JPS62180379A - Color image forming device - Google Patents

Abstract

PURPOSE:To provide an image with a feeling of natural luster and proper contrast by transferring black toner as the uppermost layer of a transfer material and setting the fusion temperature of black toner 3-12 deg.C higher than when the fusion viscosity is 10<5>CP than when the fusion viscosity of toner of other colors is 10<5>CP. CONSTITUTION:A color image forming device which heats and fixes a toner image on the transfer material to obtain a multicolor image transfers black toner as the uppermost layer of the transfer material and sets the fusion temperature of the black toner 3-12 deg.C higher when the fusion viscosity is 10<5>CP than when that of toner of other colors is 10<5>CP. In this case, the difference in fusion temperature between the black toner and toner of other colors is preferably 4-10 deg.C. The fusion temperature of the black toner is higher than that of the toner of other colors at a four-color superposed part where the black toner forms the uppermost layer, so the degree of fusion of the black toner is suppressed. Consequently, the luster of the black toner is reduced and the four-color superposed image is given a feeling of natural luster and proper contrast.

Description

[Detailed description of the invention] LJLL! The present invention relates to a multicolor image forming apparatus, and more particularly to a multicolor image forming apparatus capable of producing full color or multicolor images by single-frame photography or electrostatic recording.

Conventionally, a latent image based on color image information is formed on a latent image carrier such as an electrophotographic photoreceptor, the latent image is developed with a toner of a corresponding color, and then the toner image is transferred onto a transfer material. A method and apparatus are known in which a multicolor image is produced by heating and fixing the toner image on the transfer material after transferring the image form I&R to t&r.

However, the multicolor image thus obtained.

When the number of sails in a toner image is large, an unnaturally strong gloss and high contrast occur in those parts, which is a problem. For example, when reproducing the colors of a multicolor original using four-color toners: cyan, magenta, yellow, and black, two or three-color toners obtain good color mixing properties for chromatic images, and When the heat fixing temperature is set so that the gloss is moderate, the gloss of the part where the four color toners are concentrated, that is, the black reproduction image of the original (hereinafter referred to as "1.j-image"), becomes extremely strong. This is undesirable and furthermore, the density of the black image becomes substantially higher, resulting in an unnaturally high image contrast, which is also undesirable.

The reason for this is that when the toner layer becomes thicker, the toner adheres closely to the image area without any gaps, and when the toner melts during fixing, the image area surface becomes flat and the incident light is strongly reflected in a specific direction like a specular reflection. On the other hand, if the toner layer is relatively thin, the toner adhesion in the image area is rough, and even after fixing, the image area surface is uneven and the incident light is diffusely reflected on the surface, resulting in gloss. This is thought to be because the image density becomes weaker and the image density is suppressed to a relatively low value.

In order to deal with the problem described in , lowering the heat fixing temperature of the toner image on the transfer material will reduce the amount of toner in the two or three color areas even if the fixing temperature is such that the image cannot be rubbed off. The melting was insufficient, causing problems such as chromaticity in the image area and lack of light σ.Also, when suppressing the adhesion SIX of the toner onto the transfer material in order to improve the fixing performance, There is a problem that image density of images other than black images decreases.

i Saranijo order ``One object of the present invention is to solve the above-mentioned conventional problems.

f! reduces the gloss and image density of black images and creates color images with natural gloss and appropriate contrast. An object of the present invention is to provide a color image forming apparatus that achieves good color reproduction in J and IL.

The above object is achieved by a color image forming apparatus according to the present invention. In summary, the present invention forms a latent image based on color image information on a latent image carrier, develops the latent image with at least two corresponding toners including a black toner, and then transfers the toner image onto a transfer material. In a color image forming apparatus that obtains a multicolor image by repeating the image forming process of transferring the toner image onto the transfer material E, the toner image on the transfer material E is heat-fixed.
The melting temperature of the black toner when the melt viscosity of one color toner is 10' CP when it is transferred in layers is 3° ( !−
This is a color image forming apparatus characterized in that the temperature is raised by 12 degrees Celsius.

To further explain, according to the present invention, the melting temperature of the black toner when the melt viscosity is 10'CP as described above is at least 3°C higher than the melting temperature of the other color toners when the melt viscosity is 105cF. It is necessary to raise the temperature to a high temperature, but if it is too high, the gloss of the image will be completely lost and the black toner will be insufficiently fixed, so the temperature should be set to 12° C. or lower.

Preferably, the difference in melting temperature between the toner and the other color toners is between 4°C and 10°C.

According to the present invention, the black toner is transferred as the top layer of the transfer material, but in the four-color area where the black toner is the top layer, the melting temperature of the black toner is lower than that of the other color toners. By making it higher, the degree of melting of the black toner can be suppressed, thereby reducing the gloss of the black toner and giving a four-color image a natural gloss and appropriate contrast. As described above, it is sufficient that the toner has a sufficient fixing property to the extent that it cannot be rubbed off, and there is no need to mix it with toners of other colors, and there is no need for transparency.

According to the present invention configured as described above, for example, when forming a full-color image using toners of four colors: cyan, magenta, yellow, and black, cyan, magenta, and yellow toners are used in two to three colors. The colored portions are sufficiently fused, thus creating color mixing and imparting transparency to the toner, allowing for good color 1'T rendering. At the same time, the melting of the black toner is suppressed in the 4-color layered portion with black toner as the last layer, reducing gloss and providing the 4-color layered image with a natural gloss and appropriate contrast. As mentioned above, the black image area does not need to be mixed with toner of other colors, nor does it need to be transparent.

In addition, the present invention is not only effective in the case of a four-color image with black toner as the top layer, but also in the case of a black image when performing under color removal (UCR) image processing with a digital color copying machine, etc. Therefore, it is also effective for images in which one or two colors of cyan, magenta, and yellow toners are dried together with black toner as the top layer, or images of colors close to black.

As an additional effect of the present invention, when fixing is performed using a heat roller fixing device, it is possible to prevent offset to the fixing roller, which tends to occur in areas where toner is thick, such as a black image. This is because the black toner in the uppermost layer is fixed at a temperature considerably lower than the fixing temperature that causes hot offset, so that it acts as a barrier layer for the offset prevention 1 against the color toners in the lower layer.

Next, an image forming apparatus according to the present invention will be described in more detail with reference to the drawings. FIG. 1 shows a sectional view of essential parts of an electrophotographic copying machine for forming full-color copied images to which the present invention can be applied.

In the copying machine shown in FIG. 1, a photosensitive drum l, which is a latent image carrier, rotates in the direction of the arrow. Around it are a charger 2, an exposure optical system 3, a developing device 4, a transfer system 5. A cleaning device 6 is then provided. Optical system 3 is document scanning section 3
a and a color separation filter part 3b. Also, the developing device 4
is integrally equipped with a yellow developer 4Y using yellow toner, a magenta developer 4M using magenta toner, a cyan developer 'JA4C using cyan toner, and a black developer 4B using black toner.

Each developing device is removably held on a support 4a and has a central shaft 4b.
The transfer system 5 has a drum 5b having a gripper 5a and a transfer discharger 5C inside the drum 5b.

A full-color image is formed by sequentially transferring color toner and black toner onto a transfer material supported by a transfer drum 5b, as in a conventional copying machine. This transfer material is supplied from a cassette 7, and the transfer material that has completed the transfer process is separated by a separating means 8, and transferred to a tray via a fixing device 9.
It is discharged into O, l-.

Next, one embodiment of the present invention will be explained.

A group of toners used in the present invention were manufactured in four types (Examples 1 to 4), and the melt viscosity of the toner in each example was 10'.
The melting temperature T of the toner when exhibiting CP was measured. Table 1 shows the measurement results of the binder resin and melting temperature used in each example.
is shown.

Further, as the colorants of the toners used in each example, a carbon black pigment was used for black, a phthalocyanine dye was used for cyan, a 77 traquinone dye was used for magenta, and an azo dye was used for yellow.

Additives such as a suitable charge control agent were added as necessary.

The viscosity of each toner was measured using a constant temperature bath that could directly heat the sample and rotor. The measurement was carried out using a rotational viscometer for i, 5 viscosity.

In the toner group of Example 1, polyester resin (a) was used as the resin for each cyan, magenta, and yellow toner, and polyester resin (b), which has a higher molecular weight than the polyester resin (a), was used as the resin for the black toner. The melting temperature T of the black toner is 3° C. higher than that of the cyan toner, which has the highest melting temperature T among the other three color toners.

Using the toner group of Example 1, a full-color image was formed on a transfer paper from a multicolor original using the color copying machine shown in FIG. The surface temperature of the fixing roller of the heat roller fixing device is approximately 155°C.
Although fixing was carried out under constant control, the image was sufficiently fixed in areas with only one color and areas with two to four colors, and no offset occurred in the fixing roller. In particular, the toner was sufficiently melted in areas where two to three colors of the image overlapped, and good color development of red, green, blue, etc. was obtained.

In addition, in the black image, the melting of the black toner in the top layer was suppressed, and the gloss was almost the same as that of the cyan, magenta, and yellow toner beaded portion (brown image), and a moderate gloss was obtained. Furthermore, the C degree of the black image decreased, resulting in an image with a soft feel.

When the toner groups of Examples 2 and 3 were used, the melting temperature T of the black toner was 4°C and 1°C lower than that of the cyan toner, respectively.
Although the temperature was 0°C higher, when image formation was performed in the same manner as in Example 1 using a group of toners of each iA example,
There were no more favorable results than in Example 1.

In addition, when toner 11 of Example 4 is used, bluff)
The molten salt II T of the toner was 12°C higher than that of the cyan toner, but when images were formed in the same manner as in Example 1 using this toner group, the effect of the present invention was obtained, but the gloss of the black image was In addition, the fixability of the black toner was slightly insufficient, and as compared to Examples 2 and 3, the image quality was not as desirable.

The group of toners shown in Comparative Example 1 in Table 1 is a conventional toner group, and when an image was formed in the same manner as in Example 1 using this group of toners, a black image was obtained. The gloss was stronger and the density was about 1.8 (1°5 in the case of Example 1) by 1 nig, which was not preferable.

In addition, a group of toners shown in Comparative Example 2 in Table 1 contained polyester resin (C) (polyester resin (a)) in the black toner resin.
) and the polyester resin (b) have an intermediate molecule j-. ), the melting temperature T of the black toner was 2° C. higher than that of the cyan toner, but compared to Example 1, the effect of the present invention was insufficient and the image quality was not much different from Comparative Example 1.

[19] Historically, a group of toners shown in Comparative Example 3 in Table 1 was prepared by adding polystyrene resin (a) to the black toner resin.
Although the melting temperature T of the black toner is 13°C higher than that of the cyan toner, the gloss of the black image is almost gone compared to Example 4, and the fixability of the black toner is was also insufficient, and favorable results could not be obtained.

In the present invention, the binder resin of the toner is not limited to those shown in Table 1; for example, silicone resins, epoxy resins, etc. may also be used.

Further, in the present invention, the heat fixing means is not particularly limited, and may be a means for irradiating infrared rays, for example.

Furthermore, the present invention is effective not only for forming full-color images, but also for forming two-color images using red toner and black toner (a black image is formed by using red toner and black toner). It is.

Since the image forming apparatus according to the present invention is configured as described above, it can reduce the gloss and image density of a black image and produce a color image with natural gloss and appropriate contrast. 1
This has the effect that one better color 1q appearance can be achieved.

[Brief explanation of drawings]

Figure 1 shows a color image to which the present invention can be applied.
(Cross-sectional view of the 'Ai section of the copying machine. 1: Photosensitive drum (image carrier) 2: Charger 3: Exposure optical system 4: Developing device 5: Transfer system 9: Heat roller fixing device

Claims (1)

[Claims] 1) Form a latent image based on color image information on a latent image carrier, develop the latent image with at least two corresponding toners including black toner, and then apply the toner image to a transfer material. In a color image forming apparatus that obtains a multicolor image by repeating the image forming process and then heating and fixing the toner image on the transfer material, the black toner is transferred so as to become the top layer of the transfer material, A color characterized in that the melting temperature of the black toner when the melt viscosity is 10^5 CP is 3 to 12 °C higher than the melting temperature of the other color toners when the melt viscosity is 10^5 CP. Image forming device. 2) The method according to claim 1, wherein the melting temperature of the black toner is 4°C to 10°C higher than the melting temperature of toners of other colors.