DE1797513C3 - - Google Patents

Description

35

The invention relates to an electrophotographic process for reproducing a continuously toned color Image on an insulating layer consisting of an organic binder, at least «; an essentially colorless starting dye compound is dissolved, which upon exposure to at least one component of the layer reacts to form a dye, which of the layer imparts photoconductive properties.

In general, it is a characteristic of commercially available electrophotographic recording materials that that they produce sharp contrasts. It is therefore in the case of commercially available recording materials, such as, for example, those that have a photoconductive, insulating layer made of selenium or zinc oxide dispersed in an organic binder the improvement of the reproduction of halftone originals is desirable. Also is a Improvement in the reproduction of extensive, strongly colored areas is desirable. One has endeavors to achieve the desired improvements through the use of halftone techniques in the reproduction process to achieve. However, the raster techniques required additional equipment for reproduction, the light sources are used less well and / or the maximum achievable image density is reduced.

It is known (German Auslegeschrift 1 098 814), in the photoconductive layer of an electrophotographic recording material by adding inert substances of a certain grain size to form a grid. This is primarily intended to create the edge effect be reduced. The disadvantage of this is that the maximum achievable at the same time due to the addition Darkness is reduced. It is also known (French patent specification 1210 685), the spectral To improve the sensitivity of an electrophotographic recording material by Zinc oxide embeds in point-like areas in a photoconductive layer, these point-like Areas from 2 to 98% of the surface of the photoconductive layer can occupy and one layer with areas of different sensitivity.

The object of the invention is to provide an electrophotographic process which an improvement in the reproduction of halftone originals allows and a softer gradation over the entire gray scale leads to the deepest degrees of blackening.

In a method of the type mentioned at the outset, this object is achieved according to the invention in that that the layer is exposed with a grid, whereby in the layer the dye in accordance is formed with the grid that the layer is electrostatically charged, that imagewise an electrostatic latent image is formed on the layer and that the latent image increases a visible reproduction of the original is developed.

To develop the latent image into a visible representation of the original, is preferred a finely divided developer material applied to the latent image on the layer. Furthermore, the layer be coated with a material that is insoluble in this and an adhesive film with a Thickness up to 500 A form «.

One or more colorless starting dye compounds are used to produce the insulating layer dissolved and added to a solution of an organic binder. One can use this solution a suitable mat slipped on and left to dry, or you can make it a self-supporting Film shedding. The binder not only has the function of a binder, it also reacts in the solid state on exposure to the dye starting compound with the formation of a third substance, which acts as a photoconductive compound. The photoconductive compound is an in situ from the Dye starting compound formed dye. the This photoconductive compound is formed when the layer formed is exposed to actinic compound Radiation, such as B. with infrared, visible and / or ultraviolet light.

An essential step in the process of the invention is that the dye is so is formed that a substantially uniform geometric pattern of discrete, photoconductive Areas on the insulating layer arises. For this purpose, the insulating layer is replaced by a suitable one Original exposed. For example, the insulating layer can briefly be exposed to ultraviolet light falling through a contact halftone photographic screen plate. That way becomes a point or line shaped grid structure stirred into the insulating layer. The radiation causes dye formation in the exposed areas, whereby the layer becomes photoconductive at these points. The unexposed center of a point or a line contains little or no dye (photoconductor) and is in an electrophotographic

see procedures the least sensitive. Outside the center of the point or line will be increasing Amounts of dye are formed, which increases the photosensitivity.

In most cases, significantly less than 1% of the colorless starting dye compound has to be converted into the dye (photoconductor) in order to ensure maximum sensitivity. The formation of more dye merely increases the amount of dye in the insulating layer without increasing the photosensitivity. In this way photoconductive layers are produced which contain only small amounts of a photoconductor and which are essentially transparent to light of the visible spectrum, have a dark resistance of at least 10 ⁹ ohm-cm and a specific resistance which is at least two orders of magnitude lower in the photoconductive areas of irradiation.

The processor can thus be supplied with an electrophotographic recording material, the properties of which he can determine himself by exposing a grid of his own choice. Care only needs to be taken to avoid accidental exposure of the material prior to use. The processor must then, if he wants to produce a halftone image (or, if necessary, at some point beforehand) select a suitable halftone (dot or line) screen transparency, expose the insulating layer through this screen transparency, which causes dye formation in the layer light-sensitive grid pattern is incorporated. The layer is then electrostatically charged and exposed through a continuous tone image, producing an electrostatic latent image which is developed into a visible image.

The method according to the invention makes it possible, with the simplest possible use of the recording material, to produce halftones in significantly finer gradations can be reproduced than was previously the case, and that extensive areas of equal contrast appear without disturbing shading in the copy. It is also of commercial importance that the recording material can initially also be delivered to the consumer without screening, who then use the a grid plate can build the desired grid type into the recording material itself.

Preferred binders that react with dye starting compounds are the following:

1. Chlorinated paraffins,

2. polyvinylidene chloride,

3. polyvinylidene chloride copolymers,

4. Vinyl chloride copolymers.

The following binders can also be used if they are combined with the above or with mixed with other non-volatile halogenated organic substances.

5. Polystyrene and styrene copolymers,

6. butadiene copolymers,

7. polyacrylates and acrylic copolymers,

8. Solid uncured epoxy resins,

9. Hydrocarbon terpene resins.

In the case of copolymers, the monomers not mentioned are vinyl acetate, vinyl alcohol, Acrylonitrile, acrylic ester.

There are numerous dye starting compounds

which are soluble in one of the above binders and can react with it. Preferred Dye starting compounds have the general formula

wherein R ₁ and R _{2 are} mono-alkylamino, di-alkylamino, monoarylamino or alkylarylamino, X is hydrogen or

J'V

denotes, where R ₃ is a hydrogen atom or methyl, methoxy, R, - or

and where R ₄ . and R ₅ denotes hydrogen, methyl or methoxy groups.

These dye starting compounds are leuco bases from which the dyes can be prepared by oxidation in the presence of a suitable anion. The anion is provided by the binder or other halogen-containing compound. The oxidation takes place through irradiation.
Dye starting compounds can be used which give photoconductive materials with a certain spectral sensitivity and with a certain degree of transmittance. The following two dye starting compounds are inexpensive and are therefore preferred.

1. The leuco base of malachite green,

3is- (4,4'-dimethylaminophenyl) -phenyl-methane;

(4,4'-tetramethyl-diaminotriphenyl-methane)

(CH ₃ J ₂ N

N (CH ₃ J ₂

2. The leuco base of crystal violet,

Tris (4,4 ', 4 "-dimethylaminophenyl) methane;

(4 ₍ 4 ', 4 "-hexamethyItriamino-triphenylmethane)

(CH ₃ ) ₂ N

-N (CH ₃ ),

In addition to these dye starting compounds, the following are suitable:

7. Tris- (4,4 ', 4 "-phenylaminophenyl) -meihan

3. Bis- (4,4'-dimethylaminophenyl) -4 "-methoxy-

phenyl-methaa;

(4,4'-tetramethyl-diamino-4 "-methoxytriphenyl-methane)

OCH ₃

4. bis (4,4'-dimethylaminophenyl) -4 "-tolyl-ynethane; (4,4'-tetramethyl-diamino-4 "-methyl-triphenyl-

methane)

CH ₃

Ν — H
H

-N-

8. Bis- (4,4-ethylphenylaminophenyl) -phenyl-methane

QH ₅

C ₁ H

-N

9. Bis- (4,4-methylaminophenyl) -4 "-toyl- ^methane

CH ₃

(CHj) ₂ N- ^ yz-χ >

"N (CHj) ₂

5. Bis- (4,4'-ethyl-benzylaminophenyl) -

phenyl methane; 4,4'-benzylidene-bis- (N, N-ethyl-benzyl-aniline)

VN-CH ₃

C ₂ H ₅

CH ₂

C ₂ H ₅

10. Bis- (4,4'-dimethylaminophenyl) -2 ", 4" -dimethoxyphenyl methane

OCH ₃

OCH,

CH ₂

6. Bis- (4,4'-morpholinophenyl) -phenyl-methane

H ₂ H ₂
CC

CC
H ₂ H ₂

H ₂ H ₂ CC

CC H ₂ H ₂

11. Bis- (4,4 -dimethylaimnophenyl) -2 ", 4" -xylyl-raethane

CH ₃

CH,

12. Bis (4,4-phenylaminophenyl) -4 "-ethylaminophenyl-methane

13. Bis- (4,4'-methylaminophenyl) -4 "-methoxyphenyl-methane

OCH ₃

14. Bis (4,4-methylaminophenyl) -4 "-tolyl-methane

CH,

N-CH,

15. Bis (4,4'-methylaminophynyl) -2 ", 4" -dimethoxyphenyl methane

16. Bis (4,4'-methy] aminophenyl) -2 ", 4" -xylyl-methane CH ₃

17. Tris (4,4 ', 4 "-Elhylphenylaminophenyl) methane

CjH ₅

Suitable solvents for the binder and the dye starting compound are: methyl ethyl ketone, toluene or mixtures thereof. In some cases it is desirable that a photoconductive layer or coating be as transparent to radiation as possible. For the production of _{transparent insulating layers, IV 3} parts by weight or less of the starting dye compound are used per 10 parts by weight of the binder.

The insulating layers can vary in physical properties or their appearance various modifying agents can be added provided that they improve the electrical properties not affect. For example, flexibility can be increased by having low Adds amounts of a plasticizer, such as. B. tricresyl - phosphate, butylphthalyl - butyl - glycolate, Tris - (2,3 - dibromo - propyl) - phosphate and di- (2-ethylhexyl) -phthalate.

Increased flexibility can also be achieved by using different binders with one another combined. For example, blends of polyvinyl chloride with chlorinated paraffins result or hydrocarbon terpene resins, highly flexible insulating layers.

If an insulating layer is produced that does not contain a dye parent compound in one halogenated binder is present in dissolved form, a non-volatile halogenated compound is also used added, such as B. Tris - (2,3 - dibromopropyl) phosphate or compatible chlorinated paraffin.

To stabilize the dye starting compound, i. H. to avoid premature dye formation. a stabilizer is added to the insulating layer. Suitable stabilizers are compounds the formula

(C ₈ H ₁₇ ) ₂ - Sn - (S - CH ₂ - COOC ₈ H, ₇ ) ₂

or solid, unreacted epoxy resins.

The insulating layers can be self-supporting or they can be on suitable substrates be formed.

Recording materials with photoconductive layers according to the invention are suitable for production of halftone images. To do this, a uniform electrostatic charge is applied to the photoconductive layer applied and imagewise exposed, whereby an electrostatic image is generated on the layer, which is developed by applying finely divided electroscopic developer particles in a known manner. When charging, it is particularly useful when using coated paper or self-supporting layers.

309 682 "2 51

Th expediently, electrostatic charges of one polarity on one side of the recording material and at the same time on the other ropes of the recording material to apply electrostatic charges of opposite polarity.

With the aid of the method according to the invention, copies of color images can also be produced. For this purpose, the pre-rasterized recording material is charged and exposed through suitable color filters, that a latent electrostatic image is generated on it, that of a color component of a colored original is equivalent to. This electrostatic latent image is then developed with a color developer that responds to this one color. Charging and exposure are repeated for a different color, like this that a second electrostatic image is generated on the same recording material. This second electrostatic image is then developed into the appropriate color with a suitable color developer. This process is repeated as many times as necessary to reproduce all of the color components of the original image is necessary. The color images obtained in this way are fixed on the by heating Softening temperature of the layer.

Example 3

B e i s ρ i e 1 1

^25th

1.5 parts by weight of a vinyl chloride copolymer are dissolved in 15.5 parts by weight of methyl ethyl ketone and after complete dissolution with 1.0 part by weight of the leuco base, bis- (4,4'-dimethyl-aminophenyl) -phenyl-methane offset.

The obtained solution is coated on an aluminum plate and then dried. The coated Aluminum plate can be heated moderately to speed drying. An excessive one Heating (2 to 3 minutes at a temperature of 180 to 200 ° C) causes dye formation. The risk of undesired dye formation can be reduced by the fact that the layer in the Vacuum dries without heating.

A transparent, positive 60-line grayscale grid is placed on top of the layer and marked with a 4 watt UV lamp exposed for 15 minutes from a distance of 15.2 cm. The exposure times can can be significantly shortened when using high pressure mercury vapor lamps or mercury arc lamps used as light sources for the ultraviolet rays.

Such a recording material contains a line grid in which along the center of each The sensitivity of the raster stripe is low or nonexistent, since there is no dye here was formed. Sensitivity and dye formation increase towards the two edges of each strip gradually up to a maximum, whereby the dye formation is caused by a weak, green color in the per se transparent layer

is shown. ". . ,,
^{6 ö} example 2

With a solution of 16.8 parts by weight of a vinyl chloride mixture polymerizats, 5.6 parts by weight of a solid, uncured epoxy resin and 16.5 parts by weight the leuco base is bis (4,4'-dimethyl-aminophenyl) -phenyl-methane and methyl ethyl ketone a slide glass coated in the manner described in Example 1. By UV rays passing through If a grid of points fall, a very pale greenish-yellow grid is produced.

1 part by weight of a copolymer of 91 ". Vinyl chloride and 9% vinyl acetate is in 20 CJe parts by weight of methyl ethyl ketone dissolves ge under heating. After cooling down to room temperature 0.75 parts by weight of bis (4,4'-dimethylaniino phenyl) phenyl methane are added and dissolved A mirror-smooth aluminum plate is coated with the solution, the solvent is evaporated off and mechanically stripped the layer from the aluminum plate. You get a self-supporting one electrophotographic recording material having the same sensitivity as in Example 1 indicates. A grid is generated as in Example 1, with the irradiation either before or after deir mechanical stripping from the aluminum plate takes place.

Example 4

As in Example 1, an aluminum plate is made with a solution of 10 parts by weight of a vinyl chloride-acetate copolymer (15% solids in Methyl ethyl ketone), 0.20 parts by weight bis (4,4'-methylaminophenyl) - 4 "methoxyphenyl - methane and 5 parts by weight of toluene coated and processed. The sensitivity of the photoconductive layer differs slightly from that of the examples! and 2 from. The grid shows a greenish-blue color.

Example 5

If a comparatively strong coloring: b / u. Color of the grid does not interfere, a layer as in Example 2 can be produced from the following substances will:

10 parts by weight of a solution of a vinyl chloride / vinyl acetate mixed polymer (15% solids in equal parts of methyl ethyl ketone and toluene).

0.5 parts bis (4,4'-dimethylaminophenyl) phenyl

methane,
0.2 parts bis - (4,4 ', 4 "- dimethylaminophenyl) -

methane,
0.3 parts bis (4,4'-dimethylaminophenyl) - 4 "-

methoxyphenyl methane,
7 parts of methyl ethyl ketone as a solvent.

This layer has a broader spectral sensitivity than any "of the" layers of FIG Examples 1 to 4. The screen is reddish-blue in color.

Example 6

Very thin transparent layers can be produced from the following substances as in Example 2 will:

1.5 parts by weight of a styrene-butadiene copolymer,

I part by weight of bis (4,4'-dimethylaminophenyl) phenyl methane,

20 parts of solvent (equal parts of methyl ethyl ketone and toluene),

0.1 part by weight of tris (2,3 - dibromo - propyl) phosphate.

If conductive glass is used as the substrate, a transparent recording material is obtained, whose grid shows little color.

Claims (3)

Patent claims: 1. Electrophotographic process for reproduction of a continuously toned image on an insulating layer made of an organic The binder consists of at least one essentially colorless starting dye compound is dissolved, which upon exposure to at least one component of the layer under formation of a dye, which imparts photoconductive properties to the layer, thereby reacts characterized in that the layer is moistened with a grid, whereby in the layer the Dye is formed in accordance with the grid that the layer is electrostatically charged that an electrostatic latent image is formed imagewise on the layer and that the electrostatic latent image develops into a visible representation of the original will. 2. The method according to claim 1 _T, characterized in that a finely divided developing material is applied to the latent image on the layer for developing the latent image in a visible reproduction of the original. 3. The method according to claim 1, characterized in that the layer with a material is coated, which is insoluble in this and an adhesive film with a thickness up to 500 Ä forms.