JPH04274443A - Developer for electrostatic charge image and image forming method - Google Patents

Abstract

PURPOSE:To obtain an image faithful to a latent image without depending on the condition of a transfer material and, especially, to obtain the high quality image without the omission of transfer by making developer contain magnetic toner containing binding resin and magnetic powder, and specified resin particulates at a specified rate. CONSTITUTION:A conductive transfer roller 2 which abuts on an electrostatic charge image holding body(photosensitive body) 1 is constituted of a core bar 2a and a conductive elastic layer 2b, and bias voltage is impressed on the core bar 2a by a constant voltage power source 3. The electrostatic charge image on the photosensitive body 1 is developed with the developer for an electrostatic charge image so as to form a developed image. The developed image is electrostatically transferred to the surface of the transfer material by allowing the roller 2 to abut on the surface of the photosensitive body 1 through the transfer material. In such a case, the developer containing at least 100 pts.wt. magnetic toner containing the binding resin and the magnetic powder and 0.01-1.0 pts.wt. resin particulates whose surfaces are treated by fatty acid or the derivative of fatty acid and whose average grain size is 0.03-2.0mum is used as the developer for the electrostatic charge image.

Description

[Detailed description of the invention]

0001

[Industrial Field of Application] The present invention is applicable to electrophotography, electrostatic recording,
The present invention relates to an electrostatic image developer and an image forming method for visualizing an electrostatic image in an image forming method such as electrostatic printing.

More specifically, the present invention relates to an electrostatic image developer and an image forming method used in electrophotography, which includes a transfer step in which an electrostatic image carrier and a transfer means are brought into contact with each other.

0003

2. Description of the Related Art In an image forming apparatus that includes a step of electrostatically transferring a transferable toner image formed on the surface of an electrostatic image carrier to a sheet-like transfer material mainly made of paper, a rotating cylindrical, An electrostatic image carrier running in an endless manner, such as an endless belt, is used, and a transfer device to which a bias is applied is pressed against it, and the transfer material is passed between the two to transfer the toner image on the electrostatic image carrier side. An apparatus configured to transfer images onto a transfer material, for example, an apparatus as disclosed in Japanese Patent Application Laid-Open No. 59-46664, has already been proposed.

Compared to transfer means using corona discharge, which has been widely used in the past, such a device is capable of holding an image on a transfer material by adjusting the pressing force of a transfer roller against an electrostatic image carrier. Since the adsorption area to the body can be expanded and the transfer material is actively pressed and supported at the transfer site, there is no risk of transfer misalignment due to poor synchronization by the transfer material conveyance means or loops or curls in the transfer material. However, it is easy to meet the demands for shortening the transfer material conveyance path and reducing the diameter of the image holding body due to the miniaturization of this type of image forming apparatus in recent years. Since the transfer current is supplied from the contact portion, it is necessary to apply a certain amount of pressure to the transfer device.

On the other hand, when such contact pressure is applied, pressure is also applied to the toner image on the electrostatic image carrier, causing aggregation. Furthermore, if the surface of the electrostatic image carrier is made of resin, toner aggregates will adhere to the image carrier, inhibiting transfer to the transfer material, and in extreme cases, Transfer of the strong portions is not performed, resulting in image loss.

[0006] This phenomenon becomes particularly noticeable in the line portion of 0.1 to 2 mm. That is, edge development occurs in the line portions, where a large amount of toner is deposited, aggregation is likely to occur due to pressure, and defects are likely to occur due to transfer. At this time, the output image is a copy with an image formed only on the outline, which is called "transfer void." FIG. 1 shows an example of a copy. FIG. 1(a) is an image transferred by corona transfer, and FIG. 1(b) is a hollow image transferred by a transfer roller.

[0007] Such "transfer voids" are 100 g/cm
This problem is particularly noticeable when using thick paper with a thickness of 2 or more, OHP films with high smoothness, and when copying the second side. Since the thickness of the transfer material is thick for cardboard, film, etc., it is thought that the effect on the transfer electric field is small and that the pressure is strong and hollows are likely to occur.

[0008] Furthermore, when copying the second side, when it passes through the fixing device during image formation on the first side, a release agent contained in it to prevent offset is attached to the transfer material from the fixing device, and when the second side is transferred. It is thought that this prevents the toner from adhering to the transfer material, making it more likely that voids will occur.

As described above, in the case of a transfer device using an abutting member, although there are many advantages such as miniaturization and low power consumption, the conditions for the transfer material are narrower.

[0010] In recent years, as image forming apparatuses such as electrophotographic copying machines have become widespread, their uses have also expanded in a wide variety of ways.
The requirements for image quality are also becoming stricter. When copying images such as general documents and books, it is necessary to reproduce them extremely finely and faithfully without any interruptions, even down to the smallest characters, and the problem of "transfer blanks" must be improved. It won't happen.

[0011]

[Problems to be Solved by the Invention] In view of the problems of the prior art described above, the objects of the present invention are as follows: (1). In an image forming method using pressure transfer such as a contact transfer method, an image forming method including an electrostatic image developer and a transfer step that can obtain a high-quality image that is faithful to a latent image regardless of the conditions of the transfer material. ■. To provide an electrostatic image developer and an image forming method in which there is no phenomenon such as "transfer voids" or the phenomenon is suppressed; 2. An object of the present invention is to provide an electrostatic image developer and an image forming method that provide high-quality images without "transfer voids" even when using various transfer materials such as thick transfer paper.

0012

[Means and operations for solving the problem] The above object is to develop an electrostatically charged image on a photoreceptor (electrostatically charged A toner 1 in which the image carrier) and the transfer means are in contact with each other, and the developer contains at least a binder resin and magnetic powder.
00 parts by weight and 0.01 to 1.0 parts by weight of resin fine particles whose surfaces are treated with a fatty acid or a fatty acid derivative and have an average particle size of 0.03 to 2.0 μm, and an electrostatic image developer containing the same. It has been found that this can be achieved by an image forming method using.

First, the transfer device used in the present invention will be described. Examples include a transfer roller as shown in FIG. 2 or a transfer belt as shown in FIG. 3. FIG. 2 is a schematic side view of the main parts of a typical image forming apparatus of this type, and the illustrated apparatus has a cylindrical electrostatic image carrier ( (hereinafter referred to as photoreceptor)
1. A conductive transfer roller 2 is disposed in contact with the roller.

[0014] Around the photoreceptor 1, there is a primary charger for uniformly charging the surface of the photoreceptor 1, and a light image such as an image-modulated laser beam or light reflected from a document is projected onto the charging surface. , an exposure section that attenuates the potential of the area to form an electrostatic latent image, a developer, a cleaner that removes residual toner that remains on the surface of the photoreceptor even after transfer, and other members necessary for image formation are provided. Needless to say, all of these have been omitted.

The transfer roller 2 is composed of a metal core 2a and a conductive elastic layer 2b, and the conductive elastic layer 2b is made of urethane, EPDM, or the like in which a conductive material such as carbon is dispersed, and has a volume resistivity of approximately 106 to 1010 Ω·cm. It is composed of an elastic body. A bias is applied to the core metal 2a by a constant voltage power supply 3. The device shown in FIG. 3 is based on a transfer belt. The transfer belt 6 is supported and driven by a conductive roller 7.

The present invention is particularly effective for image forming apparatuses in which the surface of the electrostatic image carrier 1 is made of an organic compound. In other words, when an organic compound forms the surface layer, it has good adhesion with the binder resin contained in the toner, and especially when the same material is used, a chemical bond occurs at the contact point, resulting in poor transferability. This is because it decreases.

The surface material of the electrostatic image carrier used in the present invention includes silicone resin, vinylidene chloride, ethylene-vinyl chloride, styrene-acrylonitrile, styrene-methyl methacrylate, styrene, polyethylene terephthalate, polycarbonate, etc. Copolymerization, blending, etc. of other monomers or exemplified resins can also be used.

Further, in the present invention, the diameter of the photoreceptor 1 is 50 m.
This is particularly effective for image forming apparatuses with a size of m or less. That is, in the case of a small-diameter photoreceptor, even if the linear pressure is the same, the curvature is large, so pressure concentration tends to occur at the contact portion. It is thought that the same phenomenon occurs with belt photoreceptors, and it is also effective for image forming apparatuses in which the curvature at the transfer section is 25 mm or less.

The electrostatic image developer of the present invention is capable of faithfully reproducing even the fine lines of a latent image formed on a photoreceptor, and is capable of reproducing dot latent images such as halftone dots and digital dots. It provides an image with excellent gradation and resolution.

Photoreceptor 1 and transfer means 2, 6 in the present invention
It is preferable that the contact pressure with the linear pressure is 3 g/cm or more. Note that the linear pressure (g/cm) is calculated using the following formula.

(Linear pressure: g/cm) = (Total pressure applied to the transfer member)/(Length of contact) If the contact pressure is less than 3 g/cm, the transfer member may shake,
Transfer defects may occur due to insufficient transfer current, which is undesirable. Particularly preferably, it is 20 g/cm or more.

The reason why such an effect is obtained in the developer according to the present invention is not necessarily clear, but it is presumed as follows. That is, in the developer according to the present invention, the average particle size of the surface treated with a fatty acid or a fatty acid derivative is 0.03 to 2.0 μm (more preferably 0.0 μm).
One of the characteristics is that it contains 0.01 to 1.0 parts by weight (more preferably 0.03 to 0.5 parts by weight) of fine resin particles having a diameter of 5 to 1.0 μm.

According to this, in the transfer process in which the electrostatic image carrier 1 used in the present invention and the transfer means are in contact with each other,
The fine resin particles contained in the developer according to the present invention adhere to the toner particles in the developer and act like spacer particles to prevent the toner particles from coming into close contact with the electrostatic image carrier. By treating with fatty acids or fatty acid derivatives, it becomes possible to constantly supply a small amount of fatty acids or fatty acid derivatives onto the electrostatic charge image carrier, improving the releasability between toner particles and the electrostatic charge image carrier, and improving the releasability of toner particles and the electrostatic charge image carrier. It is believed that even in contact transfer, it becomes possible to transfer the toner developed on the electrostatic image carrier to the transfer material well.

In the present invention, the resin fine particles have a particle size of 0.
If the particle size is smaller than 0.03 μm, the function as a spacer particle between the electrostatic image carrier and the toner becomes extremely weak.
No effect on "transfer blanks" was observed. On the other hand, if the particle size is larger than 2.0 μm, it becomes difficult for resin particles to exist between the electrostatic image carrier and the toner, and the effect against "transfer voids" becomes weak.

Regarding the amount of resin fine particles added, if it is less than 0.01 part by weight per 100 parts by weight of toner particles, the effect on "transfer voids" will be small, and the amount added will be 1.0 parts by weight. If the amount exceeds 1, the amount of charge on the developer becomes unstable, and so-called "scattering" occurs, in which toner particles are scattered on the image.

[0026] The particle size of the resin fine particles in the present invention can be measured by various methods, but in the present invention, it was measured using an electron micrograph. That is, electron microscope S-8
00 (Hitachi) at a magnification of 10,000 to 20,000 times, and randomly selected 10
0 to 200 particles were extracted, and the diameter of each was measured using a device such as a caliper, and the averaged value was defined as the particle size of the resin fine particles.

The resin fine particles used in the present invention are produced by a soap-free polymerization method, an emulsion polymerization method, or the like. Preferably, fine resin particles obtained by polymerizing monomers such as styrene, acrylic acid, methyl methacrylate, butyl acrylate, and 2-ethylhexyl acrylate alone or in combination of two or more exhibit good effects. In addition, it may be crosslinked with divinylbenzene, etc., and the surface may be made of metal or
A preferred embodiment of the present invention is that the material is treated with metal oxides, pigments, dyes, surfactants, etc.

The fatty acids or fatty acid derivatives used in the present invention include, but are not limited to, fatty acids or derivatives thereof such as lauric acid, palmitic acid, stearic acid, and oleic acid.

[0029] Furthermore, known techniques can be used for the treatment of fatty acids and fatty acid derivatives. For example, fine resin particles and fatty acids and fatty acid derivatives may be directly mixed using a mixer such as a Henschel mixer, or fine resin particles may be directly mixed with fatty acids and fatty acid derivatives using a mixer such as a Henschel mixer. A method of spraying liquid fatty acids may also be used.

The binder resin of the toner according to the present invention is as follows:
Monopolymers of styrene and its substituted products such as polystyrene and polyvinyltoluene, styrene-propylene copolymers, styrene-vinyltoluene copolymers, styrene-vinylnaphthalene copolymers, styrene-methyl acrylate copolymers, styrene- Ethyl acrylate copolymer, styrene-butyl acrylate copolymer, styrene-octyl acrylate copolymer, styrene-dimethylaminoethyl acrylate copolymer, styrene-methyl methacrylate copolymer, styrene-methacrylate ethyl ester copolymer, styrene-butyl methacrylate copolymer, styrene-dimethylaminoethyl methacrylate copolymer, styrene-
Vinyl methyl ether copolymer, styrene-vinyl ethyl ether copolymer, styrene-vinyl methyl ketone copolymer, styrene-butadiene copolymer, styrene-isoprene copolymer, styrene-maleic acid copolymer, styrene-maleic copolymer Styrenic copolymers such as acid ester copolymers, polymethyl methacrylate, polybutyl methacrylate, polyvinyl acetate, polyethylene, polypropylene, polyvinyl butyral, polyacrylic acid resins,
Rosin, modified rosin, terpene resin, phenolic resin,
Aliphatic or alicyclic hydrocarbon resin, aromatic petroleum resin,
Paraffin wax, carnauba wax, etc. can be used alone or in combination.

As the magnetic fine particles contained in the magnetic toner according to the present invention, a substance that is magnetized by being placed in a magnetic field is used, and powders of ferromagnetic metals such as iron, cobalt, and nickel, or magnetite and γ are used. -Alloys and compounds such as -Fe2O3 and ferrite can be used.

[0032] These magnetic fine particles preferably have a BET specific surface area of 1 to 20 m2/g, particularly 2
．． Preferably, the magnetic powder has a Mohs hardness of 5 to 12 m2/g, and more preferably a Mohs hardness of 5 to 7. The content of this magnetic powder is preferably 10 to 70% by weight based on the weight of the toner.

The toner of the present invention preferably has a negative charge, and may contain a charge control agent if necessary, such as a metal complex salt of a monoazo dye, salicylic acid, alkylsalicylic acid,
A negative charge control agent such as a metal complex salt of dialkyl salicylic acid or naphthoic acid is used.

Further, as coloring materials that can be further added to the toner according to the present invention, conventionally known carbon black,
Copper phthalocyanine etc. can be used.

[0035] Further, it is more preferable to use the developer of the present invention with the addition of silicic acid fine powder, and the silicic acid fine powder is used in the so-called dry method or fume produced by vapor phase oxidation of a silicon halide compound. Both dry silica called dosilica and so-called wet silica manufactured from water glass etc. can be used, but there are few silanol groups on the surface and inside the silica fine powder, and Na2O, S
Dry silica free of production residues such as O32- is preferred.

[0036] In addition, in the case of dry silica, it is also possible to obtain a composite fine powder of silica and other metal oxides by using other metal halide compounds such as aluminum chloride or titanium chloride together with silicon halide compounds in the manufacturing process. and includes them as well. The particle size is desirably within the range of 0.001 to 2 μm as an average primary particle size, particularly preferably 0.002 to 0.0 μm.
．． It is preferable to use silica fine powder within the range of 2 μm. Further, for the hydrophobization treatment, a conventionally known hydrophobization treatment agent such as silicone oil and a method are used.

The developer of the present invention may further contain other additives, such as a fixing aid (such as low molecular weight polyethylene), or a metal such as tin oxide as a conductivity imparting agent, as long as it does not have a substantial adverse effect. Oxides and the like may also be added.

[0038] In manufacturing the toner according to the present invention,
It can be obtained by thoroughly kneading the constituent materials using a thermal kneader such as a hot roll, kneader, or extruder, followed by mechanical pulverization and classification, or by dispersing the materials in a binder resin solution and then spray drying. Alternatively, various methods can be applied, such as a polymerization method and a toner production method in which a toner is obtained by mixing a predetermined material with a monomer that constitutes a binder resin to form an emulsified suspension and then polymerizing it.

[0039]

[Examples] The present invention will be explained in detail below using examples, but these are not intended to limit the invention in any way. Note that all parts in the following formulations are parts by weight.

(Production Example 1) Styrene-n-butyl acrylate copolymer
…100 parts (Copolymerization weight ratio 8:2 Mw=260,000) Magnetic fine powder (BET value 8.4 m2/g) …
60 parts Negative charge control agent (monoazo dye-based chromium complex) ...0.8 parts Low molecular weight polypropylene (Mw=6000)
… 3 parts of the above mixture was heated to 140°C.
Melt-knead the mixture with an axial extruder, then coarsely crush the cooled mixture with a hammer mill, finely crush the coarsely crushed product with a jet mill, and air-classify the resulting finely crushed powder to obtain a weight average particle size (D4). Negatively chargeable toner particles (I) of 11.5 μm were obtained.

(Production Example 2) Styrene-2-ethylhexyl acrylate
-maleic acid n-butyl half ester copolymer
...100 parts (copolymerization ratio 7:2:1, Mw
= 220,000) Magnetic fine powder (BET value 7.6m2/g
)...100 parts Negative charge control agent (salicylic acid-based chromium complex)
... 1 part low molecular weight polypropylene (
Mw=6000)...
3 parts A negatively charged magnetic toner (II) having a weight average particle diameter (D4) of 6.5 μm was obtained using the above components in the same manner as in Production Example 1.

(Production Example 3) Styrene-n-butyl acrylate copolymer
...100 parts (copolymerization weight ratio 7.5:2.5, Mw=290,000) Magnetic fine powder (B
ET value 8.2m2/g)
... 60 parts Negative charge control agent (ditertiary butyl chromium complex) ... 2 parts Low molecular weight polypropylene (Mw = 6000)
...4 parts The above components were used in the same manner as in Production Example 1 to obtain a positively charged magnetic toner (III) having a weight average particle diameter (D4) of 11.0 μm.

(Example 1) Magnetic toner of Production Example 1 (negatively charged magnetic toner (I)
)...100 parts Hydrophobic silica fine powder (BET200m2/g)...
0.5 part Resin fine particles surface-treated with isopalmitic acid...0.05 part
(Particle size: 0.63 μm) The above mixture was mixed in a Henschel mixer to prepare a developer. Using the developer, an image forming apparatus (Canon LBP-8II modified to a contact transfer method as shown in FIG. 2) was heated at 30°C, 6
3000 images were printed continuously under a 5RH environment. still,
The transfer roller condition is that the surface rubber hardness of the transfer roller is 26.
°, a transfer current of 2.4 μA, and a contact pressure of 60 g/cm.

As a result, even after the 3000th printing, a good image was obtained without any "transfer voids" as shown in FIG. 1(a) and without any scattering on the image.

(Example 2) Magnetic toner of Production Example 2 (negatively charged magnetic toner (II)
)) ...100 parts Hydrophobic silica fine powder (BET250m2/g)
…1.2 parts Resin fine particles surface-treated with stearic acid …
0.8 parts (particle size: 0.88 μm) of the above mixture was mixed in a Henschel mixer to prepare a developer. Using this developer, the copy speed of the LBP8II modified machine was set to 4 sheets/min, and the transfer current of the transfer roller was set to 1.2 μA.
Image quality was evaluated in the same manner as in Example 1, except that the contact pressure was 38 g/cm.

As a result, even after the 3000th printing, a good image was obtained without any "transfer voids" as shown in FIG. 1(a) and without any scattering on the image.

(Example 3) Magnetic toner of Production Example 3 (positively charged magnetic toner (II)
I)) ...100 parts Hydrophobic silica fine powder (BET200m2/g)
...0.8 part Resin fine particles surface-treated with palmitic acid methyl ester ...0.1 part
(Particle size: 0.45 μm) The above mixture was mixed in a Henschel mixer to prepare a developer. Using the developer,
Image quality was evaluated in the same manner as in Example 1, except that the contact pressure of the transfer roller was 42 g/cm.

As a result, even after the 3000th printing, a good image without any "transfer voids" as shown in FIG. 1(a) was obtained.

(Example 4) Magnetic toner of Production Example 1 (negatively charged magnetic toner (I)
)...100 parts Hydrophobic silica fine powder (BET250m2/g)
...0.4 part Resin fine particles surface-treated with oleic acid ...
0.03 parts (particle size: 0.05 μm) of the above mixture was mixed in a Henschel mixer to prepare a developer. Using this developer, the contact pressure of the transfer roller was 53 g/c.
Image quality was evaluated in the same manner as in Example 1, except that m was used.

As a result, even after the 3000th printing, a good image with no "transfer voids" as shown in FIG. 1(a) and no scattering was obtained.

(Comparative Example 1) Magnetic toner of Production Example 1 (negatively charged magnetic toner (I)
)...100 parts Hydrophobic silica fine powder (BET80
m2/g)...0.2 part The above mixture was mixed in a Henschel mixer to prepare a developer. Images were evaluated in the same manner as in Example 1, except that the developer was used and the contact pressure of the transfer roller was 60 g/cm.

As a result, "transfer voids" as shown in FIG. 1(b) were observed, and the result was a defect that could be judged to be practically unacceptable.

(Comparative Example 2) Magnetic toner of Production Example 3 (positively charged magnetic toner (II)
I))...100 parts Hydrophobic silica fine powder (BET20
0m2/g) ...0.5 part Resin fine particles (particle size 2.3μm)
...0.4 part The above mixture was mixed in a Henschel mixer to prepare a developer. Images were evaluated in the same manner as in Example 1, except that the developer was used and the contact pressure of the transfer roller was 60 g/cm.

As a result, "transfer voids" as shown in FIG. 1(b) were observed, and the result was a defect that could be judged to be practically unacceptable.

[0055]

As explained above, according to the electrostatic developer and image forming method of the present invention, an image faithful to the latent image can be obtained regardless of the conditions of the transfer material, and in particular, "transfer voids" can be prevented. No high quality images can be obtained.

[Brief explanation of the drawing]

FIG. 1 is an example of a copy according to the present invention, and FIG. 1(a)
is an image obtained by corona transfer, and FIG. 1(b) is an image obtained by a transfer roller.

FIG. 2 shows an example in which a roller is used as the transfer means.

FIG. 3 shows an example in which a belt is used as the transfer means.

[Explanation of symbols]

1 Electrostatic image carrier (photoreceptor) 2 Transfer roller 2a Core metal 2b Elastic layer 3 Power supply 6 Transfer belt 7 Conductive roller

Claims (2)

[Claims] Claim 1: A magnetic toner containing at least 100 parts by weight of a binder resin and magnetic powder, the surface of which is treated with a fatty acid or a fatty acid derivative, and has an average particle size of 0.03 to 2.0 μm.
An electrostatic image developer characterized by containing 0.01 to 1.0 parts by weight of fine resin particles. 2. Developing the electrostatic image on the electrostatic image carrier with an electrostatic image developer to form a developed image, and bringing a transfer means into contact with the surface of the electrostatic image carrier via a transfer material. In the image forming method comprising the step of electrostatically transferring the developed image onto the surface of a transfer material, as the electrostatic image developer, claim 1
An image forming method characterized by using the electrostatic image developer described above.