Braiding and Creping Equipment

Abstract

A blade (6) for creping a paper web (1) from a dryer cylinder (3), said blade having a front surface (2) and a front bevel surface (10) impacted by the paper web and contacting the dryer cylinder with said front surface and said front bevel surface meeting at a contact edge (8), said front bevel surface exhibiting a 3D surface roughness Sa>0.7 μm and / or Sz>18 μm and / or Sq>1.0 μm as measured by ISO 25178.

Description

[Technical field]

[0001] The present invention relates to a blade for creping a paper web from a dryer cylinder as defined in the preamble of claim 1, as well as to a creping device equipped with such a blade.

[0002] The use of creping blades to crepe a paper web from a dryer cylinder is well known in the manufacture of paper, and particularly tissue paper.

[0003] Creped is defined as a crimped paper characteristic produced by consolidating a sheet of paper on a roll with a doctor blade, thereby creating an effect that mimics creping. The creping process creates periodic folded microstructures in the tissue that can demonstrably improve tissue qualities such as softness, loft, elongation, and absorbency properties.

[0004] First, a continuous wet web is pressed and adhered to the surface of a dryer cylinder, commonly called a Yankee, using adhesive chemicals. During the drying process, bonds between the cellulose fibers are created. After drying with hot steam and hot air around the Yankee dryer, the web is stripped from the surface by a doctor blade, forming a folded structure. The action of the doctor blade, more specifically called a creping blade, can disrupt the internal structure of the paper sheet by severing the interfiber bonds. Creping the paper sheet away from the Yankee dryer in a controlled and uniform manner defines the production of conventional tissue products.

[0005] Various types of fibers can be used as raw materials for the production of tissue paper. The various types of fibers are usually classified according to their source (virgin or recycled), the type of manufacturing process (chemical, semi-chemical, mechanical, bleached, unbleached) and the type of biomass (hardwood, softwood, non-wood).

[0006] Tissue manufacturers use a variety of machine technologies. Light dry creping (LDC) is the most common technique. In this case, the wet fibers are dried against the Yankee dryer surface at about 65% moisture content and reach the creping doctor blade at about 90-95% dryness. In the alternative conventional wet creping technique, the paper is creped at less than 85% web dryness at the creping doctor blade. Through air drying (TAD) is another notable technique. This technique has obvious disadvantages such as higher capital cost and higher energy consumption than conventional creping machines, but can produce tissue products with higher bulk, softness and absorbency among others. Other alternative techniques include creped through air drying (CTAD), uncreped through air drying (UCTAD), double re-creping (DRC), Advanced Tissue Molding System (ATMOS) and New Tissue Technology (NTT). All techniques have their own advantages and disadvantages and provide more or less advantages to the main tissue properties.

[0007] Tissue products have a wide variety of types and applications, including facial tissue, toilet paper, kitchen towels, hand towels, napkins, and handkerchiefs. For all of these products, the doctor blade specifications and settings are crucial to provide the necessary tissue qualities such as softness, bulk, and absorbency.

[0008] Bulk is a well-known quantity in papermaking and is defined as the volume that a given weight of paper occupies, and is the inverse of density. Paper thickness (i.e., caliper) and bulk are important tissue properties since they are closely related to absorbency. Absorbency (absorption rate and capacity) is an important property for towels and other tissue products whose purpose is to wipe away liquids. Water holding capacity (WHC), measured in g / g, is one metric commonly used to evaluate absorbency. As known to those skilled in the art, the following equation can be used to show the relationship between paper thickness, bulk and absorbency of tissue: Umbrella (cm 3 / g)=1 / density(g / cm 3 ) = Dry thickness (μm) / Basis weight (g / m 2 ) WHT(g / g) 60-75% of the volume

[0009] The effect of the creping doctor blade itself on tissue properties has been considered in limited studies and prior art, some of which present general blade geometries and specific blade designs.

[0010] The '429 patent includes a creping blade having a cutting or creping angle of about 72° or less, preferably 52° to 64°. As explained, the bulk and absorbency of the finished web can be further improved by using a reverse angle creping blade with such specifications.

[0011] U.S. Patent No. 6,425,983 discloses a creping blade with a plurality of notches on its upper surface, i.e., a wavy creping blade, As described, the notches are configured to increase the thickness of the cellulosic web as the creping blade crepes the cellulosic web from the outer surface of a rotatable cylinder.

[0012] GB 2128551 discloses scraper blades with wear-resistant material on the blade tips according to different embodiments. Indeed, coating the blade tips that are intended to contact the Yankee dryer surface with wear-resistant material is advantageous for extending product life and keeping the creping process very stable over that period.

[0013] What is lacking in the prior art is an alternative option to further increase bulk. Thus, there is a need for tissue producing customers in the paper industry to have an innovative creping blade that can itself increase tissue bulk and absorbency properties.

[0014] SUMMARY OF THE PRESENT EMBODIMENT It is therefore an object of the present invention to provide an improved blade which overcomes the shortcomings of the prior art.

[0015] A second object of the present invention is to provide a creping blade that can positively affect paper thickness (ie, caliper) and tissue bulk in a controlled manner.

[0016] A third object of the present invention is to provide a creping blade capable of improving tissue absorbency.

[0017] A fourth object of the present invention is to provide a versatile solution that is relatively simple to manufacture and can be combined with multiple blade designs.

[0018] All of the problems have been solved by a blade for creping a paper web from a dryer cylinder according to claim 1 as well as by a creping device comprising such a blade according to claim 13.

[0019] Advantageous embodiments are set forth in the dependent claims.

[0020] In the context of this application, the terms "blade" and "creping blade" are used synonymously unless otherwise specified.

[0021] A blade is introduced for creping the paper web from the surface of a dryer cylinder, the blade having a front surface and a front bevel surface that is impacted by the paper web, the front surface and the front bevel surface contacting the dryer cylinder with a contact edge.

[0022] According to the present invention, the front bevel surface has a 3D surface roughness measured by ISO25178, Sa>0.7μm and / or Sz>18μm and / or Sq>1.0μm Shows.

[0023] In many realizations of such blades, all roughness values ​​exceed a threshold having roughness values ​​of Sa>0.7 μm and Sq>1.0 μm and Sz>18 μm.

[0024] However, for blades according to embodiments of the present invention, it is likely that one or two of these roughness measurements will be below this threshold.

[0025] In a preferred embodiment, Sz is greater than 18 μm, in particular 25 μm or greater.

[0026] The dryer cylinder may be a Yankee cylinder.

[0027] Referring to the ASM (American Society of Materials) Handbook, Vol. 5, 1994-Surface Engineering (pp. 136-138), surface topography is defined by the combination of three specific features: surface roughness, surface waviness, and surface morphology.

[0028] As mentioned above, the prior art is concerned only with the effect of macroscopic topographical features such as waviness ("wavy creping blade") and surface shape (eg, "creping angle") on paper properties.

[0029] In the prior art, when considering microscopic topography, the goal is to reduce the roughness as much as possible to reduce wear and abrasion.

[0030] The blade has a front face facing towards the dryer cylinder and a rear face facing away from the dryer cylinder. The distance between the front and rear faces defines the thickness of the blade (x-direction). Typically, the blade thickness is between 600 μm and 1500 μm. The front and rear faces are typically parallel over at least a portion of the width of the blade (y-direction). The length of the blade (z-direction) typically extends over several metres and corresponds to the cross grain (CD) dimension of the intended dryer cylinder.

[0031] In particular, it should be noted that the front surface of the blade can have multiple surfaces. For example, when the main surface comes into contact with the rotating dryer cylinder, a so-called sliding wear surface will be formed. In order to better accommodate the sliding surface and for easier engagement of the blade with the dryer surface, a bevel proximal angle can be formed at the blade tip during creeping blade manufacture. The sliding wear surface and the bevel proximal portion are considered as part of the front surface.

[0032] The front bevel surface is a portion of the top surface of the blade. The front bevel surface is the surface adjacent to the front surface and extends through the thickness of the blade. When used as a creping blade, the paper web typically impacts this portion of the blade at very high speeds, e.g., 2000 m / min. The top surface of the creping blade may extend up to 1500 μm, but typically only the first 150 μm from the blade contact point is impacted by the paper web, significantly affecting the paper bulk.

[0033] From experience, the paper web strikes the front bevel surface at an average distance of 100 μm to 150 μm from the blade contact point in the x direction. The front bevel surface therefore extends at least 150 μm from the blade contact point in the x direction. In this region of 150 μm, the above roughness requirement is absolutely necessary. In many cases, it is beneficial to extend the roughness in the x direction more than 150 μm. For example, a distance of at least 250 μm or at least 350 μm from the blade contact point may be provided with the preferred roughness. This may be advantageous to ensure that a sufficiently large front bevel surface with the desired roughness is guaranteed even after the blade has been worn to some extent.

[0034] Although not essential to the invention, in many applications the required roughness is provided over the entire top surface of the blade extending up to 1500 μm from the contact point of the blade, as this can be readily achieved by standard techniques such as thermal spraying or sandblasting events, whereas more sophisticated methods such as laser engraving can be used to create the required roughness over only a portion of the top surface of the blade.

[0035] The surprising observation on which the present invention is based is that even very small features of the surface topography of the front bevel surface can affect the blade creping process, i.e., the specific mechanism of forming the tissue structure. More specifically, it was found that a higher roughness of the creping blade surface impacted by the paper web - the front bevel surface - changes the stresses during removal of the paper web from the dryer cylinder, so that more fiber bonds are broken and / or distorted. This always leads to a different fiber structure arrangement. This finding was surprising, since the general knowledge in the technical field was that the blade, especially the tip, should be as smooth as possible to reduce wear on the blade and in the dryer. The applicant's discovery is that such knowledge applies to the area contacting the cylinder, but that the front bevel surface is desirably made rather rough.

[0036] This principle of increasing bulk by breaking / deforming the fiber structure with roughness on the front bevel surface is perfectly understandable. However, in the applicant's initial tests, the correlation between the measured roughness and the bulk increase was not very significant. After extensive experimentation by the applicant, another very surprising discovery was made: the roughness measurements used as a standard do not accurately represent the surface roughness that affects the bulk of the paper!

[0037] In many cases, blades according to aspects of the invention are manufactured and sold with a front bevel surface exhibiting a desired roughness. However, it is possible that a new blade will be outside the claimed roughness range when installed, but that the blade will reach this roughness after a period of operation due to wear or special treatment. Both types of blades are covered according to the present application.

[0038] Those skilled in the art know that typically 3-6 roughness parameters are required to adequately characterize the topography of a surface.

[0039] Industrial standards are usually: ISO 4287 : Geometrical Product Specifications (GPS) - Surface texture: Profile method - Terminology, definitions and surface texture parameters - Measurement.

[0040] The standard supports two-dimensional (2D) or linear roughness measurements and provides the following values: Ra: arithmetic mean deviation of the roughness profile (amplitude parameter μm) Rz: Maximum height of the roughness profile (amplitude parameter μm) Rq: Root mean square deviation of the roughness profile (amplitude parameter μm) Rc: average height of the roughness profile elements (amplitude parameter μm) Rt: Total height of the roughness profile (amplitude parameter μm)

[0041] Due to the two-dimensional nature of these values, they do not adequately characterize the surface structure that affects the bulk of the paper (also called "active roughness"), which is discussed in more detail below.

[0042] The applicant ISO 25178 : Geometrical Product Specifications (GPS) - Surface texture: Area method - Roughness measurement by metrology characteristics for areal topography method was found to be more appropriate. This standard supports three-dimensional (3D) or areal roughness measurement and provides the following values:

[0043] Sa: arithmetic mean height (height parameter μm) Sz: Maximum height (height parameter μm) · Sq: Root mean square height (height parameter μm).

[0044] To perform these measurements, a Universal Profilometer UP-24 from Rtec Instruments (non-contact, high-speed 3D measurement, line and surface measurement technology) can be selected. All 3D roughness measurements shown in this application were performed with such an instrument. 2D measurements were also performed with this instrument.

[0045] As it is important that roughness values ​​are determined with high precision, non-contact measurements such as those made by the UP-24 are preferred, as contact measurements run the risk that the stylus cannot penetrate narrow holes to the same depth as non-contact instruments, thus reducing the accuracy of the measurements.

[0046] The parameter settings for the profile meter are given in the table below: [Table 1]

[0047] These experiments showed that the 3D surface values ​​represent the "active roughness" quite accurately. Roughness values ​​of Sa>0.7 μm and / or Sz>18 μm and / or Sq>1.0 μm were found to have a significant impact on bulk.

[0048] In a preferred embodiment, the roughness values ​​may be in the following ranges: Sa 0.7μm~9μm, especially 2μm~6μm and / or Sz 18μm to 100μm, in particular 25μm to 70μm and / or Sq 1.0μm~11μm, especially 2.5μm~7μm.

[0049] It has been observed that the bulk of a tissue product can be increased with increasing roughness of the front bevel surface, but other properties of the tissue product may deteriorate. As an example, the product may develop pinholes or the aesthetic appearance of the visible tissue surface may be impaired. For some tissue products, these properties may be inconsequential. However, for other tissue products, these properties can only be tolerated to a certain extent. The above ranges often provide a good compromise between increased bulk and deterioration of other properties.

[0050] The above mentioned roughness values ​​can be achieved by periodic and non-periodic surface structures, where periodic structures can have significant and detrimental effects on the tissue, and non-periodic surface structures are usually preferred to optimize bulk by breaking / distorting the fiber structure due to the roughness of the front bevel surface.

[0051] One advantage of the present invention is the fact that it can be combined with multiple blade designs.

[0052] Thus, the macroscopic shape of the front bevel surface may for example be flat or it may have a macroscopic topography, in particular a wavy topography.

[0053] The angle between the front surface and the front bevel surface is called the bevel angle β. The bevel angle may be set between 60° (negative front bevel surface) and 110° (positive front bevel surface), preferably between 70° and 95°.

[0054] The upper surface of the creping blade may extend up to 1500 μm, but the first 150 μm or 250 μm have the most impact on the bulk of the paper. From experience, the paper web strikes the front bevel surface at an average distance of 100 μm to 150 μm in the x-direction from the blade contact point. This surface is therefore an important consideration in the present invention. Roughness values ​​of Sa>0.7 μm and / or Sz>18 μm and / or Sq>1.0 μm may only be present in the first 150 μm or 250 μm of the upper surface of the blade, since this is usually the technically important front bevel surface. At a larger distance from the contact edge, for example 350 μm or 500 μm, different roughness values ​​may be possible without adversely affecting the bulk of the paper.

[0055] In most applications the blade comprises a steel strip (=steel blade).

[0056] The criteria for the steel strips most suitable for this application are described by the DIN EN 10132-4 standard. The standardized designations, chemical compositions and associated physical and mechanical properties of the steels are described in the DIN EN 10132-4 standard. To achieve optimal elastic "spring" properties, these steel strips are usually heat treated. As a result, these high strength, hardened and heat treated high carbon steels usually have hardnesses in the range of 350HV to 600HV as measured by the Vickers (HV) test. Other alternative steels, such as stainless steel references, can be used, but the hardness specifications will be similar.

[0057] Such steel blades may have a wear resistant material on the blade tip (coated and polished).

[0058] It is also possible for the blade to have a thermal spray coating, for example of a ceramic-based material. To protect the blade tip, which is the most active part likely to be exposed to mechanical stresses and wear, wear-resistant deposits can be advantageously applied. Different deposit embodiments can be suitable for partial or total protection of different areas at the blade tip. As a result, a longer life and more stable operating conditions are achieved. Typical deposit types, for example those made of or containing at least one metal oxide, at least one metal nitride or at least one metal carbide, can be recommended for this application. More specifically, it has been found that materials based on carbides, in particular references based on tungsten carbide, are well suited to meet the requirements of the invention. In fact, most carbides are extremely hard and are recommended for wear-resistant purposes. The materials are usually in the form of a composite consisting mostly of carbide particles homogeneously distributed in a matrix, i.e. a metal matrix. The metal matrix acts as a binder supporting a hard and brittle reinforcing phase. Cermet is the general name for such composites. Usually, the volume of the matrix or binder phase is less than 30% of the total volume of the cermet. One of the important criteria in selecting cermet references from suppliers is the carbide size. Although the processing parameters obviously influence the final roughness of the deposit, it has been confirmed that the higher the selected primary carbide particle size, the greater the resulting surface roughness. As an example, when used to manufacture some of the products according to the invention, the average carbide size was in the range of 0.5 μm to 15 μm. The processing technique for applying such cermets is thermal spraying, more specifically high velocity flame spraying. The hardness of the deposits typically obtained, measured in Vickers (HV) tests and on material cross sections, is in the range of 900 to 1700 HV. In many applications, the hardness of the deposit is two to four times that of the base steel substrate.

[0059] All of these types of blades can be provided with a 3D surface roughness on the front bevel surface according to one aspect of the present invention.

[0060] The working surfaces of the blades intended to contact the Yankee surface are desirably smooth and are usually finished to a low roughness level. Typical roughness specifications are Ra<0.4 μm and Rz<4.0 μm. Although the objective of the present invention is to purposefully increase the 3D roughness of the front bevel surface, it is clear that the adjacent surfaces intended to contact the Yankee dryer must maintain a surface roughness within the above "smooth" specification range. Smoother contact surfaces, e.g., Ra<0.2 μm and / or Rz<2.0 μm, are also common.

[0061] The desired 3D roughness of the front bevel surface can be achieved in a variety of ways. For example, almost any manufacturing process could potentially be used to modify the topography of the surface with the goal of increasing the surface roughness. Principles of surface alteration or surface modification may be included. Such surface treatment processes may include mechanical (e.g., machining, blasting), chemical (etching, coating), thermal (heat treatment, energy beam, coating, deposition) and / or electrical (energy discharge) effects with or without the addition of more material (e.g., coated or deposited layers).

[0062] For example, a post-treatment in the form of sandblasting can be applied to increase the roughness to the desired level. Alternatively, if a thermal spray coating is applied, the process can be adapted to achieve the desired 3D roughness. In this case, the post-treatment can be omitted.

[0063] In accordance with the present invention, it is not necessary to have isotropic properties or roughness characteristics, however this is often the result herein as selected post-processing and manufacturing methods tend to promote such isotropy.

[0064] In paper machines, especially tissue machines, the blade according to the invention is used in combination with a dryer cylinder, especially a Yankee cylinder, in the form of a creping device.

[0065] In this case it may be beneficial for the contact angle α between the blade and the dryer cylinder to be between 5° and 35°, preferably between 15° and 25°.

[0066] It should be appreciated that during use, the blade tip at its contact edge with the Yankee surface will experience some wear along a line that makes this angle α, resulting in a sliding wear surface, and a small sliding wear angle is preferred to prevent damage to the Yankee surface.

[0067] A bevel proximal angle can be formed at the blade tip during creeping blade manufacture to better accommodate the sliding surface and for easier blade engagement with the Yankee surface. Typically, the bevel proximal angle is less than the intended contact angle α. In preferred applications, the bevel proximal angle can be selected to be less than 15°, for example, 2°, 5°, 8° or 10°.

[0068] Alternatively or additionally, it may be beneficial if the pocket angle δ between the tangent to the dryer cylinder at the blade tip contact and the front bevel surface is between 115° and 35°, preferably between 95° and 65°, more preferably between 85° and 70° (pocket angle is sometimes also called cutting angle or creping angle).

[0069] The bevel angle β is a blade design parameter, while the pocket angle δ is the result of the bevel angle β and the contact angle α, which determines the quality of the crepe structure. The angle δ is measured between the tangent to the Yankee surface at the blade tip contact edge and the front bevel surface of the creping blade, i.e., the web impact surface. In principle, an increase in δ with any reduction in α and / or β leads to an improvement in softness while reducing thickness.

[0070] The invention is further illustrated by the following figures and examples, without the invention being limited to these embodiments. [Brief description of the drawings]

[0071] [Figure 1] 1 is a schematic side view of a portion of a tissue machine including a creping device according to one embodiment of the present invention; [Figure 1a] 1 is a schematic diagram illustrating a blade according to one aspect of the present invention. [Diagram 2] 2a-d are schematic cross-sectional views of the crepe development principle showing one of the four stages of creping from micro-crepe to macro-crepe formation. [Diagram 3] FIG. 1 illustrates a portion of a creping device with a creping blade according to another embodiment of the present invention. [Figure 4] This is a general diagram of the prior art (American Society of Materials Handbook, Vol. 5, 1994 - Surface Engineering, p. 136). [Diagram 5] 1 is a graph showing 2D roughness values. [Figure 6] 1 is a graph showing 2D roughness values. [Figure 7] 1 is a graph showing 3D roughness values. [Figure 8a] 1 is a scanning microscope photograph of a front bevel surface of the prior art. [Figure 8b] 1 is a scanning microscope photograph of a front bevel surface according to one embodiment of the present invention. [Figure 9a] FIG. 1 illustrates the topography of a front bevel surface according to the prior art. [Figure 9b] FIG. 2 illustrates the topography of a front bevel surface according to one embodiment of the present invention.

[0072] At the beginning of the tissue paper manufacturing process, the stock or furnish, i.e. a highly diluted slurry of pulped wood fibres, is fed into the tissue machine by the headbox and distributed evenly along the entire width of the machine in the gap between two rolls. One roll is provided with a wire, i.e. screen cloth, the other with a felt, i.e. heavy cloth. The wet web 1 adheres to the felt and follows it into the machine at a high running speed. Dewatering takes place before it reaches the absorbing press roll 2 and the dryer cylinder 3 in the form of a large Yankee dryer 3. The size of the Yankee dryer 3 can be defined by a diameter of about 5 m (and up to 7.3 m) and a length (in the cross machine direction CD) of about 5.5 m (and up to 7.8 m). The length of the Yankee dryer is slightly greater than the width of the paper sheet 1. Coating chemicals may be sprayed by a series of nozzles 4 to promote adhesion between the sheet 1 and the Yankee dryer 3 and to protect the metal surface of the cylinder 3. The drying process is carried out by a steam heated Yankee cylinder 3 and by a hot air stream from a hood 5. The lightweight fibrous sheet, moving at a speed of up to 2400 m / min, impinges on the front bevel surface 10 of the creping blade 6 and is peeled off from the Yankee 3 surface. The size of the creping blade 6 can be defined by its length (up to 7.8 m measured in the z-direction or CD), width (50-150 mm measured in the y-direction), and thickness (0.6-1.5 mm measured in the x-direction). The creped structure of the tissue paper 7 is then formed. At the end of this process, the finished tissue paper 7 is wound onto a large jumbo reel at a slower speed than the Yankee 3.

[0073] 1a shows an exemplary blade 6 according to one embodiment of the present invention, having a leading surface 20, a trailing surface 30 and a top surface 40. The leading surface 20 extends generally parallel to the trailing surface 30, except at the surface of the proximal portion 21 of the bevel. The blade 6 is a steel blade 6 having a wear-resistant coating 25. In this case, the coating 25 covers all of the top surface 40 and a portion of the leading surface 20. Depending on the application, other areas of the blade 6 may be coated with the wear-resistant coating 25, for example, only a portion of the top surface 40 may be coated with the wear-resistant coating 25.

[0074] One purpose of the coating 25 may be to increase hardness. Typical steels used as base substrates have a Vickers hardness of 350HV to 600HV, but the hardness of the resulting coating 25 may range from 900HV to 1700HV. Typically, the hardness of the deposit 25 is two to four times that of the base steel substrate.

[0075] The front bevel surface 10 is on the upper surface 40 of the blade and extends in the x-direction from the contact edge 8. The front bevel surface 10 extends in the x-direction for at least 150 μm, preferably for more than 250 μm. According to the invention, the front bevel surface 10 has a relatively high roughness, i.e. Sa>0.7 μm and / or Sz>18 μm and / or Sq>1.0 μm.

[0076] The other parts of the blade 6, i.e. the proximal portion 21 or the front surface 20, are preferably smooth. These surfaces of the blade may have a roughness of Ra<0.4 μm and Rz<4.0 μm.

[0077] 2a-d provide a detailed look at the creping mechanism, revealing a four-step process involving the development of microscopic crepes 71 that are grouped into larger macroscopic crepes 73 by the action of the doctor blade 6.

[0078] Creping delaminates the internal physical structure of the paper web 1, forcing fiber bonds to weaken or break, and forcing fibers to twist, distort or break. Microscopic crepes 71 form (first stage), overlap each other (second stage), and once the pile 72 is high enough (third stage), the macroscopic crepes 73 fall to form the macroscopically creped and structured final product 7 (fourth stage). The delamination process tends to produce a thicker, more absorbent, and cushioned tissue product with a higher water holding capacity than folded creping. Creping is a complex interaction of many factors. Control of the creping process is important to produce tissue 7 with high loft, absorbency, softness, and elongation.

[0079] In FIG. 3, various angles are shown which are used in the present application to define the geometric situation at the tip of the blade 6. The blade 6 has a front surface 20 facing towards the Yankee cylinder 3 and a rear surface 30 facing away from the Yankee cylinder 3. The sliding wear angle α is the contact angle between the Yankee dryer 3 and the creping blade 6. This angle is directly related to the blade holder angle and the elastic displacement of the blade 6 under a given load condition. Typical values ​​for α are in the range of 5°-35°, usually about 19°. It should be understood that during use, the blade tip at the contact edge 8 with the Yankee 3 surface will experience a certain wear on the line that forms this angle α. As a result, a sliding wear surface 9 is created. In order to better accommodate the sliding surface and for easier engagement of the blade with the Yankee 3 surface, a bevel proximal portion 21 angle can be formed at the blade tip during the creeping blade manufacture. Such a bevel proximal portion 21 angle may be selected, for example, from 5°-10°. Typically, this bevel front 21 angle is smaller than the sliding wear angle α. A small sliding wear angle is preferred to prevent damage to the Yankee 3 surface. The bevel angle β is a design parameter of the blade 6. Typical values ​​of β range from 60° (negative front bevel surface) to 110° (positive front bevel surface). The resulting angle δ, also called the creep work angle or pocket angle, is important for the quality of the creep structure. The angle δ is measured between the tangent to the Yankee 3 surface at the blade tip contact 8 and the front bevel surface 10 of the creping blade 6, i.e., the web impact surface.

[0080] In principle, an increase in δ with any decreasing effect on α and / or β leads to an improvement in softness while reducing the thickness. It is important here to know from experience that the paper web 1 impinges on the front bevel surface 10 at an average distance of 100 μm to 150 μm from the blade contact point 8 in the x direction. This surface, which in most cases extends to about 250 μm from the blade contact point 8, is therefore the key point to be considered in the present invention. Finally, the take-off angle θ is a direct function of the rewinder position and the web tension. Standard geometries can be selected to fit the creping pocket and to obtain the correct creping quality.

[0081] The interaction between the paper web 1 and the front bevel surface 10 plays a key role in the formation of the creped structure and the properties of the final tissue 7. It is therefore important to focus on this surface 10 and to better define its properties. Those skilled in the art know the technical definition, for example from the ASM Handbook, that most surfaces have regular and irregular spacings that tend to form a pattern or texture on the surface. Based on the general Figure 4 from the ASM Handbook, the topography of the resulting surface is defined by a combination of three specific features, namely: - surface roughness 11, i.e. high frequency irregularities on the surface resulting from the interaction of the material microstructure with the surface treatment; - surface waviness 12, i.e. medium frequency irregularities on the surface on which the surface roughness is superimposed, Surface shape, i.e. the overall shape of the surface, e.g. flatness, roundness etc., ignoring roughness and waviness.

[0082] The lay 13 is another important feature of the surface. It is a machining pattern with a well-defined direction. The lay is an important consideration since the surface topography measurement varies depending on the direction in which the measurement is performed. For this reason, a surface roughness measurement defined as an area is recommended. This is applied in particular to characterize the topography in the critical front bevel surface 10, i.e. in a specific region close to the blade contact point 8, where the impact of the paper web occurs.

[0083] Example 1 The following example highlights the importance of 3D roughness measurements to properly characterize the “active roughness” of the front bevel surface 10 .

[0084] Three different base materials were selected: S1-Standard steel base material S2 - Steel substrate with wear-resistant material on the blade tip (coated and polished) S3 - Steel substrate with multiple notches on the blade tip (wavy blade)

[0085] Two special surface treatments were used separately or in combination to vary the texture of the particular front bevel surface 10 of the blade 6. It is important to mention that the surface of the front surface 20 adjacent to the front bevel surface 10 and in contact with the Yankee dryer 3 in the area indicated by the numeral 8 should not be roughened. In order to avoid damaging (e.g., scratching) the Yankee dryer surface 3, it is recommended that this contact surface, which may become the aforementioned sliding wear surface 9 during use, be kept as smooth as possible. Typical roughness specifications for these contact surfaces are Ra<0.4 μm and Rz<4.0 μm.

[0086] T1 - Thermal spray coating of ceramic materials (When sprayed, no surface finishing / no grinding or polishing) T2-Sandblasting with angular alumina particles (Size: F180, 1 spray nozzle, distance 50mm, pressure 4 bar)

[0087] Based on these three substrates S1-S3 and the two surface treatment processes T1 and T2, a series of 15 blade samples, labeled A-O, was produced by standard methods (i.e. the basic structure is supplied or produced by the prior art). Blade samples A, B, C, D were kept as 100% references from the prior art, while all others underwent one (samples E, N, O) or two (samples F-M) additional and subsequent surface treatments to meet the requirements of the present invention. The post-treated blade samples E-O were intended to be gradually processed so that the resulting roughness of the front bevel surface 10 increases. Blade samples M, N, and O are expected to be the roughest of the series, but the resulting roughness values ​​cannot be said to be maximum values ​​to set an upper limit for the present invention.

[0088] The following table shows the main manufacturing process steps and parameters for making the reference blade sample and the blade sample according to the invention. When multiple process steps are involved, the chronological order always runs from top to bottom in this table. The entire top surface 40 of samples E-O was post-treated, but it is important to note that this is where the paper web 1 impacts the front bevel surface 10, so the front bevel surface 10 can be limited to about 150 μm or 250 μm (0.25 mm) from the blade contact point 8.

[0089] [Table 2]

[0090] For these 15 samples, the roughness values ​​of the front bevel surface were measured in three ways: 2D transverse (ISO 4287), 2D longitudinal (ISO 4287) and 3D (ISO 25178). The results are shown in the table below (all values ​​in μm).

[0091] [Table 3]

[0092] Figures 5-7 show the progression of the above roughness parameters for each blade sample (A-O) to better illustrate the relationships. Figures 5 and 6 show that the roughness values ​​in the longitudinal and transverse directions are nearly aligned. This confirms the uniformity of the surface texture in the two main directions, i.e., longitudinal (MD) and transverse (CD).

[0093] In accordance with the present invention, it is not necessary to have isotropic properties or roughness characteristics in these directions, however, the results presented herein are as follows, since the selected post-processing and manufacturing methods tend to promote such isotropy.

[0094] Comparing these graphs with the last graph of FIG. 7, the 3D surface roughness measurements tend to be less disturbed by the more constant progression of the post-processed blade samples E to O. It should be recalled that the initial goal was to gradually increase the roughness of the front bevel surface 10. In each case, the 3D surface roughness measurements clearly better represent the overall surface roughness characteristics. This is why only the three relevant roughness parameters Sa and / or Sz and / or Sq are taken into account for the roughness specification according to the invention. Compared to the reference blade samples A to D, the enhanced surface roughness of the blade samples according to the invention is characterized by the following specifications: Sa>0.7 μm and Sz>18 μm and Sq>1.0 μm. In these examples, all three of these roughness parameters show more or less the same trend from sample to sample, but this is not necessary. Also, a given sample may have, for example, a relatively high Sz value (e.g., 30 μm or 40 μm) while having fairly low values ​​for Sa and Sq (e.g., about 1.3 μm, 1 μm or less), and still provide a useful blade.

[0095] To visually illustrate the surface structure according to one embodiment of the present invention, Figures 8a and 8b show scanning electron microscope (SEM) photographs of two different top surface 40 surfaces. Figure 8a is taken of Sample A, a standard steel substrate of the prior art, whereas Figure 8b is taken of Sample N, the same base substrate, but treated with thermal spraying and sandblasting. Thus, Figure 9a shows a topographical measurement of the blade of Figure 8a, and Figure 9b shows a topographical measurement of the blade of Figure 8b.

[0096] [Table 4]

[0097] The differences between the two blades are clearly visible. Sample A in FIG. 8a has a smooth and shiny surface at top side 40. The grinding process corresponding to rays 13 results in diagonally oriented lines. Apart from these lines and occasional small point-like disturbances, the surface is very smooth.

[0098] In contrast, sample N in FIG. 8b shows a very rough and jagged surface. There is no impression of gloss. In this example, the structure appears isotropic and shows no predominant direction. Figuratively speaking, the prior art blade looks like a sandy beach, whereas the blade according to an embodiment of the present invention looks more like a bird's-eye view of an alpine region. In FIG. 8, the front bevel surface 10 extends across the entire top surface 40 of the blade.

[0099] The topographic measurements in Figures 9a and 9b emphasize the visual impression. Here again, the x-direction is the thickness direction of the blade 6 and the z-direction is parallel to the surface of the Yankee 3. The topographical height - the difference between the deepest valley and the highest peak - is about 2 μm for Sample A, while the value for Sample N is about 60 μm. The height of Sample N is therefore about 30 times higher than that of Sample A. This corresponds very well to the Sa / Sz / Sq values. For each of these three roughness measurements, Sample N is about 30 times higher than Sample A. This also emphasizes the fact that these values ​​are best suited to characterize the front bevel surface of blades within the scope of the present invention.

[0100] A number of comparative tests were carried out in practical conditions to evaluate the performance of the creeping blades according to the invention (prototype reference number - Pr n°) compared to those of the prior art (standard reference number - Sr n°). These creeping blades are manufactured according to the samples shown in Example 1.

[0101] The prototype reference number n° or standard reference number n° is linked to the internal production number n° and will show the correspondence with the sample label.The following two examples present the results of tests on tissue mills producing different types of crepe paper.

[0102] Example 2 The first test was carried out with the following operating conditions and settings: -Paper web made from 100% virgin fibers -Handkerchief / Facial tissue grade -Tissue weight: 10.5~11g / m 2 -Tissue basic thickness (dry): 42μm -Metal-coated Yankee dryer surface - Yankee dryer speed 1650m / min - Coating chemical weight 5.9g / m 2 -Creping blade size: 1.0 x 120 x 5850mm (thickness x width x length) -Bevel angle β 75° (-15° negative front bevel surface) -Sliding angle α 21° -Pocket angle δ 84°

[0103] The objective of the test was to increase the thickness of the tissue paper and therefore the tissue bulk in order to obtain gains in subsequent process steps in the conversion. Indeed, it is an economic gain to sell less product (thicker and therefore more airy product) for the same price. As known to those skilled in the art, fiber costs are by far the highest cost in papermaking and can reach 50% of all production costs. Therefore, even a relatively small saving in fiber consumption, for example 1% or 2%, can significantly increase the profitability of production.

[0104] Particularly in the case of facial tissue and handkerchief products, smooth softness is an important requirement that must never be compromised.

[0105] The following three blades were tested for the relevant production times (h) mentioned above: Sample label B = Sr 6835 (27h) Criteria for Sample label E=Pr 8614(22h) and Sample label N=Pr 8661(22h).

[0106] According to the customer, positive results were obtained. Improvements were measured based on the increase in dry thickness of the tissue over time compared to the baseline and are summarized below:

[0107] Tissue base thickness Reference blade Sr 6835(B) 42μm New Blade Pr 8614(E) +1.5~+2.5% New Blade Pr 8661(N) +3.0~+4.0%

[0108] Interestingly, it was noticed that the tissue surface appears more homogenous and has less cross-grain (CD) markings, i.e. creeping bars. This is explained as a direct effect of the surface texture and the higher roughness which scatters the fibers in more directions. As a result, the fiber distribution at the tissue surface becomes more uniform.

[0109] As indicated in the definition, bulk is dependent on the basis weight of the tissue paper. With this in mind, it was stated that the maximum bulk increase in the above specific tissue application is expected to be 10% using the optimized creping blade according to the present invention.

[0110] Example 3 For the second test, it was decided to target an application where bulk gain was the primary goal. The following operating conditions and settings were used: -Paper web made from 100% virgin fibers -Kitchen towel / absorbent tissue grade -Tissue weight: 19~20g / m 2 -Tissue basic thickness (dry): 110μm - Metallized Yankee dryer surface - Yankee dryer speed 1600m / min -Creping blade size: 1.2 x 105 x 3200mm (thickness x width x length) -Bevel angle β 90° (square front bevel surface) - Sliding angle α 16°~21° (values ​​cannot be measured more precisely since production time was limited to only about 1 hour) -Pocket angle δ 69°~74°

[0111] The purpose of the test was to increase the bulk of the tissue paper and its absorbency. Indeed, these tissue quality aspects are important in the case of kitchen towels. The softness of the tissue is not of primary importance, while the elongation of the tissue paper measured in the machine direction (MD) and cross direction (CD) is taken into account.

[0112] The following three blades were tested during the limited production time (h) mentioned above: Sample label A = steel blade as reference Sample label I = Pr 9401 (1.2h) and Sample label K=Pr 9426(1.2h)

[0113] It should be noted that the current steel blade is not a product supplied by the inventor and therefore has no standards. However, it is the most common and basic type of creping blade and is well known to those skilled in the art. The main drawbacks relate to short life span, limited stability of the creping process, and variability in tissue quality.

[0114] Positive preliminary results have been observed according to the customer. Improvements based on various tissue quality parameters and other related results have been measured and are summarized below:

[0115] Dry tissue base thickness: Steel blade standard 110μm New Blade Pr 9401(I) +5% New Blade Pr 9426(K) +25%~30%

[0116] umbrella: Steel blade standard 5.7cm 3 / g New Blade Pr 9401(I) +5% New Blade Pr 9426(K) +20%~25%

[0117] The extremely good results achieved when using the creping blade Pr 9426 were treated as if the tissue surface had a square pattern of intensity, clearly visible. This embodiment is characterized by markings on the tissue surface in both cross grain (CD) and long grain (MD). This may be acceptable for some applications, but may not be acceptable from a tissue quality or aesthetic point of view, depending on the type of tissue, its final purpose and / or other customer acceptance. This is a major disadvantage of blades with notches on the front bevel surface, especially when the depth of the waviness and the size of the notches are important. The notches, spaced about 1 mm apart, are large enough to assume mechanical deformation or embossing of the paper web when the surface is impacted during creping.

[0118] Other tissue grades, such as toilet paper, can also be made using a blade according to the present invention. [Explanation of symbols]

[0119] 1 Paper and Web 2 Absorption press roll 3 Dryer cylinder, Yankee 4 Spray nozzle 5. Food 6 Creping Blade 7 Macroscopically creped tissue paper 8 Contact Edge 9 Sliding wear surface 10 Front bevel surface 11 Roughness 12 Swell 13 Ray 20 Front 21 Front part of bevel 25 Wear-resistant coating 30 Rear 40 Top side 71 Microscopic Crepe 72 Microscopic Crepe Pile 73 Macroscopic Crepes

Claims

1. A blade (6) for creping a paper web (1) from the surface (3) of a dryer cylinder, wherein the blade (6) has a front face (20) and a front bevel face (10), the front face (20) and the front bevel face (10) are in contact at a contact edge (8), the contact edge (8) contacts the dryer cylinder (3), in the blade (6), the front bevel face (10) extends at least 150 μm from the contact edge (8) in the thickness direction of the blade (6) and is subjected to an impact by the paper web (1), the front bevel face (10) has a 3D surface roughness measured by ISO 25178, Sa > 0.7 μm and / or Sz > 18 μm and / or Sq > 1.0 μm A blade (6), characterized in that it satisfies the above conditions.

2. The front bevel face (10) has a 3D surface roughness measured by ISO 25178, Sa is 0.7 μm to 9 μm and / or Sz is 18 μm to 100 μm and / or Sq is 1.0 μm to 11 μm The blade (6) according to Claim 1, wherein the front bevel face (10) satisfies the above conditions.

3. The bevel angle β between the front face (20) and the front bevel face (10) is 60° to 110°, preferably 70° to 95°. The blade (6) according to Claim 1 or 2.

4. The macroscopic shape of the front bevel face (10) is flat or has a macroscopic topography, particularly a wavy topography. The blade (6) according to Claim 1 or 2.

5. The front bevel face (10) extends at least 250 μm, preferably at least 350 μm, from the contact edge (8), and particularly extends over the entire upper surface (40) of the blade (6). The blade (6) according to Claim 1 or 2.

6. The blade (6) is a steel blade, particularly including steel having a hardness in the range of 350 HV to 600 HV as measured by a Vickers (HV) test. The blade (6) according to Claim 1 or 2.

7. The blade includes a deposit of a wear-resistant material (25), particularly a ceramic-based material (25). The blade (6) according to Claim 6.

8. The ceramic-based material (25) includes at least one of metal oxides, metal carbides, metal nitrides, or combinations thereof. The blade (6) according to Claim 7.

9. The blade (6) according to claim 8, wherein the ceramic-based material (25) is in the form of a composite material containing particles of at least metal oxide, metal carbide or metal nitride distributed in a metal matrix material.

10. The blade (6) according to claim 7, wherein the hardness of the deposit is in the range of 900 to 1700 HV as measured by a Vickers (HV) test.

11. The blade (6) according to claim 1 or 2, wherein at least a part of the front surface (20) has a roughness of Ra < 0.4 μm and Rz < 4.0 μm.

12. The blade (6) according to claim 1 or 2, wherein the blade (6) has a thickness in the x-direction of 600 μm to 1500 μm.

13. A creping apparatus comprising a dryer cylinder (3) and a blade (6), wherein the blade (6) is the blade (6) according to claim 1 or 2.

14. The creping apparatus according to claim 13, wherein the contact angle α between the blade (6) and the dryer cylinder (3) is 5° to 35°, preferably 15° to 25°.

15. The creping apparatus according to claim 13, wherein the pocket angle δ between the tangent to the dryer cylinder (3) at the blade tip contact portion (8) and the front bevel surface (10) is 115° to 35°, preferably 95° to 65°, more preferably 85° to 70°.

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