ENDLESS ABRASIVE ARTICLE WITH NON-STRIPING FUNCTIONALITY

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to European Patent Application No. 24167320.1, filed on Mar. 28, 2024, the disclosure of which is hereby incorporated by reference in its entirety.

FIELD OF DISCLOSURE

The disclosure relates to an endless abrasive article having a non-striping functionality. The abrasive article comprises an antistatic, flexible backing and an abrasive layer comprising a plurality of cavities arranged in a series of parallel rows, the cavities being substantially free of abrasive grains. The parallel rows provide inclined segments of abrasive layer uninterrupted by any cavity between said parallel rows. The disclosure also relates to a production method for an endless abrasive article.

BACKGROUND

Abrading or abrasion refers to surface treatment that aims at altering a surface. Abrading may cause a smoothening effect or a roughening effect on a surface of a workpiece or at least a part of the workpiece surface by removing material from the workpiece surface. Abrasion may be used to generate or increase scratch patterns onto the workpiece surface. On the other hand, abrasion may be used to fade or decrease scratch patterns from the workpiece surface. In a case where abrasion precedes painting or coating, abrasion may be performed to ensure that paint, varnish or any other coating is received by a smooth surface. Abrasion is one of the most important steps in determining the end finish and quality of a product.

Abrasion may be performed to various surface materials, such as wood, metal, putties, composites, plastics, minerals or different coatings such as primers, paints or varnishes. Abrasion is performed by an article which comprises abrasive material. The article may be called an abrasive product, a sanding product, or an abrasive article.

Abrasion removes material from the surface of the workpiece. The removed material, or debris, unless efficiently removed, may clog the abrasive article surface or lead to further scratching of the workpiece, due to abrasive grains becoming loose within the debris. In demanding surface finishing applications, such as the removal of coatings, such as paints or lacquers, may also become problematic due to coatings which contain substances that are hazardous to environment or health, unless properly handled and collected.

Abrasive products having cavities for collecting the debris are known. Reference is made to European patent 1 733 844, disclosing an abrasive product having an underlay with an upper surface provided with holes obtained by laminating a cavity layer to a base layer. However, there are still problems associated with these products, which often comprise a backing made of a fiber-based material, such as paper. When produced by a conventional method, a layer of adhesive coating extends to the bottom of the cavities, diminishing the free volume of the cavity available for debris collection. Further, the cavities of conventional products are often produced by means of cutting blades, such as by perforating or piercing one or more layers of the product. The sharpness of a blade which is used to cut through an abrasive layer that comprises abrasive grains is reduced very rapidly, whereby the blade needs to be replaced with a new one. Moreover, upon cutting paper, the blade breaks the integrity of the fiber network, which leads to a degradation of the strength characteristics of the material. The tensile strength of a fiber-based material, such as paper, is based on the integrity of the fiber network therein. Therefore production means, wherein one or more layers of an abrasive product are cut through by a blade, reduce the tensile strength of the product when used in machine abrasion. This is a particular challenge with an abrasive article that is intended to be used in a belt sander, since an abrasive article, when used in a belt sander, requires tension. Thus, abrasive articles with enhanced strength and efficient debris collection are needed, together with manufacturing methods thereof.

There is also a problem associated with excess use of raw material associated with traditional production methods, which involve post-processing. By post-processing it is meant that the traditional methods rely on production of intact layers, which are afterwards processed by removing material from selected parts of the produced items. The post-processing may involve, for example, removal of selected regions of an abrasive layer or an adhesive make coat, for example by means of a de-burring tool, a water-jet device or a high intensity laser beam. The post-processing may also or in alternative involve removing selected regions by means of cutting blades, such as by perforating or piecing, as disclosed above, whereby the backing material or all layers of the abrasive product may be arranged to comprise cavities. However, post-processing of material is afterwards removed from a produced item, by perforation or piercing is considered waste and is not suitable for re-use.

Further, a risk of stripe formation on the surface of the workpiece is not solved using conventional abrasive products. When using a conventional abrasion product on a belt sander, the abrasion may result in visible stripes on the workpiece surface, especially with macrogrit designations in the range of P40 to P220. Thus, abrasive articles are needed that can provide a smooth abrasion result.

Abrasive articles typically comprise abrasive grains fixed onto a backing by means of an adhesive make coat. The adhesive make coat is cured to tightly bound the abrasive grains onto the backing. Conventionally, the adhesive is cured by heat, i.e., thermal curing. Conventional adhesives are often water-based dispersions, the curing of which consumes high amounts of energy (electricity and/or heat). Thermal curing processes typically require a hang drier to be used to reduce the size of the curing oven. In the hang drier, the backing on which the make coat and the abrasive grains are attached, propagates from roll to roll in a multiple roll arrangement, with folds between any two subsequent rolls. Thus, the backing turns in a vertical orientation while still being wet, whereby the make coat composition and the abrasive grains may move due to gravity, distorting the pattern defining the cavities. Thus, processes in which the cavity pattern maintains its well-defined structure during curing are needed.

Sustainable processes that can reduce the environmental impact of abrasive articles while improving the performance of said abrasive articles are thus needed.

SUMMARY

The disclosure solves the problems discussed above by providing a multi-layer abrasive article and a method for manufacturing the same.

This object is achieved by an endless abrasive article and its production method characterized by what is stated in the independent claims. Advantageous embodiments and variants of the disclosure are described in the dependent claims.

An endless abrasive article is provided herein. The endless abrasive article comprises a circumference and a substantially constant width, which is defined by a first edge and a second edge, an antistatic, flexible backing, and an abrasive layer comprising a layer of abrasive grains fixed onto the backing by means of an adhesive make coat. The abrasive layer comprises a plurality of cavities arranged in a predefined manner, more precisely, in a series of parallel rows. The cavities can be produced on the backing upon manufacturing the abrasive layer by means of a screen printing tool, and can thus be arranged to be substantially free of the adhesive make coat and substantially free of abrasive grains fixed onto the backing. Individual neighboring cavities in a row are separated from each other by a first distance. Adjacent parallel rows are separated from each other by a second distance in a direction parallel with the width of the endless abrasive article. The parallel rows further define an inclined direction, which refers to an angle between the inclined direction and the edges of the abrasive article, wherein the edges are parallel with the intended travelling direction of the endless abrasive article. The angle may be selected to provide an optimal arrangement of inclined segments of abrasive layer uninterrupted by any cavity between adjacent parallel rows in the inclined direction. Dimensions of the inclined segment are advantageously selected such that striping patterns caused by abrasion, when the endless abrasive article is used in a belt sander can be minimized. In other words, the arrangement of inclined segments on the surface of an endless abrasive article may be used for increasing smoothness and for reducing the formation of stripes on an abraded surface.

The cavities are configured to collect abrasion debris during use of the abrasive article. Thus, a smooth and scratch-free abrasion result may be obtained. When the abrasion debris is collected in the cavities, clogging of the abrading surface of the abrasive article by the abrasion debris is reduced.

Typically, during abrasion sanding pressure is applied on the abrasive product and the tips of abrasive grains protruding from the abrasive layer may crack such that fragments become separated from the abrasive grains. The cavities are also configured to collect such abrasive grain tip fragments. When collected in the cavities, scratching of the workpiece surface by the separated tips is reduced.

Upon use of the abrasive article in a belt sander, the abrasive article rotates around rotating elements, such as wheels. When the abrasive article turns around the rotating element, the cavities are emptied from the collected abrasion debris and separated fragments of abrasive grain tips, e.g., by gravity or suction. Thus, when contacting the workpiece surface again, the cavities are able to collect more abrasion debris. The cavities must be completely emptied upon rolling the abrasive article around the rotating element of the belt sander to ensure efficient debris collection on the next contact with the workpiece surface.

In the course of this specification, the term antistatic should be understood as a property of an object capable of reducing, removing, or preventing the buildup of static electricity. Some electrical conductivity is typically required to make an object antistatic.

The abrasive article provided herein has antistatic properties that ensure that the cavities are emptied upon turning around rotating elements when the abrasive article is used in a belt sander. Antistatic properties of the abrasive article ensure that the abrasion debris, often prone to the buildup of static electricity, does not remain in the cavities or on the surface of the abrasive article due to electrostatic interactions. The antistatic properties of the abrasive article thus enable a smooth and high-quality abrasion result on each contact of the abrasive article with the workpiece surface.

The antistatic, flexible backing provides the abrasive article with antistatic properties that are required for the high-quality and scratch-free abrasion result.

The endless abrasive article provides cavities substantially free of any adhesive make coat. Thus, the free volume of each cavity usable for debris collection is maximized. As a result, debris collection while abrading is enhanced, providing a smooth abrasion result.

Experimental results indicate that the best abrasion result, in respect of surface smoothness, is achieved when the angle of inclination on the endless abrasive article, as disclosed above, is substantially 8°, preferably in the range of 7.8 to 8.2°. The surface of a workpiece is substantially stripe-free when abraded with a belt sander using the endless abrasive article provided herein. The cavities organized in the presented pattern with the specified inclination angle enables a stripe-free abrasion result even with coarse abrasive grain sizes, e.g., abrasive grains having a grit designation in the macrogrit range (P40-P220).

In another aspect, a manufacturing method for an endless abrasive article suitable for use in machine abrasion with dust extraction is provided. The method comprises applying a pattern of an adhesive make coat on top of an antistatic, flexible backing, the pattern defining a plurality of uncoated areas that will not receive the adhesive make coat. The method typically further comprises attaching a plurality of abrasive grains on the patterned make coat. The plurality of uncoated areas in the pattern will not receive the abrasive grains. The presented method typically further comprises curing the make coat, thereby binding the abrasive grains to the make coat.

UV curing has the advantage of higher energy efficiency compared to conventional thermal curing. Thermal curing is based on evaporation of a solvent, which requires high amounts of energy. UV curing, on the other hand, is based on a photoinitiated radical polymerization reaction, whereby the energy consumption of the curing process is greatly reduced. Furthermore, space savings in production plants may be obtained using the UV curing method, since an UV curing equipment takes up less space than a conventional thermal curing oven.

The pattern in the make coat enables direct patterning of the abrasive grains upon attaching said abrasive grains on the make coat. This results in smaller material usage compared to conventional methods. Removal of material from the abrasive layer when producing the abrasive article is reduced or even completely avoided by using bottom-up approach of the presented method.

Together with the abrasive grains attached onto the patterned make coat, the uncoated areas in pattern of the make coat define a plurality of cavities arranged in a series of parallel rows. The cavities are typically substantially free of the adhesive make coat and substantially free of abrasive grains fixed onto the backing. Individual cavities in a row are separated from each other by a first distance. Adjacent parallel rows are separated from each other by a second distance in a direction parallel with the width of the abrasive article. The parallel rows define an inclined direction, wherein an angle between the inclined direction and the edges of the abrasive article is substantially 8°, preferably in a range of 7.8 to 8.2°. The angle provides inclined segments of abrasive layer uninterrupted by any cavity between adjacent parallel rows, in the direction of the inclined direction.

The method makes it possible to produce an abrasive article comprising cavities that are substantially free of the adhesive make coat and substantially free of the abrasive grains. Thus, it is possible to produce cavities with a larger free volume designed for debris collection compared to conventional methods. The larger cavities provide a more efficient debris collection, resulting in a smooth abrasion result.

The method facilitates the production of abrasive articles that can provide a substantially stripe-free abrasion result on a surface of a workpiece when used in a belt sander for abrading the workpiece. Extensive research has shown that the best abrasion result is achieved when the angle of inclination is substantially 8°, preferably in the range of 7.8 to 8.2°.

The presented method is more efficient in terms of raw material usage compared to conventional methods for producing abrasive articles comprising cavities. As disclosed above, the bottom-up approach of the presented method is based on adding material and building up the abrasive layer, not on removing material from an existing layer.

The presented method may be solvent-free, whereby both the energy efficiency and environmental and occupational safety of the method may be improved. The adhesives used for the presented method may be processed with less energy-consuming curing techniques. The solvent-free processing method also reduces the amount of solvent waste to be treated, and diminishes the health hazards on workers when handling said adhesives.

Further, a kit of parts comprising an abrading apparatus and the presented abrasive article, or an abrasive article obtainable by the presented method is provided.

SHORT DESCRIPTION OF THE FIGURES

In the figures, S_x, S_y and S_x denote orthogonal directions.

FIG. 1 is a schematic, three dimensional illustration of an endless abrasive article BLT1 that has a substantially constant width W_B parallel with the edges EDGE1, EDGE2 and a circumference defining a linear length L_B, determinable in a travelling direction DIR_MD of the endless abrasive article.

FIG. 2 is a schematic top-view illustration of a surface section of the endless abrasive article BLT1 having a substantially constant width, which comprises a plurality of cavities arranged in parallel rows which define an inclined direction, wherein an angle between the inclined direction and the edges of the abrasive article is substantially 8°, preferably in a range of 7.8 to 8.2°, which provides inclined segments of abrasive layer uninterrupted by any cavity between adjacent parallel rows that enable to reduce or eliminate the formation of a stripe pattern on an workpiece surface, upon using the endless abrasive article on a belt sander.

FIG. 3a-3b are schematic, cross-sectional illustrations of the endless abrasive article BLT1 having a substantially constant width.

FIG. 4 shows comparative experimental results of abrasion test simulations performed with endless abrasive articles comprising different inclined directions. Each endless abrasive article had the same width. Each endless abrasive article further comprised cavities having the same dimensions and distance from each other within a parallel row, which cavities were arranged in parallel rows which define an inclined direction. The parallel rows in all endless abrasive articles were also separated from each other by the same distance. The surface pattern of endless abrasive article therefore differed only in the angle between the inclined direction and the edges of the abrasive article, which was varied in a range of 7 to 8.5° between the endless abrasive articles.

FIG. 5 schematically presents a production method for manufacturing an endless abrasive article with non-striping functionality.

DETAILED DESCRIPTION

Abrasive Article

Referring to FIG. 1, an endless abrasive article BLT1 suitable for use in machine abrasion with a belt sander is provided. The endless abrasive article comprises a circumference having a linear length L_B and a substantially constant width W_B, wherein the width W_B is defined by a first edge EDGE1 and a second edge EDGE2. The endless abrasive article BLT1 is intended to be mounted on a belt sander, and may therefore have a preferred travelling direction DIR_MD. The travelling direction DIR_MD is parallel with the edges EDGE1, EDGE2 and the linear length L_B of the article BLT1. The abrasive article BLT1 may further comprise an antistatic, flexible backing BCK1, and an abrasive layer ABR1.

Referring to FIGS. 2 and 3a. the abrasive layer ABR1 comprises a layer of abrasive grains 15 fixed onto the backing by means of an adhesive make coat 11. The abrasive layer ABR1 comprises a plurality of cavities 14 arranged in a series of parallel rows R_k, R_k+1. The parallel rows R_k, R_k+1 are defined as lines extending through the center points of cavities in a respective row R_k, R_k+1. Advantageously, the cavities 14 are arranged to be substantially free of the adhesive make coat 11, whereby cavities 14 which are substantially free of abrasive grains 15 fixed onto the backing BCK1 may be provided. Individual cavities 14 in a row are separated from each other by a first distance d1. The first distance d1 is defined as an edge-to-edge distance between two adjacent individual cavities 14 in a row R_k, R_k+1, wherein the two adjacent individual cavities refer to two neighboring cavities 14 in a given row R_k, R_k+1 extending in a direction parallel with an inclined direction DIR_IN. Adjacent parallel rows R_k, R_k+1 may be separated from each other by a second distance d2 in a direction S_x parallel with the width W_B of the abrasive article BLT1. The parallel rows R_k, R_k+1 define an inclined direction DIR_IN, which is at an angle α1 to the edges EDGE1, EDGE2. The area between two adjacent parallel rows R_k, R_k+1 in the inclined direction DIR_IN defines inclined segments REG1 of abrasive layer ABR1 which are uninterrupted by any cavity 14 The angle α1 is defined as an angle between the inclined direction DIR_IN and an imaginary centerline Ax1, which is parallel with the edges EDGE1, EDGE2. The imaginary centerline Ax1 divides the endless abrasive article into two reflectionally symmetrical sides, whereby the angle α1 may be defined in any direction which deviates from the imaginary centerline Ax1. The angle α1 provides inclined segments REG1 of abrasive layer ABR1 uninterrupted by any cavity 14 between adjacent parallel rows R_k, R_k+1 in the inclined direction DIR_IN. Advantageously, the angle α1 is substantially 8°, preferably in a range of 7.8 to 8.2°.

Each individual cavity 14 comprises a circular shape with a diameter d3. As the abrasive layer contains abrasive grains 15 fixed onto the backing elsewhere except where cavities 14 exist, the share of the total surface area of the cavities 14 to the total surface area of the abrasive article BLT1 has an effect to the debris collection. Advantageously, the total surface area of the cavities 14 is in the range of 10-20%, most preferably in the range of 14-16% of the total surface area of the abrasive article BLT1. The total surface area of the abrasive article BLT1 is determined as the width W_B multiplied by the circumference L_B. The circular shape of the cavity 14 provides an advantage of enhanced debris collection performance compared to, e.g., polygonal-shaped cavity. The cavities may form a symmetrical pattern on the abrasive layer, such as a hexagonal pattern. A hexagonal pattern is advantageous for reducing the travelling distance from any given point on the abrasive layer ABR1 surface to the edge of a cavity 14. Furthermore, the circular shape of the cavities enhances the tearing resistance of the abrasive layer compared to cavities having sharp, vertex points, such as polygon-shaped cavities. The circular shape of the cavities further enables to minimize the generation of rupture points on the cavity edges.

In a typical abrasive article, ratio of the first distance d1 to the second distance d2 is in the range of 1:2 to 2:1.

Advantageously, the ratio of the first distance d1 to the width of the abrasive article W_B is in the range of 1:1 to 1:800

The width W_B of the abrasive article is in the range of 5 mm-3000 mm.

Adhesive materials used to produce the adhesive make coat 11, in other words, make coat adhesives, may be selected from compositions that can be cured. The make coat adhesives may be selected from compositions that can be cured by thermal curing, ultraviolet radiation (UV) curing, or electron beam (EB) curing.

The curable composition may comprise at least one unsaturated oligomer in an amount of up to 80 wt-%, such as 20-80 wt-%, of the total weight of the curable composition prior to curing. The at least one unsaturated oligomer may be aromatic or aliphatic. Preferably, the at least one unsaturated oligomer is selected from the group comprising polyurethanes, polyesters, polyethers, polyetheresters, epoxies, polysiloxanes, and any combination thereof. The curable composition may further comprise at least one unsaturated mono-, di-, tri- or poly-functional monomer in an amount of up to 90 wt-% of the total weight of the UV-curable composition prior to curing, such as 20-90 wt-%. The at least one unsaturated mono-, di-, tri- or poly-functional monomer may be selected from the group comprising acrylates, methacrylates, and any combination thereof. The curable composition may further comprise at least one component selected from a solvent, a filler, a surface modifier, an adhesion promoter, and any combination thereof.

Examples of oligomers based on aromatic urethane which are commercially available are Laromer UA9031V (BASF), BR-403 (Bomar), Ebecryl 215 (Allnex) or CN978 (Sartomer). Examples of oligomers based on aliphatic urethane which are commercially available are Laromer 8739 (BASF), Photomer 6210 (IGM Resins), Ebecryl 230 (Allnex), Genomer 4425 (Rahn) or CN 9001 (Sartomer). Examples of epoxy-based oligomers which are commercially available are Laromer LR 8986 (BASF), Photomer 3015 (IGM Resins), Ebecryl 600 (Allnex), Genomer 2235 (Rahn) or CN 104 (Sartomer). Examples of polyester-based oligomers which are commercially available are Laromer LR 8800 (BASF), Ebecryl 853 (Allnex) or CN 292 (Sartomer). Examples of polyether-based oligomers which are commercially available are Ebecryl 81 (Allnex) or Genomer 3364 (Rahn). Ricacryl 3500 (Sartomer) is an example of commercially available methacrylated polybutadiene oligomer.

Examples of monofunctional monomers are ethyl diethylene glycol acrylate (EDGA), ethoxylated nonylphenol acrylate, lauryl acrylate, tridecyl acrylate, isodecyl acrylate (IDA), 2-phenoxy-ethyl acrylate (PEA), hexadecyl acrylate, tetrahydrofurfuryl acrylate, isobornyl acrylate, vinyl caprolactam, acryloylmorpholine, butanediol acrylate, N-vinyl-2-pyrrolidone, octyldecyl acrylate, 4-(t-butyl)cyclohexyl acrylate (TBCH), caprolactone acrylate, dihydrodicyclopentadienyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, N-vinylformamide, vinyl acetate and their mixtures.

Examples of di-, tri,- or polyfunctional monomers are 1,6-hexanediol diacrylate (HDDA), tripropylene glycol diacrylate (TPGDA), dipropylene glycol diacrylate (DPGDA), polyethylene glycol diacrylate (PEGDA), neopentyl glycol diacrylate (NPGDA), ethoxylated neopentyl glycol diacrylate, propoxylated neopentyl glycol diacrylate, tetraethylene glycol diacrylate, 1,4-butanediol diacrylate (BDDA), ethoxylated bisphenol A diacrylate, trimethylolpropane triacrylate (TMPTA), glycerol triacrylate (GPTA), pentaerythritol triacryl-ate (PETA), ethoxylated trimethylpropane triacrylate (EO-TMPTA), propoxylated glyceryl triacrylate, tris-(2-hydroxyethyl)isocyanurate triacrylate, pentaerythri-tol tetraacrylate (PETTA), ethoxylated pentaerythritol tetraacrylate, ditrimethylolpropane tetraacrylate (DiTMPTTA), dipentaerythritol pentaacrylate (DiPEPA) and their mixtures.

The curable composition may comprise a solvent. The solvent is typically selected from the group comprising water, polar organic solvents such as alcohols, and nonpolar organic solvents such as alkanes and aromatics. Preferably, the solvent is water.

Alternatively, the curable composition not comprise a solvent. In other words, the curable composition may be a solvent-free adhesive. Solvent-free adhesives have an advantage of having a higher solid content, whereby the viscosity of the adhesive is also higher. This may result in a better resolution in the pattern of the make coat 11.

In case the adhesive make coat is curable using ultraviolet radiation (UV), the curable composition may further comprise at least one photoinitiator in an amount in the range of 0.1-10 wt-% of the total weight of the curable composition prior to curing. The at least one photoinitiator may be selected from the group comprising Norrish type I photoinitiators, Norrish type II photoinitiators, such as benzophenone and its derivatives, and any combination thereof.

Examples of suitable Norrish type I photoinitiators include 2-hydroxy-2-methyl-1-phenylpropan-1-one, benzoin ethers, for example benzoin methyl ether, benzoin ethyl ether, benzoin butyl ether and benzoin isopropyl ether, acetophenone derivatives, for example 2,2-diethoxy-acetophenone (DEAP), (1-hydroxycyclohexyl)acetophenone, 2-hydroxy-2,2-dimethylacetophenone (HDMA) or 2,2-dimethoxy-2-phenylacetophenone (DMPA), benzil ketals, hydroxyalkylphenones, morpholinoketones or acylphosphine oxides, for example (2,4,6-trimethyl-benzoyl)diphenylphosphine oxide and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (BAPO),

Examples of suitable Norrish type II photoinitiators include benzo-phenone and its derivatives, for example p-chloro-benzophenone or p-phenyl-benzophenone, benzyl, xanthone, thioxanthone and its derivatives, such as 2-ethylthioxanthone, 2-chlorothioxanthone (2CTX), 2-isopropylthioxanthone or 1-chloro-4-propoxythioxanthone, anthraquinone or ketocoumarins.

The adhesive make coat layer 11 may have a coat weight of at least 1 g/m², preferably at least 3 g/m², more preferably at least 5 g/m², expressed as weight of the adhesive make coat applied per square meter of the backing. The adhesive make coat layer 11 may have a coat weight smaller than or equal to 50 g/m², preferably 40 g/m², more preferably 25 g/m², even more preferably 10 g/m², as weight of the adhesive make coat applied per square meter of the backing. When preparing the make coat 11 using screen printing, the coat weight may be in the range of 3-40 g/m² when using solvent-based, such as water-based make coat adhesives, or in the range of 5-40 g/m² when using solvent-free make coat adhesives. When using rotary gravure printing, the coat weight may be in the range of 1-40 g/m², regardless of whether a solvent-based or solvent-free make coat adhesive is used.

The abrasive grains 15 may have a grit designation in the range of P40-P3000, determined according to FEPA standard 43-2:2017(en). Abrasive grains having a grit designation in the range of P40-P220 are referred to as macrogrits, and abrasive grains having a grit designation in the range of P240-P3000 are referred to as microgrits. The microgrit range may further be divided into two sub-ranges, wherein the first range, denoted as fine abrasive grains, comprises grit numbers P240 to P1200, while the second range, denoted as superfine abrasive grains, comprises grit numbers P1500 to P3000. For example, P240 corresponds to grains which have a grain size distribution of less than 59 μm, when defined by median grain size dew-value, by means of sedimentation. A larger grit designation value indicates grains having a smaller average size. In very demanding surface finishing applications, abrasive grains may have a grit designation equal to or higher than P600. In highly demanding surface finishing applications, abrasive grains may have a grit designation equal to or higher than P800. Advantageously, the grit designation value is selected based on the intended application.

The abrasive grains 15 may be attached to the make coat 11 by means of spray coating, slurry coating, dip coating, or electrostatic coating, preferably by slurry coating or electrostatic coating.

The layer of abrasive grains 15 may be obtainable by electrostatic coating, whereby the layer of abrasive grains 15 is electrostatically oriented, such that the abrasive grains 15 comprise tips 16 which point away from the make coat in a substantially horizontal direction S_z.

Alternatively, the layer of abrasive grains 15 may be obtainable by slurry coating.

Particularly, the layer of abrasive grains 15 in the macrogrit designation range is obtainable by electrostatic coating. The layer of abrasive grains (15) in the microgrit designation range may be obtainable by slurry coating.

Slurry coating refers to a process wherein a slurry comprising the abrasive grains 15 is applied onto the backing surface, e.g., by means of a roller. The slurry may further comprise, e.g., water, emulsifiers, wax, surface tension modifiers, oil, solvents, viscosity modifiers, or any combination thereof. When used to attach abrasive grains in the microgrit range, the slurry coating method may provide the abrasive article with surface properties that facilitate a smoother abrasion result.

The abrasive grains 15 may be attached to the make coat 11 by means of electrostatic coating. Electrostatic coating refers to a process wherein the abrasive grains are pulled up towards a backing comprising a make coat by a sufficiently high electric voltage. This generates an electric field, wherein the grains orient themselves while travelling through air. This results into the dull end of the abrasive grains to become embedded into the make coat while the pointed, sharp end of the abrasive grain protrudes away from the make coat. Examples of materials used in abrasive grains 15 are aluminum oxide, silicon carbide, zirconia, alumina zirconia, diamond, cubic boron nitride or any combinations thereof. Preferably, the abrasive grains are aluminum oxide or silicon carbide, or a combination thereof. The abrasive article BLT1 may contain a plurality of abrasive grains 15 which are of the same material or which may consists of a mixture of grains, which are of different grain types. The electrostatic coating method has the advantage of orienting the abrasive grains 15 such that the pointed, sharp end of the abrasive grain protrudes away from the make coat. This electrostatic orientation provides for sharper grains within the abrasive layer ABR1, providing a higher removal rate of debris from the workpiece surface. The sharp abrasive layer unexpectedly shows a stripeless abrasion result with the inclination angle α1 of substantially 8°, preferably 7.8 to 8.2°, even when used on soft working surfaces such as wood.

The abrasive grains 15 are typically applied on top of the make coat in a coat weight in the range of 10-300 g/m². The coat weight is expressed as weight of the abrasive grains applied per square meter of the backing. For abrasive grains in the macrogrit designation range, the abrasive grains 15 typically have a coat weight in the range of 10-300 g/m², such as in the range of 25-200 g/m². For abrasive grains in the microgrit designation range, the abrasive grains 15 typically have a coat weight in the range of 10-200 g/m², preferably in the range of 10-100 g/m².

The antistatic, flexible backing BCK1 may be made of paper. In the course of this disclosure, paper should be understood as a sheet-like product comprising cellulose-containing natural fibers. Antistatic paper should be understood as paper that has the property of reducing, removing, or preventing the buildup of static electricity on surfaces of the backing. The antistatic properties of the backing is based on the ability of the paper to dissipate electrical charge over the surface of the paper. Hygroscopicity of an antistatic paper is low enough to prevent the buildup of static electricity onto the paper surface. The antistatic property of the paper contributes to preventing clogging of the abrasive article with abrasion debris and thus increases the lifetime of the product. Paper as a material for the antistatic, flexible backing BCK1 has several advantages, such as recyclability and flexibility (especially in the out-of-plane direction). Moreover, paper has elastic properties and tear resistance required for use of the abrasive article in a belt sander under tension.

Grammage of the paper may be at least 100 g/m², preferably at least 200 or at least 250 g/m². Grammage of the paper may be equal to or smaller than 500 g/m², preferably 400 g/m² or 300 g/m². Grammage of the paper may be in the range of 100-500 g/m², preferably in the range of 200-400 g/m², more preferably in the range of 250-300 g/m².

Thickness of the paper may be at least 200 μm, preferably at least 250 μm. Thickness of the paper may be equal to or smaller than 500 μm, preferably 400 μm. Thickness of the paper may be in the range of 200-500 μm, preferably in the range of 250-400 μm.

A paper which is suitable for use as an antistatic flexible backing provides the abrasive article with tensile and tear strength characteristics that enable the abrasive article to be used for machine abrasion in a belt sander under tension.

Advantageously, the paper has a sheet resistance that is capable of providing the abrasive article with antistatic properties that enables to prevent the buildup of debris and fragments separated from abrasive grain tips in the cavities due to static electricity. Advantageously, the paper provides the abrasive article with a surface resistivity which is in the static dissipative or conductive range. A material is considered to be static dissipative when the surface resistivity is in the range of 10⁶ to 10¹¹Ω, and conductive when the surface resistivity is in the range of less than or equal to 10⁵Ω, when measured according to the ASTM standard D-257.

The endless abrasive article BLT1 further comprises an adhesive size coat 11, such that the abrasive grains 15 are surrounded by said adhesive size coat 12 adhered on top of the make coat 11. The size coat is meant to tightly envelop the abrasive grains 15 from other sides, such that once the adhesive size coat is cured, the abrasive grains 15 are firmly supported also horizontally in direction S_x by the adhesive size coat 12.

Adhesive materials used to produce the adhesive size coat 12, i.e., size coat adhesives may be selected from compositions that can be cured by electron beam (EB) curing. The electron beam curable (EB-curable) compositions provide the size coat layer 12 when cured. The EB-curable compositions provide a hard but elastic size coat layer 12, and thus they provide the abrasive article with increased durability and tensile energy absorption capacity.

The EB-curable composition may comprise at least one unsaturated oligomer in an amount of up to 80 wt-%, such as in the range of 20-80 wt-%, of the total weight of the EB-curable composition prior to curing. The at least one unsaturated oligomer may be aromatic or aliphatic. Preferably, the at least one unsaturated oligomer is selected from the group comprising polyurethanes, polyesters, polyethers, polyetheresters, epoxies, polysiloxanes, and any combination thereof. The EB-curable composition may further comprise at least one unsaturated mono-, di-, tri- or poly-functional monomer in an amount of up to 90 wt-% of the total weight of the EB-curable composition prior to curing, such as in the range of 20-90 wt-%. The at least one unsaturated mono-, di-, tri- or poly-functional monomer may be selected from the group comprising acrylates, methacrylates, and any combination thereof. The EB-curable composition may further comprise at least one component selected from a solvent, a filler, a surface modifier, an adhesion promoter, an antistatic agent, and any combination thereof.

Examples of oligomers based on aromatic urethane which are commercially available are Laromer UA9031V (BASF), BR-403 (Bomar), Ebecryl 215 (Allnex) or CN978 (Sartomer). Examples of oligomers based on aliphatic urethane which are commercially available are Laromer 8739 (BASF), Photomer 6210 (IGM Resins), Ebecryl 230 (Allnex), Genomer 4425 (Rahn) or CN 9001 (Sartomer). Examples of epoxy-based oligomers which are commercially available are Laromer LR 8986 (BASF), Photomer 3015 (IGM Resins), Ebecryl 600 (Allnex), Genomer 2235 (Rahn) or CN 104 (Sartomer). Examples of polyester-based oligomers which are commercially available are Laromer LR 8800 (BASF), Ebecryl 853 (Allnex) or CN 292 (Sartomer). Examples of polyether-based oligomers which are commercially available are Ebecryl 81 (Allnex) or Genomer 3364 (Rahn). Ricacryl 3500 (Sartomer) is an example of commercially available methacrylated polybutadiene oligomer.

Examples of monofunctional monomers are ethyl diethylene glycol acrylate (EDGA), ethoxylated nonylphenol acrylate, lauryl acrylate, tridecyl acrylate, isodecyl acrylate (IDA), 2-phenoxy-ethyl acrylate (PEA), hexadecyl acrylate, tetrahydro-furfuryl acrylate, isobornyl acrylate, vinyl capro-lactam, acryloylmorpholine, butanediol acrylate, N-vinyl-2-pyrrolidone, octyldecyl acrylate, 4-(t-butyl)cyclohexyl acrylate (TBCH), caprolactone acrylate, dihydrodicyclopentadienyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, N-vinylformamide, vinyl acetate and their mixtures.

Examples of di-, tri,- or polyfunctional monomers are 1,6-hexanediol diacrylate (HDDA), tripropylene glycol diacrylate (TPGDA), dipropylene glycol diacrylate (DPGDA), polyethylene glycol diacrylate (PEGDA), neopentyl glycol diacrylate (NPGDA), ethoxylated neopentyl glycol diacrylate, propoxylated neopentyl glycol diacrylate, tetraethylene glycol diacrylate, 1,4-butanediol diacrylate (BDDA), ethoxylated bisphenol A diacrylate, trimethylolpropane triacrylate (TMPTA), glycerol triacrylate (GPTA), pentaerythritol triacrylate (PETA), ethoxylated trimethylpropane triacrylate (EO-TMPTA), propoxylated glyceryl triacrylate, tris-(2-hydroxyethyl)isocyanurate triacrylate, pentaerythritol tetraacrylate (PETTA), ethoxylated pentaerythritol tetraacrylate, ditrimethylolpropane tetraacrylate (DiTMPTTA), dipentaerythritol pentaacrylate (DiPEPA) and their mixtures.

The EB-curable composition may comprise an antistatic agent. The antistatic agent may be selected from the group comprising graphite, carbon black, soot, metal particles, and any combination thereof, preferably graphite in the form of particles having a diameter in the range of 1-15 μm. A preferred EB-curable composition comprises graphite particles in the range of 5-25 wt-% of the total weight of the EB-curable composition prior to curing, more preferably in the range of 6-8 wt-%. The antistatic agent should be selected such that the abrasive article has a surface resistivity in the static dissipative or conductive range. A material is considered to be static dissipative when the surface resistivity is in the range of 10⁶ to 10¹¹Ω, and conductive when the surface resistivity is in the range of less than or equal to 10⁵Ω, when measured according to the ASTM standard D-257.

The EB-curable composition may comprise a filler in an amount of up to 60 wt-%, such as in the range of 20-60 wt-%, of the total weight of the EB-curable composition prior to curing.

The antistatic agents, in addition to the antistatic backing, provide the abrasive article with the required antistatic properties to prevent the buildup of abrasion debris and fragments separated from abrasive grain tips in the cavities due to static electricity. Thus, a smooth, high-quality, scratch-free abrasion result may be obtained. The antistatic size coat may reduce clogging of the surface of the abrasive article, thus enhancing the abrasion result and prolonging the lifetime of the abrasive article.

The adhesive size coat layer increases the tear resistance of the abrasive article, thus protecting the backing material from tearing. The electron beam curing process used to cross-link the size coat adhesive is energy-intensive and may weaken the tear resistance of the backing. The adhesive size coat layer covers substantially the entire surface area of the abrasive article, and thus protects the backing material from the energy-intense electron beam at the cavity sites upon the curing process. As a result, an abrasive article having a high tear strength is provided.

The adhesive size coat layer 12 may have a coat weight of at least 1 g/m², preferably at least 5 g/m², more preferably at least 30 g/m², expressed as weight of the adhesive size coat applied per square meter of the backing. The adhesive size coat layer 12 may have a coat weight smaller than or equal to 300 g/m², preferably 200 g/m², more preferably 75 g/m², as weight of the adhesive make coat applied per square meter of the backing. For abrasive grains in the macrogrit designation range, the adhesive size coat layer 12 may have a coat weight in the range of 5-300 g/m², preferably in the range of 30-200 g/m². For abrasive grains in the microgrit designation range, the adhesive size coat layer 12 may have a coat weight in the range of 1-100 g/m², preferably 5-75 g/m².

The ratio of the coat weight of the abrasive grains 15 to the coat weight of the adhesive size coat 12 is typically in the range of 1:2 to 2:1.

Referring to FIG. 3b, the endless abrasive article BLT1 may optionally comprise a super-size coat 13, such that the abrasive grains 15 are surrounded by said super-size coat 13 adhered on top of the size coat 12. A super-size coat 13 is typically used with fine abrasive grains having grit designations in the microgrit range. The super-size coat 13 is typically cured, e.g., by thermal curing or using ultraviolet radiation.

The super-size coat 13 typically comprises a mixture of stearates and a polymer dispersion that can be cured. Examples of suitable curable polymer dispersions include polyacrylates and polyurethanes, preferably as an aqueous dispersion. Preferably, the super-size coat 13 further comprises stearates, such as calcium stearates, magnesium stearates, zinc stearates, or any combination thereof. The super-size coat 13 may comprise stearates that are produced by melting followed by curing. Melting the stearates provides the super-size coat 13 with transparency.

The super-size coat 13 acts as a protective layer and also lubricates the debris forming into the space between the workpiece OBJ1 surface and the abrasive article BLT1, especially in areas that do not comprise the cavities 14. The debris lubrication has the effect of reducing clogging. This also prolongs the lifetime of the abrasive article BLT1.

Each cavity 14 has a height which extends in direction S_z away from the flexible backing BCK1 within the abrasive layer ABR1.

The individual cavities 14 of the plurality of cavities are preferably identical with each other.

Manufacturing Method of Abrasive Article

Referring to FIG. 5, a method for manufacturing an endless abrasive article suitable for use in machine abrasion with dust extraction is provided. The method comprises applying 101 a pattern of an adhesive make coat 11 on top of a flexible backing BCK1. The pattern may define a plurality of uncoated areas that will not receive the adhesive make coat 11. A plurality of abrasive grains 15 may subsequently be attached 102 on the patterned make coat 11. The plurality of uncoated areas in the pattern typically does not receive the abrasive grains 15. The method typically further comprises curing 103 the make coat 11, thereby binding the abrasive grains to the make coat 11. Thereby, an abrasive layer ABR1 is formed.

The pattern of adhesive make coat 11 may be applied by screen printing, inkjet printing, rotary gravure, or contact printing.

In a preferred method, the pattern of adhesive make coat 11 is applied 101 by screen printing using a cylindrical roll screen. The cylindrical roll screen comprises a two-layer mesh, through which the adhesive make coat is applied onto the surface of the backing.

The two-layer mesh typically comprises a conventional screen printing mesh, such as a nickel mesh arranged as a first layer. The first layer is configured to define the amount of adhesive make coat to be applied onto the surface of the backing.

In the method, a target coat weight of the adhesive make coat layer 11 may be at least 1 g/m², preferably at least 3 g/m², more preferably at least 5 g/m², expressed as weight of the adhesive make coat applied per square meter of the backing. The target coat weight of the adhesive make coat layer 11 may be smaller than or equal to 50 g/m², preferably 40 g/m², more preferably 35 g/m², even more preferably 10 g/m², as weight of the adhesive make coat applied per square meter of the backing. When preparing the make coat 11 using screen printing, the target coat weight may be in the range of 3-10 g/m² when using solvent-based, such as water-based make coat adhesives, or in the range of 5-40 g/m² when using solvent-free make coat adhesives. When using rotary gravure printing, the target coat weight may be in the range of 1-35 g/m², regardless of whether a solvent-based or solvent-free make coat adhesive is used.

The two-layer mesh may comprise a second, non-continuous layer defining the pattern of uncoated areas. The second layer typically comprises screening elements configured to prevent the application of the make coat adhesive on the uncoated areas. The screening elements may be composed of, e.g., a polymer or a metal.

Typically, the uncoated areas in the make coat 11 that will not receive the make coat 11 or the abrasive grains 15 define a plurality of cavities 14 arranged in a series of parallel rows R_k, R_k+1. The cavities 14 are typically substantially free of the adhesive make coat 11 and substantially free of abrasive grains 15 fixed onto the backing. Neighboring individual cavities 14 in a row R_k, R_k+1 are separated from each other by a first distance d1. Adjacent parallel rows R_k, R_k+1 are separated from each other by a second distance d2 in a direction S_x parallel with the width W_B. The parallel rows R_k, R_k+1 define an inclined direction DIR_IN wherein an angle α1 between the inclined direction DIR_IN and the edges EDGE1, EDGE2 of the abrasive article is substantially 8°, preferably in a range of 7.8 to 8.2°. The angle α1 provides inclined segments REG1 of abrasive layer ABR1 uninterrupted by any cavity 14 between adjacent parallel rows R_k, R_k+1.

The method may comprise curing the adhesive make coat 12 using thermal curing, ultraviolet radiation (UV), or electron beam curing (EB).

The adhesive make coat 11 may be cured by thermal curing. Thermal curing refers to a chemical process in which a prepolymer is converted into a polymer and then into a network, upon application of heat. Typically, thermal curing is carried out in a curing oven in which the backing on which the adhesive make coat composition is applied, is slowly propagating and cures upon evaporation of solvent caused by the heat. For example, resistive heating or infrared (IR) radiation may be used as a heat source.

The adhesive make coat 11 may be cured using ultraviolet radiation. UV curing is a process in which ultraviolet light is used to initiate a photochemical reaction that generates a crosslinked network of polymers. Compared to, e.g., thermal curing, UV curing is considered a low-temperature process, a high-speed process. UV curing processes may be solventless, because the curing occurs via direct polymerization rather than by evaporation.

UV curing requires the make coat adhesive to be UV-curable. Suitable UV-curable make coat adhesives may be selected from a group comprising polyesters, mono- and difunctional urethane acrylate polymers, and any combination thereof.

UV curing processes typically require the use of at least one photoinitiator, Preferably, the photoinitiator is selected from the group comprising Norrish type I photoinitiators, Norrish type II photoinitiators, such as benzophenone and its derivatives, and any combination thereof.

Examples of suitable Norrish type I photoinitiators include 2-hydroxy-2-methyl-1-phenylpropan-1-one, benzoin ethers, for example benzoin methyl ether, benzoin ethyl ether, benzoin butyl ether and benzoin isopropyl ether, acetophenone derivatives, for example 2,2-diethoxy-acetophenone (DEAP), (1-hydroxycyclohexyl)acetophenone, 2-hydroxy-2,2-dimethylacetophenone (HDMA) or 2,2-dimethoxy-2-phenylacetophenone (DMPA), benzil ketals, hydroxyalkylphenones, morpholinoketones or acylphosphine oxides, for example (2,4,6-trimethyl-benzoyl)diphenylphosphine oxide and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (BAPO),

Examples of suitable Norrish type II photoinitiators include benzo-phenone and its derivatives, for example p-chloro-benzophenone or p-phenyl-benzophenone, benzyl, xanthone, thioxanthone and its derivatives, such as 2-ethylthioxanthone, 2-chlorothioxanthone (2CTX), 2-isopropylthioxanthone or 1-chloro-4-propoxythioxanthone, anthraquinone or ketocoumarins.

The UV curing process has an advantage of being a high-speed process, e.g., when compared to conventional thermal curing. The radical polymerization process reaches a reaction equilibrium rather quickly, and the polymerization reaction proceeds to a complete state where substantially all monomers have reacted to give the cured polymer structure. Ultraviolet radiation thus provides a fast and reliable process for the curing.

The adhesive make coat 11 may be cured using electron beam (EB) curing. EB curing is a curing method based on a polymerization process, in which a substrate is coated with a curable adhesive, possibly diluted with a reactive dilutant. When applying energy in the form of an electron beam, the coating polymerizes, thus solidifying, i.e., curing said coating. Electron beam curing has an advantage over, e.g., thermal curing, of being solvent-free, thus reducing or even completely avoiding emissions of volatile organic compounds (VOCs). Electron beam curing is less energy consuming compared to thermal curing, and does not require large amounts of heat.

Typically, an electron beam with acceleration voltage in the range of 200-400 kV may be used. Such electron energies typically result in a radiation dose in the range of 15-50 kGy.

Although being largely similar to curing by ultraviolet (UV) radiation, electron beam curing has certain advantages over UV curing. UV curing is based on polymerization reactions catalyzed by photoinitiators. Since electron beams are more energetic than UV radiation, curing based on an electron beam may avoid the photoinitiator, making the curing process simpler and more straightforward. No special additives or catalysts are required. As a consequence of avoiding the photoinitiator, monomers or oligomers with higher solids content and viscosity may be used. Typically, these monomers are also more durable than monomers suitable for UV curing. The radical polymerization reaction proceeds to a complete state more quickly than by UV curing, ensuring that substantially all monomers have polymerized, i.e., cross-linked. Thus, EB curing provides a more rigid and strong polymer layer compared to UV curing. The more rigid polymer provides the abrasive article with increased durability and tensile energy absorption capacity.

Furthermore, electron beams can penetrate to the material unlike UV radiation that is confined to the surface. Electron beams may typically penetrate up to 200 μm beneath the surface of the layer to be coated. Electron beam curing can thus be used to cure thick coating layers, still providing superior surface adhesion and a high-performance surface finish.

Electron beam curing is more energy efficient than conventional curing methods. Moreover, the electron beam curing system takes up less space than conventional thermal curing ovens, simplifying the layout of production facilities.

Both the UV curing and EB curing have the advantage over conventional thermal curing that the shape of the uncoated areas in the make coat 11 is maintained intact during the curing process. Both the EB curing and UV curing processes are faster than conventional thermal curing, whereby the use of a hang drier within the curing apparatus may be avoided. In UV and EB curing, the curing reaction propagates faster than in thermal curing, such that the backing may lay flat within the curing apparatus during the curing. Thus, neither the make coat adhesive nor the abrasive grains move during the curing process, whereby the pattern defining the cavities is maintained during the curing, providing a well-defined cavity pattern in the product.

The method further comprises attaching 102 the abrasive grains 15 to the make coat 11, preferably by means of electrostatic coating. Electrostatic coating refers to a process, wherein the abrasive grains are pulled up towards a backing comprising a make coat by a sufficiently high electric voltage. This generates an electric field, wherein the grains orient themselves while travelling through air. This results into the dull end of the abrasive grains to become embedded into the make coat while the pointed, sharp end of the abrasive grain protrudes away from the make coat. Examples of materials used in abrasive grains 15 are aluminum oxide, silicon carbide, zirconia, alumina zirconia, diamond, cubic boron nitride or any combinations thereof. Preferably, the abrasive grains are aluminum oxide or silicon carbide, or a combination thereof. The abrasive article BLT1 may contain a plurality of abrasive grains 15 which are of the same material or which may consists of a mixture of grains, which are of different grain types.

The abrasive grains 15 are typically applied on top of the make coat in a coat weight in the range of 10-300 g/m², preferably in the range of 20-200 g/m². The coat weight is expressed as weight of the abrasive grains applied per square meter of the backing. For abrasive grains in the macrogrit designation range, the abrasive grains 15 typically have a coat weight in the range of 10-300 g/m², such as 25-200 g/m². For abrasive grains in the microgrit designation range, the abrasive grains 15 typically have a coat weight in the range of 10-200 g/m², preferably 10-100 g/m².

The method may further comprise applying 103 a layer of an adhesive size coat 12 on top of the patterned make coat 11 and the plurality of abrasive grains 15. The size coat is meant to tightly envelop the abrasive grains 15 from other sides, such that once the adhesive size coat is cured, the abrasive grains 15 are firmly supported also horizontally in direction S_x by the adhesive size coat 12. The method may further comprise curing 105 the adhesive size coat 12 using electron beam curing, thereby forming the abrasive layer ABR1. The adhesive size coat 12 may be substantially free of photoinitiators.

Applying the adhesive size coat 12 increases the tear resistance of the abrasive article, thus protecting the backing material from tearing. The electron beam curing process used to harden the size coat adhesive is energy-intensive and may weaken the tear resistance of the backing. The adhesive size coat layer covers substantially the entire surface area of the abrasive article, and thus protects the backing material from the energy-intense electron beam at the cavity sites upon the curing process. Thus, an abrasive article having a high tear strength may be produced.

The adhesive size coat layer 12 may be applied at a target coat weight of at least 1 g/m², preferably at least 5 g/m², more preferably at least 30 g/m², expressed as weight of the adhesive size coat applied per square meter of the backing. The adhesive size coat layer 12 may be applied at a target coat weight smaller than or equal to 3000 g/m², preferably 200 g/m², more preferably 75 g/m², as weight of the adhesive make coat applied per square meter of the backing. For abrasive grains in the macrogrit designation range, the adhesive size coat layer 12 may be applied in a target coat weight in the range of 5-300 g/m², preferably 30-200 g/m². For abrasive grains in the microgrit designation range, the adhesive size coat layer 12 may be applied in a target a coat weight in the range of 1-100 g/m², preferably 5-75 g/m².

The ratio of the coat weight of the abrasive grains 15 to the coat weight of the adhesive size coat 12 is typically in the range of 1:2 to 2:1.

The adhesive size coat layer may be applied using conventional application techniques, e.g., by using a roller.

Viscosity of the size coat adhesive prior to curing may be higher when using electron beam curing compared to UV curing. Typically, the size coat adhesive has a viscosity in the range of 15-1500 mPa, such as in the range of 15-100 mPa or in the range of 100-1500 mPa. Viscosities in the 15-100 mPa viscosity range are measured using a rheometer (Anton Paar). Viscosities in the 100-1500 mPa range are measured using a Brookfield viscometer according to the standard ISO 2884-2. All viscosities are measured at 20° C.

The antistatic agent may be selected from the group comprising graphite, carbon black, soot, metal particles, and any combination thereof, preferably graphite in the form of particles having a diameter in the range of 1-15 μm.

Electron beam curing is a curing method based on a polymerization process, in which a substrate is coated with a curable adhesive, possibly diluted with a reactive dilutant. When applying energy in the form of an electron beam, the coating polymerizes, thus solidifying, i.e., curing said coating. Electron beam curing has an advantage over, e.g., thermal curing, of being solvent-free, thus reducing or even completely avoiding emissions of volatile organic compounds (VOCs). Electron beam curing is less energy consuming compared to thermal curing, and does not require large amounts of heat.

The method may comprise curing the adhesive size coat 12 by electron beam curing. Typically, an electron beam with acceleration voltage in the range of 200-400 kV is used. Such electron energies typically result in a radiation dose in the range of 15-50 kGy.

Although being largely similar to curing by ultraviolet (UV) radiation, electron beam curing has certain advantages over UV curing. UV curing is based on polymerization reactions catalyzed by photoinitiators. Since electron beams are more energetic than UV radiation, curing based on an electron beam may avoid the photoinitiator, making the curing process simpler and more straightforward. No special additives or catalysts are required. As a consequence of avoiding the photoinitiator, monomers or oligomers with higher solids content and viscosity may be used. Typically, these monomers are also more durable than monomers suitable for UV curing. The radical polymerization reaction proceeds to a complete state more quickly than by UV curing, ensuring that substantially all monomers have polymerized, i.e., cross-linked. Thus, EB curing provides a more rigid and strong polymer layer compared to UV curing. The more rigid polymer provides the abrasive article with increased durability and tensile energy absorption capacity.

Furthermore, electron beams can penetrate to the material unlike UV radiation that is confined to the surface. Electron beams may typically penetrate up to 200 μm beneath the surface of the layer to be coated. Electron beam curing can thus be used to cure thick coating layers, still providing superior surface adhesion and a high-performance surface finish.

Electron beam curing is more energy efficient than conventional curing methods. Moreover, the electron beam curing system takes up less space than conventional thermal curing ovens, simplifying the layout of production facilities.

The electron beam curing provides an additional advantage when used to cure pigmented or colored adhesive size coat compositions. For example, graphite, when used as an antistatic agent, provides the adhesive size coat 12 with black color, whereby curing using ultraviolet radiation is not possible. When using electron beam curing, it is possible to cure the adhesive size coat layer 12 regardless of its color or opacity properties.

The method may further comprise applying 106 a layer of a super-size coat 13 on top of the patterned make coat 11, the plurality of abrasive grains 15 and the adhesive size coat 12, such that the abrasive grains 15 are surrounded by said super-size coat 13 adhered on top of the size coat 12. The method may further comprise curing 107 the super-size coat 13.

A super-size coat 13 is typically applied to abrasive articles with abrasive grains having grit designations in the microgrit range.

The super-size coat 13 typically comprises a mixture of stearates and a polymer dispersion that can be cured. Examples of suitable curable polymer dispersions include polyacrylates and polyurethanes, preferably as an aqueous dispersion. Preferably, the super-size coat 13 further comprises stearates, such as calcium stearates, magnesium stearates, zinc stearates, or any combination thereof. The super-size coat 13 may comprise stearates that are produced by melting followed by curing. Melting the stearates provides the super-size coat 13 with transparency.

The super-size coat layer 13 may be applied at a target coat weight of at least 1 g/m², preferably at least 5 g/m², expressed as weight of the adhesive size coat applied per square meter of the backing. The super-size coat layer 13 may be applied at a target coat weight smaller than or equal to 30 g/m², preferably 25 g/m², as weight of the adhesive make coat applied per square meter of the backing. The target coat weight may be in the range of 1-30 g/m², preferably 2-25 g/m². The super-size coat 13 is typically used with abrasive grains in the microgrit designation range.

Applying the super-size coat 13 provides the abrasive article with a protective layer and also lubricates the debris forming into the space between the workpiece OBJ1 surface and the abrasive article BLT1, especially in areas that do not comprise the cavities 14. The debris lubrication has the effect of reducing clogging. This also prolongs the lifetime of the abrasive article BLT1

EXAMPLES

Example 1. Simulation of Stripe Patterns

Reference is made to FIG. 4. Stripe patterns produced by the abrasive article BLT1 when used on a belt sander where simulated at different angles angle α1 between the inclined direction DIR_IN and the edges EDGE1, EDGE2 of the abrasive article ranging from 0° to 172°.

The pattern with each angle α1 was drawn as a black and white picture. The amount of black and white pixels were calculated along a 1 pixel-wide line in the machine direction DIR_MD. The ratio of number of black pixels to the number of white pixels was translated into a greyscale and plotted. Results for the simulated stripe patterns are shown in FIG. 4 for inclination angles α1 of 7°, 7.5°, 8°, and 8.5°. As evident from the results, the best abrasion result was achieved when the angle of inclination was substantially 8°, such as in the range of 7.8 to 8.2°. This enabled a non-striping abrasion.

Example 2. Coat Weight of Adhesive Lavers for Different Grit Designations

Table 1 presents target coat weights of the adhesive make coat 11, the abrasive grains 15, the adhesive size coat 12, and the super-size coat 13 for different grit designations. The coat weights are expressed as weight of the respective component applied per square meter of the backing.

TABLE 1
Grit		Abrasive		Super-size
designation	Make coat	grains	Size coat	coat
range	g/m2	g/m2	g/m2	g/m2
P80-P220	5-40	25-200	30-200	—
P240-P3000	5-25	10-100	5-75	2-25

It is to be understood that many variations to the experimental studies above may be conceived. The disclosure above, including the appended figures, is provided to aid understanding of the disclosure, which is defined by the appended claims.