CA1110026A

CA1110026A - Squeegee roller and method of making same

Info

Publication number: CA1110026A
Application number: CA311,156A
Authority: CA
Inventors: Benzion Landa
Original assignee: Savin Corp
Current assignee: Savin Corp
Priority date: 1977-11-09
Filing date: 1978-09-12
Publication date: 1981-10-06
Also published as: GB2007580A; GB2007580B; IT1099827B; DE2848544A1; IT7829115A0; FR2408861A1; JPS5470048A

Abstract

ABSTRACT OF THE DISCLOSURE

My invention compises positioning a shaft concentric with a glass tube and casting con-cellular elastomeric polyurethane around the shaft, curing the same to form a polyurethane squeegee roller around the shaft, and then removing the finished roller from the glass tube. The glass tube is internally coated with a release agent to facilitate the removal of the finished roller from the tube. The shaft may be coated with an insulating adhesive between the end portions thereof to assist in securing the polyurethane roller to the metal shaft. The finished roller made by my method will have a Shore A durometer value of between 20 and 40 and a surface finish of between 2 and 10 micro-inches.

Description

My invention relates to a method of producing cast polyuret'~ne elastomeric squeegee rollers having a surface finish of between 2 and 10 micro-inches and to the rollers produced by that method.
Background of the Invention In order to be able to remove excess developer liquid from the surface of a photoconductive drum by means of a squeegee roller, it is vital that the squeegee roller possess an extremely smooth surface finish of between two and ten micro-inches. If the surface finish is not sufficiently smooth, the remarkable results obtained by a roller made by the instant method will not be achieved. There will be streaking and tailing of liquid which is not removed, so that the developed image becomes distorted and blurred.
The desirability of removing excess liquid from the surface of a photoconductive drum by means of a polyurethane squeegee roller is taughtiby Smith et al .

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1~10026 Patent 3,955,533~ There is no disclosure in this patent of the method of making the squeegee roller and no teaching of the instant invention, as will be pointed out more fully hereinafter.
It also has been suggested by Hunstiger, in Patent 3,384,051, to pass a sheet of paper coated on both sides with a photoconductive material and bearing a latent electrostatic image through a bath of liquid developer snd then through a nip formed by a drum of solid polished aluminum or chromium or Teflon (trademark) coated metal and a roller of cast solid polyurethane elastomer. The object of the arrangement is to maintain the non-image side of the electrophotoconductive coated paper dry, so that the dry side can be used again to form an electrostatic image and developed on the opposite side of the first image. While the specification does not describe it, Claim 1 of Hunstiger indicates that excess carrier liquid will be removed from the developed surface of the image-bearing member. Any slippage which occurs will occur on the polished metal roller of the pair. There is no disclosure whatever, in Hunstiger, of the method of making the roller nor of the critical nature of the smoothness of the polyurethane roller.
Hill Patent 3,2~3,728 discloses a process of making an ink-applying roller for use in the lithographic field. The Hill process, however, makes no reference to il/ -2-Y)26 the salient feature of the instant invention--namely, the sur-face smoothness of the roller, which produces remarkable and unexpected results.
Seanor et al Patent 3,959,574 discloses a biasable polyurethane roller for use in transferring developed electro-static images ~y means of a directional force field from a photo-conductor to plain paper. The resistivity of the polyureth~ne is a critical feature o~ Seanor et al, and there is no disclosure whatever of the salient characteristic of the instant invention --namely, the smoothness of the surface of the ~olyurethane roller.
Lindsay Patent 3,914,817 has for its obiect the re-moval of dust particles from a photographic film and, for this purpose, uses a pair of Neoprene rollers. Furthermore, the sur-faces of the neoprene rollers are such that they are "tacky", so that they may pull dust particles from the surface of the film being cleaned. This patent does disclose a surface finish of under 20 micro-inches, but does not teach the unexpected and re-markable results obtained with the instant invention. The mater-ial is Neoprene, and not polyurethane, and Lindsay's rollers are non-analogous art. Removing dust from photographic negatives by tacky rollers is one thing, but drying the liquid-developed photoconductive surface bearing the developed image is quite another.

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Pg/ i - 3 -~lO(~Z6 I have previously devised a method in which a roller could be produced by supporting a shaft centrally of a highly polished tu~ular mold made from a precision drawn tube. The fabrication of such molds required polishing their interior surface, which was an expensive and time-consuming task.
Furthermore, it was difficult to obtain an interior surface of the mold to a finish of less than 8 micro-inches. A finish of this fineness was required to produce a cast roller having a surface image of less than 10 micro-inches. It is known that the surface roughness of a sand casting, a saw cut, or a rough turning is between 500 and 1000 micro-inches root-mean-square (rms~. This can be reduced to 100 micro-inches by further turning or milling and then to about 20 micro-inches by grinding. Superfinishing requires an abrasive block, contoured to match the surface to be finished, and a combination of light pressure and a~generous supply of collant lubricant. This will produce a surface of from 1 to 5 micro-inches. It will be apparent to those skilled in the art that the production of metal tubes to be used as molds for the

2~ casting of my polyurethane rollers having the required smoothness is extremely expensive.

~ esides roughness, there is the question of waviness to be considered. A surface may be described as peak-to-peak heignt of roughness or waviness. Throughout this specification, the term "micro-inches" will he used to mean root-mean-square, as defined by:

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l~lQQ26 rmS = ~ 2 where "y" is the height of the surface above the mean, "x"
is the horizontal distance between peaks, and "L" is the horizontal distance over which readings are taken.
Broadly speaking, therefore, the present in-vention provides a method o~ making a squcegee roller ha~ring a surface finish of between two and ten micro-inches including the steps of coating the interior of a drawn vitreous tube with a release agent comprising a solution of between 0.5 percent and 1.5 percent by weight of a wax having a melting point below 100C. in an or~anic solvent, positioning a metal sha~t concentric with the tube, depositing elastomeric poly-urethane within the tube around the shaft, curing the polyure-thane, and then removing the roller from the tube.
The above method will produce a squeegee roller comprising a shaft and a cast elastomeric polyurethane cylinder positioned around the shaft, the surface of the roller having a ~inish between 2 and 10 micro-inches.
In the accompanying drawings which form part of the instant specification and which are to be read in coniunction therewith, and in which like reference numberals are used to in-dicate like parts in the various views:
FIGURE 1 is a flow diagram showing the steps of my process, with necessary steps indicated by solid lines and option-al steps indicated by dashed lines.
FIGURE 2 is a diagramma-~ic ~riew, with parts sho~n~
in section, of a battery o~ glass tubes containing ~inislle~
ro~lers made in accordance with my inventi~n be~ore their remo~al -- from the mol~s.
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l~QOX6 FIGU~E 3 is a perpsective view of a roller made in accordance with my invention.
FIGURE 4 is a sectional view taken along the line 4-4 of FIGURE 3.
Description of the Preferred Embodiment Referring now to the drawings, the shaft may be of any appropriate diameter. In the preferred e~bodiment, I
finish the shaft end portions to avoid having to handle the finished roller unnecesarily after it has been produced. After the end portions of the shaft are finished, the shaft may be machined between the end portions if desired. The roughness of the shaft between the end portions may serve to bond the polyurethane to the shaft.
Preferably, I coat the shaft between the finished ends with a thin coating (of the order of 0.05 mm.) of a high , dielectric epoxy resin to insulate the shaft from the polyurethane.
In my prior method, where polished metal molds were used, a finished roller was removed from a mold by first heating the mold to slightly expand it and then removing the roller from the mold. Owing to the smoothness of the glass, I have founa that it is preferable to coat the inside of the glass tube with a very thin coating of a release agent. I form an extremely thin coating hy dissolving from be~ween 0.5 percent to 1.5 percent hy weight of a wax in a solvent. A preferred solution is 1~ ~y wei~ht of carnauba wax in trichloroethylene solvent. Any so}uble wax in which ywl/~; - 6 -~10026 the solvent does not adversely affect the polyurethane can be used for example:
Carnauba wax, which has a melting point of approximately 86C.
Indian wax, which has a melting point of ap~roximately 61~C.
Reeswax, which has a melting point of approximately 62C.
Sugar cane wax, which has a melting point of approximately 77C.
Chinese insect wax, which has a melting point of approximately 83C.
Castor wax, which has a melting point of ~ ap~roximately 85~C.
:~ A simple and preferred method of coating the Pyrex (trademark) glass tube is to dip it in a solution of the release agent After this is done, the coated glass tube is positioned in a fixture adapted to hold the glass tube precisely perpendicular and concentric to an axis. A shaft : 20 is then inserted into the fixture, the lower end of the shaft being coaxial with the glass tube. Means are provided for adjusting the upper end of the shaft so the entire shaft will be concentric or coaxial with the glass tube mold.
The polyurethane is prepared from polybutadiene polyol and a diisocyanate, being a reaction product of about 80% by weight of the polyol and about 20% by weight ywl/~ 7 -lllOOZ6 of the diiocyanate. Oel-er polyurethanes, such as the reaction product of castor oil and 2,4-tolylene diisocyanate, may be used. The reagents are mixed at a temperature of approximately 130F and then poured into the mold to the desired level.
The mold is then placed in a curing oven and the temperature elevated to 265F and held at this temperature for a period of about 4 hours. It is understood that the temperatures and times for curing are those specified by various manufacturers of the polyurethane forming reagents and any appropriate temperature may be used, depending on the particular reagents involved. After the polyurethane has been cured, the mold is removed from the oven and allowed to cool to room temperature.
In cooling, the polyurethane roller contracts slightly so that, when a solvent is poured into the top of the mold, it dissolves the wax release agent and the finished roller slips out of the glass mold like wet soap.
Referring now to Figure 2, there is shown a battery of molds formed of glass tubes 2, of which there can be any appropriate number, positioned on a support 4 of a fixture.
The bottom of each glass tube 2 is cut so that it forms a right angle with the tube axis. The support 4 is leveled by appropriate means (not shown). A templet 6 is posi~ioned on the support 4 so that each glass tube will be concentric with the axis of each opening ~ through which each shaft 10 extends.
An abutment 12 is provided for each shaft to position its lower end. Each shaft may be coated intermediate its end 1~10026 portions with a thin coating 14 of insulating epoxy resin.
The center of the upper end 16 of each shaft 10 is positioned to be aligned with the axis of each glass tube 2 by means of a plumb bob 18. Adjusting screws 20 supported in a fixture 22 are positioned 120 apart. They can be manipulated to position the center of the shaft so that it is vertical or coaxial with its tube 2. After the shaft has been concentrically positioned within the glass tube, the polyurethane 24 is poured into the glass tube 2 and then cured and removed as described hereinabove.
The finished roller exhibits remarkable properties.
When placed horizontally on a vertical windowpane, it adheres to the glass pane as if magnetically held thereto and slowly rolls downward by gravity. In the prior art, an 8-1/2" x 11"
sheet of paper coated with a photoconductor, passing through a development bath and through squeegee rollers of the prior art, will have a surface liquid of between 120 and 150 mg.
These conventional rollers of the prior art generally have an upper metal type roller, sometimes coated with Teflon*, and a lower rubber roller which presses the developed and wet paper against the upper roller. The upper roller is usually polished to prevent it from picking up part of the image and reprinting it or offsetting it on the next sheet of paper to be processed.
Using two of my rollers as squeegee rollers for the developed photoconductor-coated paper coming out of the developing bath, ~ Trade~ark ~ s -l~lQ026 there is only between 10 and 30 mg. of developer liquid on the paper sheet. Strangely enough, this improvement obtains almost irrespective of the pressure between the rollers. It will be clear to those skilled in the art that there is between 400% and 1500Z improvement in efficiency by the use of my rollers in the removal of surface liquid. Since most liquid developers comprise a light hydrocarbon as a dispersant, the evaporation of hydrocarbon vapors into the printing room - is vastly reduced. This not only lessens the odor, but avoids a health hazard where the hydrocarbon-containing liquid developers are used in an office copier located in an enclosed space.
Because of the smoothness of my squeegee rollers ~between 0 and 10 micro-inches), they appear to have a highly polished surface. They are so efficient that a light wiper for the roller on the image side prevents reprinting. r have found that the image quality is improved by reducing the water absorption of the roller. This is accomplished by using a hydrophobic polyurethane elastomer or by using a filler material which prevents water absorption into the polyurethane. The insulation of the rollers from ground also helps image clarity.
Both rollers are reasonably soft, having a Shore A hardness of between 20 and 40. A pair of my rollers act as an efficient dynamic seal; that is, they make continuous contact with the section of the paper which lies between the nip and act as a i 1J; ~ -10-1~10Q2~;

dam and prevent li~uid from passing through this dam. Owing to the relative softness of the rollers, there is conformation to the micro-irregularities present in the paper.
It will be seen that I have accomplished the objects of my invention. I have provided a method of making an improved s~ueegee roller which is inexpensive and efficient. The squeegee roller made by my invention exhibits unexpected and remarkable properties, in that it enables liquid-developed electrostatic images on photoconductive paper to leave the copy machine substantially dry, without the necessity of applying heat, and without blurring the developed image. Squeegee rollers made by my invention have an extremely smooth surface of between 2 and 10 micro-inches, owing to the fact that they are cast in glass tubes instead of the usual molds where the desired smoothness is extremely difficult and expensive to obtain.
It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of my claims. It is further obvious that various changes may be made in details within the scope of my claims without departing from the spirit of my invention. It is, therefore, to be understood that my invention is not to be limited to the specific details shown and described.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of making a squeegee roller having a surface finish of between two and ten micro-inches includ-ing the steps of coating the interior of a drawn vitreous tube with a release agent comprising a solution of between 0.5 percent and 1.5 percent by weight of a wax having a melt-ing point below 100°C. in an organic solvent, positioning a metal shaft concentric with said tube, depositing elasto-meric polyurethane within said tube around said shaft, curing the polyurethane, and then removing the roller from the tube.

2. A method of making a squeegee roller having a sur-face finish of between two and ten micro-inches including the steps of coating the interior of a drawn vitreous tube with a release agent comprising a solution of between 0.5 percent and 1.5 percent by weight of a wax having a melt-ing point below 100°C. in an organic solvent, coating a metal shaft with a dielectric adhesive, positioning the shaft con-centric with said tube, depositing elastomeric polyurethane within said tube around said shaft, curing the polyurethane, and then removing the roller from the tube.

3. A method of making a squeegee roller having a sur-face finish of between two and ten micro-inches including the steps of coating the interior of a drawn vitreous tube with a release agent comprising a solution of about one per-cent of a wax having a melting point below 100°C. in an organic solvent, positioning a metal shaft concentric with said tube, depositing elastomeric polyurethane within said tube around said shaft, curing the polyurethane, and then removing the finished roller from said tube.