GB1598236A

GB1598236A - Ink metering apparatus

Info

Publication number: GB1598236A
Application number: GB10928/78A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1977-03-21
Filing date: 1978-03-20
Publication date: 1981-09-16
Also published as: BR7801711A; SE433829B; CA1127453A; FR2408458B1; IT7809381A0; SE7802884L; JPS53116905A; DD135368A5; CS178278A2; IT1103722B; DE2812998A1; JPS622991B2; DE2812998C2; CS231162B2; FR2408458A1

Description

(54) INK METERING APPARATUS (71) I, HAROLD PHILLIP DAHL GREN, a Citizen of the United States of America, of 3305 Manor Way, Dallas, Texas 75235, United States of America, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement : This invention concerns ink metering apparatus.

Inkers for printing plates which have achieved commercial acceptance generally comprise from two to four form rollers which are positioned in rolling engagement with a printing plate. Each of the form rollers is usually in rolling engagement with one or more vibrator rollers to which ink is applied by a multitude of rollers in a train of rollers of varying diameters arranged in pyramid fashion.

Ink is delivered to the train of rollers over a ductor roller which oscillates into and out of engagement with a film of ink formed by a flexible doctor blade urged into engagement with the hard surface of an ink fountain roller by a multiplicity of ink keys.

The ink film formed on the ink fountain roller has been too thick and too irregular for application directly to a printing plate for quality printing. These inkers which include a multiplicity of rollers are intended to reduce the thickness of the ink film and to deliver a film of uniform thickness to the printing plate.

However, since the ink film on each form roller is not totally replenished on each revolution of the form roller, image ghosting and ink accumulation and starvation is not eliminated.

The multiple roller inkers require complex drive trains and are relatively expensive to purchase initially and to maintain thereafter.

In an attempt to eliminate both the expense and the disadvantages of multiple roller inkers, many recent attempts have been made to develop inkers wherein a fresh film of ink is metered onto a form roller which is urged into pressure relation with a printing plate to elimi- nate the train of rollers, to eliminate image ghosting, and to eliminate ink accumulation and starvation.

United States Patent No. 3,283,712 describes an inking system devised to overcome ghosting. The system comprises two rollers of substantially equal diameter urged together in pressure indented relation to form a nip, surfaces of the rollers adjacent the nip moving in opposite directions. One of the rollers was cleaned by a pair of doctor blades, and the rollers were urged together such that the local pressure at any point selected along the contact generatrix or nip was greater than a "critical pressure threshold", such that, theoretically, one of the rollers carried a film of ink of constant thickness throughout the length of the roller to be applied directly to a printing plate without being contacted by equalizer rollers.

The theory of operation set forth in the aforementioned patent failed to take into consideration the fact that viscosity, surface tension, cohesion of ink molecules, and adhesion of ink molecules to molecules on surfaces of the rollers are all related to temperature of the ink. Thus, since adjacent surfaces of the rollers at the nip moved in opposite directions and since pressure was not uniform along the length of the nip, temperature generated by adjacent surfaces moving in opposite directions would result in substantial variations in temperature along the length of the rollers and of ink carried by the rollers.

In addition to the irregular temperature distribution across the length of the rollers, inkers built in accordance with teachings of the aforementioned patent required substantial power for rotating the rollers and adjustment of the thickness of a film of ink metered through the nip was very sensitive because slight changes in surface speed of the roller which had been completely cleaned of ink resulted in drastic changes in the film of ink carried by the other roller.

It was also observed that the surface of the resilient roller tended to vibrate or chatter as it moved through the nip and encountered substantial forces as a result of being in pressure indented relation with the surface of the other roller moving in the opposite direction which resulted in' printing streaks which extended transversely of the direction of travel of the sheet through the printing press. Experience has revealed that conventional viscous ink could not be used in this inking system.

It appears that the inker disclosed in the aforementioned patent has failed to achieve commercial success because of its inability to meter a film of uniform thickness suitable for inking a printing plate and because of successive power requirements for driving the rollers when adjacent surfaces move in opposite directions and when heavily pressed together.

Ideally, a stationary metering unit requiring no drive in addition to that required for rotating a single form roller would appear to be a solution to the problems presented by previous inkers. Attempts have been made to employ doctor blades as ink metering units, but these attempts have universally met with failure. Doctor blades are successfully used as ink wiping units in inkers having a train of rollers for distributing and smoothing the ink, but such blades have not proven suitable for use as the sole ink metering unit for a resiliently surfaced form roller.

Printing ink is generally an oily viscous substance which is highly pigmented and formulated to be sticky or tacky so that the ink will properly adhere to image areas of the printing plate. When the image area of the printing plate transfers ink directly to paper or to a blanket cylinder which in turn transfers ink to paper, small paper fibres, lint and fragments of coating material may adhere to the surface of the plate cylinder. The plate causes the foreign substance to be applied to the surface of the ink applicator roller. If the surface of the ink applicator roller is moved directly into the reservoir and then wiped or scraped by a conventional doctor blade, the foreign substance tends to collect at the edge of the doctor blade which results in formation of an irregular film of ink on the surface of the roller. For this reason, in addition to the erratic behaviour of the surface of the resilient roller under dynamic conditions, no inking device has been devised heretofore which is capable of supporting a doctor blade for metering a uniform film of ink directly onto the surface of a resilient roller in rolling engagement with a printing plate.

United States Patent No. 3,298,305 discloses an inking mechanism having a stationary, rigidly supported edge held in a position to significantly indent a resilient roller surface such that a film forming portion on the inking mechanism would form a thin uniform film of ink which was delivered through a slot in the inking mechanism and applied to the roller surface. The edge was described as being positively locked in position to prevent any lifting by the ink film on the roller so as not to detrimentally affect the hydrodynamic effect.

I have observed that uniform pressure cannot be obtained between the rigidly positioned edge and the surface of a resilient roller under dynamic conditions because the apparent modulus of elasticity of the resilient surface on the roller increases as the rate of cyclic loading increases. The dimensions of the resilient form roller also vary under dynamic conditions, if the resilient surface is subjected to cyclic loading, since resilient materials have a memory and do not immediately recover to an original dimension after being compressed. Further, vibration in the resilient roller surface is induced by substantial indentation of the surface since the resilient cover is stacked up as a result of compressive loading on one side of the stationary rigid edge and is under tension on the other side of the edge. Vibration in the axis of the roller relative to a stationary rigid edge which results from movement of the surface of the roller into and out of the gap in the plate cylinder is not readily isolated from a rigidly supported edge.

It is further noted that a mechanism as described in Patent No. 3,298,305, which wipes the ink with a rigidly supported edge does not efficiently and effectively form a thin uniform film. Furthermore, a rigid mechanism does not readily or easily yield to conform to surface variations of the roller and, therefore, yields a non-uniform ink film in ranges of desirable thicknesses.

United States Patent No. 4,007,682 discloses a method of inking a resilient surfaced form roller wherein an ultra-thin doctor blade is mounted at a reverse angle to the ink to split the ink and apply the ink to the roller in the desired thickness when relative motion is provided between the roller and the doctor blade.

The doctor blade is described as being fiexible, for example, a blade constructed of Swedish steel having a thickness of 0.008 inches (0.20 mm) in one example and a thickness of 0.015 inches (0.38 mm) in another example.

The disclosure of Patent No. 4,007,682 states that when an ink of high viscosity is used and the rate of relative motion between the roller surface and the edge of the blade is high, a sharp blade will "float" along on the ink surface, but the lead edge of the doctor blade should be cylindrical having a radius of curvature equal to one-half the thickness of the blade when less viscous inks are used. The disclosure states that the velocity of the roller surface relative to the doctor blade is adjusted to interact with the ink viscosity, blade geo- metry and downward force on the blade to cause the ink to be carried into the nip between the blade and the roller surface whereby its viscous resistance to shear forces creates an upward pressure causing the doctor blade to "float" over the ink film it produces. The surface speed of the roller is varied for varying the thickness of the film of ink formed thereon.

The disclosure states that rotation of the inking roller at 68 inches (172.72 cm) per second pro vides a uniform coating of ink 5 microns thick and that when the rotation speed of the inking roller is increased to 172 inches (436.88 cm) per second a layer of ink 12 microns thick is formed.

I have observed that a wedge-shaped entrance surface on an ultra-thin flexible doctor blade lightly urged toward a roller surface, as described in Patent No. 4,007,682, causes the flexible blade to hydroplane such that the ink film thickness changes with press speed resulting in colour density variation on printed sheets. It has further been noted that a significant radius on the edge of the blade forms an area in which small paper fibres and lint, commonly referred to as "hickeys", collect which results in formation of an irregular film of ink on the surface of the roller.

Further, it appears that the cylindrical end on the doctor blade disclosed in Patent No.

4,007,682 is not shaped to deflect the roller surface away from the lower surface of the doctor blade and, therefore, ink carried by the surface of the roller will trail the lower surface of the doctor blade causing an accumulation of ink on the surface of the doctor blade which will result in dripping and destruction of the uniformity of the ink film formed by the blade.

The invention described herein addresses the problem of forming a film of printing ink of uniform thickness on a resilient roller surface and moving the film of ink into engagement with the image area on a printing plate while eliminating trains or rollers in inking systems, eliminating the necessity for consumption of excessive power for metering a thin uniform ink film, eliminating problems attendant to collection of "hickeys", providing a metering member which does not detrimentally stress a resilient roller surface so as to impart vibration to the resilient roller surface, and providing a metering member which forms a uniform film, the thickness of which is independent of press speed.

The present invention provides liquid metering apparatus comprising a roller having a resilient water surface and means operative, upon rotation of the roller, for forming, from a liquid film of irregular thickness carried by the roller, a thin liquid film of uniform thickness, said means comprising a metering member pressed substantially radially inwards of the roller characterised in that said metering member has a metering edge and a trailing edge and presents, to the irregular liquid film, a substantially flat metering surface on the metering member adjacent the metering edge, and is pressed so that both the metering edge and the trailing edge are indented into the resilient roller surface. Preferably the metering edge is indented into the roller surface by a distance which is equal to or greater than the distance by which the trailing edge is so indented.

The surface of the roller moving from engagement with the printing plate is moved through a reservoir of ink such that an excess of ink is applied to the surface of the roller.

The metering member is positioned in relation to the resilient surface of the roller to form an orifice through which a thin uniform film of ink is extruded which adheres to the resilient surface of the roller.

The metering member can be resiliently mounted such that a polished flexible edge thereon moves relative to the axis of the resilient covered roller and is urged towards the resilient surface of the roller to maintain a substantially constant pressure relationship relative to the roller surface along the entire length of the roller and circumferentially thereabout.

The polished flexible edge of the metering member should be rigidly supported in a direction generally tangent to the roller surface and shaped and oriented to deform the resilient roller surface to minimize wetting of a sub stantial surface area of the metering member downstream of the polished edge to cause separation of ink from the metering member adjacent the polished edge. The lower surface of the metering member can be shaped and/or positioned such that ink on the indented resilient roller surface does not separate from the roller surface and attach itself to the lower surface of the metering member when rebounding from a compressed position occupied as a result of passing the flexible polished edge of the metering member.

Flow of ink in the reservoir toward the metering member will normally be turbulent due to the structure of the metering member adjacent the reservoir, thus causing lint and other foreign matter to generally be rejected from an area of high pressure immediately adjacent the leading edge of the metering member. This lint and foreign matter is retained in the reservoir and therfore lodging of particles against the edge of the metering member is also minimized. Flow of ink carried by movement of the surface of the resilient roller toward the polished edge of the metering member experiences a rapid increase in pressure and flow becomes laminar immediately adjacent the polished edge. Velocity of the ink increases as it moves through an orifice between the resilient surface of the roller and the polished edge of the metering member. Immediately downstream from the orifice, the ink separates from the polished surface and is retained on the resilient surface of the roller.

The polished edge of the metering member can be urged toward the resilient surface of the applicator roller by a static force in a range between about one and six pounds per linear inch (0.177 to 1.063 Kg per linear cm) of the length of the edge, the force being sufficient to indent the roller surface along the entire length of the roller surface and being dependent upon the modulus of elasticity of the resilient roller, the cover thickness, the viscosity of the ink and other characteristics of the ink. The polished edge of the metering member slightly indents the surface of the resilient roller, for example about 0.03 inches (0.76 mm) on a 40 Shore A durometer roller having a cover thickness of approximately 5/16 inches (7.94 mm). As the roller rotates, the polished edge of the metering member moves relative to the axis of the roller to maintain a condition of equilibrium such that the edge forms an orifice which automatically moves radially relative to the axis of the roller to form a film of uniform thickness longitudinally of the roller surface and circumferentially thereabout although the roller surface is not perfectly round and not free of slight waviness.

The invention further provides a method of metering liquid in liquid metering apparatus, which comprises supplying the liquid as a film of irregular thickness to the outer surface of a roller, which outer surface is resilient, rotating said roller, and pressing a metering member substantially radially inwards of said roller so that a metering edge and a trailing edge of said metering member are indented into said resilient outer surface of the roller, and a substantially flat metering surface adjacent said metering edge is presented to the liquid film of irregular thickness.

The polished edge on a metering surface should be urged into pressure indented relation with the resilient roller surface such that the angle of the metering surface relative to a radius of the roller is adjustable to adjust the thickness of the film carried by the roller surface past the polished edge.

The invention will be described further by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a cross-sectional view taken transversely through a printing press; Fig. 2 is an enlarged fragmentary crosssectional view illustrating the relationship of the metering member relative to a resilient covered roller; Fig. 3 is an enlarged diagrammatic illustration of a first embodiment of the metering member and a portion of the resilient surface of the applicator roller under dynamic conditions; Fig. 4 is a diagrammatic illustration showing that as force urging the metering member into pressure indented relation with a roller surface is increased a minimum ink film thickness is reached; Fig. 5 is a diagrammatic view similar to Fig.

4 illustrating a family of curves; Fig. 6 is a diagrammatic illustration showing variation in colour density laterally across a printed sheet in response to changes in force urging an edge of the metering member into pressure relation with a resilient surface; Fig. 7 is a diagrammatic illustration showing variation in position of an edge on the metering member as a resilient covered roller rotates at a constant speed and also at changing speeds; Fig. 8 is a diagrammatic illustration that ink film thickness is independent of press speed; and Fig. 9 is a diagrammatic illustration showing the colour density on a printed sheet.

Numeral references are employed to designate like parts throughout the various figures of the drawing.

Referring to Figs. 1 and 2, the numeral 1 generally designates an inker incorporating ink metering apparatus of the invention and having spaced side frames 2 movably secured to side frames 3 of a printing press having a conventional plate cylinder P, a blanket cylinder B, and an impression cylinder I mounted therein for printing on a web W or a sheet of paper.

A support member 5 is provided to adjustably secure a metering member 10 between side frames 2 and to position metering member 10 in relation to a resilient covered applicator roller 40. Opposite ends of the applicator roller 40 are rotatably secured to the side frames 2 in suitable bearings and the applicator roller 40 is driven by any suitable drive means such as a chain 4 drivingly connecting a sprocket on the plate cylinder P to a sprocket on a clutch (not shown) at an end of the applicator roller 40.

The surface speed of the applicator roller 40 is preferably equal to the surface speed of the plate cylinder P. However, the surface speed of the applicator roller 40 can be about ten percent faster or slower than the surface speed of the plate cylinder P to facilitate cleaning non-image areas of the plate cylinder P.

End dams 6 are secured to the support member 5 and are urged into sealing relation with opposite ends of the applicator roller 40 and the metering member 10 to form a reservoir R from which ink is metered onto the surface of the applicator roller 40. One or more vibrator rollers 8 are positioned in rolling engagement with ink on the surface of the applicator roller 40 for smoothing any surface irregularities which may appear in the ink film before the ink film is carried by the surface of the roller 40 to the surface of a printing plate P1 on the plate cylinder P. The vibrator rollers 8 are in rolling engagement with ink on the surface of the applicator roller 40 and serve not only to smooth out surface irregularities, but also to change a slick metered finish to smooth matt-like finish for conditioning the ink film for proper printing to an image on a printing cylinder.

It will be appreciated that as the surface of the applicator roller 40 moves away from the surface of the printing plate pl the surface is submerged in ink and an excess of ink is applied thereto at the reservoir R.

If the inking system is employed for lithographic printing, wherein dampening fluid is applied to the surface of the printing plate P' on the plate cylinder P, means are provided for evaporating such dampening fluid from the surface of the roller 40 to prevent accumulation of excessive dampening fluid in the reservoir R. As illustrated in Fig. 1 of the drawing, a hollow perforated tube 9 extends transversely between the side frames 2 and has formed therein apertures through which dried compressed air is delivered for causing a stream of dry air to be directed toward the surface of the roller 40. An end of the tube 9 is connected by a hose to an air compressor (not shown).

Also, when dampening fluid is used with the inker of the present invention, a greater than normal proportion of alcohol to water may be employed to speed evaporation of the dampening fluid which remains on the applicator roller 40 as it moves away from the printing plate pl. In fact, the dampening solution could contain more than the normal 5 to 25 oSO alcohol to insure rapid evaporation of the dampening solution from the applicator roller 40 during travel between the plate P' and the ink metering member.

As will be hereinafter more fully explained, to provide precision control of the viscosity of ink in the reservoir R and to vary the viscosity of the ink in the reservoir R, flexible tubes 7 are connected to deliver fluid, such as water of controlled temperature and at a controlled flow rate, into one end of a passage 5l in the support member 5 and out of the other end of the passage 51.

For high speed web printing, the physical properties of ink film 130 formed between the metering member 10 and resilient cover 44 of the roller 40 may be controlled by temperature control of a fluid passing through the vibrator rollers 8 and through a passage in core 42 of the roller 40. It has been found that a high flow rate produces only a small temperature change along the length of a roller and that by monitoring and controlling the ouput temperature, heat can be dissipated and ink temperature controlled such that the physical properties of the generated film are held substantially constant throughout the length of a production run.

Therefore, by cooling and/or heating fluid passing through the support member 5 and roller core 42, the ink viscosity at the shear nip is controlled to maintain a constant desirable ink film for proper printing to the plate P'.

A preferred embodiment of the ink metering member 10 is illustrated in Fig. 3 of the drawings.

As shown, the ink metering member 10 has a smooth polished highly-developed precision metering edge 25 which is formed at the juncture of surfaces 24 and 26.

The edge 25 preferably extends, in length, for a distance within a range of from 10 to 100 inches 25.4 to 254 cms) and is defined by polished portions on the surfaces 24 and 26.

The polished portions of the surfaces 24 and 26 meet to form an angle of approximately 90 degrees. Although a 90 degree angle between the polished portions has been found to be very effective for forming the precision edge 25, the edge 25 may also be formed with the polished portions at other angles of less than 120 degrees and greater than 60 degrees.

The edge 25 is formed on relatively hard material, and normally metal is used. The material preferably has a hardness in a range between Rockwell C10 and Rockwell C60, and preferably about Rockwell C50.

The metering member 10 is preferably a resilient metallic material having a modulus of elasticity in a range between 15 and 30 X 10 psi (2.1 X 106 Kg. per sq. cm.) and preferably about 29 X 10 psi (2.03 X 106 Kg. per sq. cm).

The metering member 10 has been formed with good results from a strip of stainless steel of the type employed in the construction of compressor valves which is commercially avail- able from Uddeholm and distributed as UKB stainless 716. The stainless steel strip had a thickness of 0.031 inches (0.79 mm) and a width of 3.5 inches (88.9 mm). The strip of material had a bright extra fine polished surface finish, deburred edges, extra accurate flatness and normal straightness. Since the strip of stainless steel material was hardened and tempered, it was resistant to corrosion in the presence of air, water and most organic acids in dilute form at room temperature.

The strip of stainless steel was selected for its hardness, flatness, resilience and fine surface finish to provide high wear resistance and good fatigue properties.

Prior to polishing, the edge 25 at the juncture of the surfaces 24 and 26 defined a line consisting of ragged notches forming a ragged edge contour. To form a precision straight edge to define an unbroken line across the extent of the metering member 10, several segment s of the strip material were clamped together and the surfaces 24 thereof were simultaneously ground and then honed with a fine-grit stone as a first step in forming the polished edge 25.

A pair of strips from whcih the metering members 10 were to be formed were then clamped in a vice with a spacer between the strips, the surfaces 24 on each of the strips being positioned in a common plane so as to support a sanding block. The surfaces 24 on each of the strips with sequentially smoothed with sandpaper having grit sizes 320, 400 and 600 and then polished with crocus cloth.

As a third step, the pair of stainless steel strips were positioned on a flat horizontal surface such that each said surface 24 was adjacent the other surface 24, the upper surface 19 on each strip being supported on a spacer such that the edge 24 was inclined at an angle of about 0.2 degrees from a vertical line.

Polished portion 26 of each lower surface 28 was sequentially smoothed with sandpaper hav ing grit sizes 320, 400, and 600 and then polished with crocus cloth.

If a feather edge forms on the metering member 10 while the relevant portions of the surfaces 24 and 26 are being sanded and polished, the feather should be removed. Then the feather, or wire-like irregular edge, is removed, a microscopic curve is formed on the edge 25. Thus, in the process of polishing or "sharpening" the edge 25, the acuteness of the edge 25 should be altered somewhat to form a non-cutting, non-film-piercing edge. This process produces a fine continuous smooth straight polished highly-developed edge 25 having minimal surface irregularities. There should be no small notches or protrusions in the edge 25. The developed edge 25 formed by the polished portions of the surfaces 24 and 26 is a very fine edge which has been polished to bring it to a highly developed finish, and as nearly perfect condition as possible.

The edge 25 is finished to a surface finish approximating that of the edge of a razor blade. However, it will be appreciated that the angle between the polished portions of the surfaces 24 and 26 is significantly greater than a bevel angle such as is provided on a razor and thus a blunt non-cutting and non-piercing edge is formed. Actually, the portion 24 blends into portion 26 through the edge 25 to form a continuous polished surface adjacent the edge 25.

The material used to form the edge 25 must not only be hard and capable of being formed to provide a blunt fine polished unbroken edge, but the material must also be flexible along the length of the edge 25. In fact, the edge 25 must be quite flexible in a lengthwise direction so that, when urged into pressure-indented relation with the resilient surface of the applicator roller 40, the edge 25 will be flexed, yielding to the influence of the surface of the roller 40 to conform the edge 25 and the surface of the roller 40 to form a uniform indented area along the length of the roller 40.

As will be hereinafter more fully explained, the surface of the roller 40 has a thickness of approximately 0.25 inches (6.35 mm) and a resilience of about 40 SHORE A durometer.

This flexure of the edge 25 to obtain conforma tion with the surface of the roller 40 should be possible without excessively inden thickness of the material between surface 281 and surface 29 is approximately 0.030 inches (0.76 mm).

Surface 28a intersects the polished surface 26 at an angle Al in a range between 30 and 90 degrees as shown, The upper portion of the surface 24 of the metering member 10 is bevelled at an angle of approximately 30 degrees to form surface 22.

In the illustrated embodiment of the metering member 10, the polished surface 24 extends upwardly from the polished edge 25 by a distance approximately equal to the depth of the relieved area 27, or approximately 0.020 inches (0.508 mm) to intersect the surface 22. It should be readily apparent that the polished surface 26 supports the polished edge 25. If the surfaces 24 and 28a are parallel, the surface 26 can be refinished without changing the load bearing characteristics of the polished edge 25 of the metering member 10.

However, it should be readily apparent that the surface 22 may be formed to extend through the polished edges 25, if it is deemed expedient to do so, such that the polished surface 24 and the surface 22 would lie in a common plane.

The relief angle Al should be sufficient to cause an ink film, carried by the surface of the roller 40, to depart and separate from the surface 26 without accumulating either on the surface 26 or the surface 28a to cause ultimate dripping of the accumulated ink to cause nonuniformity.

The applicator roller 40 comprises the core 42, which is of hollow rigid tubular form, having the resilient cover 44, which is nonabsorbent, secured thereto, the cover 44 having a uniformly smooth and resilient outer surface 45. The cover 44 on the applicator roller 40, while being resilient, is relatively firm, for example in a range between 30 and 90 Shore A durometer.

The cover 44 on the applicator roller 40 is preferably formed of a resilient urethane, polyurethane or rubber-like material attached to the metallic core 42.

The cover 44 on the applicator roller 40 should have high tensile strength, excellent tear and abrasion resistance, and resistance to oils, solvents and chemicals. The cover should, furthermore, have low compression set, good recovery, and uniform ink receptivity. A suitable cover can be formed using a resin commercially available under the registered trademark "Solithane" available from Thiokol Chemical Corporation of Trenton, New Jersey, in combination with suitable plasticizers to form a resilient cover of about 40 Shore A durometer.

After the resilient cover 44 has been formed, the roller 40 may have a slick glazed outer skin or film over the surface thereof which is renewed by grinding. After grinding, the plastic surface is sanded by using 180 grit sandpaper to form a surface of uniform roughness over the outer surface 45 of the resilient cover 44.

Microscopic reservoirs, in which ink is retained, assure that a continuous film of ink is maintained on the outer surface 45 of the applicator roller 40. Final finishing, using various sandpapers to 400 grit, is done to insure a velvet smooth surface free of "orange peel" or other surface irregularities. As will be hereinafter more fully explained, adhesive force between molecules of ink and molecules of the outer surface 45 of cover 44 must exceed the cohesive force between ink molecules to permit shearing the ink to form a controlled film of ink on the surface 45 of applicator roller 40.

It will be appreciated that it is physically impractical, if not impossible, to construct the roller 40 such that the surface 45 is perfectly round in a circumferential direction, perfectly straight in a longitudinal direction, and precisely concentric to the axis of the core 42. The straightness of the surface 45 on the roller 40 can be economically held within a tolerance of about 0.002 inches (0.051 mm) along the length of the roller 40 and the radial eccentricity can be economically held within a tolerance of about 0.0015 inches (0.038 mm).

A Shore A durometer test is generally used to indicate the hardness of a resilient roller cover by measuring resistance to penetration at a constant temperature of about 76 degrees F (Appx 24.5 0C) while the resilient cover is stationary. The apparent hardness of a resilient surface under dynamic conditions deviates radically from the hardness indicated by the durometer test under static conditions. The spring constant of a resilient material also increases slightly as deformation increases.

As the frequency of loading of a resilient member increases, the dynamic modulus or apparent modulus of elasticity increases causing the cover to appear as a harder, stiffer material. However, cyclic loading of a resilient member results in generation of internal heat, with the increase in temperature resulting in a decrease in the durometer and therefore the modulus of elasticity of the resilient cover.

Further, since the surface 45 of the cover 44 on the roller 40 is preferably in pressureindented relation with the surface of the plate cylinder P, this plate cylinder P having a gap extending longitudinally thereof, this cyclic loading will result in generation of heat at an irregular rate circumferentially of the surface 45. Such temperature differences over the surface 45 may cause an appreciabie variation in the radial distance from the axis of the roller 40 to points over the surface 43, because the coefficient of thermal expansion of elastomeric materials employed for forming resilient roller covers is several times the coefficient of thermal expansion of steel.

As shown, the roller 40 can be different in diameter from the plate cylinder P without adversely affecting metering of the ink film 130 since the metering member 10 produces a continuous ribbon of ink regardless of the prior impression and regardless of thermal changes within the roller cover 44.

Referring back to Fig. 1 of the drawings, the support member 5 for supporting the metering member 10 in cantilever fashion comprises an elongate rigid support bar 50 having a ground and true flat face 52 on one side thereof and a surface 54 angularly disposed relative to flat face 52 forming a shoulder 55 which extends longitudinally of support bar 50. Journals 56 extend outwardly from opposite ends of the support bar 50 and are rotatably secured in a self-aligning bushing 57 in bearing blocks 60 having outwardly extending projections 58 adjacent opposite sides thereof.

Each of the projections 58 has an elongate slot formed therein through which anchor bolts 52 extend for securing bearing blocks 60 to the inker side frame 2.

Four elevating screws 64 extend through threaded passages in projections 58 on bearing blocks 60 and engage a surface 65 on the inker side frame 2 for movement of the support bar 50 in a vertical direction, as illustrated in Fig. 1.

Lateral adjustment screws 66 extend through threaded apertures in outward extending lugs 68 on the inker side frame 2 and engage an end surface 66' on the projections 58.

From the foregoing it should be readily apparent that the position of the bearing block 60 is adjustable vertically and horizontally, as viewed in Fig. 1 of the drawing, for movement of the support bar 50 relative to axis C of the roller 40.

An arm 70 is bolted or otherwise secured to the end of a journal 56 on the support bar 50 and is urged by a piston rod 71 of a fluid pressure actuated cylinder 72 into engagement with an end of a stop screw 74 threadedly secured to an arm 75 bolted or otherwise secured to the bearing block 60. It should be readily apparent that the support bar 50 is rotatable relative to the bearing block 60 by adjustment of the position of the end of the stop screw 74 relative to the arm 75.

A pressure regulator Rl is installed in order to set the inlet pressure in the cylinder 72 sufficient to hold the arm 70 firmly against the screw 74 for all indentations of the edge 15 into the surface 45 of the cover 44.

The metering member 10 is secured to the flat face 52 on the support bar 50 by bolts 76 extending through spaced apertures in a clamp member 78, through oversized spaced apertures extending through the cantilever beam adjacent the rear edge thereof. The bolts 76 are threadedly secured in threaded passages formed in the support bar 50. The bolts 76 and the clamp 78 cooperate such that the metering member 10 is uniformly attached or supported by the support bar 50 such that the edge 15 has a uniform spring rate along its length.

In the embodiment of the apparatus illustrated in Fig. 1, the stop screw 74 is remotely controlled by a direct current electrically driven motor 80 secured to the arm 75 by a support bracket 81. If it is deemed expedient to do so, a gear reducer may be positioned between the motor 80 and the screw 74 to further control the speed of rotation of the screw 74. A splined coupling 76a is connected between the screw 74 and the output shaft of the motor 80. The motor 80 may be of the kind commercially available from Globe Industrials Division of TRW, Inc., of Dayton, Ohio.

Conductors 82 and 84 extend between the motor 80 and a motor position control unit 85. The motor position control unit 85 is of conventional design and comprises a direct current source and a three position switch.

The motor position control unit 85 has a digital readout indicator 86 associated therewith to indicate the position of a rotary potentiometer (not shown) at the end of the stop screw 74 which engages the arm 70 to provide visual indication of the position of the support bar 50 for the metering member 10. The motor position control unit 85 is secured to the side frame 3 of the printing press in the embodi ment illustrated in Fig. 1 of the drawings.

However, an additional motor position control unit 85 is preferably positioned adjacent the delivery end of the printing press so that the position of the metering member 10 can be adjusted remotely as printed sheets are in spected to adjust colour density of ink as required.

The side frames 2 are pivotally secured by a shaft 90 to press side frames 3 adjacent oppo site sides of the printing press. A fluid pressure actuated throw-off cylinder 92 is pivotally secured to lugs 93 secured to the side frames 3 of the printing press and has a piston rod 94 pivotally secured to a lug 95 welded or otherwise secured to inker side frames 2. An on-stop adjustment screw 96 is threadedly secured to a respective lug secured to the press side frame 3 and is positioned to engage the inker side frame 2 when pressure between the outer surface 45 of the applicator roller 42 and printing plate P' has been properly estab lished. An off-stop adjustment screw 98 is threadedly secured to a respective lug welded or otherwise secured to printing press side frame 3 to engage the inker side frame 2 when the piston rod 94 in the throw-off cylinder 92 is extended thereby to separate the surface 45 of the applicator roller 40 from the surface of the printing plate pl.

As hereinbefore described, the end dams 6 are urged into sealing relation with the opposite ends of the applicator roller 40 and define opposite ends of the reservoir R. An ink retainer member 100 is positioned in sealing relation with the surface 45 of the applicator roller 4(), as illustrated in Figs. 1 and 2 of the drawings, and has opposite ends secured to the end dams 6. Lower edge 102 of the ink retainer member 100 is preferably spaced slightly from the surface 24 of the ink metering member 10, for example by 0.025 inches (0.635 mm).

The ink retainer member 100 defines the entrance side of the reservoir R.

The exit side of the reservoir R is defined by a member 105 secured to the support bar 50 by bolts 106. A lower seal 108 adjacent the member 105 is positioned adjacent the upper surface 19 of the metering member 10 to prevent flow of ink from the reservoir R onto the upper surface 19 of the metering member 10 to form an area of stagnation in which ink ceases to flow. Since ink is thixotropic, the viscosity of ink is significantly reduced when the ink is in motion as compared to the viscosity of ink which is not in motion.

As illustrated in Fig. 1 of the drawings, an ink agitator 110 is secured to ink retainer 100 for agitating ink in the reservoir R.

The ink agitator 110 is of conventional design and is commercially available from Baldwin-Gegenheimer of Stanford, Connecticut.

The ink agitator 110 generally comprises a rack and pinion which extends longitudinally across the upper portion of the reservoir R and carries a mixing head driven by a chain which is driven by a constant speed motor. As the mixing head aproaches the end dam 6 adjacent one end of the applicator roller 40, it reverses direction and moves to the other end of the reservoir. The agitator rotates within the ink to laterally stir or shear the ink to prevent irregularities in viscosity along said reservoir.

The operation and function of the apparatus hereinbefore described is as follows: The metering member 10 is aligned and attached to the face 52 of the support bar 50 by the bolts 76. Anchor bolts 52a are loosened to permit movement of the bearing blocks 60 relative to the inker side frame 2.

The lateral adjustment screws 66 are employed for moving the bearing block 60 relative to the applicator roller 40 for alignment of the edge 25 on the metering member 10 relative to the surface 45 on the resilient cover 44 of the applicator roller 40.

The elevating screws 64 are employed for adjusting the angular relationship between the surface 24 of the metering member 10 relative to a radius of the applicator roller 40.

After the edge 25 on the metering member 10 has been aligned with the surface of the applicator roller 40 and the angular relationship between the surface 24 and a line extending radially of the applicator roller 40 has been established anchor bolts 52a are tightened, rigidly securing the bearing blocks 60 relative to the side frames 2. The edge 25 is now in position in "kissing" contact with the surface 45 of the applicator roller 40. An amount of ink in excess of that needed to ink the plate P' on the plate cylinder P is provided from the reservoir R to the surface of the applicator roller 40 which is approaching the metering surface 24 of the metering member 10.

After the edge 25 has ben moved into kissing contact with the surface 45, the stop screw 74 is rotated, thereby pivoting the support bar 50 from the position illustrated in full lines in Fig. 2 of the drawings to the position illustrated in dashed lines.

This results in deflection of the cantilever beam and the flexible polished edge 25 is urged into pressure-indented relation to conform with the resilient surface of the applicator roller 40. Rotation of the roller 40 now moves ink from the reservoir R into contact with the edge 25 and th emetering surface 24 thus shearing ink of finite thickness on the surface 45 to a film 130 which may be altered in thickness as will be hereinafter more fully explained.

Assuming that the edge 25 is on a cantilever beam rigidly supported at one end, the equa tion of the elastic curve is Y = F(2L' - 3L2 x +x3) + 6EI.

In the prototype, a distance between the shoulder 55 and the metering surface 24 of the metering member 10, which would be the un supported end the cantilever beam, was 1.625 inches (41.275 mm), the distance between surfaces 18 and 19 was 0.031 inches (0.787 mm) and a static load of four pounds per inch of width (0.72 Kg per cm) was applied at the edge 25. The modulus of elasticity E of the metering member 10 was 27 X 106 psi (1.89 X 106 Kg. per sq. cm).

The moment of inertia I of a rectangular area is equal to bh8 + 12, where b is equal to the width of the base of the rectangular area and h is equal to the height of the rectangular area. The moment of inertia I of the metering member 10 having a thickness of 0.031 inches (0.787 mm) was calculated to be 2.4 X 10-6 per inch (0.945 X 10-6 per cm) of width of the cantilever beam.

At the unsupported end of the cantilever beam, x is equal to 0, and therefore, the deflection Y is equal to FL . 3EI. Therefore, it was calculated that the deflection of the un- supported end of the cantilever beam should be approximately 0.088 inches (2.235 mm) when a load of four pounds per inch of width (0.177 Kg per cm) is applied to the edge 25.

Therefore, it was concluded that the spring constant for the cantilever beam would be 0.022 inches (0.56 mm) of deflection per pound (0.45 Kg) of force applied to the edge 25, or 45 pounds per inch (7.965 Kg per cm) of the width of edge 25.

It is, of course, appreciated that the equation of the elastic curve set forth above is only approximate for calculating the deflection of the edge 25 since the metering member 10 is not rigidly supported or clamped at the shoulder 55 on the support bar 50. However, it will be readily apparent that the edge 25 is resiliently urged in a direction radially of the applicator roller 40.

The deflection or the distance moved by the edge 25 on the metering member 10, in the above example, was measured to be 0.20 inches (5.08 mm) when an average static force of four pounds per inch (0.708 Kg. per cm) was applied to the edge 25. Dividing the force of four pounds per inch (0.708 Kg. per cm) by the deflection of the metering member 10 reveals that the spring constant of the metering member 10 is low and approximately 20 pounds per inch (3.54 Kg. per cm of deflection). The spring constant calculated from the actual deflection of resilient member 10 differs from the approximate spring constant calculated above. However, the differences in the spring constant as approximately calculated and as actually measured was predicted.

As will be hereinafter more fully explained, the combined distance that the edge 25 is deflected plus the distance that edge 25 is indented into the roller surface should be substantially greater than the maximum space between points on the roller surface 45 and the edge 25 when the surface 45 and the edge 25 are urged into kissing contact. For example, irregularities or manufacturing imperfections in the roller surface 45 and slight waviness of the edge 25 might result in a maximum deviation of 0.002 inches (0.or mm) error such that the surface 45 and the edge 25 do not conform when first touched together. If the edge is deflected 0.20 inches (5.08 mm) and indented into the surface 45 a distance 0.030 inches (0.76 mm) the initial deviation of 0.002 inches (0.05 mm) would be about 1 % of the combined distance of 0.23 inches (5.84 mm). Since the edge 25 and the cover 44 are resilient, the edge 25 and the surface 45 will flex and conform to each other. When thus conformed, pressure along the stripe area will be substantially constant and the effect of small differences will be insignificant.

The combined distance of deflection and indentation is preferably more than ten times the initial deviation, such that the maximum error after the edge 25 and the surface 45 are urged into pressure-indented relation will be less than ten percent, to maintain an ink film thickness which will print what is considered by printers as acceptable uniformity of colour density. However, for what is referred to as "very tight" control, colour density should not vary more than five percent over the surface of a sheet.

As illustrated in Fig. 3 of the drawings, the edge 25 on the metering member 10 is urged into pressure-indented relation with the surface 45 of the applicator roller 40 such that both the metering edge 25 and the trailing edge 28b are indented therein and the resilient material is stacked up, up-stream from the surface 24 forming a bulge or wave 120 in the cover 44 while a groove or channel is formed in the cover 44 downstream from the edge 25. This forms an orifice through which ink is extruded, the orifice being bounded on one side by a portion of the surface 24 and the edge 25 and bounded on the other side by a portion of the surface 45, probably between the crest of the bulge 120 and the portion of the surface 45 immediately adjacent the polished edge 25.

As the cantilever beam permits the flexible edge 25 to follow the contour of the applicator roller 40, the orifice automatically moves radially relative to axis C of the applicator roller 40. Since the orifice is formed by the cooperation of the opposing flexibly biased edge 25 and the resilient surface 45 of the applicator roller 40, this movement is desirable if a constant pressure relationship is to be maintained on the ink extruded through the orifice. The surface 45 of the applicator roller 40 will constantly change in contour as the roller rotates, due to elastic memory, temperature changes, and variations in the dynamic modulus of elasticity, as hereinbefore discussed. Consequently, it is important that the edge 25 should automatically move radially and flex lengthwise to follow this changing contour.

It should be noted that ink carried by the surface 45 of the applicator roller 40 impinges against the metering surface 24, creating a region of turbulent flow adjacent the crest of the bulge 120 in the resilient roller surface 45.

Thus, although the edge 25 is resiliently urged downwardly as viewed in Fig. 3, the metering surface 24 is shaped and positioned to prevent lifting of the edge 25 by hydrodynamic forces exerted on the metering member 10 by the ink.

This condition is established by positioning the polished edge 25 such that it is closer to the control axis C of the applicator roller 40 than any other point of the metering member 10.

The blunt polished edge 25 favourably deforms the resilient cover 44 on the applicator roller 40 to form a metering orifice for forming a film of ink of precisely controlled thickness.

The lower surface of the metering member 10 has been formed such that the surface 28a at the heel of the polished surface 26 and bounding the relieved area 27 is angularly disposed relative to the direction of movement of the ink film 130 such that the roller surface 44 cannot resile to a position wherein the ink film 130 contacts the surface 28', and in the illustrated case the trailing edge 28b is indicated into the surface 44 to a lesser amount than the metering edge 25.

Thus, the metering member 10 is shaped or positioned to cause the ink film 130 to separate immediately from the metering member 10 prior to the surface of the metering member 10 returning to its relaxed, nonindented, position.

During testing of the apparatus hereinbefore described, it was discovered that as the force urging the edge 25 into pressure-indented rela tion with the surface 45 is initially increased, the thickness of film 130 is decreased to a minimum thickness; and then, with further increase in force, the film 130 begins to increase in thickness.

Referring to Fig. 4 of the drawings, it will be noted that this surprising phenomenon occurs as the force urging edge 25 on the cantilever beam metering member 10 toward the surface 45 of the roller 40 is increased.

When a light force per linear unit of length of edge 25 was employed for urging the edge 25 into pressure relation with the surface 45 colour density decreased as load was applied' and was uniform circumferentially of the surface 45 of the roller 40. However, with this light loading, colour density was not uniform laterally across the length of the roller 40. As the force was increased, the ink film thickness on the roller was reduced until a somewhat heavier load per unit of width of edge 25 was reached. The ink film thickness then began to increase as the force urging the polished edge 25 toward the central axis C of the roller 40 was increased. Otherwise stated, as the force was increased, the film thickness first was reduced and then began to increase as further load was applied. However, colour density became extremely uniform laterally across the length of roller 40 when the load approached a static average force of four pounds per inch (0.708 Kg. per cm) on the edge 25.

This phenomenon, where at a threshold pressure the ink film thickness suddenly ceases eo decrease and begins to increase as force on the edge 25 becomes higher, has been observed when the edge 25 constitutes the lower forward edge of a cantilever beam metering member.

Fig. 3 shows the metering member 10 in such indented relation with the surface 45 of the roller 40 at a position such that edge deflecting load, pressure and indentation and, therefore ink film thickness (which determines is substantially constant.

Referring to Fig. 4, it should be observed that the thickness of the ink film 130 varies as a function of the indentation of the polished edge 25 into the resilient surface 44 of the applicator roller 40. As described above, as the indentation increases, the thickness of the ink film 130 decreases rapidly to a minimum and then begins increasing. Irregularities or imperfections in the surfaces of the metering member 10 and the applicator roller 40 are easily seen in the metered ink film 130 until the polished edge 25 is indented to a point where the variation in edge deflection, for example, less than ten percent. At this point, the ink film 130 becomes more regular and uniform and remains substantially uniform as the polished edge 25 is further deflected and indented into the surface 45 of the applicator roller 40.

It has been observed that the thickness of the minimum ink film, as depicted at the bottom of the curve in Fig. 4, is controlled by the angle of the metering surface 24 relative to the radius of the roller 40.

Referring to Fig. 3 of the drawings, when the metering surface 24 is pivoted about the polished edge 25 from the illustrated position, wherein the metering surface 24 leans toward the crest of the bulge 120, in a clockwise direction as viewed in Fig. 3, to a position wherein the metering surface 24 passes a line extending radially of the roller 40, the minimum film thickness indicated in Fig. 4 is changed. Thus, by adjusting the angle between the metering surface 24 and a radius of the roller 40, a family of curves as illustrated in Fig. 4 will be generated as illustrated in Fig. 5.

From the foregoing it should be readily apparent that the thickness of the ink film 130 can be adjusted by rotating the metering surface 24 about the polished edge 25 or by increasing indentation of the polished edge 25 into the resilient surface 45 of the applicator roller 40.

It has also been observed that the thickness of the film 130 can be changed by varying the viscosity of the ink in the reservoir R. Thus, by adjusting the temperature of water or other suitable liquid through the tubes 7 and the passage 51 in the support bar 50, the viscosity of the ink in the reservoir R can be adjusted.

It should be noted that the minimum film thickness obtainable, as a result of adjusting the angular relationship between the metering surface 24 and a radius of the roller 40 may result in completely removing ink from the surface of the roller 40 prior to the point at which the film thickness begins to increase.

Thus, to prevent damage to the surface of the roller 40, the ink film thickness should be observed while adjustments are being made.

When the film 130 becomes very thin, the applicator roller 40 should be stopped while the force urging the polished edge 25 into pressure-indented relation with the roller 40 is increased. After the force has been increased sufficiently to pass through the minimum film thickness threshold, the roller 40 can be rotated without fear of loss of lubricating qualities of the film 130.

Fig. 6 diagrammatically illustrates the phenomenon hereinbefore discussed, which results in increasing uniformity of colour density of the ink on a printed sheet as the force resiliently urging the edge 25 into pressure-indented relation with the surface 45 of the roller 40 is increased.

As hereinbefore described in the remarks relating to Fig. 9 of the drawings, colour density of ink printed on a sheet was measured at points over the surface of the sheet. Maximum and minimum colour density readings were recorded. Sheets were selected which were printed with different loads applied to the edge 25 on the metering member 10.

It will be noted that the variation in colour density between the maximum and minimum on a sheet decreased as force urging the polished edge 25 into pressure-indented relation with the resilient cover 44 of the roller 40 was increased, as indicated by the length of lines D1, D2, D3 and D4 in Fig. 6.

It will be appreciated that when the force urging the edge 25 into pressure-indented relation with the surface 45 was increased, the metering member 10, being a cantilever beam, was deflected; the resilient cover 44 on the roller 40 was deflected or indented; and the edge 25 was deformed slightly along the length thereof such that the edge 25 and the surface 45 of the roller 40 immediately adjacent thereto were conformed, even though the edge 25 and the surface of the roller 40, when positioned in kissing contact, did not perfectly conform.

Thus, deflection of the metering member 10, deflection of the edge 25 along the length thereof, and indentation of the cover 44 all contribute to attaining the proper ink film thickness and uniformity of colour density over the surface of a printed sheet.

Referring to Figs. 4 and 6 of the drawings, it will be noted that the ink film thickness decreases to a minimum and then begins to increase as the force urging the edge 25 into pressure-indented relation with the roller surface 45 is increased. Thus, the same ink film thickness is achieved at two different points on the curve. However, as indicated by the difference in the lengths of lines D2 and D4 in Fig.

6 of the drawings, variation in colour density is different at the two points on the curve.

Referring to Fig. 7 of the drawings, a dial indicator was attached to the support bar 50 and positioned in engagement with the upper surface 19 adjacent the metering surface 24 of the metering member 10. As the applicator roller 40 was rotated, a total dial indicator reading of 0.0006 inches (0.0152 mm) was observed. This indicated that the runout in the radius of the surface of the roller 40 was 0.0003 inches (0.0076 mm) and that edge 25 on metering member 10 moved 0.0006 inches (0.0152 mm) upon each revolution of the roller 40. As the surface speed of the roller 40 was increased, the magnitude of movement of the edge 25 remained substantially the same at different surface speeds of the roller 40. How ever, the total deflection of the metering mem ber 10 increased somewhat as the surface speed of the roller 40 increased. Thus, the polished edge 25 on the metering member 10 automatically moves relative to the axis C of the applicator roller 40 upon each revolution of the applicator roller 40 and in response to changes in speed of the applicator roller 40.

Referring to Fig. 8 of the drawings, it will be noted that ink film thickness remained sub stantially constant over a broad speed range and therefore is substantially independent of the surface speed of the applicator roller 40.

As hereinbefore described, the edge 25 of the metering member 10 automatically moves radially as the applicator roller 40 rotates.

However, the metering member 10 is positioned such that the metering surface 24 and the polished edge 25 are rigidly supported in a tangential direction. It will be noted that the force imparted to the metering surface 24, as a result of ink impinging thereagainst, is directed substantially tangentially of the appli cator roller 40 and the metering member 10 is angularly positioned such that it is very stiff in a direction generally tangential to the appli cator roller 40.

While it is necessary that the metering mem ber 10 should be positioned resiliently to urge the edge 25 in a radial direction, the metering member 10 must be of sufficient thickness to permit formation of the metering surface 24 and the polished edge 25 thereon. The metering member 10 should not be too thin because, when compressive force is exerted in a plane of a thin plate, it will tend to buckle and dis tort in much the same manner as a long thin axially-loaded column.

The colour density of ink printed onto a sheet was measured using a "SOS--40" digital reflection densitometer, commercially available from CONSAR Corporation of Garland, Texas. The colour density readings of process yellow longitudinally and transversely of the printed sheet are indicated in Fig. 10 of the drawings. It will be noted that lateral colour control is within a very tight range and that longitudinal control is also very tight. Other process colours; namely magenta, cyan and black were measured with equally good colour control.

The data diagrammatically illustrated in Fig. 10 of the drawings indicates that a uniform film is being metered by the metering member 10 onto the surface 45 of the applicator roller 40.

It has been observed that the power required for driving a printing press having the inking system hereinbefore described is not significantly different from the power required for driving printing presses equipped with conventional inkers. However, as hereinbefore explained, any ghosted image on the surface of the applicator roller 40 which is moving from the plate P' toward the entrance side of the reservoir R is completely erased and a fresh film of ink is metered and offered to the printing plate P' upon each revolution of the applicator roller 40. Thus, ghosting is eliminated. Further, the metering member 10 constructed and supported as hereinbefore described is capable of metering a film which is sufficiently thin and sufficiently uniform for inking the printing plate to provide very high quality multi-colour printing. Colour density can be changed immediately by merely adjusting the position of the stop screw 74, which is remotely controlled.

The metering edge 25 on the metering mem ber 10, when properly formed, causes lint and other foreign matter in the ink to be rejected from the orifice formed between the metering member 10 and the surface of the applicator roller 40. To accomplish this function, the load or metering surface 24 toward which the roller surface 45 is moving plays an important roll. The metering surface 24 forms, above the edge 25, a barrier against which the excess ink on the applicator roller 40 impinges, creating an area of turbulence as hereinbefore described.

Since the area of high pressure is formed immediately prior to movement of the ink past the polished edge 25, lint and foreign matter will tend to be rejected from this area if a low pressure path is provided in the reservoir R.

The reservoir R is preferably at atmospheric pressure.

It has been observed that so long as the metering surface 24 is maintained in a position within about 30 degrees either side of a radius of the roller 40 which passes through the polished edge 25, lint and foreign matter is not significantly collected adjacent the polished edge 25. However, the tendency for foreign matter to collect adjacent the edge 25 increases as the metering surface 24 is moved in a direction toward the crest of the bulge 120. Thus, the metering surface 24 is also maintained at an angle to maintain an area of turbulence in the reservoir R adjacent thereto. It is further noted that creation of the abrupt surface 24, substantially radially, prevents formation of hydrokinetic or hydrodynamic forces which would create a hydraulic pressure wedge which would tend to lift the polished edge 25 and thereby cause the thickness of the ink film 130 to be changed as the surface speed of the roller 40 changes. Thus, the edge 25 is hydrostatically supported by ink carried by the roller surface 45.

It will further be appreciated that other and further embodiments of the invention may be devised without departing from the scope of the invention as defined by the following

Claims

claims. WHAT I CLAIM IS:-

1. Liquid metering apparatus comprising a roller having a resilient outer surface and means operative, upon rotation of the roller, for forming, from a liquid film of irregular thickness carried by the roller, a thin liquid film of uniform thickness, said means comprising a metering member pressed substantially radially inwards of the roller characterised in that said metering member has a metering edge and a trailing edge and presents, to the irregular liquid film, a substantially fiat metering surface on the metering member adjacent the metering edge, and is pressed so that both the metering edge and the trailing edge are indented into the resilient roller surface.

2. Apparatus as claimed in claim 1 wherein the metering edge is indented mto the roller surface by a distance which is equal to or greater than the distance by which the trailing edge is so indented.

3. Apparatus as claimed in claim 1 or 2 characterised in that the metering edge is provided by the intersection between the metering surface and a support surface which confronts the resilient outer surface of the roller, and the trailing edge is provided by the intersection between the support surface and a further surface of the metering member.

4. Apparatus as claimed in claim 1, 2 or 3 characterised in that the metering member is carried by support means which permits adjustment of the angular relationship of the metering member relative to the roller, thereby to vary the relative amounts by which the metering edge and trailing edge are indented into the roller.

5. Apparatus as claimed in claim 4 characterised in that the support means includes adjustment means permitting adjustment of the extent of indentation of the metering member into the outer surface of the roller.

6. Apparatus as claimed in any preceding claim characterised in that the metering surface lies in a plane which intersects at an angle of less than 30 , a plane which is radially disposed relative to the roller and passes through the metering edge.

7. Apparatus as claimed in any preceding claim characterised in that the metering member is flexible.

8. Apparatus as claimed in claim 3 or any of claims 4 to 7 when appendant to claim 3, characterised in that the metering member is in the form of a strip having a front surface which constitutes the metering surface and, spaced away from the front surface, a recess of which a surface close to the front surface constitutes the said further surface of the metering member.

9. Apparatus as claimed in any preceding claim wherein the roller is an ink-applying roller in a printing machine and the liquid is printing ink.

10. Apparatus as claimed in claim 9 wherein the ink-applying roller applies ink directly to a printing plate.

11. Liquid metering apparatus substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

12. A method of metering liquid in liquid metering apparatus, which comprises supplying the liquid as a film of irregular thickness to the outer surface of a roller, which outer surface is resilient, rotating said roller, and pressing a metering member substantially radially inwards of said roller so that a metering edge and a trailing edge of said metering member are indented into said resilient outer surface of the roller, and a substantially fiat metering surface adjacent said metering edge is presented to the liquid film of irregular thickness.

13. A method as claimed in claim 12 where in the metering member is pressed towards the said resilient surface so that metering edge is indented therein by an amount equal to or to a greater extent than the trailing edge.

14. A method as claimed in claim 12 or 13 characterised in that the pressure between said metering member and the roller surface is increased relative to the pressure at which a given or desired thickness of liquid film is first obtained.

15. A method as claimed in claim 14 characterised in that the pressure between said metering member and said roller surface is further increased when the given or desired thickness of the liquid film is obtained until the thickness of said film has passed a minimum value and has obtained again the given or wanted thickness.

16. A method as claimed in any of claims 12 to 15, characterised in that the viscosity of the liquid carried on the roller surface is controlled.

17. A method as claimed in claim 16, characterised in that the viscosity is controlled by temperature control.

18. A method as claimed in claim 14 or 15, characterised in that the temperature of the liquid is controlled.

19. A method as claimed in any of claims 12 to 18 wherein the roller is an ink-applying roller in a printing machine and the liquid is ink.

20. A method as claimed in claim 19 wherein the ink-applying roller applies ink directly to a printing plate.

21. A method of metering liquid in liquid metering apparatus, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.