JPH07271135A - Color image forming device - Google Patents

Abstract

PURPOSE:To obtain a copied image giving calmness to a user mentally without feeling fatigue in the case of viewing many copies and stable even when the obtained image is copied by specifying ralation between the glossiness of a black image and that of a color image other than the black image. CONSTITUTION:A fixing device is incorporated with heater lamp 80 in the center, and is provided with an upper fixing roller 84 obtained by forming an LTV rubber layer 82 and a PFA tube layer 83 on the surface of a hollow aluminum roller 81 whose diameter is 40mm and a lower fixing roller 88 obtained by forming an LTV rubber layer 86 and a PFA tube layer 87 on the surface of a hololow aluminum roller 85 whose diameter is 40mm. The image is previously transferred to a recording paper under a certain condition and the glossiness of the transferred image is measured. Then, developer, fixing process and the supply amount of fixing oil are optimized so that the relation of the glossiness satisfies Gk<=15, Gc<=20 and Gk<=Gc when it is assumed that the glossiness of the black image is Gk and the glossiness of the color image other than the black image is Gc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus, and more particularly to a color image forming apparatus most suitable for a color printer such as an office.

[0002]

2. Description of the Related Art Conventionally, color image forming apparatuses have been known, and various methods are used for forming color images. For example, a method in which the toner image transfer process is repeated for each color, a photosensitive drum is prepared for each color type, and each color is transferred to the recording paper while the recording paper passes through each photosensitive drum, a color image is obtained. There is known a method for forming a toner image, a method for forming a toner image for each color type on a single photosensitive drum in a laminated manner, and a batch transfer of these multicolor images on a recording paper. The operation of the multi-color image batch transfer type color image forming apparatus will be described below.

FIG. 6 is a diagram showing a structural example of a multi-color image batch transfer type color image forming apparatus. In the figure, reference numeral 1 denotes a photosensitive drum which is an image bearing member, and is an OPC photosensitive member coated on the drum, which is electrically grounded and driven and rotated clockwise. Reference numeral 2 denotes a scorotron charger, which uniformly charges the peripheral surface of the photosensitive drum 1 at the potential VH to the potential VG.
Given by corona discharge by a grid and corona discharge wire held on. Prior to the charging by the scorotron charger 2, an exposure device using a light emitting diode or the like (for example, P
CL) 3 is used to remove the charge from the peripheral surface of the photoconductor.

After uniformly charging the photoreceptor, the image exposing means 10
Thus, image exposure is performed based on the image signal. The image exposure means 10 uses a laser diode (not shown) as a light emitting source, performs scanning while the optical path is bent by a reflecting mirror 12 via a rotating polygon mirror 11, fθ lens, etc., and rotation of the photosensitive drum 1 (sub scanning). Form an electrostatic latent image. Here, the character portion is exposed to form an inverted latent image in which the character portion has a lower potential VL.

At the periphery of the photoconductor drum 1, there is provided a developing device 20 in which a developer containing toner such as yellow (Y), magenta (M), cyan (C), black (K) and a carrier is incorporated. First, the development of the first color is performed by the developing sleeve 21 which has a magnet built therein and holds the developer and rotates. The developer is composed of a carrier in which ferrite is used as a core and an insulating resin is coated around the core, and a toner in which a pigment as a main material and a charge control agent, silica, titanium oxide and the like are added, The developer is regulated to a layer thickness (developer) of 100 μm to 600 μm on the developing sleeve 21 by the layer forming means and is conveyed to the developing area.

The gap between the developing sleeve 21 and the photosensitive drum 1 in the developing area is larger than the layer thickness (developer) of 0.2.
The thickness is set to mm to 1.0 mm, and the AC bias having the voltage value VAC and the DC bias having the voltage value VDC are superimposed and applied during this period. Since VDC and VH and toner charge have the same polarity,
The toner that has been given the opportunity to leave the carrier by VAC does not adhere to the VH portion, which has a higher potential than VDC,
It adheres to the VL portion having a lower potential than VDC and is visualized (reversal development).

After the visualization of the first color is completed, the image forming process of the second color is started, the uniform charging is performed again by the scorotron charger 2, and the electrostatic latent image based on the image data of the second color is exposed by the image exposing means. Formed by 10. At this time, the charge removal by the exposure device 3 performed in the image forming process of the first color is not performed because the toner attached to the image portion of the first color scatters due to the rapid decrease in the potential around the image.

Again, an electrostatic latent image similar to that of the first color is formed on a portion of the photoconductor having a potential of VH all over the peripheral surface of the photoconductor drum without the image of the first color and developed. However, in the portion where the image with the first color image is developed again, the toner adhering to the first color shields light and an electrostatic latent image of potential VM is formed by the electric charge of the toner itself, so that VDC Development is performed according to the potential difference of VM. In the part where the images of the first and second colors overlap,
When the development of the first color is performed by forming an electrostatic latent image of VL, the balance between the first color and the second color is lost, so the exposure amount of the first color may be reduced to an intermediate potential of VH>VM> VL. is there.

An image forming process similar to that of the second color is performed for the third and fourth colors, and a visible image of four colors is formed on the peripheral surface of the photosensitive drum 1. On the other hand, the recording paper P carried out from the paper feeding cassette 15 via the half-moon roller 16 is temporarily stopped, and when the transfer timing is adjusted, the paper feeding roller 17
The paper is fed to the transfer area by the rotation operation of.

In the transfer area, a transfer roller 18 is pressed against the peripheral surface of the photosensitive drum 1 in synchronism with the transfer timing, and the supplied recording paper P is nipped and a multicolor image is transferred at once. To be done.

Next, the recording paper P is de-charged by the separating brush 19 which is brought into pressure contact with each other almost at the same time, separated by the peripheral surface of the photosensitive drum 1 and conveyed to the fixing device 30, where the heat roller 31 and the pressure roller 32 are heated. After the toner is fused by applying pressure, the toner is ejected to the outside of the apparatus through the paper ejection roller 41. Incidentally, the transfer roller 18 and the separation brush 1 described above.
After the recording paper P has passed through, 9 is retracted from the peripheral surface of the photosensitive drum 1 to prepare for the formation of the next toner image.

On the other hand, the photosensitive drum 1 from which the recording paper P is separated
Removes and cleans the residual toner by pressing the blade 51 of the cleaning device 50, and again receives the charge removal by the exposure device 3 and the charge by the scorotron charger 2 to start the next image forming process. The blade 51 moves immediately after cleaning the surface of the photoconductor and retracts from the peripheral surface of the photoconductor drum 1.

Note that the image forming apparatus shown in the figure can also be manually fed in addition to being fed by an automatic sheet feeding mechanism. The recording paper P manually fed by the manual feed tray 60 is conveyed by the rotation of the pickup roller 61,
The sheet is fed to the transfer area through the same process as the sheet feeding from the sheet feeding cassette 15 described above.

[0014]

In the conventional full-color image forming apparatus as described above, the image quality in the full-color use is generally emphasized, and the glossiness of the image portion is maintained regardless of which transfer paper is used. It was designed to be high. Therefore, an image formed on a low-gloss transfer paper also has high glossiness, and the difference in glossiness between the non-image area and the image area is large, which gives the viewer a feeling of strangeness.

In particular, in the case of a copy image of a monochrome character image for business use, since the character itself has high gloss, there is a problem that the character becomes difficult to read due to reflection. To solve such a problem, by designing the viscoelastic property of the black toner when melted to be higher than that of the color toner, the glossiness of a monochrome image (that is, a character image) is lowered, and the color image is A technique for creating a copied image having high gloss has been proposed (Japanese Patent Laid-Open No. 63-
No. 300254). In this case, since the fixing performance of the black toner and the fixing performance of the color toner are greatly different, the fixing condition for fixing both toners is extremely narrow, and the problems such as offset and insufficient fixing strength are likely to occur. As another means, a technique has been proposed in which a transparent toner is fixed on the entire surface of a copied image to make the gloss uniform and control (JP-A-4-204670), but a huge amount of transparent toner is used. However, there is a problem that it is not practical because it consumes the toner, makes the device complicated due to the addition of the developing process of the transparent toner, and lowers the copy productivity.

Conventionally, it is preferable that the glossiness of black is low and the glossiness of color is high. In the related art, there is no upper limit on the glossiness of color. The present inventor has found that when the color printer is used as a color printer, the image quality is psychologically rather bad if the glossiness of the color is too high. Since the color printer image is an original image, if the glossiness is high, there is a problem that it is difficult to obtain a stable copy image due to the scanner characteristics (including image processing) of the copying machine used for copying.

The present invention has been made in view of the above problems, and provides psychological comfort to the user, does not cause fatigue even when a large number of sheets are viewed, and is stable even when copying the obtained image. It is an object of the present invention to provide a color image forming apparatus capable of obtaining a copied image.

[0018]

SUMMARY OF THE INVENTION The present invention which solves the above-mentioned problems forms an image by forming a color image using yellow (Y), magenta (M), cyan (C) and black (K) toners. In the device, the glossiness of the black image is Gk, and the glossiness of the color image other than the black image is Gk.
It is characterized in that the relationship of glossiness is such that Gk ≦ 15, Gc ≦ 20 and Gk ≦ Gc.

[0019]

According to the present invention, by setting an upper limit on the glossiness of black (black) and color images, it is possible to prevent the glossiness from becoming higher than necessary. Therefore, according to the present invention, it is possible to psychologically give the user peace of mind, do not feel fatigue even when viewing a large number of sheets, and obtain a stable copy image even when copying the obtained image.

[0020]

EXAMPLE As described above, the present invention sets an upper limit on the glossiness of each color, but feedback is provided to the image forming process so that the glossiness of the image transferred to the recording paper does not exceed the upper limit. It does not call. According to the present invention, an image is transferred to a recording paper under a certain condition in advance, the glossiness of the transferred image is measured, and the glossiness of the black image is set to Gk, and the glossiness of the color image other than the black image is set to Gc. The developer, the fixing process, the supply amount of the fixing oil, etc. are optimized so that the relations are Gk ≦ 15, Gc ≦ 20 and Gk ≦ Gc (1). Therefore, once an optimized color image is obtained, by fixing the optimum conditions, it is possible to always obtain a color image having a desirable gloss.

Here, the glossiness used in the present invention will be defined. The glossiness was defined according to JIS Z8741 method 2. Method 2 is mainly applied when measuring the specular gloss of paper (hereinafter simply referred to as gloss).

FIG. 1 is a conceptual diagram of the measuring device. Light source 70
Irradiates the sample 72 through the optical system 71. The reflected light of the sample 72 is received by the light receiver 74 via the optical system 73. S1 and S2 are slits. α1 is the opening angle of the optical image, β1 is the opening angle in the vertical plane, α2 is the opening angle of the light receiver, and β2 is the opening angle in the vertical plane. The glossiness G is expressed by the following equation, where φ is the specular reflected light flux from the surface of the sample 72 and φs is the reflected light flux from the standard surface with respect to the designated incident angle θ shown in the figure.

G = (φ / φs) × (glossiness of the used standard surface) (2) Here, the glossiness of the used standard surface is 100.0.
Therefore, the glossiness is represented by a numerical value of 100 or less.

Since the glossiness of the image portion is an expression of the fixing state of the toner image formed on the image support, the glossiness depends on the viscoelastic characteristics of the toner, the mechanical constitution of the fixing process, the fixing conditions and the like. Can change. In actual use in a copying machine or printer, it is practically difficult to sequentially change the viscoelastic properties of the toner and the mechanical constitution of the fixing process depending on the passage of the image support having various glossiness.
A means for controlling the glossiness of the image portion by sequentially changing the fixing conditions is practical.

Specifically, the roller temperature and the fixing linear velocity in the heat roller fixing device generally used as the fixing process in the electrophotographic method may be changed according to the glossiness of the image support. In this case, since the glossiness of the image portion correlates with the amount of fixing heat energy given to the toner, in order to obtain high glossiness, the roller temperature is increased and / or the fixing linear velocity is decreased to lengthen the heating time. On the contrary, in order to achieve low gloss, control is performed such that the roller temperature is lowered and / or the fixing linear velocity is increased to shorten the heating time. Even in this case, changing the roller temperature causes a waiting time for raising or lowering the temperature. Therefore, controlling the glossiness of the image only by changing the fixing linear velocity does not require the waiting time. Is also preferable.

As described above, as long as the present invention can be achieved, the viscoelastic properties of the toner and the mechanical constitution of the fixing process are not limited, but further for facilitating the variable range of the glossiness of the image. The preferred use form is described below.

As a toner design, its viscoelastic properties should be most considered. The viscoelastic property that facilitates achievement of the present invention has higher elasticity than that of a conventional full-color copy such as a sharp melt, and it is important to design with emphasis on offset resistance. It is particularly preferable because the latitude for a wide range of fixing conditions for changing the value becomes wide.

As the binder resin, one having a partially crosslinked molecular structure for exhibiting the above-mentioned viscoelastic properties is particularly preferable as compared with a non-crosslinked resin structure, but the degree of crosslinking in this case is It is preferable that the binder resin has a chloroform-insoluble content of less than 30% by weight. When the chloroform insoluble content is 30% by weight or more, the elasticity of the toner when melted is too high, and it becomes difficult to control the glossiness.

The insoluble matter of chloroform is measured by the following method. Binder resin was finely pulverized and 5.00 g of a sample that passed through a 40 mesh node was collected and put in a container together with 5.00 g of filter aid Radiolite (# 700), and 100 g of chloroform was injected into this container, and then a ball mill was used. Place on a pedestal and rotate for 5 hours or more to sufficiently dissolve the sample in chloroform. On the other hand, a filter paper having a diameter of 70 mm is placed in the pressure filter, 5.00 g of radiolite is uniformly pre-coated on the filter paper, and a small amount of chloroform is added to bring the filter into close contact with the filter.

Next, the contents of the container were poured into the filter while thoroughly washing the wall surface deposits in the container with chloroform, and then the filter lid was closed and filtration was performed under a pressure of 4 kg / cm ² or less. To do. After the outflow of chloroform has stopped, fresh chloroform is added to wash the residue on the filter paper, and pressure filtration is performed again. After the above operation is completed, the filter paper in the filter, the residue on the filter paper, and the radiolite are all placed on a Petri dish and placed in a vacuum dryer, under the conditions of a temperature of 80 ° C to 100 ° C and a pressure of 100 mmHg. The total weight a (g) of the dry solid obtained by drying for 10 hours at
The chloroform insoluble content Z (% by weight) is calculated by the following formula.

[0031]

[Equation 1]

Regarding the chemical structure of the binder resin,
It is possible to select from a general range including conventionally known ones. Specific examples of the binder resin include styrene, acrylic acid and its ester compound, methacrylic acid and its ester compound, homopolymers or copolymers of acrylonitrile and the like, polyester, polyurethane and polyamide.

Besides the binder resin as a constituent material of the toner, a colorant, a release agent, a charge control agent, an external additive, which are required,
With regard to materials such as lubricants, those widely used in general can be selected and used.

Specific examples of the colorant include carbon black and nigrosine dye as the black colorant. As a yellow colorant, a benzidine yellow pigment such as C.I. I. Pigment Yellow
No. 12, the same 13, the same 14, the same 15, the same 17, the same 5
5, the same 83, the same 174 and the like. Examples of the magenta colorant include quinacridone magenta pigments such as C.I. I. Pigment Red No. 122, an azo lake magenta pigment C.I. I. Pigment R
ed No. 57-1 etc. can be mentioned. Examples of cyan colorants include C.I. which is a copper phthalocyanine pigment.
I. Pigment Blue No. 15 and 15-
3, the same 15-4, the same 15-5 and the like.

Specific examples of the releasing agent include low molecular weight polyethylene, low molecular weight polypropylene, amide wax,
Examples thereof include polyhydric alcohol esters. The charge control agent, which constitutes a part of the color toner, is preferably colorless or white, and specific examples thereof include salicylic acid or zinc salt of salicylic acid dielectric. Specific examples of the external additive include inorganic particles such as silica, alumina and titania, organic particles such as silicon resin particles and fluororesin particles, and lubricants such as metal salts of higher fatty acids.

In the mechanical constitution of the fixing device, it is preferable to use an elastic roller as a roller (hereinafter referred to as a fixing roller, which corresponds to the heat roller 31 in FIG. 6) on the side where the toner layer on the image support comes into direct contact. That is, when the fixing roller has elasticity, the fixing roller surface itself deforms and presses against the unevenness of the unfixed toner image surface, so that the toner image can be uniformly heated and pressed, and the glossiness can be improved. The variable range of can be widened. In this case, the elasticity of the fixing roller is preferably 50 ° or more and 85 ° or less in hardness. If the hardness is less than 50 °, the amount of deformation of the fixing roller becomes excessive, which causes a problem in the paper passing property of the image support. When the hardness is higher than 85 °, the deformation of the surface of the fixing roller becomes insufficient, and it becomes impossible to uniformly heat the toner layer.

A roller (hereinafter referred to as a pressure roller) on the side which is pressed against the fixing roller via the image support.
It is preferable that the pressure roller 32 has a hardness equal to or higher than that of the fixing roller in order to sufficiently press the fixing roller against the surface of the unfixed toner image. In order to impart elasticity of such an appropriate hardness to the fixing roller and the pressure roller, an elastic rubber layer made of silicone rubber, fluororubber or the like may be provided on the roller surface. Note that these hardnesses are measured by an Asker C hardness meter.

Further, in order to impart releasability for the purpose of preventing offset, polyvinylidene fluoride (P
It is preferable to provide a low surface energy coating layer made of VF), polytetrafluoroethylene (PTFE), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), and / or apply silicone oil or the like.

Specific examples of the present invention will be described below.
It should be noted that these examples do not limit the present invention in any way. In addition, "parts" in the examples mean "parts by weight". (Structure of Developer) Production of Toner 1 (K1, Y1, M1, C1) As a binder resin, a polycondensate composed of bisphenol A / propylene oxide, terephthalic acid and trimellitic acid, and having an insoluble content in chloroform of 10 100% by weight of polyester resin, 10 parts of carbon black as a colorant, 3 parts of a low molecular weight polypropylene wax as a release agent, and 3 parts of melt kneading and pulverizing,
After classification, colored particles having a volume average particle diameter of 8.5 μm were obtained. Next, to 100 parts of the colored particles, 0.5 part of hydrophobic silica and 1.0 part of hydrophobic titania were added and mixed to prepare a black toner; K1 which is an example of the present invention. . The softening point of the above polyester resin was 140 ° C.

As in the case of the production of K1, instead of carbon black as a colorant, C.I. I.
Pigment Yellow No. 17: 8 parts were used to obtain a yellow toner Y1 which is an example of the present invention. As in the case of the production of K1, K.C. I.
Pigment Red No. 122; 8 parts, magenta toner M1 which is an embodiment of the present invention.
Got As in the case of the production of K1, C.I. I. Pig
ment Blue No. Cyan Toner C1, which is an example of the present invention, was obtained by using 4 parts of 15-3; Manufacture of Toner 2 (K2, Y2, M2, C2) Manufacture was performed in the same manner as Toner 1 except that the polyester resin of Toner 1 had a softening point of 135 ° C. Production of Toner 3 (K3, Y3, M3, C3) Toner 1 was produced in the same manner as Toner 1 except that the softening point of the polyester resin of Toner 1 was 110 ° C.

The above-mentioned toner has a styrene-methyl melcrylate resin coating layer on the surface and has a volume average particle diameter of 45.
Ferrite core carrier with μm and toner density 7
% So as to be mixed and used as a two-component developer.

A copy image was output using the above-mentioned developer, and evaluation and comparison were performed. For image output, a full-color copying machine "DC9028" manufactured by the present applicant, in which the fixing device was modified to the following configuration, was used. (Structure of Fixing Device) FIG. 2 is a view showing an example of the structure of the fixing device of the present invention. Heater lamp 80 (halogen lamp, 600
W) is built in at the center, and an LTV rubber layer 82 and a PFA tube layer 83 are provided on the surface of a hollow aluminum roller 81 having a diameter of 40 mm.
Lower fixing roller (pressurizing roller) in which the LTV rubber layer 86 and the PFA tube layer 87 are formed on the surfaces of the upper fixing roller 84 on which is formed a hollow aluminum roller 85 having a diameter of 40 mm.
And 88. In the figure, 89 is a cleaning roller, and 90 is an oil application roller impregnated with silicon oil. In this apparatus, a combination of the fixing roller and the pressure roller having the hardness shown in FIG. 3 was prepared, and the surface temperature of the fixing roller and the fixing linear velocity were appropriately changed according to the glossiness of the image support.

The subject image was evaluated by measuring the glossiness of the image support and the glossiness of the image area.
The evaluation results are shown together in FIG. This measurement was performed using a high-quality paper as an image support. The vertical axis is satisfaction,
The horizontal axis represents the gloss level. f1 is a chromatic color Gtc and an achromatic color Gt
The difference of k, f2 is chromatic color, and f3 is black.
Satisfaction was evaluated by sensory evaluation for various image samples prepared by the method described in the above examples. As a result, it was found that the achromatic color (black) glossiness is preferably 15 or less, and the chromatic color glossiness is preferably 20 or less. When the achromatic color (black) has a glossiness of 10 or less, the glossiness of the output image is suppressed and it is easy to see, which is particularly preferable. Moreover, it has been found that better results can be obtained when the glossiness of the achromatic color is smaller than that of the chromatic color. The above results can be expressed by the following equations as described above.

Gk ≦ 15, Gc ≦ 20 and Gk ≦ Gc (1) Furthermore, when both an achromatic color and a chromatic color are present on the same image sample, the difference in glossiness between the chromatic color and the achromatic color is 15 or less. Was found to be preferable. In particular, it has been found that it is more preferable that the difference in glossiness between chromatic color and achromatic color is between 0 and 10. The above results can be expressed as follows.

0 ≦ (Gc−Gk) ≦ 10 (4) However, when a plurality of chromatic colors are used, the glossiness of the chromatic color having the largest glossiness is used.

In the above-described embodiments, the case where the developer and fixing process are optimized to realize the present invention has been described, but the present invention is not limited to this. The fixing oil and other image forming processes may be optimized as long as they can be optimized so as to satisfy the expression (1).

The present invention can be applied to the case of realizing a full-color image in which the primary colors Y, M, C, and K are used and toner is superimposed on a maximum of three layers.
When applied to a color printer using seven colors of C, K, R, G, and B, the effect that the fixed image gives the user psychological comfort and the fatigue is not felt even when a large number of sheets are viewed becomes remarkable.

If the particle size of each toner particle is 10 μm or less and the toner layers are stacked up to a maximum of two layers, the glossiness is optimum and an output image (fixed image) that is easy to see can be obtained. In this case, the thickness of the two layers is preferably 1.8 times or less the thickness of the single layer.

[0049]

As described above in detail, according to the present invention, yellow (Y), magenta (M), cyan (C).
In an image forming apparatus that forms a color image using black and black (K) toner, the glossiness of the black image is G
k, Gc is the glossiness of a color image other than the black image, and the relations of the glossinesses are Gk ≦ 15, Gc ≦ 20 and Gk ≦ Gc. It is possible to provide a color image forming apparatus capable of obtaining a stable copy image even when the obtained image is copied without causing fatigue even when viewed on a sheet.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of a glossiness measuring device.

FIG. 2 is a diagram showing a configuration example of a fixing device of the present invention.

FIG. 3 is a diagram showing hardness of a fixing roller and a pressure roller.

FIG. 4 is a diagram showing evaluation results of copied images.

FIG. 5 is a diagram showing an example of satisfaction evaluation according to the present invention.

FIG. 6 is a diagram illustrating a configuration example of a color image forming apparatus.

Claims (7)

[Claims] 1. An image forming apparatus for forming a color image using yellow (Y), magenta (M), cyan (C) and black (K) toners, wherein the glossiness of the black image is other than Gk and other than the black image. The color image forming apparatus is characterized in that the glossiness of the color image is Gc, and the glossiness relationships are Gk ≦ 15, Gc ≦ 20 and Gk ≦ Gc. 2. The yellow (Y), magenta (M),
The color image according to claim 1, wherein the types of colors expressed using cyan (C) and black (K) toners are seven colors of Y, M, C, K, R, G, and B. Forming equipment. 3. The particle size of each toner particle is 10 μm or less,
The color image forming apparatus according to claim 1, wherein the toner layers are formed so that only two toner layers are stacked at the maximum. 4. The color image forming apparatus according to claim 3, wherein the thickness when the toner layers are stacked is set to be 1.8 times or less the thickness of a single toner layer. 5. The gloss Gk of the black is Gk ≦ 1.
The color image forming apparatus according to claim 1, wherein the color image forming apparatus is 0. 6. The color image forming apparatus according to claim 1, wherein a difference in glossiness between the color image and the black image is 0 ≦ (Gc−Gk) ≦ 10. 7. The method according to claim 1, wherein at least one of a developer, a fixing process, and a fixing oil supply amount is optimized so as to satisfy each of the above conditions. The described color image forming apparatus.