NL1012507C2 - Conductive role. - Google Patents

Abstract

Conductive article, for example a roller, a doctor blade or a flat or curved plate, at least comprising a conductive sleeve and a covering layer, the covering layer containing a conductive polymer and a film-forming polymer, and method for fabricating such an article, at least comprising the application of a covering layer to a conductive sleeve, wherein the covering layer is formed by the application, to the sleeve, of a mixture of a conductive polymer and a film-forming polymer.

Description

- 1 - PN 3729 CONDUCTIVE ROLE 5

The invention relates to a composition with an adjustable electrical conductivity. The invention also relates to a conductive object in which a covering layer formed by means of the composition is present around a conductive jacket and to a method for manufacturing such an object comprising applying a layer of the composition to a conductive jacket. .

Such conductive objects, in particular rollers, scraper blades and flat or curved plates, are widely used in electrophotographic and xerographic printing and copying equipment, faxes and other office equipment 20, for example as a charge transport roller for electrostatic charging of a photosensitive drum, as a developing roller for developing an electrostatic latent image on the surface of that drum in a visible toner image, as an image transfer roller for transferring the toner image to a copy or as a scraper blade for controlling the thickness of a toner layer. With hollow rolls, the inside can also be covered with a conductive coating. In operation, the rollers, knives or plates may always be in contact with a co-operating element, for example a photosensitive drum, or there may be a small distance between the object and the co-operating element.

When, in the case of, for example, a roller, it is always in contact with, for example, a drum, it generally consists of a conductive core, usually a metal rod, around which a likewise conductive, elastic jacket is arranged. This jacket consists of an elastic material which is pressed in when the roller is pressed against a co-operating roller or surface, on which load must be applied or discharged. An electrical voltage is applied to the roller to supply the load to be transferred. On the one hand, to limit the current through the roller and the co-operating elements with which the roller is brought into contact, but on the other hand to transfer the desired amount of electrical charge sufficiently quickly, the electrical resistance of the roller must be within certain limits. For this purpose, a coating is usually applied to the jacket, which gives the roller as a whole a desired resistance. The electrical resistance of the core and jacket connected in series with the resistance of the covering layer is preferably chosen so small that the covering layer in fact determines the total resistance. The resistance of the roller is measured as the resistance between the place where the roller is brought into contact with the tension to be applied during operation, as a rule the axis of the roller and a point of the outer circumference of the roller.

In operation, if the roller does not come into contact with a co-operating roller or plane, the sheath 1012507-3 can also consist of a non-elastic material and the sheath can, for example, also be made of metal. This is, for example, as a rule the case with magnetic developing rolls. In that case, too, a covering layer 5 is provided which determines the ultimate electrical resistance of the roller.

What has been said above for rolls also applies to scrapers and plates where the mutual relationship of the different layers is concerned. At least one layer, the jacket, is always present with a high conductivity with a coating applied thereon which determines the ultimate electrical conductivity. Any differences lie in their shape and construction. However, these do not form part of the present invention and are known per se in the relevant technical field. When reference is made to a roll hereinafter, the disclosure also applies to scraper blades 20 and flat or curved plates, taking into account any constructional differences.

Said coatings are generally formed from a composition comprising a non-conductive binder and a finely divided conductive material therein.

US Pat. No. 5,597,652 discloses a conductive roller coating composition comprising nylon, urethane or rubber as binder and metal oxides or carbon black as conductive material. The resistance of a coating formed from that composition depends on the ratio of binder-conducting material.

1 0 12 * 5 Ό 7 - 4 -

A drawback of this known composition is the poor adjustability of the electrical resistance of a coating made with the composition. Depending on the concentration of the conductive material, the resistance of the known composition appears in fact to assume two values, with a steep transition range between them, from a certain concentration, called the percolation threshold. One extreme value is determined by the resistance 10 of the binder, which is generally very high. The other extreme value is determined by that of the conductive material which forms conductive paths therein from a certain concentration in the binder. The difference between the two extreme values, determined from the specific resistance of the material to be further defined hereinafter, can be very large and usually amounts to a factor of 10B to 1011. The values suitable for practical use for the resistance of the coating of conductive objects for example rolls in electro-20 photographic equipment, for example of a charge transport roll, is precisely situated between the two mentioned extreme values and thus in the steep transition range. This makes it particularly difficult to reproduce reproducibly from the known composition a coating with a suitable desired electrical resistance.

A coating's resistance could also be affected by its thickness. However, the thickness of a coating is also bound to certain narrow limits. On the one hand, short-circuiting by 1012507 - 5 - pinholes or breakdown must be prevented, which imposes a lower limit on the thickness. On the other hand, in the case of rolls which must be compressible, the cover layer must be flexible enough to be able to follow the compression of the elastic jacket without becoming loose or breaking, which imposes an upper limit on the thickness. Thickness variations therefore in most cases offer little or no possibility to influence the resistance of the coating.

The object of the invention is to provide a composition from which a coating on a conductive roller can be manufactured with an electrical resistance in the suitable and desired range for the described coatings.

This object is achieved according to the invention in that the composition contains an intrinsically conductive polymer and a film-forming polymer.

It has been found that the resistance of this composition, compared to that of the known composition, changes much more uniformly with changing concentration of the conductive material, in this case the intrinsically conductive polymer. In particular, the composition according to the invention does not show the steep transition range between high and low electrical resistance. With the composition according to the invention it is possible in a simple and reproducible manner to apply cover layers on rolls, the electrical resistance of which has a desired value at a layer thickness that lies between the practically permissible limits.

1 012 SO 7 - 6 -

In the composition, the film-forming polymer acts as a binder in which the intrinsically conductive polymer is distributed and provides the conductive properties.

Suitable intrinsically conductive polymers for use in the composition according to the invention are, for example, polyacetylene, polyphenylene, poly (paraphenylene-vinylene), polypyrrole, polyfuran, polythiophene and polyaniline and conductive substituted forms of these polymers and mixtures of two or more of the said compounds . Very suitable are polypyrrole, polythiophene and conductive substituted forms of these polymers and mixtures of two or more of said compounds.

The intrinsically conductive polymer can be present as such in the composition according to the invention, but can also be bound to a suitable carrier. Very suitable compositions are those in which the conductive polymer, on its own or on a support, and the organic polymer are present in dispersant in dispersed form. A dispersion is here understood to mean any mixture of a dispersing agent with a conductive and / or film-forming polymer sufficiently finely divided therein for the intended use, for instance a dispersion, a suspension or even a solution.

Suitable film-forming polymer for use as a binder in the composition are organic polymers capable of forming a film.

Examples of these are polyvynilidene chloride, 1012507 (- 7 - polymethacrylates, polyurethanes, polyvinyl acetate and polyvinyl alcohol. Preferred are polymers which, for example, can be applied as latex in the form of a dispersion in a dispersing agent, preferably water, and which during and / or can form a film after removal of the dispersant Very suitable are polyurethane resins, which have a high degree of abrasion resistance and are often more flexible A film here is understood to be a continuous layer which is substantially impermeable to components from the underlying coat.

Very suitable for use in the composition according to the invention are those film-forming polymers which form a film with sufficient flexibility, for example with a reversible elastic elongation of at least 50%. Film-forming polymers should also be understood to include precursors therefor, for example momomers, oligomers or prepolymers which can polymerize to form a film or, for example, two-component systems whose components can react, for example, cross-link, to form a polymeric film. The film-forming polymer is usually used in the form of a solution or dispersion, for environmental reasons, preferably in the form of an aqueous solution or dispersion. It must also be possible to disperse the conductive polymer in this dispersion. The skilled person can easily experimentally select the workable combinations of 30 available dispersants for a given film-forming polymer and a particular conductive polymer. In particular, waterborne dispersions of most of said organic polymers as of intrinsically conductive polymers are well known and available.

The invention also relates to a method for manufacturing a conductive object, in particular a roller, a scraper blade or a flat or curved plate, which comprises at least one conductive jacket and a covering layer, in which the covering layer is formed by applying the jacket of a mixture of a conductive polymer and a film-forming polymer.

Methods known per se are suitable for applying a coating on the conductive jacket to produce a conductive roller, scraper blade or plate. Here, first of all, a composition according to the invention is prepared, preferably a dispersion of the film-forming polymer and the intrinsically conductive polymer in a suitable dispersant. It is very suitable to mix the intrinsically conductive polymer with a dispersion of the film-forming polymer. The dispersed mixture can then be applied to the jacket of the article using techniques known per se. Examples of such techniques are immersion (dip coating), basting (flow coating), spraying with or without propellant (air spray or airless spray) if desired on an electrostatically charged surface and applying with a 1012507 l-9 roller or brush. The choice of a particular technique is determined to a certain extent by economic factors, but also to a large extent by the requirement that the coating can be applied in the desired thickness and with the least possible spread in thickness.

In manual operation it is feasible to apply several thin layers, for example by dip coating in a relatively low-viscous composition or electrostatic spraying. In industrial production, 10 dip coating in a relatively more viscous composition is a suitable technique. After application of the composition, the applied layer is treated such that it is covered in a film. This can be, for example, the mere removal of the solvent 15, but also curing at elevated temperature in the presence of a cross-linking agent. The suitable and conventional techniques for the above-mentioned film-forming polymers are known to the person skilled in the art.

The adhesion of the formed film to the jacket can be enhanced by the addition of adhesion promoters known per se. The coating can also be applied, in case the jacket consists of rubber, on a jacket of which the material is still

Vs? is not fully vulcanized. After the coating has been applied, complete vulcanization of the jacket material is then effected. It has been found that this has a favorable influence on the adhesion of the coating to the jacket. Also, the jacket surface can be corona treated to improve adhesion. Also, to obtain the desired processing properties, for example, flow improvers, thickeners and surface tension reducing agents can be added to the composition. Also, the surface roughness of the jacket 5 can affect the uniformity of the film formed. This surface roughness is preferably below 15 μτη. Greater roughness gives rise to unevenness in the coating which has a negative influence on the quality of, for example, copies made with the aid of an object provided with the coating, in particular a roll. Preferably, the surface roughness is at most 10 μιη and at least 3 μτη. Coatings with lower roughnesses are so smooth that the cohesion in the dispersion applied to a jacket may exceed the adhesion between dispersion and jacket material. This can lead to contraction of the applied dispersion and thus to an uneven thickness of the coating.

The invention also relates to a conductive object, in particular a roller, scraper blade or a flat or curved plate, at least comprising a conductive jacket and a covering layer containing an intrinsically conductive polymer in a polymer film.

Due to the presence of the specific coating, such an object proves to have good electrical conductivity and high wear resistance. Also, the presence of the cover layer 30 does not appear to adversely affect the compressibility of the jacket, if required. As a result, the object has a long life in a copier or printing machine and excellent copies or prints can be obtained. Also, the cover layer 5 appears to be resistant to the compression of the article upon contact with co-operating rollers or other surfaces.

The central part of an compressible guiding roller is usually but not necessarily made of metal. At least one jacket portion consists of an elastic, in particular compressible, material, for example a natural or synthetic rubber, a thermoplastic polymer or thermoplastic vulcanizate or a microcellular rubber. EPDM and SBR are very suitable examples for use in the article according to the invention.

This material is conductive, usually because a conductive material is dispersed therein. Soot is usually used as a conductive material, but other known and usual materials can also be used in the jacket of the article according to the invention, if it consists of a conductive material, for example rubber. As a rule, the electrical resistance of the conductive casing 25 is between 100 and 10000 Ω, that of any metal core present is negligibly small relative to it. Conductive objects, for example rollers, which do not come into contact with a co-operating roller or other element can be built entirely of metal and then have negligible electrical resistance. Non-ferrous metals, for example aluminum, or in any case non-magnetic materials, for example suitable stainless steels, are used for magnetic developing rolls. Such roles and their construction and construction are known per se.

The resistance of the cover layer should be between 105 and ΙΟ7 Ω when applying a voltage between 100 and 900 V and is preferably substantially i-5 in the said voltage range and more preferably varies less than 1 decade and even less than 0.5 decade over the entire voltage range.

The thickness of the coating must be such that short circuit is prevented. In practice, it has been found that a thickness of 20 µm is sufficient for this. Preferably, the thickness is greater than 50 µm and more preferably greater than 80 µm. For any desired elastic properties, a thickness of less than 400 µm is desired. Preferably thickness is less than 200 µm and more preferably less than 150 µm. The requirements imposed on the resistance of the coating and the thickness thereof determine the desired specific resistance p in Q.m of the coating material. The specific resistance is determined by placing two electrodes with an area A at a distance of 1 from each other on the material to be measured and determining the resistance R from the measured current at an applied voltage.

30 1012507 - 13 -

The specific resistance is then calculated as: p = R.A / 1 [Ω.τη].

5 Suitable coating materials have a specific resistance between 2 x 105 and ΙΟ7 Ω.τη or 2 x 107 and ΙΟ9 Ω.ατι

The invention will be elucidated on the basis of the following examples.

10

Examples

A conductive roller with a length of 225 mm and a total diameter of 11.5 mm is assumed. The roller consists of a steel core with a diameter of 6.0 mm surrounded by a sheath of a styrene-butadiene rubber with a hardness of 30 Shore A, in which 20% by weight of a conductive carbon black (DENKA BLACK from Denki KK) is dispersed.

26 Example I

Four compositions for the application of a conductive coating were prepared as follows. An aqueous dispersion of a mixture of "7 / polyethylene dioxythiophene and polystyrol sulfonate 25 (Baytron P from Bayer, conductive polymer content in the dispersion 1.3 wt%) was adjusted to pH 7.5 using 5 wt% ammonia and then added an aqueous dispersion of a polyurethane binder (Permutex EX-55-038 from Stahl Holland, content of polyurethane in the dispersion 40% by weight) and dispersed therein by stirring.

The weight ratios of the two dispersions and the content of conductive polymer in the composition were as in Table 1.

5

Tabgl 1

Permutex EX- Baytron P Baytron P

55-038 grams gram content wt% 6673 3377 1.63% 6372 3? T8 1.86% 5974 4076 '2.17% 53.2 46.8 2.78% ~

The composition was applied to the outer circumference of the roller by repeated dip coating 10 times to a total thickness of between 80 and 100 µm. Each layer was dried at room temperature. After reaching the desired thickness, the roll was held at 80 ° C for 1 hour to cure the composition.

Three roles were created with each of the compositions. The resistance at 800V was measured on each of the rollers, measured between one end of the metal core and a point on the jacket circumference. In Figure 1, the average resistance of the rolls at each content of intrinsically conductive polymer is plotted against this content. The solid line represents a least squares fit to the measurement points. It can be seen that the resistance 25 changes gradually with increasing content of intrinsically conductive polymer so that a desired resistance can be adjusted with good accuracy by adjusting the content of intrinsically conductive polymer in the composition.

5

Example II

Six formulations for applying a conductive coating were prepared by adding to an aqueous dispersion of polyurethane-coated polyurethane particles (Conquest XP-1000 from DSM Solutech, content of conductive polymer + carrier in the dispersion 20% by weight). aqueous dispersion of a polyurethane (Permutex RA-1035 from Stahl Holland, polyurethane content 40% by weight in the dispersion) and dispersed therein by stirring. The weight ratios of the two dispersions in the composition and the conductive polymer content in the composition were as in Table 2.

20 Table 2

Permutex RA ConQuest ConQuest 1035 XP1000 XP1000 gram gram content wt% _ _ 17.6% 70 3Ö 17.6% 65 35 21.2% 60 40 25.0% 50 50 '33.3% _40_ 60 42.9%

The composition is applied by means of repeated dip coating to the roller jacket to a thickness of 85-100 μνα by means of repeated dip coating. Each layer is dried in between at room temperature. After reaching the desired thickness, the roll is held at 80 ° C for 1 hour to cure the composition.

Three roles were created with each of the compositions. Resistance at 800V was measured on each of the rollers, measured between one end of the metal core and a point on the jacket circumference. In Figure 2, the average resistance of the rolls at each content of intrinsically conductive polymer is plotted against this content. The solid line represents a least squares fit to the 15 measurement points.

It can be seen that the resistance changes relatively slowly with increasing intrinsically conductive polymer content so that a desired resistance can be adjusted with good accuracy by adjusting the intrinsically conductive polymer content in the composition.

Example III

In the manner described in Example I, six rolls are provided with a conductive coating. For a first three rolls the composition from Example I with a concentration of 2.17% is used and for the second three rolls a corresponding composition with the difference that the urethane resin Impranil 85UD acts as binder.

1012507 - 17 - from Bayer is used.

The resistance of each roll measured between one end of the metal core and a point on the circumference of the roll of the roll was measured as a function of the applied voltage. The results are shown in Figure 3. The dotted lines represent the results of the first three rolls, the solid lines those of the second three.

The resistance appears to exhibit a sufficiently small variation for the intended use of the rollers, depending on the applied tension. The reproducibility is also more than sufficient for use of the rolls in electrophotographic and xerographic devices.

15

Example IV

Eight rolls were prepared by the method of Example I with a dispersion of Baytron P (Bayer) and Impranil 85 UD (Bayer) with a conductive polymer content in the final coating of 2.17% by weight. The thickness of the coating was between 85 and 97 µm. With an applied tension of 800 V, the resistance along the longitudinal direction of the rollers was determined at distances of 1 cm. The average values of the resistance and the standard deviation as a function of the location on the roll are shown in Figure 4. The average resistance appears to be almost constant over the entire mantle surface and the spread remains well within the limits. 1012507 - 18 - for application of the rolls in electrophotographic and xerographic devices.

1012507

Claims (11)

1. Conductive rubber article, at least comprising a conductive rubber jacket and a cover layer, characterized in that the cover layer contains a conductive polymer and a film-forming polymer. The article of claim 1, wherein the conductive polymer is selected from the group consisting of polyacetylene, polyphenylene, poly (paraphenylene-vinylene), polypyrrole, polyfurane, polythiophene, polyaniline, and conductive substituted forms of these polymers and mixtures of two or more of said compounds. The article of claim 1 or 2, wherein the conductive polymer is selected from the group consisting of, polypyrrole, polythiophene, and conductive substituted forms of these polymers and mixtures of two or more of said compounds. 4. An article according to any one of claims 1-3, wherein the film-forming polymer is selected from the group consisting of polyvynilidene chloride, polymethacrylates, polyurethanes, polyvinyl acetate and polyvinyl alcohol. The article of claim 4, wherein the film-forming polymer is a polyurethane. 6. An article according to any one of claims 1-5, wherein the rubber jacket has a surface roughness between rubber 3 and 10 µm. 1012507 ¥ - 20 - An article according to any one of claims 1-6, wherein the thickness of the cover layer is between 50 and 150 µm. 8. Object according to any one of claims 1-7, wherein the object is a roller or a scraper blade. 9. A method of manufacturing a conductive article according to any one of claims 1-8, at least comprising applying a coating on a conductive rubber jacket, characterized in that the coating is formed by applying a coating to the jacket. mixture of a conductive polymer and a film-forming polymer. The method of claim 9, wherein the mixture is applied in the form of a dispersion. The method of claim 10, wherein the mixture is applied in the form of an aqueous dispersion. 1012507