CA1064780A - Applicators - Google Patents

Abstract

NOVEL APPLICATORS

ABSTRACT OF THE DISCLOSURE
A method of producing liquid developer dispensing rolls is given whereby a thin surface on a resilient member supported by a hard shaft is imparted with a pattern to form an applicator.

Description

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This invention relates to ~he development of electrostatic latent images. More particularly, this invention relates to the development of electrostatic latent images by the use of liquid toners or developers.
Specifically, this invention relates to methods and apparatus for dispensing liquid toner or developer to a receiving surface.
In the process of electrostatographic imaging as disclosed, for example, in United States Patent No.

2,297,691, a plate comprising a layer of photoconductive insulating material on a conductive backing, is given a uniform electric charge over its surface and is then exposed to the subject matter or copy to be reproduced, usually by conventional projection techniques. This exposure discharges the plate in areas according to the radiation intensity thereby creating an electrostatic latent image on or in the photoconductive layer. Development of the latent image is accomplished with an electrostatically charged, finely-divided, developing material or toner which is brought into surface contact with the photoconductive layer and is held thereon electrostatically in a pattern corresponding to the electrostatic latent image. Thereafter, the developed powder image is usually transferred to a support surface, such as paper, to which it may be fixed by any suitable means.
Development of an electrostatic latent image may also be achieved with liquid rather than dry developer materials. In this technique, electrostatic latent images are developed generally using the liquid development formulations, processes and apparatus generally disclosed .'' - 1 -~L~6~7~
in United States Patents 3,084,043 and 3,806,354 which are herein incorporated by reference. In these methods, an electrostatic latent image formed as mentioned above is developed or made visible by presenting to the imaging surface a liquid toner or developer on the surface of an applicator roll or developer dispensing member having a plurality of raised portions or "lands" defining a substantially regular patterned surface and a plurality of portions depressed below the raised portions or "valleys".
The depressed portions of the applicator roll member contain a layer of liquid toner which is maintained out of contact with the electrostatographic imaging surface.
Development is achieved by moving the developer dispensing j member loaded with liquid developer in the depressed portions into developing configuration with the imaging surface. The liquid developer is attracted from the depressed portions of the applicator surface to develop the image bearing surface. The developer liquid may be pigmented or dyed. The development system disclosed in 2~ United States Patent 3,084,043 which is sometimes called "out of contact" de~elopment differs from electrophoretic development systems where substantial contact between the liquid developer and both the charged and uncharged areas of an electrostatic latent imaging surface occurs during deveIopment.
The applicator rolls employed in out of contact liquid development processes are carefully produced and are of substantially uniform characteristics. The working surface of such rolls for application of a liquid developer to an electrically charged photoreceptive surface 7~3~

is composed, for example, of a multihelicoid thread pattern having up to about 300 threads per inch at about 45 right or left hand lead. Other angles from about 20 to about 80 from axis may be used. The thread configuration is typically about 0.0005 inch pitch, about 0.001 inch top land, and with about 35 to 65 micron depth. The overall roll size may be typically about 1.5 inch in diameter and approximately 9 inches in length, exclusive of journals.
The applicator rolls generally run either in touching contact or in very close proximity to the latent image bearing surface. This surface may be of any dielectric material or it may be a photoreceptor. The photoreceptor may comprise a suitable sensitive material coated on any suitable base. Any suitable photoconductive material and substrate may be employed. Preferred photoconductors are selenium, selenium alloys, and hallogen-doped selenium, but organic photoconduc~ors may be used. Typical substrates are nickel, brass and aluminum. If desired, there may be an interfacial layer between the photoconductive matarial and the substrate to provide selected adhesive or electrical properties and there may be an insulating coating over thé photoreceptor.
As an additional alternative, a web may be interposed over the photoreceptor between the photoreceptor and the applicator.
In such an arrangement, liquid toner or developer is developed onto the web and later is transferred from the web to a receiving substrate.
It should be quite evident that the two structures, the photoreceptor and the applicator roll, must operate in close conformance and tolerances with one another in order to form a high quality image.

G4~80 In compact electrostatic copying devices, the photoreceptor and applicator roll are typically small diameter cylinders to facilitate operation in confined space. However, belt-like surfaces are also employed. Such operation typically occurs at speeds of about four to ten inches per second, although moving contact resulting in the transfer of liquid developer from an applicator to a photoreceptor can occur at speeds ranging generally from about 2 to about 70 inches per second. Liquid development of images at such speeds makes cooperation of the photoreceptor and applicator roll necessary.
Once the developer is properly applied to the applicator roll and its patterned or gravure-like surface, the developer must be cleaned from the lands or raised portions prior to to contact with the latent image bearing ~` 15 surface. This requires close conformance and tolerances between the applicator surface and a doctoring mechanism such as a blade or web. Effective doctoring or cleaning of excess developer from the applicator roll land surfaces will also result in removal of at least some of the developer from the applicator roll valleys due to surface tension characteristics of the developer.
The quality of the applicator roll is a critical issue in the out of contact liquid development process.
;~ Materials which are useful in manufacturing the applicator roll are limited~ The surface conformance between a hard metal applicator roll and a hard photoreceptor surface is very critical since very poor development occurs if there is any non-uniform separation, yet photoreceptor damage results if a hard applicator roll is too close, not in perfect alignment, and not straight with the photoreceptor.

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Producing a high quality finished metal roll under commercial conditions having little tolerance deviation is technically difficult. Mechanical engraving requires a num~er of steps. A master layout of the pattern, opposite hand, many times size, is made on a polyethylene terephthalate resin material; the master layout is photographically reduced to the proper size, again on a clear polyethylene terephthalate resin material; and then the master pattern is transferred to a hardened and ground tool steel master engraving cylinder by a photoetching process. Only the pattern outline is transferred, not the pattern depth; the photoetched master engraving cylinder is mechanically etched by a master engraving to the desired depth and contour. This step is critical and requires great skill. The tools and equipment used are relatively simple and very similar to a jeweler's etching equipment.
Subsequent engraving success deplends almost entirely on the skill of the master engraver; the master cylinder is then used to make master mills for the engraving of rolls; a ~-~ roll blank is machined to tolerance by conventional means.
An extension is left on one end and this is used to drive the roll during the mechanical engraving process After engraving, the extension is machined off. The roll material is usually AlSl, 1015 or 1020 steel; the roll is now ready for engraving. During the engraving process, the roll is placed in a special lathe designed for this purpose. The roll is placed in the machine with the roll journals supported by bronze "U" shaped bearings. The extension that is left on the roll is engaged in a floating chuck that drives the roll during the engraving process. The mastPr engraving mill is mounted in a tool holder directly above the roll. The tool )6~7~3~

holder rests on the lathe bed and is driven back and forth by a lead screw. Th~ master mill freely floats in the "U" shaped bronze bushings in the tool holder. By means of an adjusting wheel, it is brought in contact with the rotating blank roll, picks up the speed of the blank roll and is driven by frictional contact. The advance along the blank roll is controlled by the lead screw driving the tool holder. The blank roll rotates very slowly, usually no more than 15 rpm. The advance of the master mill along the length of the blank roll is also very slow, approximately 1 inch over 3 minutes for small rolls and considerably slower for larger rolls. On larger rolls it is nearly impossible to see the mill advance down the roll as it is moving so slowly. The master mill is rarely bottomed in a single pass. Usually at least two passes are required on every roll and sometimes considerably more. The amount of infeed per pass is at the discretion of the operator. During engraving, the roll is continuously flooded with lubricant.
After engraving, the journal extension is machined off, and the roll is degreased and given a flash coating of copper;
the final step consists of plating with a thin coat of hard chromium. Both plating operations require considerable skill and the usual plating setup normally would not plate completely and uniformly into such intricate configurations.
Other roll manufacturing processes which are simpler in nature have one or more deficiencies. For example, multi-die thread cutting has some feasibility for producing a multihelicoid pattern, however, it is very difficult to obtain about a 45 lead angle with this process, the maximum lead angle obtainable usually being about 25 from the :

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normal to the axisO In producing a multihelicoid pattern on an applicator roll, usually a minimum of 150 threads per inch are desirable and about 180 threads per inch are preferred.
With multi-die thread cutting, it is difficult to produce a die of about 180 threads per inch. Further, a special chucking machine that can feed small rolls at about 0.5 inch per revolution is required for a small roll such as one about one inch in diameter and about 9 inches in length. However, even this rate of feed is quite slow and compounded with the considerable amount of set up time required, this process provides low rates of productivity. Photo engraving/chemical etching also has some feasibility for producing patterned rolls except for one major drawback. That is, it is very difficult to line up and join the ends of the overlay to produce a continuous pattern. A further limitation is that the ma~imum etched depth obtainable is usually about 25 microns~
Cylindrical panographic engraving equipment can produce a multihelicoid pattern, but again the alignment of the thread pattern is a problem the same as occurs in the photo-engraving process. An electronic automatic cylinder engraving machine may produce about a 180 TPI at about a 45 lead angle multihelidoid pattern, or other patterns, on a con-tinuous cylindrical surface. However, since it is a true engraving process, it is slow and thus costly. Electro-chemical grinding is also unsatisfactory for fabricating a roll having about 180 TPI because the finest grinding wheel has an individual particle size nearly as large as the largest thread feature.

~64 ~'~3C) With these and other problems associated with metal applic~tor rolls, attempts have been made to use polymers and other elastomeric materials. Thermal expansion, swelling, elastic recovery, and pattern distortion are all problems which have made the use of such materials difficult.
Casting techniques using such materials appear to be impractical. Open casting attempts have generally failed because of poor concentricity control and unreliable mold filling. Spin casting is generally associated with shell-mounting difficulties.
Since nearly all presently known processes for ~ manufacturing applicator rolls in sufficient quantities ; are dificient in one or more vital areas, there is a con-tinuing need for an improved roll and method of fabricating the rolls.
In accordance with an aspect of this invention there is provided a method for making an applicator roll having a hard, dimensionally stable, thin, thermosetting surface carrying the desired applicator surface pattern coated over a resiIient layer which is supported by a hard metal shaft.
In accordance wlth another aspect of this invention there is provided a method of forming a patterned applicator roll for developing electros~atographic images compxising:
forming a resilient surface on a hard shaft, coating said resiLient surface with a thin uncured thermosetting polymeric material, imprinting a pattern onto the surface of said uncured thermosetting polymeric material, and curing said thermosetting polymeric material.
In accordance with another aspect of this invention there is provided a method of making the desired fine-textured applicator roll comprising embossing a resilient-sleeve .

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covered steel shaft which is coated with a thin, uncured thermosetting material. After receiving the imprint of the desired pattern, the embossed blank is separated from the master and heat cured Embossing is usually performed by passing a flat sheet of material termed the blank through an interface zone created by a master, the patterned roll, and a back-up roll. The embossing roll pulls the blank through the nip, impressing an exact replica of its inverse pattern into the relatively soft surface. Since the flat shaet is generally continuous, there is no need to match first and last teeth of the embossed pattern. This technique can also be used to emboss a continuous pattern on circumferential or endless surfaces, providing the pattern pitch is sufficiently fine ~ and the material structurally weak enough to allow formation of integral numbers of "teeth" or lands.
Non-integral teeth, such as formed during the fir~ revolution of a blank whose circumference is mismatched ; with the master's, can be integrally formed by movement of material around the circumference during embossing. The quality of the tooth profile depends upon the pitch diameter established within the blank's surface. The process of averaging out non-integral tooth errors is quite complicated and involves continual redistribution of material and reformation of pitch diameters throughout the process. During embossing, last-tooth error averaging is a function of the physical properties of the coating material and its sub-strate. The floating support of the blank allows the continual formation of pitch circumferences, depending upon the variation of nip pressure and coating viscosity. This ~647131) tooth averaging phenomenon continues to occur until a stable pitch circumference is established. Failure to stabilize the pitch circumference will result in pattern distortions.
Any hard shaft material may be employed in this -~ invention. Steel, stainless steels, nickel, brass or any other like material may be used. It is preferred to use conductive materials.
An elastomer or elastomeric-like, resilient material is used to cover the shaft. Materials such as nitril-butadiene rubber, resilient polyurethane rubber ;
silicone rubber, isoprene rubber, chloroprene rubber, styrene-butadiene rubber, butadiene rubber, and the like may be employed. These materials should have a Shore A hardness of from about 50 to 90 but values of about 70 are preferred.
Wall thicknesses of this resilie1lt material should be from about 0.05 to about one inch; thicknesses of from about 0.09 ; to about 0.20 inch are preferred.
Particularly preferred resilient substrate materials include nitrile rubber tubing, Compound 3431 modified, and molded conductive neoprene (105 ohm-cm), 70 Shore A, both ~rom American Roller Co., Union Grove, Wisconsin, and molded conductive polyurethane (105 ohm-cm) 70 Shore A, from Garlock, Inc., Rochester, New York.
The resilient substrate material may be in the form of tubing which is placed around the hard metal shaft or material molded around the shaft. Injection molding of the resilient, elastomeric-like material is preferred.

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Preparation of the blank is an important step in the manufacture of an applicator. While minor surface errors of the blank may be averaged out during final coating, existence of these can affect the efficiency of the process.
A finish grind operation for sizing and straightening may be desirable if necessary in order to have a uniform quality final product.
One important characteristic of this invention lies in the surface coat. It has been found that a thin layer of thermosetting material applied to the resilient covered shaft, gives the applicator roll of this invention dimensional stability coupled with the resiliency necessary to provide for good photoreceptorjapplicator roll system conformance without the high potential of damage to the relatively fragile photoreceptor surface.
Many materials are useEul in providing a surface in this invention. It has been found that polyurethanes are particularly useful in this invention. A fine applicator pattern is faithfully formed in the elastomer, and if uncured, this pattern must be retained until the coating is fully cured.
The quality of the rolls are normally controlled in large ~measure by the viscoelastic properties of the elastomeric coating and by its curing behavior. Embossing is the preferred way to create the desired pattern.
Early in embossing, the stress level is very high because contact is restricted to the lands of the master. As the material deforms, the contact area increases until total contact is reached and the stress level is lower.
After total contact there is no longer gross deformation, but internal viscous flow continues to redistribute stress in .. -- 11 --7~0 the elastically deformed material and this stress relaxation serves to reduce the magnitude of the elastic recovery.
For preferred embossing, the coating should have a low viscosity and a high elastic modulus (low elastic compliance). However, the need for tracking of the master lands in the formed grooves places a lower limit on this viscosity. Also, the cohesive (viscoelastic) strength must be greater than the adhesive attraction to the master roll to prevent "hot offsetting".
In using many materials, when the formed roll is removed from the embossing fixture, residual elastic recovery tends to decrease the depth of the grooves; this is called ; "slump". Surface tension will also promote leveling. Thus,the viscosity of the material must be high to counteract these forces, but unfortunately, viscosity normally decreases - with increases in temperature which are usually associated with curing.
Thixotropy of the coating material resists the leveling forces, chiefly elastic recovery and surface tension, until the material is cured. Thixotropy describes a charge in viscosity with time at constant shear rate. Viscosity decreases after an increased shear rate is imposed upon a material and eventually reach an equilibrium value. If the shear rate is reduced or removed, the viscosity will increase with time until a higher equilibrium value is reached. Initial viscosity is a function of shear history. Thixotropy is believed due to a change in intermolecular forces, molecular ordering, or in filled systems, the interparticle attachments. The energy input from a shear field breaks down the order or 7Z~0 attachments, and when the shear field is removed, thermal motion permits reordering or rebonding.
It has been found that uncured polyurethane material which has carbon black pigment dipsersed therein so that the volume resistivity is about 105 ohm-cm has the pxoper properties to be embossed in such systems.
The excellent properties of the pigmented urethane elastomer are believed directly due to the controlled thixo-tropy which is controlled by the carbon black structure~
Improved materials are obtained by the addition of less than about 20 percent by weight fumed silica which improves the thixotropy. Well dispersed amounts of about 2 to about 8 percent are preferred.
Any blocked urethane which has an un~locking temperature of greater than about 100C and preferably between 120 and 175C may be employed. Preferably such materials are diluted with solvents such as xy:Lene and/or toluene to a viscosity of about 100 centipoise for application.
The urethane is sprayed, dipped, or applied in any ; ~ 20 other conventional way to provide a uniform coating of between 4 and 12 mils. A thickness of 5 to 7 mils is preferred.
,~ One technique for accomplishing uniform coating is spraying. This is within the average skill of the artO It has been found useful to apply about two mils per pass using a pot pressure of 20 psi and an airline pressure of 45 psi. Three passes will generally coat the resilient covered shaft.
The coated roll should be allowed to dry thus releasing the solvents prior to embossing. A period of from a few minutes to 24 hours is required depending upon 4~80 the solvents employed. After this time the viscosity is stabilized which allows for optimum embossing.
An engraved metal master prepared in accordance with techniques previously described or any other high quality technique-is prepared employing the negative of the pattern to be produced. The embossing master and the blank are brought together and rotated for a period of time under pressure to impact the desired pattern in the surface of the blank.
Embossing may be accomplished at any temperature but it has been found that rolls of improved quality are achieved where the operation is conducted at room temperature, that is temperatures of from about 18 to about 35C. The viscosity of the thixotopic polyurethane is sufficiently high at room temperatures that offsetting does not occur.
Under these conditions a mold re:Lease agent is not necessary, but such an agent may be optiona:Lly used.
The master is brou~ht :into contact with the urethane coated resilient covered shaft and rotated while contact pressure is increased. Any effective contact force ; may be employed but it is preferred to use pressures of about 20 to about 30 pounds per lineal inch when embossing at room temperature. Contact is maintained for from 2 to about 20 minutes but can be extended in the case of poorly coated blanks. After a few revolutions, a rippling or "flowing" of the pattern may be observed which is a re-orientation of material to eliminate last-tooth errors.
This pattern flow is really the phenomenon of cross threading appearing and disappearing. Separation may be accomplished by sudden release.

~L~G~78~) Upon release, the uncured urethane surfaced, patterned applicator roll is cured. Any curing technique mav be employed. The roll may be placed in a hot air oven at between about 100C and about 225C and cured for from one to fifteen minutes or so. Typically, baking at 120C for from 10 to 12 minutes will unblock the urethane and initiate curing. Materials having higher thixotropic characteristics can be cured more rapidly thereby avoiding material deformation if such a tendency is found. Following the heating step, the roll should be allowed to stand at room temperature for from about 18 to about 72 hours to develop full properties.
Curing may be accomplished simultaneously with embossing. In this step, the coated roll is heated for from about 4 to about 10 minutes at temperatures of from about 150 to 90C prior to embossing. The embossing step is then caxried out as described above except that a radient heat source is employed to maintain the surface temperature.
~ Upon release, the cured embossed roll should be allowed to stand for from 18 to to about 72 hours for full property development.
There are many effective modifications to the embossing technique of this invention. The following non-limiting examples further define and demonstrate the invention. A11 parts and percentages are by weigth unless otherwise stated.

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EXAMPLE I
A steel shaft having a length of 12 inches and a diameter of about 0.75 inch was covered with about 0.20 inch wall thickness of a molded, conductive Neoprene rubber.
The Neoprene rubber, available from American Roller Company, Union Grove, Wisconsin, was blended with carbon black in a roll mill to achieve a resistivity of 105 ohm-cm and a hardness of 70 Shore A prior to ~eing injection molded about the steel shaft and simultaneously cured. The coated shaft was ground to a constant diameter.
The surface of the ground covered shaft was ; spray coated with a five mil dry thickness of a solvent based, end blocked, thermosetting polyurethane elastomer containing dispersed carbon black to achieve a volume resistivity of 105 ohm-cm and fumed silica to enhance its thixotopic properties. This material is available from Hughson Chemical Company, a division of Lord Corporation, Erie, Pennsylvania under the trade designation Chemglaze TS-1960-71. This material is strongly shear thinning; at 40C, the viscosity ~` 20 decreased from 107 poise to 106 poise when the shear stress is increased from 4.0 x 104 to 1.25 x 105 dynes per'square centimeter. The thixotropic yield stresses were 5 x 104 and 9 x 104 dynes per square centimeter at 65C and 56C, respectively. The urethane cures at 150C.
The uncured urethane coated, neoprene covered steel shaft was mounted on centers. A cleaned engraved steel master was employed having a uniform pattern of helical ; grooves, 65 ~m in depth, inclined at 67 1/2 to the roll axis, and spaced at 180 threads per inch. This patterned ~9~713~) master was engaged with the rotating urethane coated blank and driven through frictional contact with it. The embossing process was achieved by the intimate contact between the surfaces of the urethane coated blank and the engraved steel master. The pressure between the two surfaces is increased to a maximum of 25 pounds per lineal inch of roll while the two rolling surfaces increase in speed to 60 revolutions per minute. Embossing is continued for about 10 minutes and at the end of the process separation is achieved by a spring mounted quick release mechanism in order to avoid destruction of the freshly embossed pattern.
The embossed roll is placed in a hot air oven having a temperature of 120C for about ten minutes which fixes the surface of the pattern by curing. Full depth curing is accomplished by letting the roll stand at room temperatuxe for about 48 hours.
` ~ EXAMPLE II
The process of Example I was repeated in every detail except that prior to embossing the coated roll was heated in a hot air oven for about eight minutes at a temperature of 125C to partially precure the polyurethane.
The roll was then mounted and engaged for embossing. The engraved master and the precured blank undergoing embossing were placed under radient heat such that the surface ~;; 25 temperature of the urethane was about 120C. The embossing , and curing were accomplished simultaneously and after about 10 minutes the roll was comple-ted.
EXAMPLE III
, The process of Example I was substantially repeated producing different rolls to demonstrate that the process ~4'7~0 had wide latitude in its variables. The results from a representative number of these tests made after substantial development was complete is shown below.

RDLL S~E~F SLE~ CQATING C~æD L~ND HGr. SURFACE LAND
NO. DURDMEIER IHIC~ESS THIC~ESS DEPTH DEVIATION ~V~S RADIUS
` (SHORE A) (inches) (inches) (microns) (microns) (microns) (microns) AM~53 73 0.095 0.004 46 4.8 40 24 AM~54 73 0.095 0.004 44 2.5 42 34 G-66 75 0.119- 0.006 43 6.2 32 ?
10R-45 83 0.183 0.005 51 ? ? ?
G-33 ? 0.09 0.004 55 3.8 25 ?
#3 75 0.0g 0.004 53 3.8 21 29 G-50 76 0.09 0.009 42 6.2 15 40 G-46 75 0.09 0.006 ~3 3.8 15 36 R-42 83 0.205 0.006 45 6.2 38 40 Although specific materials and conditions are set ; forth in the foregoing examples, these are merely intended as illustrations of the present invention. Various other suitable roll materials such as those listed above may be 20 substituted for those in the examples with similar results.
Other materials may also be added to the roll matèrials to sensitize, synergize or otherwise improve the fabricating properties or desirable properties of the process.
Other modifications of the present invention will occur to those skilled in the art upon a reading of the present disclosure. These are intended to be included within the scope of this invention.

Claims (10)

WHAT IS CLAIMED IS:

1. A method of forming a patterned applicator roll for developing electrostatographic images comprising:
forming a resilient surface on a hard shaft, coating said resilient surface with a thin uncured thermosetting polymeric material, imprinting a pattern onto the surface of said uncured thermosetting polymeric material, and curing said thermosetting polymeric material.

2. The method according to Claim 1 wherein the pattern is embossed onto the surface of said uncured thermo-setting polymer.

3. The method according to Claim 1 wherein said uncured thermosetting polymeric material is from about 4 to about 12 mils in thickness.

4. The method according to Claim 1 wherein said uncured thermosetting polymeric material comprises a urethane.

5. The method according to Claim 4 wherein said urethane has added thereto carbon black pigment in an amount sufficient to impart a volume resistivity in said coating of 105 ohm-centimeters.

6. The method according to Claim 4 wherein said urethane has added thereto less than about 20 percent by weight fumed silica.

7. The method according to Claim 1 wherein said resilient surface has a Shore A hardness of from about 50 to about 90.

8. The method according to Claim 1 wherein said resilient surface has a wall thickness of from about 0.05 to about one inch.

9. The method according to Claim 1 wherein said resilient surface has a Shore A hardness of about 70.

10. The method according to Claim 1 wherein said imprinting and curing occur simultaneously.