JPS63306461A - Toner for developing electrostatic latent image - Google Patents

Abstract

PURPOSE:To retard migration of a surface active agent to a photosensitive body during a copy cycle and to make the degree of electric charge of a toner by producing a dry type toner by coating the surface of particles of a mother material for the toner contg. the surface active agent with small particles buried therein. CONSTITUTION:The titled toner is produced by coating small particles B having a same softening point T1 as particles A of a heat-fixing mother material contg. a surface active agent, or a softening point higher than T1, or having substantially no softening point, wherein said small particles B consist primarily of an org. high molecular material having smaller mean particle size than the mean particle size of A and are buried to a depth smaller than the particle size of the small particles B. The particles A of the mother material consist primarily of a hot-melting resin contg. further a surface active agent as resistance regulating agent. On one hand, the small particles B have a function for inhibiting migration of the surface active agent toward the photosensitive body by preventing direct contact of the photosensitive body with the mother material particles. By this constitution, the photosensitive body is prevented from defect of charge due to migration of surface active agent toward the photosensitive body.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a dry toner for developing electrostatic latent images, which is particularly suitable as a color toner.

As is well known, dry toner used to develop electrostatic latent images formed on electrophotographic photoreceptors, electrostatic recording materials, etc., is made of high-resistance heat-melting resins such as styrene resins and acrylic resins, and colorants. The main component is magnetic powder, and magnetic powder is added as needed. This dry toner is mixed with a carrier such as magnetic powder or glass beads and used as a developer. During development, the toner is frictionally charged with the carrier so that it is electrostatically attracted to and adheres to the electrostatic latent image. The toner must be appropriately charged in the agent, and the amount of charge is ±5 to 25
It is approximately μc/g, and the development efficiency decreases even if it is larger or smaller than this value. On the other hand, if the toner has high electrical resistance,
As the copy cycle is repeated, the amount of toner charge tends to increase. This tendency is particularly noticeable in toners for color copying because they use dyes that are highly resistive as coloring agents. Therefore, it is also practiced to adjust the amount of charge of the toner by dispersing and containing a blending surfactant known as an antistatic agent for plastics in the toner particles.

However, since these surfactants are low-molecular substances, they are difficult to mix with the base resin, and therefore tend to bleed out from the toner surface over time. In the case of general electrophotography, the surfactant exuded in this way is transferred onto the photoreceptor to form a film through the repetition of the copy cycle of charging the photoreceptor, image exposure, development, and transfer to paper. Improvements to this type of toner were desired to interfere with body charging.

-15 An object of the present invention is to provide a toner for developing electrostatic latent images that can prevent charging problems on the photoreceptor due to migration of the surfactant to the photoreceptor, despite the use of a surfactant. be.

As shown in FIG. 1, the dry toner for developing an electrostatic latent image of the present invention has a surface of heat-fixable base particles A containing a surfactant.
An organic polymer having a softening point equal to or higher than the softening point of the base particles A, or having substantially no softening point and an average particle size smaller than the average particle size of the base particles A. It is characterized in that small particles B mainly composed of molecular substances are embedded and coated at a depth less than the particle size of the small particles B.

In the present invention, the base particles A mainly contain a thermofusible resin and further contain a surfactant as a resistance adjuster. If necessary, a charge imparting agent, a coloring agent and/or a magnetic material are added thereto to perform the main function as a toner, that is, a heat fixing function. Although the coloring agent may be contained in the small particles B, it is usually contained in the base particles A. Also, base particle A
and small particles B.

On the other hand, small particles B are mainly composed of an organic polymer substance, to which, if necessary, a coloring agent and/or a magnetic substance are added as in the case of the base particles, and are mainly formed by direct contact between the photoreceptor and the base particles. It has the function of preventing contact and preventing migration of the surfactant to the photoreceptor.

The average particle size of the base particles A must be larger than that of the small particles B, and the softening point must be equal to or lower than the softening point of the small particles B.

Specifically, the average particle diameter of the base particles A is preferably about 5 to 25 μm, which is the same as the average particle diameter of conventional dry toners, since they form the base of the dry toner of the present invention. When the average particle size is less than 5μ, the amount of spent toner relative to the carrier increases,
Deterioration of the developer and toner melting to the sleeve may occur.
If it is larger than 25 μm, the resolution will be poor. Further, the softening point of the base particles A is preferably 80°C or lower. Softening point is 80
If the temperature is higher than .degree. C., fixing failure is likely to occur even if the coverage of the small particles B (as the projected area of the small particles B on the surface of the base particle A) is low.

On the other hand, the small particles B must have an average particle size smaller than that of the base particles A, and a softening point that is equal to or higher than the softening point of the base particles, or must have substantially no softening point. Must be.

Specifically, the average particle size of the small particles B is 0.1 μm or more,
It is preferable that the average particle diameter of the base particles A is 1/4 or less. When the average particle size is less than 0.1 μm, the original function of small particles B, which is to prevent the transfer of surfactant from base particles A to the photoreceptor, cannot be achieved, and also in terms of manufacturing, small particles B cannot be used as base particles. When buried in A, the toner tends to aggregate, making manufacturing difficult. Further, when the particle size of the small particles B is larger than 1/4 of the particle size of the base particles A, the small particles B are not sufficiently embedded in the base particles A during fixing, which tends to cause fixing failure.

Furthermore, the coverage rate of the small particles B on the surface of the base particle is 40 to 100.
% range is preferable. If it is less than 40%, the effect of preventing the surfactant from transferring to the photoreceptor is small, and if it is 100%
If it exceeds this value, the small particles B will not be sufficiently embedded in the base particles A during fixing, which tends to cause fixing failure.

The coverage α (X100%) of the small particles B is determined as follows. That is, the diameter (as an average particle size) and true specific gravity of the small particles B are respectively d, the diameter (as an average particle size) and true specific gravity of the ρ phase base particle A are kd and ρ dog, respectively, and the weight of one base particle. where W* is the weight of n small particles per one base particle, and the projected area of each base particle is (:
) 2, so Wyu ρ6 k Wt ρsmall 4...
・ Obtain (3). Here, when the particle size ratio k and true weight ratio ρ*/ρ small of the base particle A and small particle B are known, W small/W*
When the appropriate coverage α (X 100%) was determined by varying the ratio, it was found to be in the range of 40 to 100%.

Examples of materials used for the base particles include:

Polystyrene, chloropolystyrene, poly-α-methylstyrene, styrene-chlorostyrene copolymer, styrene-propylene copolymer, styrene-butadiene copolymer, styrene-vinyl chloride copolymer, styrene-vinyl acetate copolymer, Styrene-maleic acid copolymer, styrene-acrylic ester copolymer (styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-butyl acrylate copolymer, styrene-
Octyl acrylate copolymer.

Styrene-phenyl acrylate copolymer, etc.), styrene-methacrylate ester copolymer (styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-butyl methacrylate copolymer, styrene-methacrylate copolymer) acid phenyl copolymer, etc.), styrene-
Styrenic resins such as α-methyl chloroacrylate copolymer, styrene-acrylonitrile-acrylic acid ester copolymer (styrene or a monopolymer or copolymer containing a styrene substitute), vinyl chloride resin, styrene-acetic acid Vinyl copolymer, rosin-modified maleic acid resin, epoxy resin, polyester resin, polyethylene, polypropylene, ionomer resin, polyurethane resin, ketone resin,
Ethylene-ethyl acrylate copolymer.

Examples include heat-melting resins such as xylene resin and polyvinyl butyral, and waxes such as natural or synthetic waxes.

These may be used alone or in combination.

Surfactants used as resistance modifiers for base particles include alkylamine ethylene oxide adducts, alkylphenol ethylene oxide adducts, tallow acid diisopropazuramide, stearic acid polyethylene glycol ester, and lauric acid sorbitan ester ethylene oxide adducts. Examples include the body. These may also be used alone or in combination. In order to incorporate the surfactant into the base particles, the surfactant may be melted and kneaded together with the base particle material, and then crushed and classified to a desired particle size, in the same manner as in the production of a normal dry toner.

On the other hand, as an organic polymer substance for small particles B, base particles A
Depending on the softening point of the resin, it is possible to select from among the above-mentioned base materials, and materials that are not suitable as base resins and have substantially no softening point, such as silicone resins and benzoguanamine formaldehyde condensates, etc. Can be used selectively.

Coloring agents include carbon black, chromium-containing monoazo dye, nigrosine dye, aniline blue, carfoil blue, chrome yellow, ultramarine blue, quinoline yellow, methylene blue chloride, monastral blue, malachite green oxalate, lamp black, rose bengal, monas. Examples include Toral Red, Sudan Black BM, and mixtures thereof. Co, Fa as magnetic material
, metal powder such as Ni; A Q , Co, Cut F
ee P b, Nxg Mgy Sns Zzp Au
g Metal alloys or mixtures such as AgeSe and Tie Wt Zr; metal oxides such as iron oxide and nickel oxide, or metal compounds containing the same; ferromagnetic ferrite; or mixtures thereof.

Furthermore, the toner of the present invention may be used to improve fluidity or the like.

Fine powder of silica, alumina, titanium oxide, etc. can be added and mixed.

In order to produce the dry toner of the present invention, base particles A containing a surfactant may be heated and softened to a temperature near the softening point of the particles as described above, and small particles B may be added thereto and mixed by stirring. . In this way, the toner of the present invention is obtained with the small particles B embedded in the surface of the base particles A, but the depth of the embedding is determined by the stirring conditions, heating temperature, etc., so that the average of the small particles B is Controlled below particle size.

The toner of the present invention as described above can be used as a one-component dry developer by containing a magnetic material in the base particles A and/or small particles B, or as a two-component dry developer by mixing with a magnetic material. Ru.

The present invention will be explained below by way of examples. Note that all parts are parts by weight.

Example 1 90 parts of styrene-methyl acrylate copolymer and 10 parts of carbon black were hot-melted and kneaded with 2 parts of laurylamine ethylene oxide adduct, which is an amphoteric surfactant, and pulverized and classified to obtain an average particle size of 17 μm and softened. Base particles were prepared at a temperature of 70°C. The volume resistivity of this base particle is 1010Ω■
5 Meanwhile, 90 parts of styrene-methyl acrylate copolymer, 8 parts of carbon black, and 3 parts of chromium-containing monoazo dye were kneaded, crushed, and classified to give an average particle size of 3.5 μm.
(softening point is almost the same as the base particle).

Next, this small particle and the base particle are mixed at a ratio of 0.49/1. ．． 0
Mix at a weight ratio of 8.
The mixture was stirred for 1 hour in an atmosphere at 0°C. The coverage of small particles in the obtained dry toner is ρ large/ρ or ≠1.0 to about 6
It was 0%. Also, the volume resistivity of this toner is 101
It was 2Ω■.

Next, 3 parts of the above toner was added to 100 parts of a carrier made of ferrite powder with an average particle size of 100 μm coated with polymethyl methacrylate to a thickness of 1 μm to prepare a two-component dry developer, and continuous copies were made using a Ricoh copier FT5510. I did it. As a result, as shown in Figure 1, the amount of charge of the toner in the developer was -15 to -20 μc during continuous copying of 100,000 sheets.
/g, and the image quality after continuous copying was as good as the initial one.

Comparative Example 1 Base particles were prepared in the same manner as in Example 1 except that the amphoteric surfactant was removed from the base particles, and further using these base particles, 2
Created a component-based dry developer.

At this time, the volume resistivity of the toner was 1 oISΩ], and the amount of charge of the toner in the developer was -25 μc/g.

When this developer was used for continuous copying with an FT5510 (using a selenium photoreceptor drum), the charge amount increased to 145 μc/g after 1000 copies as shown in Figure 2, and the image density was approximately 0.5. As a result, the image quality deteriorated significantly.

Comparative Example 2 A base particle was prepared in the same manner as in Example 1 except that 2 parts of a chromium-containing monoazo dye was further added as a material for the base particle, and this was used as it was (without embedding small particles) as a dry toner. A two-component dry developer was prepared in the same manner as in Example 1. The amount of charge at this time was -16 μc/g. Next, when this developer was placed in FT5510 and continuous copying was performed, the image density was 0.5 after 500 copies, and the image was unclear. When I observed the photoreceptor drum, I found that
It was found that a cloudy surfactant film was formed on the surface and insufficient charge was deposited on the photoreceptor.

Example 2 90 parts of styrene-butyl methacrylate copolymer, 10 parts of carbon black and 2 parts of nigrosine dye were added to Example 1.
In the same manner as above, small particles with an average particle diameter of 4 μm and a softening point of 70° C. were produced. Next, the base particles prepared in Example 1 and these small particles were mixed at a weight ratio of 110.66, and the mixture was treated in the same manner as in Example 1 to produce a toner. The coverage rate of small particles in this toner was about 70% of ρ*/ρ small #1.

Next, a two-component dry developer was prepared using this toner in the same manner as in Example 1, and it was set in a Ricoh copier FT7500 (using an organic photoconductive photoreceptor drum), and 10,000 copies were made. The amount of charge is +20~+25μc
/g, and the high image quality was maintained as it was at the beginning. At this time, no cloudy film as observed in Comparative Example 2 was observed on the photoreceptor drum.6 Example 3 90 parts of polyester resin, 10 parts of carbon black, and 2 parts of polyethylene glycol stearate were melted. The mixture was kneaded, pulverized, and classified to produce base particles having an average particle diameter of 15 μI and a softening point of 65°C. On the other hand, as a small particle (C
Prepare methylpolysiloxane particles represented by H, Sin, , ) n with an average particle diameter of 2 μm and a softening point of 200° C. or higher, and mix the small particles and base particles at a weight ratio of 1/2.7,
Thereafter, this was treated in the same manner as in Example 1 to produce a dry toner. The coverage of small particles in this toner was about 64%, with ρ*/ρ small valve being 0.91.

Next, 3.5 parts of the toner was added to 100 parts of the polymethyl methacrylate coated carrier used in Example 1 and mixed.
Make a component-based dry developer and apply it to the Ricoh copier FT6.
080 (uses a selenium-based photoreceptor) and made 10,000 copies, the charge amount was stable at -20 to -25 μc/g, and the image quality after continuous copying was as good as the initial one. Ta. Note that no film formation on the photoreceptor was observed.

Effects - Supervised by Coco As described above, the dry toner of the present invention has small particles buried and coated on the surface of surfactant-containing base particles, so that during the copy cycle, the surfactant migrates to the photoreceptor and film formation due to them is prevented. This has the advantage that the amount of charge on the toner is stable and there is no film contamination on the photoreceptor.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional model diagram of the toner of the present invention, and FIG. 2 is a curve diagram showing changes in charge amount during continuous copying of donors prepared in Example 1 and Comparative Example 1.

Claims (1)

[Claims] 1. The surface of the heat-fixable base particles A containing a surfactant has a softening point equal to or higher than the softening point of the base particles A, or has substantially no softening point, and Electrostatic latent image development in which small particles B mainly composed of an organic polymer substance having an average particle diameter smaller than the average particle diameter of the base particles A are embedded and coated at a depth less than the particle diameter of the small particles B. toner.