JPH05158283A - Electrostatic charge image developing white toner - Google Patents

Abstract

PURPOSE:To provide the white toner with the charged level stabilized and without causing the fogging and scattering of the toner and spent carrier by melting the toner with the mechanical shearing force to reform its surface. CONSTITUTION:This electrostatic charge image developing white toner contains thermoplastic resin and titanium dioxide and is melted by the mechanical shearing force to reform the surface. Namely, the titanium dioxide exposed on the core grain is coated with resin by the mechanical shearing force, hence the surface reflectivity is improved, the hiding power is further enhanced, and a white toner with the chargeableness capable of being improved is obtained. In this case, only the toner surface is heated in surface reforming, a strong impulsive force is repeatedly exerted on the sample in a short time, and the method using mechanical shearing force is appropriately used. By such surface refining, the pigment 4 exposed on the surface is partly or wholly coated with the binder resin by the partial melting, deformation, etc., of the toner surface.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a toner for developing an electrostatic charge image,
In particular, it relates to white toner.

[0002]

2. Description of the Related Art Generally, electrophotographic copy images are black, but recently, it is also possible to obtain copy images of various colors (color images). Among the color images, the white image is formed from white toner on a colorant such as black, and has a visual beauty different from that of the black image. The white toner is composed of a white pigment typified by titanium dioxide, a binder resin, and other additives, and when forming a copy image from the white toner, the hiding property is particularly required. The concealment characteristic is the ability to make the base material of paper or the like invisible when the toner is fixed on the paper or the like.
In the case of a black image, even if the hiding property is not so sufficient, the image does not give a noticeable blurring effect.However, in the case of a white image, the image is not blurred even if the hiding property is similar to that of the black image. Feel The conventional white toner has an insufficient hiding property, and it is not possible to obtain a clear white image that does not give a feeling of unclearness.

In order to improve the hiding property, it is sufficient to increase the amount of titanium dioxide, which is a white pigment, but in the white toner, the amount of the pigment contained must be considerably increased as compared with the black toner. However, since titanium dioxide has a low charge level, increasing the amount of titanium dioxide added decreases the chargeability. In addition, when such a large amount of titanium dioxide is contained, the amount of titanium dioxide exposed on the toner surface increases, the initial charge level further decreases, and titanium dioxide is liberated, resulting in spent on the carrier. However, there was a tendency that the chargeability was deteriorated, toner scattering, background fog and the like were worsened.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a white toner which has a stable charge level and which does not cause background fog of the white toner, toner scattering, and spent on the carrier. The above object is achieved by modifying the surface of white toner particles.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a white toner containing at least a thermoplastic resin and titanium dioxide, which is surface-modified by melting due to mechanical shearing force to develop an electrostatic charge image developing white toner.

The resin constituting the toner is not particularly limited as long as it is generally used as a binder in toner, and examples thereof include polystyrene resin, poly (meth) acrylic resin, polyolefin resin, Thermoplastic resin such as polyamide resin, polycarbonate resin, polyether resin, polysulfone resin, polyester resin, epoxy resin, or thermosetting such as urea resin, urethane resin, urea resin, epoxy resin, etc. Resins and their copolymers, block polymers, graft polymers and polymer blends are preferably used. Incidentally, the binder resin used in the toner of the present invention is not limited to, for example, one in a completely polymer state as in a thermoplastic resin,
As the thermosetting resin, those containing an oligomer or a prepolymer, a crosslinking agent and the like can be used.

A binder resin having a softening temperature of 100 to 150 ° C., preferably 100 to 130 ° C. is used.
If the softening temperature is out of the above range, problems such as offset and defective fixing occur. In particular, if the softening temperature is lower than 100 ° C., the surface of the toner may dissolve during storage of the toner or stirring in the developing device, and the toner may aggregate.

Further, as the binder resin, one having a glass transition temperature of 55 ° C. to 80 ° C. is used. If the glass transition temperature is out of that range, the
Alternatively, there is a problem of aggregation during stirring in the developing device.

Examples of the white pigment used in the white toner of the present invention include titanium dioxide, zinc white, antimony white, and zinc sulfide. These may be used in combination with titanium dioxide. Titanium dioxide is particularly preferable.
Titanium dioxide may be produced by any method such as a sulfuric acid method, a hydrochloric acid method, a gas phase method, etc., and its crystal form may be anatase type, rutile type or brookite type crystal form. The white pigment has a particle size of 0.05 μm to 0.5 μm, preferably 0.1 μm to
The one with 0.4 μm is used. Sufficient hiding power cannot be obtained if the particle size is smaller than 0.05 μm. On the other hand, if the particle size is larger than 0.5 μm, the binding property with the binder resin is poor, so that toner scattering and accompanying toner fogging occur.

The white toner of the present invention may be prepared by melt-kneading a binder resin and the above white pigment together, or fine particles of the white pigment are formed on the surface of resin particles (mother particles) made of the binder resin. It may be attached by Van der Waals force or electrostatic force.

When the white raw material is melted and kneaded with the binder resin, the amount of the white pigment added is 15 to 60 parts by weight, preferably 20 to 50 parts by weight, based on 100 parts by weight of the binder resin. When the amount of the white pigment exceeds 60 parts by weight, the binding property and the dispersibility of the pigment and the binder resin are deteriorated, and the moisture resistance is deteriorated, the toner is scattered, the fog and the fixability are improved even if the surface is modified in the subsequent steps. Adversely affect. If the amount of the white pigment is less than 15 parts by weight, sufficient hiding property cannot be obtained.

In the present invention, the white toner containing at least the thermoplastic resin and the white pigment obtained as described above is subjected to surface modification by mechanical shearing force. By such treatment, the titanium dioxide exposed on the core particles is coated with a resin, whereby the surface reflectance is improved, the hiding power is further obtained, and a white toner capable of improving the charging property can be obtained. it can.

The surface modification is preferably carried out by increasing only the temperature of the toner surface, repeatedly applying a large impact force to the sample in a short time, and using the mechanical shearing force. Due to the surface modification, the surface-exposed white pigment is wholly or partially covered with the binder resin due to partial melting or deformation of the toner surface. Therefore, it is considered that the adverse effects of the surface-exposed white pigment are suppressed.

As a method of generating this mechanical shearing force, for example, a high-speed air current impact method can be carried out by using a hybridizer as shown in FIG. Input port (1)
Samples supplied from 5000 to 16000 rpm
An impact force is received by the rotary blades (2) that rotate at. Further, the sample powder is dispersed in the centrifugal direction from the center of the device by the air flow caused by the rotation of the blades. The powder diffused to the surroundings is returned to the center of the apparatus again through the circulation pipe (3). As a result, the sample is repeatedly subjected to a large impact force in a short time. Since the temperature locally rises due to this mechanical impact force, only the surface of the toner particles is melted to thermally make the surface spherical, and at the same time, the surface exposed white pigment is coated with the resin. Therefore, as shown in FIG. 2, the fine particles (4) of the white pigment that are exposed on the surface or are free, or adhered to the surface of the toner core particle by the van der Waals force or electrostatic force are fused and fixed. You can At this time, since only the surface temperature rises due to impact, surface modification can be performed without changing the shape of the core particles themselves.

Further, in the white toner of the present invention, not only the surfaces of the core particles are melted, but also the thermoplastic resin particles are adhered by the action of van der Waals force and electrostatic force,
Thereafter, the resin particles may be subjected to surface modification by mechanical shearing force to melt the resin particles, and an outer shell resin layer (5) formed on the toner surface as shown in FIG. 3 may be provided. The outer shell resin layer not only covers the white pigment fine particles (4) exposed on the surface, but also improves the surface reflectance of the white toner, further provides the hiding power, and improves the charging property. Will be able to.

As the surface modification device for generating mechanical shearing force of the present invention, a hybridization system (manufactured by Nara Machinery Co., Ltd.) applying a high-speed air impact method, a cosmos system (manufactured by Kawasaki Heavy Industries, Ltd.), a dry mechanochemical Mechanofusion system (manufactured by Hosokawa Micron), mechanomill (manufactured by Okada Seiko Co., Ltd.), suffusing system (manufactured by Nippon Pneumatic Co., Ltd.) applying the reforming method in hot air, and dispercoat applying the wet coating method. (Manufactured by Nisshin Seifun Co., Ltd.) and Coatmizer (manufactured by Freund Sangyo Co., Ltd.) are preferably used. However, of course, it is not limited to such a device.

The resin used for forming the outer shell resin layer of the present invention is a styrene resin granulated by a wet polymerization method such as an emulsion polymerization method, a soap-free emulsion polymerization method or a non-aqueous dispersion polymerization method, or a gas phase method. Various thermoplastic resin particles such as a (meth) acrylic resin, a benzoguanamine resin, a melamine resin, a Teflon resin, a silicone resin, a polyethylene resin and a polypropylene resin are used alone or in combination of two or more kinds.

Softening temperature T of thermoplastic resin particles for surface modification
m is 100 to 200 ° C, preferably 110 to 180 ° C. If the softening temperature of the thermoplastic resin forming the toner surface is lower than 100 ° C., offsetting is likely to occur, causing a problem in fixability. Since the surface is modified by mechanical shearing force, it is preferable that Tm is as low as possible.
If the temperature exceeds 00 ° C, it becomes difficult to dissolve the thermoplastic resin particles for surface modification, and the surface modification cannot be performed well.

The particle size of the surface-modifying thermoplastic resin particles is
0.1 μm to 3 μm, preferably 0.2 μm to 0.7 μm
Is. If the particle size exceeds 3 μm, it is difficult to adhere to the core particle surface due to Van der Waals force and electrostatic attraction,
Further, it becomes difficult to form a coating film. It is difficult to manufacture thermoplastic resin particles of less than 0.1 μm.

The amount of thermoplastic resin particles used for surface modification is 5 with respect to 100 parts by weight of the white toner which is the core particles.
-50 parts by weight, preferably 10-30 parts by weight. When the amount of thermoplastic resin particles added is less than 5 parts by weight, it becomes difficult to form an outer shell layer that completely covers the core particles, and when it exceeds 50 parts by weight, it is evenly distributed on the toner core particles. It becomes difficult to form a perfect outer shell layer.

The resin layer may further contain a charge control agent and / or a white pigment. In this case,
The charge control agent and / or particles of titanium dioxide may be adhered to the surface of the toner core particles by Van der Waals force or electrostatic force together with the above resin particles to be subjected to surface modification.

A charge control agent may be further added to the white toner of the present invention. As the charge control agent, one that can give positive or negative charge by frictional charging, and its type, amount used, etc. must be selectively adjusted so as not to impair the whiteness and hinder the hiding power. The charge control agent may be contained in the outer shell resin coating layer or may be attached to the outer shell coating layer surface or the toner surface by Van der Waals force or electrostatic force.
The charge control agent attached to the surface may be further immobilized by surface modification.

The positive charge control agent preferably used in the white toner of the present invention is, for example, a quaternary ammonium salt P-.
51, polyamine compound P-52 (manufactured by Orient Chemical Industry Co., Ltd.), imidazole compound and the like. As the negative charge control agent, for example, chromium complex salts E-81, 82
(Orient Chemical Co., Ltd.), zinc complex salt E-84 (Orient Chemical Co., Ltd.) and the like.

The addition amount of the charge control agent should be appropriately selected depending on the kind of toner, the additive of toner, the kind of binder resin and the like, and the developing system of toner (two component or one component). When it is contained in the core particles of the toner produced by the pulverization method, it is 0.1 to 20 parts by weight, preferably 1 to 10 parts by weight, relative to 100 parts by weight of the toner-constituting resin. If it is less than 0.1 parts by weight, the desired charge amount cannot be obtained, and if it is more than 20 parts by weight, the charge amount becomes unstable and the fixing property is deteriorated.

On the other hand, when the charge control agent is used by being adhered and fixed on the surface of the toner, it is 0.001 to 10 parts by weight, preferably 0.05 to 2 parts by weight based on 10 parts by weight of toner particles.
Parts by weight, more preferably 0.1 to 1 parts by weight. 0.
If the amount is less than 001 parts by weight, the amount of the charge control agent present in the surface layer of the toner particles is small and the charge amount is insufficient. If the amount is more than 10 parts by weight, the adhesion of the charge control agent to the toner surface becomes non-uniform and the toner is not used. Release of the charge control agent from the toner surface poses a problem.

The toner of the present invention contains
You may use together an offset prevention agent. As an anti-offset agent, various waxes, particularly low molecular weight polypropylene, polyethylene, or oxidized polypropylene,
Polyolefin wax such as polyethylene is preferably used. Further, as these waxes, those having a number average molecular weight (Mn) of 1000 to 20000 and a softening point (Tm) of 80 to 150 ° C. are preferable. Number average molecular weight is 10
When the softening point is 00 or lower, or the softening point is 80 ° C. or lower, the resin cannot be uniformly dispersed with the binder resin in the toner, and only the wax elutes on the toner surface, resulting in undesirable results during storage or development of the toner. In addition, it may cause photoconductor contamination such as filming. Further, the number average molecular weight exceeds 20,000, or the softening point is 1
If the temperature exceeds 50 ° C., not only the compatibility with the binder resin deteriorates, but also the effect of incorporating a wax such as high temperature offset resistance cannot be obtained. From the viewpoint of compatibility, when used together with a binder resin having a polar group, a polar wax is desirable.

To the white toner of the present invention, a fluidizing agent such as silica, aluminum oxide, titanium dioxide or magnesium fluoride may be added alone or in combination for improving the fluidity. It is mixed and applied to a copying machine as a two-component developer. Hereinafter, the present invention will be described in more detail with reference to examples.

[0028]

Example A white toner was manufactured with the following formulation. Example 1 Ingredient parts by weight Styrene-acrylic resin 100 (Tm = 118 ° C., Tg = 68 ° C.) Titanium oxide (Ishihara Sangyo Kaisha: CR-50) 40 Styrene-dimethylamino-ethyl acrylate copolymer resin 10 (60:40, Tg = 56 ° C., amine value = 174)

The above materials were thoroughly mixed with a Henschel mixer, kneaded with a twin-screw extruder, and then cooled. The kneaded material was roughly crushed, then crushed by a jet crusher, and classified by air to obtain particles having a particle size of 5 to 25 μm (average particle size 13.1 μm). Next, the hybridization system NH
Using S-1 type (manufactured by Nara Machinery Co., Ltd.), 7,000 rp
m for 3 minutes to make the toner surface spherical. Thereafter, 0.2 part by weight of Aerogel R972 (hydrophobic silica: manufactured by Nippon Aerosil Co., Ltd.) was mixed to prepare a toner 1.

Example 2 Implementation was carried out except that 1 part by weight of Bontron P-51 (manufactured by Orient Chemical Co.), which is a charge control agent, was added at the time of surface modification by the hybridization system NHS-1 type (manufactured by Nara Machinery Co., Ltd.). Toner 2 was manufactured in the same manner as in Example 1.

Example 3 Component parts by weight : Styrene-acrylic resin 100 (Tm = 110 ° C., Tg = 65 ° C.) Titanium oxide (Titanium Industry Co., Ltd .: KR310) 30 Low molecular weight polypropylene (Sanyo Chemical Co., Ltd .: Viscole) 550P) 5

The above materials are used in the same manner as Toner 1 for 5 to 25
A particle size of μm (average particle size 12.5 μm) was obtained. Polymethylmethacrylate resin particles (average particle size 0.4 μm, Tg = 8) based on 100 parts by weight of the fine powder obtained here.
10 parts by weight (3 ° C., Tm = 170 ° C.) were put in a Henschel mixer, and mixed and stirred at 1500 rpm for 2 minutes to attach the thermoplastic resin particles to the surface of the fine powder by Van der Waals force and electrostatically. Next, using a hybridization system NHS-1 type (manufactured by Nara Machinery Co., Ltd.), immobilization treatment was performed at 6000 rpm for 3 minutes. To 100 parts by weight of the toner obtained here, hydrophobic silica R-
0.2 parts by weight of 974 (manufactured by Nippon Aerosil Co., Ltd.) were placed in a Henschel mixer, and mixed and stirred at a rotation speed of 1500 rpm for 1 minute to obtain a toner 3.

Example 4 In Toner 3, 1 of the methylmethacrylate resin particles was used.
Charge control agent, Bontron P-51 instead of 0 part by weight
Toner 4 was obtained in the same manner as Toner 3, except that 2 parts by weight (manufactured by Orient Chemical Co., Ltd.) and 10 parts by weight of methyl methacrylate resin particles were used.

Comparative Example 1 Toner 5 is a fine powder having an average particle diameter of 13.1 μm before the surface treatment by the hybridization system in Toner 1.

Production Example of Carrier In order to use the toner for the evaluation described later, a binder type carrier was produced as follows. Ingredient parts by weight • Polyester resin (Kao: NE-1110) 100 • Inorganic magnetic powder (Toda Kogyo: EPT-1000) 500 • Carbon black (Mitsubishi Kasei: MA # 8) 2

The above materials were thoroughly mixed by a Henschel mixer, pulverized, and then melt-kneaded by using an extrusion kneader set at a cylinder portion of 180 ° C. and a cylinder head portion of 170 ° C. The kneaded product was cooled, coarsely pulverized, finely pulverized with a jet mill, and further classified with an air classifier to obtain a magnetic carrier having an average particle diameter of 55 μm.

Evaluation of Particle Diameter of Particles The particle diameters of the toner and carrier were measured as follows. (1) Toner particle size Toner average particle size is measured by a Coulter counter TA-I.
It was determined by measuring the relative weight distribution by particle size using a type I (manufactured by Coulter Counter) with an aperture tube of 100 μm.

(2) Carrier particle size The carrier particle size is Microtrack model 7995-
It measured using 10 SRA (made by Nikkiso Co., Ltd.), and calculated | required the average particle diameter.

Evaluation method for various physical properties Charge amount (Q / M) 50 g of the obtained toner 2 g and the above-mentioned carrier 28 g
Put it in a plastic bottle of cc, put it on a rotating stand, and 1200 rpm
After rotating for 10 minutes, the charge amount was measured. Further, the amount of charge after exposure for 24 hours at 35 ° C. and relative humidity of 85% was measured, and the moisture resistance was also examined.

Evaluation of image formation The toner obtained in each of the examples and the above carrier were mixed at a ratio of toner / carrier = 8/92 to prepare a two-component developer. Using this developer, various images shown in Table 1 were evaluated for Examples 1 to 4 and Comparative Example 1 using EP-470Z (manufactured by Minolta Camera Co., Ltd.).

(1) Background Fogging As described above, in the combination of various toners and carriers, images were printed using the above copying machine. For the fog on the image, evaluate the toner fog on the black background image,
It was ranked. It can be practically used in a rank or more, but is preferably in a rank or more.

(2) Hiding power Evaluation was made by the luminous reflectance when the toner was fixed on black paper (reflectance of 8% or less). The hiding power of the white toner is such that the luminous reflectance is less than 15% ×, 15 to 25% is Δ, and 25%
The above is marked with a circle. When it is Δ, it can be used practically, but when it is O or more, it is desirable.

[0043] carried out for 1 million copies of the printing test using a printing durability test B / W ratio of 6% chart, the charge amount, the evaluation of the background fogging and hiding power went.
The results are shown in Table 1. In Table 1, ◯ means a practically usable area, and × means a practically problematic area.

[0044]

[Table 1]

[0045]

EFFECTS OF THE INVENTION By providing surface modification of a white toner containing a large amount of white pigment, it is possible to provide a white toner having a high hiding power, in which the chargeability of the toner is reduced, toner scattering and background fog are improved. Further, by providing a resin layer on the surface of the toner, the surface reflectance, chargeability and hiding power can be further improved and a clear white image can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an example of a toner surface modification device.

FIG. 2 is a diagram showing a schematic configuration example of the toner of the present invention.

FIG. 3 is a diagram showing a schematic configuration example of the toner of the present invention.

[Explanation of symbols]

1; charging port, 2; rotary blade, 3; circulation pipe, 4; white pigment fine particles, 5; outer shell resin layer

Claims (2)

[Claims] 1. A white toner for developing an electrostatic charge image, wherein a white toner containing at least a thermoplastic resin and titanium dioxide is surface-modified by being melted by a mechanical shearing force. 2. A white toner for developing an electrostatic charge image, which is a white toner containing at least a thermoplastic resin and titanium dioxide, which has an outer shell layer which is melted by mechanical shearing force to form a film.