JPS62273573A - Preparation of electrophotographic toner - Google Patents

Abstract

PURPOSE:To maintain electrified quantity and developability constant by premixing a fixing resin with carbon black at a temperature lower than the softening point of the resin under the conditions of rendering the dielectric loss tangent of the toner to be produced to the minimum value or nearly to it, melting and kneading the obtained mixture, and granulating it. CONSTITUTION:100pts.wt. of the fixing resin, such as a styrene acrylic resin, are premixed with 10pts.wt. of the carbon black as a colorant and 1pt.wt. of wax as a releasing agent for preventing offset at a temperature of 20 deg.C lower than the softening point of the resin under the conditions of rendering the dielectric loss tangent of the toner to be produced to the minimum value or nearly to it by using a mixing mill for a prescribed time. The premixing conditions for minimizing the dielectric loss tangent of the toner to be finally obtained can be determined by preinvestigating the relationship between the premixing time and the dielectric loss tangent of the toner composed of the constituents prescribed in proportions and their kinds, thus permitting the electrifiability characteristics and developability characteristics to be always maintained in a constant superior level.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for producing toner for electrophotography, and more specifically, it relates to a method for producing toner for electrophotography, and more specifically, it relates to a method for producing a toner for electrophotography, and more specifically, it relates to a method for producing toner for electrophotography, and more specifically, it relates to a method for producing toner for electrophotography, and more specifically, it relates to a method for producing a toner for electrophotography, and more specifically, it relates to a method for producing toner for electrophotography, and more specifically, it relates to a method for producing toner for electrophotography, and more specifically, it relates to a method for producing toner for electrophotography, and more specifically, it relates to a method for producing toner for electrophotography, and more specifically, it relates to a method for producing toner for electrophotography. The present invention relates to a method for producing an excellent electrophotographic toner.

(Prior Art) Electrophotographic toner for copying machines is manufactured by dispersing carbon blank as a colorant in a fixing resin medium and forming the dispersed composition into particles.

In producing the dispersion composition, the toner components are dry blended, and the resulting dry blend is melted, kneaded, and kneaded. During granulation, the melt-kneaded product is pulverized and then classified to obtain toner particles having a particle size of -5 to 35 μm in the shell.

(Problems to be Solved by the Invention) Conventionally, methods for evaluating the degree of dispersion of carhoprank particles in a fixing resin medium have been conducted using an appropriate method, partly because the particle size of carbon black is significantly Wlm. Things were not well known, and evaluations were only based on theories and feelings, which led to variations in evaluations and also made relative comparisons difficult.

As a result, the produced electrophotographic toner has significant variations in development characteristics such as charge amount and image density depending on the loft, making it difficult to stably and sustainably produce electrophotographic toner of a constant quality. Ta.

Therefore, the present invention provides a method for stably and sustainably producing an electrophotographic toner in which the dispersion state of carbon black in a fixing resin medium is maintained in the best state and the amount of charge and development characteristics are always constant. The challenge is to provide the following.

(Means for Solving the Problems) The present inventors have discovered that when producing an electrophotographic toner from a composition containing a fixing resin and carbon black by a melt-kneading method, the fixing resin and carbon black are mixed together. The dispersion state of carbon black in the fixing resin is best maintained by pre-mixing so that the dielectric loss tangent of the generated toner is at the minimum value or a value close to it at a temperature lower than the softening point of the resin. However, it has been found that this is important in maintaining the charging characteristics and developing characteristics at a certain level and preventing the toner from deteriorating over time.

(Function) The present inventors discovered the following simple fact in the process of arriving at the present invention. That is, as a fixing resin medium, 100
Parts by weight of styrene-acrylic resin, 10 parts by weight of carbon black as a color rejuvenator, and 1 part by weight of wax as a release agent (offset inhibitor) are mixed at a temperature of 20° C. using a grinding mixer such as a Henschel mixer. and kneading the pre-mixed mixture at 150 to 180°C,
After cooling, the dielectric loss tangent (tan δ) of the toner obtained by pulverization and one classification was measured.

Further, for each toner, the toner was placed between the preparations, the toner was melted to form a thin layer of the melted dispersion composition, and the dispersion state was examined by microscopic observation using transmitted light.

According to the measurement results, as shown in Figure 1, the dielectric loss tangent (tan δ) of the produced toner changes as the grinding and mixing time
It is understood that the dielectric loss tangent decreases up to a certain time, but after this certain time, the dielectric loss tangent again increases, and the dielectric loss tangent shows a minimum value at a certain premixing time. On the other hand, according to the dispersion evaluation using the preparation method described above, the dispersibility is best at the mixing time at which the dielectric loss tangent shows the minimum value, and even when the mixing time is shorter or longer than this,
It was confirmed that the dispersibility deteriorated.

The present inventors discovered for the first time that the dielectric loss tangent of the toner changes depending on the dispersion state of carbon black in the toner, and that the dielectric loss tangent of the toner is the minimum in the best dispersion state. This was completely unknown until now.

The above findings in the present invention were discovered as a phenomenon, and although the theoretical explanation thereof has not yet been made, it is thought to be of the first order. That is, carbon black has a secondary particle structure in which its secondary particles are tightly bound together in clusters, but under the above-mentioned pre-mixing conditions, the secondary particle structure of carbon black is mechanically destroyed. It is considered that carbon black is mixed with resin particles in the form of primary particles or a form close to primary particles. It is presumed that when the pre-mixing time passes the optimum time, the carbon black particles, whose secondary particle structure has been destroyed, re-agglomerate using the destroyed resin fine particles as a binder and become coarse, resulting in poor dispersion. In addition, the reason why the dielectric voltage JJF (tan δ) shows the minimum value in the best dispersion state of carbon black is that in the atomized dispersion state of carbon black, the contact interface between the carbon black particles and the resin continuous phase is large. On the other hand, when carbon black is coarsely dispersed, the contact interface between the carbon black particles is large, but the contact interface between the carbon black particles and the resin is small, and the former In this case, the electrical resistance of the dispersion system increases due to the increase in the contact interface between the carbon black particles and the resin, and this is considered to be the reason why the dielectric loss tangent becomes the minimum.

In the present invention, as shown in FIG. 1, the relationship between the pre-mixing time and the toner dielectric loss tangent is investigated in advance for toner components of a certain type and a certain mixing ratio. It is possible to determine premixing conditions that minimize the

Incidentally, even if the dielectric loss tangent of the final toner is not strictly speaking the minimum value, a value near the minimum value 1, for example, within +8%,
In particular, if the condition is within +5%, the best dispersion state of carbon black in the toner can be obtained.

(Operations and Effects of the Invention) According to the present invention, due to one or more functions, the dispersion state of carbon black in the fixing resin medium is always maintained at its best, and the charging characteristics and development characteristics are always maintained at a certain excellent level. The advantage is that electrophotographic toner can be produced stably and continuously. This toner has good dispersibility of carbon black in the resin, so it has good mechanical strength, especially abrasion resistance, and good fixing properties, so it can be used as an electrophotographic toner for high-speed copying. Useful.

(Description of Preferred Embodiments of the Invention) In the present invention, any of the fixing resins used in this type of toner, such as acrylic, styrene, and polyester, can be used as the fixing resin. . However, in order to enable heat setting at a relatively low temperature without offset and to improve the fastness of the fixed image, it is necessary to
It is desirable to use a styrene-acrylic resin having a melt viscosity of 1×105 poise or higher and a glass transition temperature (tg) of 55° C. or higher.

The styrenic monomer used in the copolymer of the present invention includes:
In the following formula, R1 is a hydrogen atom, a lower C'fR prime number (4 or less) alkyl group, or a halogen atom, R2 is a substituent such as a lower alkyl group or a halogen atom, and n is 2 or less including zero. Examples of monomers represented by the following integer include styrene, vinyltoluene, α-methylstyrene, α-chlorostyrene, vinylxylene, and vinylnaphthalene.

Among these, styrene is preferred.

The other acrylic monomer is: ■ CH2=C (2) C-〇-R4 In the formula, R3 is a hydrogen atom or a lower alkyl group, and R
j is a hydrogen atom or an alkyl group having up to 18 carbon atoms, monomers represented by, for example, ethyl acrylate, methyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, acrylic liquor, Such as methacrylic acid. In addition to the above-mentioned acrylic monomers, other ethylenically unsaturated carboxylic acids or their anhydrides, such as maleic anhydride, fumaric acid, maleic acid, crotonic acid, and itaconic acid, can also be used.

In order to impart the above-mentioned properties, the fixing resin contains a styrene monomer (A) and an acrylic monomer (B).
A+B=50+50 to 90.10, particularly preferably in the range of 60:40 to 85:15.

It also has a relatively low viscosity at low temperatures (loo'c) and high temperatures (1
In order to obtain a copolymer resin having a relatively high viscosity at a temperature of 20°C, the copolymer must have a relatively high molecular weight side and a relatively high molecular weight side as determined by ffi quantity measurement by gel perminiscence chromatography (GPC). In the 0 weight molecular weight distribution, which is generally required to have a molecular weight distribution having multiple peaks on the relatively low molecular weight side, the high molecular weight side peak is
Generally, it is in the range of 50,000 or more, especially 70,000 or more, and the -Bandai molecular weight side peak is 50,000 or less, especially 40,000 or less, and it is 1 more than the high molecular weight side peak.
It is desirable to have a low molecular weight of 0,000 or more.

A copolymer with such a molecular weight distribution can also be produced by controlling one molecular weight distribution in a single polymerization step, but generally, a copolymer corresponding to a peak on the high molecular weight side and a copolymer corresponding to a peak on the low molecular weight side are produced. It can be easily obtained by blending with the corresponding copolymer.

A particularly suitable fixing resin is:

(1) copolymers of styrene and acrylic esters and/or methacrylic esters with a Mil of 80,000 to 200,000; (11) copolymers of styrene and maleic anhydride, acrylic esters, and methacrylic esters; A blend of at least one copolymer with an M4 of 10.000 to 50.000, in particular 10 to 70% by weight of copolymer (11) per copolymer (1), especially 15% by weight. It is present in the range of 50% by weight.

As the carbon black, any carbon black such as furnace black and channel black can be used. Carbon black is preferably used in an amount of 3 to 15 parts by weight, particularly 5 to 12 parts by weight, per 100 parts by weight of the fixing resin. When the amount is less than the above ratio, the blackness of the toner is insufficient, and when it is more than the above amount ratio, the fixing properties are decreased, or the charging properties and development characteristics are deteriorated.

The toner according to the invention may be blended with other ingredients known per se according to known formulations. For example, for use as an electrostatic toner, charge control agents known per se, such as oil-soluble dyes such as nigrosine base (CI5045), oil black (CI26150), and spirone black, naphthenic acid metal salts, fatty acid metal Stone soap, resin acid soap, metal-containing azo dye, etc. can be blended in an amount of 0.1 to 5% by weight based on the fixing agent. Further, silicone oil, low molecular weight olefin resins, various waxes, etc. may be used in an amount of 1 to 5% by weight based on the fixing agent for the purpose of assisting release properties.

In the present invention, the above-mentioned toner components are premixed in a dry manner, that is, at a temperature lower than the softening point of the resin. This premixing is advantageously carried out using a grinding mixer in which the secondary particle structure of the carbon black is destroyed. Suitable examples of attrition mixers are Henschel mixers, ball mills, vibratory mills, tube mills, etc.

Final toner? The value of the A electric dissipation tangent (tan δ) itself varies depending on the type and amount of the fixing resin and carbon black, and is difficult to define generally. For example, when the molecular weight of the resin becomes large, the tan δ becomes small, and when the concentration of polar groups in the resin becomes high (tan δ becomes large).Furthermore, when the volume ratio of carbon black in the toner increases, tan δ becomes large.However, in any of these cases, tan δ becomes large. According to the present invention, it is sufficient to determine premixing conditions that minimize the value of tan δ for a given toner composition.

After melt-kneading the premix and cooling this kneaded composition,
A toner is obtained by pulverizing this and sieving if necessary. Of course, there is no particular problem in performing rapid mechanical stirring in order to round off irregularly shaped particles.

Although the particle size of the toner particles is related to resolution and other factors, it is generally desirable that the particle size is in the range of 5 to 35 microns.

In the electrostatographic reproduction method using the toner of the invention, the formation of the I electrostatic latent image can be carried out in any manner known per se, for example after uniformly charging the photoconductive 7111 layer on the conductive substrate. , an electrostatic latent image can be formed by imagewise exposure.

Development of an electrostatic image is facilitated in the case of a two-component toner by mixing it with a magnetic carrier and bringing a magnetic brush of the toner into contact with the substrate.

The toner image formed by development is transferred onto copy paper,
Fixing is performed by bringing this toner image into contact with a heating roll.

(Example) Toner constituent material formulation Styrene/acrylic resin 100 parts Carbon blank 8.5 parts Wax
1.8 parts static control agent 2
15.30, 45% of the above ingredients in a hennonyl mixer
．． Pre-mix for 80 minutes at different times and knead at 160-1
A toner was prepared at 70°C.

As shown in Figure 1, tan δ is (center grain size 12 m), of which 45 minutes (tan δ = 0.0052) and 60 minutes (t
and δ = 0.0057).

Blow-off belt? The variation in the amount of charge was slightly larger for the 60 minute toner. This toner was made into a developer using an acrylic coat carrier.

An image test was carried out using Mita DC-3132. As a result, the initial image was obtained. However, after 6000 sheets of printing, the toner for 60 minutes caused toner scattering inside the machine, and the transfer efficiency also decreased. In addition, a transfer bald phenomenon also occurred.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between pre-mixing time and toner dielectric loss tangent.

Claims (3)

[Claims] (1) The fixing resin and carbon black are premixed at a temperature lower than the softening point of the resin under conditions such that the dielectric loss tangent of the generated toner is at or near the minimum value, and the resulting mixture is mixed. A method for producing toner for electrophotography, which is characterized by melt-kneading and granulation. (2) The manufacturing method according to claim 1, wherein the fixing resin is a styrene-acrylic resin. (3) The method according to claim 1, wherein carbon black is used in an amount of 5 to 12 parts by weight per 100 parts by weight of the fixing resin.