Structured abrasive

Abstract

Structured abrasive (6), comprising - a track-shaped base (1) and - a grinding layer (18), characterized in that the abrasive layer (18) has hardened convex accumulations (2) of a binder-grain mixture (15), wherein on the track-shaped substrate (1) free areas (21) remain between the convex accumulations (2), wherein the convex accumulations (2) have an at least partially random arrangement on the track-shaped substrate (1).

Description

[0001] The invention relates to a structured abrasive.

[0002] Structured abrasives are used primarily for machining metal workpieces and are available in various grits. The abrasive generally has a backing, e.g., a sheet-like backing made of a rigid or flexible material, onto which a binder layer, e.g., a phenol-based one, and abrasive grains are applied. The grains can be made of α-aluminum oxide or other materials.

[0003] The grains can be broken abrasive grains; furthermore, shaped abrasive grains are known which are individually shaped, dried and / or sintered / calcined, e.g., by a sol-gel process, and which, due to their uniform shape and appropriate alignment, enable uniform abrasive engagement.

[0004] For example, US Pat. No. 5,984,988 A discloses a manufacturing process in which the binder layer and the grains are applied to the substrates by scattering pre-formed grains, e.g., gravimetrically or electrostatically, so that they are absorbed into the already applied binder layer. This temporarily fixes the grain to the substrate. The binder layer is then cured. Examples of known curing methods include thermally initiated, radiation-cured, and chemical curing using appropriate binders or hardeners / initiators.

[0005] Gravimetric or electrostatic grain spreading has the disadvantage that the production process involves several individual steps, which can negatively impact process reliability. Hardening the entire binder-coated surface of the backing is also energy-intensive. Abrasives produced using gravimetric or electrostatic spreading have the disadvantage that the surface of the abrasive is uneven at the microscale, as the height of the abrasive can vary, for example, when multiple grains are stacked on top of each other.

[0006] Alternatively, WO 9415752 A1, for example, discloses a method in which a binder-grain mixture is applied to a molding tape, which contains indentations. The tape is then brought into contact with a substrate, so that the binder-grain mixture on the molding tape or in the indentations adheres to the substrate over its entire surface. The molding tape and the substrate are then jointly exposed to electromagnetic radiation, which penetrates the molding tape and hardens the binder. Finally, the molding tape is separated from the finished abrasive.

[0007] This process has the disadvantage that hardened residues of the binder-grain mixture remain on the impression belt or in the recesses of the impression belt, necessitating cleaning of the impression belt or resulting in a loss of process continuity. The impression belt is also a wear part that will need to be replaced after a certain period of time. High-energy UV radiation, in particular, contributes to the embrittlement of the impression belt. The abrasives produced with the impression belt have the disadvantage that the flexibility of the entire abrasive is impaired due to the fully adhering and hardened binder-grain mixture to the substrate.

[0008] The object of the invention is therefore to provide a structured abrasive which enables safe, cost-effective production and good grinding properties.

[0009] This object is achieved by a structured abrasive according to claim 1. The subclaims specify preferred developments.

[0010] Advantageously, a method for producing a structured abrasive comprises the following steps: a) Providing a web-shaped base, b) Providing a binder-grain mixture, c) Applying the binder-grain mixture as convex accumulations, e.g. hemispherical structures, by screen printing onto the web-shaped base as an abrasive layer, leaving open areas on the web-shaped base and d) partial or complete curing of the applied binder-grain mixture by radiant energy.

[0011] The binder-grain mixture preferably comprises curing initiators such as Type I or Type II photoinitiators for curing by UV radiation energy and / or thermal peroxide-based initiators and / or thermal azo compound-based initiators for curing by thermal radiation energy.

[0012] Furthermore, the binder-grain mixture may contain fillers such as chalk, cryolite, potassium tetrafluoroborate (KBF4), wollastonite and / or kaolin.

[0013] Additives that can be used in the binder-grain mixture include pyrogenic silica to adjust the rheology, silane compounds to promote adhesion between the binder and the abrasive grain, defoamers, deaerators, dispersing additives, flow control agents, and / or color pigments.

[0014] The web-shaped substrate as well as the binder and the grains of the binder-grain mixture can further contain a variety of different materials, which are described in more detail in the following subclaims and can be combined with the above-mentioned curing initiators, fillers and / or additives.

[0015] The at least partial or complete curing by radiant energy can be achieved by a type of radiant energy, for example, UV, electron, thermal radiation energy, especially infrared radiation, or by a combination of different types of radiation energy. Curing by UV radiation energy is particularly preferred, as it enables particularly energy-efficient and positionally precise curing of the binder-grain mixture.

[0016] The convex accumulations applied by screen printing have a height h and a base area with a diameter d (see alsoFig. 3A), wherein the base surface is arranged on the side of the convex accumulations facing the substrate.

[0017] The accumulations, which are convex in their basic form, may have a non-ideal convex shape in some areas; for example, the convex basic form may have dents and / or notches.

[0018] Preferably, the convex clusters correspond to hemispherical structures. In this case, hemispherical is not to be understood in the strict mathematical sense, where the height h would have to correspond to half the diameter d of the base, but merely describes the basic shape of the applied structures. Structures that correspond to an indented, truncated, or elongated hemisphere, such that the height h of the hemisphere is not equal to half the diameter d of the base, fall under the term hemispherical structure for the purposes of this patent application, just like semi-elliptical structures. Other shapes, such as cubes or polygons with a height, fall under the term convex clusters.

[0019] The application process is preferably carried out using a screen printing process that uses a roller-shaped screen printing stencil (rotary screen printing). This allows for a continuous process. However, the use of screen printing stencils in other forms, such as flat screen printing frames, is also conceivable. Other known screen printing processes can also be used.

[0020] The binder-grain mixture preferably has a viscosity such that it exhibits good processability during the printing process. Viscosities in the range of 1000 mPa*s to 10,000 mPa*s are advantageous, optimally 3000 mPa*s to 8000 mPa*s (at 20°C and a shear rate of 100 1 / s). The shape of the convex clusters is largely retained after application, but at least until partial or complete curing. Therefore, a pseudoplastic behavior of the binder-grain mixture is required.

[0021] A process for producing the abrasive according to the invention has the advantage that high process reliability is possible thanks to the described single-step process. Furthermore, structured abrasives can be produced cost-effectively.

[0022] Furthermore, the shape of the convex clusters allows for optimal penetration of the radiation energy during at least partial or complete curing, allowing greater layer thicknesses of the abrasive layer to be fully cured than with a conventional, full-surface application. This advantage is made possible, in particular, by the elimination of a molding band, which absorbs a large portion of the radiation energy. This avoids the combined curing of UV radiation and additional thermal energy, which is necessary when the layer thickness is too high or the radiation intensity is too low.

[0023] In the case of hemispherical structures as convex accumulations, the energetically most favorable form with regard to the surface tension of a body is present, so that the application and curing of the binder-grain mixture are always uniform and reproducible.

[0024] According to the invention, it is further provided that a structured abrasive has a web-shaped base and an abrasive layer, wherein the abrasive layer has hardened convex accumulations, e.g. hemispherical structures, made of a binder-grain mixture, and wherein free areas remain on the web-shaped base between the convex accumulations.

[0025] The binder-grain mixture can contain the above-mentioned fillers, additives and / or curing initiators.

[0026] The convex clusters preferably have substantially the same height. The grains of the binder-grain mixture are distributed substantially homogeneously in the cured convex clusters.

[0027] The structured abrasive according to the invention has the advantage that, due to the convex clusters, a homogeneous surface finish is produced when grinding a workpiece. This is made possible in particular by convex clusters of essentially equal height. Alternatively, however, different heights of the convex clusters can also be provided; preferably, the height of the convex clusters can be distributed in a range from 5% to 30% of the average height.

[0028] Furthermore, a homogeneous distribution of the grains in the binder-grain mixture in the cured convex aggregates achieves a high self-sharpening effect, which leads to good grinding performance, especially stock removal and durability of the structured abrasive.

[0029] The convex clusters have base surfaces on the side facing the web-shaped backing, whereby the base surfaces of the convex clusters do not cover the entire surface of the web-shaped backing. The flanks on the web-shaped backing provide the structured abrasive with very high flexibility. Furthermore, these flanks create chip spaces between the convex clusters, ensuring high stock removal and good heat dissipation.

[0030] Furthermore, the convex clusters offer a "rounded tip" at the beginning of a grinding process, unlike other geometric shapes such as cuboids or rectangles. Due to the small surface area that engages the material surface at the beginning of the grinding process, an initial breakup of the convex clusters is facilitated and the resharpening process is activated. Afterward, a uniform reduction of the abrasive down to the backing is possible (see Fig. 3A to 3C).

[0031] Compared to other geometric shapes such as pyramids or cones, convex clusters in the form of hemispherical structures do not offer a linear increase in the surface area of ​​the abrasive layer directly involved in the grinding process with a workpiece, but rather an exponential increase. This allows the user to maintain a more constant contact pressure throughout the entire grinding process. Furthermore, the hemispherical structure provides the user with a longer service life, as hemispherical structures have a higher geometry-related abrasive mass volume than, for example, pyramids.

[0032] According to one embodiment of a method for producing the abrasive according to the invention, the method comprises the following steps before the step of applying the binder-grain mixture to the substrate: a) Applying a primer layer as adhesion promoter to the web-shaped substrate and b) optional at least partial curing of the primer layer by radiant energy.

[0033] The primer layer preferably consists of UV-curable (meth)acrylates with surface-affine functional groups.

[0034] A primer layer can improve the adhesion of the binder-grain mixture to the web-like backing, thereby increasing the mechanical stability and durability of the resulting abrasive. The at least partial or complete curing of the primer layer, as well as its general use, are merely optional, as this step can be omitted and the primer layer is cured by radiant energy during the at least partial or complete curing of the applied binder-grain mixture.

[0035] One embodiment of the structured abrasive has a primer layer as an adhesion promoter between the web-shaped backing and the abrasive layer, which enables the advantages already described.

[0036] According to one embodiment, the screen printing process uses a screen printing stencil, - which has a wall thickness in the range 100 to 1100 µm, preferably in the range 150 to 900 µm, and / or - which has a number of 15 to 250, preferably 20 to 160 recesses per inch, and / or - the recesses have a diameter in the range 400 to 6000 µm, preferably 420 to 4000 µm, and / or - which has randomly arranged recesses in some areas.

[0037] The screen printing stencil is preferably formed by a roller with recesses, along which the web-like substrate is guided. The binder-grain mixture is guided into the interior of the roller and, with the aid of a squeegee, is applied through the recesses onto the web-like substrate. The recesses are preferably round, but other shapes such as squares, triangles, polygons, or polygons are also possible.

[0038] A wall thickness in the range of 100 to 1100 µm allows for the application of a layer thickness sufficient for a long abrasive life, depending on the size of the convex clusters. Wall thicknesses in the range of 100 to 500 µm, preferably 150 to 400 µm, have proven particularly advantageous for hand sanding. Wall thicknesses in the range of 400 to 1100 µm, preferably 450 to 900, have proven particularly advantageous for machine sanding. For hand sanding, thinner layer thicknesses are sufficient because less pressure is applied to the workpiece than with machine sanding applications. The lower pressure extends the abrasive life.

[0039] In addition, thinner wall thicknesses of the screen-printed stencils allow for smaller clusters to be printed without the clusters merging. Smaller clusters increase the flexibility of the abrasive, which is particularly advantageous in hand-sanding applications.

[0040] The number of notches per inch, along with the size of these notches, determines how much of the sheet-like backing is covered by the bases of convex clusters and how much of the surface remains as open space. This, in turn, significantly influences the flexibility of the structured abrasive article.

[0041] The diameter of the recesses, the layer thickness of the stencil and the squeegee position within the stencil have a relevant influence on the dimensions, in particular height h and diameter d of the convex accumulations.

[0042] The size of the convex clusters can thus be quickly and easily changed by using a different screen printing stencil, preferably without changing the binder-grain mixture formulation. The required pressure of the structured abrasive to be produced during the grinding process depends on the choice of the size of the convex clusters, with larger convex clusters requiring more pressure during grinding than smaller convex clusters. Thus, the process enables the flexible production of different structured abrasives. This allows the structured abrasive to be specifically optimized for different applications, preferably without adjusting the formulation.

[0043] Convex clusters, which are created using screen-printed stencils with cutouts ranging from 250 µm to 6000 µm, preferably 420 to 4000 µm, have the advantage of producing an abrasive product capable of producing particularly high-quality surfaces. For this purpose, only minimal pressure is required during grinding, for example, with convex clusters in the form of hemispherical structures. The durability of the abrasive can also be influenced by the selection of the convex clusters. A further advantage is the high flexibility of the abrasive, which allows it to adapt well to the workpiece during the grinding process.

[0044] Screen printing stencils with cutouts in the range of 250 to 1500 µm produce small convex clusters for particularly flexible abrasives used in hand grinding. Cutouts in the range of 1500 to 5000 µm are preferably used in machine grinding, which requires higher pressure and durability during the grinding process.

[0045] Due to the randomly arranged recesses on the screen printing stencil, the convex accumulations on the web-like substrate are also randomly arranged in some areas. “Randomly arranged in some areas” is understood in particular to mean that the positions of the centers of the convex accumulations on the web-like substrate do not follow an ordered, repeating pattern in one area, for example, they are not arranged in a square grid. The size of the random area can be freely chosen within limits. For example, within a circle with a diameter eight times the average diameter of the convex accumulations, no ordered, repeating pattern of the centers of the convex accumulations located in the circle should be recognizable, whereby the position of the circle can be freely chosen. However, after one revolution of the screen printing roller at the latest, the relative arrangement of the convex accumulations repeats itself.The advantage achieved by the randomly arranged convex accumulations in some areas is that the homogeneity of the grinding pattern on a workpiece to be machined is further improved.

[0046] In one embodiment of the structured abrasive, the arranged convex accumulations have base surfaces on the side facing the web-shaped substrate, wherein the convex accumulations have a diameter d in the range from 250 to 6000 µm, preferably 420 to 4000 µm, more preferably 600 to 3000 µm and a height h in the range from 100 to 1300 µm, preferably 150 to 900 µm, more preferably 300 to 700 µm, more preferably 500 to 1100 µm, and / or the base surfaces cover 20% to 75%, preferably 50% to 70% of the web-shaped substrate and / or the base surfaces have a distance a from one another in the range from 0 to 3500 µm, preferably 50 to 3000 µm and / or the open areas make up 80% to 25%, preferably 30% to 50% of the web-shaped base.

[0047] A distance of 0 µm between the bases of the hemispheres is possible during production. However, the hemispheres should preferably have a distance of at least 50 µm to ensure the flexibility of the abrasive.

[0048] The advantages already mentioned apply to the dimensions of the hemispherical structures.

[0049] Covering 20% ​​to 75% of the sheet base with the base areas of the convex mounds corresponds to the number of recesses per inch described above and has the same advantages.

[0050] A proportion of 80% to 25% free surfaces ensures the flexibility of the abrasive.

[0051] By maintaining a distance a between the base surfaces in the range of 0 to 3500 µm, preferably 50 to 3000 µm, it is ensured that no full-surface binder layer is applied to the web-shaped backing. This allows the web-shaped backing to retain its full flexibility between the convex accumulations. Even workpieces to be ground with tight radii can be processed without any problems. Distances a of 50 to 1500 µm are advantageous for hand grinding and 500 to 3000 µm for machine grinding. Furthermore, the distance a contributes to the dissipation of heat, as the chip can quickly leave the grinding zone. In addition, it can no longer damage the surface of the structured abrasive. By specifically creating the contact points in the grinding process through the number of convex accumulations, the heat input into the workpiece is directly influenced. A more open structure transfers less heat into the workpiece.

[0052] In a further embodiment of the structured abrasive, the convex accumulations have a partially random arrangement on the web-shaped substrate

[0053] As already described, the homogeneity of the grinding pattern on a workpiece is improved by a random arrangement of the hemispherical structures in certain areas. The above statements apply analogously to the term "random arrangement in certain areas."

[0054] In a further embodiment of the structured abrasive, at least one of N convex accumulations following one another in the longitudinal direction L of the web-shaped base is offset by at least an offset distance v of greater than 5% of their mean diameter orthogonal Q to the longitudinal direction L of the web-shaped base, wherein the offset distances v of the N convex accumulations considered differ and wherein N = 3, preferably N = 5, more preferably N greater than 9.

[0055] An offset of N consecutive convex clusters in the longitudinal direction L of the web-shaped backing by an offset distance v of at least 5% of their average diameter orthogonal Q to the longitudinal direction L of the web-shaped backing represents a criterion for randomness, which enables a sufficiently homogeneous grinding pattern. Furthermore, the random arrangement can prevent the formation of kinks in the abrasive, compared to abrasives with evenly arranged convex clusters. This prevents the creation of so-called chatter marks on the workpiece. The larger N is selected, the larger the area in which the convex clusters are randomly distributed.

[0056] The longitudinal direction L of the web-shaped backing corresponds to the subsequent grinding direction of the structured abrasive and is defined by the longest dimension of the web-shaped backing. The orthogonal direction Q lies in the plane of the web-shaped backing and is orthogonal, i.e., transverse to the longitudinal direction L. The mean diameters are calculated in a known manner by averaging the diameters d of the considered hemispherical structures analogous to the FEPA standard. The offset distance v is determined as the deviation of the respective centers of the convex accumulations in direction Q from the longitudinal direction L. For further illustration of the individual quantities L, Q, v, d, the Fig. 4.

[0057] According to one embodiment of the structured abrasive, the binder of the binder-grain mixture comprises the following components of a group formed by: - Polyester acrylates, - polyether acrylates, - Epoxyacrylates, - Urethane acrylates as oligomeric components - Acrylate monomers - Methacrylate monomers

[0058] The use of an acrylate binder enables the structured abrasive to exert less pressure during the sanding process than would be the case with conventionally coated abrasives with phenol-based binders.

[0059] The use of UV-curable binders enables particularly energy-efficient and targeted curing of the binder using UV light.

[0060] The process for producing the abrasive according to the invention requires less space in the production plant than would be the case with conventionally coated abrasives with phenolic resin-based binders. Furthermore, a shorter production time and thus a higher throughput relative to the plant size are possible than with conventionally coated abrasives with phenolic resin-based binders.

[0061] The following proportions have been found to be particularly advantageous for the binder-grain mixture: • Acrylate monomer: 0%-60%, especially 5%-40% • Acrylate oligomer: 0%-60%, especially 2% to 35% • Filler: 0%-40%, especially 8% to 30% • UV initiator: 0.1%-6%, especially 0.3%-5% • Abrasive grain: 30%-75%, especially 35% to 70%

[0062] According to a further embodiment of the structured abrasive, the web-shaped backing consists of a group formed by: - Cotton, - Polyester, - mixed fabrics, - paper, - Vulcanized fiber.

[0063] The blended fabric is preferably highly flexible, medium flexible, flexible, medium stiff, stiff or very stiff.

[0064] This means that a wide range of common web-shaped backings can be used, making the structured abrasive suitable for a wide variety of applications.

[0065] According to a further embodiment of the structured abrasive, the grains of the binder-grain mixture consist of a group formed by: - normal corundum, - semi-precious corundum, - Corundum, - ceramic aluminum oxide, - Zirconia corundum, - silicon carbide, - Diamond, - Cubic boron nitride, - Sol-gel aluminum oxide - formed sol-gel alumina.

[0066] An appropriate selection of grains enables the use of grain properties that are individually tailored to the application of the structured abrasive.

[0067] Semi-precious corundum is preferably used as it offers a good cost-benefit ratio for a wide range of applications.

[0068] According to a further embodiment of the structured abrasive, the grains of the binder-grain mixture have an average diameter in the range of 7 to 200 µm, preferably 7 to 125 µm.

[0069] The mean diameter of the grains is determined analogously to the FEPA standard from the mean values ​​of the diameters of the grains considered.

[0070] Grains with average diameters in the range of 7 to 200 µm have proven particularly advantageous because this grain size range covers surface finishing applications up to a mirror finish. In this grain size range, the binder system is capable of holding the abrasive grain in place while simultaneously ensuring sufficient self-sharpening of the abrasive.

[0071] According to a further embodiment of the structured abrasive, the volume ratio of grains to binder in the binder-grain mixture is in the range of 0.4 to 1.5, preferably in the range of 0.5 to 1.2.

[0072] A corresponding volume ratio has proven to be particularly advantageous because in this range optimal grinding performance is consistent with a suitable processing viscosity for the screen printing process.

[0073] According to a further embodiment of the structured abrasive, the flanks are interconnected and form a two-dimensional network structure.

[0074] The two-dimensional network structure forms in the plane of the web-shaped substrate and enables sufficient flexibility of the structured abrasive.

[0075] The invention is explained in more detail below with reference to the accompanying drawings. They show: Fig. 1 shows an exemplary structure of an apparatus for carrying out a method for producing a structured abrasive; Fig. 2 an enlarged section of the device Fig. 1; Fig. 3A, Fig. 3B, Fig. 3C is a schematic side view of a grinding process with a structured abrasive; Fig. 4 a schematic top view of a structured abrasive.

[0076] In Fig. 1 shows an exemplary structure of a device for carrying out a method for producing a structured abrasive 6. The method comprises the following steps: a) Providing a web-shaped base 1, b) applying a primer layer 19 as an adhesion promoter to the web-shaped substrate 1, c) at least partially curing the primer layer 19 by radiation energy. d) Providing a binder-grain mixture 15, e) applying the binder-grain mixture 15 as convex accumulations 2, e.g. hemispherical structures, by a screen printing process onto the web-shaped base 1 as an abrasive layer 18, whereby free surfaces 21 remain on the web-shaped base 1, f) at least partial or complete hardening of the applied binder-grain mixture 15 by radiation energy and g) Rolling up the web-shaped base 1.

[0077] Step a) is performed by unwinding the web-shaped base 1 from a roll. The web-shaped base 1 consists of cotton, polyester, blended fabric, paper, and / or vulcanized fiber. Any combination of the aforementioned components is possible. The web-shaped base 1 is guided through the entire device via rollers, completing steps a) to g) of the process.

[0078] Step b) is carried out by supplying primer 19 provided in a primer container 8 to a primer doctor blade 10, for example by a pump (not shown), wherein the primer 19 is applied as a primer layer 19 to the web-shaped substrate 1 by means of the primer doctor blade 10. The primer layer 19 preferably consists of surface-affine acrylate compounds, which represents a particularly good adhesion promoter.

[0079] Subsequently, in step c), the primer layer 19 is at least partially cured using a primer blaster 12. It is also possible to not cure the primer layer 19 at all at this time. Instead, the primer layer 19 is cured only in step f), together with the applied binder-grain mixture 15.

[0080] To remove any dust, gases, and / or vapors that may be generated during steps b) and c), an extraction system 7 is provided. This prevents contamination and ensures a safe working environment.

[0081] Then step e) takes place, whereby this step is Fig. 2 is shown in detail. Fig. 2 shows the section of the device from Fig. 1 in an enlarged view, in which the web-shaped substrate 1 coated with the primer 19 is passed between the screen printing stencil 16 and the counter-pressure roller 17.

[0082] The binder-grain mixture 15 is conveyed from a mixing container 9, in which the binder-grain mixture 15 is prepared, into the interior of the roller-like screen printing stencil 16, for example, by a pump or screw conveyor (not shown). By means of a squeegee 11 attached to a squeegee holder 14, the binder-grain mixture 15 is pressed from the inside through the roller-like screen printing stencil 16 onto the web-like substrate 1 coated with the primer 19. The dashed arrow outlines the flow of the binder-grain mixture 15 within the roller-like screen printing stencil 16. The solid arrow outlines the direction of rotation of the roller-like screen printing stencil 16, wherein the squeegee holder 14 is arranged within the roller-like screen printing stencil 16 in such a way that it does not rotate and the squeegee 11 is stationary.

[0083] Through recesses in the screen printing stencil 16, convex accumulations 2, preferably hemispherical structures, consisting of the binder-grain mixture 15 are applied to the web-shaped substrate 1. The convex accumulations 2 form the abrasive layer 18 of the structured abrasive 6. Free spaces 21 exist between the convex accumulations 2. The viscosity of the binder-grain mixture 15 is selected such that the shape of the convex accumulations 2 is largely retained between steps e) and f).

[0084] In step f), the applied binder-grain mixture 15 is at least partially or completely hardened by means of a radiator 13.

[0085] Depending on the binder 4, even partial curing using a blaster 13 is sufficient, since complete curing can be achieved, for example, through subsequent thermal treatment. However, complete curing of the binder-grain mixture 15 is preferred.

[0086] To remove any dust, gases, and / or vapors that may be generated during step f), an extraction system 7 is also provided. This ensures a safe working environment.

[0087] Finally, in step g), the web-shaped substrate 1 is rolled up, which is now coated with a primer layer 19 and convex accumulations 2 of a binder-grain mixture 15 arranged thereon, whereby a structured abrasive 6 is provided.

[0088] After step f), the web-shaped base 1, which is coated with primer layer 19, convex accumulations 2 as abrasive layer 18, can be coated with additional layers (not shown).

[0089] Fig. 3A to 3C show a schematic side view of a grinding process with a structured abrasive 6. The Fig. 3A to 3C represent different degrees of wear of one and the same structured abrasive 6, which wears during the grinding process on a workpiece 5.

[0090] The structured abrasive 6 has a web-shaped base 1, on which the convex accumulations 2 forming an abrasive layer 13, which in this case correspond to hemispherical structures, are arranged from a binder-grain mixture 15. In the case of the Fig. In the example of the structured abrasive 6 shown in Figures 3A to 3C, no primer layer 19 is shown, but it may be present. The convex clusters 2 have a base area 20 with a diameter d and a height h. The convex clusters 2 are spaced apart by a distance of a.

[0091] The dimensions of the convex clusters 2 are in the range of 250 to 6000 µm for the diameter d and in the range of 100 to 1100 µm for the height h.

[0092] The distance a of the base surfaces 20 of the hemispherical structures 2 is in the range from 0 to 3500 µm.

[0093] The convex accumulations 2 consist of a binder-grain mixture 15, which consists of binder 4 and grains 3.

[0094] The volume ratio of grains 3 to binder 4 is in the range of 0.4 to 1.5, preferably in the range of 0.5 to 1.2.

[0095] The binder is formed by acrylates, polyester acrylates, polyether acrylates, epoxy acrylates, urethane acrylates as oligomeric components, acrylate monomers, and / or methacrylate monomers.

[0096] The grains are formed by normal corundum, semi-precious corundum, precious corundum, ceramic aluminum oxide, zirconium corundum, silicon carbide, diamond, cubic boron nitride, sol-gel aluminum oxide and / or formed sol-gel aluminum oxide.

[0097] Furthermore, the binder-grain mixture 15 can have the following components: - Curing initiators such as Type I or Type II photoinitiators for curing by means of UV radiation energy and / or thermal peroxide-based initiators and / or thermal azo compound-based initiators for curing by means of thermal radiation energy, - fillers such as chalk, cryolite, potassium tetrafluoroborate (KBF4), wollastonite and / or kaolin, and / or - Additives such as pyrogenic silica to adjust the rheology, silanes to promote adhesion between binder and abrasive grain, defoamers, deaerators, flow control agents, and / or color pigments in the binder-grain mixture.

[0098] An advantage of the structured abrasive 6, comprising an abrasive layer 18 with convex accumulations 2 in the form of hemispherical structures is Fig. 3A to 3C: Compared to other geometric shapes such as pyramids or cones, there is no linear increase in the surface area of ​​the abrasive layer 18 directly involved in the grinding process with the workpiece 5, but rather an exponential increase. This allows the user to maintain a more constant contact pressure of the structured abrasive 6 throughout the entire grinding process. Furthermore, with the hemispherical structure, the user achieves a longer service life of the structured abrasive 6, since there is a higher abrasive mass volume than, for example, with a pyramid.

[0099] Fig. 4 shows a schematic top view of a structured abrasive 6, having convex accumulations 2 in the form of hemispherical structures consisting of a binder-grain mixture 15 with diameter d.

[0100] The convex clusters 2 are arranged in regions on a web-like substrate 1 due to the selection of a screen printing stencil 16, which has randomly arranged recesses in certain regions. Between the convex clusters 2 are open spaces 21, which form a two-dimensional network structure 22. This enables a high degree of flexibility of the structured abrasive 6.

[0101] A measure of the randomness of the arrangement is the offset v of the centers of the convex accumulations 2 in a direction Q transverse to the longitudinal direction L of the web-shaped base 1. The longitudinal direction L of the web-shaped base 1 corresponds to the later grinding direction of the structured abrasive 6.

[0102] The centers of five successive hemispherical structures 2 in the longitudinal direction L of the web-shaped base 1 are offset by an offset distance v of at least 5% of their mean diameter transversely (also orthogonally) Q to the longitudinal direction L of the web-shaped base, whereby the offset distances v of the five considered convex accumulations 2 differ.

[0103] This improves the homogeneity of the grinding pattern on a workpiece to be machined. Reference symbol (part of the description) 1 sheet-like base 2 convex clusters 3 grains 4 Binders 5 Workpiece 6 structured abrasive 7 Extraction 8 primer containers 9 mixing containers 10 primer squeegees 11 squeegees 12 primer spotlights 13 spotlights 14 Squeegee holder 15 Binder-grain mixture 16 Printing screen / screen printing stencil 17 Counterpressure roller 18 grinding layer 19 Primer / Primer layer 20 Base area of ​​the convex accumulations 21 open spaces 22 Network structure of open spaces L Longitudinal direction of the web-shaped base Q Transverse direction of the web-shaped base d Diameter of the grains h height of the grains a Distance between two hemisphere structures v Offset distance of the hemisphere structures in the transverse direction QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] US 5984988 A

[0004] WO 9415752 A1

[0006]

Claims

[1] Structured abrasive (6), comprising - a web-shaped base (1) and - an abrasive layer (18), characterized by that the abrasive layer (18) has hardened convex accumulations (2) made of a binder-grain mixture (15), whereby free areas (21) remain on the web-shaped base (1) between the convex accumulations (2), wherein the convex accumulations (2) have an at least partially random arrangement on the web-shaped base (1). [2] Structured abrasive (6) according to claim 1, additionally comprising a primer layer (1) as an adhesion promoter between the web-shaped base (1) and the abrasive layer (18). [3] Structured abrasive (6) according to claim 1 or 2, wherein the convex accumulations (2) have base surfaces (20) on the side facing the web-shaped base (1) and - have a diameter (d) in the range of 250 to 6000 µm, preferably 420 to 4000 µm, more preferably 600 to 3000 µm and a height (h) in the range of 100 to 1300 µm, preferably 150 to 900 µm, and / or the base areas (20) cover 20% to 75%, preferably 50% to 70% of the web-shaped base (1) and / or - the base surfaces (20) have a distance (a) from each other in the range from 0 to 3500 µm, preferably 50 to 3000 µm and / or - the open areas (21) make up 80% to 25%, preferably 30% to 50% of the web-shaped base (1). [4] Structured abrasive (6) according to one of claims 1 to 3, wherein at least one of N successive convex accumulations (2) in the longitudinal direction (L) of the web-shaped base (1) is offset at least by an offset distance (v) of greater than 5% of their average diameter orthogonal (Q) to the longitudinal direction (L) of the web-shaped base (1), where the offset distances (v) of the N considered convex clusters (2) differ, where N = 3, preferably N = 5, more preferably N greater than 9. [5] Structured abrasive (6) according to one of claims 1 to 4, wherein the binder (4) of the binder-grain mixture (15) comprises the following components from a group consisting of: - Polyester acrylates, - polyether acrylates, - Epoxyacrylates, - Urethane acrylates as oligomeric components with at least 2 vinyl groups, - acrylate monomers with at least 2 vinyl groups, - methacrylate monomers with at least 2 vinyl groups. [6] Structured abrasive (6) according to one of claims 1 to 5, wherein the web-shaped base (1) consists of a group formed by: - Cotton, - Polyester, - mixed fabrics, - paper, - Vulcanized fiber.

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