Blade and production methods

Abstract

The invention relates to a blade, in particular a doctor blade or sealing blade, for contacting a moving surface in a paper machine, wherein the blade has a facet side contacting the moving surface and a holder side facing away from same, and a length L extending in the width direction of the paper machine when the blade is used as intended, wherein the blade comprises a first polymer component which provides the facet side of the blade and a second polymer component which provides the holder side. The invention also relates to methods for producing a blade of this type.

Description

[0001] Blade and manufacturing process

[0002] The invention relates to a blade, in particular a doctor blade or sealing blade for contacting a running surface in a paper machine according to the preamble of claim 1 and to methods for producing such blades.

[0003] Blades are used at various points in the papermaking process. Doctor blades are used in paper machines, among other things, for cleaning roll surfaces. Sealing blades are used to operate vacuum-based dewatering zones more efficiently.

[0004] Such blades can be made from thermoplastic base materials, such as polyethylene (PE), polyphenylene sulfone (PPSU), or polyvinylidene fluoride (PVDF), polyamide (including PA 10.10), or other suitable thermoplastics, or from fiber-reinforced thermosets, e.g., based on cross-linked epoxy resin systems. The production of such blades from thermoplastics is known per se, for example, from WO00015904 A1 and the utility model DE 203 10 750 U1.

[0005] Blades made of thermoplastic base material are manufactured, among other things, by extrusion, as described in DE 203 10 750 U1. Using the appropriate extrusion tool (die), either a rectangular profile or the finished blade profile can be produced. A blade produced in this way, or in the case of a rectangular profile, the blade blank, has no seams and can be referred to as an "endless blade," which is wound, for example, as a coil of 100 linear meters in length.

[0006] Due to tribological effects, contact with moving surfaces causes the blade to wear during use in the paper machine. Due to the loss of cleaning and sealing properties, it must be replaced at regular intervals. Typically, more than 80% of the remaining width of a blade remains after it is replaced. This generates a significant amount of waste material.

[0007] Although thermoplastic materials can often be reshaped and reused through thermal treatment, the thermal and mechanical stresses during recycling cycles caused by the regranulation and extrusion process lead to a degradation of the plastic molecular chains, resulting in a loss of mechanical properties, particularly the strength of the polymer material. Depending on the usually unknown number of recycling cycles, the quality of such polymer materials can also vary considerably.

[0008] However, for use as a blade in a paper machine, a consistent and high quality of the final product, especially high strength, is essential.

[0009] Therefore, a high proportion of fresh raw material is generally used in the production of scraper blades and sealing strips made of thermoplastic material.

[0010] The remaining blade material, which as mentioned can make up 80% or more of the total blade material, cannot be used for new blades and is now disposed of as waste.

[0011] The process of chemical recycling, in which the cross-linked polymers are chemically broken down into their individual molecules, is possible in principle, but is currently very complex and generates additional waste that must be taken into account.

[0012] The object of the invention is to overcome the problems of the prior art. In particular, it is an object of the invention to reduce the waste of polymer material during the life cycle of a scraper or sealing blade. It is also an object of the invention to propose blades that do not exhibit any qualitative limitations compared to previous blades.

[0013] The object is achieved according to the invention by a blade according to claim 1 and by methods for producing a blade according to claims 6 and 7. Further advantageous embodiments of the present invention can be found in the subclaims.

[0014] Proposed is a blade, in particular a doctor blade or sealing blade for contacting a running surface in a paper machine, wherein the blade has a face side contacting the running surface and a holder side facing away from it, as well as a length L that extends in the width direction of the paper machine when the blade is used as intended. According to the invention, the blade comprises a first polymer component that provides the face side of the blade and a second polymer component that provides the holder side.

[0015] In particularly preferred embodiments, it can be provided that the first polymer component comprises or consists of new polymer material, while the second polymer component comprises or consists of reused polymer material.

[0016] The reused polymer material can be wholly or partly a regranulated polymer material.

[0017] Alternatively or additionally, the reused polymer material may be, in whole or in part, a recycled polymer material.

[0018] For the purposes of this application, regranulated material is defined as follows: Excess extruded material that is processed back into granules for re-extrusion. Although this material has not yet been used for its original purpose, it has already undergone thermal and mechanical stress during the extrusion process.

[0019] Recycled material within the meaning of this application, however, has already been used for its intended purpose. It is also conceivable in the future to use previously used scraper blades, which may be cleaned and granulated, to re-extrude the resulting recyclate. Since recycled material is usually granulated again for reuse, recycled material can be considered a special case of regranulated material.

[0020] The invention is based on the idea that the high demands on the quality and uniformity of the polymer material are only required in the area of ​​the blade tip ("bevel"), which is in contact with the running surface to achieve a good cleaning or sealing effect. The remaining part of the blade, which represents by far the largest part of the blade, essentially serves to secure the blade. In this area, the stress on the material is significantly lower than in the bevel area.

[0021] Therefore, according to aspects of the present invention, the blades are constructed from two polymer materials. A first polymer component, which provides the blade's face side and typically has high material quality requirements. Furthermore, a second polymer component, which forms the blade's holder side. This second polymer component must meet less stringent requirements, so a lower-quality material can also be used.

[0022] Very attractive designs are those in which the same polymer type is used for both polymer components (e.g., PE, PPSU, PVDF, or polyamide, especially PA10.10). The first polymer component consists entirely or largely of virgin material, while the second polymer component consists entirely or largely of material that has been regranulated or recycled once or several times. (By "largely" here, we mean at least 80% by weight or more). Two such components bond very well together, so that the resulting blade is largely homogeneous. The face side and the holder side differ primarily in the length of the plastic molecular chains.

[0023] It is also possible to deliberately distinguish the two polymer components, for example, by adding dyes. This makes the residual volume of the first polymer component easily visible, even during blade operation. This also makes it easy for the operator to assess whether the blade can still be used safely, or whether the volume of the first polymer component has already been worn down to such an extent that an imminent blade replacement is necessary.

[0024] It may be particularly advantageous for the proportion of the second polymer component to be more than 50 wt%, in particular more than 10 wt%, preferably between 70 wt% and 90 wt%. A high proportion of the second polymer component in the blade allows for a high proportion of regranulated or recycled polymer to be used.

[0025] Since 80 wt% or more of the blade volume is usually left when the blades are replaced, a very large part of the blade can be made of the second polymer component.

[0026] Various methods can be imagined for producing such a blade.

[0027] Thus, a method for producing a blade is proposed, according to which the blade is produced by coextrusion of the first polymer component and the second polymer component.

[0028] By using two extruders connected in parallel and appropriately designed nozzles, it is possible to use both regranulated or recycled material and virgin material. A first extruder supplies the first polymer component, and a second extruder supplies the second polymer component. The two polymer components are then combined in a nozzle. The blade or blade blank, consisting of both polymer components, then emerges from the nozzle outlet.

[0029] In this process, the new blade is re-extruded in its entirety.

[0030] In an alternative method, the holder side of the blade can be provided, and the face side of the blade can be formed by extruding the first polymer component onto the holder side. It can be advantageous for the holder side of the blade to be obtained by reprocessing one or more old blades. To reprocess the old blades, for example, the face side can be removed. This can simply be sawn off. This reprocessing can ensure, for example, a constant starting width.

[0031] Advantageously, at least 30%, in particular at least 50% of the original blade width is retained during reprocessing.

[0032] The sawn-off material can, if desired, be regranulated and used as a component of the second polymer component in a blade according to further aspects of the invention.

[0033] New blades are typically manufactured in the form of "endless blades," which are wound, for example, into a coil of 100 linear meters. The blades are then cut from these coils according to the required length.

[0034] Such endless blades can be easily manufactured using coextrusion.

[0035] If the holder side of the blade is provided by old blades, a plurality of old blades must be arranged next to each other in the length direction L to produce a coil. The butt seams between the old blades can be fused together, for example, using heated rollers or a suitably designed tool (nozzle), so that the holder side of the blade is also continuous without gaps or joints.

[0036] In one embodiment of the method, the holder side of the blade can be passed through the extrusion die during the extrusion of the first polymer component. In contrast to coextrusion, this method requires only one extruder for the first polymer component. The second polymer component is introduced into the extrusion die in the form of a solid blade. The finished blade or a blade blank then emerges from the extrusion die, with the first polymer component attached to the holder side.

[0037] Alternatively, the first polymer component can be extruded from the extruder onto the blade holder side. In this case, the old blades are not inserted into the extrusion die. The first polymer component is applied to the old blades outside the extrusion die and bonded to them.

[0038] Regardless of the process chosen, it can be advantageous to follow the extrusion process with subsequent fixation, particularly in the form of pressing. This pressing process can be carried out, for example, in a step press or in a roller nip.

[0039] The invention is explained below with reference to figures. The invention is not limited to the embodiments shown here. The figures show in detail:

[0040] Figures 1a and 1b show a method and a blade according to one aspect of the invention

[0041] Figures 2a to 2d show a method and a blade according to another aspect of the invention.

[0042] Figure 1a shows the production of the blade 5 according to one aspect of the invention by coextrusion of the first polymer component 6 and the second polymer component 7.

[0043] Two parallel extruders 1a, 1b are used. The first extruder 1a supplies a first polymer component 6 in the form of fresh polymer material 6. The second extruder 1b supplies a second polymer component 7 in the form of regranulated or recirculated polymer 7.

[0044] The two polymer components 6, 7 are then combined in a suitable nozzle 4. The blade 5 or blade blank, which consists of both polymer components 6, 7, then emerges from the nozzle outlet.

[0045] In this process, the new blade 5 is re-extruded in its entirety. The blade 5 has a width b of first polymer component 6 on the face side 2, and a width a of second polymer component 7 on the holder side 3. Such a blade 5 is shown from the side in Figure 1b. It is possible that the extrusion only produces a blade blank 5, for which further processing steps such as grinding the face 2 are necessary before the actual application. Figure 1b shows a blade 5 with such a grind. Very attractive designs are those in which the same type of polymer is used for the two polymer components 6, 7 (e.g. PE, PPSU, PVDF or polyamide, in particular PA 10.10), wherein the first polymer component 6 consists entirely or largely of fresh material, while the second polymer component 7 consists entirely or largely of material that has been regranulated or recycled once or several times.(By "largely" here, we mean at least 80% by weight or more.) Two such components 6, 7 bond very well with each other, so that the resulting blade 5 is largely homogeneous. The blade side 2 and the holder side 3 differ primarily in the length of the plastic molecular chains.

[0046] In this coextrusion process, the ratio a / b of the two polymer components 6.7 can be chosen very freely.

[0047] It may be particularly advantageous for the proportion of the second polymer component 7 to be more than 50 wt.%, in particular more than 60 wt.%, preferably between 70 wt.% and 90 wt.%. A high proportion of the second polymer component 7 in the blade 5 allows for the use of a high proportion of regranulated or recycled polymer.

[0048] Alternatively, the proportion of the second polymer components 7 may also be less than 50 wt%.

[0049] Figures 2a to 2d describe an alternative manufacturing method for a blade 5 according to further aspects of the invention. The starting point is a used blade 5a. Through use, the face side 2 is worn, and the old blade 5a is therefore no longer usable. However, the holder side 3 is virtually unaffected (Figure 2a). Therefore, a strip of width b is severed in the length direction L. This can be done very easily, for example, by chipping. Advantageously, at least 30%, in particular at least 50%, of the original blade width is retained during reconditioning.

[0050] What remains is a strip of width a on the holder side 3 (Figure 2b). This strip consists of a polymer component 7, which is reused in the new blade 5 without being extruded again. Instead, in the next step (Figure 2c), a first polymer component 6 is extruded using an extruder 1 and applied to the remaining strip. Here, too, the connection between the two components 6, 7 is particularly good if the same type of polymer is used for both components 6, 7 (e.g., PE, PPSU, PVDF, or polyamide, in particular PA 10.10), with the first polymer component 6 consisting entirely or largely of fresh material.

[0051] Thus, a blade 5 according to one aspect of the invention is also created (Figure 2d).

[0052] New blades 5 are typically manufactured in the form of a "continuous blade," which is wound, for example, into a coil of 100 linear meters in length. The blades 5 are then cut from these coils according to the required length.

[0053] Such endless blades can be easily manufactured using coextrusion.

[0054] If the holder side 3 of the blade 5 is provided by old blades 5a, a plurality of old blades 5a must be arranged next to one another in the length direction L to produce a coil. The butt seams between the old blades 5a can be fused together, for example, using heated rollers or a suitably designed tool (nozzle), so that the holder side 3 of the blade 5 is also continuous without gaps or joints.

[0055] List of reference symbols

[0056] 1 , 1a, 1b Extruder

[0057] 2 Wading side 3 Holder side

[0058] 4 nozzle, extrusion tool

[0059] 5 blade

[0060] 5a old blade

[0061] 6 first polymer component 7 second polymer component

[0062] L Length direction b Width of the first polymer component a Width of the second polymer component

Claims

Patent claims 1 . Blade (5), in particular a doctor blade (5) or sealing blade (5) for contacting a running surface in a paper machine, wherein the blade (5) has a face side (2) contacting the running surface and a holder side (3) facing away from it, and a length L which, when the blade (5) is used as intended, extends in the width direction of the paper machine, characterized in that the blade (5) comprises a first polymer component (6) which provides the face side (2) of the blade (5), and a second polymer component (7) which provides the holder side (3), wherein the first polymer component (6) and the second polymer component (7) consist in particular of the same type of polymer, preferably of a PE, PPSU, PVDF or a polyamide.

2. Blade (5) according to claim 1, characterized in that the first polymer component (6) comprises or consists of new polymer material, while the second polymer component (7) comprises or consists of reused polymer material.

3. Blade (5) according to claim 2, characterized in that the reused polymer material is wholly or partly a regranulated polymer material.

4. Blade (5) according to one of claims 2 or 3, characterized in that the reused polymer material is wholly or partly a recycled polymer material.

5. Blade (5) according to one of the preceding claims, characterized in that the proportion of the second polymer component (7) is more than 50 wt%, in particular more than 60 wt%, preferably between 70 wt% and 90 wt%.

6. Method for producing a blade (5) according to one of the preceding claims, characterized in that the blade (5) is produced by coextrusion of the first polymer component (6) and the second polymer component (7).

7. A method for producing a blade (5) according to any one of claims 1 to 5, characterized in that the holder side (3) of the blade (5) is provided, and the wad side (2) of the blade (5) is formed by extrusion of the first polymer component (6) on the holder side (3).

8. Method according to claim 7, characterized in that the holder side (3) of the blade (5) is obtained by reconditioning one or more old blades (5a), wherein in particular the wad side (2) is removed during the reconditioning of the old blades (5a).

9. Method according to one of claims 7 to 8, characterized in that during the extrusion of the first polymer component (3) the holder side (3) of the blade (5) passes through the extrusion tool (4).

10. Method according to one of claims 7 to 9, characterized in that the first polymer component (6) is extruded from the extruder (1, 1a, 1b) onto the holder side (3) of the blade (5).

11. Method according to one of claims 7 to 10, characterized in that after the extrusion process, a subsequent fixing takes place, in particular in the form of a pressing.

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