines (diethylamine, dibutylamine, butylamine, laurylamine, etc.), and those obtained by blocking them (ketimine compounds).

  The weight average molecular weight of the urea-modified polyester is usually 10,000 or more, preferably 20,000 to 10,000,000, and more preferably 30,000 to 1,000,000. If it is less than 10,000, the hot offset resistance deteriorates. The number average molecular weight of the urea-modified polyester or the like is not particularly limited when the above-mentioned unmodified polyester is used, and may be a number average molecular weight that can be easily obtained to obtain the weight average molecular weight. When the urea-modified polyester is used alone, its number average molecular weight is usually 2000-15000, preferably 2000-10000, more preferably 2000-8000. When it exceeds 20000, the low-temperature fixability and the glossiness when used in a full-color apparatus are deteriorated.

  By using the unmodified polyester and the urea-modified polyester in combination, the low-temperature fixability and the gloss when used in the full-color image forming apparatus 100 are improved. Therefore, it is preferable to use the urea-modified polyester alone. The unmodified polyester may include a polyester modified with a chemical bond other than a urea bond.

  The unmodified polyester and the urea-modified polyester are preferably at least partially compatible with each other in terms of low-temperature fixability and hot offset resistance. Therefore, it is preferable that the unmodified polyester and the urea-modified polyester have a similar composition.

  The weight ratio of unmodified polyester to urea-modified polyester is usually 20/80 to 95/5, preferably 70/30 to 95/5, more preferably 75/25 to 95/5, and particularly preferably 80 /. 20-93 / 7. When the weight ratio of the urea-modified polyester is less than 5%, the hot offset resistance is deteriorated, and it is disadvantageous in terms of both heat-resistant storage stability and low-temperature fixability.

  The glass transition point (Tg) of the binder resin containing unmodified polyester and urea-modified polyester is usually 45 to 65 ° C, preferably 45 to 60 ° C. If it is less than 45 ° C., the heat resistance of the toner deteriorates, and if it exceeds 65 ° C., the low-temperature fixability becomes insufficient.

  In addition, since the urea-modified polyester is likely to be present on the surface of the obtained toner base particles, the heat-resistant storage stability tends to be good even when the glass transition point is low as compared with known polyester-based toners.

(Coloring agent)
As the colorant, all known dyes and pigments can be used. For example, carbon black, nigrosine dye, iron black, naphthol yellow S, Hansa yellow (10G, 5G, G), cadmium yellow, yellow iron oxide, ocher , Yellow lead, titanium yellow, polyazo yellow, oil yellow, Hansa yellow (GR, A, RN, R), pigment yellow L, benzidine yellow (G, GR), permanent yellow (NCG), Vulcan fast yellow (5G, R), Tartrazine Lake, Quinoline Yellow Lake, Anthrazan Yellow BGL, Isoindolinone Yellow, Bengala, Red Dan, Lead Zhu, Cadmium Red, Cadmium Mercury Red, Antimon Zhu, Permanent Red 4R, Para Red, Phi Sayred, Parachlor Ortonito Aniline Red, Resol Fast Scarlet G, Brilliant Fast Scarlet, Brilliant Carmine B, Permanent Red (F2R, F4R, FRL, FRLL, F4RH), Fast Scarlet VD, Belkan Fast Rubin B, Brilliant Scarlet G, Resol Rubin GX, Permanent Red F5R , Brilliant Carmine 6B, Pigment Scarlet 3B, Bordeaux 5B, Tolujing Maroon, Permanent Bordeaux F2K, Helio Bordeaux BL, Bordeaux 10B, Bon Maroon Light, Bon Maroon Medium, Eosin Lake, Rhodamine Lake B, Rhodamine Lake Y, Alizarin Lake, Thio Indigo Red B, Thioindigo Maroon, Oil Red, Quinacridone Red, Pyrazolone Red Polyazo Red, Chrome Vermillion, Benzidine Orange, Perinone Orange, Oil Orange, Cobalt Blue, Cerulean Blue, Alkaline Blue Lake, Peacock Blue Lake, Victoria Blue Lake, Metal Free Phthalocyanine Blue, Phthalocyanine Blue, Fast Sky Blue, Indanthrene Blue (RS, BC), indigo, ultramarine blue, bitumen, anthraquinone blue, fast violet B, methyl violet lake, cobalt purple, manganese purple, dioxane violet, anthraquinone violet, chrome green, zinc green, chromium oxide, pyridian, emerald green, pigment Green B, Naphthol Green B, Green Gold, Acid Green Lake, Malachite Green Lake, Lid Russian nin green, anthraquinone green, titanium oxide, zinc white, litbon and mixtures thereof can be used. The content of the colorant is usually 1 to 15% by weight, preferably 3 to 10% by weight, based on the toner.

  The colorant can also be used as a master batch combined with a resin. As a binder resin to be kneaded together with the production of a master batch or a master batch, a polymer of styrene such as polystyrene, poly-p-chlorostyrene, polyvinyl toluene, or a substituted product thereof, or a copolymer of these and a vinyl compound, Polymethyl methacrylate, polybutyl methacrylate, polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene, polyester, epoxy resin, epoxy polyol resin, polyurethane, polyamide, polyvinyl butyral, polyacrylic acid resin, rosin, modified rosin, terpene resin, fat Aromatic or alicyclic hydrocarbon resins, aromatic petroleum resins, chlorinated paraffins, paraffin waxes and the like can be mentioned, and these can be used alone or in combination.

(Charge control agent)
Known charge control agents can be used, such as nigrosine dyes, triphenylmethane dyes, chromium-containing metal complex dyes, molybdate chelate pigments, rhodamine dyes, alkoxy amines, quaternary ammonium salts (fluorine-modified 4 Secondary ammonium salts or compounds, tungsten simple substances or compounds, fluorine activators, salicylic acid metal salts, and metal salts of salicylic acid derivatives. Specifically, Bontron 03 of a nigrosine dye, Bontron P-51 of a quaternary ammonium salt, Bontron S-34 of a metal-containing azo dye, E-82 of an oxynaphthoic acid metal complex, E-84 of a salicylic acid metal complex , Phenolic condensate E-89 (above, Orient Chemical Industries, Ltd.), quaternary ammonium salt molybdenum complex TP-302, TP-415 (above, Hodogaya Chemical Co., Ltd.), quaternary ammonium salt copy Charge PSYVP2038, copy blue PR of triphenylmethane derivative, copy charge of quaternary ammonium salt NEG VP2036, copy charge NX VP434 (manufactured by Hoechst), LRA-901, LR-147 which is a boron complex (manufactured by Nippon Carlit) ), Copper phthalocyanine, perylene, quinacridone, azo face And other polymeric compounds having functional groups such as sulfonic acid groups, carboxyl groups, and quaternary ammonium salts. Of these, substances that control the negative polarity of the toner are particularly preferably used.

  The amount of charge control agent used is determined by the type of binder resin, the presence or absence of additives used as necessary, and the toner production method including the dispersion method, and is not uniquely limited. Preferably, it is used in the range of 0.1 to 10 parts by weight with respect to 100 parts by weight of the binder resin. The range of 0.2 to 5 parts by weight is preferable. When the amount exceeds 10 parts by weight, the chargeability of the toner is too high, the effect of the charge control agent is reduced, the electrostatic attraction with the developing roller is increased, the developer fluidity is lowered, and the image density is lowered. Invite.

(Release agent)
As a release agent, a low melting point wax having a melting point of 50 to 120 ° C. works more effectively as a release agent in the dispersion with the binder resin between the fixing roller and the toner interface. The effect on high temperature offset is exhibited without applying a release agent such as oil. Examples of such a wax component include the following. Examples of waxes and waxes include plant waxes such as carnauba wax, cotton wax, wood wax, rice wax, animal waxes such as beeswax and lanolin, mineral waxes such as ozokerite and cercin, and paraffin, microcrystalline, And petroleum waxes such as petrolatum. In addition to these natural waxes, synthetic hydrocarbon waxes such as Fischer-Tropsch wax and polyethylene wax, and synthetic waxes such as esters, ketones, and ethers can be used. Furthermore, fatty acid amides such as 12-hydroxystearic acid amide, stearic acid amide, phthalic anhydride imide, chlorinated hydrocarbon, and low molecular weight crystalline polymer resin, poly-n-stearyl methacrylate, poly-n- A crystalline polymer having a long alkyl group in the side chain such as a homopolymer or copolymer of polyacrylate such as lauryl methacrylate (for example, a copolymer of n-stearyl acrylate-ethyl methacrylate, etc.) can also be used. .

  The charge control agent and the release agent can be melt-kneaded together with the master batch and the binder resin, and of course, they may be added when dissolved and dispersed in the organic solvent.

(External additive)
Inorganic fine particles are preferably used as an external additive for assisting the fluidity, developability and chargeability of the toner particles. The primary particle diameter of the inorganic fine particles is preferably 5 × 10 −3 to 2 μm, and particularly preferably 5 × 10 −3 to 0.5 μm. Moreover, it is preferable that the specific surface area by BET method is 20-500 m <2> / g. The use ratio of the inorganic fine particles is preferably 0.01 to 5 wt% of the toner, and particularly preferably 0.01 to 2.0 wt%.

  Specific examples of the inorganic fine particles include, for example, silica, alumina, titanium oxide, barium titanate, magnesium titanate, calcium titanate, strontium titanate, zinc oxide, tin oxide, quartz sand, clay, mica, wollastonite, diatomaceous earth. Examples include soil, chromium oxide, cerium oxide, bengara, antimony trioxide, magnesium oxide, zirconium oxide, barium sulfate, barium carbonate, calcium carbonate, silicon carbide, and silicon nitride. Among these, as the fluidity imparting agent, it is preferable to use hydrophobic silica fine particles and hydrophobic titanium oxide fine particles in combination. In particular, when stirring and mixing are performed using particles having an average particle size of 5 × 10-2 μm or less, the electrostatic force and van der Waals force with the toner are remarkably improved. Even when stirring and mixing inside the developing device is performed, a fluidity-imparting agent is not detached from the toner, a good image quality that does not cause fireflies and the like is obtained, and a reduction in residual toner is further achieved. .

  Titanium oxide fine particles are excellent in environmental stability and image density stability, but have a tendency to deteriorate the charge rise characteristics. Therefore, if the amount of titanium oxide fine particles added is larger than the amount of silica fine particles added, this side effect is affected. It can be considered large. However, when the added amount of the hydrophobic silica fine particles and the hydrophobic titanium oxide fine particles is in the range of 0.3 to 1.5 wt%, the charge rising characteristics are not greatly impaired, and the desired charge rising characteristics can be obtained, that is, repeated copying. Stable image quality can be obtained even if

  Next, a toner manufacturing method will be described. Here, although a preferable manufacturing method is shown, it is not limited to this.

(Toner production method)
1) A toner material solution is prepared by dispersing a colorant, unmodified polyester, a polyester prepolymer having an isocyanate group, and a release agent in an organic solvent.
The organic solvent is preferably volatile with a boiling point of less than 100 ° C. from the viewpoint of easy removal after toner base particle formation. Specifically, toluene, xylene, benzene, carbon tetrachloride, methylene chloride, 1,2-dichloroethane, 1,1,2-trichloroethane, trichloroethylene, chloroform, monochlorobenzene, dichloroethylidene, methyl acetate, ethyl acetate, methyl ethyl ketone, Methyl isobutyl ketone and the like can be used alone or in combination of two or more. In particular, aromatic solvents such as toluene and xylene and halogenated hydrocarbons such as methylene chloride, 1,2-dichloroethane, chloroform, and carbon tetrachloride are preferable. The usage-amount of an organic solvent is 0-300 weight part normally with respect to 100 weight part of polyester prepolymers, Preferably it is 0-100 weight part, More preferably, it is 25-70 weight part.

  2) The toner material liquid is emulsified in an aqueous medium in the presence of a surfactant and resin fine particles.

  The aqueous medium may be water alone or an organic solvent such as alcohol (methanol, isopropyl alcohol, ethylene glycol, etc.), dimethylformamide, tetrahydrofuran, cellosolves (methyl cellosolve, etc.), lower ketones (acetone, methyl ethyl ketone, etc.). It may be included.

  The amount of the aqueous medium used relative to 100 parts by weight of the toner material liquid is usually 50 to 2000 parts by weight, preferably 100 to 1000 parts by weight. If the amount is less than 50 parts by weight, the dispersion state of the toner material liquid is poor and toner particles having a predetermined particle diameter cannot be obtained. If it exceeds 20000 parts by weight, it is not economical.

  Further, in order to improve the dispersion in the aqueous medium, a dispersant such as a surfactant and resin fine particles is appropriately added.

  As surfactants, anionic surfactants such as alkylbenzene sulfonates, α-olefin sulfonates, phosphate esters, alkylamine salts, amino alcohol fatty acid derivatives, polyamine fatty acid derivatives, amine salt types such as imidazoline, Quaternary ammonium salt type cationic surfactants such as alkyltrimethylammonium salt, dialkyldimethylammonium salt, alkyldimethylbenzylammonium salt, pyridinium salt, alkylisoquinolinium salt, benzethonium chloride, fatty acid amide derivative, polyhydric alcohol Nonionic surfactants such as derivatives, for example, amphoteric surfactants such as alanine, dodecyldi (aminoethyl) glycine, di (octylaminoethyl) glycine and N-alkyl-N, N-dimethylammonium betaine And the like.

  Further, by using a surfactant having a fluoroalkyl group, the effect can be obtained in a very small amount. Preferred anionic surfactants having a fluoroalkyl group include fluoroalkyl carboxylic acids having 2 to 10 carbon atoms and metal salts thereof, disodium perfluorooctanesulfonyl glutamate, 3- [ω-fluoroalkyl (C6-C11 ) Oxy] -1-alkyl (C3-C4) sodium sulfonate, 3- [ω-fluoroalkanoyl (C6-C8) -N-ethylamino] -1-propanesulfonic acid sodium, fluoroalkyl (C11-C20) carvone Acids and metal salts, perfluoroalkylcarboxylic acids (C7 to C13) and metal salts thereof, perfluoroalkyl (C4 to C12) sulfonic acids and metal salts thereof, perfluorooctanesulfonic acid diethanolamide, N-propyl-N- ( 2-Hydroxyethyl) Perful Olooctanesulfonamide, perfluoroalkyl (C6-C10) sulfonamidopropyltrimethylammonium salt, perfluoroalkyl (C6-C10) -N-ethylsulfonylglycine salt, monoperfluoroalkyl (C6-C16) ethyl phosphate, etc. Can be mentioned.

  Product names include Surflon S-111, S-112, S-113 (Asahi Glass Co., Ltd.), Florard FC-93, FC-95, FC-98, FC-129 (Sumitomo 3M Co., Ltd.), Unidyne DS-101. DS-102 (manufactured by Daikin Industries, Ltd.), Megafac F-110, F-120, F-113, F-191, F-812, F-833 (manufactured by Dainippon Ink, Inc.), Xtop EF-102, 103, 104, 105, 112, 123A, 123B, 306A, 501, 201, 204 (manufactured by Tochem Products), and Fgentent F-100, F150 (manufactured by Neos).

  Moreover, as the cationic surfactant, aliphatic quaternary ammonium such as aliphatic primary, secondary or secondary amic acid, perfluoroalkyl (C6-C10) sulfonamidopropyltrimethylammonium salt which has a right fluoroalkyl group is used. Salts, benzalkonium salts, benzethonium chloride, pyridinium salts, imidazolinium salts, trade names include Surflon S-121 (Asahi Glass Co., Ltd.), Florard FC-135 (Sumitomo 3M Co., Ltd.), Unidyne DS-202 (Daikin Industries) Smoke), Megafac F-150, F-824 (Dainippon Ink Co., Ltd.), Xtop EF-132 (Tochem Products), Footage F-300 (Neos), and the like.

  The resin fine particles are added to stabilize the toner base particles formed in the aqueous medium. For this reason, it is preferable to add so that the coverage existing on the surface of the toner base particles is in the range of 10 to 90%. For example, polymethyl methacrylate fine particles 1 μm and 3 μm, polystyrene fine particles 0.5 μm and 2 μm, poly (styrene-acrylonitrile) fine particles 1 μm, trade names are PB-200H (manufactured by Kao), SGP (manufactured by Soken), Techno Examples include polymer SB (manufactured by Sekisui Chemical Co., Ltd.), SGP-3G (manufactured by Sokensha), and micropearl (manufactured by Sekisui Fine Chemical Co., Ltd.).

  In addition, inorganic compound dispersants such as tricalcium phosphate, calcium carbonate, titanium oxide, colloidal silica, and hydroxyapatite can also be used.

  As a dispersant that can be used in combination with the above resin fine particles and inorganic compound dispersant, the dispersed droplets may be stabilized by a polymer protective colloid. For example, acrylic acid, methacrylic acid, α-cyanoacrylic acid, α-cyanomethacrylic acid, itaconic acid, crotonic acid, fumaric acid, maleic acid or maleic anhydride and other (meth) acrylic monomers containing hydroxyl groups Bodies such as acrylic acid-β-hydroxyethyl, methacrylic acid-β-hydroxyethyl, acrylic acid-β-hydroxypropyl, methacrylic acid-β-hydroxypropyl, acrylic acid-γ-hydroxypropyl, methacrylic acid-γ-hydroxy Propyl, acrylic acid-3-chloro-2-hydroxypropyl, methacrylic acid-3-chloro-2-hydroxypropyl, diethylene glycol monoacrylate, diethylene glycol monomethacrylate, glycerol monoacrylate, glycerol monomethacrylate Luric acid esters, N-methylol acrylamide, N-methylol methacrylamide, etc., vinyl alcohol or ethers with vinyl alcohol, such as vinyl methyl ether, vinyl ethyl ether, vinyl propyl ether, or compounds containing vinyl alcohol and a carboxyl group Esters such as vinyl acetate, vinyl propionate, vinyl butyrate, acrylamide, methacrylamide, diacetone acrylamide or their methylol compounds, acid chlorides such as acrylic acid chloride, methacrylic acid chloride, vinyl pyridine, vinyl pyrrolidone, vinyl Nitrogen compounds such as imidazole and ethyleneimine, or homopolymers or copolymers such as those having a heterocyclic ring thereof, polyoxyethylene, poly Xoxypropylene, polyoxyethylene alkylamine, polyoxypropylene alkylamine, polyoxyethylene alkylamide, polyoxypropylene alkylamide, polyoxyethylene nonylphenyl ether, polyoxyethylene lauryl phenyl ether, polyoxyethylene stearyl phenyl ester, polyoxy Polyoxyethylenes such as ethylene nonylphenyl ester, celluloses such as methyl cellulose, hydroxyethyl cellulose, and hydroxypropyl cellulose can be used.

  The dispersion method is not particularly limited, and known equipment such as a low-speed shear method, a high-speed shear method, a friction method, a high-pressure jet method, and an ultrasonic wave can be applied. Among these, the high-speed shearing method is preferable in order to make the particle size of the dispersion 2 to 20 μm. When a high-speed shearing disperser is used, the rotational speed is not particularly limited, but is usually 1000 to 30000 rpm, preferably 5000 to 20000 rpm. The dispersion time is not particularly limited, but in the case of a batch method, it is usually 0.1 to 5 minutes. The temperature during dispersion is usually 0 to 150 ° C. (under pressure), preferably 40 to 98 ° C.

  3) At the same time as the preparation of the emulsion, the amines (B) are added to cause a reaction with the polyester prepolymer (A) having an isocyanate group.

  This reaction involves molecular chain crosslinking and / or elongation. The reaction time is selected depending on the reactivity between the isocyanate group structure of the polyester prepolymer (A) and the amines (B), but is usually 10 minutes to 40 hours, preferably 2 to 24 hours. The reaction temperature is generally 0 to 150 ° C, preferably 40 to 98 ° C. Moreover, a well-known catalyst can be used as needed. Specific examples include dibutyltin laurate and dioctyltin laurate.

  4) After completion of the reaction, the organic solvent is removed from the emulsified dispersion (reactant), washed and dried to obtain toner base particles.

  In order to remove the organic solvent, the temperature of the entire system is gradually raised in a laminar stirring state, and after giving strong stirring in a certain temperature range, the solvent base is removed to produce spindle-shaped toner base particles. . Further, when an acid such as calcium phosphate salt or an alkali-soluble material is used as the dispersion stabilizer, the calcium phosphate salt is dissolved from the toner base particles by a method such as dissolving the calcium phosphate salt with an acid such as hydrochloric acid and washing with water. Remove. It can also be removed by operations such as enzymatic degradation.

  5) A charge control agent is injected into the toner base particles obtained above, and then inorganic fine particles such as silica fine particles and titanium oxide fine particles are externally added to obtain a toner.

  The injection of the charge control agent and the external addition of the inorganic fine particles are performed by a known method using a mixer or the like.

  Thereby, a toner having a small particle size and a sharp particle size distribution can be easily obtained. Furthermore, by giving strong agitation in the process of removing the organic solvent, the shape between the true spherical shape and the rugby ball shape can be controlled, and the surface morphology is also controlled between the smooth shape and the umeboshi shape. be able to.

  The toner according to the present invention has a substantially spherical shape and can be represented by the following shape rule.

  FIG. 6 is a diagram schematically showing the shape of the toner of the present invention. In FIG. 6, when a substantially spherical toner is defined by a major axis r1, a minor axis r2, and a thickness r3 (where r1 ≧ r2 ≧ r3), the toner of the present invention has a major axis and a minor axis. Ratio (r2 / r1) (see FIG. 6 (b)) is 0.5 to 1.0, and the ratio of thickness to minor axis (r3 / r2) (see FIG. 6 (c)) is 0.7 to It is preferable to be in the range of 1.0. When the ratio of the major axis to the minor axis (r2 / r1) is less than 0.5, the dot reproducibility and transfer efficiency are inferior because of being away from the true spherical shape, and high-quality image quality cannot be obtained. On the other hand, if the ratio of thickness to minor axis (r3 / r2) is less than 0.7, the shape is close to a flat shape, and a high transfer rate like a spherical toner cannot be obtained. In particular, when the ratio of the thickness to the minor axis (r3 / r2) is 1.0, the rotating body has a major axis as a rotation axis, and the fluidity of the toner can be improved.

  Note that r1, r2, and r3 were measured with a scanning electron microscope (SEM) while changing the angle of field of view and taking pictures.

Below, the effect for each claim is explained.
3. The image forming apparatus according to claim 1, wherein only one set (four) of the first image carrier is used, and the color order of the toner on the first surface of the paper and the color order of the toner on the second surface are as follows. Therefore, it is possible to make a one-pass duplex copy with stable color image quality without changing the color of each side without increasing the size of the apparatus (providing two sets (eight) first image carriers). It becomes possible to provide.

In the image forming apparatus according to claim 3 and 4, since the volume resistance value of the intermediate transfer member is 10 ⁶ to 10 ¹³ (Ω · cm) and the material is polyimide, the toner image can be easily held. In addition, since the toner releasability is also excellent, it is possible to provide an image forming apparatus having excellent transferability to paper.

  6. The image forming apparatus according to claim 5, wherein the toner used has a volume average particle diameter of 3 to 8 μm and a ratio (Dv / Dn) of volume average particle diameter (Dv) to number average particle diameter (Dn) of 1. By setting the range to 0.001 to 1.40, the toner charge amount distribution becomes uniform, a high-quality image with little background fogging can be obtained, and in the electrostatic transfer method, the transfer rate is increased. Can do.

  7. The image forming apparatus according to claim 6, wherein the toner to be used has a shape factor SF-1 in the range of 100 to 180 and a shape factor SF-2 in the range of 100 to 190, whereby the toner has a spherical shape. Since the contact state between the toner and the toner or the toner and the photoconductor becomes point contact, the adsorbing force between the toners becomes weak and the fluidity becomes high, and the adsorbing force between the toner and the photoconductor is also weak. Thus, the transfer rate can be increased. However, if the shape factor SF-1 exceeds 180 and SF-2 exceeds 190, the transfer rate is lowered, which is not preferable and thus excluded from the range.

  8. The image forming apparatus according to claim 7, wherein a toner material liquid in which at least a polyester prepolymer having a functional group containing a nitrogen atom, a polyester, a colorant, and a release agent is dispersed in an organic solvent is used. A toner can be produced by preparing a toner obtained by crosslinking and / or elongation reaction in an aqueous medium.

  In the image forming apparatus according to the eighth aspect, the toner to be used has a substantially spherical shape.

  In the image forming apparatus of the ninth aspect, the shape of the toner to be used is defined by the major axis r1, the minor axis r2, and the thickness r3 (provided that r1 ≧ r2 ≧ r3), and the major axis r1 and the minor axis are short. The ratio (r2 / r1) to the axis r2 is in the range of 0.5 to 1.0, and the ratio (r3 / r2) of the thickness r3 to the minor axis r2 is in the range of 0.7 to 1.0. Thus, the following effects can be obtained. When the ratio of the major axis to the minor axis (r2 / r1) is less than 0.5, the dot reproducibility and transfer efficiency are inferior because of being away from the true spherical shape, and high-quality image quality cannot be obtained. On the other hand, if the ratio of thickness to minor axis (r3 / r2) is less than 0.7, the shape is close to a flat shape, and a high transfer rate like a spherical toner cannot be obtained. In particular, when the ratio of the thickness to the minor axis (r3 / r2) is 1.0, the rotating body has a major axis as a rotation axis, and the fluidity of the toner can be improved.

  Each embodiment described above is a preferred embodiment of the present invention, and various modifications can be made without departing from the gist of the present invention.

1 Body 2 Feeder
a, b, c, d First image carrier L Static eliminating device 5 Photosensitive drum 6 Cleaning device 7 Charging device 8 Developing device 9 Exposure device 10 First intermediate transfer belt 11 Support roller 20 Transfer roller 25 Cleaning device (first intermediate) Transfer belt)
28 Registration Roller (pair)
30 Paper discharge stack 31 Guide 32 Paper discharge roller (pair)
40 Fixing Device 100 Second Intermediate Transfer Belt 120 Transfer Roller 113 Support Roller CH Charger

JP 2006-227292 A JP 2004-109921 A

Claims (9)

Four first image carriers each carrying four color toner images, a second image carrier comprising a first intermediate transfer belt, a third image carrier comprising a second intermediate transfer belt, and the first image A first transfer unit that transfers a toner image from the carrier to the second image carrier; and a second transfer unit that transfers the toner image from the second image carrier to the third image carrier or a recording medium. ,
A plurality of toner images formed using the first image carrier are held on the third image carrier by the first transfer unit and the second transfer unit, and the toner images are formed on both sides of the recording medium. In the image forming apparatus provided with a fixing device that simultaneously fixes the toner image to both sides of the recording medium after the transfer,
An image forming apparatus, wherein each station of the first image carrier has a plurality of development colors. When forming images on both sides of the recording medium,
By switching the color of the toner at each station of the first image carrier between the time when the first surface toner image is formed and the time when the second surface toner image is formed, the toner image on the recording medium is changed. 2. The image forming apparatus according to claim 1, wherein the color order of the toner on the first surface is the same as the color order of the toner on the second surface.   3. The image forming apparatus according to claim 1, wherein at least one of the second image carrier and the third image carrier comprises an endless belt made of polyimide. 3. The image formation according to claim 1, wherein at least one of the second image carrier and the third image carrier has a volume resistance of 10 ⁶ to 10 ¹³ (Ω · cm). apparatus.   The toner used has a volume average particle diameter of 3 to 8 μm and a ratio (Dv / Dn) of volume average particle diameter (Dv) to number average particle diameter (Dn) in the range of 1.00 to 1.40. 5. The image forming apparatus according to claim 1, wherein the image forming apparatus is provided.   6. The toner according to claim 1, wherein the toner used has a shape factor SF-1 in the range of 100 to 180, and a shape factor SF-2 in the range of 100 to 190. The image forming apparatus described in the item.   The toner to be used is obtained by crosslinking a toner material solution in which at least a polyester prepolymer having a functional group containing a nitrogen atom, polyester, a colorant, and a release agent is dispersed in an organic solvent in an aqueous medium. The image forming apparatus according to claim 1, wherein the image forming apparatus is a toner obtained by an extension reaction.   The image forming apparatus according to claim 1, wherein the toner used has a substantially spherical shape.   The shape of the toner is defined by a major axis r1, a minor axis r2, and a thickness r3 (where r1 ≧ r2 ≧ r3), and the ratio (r2 / r1) between the major axis r1 and the minor axis r2 is 0. The image formation according to claim 8, wherein the ratio (r3 / r2) of the thickness r3 to the minor axis r2 is in the range of 0.7 to 1.0. apparatus.

Images