JPS5854382B2 - electrostatographic photoreceptor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This application is based on US Patent Application No. 5 filed on June 3, 1974.
CIP of erial A476024, and this application is US Patent Application No. 5er filed on May 29, 1974.
ial A474296 CIP.

The present invention relates to electrostatographic reproduction, electrostatographic photoreceptors, and methods of processing the photoreceptors for use in electrostatographic reproduction machines.

Originally Carlson's US Patent A22
This type of reproduction, described in US Pat. No. 9,769, involves as an initial step the uniform charging of a plate or drum containing a conductive substrate, usually bearing on its surface a non-conductive barrier layer covered by a photoconductive insulating layer.

This is followed by image configuration.
) exposing the plate or drum to activating radiation, which causes dissipation of the electrostatic charge in the exposed areas, while the unexposed areas retain the charge in a pattern known as a latent image.

The latent image is developed by contacting the latent image with an electroscopic marking material, commonly referred to as a toner.

This material is electrostatically attracted to the latent image, which by definition is located in the portion of the photoreceptor that was not exposed to the activating radiation.

This toner image is subsequently transferred to paper and fused thereto to form a permanent copy.

Following this, the latent image is erased by discharging the drum and excess toner is washed therefrom to prepare the drum for the next cycle.

The photoconductive insulating material is characterized in that it has a relatively high electrical resistance in the dark, and this resistance decreases significantly upon exposure to activating radiation.

2,4,7-dolinitro9 in polyvinylcarbazole
- Both organic materials such as fluorenone and inorganic materials such as amorphous selenium have been successfully used as photoconductive materials in electrostatographic reproduction machines.

In some cases it has proven desirable to coat the photoconductive material with certain materials to protect it from physical damage or to facilitate the removal of toner during the cleaning process.

Examples of coating materials are organic resins that form an insulating film and are transparent or translucent to the activating radiation.

Coatings known to those skilled in the art are generally not regarded as contributing to improved copy quality.

The present invention includes coating the photoreceptor with a material that not only protects the photoconductive material from abrasion and environmental chemical contaminants, but also enhances the quality of copies made from the coated photoreceptor. .

Copy reinforcement involves the creation of increased copy contrast and the reduction or elimination of undesirable conditions in which copies suffer from background development.

Amorphous selenium has many desirable properties that make its use extremely beneficial in electrostatographic reproduction machines.

However, the advent of high speed copiers making only one or two copies per drum revolution necessitated the use of photoconductive materials that discharge at a faster rate than pure selenium.

This is the case, since an increase in copying speed is obtained by increasing the speed of drum rotation.

Therefore, the photoreceptor must be able to go through charge, exposure, development, transfer, discharge and wash cycles very quickly.

Research has shown that the rate at which selenium can pass through this cycle can be increased by combining selenium and arsenic to form an alloy.

Additionally, the use of selenium/arsenic alloys results in photoreceptors that are sensitive to longer wavelengths of light.

This concept is described in further detail in Ullrich US Pat. No. 2,803,542.

Thus, selenium alloys containing from about 0.3 to about 48.7 weight percent arsenic are advantageously used as photoconductive materials in high speed electrostatographic reproduction machines.

These arsenic-containing selenium alloys have print deletion (dele)
However, it has been found to suffer from a drawback which has become known as tion.

This development is observed in copies as blank areas that gradually become larger until the copy quality becomes unacceptable.

What causes print deletion is not fully understood, but it is believed that materials found around where the copier is placed react with the arsenic in the photoconductor, causing the charge to dissipate shortly after the charging process. It is believed to contain components that form acceptable conductive reaction products.

As a result, no latent image is formed in these areas and print deletion occurs.

Another drawback associated with the use of selenium/arsenic alloys as photoconductive materials in electrostatography is the long recovery time from photofatigue.

Care must be taken to prevent the alloy from being exposed to light as that exposure will render the material non-photoresponsive over relatively long periods of time.

It is desirable and an object of the present invention to provide new coatings for electrostatographic photoreceptors.

Another object is to provide this coating which enhances the quality of copies produced by the coated photoreceptor.

Another object is to provide this coating that reduces or eliminates copy deletion and photofatigue recovery problems associated with the use of selenium/arsenic alloys as photoconductors.

The present invention comprises (a) a conductive substrate; (b) a layer of photoconductive insulating material in operative contact with the conductive substrate; and (c) (i) methyl methacrylate, n-butyl acrylate and acrylic or methacrylic acid. (11) a crosslinkable polymer composition comprising a first polymer that is an addition polymerization product; and (11) a second polymer that is an addition polymerization product of styrene and maleic anhydride. An improved electrostatographic photoreceptor comprising an organic coating on top of a layer.

The present invention is based on the discovery that coating the photoconductive insulating layer of an electrostatographic photoreceptor with a thin but effective layer of the coating material described above imparts unexpected beneficial properties to the photoreceptor. There is.

This improvement relates to overcoming copy deletion and slow recovery from photofatigue problems associated with the use of certain photoconductive alloys, as well as generally improving copy quality.

Typical organic coating materials contemplated for use in the present invention include methyl methacrylate, n-butyl acrylate and the product of addition polymerization of acrylic acid or methacrylic acid as the first polymer.

The second polymer, sometimes referred to as a leveling agent, is the product of copolymerization of styrene and maleic anhydride.

In a typical coating, the first polymer comprises about 75 to 90 mole percent of the film and contains about 45 to 65 mole percent methyl methacrylate, 25 to 40 mole percent n-butyl methacrylate, and 5 to 15 mole percent Contains acrylic or methacrylic acid.

The second polymer usually accounts for 10 to 25% by weight of the film and contains styrene and maleic anhydride in a molar ratio of 2:1 to 1:1.

Copolymers of styrene and maleic anhydride, commonly referred to as SMA resins, typically contain a ratio of styrene to maleic anhydride of either 2:1 or 1:1; A composition in which is between the extreme values necessarily contains a mixture of SMA resins.

These S with a 2:1 styrene/maleic anhydride ratio
MA resins are generally preferred.

The coating is conveniently applied from a synthetic binary, ie, a finely divided dispersion of polymer particles in an aqueous carrier.

Typically, the carrier contains a basic material such as ammonia or an amine, such as ethylamine, isopropylamine, isobutylamine, etc., to form salts with weakly ionized carboxylic acid groups and thereby increase the solubility of the polymer. do.

This latex dispersion is described in further detail in US Pat. No. 3,799,901.

Alcohol and/or alcohol in combination with basic materials such as amines
Another method of making suitable latices using organic solvents such as chlorinated hydrocarbons is described in U.S. Patent A32961.
72.

The polymer coating is easily applied from the latex dispersion by applying a thin film to the photoreceptor surface and allowing the carrier to evaporate.

Metal crosslinking components are commonly used to impart toughness to films formed by latex dispersions.

Thus, by introducing a crosslinking material such as an oxide, hydroxide or salt of a polyvalent metal, e.g. zinc or zirconium, along with sufficient base to dissolve the aqueous dispersion of the polymer, the metal can be freed from carboxyl groups. This solution helps cross-link the polymer and forms a tough film when molded.

This cross-linking is ionic in nature, but when ammonia is the base, the use of a metal cross-linking agent with a nialic or methacrylic acid-containing polymer may improve the film-forming properties of the resulting material. Desirable due to increased performance.

Incorporation of SMA resins into polymer dispersions is particularly beneficial when metal crosslinkers are used since the most critical issue with these systems is storage stability.

This is the case, because in the absence of metal ions, the solution is somewhat susceptible to kelization and flocculation.

The SMA resin serves the purpose of acting as a leveling agent and increasing the freeze-thaw and thermal stability of the coating formulation.

This aqueous latex solution selectively contains, in addition to the two polymers, a base and a metal crosslinker, a volatile plasticizer.

This plasticizer is usually present because it is desirable to formulate materials that will form continuous films that exhibit a fairly high level of abrasion resistance upon application to a substrate.

In order to produce a continuous film, the coating composition must have a minimum film forming temperature (MFT) below the application temperature.

In order for the dried film to be sufficiently serviceable, its glass transition temperature (Tg) should be above its service temperature.

The minimum film forming temperature is a function of polymer-T, and plasticizer content, so low MFT (before plasticizer evaporation) and high Tg
It is practice in the coatings industry to incorporate volatile plasticizers into formulations to obtain (after evaporation of the plasticizer).

In descending order of volatility, examples of volatile plasticizers are pyrrole, propylene glycol, n-octatool, hexylene glycol, dipropylene glycol methyl ether, tributyl citrate and tributoxyethyl phosphate.

Additionally, caprolactam is sometimes used in commercial floor finishes to serve as a dual volatile plasticizer and gloss enhancer.

For purposes of this invention, the thickness of the polymer coating is not critical, but some experimentation may be required to determine the optimal coating thickness for a given photoconductive material. It will be clear to those skilled in the art.

Typical coating thicknesses range from about 0.1 to about 10 microns.

As mentioned above, the cause or causes of copy deletion are not well known or understood.

- Type copy deletions are being replicated under controlled conditions.

This type is known as amine-induced copy deletion.

The amines present in the periphery of the arsenic-rich photoreceptor react with the surface of the photoreceptor to form a film that interferes with charge retention in this area and prevents a developable latent image from forming. It seems that it will.

The application of films of the type described herein overcomes not only amine-induced print deletion, but also causes of print deletion due to other harmful materials present in the particular surroundings.

The invention is further illustrated by the following examples.

EXAMPLE ■ An electrostatographic reproduction machine having as a photoreceptor an aluminum drum coated with an alloy of approximately 63% selenium and 37% arsenic by weight was placed in a room with an atmosphere intentionally contaminated with cyclohexylamine. Place it in

This atmosphere is known to cause copy deletion when the amine contacts the photoconductive alloy, and this effect is seen in about 2 hours.

Half of the photoconductor was transferred to Armstrong in May 1974.
Cover with Solarian Floor Finish (trade name) obtained from Koch Company.

Analysis of the coating material indicates that it contains about 70 to 8% of 45 to 65% methyl methacrylate, 25 to 40% n-butyl acrylate, and 5 to 15% methacrylic acid.
It is shown to be a latex containing about 20% solids by weight, including 0% by weight colloidal sized particles of the terpolymer.

Furthermore, the molar ratio of styrene to maleic anhydride is 2:
There is between 8 and 23% by weight of SMA resin that is 1.

A small amount of zinc is present as a crosslinker.

This formulation also contains 1 to 2% tributoxy ether phosphate, 4 to 6% caprolactam (monomer), 1 to 2% glycerin, 0.5% ammonia and about 1%
% diethylaminoethanol.

Plasticizer (tributoxyethyl phosphate, caprolactam)
, gloss enhancers (caprolactam, glycerin) and emulsifiers (ammonia, diethylaminoethanol) play no role in the xerographic process, so their presence is not necessary after the film is put down, and other materials are added to it. Substitutions may be made to aid in action.

applying a sponge containing the material to the drum surface;
The coating is then carried out by rotating the drum several times while moving the sponge parallel to the axis of rotation.

After application, this layer is carefully dried to form a substantially uniform film.

After 2 hours of copying using the machine in the normal xerography mode where the machine pauses for 5 minutes between each fourth copy, a progressively worsening copy deletion effect occurs on the uncoated side of the photoreceptor. Be looked at.

Conversely, copy deletions are seen on the side of the photoreceptor that has a coating.

Foster copies were made using treated photoreceptors without any signs of copy deletion on the coated side.

EXAMPLE ■ Uncoated photoreceptors are exposed to fluorescent laboratory light for approximately 45 minutes as described in Example ■.

Reinsert the drum into the copier and operate in normal xerographic mode.

This photoreceptor is normally unresponsive due to photofatigue of the photoconductor.

Extreme light exposure resulted in low contrast copies from photofatigued plates.

This condition continued through approximately 100 copies without any improvement, at which point the experiment was stopped.

Only after several hours of storage in the dark did the photoreceptor behave with normal contrast. Exposure to lighting.

When the photoreceptor is reinserted into the copier, it is found that after about three copies the photoconductive material exhibits a normal high contrast photoresponse.

This quick recovery and rapid stabilization allows the electrical parts of the machine to set up within minutes after reinserting the drum into the copier.

This is a significant additional unexpected advantage of the coating of the present invention.

Electrostatographic copies made using coated photoreceptors according to the present invention utilize uncoated photoreceptors for both reduced background development and greater contrast between image and background areas of the copy. Better than anything made by someone else.

EXAMPLE ■ Coating the photoreceptor described in Example ■ in a manner similar to that described in Example ■ using the following commercially available floor finishes; (a) metallized acrylic/styrene copolymer; Q))
an alkali-soluble maleic resin, and (c) a polyethylene wax.

Super Glo Coat (S Glo CoatR)
) per (product name) as Racine, Uis kelp varnish.
This material, marketed by See, Johnson & Saiz, is applied from an aqueous dispersion containing glycol ether, tributoxyethyl phosphate, formaldehyde and traces of surfactant.

The coating material can be easily applied to the drum in the sense that it can be applied to form a uniform coating.

However, copies made from coated drums are unacceptable due to the presence of dark backgrounds and hairy images.

The copy quality was clearly inferior to that obtained with an uncoated drum, and clearly superior to copies made using an uncoated drum using a drum coated with the coating material described in Example ■. in sharp contrast to the quality of the copies obtained.

Photoconductors that may be coated by the method of the present invention are not limited to those specifically described, ie, high arsenic/selenium alloy photoconductors, but include a wide variety of photoconductors.

Thus, for example, reinforcement in copying materials is possible when the photoconductive material is an organic material, such as TN in poly(vinylcarbazole).
F, or by coating the photoreceptor with an inorganic photoconductor in an insulating organic resin, such as Cd5Se in polyurethane.

In the above example, the organic coating is applied from an aqueous solution containing colloidally sized particles of resinous material.

It is not important that the coating is applied in this manner and that other coating methods known to those skilled in the art could be used.

The present invention includes the following aspects.

The photoreceptor of claim 1, wherein: (1) the first polymer comprises 75 to 90% by weight of the coating layer and the second polymer comprises 10 to 25% by weight of the film.

(2) the first polymer comprises about 45 to 65 mol% methyl methacrylate, 25 to 40 mol% n-butyl acrylate, and 5 to 15% acrylic acid or methacrylic acid; 2:1 to 1:
The above (1) containing styrene and maleic anhydride in a molar ratio of 1
) photoreceptors.

(3) The photoreceptor of item 2) above, wherein the molar ratio of styrene to maleic anhydride is 2:1.

(4) The photoreceptor of claim 1, wherein the first polymer is crosslinked by a polyvalent metal across the carboxyl groups of acrylic acid or methacrylic acid.

(5) The above (4) in which the polyvalent metal is zinc or zirconium
) photoreceptors.

(6) The photoreceptor of (5) above, wherein the polyvalent metal is zinc.

(7) The photoreceptor of claim 1, wherein the photoconductive insulating material is an alloy of selenium and arsenic.

(8) The photoreceptor of (7) above, wherein the alloy contains about 0.3 to about 487% by weight arsenic.

(9) The photoreceptor of item 8) above, wherein the alloy contains about 63% selenium and 37% arsenic.

00) The light of claim 2, wherein the alloy comprises about 63% selenium and about 37% arsenic; the first polymer contains methacrylic acid and the ratio of styrene to maleic anhydride is 2:1. receptor.

(11) The photoreceptor of 00 above, in which the carboxyl group of methacrylic acid is crosslinked with either zinc or zirconium.

(12) The photoreceptor of 01 above, wherein the crosslinking metal is zinc.

(13) The method according to claim 3, wherein the photoreceptor has an alloy containing selenium and arsenic as a photoconductive material.

04) The method of (13) above, wherein the alloy contains about 0.3 to about 487% by weight arsenic.

(15) The method of α7 above, wherein the alloy contains about 63% selenium and 37% arsenic.

(16) The ratio of styrene to maleic anhydride is l:1
The method according to claim 3.

Claims (1)

Claims: 1 (a) a conductive substrate; (b) a layer of a photoconductive insulating material in operative contact with the conductive substrate; and (c X i ) methyl methacrylate, n-butyl acrylate and acrylic acid or A first polymer that is an addition polymerization product of methacrylic acid; and (11) a second polymer that is an addition polymerization product of styrene and maleic anhydride. an organic coating on a photoconductive layer of . Z (a) Applying a thin film from an aqueous dispersion to the surface of the photoreceptor containing the following ingredients: (i) 45 to 65% methyl methacrylate, 25%
from 5 to 40% n-butyl acrylate and from 5 to 1
70, formed by addition polymerization of 5% methacrylic acid.
(ii) an addition polymerization product of styrene and maleic anhydride having a molar ratio of styrene to maleic anhydride of 2:1 to 1:1; and (110) 1 to 2% tributoxyethyl phosphate, 4 to 6% caprolactam (monomer), 1 to 2% glycerin, 0.5% ammonia and about 1%, with the remainder being a small amount of zinc. and (b) drying the applied dispersion to form a hard film.