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(11) | EP 0 109 725 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Improved printing ink proofer |
| (57) A method and apparatus for preparing a proof or sample of an ink (as herein defined)
as a preliminary to its being employed in a printing or coating process to enable
its colour and coating capability to be determined. A quantity of the ink is applied to a first roller the surface of which is engraved. The ink is evenly distributed over the roller using a doctor-blade set as to wipe the roller surface clean and leave the ink only in the engraving. A second roller of resiliently deformable material is moved into contact with the inked roller so causing ink to be transferred to the surface of the second roller until equilibrium is reached and a sheet of the substrate to be inked or coated is introduced into the nip between the two rollers. Means is provided for cleaning the rollers after use. The second roller may be formed from two or more separate rollers spaced apart so as to define separate inking surfaces or may be in the form of a single roller having one or more annular grooves to define the different inking surfaces required. |
Field of invention
[0001] rhis invention concerns a printing ink proofer and an improved method of proofing an ink or like materials.
Background to the invention
[0002] The testing of inks inter alia for colour has previously entailed the application of controlled quantities of the ink onto a small scale printing machine and producing one or more sample prints or proofs to enable the covering qualities and colour of the ink to be ascertained.
[0003] The accuracy of such tests has relied on the accuracy in the measurement of the volume of ink applied to the machine, and this in turn tends to be directly attributable to the skill and care exercised by the operator.
[0005] It is an object of the present invention to provide an improved proofer for checking on the coating capability and colour of inks on paper and board and like materials.
Definition
[0006] In the context of this application the expression 'ink' is intended to cover any liquid or fluid or paint or paste-like material employed in a coating or printing process.
Summary of the invention
[0007] According to one aspect of the present invention a method of preparing a proof or sample of an ink (as herein defined) as a preliminary to its being employed in a printing or coating process to enable its colour and coating capability to be determined comprises the steps of:-
1) applying a quantity of ink to a first roller formed of resiliently deformable material;
2) bringing the first roller into contact with a second roller axially longer than the first, and engraved so as to form a large number of microscopic depressions therein into which the ink can become trapped;
3) causing the ink to become evenly distributed over that part of the axial length of the second engraved roller which corresponds to the axial length of the first roller, using a so-called doctor blade set so as to wipe the engraved roller surface clean leaving the ink only in the depressions;
4) controlling the pressure between the two rollers so as to first cause ink to be transferred from the depressions onto the surface of the second roller until equilibrium is reached;
5) introducing into the nip between the two rollers a sample of sheet material which is the same as or similar to that to which the ink is to be applied in a subsequent printing process and causing the ink on the surface of the first resiliently deformable roller to be applied as a coating to the said sheet material;
[0008] The resulting coating is found to be readily reproducible to a high level of accuracy by merely allowing the two rollers to continue to rotate together and re-establish a position of inking equilibrium before inserting another sample of sheet material therebetween.
[0009] If a reduced tone (or undertone) effect is required, a length of the sample of sheet material is selected so as to be greater than the circumference of the transfer roller so that the sheet material will still be located in the nip after a complete revolution of the two rollers thereby preventing re-inking during the second revolution. During this latter, the ink available for coating the sheet material is that remaining in the depressions after the first pass of the sheet material.
[0010] Preferably the doctor blade is adjustable in both proximity and angle of inclination to the surface of the engraved roller. Typically the angle between the plane of the blade and the normal to the roller surface at the point of contact between the blade and the roller surface, is in the range 70° - 85°.
[0011] Preferably force is applied to the hingeing frame to urge the first roller into contact with the second roller with the desired pressure therebetween.
[0013] In order to simulate different printing techniques, a number of differently engraved rollers may be provided and the appropriate one is selected according to the technique which is to be simulated.
[0014] Although reference has so far only been made to a single first roller, it is to be understood that the method is applicable to apparatus in which there is more than one first roller and in which the inking surfaces of the two or more first rollers are separate one from the other by virtue of grooves provided in the surface of the rollers if not actual axially spacing of the rollers along a shaft. The invention thus allows two or more different colours of ink or different types of ink or different shades of ink to be applied to different ones of the first rollers and for two proofing coatings to be laid down on the sheet material during a single pass between the rollers. This is of particular advantage where a direct comparison under the same conditions is required between one ink and another.
[0016] The method is particularly applicable to thick paste-like inks and relies for its success on the fact that the doctor blade can be set to clean the engraved roller just before the latter is due to engage the resilient roller and form the nip therebetween and a sheet of paper or similar sheet material introduced into the nip will therefore only have ink applied to that surface of the sheet material facing the resilient roller.
[0017] The pressure between the rollers is adjusted so that this desirable result is in practice normally obtained.
[0018] According to another aspect of the invention, apparatus for performing the method of the invention comprises:
1) a first engraved roller having a plurality of microscopic depressions in its surface;
2) a doctor blade adjustably mounted relative to the first roller, for co-operating with the roller to remove surplus ink from the surface of the roller and leave ink only in the depressions;
3) at least two second rollers each of resiliently deformable material and axially separate at least at their inking surfaces, mounted for rotation about an axis parallel to the axis of rotation of the first, engraved, roller, and movable under pressure into contact with the engraved roller, and away therefrom, as required;
4) means for adjusting the pressure exerted between the rollers;
5) drive means for rotating at least the engraved roller at a controlled speed, and
6) sheet collecting means on the discharge side of the nip between the rollers for receiving and supporting a sheet of paper or like material after the latter has passed between the rollers and had ink applied thereto from the rollers.
[0019] By providing two separate rollers or at least a single roller having two separate inking surfaces separated by an annular groove, with the total extent of the resiliently deformable roller being less than that of the engraved roller, so different inks can be laid down as coatings on a single sheet of paper or like sheet material passed between the inked rollers and the engraved roller with the coating, as provided by the method of the invention, being laid down from the ink contained on the surfaces of the resiliently deformable rollers. In this way, direct comparison can be made between one ink and another.
[0020] It is to be understood that any number of separate inking surfaces may be provided by an appropriate number of subdivisions of the cylindrical surface of a single resiliently deformable roller or by means of a corresponding number of separate rollers mounted on a single shaft.
[0023] Preferably means for indicating the speed of rotation of the engraved roller, is provided. Typically a tachometer is employed or alternatively a shaft encoder and electronic-pulse counter and display are provided. Preferably means is provided for adjusting the pressure exerted between the two rollers and for indicating said pressure.
[0024] Preferably means is provided for cleaning the rollers after use, typically in the form of a solvent both with or without solvent applicator roller and transfer rollers.
[0025] Preferably means is provided for adjusting both the angle and spacing of the doctor blade relative to the engraved roller.
[0026] The engraving of the first roller is typically such as to provide between 100 and 400, typically 300, cavities per inch in both axial and circumferential directions of - measurement around the first roller, ie typically 90,000 cavities per square inch of surface.
[0027] Typically the cavities are 6/10 of a thousandth of an inch, ie approximately 14 microns, deep, but deeper or shallower cavities may be employed in the range 0.2 to 2.00 thousandths of an inch.
[0029] Conveniently each second roller is of natural or synthetic rubber material or a plastics material such as polyurethane or a composite of rubber and plastics material.
[0030] Preferably the second rollers are mounted in a hingeing frame and-are movable from an elevated position clear of the engraved roller, into a lower position in contact with the engraved roller.
[0031] Since printing ink and the like are often highly inflammable, the drive means for rotating the engraved roller is conveniently an air motor, and speed control is achieved by controlling the volume of air available to the air motor.
[0032] Typically the doctor blade is formed from a blade some two thousandths of an inch thick and a thicker rigid backing plate, and the two are sandwiched in a chuck, itself mounted for movement relative to the engraved roller.
[0033] Preferably both the resilient rollers and the engraved roller are mounted on shafts which are adapted to be readily inserted into and removed from, bearing assemblies and driving means is provided at least at one end for engaging one of the shafts and rotating same, so that different rollers can be substituted at will.
[0034] Typically an air motor is provided for driving the engraved roller shaft through reduction gearing so that the final speed of rotation of the shaft is of the order of 100 revolutions per minute. In a typical installation the motor will rotate at a speed of around 3000 rpm under no-load, reducing to approximately 1500 rpm under load and the reduction gearing (or gearbox) has a ratio of 18:1.
[0035] The method of applying the ink to the rollers (typically the resiliently deformable rollers) prior to the establishment of equilibrium and the passage of a sheet material between the rollers, is most conveniently attained using a spatula or the like and simply positiflning a suitably sized blob of ink on to the surface of the roller to which the ink is to be applied. Running the rollers together and using the doctor blade will cause the ink to spread out and form an even film over the surface of the resiliently deformable roller to which the ink has been applied after equilibrium has been established.
[0036] Alternatively and in some ways more preferably, ink applicator means may be provided for applying ink from a suitable reservoir or container to the cylindrical surface of the roller to which the ink is to be applied. The ink applicator may in fact form part of or be associated with a cleaning device for cleaning the roller and removing therefrom all trace of the ink film applied thereto and to this end the ink applicator may be on one side and the ink remover on the other side of a rocking member which can be tilted so that either one or the other engages the roller.
[0037] The invention will now be described by way of example with reference to the accompanying drawings.
Description of the drawings
[0038]
Figure 1 is a perspective view of one embodiment of the invention;
Figure 2 is a side elevation of the apparatus shown in Figure 1;
Figure 3 is a front view of the apparatus of Figure 1, and
Figure 4 is a plan view thereof.
Detailed description of the drawings
[0039] A printing tester or proofing press is shown in the drawings as comprising a baseplate 10 carrying supports 12 and 14 for an engraved roller 16 carried by a shaft 18 which is rotatably received in half bearings at 20 and 22 and includes a drive take-up pin 24 which is engaged by a driving pin 26 extending off centre from a rotating plate 28 comprising the output of a gearbox 30.
[0040] The supports 12 and 14 include two elevated sections 32 and 34 within which are held captive the ends of a support shaft 36 on which are rigidly mounted two radius arms 38 and 40 which carry between their ends a shaft 42 on which is rotatable a rubber roller 44 serving as a transfer - roller for co-operating with the engraved roller 16. The roller 44 includes a circular central annular groove 43 to define two inking surfaces 45 and 47.
[0041] The roller 44 is movable into engagement with the roller 16 by rotation of the shaft 36 and to this end an arm 46 is rigidly attached to one end of the shaft 36 and as shown in Figure 2, is acted on at its lower end by a pneumatic ram 48 the piston of which is movable outwardly to rotate shaft 36 clockwise as shown in Figure 2. The retracted position is shown at 46'.
[0042] A doctor blade, best seen in Figure 2, comprising a chuck 50 and blade 52, is movable relative to a support 54 by screw adjusters 56. Angle as well as spacing from the cylinder 16 is adjustable.
[0043] 4n air motor 58 is mounted within the gearbox housing 30 as shown in Figure 2, and gears (not shown in detail) transmit drive therefrom to the shaft 18 as described.
[0044] As best seen in Figures 1 and 4, a control panel 60 is provided with an ON-OFF switch 62, motor speed control 64, UP-DOWN switch 66 and speed of rotation indicator 68.
[0045] Although not shown in detail the speed indicator 68 is an LED display device for displaying digits indicating the rotational speed in RPM and an electronic revolution counting device is provided with a shaft encoder (not shown) on the shaft 18.
[0046] Figure 3 shows the nip between the two rollers 16 and 44. between which a sheet of paper or the like is to be introduced, to obtain the proofing inking.
[0047] Figure 4 shows inter alia meshing gears 72, 74 in the gearbox and illustrates the roller 44 in its lowered position particularly overlying the roller 16.
[0048] In use ink is applied to the inking surface 45 and/or 47 of the inking roller 44 and the latter is lowered on to the engraved roller 16. Mutual inking occurs with effective removal of the surplus ink from the surface of the roller 16 by means of the doctor blade and eventually equilibrium is reached in which a film of ink exists around the surfaces 45 and 47 of the roller 44 and the surface of the roller 16 is effectively free of ink, the latter being trapped in the cavities in the surface of the roller 16 formed by the engraving of the roller.
[0049] At this stage a sheet of paper or like sheet material can be introduced into the nip between the rollers 44 and 16 and a coating of ink will be applied from the inking surfaces 45 and 47 (if both have been inked) on to the surface of the sheet material which cooperates with the inking surfaces whilst little or no ink is applied to the underside of the paper from the engraved roller because of the action of the doctor blade.
[0050] The process is thus an exact opposite of a standard printing process in which ink is applied to an engraved roller for application from the engraved roller to a sheet of paper pressed into contact therewith in a nip formed between the ink engraved roller and non-inked resilient rollers. As is well known, in printing machines, any roller running with the inked engraved roller is not normally brought into contact with the latter, but only into contact with the back of a sheet of paper or like sheet material which itself is run in contact with the engraved inked roller and acts as a barrier between the inked surface of the engraved roller and the pressure rollers. In the event that ink is accidentally applied to pressure rollers in an ordinary printing machine, the machine has to be stopped and the accidentally inked pressure rollers cleaned before printing can recommence.
a) applying a quantity of ink to a first roller formed of resiliently deformable material;
b) bringing the first roller into contact with a second roller, axially longer than the first roller and engraved so as to form a large number of microscopic depressions therein into which the ink can become trapped;
c) causing the ink to become evenly distributed over that part of the axial length of the second engraved roller, which corresponds to the axial length of the first roller using a so-called doctor blade set so as to wipe the engraved roller surface clean so leaving the ink only in depressions;
d) controlling the pressure between the two rollers so as to first cause ink to be transferred from the depressions onto the surface of the second roller until equilibrium is reached;
e) introducing into the nip between the two rollers a sample of sheet material which is the same as or similar to that to which the ink is to be applied in a subsequent printing process and causing the ink on the surface of the first resiliently deformable roller to be applied as a coating to the said sheet material.
a) a first engraved roller having a plurality of microscopic depressions in its surface;
b) a doctor blade adjustably mounted relative to the first roller, for co-operating with the roller to remove surplus ink from the surface of the roller and leave ink only in the depressions;
c) second roller means of resiliently deformable material presenting at least two axially separate cylindrical inking surfaces, mounted for rotation about an axis parallel to the axis of rotation of the first, engraved, roller, and movable under pressure into contact with the engraved roller, and away therefrom, as required;
d) means for adjusting the pressure exerted between the rollers;
e) drive means for rotating at least the engraved roller at a controlled speed, and
f) sheet collecting means on the discharge side of the nip between the rollers for receiving and supporting a sheet of paper or like material after the latter has passed between the rollers and had ink applied thereto from the rollers.