US3545381A - Method of cleaning printing surfaces after printing soft tissue paper - Google Patents

Description

United States Patent [72] Inventor Jorgen L.Jorgensen Forest Park, Ohio [2]] Appl. No. 706,894

[22] Filed Feb. 20, 1968 [45] Patented Dec. 8, 1970 [73] Assignee The'Procter & Gamble Company Cincinnati, Ohio a corporation of Ohio [54] METHOD OF CLEANING PRINTING SURFACES AFTER PRINTING SOFT TISSUE PAPER 416, 423, 424; l18/(Inquired), 203; l5/(lnquired), 256.51, 256.52

[56] References Cited UNlTED STATES PATENTS 2,525,982 10/1950 Wescott 101/425 2,832,289 4/1958 Mitchell etal 101/425 Primary Examiner Robert E. Pulfrey Assistant Examiner-Eugene H. Eickholt Attorney.lohn V. Gorman ABSTRACT: A method of printing soft tissue paper and-immediately cleaning the printing surfaces by contacting the printing surfaces with a cleaning roll having a resilient, absorbent outer sleeve which is moistened with an ink-compatible solvent. The cleaning roll is brought III/to contact with the roll or surface having the printing elements thereon and by pressing the two together to provide sufficient contact pressure, a portion of the solvent in the sleeve of the cleaning roll is deposited on the printing surface to prevent the ink thereon from drying, and thereby pulling loose fibers from the paper which is to be printed. The roll also serves to remove any of the fibers which may have been deposited on the printing surfaces.

mnammum 8mm Y 53545381 Jorgen L. Jorgensen BACKGROUND OF THE INVENTION This invention relates to a method of printing soft tissue paper and immediately cleaning the associated printing surfaces and, more particularly, it relates to a method of continuously printing soft, loose-surfaced paper and cleaning the printing surfaces by contacting them with a solvent moistened, resiliently surfaced cleaning roll immediately after printing, to thereby materially reduce the buildup of lint and'fibers on the printing surfaces when soft tissue paper and the like is being printed.

The use of resiliently surfaced rolls to clean rotary printing surfaces is well known in the art. For example, US. Pat. No. 2,731,916, granted Jan. 24, 1956 to W. Koch, shows a cleaning roll having a liquid-absorbing outer sleeve which is adapted to be brought into contact with a rotary printing cylinder during the intermittent periods that cleaning of the surface of the printing cylinderis performed. The cleaning roll both applies cleaning liquid to the surface of the printing cylinder and subsequently removes the cleaning liquid to provide a clean, dry printing cylinder.

None of the prior art teachings, however, relates to the cleaning of printing apparatus used to decorate thin, soft tissue paper of the type from which facial tissues, paper towels, and the like are made. Those materials have a soft, relatively loose-fibered surface that is substantially different from that of conventional printing papers, which have a relatively dense surface of compacted fibers. Since the tissue webs are soft-surfaced and loose-fibered, the printing surfaces with which such we'bs are brought into contact are frequently covered with loose fibers and lint fromprevious impressions to the extent that printers are'faced with the problem of frequent press shutdowns in order to manually wash the printing surfaces with solvent to remove the lint, fibers, and dried ink and thereby permit the resumption of high quality printing.

SUMMARY OF THEINVENTION sorbent exterior surface and a nonresilient core. The contact of the cleaning roll and printing surfaces takes place across substantially the entire width of the printing surface. The cleaning roll is rotated while in contact with the printing plate andhas an ink-compatible solvent applied to thesurface thereof. The cleaning roll and printing plate are pressed together with a contact pressure of less than about 1.0 pound per linear inch.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a perspective view, partially broken away, showing printing apparatus with which the method of the present invention can be practiced; and

FIG. 2 is a cross-sectional view taken along the line 2-2 of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will hereinafter be describedin connection with the printing of various materials in web form by means of the flexographic printing process, wherein a thin, curved rubber printing plate having raised printing elements thereon is used to provide the impression on the printed web.

' the printing surfaces with a cleaning roll having a resilient, ab- 1 However, it is not intended that the applicability of the present invention be limited to the specifically disclosed printing process and it will be apparent to those skilled in the art that the method hereinafter disclosed is suitable for use with other printing processes, such as, for example, the, letterpress process, and is suitable for use on sheet-fed printing equipment in addition to web-fed equipment. Moreover, the term printing plate" as hereinafter used is intended to include both curved printing plates which are affixed to rotary printing cylinders, and flat printing plates such as those used on flat bed, reciprocating printing presses.

Referring now to the drawing, there is shown a single station printing apparatus 10 whereby a single color impression of a predetermined pattern is applied to a continuous web 11 of material which is to be printed. The printing apparatus 10 can be positioned downstream from an unwind stand (not shown) from which a previously wound roll of the web 11 is continuously unwound, or it can be positioned at the end of a papermaking machine (not shown) to receive paper which has undergone the requisite drying steps. A number of such printing stations can be serially arranged topermit the printing of multiple colors on a single web 11, but to simplify the description the ensuing discussion will be directed to a single printing station. It is to be understood, however, that the method disclosed is not intended to be limited to use with such a single station arrangement.

The single station printing apparatus 10 shown in FIGS. 1 and 2 of the drawing, exclusive of the cleaning roll hereinafter described, is essentially a conventional, web-fed, single color, flexographic printing press of the type well known to those of ordinary skill in the art, and the parts thereof are carried in and supported by frame 12. Web 11 passes around an impression cylinder 13, against which a cooperating p!ate roll 14 is in continuous contact. A thin rubber printing plate 15 having raised surfaces to define the image to be printed on the web is securely attached to the peripheryof the plate roll 14. Impression cylinder 13 rotates at the same peripheral speed as that of printing plate 15 on plate roll 14 and serves as the nonyielding backup surface with which printing plate 15 cooperates to transfer the ink from the raised surfaces thereof to web 11 passing between the two rolls. Both impression cylinder 13 and plate roll 14 are rotatably supported in frame 12.

The ink used to print web 11 is supplied from ink reservoir 16. The ink level in reservoir 16 can be maintained at a predetermined height by a suitable conventional float valve (not shown), which controls the flow of ink to reservoir 16 in a manner well known to those skilled in the art. Fountain roll 17 is rotatably mounted in frame 12 and is positioned so that a portion of its periphery lies below the surface of the ink in ink reservoir 16. In the course of rotating through the ink, a thin film of the ink adheres to the surface of fountain roll 17 and is transferred to contacting Anilox roll 18, which is also rotatably supported in frame 12. Anilox roll 18 is in line contact with fountain roll 17 and has a multiplicity of minute recesses on its surface, which act as ink receptors and transferrers. Both fountain roll 17 and Anilox roll 18 are typically made of steel and the recesses in the latter are formed therein by means ofa photoengraving process which is well known to those skilled in the art. By virtue of the minute recesses therein, Anilox roll 18 provides improved control of ink distribution as compared with the relatively uncontrolled distribution that .would take place if a smooth-surfaced roller without recesses were to be used in place of Anilox roll 18.

The ink is transferred from fountain roll 17 to Anilox roll 18 i where it enters the recesses therein and is carried by the 17 and subsequently transferred to the raised printing surfaces on printing plate 15. The ink from the recesses in the surface of Anilox roll 18 is uniformly deposited on the raised surfaces of printing plate 15 following which the ink is transferred to the web by the cooperative action of printing plate 15 and impression cylinder 13. Each of the rolls 13, l4, l7, and 18, in addition to being rotatably mounted in support frame 12, is independently driven as by means of a gear train arrangement powered by a motor, none of which is is shown but is typical of such systems well known in the art.

Printing apparatus of the character hereinabove described has been used to provide the desired printing effects on a wide variety of substrates. For example, this type of apparatus can be used to print paper, polymeric and cellulosic films, metallic foils, and the like. However, it has been found that when very soft and light paper of the character from which sanitary paper products such as, for example, paper towels, toilet tissue, facial tissues, and paper napkins are made, and is printed, because of the nature of the surface of this type of paper a considerable and rapid buildup of loose fibers and lint takes place on the printing surface. This buildup necessitates frequent shutdowns of the printing surface. This buildup necessitates frequent shutdowns of the printing equipment to pen-nit the printing surfaces to be periodically completely washed with solvent to remove accumulated lint and fibers. Otherwise, if not removed, the excessive buildup of lint and fibers causes the desired printing image to become blurred or otherwise appear altered because of the random orientation of these ink-carrying fibers on the raised printing surfaces.

Paper with which the method comprising the present invention finds particular utility is creped tissue paper having a soft, loose-fibered surface and having a basis weight (i.e., the weight, air-dry, of a ream comprising 3000 square feet of paper after creping) which ranges from about 8 to about 35 pounds. For example, the tissue paper from which facial tissues are made generally has a basis weight which ranges from about 8.5 pounds to about 1 3 pounds, while tissue paper from which toilet tissue is made generally has a basis weight which ranges from about l pounds to about 14 pounds. Paper toweling stock, on the other hand, has a basis weight ranging from about 15 pounds to about 35 pounds. Although of a somewhat higher basis weight, the paper toweling stock still exhibits the soft surface which is characteristic of tissue products and, as a result, it can produce the above-described adverse effects because of the nature of its soft, loose-fibered surface.

The inks used in this type of printing operation are generally .of the solvent-based variety. Water, ethyl alcohol, a combination of ethyl alcohol and ethyl acetate, or a combination of methyl cellosolve and ethyl alcohol, are examples of solvents suitable for flexographic inks. Since the inks are relatively fast drying, after the ink from printing plate 15 is transferred from plate 15 to web 11, the thin layer of ink remaining on the plate 15 immediately after the impression has been made becomes tacky and loose fibers on web 11 thus adhere to printing plate 15. With the existing printing techniques, when the printing surfaces again contact Anilox roll 18, whereupon additional ink is deposited on the raised printing surfaces and on the lint and fibers attached thereto, as stated above, the presence of the fibers and lint tends to blur the pattern which it is desired to print on the web and successive impressions magnify the problem. One way to overcome this problem is to increase the amount of solvent in the ink so that it does not dry to the point of attracting the lint and loose fibers. However, this approach has an adverse effect in that it dilutes the ink, thereby reducing the color intensity of the printed web. It also increases the drying time, thereby precluding the immediate winding of the web into rolls.

The present method overcomes the above-described problems by continuously contacting the printing surfaces with a cleaning roll 19, having a soft, resilient cellular sleeve which overlies a metal core 21 and is either frictionally attached thereto or permanently fastened thereto as by gluing. Resilient sleeve 20 is preferably moistened with the same solvent as that incorporated in the ink being used. As shown in FIGS. 1 and 2, cleaning roll 19 is positioned directlyabove plate roll 14, but it can be placed at any position whereby it will encounter the raised printing surfaces of plate 15 after these have contacted moving web 11 and before they contact Anilox roll 18 to pick up the ink for the subsequent impres- The radial thickness of sleeve 20 is preferably greater than about one-half inch to permit substantial deflection thereof so that a portion of the solvent applied to cleaning roll 19 can be squeezed therefrom and thereby wet the printing surfaces of printing plate 14. After being so compressed, the release of pressure on cells of absorbent sleeve 20 causes a slight negative pressure on the absorbent exterior surface of cleaning roll 19 and the surface cells attract foreign material on the printing surface. Thus, any lint which had been deposited on the raised printing surfaces is daubed or blotted therefrom or removed by means of the suction which exists in the cells as they return to their former, uncompressed condition.

Sleeve 20 can be formed from a resilient cellular material having an open cell structure, such as sponge rubber or the like. However, it must be a material which is compatible with the ink being used so that the solvents employed do not have an adverse effect on it. Preferably, it is formed from a relatively inert, foamed polymeric material. A suitable such material for this purpose is an open cell polyurethane foam having a medium firm density of about 2.2 pounds per cubic foot, identified as Catalog No. UU34 and available from the B. F. Goodrich Company, Akron, Ohio. The preferred foam covering has a density of from about 1 pound per cubic foot to about 6 pounds per cubic foot.

Sleeve 20 of cleaning roll 19 can be kept moist be means of spray nozzle 22, which sprays solvent onto the surface of sleeve 20 as shown in FIGS. 1 and 2. Spray nozzle 22 can be supported on lead screw 23, which can be suitably rotated and positioned in support frame 12 so that it traverses the entire axial length of the cleaning roll 19. Alternatively, a series of fixed nozzles can be employed but the traversing arrangement herein disclosed is preferred to provide closer control over the quantity of solvent applied to the cleaning roll.

The amount of solvent applied to sleeve 20 should be sufficient to keep the roll moist but not to the degree that excess solvent runs off the surface. Excess solvent that either runs from the surface of sleeve 20 or is squeezed therefrom will be deposited on the surface of plate 15 and when ink for the next impression is applied thereto by Anilox roll 18, the excess solvent will dilute the ink so applied, which would reduce the color intensity of the printed matter and increase the drying time of the ink since more solvent must be evaporated. The solvent can be applied at a rate of from about 0.0001 to about 0.0012 grams/inch of axial length of cleaning roll/foot of web travel/minute at normal press speeds which can range from about to about 2000 feet per minute but are usually of the magnitude of about 1000 feet per minute. Preferably, the solvent flow rate ranges from 0.0002 to about 0.0008 grams/inch of axial length of cleaning roll/foot of web travel/minute. If less than about 0.0001 grams/inch of axial length of cleaning roll/foot of web travel/minute of solvent is applied to the surface of the cleaning roll, the printing surface will not be adequately cleaned; if more than about 0.0012 grams/inch of axial length of cleaning roll/foot of web travel/minute of solvent is applied, the ink will be excessively diluted.

The contact pressure between cleaning roll 19 and plate roll 14 should be sufficient to cause some deflection of sleeve 20 in order to provide adequate contact with the raised printing elements of plate 15. Preferably, the contact pressure is such as to result in an inwardly deflected area on sleeve 20 which ranges from about A inch to about 1% inches in a circumferential direction (see FIG. 2). In terms of force units, the contact pressure is preferably in the range of from about 0.1 to about l.0 pounds per linear inch. If the pressure is too heavy, excessive solvent is squeezed from its resilient surface and the lint previously picked up by the resilient surface could be redeposited on the surface of the printing plate and thereby adversely affect the printing operation.

Preferably, cleaning roll 19 extends along the entire axial length of plate roll 14 to insure that all the raised printing surfaces are contacted by the solvent-containing sleeve 20 once each revolution of the plate roll. Cleaning roll 19 can be frictionally driven by plate roll 14 so that the peripheralvelocity of the two rolls is substantially the same. Alternatively, however, cleaning roll 19 can be independently driven and can be arranged to rotate at a peripheral speed different from that of plate roll 14. In the latter case, a scrubbing action will be provided on the raised printing surfaces. A scrubbing action can also be provided by axially reciprocating cleaning roll 19 while it is in contact with plate roll 14. This type of motion can be imparted to cleaning roll l9 by axially spring biasing the supporting shaft of the roll against the edge of an eccentric disk cam (not shown) which is independently rotated.

As an example of the method comprising the present invention, a web of creped tissue paper was printed on a flexographic printing press which included a cleaning roll of the character hereinbefore described. The creped tissue paper way a soft, loose-fibered two-ply web having a combined basis weight of 20 pounds. Each individual ply had a basis weight of pounds and had been creped to provide a sheet having percent crepe. The printing press employed was of the flexographic type designated as Model HDP 105 manufactured by the Dietz Machine Co. The Anilox roll which was used had 200 cells per inch with each cell averaging 0.0009 inch in depth. The printing plate had a raised printed pattern thereon comprising 4 percent of the total plate area. A water-based flexographic ink from the H. Blacker .lnk Co., Cincinnati, Ohio, was used.

The cleaning roll was positioned against the plate roll at a contact pressure of 0.2 pounds per linear inch and comprised an aluminum core 105 inches long and 3% inches outer diameter. A 1 inch thick sheet of polyurethane foam having a density of 2.2 pounds per cubic foot was applied to the core. The polyurethane foam was of the medium density type and was designated type UU34, available from the B. F. Goodrich Co., Akron, Ohio. The cleaning roll was driven by the frictional contact with the plate roll, and water (solvent) was applied to the surface of the roll at a rate of 0.0003 grams/inch of axial length of cleaning roll/foot of web travel/minute.

The two-ply web was conveyed to and through the press at a speed of 800 feet per minute. When the cleaning method of the present invention was employed, the press was operated satisfactorily to print the tissue paper continuously for a period of 7% hours. When the equipment was operated without the present cleaning method, the press was operated satisfactorily for a maximum period of only 30 minutes. At

fiber buildup.

Similar results can be obtained if different inks are used, which, of course, necessitates a different solvent, and the solvent flow rateranges from about 0.0001 to about 0.0012 grams/inch of axial length of cleaning roll/foot of web travel/minute.

While particular embodiments of the invention have been illustrated and described, it will be obvious to those skilled in the art that various changes and modifications can be made a without departing from the spirit and scope of the invention, and it is intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.

I claim:

1. In the printing of an absorbent, fibrous substrate having a soft, loose-fibered surface, wherein printing ink is supplied from a reservoir to. a printing surface and the printing surface is brought into contact with said substrate to transfer said ink thereto in a predetermined pattern, the method of cleaning the printing surface comprising:

a. continuously contacting and moistening said printing surface with a rotating cleanin roll concurrently with said printing, said cleaning roll avmg a resilient, absorbent exterior surface and a substantially nonresilient core, the axis of which is substantially parallel to said printing surface, said cleaning roll being in contact with said printing surface across substantially the entire width thereof at a position wherein said contact occurs subsequent to the transfer of ink to the substrate but before additional ink is supplied to said printing surface from said reservoir;

b. applying an ink-compatible solvent to the surface of said cleaning roll whereby to maintain said cleaning roll in moist condition, said solvent being applied at a rate of from about .0001 to about .0012 grams/inch of axial length of cleaning roll/foot of substrate travel/minute; and

c. maintaining said contact between. said cleaning roll and said printing surface by pressing the same together by a a force in the range of from about Otl to about 1.0 pounds per linear inch of contact.

2. The method of claim 1 including; the additional step of frictionally driving said cleaning roll with said printing surface so that the peripheral speed of said cleaning roll is substantially the same as the peripheral speed of said printing surface.

3. The method of claim 1 including the additional step of independently driving said cleaning roll at a linear speed at the periphery thereof less than the linear speed at the periphery of said printing surface.

4. The method of claim 1 including. the additional step of periodically axially reciprocating said cleaning roll while it is in contact with said printing surface.

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