DOCTOR

Abstract

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).

Claims

1. A doctor blade comprising: a doctor blade edge; a doctor blade body; and a curved blade profile which is formed between the doctor blade edge and the doctor blade body, wherein a) the curved blade profile has a square or cuboidal course f(x) from the doctor blade edge to the doctor blade body, and/or b) the curved blade profile has a course f(x), from the doctor blade edge to the doctor blade body, having at least one turning point.

2. A doctor blade according to claim 1, wherein 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 (20) having a thickness s at the doctor blade edge and a thickness t at the doctor blade body:
f=ax.sup.3+bx.sup.2+cx+d, wherein the following applies for the constants a, b, c, d: a) (a and b and c)0, (a or b)>0 and d=st, or b) (a and c)>0, b<0 and d=st.

3. A doctor blade according to claim 2, wherein, for the cuboidal course f(x) of the curved blade profile, the following applies for the constants a, b, and c: 0.000485a0.0021953, 3.33158b4.545127, and 1.468371c25.0128.

4. A doctor blade according to claim 2, wherein for the cuboidal course f(x) of the curved blade profile, the following applies for the constants a, b, and c: 0.00068a0.00158, 3.3321b4.5416, and 10.19478c10.2501.

5. A doctor blade according to claim 2, wherein, for the square course f(x) of the curved blade profile, the following applies for the constants a, b, and c: a=0, 3.335997b4.565214, and 1.457449c25.96338.

6. A doctor blade according to claim 2, wherein, for the square course of the curved blade profile, the following applies for the constants a, b, and c: a=0, 3.33829b4.55603, and 10.017947c10.21459.

7. A doctor blade according to claim 2, wherein the following applies for the thickness s of the doctor blade at the doctor blade edge and the thickness t of the doctor blade at the doctor blade body: 60 ms125 m and 150 mt200 m.

8. A doctor blade according to claim 1, wherein the doctor blade is manufactured from a ground steel strip.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In the drawings:

[0051] FIG. 1a is a schematic view of a state of the art printing mechanism of an intaglio printing press showing a mode of operation of a doctor blade;

[0052] FIG. 1b includes schematic views a), b) and c) showing states of a state of the art doctor blade;

[0053] FIG. 1c includes schematic view a) showing a state of the art doctor blade and view b) showing the same doctor blade with an edge pressed onto the surface of the printing cylinder;

[0054] FIG. 2a is a perspective view of a doctor blade according to the invention;

[0055] FIG. 2b is a plan view of the doctor blade of FIG. 2a;

[0056] FIG. 2c is a cross-sectional view of the doctor blade of FIG. 2a;

[0057] FIG. 3a and FIG. 3b are views in each case showing a doctor blade having a cuboidal course of the curved blade profile according to the invention;

[0058] FIG. 4a and FIG. 4b are views in each case showing a doctor blade having a square course of the curved blade profile; and

[0059] FIG. 5 shows a doctor blade having a curved blade profile which has a turning point.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0060] Referring to the drawings, FIG. 2a is a perspective view of a specific embodiment of a doctor blade 20 according to the invention. The doctor blade 20 consists of a ground steel strip and has a doctor blade edge 21 which 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 edge 21 having an inclination relative to the horizontal is always shown. For detachably fastening the doctor blade 20 to a holder (not shown), the doctor blade 20 has a doctor blade body 22, on the side opposite the doctor blade edge 21, which body is delimited by two flat surfaces, specifically the doctor blade upper side 23 and the doctor blade underside 24. A curved blade profile 25 which has a square or cuboidal course extends between the doctor blade edge 21 and the doctor blade body 22. Doctor blades 20 of this kind typically have a length L.sub.3 of 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 blades 20 of this kind typically, depending on the application, have a width L.sub.4 of 80 mm to 4000 mm.

[0061] FIG. 2b is a plan view of a doctor blade 20 of this kind, comprising the doctor blade edge 21, the curved blade profile 25 and the doctor blade body 22.

[0062] FIG. 2c is a cross-sectional view of the doctor blade 20 which has the thickness s at its doctor blade edge 21 and the thickness tin the region of the doctor blade body 22. The curved blade profile 25 of length L.sub.5, which, in the embodiment of the present embodiment that is shown, has either a square or a cuboidal course, extends between the doctor blade edge 21 and the doctor blade body 22.

[0063] 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 profile 25, 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 blade 20 at the doctor blade edge 21 thereof, and the thickness t of the doctor blade 20 at the doctor blade body 22 thereof, which can be selected depending on the requirements. In each case, a specific embodiment of the square and cuboidal course of the doctor blade 20 are shown in FIGS. 3a, b and 4a, b, wherein FIG. 3a, b show a square course f(x) and FIG. 4a, b show a cuboidal course f(s) of the curved blade profile 25. In all the embodiments show, for the sake of simplicity uniform thicknesses s, t of the doctor blade 20 at its doctor blade edge 21 and its doctor blade body 22 are assumed. Furthermore, the course f(x) of the curved blade profile 25, represented functionally in each case, relates to a doctor blade 20, the doctor blade edge 21 of which, at the transition to the ground region of the blade profile 25, is located on the y-axis of a cartesian coordinate system, and the doctor blade upper side 23 of which coincides with the x-axis of the coordinate system.

[0064] Proceeding herefrom, FIG. 3a shows 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, f.sub.1(x) represents the square course f(x) of the curved blade profile 25, for which the following applies: a=0, b=4.565214, c=25.96338, s=70 m a=and t=200 m.

[0065] f.sub.2(x) represents the square course f(x) of the curved blade profile 25, for which the following applies: [0066] a=0, b=3.335997, c=1.457449, s=70 m and t=200 m.

[0067] FIG. 3b shows 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 profile 25. According thereto, f.sub.3(x) represents the square course f(x) of the curved blade profile 25, for which the following applies: [0068] a=0, b=4.55603, c=10.21459, s=70 m and t=200 m.

[0069] Within the context of the preferred embodiment, f.sub.4(x) represents the square course f(x) of the curved blade profile 25, for which the following applies: [0070] a=0, b=3.33829, c=10.017947, s=70 m and t=200 m.

[0071] In a similar manner, FIG. 4a, b show a specific embodiment of a doctor blade 20 according to the invention, in the case of which a cuboidal course of the curved blade profile 25 is provided. Specifically, FIG. 4a, b in 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, f.sub.5(x) represents the cuboidal course f(x) of the curved blade profile 25, for which the following applies: [0072] a=0.0021953, b=4.545127, c=25.0128, s=70 m and t=200 m.

[0073] f.sub.6(x) represents the cuboidal course f(x) of the curved blade profile 25, for which the following applies: [0074] a=0.000485, b=3.33158, c=1.468371, s=70 m and t=200 m.

[0075] FIG. 4b shows 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 profile 25. According thereto, f.sub.7(x) represents the cuboidal course f(x) of the curved blade profile 25, for which the following applies: [0076] a=0.00158, b=4.5416, c=10.2501, s=70 m and t=200 m.

[0077] Within the context of the preferred embodiment, f.sub.8(x) represents the cuboidal course f(x) of the curved blade profile 25, for which the following applies: [0078] a=0.00068, b=3.3321, c=10.19478, s=70 m and t=200 m.

[0079] Within the context of specific embodiments of the present invention, variations of the thickness s of the doctor blade 20 at the doctor blade edge 21 and the thickness t of the doctor blade 20 at the doctor blade body 22 are provided in such a way that 60 ms125 m and 150 mt200 m applies. Proceeding herefrom, curved blade profiles 25 having a square or cuboidal course f(x) result, wherein lengths L.sub.5 of the blade profile 25 between 0.8 mm and 4.9 mm can be specified.

[0080] Finally, FIG. 5 shows a doctor blade 20 having a curved blade profile 25 between the doctor blade edge 21 and the doctor blade body 22, wherein the course f(x) has a turning point 26. The turning point 26 is the intersection point of a first region L.sub.61 and a second region L.sub.62 of the curved blade profile 25, wherein the first region L.sub.61 has a right-hand curvature, proceeding from the doctor blade edge 21, and the second region L.sub.62 has a left-hand curvature. In other words, a tangent applies to the curved blade profile 25 changes sides at the turning point 26. In the embodiment shown, the gradient of the curved blade profile 25 vanishes at the turning point 26, such that the turning point 26 coincides with a saddle point. Specifically, the following applies at the turning point 26: f(x)=f(x)=0. Alternatively thereto, embodiments (not shown) are also provided in which the course f(x) of the curved blade profile 25 has a positive gradient at the turning point 26.

[0081] The region L.sub.62, i.e. the region between the turning point 26 and the doctor blade body 22, has a course f(x), as has been described above in connection with a doctor blade 20, 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 L.sub.61. Therefore, at the turning point 26 the doctor blade 20 has a thickness s. In this case, the turning point 26 is located within the front half of the blade profile, as a result of which the following applies: L.sub.61L.sub.62. As a result, a doctor blade 20 having a turning point 26 has a doctor blade edge having a comparatively small thickness s*. Specifically, the following applies for s*: 40 ms*s.

[0082] The course f*(x) in the region L.sub.61 follows 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:

f*(x)a*x.sup.3+b*x.sup.3+c*x+ts*.

[0083] In this case, the following applies: [0084] a*>a, b*0, 0<c*100, 150 mt200 m and 40 ms*<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*x.sup.3+b*x.sup.3+c*x+ts*.

[0085] In this case, the following applies: [0086] a*=0, b*<0, 0<c*100, 150 mt200 m and 40 ms*<s.

[0087] While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.

REFERENCE CHARACTERS

[0088] 1 intaglio printing press [0089] 2 printing cylinder [0090] 3 dye bath [0091] 4 doctor blade device [0092] 5 doctor blade holder [0093] 6 doctor blade (prior art) [0094] 61 doctor blade (prior art) [0095] 62 doctor blade (prior art) [0096] 7 support doctor blade [0097] 8 impression cylinder [0098] 9 paper web [0099] 10 direction of rotation [0100] 11 doctor blade edge [0101] 12 blade profile [0102] 13 doctor blade body [0103] 14 doctor blade underside [0104] 20 doctor blade [0105] 21 doctor blade edge [0106] 22 doctor blade body [0107] 23 doctor blade upper side [0108] 24 doctor blade underside [0109] 25 blade profile [0110] 26 turning point [0111] a, a* constant [0112] b, b* constant [0113] c, c* constant [0114] d constant [0115] F force direction [0116] s, s* thickness of the doctor blade at the doctor blade edge [0117] t thickness of the doctor blade at the doctor blade body [0118] d.sub.1,2 thickness of the doctor blade in the region of the blade profile [0119] R radius [0120] L.sub.1,2 width of the contact surface [0121] L.sub.3 doctor blade length [0122] L.sub.4 doctor blade width [0123] L.sub.5 length of the blade profile [0124] L.sub.61 region of the blade profile having a right-hand curvature [0125] L.sub.62 region of the blade profile having a left-hand curvature [0126] f(x), f*(x) course of the blade profile