Endless Abrasive Article with Non-Striping Functionality

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.

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.

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.

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.

Referring to, an endless abrasive article BLTsuitable for use in machine abrasion with a belt sander is provided. The endless abrasive article comprises a circumference having a linear length Land a substantially constant width W, wherein the width Wis defined by a first edge EDGEand a second edge EDGE. The endless abrasive article BLTis intended to be mounted on a belt sander, and may therefore have a preferred travelling direction DIR. The travelling direction DIRis parallel with the edges EDGE, EDGEand the linear length Lof the article BLT. The abrasive article BLTmay further comprise an antistatic, flexible backing BCK, and an abrasive layer ABR.

Referring to. the abrasive layer ABRcomprises a layer of abrasive grainsfixed onto the backing by means of an adhesive make coat. The abrasive layer ABRcomprises a plurality of cavitiesarranged in a series of parallel rows R, R. The parallel rows R, Rare defined as lines extending through the center points of cavities in a respective row R, R. Advantageously, the cavitiesare arranged to be substantially free of the adhesive make coat, whereby cavitieswhich are substantially free of abrasive grainsfixed onto the backing BCKmay be provided. Individual cavitiesin a row are separated from each other by a first distance d. The first distance dis defined as an edge-to-edge distance between two adjacent individual cavitiesin a row R, R, wherein the two adjacent individual cavities refer to two neighboring cavitiesin a given row R, Rextending in a direction parallel with an inclined direction DIR. Adjacent parallel rows R, Rmay be separated from each other by a second distance din a direction Sparallel with the width Wof the abrasive article BLT. The parallel rows R, Rdefine an inclined direction DIR, which is at an angle αto the edges EDGE, EDGE. The area between two adjacent parallel rows R, Rin the inclined direction DIRdefines inclined segments REGof abrasive layer ABRwhich are uninterrupted by any cavityThe angle αis defined as an angle between the inclined direction DIRand an imaginary centerline Ax, which is parallel with the edges EDGE, EDGE. The imaginary centerline Axdivides the endless abrasive article into two reflectionally symmetrical sides, whereby the angle αmay be defined in any direction which deviates from the imaginary centerline Ax. The angle αprovides inclined segments REGof abrasive layer ABRuninterrupted by any cavitybetween adjacent parallel rows R, Rin the inclined direction DIR. Advantageously, the angle αis substantially 8°, preferably in a range of 7.8 to 8.2°.

Each individual cavitycomprises a circular shape with a diameter d. As the abrasive layer contains abrasive grainsfixed onto the backing elsewhere except where cavitiesexist, the share of the total surface area of the cavitiesto the total surface area of the abrasive article BLThas an effect to the debris collection. Advantageously, the total surface area of the cavitiesis in the range of 10-20%, most preferably in the range of 14-16% of the total surface area of the abrasive article BLT. The total surface area of the abrasive article BLTis determined as the width Wmultiplied by the circumference L. The circular shape of the cavityprovides 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 ABRsurface to the edge of a cavity. 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 dto the second distance dis in the range of 1:2 to 2:1.

Advantageously, the ratio of the first distance dto the width of the abrasive article Wis in the range of 1:1 to 1:800

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

Adhesive materials used to produce the adhesive make coat, 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.

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

The abrasive grainsmay 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 grainsmay be attached to the make coatby means of spray coating, slurry coating, dip coating, or electrostatic coating, preferably by slurry coating or electrostatic coating.

The layer of abrasive grainsmay be obtainable by electrostatic coating, whereby the layer of abrasive grainsis electrostatically oriented, such that the abrasive grainscomprise tipswhich point away from the make coat in a substantially horizontal direction S.