EP4417367A1 - Method for producing a structured abrasive product and structured abrasive product - Google Patents

Abstract

Structured abrasive (6) and method for its production, the method comprising the following steps: a) providing a web-shaped base (1), b) providing a binder-grain mixture (15), c) applying the binder-grain mixture as convex accumulations (2), e.g. hemispherical structures, by a screen printing process to the web-shaped base as an abrasive layer (18), wherein free spaces (21) remain on the web-shaped base, and d) partially or completely hardening the applied binder-grain mixture by radiation energy (13), so that the structured abrasive has a web-shaped base and an abrasive layer, wherein the abrasive layer has hardened convex accumulations made of a binder-grain mixture, and wherein free spaces remain on the web-shaped base between the convex accumulations.

Description

The invention relates to a structured abrasive and a method for its production.

Structured abrasives are used in particular for machining metal workpieces and are available in different grain sizes. The abrasive generally has a base, e.g. a web-shaped base made of a solid or flexible material, onto which a binder layer based on e.g. phenol and abrasive grains absorbed in the binder layer are applied. The grains can be made of α-aluminum oxide or other materials.

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 suitable alignment, enable uniform abrasive engagement.

From the US5984988A For example, a manufacturing process is known in which the binding agent layer and the grains are applied to the substrates by scattering pre-prepared grains, e.g. gravimetrically or electrostatically, so that they are absorbed into the binding agent layer that has already been applied. This temporarily fixes the grain on the substrate. The binding agent layer is then cured. Thermally initiated, radiation-curing, and chemical curing using appropriate binding agents or hardeners/initiators are known.

The gravimetric or electrostatic spreading of the grains has the disadvantage that the production process involves several individual steps, which can have a negative impact on process reliability. The hardening of the entire surface of the substrate coated with binder is also energy-intensive. Abrasives produced by gravimetric or electrostatic scattering have the disadvantage that the surface of the abrasive is uneven on a microscale, since in particular the height of the abrasive can vary, e.g. when several grains are superimposed.

Alternatively, for example, from the WO 9415752 A1 A method is known in which a binder-grain mixture is placed on a molding tape, whereby the molding tape contains depressions and is then brought into contact with a base so that the binder-grain mixture on the molding tape or in the depressions of the molding tape adheres to the base over its entire surface. The molding tape and the base are then exposed together to electromagnetic radiation, which passes through the molding tape and hardens the binder. Finally, the molding tape is separated from the finished abrasive.

This process has the disadvantage that hardened residues of the binder-grain mixture remain on the impression belt or in the depressions of the impression belt, which makes it necessary to clean the impression belt or to accept losses in process continuity. The impression belt is also a wearing part that will have to be replaced after a certain time. In particular, the high-energy UV radiation 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 by the hardened binder-grain mixture adhering to the entire surface of the substrate.

The object of the invention is therefore to provide a structured abrasive and a method for its production which enable safe, cost-effective production and good grinding properties.

This object is achieved by a method for producing a structured abrasive according to patent claim 1 and by a structured abrasive according to patent claim 5. The subclaims specify preferred developments.

The structured abrasive according to the invention can be produced in particular by a process according to the invention.

1. a) Bereitstellen einer bahnförmigen Unterlage,
2. b) Bereitstellen einer Bindemittel-Korn-Mischung,
3. c) Auftragen der Bindemittel-Korn-Mischung als konvexe Anhäufungen, z.B. Halbkugelstrukturen, durch ein Siebdruckverfahren auf die bahnförmige Unterlage als Schleifschicht, wobei Freiflächen auf der bahnförmigen Unterlage verbleiben und
4. d) teilweises oder vollständiges Härten der aufgetragenen Bindemittel-Korn-Mischung durch Strahlungsenergie.

According to the invention, the method for producing a structured abrasive comprises the following steps:

1. a) Providing a web-shaped base,
2. b) Providing a binder-grain mixture,
3. c) applying the binder-grain mixture as convex accumulations, e.g. hemispherical structures, by screen printing onto the web-shaped substrate as an abrasive layer, leaving open areas on the web-shaped substrate and
4. d) partial or complete hardening of the applied binder-grain mixture by radiant energy.

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

Furthermore, the binder-grain mixture can contain fillers such as chalk, cryolite, potassium tetrafluoroborate (KBF ₄ ), wollastonite and/or kaolin.

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.

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.

The at least partial or complete hardening by radiation energy can be carried out by any type of radiation energy, for example UV, electron, thermal radiation energy, especially infrared radiation, or by a combination of different types of radiation energy. Curing using UV radiation energy is particularly preferred because it enables particularly energy-efficient and positionally precise curing of the binder-grain mixture.

The convex accumulations applied by screen printing have a height h and a base area with a diameter d (see also Figure 3A ), with the base area being arranged on the side of the convex accumulations facing the substrate. The convex accumulations preferably correspond to hemispherical structures, whereby hemispherical in this case is not to be regarded in the strict mathematical sense, whereby the height h would have to correspond to half the diameter d of the base area, but should merely describe the basic shape of the applied structures. Structures which correspond to an indented, truncated or elongated hemisphere, so that the height h of the hemisphere is not equal to half the diameter d of the base area, as well as semi-elliptical structures, fall under the term hemispherical structure within the meaning of this patent application. Other shapes, such as cubes or polygons with a height fall under the term convex accumulations.

The application process is preferably carried out using a screen printing process that has a roller-shaped screen printing stencil (rotary screen printing). This enables a continuous process. However, it is also conceivable to use screen printing stencils in a different form, for example using flat screen printing frames. Other known printing processes can also be used.

The binder-grain mixture preferably has a viscosity such that it is easy to process during the printing process. Viscosities in the range of 1000 mPa*s to 10000 mPa*s are advantageous, ideally 3000 mPa*s to 8000 mPa*s (at 20°C and a shear rate of 100 1/s). The shape of the convex accumulations is largely retained after application, but at least until partial or complete hardening. The binder-grain mixture therefore needs to exhibit structural viscosity.

The method according to the invention has the advantage that a high level of process reliability is possible through the single-stage method described. In addition, structured abrasives can be produced in a cost-effective manner.

Furthermore, the shape of the convex accumulations enables optimal penetration of the radiation energy during at least partial or complete hardening, which means that greater layer thicknesses of the grinding layer can be hardened than with a conventional, full-surface application. This advantage is made possible in particular by the absence of a molding tape, which absorbs a large proportion of the radiation energy. This avoids combined hardening from UV radiation and additional thermal energy, which is necessary when the layer thickness is too high or the radiation intensity is too low.

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 hardening of the binder-grain mixture are always uniform and reproducible.

According to the invention, it is further provided that a structured abrasive, which was preferably produced according to a method according to the invention, 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.

All features of the structured abrasive can be combined with the process according to the invention.

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

The convex accumulations preferably have substantially the same height. The grains of the binder-grain mixture are distributed substantially homogeneously in the hardened convex accumulations.

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

Furthermore, a high self-sharpening effect is achieved through a homogeneous distribution of the grains in the binder-grain mixture in the hardened convex accumulations, which leads to good grinding performance, in particular removal and durability of the structured abrasive.

The convex accumulations have base areas on the side facing the web-shaped base, whereby the base areas of the convex accumulations do not cover the entire surface of the web-shaped base. The open spaces on the web-shaped base provide the structured abrasive with a very high level of flexibility. In addition, these open spaces create chip spaces between the convex accumulations and ensure high stock removal and good heat dissipation.

Furthermore, the convex accumulations offer a "rounded tip" at the beginning of a grinding process, unlike other geometric shapes such as cuboids or rectangles. Due to the small area that penetrates into a material surface at the beginning of the grinding process, the initial breaking up of the convex accumulations is facilitated and the resharpening process is activated. After this, a uniform removal of the abrasive down to the carrier is possible (see Fig. 3A to 3C ).

Compared to other geometric shapes such as pyramids or cones, convex accumulations in the form of hemispherical structures do not offer a linear increase in the surface of the grinding layer directly involved in the grinding process with a workpiece, but an exponential one. This results in a more constant This allows the user to apply pressure throughout the entire grinding process. In addition, the user achieves a longer service life with a hemispherical structure, as the hemispherical structures have a higher geometry-related abrasive mass volume than, for example, pyramids.

1. a) Auftragen einer Primerschicht als Haftvermittler auf die bahnförmige Unterlage und
2. b) optionales zumindest teilweises Härten der Primerschicht durch Strahlungsenergie.

According to one embodiment of the method, the method comprises the following steps before the step of applying the binder-grain mixture to the substrate:

1. a) Applying a primer layer as an adhesion promoter to the web-shaped substrate and
2. b) optionally at least partially curing the primer layer by radiant energy.

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

A primer layer can improve adhesion of the binder-grain mixture to the web-shaped substrate, thereby increasing the mechanical stability and durability of the abrasive produced. The at least partial or complete hardening of the primer layer and its general use are merely optional, as this step can be omitted and the primer layer is also hardened by radiation energy when the applied binder-grain mixture hardens at least partially or completely.

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

• die eine Wandstärke im Bereich 100 bis 1100 µm, vorzugsweise im Bereich 150 bis 900 µm aufweist, und/oder
• die eine Anzahl von 15 bis 250, vorzugsweise 20 bis 160 Aussparungen pro Zoll aufweist, und/oder
• die Aussparungen mit einem Durchmesser im Bereich 400 bis 6000 µm, vorzugsweise 420 bis 4000 µm aufweist, und/oder
• die bereichsweise zufällig angeordnete Aussparungen aufweist.

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
• which has recesses with a diameter in the range 400 to 6000 µm, preferably 420 to 4000 µm, and/or
• which has randomly arranged recesses in some areas.

The screen printing stencil is preferably formed by a roller with recesses, past which the web-shaped substrate is guided, whereby the binding agent-grain mixture is guided into the interior of the roller and is passed through the recesses onto the web-shaped substrate with the help of a squeegee. The recesses are preferably round, but other shapes such as squares, triangles, polygons or polygons are also possible.

A wall thickness in the range of 100 to 1100 µm makes it possible to apply a layer thickness that is sufficient for a long service life of the abrasive, depending on the size of the convex accumulations. Wall thicknesses in the range of 100 to 500 µm, preferably 150 to 400 µm, have proven to be particularly advantageous for hand grinding. Wall thicknesses in the range of 400 to 1100 µm, preferably 450 to 900, have proven to be particularly advantageous for machine grinding. In hand grinding, thinner layer thicknesses are sufficient because less pressure is applied to the workpiece than in machine grinding applications. The lower pressure means that the service life of the abrasive is longer.

In addition, thinner wall thicknesses of the screen printing stencils allow smaller clusters to be printed without the clusters flowing into one another. Smaller clusters increase the flexibility of the abrasive, which is an advantage especially in hand sanding applications.

The number of recesses per inch, together with the size of these recesses, indicates how much of the surface area of the web-shaped backing is covered by base areas of convex accumulations and how much area remains as free space. This in turn significantly influences the flexibility of the structured abrasive article.

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 the height h and diameter d of the convex accumulations.

The size of the convex accumulations can thus be changed quickly and easily by using a different screen printing stencil, preferably without changing the recipe of the binder-grain mixture. The pressure required for the structured abrasive to be produced during the grinding process depends on the choice of the size of the convex accumulations, with large convex accumulations requiring more pressure during grinding than smaller convex accumulations. The process thus makes it possible to flexibly produce different structured abrasives. This means that the structured abrasive to be produced can be specifically optimized for different applications, preferably without making a recipe adjustment.

Convex accumulations, which are produced using screen printing stencils with recesses in the range of 250 µm to 6000 µm, preferably 420 to 4000 µm, have the advantage that an abrasive product can be produced that can produce particularly high-quality surfaces. For this purpose, only a small amount of pressure is required when grinding, for example with convex accumulations in the form of hemispherical structures. The durability of the abrasive can also be influenced by the selection of the convex accumulations. Another advantage is the high flexibility of the abrasive, which can therefore adapt well to the workpiece during the grinding process.

Screen printing stencils with recesses in the range of 250 to 1500 µm produce small convex accumulations for particularly flexible abrasives that are used in hand grinding. Recesses in the range of 1500 to 5000 µm are preferably used in machine grinding, where there are higher demands on pressure and durability during the grinding process.

Due to the randomly arranged recesses on the screen printing stencil, the convex accumulations on the web-shaped base are also randomly arranged in some areas. "Randomly arranged in some areas" means In particular, this means that the positions of the centers of the convex accumulations on the web-shaped substrate in one area do not follow an ordered, repeating pattern, for example they are not arranged in a square grid. The size of the random area can be freely selected within limits. For example, within a circle with eight times the diameter of the average diameter of the convex accumulations, no ordered, repeating pattern of the centers of the convex accumulations in the circle should be recognizable, whereby the position of the circle can be freely selected. However, after one revolution of the screen printing roller at the latest, the relative arrangement of the convex accumulations repeats itself. The advantage of the convex accumulations being randomly arranged in some areas is that the homogeneity of the grinding pattern on a workpiece to be processed is further improved.

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 substrate.

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

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

Covering 20% to 75% of the sheet substrate with the bases of the convex mounds corresponds to the number of recesses per inch described above and has the same advantages.

A proportion of 80% to 25% open space ensures the flexibility of the abrasive.

A distance a between the base surfaces in the range of 0 to 3500 µm, preferably 50 to 3000 µm, ensures that no full-surface binder layer is applied to the web-shaped base. This allows the web-shaped base 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. The distance a also helps to dissipate 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 also directly influenced. A more open structure introduces less heat into the workpiece.

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

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

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 average 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.

An offset of N successive convex accumulations in the longitudinal direction L of the web-shaped base by an offset distance v of at least 5% of their average diameter Q orthogonal to the longitudinal direction L of the web-shaped base 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 spaced convex accumulations. 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 accumulations are randomly distributed.

The longitudinal direction L of the web-shaped base corresponds to the subsequent grinding direction of the structured abrasive and is defined by the longest extension of the web-shaped base. The orthogonal direction Q lies in the plane of the web-shaped base and is orthogonal, i.e. perpendicular to the longitudinal direction L. The average diameters are calculated in a known manner by averaging the diameters d of the hemispherical structures considered, analogous to the FEPA standard. The offset distance v is determined as the deviation of the respective centers of the convex accumulations in the direction Q from the longitudinal direction L. For further illustration of the individual sizes L, Q, v, d, reference is made to the Fig.4 referred to.

• Polyesteracrylate,
• Polyetheracrylate,
• Epoxyacrylate,
• Urethanacrylate als oligomerer Bestandteile
• Acrylatmonomere
• Methacrylatmonomere

According to one embodiment of the method or the structured abrasive, the binder of the binder-grain mixture comprises the following components of a group formed by:

• Polyester acrylates,
• Polyetheracrylates,
• Epoxy acrylates,
• Urethane acrylates as oligomeric components
• Acrylate monomers
• Methacrylate monomers

The use of an acrylate binder allows a lower pressure of the structured abrasive during the grinding process than is possible with conventionally coated abrasives with phenol-based binders.

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

The process requires less space in the production plant than would be the case with conventionally scattered abrasives with phenolic resin-based binders. In addition, a shorter production time and thus an increased throughput in relation to the plant size is possible than with conventionally scattered abrasives with phenolic resin-based binders.

• Acrylatmonomer: 0%-60%, insbesondere 5%-40%
• Acrylatoligomer: 0%-60%, insbesondere 2% bis 35%
• Füllstoff: 0%-40%, insbesondere 8% bis 30%
• UV-Initiator: 0,1 %-6%, insbesondere 0,3%-5%
• Schleifkorn: 30%-75%, insbesondere 35% bis 70%

The following proportions have been found to be a particularly advantageous composition of 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%

• Baumwolle,
• Polyester,
• Mischgewebe,
• Papier,
• Vulkanfiber.

According to a further embodiment of the method or of the structured abrasive, the web-shaped substrate consists of a group formed by:

• Cotton,
• Polyester,
• mixed fabrics,
• Paper,
• Vulcanized fiber.

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

This means that a wide range of common web-shaped substrates can be used, making the structured abrasive suitable for a wide range of applications.

• Normalkorund,
• Halbedelkorund,
• Edelkorund,
• keramisches Aluminiumoxid,
• Zirkonkorund,
• Siliziumcarbid,
• Diamant,
• Cubisches Bornitrid,
• Sol-Gel Aluminiumoxid
• geformtes Sol-Gel Aluminiumoxid.

According to a further embodiment of the method or 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 alumina
• formed sol-gel alumina.

An appropriate choice of grains enables the use of grain properties that are individually tailored to the application of the structured abrasive.

Preferably, semi-precious corundum is used as it offers a good cost-benefit ratio for a wide range of applications.

According to a further embodiment of the method or 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.

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

Grains with average diameters in the range of 7 to 200 µm have proven to be particularly advantageous because this grain size range covers the application of surface finishing up to a mirror-like surface. In this grain size range, the binding system is able to hold the abrasive grain and at the same time ensure sufficient self-sharpening of the abrasive.

According to a further embodiment of the method or 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.

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

According to a further embodiment of the method or of the structured abrasive, the free surfaces are interconnected and form a two-dimensional network structure.

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

Fig. 1

einen beispielhaften Aufbau einer Vorrichtung zur Durchführung eines Verfahrens zur Herstellung eines strukturierten Schleifmittels;

Fig. 2

einen vergrößerten Ausschnitt der Vorrichtung aus Fig.1;

Fig. 3A, 3B, 3C

eine schematische Seitenansicht eines Schleifvorgangs mit einem strukturierten Schleifmittel;

Fig. 4

eine schematische Topsicht eines strukturierten Schleifmittels.

The invention is explained in more detail below with reference to the accompanying drawings. They show:

Fig.1

an exemplary structure of a device for carrying out a method for producing a structured abrasive;

Fig. 2

an enlarged section of the device Fig.1 ;

Fig. 3A, 3B, 3C

a schematic side view of a grinding process with a structured abrasive;

Fig.4

a schematic top view of a structured abrasive.

1. a) Bereitstellen einer bahnförmigen Unterlage 1,
2. b) Auftragen einer Primerschicht 19 als Haftvermittler auf die bahnförmige Unterlage 1,
3. c) zumindest teilweises Härten der Primerschicht 19 durch Strahlungsenergie.
4. d) Bereitstellen einer Bindemittel-Korn-Mischung 15,
5. e) Auftragen der Bindemittel-Korn-Mischung 15 als konvexe Anhäufungen 2, z.B. Halbkugelstrukturen, durch ein Siebdruckverfahren auf die bahnförmige Unterlage 1 als Schleifschicht 18, wobei Freiflächen 21 auf der bahnförmigen Unterlage 1 verbleiben,
6. f) zumindest teilweises oder vollständiges Härten der aufgetragenen Bindemittel-Korn-Mischung 15 durch Strahlungsenergie und
7. g) Aufrollen der bahnförmigen Unterlage 1.

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:

1. a) Providing a web-shaped base 1,
2. b) applying a primer layer 19 as an adhesion promoter to the web-shaped substrate 1,
3. c) at least partially curing the primer layer 19 by radiation energy.
4. d) Providing a binder-grain mixture 15,
5. e) applying the binder-grain mixture 15 as convex accumulations 2, e.g. hemispherical structures, by a screen printing process onto the web-shaped substrate 1 as an abrasive layer 18, whereby free surfaces 21 remain on the web-shaped substrate 1,
6. f) at least partial or complete hardening of the applied binder-grain mixture 15 by radiation energy and
7. g) Rolling up the web-shaped base 1.

Step a) is carried out by unwinding the web-shaped base 1 from a roll. The web-shaped base 1 consists of cotton, polyester, mixed 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, whereby steps a) to g) of the method are carried out.

Step b) is carried out by supplying primer 19 provided in a primer container 8 to a primer doctor blade 10, for example by means of a pump (not shown), wherein the primer 19 is applied to the web-shaped substrate 1 as a primer layer 19 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.

Subsequently, in step c), the primer layer 19 is at least partially hardened by means of a primer emitter 12. It is also possible to no hardening of the primer layer 19 is provided. Instead, the hardening of the primer layer 19 only takes place in step f), together with the applied binder-grain mixture 15.

In order 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.

This is followed by step e), whereby this step is Figure 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.

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 conveyor screw (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-shaped base 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.

Convex accumulations 2, preferably hemispherical structures, consisting of the binder-grain mixture 15 are applied to the web-shaped substrate 1 through recesses in the screen printing stencil 16. The convex accumulations 2 form the abrasive layer 18 of the structured abrasive 6. There are free areas 21 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).

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

Depending on the binding agent 4, partial hardening by means of a radiator 13 is sufficient, since complete hardening is achieved, for example, by subsequent thermal treatment. However, complete hardening of the binding agent-grain mixture 15 is preferred.

In order 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.

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.

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

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.

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

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

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

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

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

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

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

• Härtungsinitiatoren wie Photoinitiatoren vom Typ I oder Typ II für eine Härtung mittels UV-Strahlungsenergie und/oder thermische peroxidbasierte Initiatoren und/oder thermische azoverbindungsbasierte Initiatoren für eine Härung mittels thermischer Strahlungsenergie,
• Füllstoffe wie Kreide, Kryolith, Kaliumtetrafluoroborat (KBF₄), Wollastonit und/oder Kaolin, und/oder
• Additive wie Pyrogene Kieselsäure zur Einstellung der Rheologie, Silane zur Haftvermittlung zwischen Bindemittel und Schleifkorn, Entschäumer, Entlüfter, Verlaufshilfsmittel, und/oder Farbpigmente in der Bindemittel-Korn-Mischung.

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 (KBF ₄ ), wollastonite and/or kaolin, and/or
• Additives such as pyrogenic silica to adjust the rheology, silanes to promote adhesion between the binder and the abrasive grain, defoamers, deaerators, flow aids, and/or color pigments in the binder-grain mixture.

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 do not result in a linear increase in the surface of the grinding layer 18 that is directly involved in the grinding process with the workpiece 5, but rather an exponential increase. This enables the user to apply a more constant pressure to the structured abrasive 6 during the entire grinding process. In addition, the user achieves a longer service life for the structured abrasive 6 with the hemispherical structure, since there is a higher abrasive mass volume than with a pyramid, for example.

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.

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

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.

The centers of five consecutive 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 convex accumulations 2 considered differ.

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 accumulations

3

grain

4

binder

5

workpiece

6

structured abrasive

7

Extraction

8

Primer container

9

Mixing container

10

Primer squeegee

11

Squeegee

12

Primer Spotlight

13

Spotlights

14

Squeegee holder

15

Binder-grain mixture

16

Printing screen / screen printing stencil

17

Counter pressure roller

18

Grinding layer

19

Primer/ Primer layer

20

Base area of 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 grains

h

Height of grains

a

Distance between two hemisphere structures

v

Offset distance of the hemisphere structures in transverse direction

Claims (15)

Method for producing a structured abrasive (6), comprising the following steps: a) providing a web-shaped base (1), b) providing a binder-grain mixture (15), c) applying the binder-grain mixture (15) as convex accumulations (2) by a screen printing process onto the web-shaped substrate (1) as an abrasive layer (18), whereby free surfaces (21) remain on the web-shaped substrate (1) and d) partially or completely hardening the applied binder-grain mixture (15) by radiation energy. A method according to claim 1, wherein the method comprises the following steps prior to the step of applying the binder-grain mixture (15): a) applying a primer layer (19) as an adhesion promoter to the web-shaped substrate (1) and b) optionally at least partially curing the primer layer (19) by radiation energy. Method according to one of the preceding claims, wherein the screen printing method uses a screen printing stencil (16) which has one or more of the following properties: - a wall thickness in the range 100 to 1100 µm, preferably in the range 150 to 900 µm, - a number of 15 to 250, preferably 20 to 160 recesses per inch; - Recesses with a diameter in the range 250 to 6000 µm, preferably 420 to 4000 µm, more preferably 600 to 3000 µm, - Randomly arranged recesses in some areas. Method according to one of the preceding claims, wherein the at least one step of curing by radiant energy is carried out by means of UV, electron and/or thermal radiant energy. 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), wherein free spaces (21) remain on the web-shaped base (1) between the convex accumulations (2). Structured abrasive (6) according to claim 5, additionally comprising a primer layer (1) as an adhesion promoter between the web-shaped substrate (1) and the abrasive layer (18). Structured abrasive (6) according to claim 5 or 6, 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 of 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). Structured abrasive (6) according to one of claims 5 to 7, wherein the convex accumulations (2) have an at least partially random arrangement on the web-shaped base (1) Structured abrasive (6) according to one of claims 5 to 8, wherein at least one of N successive convex accumulations (2) in the longitudinal direction (L) of the web-shaped base (1) is offset by at least 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. Structured abrasive (6) according to one of claims 5 to 9, wherein the binder (4) of the binder-grain mixture (15) contains the following components from a group consisting of: - Polyester acrylates, - polyether acrylates, - Epoxy acrylates, - 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, has. Structured abrasive (6) according to one of claims 5 to 10, wherein the web-shaped substrate (1) consists of a group formed by: - Cotton, - Polyesters, - mixed fabrics, - Paper, - Vulcanized fiber. Structured abrasive (6) according to one of claims 5 to 11, wherein the grains (3) of the binder-grain mixture (15) 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 - molded sol-gel alumina. Structured abrasive (6) according to one of claims 5 to 12, wherein the grains (3) of the binder-grain mixture (15) have an average diameter (d) in the range of 7 to 200 µm, preferably 7 to 125 µm. Structured abrasive (6) according to one of claims 5 to 13, wherein the volume ratio of grains (3) to binder (4) in the binder-grain mixture (15) is in the range of 0.4 to 1.5, preferably in the range 0.5 to 1.2. Structured abrasive (6) according to one of claims 5 to 14, wherein the free surfaces (21) are interconnected and form a two-dimensional network structure (22).

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