US3542579A

US3542579A - Electrostatic image development

Info

Publication number: US3542579A
Application number: US762451A
Authority: US
Inventors: Robert W Gundlach
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1964-12-28
Filing date: 1968-09-25
Publication date: 1970-11-24
Anticipated expiration: 1987-11-24
Also published as: DE1497233A1; FR1465790A; DE1497233B2; NL6516798A; GB1133462A

Description

R. W. GUNDL ACH ELECTROSTATIC IMAGE DEVELOPMENT Nov. 24, 1970 Filed Sept. 25, 1968 I III I IIIIIIIIIIII. \7*\/\ "*0 O xmm INVENTOR. ROBERT W. GUNDLACH 42 frQ 5 ATTOR/V United States Patent 015cc 3,542,579 Patented Nov. 24, 1970 US. Cl. 11717.5 Claims ABSTRACT OF THE DISCLOSURE The method and apparatus for the development of electrostatic images wherein xerographic developer material is applied to a photoreceptive surface bearing a latent electrostatic image by a combination of cascade and powder cloud development.

RELATED APPLICATIONS This application is a continuation of applicants prior copending application Ser. No. 421,297 filed Dec. 28, 1964, now abandoned.

BACKGROUND OF THE INVENTION This invention relates to latent electrostatic image development and, more particularly, to a method and apparatus for developing a visible image from a latent electrostatic image by means of a combination of cascade and powder cloud development.

More specifically, this invention relates to a method and apparatus for the development of latent electrostatic images wherein electroscopic developing material is used to develop a latent electrostatic image by sequentially contacting the latent electrostatic image with a suspension of toner powder and cascading electroscopic developer material.

Latent electrostatic images may be formed, for example, by the electrographic or xerographic process. Whether a latent electrostatic image is formed by selective deposition of electrical charges on a suitable substrate or by uniformly electrically charging a suitable substrate and selectively dissipating the electrical charges, it is necessary to contact the image with electroscopic toner powder in order to render this latent electrostatic image visible.

One suitable type of image development is disclosed in Edward N. Wise US. Pat. No. 2,618,552 wherein the development of a latent electrostatic image is accomplished by rolling or cascading a developer material, including carrier particles having toner powder particles electrostatically adhering thereto, across th latent image bearing surface. The materials comprising the toner powder or particles and carrier particles are selected in accordance with their triboelectric relationship such that an electrical charge is imparted to the toner powder and carrier material upon inter-mixing so that the toner particles adhere to and coat the surface of the carrier material. As the developer material is cascaded across a latent electrostatic image, the electroscopic toner powder is attracted to the latent electrostatic image from the carrier material due to a greater magnitude of electrical charge. As the developer material cascades or rolls across a latent electrostatic image bearing surface, these toner particles are generally electrostatically deposited on and secured to the charged portions of the latent image and not deposited on the uncharged or background portions of the image bearing surface.

In the cascade development method it has been found that, due to the magnitude of the triboelectric attraction between the carrier particles and the toner powder, areas of greatest charge differential are developed by this method to the exclusion of those areas having a slight charge differential. Since the cascade development method requires that the attraction between the toner particles and the latent electrostatic image must be of a greater magnitude than the attractive force between the toner particles and the carrier material, the cascading developer material is generally effective only in areas of greatest charge differential, that is the latent electrostatic image tends to be developed more heavily around the edges than in the central portions of a uniformly charged area. Since the electrical field is much stronger at the edges of a uniformly charged area, the edge portion is developed by the cascading developer material because the strength of the electrical field is sufficient to attract the toner particles from the carrier material. However, the central portion of a uniformly charged area, the electric field is substantially less than at the edge portion due to the contiguous electrical charges of the same polarity. Therefore, th electric field is not strong enough to attract the tonner particles from the carrier material and this central portion is not developed by the cascading developer material.

One attempt to overcome these difficulties has been the utilization of a development electrode in the developer apparatus. However, the use of a development electrode has not been entirely satisfactory in that the cascading developer material tends to become constricted between the latent electrostatic image bearing surface and the development electrode due to the narrow spacing required for an effective development electrode. Also, when a development electrode is utilized in an apparatus having an endless latent electrostatic image bearing surface, the close spacing required between the image bearing surface and the development electrode results in abbrasion of the latent electrostatic image bearing surface.

A further problem associated with cascade development systems has been that as the developer material is cascaded across the latent electrostatic image during the cascading process, the carrier material may become sufficiently depleted of toner powder (toner starvation) such that the partially denuded carrier material will have an electrical charge of a magnitude sufiicient to remove toner powder which has been previously deposited on the latent electrostatic image. This removal of previously deposited toner powder degrades the developed image and produces variations in the image density referred to in the art as image striations.

Another method of developing latent electrostatic images is disclosed in C. F. Carlson US. Pat. No. 2,217,- 776 and is referred to as powder cloud development. This method of development utilizes a substantially uniform suspension of electroscopic toner particles suspended or dispersed in a gaseous carrier. These particles are generally given an electrostatic charge during the formation of an aerosol, and then this aerosol or powder cloud is presented to the surface of a latent electrostatic image bearing member to develop a visible image thereon. Since the electroscopic toner powder is not adhering to an oppositely charged body as in cascade development, the electric fields of the latent electrostatic image do not have to compete with the electrostatic attraction of a carrier material and, therefore, the central portions of a charged area whereat the charge differential is very small are developed by this electroscopic toner powder cloud. However, as the areas of minimum charge differential occur not only in the central portion of a latent electrostatic image but also in areas of residual electrostatic charge such as background, the powder cloud development technique develops substantially all electrostatic charges including background and, therefore, is limited in its applications.

Further problems associated with powder cloud development include image streaking due to the high velocity conditions necessary to generate the toner powder cloud, and agglomeration of the toner powder as it is attracted onto oppositely charged or electrically grounded surfaces and subsequently torn loose by various mechanical forces exerted on that surface. Also, due to the nature of the electric field of the latent image, toner powder deposition along the areas having a high charge differential (edge portion) is minimal resulting in a defect referred to in the art as a halo effect. The uniformity of development and the speed of development are generally not sufiicient to utilize such a development process in a commercial application. Moreover, the inclusion of a development electrode in this system has created a problem of high background in cases of insufficient exposure.

Although much effort has been invested in the improvement of powder cloud development, as evidenced in Landrigan U.S. Pat. 2,725,304; Hayford U.S. Pat. No. 2,862,646; Carlson U.S. Pat. No. 2,918,900; and Richter U.S. Pat. No. 2,943,950 which are only exemplary samples of this type of development, the technique is not widely used in commercial applications because of its relative complexity and cost. Generally, these devices include a source of toner powder and means to suspend it in a gas in the form of an aerosol which is accomplished by agitating the powder and gaseous atmosphere and allowing the gas to expand. Depending upon the particular powder cloud generator, the creation of the aerosol may require the utilization of vanes or heaters to stir up the powder, sources of high pressure gas including compressors, regulating valves, and the like, and means to convey the aerosol for presentation to the latent electrostatic image. Furthermore, the introduction of gas from a high pressure source must be accomplished by a filtered exhaust system to carry away equal quantities of the electroscopic toner powder bearing aerosol.

SUMMARY OF THE INVENTION The present invention comprises a unique development system wherein the benefits of cascade and powder cloud development may be exploited and the problems hereto fore associated with each of these development systems when utilized separately are minimized. In addition, it has been found that by utilizing the novel development method disclosed herein an extremely high quality image reproduction development system is obtained. By uniquely r combining the powder cloud and cascade development techniques in a sequential manner as disclosed herein in one embodiment an extremely high quality latent electrostatic image development method is obtained by an initial contact of the latent electrostatic image with a powder cloud and a subsequent contact with cascading developing material whereby the areas of low and high charge differential are developed, respectively, and the background or developed residual charge areas are removed from the image bearing surface.

As the latent electrostatic image bearing surface is contacted by a cloud of electroscopic toner particles, the areas of the latent electrostatic image having a low charge differential are developed, and the portion of the image bearing surface having residual electrical charges or background is developed, too. The subsequent cascading of the developer material across the electrostatic image bearing surface, which has been partially developed by exposure to the cloud of toner particles, completes image development by developing the portion of an image having a high charge differential. The partially denuded carrier material, which has given up a portion of the toner powder adhering to its surface to form a visible image, removes the background developed by the powder cloud. This scavenging of the toner powder in non- 4 image configuration or background removes the background thereby improving the quality of the developed image and eliminates image striations occasioned by the toner starved carrier material.

It is, therefore, an object of this invention to improve methods and apparatus for the development of latent electrostatic images.

Another object of this invention is to utilize the advantages of cascade development and powder cloud development in a single development system.

Still another object of this invention is to inexpensively and conveniently develop latent electrostatic images in an automatic development operation.

Yet another object of this invention is to develop continuous toned images such as photographs, radiographs, and large solid dark areas with a minimum of background development.

A further object of this invention is to develop both edge and solid areas of a latent electrostatic image substantially free of background development.

DESCRIPTION OF THE DRAWINGS Further objects of this invention, together with additional features contributing thereto and advantages occuring therefrom, will be apparent from the following description of several embodiments of the invention when read in conjunction with the accompanying drawings, wherein:

FIG. 1 is an ellarged fragmentary sectional view illustrating the field lines emanating from a latent electrostatic image;

FIG. 2 is an enlarged fragmentary sectional view illustrating the effect on an electrostatic field as shown in FIG. 1 by the inclusion of an electrode;

FIG. 3 is a schematic side sectional view of apparatus for development of a latent electrostatic image used in the present invention;

FIG. 4 is a schematic sectional view of a drum type xerographic machine according to the invention; and,

FIG. 5 is a partial schematic sectional view illustrating an alternative embodiment to that shown in FIG. 4 according to the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS Illustrated in FIG. 1 is an exposed xerographic plate 10 having conductive backing member 6 and photoconductive insulating layer 7. On or near the surface of insulating layer 7, is an electrostatic latent image designated by plus marks 9. Also shown are the electrostatic lines of. force characteristic of a latent electrostatic image. The plus marks on the layer indicate a charged area of the electrostatic latent image corresponding to a dark area of the original image which was used in making the exposure. It would obviously be desirable to develop this area heavily with toner powder in order that the resulting picture would have a dark area corresponding to the dark area in the original. However, it will be noted that the field lines near the center of the image which extend farthest from the image are much weaker than those near the edges which extend only a short distance. Because of this field configuration and the toner-carrier adherence which must be overcome to deposit toner in charged plate areas, the edge areas, i.e. the areas that have the greatest field attraction, are developed and the relatively weaker areas in the middle of a charged area are left undeveloped by the cascade technique. On the other hand, it will be apparent that in the case of powder cloud development, where the toner is freely floating in air away from the plate surface, good development is obtained in the middle areas by the relatively weak but farther reaching field lines emanating from the center of the image while the shorter but stronger fringe field lines are not seen by these relatively remote particles because they are shielded by the weaker but farther reaching field lines. In cascade, the

toner sees these short lines because the developer is flowed across the plate in actual surface contact with it. Therefore, it is seen that cascade development and powder cloud development, practically speaking, compensate each other by developing the edge and solid areas, respectively.

FIG. 2 illustrates the improvement obtained by adding a control grid 12. Grid 12 provides a conductor spaced in front of layer 7, thereby producing a capacitance between layer 7 and grid 12. This tends to intensify the number of lines of force extending outwardly from the charges on layer 7 and reduce the number extending through layer 7 to its conductive backing. The grid also tends to straighten out the lines of force at the edges of the charged area so that, for example, in powder cloud development, particles floating in this region will be more strongly attracted to all parts of the charged area. Grid 12 may be held at the same potential as plate or, if desired, further control of development may be achieved by placing a potential on the grid which is different from the potential of the plate. For example, if a small residual potential still exists in the areas of greatest illumination, (and these areas should remain white in the final developed image) biasing the screen electrode to match this residual potential will result in a minimum toner deposit in those areas.

Referring now to FIG. 3 of the drawings, there is illustrated a preferred powder cloud generator for use in the developing system of this invention. As in FIG. 2, a screen grid 13 is placed substantially coextensive with the image bearing surface of xerographic plate 10 so that the electrostatic lines of force that emanate outwardly from the different potential areas on the image tend to flow mostly to the screen. The screen should be spaced no more than .030 inch from the image for optimum field conditions. On the side of screen 13 opposite that of plate .10 is a conductive chute 18 for conveying developer material 14 poured from container 16.

Developer material 14 preferably takes the form of any suitable electroscopic toner mixed with a suitable granular carrier. Typical compositions for this mixture and for toners per se are more fully described in U.S. Pats. 2,618,551 to Walkup; 2,618,552 to Wise; 2,638,416 to Walkup and Wise; 2,788,288 to Rheinfrank; 2,753,308 to Landrigan; 2,891,011 and 3,079,342 to Insalaco; and Re. 25,135 to Carlson. The size and color of the toner particles depend upon the purpose intended as, for example, the size of xerographic toner in US. Pat. 3,079,342 is about 1 to about 30 microns. These toners usually consist of an electroscopic resin and a colorant such as any suitable organic or inorganic pigment or dye. The carrier particles on the other hand generally range from 300-500 microns.

A potential 15 of the same polarity as the electroscopic toner particles is applied to chute 18. Toner particles are driven from their carrier granules due to the electric field created between chute 18 and screen 13, forming a cloud of unipolarized particles having a mutual repulsion force between them. The cloud moves through screen 13, which prevents the passage of the larger carrier, into the electric field created between plate 10 and screen 13 and deposits in conformity with the electrostatic image on plate 10. By biasing screen 13 slightly with respect to xerographic plate 10 to precisely match the residual surface potential of the most highly exposed areas, it is possible to help prevent any background deposits on the plate.

Screen 13 may comprise any open work conductive material, such as, a fine mesh conductive screen. The choice of mesh size or opening pattern is dependent upon such features as having sufficiently large openings to avoid plugging up of openings by the toner particles on the one hand and sufficiently small openings on the other hand to prevent the passage of the carrier granules through the screen and also to avoid distortion of the electric field. Although FIG. 3 shows the position of the screen to be below that of the plate, it is by no means intended that the screen could not be placed in any other suitable position such as above the plate between it and the chute.

The potential applied to the chute should be of sufficient magnitude to overcome the electrostatic attraction between the carrier granules and toner particles and to propel such particles in the direction of the screen. A potential of 4,000 volts has been found to work very well for a quarter inch spacing between chute and screen. By varying the intensity of the field, of course, it is possible to accelerate the action of the particles. The polarity of the chute should be the same as the polarity of the charged toner particles. Therefore, if negatively charged toner pgrticles are used, a negative potential is applied to the c ute.

The cloud is capable of being dispersed in any suitable insulating fluid medium either of the gas or liquid type. Typical examples of such fluids are air, carbon dioxide, nitrogen, oxygen, Sohio Odorless Solvent (a kerosene fraction available from Standard Oil of Ohio), Freon 113 (trichlorotrifluoroethane), etc. As can be readily appreciated, the cloud generating system described above, hereinafter referred to as cascloud, is both simple and efiicient, thereby rendering it adaptable for use with other development systems. In this respect it should be noted that there is no bulky or complicated apparatus needed for this system, but merely a pair of spaced elements and a potential source. It is for this reason especially that this system is readily adaptable for use in a conventional cascade development system as will presently be shown.

In FIG. 4, there is shown a schematic sectional view of a drum type xerographic machine according to the invention. The principal element of the machine is xerographic drum 21 of a conductive material which is covered on its outer surface with a layer of photoconductive insulating material such as vitreous selenium. Drum 21 is rotatable about its axis in the direction indicated by conventional means, not shown. An electrostatic image is formed on drum 2.1 by means of a corona charging device 22 which deposits a uniform charge on the surface of photoconductive insulating layer. The drum then passes a projector 20 which exposes the charged photoconductor to a light image of the original to be reproduced thus discharging portions of the charged photoconductor which are struck by light. Other means of forming electrostatic latent images including means for forming images on ordinary insulating surfaces are known in the art and may be used instead of the one shown.

After image development, which will be described later, the developed image is transferred from drum 21 to a web of paper or the like 29 between guide rolls 28 acting to position web 29 against drum 21 by a second corona discharging device 27. A heating element 24 is positioned to heat the transferred image and thus fix it permanently bonded to the paper web 29. A rotating cylindrical cleaning brush 23 contacts drum 21 subsequent to image transfer and removes any residual image material from the drum thus readying it for reuse. Many other equivalent charging, exposure, transfer and fusing techniques known in the art may be employed in connection with the present invention.

Image development is effected by apparatus including a bucket conveyor 34 operating in a housing '35. Conveyor 34 moves developer material 31 from a supply at the bottom of housing 35 to a point above drum 21 and then drops developer onto drum 21 over which the developer material cascades. As developer material '31 cascades over drum 21, the toner particles are selectively detached from the carrier praticles and deposit on the surface in accordance with the fields genearted by the latent electrostatic image thereon, thus forming a visible image. The remaining material falls into and is guided down chute 32 as it continues its movement across the drum. Since the cloud generating chute accepts residual developer by gravity feed from the cascade system and requires no additional moving parts to form a powder cloud, it is very well suited for use with the cascade syst em. A potential is applied to chute 32 in the manner discussed above in the embodiment of FIG. 3 resulting in a cascloud development of the image surface of drum 21 in the areas adjacent screen member 33. As already mentioned, it is desirable to position the screen close enough to the drum to obtain Optimum field conditions taking into account, of course, drum machine flatness tolerances. Any remaining developer material falls into the bottom of housing 35 where it is available for a recycling on conveyor 34.

Obviously, by reversing the direction of rotation of the

drum

21 or 21, it is possible to have cascloud development followed by cascade development which is a preferred sequence because it is possible to take advantage of the scavenging effect of the carrier materials to remove loosely adhering toner from background areas. Alternatively, the cascloud developer system may be positioned above the cascade developer system as shown in FIG. 5.

In the embodiment of FIG. 5, primes have been added to the numerals shown in FIG. 4 to show like parts. Developer material 31 is fed into the channel formed by screens 33 and chute 32' effectuating cloud development as discussed above in FIGS. 3 and 4. The remaining developer material, which is now detoned, rolls across the surface of drum 21 as in ordinary cascade where further toner deposits are made and surplus toner recovered from background areas. Besides the better quality of reproduction obtained from this scavenging action, it also obviates the criticality of exposure normally present in cloud development systems with an electrode. As mentioned above, by reversing the direction of rotation, it is possible to change the sequence of development.

As can be readily appreciated, the development system of this invention achieves both solid area and edge development in a single continuous system. Development is not affected by the weaknesses of the field in the middle of charged areas as is the case in cascade development. On the other hand, because of the simplicity of the cloud generating system, the advantage of good edge development in cascade is still retained. What is more astonishing is that even for ordinary line copy reproductions, development by the invention proved superior to that of ordinary cascasde. In the past, it has not been possible to obtain complete development especially for continuous toner images. The development system of the invention makes possible the complete and rapid development of any pattern by electrophotography. Moreover, the advantage of a cleaning action after cloud development as when cloud is followed by cascade is novel in and of itself. Thus, there ,is achieved a unique development system for an electrostatic latent image which is both simple and inexpensive but gives complete development in all respects with a clean background.

While the specific embodiments shown and described in this specification and drawings are admirably adapted to fulfill the stated objects, it should be understood that it is not intended to confine the invention to these disclosed embodiments since the invention itself is susceptible of embodiment in many various forms.

What is claimed is: 1. A method of developing a surface bearing a latent electrostatic image which comprises the steps of passing a quantity of latent electrostatic image developer material including toner powder and particulate carrier material in a path of movement adjacent a latent electrostatic image bearing surface,

impelling said passing developer material including toner powder and carrier material towards said latent electrostatic image bearing surface,

intercepting said developer material to prevent said particulate carrier material from contacting said lat- 8 ent electrostatic image bearing surface and separating a portion of toner powder from said developer material for passing said portion of toner powder into development contact with said latent electrostatic image bearing surface to develop a latent image thereon, and

cascading the remaining developer material over said image bearing surface to effect a complete development of said image and removal of toner powder in non-image areas.

2. The method of claim 1 wherein said developer material remaining after having a portion of the toner powder separated therefrom is cascaded in a path of movement conforming to the peripheral surface of the latent electrostatic image bearing surface.

3. The method of claim 1 including further impelling said portion of toner powder separated from said developer material toward said latent electrostatic image bearing surface to partially develop a visible image thereon.

4. The method of claim 3 wherein said developer material remaining after having a portion of the toner powder separated therefrom is cascaded in a path of movement conforming to the peripheral surface of the image bearing surface to effect a complete visible development of said image.

5. Apparatus for developing a visible image on a latent electrostatic image bearing surface including means for cascading latent electrostatic image developer material comprising a mixture of charged toner powder and carrier material across a latent electrostatic image bearing surface to partially develop a visible image thereof,

means positioned adjacent said latent electrostatic image bearing surface to guide the developer material after being cascaded over said image bearing surface,

a foraminous member positioned between said guide means and said image bearing surface having openings larger than said toner powder and smaller than said carrier material,

means to apply a potential to said guide means of a magnitude and a polarity sufiicient to separate a portion of the toner powder from said developer material and to propel said toner powder through said foraminonus member to said image bearing surface for completely developing a visible image thereof.

6. The apparatus of claim 5 wherein said foraminous member is electrically biased to a magnitude and polarity such that the toner powder separated from the developer mixture and propelled through said foraminous member is deposited substantially on the latent electrostatic image.

7. The apparatus of claim 5 wherein said foraminous member comprises a screen.

8. The apparatus of claim 7 wherein said screen is electrically biased to a magnitude and polarity such that the toner powder separated from the developer mixture and propelled through said foraminous member is deposited substantially on the latent electrostatic image.

9. Apparatus for developing a visible image on a latent electrostatic image bearing member by the application of developer material comprising toner powder and carrier material, the apparatus including a foraminous member having openings larger than toner powder and smaller than carrier material positioned adjacent the surface of a latent electrostatic image bearing member,

means positioned adjacent to said foraminous member for introducing a quantity of latent electrostatic image developer material thereonto, and

having an electrical charge of a polarity and magnitude sufiicient to separate a portion of the toner powder from said developer material and to propel said portion of toner powder through said foraminous member to said latent electrostatic image bearing member for partially developing a visible image thereon, and

said foraminous member extending to a position such that said developer material remaining after having a portion of the toner powder removed therefrom is cascaded over said partially developed image bearing surface to effectuate complete development of the image thereon.

10. The apparatus of claim 9 wherein said means positioned adjacent to said foraminous member to introduce a quantity of developer material onto said foraminous member comprises a chute including a dependent trailing guide portion extending substantially the length of said foraminous member.

11. The apparatus of claim 9 wherein said forarninous member is electrically biased to a magnitude and polarity such that the toner powder separated from the developer mixture and propelled through said foraminous member is deposited substantially on the latent electrostatic image.

12. The apparatus of claim 9 wherein said foraminous member comprises a screen.

13. The apparatus of claim 12 wherein said screen is electrically biased to a magnitude and polarity such that the toner powder separated from the developer mixture and propelled through said foraminous member is deposited substantially on the latent electrostatic image.

14. Apparatus for developing a latent image on an electrostatic image bearing member, comprising means for cascading a mixture of charged toner particles and larger carrier beads across the surface of said image bearing member,

a chute adjacent the surface of said member positioned to collect the mixture after it is cascaded,

a screen intermediate said chute and said member, the openings in said screen being larger than said toner particles and smaller than said carrier beads,

means to apply a potential to said chute of the same polarity as the charge on said toner particles, said potential being of a magnitude sufficient to separate a portion of the toner particles from the carrier beads in the collected mixture and repel them through said screen towards said image bearing member, and

means to move said image bearing member relative to said cascading means and said chute and screen whereby both edge and solid area development of said latent image is accomplished in a continuous system.

15. Apparatus for developing an image on a latent electrostatic image bearing member comprising an electrode chute adjacent a portion of the surface of an image bearing member,

a conductive screen intermediate said chute and said image bearing member,

said screen having openings of a size which will pass toner particles but not carrier beads,

means to apply a potential to said chute of a polarity and magnitude suflicient to repel a portion of toner particles from carrier beads through said screen towards said image bearing member,

means to feed a mixture of charged toner particles and carrier beads between said screen and said chute to form a cloud of toner particles of the portion of toner particles repelled from said carrier beads, and to cascade the remaining toner particles and carrier beads over said image bearing surface, and

means to move said image bearing member past said chute.

References Cited UNITED STATES PATENTS 2,784,109 3/1957 Walkup 117--17.5 2,808,023 10/1957 Hayford 117-17.5 X 2,808,328 10/1957 Jacob 117-17.5 X 2,862,472 12/ 1958 Carlson 11717.5 X 2,927,554 3/1960 Oldenboom 118-637 2,940,864 6/ 1960 Watson 11717 3,008,826 11/1961 Mott et al. 117-17.5 X 3,011,473 12/1961 Gundlach 117--17.5 X 3,011,474 12/1961 Ulrich 11717.5 X 3,140,175 7/1964 Kaprelian 117-17.5 X 3,241,483 3/1966 Dutr' 11717.5 X 3,257,223 6/1966 King 11717.5 3,294,017 12/1966 St. John 11717.5 X 3,306,193 2/1967 Rarey et a1. 101-114 WILLIAM D. MARTIN, Primary Examiner E. J. CABIC, Assistant Examiner U.S. Cl. X.R.