Gapless tubular printing blanket - Patent Review 5323702

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FIELD OF THE INVENTION

The present invention relates to printing blankets for blanket cylinders in web offset printing presses, and particularly relates to a gapless tubular printing blanket.

BACKGROUND OF THE INVENTION

A web offset printing press typically includes a plate cylinder, a blanket cylinder and an impression cylinder supported for rotation in the press. The plate cylinder carries a printing plate having a rigid surface defining an image to be printed. The blanket cylinder carries a printing blanket having a flexible surface which contacts the printing plate at a nip between the plate cylinder and the blanket cylinder. A web to be printed moves through a nip between the blanket cylinder and the impression cylinder. Ink is applied to the surface of the printing plate on the plate cylinder. An inked image is picked up by the printing blanket at the nip between the blanket cylinder and the plate cylinder, and is transferred from the printing blanket to the web at the nip between the blanket cylinder and the impression cylinder. The impression cylinder can be another blanket cylinder for printing on the opposite side of the web.

A conventional printing blanket is manufactured as a flat sheet. Such a printing blanket is mounted on a blanket cylinder by wrapping the sheet around the blanket cylinder and by attaching the opposite ends of the sheet to the blanket cylinder in an axially extending gap in the blanket cylinder. The adjoining opposite ends of the sheet define a gap extending axially along the length of the printing blanket. The gap moves through the nip between the blanket cylinder and the plate cylinder, and also moves through the nip between the blanket cylinder and the impression cylinder, each time the blanket cylinder rotates.

When the leading and trailing edges of the gap at the printing blanket move through the nip between the blanket cylinder and an adjacent cylinder, pressure between the blanket cylinder and the adjacent cylinder is relieved and established, respectively. The repeated relieving and establishing of pressure at the gap causes vibrations and shock loads in the cylinders and throughout the printing press. Such vibrations and shock loads detrimentally affect print quality. For example, at the time that the gap relieves and establishes pressure at the nip between the blanket cylinder and the plate cylinder, printing may be taking place on the web moving through the nip between the blanket cylinder and the impression cylinder. Any movement of the blanket cylinder or the printing blanket caused by the relieving and establishing of pressure at that time can smear the image which is transferred from the printing blanket to the web. Likewise, when the gap in the printing blanket moves through the nip between the blanket cylinder and the impression cylinder, an image being picked up from the printing plate by the printing blanket at the other nip can be smeared. The result of the vibrations and shock loads caused by the gap in the printing blanket has been an undesirably low limit to the speed at which printing presses can be run with acceptable print quality.

Another problem caused by the gap at the adjoining ends of a conventional printing blanket is the circumferentially extending void defined by the width of the gap. The void defined by the width of the gap interrupts and reduces the circumferential length of the printing surface on the blanket cylinder. This causes an area of the web to remain unprinted each time the blanket cylinder rotates. Such unprinted areas of the web reduce productivity and increase waste. In addition, such a conventional printing blanket is not easily properly attached to a blanket cylinder. As a result there can be considerable press downtime, which can be expensive. Furthermore, the blanket cylinder itself must be equipped with means for engaging the opposite ends of the printing blanket to hold them in place.

Another problem associated with conventional printing blankets is caused by the pressure exerted against the flexible surface of the printing blanket by the rigid surface of the printing plate at the nip between the blanket cylinder and the plate cylinder. The flexible surface of the printing blanket is indented by the rigid surface of the printing plate as it is pressed against the printing plate upon movement through the nip. At the center of the nip, the cylindrical contour of the rigid printing plate impresses a corresponding cylindrical depression in the flexible printing blanket. When a depression is pressed into the flexible printing blanket, bulges tend to arise on each of the two opposite sides of the depression. Such bulges appear as standing waves on the surface of the printing blanket on opposite circumferential sides of the nip. A point on the surface of the printing blanket moves up and over such standing waves as it enters and exits the nip. Compared with a point on the rigid cylindrical surface of the printing plate, a point on the flexible surface of the printing blanket traverses a greater distance as it moves past the nip. The speeds of those surfaces therefore differ at the nip. A difference in surface speeds causes slipping between the surfaces which can smear the ink transferred from one surface to the other.

Printing blankets are known to include compressible rubber materials which compress under the pressure exerted against the printing blanket by the printing plate at the nip therebetween. Compression of the printing blanket at the nip reduces the tendency of bulges to form at opposite sides of the nip. Standing waves which could smear the ink on the rotating printing blanket are thus reduced, but repeated compression and expansion of the compressible rubber material can cause the printing blanket to overheat.

SUMMARY OF THE INVENTION

The present invention provides a tubular printing blanket which enables a printing press to run at high speeds without excessive vibration or shock loads, without slipping of printing surfaces which could smear the ink, and without overheating.

In accordance with the present invention, a tubular printing blanket for a blanket cylinder in an offset printing press comprises a cylindrical sleeve movable axially over a blanket cylinder, a compressible layer over the sleeve, and an inextensible layer over the compressible layer. The compressible layer comprises a first seamless tubular body of elastomeric material. The body of elastomeric material has a plurality of voids which impart compressibility to the body. The inextensible layer comprises a second seamless tubular body of elastomeric material containing a tubular sublayer of circumferentially inextensible material. The tubular printing blanket further has a gapless cylindrical printing surface which is preferably formed on a seamless tubular printing layer.

The tubular printing blanket constructed in accordance with the invention advantageously has a seamless and gapless tubular form throughout its various layers, including a continuous, gapless cylindrical printing surface. When the tubular printing blanket moves through the nip between a blanket cylinder and a plate cylinder, the cross-sectional shape of the tubular printing blanket at the nip remains constant. The pressure relationship between the tubular printing blanket and the printing plate thus remains constant while the printing press is running, and movement of the tubular printing blanket through the nip does not cause vibrations or shock loads. Furthermore, because there is no gap at the surface of the tubular printing blanket, there is less waste and greater productivity.

Additionally, the inextensible layer of the tubular printing blanket prevents the formation of standing waves on the outer printing surface which could smear the inked image.

In the preferred embodiments of the present invention, the voids in the compressible layer of the tubular printing blanket are microcells. The microcells are formed by compressible microspheres located uniformly throughout the first tubular body of elastomeric material. The compressible layer preferably includes a compressible fabric material along with the compressible microspheres. The compressible fabric material is included as a thread wound helically through the compressible layer and around the underlying cylindrical sleeve. The thread heats up less than the surrounding elastomeric material during use of the tubular printing blanket, and thus enables the tubular printing blanket to run cooler.

In a preferred method of manufacturing the tubular printing blanket, the compressible layer is formed by coating a compressible thread with a mixture of rubber cement and microspheres, and wrapping the coated thread in a helix around the cylindrical sleeve. The inextensible layer is similarly formed by coating an inextensible thread with a rubber cement that does not contain microspheres, and wrapping the coated thread in a helix around the underlying compressible layer. The inextensible thread thus defines a circumferentially inextensible tubular sublayer which imparts inextensibility to the inextensible layer. The printing layer is formed over the inextensible layer by wrapping an unvulcanized elastomer over the inextensible layer and securing it with tape. The taped structure is vulcanized so that a continuous seamless tubular form is taken by the overlying layers of elastomeric material.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features of the present invention will become apparent to those skilled in the art upon reading the following description of preferred embodiments of the invention in view of the accompanying drawings, wherein:

FIG. 1 is a schematic view of a printing apparatus including a tubular printing blanket in accordance with the present invention;

FIG. 2 is a schematic perspective view of the printing blanket shown in FIG. 1;

FIG. 3 is a sectional view taken on line 3--3 of FIG. 2;

FIG. 4 is an enlarged sectional view of a portion of the printing apparatus of FIG. 1;

FIG. 5 is a view of the prior art;

FIG. 6 is a schematic view illustrating a method of constructing a tubular printing blanket in accordance with the present invention;

FIG. 7 is a partial sectional view of a tubular printing blanket in accordance with an alternate embodiment of the present invention;

FIGS. 8A through 8C are schematic views showing methods of constructing the tubular printing blanket of FIG. 7;

FIGS. 9A and 9B are schematic views of a part of a tubular printing blanket in accordance with another alternate embodiment of the present invention;

FIG. 10 is a schematic view of a part of a tubular printing blanket in accordance with another alternate embodiment of the present invention;

FIGS. 11A and 11B are schematic views of a part of a tubular printing blanket in accordance with yet another alternate embodiment of the present invention;

FIG. 12 is a partial sectional view of a tubular printing blanket in accordance with an additional alternate embodiment of the present invention; and

FIG. 13 is a partial sectional view of still another alternate embodiment of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

As shown schematically in FIG. 1, a printing apparatus 10 includes a blanket cylinder 12 with a tubular printing blanket 14 constructed in accordance with the present invention. The printing apparatus 10, by way of example, is an offset printing press comprising a plurality of rolls for transferring ink from an ink fountain 16 to a printing plate 18 on a plate cylinder 20. The tubular printing blanket 14 on the blanket cylinder 12 transfers the inked image from the printing plate 18 to a moving web 21.

A fountain roll 22 picks up ink from the ink fountain 16. A ductor roll 24 is reciprocated between the fountain roll 22 and a first distributor roll 26 in order to transfer ink from the fountain roll 22 to the first distributor roll 26, as indicated in FIG. 1. A plurality of successive distributor rolls 26 transfers ink from the first distributor roll 26 to a group of form rolls 28, which, in turn, transfers the ink to the printing plate 18 on the plate cylinder 20. A second blanket cylinder 30 with a second tubular printing blanket 32 is shown only partially in FIG. 1 to represent a second printing apparatus for printing simultaneously on the opposite side of the web 21. The blanket cylinders 14 and 30 serve as impression cylinders for each other. The rolls and cylinders are interconnected by gears and are rotated by a drive means 34 in a known manner. The ductor roll 24 is moved by a reciprocating mechanism 36 in a known manner.

The tubular printing blanket 14 has a continuous, gapless inner cylindrical surface 40 firmly engaged in frictional contact with the cylindrical outer surface 42 of the blanket cylinder 12. The blanket cylinder 12 has a central lumen 44 and a plurality of passages 46 extending radially from the central lumen 44 to the cylindrical outer surface 42. A source 50 of pressurized gas communicates with the central lumen 44 in the blanket cylinder 12, and is operable to provide a flow of pressurized gas, preferably air at 90 lbs. per square inch, which is directed against the inner cylindrical surface 40 of the tubular printing blanket 14 from the central lumen 44 and the radially extending passages 46.

When a flow of pressurized air is directed against the cylindrical inner surface 40 of the tubular printing blanket 14, the cylindrical inner surface 40 is elastically deformed in a slight amount to increase the diameter thereof. The tubular printing blanket 14 is then easily moved telescopically on or off the blanket cylinder 12. When the flow is stopped, the inner cylindrical surface 40 of the tubular printing blanket 14 elastically contracts to its original size to grip the outer surface 42 of the blanket cylinder 12. The tubular printing blanket 14 is then firmly engaged in frictional contact with the blanket cylinder 12 and will not move relative to the blanket cylinder 12 during operation of the printing apparatus 10.

As shown in FIG. 3, the tubular printing blanket 14 comprises a plurality of layers. The layers include a relatively rigid backing layer 60 and a number of flexible layers supported on the backing layer 60. The flexible layers include first and second compressible layers 62 and 64, an inextensible layer 66, and a printing layer 68.

The backing layer 60 is defined by a cylindrical sleeve 70 on which the inner cylindrical surface 40 is located. The cylindrical sleeve 70 is elastically expandable diametrically in a slight amount to enable telescopic movement of the tubular printing blanket 14 over the blanket cylinder 12, as described above. The cylindrical sleeve 70 is preferably formed of metal, such as nickel with a thickness of approximately 0.005 inches, which has been found to have the requisite rigidity, strength and elastic properties. Specifically, the nickel sleeve 70 has a modulus of elasticity of approximately 20.times.10.sup.6 lbs. per square inch. Alternately, the cylindrical sleeve 70 can be formed of a polymeric material such as fiberglass or plastic, e.g. Mylar.TM., having a thickness of approximately 0.030 inches.

Two coats of primer 71 and 72 help to bind the first compressible layer 62 to the backing layer 60. If the backing layer 60 is a nickel cylinder, the primer coat 71 is preferably Chemlok 205, and the primer coat 72 is preferably Chemlok 220, both available from Lord Chemical.

The first compressible layer 62, as shown in FIG. 3, comprises a seamless tubular body 74 of elastomeric material. The tubular body 74 has a plurality of voids which impart compressibility to the tubular body 74. In the preferred embodiment of the invention shown in the drawings, the voids are microcells which are formed by a plurality of compressible microspheres 76 encapsulated in the tubular body 74. The voids in the tubular body 74 could alternatively be formed by encapsulated particles of compressible material other than the microspheres 76, or by blowing, leaching, or other known methods of forming voids in an elastomeric body to impart compressibility to the elastomeric body.

The first compressible layer 62 further comprises a compressible thread 80 extending helically through the tubular body 74 and around the backing layer 60. The thread 80 is bonded to the elastomeric material of the tubular body 74, and is most preferably impregnated with the elastomeric material and with the microspheres 76. The second compressible layer 64 similarly comprises a seamless tubular body 90 of elastomeric material, a plurality of compressible microspheres 92 encapsulated in the tubular body 90, and a compressible thread 94 extending helically through the tubular body 90 and around the first compressible layer 62.

The elastomeric material of which the seamless tubular bodies 74 and 90 are formed is preferably mixed with the microspheres 76 to form a compressible, composite rubber cement having the following composition:

______________________________________ PARTS ______________________________________ 1. Copolymer of Butadiene and 480.00 Acrylonitrile with 50 parts DOP 2. Soft sulfur factice 40.00 3. Acrylonitrile/Butadiene copolymer 80.00 4. Medium thermal carbon black 360.00 5. Barium Sulfate 80.00 6. Dioctyl Phthalate 40.00 7. Benzothiazyl Disulfide accelerator 8.00 8. Tetramethyl-Thiuram Disulfide 4.00 accelerator 9. Sulfur with magnesium carbonate 4.00 10. Zinc Oxide activator 20.00 11. Butyl Eight 2% by weight of adding lines 1 thru 10 12. Microspheres 6% by weight of adding lines 1 thru 11 13. Toluene 2.5 times weight of adding lines 1 thru 12 ______________________________________

The microspheres 76 and 92 are preferably those known by the trademark Expancel 461 DE from Expancel of Sundsvall, Sweden. Such microspheres have a shell consisting basically of a copolymer of vinylidene chloride and acrylonitrile, and contain gaseous isobutane. Other microspheres possessing the desired properties of compressibility can also be employed, such as those disclosed in U.S. Pat. No. 4,770,928.

The compressible threads 80 and 94 are preferably cotton threads having diameters of approximately 0.005 to 0.030 inches, and most preferably having diameters of approximately 0.015 inches. The individual windings of thread, i.e. adjacent circumferential sections thereof, are preferably spaced axially from each other a distance of approximately 0.01 inches. Such close spacing assures that there are no substantial gaps between adjacent windings. Alternately, the threads 80 and 94 can be of other compressible materials, or can be replaced with compressible tubes, e.g., hollow fibers.

The inextensible layer 66 comprises a seamless tubular body 100 of elastomeric material and a longitudinally inextensible thread 102 within