JPH02201453A - Image forming method - Google Patents

Abstract

PURPOSE:To completely fix toners without allowing an unfixed part to remain by developing the electrostatic latent image formed on an image carrier with the chromatic toners, then developing the entire surface of an image forming region with the colorless transparent toner. CONSTITUTION:The electrostatic latent image corresponding to the original image formed on the image carrier is developed with the chromatic toners by an ordinary developing method and further, the entire surface is developed by the transparent toner which does not disturb the toner image formed with the chromatic toners to stick the toners and to increase the absolute amt. of the toners to be transferred onto transfer paper so that the fixing power is improved by the heat conductivity and tacky flocculating force of the toners. The transparent toner exists between the chromatic toners 22 dispersed sparesely on the transfer paper 21 and the toners are held stuck securely onto the transfer paper by the adhesive property between the molten toners 23. The chromatic toner image corresponding to the original image is completely fixed in this way without degrading the image quality.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a developing method that can prevent the occurrence of unfixed images in electrophotography, electrostatic printing, and the like.

(Prior Art) In recent years, the uses of image forming apparatuses using electrophotography have expanded, and various image forming apparatuses have been developed and used. FIG. 2 shows an industrial copying machine as a typical example of a so-called wide-width industrial image forming apparatus.

In such an industrial copying machine, transfer paper fed onto a paper feed tray 2 passes through a paper feed roller 3 and a registration roller 4 to reach a feed roller 5. Furthermore, the transfer paper is attached to the photosensitive drum 6.
By passing through the transfer section 8 between the photosensitive drum 6 and the transfer charger 7, the toner image formed on the surface of the photosensitive drum 6 is transferred to the transfer paper.

The toner image transfer paper further passes through a fixing section 9, where the toner image is fixed. Thereafter, the transfer paper is discharged to a paper discharge tray 11 via a paper discharge roller 10.

In such an industrial copying machine, the fixing section 9 has a heat roller 12 and two rollers 14a and 14b for pressing the transfer paper 13 against the heat roller 12, as shown in FIG. The belt 15 is made up of a belt 15.

In the case of industrial copying machines, the transfer paper size is A1,
Since large objects such as AO are handled, wrinkles tend to occur in the transfer paper, and by using the belt 15 described above, the pressure detection force on the heat roller is weakened and wrinkles are prevented. The bulge part) is widened to supplement the fixing power.

(Problems to be Solved by the Invention) The manuscripts used in the above-mentioned industrial copying machines are generally blueprints for architectural drawings (diazo large copying machines).
is often used. However, in this blueprinting, since the non-image areas are also colored pale blue, areas with low image density (areas with little toner) are formed as halftones due to toner on the transfer paper. Then, when such transfer paper is fixed in the fixing section that uses the above-mentioned belt with weak pressure,
Areas with low image density (areas with little toner) are often ejected with poor fixation. As the toner particles are packed together, the heat from the heat roller is sufficiently distributed throughout the toner due to the thermal conductivity and adhesive cohesive force of the toner particles, and even with a low pressure contact force, the heat roller is effectively transferred to the toner. Fixation is performed by the action of heat, but in areas where the image density is low, such as non-image areas, the toner is sparsely dispersed, as shown in Figure 4, so individual toner particles are only sufficiently melted. This is because the heat is not transferred, and the paper is ejected from the copying machine in an unfixed or incompletely fixed state.Similarly, in the case of gray images, foggy toner, etc., the toner is unfixed or has not been fixed. Sometimes the copy is ejected from the copying machine in an incomplete state.

For this reason, a problem arises in that hands, clothes, etc. are stained by unfixed toner from the transfer paper discharged from the main body of the image forming apparatus.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an image forming method in which toner transferred onto a transfer paper is completely fixed without leaving any unfixed areas.

(Means for Solving the Problems) According to the present invention, after developing the electrostatic latent image formed on the image carrier with colored toner, the entire image forming area is developed with a colorless transparent toner, thereby achieving the above-described problems. The purpose is achieved.

In other words, the present invention develops an electrostatic latent image corresponding to a document image formed on an image carrier with colored toner using a normal developing method, and further uses transparent toner that does not disturb the toner image formed with colored toner. The entire surface is developed to adhere toner, the absolute amount of toner transferred onto the transfer surface is increased, and the fixing power is improved by the thermal conductivity and adhesive cohesive force of the toner particles. As shown in FIG. 1, transparent toner exists between the colored toners sparsely dispersed on the transfer surface, and the fused toner particles adhere firmly to the transfer paper due to their mutual adhesion.

Usually, the binder resin used for colored toners includes styrene polymers, acrylic polymers, styrene-acrylic polymers, polyethylene, chlorinated polyethylene, polypropylene, olefin polymers such as ionomers, polyvinyl chloride, polyester, polyamide, polyurethane,
Examples include various polymers such as epoxy resin, diallyl phthalate resin, silicone resin, ketone resin, polyvinyl butyral resin, phenol resin, rosin-modified phenol resin, xylene resin, rosin-modified maleic acid resin, and rosin ester. Among these, styrene polymers, acrylic polymers, or styrene-acrylic polymers, particularly styrene-acrylic polymers, are preferred because they are easy to control in terms of crushability and molecular weight distribution. These may be used alone or in combination of two or more.

Colorants that make up colored toner include carbon black, lamp black, chrome yellow Hansa yellow,
Benzidine Yellow, Bethlen Yellow, Quinoline Yellow, Permanent Orange GTR, Pyrazolone Orange, Palkan Orange, Watch Young Red, Permanent Red, Brilliant Carmino 3B, Brilliant Carmine 6B, Danibon Oil Red Pyrazolone Red, Lysole Red, Rhodamine B Lake , Lake Red 010-Z Bengal, Aniline Blue Ultramarine Blue, Calco Oil Blue, Methylene Blue Chloride, Phthalocyanine Blue Phthalocyanine Green, Malachite Green Off-Salate, etc. or C,1,5o
lvent Yellow 60SC.

1.5olvent Red 27, C, 1,5olv
Examples include oil-soluble dyes such as enL Blue 35. These colorants are used alone or in a mixture of two or more, and are used in an amount that provides sufficient image density, for example, 1 to 30 parts by weight, preferably 2 parts by weight, per 100 parts by weight of resin.
20 parts by weight is used.

In addition, in order to control the charge of the toner, the above-mentioned toner may contain a charge control agent such as an oil-soluble dye such as nigrosine dye, oil black, or spirone black, or manganese such as naphthenic acid, salicylic acid, octylic acid, fatty acid, or resin acid. iron,
Metal soaps such as metal salts of cobalt, nickel, lead, zinc, cerium, calcium, aluminum, etc., metal-containing azo dyes, pyrimidine compounds, alkyl salicylic acid metal chelates, etc. are added in an amount of 0.00% per 100 parts by weight of the binder resin.
The preferred amount may be adjusted within the range of 1 to 10 parts by weight.

Further, an anti-offset agent may be added to the toner to prevent the toner from adhering to the fixing roller.
For example, low molecular weight polypropylene, low molecular weight polyethylene, various waxes such as paraffin wax, low molecular weight olefin polymers of olefin monomers having 4 or more carbon atoms, fatty acid amide, silicone oil, etc. are added at 0.00% per 100 parts by weight of the binder resin. Preferably, the content is 5 to 15 parts by weight.

As the binder resin used in the colorless transparent toner of the present invention, one having excellent transparency is used. It is preferable to use a resin that has high adhesion to the colored toner when melted, and it is preferable to use a resin in the same series as the colored toner.

For example, styrene-based and styrene-acrylic polymers have a weight average molecular weight of 15,000 to 2 Q OQ.
OO, particularly preferably in the range of 20,000 to 150,000.

This colorless and transparent toner preferably has a low viscosity when melted and permeates a wide area during fixing, and generally has a melt viscosity in the range of 10' to 105 (poise) at 120°C, and particularly has a melt viscosity of 6X10' at 110°C. ~6X
It is preferably in the range of 10' (poise).

If the melt viscosity of the transparent toner is too low outside the above range,
Even if unfixed toner is prevented from entering, it may adhere to the fixing roller and cause offset. On the other hand, if the melt viscosity is too high outside the above range, the fixing properties cannot be improved.

Further, a charge control agent and an offset preventing agent may be added to the colorless transparent toner, and those having high transparency are selected from among those used for the colored toner described above. The amount used is 1 to 2 parts by weight per 100 parts by weight of the binder resin.
0 parts by weight is common.

The particle size of these colored toners and colorless transparent toners is preferably 5 to 30 μm, particularly preferably 7 to 20 μm.

The present invention provides a developing device equipped with colorless and transparent toner on the downstream side of the rotational direction of the image bearing member, in addition to a normal developing device equipped with colored toner provided facing each other on the image bearing member. This is done by applying a colorless transparent toner to the entire image forming area developed with colored toner on the image carrier by so-called bias development in which a bias potential of the same polarity as is applied.

The bias development potential varies depending on the photoreceptor and development system used, but the amount of toner present on the transfer paper during transfer is generally 0.3 to 2.0 mg/cm", preferably 0.5 to 1.5 mg/cm". It is recommended to determine the development potential. If the amount of toner present is too large outside this range, an offset phenomenon is likely to occur during fixing. Furthermore, if the amount of toner present is too small, the fixing performance cannot be improved.

Although the present invention is effective for image forming apparatuses equipped with the above-mentioned belt fixing device, it is also applicable to devices equipped with a fixing device consisting of a pair of heated and pressurized rollers when a low-pressure fixing method is adopted. It goes without saying that it can be done.

(Example) 90% by weight of styrene-acrylic copolymer as a binder resin, 7.5% by weight of carbon black as a coloring agent, and 1.5% by weight of a low molecular weight polypropylene as an anti-offset agent.
After melting and dispersing 1.0% by weight of negative polar dye as a charge control agent using a heating roll mill, coarsely pulverizing,
By classifying, a powder toner having an average particle size of 5 to 20 μm was prepared. The toner charge amount was measured by the blow-off method and was found to be -29 μc/g.

98.5% by weight of Nistyrene-acrylic copolymer, 1.0% by weight of low molecular weight polypropylene as an anti-offset agent
A transparent toner having an average particle size of 5 to 19 μm was prepared by melting and dispersing 0.5% by weight of a negative polar dye as a charge control agent using a heated roll mill, followed by coarse pulverization and classification. The toner charge amount was measured by a blow-off method and was found to be 12 μc/g. When the melt viscosity was measured using a flow tester (product name manufactured by Shimadzu Corporation) under a load of 20 kgf, the melt viscosity at 110°C was 5xl.
The melt viscosity at 120'C was 9X10' (poise).

Each toner was mixed with a ferrite carrier at a toner concentration of 3.8.
% to prepare a developer.

A belt-type fixing device with a heat roller whose surface temperature is set at 135° C. and a nip width of 25 ml11, a first developing device that develops black toner, and a colorless toner disposed on the downstream side in the rotational direction of the photoreceptor. In a wide-width industrial copying machine equipped with a second developing device that uses transparent toner, a blue-printed original with a solid area and a fine line image is processed by setting the surface potential of the photoreceptor to +800V and using black toner. The bias potential of the first developing device is set to +200cm, and the bias potential of the second developing device equipped with colorless transparent toner is set to -400cm.
Setting (3) was used to perform development with black toner and bias development with transparent toner.

As a result, the solid areas and fine line images were faithfully reproduced in the original, and although the density of the non-image areas was slightly lighter than in the original, the toner was completely fixed and the toner remained even when rubbed by hand. It didn't come loose and didn't get my hands dirty.

(Effects of the Invention) According to the present invention, a colored toner image corresponding to a document image can be completely fixed without deteriorating the image quality.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a toner image fixed on a transfer paper by the image forming method of the present invention. FIG. 2 is a schematic cross-sectional view of a wide-width industrial copying machine, and FIG. 3 is an enlarged view of the main parts of the fixing section. FIG. 4 is a schematic diagram showing a toner image on transfer paper in an unfixed state. 21... Transfer paper 22... Colored toner 23...
Melted colorless transparent toner

Claims (2)

[Claims] (1) An image forming method characterized by developing an electrostatic latent image formed on an image carrier with a colored toner, and then developing the entire image forming area with a colorless transparent toner. (2) The image forming method according to claim 1, wherein the colorless transparent toner has a melt viscosity at 120° C. of 1×10^4 to 1×10^5 (poise).