JPH0677160B2 - Black insulating paper for electrophotography and electrophotographic copying method using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a black insulating paper for electrophotography which can obtain a color image, especially a reverse image on black paper in an electrophotographic copying process, and electrophotographic copying using the same. Regarding the method.

(Prior Art) In the electrophotographic copying method, in addition to a normal positive image copying system for forming a positive electrostatic latent image from a positive original to obtain a positive copy, a negative original such as microfilm or a laser beam or There is a reverse image copying system in which a negative electrostatic latent image is formed by a light image of a light emitting diode array and then inverted to obtain a positive copy.

A normal copying machine is provided with only a normal image copying system, and it is premised that a white positive original in the background portion is obtained from a white positive original in the background portion. Therefore, it is not possible to obtain a white positive image in the background from a negative black image in the background. However, slides and some foreign pamphlets or catalogs have manuscripts with negative images, which are difficult to read if they are copied as normal images. Therefore, it is desired that these originals be used as positive images by reverse image copying.

Under such circumstances, a copying machine having both a normal image copying system and a reverse image copying system has been proposed. This copying machine includes, for example, a copying machine including a photoconductor that can be charged in both positive and negative polarities and a charging device. However,
The number of photoconductors that can be charged in both polarities is limited, and their sensitivity and durability are limited. There is a great difference in the sensitivity of the photoconductor and other electrophotographic characteristics between the positive charging and the negative charging, and it becomes difficult to adjust the density and image quality of the positive image and the reverse image to be constant. A copying machine using positive and negative polar toners is also known. However, this copying machine requires two types of toners, and also requires electrical control such as switching the application of bias voltage to the developing section. As described above, a copying machine having both a normal image copying system and a reverse image copying system requires a complicated mechanism and control.

In order to solve such a drawback, a normal toner image copying machine is used to form a desired color area on a transfer paper with a colored toner (for example, black toner), and then the colored toner is formed on this area. Attempts have been made to copy images with toners of different colors (for example, black toner and white toner). However, this method requires copying twice, which makes the operation complicated. Wrinkles and curls are generated in the obtained copied image by the two copies.

As a simple method for obtaining a reverse image with a normal copying machine, a method of copying an image using white toner on black paper can be considered. However, in general, black paper contains carbon black for the purpose of improving color development and preventing static electricity. Therefore, this black paper is conductive, and the toner image cannot be transferred by a copying machine for electrophotography.

(Problems to be Solved by the Invention) The present invention is intended to solve the above-mentioned conventional problems, and an object of the present invention is to provide a black electrophotographic black capable of transferring an image to an electrophotographic copying machine. An object is to provide an insulating paper and an electrophotographic copying method using the same. Another object of the present invention is to provide a black insulating paper for electrophotography, which can provide a reverse image by an ordinary copying machine, and an electrophotographic copying method using the same.

(Means for Solving the Problems) In the present invention, a black insulating paper is prepared in place of the conventional black paper which is electrically conductive, and the black insulating paper is used to make a copy using a normal positive image copying machine. This was completed based on the inventor's knowledge that a clear inverted image can be easily obtained.

The black insulating paper for electrophotography of the present invention has a surface specific resistance of 10
^{It is 9} Ω or more and the volume resistivity value is 5 × 10 ⁹ Ω · cm or more, which achieves the above object.

The electrophotographic copying method of the present invention is an electrophotographic copying method using the black insulating paper, which includes copying an inverted image on the black insulating paper with white toner, thereby achieving the above object. To be done.

In the electrophotographic copying process, the electric resistance value of the transfer paper influences the transfer efficiency and the image quality of the toner image or the electrostatic latent image. If the electrical resistance of the transfer paper is not high enough, the charge from the transfer corotron or bias roll is grounded through the paper, and the electric field necessary to cause transfer is not formed. Therefore, the transfer efficiency is reduced. Further, if the electric resistance value of the transfer paper is too low, electric charges are leaked through the paper, the transfer electric field is lowered, and the toner image is lost. The relationship between the surface specific resistance value (Ω) of the transfer paper and the transfer efficiency (%) is shown in FIG. FIG. 2 shows the relationship between the surface specific resistance value (Ω) of the transfer paper and the occurrence rate (%) of the toner image missing when copying is performed using this transfer paper. As is clear from FIGS. 1 and 2, the transfer efficiency of the transfer paper drops remarkably when the surface specific resistance value is around 10 ⁹ Ω and falls below this value. Similarly, the rate of occurrence of missing toner images is 10 ⁹
It drops sharply below Ω. Therefore, the surface resistivity of the black insulating paper of the present invention was set to 10 ⁹ Ω or more. The volume resistivity value is set to 5 × 10 ⁹ Ω · cm or more based on the same data. If the surface specific resistance value of black insulating paper is below 10 ⁹ Ω or the volume specific resistance value is below 5 × 10 ⁹ Ω · cm, the transfer efficiency will be reduced even if copying is performed using this black insulating paper. However, a clear electrophotographic copy image cannot be obtained. The toner image is also lost.

This black insulating paper is obtained, for example, by mixing an insulating black pigment with raw pulp in the existing paper manufacturing process.
In the paper manufacturing process, raw pulp is suspended in water and then beaten. The beaten pulp is mixed with size, filler, dye and the like. Then, it is made into paper and wound or cut to obtain a roll or cut paper, respectively. Insulating black pigment, along with size, fillers, dyes, etc., is added to the beaten raw pulp during the compounding process in the manufacture of this paper. Insulating black pigment, for example, carbon black, graphite, cyanine black, obtained by coating a conductive black pigment in an insulating transparent resin such as _{CuCr 2 O 4, CuFe 2 O} 4 -CuMn 2 O 4. Examples of the insulating transparent resin include polystyrene; styrene-based copolymers such as polystyrene-butadiene copolymer and styrene-acrylic copolymer; polyethylene, polyethylene-vinyl acetate copolymer, polyethylene-vinyl alcohol copolymer. Such ethylene copolymers; phenolic resins; epoxy resins; allyl phthalate resins; polyamide resins;
Polyester resin: Maleic acid resin is available. To coat the conductive black pigment with the insulative transparent resin, the same method as that for producing a normal electrophotographic toner is used. In this method, first, a conductive black pigment and an insulative transparent resin are mixed by a mixer, and then heated, melted and kneaded by a hot roll mill. Next, the kneaded product is pulverized by a feather mill or jet mill and then classified to obtain an insulating black pigment having a desired particle size. By classification, the insulating black pigment preferably has an average particle size of 10 μm or less. If it exceeds 10 μm, a clear electrophotographic copy image cannot be obtained even if copying is performed using a black insulating paper produced using this insulating black pigment.

The black insulating paper of the present invention is also obtained by applying or impregnating a conductive black paper with an insulating transparent resin. As the insulating transparent resin, the same resin as the resin used for coating the conductive black pigment is used. This resin is usually dissolved in a suitable solvent and applied or impregnated on conductive black paper. A black insulating paper can be obtained by laminating an insulating transparent film on a conductive black paper. As the insulating transparent film, polyethylene terephthalate, poly-4-methylpentene-1, polyolefin resin or the like is formed into a film and used. Alternatively, the resin film for a film may be formed on both surfaces of the conductive black paper by a lamination method such as an extrusion laminating method.

Also, the black insulating paper of the present invention can be obtained by printing, coating or impregnating white paper with an insulating black pigment. As the white paper, a normal transfer paper used for copying electrophotography is used.
For the insulating black pigment, the same material as the insulating black pigment mixed with the raw material pulp is used in the method of obtaining the black insulating paper. This method of preparing an insulating black pigment can also be obtained by coating a conductive black pigment such as carbon black or graphite with an insulating transparent resin as described above. The same resin as described above is used as the insulating transparent resin.

The black insulating paper thus obtained is used as a transfer paper in the usual electrophotographic copying process. With this black insulating paper, for example, a reverse image is copied by an ordinary copying machine as follows.

By exposing the document, an electrostatic latent image corresponding to the document image is formed on the photoconductor. This latent image is developed with, for example, white toner. The toner image is then electrostatically transferred to black insulating paper and heat fixed. As a result, a reverse image of the original image (a negative image for a positive original) is formed on the black insulating paper. In the electrophotographic copying process, a known process is adopted except that a white toner is used as the toner, and no special operation is required.

The white toner contains a white colorant, a binder resin and a compounding agent (charge control agent, release agent, etc.).

As the white colorant of this toner, zinc white, titanium oxide, tin oxide, antimony white, zinc sulfide, zinc oxide, barium carbonate, clay, silica, white carbon, talc, alumina, pearlite, etc. are used.

As the charge control agent for the toner, a colorless or white colorant known per se is used as it does not adversely affect the color tone of the white toner. For the purpose of controlling the positive charge, organic compounds having a basic nitrogen atom such as basic dyes, aminopyrine, pyrimidine compounds, polynuclear polyamine compounds, aminosilanes or fillers surface-treated with them are used, and For the purpose of controlling the negative charge, a carboxy group-containing compound such as a metal chelate of alkylsalicylic acid is used. These charge control agents are preferably used in an amount of 1 to 10% by weight per toner.

Further, as a release agent for this toner, silicone oil, low molecular weight olefin resins, various waxes, etc. are used.

The white toner is obtained by melt-kneading the above components, cooling and then pulverizing and classifying the components. It can also be obtained by dispersing the toner compounding agent in the resin solution and then spray granulating it.

As the binder resin for the white toner, for example, the same resin as the above-mentioned insulating transparent resin is used.

(Examples) The present invention will be described below with reference to Examples.

Example 1 Styrene-acrylic copolymer (Pryolite ACL; manufactured by Goodyear) 100 parts by weight Carbon black (Printex L, manufactured by Degussa) 20 parts by weight After blending the above formulation and premixing with a Henschel mixer, biaxial It was melt-kneaded with an extruder and allowed to cool. The kneaded product was roughly pulverized with a cutting mill and then finely pulverized with an ultrasonic jet mill PJM-100 to obtain an insulating black pigment having an average particle size of 8 μm.

This insulating black pigment was mixed with the size, filler, dye, etc. into beaten raw pulp. Then, a black insulating paper was obtained by a known paper manufacturing process.

The surface resistivity of the obtained black insulating paper is 1.5 × 10 ¹⁰ Ω,
The volume resistivity value was 2.1 × 10 ¹¹ Ω · cm.

Using this black insulating paper as a transfer paper and white toner containing titanium oxide as a white colorant, a white image was formed on the black insulating paper by a usual copying method. This white image was clear and no wrinkles or curls were found in the image.

Example 2 Commercially available conductive black paper in which carbon black was dispersed (Belcourt 70, surface specific resistance value 1.5 to 2 × 10 ⁶ Ω, volume specific resistance value 1.2 × 10 ⁸ Ω · cm) and polyvinyl butyral 20
A wt% methanol solution was applied. The coating was performed on both sides of the conductive black paper with a layer thickness of 2 to 10 μm or more.

The surface resistivity of the obtained black insulating paper is 1.2 × 10 ¹⁰ Ω,
The volume resistivity value was 1.8 × 10 ¹¹ Ω · cm.

Using this black insulating paper as a transfer paper and white toner containing titanium oxide as a white colorant, a white image was formed on the black insulating paper by a usual copying method. This white image was clear and no wrinkles or curls were found in the image.

Example 3 A black insulating paper was obtained in the same manner as in Example 2 except that a 20 wt% methanol solution of polyvinylpyrrolidone was used instead of the 20 wt% methanol solution of polyvinyl butyral.

The surface resistivity of the obtained black insulating paper was 8.0 × 10 ⁹ Ω, and the volume resistivity was 1.5 × 10 ¹¹ Ω · cm.

Using this black insulating paper as a transfer paper and white toner containing titanium oxide as a white colorant, a white image was formed on the black insulating paper by a usual copying method. This white image was clear and no wrinkles or curls were found in the image.

Example 4 A black insulating paper was obtained in the same manner as in Example 2 except that a 20 wt% methanol solution of an acrylic polymer (L-53P) was used instead of the 20 wt% ethanol solution of polyvinyl butyral. .

The surface resistivity of the obtained black insulating paper is 3.0 × 10 ¹⁰ Ω,
The volume resistivity value was 5.2 × 10 ¹¹ Ω · cm.

Using this black insulating paper as a transfer paper and white toner containing titanium oxide as a white colorant, a white image was formed on the black insulating paper by an ordinary copying method. This white image was clear and no wrinkles or curls were found in the image.

Example 5 The insulating black pigment obtained in Example 1 was dissolved in toluene at a concentration of 25% by weight. This solution was applied to a normal white transfer paper for electrophotographic copying in a thickness of 5 μm.

The surface resistivity of the obtained black insulating paper is 4.8 × 10 ¹⁰ Ω,
The volume resistivity value was 5.6 × 10 ¹¹ Ω · cm.

Using this black insulating paper as a transfer paper and white toner containing titanium oxide as a white colorant, a white image was formed on the black insulating paper by a usual copying method. This white image was clear and no wrinkles or curls were found in the image.

(Effect of the Invention) Since the black insulating paper for electrophotography of the present invention is excellent in insulating property as described above, a reverse image can be easily obtained by performing ordinary electrophotographic copying with white toner as a transfer paper. .
There is no need for a special copying machine or complicated control as in the past.
There is no need to make two copies. The resulting copied image is clear with no wrinkles or curls.

As a result, the electrophotographic copying method using the black insulating paper of the present invention is useful in obtaining a positive image copy from a negative original.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the surface resistivity of transfer paper and the transfer efficiency when electrophotographic copying is performed using this transfer paper, and FIG. 2 is the surface resistivity of transfer paper. 6 is a graph showing the relationship with the occurrence rate of toner image bleeding when electrophotographic copying is performed using this transfer paper.

Claims (14)

[Claims] 1. A black insulating paper for electrophotography having a surface resistivity of 10 ⁹ Ω or more and a volume resistivity of 5 × 10 ⁹ Ω · cm or more. 2. The beaten raw pulp is sized, filled, and
The black insulating paper for electrophotography according to claim 1, which is obtained by mixing an insulative black pigment with the raw material pulp in a mixing step in the production of a paper in which a dye or the like is mixed. 3. The black insulating paper for electrophotography according to claim 1, which is obtained by coating or impregnating a conductive black paper with an insulating transparent resin. 4. The black insulating paper for electrophotography according to claim 1, which is obtained by laminating an insulating transparent film on a conductive black paper. 5. The black insulating paper for electrophotography according to claim 1, which is obtained by printing, coating or impregnating an insulating black pigment on white paper. 6. The black insulating paper for electrophotography according to claim 2 or 5, wherein the insulating black pigment is formed by coating a conductive black pigment with an insulating transparent resin. 7. The conductive black pigment is carbon black, graphite, cyanine black, CuCr ₂ O ₄ and C.
The black insulating paper for electrophotography according to claim 6, which is at least one of uFe ₂ O ₄ —CuMn ₂ O ₄ . 8. An electrophotographic copying method using black insulating paper for electrophotography, which has a surface specific resistance value of 10 ⁹ Ω or more and a volume specific resistance value of 5 × 10 ⁹ Ω · cm or more, An electrophotographic copying method including copying a reverse image on a black insulating paper with white toner. 9. The black insulating paper is obtained by mixing an insulating black pigment with the raw material pulp in a blending step in the production of paper in which a beaten raw pulp is blended with a size, a filler, a dye and the like. The electrophotographic copying method according to claim 8. 10. The electrophotographic copying method according to claim 8, wherein the black insulating paper is obtained by coating or impregnating a conductive black paper with an insulating transparent resin. 11. The black insulating paper is obtained by laminating an insulating transparent film on a conductive black paper.
Electrophotographic copying method described in paragraph. 12. The electrophotographic copying method according to claim 8, wherein the black insulating paper is obtained by printing, coating or impregnating an insulating black pigment on white paper. 13. The electrophotographic copying method according to claim 9, wherein the insulating black pigment is formed by coating a conductive black pigment with an insulating transparent resin. 14. The conductive black pigment is carbon black, graphite, cyanine black, CuCr ₂ O ₄ and C.
The electrophotographic copying method according to claim 13, which is at least one of uFe ₂ O ₄ —CuMn ₂ O ₄ .