DE1278242B - Electrophotographic recording material - Google Patents

Description

Electrophotographic Recording Material The invention relates to an electrophotographic recording material with a photoconductive Zn0 binder layer, the compounds containing carboxyl groups or derived from compounds containing carboxyl groups Contains compounds, and optionally further layers.

It is known to be sufficient to achieve a ZnO binder layer high dark resistance to use a binder whose electrical conductivity is so small that the mixture has a markedly higher dark resistance than the photoconductor has itself.

Suitable binders are described in Dutch patent 95 533 and in Belgian patents 533 514 and 587 301. The halogenated Polymers and polycondensates of British Patent 964 885, which are in the Belgian patents 588 049 and 589 996 described photoconductive polymers and the following compounds are also suitable as binders. A. Natural substances and modified natural products a) rosin and esterified rosin. b) Dammar resin.

c) Colophony modified with phenol-formaldehyde resin.

d) Maleate resin made with rosin. e) ethyl cellulose acetate.

f) oxyethyl cellulose acetate. g) cellulose acetate stearate. h) ethyl cellulose stearate.

B. Vinyl Polymers and Substituted Vinyl Polymers I. Photoconductive Vinyl polymers a) the vinyl polymers described in Belgian patent 588 048.

b) the vinyl polymers described in Belgian patent specification 588 050, z. B. the copolymer of 74.5 percent by weight of N-vinyl carbazote and 25.5 percent by weight Acrylic acid ethyl ester.

1I. Polyvinyl ester a) polyvinyl acetate.

b) Copolymer of 90 percent by weight vinyl acetate and 10 percent by weight Crotonic acid.

c) Copolymers of vinyl acetate and a vinyl alcohol ester of Lauric acid, stearic acid or palmitic acid, e.g. B. a copolymer of vinyl acetate and vinyl stearate (92.5, / 7.5; 85; '15; 70/30 or 25/75 percent by weight) or a Mixed polymer of vinyl acetate and vinyl laurate (80/20; 75/25; 60/40 or 50/50 Weight percent).

d) polyvinyl stearate.

e) copolymer of vinyl acetate and maleic acid, which is as follows is prepared: A solution of 300 g of maleic anhydride and 238 g of vinyl acetate is heated and 1.12 g of azobisisobutyronitrile in 3 l of thiophene-free benzene for 9 hours at 75 ° C, The precipitated polymer is suctioned off and washed with methylene chloride. The polymer is air-dried at room temperature, the anhydride groups becoming acid groups hydrolyze. Then it is dried at 40 ° C. Yield: 344 g. III. Vinyl chloride polymers and copolymers a) polyvinyl chloride.

b) Copolymer of 75 percent by weight vinyl chloride and 25 percent by weight Vinyl isobutyl ether.

c) Copolymer of 91 percent by weight vinyl chloride, 3 percent by weight Vinyl acetate and 6 percent by weight vinyl alcohol.

d) Copolymer of 85 percent by weight vinyl chloride, 14 percent by weight Vinyl acetate and 1 percent by weight maleic anhydride. IV styrene polymers and copolymers a) polystyrene.

b) Copolymer of 40 percent by weight of styrene and 60 percent by weight Maleic acid monoisobutyl ester.

c) Copolymer of styrene and methacrylic acid, prepared as follows is: A solution of 645 g of methacrylic acid, 156 g of styrene and 2 g of azobisisobutyronitrile is heated in 800 cm carbon tetrachloride and 7.2 cm thiophene-free benzene for 12 hours Reflux and vigorous stirring. The precipitate formed is filtered off with suction; with Washed hexane and dried at 40 to 50 ° C.

d) Copolymer of 80 percent by weight of styrene and 20 percent by weight Butadiene.

e) Copolymer of 20 percent by weight dimethyl itaconate and 80 weight percent styrene.

f) A copolymer of the structure V. Polymethacrylic acid esters a) Polymethacrylic acid n-butyl ester. b) ethyl polymethacrylate. c) methyl polymethacrylate.

V1. Polyvinyl acetals and copolymers a) One 18.2% vinyl alcohol units containing polyvinyl butyral.

b) mixed polymer of 80 percent by weight vinyl butyral, 17.5 to 20 Percent by weight vinyl alcohol and up to 2.5 percent by weight vinyl acetate.

c) One containing 5.6% vinyl alcohol and 9.5-13% vinyl acetate units Copolymer of vinyl formal, vinyl alcohol and vinyl acetate. C. Polycondensates a) Phthalic acid pentaerythritol ester. b) polyterpenes.

c) Polyester from phosphoric acid and hydroquinone. d) -Polyphenylphosphonic acid hydroquinone ester.

e) Polyphosphite, which is produced as follows: One heats in a wide tube on a propylene glycol bath (boiling point 177 ° C) a mixture of 27.6 g of diethyl phosphite (Inorg. Synth. Vol. IV, p. 58), 15 g of glycol and 13 mg of anhydrous Zinc acetate, with 23 cm 'of ethanol being split off. After distillation of this amount of ethanol the tube is switched on to a vacuum of 5 mm Hg for 2 hours. A light-colored, viscous product.

f) Polyester from fumaric acid and 2,2-bis- (4-oxyphenyl) -propane (Belgian Patent 563 173). g) Polyester from 4,4'-dicarboxyphenyl ether and 2,2-bis (4-oxyphenyl) propane (Belgian patent 563 173).

h) Polyester from 1,3-disulfobenzene and 2,2-bis- (4-oxyphenyl) -propane and polyesters from diphenyl-p, p'-disulfonic acid and 2,2-bis- (4-oxyphenyl @ propane (Belgian Patent 565,478).

i) Polyester from isophthalic acid and neopentyl glycine (Belgian patent specification 563173). j) The polyesters described in Belgian patent 565 478, z. B. the polyester from diphenyl-p, p'-disulfonic acid and 2,2-bis (4-oxyphenyl) propane.

k) The polycarbonates described in Belgian patent specification 563 346, z. B. a polycarbonate made from 2,2-bis (4-oxyphenyl) propane.

D. Other polymers a) Polyindene.

b) polycyclopentadiene. c) silicone resin.

d) 100% cyclic rubber. e) chlorinated polypropylene.

f) One by condensation of an aliphatic ketone with formaldehyde manufactured ketone resin. You can also use low molecular weight compounds or mixtures of low and high molecular weight compounds or unpolymerized compounds use that are polymerized, condensed or crosslinked in situ.

The disadvantage is that most binders because of their inadequate mechanical properties and / or casting characteristics as well as because of their considerable Are not suitable for use on an industrial scale.

The object of the invention is to reduce the dark resistance of zinc oxide in Zn0 binder layers to increase without being bound to special binders.

The object of the invention proceeds from an electrophotographic Recording material with a photoconductive ZnO binder layer containing carboxyl groups or contains compounds derived from carboxyl-containing compounds, and optionally further layers and is characterized in that it at least one aliphatic mono- or polybasic carboxylic acid with water-solubilizing agents Groups, their salt or their reaction product with Zn0 and optionally at least a compound belonging to one of the compound classes a) to d) in free form, in salt form and / or as a reaction product with Zn0 contains: a) Aliphatic single or polybasic sulfonic acids, b) aliphatic boric acid compounds, c) aromatic ones mono- or polybasic carboxylic acids or carboxylic acid anhydrides, d) aromatic sulfonic acid compounds.

Examples of groups which make water solubilizing are the hydroxyl group and called the carbonyl group. As examples of the aliphatic monobasic or polybasic Carboxylic acids with water-solubilizing groups are lactic acid, tartaric acid, citric acid, Lactic acid, a-oxycaproic acid, 9,10-dioxyoctadecanoic acid, 2,3-dioxyoctadecanoic acid, Levulinic acid, 2-oxypentanoic acid and 2-oxy-4-methylpentanoic acid.

The zinc oxide is water-solubilizing with at least one such carboxylic acid Groups brought into contact at each stage of the manufacturing process of the recording material can take place, so both before, during or after Preparation of the coating liquid from which the photoconductive layer is formed is, or after their application to a layer support. The carboxylic acid can be used both as such and in their salt form, however the acid form is preferred.

As examples of the optionally with the carboxylic acid, its salt or their reaction product with ZnO compounds of the above-mentioned classes of compounds a) to d) in free form, in salt form and / or as a reaction product with ZnO the following mentioned: a) methanesulfonic acid and 1-butanesulfonic acid, b) monododecylboronic acid and monononadecylboric acid, c) pyromellitic acid, 4,4'-stilbene dicarboxylic acid and phthalic anhydride and d) benzenesulfonic acid, toluenesulfonic acid and 2,2'-stilbene disulfonic acid. Man has found that in most cases the adsorption of the compounds before especially that of the acidic particles, which run very quickly on the surface of the zinc oxide grain. Around However, to achieve the desired effects, it is not necessary that all Grains or grain agglomerates are covered by the compound. One achieves. the desired Effects also when the photoconductive layer is made from a mixture of untreated and treated zinc oxide.

The compound comes into contact with the zinc oxide in the following manner brought: 1. The low-boiling point is left in a column or in a rotating drum Compound in gaseous form react with the zinc oxide. Then the zinc oxide is dispersed in a solution or dispersion of the binder.

2. The water-soluble or water-dispersible compound is added to an aqueous dispersion of the zinc oxide. Centrifuge or filter the treated zinc oxide, dries it and disperses it in a solution of a Binder.

3. The zinc oxide is dissolved or dispersed in an organic solvent, in that the compound applied is soluble or dispersible, and sets the required Crowd connection too. A binding agent can then be added immediately.

4. The zinc oxide, a binder and a solvent are dispersed for the binder together, for example by grinding for 2 to 36 hours in a ball mill and sets one or more before, during or after grinding of connections to.

5. A coating liquid is applied to a paper support with the compounds and optionally a binder. As an alternative the paper is impregnated with a compound during or after its manufacture. A second layer, the untreated zinc oxide, is applied to this layer and contains a binder. During the application of the second layer and / or the compound diffuses out during storage of the recording material the first layer to the zinc oxide and is adsorbed on this. This method allows to achieve a double effect. When using a connection which is acidic and also electrically conductive, cannot diffused to the ZnO Part in the first layer allow a charge to be dissipated during irradiation.

6. A dispersion of untreated zinc oxide in a binder. You wear one on top of this layer Layer on one or more of the compounds and, if necessary, a binder contains. During the application of the layer and / or while the This compound diffuses from the second layer to the recording material Zinkokyd in the first layer. This method is preferably used if the surface characteristics of the zinc oxide layer are to be changed. By Suitable binders for the second layer can either be the adhesion of the toner increase, which leads to an improved fixation, or decrease, which is in expresses a better transfer of the toner image to an image receiving material.

The dark resistance of the zinc oxide layers shows a maximum when you use increasing amounts of the compound: If you use salts, you need a lot higher amounts to achieve the same effect than with free acids. The amount of salt varies between 0.5 and 40 percent by weight, based on the Zn0. The dark resistance of ZnO is described in one of W. S i m m, Chemie-Ingenieur-Technik, 31 (1959), 44 Measuring cell measured.

The dark resistance of a photoconductor-binder layer is measured with ohmic contacts or with blocking contacts. If electrolytically developed, e.g. B. according to the Belgian patent 561203, is measured with ohmic contacts, if developing with a toner, is measured with blocking contacts. The procedure is as follows: Zinc oxide, which is dispersed in a binder, is poured onto a substrate with a relatively high conductivity; z. B. made of paper or metal. The conductive layer is 10 to 15 #tm thick. The recording material is stored in the dark for 15 hours and then conditioned under the required humidity and temperature conditions. The electrophotographic recording material is then placed with its conductive layer support on a grounded metal plate and charged electrostatically to saturation with the negative pole of a high voltage source of 6000 to 7000 volts; this saturation is reached in most cases after 5 to 10 seconds. The recording material is removed from the grounded metal plate and the dark discharge is recorded continuously, e.g. B. by means of an electrometer with a vibrating electrode, e.g. B. with the electrometer described by CJ Young and HG Greig in RCA Review (1954), XV, p.469, connected to a recording device. The measurement of the field strength begins exactly 5 seconds after the end of the charging process. The measurement results are expressed in volts / cm. The relaxation time, ie the time that elapses from the beginning of the measurement at the field strength Fo to the moment in which this value becomes is reduced (e is the base of the natural logarithm), and the field strength can be read from the dark discharge curve. It can be assumed with some probability that the adsorption of the compound on the zinc oxide grains gives rise to the reduction of the electrical leakage at the grain surface of the zinc oxide. Making the zinc oxide grains hydrophobic in the usual sense is out of the question because the dark resistance can also be increased by adding a water-soluble antistatic (electrically conductive) phosphoric acid derivative, e.g. B. where x = 1 or 2, y = 3-x, a = 1,2 or 3, b = 3-a, X = hydrogen or ethyl. The Maxwell relation r = e.FO.n in which r = the relaxation time in seconds, F = the dielectric constant of the layer, measured at - 1000 Hz (f varies in the layers considered here mostly from 2.5 to 5), eo = the dielectric constant of the vacuum, namely o = the dark resistance of the layer in ohm cm, gives the relationship between the relaxation time, the dielectric constant and the dark resistance. The binders can be divided into two groups, depending on whether the specific dark resistance is higher or lower than that of the treated zinc oxide.

Binders whose specific dark resistance is higher than that Dark resistance of the treated zinc oxide, are the compounds a), b), c) and d) of the abovementioned class A, the compounds a) and b) of the class B, I, the compounds a), b), c), d), e) and f) of class B, III, the compounds a), d), e), f), g) and h) Class B, IV, the compounds a), b), c) and d) Class B, V, the Compounds a), c), d), e), f), g), h), i), j) and k) of class C, the compounds a), b), c), d), e), f) and g) of class D.

Binders whose specific dark resistance is lower than the dark resistance of the treated zinc oxide, are the compounds e), 0, g) and h) of class A, the compounds a), b), c), d) and e) of class B, II, the Compounds b), c) and i) of class B, IV, the compounds a), b) and c) of Class B. IV. The compound b) of class C. The latter possess binders does not have a high specific electrical resistance, which is why it was not previously called Binders for photoconductors were considered suitable.

The invention achieves that binders that. earlier because of their too low specific resistance could not be used the production of photoconductive layers can be used because by the invention of the dark resistance of Zn0 is increased. Another increase the dark resistance is obtained if at least one of the above is used Connection classes a) to d) also brings in connection belonging to it. In the end the invention also makes it possible to determine the ratio of zinc oxide to binder up to 7 parts by weight of zinc oxide to 1 part by weight of binder, what in turn enables the production of more sensitive photoconductive layers.

According to one embodiment of the invention, the recording material contains Lactic acid, phthalic acid or phthalic anhydrides, what a technically special interesting increase in dark resistance.

According to a further embodiment of the invention, the photoconductive or a layer adjacent to the photoconductive layer between 0.1 and 10, preferably between 0.1 and 3 percent by weight (based on the weight of the Zn0) the substituted aliphatic carboxylic acid, the salt of such a carboxylic acid or its or its reaction product with Zn0.

According to a further embodiment of the invention, the photoconductive Layer between 7 and 27 parts by weight of Zn0 on 3 parts by weight of binder.

The above amounts produce electrophotographic ones which are particularly useful in technical terms Recording materials.

According to a further embodiment of the invention, the photoconductive Layer as a binder from a copolymer of vinyl acetate and an ester an aliphatic carboxylic acid with at least 12 carbon atoms and vinyl alcohol.

The presence of such a polymer offers the advantage of the binder from a water-miscible alcohol, such as ethanol, instead of toxic chlorinated ones To be able to apply hydrocarbons or aromatic hydrocarbons and nevertheless a flexible, but mechanically strong photoconductive layer without plasticizer content.

Example 1 75 g of zinc oxide. in 500 ml of a 40 oigen solution Copolymer of 85 percent by weight Vinyl acetate and 15 percent by weight Vinyl stearate are dispersed in ethyl alcohol. 48 hours in a ball mill ground. Before pouring, 0.5 ml of lactic acid become the very stable dispersion added and the mixture stirred thoroughly.

"The application to a substrate made of barytized paper by 90 g / m 'is carried out with the aid of a doctor blade device in such a way that 1 l of the dispersion covered an area of 15 m2.

After drying, the layer obtained is charged with a corona discharge. After they have been exposed for 4.5 seconds through a slide with a 100 watt lamp set up at a distance of 10 cm, the charge image is developed using an electrophotographic developer made from iron powder as a carrier and a toner. After fixing by heating, a strong and high-contrast image is obtained, even at high relative humidity. Example 2 0.1 ml of lactic acid are added to 100 ml of a 2% strength alcoholic solution of a copolymer of 85% by weight of vinyl acetate and 15% by weight of vinyl stearate. This solution is used to apply a layer to a paper support (60 g (m)). A layer of a suspension composed as follows and thoroughly ground for 24 hours is applied to this: vinyl acetate-vinyl stearate copolymer (85/15). .......... 4 g ethyl alcohol, 96%............ 100 ml zinc oxide .................. .... 15 gl% solution of Rhodamine B (C.1. 45170) in ethanol ....... 94 ml The layer is applied with a squeegee in such a way that 12 in 'are covered per liter.

Lactic acid diffuses out during spreading and storage the lower in the photoconductive layer, so that the lactic acid with the zinc oxide comes into contact and reacts with it. It was found that the photoconductive Layer in this way can be applied more evenly than if the lactic acid the Zn0 suspension is added. The extension of the relaxation time in this Recording material is very clearly perceptible. Example 3 10 g of zinc oxide become dispersed in 100 ml of water and ground in a ball mill for 24 hours. After this 2 ml of isopropyl alcohol and 4 ml of a polyvinyl acetate latex are ground with vigorous stirring admitted. Then, with stirring, 0.6 ml of a 10% aqueous lactic acid solution are added added to the dispersion.

The dispersion is then made by dipping onto a support Baryta paper applied in such a way that 1 1 10 in 'covered.

After drying, the recording material is stored at 20C and 50% relative humidity charged, imagewise exposed and with a carrier-toner developer developed. When compared with a recording material that does not contain lactic acid is added, the result is a higher-contrast and sharper image with good opacity. Example 4 1500 g of zinc oxide are mixed with a solution of 120 g of a copolymer from 85 percent by weight vinyl acetate and 15 percent by weight vinyl stearate in 3 liters of ethanol mixed and ground in a ball mill for 24 hours. The dispersion is with a Solution of 800 g of the copolymer of 85 percent by weight vinyl acetate and -15 Percent by weight vinyl stearate diluted in 21% methanol. This dilute dispersion is divided into 50 ml portions, and each 50 ml portion is made up of 4 percent by weight Solution of the copolymer of 85 percent by weight vinyl acetate and 15 percent by weight Vinyl stearate was added to ethanol.

Each serving comes with one of the following compounds in the specified Amount offset (percent by weight of zinc oxide). The addition takes place under strong Stir. Calcium lactate. . . . . . . . . . . . . . 0.6 to 10% copper lactate. . . . . . . . . . . . . . . 0.6 to 3% ammonium lactate. . . . . . . . . . . 0.6 to 10% Finally, 0.4 ml of a 10% solution of Rose Bengal is added to each serving (C.1. 45435 and 45440) in ethanol are added, and each portion is then for another 4 hours ground.

The various dispersions are then applied to one with a doctor blade Finally, for each portion, 0.4m1 of a 1 % solution of Rose Bengale (C.1. 45435 and 45440) in ethanol was added, and each The portion is then ground for another 4 hours.

The various dispersions are then applied to one with a doctor blade Layer support made of barytaised paper of 90 g / m 'applied. After drying the various samples are tested for their moisture resistance. The at Dark decay curves of these recording materials measured at 22 ° C. and 50% relative humidity show greater relaxation times than the recording materials without these Links.

Claims (5)

Claims: 1. Electrophotographic recording material with a photoconductive Zn0 binder layer that contains carboxyl groups or contains compounds derived from carboxyl-containing compounds and, if appropriate further layers, characterized in that there is at least one aliphatic mono- or polybasic carboxylic acid with water-solubilizing groups, their salt or their reaction product with ZnO and optionally at least one of the Compound classes a) to d) belonging to compound in free form, in salt form and / or contains as reaction product with Zn0: a) Aliphatic monobasic or polybasic Sulfonic acids, b) aliphatic boric acid compounds, c) aromatic monobasic or polybasic Carboxylic acids or carboxylic acid anhydrides, d) aromatic sulfonic acid compounds. 2. Recording material according to claim 1, characterized in that it contains lactic acid, Contains phthalic acid or phthalic anhydride. 3. Recording material according to claim 1, characterized in that the photoconductive or one of the photoconductive Layer adjacent layer between 0.1 and 10, preferably between 0.1 and 3, Percentage by weight (based on the weight of the Zn0) of the substituted aliphatic Carboxylic acid, the salt of such a carboxylic acid or its or its reaction product with Zn0 contains. 4. Recording material according to claim 1; characterized, that the photoconductive layer is between 7 and 27 parts by weight of Zn0 to 3 parts by weight Contains binding agent. 5. Recording material according to claim 1, characterized in that the photoconductive layer contains, as a binder, a copolymer of vinyl acetate and an ester of an aliphatic carboxylic acid having at least 12 carbon atoms and vinyl alcohol. Documents considered: German Auslegeschrift No. 1 101 146.