DOCTOR

A doctor (20), in particular for printing cylinders and coating systems, includes a doctor edge (21), a doctor body (22), and a curved blade profile (25) which is formed between the doctor edge (21) and the doctor body (22). In order to produce a doctor (20) which reduces the maintenance requirements of a gravure, flexographic, offset and/or digital printing machine and increases the service life of a doctor (20), according to the invention the extension of the curved blade profile (25) from the doctor edge (21) to the doctor body (22) is square or cuboid and/or the extension of the curved blade profile (25) from the doctor edge (21) to the doctor body (22) has at least one turning point (26).

TECHNICAL FIELD

The present invention relates to a doctor blade, in particular for printing cylinders and coating systems, comprising a doctor blade edge, a doctor blade body, and a curved blade profile that is formed between the doctor blade edge and the doctor blade body.

BACKGROUND

Doctor blades of the type in question are known in particular for intaglio, flexographic, offset and digital printing presses.FIG.1ashows, by way of example, in order to explain the mode of operation of a doctor blade, a schematic view of a printing mechanism of an intaglio printing press1. In the intaglio printing method, elements to be imaged are introduced as depressions, known as wells, into the surface of a printing cylinder2, which rotates within a dye bath3and there absorbs ink on the entire surface. By means of a doctor blade device4which is arranged downstream in a direction of rotation10and has a doctor blade holder5, a doctor blade6held therein, and an (optional) support doctor blade7, excess ink is scraped or wiped off the surface of the printing cylinder2, such that the ink remains only in the wells of the printing cylinder2. The ink remaining in the wells is subsequently transferred onto a paper web9which is guided, for this purpose, between the printing cylinder2and a counterrotating impression cylinder8. Viewed in the direction of rotation10of the printing cylinder2, the printing cylinder2subsequently absorbs ink in the dye bath3again, and a continuous printing process results.

In order to carry out the mentioned printing methods, typically doctor blades are used which are designed as a steel strip that is ground in the manner of a knife.FIG.1b, cshow, by way of example, two different doctor blades that are known according to the prior art, in each case during use as intended and in the unloaded state.

FIG.1bshows, in partial figure a), a doctor blade61in the unloaded state, the blade profile12of which, proceeding from the doctor blade edge11, initially has a linear portion which transitions, via a circular portion of radius R, into the doctor blade body13. The doctor blade edge11is inclined by an angle of approximately 70° relative to the linear upper face of the blade profile12. During scraping, the doctor blade61according to partial figure b) is pressed, by the doctor blade edge11thereof, onto the printing cylinder2in the force direction F, such that a contact surface of width L1results. On account of the rotating printing cylinder2, the doctor blade61is deflected, at the doctor blade edge11thereof, by an amount in the direction of rotation10of the printing cylinder2, such that a bending stress acts on the doctor blade61. It has been found in practice that doctor blades61of this kind tend, with increasing wear and the resultant increasing bending stress, to rest tangentially on the surface of the printing cylinder2, as is shown in partial figure c), which results, however, in a comparatively wider contact surface L2and a reduction in the line pressure with which the doctor blade61presses on the printing cylinder2. As a result, the doctor blade61floats at least in part, and the result from the doctor blade is insufficient on account of wear, because residual ink remains, in part, on the printing cylinder2, even outside of the wells, and thus it is not possible to achieve a perfect result from the doctor blade. The service life of a doctor blade61of this kind is therefore limited, as a result of which the doctor blade61has to be changed at regular intervals, which is disadvantageously associated with labor-intensive mounting of a new doctor blade61and the maintenance-related downtime of the intaglio printing press1.

FIG.1cshows, in partial figure a), a doctor blade62which has a blade profile12having a linear gradient of approximately 2° relative to the doctor blade underside14, such that the doctor blade thickness d1, d2increases as the distance from the doctor blade edge11increases. During use as intended of a doctor blade62of this kind (cf. partial figure b), the doctor blade edge11is pressed onto the surface of the printing cylinder2. As the wear increases, the specific line pressure decreases on account of the increasing contact surface, as a result of which, in the case of this doctor blade geometry too, the result from the doctor blade is unsatisfactory on account of wear, and the doctor blade62has to be changed in order to still achieve a perfect result from the doctor blade. The disadvantages discussed above, with regard to the maintenance work required due to wear, result in the case of the doctor blade62according toFIG.1c, too.

Doctor blades of the type in question are furthermore used in coating systems, in order, for example, to apply hot or cold seal adhesives in thin layers to paper, cardboard packaging, or films.

SUMMARY

Proceeding herefrom, the object of the present invention is that of providing a doctor blade which reduces the maintenance outlay for an intaglio printing press, flexographic printing press, offset printing press, digital printing press, and/or a coating system, and increases the service life of a doctor blade.

This object is achieved by the doctor blade according to the invention. According to the invention, it is first provided that the curved blade profile has a square or cuboidal course from the doctor blade edge to the doctor blade body. In particular, this is intended to mean a course in which the thickness of the doctor blade increases in a square or cuboidal manner from the doctor blade edge to the doctor blade body. Due to this special doctor blade geometry, in particular in the region of the curved blade profile, a substantially constant line pressure which is independent of wear is achieved, because the change in the bending of the blade profile and the associated change in the bending stress compensates the change in the contact surface between the doctor blade and the printing cylinders, and thus the doctor blade edge. This leads to a constant and perfect result from the doctor blade, which is as far as possible independent of the wear of the doctor blade, which is directly apparent from a reduced maintenance outlay for a printing machine and a longer service life of a doctor blade of this kind.

Alternatively, and/or in addition it is provided according to the invention that the curved blade profile has a course from the doctor blade edge to the doctor blade body which has at least one turning point. In this case, the turning point can coincide with a point of the course at which the course has a positive or a negative gradient, or at which the gradient disappears, such that the turning point simultaneously forms a saddle point. In particular a region having a (slightly) falling gradient between the turning point and the doctor blade body, and thus having a (slight) thickness increase in the curved blade profile results in a reduced warm-up time, i.e. the time in which the contact with the printing cylinder transitions from punctual to areal resting, on account of the wear.

Preferred embodiments of the present invention are specified below and in the dependent claims.

Within the context of a first advantageous embodiment of the present invention, it is provided that the following applies for the course f(x) of the curved blade profile, from the doctor blade edge to the doctor blade body, of the doctor blade having a thickness s at the doctor blade edge and a thickness t at the doctor blade body:

In this case, within the context of a first preferred embodiment the following applies for the constants a, b, c, d:(a and b and c)≥0, (a orb)>0 and d=s−t.

In other words, the constants a, b and c are in each case greater than or equal to zero, wherein at least one of the constants a orb must be “much greater” than zero. In this respect, the course f(x) of the curved blade profile has at least one portion, between the doctor blade edge and the doctor blade body, which increases in a square or cuboidal manner. In this case, here and in the following the functionally represented course f(x) of the curved blade profile relates to a doctor blade, the doctor blade edge of which, at the transition to the ground region of the blade profile, is located on the y-axis of a cartesian coordinate system, and the doctor blade upper side of which coincides with the x-axis of the coordinate system.

Alternatively, the following applies for the constants a, b, c and d:(a and c)>0, b<0 and d=s−t.

On account of the negative constant b, the turning point of the course f(x) shifts into the positive half plane (x>0), and thus into the region between the doctor blade edge and the doctor blade body. This results in the advantages of the curved blade profile already mentioned above.

The above-described range limits for the constants a, b, c and d lead, depending on magnitude, to different courses of the curved blade profile, which will be discussed in the following only by way of example.

Fora>0, b=0, c=0 and d=s−t, ora>0, b>0, c=0 and d=s−t
a course of the curved blade profile that rises in a cuboidal manner results, wherein the gradient vanishes at the doctor blade edge. In other words, the blade profile is oriented in parallel with the doctor blade underside, in the region of the doctor blade edge, and a grinding angle at the doctor blade edge of 0° results.

Fora>0, b=0, c>0 and d=s−t, ora>0, b>0, c>0 and d=s−t
a course of the curved blade profile that rises in a cuboidal manner results, having a positive gradient at the doctor blade edge. In this case, the grinding angle at the doctor blade edge is >0°.

For a=0, b>0, c=0 and d=s−t, a course of the curved blade profile that rises in a square manner, having a vanishing gradient at the doctor blade edge results, due to which the grinding angle in the region of the doctor blade edge is 0° within the context of this embodiment too.

If the following are selected for the constants a=0, b>0, c=0 and d=s−t, a course of the curved blade profile that rises in a square manner, having a positive grinding angle at the doctor blade edge, results.

In the following, in each case embodiments having specific range information for the constants a, b and c are described.

Within the context of a preferred embodiment of the present invention, in the case of a cuboidal course f(x) of the curved blade profile, the following is provided for the constants a, b, and c:0.000485≤a≤0.0021953,3.33158≤b≤4.545127, and1.468371≤c≤25.0128.

In the case of a cuboidal course f(x) of the curved blade profile, the following preferably applies for the constants a, b, and c:0.00068≤a≤0.00158,3.3321≤b≤4.5416, and10.19478≤c≤10.2501.

In the case of a square course f(x) of the curved blade profile, within the context of an advantageous embodiment the following applies for the constants a, b, and c:a=0,3.335997≤b≤4.565214, and1.457449≤c≤25.96338.

Within the context of a particularly preferred embodiment of the invention, in the case of a square course f(x) of the curved blade profile, the following is provided for the constants a, b, and c:a=0,3.33829≤b≤4.55603, and10.017947≤c≤10.21459.

Within the context of the preferred embodiments of the curved blade profile discussed above, in each case only the constants a, b and c are discussed, which describe the change of the thickness of the curved blade profile from the doctor blade edge to the doctor blade body. The thicknesses s, t of the doctor blade both at the doctor blade edge and at the doctor blade body can be selected depending on the application, wherein preferably the following applies for the constants s, t:60 μm≤s≤125 μm and150 μm≤t≤200 μm.

In all cases, the doctor blade is preferably manufactured from a ground steel strip. Alternatively, the doctor blade can consist of a different metal, a metal alloy, aluminum or of plastics material, such as polyester.

Specific embodiments of the doctor blade according to the invention are explained in the following with reference toFIGS.2ato5. The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to the drawings,FIG.2ais a perspective view of a specific embodiment of a doctor blade20according to the invention. The doctor blade20consists of a ground steel strip and has a doctor blade edge21which is inclined by approximately 70° with respect to a horizontal and is designed to rest on a rotating printing cylinder (not shown). Alternatively to an inclination of the doctor blade edge of approximately 70°, the doctor blade edge can also be curved. In this connection, a concave curved shape, in particular having a constant radius of curvature, has proven particularly advantageous. However, for the sake of simplicity, here and in the drawings a doctor blade edge21having an inclination relative to the horizontal is always shown. For detachably fastening the doctor blade20to a holder (not shown), the doctor blade20has a doctor blade body22, on the side opposite the doctor blade edge21, which body is delimited by two flat surfaces, specifically the doctor blade upper side23and the doctor blade underside24. A curved blade profile25which has a square or cuboidal course extends between the doctor blade edge21and the doctor blade body22. Doctor blades20of this kind typically have a length L3of 20 mm to 60 mm and are wound onto transportable coils of up to 100 m. In the state when cut to length, and thus mountable, doctor blades20of this kind typically, depending on the application, have a width L4of 80 mm to 4000 mm.

FIG.2bis a plan view of a doctor blade20of this kind, comprising the doctor blade edge21, the curved blade profile25and the doctor blade body22.

FIG.2cis a cross-sectional view of the doctor blade20which has the thickness s at its doctor blade edge21and the thickness tin the region of the doctor blade body22. The curved blade profile25of length L5, which, in the embodiment of the present embodiment that is shown, has either a square or a cuboidal course, extends between the doctor blade edge21and the doctor blade body22.

The region limits for the constants a, b, c and d lead, both within the context of the square course and within the context of the cuboidal course of the curved blade profile25, to the possible courses forming a family of curves, wherein the family of curves is limited by a first curve having the smallest possible values in each case for the constants a, b and c, and a second curve having the largest possible values in each case for the constants a, b and c. The constant d merely brings about a shift of the y-axis portion, and is dependent on the thickness s of the doctor blade20at the doctor blade edge21thereof, and the thickness t of the doctor blade20at the doctor blade body22thereof, which can be selected depending on the requirements. In each case, a specific embodiment of the square and cuboidal course of the doctor blade20are shown inFIGS.3a, band4a, b, whereinFIG.3a, bshow a square course f(x) andFIG.4a, bshow a cuboidal course f(s) of the curved blade profile25. In all the embodiments show, for the sake of simplicity uniform thicknesses s, t of the doctor blade20at its doctor blade edge21and its doctor blade body22are assumed. Furthermore, the course f(x) of the curved blade profile25, represented functionally in each case, relates to a doctor blade20, the doctor blade edge21of which, at the transition to the ground region of the blade profile25, is located on the y-axis of a cartesian coordinate system, and the doctor blade upper side23of which coincides with the x-axis of the coordinate system.

Proceeding herefrom,FIG.3ashows two mutually spaced course f(x), shown in dashed lines, which represent the outer limit regions of the constants a, b and c. According thereto, f1(x) represents the square course f(x) of the curved blade profile25, for which the following applies: a=0, b=4.565214, c=25.96338, s=70 μm a=and t=200 μm.

f2(x) represents the square course f(x) of the curved blade profile25, for which the following applies:a=0, b=3.335997, c=1.457449, s=70 μm and t=200 μm.

FIG.3bshows a particularly preferred partial range of the values for the constants a, b, c, s and t within the context of a square course f(x) of the curved blade profile25. According thereto, f3(x) represents the square course f(x) of the curved blade profile25, for which the following applies:a=0, b=4.55603, c=10.21459, s=70 μm and t=200 μm.

Within the context of the preferred embodiment, f4(x) represents the square course f(x) of the curved blade profile25, for which the following applies:a=0, b=3.33829, c=10.017947, s=70 μm and t=200 μm.

In a similar manner,FIG.4a, bshow a specific embodiment of a doctor blade20according to the invention, in the case of which a cuboidal course of the curved blade profile25is provided. Specifically,FIG.4a, bin each case show two mutually spaced courses f(x), shown in dashed lines, which represent the outer limit regions of the constants a, b and c. According thereto, f5(x) represents the cuboidal course f(x) of the curved blade profile25, for which the following applies:a=0.0021953, b=4.545127, c=25.0128, s=70 μm and t=200 μm.

f6(x) represents the cuboidal course f(x) of the curved blade profile25, for which the following applies:a=0.000485, b=3.33158, c=1.468371, s=70 μm and t=200 μm.

FIG.4bshows a particularly preferred partial range of the values for the constants a, b, c, s and t within the context of a cuboidal course f(x) of the curved blade profile25. According thereto, f7(x) represents the cuboidal course f(x) of the curved blade profile25, for which the following applies:a=0.00158, b=4.5416, c=10.2501, s=70 μm and t=200 μm.

Within the context of the preferred embodiment, f8(x) represents the cuboidal course f(x) of the curved blade profile25, for which the following applies:a=0.00068, b=3.3321, c=10.19478, s=70 μm and t=200 μm.

Within the context of specific embodiments of the present invention, variations of the thickness s of the doctor blade20at the doctor blade edge21and the thickness t of the doctor blade20at the doctor blade body22are provided in such a way that 60 μm≤s≤125 μm and 150 μm≤t≤200 μm applies. Proceeding herefrom, curved blade profiles25having a square or cuboidal course f(x) result, wherein lengths L5of the blade profile25between 0.8 mm and 4.9 mm can be specified.

Finally,FIG.5shows a doctor blade20having a curved blade profile25between the doctor blade edge21and the doctor blade body22, wherein the course f(x) has a turning point26. The turning point26is the intersection point of a first region L61and a second region L62of the curved blade profile25, wherein the first region L61has a right-hand curvature, proceeding from the doctor blade edge21, and the second region L62has a left-hand curvature. In other words, a tangent applies to the curved blade profile25changes sides at the turning point26. In the embodiment shown, the gradient of the curved blade profile25vanishes at the turning point26, such that the turning point26coincides with a saddle point. Specifically, the following applies at the turning point26: f′(x)=f″(x)=0. Alternatively thereto, embodiments (not shown) are also provided in which the course f(x) of the curved blade profile25has a positive gradient at the turning point26.

The region L62, i.e. the region between the turning point26and the doctor blade body22, has a course f(x), as has been described above in connection with a doctor blade20, which has a square or cuboidal course f(x). However, the course f(x) is shifted in the positive x-direction by the length of the region L61. Therefore, at the turning point26the doctor blade20has a thickness s. In this case, the turning point26is located within the front half of the blade profile, as a result of which the following applies: L61≤L62. As a result, a doctor blade20having a turning point26has a doctor blade edge having a comparatively small thickness s*. Specifically, the following applies for s*: 40 μm≤s*≤s.

The course f*(x) in the region L61follows a cuboidal shape or a square shape that is open at the bottom. In the case of a cuboidal shape, the course f*(x) can be described generally by:

In this case, the following applies:a*>a, b*≤0, 0<c*≤100, 150 μm≤t≤200 μm and 40 μm≤s*<s. In the case of a shape that is open at the bottom, the course f*(x) can be described generally by: f*(x)≤a*x3+b*x3+c*x+t−s*.

REFERENCE CHARACTERS

1intaglio printing press2printing cylinder3dye bath4doctor blade device5doctor blade holder6doctor blade (prior art)61doctor blade (prior art)62doctor blade (prior art)7support doctor blade8impression cylinder9paper web10direction of rotation11doctor blade edge12blade profile13doctor blade body14doctor blade underside20doctor blade21doctor blade edge22doctor blade body23doctor blade upper side24doctor blade underside25blade profile26turning pointa, a* constantb, b* constantc, c* constantd constantF force directions, s* thickness of the doctor blade at the doctor blade edget thickness of the doctor blade at the doctor blade bodyd1,2thickness of the doctor blade in the region of the blade profileR radiusL1,2width of the contact surfaceL3doctor blade lengthL4doctor blade widthL5length of the blade profileL61region of the blade profile having a right-hand curvatureL62region of the blade profile having a left-hand curvaturef(x), f*(x) course of the blade profile