Manipulation of printing blankets

A container for a printing blanket comprises a cassette of dimensions sufficient at least to contain a printing blanket in wound form. The cassette comprising a casing of generally cylindrical shape having a longitudinal opening for sheet-form egression of a printing blanket from within the cassette. In one preferred embodiment, the cassette has a pressure slide attached to or integral therewith adjacent to the longitudinal opening, for pressing a printing blanket on a press cylinder when the blanket is fed onto the cylinder. The cassette is employed in the manipulation of large adhesive-backed printing blankets for web-feed offset printing presses.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 This invention relates to manipulation of printing blankets.
 2. Discussion of Prior Art
 A common means for securing an offset printing blanket onto a press
 cylinder employs a tensioning `lock-up` device located within the cylinder
 body. Employment of such a device usually necessitates a gap in the usable
 printing area of the cylinder and furthermore tends to promote undesirable
 vibration during operation of the printing press, especially at high-speed
 printing.
 It has been proposed to avoid vibration by providing a `seamless` or
 endless blanket on the printing press cylinder. Typically such blankets
 are supplied on a metal sleeve to be fitted on the cylinder. Although such
 blankets may be feasible for newly manufactured presses wherein means for
 ease of removal of the cylinder or sleeve may be incorporated in the
 design of the press, they are not a practicable option for the majority of
 existing presses. Moreover, a disadvantage of such blankets is the high
 cost of producing individual blanketed sleeves or cylinders in comparison
 with the cost of producing a sheet-form (open-ended) blanket for
 application to replace a worn or damaged similar blanket on an existing
 cylinder in the press.
 In some relatively small offset printing presses (such as those used for
 printing stationery and business forms), in which the printing cylinder
 typically has a circumference of the order of 30 cm, a negligible gap in
 the usable printing area is achieved by securing a sheet-form printing
 blanket on the cylinder by means of an adhesive which typically is in the
 form of an adhesive coating on the back of the blanket sheet and may be
 protected by a releasable cover sheet until the blanket is applied to the
 cylinder.
 Although adhesive-backed printing blankets are used for small presses,
 generally they have not been used for large web-feed printing presses
 owing to problems in handling and mounting large sheets of adhesive-backed
 blanket. Problems include manual handling difficulties and safety risk to
 persons manipulating a bulky adhesive-backed blanket, the risk of
 contamination of the adhesive backing during manipulation, and the need
 for the initial positioning of the blanket on the cylinder to be accurate
 since the capability for position-adjustment after initial application
 usually is extremely limited or non-existent without detriment to the
 blanket or the adhesive bond.
 In large high-speed printing presses, such as those used in the newspaper
 and magazine printing industry, typically the printing blanket requires to
 be replaced owing to wear at frequent intervals, for instance every one to
 three months. Speed of application of a replacement blanket onto the
 cylinder is especially important in the newspaper and magazine printing
 industry where a long down-time of a printing press could be highly
 detrimental to meeting distribution deadlines.
 SUMMARY OF THE INVENTION
 An object of the present invention is the provision of means to facilitate
 manipulation of large adhesive-backed printing blankets to enable their
 commercial application to large printing press cylinders.
 A further object of the invention is the provision of means for enabling a
 printing blanket, especially an adhesive-backed printing blanket, to be
 applied to a press cylinder accurately with increased speed.
 A further object of the invention is the provision of means for enabling
 adhesive-backed blankets to be stored, transported, handled and applied
 easily, accurately and quickly, with minimal risk of contamination of the
 adhesive, damage to the blanket and trapping of air between the blanket
 and the cylinder.
 The invention is beneficial for blankets of all sizes, with or without an
 adhesive backing. However, the benefits are especially advantageous in
 respect of large adhesive-backed printing blankets for web-feed offset
 printing presses.
 According to one aspect of the present invention there is provided
 manipulation means for a printing blanket, comprising a cassette of
 dimensions sufficient at least to contain a printing blanket in wound
 form, said cassette comprising a casing of generally cylindrical shape
 having a longitudinal opening for sheet-form egression of a printing
 blanket from within the cassette.
 According to another aspect of the invention there is provided a method of
 mounting a printing blanket on a printing press cylinder, which comprises
 feeding the blanket onto the cylinder from a cassette described in the
 immediately preceding paragraph.
 The cassette casing may have a substantially continuous cylindrical wall
 (apart from the opening for egression of the blanket), or it may have a
 discontinuous cylindrical shape, for instance a frame structure.
 The cassette may be open or closed at one or both of the casing cylinder
 ends. At least one of the ends may be closed by a cap which is removable
 for insertion of a blanket into the cassette.
 The blanket suitably is in roll-wound form inside the cassette. Preferably
 the outer, leading, end of the contained blanket is positioned adjacent to
 the longitudinal opening which suitably is an elongate gap or slot in the
 casing wall.
 If desired, the cassette may include a spindle, which may or may not be
 rotatable, about which the blanket is wound. The longitudinal central axes
 of the cassette casing and spindle may be coincident or parallel. For
 instance, the spindle axis may be off-set away from the casing axis along
 a plane passing through the position at which the blanket begins to
 diverge from the blanket roll when the blanket is fed through the
 longitudinal opening.
 Preferably the cassette casing should have sufficient rigidity to retain
 its shape during handling, feeding and loading of the blanket. Suitable
 materials include plastics and metals.
 The cassette may be reusable or disposable.
 For feeding a blanket from the cassette onto a press cylinder, the cassette
 should be mounted in a set relationship to the press cylinder. For
 instance, location means may comprise an axial spigot extending from each
 end of the cassette for location in a hole, slot or cup on the press
 structure, if desired in conjunction with detent means to prevent the
 spigots from becoming dislodged accidentally.
 Suitably the cassette is mounted such that its longitudinal axis is
 parallel to that of the press cylinder onto which the blanket is to be
 fed.
 The blanket may be fed from the cassette onto the press cylinder simply by
 pulling the leading end of the blanket through the longitudinal opening of
 the cassette, positioning the leading end of the blanket securely on the
 surface of the cylinder, and rotating the cylinder to pull the rest of the
 blanket from the cassette onto the cylinder surface.
 The cassetted blanket may be of a length to fit the cylinder exactly or it
 may be longer than the circumference of the cylinder and then trimmed to
 the correct length, e g by cutting or stamping on the cylinder.
 Alternatively the cassette may contain two or more blanket pieces for
 application to the cylinder as one piece after another in line or as one
 piece on top of another.
 When the blanket has an adhesive-coating protected by a releasable sheet,
 the protective sheet suitably is removed from the blanket continuously as
 the blanket is fed from the cassette. This may be done manually or by a
 separator blade and the released sheet may be collected in a bin or by
 winding on a roller.
 Preferably the blanket is pressed onto the cylinder during its application
 in order to ensure good bonding contact and to prevent trapping of air
 between the blanket and the cylinder.
 If desired, the blanket may be pressed onto the cylinder manually, such as
 by moving a roller under pressure over the blanket on the cylinder
 continuously from the line of initial contact.
 However, a preferred pressure means comprises a dedicated pressure roller
 or a pressure slide (skid), mounted with its longitudinal axis parallel to
 those of the cassette and cylinder and at a set distance from the cylinder
 surface at or immediately after the line of initial contact of the blanket
 with the cylinder. The maximum distance of the pressure roller or slide
 surface from the cylinder surface should not be greater than the thickness
 of the blanket being applied and may be adjustably set to apply a
 predetermined pressure on the blanket.
 The pressure slide may have a curved surface, at least at its edge portion
 proximate to the casing opening, to facilitate smooth sliding of the
 blanket over the slide surface. The pressure slide may be attached to the
 press structure or, preferably, may be attached to, or be integral with,
 the cassette casing.
 The pressure means may be mounted to be guided towards and away from the
 cylinder as required.
 If desired, the leading end portion of the blanket may be located on the
 pressure means, such as by use of a relatively weak adhesive (e g double
 sided adhesive tape), prior to mounting the pressure means at its pressure
 distance from the cylinder. The pressure means is then moved to its
 pressure distance with the leading end portion of the blanket between the
 pressure means and the cylinder. Such a procedure may be useful for
 reducing the risk of operator contact with the adhesive backing on the
 blanket since the protective sheet may be released from the leading end
 portion of the blanket more easily while the end portion is supported on
 the pressure means. The weak adhesive employed to locate the blanket end
 portion on the pressure means should be capable of releasing the blanket
 from the pressure means when the cylinder is subsequently rotated during
 feeding of the blanket onto the cylinder.
 After application of the blanket onto the cylinder, usually the cassette
 and, if employed, the pressure means are moved away from the cylinder and
 may be removed altogether from the press frame.
 The present invention is suitable for employment in conjunction with the
 invention described in our co-pending patent application filed on Dec. 29,
 1997 entitled `Printing Press Cylinders` U.S. Ser. No. 08/952,065. When
 used in conjunction with the invention described in said co-pending patent
 application, the leading edge of the blanket may be located along the
 nearer edge of the slit in the cylinder surface or overlapping the slit
 and then trimmed along the slit.
 The adhesive employed for attaching a blanket to a press cylinder must be
 stable at the temperatures created during high speed running of the
 printing press and should be resistant to solvents employed for cleaning
 the blanket.
 Preferably the adhesive should be such as to enable removal of a worn or
 damaged blanket by peeling off the cylinder with no or minimal adhesive
 residue left on the cylinder surface.
 The adhesive layer should be of low thickness and of uniform consistency in
 order to avoid conferring even small aberrations on the total blanket
 thickness.
 Accordingly, a contact adhesive usually is employed and typically such
 adhesives have a high initial bond strength which resists adjustment of
 the position of the blanket after contact with the cylinder. However,
 other types of adhesive, for instance a settable adhesive (e g heat- or
 radiation-settable) or a reaction adhesive (e g comprising a
 pressure-rupturable microencapsulated reactant), may be employed provided
 that they satisfy the requirements for a printing operation.
 The adhesive typically is employed as a pre-coating on the cylinder-side
 (back) of the blanket and is protected by a releasable sheet of flexible
 material such as paper or plastics film until immediately prior to
 application of the blanket to the cylinder.

DETAILED DISCUSSION OF PREFERRED EMBODIMENTS
 FIG. 1 shows a cassette 1 in accordance with the invention, comprising a
 cylindrical casing 2 having a longitudinal opening 3 and (optionally) a
 spindle 4. The cassette is shown in mounted relationship with a printing
 press cylinder 5 and a pressure roller 6. An adhesive-backed printing
 blanket 7 with a releasable protective cover sheet 8 on the adhesive
 backing is in wound-roll form inside the cassette. The leading end portion
 9 of the blanket 7 is shown as having been fed Out of the cassette through
 the opening 3, around the pressure roller 6 and onto the cylinder 5. The
 protective cover sheet 8 is released from the blanket continuously as the
 blanket emerges from the cassette, and the pressure roller promotes firm
 even adhesion of the blanket to the press cylinder surface as the cylinder
 is rotated about its central axis.
 FIG. 2 shows an alternative embodiment of the invention, in which like
 numerals denote features similar to those of FIG. 1, except that instead
 of the pressure roller 6 of FIG. 1 there is a pressure slide 10 which is
 integral with the cassette casing 2.