JPS5833548B2 - Photoconductive compositions and electrophotographic elements - Google Patents

Description

Detailed Description of the Invention The present invention provides an electron donor and an electron acceptor having photoconductivity or semiconductivity (in this case, the acceptor itself may or may not have photoconductivity). An electrophotographic reproduction element comprising a suitable support coated with a photoconductive coating layer comprising a donor-receiver composite formed by the present invention.

The present invention further provides for preparing a mixture of an electron donor organic compound and an electron acceptor organic compound that are photoconductive or semiconductive, thereby forming a donor-acceptor complex (wherein the acceptor itself is also photoconductive). A method of producing a photoconductive composition suitable for the production of electrophotographic reproduction elements with said composition by forming a photoconductive composition, which may or may not have.

Photoconductive compositions containing organic compounds as monomers or polymers as photoconductive elements are known.

Examples of monomers that have been produced as photoconductors include anthracene, phenanthrene, pyrene, perylene, carbazole, substituted carbazole, oxadiazole, substituted oxadiazole, and monomers containing one or more heteroaromatic rings in the aromatic ring. There are many other aromatic polynuclear compounds with or without atoms; examples of polymers that have been described in the literature as Sino-American conductors include poly-1 and poly-9-vinylanthracene, polyacenaphthylene. , poly-N-vinylcarbazole, and nitrified or halogenated poly-N
- Vinyl carbazole, especially poly-3-brome and poly-
There are substitutes of said compounds such as 3,6-dibromo N-vinylcarbazole and copolymers of 3-nitro-N-vinylcarbazole and acenaphthylene.

However, all organic photoconductors known to date have photosensitivity that is far inferior to that of common inorganic photoconductors Se and ZnO.

Therefore, until recently, organic photoconductors have not been commercially available.

Photosensitization is made possible by the use of sensitizing compounds such as photosensitizers to shift the absorption spectrum toward the visible part of the electromagnetic emission spectrum and activators to increase photosensitivity at certain wavelengths. Continuous efforts have been made over the years to improve the.

Although such efforts have long been fruitless, it appears that some significant progress has recently been made.

Electrophotographic reproduction elements can be formed by choosing as sensitizing compounds electron-accepting compounds that are capable of forming donor-acceptor complexes (π-complexes or charge-transfer complexes), especially with electron-donating photoconductive compounds. A photoconductive layer with sufficient photosensitivity is obtained.

For example, German patent no. 1111935, 1127218
Dutch Patent Application No. 7013324 (contrary to what is implied from earlier patent specifications such as No.
Published), German Patent Application No. 1572347 and I, B, M, Journ.

Res, Develop, 15.75 (1971
It appears that the ratio of donor to acceptor should be approximately 1:1, as described in the article by R.M. Schaffert, published in January 2006.

Known complex-forming receptors include, for example, tetracyanoethylene (1,38), chloranyl (1,38), 2.
3-dichloro-5,6-dicyano-p-benzoquinone (
1,47), p-benzoquinone (0,75) and 1.3
- There is 5-trinitro-2-chlorobenzene (-hycryl chloride) (0,58).

The number in parentheses after the compound indicates the measured electron affinity (E
A) is expressed in eV.

However, the best known and most commonly used complexation acceptor is the structurally similar carbazole or polyJN-vinylcarbazole, which produces a highly photosensitized composition. - trinitrofluorenone.

Recently, fluorenone-based electron-accepting compounds have also been included in the category of sensitizing compounds.

This is for example British Patent Specification No. 1245008, no.
Related to the substituted or unsubstituted 9-dicyanomethylene fluorene compound described in No. 222252.

Although this is not mentioned in the two UK patent specifications, J. Phys. Chem, 70. nr
, 12.3848-52 (1966) and 73, nr.
Japan K on 12.43812 (1969)
, Mukherjee, the 9-dicyanomethylene fluorene compound itself has photoconductivity.

Whether the sensitized complex formed is itself photoconductive or has a photosensitizing additive and/or active effect, the mechanism for forming this sensitized complex is unknown.

Therefore, a sensitizing compound that, as a result of its electron-accepting properties, is capable of forming a π-compound in cooperation with a photoconductive electron donor will hereinafter be conceptually described as an "acceptor."

Nevertheless, in fact, there are only two types of π-complex compounds that are considered to be receptors for poly-N-vinylcarbazole (to date the most attractive and longest-used photoconductor). That is, there are only the above-mentioned fluorene compounds and fluorenone compounds.

Of these two types, the most highly regarded and practically suitable compound is the 2,4,7 trinitro derivative.

Without such a limited variety of compounds, it is often difficult to develop a copying element based on an organic photoconductor that performs optimally in all cases. It should be obvious.

The present invention allows for a wide variety of acceptors for photoconductive organic donors, especially poly-N-vinylcarbazole.

It is an object of the present invention to provide an electrophotographic reproduction element which provides the same degree of satisfaction as elements known in practice.

This consists of an electron donor and an electron acceptor that have photoconductivity or semiconductivity (the acceptor itself may or may not have photoconductivity); is the following formula [wherein n=1 or 2, R and R may be equal or different (each has one or more hydrogen atoms or one or more electrons known per se] Indicates an attractive group.

This is achieved by selecting a photocopy element comprising a suitable support coated with a photoconductive coating layer containing a donor-acceptor complex characterized in that it is a compound.

A compound where n=1 is dibenzothiophene-5
-oxide and n=2 is described as dibenzothiophene-5,5-dioxide.

Some of the dibenzothiophene oxides and dioxides just mentioned are already known per se, and Pharm
, Bul 1, Tokyo, Part 5 (19
57), pp. 548-552 (already known, especially in the field of pharmaceutical sciences, it is well known to those skilled in the field of electrophotographic methods to form donor-acceptor complexes using other compounds). Therefore, the property of the compound to easily accept electrons was not known.

Of course, the use of these compounds as receptors for forming complexes in electrophotographic methods was not known, nor was it clear, as will be clear from the description below.

This is because in order to be able to form a donor-acceptor complex, one compound would actually have to give up an electron (and the donor) and the other compound would have to capture an electron. (receptor).

If the donor is kept the same, the amount of complex formed will only depend on the acceptor.

The higher the electron affinity (EA) of the receptor, the faster and/or stronger complex formation will occur.

In addition to the FA factor, there are also other factors, in particular the mutual compatibility of the donor and acceptor that allows them to approach each other sufficiently to form a complex due to their respective electron-emitting and electron-capturing properties. Atomic space factors such as the presence or absence of atomic compounds also seem to play a role in complex formation.

2.4.7-)! J nitro 9-fluorenone (T
NF) is a good active receptor, its EA is 1.18
It is eV.

In the search for new receptors, the aim should be to find receptors as satisfactory as TNF, and receptors with inferior properties are not needed.

2,4,7-dolinitro-9-dicyanomethylenefluorene (DTF) has the same spatial structure as TNF,
DTE may be considered a better receptor than TNF based on the fact that DTE has an EA of 1.44 eV.

As a result of experiments, the above prediction was found to be correct.

That is, the photoconductive layer consisting of PVK+DTP is PVK+TN.
It has considerably higher photosensitivity than photoconductive layers formed from F.

1,3,7-trinitrodibenzothiophene-3,5-dioxoid of the following formula has the same spatial structure as TNF, with only 0,98
Based on the fact that it does not have an EAL of eV, dibenzothiophene-dioxoid (DBTO2) may be considered a poorer receptor than TNF.

However, this does not seem to be the case.

That is, a photoconductive layer consisting of PVK and DBTO2 with a donor:acceptor ratio of 2:1 is composed of PVK and TBT in the same ratio.
It has the same photosensitivity as a photoconductive layer made of NF'.

The present invention adds to the two already existing classes of receptors a new class of receptors that is highly suitable for electrophotographic methods.

Particularly in combination with poly-N-vinylcarbazole, this new receptor compound is also based on organic photoconductors with respect to all properties important for reproduction elements such as discharge rate in light and dark, memory action, contrast reproduction, etc. This produces an electrophotographic reproduction element that can compare favorably with even the best reproduction elements known to date.

Dibenzothiophenes listed below.

Oxides and dioxides are mentioned as illustrations of receptors according to the invention.

3-nitro-dibenzothiophene-5-oxide 3,7-dinitro-dibenzothiophene-5-oxide 3,7-sinitro-2,6-difuromodibenzothiophene-5-oxide 2-nitro-dibenzothiophene-5・5-dioxide 3-nitrodibenzothiophene-5,5-dioxide 2-from-dibenzothiophene-5,5-dioxide 3-from-dibenzothiophene-5,5-dioxide 4-from-dibenzo Thiophene-5,5-dioxide 3,7-sinitrodibenzothiophene-5,5-dioxide 2,8-dinitro-dibenzothiophene-5,5-dioxide 2-bromo-7-nitrosybenzothiophene N-5.5
-dioxide 3-from-7-nitrodibensothiophene-5.5
-dioxide 2,8-dibromo-dibenzothiophene-5,5-dioxide 3,7-dibromo-dibenzothiophene-5,5-dioxide 3,7-dicyathudibenzothiophene-5,5-dioxide 3・7-)! , l nitrodibenzothiophene 5.5
-Dioxide 3,7-dibromo-1,9-dinitro-dibenzothiophene-5,5-dioxide 2,3,7,8-tetrachloro-dibenzothiophene-
The complex formation of 5,5-dioxidedibenzothiophene-oxide and the oxide, and hence its sensitizing effect, is dependent on the electron-withdrawing effect of the substituents, i.e., the complex formation and the sensitizing effect depend on the electron-withdrawing It is assumed that it increases in proportion to the strength.

Therefore, a nitro group that strongly attracts electrons is preferred as a substituent.

Dioxide is preferred because, on average, the suction effect of dioxide is greater than that of monooxide.

Among the dioxides themselves, the new formula [■] 1, 3, 7-) that has not yet been described in the literature! Since J nitrobenzthiophene-5,5-dioxide is the best, it is preferred to use this compound as the acceptor if possible.

In principle, the acceptors described above can be used with each of the electron-emitting photoconductors used for donor-acceptor complex formation.

In particular, very effective complexes can be formed with optionally substituted poly-N-vinylcarbazoles, monocarbazole compounds and substituted or unsubstituted 2,5-bis(4-diaminophenyl). -1・3・4
-Oxadiazole, 2,5-bis(4-dialkylaminophenyl)-1,3,4-oxadiazole or poly9-vinylanthracene can also be used to form a photosensitive donor-acceptor. Complexes can be formed.

The amount of receptor added can vary within a very wide range in relation to the amount of photoconductor.

The lower limit is determined by the amount that has an active effect on the photoconductor.

As already described in old literature, if measured according to the monomer unit, the lower limit value seems to be located near the limit of o, ooi moles per mole of photoconductor.

The upper limit is determined by the solubility of the receptor in the solvent.

This upper limit is, for example, the preferred PVK and 1.3.7
- trinitrodibendithiophene 5,5-dioxide in a molar ratio of 1:1.

Preferred amounts of receptor used range from 0.02 to 1 mole per mole of photoconductor, measured according to monomer units.

A reproduction element according to the invention is obtained by applying a donor-acceptor complex according to the invention to a suitable support with a photoconductive composition.

The support may be, for example, a metal plate or foil, or a plastic foil coated with an electrically conductive layer, which is essentially sufficiently electrically conductive, for example impregnated with an electrically conductive substance in a paper mill, or may be electrically conductive, such as a layer containing carbon, for example. It may also be formed from paper that is made conductive by adding a conductive layer thereto.

In addition to the electron donor and electron acceptor according to the present invention, the photosensitive layer also contains one or more photoconductors and/or one or more photosensitive sensitizing compounds. Also good.

If the electron donor or electron acceptor itself does not have film-forming properties, a binder may be added to impart film-forming properties.

Experience has shown that the photosensitivity of the photoconductive layer of the present invention depends on the polarity of the charge and the ratio of donor to acceptor in the complex.

Thus, the molar ratio of PVK/1.3.
It is clear that the photoconductive layer of 7-trinitrodibenzothiophene-5,5-dioxide is more photosensitive if it is negatively charged than if it is positively charged.

For ratios of about 10:1 to 25:1, the photoconductive layer is approximately equally sensitive in both cases, so a photoconductive layer with a donor to acceptor ratio of about 25=1 is When positively charged, it is more sensitive to light than when negatively charged.

The thickness of the photoconductive layer is not critical and can vary within fairly wide ranges.

A thickness of 3 to 10 microns is generally sufficient to produce a photoconductive layer suitable for practical use, although thicker layers, such as 20 microns, are also suitable.

The reproduction element of the invention can be used in both direct and indirect electrophotography.

In direct electrophotography, a latent image formed on a copying element is developed and fixed.

In indirect electrophotography, the latent image is first transferred onto a receiving material such as paper and then developed and fixed, or alternatively, the latent image is first developed and then the powder image is transferred onto the receiving material and the powder image is then transferred onto the receiving material. to take root.

The present invention further provides an electron donor-acceptor complex (the acceptor itself has no photoconductivity) by preparing a mixture of an electron donor organic compound and an electron acceptor organic compound having photoconductivity or semiconductivity. The present method relates to a method for producing a photoconductive composition which may or may not have the formula [ The compound of formula [■] is used as a receptor, and in the formula [■], n = 1 or 2, and RlR may be equal or unequal, and each one or It represents two or more hydrogen atoms or one or more electron-withdrawing groups.

Preparation of these new receptors is accomplished using common reactions in organic chemistry.

Thus J. am, Chem, Soc, 70.
1748 (1948), monooxides can be prepared starting from dibenzothiophene by oxidation with chlorine in carbon tetrachloride, followed by nitration to produce mono- and dinitro compounds.

The dioxides can also be oxidized by oxidizing dibenzothiophene with a mixture of sulfuric acid and dichromate.

Mono-, di- or trinitro compounds can be obtained by nitration.

If the starting material dibenzothiophene does not yet have a halogen substituent, the above-mentioned... A rogane substituent can be introduced into the dioxide.

Introduction of a cyano group is also carried out in a similar manner.

By nitrating a compound having a halogen group, a compound having a mixed substituent (for example, a nitro group and a halogen group) can be obtained.

The preparation of the same photoconductive compositions and their application to reproduction elements are described in the Examples below to illustrate the invention.

Example 1 PolyN dissolved in tetrahydrofuran 111r11
- 0.901 (=0.0046 mol) of vinylcarbazole is mixed with 0.82 g (-0,0023 mol) of 1,3,7-trinitrodibenzothiophene-5.5 in 101 rLl of 4-dioxane. - added to the dioxide solution.

These two solutions were heated to about 50° C. with stirring.

After the mixing was completed, the temperature of the solution was lowered to room temperature.

This solution was used to apply a photosensitive layer to an aluminum plate having a thickness of approximately 3-4 microns after drying.

The copying element thus obtained was charged to about 200 V by a positive corona discharge of 7 kV and then imaged for 2 seconds using an incandescent lamp under an enlarger with a light intensity of 40 lux in the illuminated area. was exposed, and finally developed using, for example, powdered toner.

This powdered toner could be fixed to the plate itself, or it could first be transferred to a receiving material, such as paper, and fixed thereon.

Excellent images were obtained in both of these cases.

Instead of transferring the powder image, it was also possible to transfer the latent image itself.

Copies were obtained by developing and fixing the latent image formed on the receiving material, if necessary.

Illuminate the exposed area with 10 lux of incandescent light and perform electrostatic method (
After the Tappi 50 (described in 2139A et seq. (1967)), the Victoreen Electrostudy Paper Analyzer (VictoreenElektr)
The sensitivity of the photosensitive plate formed as described above is 25% lower than the original on-layer potential of 190 V, as measured on a static paper analyzer.
It required only 41 lux/sec to reduce to .

Examples 2 and 3 1.3.7- of 0.164 S' in 1.4-dioxane of 10 rrL1) 1) Nitro-dibenzothiophene-5
- 11 ml of a 0.90 Y poly-N-vinylcarbazole solution in tetrahydrofuran was added to the 5-dioxide solution while stirring and heating.

In this case, the molar ratio of donor to acceptor was 10:1.

This solution was used to apply a photosensitive layer to aluminum foil, which had a thickness of 3-5 microns after drying.

The reproduction element thus obtained was charged to a potential of approximately -270 V by means of a negative corona discharge.

The energy required to reduce this potential to about 25% of the original potential was 75 lux/sec.

The energy value for the same photosensitive layer when positively charged was 100 Lux/sec.

Increasing the molar ratio of donor to acceptor to 20=1 reduces the photosensitivity only slightly, and for negatively charged layers it decreases to about 100
lux/sec, approximately 105 lux/sec for positively charged layers.

Example 4 Using a solution of poly-N-vinylcarbasol and 3,7-dipromut-9-dinitrodibenzothiophene-5,5-dioxide in a donor:acceptor ratio of 20:1, An aluminum support was provided with a 2-3 micron thick photosensitive layer.

When exposed with an incandescent lamp, the initial potential of 500V was changed to 125V (
-25%) is 215 Lux/37 seconds for a negatively charged plate.
seconds, and 180 lux/second for positively charged plates.

Example 5 A 3μ thick photosensitive layer containing poly-N-vinylcarbazole as donor and 3,7-sinitrodibenzothiophene-5-oxide as acceptor in a molar ratio of 20:1 on an aluminum support. was applied.

The reproduction element thus obtained is charged to about -40'OV by a negative corona discharge.

The 25% photosensitivity of this photosensitive layer was 350 Lux/sec.

Aspects of the present invention are listed below.

(1) The above C where n=1 or 2 and at least one of R and RI represents one or more nitro groups
An electrophotographic reproduction element according to claim 2, characterized in that the compound of I) is used as a receptor.

(2) The electrophotographic reproduction element according to claim 2 and item (1) above, characterized in that the compound of the formula [■] where n=2 is used as a receptor.

(3) The electrophotographic copying element according to the above item (2), characterized in that 1,3,7-trinitrodibenzothiophene-5,5-dioxide of the formula [■] is used as a receptor.

(4) 1,3,7-trinitrodibenzothiophene-5,5-dioxide.

Claims (1)

[Scope of Claims] 1. Producing a mixture from an organic compound electron donor and an organic compound electron acceptor having photoconductivity or semiconductivity, and forming an electron donor-acceptor complex through the mixture, and the electron acceptor may or may not have photoconductivity, so that when producing a photoconductive composition suitable for producing an electrophotographic reproduction element, Formula [where n is 1 or 2, R and R' are the same or different 1 or 2 or more hydrogen atoms, or 1 or 2
The above electron-withdrawing groups are shown below. ] A photoconductive composition characterized by using a compound. 2 consisting of a suitable support having a photoconductive coating layer thereon, said coating layer comprising an electron donor-accepting complex, said complex comprising an electron donor and an electron acceptor having photoconductive or semiconducting properties. in an electrophotographic reproduction element formed from a molecule of the formula [wherein n is 1 or 2, R and R are the same or different one or more hydrogen atoms or one or more electron-withdrawing groups.] An electrophotographic reproduction element characterized in that it is a compound.