CROSS-REFERENCE TO RELATED APPLICATION
This application claims the benefit of U.S. Provisional Patent Application No. 60/825,220, filed Sep. 11, 2006, the disclosure of which is incorporated by reference herein in its entirety.
The present disclosure relates to fixed abrasive articles having a molded mechanical fastener.
It is common to use certain hook-and-loop type mechanical fasteners for connecting fixed abrasive articles to abrading tools. One approach uses thin, molded male fasteners (e.g., “hooks”) with low loft loop materials, most commonly textile “loop” materials as the female components. For these uses generally low cost and appropriate attachment strength are important. The word “loop”, as used in this document, also includes low lying, free sections of fabric filaments, such as those of a textile fabric, capable of mechanically engaging with a male fastener component, this use of the word being in accordance with its current general use in the art of separable fasteners.
Engaging projections have been directly molded as disclosed for example in U.S. Pat. No. 5,315,740, which describes a re-entrant hook, i.e., a hook having a tip-portion that curves over and down toward the base sheet from the upper end of the hook to define a fiber-retaining recess on the underside of the hook. It is also known to cap molded stems on webs. Mushroom-shaped engaging projections obtained by this process are disclosed in, e.g., U.S. Pat. Nos. 5,679,302; 5,879,604; 6,287,665; and 6,627,133. U.S. Pat. No. 6,470,540 uses a hot extruded layer for deforming stems, which results in semi-spherical mushroom heads. In U.S. Pat. No. 3,550,837, a male fastener member is described wherein each engaging projection is constituted by an irregularly shaped granule with a special multifaceted surface, adhesively adhered to the base. In U.S. Pat. No. 3,922,455, nibs of various shapes are grafted onto linear filaments, the linear filaments, protruding from a base, forming the engaging elements of a male fastener component. In PCT publication WO 01/33989, particles are, with a scatter head of a scatter coater, randomly scattered, and fixed onto a base. Each engaging projection is constituted by several agglomerated particles, though some individual particles may also be left present.
There is a continuing need to provide low-cost male mechanical fasteners with advantageous properties.
In one aspect, the present disclosure provides a fixed abrasive article comprising a substrate having an abrasive surface and an attachment surface, and at least one engaging projection. The engaging projection comprises a top surface having a top surface edge and an attachment end attached to the attachment surface of the substrate. The area of attachment between the attachment end and the attachment surface is bounded by an attachment perimeter. The engaging projection also comprises a mantle surface extending from the top surface edge to the attachment perimeter. At least one profile of the mantle surface is substantially convex from a point of maximum width along the profile to the attachment perimeter.
In some embodiments, the engaging projection is directly attached to the attachment surface of the substrate. In some embodiments, the engaging projection is indirectly attached to the attachment surface of the substrate. In some embodiments, at least one intermediate layer is interposed between the attachment end of the engaging projection and the attachment surface, optionally wherein the intermediate layer is selected from the group consisting of an adhesive, a primer, a binder, a resin, a polymeric film, and combinations thereof.
In another aspect, the present disclosure provides a fixed abrasive article comprising a first substrate having an abrasive surface and an attachment surface, and an attachment layer. The attachment layer comprises a second substrate having a first surface and a second surface, wherein the first surface of the second substrate is attached to the attachment surface of the first substrate. The attachment layer further comprises an engaging projection comprising a top surface having a top surface edge, and an attachment end attached to the second surface of the second substrate. The area of attachment between the attachment end and the second surface is bounded by an attachment perimeter. The engaging projection also comprises a mantle surface extending from the top surface edge to the attachment perimeter. At least one profile of the mantle surface is substantially convex from a point of maximum width along the profile to the attachment perimeter. In some embodiments, the first surface of the second substrate is attached to the attachment surface of the first substrate via an adhesive layer, optionally wherein the adhesive layer comprises an adhesive selected from the group consisting of a pressure sensitive adhesive, a heat-activated adhesive, radiation curable adhesive, and moisture curable adhesive.
In some embodiments, the fixed abrasive articles of the present disclosure further comprise an abrasive layer at the abrasive surface of the substrate. In some embodiments, the abrasive layer is directly attached to the abrasive surface of the substrate. In some embodiments, the abrasive layer is integral with the abrasive surface of the substrate. In some embodiments, the abrasive layer is indirectly attached to the abrasive surface of the substrate.
In some embodiments, the abrasive layer comprises a make coat, abrasive particles at least partially embedded in the make coat, and, optionally, a size coat over the abrasive particles. In some embodiments, the abrasive layer comprises a primer and abrasive particles attached to the primer. In some embodiments, the abrasive layer comprises abrasive particles dispersed in a binder, optionally wherein the binder is selected from the group consisting of inorganic binders, organic binders, and combinations thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates an exemplary abrasive article according to some embodiments of the present disclosure.
FIG. 2 illustrates an exemplary engaging element according to some embodiments of the present disclosure.
FIG. 3 illustrates a cross-section of the exemplary engaging element of claim 2.
FIGS. 4a-4c illustrate the cross sections of concave engaging elements.
In one aspect, the present disclosure provides a fixed abrasive article comprising a substrate having an abrasive surface and an attachment surface. The attachment surface includes attached engaging projections, which may be used to connect the fixed abrasive article to an abrading apparatus.
Fixed abrasive articles are often used with dual action sanders (“DA sanders”) which are well known in the art. Such sanders with back-up pads may be used for light duty sanding operations such as light sanding of painted surfaces between paint coats and sanding with very fine sandpaper to remove small paint imperfections such as dust nibs from the final paint coat. This type of sanding imparts little stress to the attachment interface. Such back-up pads may also be used for medium duty sanding operations such as final preparation of a workpiece surface for primer painting and sanding a workpiece surface having a primer paint thereon in preparation for subsequent painting. Light to medium downward pressures are typically applied during these types of sanding applications and impart a moderate amount of stress on the attachment interface. However, such sanders and back-up pads are often used under heavy duty sanding operations such as paint stripping or removing excess body filler where fairly heavy downward pressure would be applied by the operator. The back-up pad is often inclined at a relatively steep angle with respect to the workpiece surface and may also be pushed into crevices and over fairly sharp contours. The paint or body filler on the workpiece surface provides substantial resistance to the abrasive surface of the abrasive article attached to the back-up pad so that a considerable sanding force is often required to remove the paint or body filler. Such aggressive, heavy sanding operations apply substantial stress on the hook and loop attachment interface.
In general, the means (e.g., mechanical attachment systems) used to attach a fixed abrasive article to, e.g., a back-up pad may be required to withstand both shear forces and peel forces. In addition, in some embodiments, the peel force may be selected to be high enough to withstand the forces encountered during use, but low enough to provide ease of removal and/or repositioning.
Generally, any known form of fixed abrasive article may be used. Exemplary fixed abrasive articles forms include discs, sheets, strips, circles, ovals, polygons, and “daisy-shapes.”
A representative fixed abrasive article 10 is shown in FIG. 1. Abrasive article 10 includes substrate 20 having abrasive surface 21 and attachment surface 22. Engaging projections 30 are attached to attachment surface 22.
Generally, any known substrate may be used, e.g., paper, polymeric films, vulcanized fiber, woven and nonwoven webs, fabrics (e.g., knitted fabrics), cloths, scrims, meshes, foams, foils, treated versions thereof, and combinations thereof. Exemplary polymeric films include extruded, blown, or cast films of polyamide, polyester, or polyolefin. Exemplary woven fabrics include plain or twill weaves of polyamide, polyester, rayon, or cotton yarns. Exemplary nonwoven fabrics include air laid, calendared, carded, or melt-blown fabrics of natural or synthetic fibers. Nonwoven fabrics may be crosslapped.
In some embodiments, is the substrate may comprise paper, including, e.g., treated, primed, or otherwise modified papers. Any of a variety of papers customarily employed as coated abrasive backings may be employed to provide the paper sheet. In some embodiments, the paper sheet is a cylinder paper. In some embodiments, the paper has a basis weight in the range of about 100 to 400 grams per square meter (gsm). In some embodiments, the paper has tensile strength at break of at least about 40 kilograms per 25 millimeters (kg/25 mm) in the machine direction, and at least about 16 kg/25 mm in the cross machine direction. An exemplary cylinder paper having a basis weight of 220 gsm is commercially available from FiberMark located in Battleboro, Vt.
In some embodiments, the substrate is foraminous, including, e.g., scrims, screens, or meshes, including treated or modified versions thereof. The foraminous substrate may be made of natural or synthetic fibers. Such substrates may be knitted or woven in a network having intermittent openings spaced along the surface of the substrate. The substrate need not be woven in a uniform pattern but may also include a nonwoven random pattern. Thus, the openings may either be in a pattern or randomly spaced. The foraminous substrate openings may be of any desired shape including, e.g., polygonal shaped (e.g. rectangular, diamond, triangular, or octagonal shaped) or a combination of such shapes.
In some embodiments, the foraminous substrate, e.g., a scrim, comprises a first set of rows of separated fibers deployed in a first direction and a second set of fibers deployed in a second direction to provide a grid including multiple adjacent openings. The substrate may also comprise an open mesh including, e.g., those selected from the group consisting of woven or knitted fiber mesh, synthetic fiber mesh, natural fiber mesh, metal fiber mesh, molded thermoplastic polymer mesh, molded thermoset polymer mesh, perforated sheet materials, slit and optionally stretched sheet materials and combinations thereof.
In some embodiments, the substrate may comprise multiple layers of the same or different materials. In some embodiments, the substrate comprises two or more polymeric films. In some embodiments, one layer (e.g., a paper, fabric, cloth, scrim or high melting point polymeric film (e.g., polyester)) may be selected to provide, e.g., the desired mechanical properties of the fixed abrasive article. In some embodiments, one layer (e.g., a low melting point polymeric film (e.g., polyethylene or polypropylene)) may be selected to provide, e.g., a surface suitable for attachment to the engaging elements. In some embodiments, at least one layer comprises a foam (e.g., an open cell foam or a closed-cell foam).
Referring to FIG. 1, abrasive layer 25 is attached to abrasive surface 21. In some embodiments, abrasive layer 25 is directly attached to abrasive surface 21. In some embodiments, one or more layers (e.g., primer layers, tie layers, adhesive layers) may be interposed between abrasive layer 25 and abrasive surface 21. In some embodiments, the abrasive layer is integral with the abrasive surface of the substrate
Generally, any known abrasive layer may used. In some embodiments, the abrasive layer comprises a plurality of abrasive particles at least partially embedded in a make coat. In some embodiments, a size coat is provided over the abrasive particles. In some embodiments, the abrasive layer comprises a primer and abrasive particles attached to the primer.
In some embodiments, the abrasive layer comprises shaped abrasive structures. In some embodiments, the shaped abrasive structures comprise a cured resin binder and abrasive particles. In some embodiments, the shaped abrasive structures are porous, e.g., in some embodiments, the shaped abrasive structures comprise interconnected pores. In some embodiments, the cured resin binder is formed by curing a particulate, room temperature solid, softenable, curable binder material. In some embodiments, the particulate curable binder material comprises organic curable polymer particles. The particulate curable polymers are capable of softening on heating to provide a curable liquid capable of flowing sufficiently so as to be able to wet either an abrasive particle surface or the surface of an adjacent curable binder particle.
In some embodiments, the abrasive layer may comprise a plurality of abrasive particles dispersed in an organic or inorganic binder. Organic and inorganic binders suitable for producing abrasive layers are known in the art.
In some embodiments, the outer surface of the abrasive layer is substantially parallel to the abrasive surface of the substrate. In some embodiments, the abrasive layer is textured, e.g., the abrasive layer may be embossed to provide an ordered and/or random pattern of raised and lowered regions. Methods of providing a textured surface are known and described in, e.g., U.S. Pat. No. 5,152,917 (Pieper et al.).
In some embodiments, an abrasive article of this invention contains an abrasive coating with at least one abrasive composite layer that includes a plurality of shaped, preferably precisely shaped, abrasive composite structures. The term “shaped” in combination with the term “abrasive composite structure” refers to both precisely shaped and irregularly shaped abrasive composite structures. An abrasive article of this invention may contain a plurality of such shaped abrasive composite structures in a predetermined array on a backing. Alternatively, the shaped abrasive composites may be in a random shape or an irregular placement on the backings.
Any known abrasive particles may be used. The average particle size of the abrasive particles can range from about 1 to 1800 micrometers (39 to 71,000 microinches), typically between 2 and 750 micrometers (79 to 30,000 microinches), and most generally between 5 and 550 micrometers (200 to 22,000 microinches). The size of the abrasive particle is typically specified to be the longest dimension of the abrasive particle. In most cases there will be a range distribution of particle sizes. In some instances, the particle size distribution is tightly controlled such that the resulting abrasive article provides a consistent surface finish on the workpiece being abraded.
Exemplary abrasive particles include fused aluminum oxide, ceramic aluminum oxide, sol gel alumina-based ceramics, silicon carbide, glass, ceria, glass ceramics, fused alumina-zirconia, natural crushed aluminum oxide, heat treated aluminum oxide, zirconia, garnet, emery, cubic boron nitride, diamond, particulate polymeric materials, metals and combinations and agglomerates thereof.
Examples of conventional hard abrasive particles include fused aluminum oxide, heat treated aluminum oxide, white fused aluminum oxide, black silicon carbide, green silicon carbide, titanium diboride, boron carbide, tungsten carbide, titanium carbide, diamond (both natural and synthetic), silica, iron oxide, chromia, ceria, zirconia, titania, silicates, tin oxide, cubic boron nitride, garnet, fused alumina zirconia, sol gel abrasive particles and the like. Examples of sol gel abrasive particles can be found in U.S. Pat. No. 4,314,827 (Leitheiser et al.); U.S. Pat. No. 4,623,364 (Cottringer et al); U.S. Pat. No. 4,744,802 (Schwabel); U.S. Pat. No. 4,770,671 (Monroe et al.) and U.S. Pat. No. 4,881,951 (Wood et al.).
The term abrasive particle, as used herein, also encompasses abrasive agglomerates, e.g., single abrasive particles bonded together with a polymer or ceramic to form an abrasive agglomerate. Abrasive agglomerates are further described in U.S. Pat. No. 4,311,489 (Kressner); U.S. Pat. No. 4,652,275 (Bloecher et al.); U.S. Pat. No. 4,799,939 (Bloecher et al.), and U.S. Pat. No. 5,500,273 (Holmes et al.). Alternatively, the abrasive particles may be bonded together by inter-particle attractive forces.
The abrasive particle may also have a shape associated with it. Examples of such shapes include rods, triangles, pyramids, cones, solid spheres, hollow spheres and the like. Alternatively, the abrasive particle may be randomly shaped.
Abrasive particles can be coated with materials to provide the particles with desired characteristics. For example, materials applied to the surface of an abrasive particle have been shown to improve the adhesion between the abrasive particle and the polymer. Additionally, a material applied to the surface of an abrasive particle may improve the adhesion of the abrasive particles in the softened particulate curable binder material. Alternatively, surface coatings can alter and improve the cutting characteristics of the resulting abrasive particle. Such surface coatings are described, for example, in U.S. Pat. No. 5,011,508 (Wald et al.); U.S. Pat. No. 3,041,156 (Rowse et al.); U.S. Pat. No. 5,009,675 (Kunz et al.); U.S. Pat. No. 4,997,461 (Markhoff-Matheny et al.); U.S. Pat. No. 5,213,591 (Celikkaya et al.); U.S. Pat. No. 5,085,671 (Martin et al.) and U.S. Pat. No. 5,042,991 (Kunz et al.).
Referring to FIGS. 2 and 3, engaging projection 30 comprises attachment end 33 attached to attachment surface 22. In some embodiments, attachment end 33 is directly attached to attachment surface 22. In some embodiments, the attachment end of a projection may be indirectly attached to the attachment surface (i.e., one or more intervening layers (e.g., primer layers, tie layers, adhesive layers, polymeric films)) may be interposed between the attachment end of a projection and the attachment surface of the substrate. Exemplary polymeric films include, e.g., low melting point polymeric films including, e.g., polyethylene and polypropylene.
Attachment perimeter 35 indicates the location where engaging projection 30 first contacts attachment surface 22, wherein the area of attachment between the engaging projection and the attachment surface of the substrate is bounded by this attachment perimeter. Edge 32 indicates the perimeter of top surface 31 of engaging projection 30. Mantle surface 34 is the surface of engaging projection 30 extending from edge 32 to attachment perimeter 35.
Referring to FIG. 3, a cross-section of engaging projection 30 taken along line 3-3 of FIG. 2 is shown. Mantle profile 44 intersects top surface 31 at intersection point 42. Edge angle 46 is defined by the interior angle between line 45, which is tangent to mantle profile 44, and line 47, which is parallel to top surface 31. In some embodiments, the edge angle is substantially constant. In some embodiments, the edge angle varies around the perimeter of the top surface of the engaging projection. In some embodiments, the edge angle is at least about 15 degrees (15°). In some embodiments, the edge angle is at least about 20°, at least about 30°, or even at least about 40°. In some embodiments, the edge angle is no greater than about 85°. In some embodiments, the edge angle is no greater than about 80°, or even no greater than about 70°.
Engaging projection 30 is a substantially convex engaging projection. As used herein, an engaging projection is “substantially convex” if its mantle profile is substantially convex. As used herein, a mantle profile is “substantially convex” if at least about 75% of the portion of the mantle profile extending from the point of maximum width 43 to attachment perimeter 35 is convex relative to reference line 40. Reference line 40 is perpendicular to attachment surface 22 and passes through center point 41 of the region of contact between engaging projection 30 and attachment surface 22. The point of maximum width is the location on the mantle profile that is furthest from reference line 40. In some embodiments, the point of maximum width corresponds to the location of the edge, i.e., the intersection between the top surface and the mantle surface of the engaging projection.
In some embodiments, at least about 80%, in some embodiments, at least about 85%, in some embodiments, at least about 90%, 95%, or even substantially 100% of the mantle profile extending from the point of maximum width to the attachment perimeter is convex relative to the reference line.
Cross sections of exemplary, substantially concave engaging projections of the prior art are shown in FIGS. 4a-4c. In each case, the portion of mantle profiles 44a, 44b, and 44c extending from point of maximum width 43a, 43b, and 43c to attachment perimeters 35a, 35b, and 35c are concave relative to reference lines 40a, 40b, and 40c, respectively.
The edge angle between the top of the deformed projection and the mantle surface may vary over a broad range. In some embodiments, an edge angle that is too small may weaken the fastener, e.g., by weakening the overhanging rim by making it too thin, subject to bending or breaking. Therefore, in some embodiments the contact angles are between, 20 degrees (20°) and 85° and, in some embodiments, between 30° and 80°. A skilled person can achieve this by suitably selecting the conditions in the method, such as the materials of the particles and the contact surface, the contact period time and other details of the contact deformation step.
In some embodiments, at least some engaging projections are provided with a mantle profile that strictly tapers from the top surface edge to the attachment perimeter. Strictly tapering means that the nearer the engaging projection gets to the substrate, the narrower the projection becomes. For example, engaging projection 30 of FIGS. 2 and 3 is strictly tapering.
Generally, in some embodiments, an engaging projection that is strictly tapering will pull engaged fibers down to the attachment surface of the substrate when a shear load is applied to the fastener without the fibers being caught at a non-tapered portion displaced from the attachment surface of the base. In some embodiments, the torque on the engaging projection is minimized so the substrate can be weaker, and, in some embodiments, can be cheaper, more flexible, and/or thinner. Furthermore, the attachment side of the fixed abrasive article may have a relatively large surface area formed by the plurality of engaging projection top surfaces, making this surface smooth to the touch, while also having a relatively low total surface area of the projection attached ends connected to the substrate, thereby increasing the flexibility of the abrasive article.
In addition to the edge angle, engaging projection 30 may be characterized by the ratio of the perimeter of top surface 31 to the height. In some embodiments the ratio of top surface perimeter to height is about 1.1 to about 50. In some embodiments, this ratio is at least about 1.2, about 1.5, or even at least about 2. In some embodiments, this ratio is no greater than about 40, no greater than about 30, or even no greater than about 25. Engaging projection 30 may also be characterized by the ratio between the perimeter of top surface 31 to attachment perimeter 35.
A variety of methods may be used to form a fixed abrasive article having one or more substantially convex engaging elements attached to its attachment surface. In some embodiments, the substantially convex engaging elements may be formed directly on the attachment surface of the substrate of the fixed abrasive article.
For example, in some embodiments, the substantially convex engaging elements may be formed from particles of a material, e.g., a thermoplastic material may be affixed to the attachment surface of the substrate, forming a multiplicity of thermoplastic projections extending from the attachment surface to corresponding terminal ends. The word “particle”, as used herein, refers to a solid, liquid or semi-liquid particle, including, for example, granules, pellets, powders and droplets. In some embodiments, the particles may be uniformly affixed to the substrate. In some embodiments, the particles may be randomly affixed to the substrate. In some embodiments, at least the terminal ends of the formed projections are constituted by the particles that were affixed to the attachment surface.
In a subsequent step, the terminal ends of the projections are contacted with the contact deformation surface of a deforming means under conditions (e.g., temperature, pressure and time) sufficient to achieve the desired deformation and, thus, the desired engaging projections. During the contact, the terminal ends of the projections are heated above a softening temperature while the attachment surface is generally kept cold enough to provide for suitable stability of both the substrate attachment surface and the portions of the engaging projections adjacent to the substrate attachment surface. The contacted surface is then cooled forming the top surface of the engaging projection.
Generally, deforming means are well known and include, but are not restricted to, hot rolls, plates, and elongated nips (e.g., variable nips). The heating of the terminal ends of the particles can be provided by, e.g., a pre-heater or the contact surface of the deforming means, or both. Exemplary preheating means include heated platens, radiant heat sources, and hot fluids (e.g., hot gases).
The skilled person will be able to select a way of keeping the base and, also, the attached ends of the projections cold enough, thereby solid enough, to prevent undesired deformation thereof. One exemplary way to achieve this includes keeping the back of the base in contact with a cooled surface.
In some embodiments, the top surface of the deformed particles, i.e. the projections, can be formed by a contact deformation surface that can be smooth. In some embodiments, the contact surface may be textured or roughened, e.g., sandpaper-like or grooved. However, in some embodiments, the contact deformation surface will be essentially flat, even if it is not planar in the true geometrical sense. In some embodiments, post treatments of the projections could be used to make the top surface not essentially flat, such as using non-contact heat treatment.
During the contacting of the heated terminal end with the contact deformation surface, a contact area is created bordered by a contact line. Along at least a part of the contact line the heated terminal end is provided with an acute contact angle.
The contact angle is influenced by the surface energies (i.e. surface tension) of the contact surface and of the heated terminal end of the material, as well as the temperature and time of contact. The formed top surface is thus bordered, at least partly, by an edge having an angle influenced by the acute contact angle. The contact angle will be affected by the surface energy of the particles, the surface energy of the contact surface, and their relative interfacial energy.
If there is essentially no molecular orientation of the particles or formed projections, the contact angle is mainly determined by the surface energies of the particle polymers and the contacting surface. The contact angle is furthermore influenced by the contact time, which should be selected appropriately. Subsequent cooling of the projections preserves the edge angles of the projections and can be selected, for example, from ambient cooling, contact cooling, cooling with fluids (e.g., gases such as air).
The substrate can be any suitable continuous or discontinuous base web such as a porous or nonporous polymer film, a laminate film, a nonwoven web, a paper web, metal films, foils or the like. The substrate could be modified by any known method such as by being printed, embossed, flame treated, laminated, particle coated, colored, or the like.
A polymer film used as a substrate can be oriented or unoriented. In some embodiments, essentially unoriented films may be desirable. The attachment surface of the substrate can be smooth or rough. For example, in some embodiments, the attachment surface can be roughened with particles previously scattered and affixed thereon.
The particles should be brought and fixed on the substrate in a way that at least the terminal ends of the projections can be formed from the particles. Projections can consist completely of the particles without any further modification of said particles. For bringing and affixing the particles to the (smooth or roughened) attachment surface, several methods are taught, e.g., random scattering and adhering, for example, in PCT publication WO 01133989, the entire disclosure of which is hereby incorporated by reference.
The material forming the substrate can be independently selected from the material forming the particles. In some embodiments, different particles of different materials, shapes and/or sizes, may be used. Also, mixtures of particles of different properties could be used. The density of the projections can be varied during the process. Also, by choosing a thin substrate, e.g. a suitable film, a thin fastener can readily be made, the thickness can be further decreased by using small particles resulting in small projections which, in some embodiments, may also function especially well with thin loop fabrics. The symmetry of the method and the deformed projections also can provide an isotropic fastener.
In some embodiments, it may be desirable to extend the contact time between the deforming surface and the particles, e.g., so that there is more time for the surface tension effects to create acute contact angles so that the engaging projections have more acute edge angles. In some embodiments, the process can be run at a lower speed. In some embodiments, an elongated variable nip that gradually compressively deforms the terminal ends of the particles or projections can be used.
The deformed projections can be solidified, e.g., by cooling, in their most compressed state. It is also possible that after the deformed projections are in their most compressed state and before the deformed projections are in their final solidified state, the deformed projections are somewhat lengthened by stretching them as they are removed from the deforming surface. For example, in some embodiments, the terminal ends of the deformed projections can be stretched from the substrate by opening a nip while they are still attached to the deforming surface, thereby causing the projections to get slimmer in their middle section.
In some embodiments, e.g., when many small projections are desired, it may be useful to form at least some deformed projections comprising one particle per deformed projection. This may make the process less expensive than forming the projections from multiple small particles, as less expensive larger particles can be used to form the projections. In some embodiments, this can be inexpensively achieved by uniformly scattering suitable polymer powder particles over a moving substrate at a suitable distance to provide the projections or particles.
In some embodiments, molecularly unoriented thermoplastic polymers are preferred for attaching the particle to the substrate in the first method. Therefore, in some embodiments of the first method, the provided thermoplastic particles are unoriented particles, which can be one or more types of particles selected from a group including: (a) granules of a powder made with size reduction from pellets; (b) granules from a reactor powder; (c) granules from a precipitated powder; and (d) droplets.
Reactor powder means polymer powder taken from a polymer manufacturing reactor, before palletizing. Granules from a reactor or precipitated powder, as used herein, also include granules, of such powder, further size-reduced. Droplets may be solid or not, when provided, brought and affixed to the front surface. Softening of the particle as they are attached to the substrate can further decrease any residual orientation in the particles.
In the first method, the affixing of the particles to the front surface of the substrate includes keeping the particles, brought to the front surface, at least partly, at a temperature above their softening temperature.
In some embodiments, the engaging projections may be formed on a carrier and subsequently transferred to the attachment surface of the fixed abrasive article. For example, in some embodiments, particles (e.g., polymer particles) may be dispersed on the surface of the carrier. Generally, the surface may be pretreated to provide a suitable surface energy and desirable release characteristics relative to the particles. In some embodiments, particles may be provided in at least a semi-liquid state or softened state of suitable viscosity. In some embodiments, the particles can be brought into this state after their deposition on the surface of the carrier by, e.g., heating. The resulting softened or semi-liquid particles are referred to as preform projections, where a “preform projection” is defined as a projection that, to at least some extent, has been preformed into the shape of the final engaging projection at the ultimate top surface end, which is in contact with the surface of the carrier, and extending to the terminal ends of the preform projection, which will ultimately provide the attachment end.
The preform projections along their edges contacting the carrier will form contact angles, which will be influenced by the surface energies of the polymer particles and the carrier surface. The polymer particles are maintained in a softened or semi-liquid state for a suitable period of time so that they may form an acute contact angle at least along a portion of their edges contacting the carrier.
The preform projections can then be at least partially solidified and brought into contact with the attachment surface of the fixed abrasive article, thereby affixing the terminal ends of the preform projections to the attachment surface, while essentially maintaining the shape of the edge formed by contact with the carrier. The preform projections can then be further solidified to a sufficient degree so that the preform projections can be released from the carrier and transferred to the attachment surface, thereby forming engaging projections attached to the fixed abrasive article. These formed engaging projections project from attachment end (now attached to the attachment surface of the substrate), to the top surface, which was formed on the carrier. The flattened tops at least partially overhang the substrate forming a rim, and are bordered, at least partly, by an edge having an angle which is influenced by the acute contact angle, as described above.
Suitable particles capable of being in a liquid or semiliquid (i.e., softened or suitably pliable) state; and capable of becoming solid are known. The particles can be, for example, droplets of liquid suspensions etc., solidifiable by irradiation, or they can be thermoplastic particles, as described above. The carrier can be any suitable carrier, e.g., a sheet-form substrate, e.g., a film, as described above.
The skilled person, familiar with the field of surface energy, surface tension and wetting, can select a combination of a suitable polymer for the particles and a carrier or the appropriate surface treatment for the carrier. The skilled person can also select particles having a suitable viscosity at the temperature of the carrier such that the particles will wet the carrier within a suitable time. The surface energy of the carrier may be formed by known materials and methods, such as siliconized surfaces, fluorochemicals, corona discharge, flame or the like.
Generally, the carrier surface should be able to release the particular polymer particles used, whether semi-liquefied or solidified. It is known that certain release surfaces can release certain polymers but are unable to release other polymers. For example, a polyethylene release surface can release suitable polypropylene particles but may not release certain polyethylene particles as they tend to weld or fuse to each other. The word “release” as used herein refers to the phenomenon where the particles are detached from the contact release surface without unacceptable damage or loss of material of the particles or preform projections.
The carrier surface can be smooth or suitably structured or roughened, e.g., grooved, as known from the art. Dispersing of the particles onto the release surface can be performed in any suitable way, for example, by scattering the particles with a scatter unit. In some embodiments, the particles are dispersed at a rate per unit surface area so that they form preform projections where one particle can form one preform projection. The particles may be distributed uniformly or randomly. The particles may also be dispersed according to a predefined pattern.
The particles can be brought into the at least semi-liquid state before, during and/or after dispersing of the particles onto the contact release surface. “At least semi-liquid” means liquid or semi-liquid. A suitable way of liquefying will depend on the properties of the selected polymer, and can include, for example, heating, thinning, solving, emulsifying, dispersing, etc.
A solidity (degree or extent of solidification) suitable for contacting and affixing the preform projections from the carrier to the attachment surface of the fixed abrasive article substrate can be decided by the skilled person, depending on the particular circumstances. It will usually, but not necessarily, require a more solid state than the one in which the preform projections have been formed on the carrier. In some embodiments, the preform projections should be solid enough to keep, at least partly, their shape while being contacted with the attachment surface. In some embodiments, the solidity is selected to maintain at least a minimum free height and also a suitable edge angle of the preform projections. Setting the necessary solidity in the preform projections will be material-dependent, and can include cooling, drying, heating, crosslinking, curing, chemical treatment, etc.
The preform projections of suitable solidity, sitting on the carrier, can be covered by the attachment surface such that the attachment surface contacts and fixes with the preform projection terminal ends. The terminal ends are the ends farthest from the carrier surface. Before contacting with the attachment surface, the preform projections can be provided or supplemented with further added dispersed particles or the like, which will attach to the preform projections. It is possible that the attachment surface is contacted with the preform projections when the preform projections are in a semiliquid state. In this case it is possible that, after the contacting and before a final solidification, the preform projections are somewhat lengthened by stretching while the preform projections are removed from the carrier thereby causing the preform projections to get slimmer in their middles.
The affixing of the attachment ends of the preform projections to the attachment surface can be obtained by, e.g., adhering with an added adhesive, resin, binder, solution, etc., and/or by crosslinking with ultraviolet irradiation. In some embodiments, affixing can be accomplished using the inherent adhesion of the contacted materials (i.e., attachment surface and/or the preform projections) or fusing. While affixing, care should be taken in order that the free overhangs or rims, and the actual heights of the preform projections are sufficiently preserved. For example, in some embodiments, an exaggerated sinking or compression of the projections into the attachment surface should be avoided. The proper solidity of the preform projections and the substrate, suitable for separating and removing both from the carrier can be decided by the skilled person, depending on the particular circumstances.
In some embodiments, the solidity of the preform projections when they are removed from the carrier will usually, but not necessarily, be a more solid state than when they are initially contacted with the attachment of the substrate. In some embodiments, the preform projections should be solid enough to keep, at least partly, their shape during the separation from the carrier. It usually primarily means keeping a suitable overall shape, with particular respect to the edge angle formed, but preserving a suitably strong bond with the attachment surface is also an important factor. The substrate itself should generally be solid enough to keep its form and allow the separation of the preform projections from the release surface. The flattened top surface of a projection as formed can be smooth but can also be somewhat roughened, e.g., sandpaper-like or grooved, as known from the art. The top surface structure will be determined by the contact release surface, which generally will be essentially flat, even if naturally not planar in the true geometrical sense. In some embodiments, post treatments could be used that would make the top surface not essentially flat, such as a noncontact heat treatment. Also it is possible that the carrier is not flat so that it can form projection top surfaces that correspond to the carrier on which they were formed.
In some embodiments of transfer methods, the attachment end of the preform projections is less likely to be affected by long contact times with the carrier as there is no pressure on the attached end. That opens a possibility of letting the surface energies work for a longer time, e.g., with a lengthened carrier in a production line. In other words, the beneficial mechanical effects of the surface tensions forming the flattened ends do not have to interfere, or “compete”, with mechanical effects originating from an already attached end. A further advantage is that, independently of the sizes of the particles or preform projections, similar contact angles can be obtained for all projections. In other words the projections all are in contact with the release surface for the same time period and under the same conditions, which is not the case if they were already attached to a substrate and at different heights, depending on the particle size, when contacting a deforming release surface as occurs in direct forming methods. In some embodiments, this gives transfer methods a high tolerance to particles of varied sizes. Further significant cost savings, and simplification, may be achieved by making the deformation apparatus unnecessary. Line speed and running width of the manufacturing line can probably be greater than ever before, with lower costs. A further advantage is that non-thermoplastic polymers, potentially having, e.g., better mechanical features, could be used.
If small numerous projections are advantageous, it may be desirable if at least some of the separate preform projections comprise exactly one polymer particle per preform projection. In some embodiments, at least some of the preform projections are provided with contact angles of between 10° and 85°, preferably 30° and 80°. In some embodiments, this would be the range of contact angles for most of the individual preform projections. In some embodiments, this range would be the mean contact angle for the preform projections.
In some embodiments, at least some engaging projections are provided with a shape in which, in each side view thereof, the engaging projection strictly tapers (preferably is strictly convex) from the flattened top or top edge to the attachment perimeter. In some embodiments, transfer methods create semi-lenticular preform projections, like water drops sitting on a suitable surface.
In transfer methods, non-thermoplastic and thermoplastic polymer particles can be used, with the selection being based on, e.g., necessary strength, required surface energy, cost, etc. In some embodiments, thermoplastics may have some advantages specific to transfer methods, which may not be obvious. First, using thermoplastic particles and softening them after their delivery will generally ensure that any residual molecular orientation will generally be released from the preform projections, at least where in contact with the carrier. Second, if the particles are thermoplastic, the viscosity of the liquefied or at least semi-liquefied material forming the preform projections can be controlled, e.g., fine-tuned (e.g. adjusted and/or optimized) on-line by controlling the material temperature. In some embodiments, such control may be precise, easy, cheap, and reversible. The viscosity has a direct influence on the extent to which the surface energies of and between the preform projections and the contact release surface affect the formed contact angles. By adjusting the viscosity using appropriately selected temperatures and heating times, the edge angle of the final engaging projections can be fine-tuned on-line. In some embodiments, transfer methods using thermoplastic particles can result in inexpensive, formed fasteners with the flexibility of adjusting the form of the fastener on-line.
If drops of liquids are deposited onto a solid carrier and if the surface energy of the carrier is somewhat higher than the surface energy (or surface tension) of the liquid, the liquid will typically perfectly wet the solid, with a contact angle of zero. With liquids, each “solid-liquid” pair has a contact angle, between zero and 180°, with which the liquid drop will, approximately, wet the solid. With semi-liquid (e.g., softened thermoplastic) particles, the process of forming a contact angle is a time-temperature phenomenon. With solid release surfaces of high surface energy, a liquid polymer will wet perfectly if given enough time. If this high surface energy release solid surface is kept hot, and a cold solid particle is placed thereon, a process is started in which the contact angle transforms over time from an initial obtuse angle towards the final zero contact angle. By interrupting this transformation process, e.g., by a suitable cooling, one can achieve any desired contact angle. Therefore high surface energy solid carriers are useful in some embodiments of the processes of the present disclosure. However, the higher the carrier's surface energy, the more difficult it may be to finally separate the carrier from the preform projections. Also if the surface energy of the carrier is too high in relation to that of the polymer particles, there is greater opportunity for forming a preform projection that is excessively wet to the carrier. The risk of over-wetting the carrier is reduced if the surface energy of the carrier is no greater than 60 mJ/m2 higher than the surface energy of the particles.
High surface energy carriers may also cause the engaging projection's edge angles to be too sharp, creating rims that are too thin and which might possibly break off during later use, creating undesired contamination. In some embodiments, it may be better to accept larger contact or edge angles to provide enhanced security against engaging projections forming with thin weak edges and rims. Therefore, in some embodiments, it may be useful to provide a carrier whose surface energy is lower than the surface energy of the particles. In this case, the edge angle in the product can be determined by material selection rather than by on-line operating parameters. Also, generally, the lower the surface energy of the carrier, the easier it is to finally detach the preform projections therefrom. However a certain degree of force needed for detaching preform projections from the contact release surface can be beneficial. Some preform projections can be weakly affixed to the attachment surface of the fixed abrasive article substrate. Namely the affixing strength is lower than desired for its intended end use resulting in some engaging projections possibly breaking loose during use. This may be a difficult defect to detect. Therefore, in some embodiments, it may be desirable if the carrier's surface energy is no less than 23 mJ/m2 lower than the surface energy of the particles. With a carrier surface energy of this level, the separation force for detaching preform projections from the contact release surface may be high enough to remove projections weakly affixed to the attachment surface thereby providing an on-line fault-detection and correction mechanism.
In some embodiments of the methods described hereinabove for thermoplastic preform projections, the affixing of the attachment surface with the terminal ends of at least some of the preform projections comprises affixing by heat or fusing. Affixing by heat can include melting one or the other of the preform projections or the attachment surface, depending on the materials and pressure etc. In some embodiments, both the preform projections and the attachment surface are allowed to potentially melt, and are thereby fused. Fusing is affixing of the preform projections to the attachment surface by heat. In this case, the preform projections are made up of particles well suited for both being shaped by the carrier surface and being affixed to the attachment surface by fusing. The particles must be liquefied enough to suitably form the desired contact angle, but must remain solid enough, to permit keeping their edge angles during the fusing. In some embodiments, it is preferred that the thermoplastic polymer particles have a melt flow rate (ASTM 1238) of between 1 and 90 grams per 10 minutes at the conditions appropriate for the selected polymer. In some embodiments, the melt flow rate at least 5, at least 10, or even at least 15 grams per 10 minutes.
In the subsequent step of some transfer methods, the affixing by heat comprises maintaining the carrier at a temperature lower than the softening temperature of the polymer particles or preform projections while contacting the attachment surface with the attachment ends of at least some of the preform projections. In some embodiments, the back surface the substrate (i.e., the abrasive surface) is heated by subjecting it to a heated gas. Furthermore, the gas pressure at the abrasive surface of the heated substrate is higher than the pressure (e.g., a gas pressure) at the attachment surface of the heated substrate, thereby pressing the heated substrate against the terminal ends of at least some of the preform projections to enhance the affixing thereof to the attachment surface. The pressure difference may be enhanced, for example, by applying vacuum from beneath the carrier or the attachment surface of the substrate.
Generally, in transfer methods it is not a great problem if the preform projections are of different heights, as long as a sufficiently pliable substrate, capable of bending down to reach the lower preform projections, is provided. In some embodiments, it is especially advantageous if the whole substrate is thermoplastic and is actually softened, thereby made soft and flexible, easily bending or even stretching when hot. If desired, the substrate can be fully softened, where fully softening means softening of all components and/or layers thereof, e.g. in case of a composite substrate, above a softening temperature.
After the separation of the substrate from the carrier, some preform projections may remain on the carrier. These are usually very tiny residual polymer particles which may melt into, and go away with, particles dispersed later. Still by regularly providing for their removal from the carrier, the process can be made more uniform and secure. Therefore, in some embodiments, the transfer method may further comprise cleaning the carrier before the dispersing of the multiplicity of polymer particles on to its surface. This may involve: (1) heating the carrier to a temperature higher than the softening temperature of both the polymer particles and the front surface of a cleaning web; (2) contacting the cleaning web with the heated carrier surface thereby softening the front surface; (3) suitably pressing the softened front surface against the heated carrier surface thereby fusing the polymer particle contamination residue into the front surface of the cleaning web; (4) providing for the carrier and cleaning web, temperatures suitable for separating the cleaning web from the carrier; and (5) separating the cleaning web from the carrier, thereby cleaning the carrier.
This cleaning method uses the thermoplastic character of both the particles and the cleaning web for cleaning the carrier. During the steps above, the small amount of residual polymer contamination goes away with, and usually disappears in the front surface of the cleaning web and the cleaning web can be reused. In some embodiments, no separate cleaning web may be required, as the substrate used for the abrasive article may be used as the cleaning web. In a continuous operation, e.g. comprising rolls or conveyors, the carrier can be cleaned with every revolution before each dispersing of particles, thus always keeping the cumulative carrier contamination at low levels.
In some embodiments, while the preform projections are being fused to the attachment surface, the substrate is above the carrier where it is supported by the preform projections and bridges the space between them. If the attachment surface is above its softening temperature, any molecular orientation therein may cause problems by shrinking at least the bridging portions of the substrate. That can be avoided, e.g., by using a composite substrate with a suitable layer resistant to shrinking. For example, a substrate comprising a polyester film or paper backing and a polyethylene layer coated thereon as a front surface can potentially withstand the shrinking that may occur in the substrate. However, if shrinkage is a problem, it is preferable if the substrate is free of molecular orientation when fusing the preform projections or particles. Molecularly oriented films can be pretreated by contacting the attachment surface of the substrate with a heated release surface (which could be the carrier), thereby rendering the attachment surface essentially molecularly un-oriented. The tight pressing of the carrier to the softened attachment surface during the cleaning step also can preform this pretreating step as long as the molecular orientation is suitably released.
In some embodiments, heated gas (preferably air) at an elevated pressure can best be provided with gas nozzles ejecting heated gas. The nozzles preferably use electric heating for heating the gas, but the heat source can be any suitable alternative heat source such as gas burners etc. In some embodiments, if the substrate is moved in front of the output orifice of the nozzles so that its attachment surface is contacted with the ejected hot gas, then the substrate softens. At the same time, the hot gas ejected from the nozzles creates and maintains a gas flow along the abrasive surface of the substrate, typically parallel to the traveling direction of the substrate. If the nozzles are fixed and the substrate is moving in a machine direction, the hot gas flow will have a direction essentially both parallel and opposite to the machine direction. The hot gas flow, e.g. hot air flow, will exert a pulling force on the softened substrate, dragging the attachment surface of the substrate that will tend to stretch the softened substrate. The faster the gas flows, the stronger this stretching effect will be. With a low throughput arrangement, i.e., with low hot gas velocities, and especially with a thick substrate, a substrate which is essentially free of molecular orientation can be used. In case of higher throughputs and higher gas flow rates, and especially with a thinner substrate, this machine direction stretching of the substrate can be very significant, which can be undesirable. For example, stretching of the substrate in a lengthwise, machine direction can make it difficult to control the thickness of the fastener or can result in rolls of unspecified length. Stretching can also lead to accidental breaking by thinning and tearing apart the substrate.
The effects of stretching can be counterbalanced by providing a suitable molecular orientation in the substrate. The problem of stretching can be solved if the substrate is provided with a heat-shrink potential in the machine direction. The heat of the gas will relax the orientation in the substrate, i.e., will tend to shrink the substrate, which will counteract stretching by the heated gas flow. Therefore, in a variation of the transfer methods, one or more gas nozzles adapted for ejecting heated gas are provided. The abrasive surface of the substrate is contacted with the heated gas ejected by the one or more gas nozzles while the substrate moves relative to the one or more gas nozzles. The direction in which the substrate is moving is the machine direction and is essentially within the plane of the substrate. The substrate preferably has a heat-shrinkability in the machine direction (the lengthwise heat shrinkability) of at least 1 percent. The affixing by heat includes heating the substrate above a heat shrink temperature thereof.
As used herein, “heat-shrinkability” in a direction shall mean, in the context of a material such as the substrate material, that the material is capable of being decreased in its length in the given direction, or dimension, in response to the transmission of thermal energy into the material. The “heat shrinkability” of the material is a percent value and equals 100 percent times the difference between its pre-shrink length and post-shrink length, divided by its preshrink length, in the given direction. The post-shrink length in a given direction of the material means the length of the material in the given direction after shrinking the material, such as at a temperature of 170° C. for 45 seconds. Shrinking can be determined, for example, by immersing the material into hot silicon oil and letting it freely shrink. It was found that using temperature of 140° C. for 14 seconds relaxes essentially all the shrink in usual polymer materials. As used herein, the “shrinking temperature” of a material refers to the temperature at which the material, exposed to an increasing temperature, starts to heat-shrink.
The advantage of this variation of the transfer methods of the disclosure is that it helps counteract stretching effects exerted on a softened substrate by ejected hot gas flow. With high production rates, lengthwise heat-shrinkability higher than 1 percent can provide improved results. Therefore, in some embodiments, it is preferable if, in this variation of the transfer methods, a substrate having a lengthwise heat-shrinkability of at least 10 percent, in some embodiments, at least 20 percent, at least 30 percent, at least 40 percent, or even at least 50 percent is provided for the contacting and the affixing depending on the forces created by the hot gas flow and the production rate.
The stretching effect exerted on the substrate by a lateral hot gas flow is less significant, or even close to zero (depending on the details of the nozzle arrangement) in the crosswise direction, i.e., in the direction perpendicular to the direction of the traveling path of the substrate (in a machine it is called the cross machine direction). Therefore, if a substrate has a high heat-shrink potential, or high heat-shrinkability in the crosswise direction, the edges of the substrate can shrink or neck in, which results in folding or wrinkling when contacted with the hot gas. Generally, this is undesirable. Therefore, in some embodiments, it is preferable if the heat-shrinkability of the substrate in its in-plane direction perpendicular to the main or machine direction is either zero, or lower than the lengthwise heat-shrinkability. “Zero crosswise heat-shrinkability”, as used herein, includes the case in which the substrate exhibits an increase in length, or stretch, rather than shrinking, in the crosswise direction when exposed to heat. The advantage of this difference in heat shrinkability is that it provides a differentiated counteraction to the differentiated dragging effects of the hot gas flow on the softened substrate in the two orthogonal dimensions. Generally the heat-shrinkability of the substrate in its in-plane direction perpendicular to the main direction (the crosswise direction) is lower than 50 percent. In some embodiments, the crosswise heat-shrinkability is lower than 40 percent, lower than 30 percent, or even lower than 25 percent, depending on the forces created by the hot gas flow and the production rate. On the other hand, the substrate heated by the hot gas will exhibit a crosswise thermal expansion which may cause wrinkles in the product. That can be counterbalanced with a suitably low, but positive level of heat-shrinkability provided in the substrate in the crosswise direction. Therefore, in some embodiments, it is preferable, if, in the aforementioned situation, the crosswise heat-shrinkability of the substrate is at least 1 percent.
As discussed above, the dragging or stretching effect in the length direction from the gas nozzles is counteracted by a lengthwise heat-shrinking, which together will generally define a final length of the formed fastener product as related to the initial length of the provided substrate. If the lengthwise heat-shrinkability of the substrate is relatively low and the gas nozzles eject a strong hot gas flow, the fastener product will be longer than the initial substrate material from which it was produced. By increasing the heat-shrink potential and perhaps decreasing the gas pressure or gas flow of the nozzles, the trend of elongated fasteners can be reversed, and the formed fastener can be shorter than the substrate from which it was made.
The release surface used for the pre-treating, i.e., the pre-treating release surface can be similar to or different from the carrier surface discussed above. The pre-treating release surface must be able to suitably release the substrate at the right time. The substrate preferably is essentially prevented from any shrinking, e.g. in order to maintain its regular dimensions, but mainly its length. This could be done by keeping the substrate attachment surface in full contact with the pre-treating release surface. For that purpose, the tack between the softened attachment surface of the substrate and the pre-treating release surface (e.g., a polytetrafluoroethylene surface) can be exploited. In order to do this, residual air between the two surfaces should preferably be removed while contacting and pressing the substrate to the pre-treating release surface. The lengthwise heat-shrinkability of the substrate is decreased to a suitable value while the crosswise heat-shrinkability rate may (and preferably will) also be decreased. The longer the contact time and higher the temperature, the more the decrease in the heat-shrinkability will be and vice-versa.
A practicable manufacturing arrangement using a pre-treating step includes using an endless release belt with a release outer belt surface kept in a circulating motion along a belt path. For pre-treating the substrate, a first portion of the outer belt surface, being at a first location of the belt path, is used as the pre-treating release surface. For forming the fastener from the pre-treated substrate, a second portion of the outer belt surface, being at a second location of the belt path suitably displaced from the first location, is used as the carrier. The substrate is provided in the form of a continuous substrate film kept in a motion synchronous with the belt, and is contacted with the outer belt surface at the first and second locations.
This solution is advantageous because a single release belt is used for pre-treating the substrate and further producing the fastener from the pre-treated substrate, which can provide for a zero length-difference between the initial substrate and the final product. This zero length-difference is desired to conveniently use the same belt, running in all of its points with the same speed, for two different purposes, i.e., for pre-treating the substrate on the one hand and for depositing the particles to form preform projections and contacting and affixing the pre-treated substrate therewith on the other hand. The release surface speed at the first location is desirably the same speed as the initial substrate speed and the release surface speed at the second location is desirably the same speed of the final formed fastener product. If the decreased value of lengthwise heat-shrinkability of the substrate provided by the pre-treating deviates from a balance value, this section of the substrate when in free contact with the belt between the first and second belt locations will tend to either get shorter or longer. That can be detected with providing a substrate film buffer with dancing roller(s) and detecting the trend of motion of the dancing roller(s). If the free section of the substrate film between the two belt locations should shorten, then the lengthwise heat-shrinkability of the pre-treated substrate could be decreased and vice versa. The lengthwise heat-shrinkability of the pre-treated substrate can be decreased more by elevating the temperature of the substrate at the first location and/or lengthening the first portion of the outer belt surface along which the belt and the substrate are in contact thereby lengthening the duration of the pre-treating of the substrate, and vice-versa. This solution has an additional advantage that the outer release belt surface is cleaned from any potential polymer particle contamination by contacting the softened thermoplastic front surface of the pre-treated substrate with the release belt with every revolution of the belt.
In both transfer and direct methods, during the forming of the heated ends of the preform projections (the transfer methods) or the deformation of the projections or particles (the direct methods), some preform projections or particles can unify with other, neighboring, preform projections or particles. “Unify” means that two neighboring preform projections or particles fuse or merge into a single preform or engaging projection. It is possible that preform projections or particles portions only fuse near their tops, their attached ends remaining separate. However, it also possible that the attached ends unify with the neighboring partner preform projections or particles. In some embodiments, only a part of the preform projections or particles unify, while the rest remain separate, this provides a variety of engaging capabilities. In some embodiments, a fastener with some unified engaging projections may provide an enhanced shear strength with respect to certain loop fabrics, e.g. low loft loops.
While not intending to be bound by any theory, the cause of this phenomenon appears to be, first, that the elongated (in top view) shape of the new engaging projection formed by the unification may resist a higher torque normal to its elongated dimension. Second, the edge angles of one of the partner merged projections, farthest from the center of the merged engaging projection, has edge angles that appear to be made more acute by the unification. It is speculated that, during the unification, the polymer material of two partner projections moves from the projections remote edges toward their new common centre, due to cohesion, which leaves a so-called receding, decreased, contact angle at the outer edge portions, farthest from the center or the contact line of the two partner projections. This allows one of ordinary skill in the art further ways to modify the engaging performance relative the particular intended engaging loop.
In some embodiments, the unifying of neighboring projections can be easily and inexpensively achieved, and controlled by adjusting some manufacturing operational parameters, e.g., by adjusting the dosing rate of particles, or by using particles of different size and/or melt properties. By increasing the density of the preform projections or particles, a point occurs where the unifying phenomenon increases. This is influenced by the kind, and the shape of the particles. For example, using less spherical, more irregular particles, generally results in an increase in unification of the particles.
In another aspect, the present disclosure provides a new fixed abrasive article, readily achievable through the methods above, having corresponding advantages.
In some embodiments, it may be advantageous if the material of the attachment surface of the substrate differs from the material of at least one engaging projections mantle surface where they are attached. In some embodiments, it may be advantageous if the material of the attachment surface of the substrate is softer than the material of the mantle surface of the at least one engaging projection as determined, for example, by differing Shore hardness values.
In some embodiments, it may be advantageous for some uses if the substrate is elastically extensible within a plane of the substrate, and the material of the mantle surface of the at least one engaging projection is non-elastomeric. The substrate can comprise elastomer materials including elastic laminates or the like. This can make an elastic product.
In some embodiments, the engaging projections may be formed directly on the attachment surface of the substrate of fixed abrasive article. In some embodiments, the engaging projections may be transferred to the attachment surface of the substrate of a fixed abrasive article.
In some embodiments, the fixed abrasive article may comprise a first substrate having an abrasive surface and an attachment surface, and an attachment layer. The attachment layer comprises a second substrate having a first surface and a second surface, wherein the first surface of the second substrate is attached to the attachment surface of the first substrate. The second substrate may be the same as or different from the first substrate. The attachment layer further comprises an engaging projection, as described above. Generally, any method suitable for forming the engaging projections (e.g., the direct and transfer methods discussed herein) may be used to provide engaging elements on the second surface of the second substrate.
In some embodiments, the second substrate may be connected (e.g., adhered, fused, bonded, laminated) to the attachment surface of the substrate. In some embodiments, the first surface of the second substrate is attached to the attachment surface of the first substrate via an adhesive layer, optionally wherein the adhesive layer comprises an adhesive selected from the group consisting of a pressure sensitive adhesive, a heat-activated adhesive.
Abrasive discs were prepared as described below with reference to each of the particular examples. These discs were then tested using the following test procedure, for purposes of comparing the performance of different discs. These examples are provided only for purposes of illustration.
Fastener Sheet Preparation
16±5 grams per square meter (gsm) polypropylene particles (200-500 micrometer diameter, “POLYAXIS PD2000”, A. Schulman, Akron, Ohio, USA) were coated onto a release surface (“CHEMGLAS 100-6”, PTFE-coated glass fiber web, Lörincz kft, Hungary). The coated release surface was passed over a hot plate set at 170±10 degrees C. to melt the polypropylene particles into liquid droplets. The molten droplets were then cooled to cause resolidification. An extruded polypropylene film (0.1 mm (0.004 inch), 91 gsm) backing was then brought into contact with the distal ends of the solidified droplets. Hot air (600±10 degrees C.) was directed onto the back side of the backing to fuse materials at the interface. The backing was then cooled to effect bonding of the solidified droplets to the backing. The solidified droplets bonded to the backing were then separated from the release surface, thereby forming a fastener sheet having engaging projections.
Examples 1 and 2
Abrasive Article Preparation
Strips of the fastener sheet were laminated to two abrasive discs having a PSA-coated backing (12.7 cm (5 inch) diameter, “360L P800, STIKIT” obtained from 3M, St. Paul, Minn.). A rubber roller was used to apply pressure to secure the fastener sheet to the PSA-backed disc. A matching backup pad for the test was prepared by applying standard loop material (100% polyamide Daytona Brush Nylon loop, available from Sitip SpA of CENE (BG), Italy) on the face of a backup pad (Model #05575, 5″ diameter, STIKIT backup pad, available from 3M Co., Maplewood, Minn.) using a transfer adhesive (3M Double Coated Polyester Tape, “442 KW”, available from 3M Co of Maplewood, Minn.).
A 3-mode test was used to evaluate the adhesion of the hook-backed abrasive prototypes to the loop-faced backup pad. The test uses a ranking between 0 and 10 with 5 being ideal, 0 being too low and 10 being too aggressive.
The test consists of 5 evaluations. The first evaluation grades the initial grasp. This is accomplished by placing the abrasive disc on the backup pad and lightly slapping the disc three times. Then, the disc edge is raised to determine the strength of the initial attachment.
The second evaluation (First Mode) is flat sanding for about 20 seconds. The disc is evaluated for any signs of wrinkles or release of grasp of the hook/loop interface on the abrasive disc edges.
The third evaluation (Second Mode) is sanding at about a 15-degree angle from the panel surface for about 20 seconds. The disc is evaluated for any signs of wrinkles or release of grasp of the hook/loop interface on the abrasive disc edges.
The fourth evaluation (Third Mode) is aggressive sanding at above a 40-degree angle from the panel surface for about 20 seconds. The disc is evaluated for any signs of wrinkles or release of grasp of the hook/loop interface on the abrasive disc edges.
The fifth (and last) evaluation is the final grasp. The disc is removed from the backup pad and the grasp of the hook with the loop evaluated.
Examples 1 and 2 were tested using the 3-mode test. The sander used was a 12.7 cm (5 inch) non-vacuum “Dynorbital-Spirit Random Orbital Sander” model #59020, available from Dynabrade, Inc., of Clarence, N.Y. The workpiece was a mild steel panel coated with a production gel coat commonly used for boat parts, commercially available from Cook Composites and Polymers of Kansas City, Mo. The test results are shown in Table 1.
Results of the 3-mode test.
Disc loose in
Various modifications and alterations of this invention will become apparent to those skilled in the art without departing from the scope and spirit of this invention.