Classifications

• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G5/00—Recording members for original recording by exposure, e.g. to light, to heat, to electrons; Manufacture thereof; Selection of materials therefor
  • G03G5/02—Charge-receiving layers
  • G03G5/04—Photoconductive layers; Charge-generation layers or charge-transporting layers; Additives therefor; Binders therefor
  • G03G5/05—Organic bonding materials; Methods for coating a substrate with a photoconductive layer; Inert supplements for use in photoconductive layers
  • G03G5/0528—Macromolecular bonding materials
  • G03G5/0532—Macromolecular bonding materials obtained by reactions only involving carbon-to-carbon unsatured bonds
  • G03G5/0546—Polymers comprising at least one carboxyl radical, e.g. polyacrylic acid, polycrotonic acid, polymaleic acid; Derivatives thereof, e.g. their esters, salts, anhydrides, nitriles, amides

Definitions

• the present invention relates to electrophotography.
• the present invention relates to the use of polymers of hydroxyalkyl esters of acrylic or methacrylic acid as binders for zinc oxide in manufacturing coated copy paper.
• the present invention relates to the use of such coated copy paper in direct electrophotographic processes.
• Electrophotography is one of several terms used to describe a reproduction or image transfer process utilizing electrical and light stimulation of conductive materials.
• Some common terms for commercial processes based on this technique are Electrofax, electrostatography, electrography, xerography, and elcctrographic recording. These processes all employ electromagnetic radiation and a photo-responsive member to obtain, on exposure to light, a latent electrostatic image on the photo-responsive member. Ordinarily, this latent electrostatic image is then converted into a positive image, off-set master, etc.
• Such tech niques areused in commercial off-set printing, computer readout, film developing, map making, long-distance copying, recording, oflice copying, and the like.
• electrophotography There are two general types of electrophotography which'have been commercially successful in the office and industrial copying field. These types, although using the same basic principle, differ in the type of photoresponsive member employed. These types of electrophotography are the direct process and the transfer process.
• the TRANSFER PROCESS relies upon the photoconductive properties of amorphous selenium. This process operates in the following manner:
• a selenium-coated aluminum drum is given a uniform electrostatic charge by exposure to a corona discharge in the dark.
• a light image of the object to be copied i.e. the object image
• a lens system in such a manner that the light strikes the charged drum, dissipating the previously-applied charge in the nonimaged area.
• the drum then carries an electrical charge in those areas corresponding to, for example, printed matter contained on the object being copied (e.g. a page of a book).
• the charged latent image is then developed by cascading an oppositely charged dry toner (or ink) across the surface of the drum.
• the powdered toner clings to the oppositely charged areas on the drum by electrostatic attraction. In this manner, a powder or toner image of the object being copied is formed on the selenium-coated drum.
• a sheet of ordinary paper i.e. paper not coated with a photoconductor
• a corona discharge The charged powder or toner is then transferred from the drum to the paper.
• the paper is then heated to, for example, 200 C. to fuse the powder on the surface of the paper and produce the fixed image.
• the direct process utilizes the same principle as the transfer process, except that a selenium-coated drum is not used. Instead, the image is directly produced on, for example, paper.
• the basis for this technique is the use of coated paper or the like containing, on the surface thereof, a finely-divided photoconductive material.
• zinc oxide is employed as the photoconductive material and is bonded to the paper 'by the use of some suitable organic binder.
• dyes are used to sensitize the zinc oxide.
• the electrical conductivity of zinc oxide shows a significant increase when subjected to light. Consequently, the zinc oxide will lose any previously applied electrical charge when exposed to light.
• the direct process operates as follows:
• the coated paper is made light sensitive by placing a uniform electrostatic charge on the coated surface in the dark by means of a high voltage corona discharge, e.g. 4000 to 6000 volts.
• the coated paper is not sensitive to light until properly charged.
• a latent image is produced on the paper by projecting an object image onto the paper, typically employing white light in the visible range.
• the original electrostatic charge carried by the paper is dissipated in all areas exposed to light and is retained in the shadowed areas, thus forming a latent electrical image on the paper.
• the latent image is similar to that described for the transfer process, except that commercial equipment is available which utilizes both liquid and dry toners.
• the toner consisting of pigmented resin and ferromagnetic particles, e.g. iron filings
• the toner is applied to the paper by a magnetic brush.
• the brush moves across the paper, the charged toner is attracted to the charges of opposite polarity on the paper.
• the pigmented resin particles are suspended in an organic liquid such as odorless mineral spirits. This liquid is then brought in contact with the paper.
• Multi-color copying can be conducted by re-charging the coated copy paper for each new color and utilizing the proper color of toner. This technique is currently applied in map copying.
• the binder for the zinc oxide (or other photoconductor) is extremely important to the success of the electrophotographic process.
• the binder should be one into which the zinc oxide (or other photoconductor) can be dispersed and-the mixture then applied to paper as a coating.
• the binder must not interfere with the photoconductive properties of the zinc oxide.
• the binder should adhere strongly to the paper and provide a flexible coating. Since the binder is ordinarily applied to a sheet of paper, it should be able to withstand 180 bends and wrinkling without cracking or chipping.
• the binder, when mixed with zinc oxide and applied to a paper substrate, should be capable of providing pleasing, clear, legible copies. To enable the photoconductor to accept a maximum electrostatic charge, it is desirable that the individual photoconductor particles be separately encapsulated by the binder.
• the binder should be capable of properly wetting the photoconductor and firmly positioning it on the paper in the photoconductive matrix. Initially, the binder must be an extremely good insulator and prevent any significant decay of the electrostatic charge on the paper (before the photoconductive coating is exposed to the light of the object image). Additionally, the binder should not interfere with the rapid dissipation of the electrostatic charge when the coated paper is ex osed to the light of the object image. Desirably, the binder should not accept or retain any appreciable residual voltage in the exposed area. The binder should not exhibit color or decompose on aging. The binder should bond readily to the pigmented developer or toner and give rise to good printing quality.
• the binder should be effective when used at very low coating weights. Additional properties which the binder should exhibit are nonyellowing tendencies, resistance to solvents (if the coated paper is to be used in combination with a liquid toner) and a resistance to flowing at the fixing or fusing temperature of the toner. Still further, the electrical properties of the coated paper should not be significantly affected by changes in humidity.
• binders have been suggested for use in manufacturing paper for direct electrophotography.
• some acrylic resins have been utilized as modifiers for the more conventional binders.
• acrylic resins have not been used to any significant extent as the primary or sole binders because of certain undesirable properties which they exhibit.
• solvent holdout the use of high molecular weight acrylic resins has increased what is known as solvent holdout. The increased solvent holdout did not allow a suitable fusing of pigment particles to the surface of the exposed paper. Consequently, the pigmented particles did not adhere and smeared. The resulting copies were of poor quality.
• copolymers contain (1) from 1 to 30% by weight (preferably 10 to 20% by weight) of a hydroxyalkyl acrylate or methacrylate, or mixture thereof, (2) from 1 to 15% by weight (preferably 1 to 5% by weight) of a copolymerizable a,/3-unsaturated carboxylic acid, or mixture thereof, and (3) the balance to make 100% of one or more copolymerizable monoethylenically unsaturated vinyl monomers which are devoid of hydroxyl groups.
• the copolymers can be prepared from these monomers by conventional techniques as shown in, for example, US.
• copolymers can be used as binders both with and without cross-linking agents such as the various aminoplasts (e.g. an melamine-formaldehyde resin) and phenolis (e.g. phenol-formaldehyde resins).
• various aminoplasts e.g. an melamine-formaldehyde resin
• phenolis e.g. phenol-formaldehyde resins
• One of the classes of monomers used in preparing copolymers for use in this invention consists of the hydroxyalkyl esters of vinyl carboxylic acids.
• Suitable hy droxyl-containing esters are the C C hydroxyalkyl esters of acrylic and methacrylic acids, as well as mixtures thereof.
• the hydroxyl groups will be in the beta (i.e. 2), gamma (i.e. 3), etc., position.
• beta-hydroxyalkyl esters of acrylic or methacrylic acids will be used.
• Suitable hydroxyalkyl esters are fl-hydroxyethyl acrylate and methacrylate, fi-hydroxypropyl acrylate and methacrylate, ,B-hydroxyhexyl acrylate and methacrylate, fi-hydroxydecyl acrylate and methacrylate, 12- hydroxystearyl acrylate and methacrylate, and the like. Hydroxypropyl acrylate and methacrylate, as well as mixtures thereof, are the preferred hydroxyalkyl esters. Hydroxypropyl methacrylate is especially preferred.
• a second class of monomers used in preparing the copolymers consists of the copolymerizable carboxylic acids.
• Any copolymerizable unsaturated carboxylic acid can be used in preparing copolymers for use in the present invention.
• Suitable acids include maleic acid, fumaric acid, itaconic acid, citraconic acid, crotonic acid, acrylic acid, methacrylic acid, and the like.
• Acrylic acid, methacrylic acid, and itaco nic acid are preferred. If desired, mixtures of these acids can be used. Often, certain of these acids are present in commercially available hydroxyalkyl esters. Thus, a single commercial raw material can provide two of the three classes of monomers needed to form the copolymers used in this invention.
• a third class of monomers used in preparing the copolymers consists of other mono-ethylenically unsaturated compounds which are free of hydroxyl and carboxyl groups and which are copolymerizable with the first two monomer classes hereinbefore mentioned.
• Other monoethylenically unsaturated compounds copolymerizable with the hydroxyl-containing and acidic monomers are the C C cyclic and acyclic esters of acrylic and methacrylic acids, acrylonitrile, methacrylonitrile, styrene, ochlorostyrene, vinyl toluene, a-methyl styrene, etc. If desired, mixtures of these vinyl monomers can be used.
• the hardness, flexibility, and adhesion of the copolymers to various substrates can be varied by adjusting the proportions of these various vinyl monomers.
• Styrene and the C -C alkyl acrylates and methacrylates, as well as mixtures thereof, are preferred.
• the copolymers of this invention can be optionally combined with aminoplast or phenolic resins.
• Suitable aminoplast resins include the alkylated and non-alkylated condensates of an aldehyde with urea, N,N-ethylene urea, dicyandiamide, and aminotriazines. If water soluble condensates are preferred, as in combination with an emulsion or water-soluble copolymer, the non-alkylated or partially alkylated water soluble aminoplasts are preferred over the more fully alkylated aminoplasts. If a solution copolymer is utilized, alkylated aminoplasts soluble in the organic solvent of the copolymer are preferred.
• Phenol-formaldehyde resins can also be used.
• the amount of aminoplast or phenolic resin used in conjunction with the copolymers will usually be from 5-100%, e.g., 1050%, based on the weight of the copolymer.
• a photoconductive material is dispersed in a solution or emulsion of the copolymer by suitable grinding techniques.
• Typical photoconductive materials are zinc oxide, zinc sulfide, silver chloride, mercuric sulfide, and other photoconductive materials known to the art.
• Zinc oxide is the preferred photoconductor.
• the zinc oxide is usually dispersed at a concentration of 4-16 parts by Weight of zinc oxide per one part of copolymer. This mixture is optionally combined with the aminoplast or phenolic resin.
• the zinc oxide is dispersed or mixed at a level of 6 to 12 parts by weight of zinc oxide per one part of copolymer, and more preferably 8-10 parts by weight of zinc oxide per one part of binder.
• the zinc oxide can first be dispersed in a suitable dispersing aid. Then, this dispersant mixture can be diluted with the copolymeric emulsion in a manner conventional to the art of pigment dispersion.
• the final binder or coating compositions will usually have a solids content (i.e., non-volatile content) of from 4070%, preferably 50-60% (the remainder being solvent or water).
• suitable dyes such as rose bengal, methylene blue, rhodamine B, dibromo-fluorescein, and various cyanine dyes can be included in the binder or coating compositions. Usually a mixture of dyes is added, incorporating complementary colors so that the dried coatings have a pleasing, off-white appearance.
• the coating compositions containing the zinc oxide, the copolymer, solvent or water, and optionally an aminoplast or phenolic resin, are then applied to a suitable substrate (usually paper, although metal, foil, etc., can be used) in any suitable fashion such as by brushing, spraying, dipping, roller coating, or the like to give a coated paper having an average of from 5-50 pounds, e.g., 8-30 pounds of deposited dry coating per 3000 square feet of coated paper surface.
• the wet coated paper can be air dried at room temperature or dried by baking, e.g., baked at 200350 F. The preferred drying temperature will depend on whether or not an aminoplast or phenolic resin is present.
• a curing temperature in the range of 150250 F., preferably l90210 F. will ordinarily be used. In the presence of an aminoplast or phenolic resin, higher temperatures are usually required to obtain maximum benefits.
• an acidic catalyst such as toluene sulfonic acid or phthalic acid serves to lower the temperature required for proper curing.
• Example 1 16 parts of methyl methacrylate, 26.6 parts of styrene, 19.9 parts of butyl methacrylate, 19.9 parts of butyl acrylate, and 37.4 parts of a commercially available xylene solution containing 40% of hydroxypropyl methacrylate and 6% of methacrylic acid were mixed together. A mixture of 1.25 parts of azo-bis-isobutyronitrile and 0.2 part of di-tertiary butyl peroxide was then added to the mixture of monomers. The resulting mixture was then sparged with nitrogen and then added dropwise during a 2 /2 hour period at 250 F.
• a 250 gram portion of zinc oxide (American Zinc Sales AZOZZZ661) was then added to 50 grams of the copolymer solution just prepared to give a weight ratio of zinc oxide to copolymer of about 10: 1.
• the zincoxide was dispersed in the solution by agitation for 5 minutes in a Hamilton-Beach mixer. The dispersion was then diluted with toluene to a 58% concentration of pigment and resin (i.e., 42% solvent).
• Example 2 a mixture of 177.6 grams of methyl methacrylate, 201.6 grams of styrene, 272.4 grams of butyl methacrylate, 272.4 grams of butyl acrylate, 97.2 grams of acrylic acid, and 147.5 grams of a 96% solution of hydroxypropyl methacrylate in xylene (which also contained 4.8 grams of methacrylic acid), 24 grams of azobis-isobutyronitrile and 12 grams of di-tertiarybutyl peroxide was added to 340 grams of ethyl Cellosolve in an autoclave.
• the monomer/catalyst mixture was added over a two-hour period to the autoclave which was maintained at a temperature of 345 350 F.
• the pressure increased to 100 p.s.i.g. during the addition.
• Additional solvent 122 grams was added to obtain a 70% NV solution.
• a booster catalyst of 3.5 grams of di-tertiarybutyl peroxide was added four hours after the monomer addition was completed.
• the total reaction time (including monomer addition) was ten hours.
• the copolymer had a final viscosity of 14 stokes at 70.2% NV.
• the acid value of the solution was 45.6.
• Example 4-11 A number of additional copolymers were prepared in the manner described in Example 1. Zinc oxide was dispersed in each of these copolymers in the manner de- Dispersion of Example 3 (grams) 5 scribed in Example 1. The amount of zinc oxide was suffi- Zinc oxide (grams) 250 250 Charge acceptance 070m) clent to give a weight ratio of Zinc oxide to copolymer of (a) At 221b./3,000 sq. ft 440 460 about 1. A dye mixture, equivalent to that of Example (b) At lb./3,000 sq. ft.
• the hydroxypropyl methacrylate was supplied as a solution from Rohm and Haas Company. It is known to be a mixture of isomeric hydroxyalkyl acrylates. The solution contains 38.5-42.5% hydroxypropyl methacrylate, a maximum of 2.0% of higher methacrylates, a maximum of 0.3% of alkylene di-methacrylate, and about 56% of methacrylic acid.
• Dark decay is the voltage drop in darkness over a 4.5 second period from the maximum charge acceptance to the start of the light decay.
• Light decay is the time required for the static charge (i.e. the accepted charge) to be dissipated to 50 volts.
• the residual voltage is the amount of static charge which is not dissipated.
• Methyl methacrylate Methacrylic acid.-.
• cobalt naphthenate e.g. 0.15% to 0.5% based on the weight of the copolymers
• cobalt naphthenate is sometimes used as a drier for oxidizing resins at levels of, for example, 0.01 weight percent
• its use at high levels in conjunction with a non-oxidizing copolymer is very unusual.
• Other known driers, e.g. lead naphthenate do not exhibit the same degree of effectiveness in non-oxidizing resins.
• hydroxyalkyl ester is a C -C hydroxyalkyl acrylate or methacrylate, or a mixture thereof.
• n e-unsaturated carboxylic acid is acrylic acid, methacrylic acid, itaconic acid, or a mixture thereof.
• hydroxyl-free vinyl monomer is styrene or a C -C alkyl acrylate or methacrylate, or a mixture thereof.
• binder composition a mixture consisting essentially of:
• composition of claim 14 as a diluent, solvent or water, or a mixture there- 15.
• the composition of claim 14 wherein the nonvolatile content of said mixture is 40 to weight percent.
• composition of claim 15 wherein said diluent is a mixture of solvent and water.
• composition of claim 14 wherein said mixture also contains sensitizing dyes for said zinc oxide and contains from 10-50 weight percent aminoplast resin based on the weight of said copolymer.
• Coated copy paper comprising paper having a cured coating on a surface thereof, said coating having been formed by applying to said paper a wet film of the binder composition of claim 14 and thereafter curing said composition on said paper, said coated copy aper having an average of from 5-50 pounds of deposited dry coating per 3000 square feet of coated paper surface.

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• Physics & Mathematics (AREA)
• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Spectroscopy & Molecular Physics (AREA)
• General Physics & Mathematics (AREA)
• Paper (AREA)
• Photoreceptors In Electrophotography (AREA)
• Color Printing (AREA)
• Printing Plates And Materials Therefor (AREA)
• Paints Or Removers (AREA)
• Printing Methods (AREA)
• Thermal Transfer Or Thermal Recording In General (AREA)

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Citations (3)

• 0
  • DE DENDAT1249891D patent/DE1249891B/de not_active Withdrawn
  • NL NL132001D patent/NL132001C/xx active
  • NL NL256317D patent/NL256317A/xx unknown
• 1960
  • 1960-09-23 SE SE9075/60A patent/SE310602B/xx unknown
  • 1960-09-28 CH CH1093360A patent/CH428803A/de unknown
  • 1960-09-29 GB GB33522/60A patent/GB973965A/en not_active Expired
• 1966
  • 1966-02-23 US US529247A patent/US3481735A/en not_active Expired - Lifetime
• 1967
  • 1967-02-17 DE DE1522562A patent/DE1522562C3/de not_active Expired
  • 1967-02-21 NL NL6702638.A patent/NL159511B/xx unknown
  • 1967-02-22 GB GB8460/67A patent/GB1178463A/en not_active Expired
  • 1967-02-23 FR FR96278A patent/FR1512257A/fr not_active Expired
  • 1967-02-23 BE BE694515D patent/BE694515A/xx unknown

Patent Citations (3)

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