US3631798A - Pneumatic doctoring of solid ink particles from intaglio plate - Google Patents

Abstract

An apparatus and method for pneumatically doctoring excess particulate printing materials from a gravure printing element by utilizing a flowing boundary layer as an air knife.

Description

United States Patent lnventor Douglas I". St. John Toledo, Ohio Apr. 23, 1970 Jan. 4, 1972 Owens-Illinois, Inc.

Continuation-impart of application Ser. No. 663,581, Aug. 28, 1967, now abandoned. This application Apr. 23, 1970, Ser. No. 31,395

Appl. No. Filed Patented Assignee PNEUMATIC DOCTORING OF SOLID INK PARTICLES FROM INTAGLIO PLATE 11 Claims, 3 Drawing Figs.

US. Cl 101/167, 101/170 Int. Cl B411 9/08 Field of Search 101/150,

155, 167, 170, DIG. 13, 1 12; 118/63, 261; 117/102 [56] ReferencesCited UNITED STATES PATENTS 2,787,556 4/1957 Haas l0l/D1G.l3 1,696,171 12/1928 Lipsius 118/63 2,604,848 7/1952 Mullen 118/63X 3,120,806 2/1964 Supernowicz... 101/426 3,296,965 1/1967 Reifetal. l0l/D1G.l3

Primary Examiner.l.

Reed Fisher At!0rneysE. J. Holler and Donald K. Wedding ABSTRACT: An apparatus and method for pneumatically doctoring excess particulate printing materials from a gravure printing element by utilizing a flowing boundary layer as an air knife.

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FVERNEQQ PNEUMATIC DOCTORING OF SOLID INK PARTICLES FROM INTAGLIO PLATE RELATED APPLICATION This is a continuation-in-part of copending application Ser. No. 663,581, filed Aug. 28, 1967 (now abandoned).

THE INVENTION This invention relates to a printing process and apparatus, and more particularly to an improvement in the doctoring of particulate or powdered inks and toners from intaglio gravure printing elements. As used herein, the term gravure element includes flat platelike elements as well as cylindrical elements.

The phrase gravure printing" refers to a printing process wherein the printed image corresponds to engravings, depressions, or cells in the surface of a gravure element. Printing materials (inks) are transferred from these engravings to the substrate to be decorated. This can be accomplished by direct transfer of the printing material from the gravure to the substrate, or indirectly through the use of an intermediate transfer element such as an offset blanket. This definition includes intaglio, rotogravure, etched plates and the like.

Gravure printing has been successfully carried out with solid printing materials in printing high quality images on a wide variety of substrates. Solid printing materials such as powdered inks and toners have advantages over conventional inks in that the need for solvents with their attendant health, safety and cost disadvantages are eliminated. Additionally, ink solubility is no longer a problem. As a further advantage of printing with solid inks, electrical fields can be employed as a means of eliminating the need for contact between the substrate and the printing element.

Conventional methods for removing the excess particulate inks from the nonprinting surface areas of intaglio gravures usually include wiping the gravure element with a thin flexible blade. This process is known as doctoring and the blade is known as a doctor blade." The blade removes the excess printing powder through physical contact with the gravure surface after the particulate ink is applied, but prior to the printing operation.

This method causes extreme wear on both the blade and the surface of the gravure element, and is therefore undesirable. More importantly, this contact between the doctor blade and the gravure surface often physically dislodges the particulate ink from the depressed printing surface. This, of course, results in hazy, fuzzy and incomplete printed images.

In view of the foregoing, it is a primary object of the present invention to provide a novel apparatus and method for doctoring particulate printing materials from intaglio printing gravure elements.

Another object of the present invention is to provide an apparatus and method for doctoring particulate inks from printing gravures which eliminates wear on both the gravure and doctor blade.

Another object is to provide a method of doctoring the excess particulate inks and toner from intaglio gravure plates and cylinders which eliminates all physical contact between the doctoring device and the gravure.

A further object is to provide a method and apparatus for doctoring solid printing materials from gravure elements through the control of the air boundary layer in contact with the element.

A still further object is to provide a method for doctoring the excess printing powders from intaglio gravures through the use of positive static air pressure in combination with boundary air flow that removes the excess printing powders from the nonprinting surfaces without dislodging the powders in the intaglio printing depressions.

Referring now to the drawings:

F 1G. 1 is a perspective view of apparatus suitable for practicing the present invention.

FIG. 2 is a side elevation of the apparatus shown in FIG. 1.

FIG. 3 is a sectional view taken along line 3-3 in FIG. 2.

In FIGS. 1-3, one form of the invention is shown in which the excess of powdered printing material 9 is removed from a flat platelike gravure printing element 10 while the printing element is conveyed beneath two juxtapositioned, contacting, counter rotating drums or rolls II and 11a by suitable conveying means such as a belt 40 driven in the direction of arrow A of FIG. 1.

The drums 11 and Ila are mounted on drive shafts l2 and 12a. These drive shafts are in turn journaled in supporting walls 15 and 15a which walls are supported by base 14. Drive shafts 12 are connected to, and driven by motors I8 and 18a. The drums can also be driven with one motor and suitable gear train arrangements.

A pair of ducts or nozzles 16 and 16a are positioned on either side of the drums 11 and lla and protrude into the gap 41 existing between the drums 11 and 11a and the gravure element 10 best shown in FIG. 3. Ducts l6 and 16a are not circular in cross section but are elongated so as to be at least coextensive with the width of the gravure element 10 as shown in FIG. 2.

Ducts l6 and 16a are each connected to both a vacuum source V and pressure sources P through regulating valve assemblies 20 and 20a which can be provided with conventional means, not shown, for adjustably regulating the rate of flow of air through the nozzles. Each valve assembly has three positions of operation so that it can be set to supply pressure or vacuum, and can also be completely shut ofl. In FIG. 3, nozzle 16a is set for pressure and nozzle 16 is set for vacuum.

In practicing the present invention a suitable printing powder is deposited in the printing depressions or cells 17 in the gravure element 10, These cells are shown greatly exaggerated in the drawings. This deposition of the powder on the gravure can be accomplished by wiping, brushing, spraying, electrostatic spraying or any other suitable means. Apparatus for depositing the powders is not shown in the drawings for the sake of clarity. During thisoperation, excess printing powder also covers substantial portions of the nonprinting surface areas. The excess printing powder is then removed by translating the gravure element 10 in close proximity, usually about 0.001 inch to about 0.5 inches, beneath the pair of highrspeed counter rotating drums 11 and 11a. The drums are counter rotating so that the peripheral surface of each drum is moving toward their point of mutual contact asthis peripheral surface passes directly over the gravure element. As a result of this drum rotation, the moving peripheral surfaces of the drums carry with them a boundary layer of air indicated in FIG. 3.

In fluid dynamics, the boundary layer is defined as a relatively thin layer of fluid flowing adjacent to a solid surface under the influence of the interfacial viscous shear existing along the fluid-solid surface boundary. Since boundary layer fluid flow is a specialized type of fluid flow (e.g. fluid flow under the influence of viscous shear) it can be controlled as any other type of fluid flow such as by the addition or subtraction of energy to or from the system. For example, low energy fluid of the boundary layer can be removed by suction or vacuum. This practice is well known and has many applications. The boundary layer can also be supplemented by introducing pressurized fluid into the system. Both of these methods are directed to controlling the thickness, velocity and direction of the boundary layer by the addition of energy to remove the pressure gradient or by actual removal of the boundary layer by suction.

In the present invention, the moving boundary layers of air are carried by the moving peripheral drum surface to the point of contact or nip 30 between the drums. Since thisboundary layer of air cannot escape from the nip between the drums, the air emerges from the nip flowing perpendicularly towardthe gravure element as shown in FIG. 3. The nip then acts as an air source and creates a positive fluid pressure (with, respect to ambient or atmospheric) in the triangular zone bounded by the gravure element and the peripheral surfaces of the drums thereabove and extending to the gaps 41 and 41a, so as to subject the gravure surface to a positive static air pressure greater than the atmospheric pressure outside the triangular area. lmmediately upon the gravure surface passing through the gap 410, a fluid pressure gradient is created with a lower instantaneous static pressure" within the gravure depressions and a higher positive static pressure above the surface. The positive static pressure above the surface is dynamically sustained so that while the pressure gradient exists a boundary layer of air adjacent the gravure surface flows from the triangular zone through the gaps 41 and 41a between the surface of the rolls and the gravure surface. it is not necessary that the juxtaposed drums be in actual contact with each other so long as the drums are close enough to each other to substantially restrict the flow of air therebetween and create a positive static pressure above the gravure. In other words, it is sufficient for the present purposes that the juxtaposed drums be in virtual contact.

It is this dynamically sustained positive static air pressure above the depressions which is greater than the instantaneous static pressure within the depressions that allows the removal of excessive printing ink material about the outer portion of the depression without removal of the material therein.

As can be seen in FIG. 3, the boundary layers of air surrounding the peripheral surface of the moving drums are flowing into the triangular zone while the boundary layer contacting the gravure element is flowing out of the triangular zone through the gap between the drums and the gravure element. It is an important feature of the present invention that particulate printing materials are not removed from the printing depressions in the gravure since the boundary layer is moving tangentially across the gravure surface while the depressions are under an instantaneous positive pressure.

The air ducts or nozzles 16 and 16a positioned exteriorly of the gaps 41 and 41a are not required in practicing the present invention, but when they are used, they serve to further control the boundary layer airflow as indicated in FIG. 3. In FIG. 3, the duct 16a is set for pressure and is directing a flow of air tangent'to the peripheral surface of the drum and at approximately an angle of 45 to the gravure element. This duct angle is not critical, so long as the angle is such as to not disturb particulate ink either in or out of cells when drums 11 and 1 1a are stationary. This positive air stream tends to increase the pressure in the triangular zone and thereby further prevents the particulate ink from being dislodged from the gravure printing depressions by keeping the total pressure (static and velocity) above atmospheric.

The nozzle 16 in FIG. 3 is positioned tangentially with respect to the drum and at an angle of approximately 45 with respect to the gravure element. This nozzle as shown is set for vacuum and has a tendency to reinforce the gravure boundary layer air current at the expense of the drum boundary layer air current. This vacuum nozzle increases the tangential airflow across the gravure at the expense of the pressure within the triangular zone. The vacuum nozzle therefore increases the rate at which the powdered ink will be doctored while decreasing the positive pressure in the triangular zone. If the pressure in the triangular zone is reduced too much, the powdered ink will become dislodged from the gravure cells.

From the foregoing it is apparent that the application of vacuum tends to increase the tangential airflow rate at the expense of positive pressure while the application of pressure tends to increase the positive pressure at the expense of tangential airflow rate. The application of vacuum or pressure can then be determined according to the requirements of each printing application.

One embodiment of this invention is an apparatus shown in FIG. 1 through 3, having the following specifications:

Counter rotating drums: Both drums were three-fourths inch in diameter and 3 inches in length having diamond knurled surfaces (96 diametral pitch). The drums were counter rotating in contact at the rate of about 15,000 r.p.m.

Boundary layer gaps: The shortest distance between the drums and the gravure element was about 0.01-0.02 inches.

Gravure element: Aluminum plate, inch thickness X 1% inch width X 6 inch length, drilled with ll8 point angle drill to the depth of the cone (as measured by the maximum cone diameter) from about 0.04 to about 0.08 inches.

Vacuum duct: 1/32 inch X 2% inch nozzle connected by Vtinch I.D. tubing to a vacuum pump capable of attaining about inch Hg vacuum at no flow conditions.

Pressure duct: Same design as vacuum duct with about 2 p.s.i.g. static pressure applied to the tubing.

Both the pressure and vacuum ducts were inclined at an angle of 45 with respect to the gravure plate, and positioned one-half inch above the plate and approximately three-fourths inch out from the minimum gap distance between the rolls and the plate (three-fourths inch from the axis of the rotation of the cylinder).

Printing material: A standard toner having a particle size of about 5-15 micron in diameter was applied to the gravure plate with a bristle brush and compacted into the printing depression.

Gravure plate speed: The plate was passed under the nozzles and drums at approximately ftJmin.

Adequate doctoring resulted using the above parameters. It was observed that the excess ink was not removed from the gravure plate by either the pressure or vacuum nozzle when the rollers were stationary.

Iclaim:

1. An apparatus for doctoring the excess printing powder from an element having gravure-type printing impressions thereon comprising, a base,

a pair of counter rotatable cylindrical drums mounted on said base, and juxtapositioned along their peripheral surfaces in a direction parallel to their axes of rotation,

means for positioning a gravure printing element in closespaced relationship beneath said drums so as to form two narrow air gaps at the region where the minimum spacing exists between the peripheral surfaces of the drums and the gravure element,

means for rotating said pair of drums at high speed and in opposite directions so as to form a zone of increased static air pressure in the triangular zone bounded by the gravure element and the peripheral surfaces of said drums whereby a tangential flow of air is inducted across said element which flow of air substantially removes the excess printing powder from the gravure element and,

means for translating said gravure element at right angles to the axes of rotation of said drums.

2. The apparatus of claim 1 further including means for inducing a flow of air into said triangular zone through one of said gaps to dynamically increase the instantaneous static air pressure in said zone relative to that pressure within the gravure impressions.

3. The apparatus of claim 2 further including means for inducing a flow of air out of said other gap tangentially across said gravure element.

4. A method for doctoring the excess printing powder from a printing element having gravure-type printing impressions comprising:

positioning a gravure printing element in close-spaced relationship beneath a pair of counter rotatable cylindrical drums, said drums being positioned in tangential contact alone their peripheral surface in a direction parallel to their axes of rotation,

rotating said pair of drums at high speeds and in opposite directions so as to form a zone to of increased static air pressure in the triangular zone bounded by the gravure element and the peripheral surfaces of said drum, and

translating said gravure element at right angles to the axes of rotation of said drums whereby tangential flow of air is induced across the element which flow of air substantially removes the excess printing powder from the gravure element.

5. An apparatus for doctoring the excess printing powder 75 from the face of a gravure-printing element having printing depressions in said face comprising means for subjecting the face of the gravure-printing element to an increase in static fluid pressure and simultaneously inducing at least one boundary layer of said fluid to flow tangentially across the face of the gravure-printing element, said means comprising a pair of cylindrical drums and means for rotatably mounting said drums juxtapositioned along their peripheral surfaces in a direction parallel to their axes of rotation, said apparatus further comprising means positioning said gravure element with its face in close-spaced relationship to said drums to form two narrow gaps at the region where minimum spacing exists between the peripheral surfaces of the drums and the face of the gravure element, whereby upon high-speed rotation of said pair of drums in opposite directions boundary layer of fluid are induced to flow adjacent the cylindrical surfaces of said drums into a generally triangular zone bounded by the face of the gravure element and the peripheral surfaces of the drums causing increased static fluid pressure within said triangular zone which is greater at the face of the gravure-printing element than the static pressure in said depressions and simultaneously at least one further boundary layer of fluid is induced to flow tangentially across the face of said gravure element away from said triangular zone and through at least one of said gaps to remove the excess printing powder without dislodging the powder contained in said depressions.

6. The apparatus of claim 5 further comprising means for moving said fluid pressure increasing and flow means and said gravure element relative to each other, whereby excess printing powder is removed from the face of the gravure element as portions of the face of the gravure element are subjected to said means.

7. The apparatus of claim 5 further comprising means for inducing a flow of fluid into said triangular zone through one of said gaps.

8. The apparatus of claim 7 further comprising additional means for inducing a flow of fluid away from said triangular zone and through said other gap tangentially across the face of said gravure element whereby the rate of tangential flow of fluid across the face of said gravure element is increased.

9. The apparatus of claim 5 wherein said means for positioning said gravure element comprises means for translating said gravure element along a path at a right angle to the axes of rotation of said drums.

10. A method of doctoring the excess printing powder from the face of a gravure-printing element having printing depressions in said face comprising rotating a pair of cylindrical surfaces in juxtapositioned relationship in opposite directions adjacent the face of the gravure printing element to cause the flow of boundary layers of fluid towards each other into a chamber defined by said cylindrical surfaces and said face whereby the static fluid pressure in said chamber is increased and is greater at the face of said gravure-printing element than the static pressure in said depressions and simultaneously at least one further boundary layer of said fluid is induced to flow tangentially across the face of the gravure-printing element to remove the excess printing powder from the face of the gravure-printing element without dislodging the powder contained in said depressions.

11. The method of claim 10 wherein said gravure element is moved along a path whereby excess printing powder is progressively removed from the face of the gravure element.

Claims (11)

1. An apparatus for doctoring the excess printing powder from an element having gravure-type printing impressions thereon comprising, a base, a pair of counter rotatable cylindrical drums mounted on said base, and juxtapositioned along their peripheral surfaces in a direction parallel to their axes of rotation, means for positioning a gravure printing element in close spaced relationship beneath said drums so as to form two narrow air gaps at the region where the minimum spacing exists between the peripheral surfaces of the drums and the gravure element, means for rotating said pair of drums at high speed and in opposite directions so as to form a zone of increased static air pressure in the triangular zone bounded by the gravure element and the peripheral surfaces of said drums whereby a tangential flow of air is induced across said element which flow of air substantially removes the excess printing powder from the gravure element and, means for translating said gravure element at right angles to the axes of rotation of said drums.

2. The appaRatus of claim 1 further including means for inducing a flow of air into said triangular zone through one of said gaps to dynamically increase the instantaneous static air pressure in said zone relative to that pressure within the gravure impressions.

3. The apparatus of claim 2 further including means for inducing a flow of air out of said other gap tangentially across said gravure element.

4. A method for doctoring the excess printing powder from a printing element having gravure-type printing impressions comprising: positioning a gravure printing element in close spaced relationship beneath a pair of counter rotatable cylindrical drums, said drums being positioned in tangential contact along their peripheral surface in a direction parallel to their axes of rotation, rotating said pair of drums at high speeds and in opposite directions so as to form a zone to of increased static air pressure in the triangular zone bounded by the gravure element and the peripheral surfaces of said drum, and translating said gravure element at right angles to the axes of rotation of said drums whereby tangential flow of air is induced across the element which flow of air substantially removes the excess printing powder from the gravure element.

5. An apparatus for doctoring the excess printing powder from the face of a gravure-printing element having printing depressions in said face comprising means for subjecting the face of the gravure-printing element to an increase in static fluid pressure and simultaneously inducing at least one boundary layer of said fluid to flow tangentially across the face of the gravure-printing element, said means comprising a pair of cylindrical drums and means for rotatably mounting said drums juxtapositioned along their peripheral surfaces in a direction parallel to their axes of rotation, said apparatus further comprising means positioning said gravure element with its face in close spaced relationship to said drums to form two narrow gaps at the region where minimum spacing exists between the peripheral surfaces of the drums and the face of the gravure element, whereby upon high-speed rotation of said pair of drums in opposite directions boundary layers of fluid are induced to flow adjacent the cylindrical surfaces of said drums into a generally triangular zone bounded by the face of the gravure element and the peripheral surfaces of the drums causing increased static fluid pressure within said triangular zone which is greater at the face of the gravure-printing element than the static pressure in said depressions and simultaneously at least one further boundary layer of fluid is induced to flow tangentially across the face of said gravure element away from said triangular zone and through at least one of said gaps to remove the excess printing powder without dislodging the powder contained in said depressions.

6. The apparatus of claim 5 further comprising means for moving said fluid pressure increasing and flow means and said gravure element relative to each other, whereby excess printing powder is removed from the face of the gravure element as portions of the face of the gravure element are subjected to said means.

7. The apparatus of claim 5 further comprising means for inducing a flow of fluid into said triangular zone through one of said gaps.

8. The apparatus of claim 7 further comprising additional means for inducing a flow of fluid away from said triangular zone and through said other gap tangentially across the face of said gravure element whereby the rate of tangential flow of fluid across the face of said gravure element is increased.

9. The apparatus of claim 5 wherein said means for positioning said gravure element comprises means for translating said gravure element along a path at a right angle to the axes of rotation of said drums.

10. A method of doctoring the excess printing powder from the face of a gravure-printing element having printing depressions in said face comprising rotAting a pair of cylindrical surfaces in juxtapositioned relationship in opposite directions adjacent the face of the gravure printing element to cause the flow of boundary layers of fluid towards each other into a chamber defined by said cylindrical surfaces and said face whereby the static fluid pressure in said chamber is increased and is greater at the face of said gravure-printing element than the static pressure in said depressions and simultaneously at least one further boundary layer of said fluid is induced to flow tangentially across the face of the gravure-printing element to remove the excess printing powder from the face of the gravure-printing element without dislodging the powder contained in said depressions.

11. The method of claim 10 wherein said gravure element is moved along a path whereby excess printing powder is progressively removed from the face of the gravure element.

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