JPH01230072A - Fixing method for polymerized full color electrophotograph - Google Patents

Abstract

PURPOSE:To eliminate cold offset and to accomplish the long life of a fixing roller by using polymerized toner where the melting point of wax included in toner forming the lowest layer on a transfer medium is made lower than the melting point of wax included in the toner forming the other upper layer CONSTITUTION:An original image is separated in terms of color and a latent image is formed every color, then developed with primary color toner and black toner corresponding to a color separation filter. The visualized images of the respective colors are sequentially superposed on a transfer member to be transferred. After obtaining a multicolor image, a heating and pressurizing roller fixes it. In such a case, the polymerized toner obtained by suspending and polymerizing a polymeric monomer system containing wax and coloring materials corresponding to the respective colors in a water-based medium is used as the toner and the melting point of the wax included the toner forming the lowest layer on the transfer medium is made lower than the melting point of the wax contained in the toner forming other upper layers. Thus, an excellent image without the cold offset can be obtained and the durability of the fixing roller can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a toner fixing method used for visualizing an electrical latent image in electrophotography, electrostatic photography, or the like.

[Prior Art 1] In recent years, there has been a rapid shift from monochrome copying to full-color copying in copying machines, and two-color copying machines and full-color copying machines are being widely studied and put into practical use.

Color image formation by full-color electrophotography generally requires 3
It reproduces all colors using toner of three primary colors: yellow, magenta, and cyan.

The method involves first passing light from the original through a color-separating light transmitting filter that has a complementary color to the toner color to form an electrostatic latent image on the photoconductive layer.Then, through a development and transfer process, the toner is transferred to the support. Then, the above-mentioned steps are performed several times in order, and the toners are superimposed on the same support while registering, and a perfect full-color image is obtained by one fixation.

For example, as proposed by the present applicant in Japanese Patent Laid-Open No. 59-26757, a color toner kit consisting of three types of toner of three primary colors is used as a full-color toner.

However, while these combinations are relatively balanced for color reproduction, their electrophotographic properties are
There are still points to be improved regarding charging characteristics other than storage stability and durability against repeated copying.

Furthermore, in the above proposal, in order to obtain black by superimposing three colors of toner, subtle differences in tone between these three colors and differences in superposition during constant development and transfer are reflected in the black tone. The complexity of color matching of each color toner during the process and the development-transfer process and fixing process of the copying process must be highly accurate, which naturally complicates the process and causes an increase in costs.

Also, Japanese Patent Application Laid-Open No. 53-68234 and U.S. Patent Sections 4 and 5
There are many applications for monochromatic color toners such as No. 18゜672, but for full color, at least three colors, preferably four colors, must be harmoniously balanced. There is no point in discussing electrophotographic characteristics.

In principle, if we have the three primary colors of yellow, magenta, and cyan, it should be possible to reproduce almost all colors through subtractive color mixing, which is why full-color copiers currently on the market has a structure in which three primary color toners are used in a superimposed manner. Ideally, this would make it possible to achieve all colors in all density ranges, but in reality, there are still many improvements to be made in terms of the spectral reflection characteristics of toner, color mixing properties when toners are superimposed, and loss of saturation due to subtractive color mixing. It has a certain point.

After intensive research to improve these problems, the applicant has
By using a new black toner for inking in addition to the three primary color toners, it has a wide range of color reproducibility and is easy to develop,
We have achieved a full color toner kit that exhibits particularly favorable characteristics in the fixing process.

In these multi-layer development systems, the toner layer during fixing is several times thicker than in monochrome development systems, so under the same fixing conditions as in monochrome systems, sufficient heat does not reach the toner in the bottom layer. As a result, the toner in the bottom layer is not melted and adheres to the fixing roller together with the melted upper layer, which is a drawback in that so-called cold offset tends to occur.

As a measure to prevent cold offset during fixing of multicolor images, Japanese Patent Publication No. 62-49622 discloses a method of lowering the softening point of the toner in the bottom layer. However, it was not possible to satisfy cold offset prevention and blocking performance.

On the other hand, solutions from the aspect of the fixing device include raising the fixing temperature, lowering the fixing speed, and increasing the contact area of the fixing roller. However, increasing the fixing temperature
Thermal deterioration of the fusing roller and increase in energy costs 9 There is a limit when taking into account the temperature rise inside the machine, and lowering the fusing speed means lowering the copying speed, which is undesirable as it leads to a reduction in the function of the copying machine. In order to increase the contact area of the fixing roller, it is necessary to increase the ease of elastic deformation of the roller. To do this, it is necessary to thicken the rubber layer of the roller, which weakens its resistance to heat and shortens the lifespan of the fixing roller. - On the other hand, as a result of sufficient melting, high-temperature offset occurs, making it necessary to apply a mold release agent such as oil to the roller. Moreover, this application of oil shortens the life of the fixing roller, creating a vicious cycle.

The above-mentioned problem also applies to the aforementioned four-color toner kit invented by the present applicant, and is a major problem to be improved.

On the other hand, a suspension polymerization method has been proposed as a method for producing toner (Japanese Patent Publication No. 36-10231). In this suspension polymerization method, polymerizable monomers and colorants (and if necessary, a polymerization initiator , crosslinking agents, charge control agents and other additives)
After uniformly dissolving or dispersing to form a monomer composition, this monomer composition is dispersed in a continuous phase (for example, an aqueous phase) containing a dispersion stabilizer using an appropriate stirrer, and at the same time a polymerization reaction is carried out. to obtain toner particles having a desired particle size.

In this suspension polymerization method, droplets of the monomer composition are generated in water, which is a highly polar dispersion medium. It has a so-called pseudocapsule structure in which it tends to exist in a certain surface layer and non-polar components do not exist in the surface layer. Utilizing this characteristic of the manufacturing method, it is possible to contain waxes with low melting points that cannot be used in the pulverization method.

By incorporating this low-melting-point wax, the toner produced by the polymerization method can achieve both contradictory properties of blocking resistance and low-temperature fixing.

In other words, since the low melting point wax is included, the thermal conductivity in the toner is improved due to the wax that melts at low temperature without reducing the anti-blocking performance.
As a result, low temperature fixing becomes possible. More preferably, since the wax melted during fixing also acts as a release agent, it is possible to prevent high-temperature offset without applying an S-type agent such as oil to the fixing roller.

[Problems to be Solved by the Invention] However, even with the above-mentioned polymerized toner having advantageous performance during fixing, when multiple development is performed in full color and a multiple transfer image is obtained, the thickness of the toner layer becomes monochromatic. Since the amount is several times that of color, the problem of cold offset remains unsolved.

An object of the present invention is to provide a toner fixing method without cold offset.

A further object of the present invention is to provide a fixing method that can prevent offset without applying a release agent to the fixing roller.

A further object of the present invention is to provide a fixing method that can extend the life of the fixing roller.

[Means and effects for solving the problem] The object of the present invention is to color separate an original image, form a latent image for each color, develop it with primary color and black toners corresponding to the color separation filter, and visualize it. In a full-color electrophotographic copying device that sequentially transfers each color image onto a transfer member to obtain a multicolor image, the toner contains at least wax and a coloring material corresponding to each color. Using a polymerized toner obtained by suspension polymerizing a polymerizable monomer system in an aqueous medium, the melting point of the wax contained in the toner forming the lowermost layer on the transfer medium is lowered by the melting point of the wax contained in the toner forming the other upper layer. This is achieved by a full-color electrophotographic fixing method in which the melting point is lower than the melting point of the wax used.

The present invention will be explained in detail below.

The present inventors have arrived at the present invention by paying attention to the fact that a polymerized toner has a quasi-capsule structure with respect to wax, and that a low melting point wax can be added without impairing blocking performance.

That is, in order to apply the polymerized toner, which extends the life of the fixing roller, to full color, it is necessary to solve the problem of cold offset after fixing multiple transfer images. Therefore, regarding the wax that melts sufficiently below the fixing temperature and can be eluted from the toner under the fixing pressure, by including a wax with a lower melting point than the other upper layers in the lowest layer of the multiple transfer image, it is possible to prevent the wax from melting when the multiple transfer image is fixed. This makes it possible to prevent cold offset.

The melting point of the wax in the present invention is preferably in the range shown below.

Melting point of the wax of the toner for the first color of development: a Melting point of the wax of the toner of the second to fourth color of development: b, c, d, then there is a relationship of a<b, c, ct, and 55°C≦a ≦60°C 55°C≦b, c, d≦70°C.

Here, the added wax does not exist in the surface layer, but there is a young resin in the surface layer that has better thermal strength than the added wax, so if the toner environment is below the melting point of the wax, blocking may occur. However, if the melting point is exceeded, the wax becomes liquid and leaches to the surface layer, causing fusion. Considering the temperature environment inside the copying machine, it is preferable that the melting point of the wax is 55°C or higher. When producing toner by turbid polymerization, additives such as wax need to be uniformly dissolved or dispersed in the monomer system, and if the melting point of the wax is too high, it will not dissolve uniformly in the monomer, making it difficult to add. As a wax, the melting point is 55-7
Paraffinic hydrocarbons in the range of 0°C are preferably used. For example, paraffin waxes include products manufactured by Nippon Oil and Nippon Seiro, and branched paraffin waxes include microcrystalline wax (Nippon Seiro). wax), micro wax (made by Nippon Oil), etc.

Further, the amount of wax added is preferably 1 to 30 parts by weight per 100 parts by weight of the polymer.

The polymerized toner used in the present invention can be obtained by the following method. In other words, a monomer system containing a suspension stabilizer is obtained by adding wax, a colorant, a polymerization initiator, and other additives to a polymerizable monomer and uniformly dissolving or dispersing them using an ultrasonic disperser, homogenizer, etc. The mixture is dispersed in the aqueous phase (ie, continuous phase) using a conventional stirrer, homomixer, homogenizer, etc. Preferably, the stirring speed and time are adjusted so that the monomer droplets have the desired toner particle size, generally a size of 30 mm or less, and after that, the same state is maintained by the action of a dispersion stabilizer. Stirring may be carried out to the extent that sedimentation of particles is prevented. The polymerization temperature is set at 40°C or higher, generally from 50 to 90°C. After the reaction is completed, the generated toner particles are collected by washing, filtration, and dried. In the hanging 7F+ polymerization method, 300 to 3 parts of water is usually added to 100 parts by weight of monomer.
000 parts by weight are preferably used as dispersion medium.

Polymerizable monomers that can be applied to the toner of the present invention include:
Styrene, low methylstyrene, m-methylstyrene,
Styrene and its derivatives such as p-methylstyrene, p-methoxystyrene, p-ethylstyrene; methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate,
Methacrylic acid esters such as n-octyl methacrylate, dodecyl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, phenyl methacrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate; methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, propyl acrylate, n-octyl acrylate, dodecyl acrylate, 2-ethylhexyl acrylate, stearyl acrylate.

Examples include acrylic acid esters such as 2-chloroethyl acrylate and phenyl acrylate; and vinyl monomers such as acrylic acid or methacrylic acid derivatives such as acrylonitrile, methacrylonitrile, and acrylamide.

These monomers can be used alone or in combination. Among the above-mentioned monomers, it is preferable to use styrene or a styrene derivative alone or in combination with other monomers as a polymerizable monomer in terms of the development characteristics and durability of the toner.

In addition, it is more preferable to polymerize the monomer by adding a polymer or copolymer having a polar group as an additive during the polymerization of the monomer. It is preferable to suspend and polymerize a polymerizable monomer system to which a copolymer or cyclized rubber is added in an aqueous phase in which the polar polymer and a dispersant with an opposite charge are dispersed. The cationic or anionic polymer, copolymer or cyclized rubber contained in the polymer system is polymerized with the oppositely charged anionic or cationic dispersant dispersed in the aqueous phase to form the toner particles. Electrostatic attraction on the surface,
By covering the particle surface with the dispersant, it prevents the particles from coalescing and stabilizes them. At the same time, the polar polymer added during polymerization collects on the surface layer of the particles that will become the toner, forming a kind of shell-like shape, The particles become pseudo-capsules. A relatively high molecular weight polar polymer, copolymer or cyclized rubber is used to give toner particles excellent blocking properties and development abrasion resistance, while a relatively low molecular weight internal material improves fixing properties. Polar polymers (including polar copolymers) that can be used in the present invention and reverse loading Examples of dispersants are shown below.

(i) Examples of the cationic polymer include polymers of nitrogen-containing monomers such as dimethylamine ethyl methacrylate and diethylaminoethyl acrylate, or copolymers of styrene, unsaturated carboxylic acid esters, etc., and the nitrogen-containing monomers. .

(i) Examples of anionic polymers include nitrile monomers such as acrylonitrile, halogen-containing monomers such as vinyl chloride, unsaturated carboxylic acids such as acrylic acid, unsaturated dibasic acids,
There are anhydrides of unsaturated dibasic acids and polymers of nitro monomers.

(iTi) As an anionic dispersant, Aerosil 12
00, 1300. There are colloidal silicas such as Kumo 380 (manufactured by Nippon Aerosil Co., Ltd.).

(iv) Examples of the cationic dispersant include aluminum oxide, fine wood-philic positively chargeable silica powder such as aminoalkyl-modified colloidal silica, and the like. Cyclized rubber may be used instead of the polar polymer.

Such a dispersant is preferably used in an amount of 0.2 to 20 parts by weight, more preferably 0.2 to 20 parts by weight, based on 100 parts by weight of the polymerizable monomer.
It is 3 to 15 parts by weight.

On the other hand, as the charge control substance to be added as necessary, commonly known ones can be used. For example, nigrosine, azine dyes containing an alkyl group having 2 to 16 carbon atoms, metal complex salts of monoazo dyes, salicylic acid, difluor Metal complex salts of kylsalicylic acid and the like are used.

As the polymerization initiator, any suitable polymerization initiator such as 2,2'-azobis-(2,4-dimethylvaleronitrile), 2,2'-7zobisisobutyronitrile, 1,1' -azobis(cyclohexane-1-carbonitrile), 2,2'-azobis-4-methoxy-2
, 4-dimethylvaleronitrile, and other azo or diazo polymerization initiators such as azobisinbutyronitrile (AIBN); benzoyl peroxide, methyl ethyl ketone peroxide, isopropyl peroxy carbonate, cumene hydroperoxide, 2,4 −
Examples include peroxide-based polymerization initiators such as dichloryl benzoyl peroxide and lauroyl peroxide.

Generally, about 0.5 to 10% of the polymerization initiator based on the weight of one polymerizable monomer is sufficient.

Further, a fluidity modifier may be mixed (externally added) with toner particles and used. Examples of the fluidity modifier include colloidal silica, fatty acid metal salts, and fine Teflon powder. In addition, fillers such as calcium carbonate and finely powdered silica are added for the purpose of increasing the volume.
It may be blended into the toner in a range of 5 to 20% by weight.

The area pressure of the fixing roller is a value obtained by dividing the total pressure applied to the roller by the contact area between the fixing roller and the fixing medium.

[Example] A detailed explanation will be given below based on examples.

All parts are by weight.

Examples 1 to 3 A monomer composition uniformly dissolved or dispersed according to the formulation shown below was dissolved in a dispersion system containing a suspension stabilizer dispersed in water.
Through #3 polymerization, toners of four colors, yellow, cyan, magenta, and black, were obtained.

〈Prescription〉 (blank below) Use these four color toners with Canon Color Laser Copier 1
Multiple development was carried out in the order of magenta, cyan, yellow, and black, and the resulting unfixed image was passed between fluorine-based fixing rollers under the fixing conditions shown in Table 1 to obtain a fixed image. No cold offset was observed in the obtained images.

Comparative Example A similar experiment was carried out using toner obtained in the same manner as in Example except that the amount of wax in the four color toners was changed to the proportions shown in Table 1.
A fixed image was obtained.

A cold offset phenomenon was observed in the obtained image.

[Effects of the Invention] As described above, according to the present invention, excellent images without cold offset can be obtained, and the durability of the fixing roller is also good.

Claims (1)

[Claims] The original image is color separated, latent images are formed for each color, developed with primary color and black toners compatible with the color separation filter, and the visualized color images are sequentially overlaid and transferred onto a transfer member to create a multicolor image. After obtaining the toner, a polymerizable monomer system containing at least wax and a colorant corresponding to each color is suspended and polymerized in an aqueous medium in a full-color electrophotographic copying machine that fixes the toner using a heating and pressure roller. Full-color electrophotography characterized by using a polymerized toner obtained by using a polymerized toner in which the melting point of the wax contained in the toner forming the lowermost layer on the transfer medium is made lower than the melting point of the wax contained in the toner forming the other upper layer. Fixation method.