Scraper and creping device

Abstract

A doctor blade (6) for creping a paper web (1) from a cylinder surface (3), the doctor blade comprising a front side (2) and a front bevel (10) impacted by the paper web, the front side and the front bevel intersecting at a contact edge (8) to contact the cylinder. The front bevel has a three-dimensional surface roughness measured according to ISO 25178 of Sa > 0.7 µm, and / or Sz > 18 µm, and / or Sq > 1.0 µm.

Description

Technical Field

[0001] The present invention relates to a doctor blade for creping a paper web from the surface of a drying cylinder (or dryer roller) and a creping device including such a doctor blade. Background Technology

[0002] As is well known, in the manufacture of paper, especially cotton paper, the paper web is creped from the drying cylinder using a creping doctor blade.

[0003] Crinkling is defined as a paper property that produces wrinkles by pressing paper onto rollers with a doctor blade, thereby creating a simulated wrinkled effect. During the creping process, periodically folded microstructures are formed in the paper, which can significantly improve the quality of the paper, such as softness, bulk, tensile strength, and absorbency.

[0004] First, using adhesive chemicals, a continuous wet paper web is pressed and adhered to the surface of a drying cylinder, commonly known as a Yankee drying cylinder. During drying, the cellulose fibers bond together. After being dried by the hot steam and air surrounding the Yankee drying cylinder, the paper web is scraped off the surface by a doctor blade and folded. The doctor blade (more specifically, a creping doctor blade) functions by breaking down the internal structure of the paper by disrupting the bonds between the fibers. Creping paper from the Yankee drying cylinder in a controlled and uniform manner is a characteristic of traditional cotton paper manufacturing.

[0005] Different types of fibers can be used as raw materials for the production of cotton paper. These fibers are generally classified according to their source (virgin or recycled), manufacturing process type (chemical, semi-chemical, mechanical, bleached, unbleached), and biological material type (hardwood, softwood, non-wood).

[0006] Cotton paper manufacturers use various machine technologies. Lightly Dry Crinkling (LDC) is the most traditional technique. In this case, the wet fibers are dried to approximately 65% ​​moisture content on the surface of the Yankee drying cylinder and reach the creping blades at approximately 90-95% dryness. In alternative conventional wet creping techniques, the paper is creped at the creping blades at less than 85% web dryness. Aerated Drying (TAD) is another important technique. While ATD has significant disadvantages, such as higher cost and energy consumption compared to conventional creping machines, it can produce cotton paper products with exceptionally high bulk, softness, and absorbency. Other alternative technologies include Crinkled Aerated Drying (CTAD), Uncreased Aerated Drying (UCTAD), Double Re-creping (DRC), Advanced Cotton Paper Forming System (ATMOS), and New Cotton Paper Technology (NTT). All of these technologies have their specific advantages and disadvantages and are more or less beneficial to the main cotton paper properties.

[0007] Cotton paper products have a wide range of types and applications, including facial tissues, toilet paper, kitchen paper towels, hand towels, napkins, and wet wipes. For all these products, the scraper specifications and settings are crucial for producing the desired cotton paper quality, such as softness, bulk, and absorbency.

[0008] Bulk density is a well-known quantity in papermaking, defined as the volume occupied by a given weight of paper, and is inversely proportional to density. It is an important property of cotton paper because paper thickness (i.e., caliper measurement) and bulk density are closely related to absorbency. Absorbency (rate and volume) is a key characteristic of paper towels and other cotton paper products used for wiping liquids. Water retention capacity (WHC), measured in g / g, is a commonly used indicator for evaluating absorbency. As those skilled in the art will recognize, the relationship between cotton paper thickness, bulk density, and absorbency can be established using the following equation: Looseness (cm) 3 / g)=1 / density(g / cm³) 3 = Dry thickness (µm) / Basis weight (g / m³) 2 ) WHT (g / g) ~ 60-75% of bulk thickness Limited research and existing technology have considered the impact of the creased blade itself on the properties of cotton paper. Some of these studies describe the general shape of the blade and specific blade designs.

[0009] US 4,482,429 A relates to a creping blade having a cutting angle or creping angle of about 72° or less, and preferably 52° to 64°. As described, by utilizing a creping blade with a reverse angle of this specification, the bulk and absorbency of the finished paper web can be further improved.

[0010] US 6,425,983 B1 discloses a creping blade having a plurality of notches on its upper surface; also known as a corrugated creping blade. As described, the notches are provided to increase the thickness of the cellulose web when the creping blade creases the cellulose web from the outer surface of a rotatable roller.

[0011] GB 2 128 551 B discloses a scraper with a wear-resistant material at the tip, based on different embodiments. Coating the scraper tip, which will contact the surface of the Yankee drying cylinder, with a wear-resistant material is indeed advantageous to increase production time and maintain high stability of the wrinkling process over a long period.

[0012] What is lacking in existing technologies are alternatives for further increasing bulk. Therefore, customers in the paper industry producing cotton paper need a new type of creping blade that can itself enhance the bulk and absorbency of cotton paper. Summary of the Invention

[0013] Therefore, the technical problem to be solved by the present invention is to provide an improved scraper that overcomes the shortcomings of the prior art.

[0014] The second technical problem to be solved by the present invention is to provide a crease scraper that can positively influence the paper thickness (i.e., caliper measurement) and the bulk of cotton paper in a controlled manner.

[0015] The third technical problem to be solved by the present invention is to provide a crease scraper that can improve the absorbency of cotton paper.

[0016] The fourth technical problem to be solved by the present invention is to provide a universal solution that is relatively easy to manufacture and can be combined with a variety of scraper designs.

[0017] The technical problem is solved by a doctor blade for creping the paper web from the surface of the drying cylinder and a creping device including such a doctor blade.

[0018] In the context of this application, the terms "scraper" and "wrinkling scraper" are used as synonyms unless otherwise expressly stated.

[0019] A doctor blade for creping a paper web from the surface of a drying cylinder is introduced. The doctor blade includes a front side and a front bevel that is impacted by the paper web. The front side and the front bevel intersect at a contact edge for contacting the drying cylinder.

[0020] According to the present invention, the three-dimensional surface roughness of the front inclined surface is measured according to ISO 25178 as follows:

[0021] Sa>0.7μm, and / or

[0022] Sz>18μm, and / or

[0023] Sq>1.0µm.

[0024] In many implementations of this scraper, all roughness values ​​exceed the thresholds of Sa > 0.7 µm, Sq > 1.0 µm to Sz > 18 µm.

[0025] However, for scrapers according to various aspects of the invention, one or both of these roughness measurements are likely to be below the threshold.

[0026] In the preferred embodiment, Sz is greater than 18 μm, especially 25 μm or greater.

[0027] The drying cylinder can be a Yankee drying cylinder.

[0028] Referring to the ASM (American Materials Society) Handbook, Volume 5 - Surface Engineering, 1994 (pp. 136-138), the morphology of a surface is defined by a combination of three specific characteristics: surface roughness, surface waviness, and surface shape.

[0029] As mentioned above, existing technologies only focus on the impact of macroscopic morphological characteristics, such as waviness (“wavy wrinkling blade”) and surface shape (e.g., “wrinkling angle”), on paper properties.

[0030] If microscale morphology is considered in the existing technology, the goal is to minimize roughness as much as possible to reduce wear and scratches.

[0031] The scraper comprises a front side facing the drying cylinder and a rear side facing away from the drying cylinder. The distance between the front and rear sides defines the thickness of the scraper (x-direction). Typically, the scraper thickness is between 600 μm and 1500 μm. The front and rear sides are usually parallel, at least for a portion of the scraper's width direction (y-direction). The length of the scraper (z-direction) typically extends several meters and corresponds to the transverse (CD) dimension of the drying cylinder to which it is prepared.

[0032] It should be noted that the front side of the scraper can include multiple surfaces. For example, if the main surface contacts the rotary drying cylinder, a so-called sliding wear surface will be formed. To better accommodate the sliding surface and make it easier for the scraper to engage with the dryer surface, a pre-tilt angle can be formed at the tip of the scraper during the manufacturing of the wrinkling scraper. The sliding wear surface and the pre-tilt angle are considered part of the front side.

[0033] The front bevel is a portion of the top side of the doctor blade. The front bevel is the surface adjacent to the front side that extends along the thickness direction of the doctor blade. When used as a creping doctor blade, the paper web typically impacts this portion of the doctor blade at very high speeds, such as 2000 m / min. Although the top side of the creping doctor blade can extend up to 1500 μm, typically only the first 150 μm from the contact point with the doctor blade is impacted by the paper web, and this primarily affects the bulk of the paper.

[0034] Based on experience, the paper web impacts the doctor blade at an average distance of 100 μm to 150 μm along the x-direction. Therefore, the front bevel extends at least 150 μm along the x-direction from the doctor blade contact point. Within this 150 μm region, the aforementioned roughness requirements are absolutely necessary. In many cases, it is advantageous to extend this roughness beyond 150 μm along the x-direction. For example, a preferred roughness can be provided at a distance of at least 250 μm or at least 350 μm from the doctor blade contact point. This helps ensure that a sufficiently large front bevel with the required roughness is maintained even after the doctor blade has worn to a certain extent.

[0035] In many applications, the necessary roughness is provided across the entire top side of the scraper, extending up to 1500 μm from the scraper contact point, as this can be easily achieved through standard methods such as thermal spraying or sandblasting, although this is not necessary for the present invention. On the other hand, more sophisticated methods, such as laser engraving, can be used to produce the necessary roughness only on a portion of the top side of the scraper.

[0036] The present invention is based on a surprising observation that even the smallest features of the surface morphology of the front bevel are affected during the creeping process of the doctor blade, i.e., in the specific mechanism of producing the paper structure. More specifically, it has been found that a higher roughness of the creeping doctor blade surface subjected to the impact of the paper web, i.e., the front bevel, does indeed alter the stress during the separation of the paper web from the drying cylinder, resulting in more fiber bonding being disrupted and / or twisted. In any case, this leads to a different fiber structure arrangement. This finding is surprising because it is generally known in the art that doctor blades, especially the tips, should be as smooth as possible to reduce wear on the doctor blade and the dryer. The applicant has found that while this applies to the area in contact with the roller, the front bevel should be made rougher.

[0037] The principle of increasing bulk by disrupting / distorting the fiber structure through the roughness of the front bevel is understandable. However, in the applicant's initial tests, the correlation between measured roughness and the increase in bulk was not strong. After conducting extensive experiments, the applicant made another surprising discovery: the roughness measurement used as a standard cannot reliably describe the surface roughness that affects paper quality.

[0038] In most cases, the scraper according to one aspect of the invention will be manufactured and sold as a scraper having a front bevel exhibiting the desired roughness. However, it is also possible that a new scraper exceeds the claimed roughness range upon installation, but achieves the required roughness after a certain period of operation due to wear or special treatment. Both types of scrapers are included in this application.

[0039] Technicians are aware that typically three to six roughness parameters are required to properly characterize the surface morphology.

[0040] Industry standards are typically measurements performed according to established standards. ISO 4287 Geometry Product Specification (GPS) - Surface Texture: Profile Method - Terminology, Definitions and Surface Texture Parameters.

[0041] This standard supports two-dimensional (2-D) or line roughness measurement and provides the following values: - Ra: Arithmetic mean deviation of the roughness profile (amplitude parameter, in micrometers) - Rz: Maximum height of the roughness profile (amplitude parameter, in micrometers) - Rq: Root mean square deviation of roughness profile (amplitude parameter, in micrometers) - Rc: Average height of the roughness profile element (amplitude parameter, in micrometers) - Rt: Total height of the roughness profile (amplitude parameter, in micrometers) Because of the two-dimensional nature of these values, they cannot accurately characterize the surface structure (which may be called "effective roughness") that affects paper bulk. This will be explained in more detail below.

[0042] The applicant found that according to the standard ISO 25178 Roughness measurement: ISO 25178 Geometry Specification for Products (GPS) – Surface texture: Area method – Metrological characteristics of area shape measurement methods – is more suitable. This standard supports three-dimensional (3-D) or surface roughness measurement and provides measured values. Sa: Arithmetic mean height (height parameter, unit: micrometers) Sz: Maximum height (height parameter, unit: micrometers) Sq: Root mean square height (height parameter, in micrometers) For these measurements, the Rtec Instruments UP-24 general-purpose profilometer (non-contact rapid 3D measurement, line and area measurement technology) can be selected. All 3D roughness measurements shown in this application were performed on this instrument. Two-dimensional measurements were also performed on these instruments.

[0043] Non-contact measurement methods like the UP-24 are preferred because accurately determining roughness values ​​is important. Contact measurements carry the risk that the stylus may not be able to penetrate narrow pits of the same depth as a non-contact instrument, leading to inaccurate measurements.

[0044] The following table shows the parameter settings for the profilometer:

[0045] Experiments show that three-dimensional surface values ​​describe "effective roughness" very accurately. For roughness values ​​Sa > 0.7 μm to / or Sz > 18 μm to / or Sq > 1.0 μm, a significant effect on porosity can be observed.

[0046] In a preferred embodiment, the roughness value can be within the following range: Sa is between 0.7µm and 9µm, especially between 2µm and 6µm, and / or Sz is between 18 μm and 100 μm, especially between 25 μm and 70 μm, and / or Sq is between 1.0 μm and 11 μm, especially between 2.5 μm and 7 μm.

[0047] It has been observed that while the bulk of cotton paper products increases with increasing roughness of the front bevel, other properties of the cotton paper products may deteriorate. For example, pinholes may appear in the product, or the visual aesthetics of the cotton paper surface may worsen. For some cotton paper products, these characteristics may be insignificant. However, for others, these properties are only acceptable to a certain extent. In many cases, the range given above represents a good trade-off between the increase in bulk and the decrease in other properties.

[0048] The aforementioned roughness values ​​can be generated by periodic and non-periodic surface structures. In order to optimize bulk by disrupting / distorting the fiber structure through the roughness of the front slope, non-periodic surface structures are generally preferred, because periodic structures may have a significant adverse effect on cotton paper.

[0049] One advantage of this invention is that it can be combined with a variety of scraper designs.

[0050] Therefore, the macroscopic shape of the front slope can be, for example, flat or can have a macroscopic shape, especially a wavy shape.

[0051] The angle between the front side and the front ramp is called the tilt angle β. The tilt angle can be set from 60° (negative front ramp) to 110° (positive front ramp), preferably from 70° to 95°.

[0052] Although the top side of the creaser blade can extend up to 1500 μm, the initial 150 μm or 250 μm primarily affects the paper bulk. Empirically, the paper web impacts the front bevel at an average distance of 100 μm to 150 μm from the blade contact point along the x-direction. Therefore, this surface is a key consideration in this invention. Roughness values ​​Sa > 0.7 μm and / or Sz > 18 μm to / or Sq > 1.0 μm may only appear at the initial 150 μm or 250 μm of the top side of the blade, as this is typically the technically relevant front bevel. Different roughness values ​​are possible at larger distances from the contact edge, such as 350 μm or 500 μm, without negatively impacting the paper bulk.

[0053] In most applications, the scraper will include a steel strip (= steel scraper).

[0054] The most suitable steel strips for this application are specified according to EN 10132-4. DIN EN 10132-4 specifies the standardized name, chemical composition, and associated physical and mechanical properties of the steel. To achieve optimal elastic "spring-like" properties, these steel strips are typically heat-treated. Therefore, these high-strength, hardened, and tempered high-carbon steels generally have a hardness ranging from 350 HV to 600 HV, measured in Vickers hardness (HV). While other alternative steels, such as stainless steel, may be used, the hardness specifications are similar.

[0055] This type of steel scraper may have abrasion-resistant material (coating and grinding) at the tip.

[0056] The scraper may also have a thermally sprayed coating, for example, based on a ceramic material. To protect the scraper tip, the moving part most likely to be subjected to mechanical stress and wear, a wear-resistant deposit can be advantageously applied. Different deposit embodiments can be applied to partially or completely protect different areas of the scraper tip. This results in a longer service life and more stable operating conditions. Typical deposit types, such as those made of at least one metal oxide, at least one metal nitride, or at least one metal carbide, or including at least one metal oxide, at least one metal nitride, or at least one metal carbide, are suggested for use in this application. More specifically, carbide-based materials, particularly those based on tungsten carbide, have been found to be very suitable for meeting the requirements of this invention. Indeed, most carbides are very hard and are suggested for wear-resistant purposes. The material is typically in the form of a composite consisting of a large number of carbide particles uniformly distributed in a matrix, i.e., a metal matrix. The latter composite acts as a binder, supporting the hard and brittle reinforcing phase. Cermet is a common name for such composite materials. Typically, the volume of the matrix or binder phase is less than 30% of the total volume of the cermet. When selecting a cermet reference from a supplier, carbide size is an important criterion. While process parameters obviously affect the final roughness of the deposit, it has been shown that a larger primary carbide grain size results in a greater surface roughness. For example, the average carbide size used to manufacture some products according to the invention ranges from 0.5 μm to 15 μm. The process technique for applying this cermet is thermal spraying, more specifically, high-speed flame spraying. Typical deposit hardness, measured in Vickers hardness (HV) across a cross-section of the material, ranges from 900 to 1700 HV. In many applications, the hardness of the deposit is two to four times that of the underlying steel substrate.

[0057] All of these types of scrapers can have a front bevel with a three-dimensional surface roughness according to one aspect of the invention.

[0058] The working surface of the scraper to be in contact with the Yankee drying cylinder should be smooth and typically finished to a predetermined low roughness level. Typical roughness specifications are Ra < 0.4 μm to Rz < 4.0 μm. While the purpose of this invention is to intentionally increase the 3D roughness of the front bevel, it is evident that the adjacent surfaces to be in contact with the Yankee drying cylinder must maintain surface roughness within the aforementioned "smooth" specification range. Furthermore, even smoother contact surfaces with Ra < 0.2 μm to / or Rz < 2.0 μm are also common.

[0059] The required three-dimensional roughness of the front bevel can be achieved in a variety of ways. Almost any manufacturing process can be used to alter the surface morphology, for example, to increase its roughness. This will involve surface alteration or surface modification principles. Such surface treatment processes can include mechanical (e.g., machining, sandblasting), chemical (etching, coating), thermal (heat treatment, energy beam, coating, deposition), and / or electrical (energy release) effects; with or without the addition of further materials (e.g., coatings or deposited layers).

[0060] For example, post-processing such as sandblasting can be applied to improve the roughness to the desired level. Alternatively, in the case of applying a thermal spray coating, the process can be adapted to achieve the required three-dimensional roughness. In this case, post-processing can be omitted.

[0061] According to the present invention, isotropic properties or roughness characteristics are not necessarily required. However, this is often the case because the chosen post-processing and manufacturing methods tend to produce such isotropy.

[0062] In papermaking machines, especially cotton paper machines, the doctor blade according to the present invention is used in conjunction with a drying cylinder, especially a Yankee drying cylinder, in the form of a creping device.

[0063] It may be advantageous here that the contact angle α between the scraper and the drying cylinder is 5° to 35°, preferably 15° to 25°.

[0064] It should be understood that during use, the scraper tip at the contact edge with the Yankee dryer cylinder surface experiences a certain amount of wear consistent with the angle α. This will result in a sliding wear surface. To prevent damage to the Yankee dryer cylinder surface, a low sliding wear angle should be preferred.

[0065] To better adapt to the sliding surface and facilitate easier engagement of the doctor blade with the Yankee drying cylinder surface, a pre-tilt angle can be formed at the tip of the doctor blade during the wrinkling doctor blade manufacturing process. The pre-tilt angle is typically smaller than the intended contact angle α. In preferred applications, the pre-tilt angle can be selected to be less than 15°, for example, 2°, 5°, 8°, or 10°.

[0066] Alternatively or additionally, it may be advantageous that the pocket angle δ between the tangent at the contact end of the drying cylinder at the tip of the scraper and the front inclined surface is 115° to 35°, preferably 95° to 65°, and more preferably 85° to 70°. (The pocket angle is sometimes also called the cutting angle or the wrinkling angle).

[0067] While the tilt angle β is a design parameter of the doctor blade, the concavity angle δ is a result of the tilt angle β and the contact angle α, and determines the quality of the creping structure. Angle δ is measured between the tangent at the contact edge of the doctor blade tip on the Yankee dryer cylinder surface and the front bevel of the creping doctor blade (also known as the web impact surface). In principle, increasing δ by reducing α and / or β leads to improved softness while simultaneously reducing thickness. Attached Figure Description

[0068] The present invention will be further described below with reference to the accompanying drawings and embodiments. The present invention is not limited to these embodiments.

[0069] Figure 1 A side view schematic diagram of a portion of a cotton paper machine having a creping device according to one aspect of the invention is shown. Figure 1a A schematic diagram of a scraper according to one aspect of the invention is shown. Figures 2a to 2d A cross-sectional schematic diagram illustrating the wrinkling development principle shows the four stages of wrinkling formation, from micro-wrinkles to macro-wrinkles. Figure 3 A portion of a wrinkling device having a wrinkling scraper according to another aspect of the invention is shown. Figure 4 A general view of the prior art is shown (Materials Society Handbook, Vol. 5, 1994, Surface Engineering, p. 136). Figure 5 and Figure 6 A graph showing the two-dimensional roughness values. Figure 7 A graph showing the three-dimensional roughness values, Figure 8a This shows an SEM image of the front bevel of the prior art. Figure 8b This shows a SEM image of the front bevel according to one aspect of the invention. Figure 9a The shape of the front slope in the prior art is shown. Figure 9b The shape of the front slope according to one aspect of the invention is shown. Detailed Implementation

[0070] At the start of the papermaking process, the raw material or feedstock, namely highly diluted pulped wood fiber pulp, is supplied to the paper machine from the headbox and evenly distributed across the entire width of the machine in the gap between two rolls. One roll has metal wire, i.e., a screen, and the other roll has felt, i.e., a thick fabric. The wet paper web 1 adheres to the felt and follows the felt into the machine at a high speed. Dehydration occurs before reaching the vacuum pressure rolls 2 and the drying cylinder 3 in the form of a large Yankee drying cylinder 3. The dimensions of the Yankee drying cylinder 3 are defined by its diameter of approximately 5 m (up to 7.3 m) and its length (cross-machine direction CD) of approximately 5.5 m (up to 7.8 m). Its length is slightly wider than the width of the paper 1. Coating chemicals can be sprayed from a series of nozzles 4 to promote adhesion between the paper 1 and the Yankee drying cylinder 3 and to protect the metal surface of the drying cylinder 3. The drying process is carried out by steam-heated Yankee drying cylinder 3 and hot airflow from a cover 5. Lightweight fiber strips move at speeds up to 2400 m / min, impacting the front bevel 10 of the crease doctor blade 6 and scraping it off the surface of the Yankee drying cylinder 3. The dimensions of the crease doctor blade 6 are defined by its length (maximum 7.8 m when measured along the z-direction or CD-direction), width (between 50 and 150 mm when measured along the y-direction), and thickness (between 0.6 and 1.5 mm when measured along the x-direction). This then forms the crease structure of the cotton paper 7. At the end of the process, the finished cotton paper 7 is wound onto a large roll at a lower speed compared to the Yankee drying cylinder 3.

[0071] Figure 1a A typical scraper 6 according to one aspect of the invention is shown, comprising a front side 20, a rear side 30, and a top side 40. The front side 20 is generally parallel to the rear side 30, except for the surface of the pre-tilted portion 21. The scraper 6 is a steel scraper with an abrasion-resistant coating 25 applied. The coating 25 covers the entire top side 40 and a portion of the front side 20. Depending on the application, other areas of the scraper 6 may be covered with the abrasion-resistant coating 25; for example, only a portion of the top side 40 may be covered with the abrasion-resistant coating 25.

[0072] One purpose of these coatings 25 can be to increase hardness. While the Vickers hardness of typical steel used as the substrate is 350 HV to 600 HV, the hardness of the resulting coating 25 can range from 900 HV to 1700 HV. Typically, the hardness of the deposit 25 is two to four times that of the base steel substrate.

[0073] The front bevel 10 is located on the top side 40 of the scraper and extends from the contact edge 8 along the x-direction. The front bevel 10 extends at least 150 μm, preferably 250 μm or more along the x-direction. According to the invention, the roughness at the front bevel 10 is relatively high, i.e., Sa > 0.7 μm and / or Sz > 18 μm and / or Sq > 1.0 μm.

[0074] The other parts of the scraper 6, namely the other parts of the front bevel 21 or the front side 20, should be smooth. These surfaces of the scraper may have a roughness of Ra < 0.4 μm and Rz < 4.0 μm.

[0075] Figures 2a-2d A detailed investigation of the wrinkling mechanism is described, revealing a four-stage process involving the development of micro-wrinkles 71, which aggregate into larger macro-wrinkles 73 under the action of the scraper 6.

[0076] Crinkling delaminates the internal physical structure of the paper web 1, forcing the fibers to weaken or break, and causing them to bend, twist, or even break. Micro-creases 71 (stage 1) are created and stacked on top of each other (stage 2). When the stacked structure 72 is high enough (stage 3), macro-creases 73 fall, producing a macro-folded and structured final product 7 (stage 4). Compared to the folding type of crease, the delamination process tends to produce thicker, more absorbent, and softer cotton paper products with greater water retention. Crinkling is a complex interplay of many factors. Managing the process is crucial for producing cotton paper 7 with high bulk, absorbency, softness, and stretchability.

[0077] Figure 3 Different angles are shown for defining the geometry of the tip of the creaser 6 in application. The creaser 6 includes a front side 20 facing the Yankee cylinder 3 and a rear side 30 facing away from the Yankee cylinder 3. The sliding wear angle α is the contact angle between the Yankee cylinder 3 and the creaser 6. It is directly related to the creaser retainer angle and the elastic deformation of the creaser 6 under a given load condition. Typical values ​​of α are between 5° and 35°, typically around 19°. It should be understood that during use, the creaser tip at the contact edge 8 in contact with the surface of the Yankee cylinder 3 will experience a certain amount of wear consistent with this angle α. This will result in the formation of a sliding wear surface 9. To better accommodate the sliding surface and make it easier for the creaser to engage with the surface of the Yankee cylinder 3, a pre-tilt angle 21 can be formed at the creaser tip during the manufacturing process of the creaser. This pre-tilt angle 21 can be selected, for example, between 5° and 10°. Typically, this pre-tilt angle 21 is smaller than the sliding wear angle α. To prevent damage to the surface of the Yankee cylinder 3, a low sliding wear angle is preferred. The tilt angle β is a design parameter of the scraper 6. Typical values ​​for β range from 60° (negative front bevel) to 110° (positive front bevel). The resulting angle δ (also known as the wrinkling angle or concave angle) is important for the quality of the wrinkled structure. Angle δ is measured between the tangent of the Yankee drying cylinder surface 3 at the scraper tip contact point 8 and the front bevel 10 (also known as the web impact surface) of the wrinkling scraper 6.

[0078] In principle, increasing δ by reducing α and / or β results in increased softness and decreased thickness. Importantly, empirically, the paper web 1 impacts the front bevel 10 at an average distance of 100 μm to 150 μm from the doctor blade contact point 8 along the x-direction. Therefore, in most cases, this surface extends to approximately 250 μm from the doctor blade contact point 8, which is a key factor to consider in this invention. Finally, the output angle θ depends directly on the rewinder position and the web tension. Standard geometries can be selected to fit the crease bag and obtain suitable crease quality.

[0079] The interaction between the paper web 1 and the front bevel 10 plays a major role in producing the wrinkled structure and the final properties of the cotton paper 7. Therefore, it is important to focus on this surface 10 and better define its characteristics. Those skilled in the art know, for example, from the technical definitions in the ASM manual, that most surfaces have regular and irregular spacing that tends to form patterns or textures on the surface. Based on the general principles derived from this source… Figure 4 The final form of the surface is composed of three specific features: - Surface roughness 11 refers to the high-frequency surface irregularities caused by the interaction between the material's microstructure and surface preparation. - Surface ripples 12, i.e., mid-frequency irregularities on the surface, with surface roughness superimposed on these mid-frequency irregularities. - Surface shape, i.e. the general shape of the surface, such as flat, round, etc., ignoring roughness and ripples.

[0080] Orientation (lay) 13 is another important feature of the surface. It is a processing pattern with a clear directionality. Orientation is an important consideration because the measurement of surface morphology will vary depending on the direction of measurement. This is why it is recommended to define the surface roughness measurement as a region. This is especially used to characterize the morphology of the critical front bevel 10; particularly in specific areas near the doctor blade contact point 8 where paper web impact occurs.

[0081] Example 1

[0082] The following example highlights the importance of three-dimensional roughness measurement in order to properly characterize the “effective roughness” of the front bevel 10.

[0083] Three different substrates were selected: S1 - Standard steel substrate S2 - Steel substrate, with wear-resistant material (coating and grinding) at the scraper tip. S3 steel substrate, with multiple notches at the tip of the scraper (corrugated scraper). Two specific surface treatments are used individually or in combination to alter the texture of a particular front bevel 10 of the scraper 6. Importantly, the surface of the front side 20 adjacent to the front bevel 10 and in contact with the Yankee drying cylinder 3 in the area connected to 8 must not be rough. It is recommended to keep this contact surface as smooth as possible to avoid damaging (e.g., scratching) the Yankee drying cylinder surface 3, which may form the sliding wear surface 9 during use. Typical roughness specifications for these contact surfaces are Ra < 0.4 μm and Rz < 4.0 μm.

[0084] T1 - Thermal spray coating based on ceramic materials

[0085] (Spray-coated, without surface polishing / grinding or polishing)

[0086] Sandblasting treatment of T2-angular alumina particles

[0087] (Size: F180, 1 nozzle, distance 50mm, pressure 4 bar)

[0088] Based on these three substrates S1-S3 and two surface treatment processes T1 and T2, a series of 15 scraper samples, labeled A to O, were manufactured according to standard methods (i.e., basic structures provided or manufactured according to existing technology). While scraper samples A, B, C, and D serve as 100% references from existing technology, all other samples have one (samples E, N, and O) or two (samples F to M) additional subsequent surface treatments to meet the requirements of this invention. The post-processed scraper samples E to O are to be gradually processed, resulting in an increased roughness of the front bevel 10. Although scraper samples M, N, and O are expected to be the roughest in the series, it cannot be said that the resulting roughness values ​​are the maximum values ​​limiting the upper limit of this invention.

[0089] The table below provides the main manufacturing process steps and parameters for manufacturing the reference doctor blade example and the doctor blade example according to the present invention. It should be noted that, in cases involving multiple process steps, the order is always from top to bottom. Although the entire top side 40 of examples E to O is post-processed, it is important that the front bevel 10 be confined to a distance of approximately 150 μm or 250 μm (0.25 mm) from the doctor blade contact point 8, as this is the location where the paper web 1 impacts the front bevel 10.

[0090]

[0091] Table 1: Scraper Examples

[0092] For these 15 samples, the roughness values ​​of the front bevel were measured in three ways: 2D measurement along the transverse direction (ISO 4287), 2D measurement along the longitudinal direction (ISO 4287), and 3D measurement (ISO 25178). The results are given in the table below (all values ​​are in meters).

[0093] Table 2: Roughness Values

[0094] Figures 5 to 7 The evolution of the roughness parameters described above for each scraper sample (A to O) is illustrated using simplified relationships. Figure 5 and Figure 6 The results show that the longitudinal and transverse roughness values ​​are very consistent. This confirms the uniformity of the surface texture along the two main directions, namely the machine direction (MD) and the transverse direction (CD).

[0095] According to the invention, it is not necessary to have isotropic properties or roughness characteristics in these directions. However, the selected post-processing and manufacturing methods tend to promote the formation of such isotropic properties or roughness characteristics.

[0096] When these charts are compared with Figure 7 When comparing the final charts, the trends of the three-dimensional surface roughness measurements are less disturbed and exhibit a more continuous evolution for the post-processed scraper samples E to O. It is important to note that the initial goal was to gradually increase the roughness of the front bevel 10. In any case, the three-dimensional surface roughness measurements clearly better represent the overall surface roughness characteristics. This is why the three relevant roughness parameters Sa and / or Sz and / or Sq are considered only for the roughness specifications according to the invention. Compared to reference scraper samples A to D, the increased surface roughness of the scraper samples according to the invention is characterized by the following specifications: Sa > 0.7 μm and Sz > 18 μm and Sq > 1.0 μm. Although in these embodiments, all three roughness parameters show more or less the same trend between samples, this is not necessarily the case. It is also possible for a sample to have, for example, fairly low Sa and Sq values ​​(e.g., about 1.3 μm, 1 μm, or even lower), while having a relatively high Sz value (e.g., 30 μm or 40 μm). This will still provide a favorable scraper.

[0097] In order to provide a visual impression of the surface structure according to one aspect of the invention, Figure 8a and Figure 8b Electron microscopy (SEM) images of two different top-side 40 surfaces are shown. Figure 8a Taken from Sample A, which is a standard steel substrate in the prior art, and Figure 8b Taken from sample N, which uses the same substrate but has undergone thermal spraying and sandblasting. Accordingly, Figure 9a It shows Figure 8a The morphology measurement of the scraper, and Figure 9b It shows Figure 8b The shape measurement of the scraper.

[0098]

[0099] Table 3: Comparison

[0100] The differences between the two types of scrapers are clearly visible. Figure 8a Sample A has a smooth and glossy top side 40. Corresponding to orientation 13, the diagonal lines are produced by a grinding process. Apart from these lines and the occasional small dot-like defects, the surface is very smooth and flat.

[0101] In comparison, Figure 8b Example N shows a very rough and jagged surface. It has a completely matte appearance. In this example, the structure appears isotropic, showing no preferred orientation. Figuratively speaking, a scraper according to the prior art looks like a sandy beach, while a scraper according to one aspect of the invention looks more like a bird's-eye view of a mountainous region. Figure 8b In the middle, the front bevel 10 extends over the entire top side 40 of the scraper.

[0102] Figure 9a and 9b The morphological measurements emphasize the visual impression. Here, the x-direction is the thickness direction of the scraper 6, while the z-direction is parallel to the surface of the Yankee drying cylinder 3. The difference in morphological height, i.e., between the deepest groove and the highest top of sample A, is approximately 2 μm, while the value for sample N is approximately 60 μm. Therefore, the height of sample N is approximately 30 times that of sample A. This corresponds very well to the Sa / Sz / Sq values. Each of these three roughness measurements for sample N is approximately 30 times higher than that for sample A. This again emphasizes the fact that these values ​​are best suited for characterizing the front bevel of a scraper within the scope of this invention.

[0103] To evaluate the performance of the wrinkling doctor blade according to the present invention (sample reference - Pr n°) compared with the prior art wrinkling doctor blade (sample reference - Sr n°), several comparative tests were conducted under real conditions. These wrinkling doctor blades will be manufactured according to the sample given in Example 1.

[0104] When a sample or standard reference n° is associated with an internal manufacturing n°, the correspondence with a standard steel doctor blade is given. The following two examples provide test results for different types of crepe paper produced by a cotton paper mill.

[0105] Example 2

[0106] The first experiment was conducted under the following operating conditions and settings: - The paper web is made from 100% virgin fiber. - Handkerchief / Face Tissue Grade - 10.5 to 11 g / m 2 cotton paper base weight - The basic thickness (dry) of the cotton paper is 42μm. - Metallized Yankee drying cylinder surface - The Yankee drying cylinder speed is 1650 m / min - 5.9 mg / m 2 amount of coating chemicals - The dimensions of the wrinkling scraper are 1.0×120×5850mm (thickness×width×length). - The inclination angle β is 75° (-15° negative front slope). - The sliding angle α is 21° - The concave angle δ is 84° The aim of the experiment was to increase the thickness of the paper, thereby increasing its bulk, so as to benefit from conversion in subsequent processing steps. Indeed, it is economically viable to sell less product (higher thickness and therefore more air) for the same price. As is known to those in the know, fiber costs are by far the highest expense in papermaking, potentially accounting for 50% of all production costs. Therefore, even relatively small savings in fiber consumption (e.g., 1% or 2%) can significantly improve the profitability of production.

[0107] As a key requirement, especially in the case of facial tissues and handkerchiefs, smoothness and softness must not be compromised.

[0108] The following three scrapers were tested within the relevant production time (hours) mentioned above: Sample label B = Sr 6835 (27 hours) is used as a reference. Sample label E = Pr 8614 (22 hours) and Sample label N = Pr 8661 (22 hours).

[0109] The customer reported positive results. Improvements were observed in measurements based on the increase in dry cotton paper thickness over time compared to the reference standard, summarized as follows: Basic thickness of cotton paper : For reference scraper Sr 6835(B) with a diameter of 42 μm The innovative scraper Pr 8614(E) shows an improvement of 1.5% to 2.5%. The innovative scraper Pr 8661(N) shows a 3.0% to 4.0% improvement. It is worth noting that the surface of the tissue paper appears more uniform, with fewer markings (also known as wrinkles) along the transverse (CD) direction. This is explained by the direct effect of surface texture and higher roughness, causing the fibers to disperse in more directions. Therefore, the distribution of fibers on the surface of the tissue paper is more uniform.

[0110] As defined, bulk depends on the basis weight of the cotton paper. With this in mind, it is claimed that using the optimized creaser according to the invention, the maximum increase in bulk in the specific cotton paper application described above is expected to be 10%.

[0111] Example 3

[0112] In the second experiment, it was decided to target an application where batch scaling was the primary objective. The following operating conditions and settings were used: - The paper web is made from 100% virgin fiber. - Kitchen paper towels / absorbent paper grades - 19 to 20 g / m 2 cotton paper base weight - The basic thickness (dry) of the cotton paper is 110μm. - Metallized Yankee drying cylinder surface - Yankee drying cylinder speed is 1600 m / min - The dimensions of the wrinkling scraper are 1.2×105×3200mm (thickness×width×length). - The tilt angle β is 90° (for the front slope of a square). - The sliding angle α is 16° to 21° (a more precise measurement is not possible due to production time being limited to approximately one hour). - The concave angle δ is 69° to 74° The purpose of the test was to increase the bulk and absorbency of the cotton paper. In fact, all aspects of cotton paper quality are crucial for kitchen paper towels. Although the softness of the cotton paper is the least important, the stretch of the cotton paper measured in both the machine direction (MD) and the transverse direction (CD) will also be considered.

[0113] The following three scrapers were tested within the relevant production time (hours) mentioned above: Sample label A = steel scraper as a reference Sample label I = Pr 9401 (1.2 hours) and Sample label K = Pr 9426 (1.2 hours) It should be noted that there are no references for current steel doctor blades, as they are not products provided by the inventor. Nevertheless, it is the most common and basic type of creping doctor blade familiar to technicians. Its main disadvantages are related to short lifespan, limited stability in the creping process, and inconsistent cotton paper quality.

[0114] The customer reported initially satisfactory results. Based on improvements in various cotton paper quality parameter measurements and other relevant results, the following summary is presented: Dry cotton paper base thickness : The reference thickness for steel scrapers is 110μm. The innovative Pr 9401(I) scraper has been improved by 5%. The innovative Pr 9426(K) scraper achieves a 25% to 30% improvement. Looseness : The reference value for steel scrapers is 5.7cm. 3 / g The innovative Pr 9401(I) scraper has been improved by 5%. Improvements of 20% to 25% for the innovative Pr 9426(K) scraper. The particularly good results achieved when using the creping doctor blade Pr 9426 are relative, as a significant square pattern is clearly visible to the naked eye on the paper surface. This is characterized by markings on the fabric surface along the transverse (CD) and machine direction (MD). While this may be acceptable for some applications, it can be unacceptable from the perspective of paper quality or aesthetics, depending on the type of paper, its end purpose, and / or further customer acceptance. This is a major drawback of doctor blades with notches on the front bevel, especially when the depth and size of the notches are relevant. Notches spaced at approximately 1 mm are large enough to be expected to cause mechanical deformation or embossing of the paper web upon impact with the surface during creping.

[0115] The scraper according to the present invention can also be used to manufacture other grades of cotton paper, such as toilet paper.

[0116] List of reference numerals

[0117] 1. Paper width

[0118] 2 Vacuum pressure rollers

[0119] 3. Yankee drying cylinder

[0120] 4 nozzles

[0121] 5. Cover

[0122] 6. Wrinkling scraper

[0123] 7. Tissue paper with slight wrinkles

[0124] 8. Contact edge

[0125] 9. Sliding wear surface

[0126] 10 front bevel

[0127] 11. Roughness

[0128] 12 ripples

[0129] 13 Orientation

[0130] 20 Front

[0131] 21 Pre-tilting section

[0132] 25 Abrasion-resistant coating

[0133] 30 rear side

[0134] 40 Top Measurement

[0135] 71 micro-pleats

[0136] 72 Stacked Structure

[0137] 73 Macroscopic folds

Claims

1. A doctor blade (6) for creping a paper web (1) from a drying cylinder surface (3), the doctor blade (6) comprising a front side (20) and a front bevel (10), the front side (20) and the front bevel (10) intersecting at a contact edge (8) for contacting the drying cylinder (3), the front bevel (10) extending at least 150 μm along the thickness direction of the doctor blade (6) from the contact edge (8) and being impacted by the paper web (1), characterized in that, The three-dimensional surface roughness of the front inclined surface (10) is measured according to ISO 25178 as follows: Sa>0.7μm, and / or Sz>18μm, and / or Sq>1.0µm.

2. The scraper (6) according to claim 1, characterized in that, The three-dimensional surface roughness of part or all of the front inclined surface (10) is measured according to ISO 25178 as follows: Sa is between 0.7 μm and 9 μm, and / or Sz is between 18 μm and 100 μm, and / or Sq is between 1.0 μm and 11 μm.

3. The scraper (6) according to claim 1 or 2, characterized in that, The angle β between the front side (20) and the front inclined surface (10) is 60° to 110°.

4. The scraper (6) according to claim 3, characterized in that, The angle β between the front side (20) and the front inclined surface (10) is 70° to 95°.

5. The scraper (6) according to claim 1 or 2, characterized in that, The macroscopic shape of the front inclined surface (10) has a macroscopic form.

6. The scraper (6) according to claim 1 or 2, characterized in that, The macroscopic shape of the front inclined surface (10) is flat.

7. The scraper (6) according to claim 5, characterized in that, The macroscopic shape of the front inclined surface (10) has a wavy morphology.

8. The scraper (6) according to claim 1 or 2, characterized in that, The front bevel (10) extends at least 250 μm from the scraper contact edge (8).

9. The scraper (6) according to claim 7, characterized in that, The front bevel (10) extends at least 350 μm from the scraper contact edge (8).

10. The scraper (6) according to claim 7, characterized in that, The front bevel (10) extends over the entire top side (40) of the scraper (6).

11. The scraper (6) according to claim 1 or 2, characterized in that, The scraper (6) is a steel scraper.

12. The scraper (6) according to claim 10, characterized in that, The scraper (6) comprises steel with a hardness in the range of 350 HV to 600 HV, the hardness being measured in Vickers hardness.

13. The scraper according to claim 10, characterized in that, The scraper includes a deposit of abrasion-resistant material (25).

14. The scraper according to claim 12, characterized in that, The scraper comprises deposits made of a ceramic-based material (25).

15. The scraper according to claim 13, characterized in that, The ceramic-based material (25) includes at least one of metal oxides, metal carbides, metal nitrides, or combinations thereof.

16. The scraper according to claim 14, characterized in that, The ceramic-based material (25) is in the form of a composite material, comprising particles of at least one metal oxide, metal carbide, or metal nitride distributed in a metal matrix material.

17. The scraper (6) according to claim 12, characterized in that, The sediment hardness, measured by Vickers hardness, ranges from 900 to 1700 HV.

18. The scraper (6) according to claim 1 or 2, characterized in that, The front side (20) has at least a partial roughness of Ra<0.4μm and Rz<4.0μm.

19. The scraper (6) according to claim 1 or 2, characterized in that, The thickness of the scraper (6) along the x-direction is between 600 μm and 1500 μm, where x-direction is the thickness direction of the scraper (6).

20. A wrinkling apparatus comprising a drying cylinder (3) and a scraper (6), said scraper (6) being a scraper according to any one of the preceding claims.

21. The wrinkling device according to claim 19, characterized in that, The contact angle α between the scraper (6) and the drying cylinder (3) is 5° to 35°.

22. The wrinkling apparatus according to claim 20, characterized in that, The contact angle α between the scraper (6) and the drying cylinder (3) is 15° to 25°.

23. The wrinkling apparatus according to any one of claims 19 to 21, characterized in that, The concave angle δ between the tangent at the contact edge (8) of the drying cylinder (3) and the front inclined surface (10) is 115° to 35°.

24. The wrinkling device according to claim 22, characterized in that, The concave angle δ between the tangent at the contact edge (8) of the drying cylinder (3) and the front inclined surface (10) is 95° to 65°.

25. The wrinkling apparatus according to claim 22, characterized in that, The concave angle δ between the tangent at the contact edge (8) of the drying cylinder (3) and the front inclined surface (10) is 85° to 70°.

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