JP2826739B2 - Image forming method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an image forming method, and more particularly to an image forming method capable of stably obtaining a high-quality image for a long period of time.

[Related Art] In recent years, development of a toner capable of fixing at a lower temperature than in the past has been strongly desired due to a demand for downsizing of a high-speed copying machine or a copying machine. Also, with the spread of negatively charged organic photoconductors, development of an image forming method using positively charged toner has become important.

[Problems to be Solved by the Invention] In order to enable fixing at a low temperature, it is necessary to lower the softening point of a binder resin for toner. Due to filming, toner spent on a carrier, reduced fluidity, reduced triboelectricity, etc., it was not possible to maintain good developability, cleaning properties, and high image quality for a long period of time.

On the other hand, in order to prevent such filming and blocking development and to improve the cleaning property, the fluidity and the triboelectric charging property, the following techniques for containing organic fine particles have been proposed.

(1) A toner in which organic fine particles B having an average particle diameter higher than the softening point of 0.1 μm or more and an average particle diameter of the particles A of 1/4 or less are embedded and coated on the surface of the heat fixing base particles A 63-1311
No. 49).

(2) It contains a positively chargeable toner and a polymerizable fine powder having an average particle diameter smaller than the toner and capable of being negatively charged and having a Tg of 50 ° C. or less.
No. 60-186858).

However, in the technique (1), when used as a two-component developer, the chargeability of the carrier and the organic fine particles is significantly different, so that the fine particles embedded on the toner surface easily migrate to the carrier, and as a result, the carrier There is a problem that the fine particles are electrostatically adhered to the surface, and the charging ability of the carrier is greatly reduced, and the durability is impaired. When fine particles having a strong positive charge are used for a positively charged toner, polytetrafluoroethylene (PTFE), a tetrafluoroethylene-perfluoroalkylvinyl ether copolymer (PTFE) generally used as a coating layer of a fixing roller is used. PFA) and other fluororesins have good electrical insulation properties,
Since the material is easily negatively charged, electrostatic adhesion to the fixing roller increases, the anti-offset property decreases, and winding around the fixing roller and remarkable fixing separation become more likely to occur.

In the technique (2), since the polymer fine powder is merely mixed, the polymer fine powder is easily released from the toner particles, and sufficient filming resistance and blocking resistance are obtained. Can not. When a large amount of fine powder is added in order to secure sufficient filming resistance and blocking resistance, the flowability is lowered and the durability is also lowered.

Further, in order to improve the offset resistance, the following technology for making the heating roller coating layer conductive has been proposed.

(3) A technique of including a low-resistance substance in the heating roller coating layer (Japanese Patent Publication No. 58-23626).

(4) A technique of including a conductive substance in the primer layer (JP-B-57-150869, JP-B-59-83181, and JP-B-59-111177).

(5) A technique in which an oxobenzoyl polyether and carbon black are contained in a heating roller coating layer (Japanese Unexamined Patent Publication No. Sho 61-61).
100777).

However, when the transfer material has a low resistance, or when the transfer material absorbs moisture in a high-temperature and high-humidity environment and the resistance of the transfer material decreases, the transfer current leaks from the heating roller, resulting in poor transfer and poor transfer efficiency. There was a drawback that caused a drop.

The present invention has been made in view of the above-described conventional problems, and uses a positively charged toner capable of improving blocking resistance, filming resistance, cleaning property, frictional charging property, fluidity, and fixing at a low temperature, Furthermore, by improving the durability of image quality, reducing the adhesion of electrostatic toner to the fixing roller, and improving the transferability under high sound and humidity, the durability of the image forming process is improved. Aim.

[Means for Solving the Problems] In order to achieve the above object, an image forming method according to the present invention is characterized in that base particles having an amorphous vinyl polymer having a softening point of 120 ° C. or lower as a binder are used, Negatively charged, and
The electrostatic latent image formed on the photoreceptor is developed using positively charged toner, which has resin particles with a volume resistivity of 10 ¹² Ωcm or more fixed by mechanical impact, and the formed toner image is transferred. After the transfer to the material, fixing is performed by a heat roller having a fluororesin coating layer having a volume resistivity of 10 ³ to 10 ¹¹ Ω · cm.

[Action] Since the toner having the requirements of the present invention has a low softening point of the binder for the base particles of 120 ° C. or lower, sufficient low-temperature fixability is exhibited, and at the same time, resin fine particles are mechanically coated on the surface of the base particles. Since the particles are fixed by the impact force, the expression of the soft property of the base particles is suppressed by the resin fine particles, and the blocking resistance, the filming resistance and the fluidity are improved.

Further, the physical adhesion of the toner to the photoreceptor is weakened by the so-called lubricating action of the resin fine particles, and the cleaning property is improved.

Further, when the photoreceptor is made of an organic photoconductor, paper powder generated from the transfer material, rosin, precipitates such as talc, corona discharge products generated due to a corona discharger in the apparatus,
Alternatively, toner and the like adhere to the photoreceptor, and under high temperature and high humidity, they absorb water, so that the surface of the photoreceptor tends to have low resistance,
Although the latent image flows and image defects (image blurring) occur, filming on the photoreceptor is prevented by the fine resin particles as described above, and an appropriate polishing performance can be obtained. A good image without image deletion can be formed.

Further, since contamination of the developing sleeve due to filming is prevented, stable developability can be obtained even when an image is formed many times in the developing step.

Also, the negatively charged resin fine particles are mechanically impacted,
Since the toner is fixed to the surface of the base particles to form a positively charged toner, the durability is remarkably improved, and the volume resistivity is 10 ³ to 10 ¹¹ Ω.
The electrostatic offset is significantly reduced by combining with a fixing heat roller having a resin coating layer of cm.
Moreover, since the volume resistivity of the fine resin particles is as high as 10 ¹² Ω · cm or more, good transferability can be maintained even under high temperature and high humidity.

[Specific Configuration] In the present invention, an amorphous vinyl polymer having a softening point of 120 ° C. or lower is used as a binder for the base particles. When the softening point exceeds 120 ° C., the fixability at a low temperature is reduced.

The softening point referred to here means that a load of 20 kg / cm ² is given by a plunger while heating a 1 cm ³ sample at a heating rate of 6 ° C./min using a Koka type flow tester (manufactured by Shimadzu Corporation). A nozzle having a diameter of 1 mm and a length of 1 mm was extruded, whereby a plunger descent amount-temperature curve (softening flow curve) of the flow tester was drawn. When the height of the S-shaped curve was h, the height was h / 2. The corresponding temperature is the softening point.

As a binder resin for the base particles, the softening point is 120 ° C.
The following may be used, and specific examples thereof include a styrene resin, an acrylic resin, a styrene-acryl resin, a polyester resin, and an epoxy resin.

The resin fine particles adhered to the surface of the base particles composed of the binder as described above are negatively chargeable with respect to iron powder, and
It has a volume resistivity of 10 ¹² Ω · cm or more, and examples thereof include a vinyl polymer or copolymer, a polyester resin, and a fluororesin. Particularly, a styrene resin, an acrylic resin, and a styrene-acryl resin are preferable. If the volume resistivity of the resin fine particles is less than 10 ¹² Ω · cm, the transferability under high temperature and high humidity becomes poor.

The glass transition point Tg of the resin fine particles is preferably 55 ° C. or higher, and is excellent in blocking resistance.

In addition, the softening point of the resin fine particles is 300 ° C or less, particularly 100 to 20 ° C.
The temperature is preferably 0 ° C., the fixability at low temperatures is excellent, and the fixation to the base particle surface is easy.

The average particle diameter of such resin fine particles is 1 μm or less, particularly 0.1 μm.
The particle size is from 02 to 0.6 μm, it is easy to fix to the surface of the base particle, can be prevented from being embedded in the surface of the base particle, and is excellent in blocking resistance.

In the present invention, the state in which the resin fine particles are fixed to the surface of the base particles means a state in which the height of the resin fine particles projecting from the surface of the base particles is 10 to 90% of the diameter of the resin fine particles. Note that such a state can be easily confirmed by observing the surface of the toner particles with a transmission electron microscope or a normal electron microscope.

In order to obtain such a state, in a system in which the base particles and the resin fine particles are both present, an impact force having a size such that the base particles are not pulverized, for example, 1/5 to 1 / l of the force normally required at the time of pulverization. What is necessary is just to apply an impact force of a magnitude of 10. Specifically, although it depends on the properties of the binder of the base particles, each base particle has a size of 1.59 × 10 ^{−3 to} 9.56 × 10 ⁻⁵ er
g, preferably from 1.20 × 10 ^{−3 to} 1.60 × 10 ⁻⁴ erg.

Other toner components used with the binder resin of the base particles include a colorant, a load control agent, a fluidizing agent,
There are various additives such as lubricants, which can be used as needed.

As the colorant, for example, carbon black, chrome yellow, Dupont oil red, quinoline yellow, phthalocyanine blue, malachite green oxalate, and others can be used.

Examples of the charge control agent include a nigrosine dye, a metal-containing azo dye, and a metal complex.

In order to further improve the viscoelasticity of the toner at the time of melting or to further improve the fixability, it is preferable to use a wax kneaded with a binder resin. Specifically, solid paraffin, low molecular weight polyolefin such as polyethylene or polypropylene, fatty acid ester, higher alcohol, amide wax and the like can be used.

Examples of the fluidizing agent include fine particles of silica, alumina, titania, barium titanate, magnesium titanate, calcium titanate, strontium titanate, zinc oxide, cerium oxide, antimony trioxide, zirconium oxide, silicon carbide, silicon nitride, and the like. Can be mentioned. Particularly, silica fine particles are preferable. Further, silica surface-treated with an amine-modified silicon compound is preferable for positively charging the toner.

The mixing ratio of these fluidizing agents is, for example, preferably 0.01 to 5% by weight, and particularly preferably 0.05 to 2% by weight of the whole toner.

Examples of the lubricant include zinc stearate, aluminum stearate, lithium stearate, stearic acid, hydrogenated castor oil, and the like. The mixing ratio of these lubricants is, for example, 0.01 to
2% by weight is preferred.

The toner according to the present invention may be used as a two-component developer by being mixed with a carrier, or may be used as a one-component developer consisting of only a magnetic toner or a non-magnetic toner without being mixed with a carrier.

As the carrier, conventionally known carriers can be used, but in order to positively charge the toner particles, ferromagnetic metals such as iron, nickel, and cobalt; alloys containing these metals; ferrites; and ferromagnetics such as magnetite. Particles of a metal compound, a fluorine resin such as vinylidene fluoride-tetrafluoroethylene copolymer, tetrafluoroethylene, 2,2,2-trifluoroethyl methacrylate, pentafluoro-n-propyl methacrylate, or a silicone resin Is preferred.

The average particle size of the carrier is preferably 20 to 200 μm, especially 3 μm.
0 to 150 μm is preferred.

As an example of a preferred method for producing the toner according to the present invention, first, a binder resin material is pulverized and classified to obtain base particles having a desired particle size as the toner. The toner particles as described above can be contained in the base particles. Then, the resin particles are added to the base particles, and the mixture is stirred by, for example, a V-type mixer, whereby the resin particles are electrostatically adhered to the surface of the base particles. Add. By performing such treatment, resin fine particles are fixed to the surfaces of the base particles.

In the case where toner components such as a colorant, a fixing property improver, a magnetic material, and other property improvers are dispersed and contained in the base particles, they are uniformly mixed in advance by an extruder or the like, and then pulverized. Classification is sufficient to obtain powder having a desired particle size. External additives such as a fluidizing agent and a lubricant may be added and mixed after the resin fine particles are fixed.

In the present invention, the resin coating layer used for the fixing heat roller has a volume resistivity of 10 ³ to 10 ¹¹ Ω · cm, and is preferably a polytetrafluoroethylene (PTFE) or a tetrafluoroethylene-perfluoroalkylvinyl ether copolymer. Metal oxides such as SnO ₂ / antimony oxide dope, TiO ₂ / SnO ₂ / antimony oxide dope, conductive zinc oxide, mica (mica), glass, ceramic hollow spheres, etc. , Aluminum, copper, zinc,
Metal coat filler coated with ferrite, etc.,
Alternatively, metal powders such as gold, silver, copper, nickel, and aluminum, and graphite and carbon black are dispersed and contained. If the volume resistivity exceeds 10 ¹¹ Ω · cm, the offset property tends to decrease. If the volume resistivity is less than 10 ³ Ω · cm, poor transfer tends to occur under high temperature and high humidity.

According to the image forming method of the present invention, the toner according to the present invention is used for developing an electrostatic latent image formed in, for example, an electrophotographic copying machine, and the obtained toner image is electrostatically transferred onto a transfer material. Then, the image is fixed by the heating roller having the above-described configuration, and a final copy image is obtained.

[Practical Examples] Hereinafter, examples of the present invention will be specifically described, but the present invention is not limited to these examples.

<Production of Binder for Base Particles> (1) Binder 1 for Base Particles (for the Present Invention) Polyester Resin (Softening Point Tsp = 115 ° C.) (2) Binder 2 for Base Particles (for the Present Invention) Styrene-acrylic resin (softening (Tsp = 110 ° C.) (3) Binder 3 for base particles (for comparison) Styrene-acrylic resin (softening point Tsp = 130 ° C.) <Production of fine resin particles> (1) Fine resin particles 1 (for the present invention) potassium persulfate Using styrene and sodium thiosulfate as initiators, 75 parts by weight of styrene, 5 parts by weight of methyl methacrylate, and 20 parts by weight of n-butyl acrylate were polymerized to obtain fine resin particles 1 having an average particle diameter of 0.4 μm.

(Glass transition point Tg = 68 ° C., softening point Tsp = 165 ° C., volume resistivity 2 × 10 ¹³ Ω · cm) (2) Resin fine particles 2 (for the present invention) Using ammonium persulfate as an initiator, methyl methacrylate 80 weight , 10 parts by weight of n-butyl acrylate and 10 parts by weight of n-butyl methacrylate were polymerized to obtain fine resin particles 2 having an average particle size of 0.06 μm.

(Glass transition point Tg = 61 ° C., softening point Tsp = 199 ° C., volume resistivity 9 × 10 ¹² Ω · cm) (3) Resin fine particles 3 (for the present invention) Same composition as resin fine particles 1 and average particle size 0.06 μm Of resin fine particles 3 were obtained.

(Glass transition point Tg = 60 ° C., softening point Tsp = 145 ° C., volume resistivity 3 × 10 ¹³ Ω · cm) (4) Resin fine particles 4 (for comparative example) In resin fine particles 2, ammonium persulfate was used as a polymerization initiator. Was replaced by 2,2'-azobis (2-amidinopropane) dihydrochloride except that the average particle size was 0.2.
4 μm resin fine particles 4 were obtained.

(Glass transition point Tg = 71 ° C., softening point Tsp = 215 ° C., volume resistivity 6 × 10 ¹² Ω · cm) (5) Resin fine particles 5 (for comparative example) 4 × 10 ¹¹
Ω · cm, resin fine particles with an average particle diameter of 0.4 μm
And

(Glass transition point Tg = 69 ° C, softening point Tsp = 165 ° C) Resin fine particles 1 to 3 and 5 all show negative chargeability with respect to spherical iron powder (DSP-135, manufactured by Dowa Iron Powder Co., Ltd.) The resin fine particles 4 were positively charged.

The volume resistivity of the resin fine particles is 40 kg for the resin fine particles.
/ pressurized with cm ^2, to form pellets of diameter 1.0cm, a thickness of about 8 mm, which scissors about 1.0cm electrode, after application of a DC 100 V, determined by measuring the current value after 30 seconds Was.

<Manufacture of Toner 1> Binder 1 for base particles 100 parts by weight Carbon black "Mogal L" (manufactured by Cabot) 10 parts by weight Paraffin wax "Sazol wax H1" (manufactured by Sasol Marketing) 3 parts by weight Alkylene bis fatty acid amide "Hoechst wax C"
(Manufactured by Hoechst) 3 parts by weight The above compositions were mixed, melted and kneaded by a heating roll, cooled, coarsely pulverized, and classified by an air classifier to obtain base particles 1 having an average particle size of 11 μm. .

5 parts by weight of the resin fine particles 1 were added to 95 parts by weight of the base particles 1 and sufficiently stirred and mixed by a V-type mixer to electrostatically adhere the resin fine particles to the base particles. Next, these are referred to as "Nara Hybridization System NH
S-1 "(manufactured by Nara Machinery Co., Ltd.), and treated for 5 minutes at a rotation speed of the impact blade of 6000 rpm, whereby resin fine particles were fixed on the surfaces of the base particles.

Further, 0.8 parts by weight of silica fine particles whose surface was treated with a polysiloxane ammonium salt and 0.2 parts by weight of zinc stearate were added to 100 parts by weight of the base particles to which the resin fine particles were fixed, and mixed with a V-type mixer. Thus, Toner 1 according to the present invention was obtained.

The toner 1 obtained here is in a state where the fine resin particles electrostatically adhered to the surface of the base particles are firmly fixed to the surface of the base particles by surface observation with an electron microscope and observation with a transmission electron microscope. It was recognized that.

<Production of Toner 2> In the production of the toner 1, after obtaining the base particles 1 in the same manner, 98 parts by weight of the base particles 1
Parts by weight were added, and the mixture was sufficiently stirred and mixed by a V-type mixer to electrostatically adhere the resin fine particles 2 to the base particles 1. Next, these were transferred to a “Nara Hybridization System NHS-1” (manufactured by Nara Machinery Co., Ltd.), and processed for 5 minutes at a rotation speed of the impact blade of 6000 rpm, whereby resin fine particles 2 were fixed on the surface of the base particles 1. .

Then, in the same manner as in the production of the toner 1, the mixture treatment of the silica fine particles and the zinc stearate was performed to obtain the toner 2 according to the present invention.

<Production of Toner 3> Base particles 2 were obtained in the same manner as in production of toner 1, except that binder 2 for base particles was used in place of binder 1 for base particles. A toner 3 according to the invention was obtained in the same manner as in the production of the toner 1 except that the base particles 2 were used.

<Production of Toner 4> Base particles 2 were obtained in the same manner as in production of toner 1, except that binder 2 for base particles was used instead of binder for base particles. A toner 4 according to the invention was obtained in the same manner as in the production of the toner 2 except that the base particles 2 were used.

<Production of Toner 5> Base particles 2 were obtained in the same manner as in production of toner 1, except that binder 2 for base particles was used in place of binder 1 for base particles.

To 97 parts by weight of the base particles 2, 3 parts by weight of the resin fine particles 3 were added, and the mixture was sufficiently stirred and mixed by a V-type mixer to electrostatically adhere the resin fine particles to the base particles 2. Next, these are referred to as “Tapra shaker mixer T2C type” (W
(Manufactured by AR Co.), and the mixture was further processed at a rotation speed of 90 rpm for 30 minutes with glass beads added, whereby resin fine particles were fixed on the surfaces of the base particles.

Then, in the same manner as in the production of the toner 1, the silica fine particles and the zinc stearate are mixed and treated to form the toner 5 according to the present invention.
I got

<Production of Comparative Toner 1> Comparative toner 1 was obtained in the same manner as in production of toner 1, except that fine resin particles were not used.

<Manufacture of Comparative Toner 2> Comparative toner 2 was prepared in the same manner except that mother particles 1 and resin fine particles 1 were simply mixed by stirring with a Henschel mixer instead of using “Nara Hybridization System NHS-1” in manufacturing toner 1. I got

<Production of Comparative Toner 3> Comparative toner 3 was obtained in the same manner as in production of toner 3, except that resin fine particles 4 were used instead of resin fine particles 1.

<Production of Comparative Toner 4> Comparative toner 4 was obtained in the same manner as in production of toner 3, except that resin fine particles 5 were used instead of resin fine particles 1.

<Production of Comparative Toner 5> Base particles 3 were obtained in the same manner as in production of toner 1, except that binder 3 for base particles was used instead of binder 1 for base particles. A comparative toner 5 was obtained in the same manner as in the production of the toner 1 except that the base particles 3 were used.

<Preparation of Developer> A carrier (average particle size: 80 μm) in which magnetic particles made of copper-zinc ferrite (manufactured by Nippon Iron Powder Co., Ltd.) are coated with 2,2,2-trifluoroethyl methacrylate, and the above toners Were mixed to prepare two-component developers each having a toner concentration of 5% by weight.

<Heat roller> Table 1 shows heat rollers 1 to 3 of the present invention and a heat roller for comparison.
The specifications of 4,5 are shown.

The volume resistivity was measured using an electrometer (a 617 programmable electrometer manufactured by Kesley) by vacuum-depositing gold on a surface of a heat roller having a resin film of 20 μm formed thereon in a size of 1 cm × 1 cm.

<Evaluation of Durability> As shown in Table 2, an electrophotographic copying machine “U-Bix1550MR” (Konica Corporation) in which each of the above-mentioned developers was combined with a heat roller and the fixing heat roller was set at a temperature of 150 ° C. Using a remodeling machine (linear velocity: 139 mm / sec), under the high-temperature and high-humidity environment (temperature: 33 ° C, relative humidity: 80%), 50,000 times of actual shooting tests were performed. The durability was evaluated by visually observing the image.
The electrophotographic copying machine “U-Bix1550MR” includes a photoconductor made of an organic photoconductor and a heating roller fixing device, and the heating roller fixing device does not include a coating mechanism of a release agent such as silicone oil. Things.

(Method of Measuring Charge Amount of Toner) The charge amount of the toner was measured by a blow-off method through a 350 mesh stainless steel net.

(Blow pressure 0.2 kg / cm ² , blow time 6 sec) The results are shown in Table 3.

From the above results, the following has become clear.

<Examples 1 to 5> The toner charge amount after copying 50,000 times was almost the same as that at the initial stage, and good image quality free from poor cleaning, image deletion and fog was maintained. Further, there was no toner blocking in the developing section and the cleaning section, the fixing property was good, no offset or wrapping around the fixing roller occurred, and the fixing roller was very little stained. Furthermore, no filming on the photosensitive drum or developing sleeve was observed at all,
The transferability was also very good. In addition, contamination inside the apparatus due to toner scattering was very small.

<Comparative Example 1> After 3000 times, the toner blocked in the developing device, and an image defect such as an image drop due to a poor developer conveyance and a large number of toner aggregates were observed on the image. Also, the charge amount after copying 50,000 times is +7 μc / g, which is significantly lower than the initial value,
In addition, toner filming is recognized on the photosensitive drum,
The image was remarkably fogged and unclear.

<Comparative Example 2> The charge amount after copying 50,000 times was +3 μc / g, which was significantly lower than that at the initial stage. Therefore, fog was noticeable after 5,000 times, and in-machine contamination due to scattering of toner and resin fine particles was observed.

<Comparative Example 3> The charge amount after copying 50,000 times is +4 μc / g, which is significantly lower than the initial value. Therefore, fog is remarkable after 5,000 times, and the inside of the apparatus due to toner scattering is severe. Observation of the carrier surface revealed that the carrier was covered with fine resin particles. Further, the toner was frequently electrostatically attached to the fixing heat roller, and image defects due to fixing heat roller contamination and wrapping around the fixing heat roller frequently occurred after 5000 times.

<Comparative Example 4> From the beginning, the transferability was poor, and transfer slippage occurred frequently.

<Comparative Example 5> Similar to Comparative Example 4, transfer slippage occurred frequently.

<Comparative Example 6> A large amount of electrostatic adhesion of toner to the fixing heat roller was observed.
After the first rotation, image defects due to fixing roller contamination and wrapping around the fixing roller frequently occurred.

<Comparative Example 7> The fixing property was poor, and the toner was easily separated from the transfer material.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-198070 (JP, A) JP-A-62-116980 (JP, A) JP-A-1-257857 (JP, A) JP-A-1- 261656 (JP, A) JP-A-63-244055 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G03G 15/20 G03G 13/20 G03G 9/087

Claims (1)

(57) [Claims] (1) A resin particle having a negative charging property with respect to iron powder and a volume specific resistance of 10 ¹² Ω · cm or more is added to base particles having an amorphous vinyl polymer having a softening point of 120 ° C. or lower as a binder. with positively charged toner was fixed by a mechanical impact force, and develops the electrostatic latent image formed on the photosensitive member, after the formed toner image was transferred onto the transfer material, a volume resistivity of 10 ³ to 10
An image forming method characterized by fixing by a heat roller having a fluororesin coating layer of ¹¹ Ω · cm.