JP2859646B2 - Image forming method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming method in which, in an electrophotographic apparatus, a transfer device is brought into contact with a latent image carrier to transfer a toner image.

2. Description of the Related Art In an image forming apparatus including a step of electrostatically transferring a transferable toner image formed on a surface of a latent image carrier to a sheet-like transfer material mainly made of paper, a rotating cylindrical, endless Using a latent image carrier that runs endlessly such as a belt, a biased transfer device is pressed against it and the transfer material passes between them, and the toner image on the latent image carrier side is transferred to the transfer material. Those configured to transfer, for example, JP-A-59-4666
An apparatus as disclosed in Japanese Patent Laid-Open No. 4 has already been proposed.

Such an apparatus adjusts the pressing force of the transfer roller to the latent image carrier by adjusting the pressing force of the transfer roller against the latent image carrier, as compared with a transfer unit using corona discharge, which has been widely used in the past. The suction area can be enlarged, and the transfer material is positively pressed and supported at the transfer portion. For this reason, there is little possibility that transfer failure due to transfer failure due to transfer material conveyance means or a loop or a curl existing in the transfer material may occur, and the transfer material conveyance path may be shortened due to the recent miniaturization of this type of image forming apparatus. It is easy to respond to requests such as reducing the diameter of the image carrier.

However, on the other hand, in a device that performs transfer by contact, a transfer current is supplied from the contact portion, so that it is necessary to apply a certain pressure to the transfer device. When the contact pressure is applied, pressure is applied to the toner image on the latent image carrier, and aggregation occurs.

Further, when the surface of the latent image carrier is made of resin, adhesion occurs between the toner aggregates and the latent image carrier, and transfer to the transfer material is inhibited. A phenomenon occurs in which a strong portion is not transferred at all and an image is lost.

This phenomenon is particularly remarkable in the line portion of 0.1 to 2 mm. This is edge development in the line area,
This is because the amount of toner is large, aggregation due to pressure is likely to occur, and loss due to transfer is likely to occur. At this time, the output image is a copy in which only the outline portion is formed,
This is called "transfer missing". FIG. 1 shows an example of an omission during transfer. In the figure, a is an image transferred by corona transfer, and b is a hollow image transferred by a transfer roller.

The “missing during transfer” is particularly remarkable in thick paper of 100 g / cm ² or more, an OHP film having a high degree of smoothness, when copying the second side, and the like.

In the case of a cardboard or a film, it is conceivable that the effect of the transfer electric field is small due to the thickness of the transfer material, and the pressure is increased, so that the sheet is likely to drop out.

Further, at the time of copying on the second side, when passing through the fixing device at the time of forming the image on the first side, a release agent contained for preventing offset from the fixing device adheres to the transfer material. It is conceivable that the contact between the sheet and the transfer material is hindered, so that hollow holes are likely to occur.

As described above, in the case of the transfer device using the contact member, the size is reduced
Although there are many advantages such as low power, the conditions for the transfer material are narrowed.

[Problem to be Solved by the Invention] An object of the present invention is to provide an image forming method that solves the above-mentioned problems.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming method by pressure transfer such as a contact transfer method, which has a transfer step of obtaining a high-quality image faithful to a latent image regardless of the conditions of a transfer material. Is to provide.

The purpose of the present invention is to check for phenomena such as “missing during transfer”
Another object is to provide an image forming method in which the phenomenon is suppressed.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming method using a developer that provides a high-quality image with no omission during transfer even when various transfer materials such as thick transfer paper are used.

Further, an object of the present invention is to provide an image forming method using a developer which is stable against environmental changes such as high temperature and high humidity and low temperature and low humidity and can always exhibit good characteristics. .

Means and Action for Solving the Problems The present inventors have found that the surface of the latent image carrier has a contact angle with water.
By having a specific amount of the insulating toner having a material capable of forming a smooth surface of 80 ° or more, the transfer device to which the transfer bias is applied is brought into contact with the latent image carrier at a linear pressure of 3 g / cm or more,
It has been found that good results can be obtained when a toner image is electrostatically transferred to a transfer material.

That is, the present invention provides a developing step of forming a toner image by developing an electrostatic latent image on a latent image carrier with an insulating toner, and transferring the toner image to a transfer material using a transfer device. In the image forming method having a step, a transfer device to which a transfer bias is applied is brought into contact with the latent image carrier at a linear pressure of 3 g / cm or more to electrostatically transfer the toner image to the transfer material. As an insulating toner, a material capable of forming a smooth surface having a contact angle of 80 ° or more with water on the surface of the latent image carrier is 0.01 to 1.0 part by weight based on 100 parts by weight of toner particles. The present invention relates to an image forming method using a toner.

The contact pressure used in the present invention is 3 g / cm as a linear pressure.
It is preferably at least 20 g / cm.

 The linear pressure is calculated by the following formula.

(Linear pressure) [g / cm] = (Total pressure applied to transfer member)
[G] ÷ (length in contact) [cm] If the contact pressure is less than 3 g, transfer failure of the transfer member and insufficient transfer due to insufficient transfer current undesirably occur.

The transfer device used in the present invention includes a transfer roller as shown in FIG. 2 or a transfer belt as shown in FIG.

FIG. 2 is a schematic side view of a main part of a typical image forming apparatus of this type. The illustrated apparatus is a cylindrical latent image carrier that extends in a direction perpendicular to the paper and rotates in the direction of arrow A. (Hereinafter referred to as photoreceptor) 1, conductive transfer roller 2 in contact with this
Is arranged.

A primary charger for uniformly charging the surface of the photoreceptor 1 and a light image such as an image-modulated laser beam and light reflected from a document are projected on the charged surface, and The exposure unit that attenuates the potential of the part to form an electrostatic latent image, a developing unit, a cleaner that removes residual toner remaining on the photoreceptor surface even after transfer, and other members necessary for image formation are provided. Needless to say, they are all omitted.

The transfer roller 2 comprises a cored bar 2a and a conductive elastic layer 2b. The conductive elastic layer 2b is an elastic body having a volume resistance of about 10 ⁶ to 10 ¹⁰ Ωcm such as urethane or EPDM in which a conductive material such as carbon is dispersed. It is made. A transfer bias is applied to the metal core 2a by the constant voltage power supply 8.

FIG. 3 shows the present invention applied to a transfer belt.
The transfer belt 9 is supported and driven by the conductive roller 10.
The pressurization of the transfer device is usually performed by pressurizing the end bearing of the core 2a or 10 of the core.

The present invention is particularly effective for an image forming apparatus in which the surface of a latent image carrier is an organic compound. When the organic compound forms the surface layer, it has good adhesion to the binder resin contained in the toner.Particularly, when using the same material, a chemical bond occurs at the contact point, and the transfer property is low. Is to be reduced.

Examples of the surface material of the latent image carrier used in the present invention include, but are not limited to, silicone resin, vinylidene chloride, ethylene-vinyl chloride, styrene-acrylonitrile, styrene-methyl methacrylate, styrene, polyethylene terephthalate, and polycarbonate. However, other monomers or copolymerization or blending between the exemplified resins can be used.

The present invention is particularly effective for an image forming apparatus in which the diameter of the latent image carrier 1 is 50 mm or less. This is because, in the case of a small-diameter drum, even if the linear pressure is the same, the curvature is large, and the concentration of pressure tends to occur at the contact portion.

It is considered that the same phenomenon occurs in the belt photoreceptor, and the present invention is also effective for an image forming apparatus having a radius of curvature of 25 mm or less at the transfer section.

 Next, the toner used in the present invention will be described.

Silicone oil represented by the following formula is used as the film-forming substance used in the present invention. Examples thereof include dimethyl silicone oil, alkyl-modified silicone oil, α-methylstyrene-modified silicone oil, chlorophenylsilcon oil, and fluorine-modified silicone oil.

Also, a fatty acid metal soap represented by the following formula: Examples include zinc stearate, zinc laurate, zinc myristate, calcium stearate, aluminum stearate and the like.

As described above, examples of the film-forming substance have been given, but the present invention is not limited thereto.

The contact angle of the surface of the latent image carrier with water is measured as follows. Using a Kyowa contact angle meter CA-DS, mount so that the sample surface is horizontal when viewed directly from a mirror.

Drop 10 μg of pure water subjected to ion exchange treatment on the surface, measure 1 / 2θ from a direct mirror, and obtain the contact angle θ
It is considered that the formation of a film that requires the following is mainly performed by a cleaning step.

In other words, on the latent image carrier, the film-forming substance that moves along with the insulating toner and remains without being transferred is broken or stretched by mechanical action in the cleaning process. A water-repellent film is formed on the latent image holding member.

The content of the film-forming substance in the toner is 10%.
It is preferably 0.01 to 1.0 part by weight based on 0 part by weight.

If the amount is less than 0.01 part by weight, the effect of addition is not recognized, and a problem concerning transfer occurs. On the other hand, if the amount exceeds 1.0 part by weight, a film is formed on other portions such as the developer carrying member, and a problem concerning developability occurs. Particularly preferably, it is 0.03 to 1.0 part by weight.

In the present invention, as the binder resin of the toner, for example,
Styrene such as polystyrene, poly-p-chlorostyrene, polyvinyltoluene, and a homopolymer of a substituted product thereof;
Styrene-p-chlorostyrene copolymer, styrene-propylene copolymer, styrene-vinyltoluene copolymer, styrene-vinylnaphthalene copolymer, styrene-
Methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-butyl acrylate copolymer, styrene-octyl acrylate copolymer, styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate Copolymer, styrene-butyl methacrylate copolymer, styrene-α-chloromethyl methacrylate copolymer, styrene-acrylonitrile copolymer, styrene-vinyl metal ether copolymer, styrene-vinyl ethyl ether copolymer Copolymer, styrene-vinyl methyl ketone copolymer, styrene-butazineene copolymer, styrene-isoprene copolymer, styrene-acrylonitrile-
Styrene copolymers such as indene copolymers; polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene, silicone resin, polyester, epoxy resin, polyvinyl butyral, rosin, modified rosin, terpene resin, phenol resin, xylene resin, fat Aromatic or alicyclic hydrocarbon resins, aromatic petroleum resins, chlorinated paraffins, paraffin waxes and the like are used alone or in combination.

In the present invention, among these resins, styrene-acrylic copolymers are preferably used. In particular, styrene-n-butyl acrylate (St-nBA) copolymer, styrene-n-butyl methacrylate (St-nBA) -NBMA) copolymer, styrene-n-butyl acrylate-2-ethylhexyl methacrylate (St-nBA-2EHMA) copolymer and the like are preferably used.

Further, as a coloring material that can be added to the toner according to the present invention, conventionally known carbon black, copper phthalocyanine, iron black and the like can be used.

The toner according to the present invention may contain a magnetic material. As the contained magnetic fine particles, a substance that is magnetized when placed in a magnetic field is used, and powders of ferromagnetic metals such as iron, cobalt, and nickel or alloys such as magnetite, γ-Fe ₂ O ₃ , and ferrite are used. Compounds can be used.

These magnetic fine particles preferably have a BET specific surface area of ^{2 to 20} m ² / g, particularly 2.5 to 12 m ² / g, and a Mohs hardness of 5 to 7 by nitrogen adsorption. The content of the magnetic powder is preferably 10 to 70% by weight based on the toner amount.

The toner of the present invention may contain a charge control agent, if necessary, such as a metal complex salt of a monoazo dye; a negative charge control agent such as a metal complex salt of salicylic acid, alkylsalicylic acid, cyalkylsalicylic acid or naphthoic acid. Used.

The toner according to the present invention is generally manufactured as follows.

The binder resin and, if necessary, the magnetic substance and the coloring agent as a colorant are uniformly dispersed by a mixer such as a Henschel mixer.

The dispersion obtained as described above is melt-kneaded with a kneader, extruder, roll mill or the like.

The kneaded material is roughly pulverized by a cutter mill, a hammer mill or the like, and then finely pulverized by a jet mill or the like.

The finely pulverized product is adjusted to a particle size distribution using a zigzag classifier or the like, and is classified into a toner.

In addition, as a method for producing the toner, a polymerization method, a capsule method, or the like can be used. The outline of these production methods is described below.

(Polymerization Toner) A polymerizable monomer, and if necessary, a polymerization initiator, a colorant, and the like are granulated in an aqueous dispersion medium.

The granulated monomer composition particles are classified into an appropriate particle size.

The monomer composition particles having a specified internal particle diameter obtained by the classification are polymerized.

After an appropriate treatment to remove the dispersant, the polymerization product obtained above is filtered, washed with water and dried to obtain a toner.

(Capsule Toner) A resin and, if necessary, magnetic powder and the like are kneaded with a kneader or the like to obtain a toner core material in a molten state.

The toner core is placed in water and stirred vigorously to produce a fine particle core.

The core material fine particles are placed in a shell material solution, and a poor solvent is dropped with stirring, and the core material is encapsulated by covering the core material surface with the shell material.

After the capsule obtained above is dried, a toner is obtained.

The present invention is particularly effective for toner produced by a process of pulverizing by wind power.

This is considered to be because the toner produced by pulverization by wind force has more irregularities and lower sphericity than other methods, so the contact area with the drum increases, and the adhesive force increases. .

Insulating toner used in the image forming method of the present invention,
Further, it is preferable to have a hydrophobic silica fine powder.

When the insulative toner is used as a negatively chargeable magnetic one-component developer, it has a negatively chargeable hydrophobic silica fine powder and a positively chargeable resin fine particle treated with a silane coupling agent and / or silicone oil, and further has a negative charge. It is preferable to have 0.01 to 3 parts by weight of the silica and 0.02 to 3 parts by weight of the fine resin particles per 100 parts by weight of the magnetic toner particles.

The silica fine powder used in the present invention is a so-called dry silica or fumed silica produced by a vapor phase oxidation of a silicon halide, and the surface thereof is treated with a silane coupling agent and / or silicone oil. It is a silica fine powder obtained.

Preferred silane coupling agents include hexamethyldisilazane (HMDS). Preferred silicone oils have a viscosity of about 50 at 25 ° C.
Those having a viscosity of up to 1,000 centistokes are used. For example, dimethyl silicone oil, methylphenyl silicone oil, α-methylstyrene modified silicone oil, chlorophenyl silicone oil, fluorine modified silicone oil and the like are preferable. For the purposes of the present invention, -OH groups,-
COO group, silicone oils containing a large amount of -NH ₂ group or the like is not preferable.

[Example] Example 1 The mixture is melted and kneaded in a twin-screw ruder heated to 160 ° C. and then cooled, and the cooled material is coarsely pulverized with a hammer mill (mechanical pulverizer) through a mesh having an opening diameter of 2 mm to about a pass, and then jet milled. (Wind crusher), 10μ
Finely ground to a degree. The finely pulverized product was classified with a DS classifier (wind classifier) so that the volume average particle size measured by a Coulter counter was 11.5 μm, to prepare negatively-charged insulating magnetic toner particles.

The insulating magnetic toner particles had a triboelectric charge amount of −13 μc / g as measured by a blow-off method with respect to the iron powder carrier.

Zinc stearate (SZ-2000 manufactured by Sakai Chemical Co.) was used as a film-forming material with respect to 100 parts by weight of the negatively-chargeable magnetic toner particles.
0.1 parts by weight, treated with HMDS, hydrophobic silica fine powder 0.4
Parts by weight were added to the respective toner particles and mixed with a Henschel mixer to obtain an insulating toner.

Using the obtained insulating toner as a one-component developer, a commercially available copying machine FC-5 (manufactured by Canon Inc .; OPC laminated negatively charged photoreceptor, drum diameter φ30) was used.
A transfer device as shown in the figure was incorporated. The conditions of the transfer roller are as follows: transfer roller expression rubber hardness 27 °, transfer current 1
μA and a contact pressure of 50 [g / cm].

The primary charging is set to -700 V, a gap is set between the photosensitive drum and the developer layer on the developing drum (including the magnet) in a non-contact manner, and an AC bias (f = 1,800 Hz, V _pp = 1,600 V) and a DC bias (V _DC (= −300 V) to the developing drum. The toner-fixed image formed and fixed by the heating and pressing roller was evaluated as follows. The results are shown in Table 1.

(1) Image density: ordinary copy paper (75 g / m ² ) 1,00
The evaluation was performed by maintaining the image density when passing 0 sheets.

○ (good): 1.35 or more, Δ (acceptable): 1.0 to 1.34, ×: (impossible): 1.0 or less (2) Transfer condition: Strict transfer conditions, 120 g / m ² thick paper passed, and transfer missing Was evaluated.

：: good, 実 用: practical, ×: impractical (3) Paper transport state: 1,000 sheets of 50 g / m ² thin paper were passed, and the occurrence of illicit transport such as skew was evaluated.

: 1: Within 1 time / 1,000 sheets, Δ: 2 to 4 times / 1,000 sheets, ×: 5 or more sheets / 1,000 sheets (4) Image quality: The toner was scattered and the roughness was visually evaluated.

：: good, Δ: practical, ×: not practical Example 2 Image formation was performed in the same manner as in Example 1 except that the contact pressure was 20 [g / cm]. The results are shown in Table 1.

Example 3 An image was formed in the same manner as in Example 1 except that the contact pressure was 5 [g / cm]. The results are shown in Table 1.

Example 4 An image was formed in the same manner as in Example 1 except that 0.1 weight part of aluminum stearate (SA-2000, manufactured by Sakai Chemical Co.) was used as a film forming material. The results are shown in Table 1.

Example 5 An image was formed in the same manner as in Example 1 except that the material for forming a film was changed to 0.1 part by weight of magnesium laurate. The results are shown in Table 1.

Example 6 An image was formed in the same manner as in Example 1, except that calcium myristate was used in an amount of 0.1 part by weight as a film-forming substance. The results are shown in Table 1.

Example 7 Silicone oil (manufactured by Shin-Etsu Chemical Co., Ltd.)
KF-96) An image was formed in the same manner as in Example 1 except that the amount was 0.05 part by weight. The results are shown in Table 1.

Example 8 An image was formed in the same manner as in Example 1 except that the amount of the film-forming substance was changed to 0.02 parts by weight. The results are shown in Table 1.

Example 9 An image was formed in the same manner as in Example 1 except that the amount of the film-forming substance was changed to 1.0 part by weight. The results are shown in Table 1.

Comparative Example 1 An image was formed in the same manner as in Example 1 except that the contact pressure was 2 g / cm. The results are shown in Table 1.

Comparative Example 2 An image was formed in the same manner as in Example 1 except that the amount of the film-forming substance was changed to 1.5 parts by weight. The results are shown in Table 1.

Comparative Example 3 An image was formed in the same manner as in Example 1 except that the film-forming substance was not added. The results are shown in Table 1.

[Effect of the Invention] In the present invention, since the developer is improved under an appropriate contact pressure in the transfer step, a high-quality image can be obtained without occurrence of omission during transfer.

[Brief description of the drawings]

FIG. 1 shows an example of missing during transfer, and FIGS. 2 and 3 are schematic side views of main parts of the image forming apparatus.

Claims (11)

(57) [Claims] A developing step of developing the electrostatic latent image on the latent image carrier with an insulating toner to form a toner image; and a transferring step of electrostatically transferring the toner image to a transfer material using a transfer device. In the image forming method, a transfer device to which a transfer bias is applied is brought into contact with the latent image carrier at a linear pressure of 3 g / cm or more, and the toner image is electrostatically transferred to the transfer material. Insulating toner having 0.01 to 1.0 parts by weight, based on 100 parts by weight of toner particles, of a substance capable of forming a smooth surface having a contact angle with water of 80 ° or more on the surface of the latent image carrier as a neutral toner. An image forming method characterized by using: 2. The image forming method according to claim 1, wherein the transfer device is a transfer roller or a transfer belt. 3. The image forming method according to claim 1, wherein the transfer device has a conductive transfer member having a volume resistance of 10 ⁶ to 10 ¹⁰ Ωcm. 4. The insulating toner according to claim 1, further comprising a substance capable of forming a lubricated surface having a contact angle with water of 85 ° or more.
The image forming method according to any one of the above. 5. A substance capable of forming a lubricated surface having a contact angle with water of 80 ° or more on the surface of the latent image carrier is represented by the following formula: The image forming method according to claim 1, which is a silicone oil represented by the formula: 6. The image forming method according to claim 5, wherein the silicone oil is a dimethyl silicone oil, an alkyl-modified silicone oil, an α-methylstyrene-modified silicone oil, a chlorophenyl silicone oil or a fluorine-modified silicone oil. 7. A substance capable of forming a lubricated surface having a contact angle with water of 80 ° or more on the surface of the latent image carrier is represented by the following formula: The image forming method according to claim 1, which is a fatty acid metal soap represented by the formula: 8. The image forming method according to claim 7, wherein said fatty acid metal soap is zinc stearate, zinc laurate, zinc myristate, calcium stearate or aluminum stearate. 9. The latent image carrier has a radius of curvature of 25 at a transfer portion.
The image forming method according to claim 1, wherein the thickness is equal to or less than mm. 10. The image forming method according to claim 9, wherein said latent image carrier has a drum shape having a diameter of 50 mm or less. 11. The image forming method according to claim 1, wherein at least the surface of the latent image carrier is formed of an organic compound.