JPH0736308A - Color image forming device - Google Patents

Abstract

(57) [Summary] [Object] It is an object of the present invention to provide a color image forming apparatus capable of reducing the glossiness of a monochrome image while maintaining good color mixing of a full color image. An image signal processing circuit 28 to which a chromatic color image signal 33 and a black image signal 34 are input determines whether or not the image signals include a chromatic color in the same page, and the determination result is determined by a determination signal 31. Output to the controller 27.
Then, when the black signal is not all pages, the controller roller 27 uniformly sets the adjustment target value of the surface temperature of the fixing roller 1 to a high temperature such as 180 ° C., and when the black signal is all pages, it is 165 ° C. or the like. Switch to low temperature.

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 capable of favorably forming a printed image after fixing to any developer from chromatic color toner to black toner.

[0002]

2. Description of the Related Art An image forming method for obtaining a color image on a recording material by superposing toner images of a plurality of colors forms an electrostatic latent image on an image carrier and successively develops it with toner images. Each time, it is transferred onto the recording material and the color toner images of plural colors are superposed on the recording material, or the toner images of plural colors are superposed on the image carrier or the intermediate recording material,
There is a method of collectively transferring these onto a recording material.

Of these, the former method is DE26077.
No. 27, Japanese Patent Laid-Open No. 50-50935 and the like are put to practical use. On the other hand, the latter method has problems such as color mixture at the time of development and deterioration of image quality at the time of retransfer, but it has an advantage such as a simple structure and is a technique which is currently attracting attention. In either method, the result shown in FIG.
The toner images T of plural colors formed on the recording material 3 as shown in FIG.
By heating and fixing, the toner images of the respective colors are mixed and a full-color image can be obtained.

An example of this type of fixing device of the heat roller type will be described below with reference to FIG. In FIG. 6, 1 is a fixing roller for melt-fixing the toner T on the recording material 3 by heating and pressing, and 2 is a pressing roller for pressing. Usually, the fixing roller 1 is often heated from the inner surface using a heater 4 such as a halogen lamp.
Therefore, it is general that the surface temperature of the fixing roller 1 is monitored by a temperature detecting element 14 such as a thermistor, and the heater 4 is turned on / off to adjust the temperature. Also,
As the color toner T, four colors of yellow, cyan, magenta, and black toner are generally used.

In the case of fixing the color toner T, unlike the case of ordinary black-and-white printing, not only the fixing property but also the melt-mixing property of each color is an important factor for proper color reproduction. Therefore, the color toner T is formulated not only for chromatic colors but also for black toner so that the melting point thereof is slightly lower than that of black toner of a black-and-white copying machine which is generally used. For example, a method of shifting the molecular weight of a material such as styrene-acrylic resin or polyester used as a binder resin to a low molecular weight side, or a method of blending a wax having a low melting point as a release agent is used.
Therefore, the fixing roller 1 is much more likely to be offset than the case of fixing with the black toner used in a normal black-and-white copying machine or printer.

Therefore, in order to prevent the offset, as shown in FIG. 6, an oil application device 5 and an application / cleaning web 7 are used to apply oil 6 such as silicone oil to the surface of the fixing roller 1. Commonly used. Also,
In order to improve the color mixing property, the low melting point toner is melted and fixed at a fixing temperature slightly higher than the fixing possible temperature so that the toners of respective colors are sufficiently melted and mixed, and the surface of the fixing roller 1 is also shown in FIG. As shown in, the surface of the core metal 10 such as Al is coated with silicone rubber 9 (HTV) having excellent elasticity and strength.
Etc.) and then the surface thereof is coated with silicone rubber 8 (LTV etc.) having excellent releasability and flexibility to improve the heat transfer efficiency by enclosing the toner. It often happens. Further, the pressure roller 2 also covers the surface of a core metal 13 such as Al with a silicone rubber 12 (HTV or the like) having an appropriate elasticity, and further coats the surface with a thin layer of fluororesin 11 to protect the toner. A structure for improving releasability is required.

Of course, the above structure may change depending on the type of the release agent oil. For example, when methyl phenyl silicone oil is used as the oil, the above configuration can be used. However, when dimethyl silicone oil is used, a swelling prevention is further performed between the silicone rubbers 9 and 10 of the fixing roller 1. A blocking layer may be provided.

In any case, in the conventional device as described above,
As described above, a toner is prepared from a low molecular weight binder or a low melting point wax having a low melting viscosity generally represented by a glass transition point or a melting viscosity generally represented by a melting index, so that each color is sufficiently mixed. By carrying out heat fixing, a good full-color image was formed.

[0009]

However, in the above-mentioned conventional apparatus, the full-color image has a good color mixing property, but on the other hand, the surface of the toner image is smoothed after fixing and the wax which is a releasing agent is also on the surface. It is easy to obtain an image with a high glossiness (usually, a gloss value is used) due to the effects such as appearing in. Further, offset due to heat is likely to occur, and in order to prevent this, it is necessary to apply a large amount of release agent such as silicone oil to the fixing roller as described above.
There is a drawback that the glossiness of the toner is further increased and the fixing device is easily contaminated with oil. Especially in recent years,
As color copiers have become more popular in the general public, the same device may copy not only full-color images but also mono-color or black-and-white images. Stronger than black-and-white copy,
It was a so-called calendar-like image.

Further, in recent years, the use of outputting a document created by a word processor or a computer as a high-quality original print using a laser beam printer or the like has been rapidly increasing. In this field, too, there is a great demand for colorization. Is increasing. However, the high-gloss image as described above is not generally preferred as a black-and-white document for office use, and therefore a high-quality image is required not only for full-color print but also for black-and-white print image. In the printer field, strong gloss during black-and-white printing is a major drawback.

An object of the present invention is to solve the above problems and to provide a color image forming apparatus capable of reducing the glossiness of a monochrome image while maintaining good color mixing of a full color image.

[0012]

According to the present invention, the above object is to provide a fixing rotary member which is in contact with an unfixed developer image, and a pressing rotary member which is in pressure contact with the fixing rotary member. A fixing means for sandwiching and heating and fixing a recording material carrying an unfixed developer image, and a determining means for determining whether the developer image is a chromatic color developer image or a black developer image. In the image forming apparatus including the above, the temperature adjustment target value of the fixing unit is changed based on the determination result of the determination unit.

[0013]

According to the present invention, the discrimination means discriminates whether the image is a chromatic color developer image or a black developer image, and the temperature control target value of the fixing means is changed based on the discrimination result. For example, in the case of a chromatic color developer image, the temperature of the fixing unit is set to a high temperature so as to obtain a good color mixing property, and in the case of a black developer image, it is set to a low temperature so as to reduce the glossiness. To set.

[0014]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

<First Embodiment> First, a first embodiment of the present invention will be described with reference to FIGS. First Embodiment FIG. 1 is a configuration diagram for explaining a first embodiment of the present invention.

In this embodiment, an example in which the present invention is applied to a color image forming apparatus using an electrophotographic laser beam printer will be described. In FIG. 1, 1 is a fixing roller, 2 is a pressure roller, and 3 is a recording material. Also, 4
Is a halogen lamp as a heat source, 5 is a device for applying an oil as a release agent, and 14 is a thermistor for measuring the surface temperature of the fixing roller 1. Since the operations of these devices have been described in detail in the conventional example, the description thereof will be omitted.

Next, the image forming method will be described. First, as the image signal, a chromatic color signal 33 and a black signal 3
4 is input to the image signal processing circuit 28. Of these, the chromatic signals 33 are B (blue), G (green), R
(Red) signal or Y (yellow), M which is the complementary color
(Magenta) and C (cyan) signals are generally used.
When performing full-color recording, it is common to handle signals that have gradations for both chromatic colors and black, while binary output is used when outputting black and white documents or business colors (monochrome characters, graphs, etc.). Signal is enough. These image signals are
The time series signal 30 is converted by the processing circuit 28 and sent to the controller 27. At this time, whether or not the image signal includes a chromatic color in the same page is simultaneously notified to the controller 27 by the determination signal 31. On the other hand, when the image signal becomes acceptable from the controller 27, the image request signal 32 requesting the transfer of the time series signal 30 is sent to the image signal processing circuit 28.

On the other hand, the controller 27 to which the time-series signal 30 is input sends a drive signal based on the time-series signal 30 to the optical system 26, and a laser diode (not shown) via a drive circuit (not shown). Drive. And
Laser light output from this laser diode is converted into scanning light by a rotating polygonal mirror (polygon) (not shown), and is irradiated onto the photosensitive drum 21. Then, the photosensitive drum 21 is uniformly charged in advance by the charging roller 22 and the like, and the charge is partially removed by scanning with the laser beam to form an electrostatic latent image.

This electrostatic latent image is developed by rotary developing means 25C, 25M, 25Y and 25BK (cyan, magenta, yellow and black) which rotate in the direction of the arrow while maintaining their own posture and are successively contacted. To be done.

On the other hand, the recording material 3 is wound around the transfer drum 23 from the cassette 41 via the pickup roller 42, the conveying roller 43, and the registration roller 44. Although a method of attracting the recording material 3 to the transfer drum 23 is not shown, generally, a grip mechanism is provided in a part of the transfer drum 23 formed of a hollow or cylindrical core metal, and the transfer drum is further electrostatically attracted. A method of adsorbing onto the insulating sheet provided in 23 is often adopted, and a corona charger for adsorbing, a bias roller, or the like is often used together.

Here, the image to be formed is a single color or Y,
The transfer rotational speed after adsorption to the transfer drum 23 differs depending on whether it is two or three colors of M, C, and BK or full color. That is, in the case of a single color, the recording material 3 is attracted onto the transfer drum 23 and then the photosensitive drum 2
After passing through the surface facing 1 and immediately separated by the separating claw 45, in the case of two or three colors, the recording material 3 passes through the surface facing the photosensitive drum 21 two or three times and undergoes multiple transfer. . Further, in the case of full-color, it is necessary to pass four times for multiple transfer. In some cases, each rotation may be further rotated to facilitate separation.

The recording material 3 carrying the toner images that have been multi-transferred as described above is nipped and conveyed between the fixing roller 1 and the pressure roller 2 and is heated and pressure-fixed. The residual toner on the photosensitive drum 21 is cleaned by the cleaner 24 after each transfer of each color.

The relationship between the surface temperature T of the fixing roller 1 and the glossiness (gloss value) of the image after fixing is shown in FIG.
As the gloss measurement method, a method of measuring the amount of reflected light in the 60 ° direction was used. As a fixing condition, a pair of a fixing roller and a pressure roller having the structure described in the conventional example shown in FIG. 7 is used, and the HTV rubber 9 of the fixing roller 1 is set to about 1 m.
m, LTV rubber 8 approximately 0.3 mm, HT of pressure roller 2
The V rubber was approximately 2 mm, the fluorine coating layer thickness was approximately 50 μm, and both the fixing roller 1 and the pressure roller 2 were brought into contact with each other with an outer diameter of 40 mm and a linear pressure of 1.6 kg / cm.

The paper feeding speed was 100 mm / sec.
In FIG. 2, since the toner layer is thick during full color printing, the smoothness is increased, and the gloss value is apparently increased (A in FIG. 2 is full color, B is in black toner printing).

The gloss value and the visually preferable area are different between the full color printing and the black and white printing as described above, and it is difficult to express uniquely because it is based on the subjective evaluation. In the case of the gloss value, the gloss is not so much noticeable up to the 40 to 50th place, and
Below, it is a level where the color mixture and the local unevenness of gloss start to be noticed. On the other hand, at the time of black-and-white printing, if the gloss value exceeds 20, it gives an unfavorable impression as a normal document, and if it is 15 or less, the level becomes unnoticeable.

Therefore, when the discrimination signal 31 from the image signal processing circuit 28 is not the black signal for all pages, the adjustment target value T _P of the surface temperature of the fixing roller 1 is uniformly set to 180 ° C., and the discrimination signal 31 is all. Only when the page black signal is generated 1
When the temperature was changed to 65 ° C., the gloss value at the time of black character printing was reduced from P in FIG. 2 to Q, and a good printed image of a document with little gloss was obtained. When a black image was fixed at T _P = 155 ° C., a state of poor fixability (toner peeling) partially occurred. Therefore, from the viewpoint of fixability, 160 ° C. or higher is considered necessary for black toner.
Further, in full color, at T _P = 165 ° C., the color mixing property and the gloss unevenness become poor. That is, when the target temperature when the black toner is a single color is T _P1 and the target temperature in other cases is T _P2 ,
T _P1 = 165 ° C to 170 ° C, T _P2 = 175 ° C to 180 ° C
It is preferable to set the position.

<Second Embodiment> Next, a second embodiment of the present invention will be described. The same parts as those of the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

In the first embodiment, the method of lowering the temperature control target value only when the discrimination signal is a black image is used, but in the present embodiment, the temperature control target value is lowered even during standby.

In general, the surface temperature of the fixing roller 1 in the non-sheet-passing state is gentler when the lamp 4 is turned off than when the heater 4 is turned on. In particular, in a system in which the core metal 10 of the fixing roller 1 and the elastic members 8 and 9 are thin and the thermal conductivity is high, the determination signal 31 is full color,
Alternatively, the target temperature T _P is switched to T _P2 (high temperature) only in the case of chromatic color, and T is set at the time of standby and black printing.
Switching _P to T _P1 (low temperature) improves the responsiveness of temperature control and lowers the standby temperature, so that the life of the fixing roller 1 is also improved. Of course, in addition to this, a target value T _P3 from power-on to standby is set, and T _P3 <T _P1 <
It may be set as T _P2 . Of the chromatic colors, the maximum value is T _P in full color, and the target value T _P is sequentially decreased until two colors are superposed according to the number of toner images to be superposed. It may be further reduced in order to set the black-only TP to the minimum value.

<Third Embodiment> Next, a third embodiment of the present invention will be described with reference to FIG. The same parts as those of the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

In the first embodiment described above, the fixing roller 1
Although the case where only the heat source is provided has been described, as shown in FIG. 3, an example in the case of the two-heater system having the heat source also in the pressure roller 2 is shown. In this case, the thermistor 1
It is also possible to detect the surface temperature of the fixing roller 1 by means of 4, and based on this, control the heater 4 on / off in accordance with the target temperature T _P as shown in Embodiment 1, and at the same time turn on / off the heater 18. As another method, according to the discrimination signal 31, in the case of a black image, instead of changing the temperature control target value T _P , the heater 4 is used.
It is also possible to divide the drive signals of Nos. 18 and 18 into 35 and 36, respectively, to turn off the heater 18 only on the pressure roller side, or to turn on the time division at a duty of 100% or less. This is because in the two-heater system, the heat of the fixing roller 1 is not carried out to the pressure roller 2 and the recording material 3 also receives residual heat from the back surface, so the relationship between the surface temperature and the glossiness in FIG. This is because it apparently shifts to the temperature side.

<Fourth Embodiment> Next, a fourth embodiment of the present invention will be described with reference to FIG. The same parts as those of the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

In the above-described first embodiment, the case where the image signal is divided into two signals of chromatic color and black system in advance has been described, but as shown in FIG.
For example, the present invention can be implemented even when only the B, G, R signals 37 are input. In this case, the B, G, and R signals are converted into Y, M, and C signals by once taking the inverse logarithmic conversion by the image signal processing circuit 28. After that, black extraction is performed, masking processing is performed, and the final Y, M, C, and BK four-color signals are converted. As a result, when B, G, and R are all maximum densities, Y, M, and C are calculated from the signal components in one page.
Disappears, leaving only the BK signal. In this way, a black signal may be sent to the controller 27 as the determination signal 31 only when the processed image signal becomes a black signal. Further, in combination with this, it is preferable to use the signal 38 indicating whether the image signal is a single color or a multicolor image within the page. By doing so, when it is possible to determine that the color is monochrome and black, the determination signal 31 can be immediately changed to black. With this configuration, the black determination signal can be generated inside the printer, so the printer can determine whether the color is chromatic or black without the need for a special black signal line to be input to the external device. In the same manner as described in Examples 1 to 3 and the like, it is possible to optimally control and output a full-color print with good color mixture and a black glossy text print.

<Fifth Embodiment> Next, a fifth embodiment of the present invention will be described. The same parts as those of the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

In the above examples, no particular consideration was given to the chromatic color toner and the black toner regarding the composition of the toner used. In fact, considering the contact property, it is said that the same binder component of the toner has good compatibility. However, for color printers,
Since it is expected that the frequency of black color will increase, it is desirable that the black toner is less likely to produce gloss, that is, a toner having a relatively high melt viscosity and melting point. At this time, there is a special circumstance that only black is not required to transmit light. From the above points, better results can be expected by changing only the black toner, the binder or external additive formulation, the wax formulation, or the toner particle size. Further, in general, the magnetic toner tends to have less gloss including the color tone of the magnetic material than the non-magnetic toner.

This embodiment is based on the above point of view. As an example, the above-mentioned TG value (glass transition point, Y, M, C chromatic toner, polyester resin as a binder.
The same shall apply hereinafter) is composed of a non-magnetic one-component toner at about 60 ° C., a black toner is a styrene-acrylic resin as a binder, and a magnetic substance is mixed to obtain the above-mentioned TG value of about 65 ° C. Composed of. At this time, when the order of multiple transfer during full color printing is reversed so that only black is transferred and the transfer is performed first, black toner becomes the lowermost layer on the recording material, and even in the full color image, the black part It was possible to prevent the occurrence of a phenomenon in which the image of became unnatural due to loss of gloss.

When the temperature control target value T _{P2 for} chromatic color printing is set to 180 ° C. and the temperature control target value T _P1 is set to 175 ° C. for black printing according to the discrimination signal 31, color mixing and black text in full color printing are obtained. I was able to more effectively balance the matte effect during printing. In addition, T
_The reason why _P1 is higher than that in Example 1 is that the melting point of the black toner is relatively high. In this way, the values of T _P1 and T _P2 can be brought close to each other, so that the temperature control target value can be switched more smoothly.

<Sixth Embodiment> Next, a sixth embodiment of the present invention will be described with reference to FIG. The same parts as those of the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

In the above-mentioned Example 5, the case where the blending of the black toner was changed to relatively increase the melt viscosity and the melting point to lower the glossiness was also explained. As described above, when the touch viscosity and the touch point of the toner are relatively increased, the offset of the toner may be prevented without applying the release agent such as the silicone oil 6 to the surface of the fixing roller 1. it can. Therefore, in such a case, when the determination signal 31 determines that the image is a black image, the temperature control target temperature T _P of the fixing roller 1 is compared with the temperature control target temperature T _P2 for the chromatic color described above. While changing to a lower T _P1 , the solenoid 51 may be driven to separate the oil application device 5 from the fixing roller 1 as shown in FIG. This not only makes it possible to suppress the gloss of black and white prints by not using release oil, but it is possible to eliminate unnecessary oil carry-out during black and white prints, resulting in oil savings. Further, oil contamination of the fixing roller 1 and surrounding members can be reduced.

In the above description, the description has been given by using the embodiment in which the toner is multi-transferred onto the recording material 3, but the present invention is exactly the same even when the intermediate recording material or other transfer means is used. It goes without saying that it can be implemented.

In the present invention, the case where the fixing temperature setting value is changed based on the discrimination result between the black character and the chromatic color is mainly described in the printer main body, but the external device, for example, the host computer is used. When performing the image print command, the host computer may change the fixing temperature setting value of the printer main body based on the result of distinguishing between black and white and chromatic color.

[0042]

As described above, according to the present invention, the discrimination means discriminates whether or not the print image is a black image, and the temperature control target value of the fixing roller is changed.
While maintaining good color mixing properties in chromatic images, especially color mixing properties in full-color images, it was possible to suppress gloss of black and white images and to output good black and white documents. Further, by adjusting the composition of the black toner so that the melt viscosity and the melting point of the black toner are relatively high, the above effect can be further improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of a device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing the relationship between the surface temperature of a fixing roller and the glossiness of an image after fixing in the apparatus of FIG.

FIG. 3 is a diagram showing a schematic configuration of a device according to a third embodiment of the present invention.

FIG. 4 is a diagram showing a schematic configuration of a device of Example 4 of the present invention.

FIG. 5 is a diagram showing a schematic configuration of a device according to a sixth embodiment of the present invention.

FIG. 6 is a diagram showing a schematic configuration of a fixing device in a conventional image forming apparatus.

FIG. 7 is a diagram showing structures of a fixing roller and a pressure roller in the apparatus shown in FIG.

[Explanation of symbols]

 1 Fixing Roller (Fixing Rotating Body) 2 Pressure Roller (Pressuring Rotating Body) 3 Recording Material 28 Image Signal Processing Circuit (Discriminating Means)

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Claims (5)

[Claims] 1. A recording material carrying an unfixed developer image is sandwiched and conveyed between the rotating body and a fixing rotator in contact with the unfixed developer image and a pressure rotator in pressure contact with the fixing rotator. In the image forming apparatus, the image forming apparatus is provided with a fixing unit that heats and fixes the image and a determining unit that determines whether the developer image is a chromatic color developer image or a black developer image. A color image forming apparatus characterized in that the temperature control target value of the fixing means is changed based on the above. 2. The color image forming apparatus according to claim 1, wherein the temperature adjustment target value is set to be smaller than a standard value when the determination result of the determination unit is a black developer image. 3. The color image forming apparatus according to claim 1, wherein the temperature adjustment target value is set to be larger than a standard value when the determination result of the determination unit is a chromatic color developer image. 4. The color image forming apparatus according to claim 1, wherein the black developer is blended so as to have a higher melt viscosity or melting point than that of the chromatic color developer. 5. When a releasing agent applying unit that comes into contact with the fixing rotator is provided and the result of the determination by the determining unit is a black developer image, the releasing agent applying unit applies the toner to the fixing rotator. The color image forming apparatus according to claim 1, wherein the release agent coating operation is canceled.