JPH03178366A - Doctor rod for adjusting volume of coating material - Google Patents

Abstract

PURPOSE: To hold a low coating weight without damaging a roll surface by forming a doctor rod in such a manner the surfaces of projecting parts are flat and exist on one cylindrical envelope, that the sum of the surface areas of the projecting parts occupy the specific ratio of the envelope and that the molded sectional depth of the entire surface has a specific value. CONSTITUTION: The peripheral surface of the doctor rod is provided with the plural projecting parts 2 and recessed parts for the purpose of volumetric flow control of a coating material to be applied particularly on a paper web or cardboard web surface during traveling. The rod is so formed that the surfaces of the projecting parts 2 are flat and exist on the one cylindrical envelope, that the sum of the surface areas of the projecting parts 2 is 10 to 50% of the cylindrical envelope and that the molded sectional depth Pt (2.5 mm) of the entire surface by DIN 4771 has the value of 30 to 150 μm. Consequently, the low coating weight may be obtain. without line traces without the occurrence of the damage on the roll surface at the time of applying the coating material on the roll surface.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention is particularly directed to a method of applying a plurality of convex portions on the circumferential surface in order to measure the volume of a coating material to be coated on the surface of a running paper web or cardboard web. The present invention relates to a coating device for a running material web, which is equipped with a doctor rod having a recess and one doctor rod as a metering element.

BACKGROUND OF THE INVENTION It is known to use doctor rods with multiple circumferential grooves when coating moving paper or cardboard webs. Such doctor rods are used to apply a metered paint film or size film to the web surface to be coated, in which case the amount of coating material applied is determined by the groove cross section. Depends on it.

The use of the doctor rod is carried out directly along the web,
That is, either an excess amount of coating material is applied to the web surface by a pre-applying mechanism and then metered to the desired coating weight by a doctor rod, or metering is carried out on the roll surface and the coating material is then transferred from the roll. is transferred to the web in the roll gear (roll nip) section. For this purpose, the web is guided through a roll nip between two rolls, with a coating mechanism being arranged along one or both rolls and in the area of the rolls where the web is not wound. Following this, a doctor rod is placed at the rear.

A doctor rod of the type mentioned at the outset is known from German Patent Application No. 37 35 889 and German Utility Model No. 84 14 413. In the coating device disclosed in the former West German patent application publication specification, the doctor rod directly contacts the paper web, and in the latter West German registered utility model specification, the doctor rod applies a coating material film to the roll surface. From the roll the coating material is then transferred to the web surface at the roll nip.

Further, the registered utility model specification also discloses a doctor rod having a wire wrapped around its circumferential surface, but it has been found that such a doctor rod wears out more quickly than expected. Furthermore,
When metering with a rubber-coated roll surface, the roll surface may be damaged under certain operating conditions.

Furthermore, West German Patent Application No. 38 41 494 (unpublished) proposes arranging a large number of knob-like protrusions on the circumferential surface of the doctor rod. The knob-like protrusion can be formed by forming a recess in the cylindrical rod, for example by etching, milling, grinding, stamping, or the like. The knob or the entire doctor rod is molded from a low-wear material, such as hard metal, hard chromed steel, glass or oxidized ceramic material.

[Problems to be Solved by the Invention] An object of the present invention is to provide a doctor rod that can obtain a low coating weight without scratches and without causing damage to the roll surface when coating the roll surface. It is.

[Means for Solving the Problems] Constituent means of the present invention for solving the above problems include (a) the surface of the convex portion is flat and located on one cylindrical envelope surface, and (b) the surface area of the convex portion is The sum is 10 of the cylindrical envelope surface.
% to 50%, and (iii) the molded cross-sectional depth of the entire surface according to DIN 4771 has a value of 30 μm to 150 μm.

Claims 2 to 10 describe particularly advantageous configurations of the doctor rod according to the invention, and claims t1 and 12 describe a coating device using the doctor rod according to the invention as a metering element. .

The functions and effects of the present invention will be clear from the description of the following examples.

[Example] Next, embodiments of the present invention will be explained in detail based on the drawings.

The doctor rod, which is only partially shown, has a large number of recesses formed by machining material on the entire circumference of a smooth rod-shaped cylindrical base 1, and the outer surface of the doctor rod is formed by the remainder of the original cylindrical circumference. Therefore, the surface of the protrusions 2 is flat and all located on one cylindrical envelope, which is different from the original cylindrical shape. It corresponds to the outer peripheral surface of the rod. In order to obtain a wear-resistant, smooth surface of the protrusions, the doctor rod according to the invention is particularly preferably manufactured by first coating a steel rod with a wear-resistant material, in particular an oxide ceramic, and then polishing it. . Next, concave portions are formed on the surface by a laser beam, and during laser processing, the coating material on the processed portion evaporates without any residue or burrs.

It is also possible to use a rod whose metal surface has been hardened and polished, and to form a large number of recesses on the metal surface with a diamond tool or by etching. Instead of using the cutting method, a large number of convex portions are attached to the rod surface, and the surface of the convex portions is then processed by grinding, polishing, etc. so that they are flattened and positioned on one cylindrical envelope surface to obtain the desired surface. The rods, which are only partially shown in FIG.
0. ).

The sum of the surface areas of the convex parts, in other words, the area that contacts the liquid web or coating roll during coating, is 10% of the cylindrical envelope surface.
~50%. Therefore, 50% of the original peripheral area ~ 9
This means that 0% has been removed. In order to obtain an even and high-quality coating, the surface should be DIN 47 with a thickness of 30 μm to 150 μm.
71 to have a forming cross-sectional depth Pt (2.5 mm). Measurements are taken in the axial direction of the doctor rod. Within the range of the abovementioned values, the variation in the profile depth is only very steep.3 The deviation of the profile depth determined by individual measurements from the average profile depth is at most 5%. Good release of the coating material from the doctor rod is achieved when the rough surface depth Rt of the side surface of the convex portion is Pt (2,5
*z) is smaller than 10% of the value.

Advantageously, the projection 2 has an elongated shape in plan view and is oriented approximately in the circumferential direction. The circumferential length of the convex portion 2 is 1 mm to 151 mm, and the axial width is 10 μm to 100 μm.
It is particularly advantageous if m. In certain applications, it may be advantageous for the projections to be continuous in the circumferential direction. The mutual spacing a of the convex portions 2 is from 150 μm to 400 μm.

In order to achieve uniform application, it has proven particularly advantageous to vary the geometrical dimensions of the projections 2 and the arrangement of the projections 2 within predetermined limits in a randomly distributed manner. The variation width for the convex width measured in the axial direction is from 10 μm to 10
0 μm, and the variation width for the distance a between the convex portions is 150 μm to 400 μm.

For certain applications it is advantageous for the doctor rod to have a substantially circumferentially oriented elongate projection. In this case, the deviation value of the vertical axis of the convex portion from the circumferential direction, that is, the inclination angle α in FIG. 1 is 10° at the maximum. The inclination angle α of the convex portion 2 can also be varied within this angular limit in a randomly distributed manner.

Even if a coating material normally used for coating paper webs or cardboard webs is used, the open cross-sectional area created between the two protrusions on one side when a longitudinal section is taken through the center of the doctor rod is the length of the doctor rod in meters. Satisfactory coatings are obtained between 15 gm2 and 80 iI12 per coat.

Particularly advantageous fields of use for the doctor rod according to the invention are:
This is a coating device (coater) that indirectly coats a paper web with a powder or pigment via a coating roll. The coating device has two press rolls through which the paper web is guided. A known application mechanism, for example a nozzle or roll application mechanism, is arranged on one or both press rolls, which applicator has a metering system following it in the direction of rotation of the press roll, the metering system being It contains a doctor rod according to the invention as a metering element. The doctor rod is supported in an elastic doctor holder and is driven in a direction opposite to the press roll. This type of coating equipment is registered as a West German utility model no. 8.
4 14 413 in detail. A particularly advantageous doctor holder for a doctor rod is disclosed in German Patent No. 3022 955.

The doctor rod of the invention is also suitable for use in coating equipment for direct metering onto the paper or cardboard web surface. The coating device has opposed rolls around which the paper or cardboard web is wound and guided. An application mechanism, for example a roll type or nozzle type application mechanism, is arranged in the winding region of the counter roll, which applies the coating material directly onto the web surface in excess. A metering element is arranged downstream of the application mechanism in the web running direction, which metering element scrapes excess coating material from the web to the desired coating weight. As metering elements, elastically supported smooth doctor rods are known, for example from German Patent No. 30 22 955. It is even more advantageous to use the doctor rod of the invention instead of this smooth doctor rod.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway view of a doctor rod according to the present invention.

Claims (1)

[Scope of Claims] 1. In a doctor rod having a plurality of convex portions and concave portions on the circumferential surface in order to measure the volume of a coating material to be applied to the surface of a paper web or cardboard web in particular, (a) The surface of the convex portion (2) is flat and located on one cylindrical envelope surface, (b) the sum of the surface areas of the convex portion (2) is 10% to 50% of the cylindrical envelope surface, and ( C) Molding cross-sectional depth Pt of the entire surface according to DIN4771
A doctor rod for volumetric metering of coating materials, characterized in that (2.5) has a value of 30 μm to 150 μm. 2. The doctor rod according to claim 1, wherein the rough surface depth Rt of the side surface of the convex portion (2) is at most 10% of the forming cross-sectional depth Pt (2.5). 3. Doctor rod according to claim 1 or 2, wherein the geometrical dimensions and/or arrangement of the projections (2) vary within predetermined limits in a random distributed manner. 4. The width (b) of the protrusions (2), which are elongated and oriented in the circumferential direction when seen in a plan view, is from 10 μm to 100 μm, and the protrusions (2) are spaced apart from each other (a) from 150 μm to 400 μm. A doctor rod according to any one of claims 1 to 3, wherein a doctor rod is provided. 5. The convex width (b) measured in the axial direction is between 10 μm and 100 μm with an accidental distribution, and the inter-convex spacing (a) is between 150 μm and 400 μm with an accidental distribution.
5. Doctor rod according to any one of claims 1 to 4, which varies between. 6. The circumferential length of the convex portion (2) is 1 mm to 15 mm.
A doctor rod according to any one of claims 1 to 5. 7. The open cross-sectional area that occurs between the convex portions (2) on one side when taken in a longitudinal section through the center of the doctor rod is 15 mm^2 to 80 mm^2 per meter of doctor rod length.
A doctor rod according to any one of claims 1 to 7. 8. Doctor rod according to one of claims 1 to 7, characterized in that the elongated projection (2) is arranged at an inclination (α) of up to 10° with respect to the circumferential direction. 9. According to one of claims 1 to 8, the protrusion (2) is produced by scraping material from a smooth cylindrical rod coated with a wear-resistant coating. Doctor Rod. 10. The doctor rod according to claim 9, wherein the recessed portion is formed in the ceramic-coated rod by laser processing. 11. A running press having two press rolls, a coating mechanism disposed on one or both press rolls, and a metering system following the coating mechanism when viewed in the direction of roll rotation. A running material web in a coating device for material webs, in particular paper webs or cardboard webs, characterized in that a doctor rod according to one of claims 1 to 10 is used as a metering element. coating equipment. 12. The material web is placed between a counter roll on which the material web is guided to be wound, a coating mechanism arranged in the material web winding range of the counter roll, and a coating mechanism disposed downstream of the coating mechanism when viewed in the web running direction. a running web of material, with a quantity system;
In particular, a coating device for paper webs or cardboard webs, characterized in that the metering system has a doctor rod according to one of claims 1 to 10 as a metering element, while the material is running. Web coating equipment.