US3926628A - Using photoconductive and non-photoconductive powders - Google Patents

Abstract

An electrostatic powder coating method comprising; exposing a charged photoconductive toner layer formed on an electrically conductive substrate to an optical image; selectively removing the irradiation discharged toner particles from the toner layer at the irradiated areas to form a toner image corresponding to the optical image; then, while the remaining charged toner layer still retains a sufficient amount of charge, electrostatically spraying a second powder having the same charge polarity as that of the toner layer over the toner image bearing surface whereby the second powder is preferentially deposited on the irradiated areas of the image bearing surface; and fusing the photoconductive toner particles and the second powder layer or fusing the second powder layer after removing the toner particles from the substrate after discharging the charged toner particles of the toner layer by uniform irradiation by heating to form a continuous film, wherein an affinity between a main resinous component of said photoconductive toner and that of the second powder is high and both main resinous components are compatible with each other when fused by heating.

Description

United States Patent [191 Honjo [4 1 Dec. 16, 1975 1 USING PHOTOCONDUCTIVE AND NON-PHOTOCONDUCTIVE POWDERS [75] Inventor: Satoru Honjo, Asaka, Japan [73] Assignee: Fuji Photo Film C0., Ltd.,

Kanagawa, Japan 22 Filed: May2, 1974 211 Appl.No.:466,451

[30] Foreign Application Priority Data May 2, 1973 Japan 48-49327 [52] US. Cl 96/1 R; 96/15 D; 427/14 [51] Int. Cl. G036 13/22 [58] Field of Search 96/1 R, 15 D, 1.4; 117/ 17.5, 21

[56] References Cited UNITED STATES PATENTS 3,245,823 4/1966 Mayo 96/15 D X 3,532,530 10/1970 Denison et a1 117/21 X 3,650,797 3/1972 Tomanek 96/15 D X 3,770,482 11/1973 Millar et al. 117/21 X 3,820,984 6/1974 Gundlach 117/21 X 3,825, 121 7/1974 Tamai 96/1 R 3,833,365 9/1974 Hiwano et al 96/1 R X Primary ExaminefRoland E. Martin, Jr. Attorney, Agent, or Firm-Gerald .l. Ferguson, Jr.; Joseph J. Baker ABSTRACT An electrostatic powder coating method comprising; exposing a charged photoconductive toner layer formed on an electrically conductive substrate to an optical image; selectively removing the irradiation discharged toner particles from the toner layer at the irradiated areas to form a toner image corresponding to the optical image; then, while the remaining charged toner layer still retains a sufficient amount of charge, electrostatically spraying a second powder having the same charge polarity as that of the toner layer over the toner image bearing surface whereby the second powder is preferentially deposited on the irradiated areas of the image bearing surface; and fusing the photoconductive toner particles and the second powder layer or fusing the second powder layer after removing the toner particles from the substrate after discharging the charged toner particles of the toner layer by uniform irradiation by heating to form a continuous film, wherein an affinity between a main resinous component of said photoconductive toner and that of the second powder is high and both main resinous components are compatible with each other when fused by heating.

7 Claims, 8 Drawing Figures US Patent Dec. 16, 1975 3,926,628

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USING PIIOTOCONDUCTIVE AND NON-PHOTOCONDUCTIVE POWDERS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to an electrostatic powder coating method combined with an electrophotographic marking process utilizing a photoconductive toner. The present invention further relates to a method carried out on a plate bearing a photoconductive toner image thereon formed electrophotographically whereby a paint powder is deposited selectively on the toner-difficient region of the marked plate to obtain a reversal paint distribution relative to the first toner image. The present invention further relates to a method of increasing adhesion between a powder paint film and a substrate on which the film is formed by selecting suitable combinations of resinous components of the photoconductive toner and the powder paint.

2. Description of the Prior Art The electrostatic powder coating method described in US. patent application Ser. No. 267,757, filed June 30, 1972, now US. Pat. No. 3,833,365, comprises, exposing a charged photoconductive toner layer formed on an electrically conductive substrate to an optical image, selectively removing the irradiation discharged toner particles from the toner layer at the irradiated areas to form a toner image corresponding to the optical image, then, while the remaining charged toner layer still retains a sufficient amount of charge,

electrostatically spraying a second power having the same charge polarity as that of the toner layer over the toner image bearing surface whereby the second powder is preferentially deposited on the irradiated areas of the image bearing surface, discharging the charged toner particles of the charged toner layer by uniform irradiation, removing the discharged toner particles from the substrate, and converting the second powder layer into a continuous film by thermal fusing.

The method described above has the defect that the first irradiation discharged toner particles are not removed completely, as a result, a small amount of toner particles exist under the second powder layer and this causes poor adhesion between the continuous film and the substrate.

A further defect of the method is that the strength of the filmis low because of the presence of a small amount of toner particles between the film and the substrate.

Another defect of the method is that the charging condition of the photoconductive toner layer and the optical exposure time are critical because the amount of the residual toner particles must be minimized to increase the adhesion between the continuous film and the substrate.

The present invention has overcome these defects by selecting suitable combinations of main resinous components of the photoconductive toner and the powder paint.

SUMMARY OF THE INVENTION between the final coating film and a substrate on which the film is formed.

A further object of this invention is to provide an electrostatic powder coating method which provides a stronger final coatingfilm.

Another object of this invention is to provide an electrostatic powder coating method so that the selection of the charging conditions'and the optical image exposure time of the photoconductive toner layer can be more easily made.

A main resinous component of the photoconductive toner is selected to have an affinity and a good compatibility with that of the paint powder when fused by heating. t I

This invention provides an electrostatic powder coating method comprising; exposing a charged photoconductive toner .layer formed on an electrically conductive substrate to an optical image; selectively removing the irradiation discharged toner particles from the toner layer at the irradiated areas to form a toner image corresponding to the optical image; then, while the remaining charged toner layer still retains a sufficient amount of electrical charge, electrostatically spraying a second powder having the same charge polarity as that of the toner layer over the toner image bearing surface whereby the second powder is preferentially deposited on the irradiated areas of the: image bearing surface; and fusing the photoconductive toner particles and the second powder particles by heating to form a continuous film, wherein the affinity between a main resinous component of the photoconductive toner and that of the second powder is high and both main resinous components are compatible with each other when fused by heating. An embodiment includes further discharging the charged toner particles of the charged toner layer by uniform irradiation and removing the discharged toner particles from the substrate, after electrostatically spraying the second powder over the toner image bearing surface.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 through FIG. 8 show the procedural steps of a preferred embodiment of the present invention.

DETAILED DESCRIPTION 'OF THE INVENTION The present invention relates to an improvement of the electrostatic powder coating method described in US. patent application Ser. No. 267,757, filled June 30, 1972. g I

This prior method has several defects. Firstly, irradiation discharged toner particles are not removed completely, and as a result, a small amount of toner particles are present under the power paint layer, resulting in poor adhesion between the final paint film and the substrate. Secondly, the strength of the final film is low because of the presence of a small amount of toner particles between the film and the substrate. Thirdly, the charging conditions and the optical exposure time of the photoconductive toner layer are critical because the amount of the residual toner particles must be minimized to increase the adhesion between the film and the substrate.

The inventor of the present invention discovered these defects resulted from the poor compatibility between the main resinous component of the photoconductive toner and that of the powder paint. Therefore, the main resinous component of the photoconductive toner is selected to have a good affinity and compatability with that of the powder paint to overcome these defects.

According to the present invention the quality of the final film is not affected by the presence of a small amount of toner particles under the powder paint layer, and there is no possibility of the coating film coming off.

Also, according to the present invention adhesion between the powder paint film and a substrate and between the photoconductive toner film obtained by thermal fusing and a substrate are equally good. Even if a photoconductive toner image has a fairly large amount of toner particles, the adhesion of a powder paint film to the substrate is quite good unlike the method described in U.S. patent application Ser. No. 267,757, filed June 30, 1972. t

In the following, the present invention will be describedin detail with reference to the accompanying drawings.

-i. Formation of a photoconductive toner image A photoconductive toner layer 1 is formed on a substrate 2 to be coated using a toner dusting apparatus 3 as shown in FIG. 1. The photoconductive toner layer is then charged negatively using a corona discharge apparatus-'4 as shown in FIG. 2. The charging of the photoconductive toner layer is preferably carried out simultaneously with the dusting, for example, using techniques' as disclosed in US. Pat. No. 3,418,972. Then, the charged toner layer is exposed toan optical image 5 to discharge the charged toner layer at the exposed area 6'as shown in FIG. 3. The discharged toner particles 8 are then removed with a suitable developing apparatus. In FIG. 4 an air stream from a nozzle 9 is used for developing.

Thus a desired toner image is'formed.

' As alternatives to the coating using a toner duster as described in the above embodiment, a method in which a conductive support o'rplate is charged with a bias voltage and a toner similar to those used in cascade development can becascaded, a method in which only the photoconductive toner is sprayed can be used and a method in which simultaneous charging and powder scattering is accomplished using an electrostatic powder spraying apparatus can be employed.

, ii. Electrostatic coating of a powder paint Then, while the remaining charged toner layer still retains a sufficient amount of charge, a non-photoconductive insulating powder paint 10 having the same charge polarity as that of the toner layer is electrostatically sprayed over the substrate. The powder paint particles 10 deposit selectively on the toner-difficient region of the substrate as a result of electrostatic repulsion affected on the paint particles by the toner particles as shown in FIG. 5. Number 11 denotes an electrostatic powder coating apparatus. Next, a uniform exposure 12 is applied to discharge completely the entire charge of the image forming toner particles 1 as shown in FIG. 6. Then, the discharged toner particles are removed by an air stream from an air nozzle 13 as Combination Resin of Photoconductive Toner 4 shown in FIG. 7 or by any other suitable means such as mechanical vibration. I

The powder paint layer thus obtained is converted into a continuous film 14 by thermal fusing using high frequency induction heating, for example, as shown in FIG. 8.

Another preferred embodiment of the present invention omits the removing procedure of the toners shown in FIG. 7 and fuses both the toners and the powder layer simultaneously. For example, such can be simultaneously accomplished where the heat capacity of the metal substrate is high using high frequency electric heating.

Also, the present invention can be applied to a coating method in which the photoconductive toner can be colored by heating. For example, aphotoconductive toner which can be suitably used is a toner containing a metallic soap, as disclosed in US. patent application Ser. No. 429,266, filed Dec. 28, 1973.

Resinous materials, which have a large affinity with each other, for the photoconductive toner and the powder paint used in the present invention comprise chemically common or similar resins. Suitable resinous materials which can be used as the resinous materials for the photoconductive toner and the powder paint can be addition polymerization thermoplastic resins having a degree of polymerization of about to 2000, condensation polymerization thermoplastic resins having a degree of polymerization of about 50 to 200 and low molecular weight cross-linking resins having a degree of polymerization of about 10 to 200. Typical examples of resinous materials considered sim ilar include epoxy resins of epichlorohydrin and bisphenol A, polyesters of ethylene glycol and terephthalic acid or isophthalic acid, copolyesters of these three monomers and an epoxy resin having a high degree of polymerization having bisphenol A thermal groups giving a phenoxy resin. Typical chemically similar resinous materials also include methacryl esters, acryl esters or styrene copolymers containing monomers such as glycidyl methacrylate, hydroxy ethyl methacrylate, hydroxy propyl methacrylate, acrylic acid, maleic anhydride or methacrylic acid and vinyl chloride-vinyl acetate copolymers. Any other resinous materials which have an affinity with each other, namely, compatibility with'each other, can be freely selected and used as main resinous components of the photoconductive toner and the powder paint. Examples of suitable compatible combinations are set forth in the table below to further illustrate combinations which can be employed. These combinations are given for the purposes of facilitating a more complete understanding of this aspect of the invention and are not to be construed as limiting the scope of the invention since the important functional characteristic lies in the compatibility of the materials employed.

' Powder Paint Resin Terpolymer More specifically suitable examples of resins which can be and generally are used for powder paints are Conbination Photoconductive Toner Resin resin used for powder coating. Typically, the following combinations are preferably chosen.

Powder Paint Resin Styrene modified alkyd resin Epoxy resin Acrylate copolymer Cross-linking acrylate resin Polyester Polyester epoxy resins and polyester resins. Suitable epoxy resins l are generally a linear condensate comprising bisphenol A and epichlorohydrin having the general formulae where n is about 2 to and having a melting point of about 80 to 135C. This epoxy resin is used as the main resinous component of the powder paint. Generally a hardening agent is employed with the epoxy resin anda hardening agent which does not cause hardening at normal temperature is preferred. Suitable hardening agents are dicyandiamide, a complex salt of bron trifluoride, an acid anhydride, etc.

Illustrative typical polyester resins for the powder paint are polyalkylene terephthalate type polymers obtained by the condensation polymerization of an alkylene glycol and a dicarboxylic acid. Suitable glycols are ethylene glycol, diethylene glycol, propylene glycol, trimethylene glycol, butane-1,3-dio1, 2,2-dimethy1- propane-1 ,3-diol, cis-2-butene'l ,4-diol, trans-2- butene-l,4-diol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol, heptamethylene glycol, octamethylene glycol, nonamethylene glycol, decamethylene glycol, undecamethylene glycol, dodecamethylene glycol. Those glycols having about 4 to 12 carbon atoms are preferred, and mixtures of glycol components can be employed where desired. Examples of dicarboxylic acids are oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, B-methyladipic acid, pimelic acid, azelaic acid, sebacic acid, nonanedicarboxylic acid, maleic acid, fumaric acid, diglycolic acid, malic acid, citric acid, terephthalic acid, isophthalic acid, phthalic acid, tetrachlorophthalic acid chlorophthalic acid, nitrophthalic acid, diphenylacetic acid, naphthalene 1,4-dicarboxylic acid, naphthalene 1,5-dicarboxylic acid, naphthalene 2, 6-dicarboxylic acid, etc.

The melting point of the above described polyester resin generally ranges from about 80 to 350C, preferably about 100 to 150C. The degree of polymerization is indicated by the intrinsic viscosity 1 and a "n ranging from about 0.4 to 1.2 at C in o-chlorophenol is preferred.

With respect to the resin of the photoconductive toner, the resin can be used for a core material or as a binder for a surface photoconductive layer. Generally, the resin as the core material is the same resin as the this can be used as the surface layer of the photoconductive toner.

Illustrativecross-linking acrylate resins are disclosed in U.S. Pat. Nos. 3,481,735 and 3,554,747.

Generally, the molecular weight of the resin for the binder of the photoconductive layer ranges from several thousand to several tens of thousands.

As will be described hereinafter in Example 3, one such example includes a powder paint containing nylon as a main resinous component and a photoconductor toner containing a polyamide resin having low degree of polymerization as a main resinous material. In general, if one of the main resinous components of the photoconductive toner and the powder paint has a low molecular weight, the range of compatibility is broad. Consequently, considerably broad range of combinations are possible. In this specification, the term main resinous component is intended to cover a resinous material which comprises more than 50% by weight of the resinous components of a photoconductive toner or a powder paint, but a resinous material at less than 50% by weight may be a main resinous component if the objects of the present invention are accomplished.

A desirable toner should retain in the dark a high electrostatic potential over a long period of time and rapidly lose its potential when irradiated. U.S. Pat. No. 3,607,363, U.S. patent application Ser. No. 615,091, filed Feb. 10, 1967, British Pat. No. 1,183,762, and 1,165,017, and French Pat. No. 1,536,725 disclose preferred structures and production methods for such photoconductive toners.

Typical structures of the photoconductive toner include a photoconductive core of an organic or inorganic photoconductor and a resinous binder having surface layer, which is able to transport a charge carrier, thereon mainly of a resinous material, a mixture of an organic or inorganic photoconductor and a binder, which is able to transport a charge carrier, mainly of a resinous material, and a glass or plastic core having a surface layer of the mixture. Toners comprising a surface photoconductive layer and insulating core material are disclosed in U.S. Pat. No. 3,607,363 and British 7 Pat. No. 1,183,762. A suitable particle size of such toners generally range from about to 80 microns and a suitable thickness of the surface photoconductive layer ranges from about 0.1 to 0.9 D, where D is the toner particle diameter. Toners, where the charge carrier generating phase and charge carrier transport phase are separated, having excellent transparency are disclosed in U.S. patent application Ser. No. 436,717,

filed on Jan. 25, 1974 and 441,861, filed on Feb. 12, 1974. An appropriate particle size for this type tonerv is about 10 to 80 microns, and the ratio of carrier generating phase in the toner is about 0.01 to 75 vol%, preferably l to 50 vol%. Toners having different structures can also be used in the present invention provided that resinous materials are included.

' A photoconductive toner which comprises a transparent core material and a photoconductive surface layer is preferred, and the transparency of core materials is such that the coefficient of absorption to light to which the photoconductive material of the surface layer is sensitive is less than 3 X 10 mm. A typical method of producing such a photoconductive toner is the vacuum deposition of selenium on the surface of a core material, the mixing of a core material in a dispersion which comprises zinc oxide, a resin and a solvent which does not dissolve the core material, and then spray-drying the mixture and spraying a core material and a photoconductive powder such as zinc oxide into an air stream containing a solvent vapor so that the zinc oxide coats the solvent swollen surface of the core material.

To accomplish the purposes of the present invention it is only necessary for at least one resinous component of core materials, charge carrier transporting layers and binders to have an affinity with a main resinous component of the powder paint and to be quite compatible with the resinous component when melted by heating.

Typical inorganic photoconductors include zinc oxide, titanium dioxide and cadmium sulfide and the oxides, sulfides selenides and tellurides of a divalent metal such as cadmium, zinc, and mercury as well as PbCrO Other inorganic photoconductors as disclosed in U.S. Pat. No. 3,121,006 can be used.

Typical organic photoconductors include X-form metal free phthalocyanine, other phthalocyanines and insoluble. vinyl anthracene derivatives. Other organic photoconductors such as a photoconductive layer comprising phthalocyanine in a resinous binder as disclosed in U.S. Pat. No. 3,357,989 (U.S. Pat. No. Re. 27,117) and polyvinylanthracene as a photoconductive material as disclosed in U.S. Pat. No. 3,464,819 can also be used.

Resinous binder materials can be sensitized using Lewis acids or spectral sensitizing dyes. Typical Lewis acids include 2,4,7-trinitro-9-fluorenone, picric acid, tetracyanobenzoquinone dimethane and 1,3,5-trinitrobenzene. Typical spectral sensitizing dyes include Auramine (CI. 41000), Methylene Blue (CI. 52015), Eosine (CI. 45380) and Fluorescein (CI. 45350).

The charge carrier transporting layer can be an organic photoconductive polymer alone, such aspoly-N- vinylcarbazole, polyacenaphthene and so on.

Spherical particles of glass, ceramics or thermosetting resins such as a phenol resin can be used as a core material of the photoconductive toner, provided that a resin having a high affinity with the powder paint is included in the surface layer on the core.

Any substrate on which the photoconductive toner layer can be formed can be used provided that its surface has a suitable electrical conductivity and that it does not exhibit a high adhesivity to a finely-divided powder. A preferred conductivity range is not less than 10 (ohm square) and there is substantially no upper limit. Typical materials include metallic plates, coated plastic films or paper. Materials which originally have a low surface conductivity such as glass, ceramics, fibers, plastics, wood, no-woven fabrics, paper, leather, synthetic leather, and film forming materials such as resins, varnishs, etc., treated so as to provide a high surface conductivity, for example, using alumina or colloidal silica can also be used.

The powder paint comprises as described above a resinous material which melts at a suitable temperature range to form a continuous film. Pigments and plasticizers can be included, if desired.

More specifically, with respect to these additives in a powder paint, where a cross-linking resin such as an epoxy resin is used, pigments, hardening agents, flow control agents, thixotropic agents, or defoaming agents can be employed as components. Suitably the powder paint contains the pigment at about 5 to 20 vol% of the total paint composition the hardening agent at less than 50 wt% to the weight of the resin employed and other additives at less than 5 wt%.

' Where a thermoplastic resin such as polyvinyl chloride is used, pigments, plasticizers, light and heat stabilizers can be'employed as components. A suitable polymerization degree for the polyvinyl chloride is about 700 to 900 The powder paint generally contains the pigment at about 5 to 20 vol% of the total paint composition, the plasticizer at less than about 20 wt% to the weight of the resin and the stabilizer at less than 10 wt% is added to the weight of the resin. Illustrative stabilizers are anti oxidation agents or metal soaps. In case of a powder paint employing a fairly crystalline thermoplastic resin such as a polyamide, a plasticizer generally is not used. Where the resin of the powder paint as a polyester, no additives are required although they may be present to provide desirable properties thereto. Powder paints containing, cross-linking acrylic resins often harden by selfcondensation, and a hardening agent at less than about 20 wt% to the weight of the resin is usually present to minimize this. Suitable powder paints which can be employed are disclosed in U.S. Pat. Nos. 2,771,378, 3,161,530, and 3,451,838.

The powder paint must be non-photoconductive when irradiated with light to which the photoconductive toner is active.

Althoughthe preferred embodiments of the present invention are described in Examples hereinafter, the following general techniques concerning desirable structures of the photoconductive'toner can be used. That is, in a photoconductive toner comprising a resinous core and a photoconductive surface layer, the 'resinous material of the core rather than that of the photoconductive surface layer should desirably have an affinity with the main resinous component of the powder paint, partly because the resinous material of the photoconductive surface layer generally must satisfy many requirements so that the layer can exhibit a high quality as a photoconductive layer and because the resinous material of the core usually occupies a larger proportion by weight of the toner than that of the photoconductive surface layer. T

In using a conventional polymer such as polyvinylcarbazole which has a high second order transition temperature as an organic photoconductive material for the photoconductive toner as disclosed in the Japanese patent application No. 10,826/73, polyvinylcarbazole can not be used as a resinous material of the powder paint, because it is difficult to melt because of its high second order transition temperature. Therefore, in such as case, combinations of resinous materials which have good compatibility with the core materials should be selected. In using linear polyesters for the charge carrier transporting layer of the photoconductive toner, a polyester-based powder paint can be combined.

According to the present invention, the possibility of obtaining a final coating film of a poor quality is greatly reduced, even if a small amount of residual photoconductive toner particles are present under the powder paint layer as shown in FIG. 6. Consequentlyjthe coating film does not disadvantageously come off. Moreover, the adhesivity of a film to a substrate is equally good at the image and non-image areas. Even an image with a fairly large amount of residual toner particles has good adhesion between the final coating film and the substrate, unlike the method as described in Japanese Patent Application No. 82136/70.

The following examples are given to illustrate the invention in greater detail. Unless otherwise-indicated, all parts, percents, ratios and the like are by weight.

EXAMPLE 1 85 parts by weight of a copolymer of styrene, methylmethacrylate, hydroxyethylacrylate and acrylic acid (60:23: :2 by weight) and 15 parts by weight of polyisocyanate blocked by phenol (Desmodur AP Stable, trade name for a product of the Bayer Go, West Germany) were dissolved a mixed solvent (60:40 by volume) of ethyl acetate and toluene. Then the solution was spray dried to form spherical particles of adiameter of 30 to 40 microns.

A homogeneous mixture of 100 parts by weight of photoconductive zinc oxide, 25 parts by weight of methylphenyl polysiloxane and 100 parts by weight of cyclohexanone was separately prepared. 30/ 1000 parts by weight of fluoroscein solved in a small amount of methyl alcohol was added to the mixture.

50 parts by weight of the above particles was mixed with 100 parts by weight of the resulting mixture, and then spray dried to form a photoconductive toner having a particle size of about 40 to 60 microns. The photoconductive toner thus obtained had a light yellowish color appearance.

The toner was stored and further dried at 40C in the dark for about hours, then was sprinkled on a steel plate at a density of 80 g/m and then the toner layer was exposed to a negative corona discharge. The initial surface electrical potential was about 320 volts. The toner layer was exposed optically to a positive image and then developed using an air stream. The toner particles remained only at the unexposed regions. While still in dark a white powder paint of a thermosetting acrylic resin (copolymer of styrene, methylmethacrylate and glycidylmethacrylate in a proportion of 40:50:10 by weight; particle size about 30 to 150 microns) and titanium dioxide was simultaneously electrostatically negatively charged and sprayed over the image-bearing surface. The powder uniformly depos ited on the background of the toner image. Both the 10 toner particles and the powder paint particles were fused by heating to 150C to form a continuous film.

EXAMPLE 2 After the powder paint coating as described in Example l, a uniform visible light exposure was applied to the image-bearing surface to dissipate the electrostatic charges of only the toner particles and then the toner particles only were removed using an air stream and recovered.

Then the powder particles werethermally fused at about 180C for about 15 minutes to form a continuous film.

The adhesion between the steel plate and the coating films obtained in Example 1 and Example 2 were examined using the Cross Cut Test and the both films were found to exhibit substantially equal results to that for a a photoconductive toner.

EXAMPLE 3 Spherical polyamide resin particles with an average particle size of 50 micronswere used as a core material.

parts by weight of a coating solution of 100 parts by weight of photoconductive zinc oxide, 15 parts by weight of silver laurate, 18 parts by weight of a copolymer of butylmethacrylate, styrene, maleic anhydride and hydroxymethylrnethacrylate (in a proportion of 40:50:3:7 by weight) and parts by weight of toluene were mixed with 500 parts by weight of the above described core material. The mixture was then sprayed into a hot air stream using a spray gun and the dried fine particles were collected. The photoconductive toner thus obtained was combined with a nylon based powder paint and processed in'the same way as described in Example I. The fusing temperature was about 200C.

Adhesion between the steel plate and the resulting film was examined using the Cross Cut Test and was found to be the same as that between the steel plate and a film obtained by a usual powder coating method which does not include image formation using the photoconductive toner.

EXAMPLE 4 40/1000 parts by weight of Eosine Y(C.I. 45380) dissolved in a small amount of methyl alcohol was added to a homogeneous mixture. of 60 parts by weight of photoconductive zinc oxide, 20 .parts by weight of metal free phthalocyamine, 20 parts by weight of a styrene modified alkyd resin, 5 parts by weight of polyisocyanate cross linking agent (the addition product of 1 mole of trimethylolpropane and 3 moles of tolylenediisocyanate) and butyl acetate. The mixture was spray dried to form fine particles of a diameter of about 20 microns.

The resulting particles were stored at 60C for one day to harden and to render them insoluble.

100 parts by weight of the particles thus obtained was added to a solution of 40 parts by weight of a linear polyester resin, 12 parts by weight of 2,4,7-trinitrofluorenone and 200 parts by weight of a mixed solvent including an equal volume of toluene and methyl isobutyl ketone. The mixture was spray dried. The thickness of the surface coating layers of the resulting particles was between 4 and 5 microns. The particles were further dried, and after dark adaptation, they were sprinkled on an aluminum plate in the dark and then pr0- 1 l cessed in the same way as described in Example 1. A powder paint of dark brown colored powder paint of a linear polyester type was used. High frequency induction heating was applied to form a continuous film. The adhesion between the substrate and the film was extremely good, an no difference in adhesivity between the image regions and non-image regions was observed.

EXAMPLE 5 80 parts by weight of soluble polyester resin, parts by weight of tetracyanoquinodimethane and 20 parts by weight of 2,4,7-trinitroflu roenone were dissolved in toluene. Zinc oxide having adsorbed thereon 20/ 1000 parts by weight of C.l. Food Blue 1 was added to the solution and mixed so as to obtain homogeniety. The resulting coating compositions was spray dried to form photoconductive toner particles having a diameter ranging from to 60 microns. Using the photoconductive toner thus obtained and the powder paint used in Example 4, the same procedure as described in Example 2 was carried out. A good image uniformly adhered to the substrate was obtained.

While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing'from the spirit and scope thereof.

What is claimed is:

1. An electrostaticpowder coating method comprising, exposing a layer of charged photoconductive toner particles formed on an electrically conductive substrate to an optical image, the photoconductive toner particles having a main resinous component;

selectively attempting to remove all of the irradiation discharged toner particles from said toner layer at the irradiated areas to form a toner image corresponding ,to said optical image where a small amount of the toner particles undesirably remain in the irradiation discharged area;

then, while the remaining charged toner layer still retains a sufficient amount of electrical charge, electrostatically spraying a second powder having a main resinous component and having the same charge polarity as that of said toner layer over the toner image bearing surface whereby said second powder is preferentially deposited on the irradiated areas of said image bearing surface;

fusing said photoconductive toner particles and said second powder particles by heating to form a continuous film, wherein the affinity between a main resinous component of said photoconductive toner and that of said second powder is high and both main resinous components are compatible with each other when fused by heating; and

discharging the charged toner particles of said charged toner layer by uniform irradiation and removing said discharged toner particles from the substrate, after electrostatically spraying said second powder over the toner image bearing surface so that all of the removed toner particles may be reused.

2. The method asdescribed in claim 1, wherein said main resinous components of said photoconductive toner and said second powder contain chemically the same materials.

3. The method as described in claim 2, wherein said chemically same materials are selected from the group consisting of an epoxy resin of epichlorohydrin and bisphenol A, a polyester of ethylene glycol and terephthalic acid or isophthalic acid, a copolyester of ethylene glycol, terephthalic acid and is o-phthalic acid, and a phenoxy resin comprising an epoxy resin having a high degree of polymerization terminated by a bisphenol A residue.

4. The method as described in claim 1, wherein said main resinous components of said photoconductive toner and said second powder contain chemically similar materials.

5. The method as described in claim 4, wherein said chemically similar materials are selected from the group consisting of a methacryl ester, an acryl ester or a styrene copolymer including monomers such as glycidyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, acrylic acid, maleic anhydride or me'thacrylic acid, and a vinyl chloride-vinyl acetate copolymer.

6. The method as described in claim 1, wherein one of said main resinous components of said photoconductive toner and said second powder has a low molecular weight.

7. The method as described in claim 6, wherein said main resinous component is a polyamide resin having a low degree of polymerization.

Claims (7)

1. AN ELECTROSTATIC POWDER COATING METHOD COMPRISING, EXPOSING A LAYR OF CHARGED PHOTOCONDUCTIVE TONER PARTICLES FORMED ON AN ELECTRICALL CONDUCTIVE SUBSTRATE TO AN OPTICAL IMAGE, THE PHOTOCONDUCTIVE TONER PARTICLES HAVING A MAIN RESINOUS COMPONENT; SELECTIVELY ATTEMPTING TO REMOVE ALL OF THE IRRADIATION DISCHARGED TONER PARTICLES FROM SAID TONER LAYER AT THE IRRADIATED AREAS TO FORM A TONER IMAGE CORRESPONDING TO SAID OPTICAL IMAGE WHERE A SMALL AMOUNT OF THE TONER PARTICLES UNDERSIRABLDY REMAIN IN THE IRRADIATION DISCHARGED AREA; THEN, WHILE THE REMAINING CHARGED TONER LAYER STILL RETAINS A SUFFICIENT AMOUNT OF ELECTRICAL CHARGE, ELECTROSTATICALLY SPRAYING A SECOND POWDER HAVING A MAIN RESINOUS COMPONENT AND HAVING THE SAME CHARGE POLARITY AS THAT OF SAID TONER LAYER OVER THE TONER IMAGE BEARING SURFACE WHEREBY SAID SECOND POWDER IS PERFERENTIALLY DEPOSITED ONT THE IRRADIATED AREAS OF SAID IMAGE BEARING SURFACE; FUSING SAID PHOTOCONDUCTIVE TONER PARTICLES AND SAID SECOND POWDER PARTICLES BY HEATING TO FORM A CONTINUOUS FILM, WHEREIN THE AFFINITY BETWEEN A MAIN RESINOUS COMPONENT OF SAID PHOTOCONDUCTIVE TONER AND THAT OF SAID SECOND POWDER IS HIGH AND BOTH MAIN RESINOUS COMPONENTS ARE COMPATIBLE WITH EACH OTHER WHEN FUSED BY HEATING; AND DISCHARGING THE CHANGED TONER PARTICLES OF SAID CHARGED TONER LAYER BY UNIFORM IRRADIATION AND REMOVING SAID DISCHARGED TONER PARTICLES FROM THE SUBSTRATE, AFTER ELECTROSTATICALLY SPRAYING SAID SECOND POWDER OVER THE TONER IMAGE BEARING SURFACE SO THAT ALL OF THE REMOVED TONER PARTICLES MAY BE REUSED.

2. The method as described in claim 1, wherein said main resinous components of said photoconductive toner and said second powder contain chemically the same materials.

3. The method as described in claim 2, wherein said chemically same materials are selected from the group consisting of an epoxy resin of epichlorohydrin and bisphenol A, a polyester of ethylene glycol and terephthalic acid or isophthalic acid, a copolyester of ethylene glycol, terephthalic acid and is o-phthalic acid, and a phenoxy resin comprising an epoxy resin having a high degree of polymerization terminated by a bisphenol A residue.

4. The method as described in claim 1, wherein said main resinous components of said photoconductive toner and said second powder contain chemically similar materials.

5. The method as described in claim 4, wherein said chemically similar materials are selected from the group consisting of a methacryl ester, an acryl ester or a styrene copolymer including monomers such as glycidyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, acrylic acid, maleic anhydride or methacrylic acid, and a vinyl chloride-vinyl acetate copolymer.

6. The method as described in claim 1, wherein one of said main resinous components of said photoconductive toner and said second powder has a low molecular weight.

7. The method as described in claim 6, wherein said main resinous component is a polyamide resin having a low degree of polymerization.

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