US3899328A - Active matrix and intrinsic photoconductive polymer of a linear polysiloxane - Google Patents

Abstract

and

in the presence of tetramethylammonium silanolate or corresponding alkali metal salt as initiators; the polymeric product, and photoconductive members utilizing such product demonstrate excellent structural and electronic properties for xerographic purposes.

A process for obtaining a substantially linear homopolymer and/or copolymeric material from a cyclic trimer such as 1,3,5trimethyl-1,3,5-tri(N-ethyl-3-carbazyl)cyclotrisiloxane alone or in combination with cyclic trimers or tetramers exemplified by the formulae

Description

United States Patent [1 1 Limburg [451 Aug. 12, 1975 ACTIVE MATRIX AND INTRINSIC PI-IOTOCONDUCTIVE POLYMER OF A LINEAR POLYSILOXANE [75] Inventor: William W. Limburg, Penfield, NY.

[73] Assignee: Xerox Corporation, Stamford,

Conn.

[22] Filed: May 7, 1973 [21] Appl. No.: 357,987

Primary Examiner-Norman G. Torchin Assistant Examiner.lohn L. Goodrow Attorney, Agent, or Firm lohn E. Crowe;i.larnes J. Ralabate; James P. OSullivan [5 7 ABSTRACT A process for obtaining a substantially linear homopolymer and/or copolymeric material from a cyclic trimer such as 1,3,5-trimethyl-1,3,5-tri(N-ethyl-3- carbazyl)cyclotrisiloxane alone or in combination with cyclic trimers or tetramers exemplified by the formulae and in the presence of tetramethylammonium'silanolate or corresponding alkali metal salt as initiators; the polymeric product, and photoconductive members utilizing such product demonstrate excellent structural and electronic properties for xerographic purposes.

I 12:.Claims, No Drawings 1 ACTIVE MATRIX AND INTRINSIC PI-IOTOCONDUCTIVE POLYMER OF A LINEAR POLYSILOXANE BACKGROUND OF THE INVENTION In the electrophotographic or xerographic art it is customary to utilize photoreceptor plates having at least an external photoconductive insulating layer and a charge conductive supporting substrate. Generally, a

photoconductive layer is uniformly electrostatically charged in the absence of light or other activating radiation end, thereafter, exposed to a light'pattern which can correspond to a negative image. The areas ofthe photoconductive layer which are so exposed selectively lose their charge much more rapidly than non-exposed areas. As a result, the photoconductive layer at least temporarily retainsa charge corresponding essentially to a latent positive image. This image can then be conveniently developed to form a visible positive image by contacting with oppositely charged pigmented particles commonly identified as toner particles which will adhere mostly to the charged areas. The resulting image may optionally be permanently affixed to the photoconductor if the imaging layer is not to be reused. This usually occurs with binder-type photoconductive films where the photoconductive imaging layer is also an integral part of the finished copy.

Where plain paper copying systems are involved, however, the latent image is conveniently developed on the imaging surface of a reusable photoconductor, or transferred to another surface such as a sheet of paper.

and thereafter developed. After a latent image is developed on the imaging surface of a reusable-type photoconductor, it is transferred'to another substrate and then permanently affixed by using any one of a variety of well-known techniques such as by overcoating with a transparent film, or by'therma'l fusion of the toner particles to the sheet. In such a copying system the materials in the photoconductive layer'must be capable of rapidly changing from an insulative, to a chargeconductive, and then back to an insulative condition to permit cyclic use of the imaging surface. Failure to re vert back to the insulative state before each succeeding I charging sequence will result in a high dark decay rate commonly referred to as fatigue. In the past, the problem has been controlled, to some extent, simply by selection of those photoconductive materials having the best known rapid swtiching capacity. Typical of such materials are anthracene, poly( N-vinylcarbazole), sulfur, selenium, selenium alloys, metabfree phthalocyanines, etc., and mixtures thereof (U.S. Pat. No. 2,297,691

While organic photoconductive materials such as poly(N-vinylcarbazole generally have good dark decay 2 3,408,185; 3,408,186; 3,408,187; 3,408,188; 3,408,189; and 3,408,190 are of interest in this area.

For all practical purposesi the amount of sensitization of 1 both v photoconductive and nonphotoconductive resins depends upon the concentration of the activator; within limits,the higher the loading, the greater the photoresponse obtained. Unfortunately, however, loadings exceeding about 10 weight percent of the photoconductive composition will usually impair mechanical and/or photoconductive properties of the sensitized composition. Excessive amounts of activator in either a photoconductive ora nonphotoconductive material of the type disclosed in the above patents will tend to crystallize outof the photoconduc tive composition.- 3

The above inhe rent limitations make it very difficult and often times impossible toobtain the much-desired marriage of a high quantum efficiency photoconductor with a tough, transparent, flexible, active matrix material having a low injection threshold. 4

One veryuseful discovery in this area utilizes various protective ,polymeric overcoats capable of holding a charge of high field strength on an external surface and also permitting selective transmittal of holes from a photoconductive layer through the polymeric-overcoat.

None of the known active matrix materials, however,

are capable of satisfying all of the important physical and electronic properties needed for modern xerographic or electrophotographic usage. I

OBJECTS OF THE INVENTION It is an object of the present invention to obtain a new class of polymeric materials having the necessary physical and electrical properties to permit a wider and more flexible use of xerographic principles for copying pur poses.

It is a further object to synthesize and utilize a new class of intrinsic organic photoconductors which can be combined with a substantial amount of an activator without unduly affecting its mechanical or photoconductive properties. i

A further object of the present invention is to discover and synthesize a new active polymeric matrix material which is compatible with high quantum efficiency photoconductor material and which retains its flexability and durability.

SUMMARY OF THE INVENTION These and other' objectsare realized by the discov- .ery, preparation and utilizationofa new class of silicon-containing polymeric materials, photoreceptor components utilizing such materials as active rnatrices and/or intrinsic photoc onductors. When used as described, the materials provide a method for obtaining increased durability, and efficiency in xerographic pho-' which are conveniently represented by the general formulae or wherein R, is defined as a lower alkyl group, preferably an alkyl of 1-8 carbon atoms such as methyl, propyl, isopropyl and octyl; a lower alkoxy such as a methoxy or propoxy; and as a lower alkyl III IV wherein R is defined as a lower alkyl group of 28 carbon atoms such as ethyl, propyl, isopropyl or octyl. and defined as an aryl group such as a phenyl group or a naphthyl group; I

R, and R are individually defined as a hydrogen, lower alkyl of 1-8 carbon atoms, halo such as chloro and bromo and cyano groups, such groups being preferably attached to one or more of the 3, 6 or 8 positions on heteroeyelic ring system (111 and on one or more of the fused aromatic rings of ring system (IV);

R of formulae 1 and 11 is defined as a polymeric end group including the residue of an initiating chain such as a tetra-methyl ammonium silanolate, or otherwise defined as a hydroxyl or ester group such as an alkyl carbonyl or an aryl carbonyl group in which the alkyl moiety usefully contains l-l8 carbon atoms and the aryl moiety is a phenyl group such as phenyl, hydroxy phenyl, an alkyl phenyl or a halo phenyl group;

R, and R are individually defined as a lower alkyl group, including alkyl groups of 1-8 carbon atoms such as methyl propyl, isopropyl and n-octyl, and preferably as an alkyl of l3 carbon atoms;

R is a polymeric end group, including hydrogen or an acyl group such as an alkyl carbonyl having an alkyl moiety of 1-18 carbon atoms and an aryl carbonyl such a phenyl carbonyl exemplified by phenylcarbonyl, alkyl substituted phenylcarbonyl or halophenylcarbonyl; and

m, n and 0 are positive numbers commensurate with a number average molecular weight of at least about 1,000 and conveniently varying from about 1,000 1,000,000 or higher, the numbers 3n and 30 being defined so as to fall within a ratio of about 3:1 to 1:8 in a random or block copolymer. For purposes of the present invention the copolymers tend to exceed the homopolymers in molecular weight, a preferred although non-exclusive range being about 1,000 50,000 for the homopolymer and about 1,000 500,000 for the copolymer, depending upon the ratio of monomeric units and the definitions of R and R The above-defined homopolymers and copolymers are found to be multifunctional in nature (i.e.. as an intrinsic photoconductor or as an active matrix) and are essentially linear, although desired amounts of cross 1 SiO l Si-O l q CH3 Table I Approximate Number Average MW R R R R Ratio P-l 1300 CH OH H 2 5 P-5 50,000 lzl Si-O (lntennediateA) Cyclimtion L:

where R is a carbazyl group, steps (c) and (d) prefera- 5 bly proceed as follows:

In the above partial reaction. Intermediate A preferably includes the following cyclic trimers:

and

Substantially thesame reaction mechanism is also found useful in obtaining cyclized tetramcr or trimer reactants such as (Intermediate B )1 wherein the R and R radicals are defined as in formulae llV supra.

Intermediate A (supra) can be easily converted to the desired 'homopolymer or to a corresponding cotetramer, (i.e., Intermediate 8), with an initiating amount of tetra alkyl ammonium silanolate or corresponding alkali metal salt thereof such as a potassium salt (30-500 ppm); optionally the reaction can proceed in the presence of a strong base such as KOH. For this purpose, the reaction temperature can vary from about C to about 160C, depending upon the optimal use of reaction solvent and the choice of reactants.

When no reaction solvent is utilized, the reaction can best proceed in the presence of tetra alkylammonium silanolate at a temperature of about 80 160C. Preferably this reaction is effected under vacuum for a period of about 3-5 hours. Extended reaction periods particularly at the higher temperature range, however, favors an increased randomness of units attributed to indiscriminate cleavage of long chains by initiator groups.

When polymerization is carried out in the presence of a reaction solvent such as tetrahydrofuran, toluene or dichloroethane, however, it is found most convenient to use one of the above initiators, particularly the corresponding potassium salt of a silanolate initiator at a temperature optimally varying from about 20C wholly or partly in place of Intermediate B.

The following examples further illustrate certain preferred embodiments of this invention.

in which R is a l-pyrenyl group, is prepared by contacting the corresponding l-bromopyrenyl reactant with a phenyllithium reactant in general accordance with the mechanism as described following Table l. The

20 resulting cyclic trimer intermediate is then dissolved in tetrahydrofurane and then contacted with about 150 ppm potassium tetramethyl silanolate at room temperature. The reaction mixture is heated to about 60C for 2 hours and then slowly raised to about 120C for an additional hour; the resulting linear homopolymer is isolated by methanol precipitation and then washed and identified as po1y( methyl-l-pyrenyl siloxane). The product is soluble in CHC1 CHC1 CHCl cyclohexanone and tetrahydrofuran, and is conveniently cast from THF-tetrachloroethane solution to obtain a clear,

hard, tough, semiflexible film. The product is tested, and. the following parameters noted:

130C, depending upon the solvent. It is also sometimes ,Hmmm Cmma found advantageous to slowly raise the reaction temperature to a maximum of about 160C during at least the last hour. Preparation of the copolymer. for in g fi lg g stance, is conveniently exemplified by the following Jrwmn Corona I Field v/LI 76 6O equation.

a l i l 3 Si 4 Si() R. CH, CH,

T 1) SiR;, R;,Si() 'N(CH;,), R,Si Si-R R -,Si 20 mo R: O R, ()Si P a s R0 wherein R are defined as above and the ratio of P1 is about 3:1 to 1:8. While a substantial variation in the monomeric ratio is possible, it is found that polymers of a higher desirable molecular weight are' obtained when both the trimer and tetramer monomers are utilized and reacted in molar amounts at least sufficient to obtain a copolymer having the indicated monomeric ratios. K

For purposes of the present invention, it is also found convenient to use the cyclic trimer,

This data suggests that a substantial number of holes are injected from a selenium photoconductor layer into the polymer overcoat and discharging the negative charge on the polymer surface.

9 sulting pyrenyl group-containing siloxane homopolymer is coded as p-2. The vacuum stripped, tested and washed product is evaluated in Tables ll-lll below.

EXAMPLE Ill (p-3) 0.01 Mole of cyclic trimer of the formula EXAMPLE IV (p-4) 0.01 Mole of cyclized dimethyl siloxane tetramer of the formula Si0 L 4 and 0.04 mole of the trimer of Example 1 are dissolved in tetrahydrofurane and agitated with about 150 ppm of potassium tetramethyl silanolate at 60C for 3 hours. The temperature of the thickened reaction mixture is then raised to about 130C for three additional hours. The resulting polymeric product (P-4) is washed and identified as an essentially random linear copolymer which is conveniently represented by the formula li-O l R: f a I wherein the ratio of p-to-q is about 3 to l and R is lpyrenyl. The product is tested and results reported in Tables n-m below.

EXAMPLE V (P-S) 0.05 Mole of cyclized dimethyl siloxane tetramer of the formula 10 and 0.07 mole of the cyclietrimer of Example III are dissolved in tetrahydrofuran and reacted as in Example IV. The resulting polymeric product is washed and identified as an essentially linear copolymer which is conveniently represented by the formula wherein p and q are in aratio of about l-tol and R. is defined as N-ethyl-3-carbazyl group. .The product is evaluated and reported in Tables llll[.

EXAMPLE Vl (P-6) 0.003 Mole of the cyclic tetramer and 0.00] mole of the cyclic trimer of Example V are admixed with ppm of tetramethylammonium silanolate and heated at about C for 2 hours in a sealed glass ampule under vacuum. The resulting copolymer coded as P-b is washed with methanol and identified as linear poly( methyl-N-ethyl-3-carbazyl-siloxy )dimethylsiloxane co polymer represented by the formula wherein R is identified as the N-ethyl-3-carbazyl group, and p and q are in a ratio of about 1:4. The methanol-washed product is tested and evaluated in Tables ll-lIl.

EXAMPLE Vll (P-7) 0.01 Mole of the cyclic trimer and 0.05 mole of the cyclic tetramer of Example V are dissolved in tetrahydrofuran and agitated in the presence of about 150 ppm potassium dimethyl silanolate initiator at about 120C. After 3 hours the reaction temperature is gradually raised to about 160C for 1 hour to obtain an essentially linear copolymer conveniently represented by the formula wherein R is N-ethyl-3-carbazyl group, and p and q are in a ratio of about l:6. The methanol-washed product is repeated in Table I.

EXAMPLE VIII (P-S) Example VII is repeated with the addition of 0.001 mole of a second cyclic trimer of the formula SiO to obtain a copolymer identified as P-8. The product is methanol-washed and reported in Table I.

EXAMPLE IX (P-9) Example VII is repeated except that the trimcr reactant is a cyclic compound of the formula EXAMPLE X Six test photoreceptor strips identified as T l and as control are prepared in the usual manner by vapor condensation of selenium alloy (60 u) onto an aluminium foil substrate. A polymeric overcoat is then cast onto the resulting selenium photoconductive layer from tetrachloroethane-tetrahydrofurane solutions of products P 26 respectively. to obtain polymeric overcoats having an average thickness of about 12 u. The resulting test components are then corona charged. checked for charge retention and discharged by exposure for seconds with a 200 watt tungsten-iodine lamp at a distance of centimeters. The control test is prepared by applying onto the selenium alloy a homopolymer resin overcoat having a molecular weight of about 500,000 consisting of monomeric units of the formula The results are reported in Table III below.

TABLE III Test Polymer The resulting copolymeric product is methanol-washed and reported in Table I.

Table II Hardness Code Polymer F lexihility Clarity vgv Vg. 0' ex. C vg. C vg. *H homopolymer C copolymer P- P-2 P-3 P-4 P-5 P-6 g good vg very good ex excellent )Coronai Dark Decay (-l Res.Volt. II) Sec) Light Res. Volt. lU Sec) Light mmocox;

Except for the control, holes injected from the selenium layer into the polymeric overcoat of T 1-5 are sufficient to discharge a functionally useful amount of the surface charge.

EXAMPLE XI Table IV Sample Polymer Charge Discharge Rate Adhesion vu sec 84 Spalling P-2 P-2 P-6 P-6 C- l C- l T-(l T-7 T-8 T-9 Control Passed wherein R is defined as a lower alkyl group;

R is defined as an aromatic polycyclic group with fused aromatic rings having at least three fused ring nuclei or a heteroaromatic group;

R is defined as a hydroxyl. or other polymeric end group;

R and R,-, are individually defined as a lower alkyl I group; R is defined as a polymeric end group; and m. n and are positive numbers commensurate with a molecular weight of at least 1,000. the respective numerical products represented by 3n and 40 having a ratio of about 3:1 to 1:8. 2. A photoconductive member utilizing the polymeric material of the formula wherein m is a positive number commensurate with a number average molecular weight of at least about 1.000;

R; and R are polymeric end groups; and

R is an alkyl group of 2-8 carbon atoms or an aryl group.

4. A xerographic photoreceptor component comprising a substrate and at least one photoconductive layer with an applied active matrix overcoat layer consisting essentially of a polysiloxane of the formulae m or wherein R, is defined as a lower alkyl. a lower alkoxy.

or lower alkyl carbonyloxy group;

R is defined as an aromatic polycyclic group with fused aromatic rings having at least three ring nuclei or a heteroaromatic group;

R is defined as a hydroxyl. or other polymeric end group;

R, and R are individually defined as a lower alkyl group;

R is defined as a polymeric end group; m. n and 0 are positive numbers commensurate with a molecular weight of at least 1,000 the respective numerical product represented by 311 and 40 having a ratio of about 3:1 to 1:8.

5. A xerographic photoreceptor component comprising a substrate and at least one photoconductive layer with an applied overcoat layer consisting essentially of the linear polysiloxane of claim 4 wherein R R and R are individually defined as an alkyl group of 1-3 carbon atoms;

R is an aromatic polycyclic group having at least three fused ring nuclei; and

R and R are polymeric end groups.

6. A xerographic photoreceptor component comprising a substrate and at least one photoconductive layer with an applied overcoat layer consisting essentially of the linear polysiloxane of claim 4 wherein R,, R and R are individually defined as an alkyl group of 13 carbon atoms; and

R is a heterocyclic group.

7. A xerographic photoreceptor component comprising a substrate and at least one photoconductive layer with an applied overcoat layer consisting essentially of a linear polysiloxane of the formula si o R6 wherein m is a positive number commensurate with a number average molecular weight of at least about 1.000;

R and R are polymeric end groups; and R is an alkyl group of 2-8 carbon atoms or an aryl group. 9. A photoconductive member of claim 1 wherein R R, and R in the polysiloxane polymeric material are individually defined as an alkyl group of l3 carbon atoms; R is an aromatic polycyclic group having at least 3 'fused ring nuclei; and R and R are polymeric end groups. 10. A photoconductive member of claim 1 wherein R, R and R in the polysiloxane polymeric material 16 are individually defined as an alkyl group of 13 carbon atoms; and;

R is a heterocyclic group.

11.. A photoconductive member of claim 10 wherein R is an aromatic polycyclic group having four fused ring nuclei.

12. A method for obtaining photoreceptor elements having improved electronic and mechanical properties for xerographic, copying purposes, said elements having at least a charge conductive substrate and a photoconductive layer the improvement comprising applying onto the substrate at least one of 1 the photoconductive layer or (2) an overcoat layer having as a polymeric component a linearpolymer represented by the formulae R, is defined as a lower alkyl group;

R is defined as an aromatic polycyclic group with fused aromatic rings having at least three ring nuclei or a heteroaromatic group;

R is defined as hydroxyl, hydroxy. or other polymeric end group;

R and R are individually defined as a lower alkyl group;

R is defined as a hydrogen or other polymeric end group and m. n and o are positive numbers comensurate with commensurate molecular weight of at least 1,000, the respective numerical products represented by 3n and 40 having a ratio of about 3:l to 1:8.

Page 1 of 2 UNITED STATES PATENT AND TRADEMARK ()FFICE CERTIFICATE OF CORRECTION PATENT N0. 3,899,328

DATED August 12, 1975 lN\/ ENTOR(S) William W. Limburg It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Abstract, insert subnumbers 3 and 4 on the two formulae to read (31-1 and (2H respectively.

Si- O Si-- O I 3 l 4 Column 1, line 48, delete "swtiching" and insert -switching a Column 3, first line below the formulae, delete or".

Column 7, line 12, delete "alkylammonium" and insert alkyl ammonium.

: Column 7, line 59, delete "P:q" and insert -p:q.

Column 7, third formula, delete "0 and insert of) Column 8, line 10, delete "Example I (p-l)" and insert -Example I (Pl)-.

Column 8, line 63, delete "Example II (p-2)" and insert --Example II (P2).

Column 8, last line, delete "ampule" and insert --ampoule--. Column 9, line 2, delete "p-Z" and insert -P2.

Column 9, line 4 delete "Example III (p-3)" and insert Example III (P-3)-.

'[SEAL] Page 2 of 2 UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3, 899, 328

DATED August 12, 1975 INVENTORG) William w. Limburg It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 9, line 25, delete "Example IV (p-4) and insert -Exa.mple IV (P4) Column 10, line ,24, delete "ampule" and insert aInpoule- Column 16, line 38 after as, insert -a-.

Column 16, line 38, delete "hydroxy" Column 16, line 44, replace commensurate" with -a.

Attest:

RUTH C. MASON Arresting Officer C. MARSHALL DANN Commissioner ufParents and Trademarks

Claims (12)

1. A PHOTOCONDUCTIVE MEMBER COMPRISING A SUBSTRATE AND AT LEAST ONE ORGANIC PHOTOCONDUCTIVE LAYER COMPRISING AN INTRINSIC POLYMERIC PHOTOCONDUCTIVE MATERIAL OF THE FORMULAE

2. A photoconductive member utilizing the polymeric material of the formula

3. A photoconductive member utilizing the polymeric material of the formula

4. A xerographic photoreceptor component comprising a substrate and at least one photoconductive layer with an applied active matrix overcoat layer consisting essentially of a polysiloxane of the formulae

5. A xerographic photoreceptor component comprising a substrate and at least one photoconductive layer with an applied overcoat layer consisting essentially of the linear polysiloxane of claim 4 wherein R1, R4 and R5 are individually defined as an alkyl group of 1-3 carbon atoms; R2 is an aromatic polycyclic group having at least three fused ring nuclei; and R3 and R6 are polymeric end groups.

6. A xerographic photoreceptor component comprising a substrate and at least one photoconductive layer with an applied overcoat layer consisting essentially of the linear polysiloxane of claim 4 wherein R1, R4 and R5 are individually defined as an alkyl group of 1-3 carbon atoms; and R2 is a heterocyclic group.

7. A xerographic photoreceptor component comprising a substrate and at least one photoconductive layer with an applied overcoat layer consisting essentially of a linear polysiloxane of the formula

8. A xerographic photoreceptor component comprising a substrate and at least one photoconductive layer with an applied overcoat layer consisting essentially of a linear polysiloxane of the formula

9. A photoconductive member of claim 1 wherein R1, R4 and R5 in the polysiloxane polymeric material are individually defined as an alkyl group of 1-3 carbon atoms; R2 is an aromatic polycyclic group having at least 3 fused ring nuclei; and R3 and R6 are polymeric end groups.

10. A photoconductive member of claim 1 wherein R1, R4 and R5 in the polysiloxane polymeric material are individually defined as an alkyl group of 1-3 carbon atoms; and R2 is a heterocyclic group.

11. A photoconductive member of claim 10 wherein R2 is an aromatic polycyclic group having four fused ring nuclei.

12. A method for obtaining photoreceptor elements having improved electronic and mechanical properties for xerographic copying purposes, said elements having at least a charge conductive substrate and a photoconductive layer, the improvement comprising applying onto the substrate at least one of (1) the photoconductive layer, or (2) an overcoat layer having as a polymeric component a linear polymer represented by the formulae