Stirface finishing of a workpiece can include sanding, buffing, polishing or other finishing processes. A wide variety of materials for such finishing have been used. For example, sandpaper of various grades and nonwoven finishing pads with abrasive coatings or additives are well known. One manufacturer of sandpaper products is Minnesota Mining and Manufacturing Company, St. Paul, Minnesota.

Sandpaper sheets in various configurations and abrasive grades, double-sided abrasive sheets ("duplex" sheets), as well as abrasive sheet material where one side has abrasive and the other side has pressure sensitive adhesive, are all well known.

Nonwoven pads having a variety of surface treatment characteristics (and in varying abrasive grades) are also available fine Minnesota Mining and Manufacturing Compaiiy. St. Paul, Nliiiiiesota, conllnel-cially referred to as SCOTCH-BRITETM pads.

Although these surface finishing materials can be used to refine nearly any surface, they have found particular application to floor refinishing techniques. It is common in floor sanding to use a nonwoven abrasive pad on a rotary sander machine as a cushion between the sander and a sandpaper sheet facing the floor.

An abrasive disk of sandpaper of the same size or larger than the circular face ofthe nonwoven pad is either mechanically fastened from its center to the sander, or mounted relative to the nonwoven pad via use of a double-sided abrasive disk or affixed by a pressure sensitive adhesive on the back of the disk to adhere the disk to the nonwoven pad. Mechanical fastening ofa sanding disk from its center requires the use of a full abrasive disk. which reduces unit pressure for sanding, limits the

ability of the sandpaper to conform to the floor surface, and wastes the abrasive in the center of the disk. Double-sided abrasive disks rely on a loose mechanical bite between the back abrasive side and the nonwoven disk to maintain those components attached for coupled rotation. The use of a pressure sensitive adhesive to mount the sandpaper to the nonwoven pad allows the placement of a disk over the face of a pad. However, the pressure sensitive adhesive may not hold well to the nonuniform fibrous face of the nonwoven pad, especially ifthe pad has any dust or debris built up on it, which is very common in finishing operations (e.g., sanding of drywall, cabinets, furniture, automobiles and similar operations that generate fine sanding dust) and in the hostile workplace environment in which such operations often take place. Increasing the density of the nonwoven pad provides additional fiber siitaces for pressure sensitive adhesive bonding, but may not be desired for other functional reasons.

For some floor finishing situations, a strip of sandpaper is mounted across the trace of an abrasive nonwoven disk to present two different abrasive surfaces to the floor for surface treatment. The sandpaper strip is secured in place relative to the nonwoven pad either by folding the sandpaper over so the abrasive is on both sides of the sandpaper sheet, or by just folding over the edges of the sandpaper sheet, or by using a pressure sensitive adhesive disposed on the back ofthe sandpaper sheet None of these attachment alternatives has resulted in a connection between the sandpaper and the nonwoven web which is sufficiently simple, reliable and repeatable in the dusty, non-uniform and hostile (and rapidly rotating) floor sanding en',ironment.

As a floor surface is treated, it may be necessary to substitute a fresh sheet of sandpaper, or it may be desired to change to a sandpaper sheet having a different abrasive grade. After initial use, this may not be possible using a pressure sensitive adhesive backed sandpaper on a nonwoven pad because the dust on the pad prevents a second sandpaper sheet from adhering to the pad. Thus, not only is a difFerent sheet of sandpaper required for flirther finishing, but a clean nonwoven pad is also required, in order to adhere the sandpaper to the nonwoven pad. The existing (dirt) nonwoven pad must be cleaned or a new nonwoven pad used. Its is

especially troublesome for applications where it is desired to arrange a sheet of sandpaper on the face of a nonwoven pad which is smaller than the nonwoven pad, so that the abrading surface presented to the floor includes not only the sandpaper but also the abrasive on the nonwoven pad itself Prior to the present invention, there liars been no truly effective means for affirmatively securing a sandpaper sheet across a portion of a nonwoven abrasive pad for use in creating an abrasive assembly which presents mllltiple abrasive surfaces for workpiece surface treatment.

SUMMARY OF THE INVENTION The present inventioii includes an abrasive assembly which presents at least two separate abrading surfaces to a workpiece for surface treatment thereof, with the two surfaces having different abrasive characteristics. The abrasive assembly comprises a nonwoven pad haviiig a major generally planar face defining a first one of the abrading surfaces, and a sheet, smaller than the planar face of the nonwoven pad, having fi-ont and back major sides. The front side ofthe sheet defines a second one of the abrading surfaces and the back side of the sheet has a plurality of hooking stems projecting therefrom releasably engaged with the face of the nonwoven pad.

The present invention also includes a method of assenibling an abrasive assembly. A nonwoven pad haing a major generally planar face is provided, with the face having abrasive characteristics and defining an engaging surface. A sheet smaller than the planar face of the nonwoven pad is also provided, with the sheet having fi-ont and back major sui-faces. The front surface of the sheet has abrasive chaiacteristics differing from those of the face of the nonwoven pad and the back surface of the sheet includes a plurality of hooking stems projecting therefrom. The method further includes the step of pressing the hooking stems on the back surface of the sheet against the engaging surFace on tile planar face of the nonwoven pad to releasably secure the sheet to the iionvoven pad.

The present invention flirther includes a method of surface treatment for a workpiece surface. The method includes providing a circular nonwoven pad having a major generally planar face, wherein the face has first abrasive characteristics and

defines an engaging surface. A sheet smaller than the planar face of the nonwoven pad is provided, and has front and back major surfaces. The front surface of the sheet has second abrasive characteristics diflbring from those of the face of the nonwoven pad, and the back surface of the sheet includes a plurality of hooking stems projecting therefrom. The hooking stems on the back surface of the sheet are pressed against the engaging surface on the planar face ofthe nonwoven pad to releasably secure the sheet to the nonwoven pad. The face of the nonwoven pad and front surface of the sheet adhered thereto are placed against the workpiece surface, and the nonwoven pad is moved relative to the work piece surface to present the abrasive characteristics of the front surface of the sheet and those portions of the nonwoven pad not covered by the sheet to the workpiece surface.

BRIEF DESCRIPTION OF TllE DRAWINGS The present invention will be further explained with reference to the drawing figul-es listed below wherein like structure is referred to by like numerals through the several views.

FIG. I is a side elevational view of a rotary floor sander having an abrasive assembly of the present invention moulted thereon.

FIG. 2 is an enlarged section view as taken at view A in FIG. 1 FIG. 3A is a bottom plan view of a first embodiment ofthe present invention.

FIG. 3B is a bottom plan view of a second embodiment of the present invention.

FIG. 3 C is a third embodimeiit of the present in'ention.

FIG. 3D is a fourth embodiment of the present invention.

FIG. 3E is a fifth embodiment ofthe present invention.

FIG. 3F is a sixth embodiment ofthe present invention.

FIG. 4A is a seventh enlbodiment ofthe abrasive assembly ofthe present invention, illustrating its application in a rectangular format.

FIG. 4B is an eighth alternative embodiment of the present invention.

While the above-identified drawings features set forth several preferred embodiments, other embodiments of the present invention are also contemplated, as noted in the discussion. This disclosure presents illustrative embodiments of the present invention by way of representation and not limitation. Numerous other modifications and embodiments can be devised by those skilled in the art which fall within the scope and spirit of the principles of this invention.

DETAILED DESCRTPTION OF THE PREFERRED EMBODIMENTS A typical rotary floor sander machine 10 is illustrated in FIG. 1. The sander 10 has a main sander housing 1 2 connected to a handle 14, which is manipulated by an operator to advance the sander 10 across the floor surface 1 6 to be worked.

While referred to herein as a "sander," the floor sander 10 can be used for other floor treatment operations such as buffing, polishing, etc., by varying the abrasiveness ofthe surface treatment material on the bottom ofthe sander 10. In the present inventive assembly, at least two materials having different "abrasive characteristics" are presented to a work piece at the same time. The abrasive characteristics for any particular type of material (e.g., sandpaper) may differ significantly in "grade" (e.g., from a very coarse grade, highly abrasive state (for stocl; renioval) to a very fine grade, almost nonabi-asive state (for polishing or buffing \oW)).

The housing 12 of the sander 10 includes a drive motor (not shown) which is activated by the operator to rotate a drive platen 1 S at the base ofthe sander 10.

A bottom face 19 ofthe drive platen 1 S is typically covered with a frictional material, such as rubber belting or sheet 20, which preferably has an array of protrusions or knobs 22 011 a bottom side 24 thereof. The rubber sheet 20 and its protrusions 22 aid in engaging whatever floor surface treatment material or intermediate pads are positioned between the drive platen 15 and the floor surface 16.

As illustrated in FIG. I, a disk-shaped nonwoven pad 30 is aligned between the rubber sheet 20 and floor surface 16. The nonwoven pad 30 has a generally planar top surface 32 facing the bottom surface 24 of the rubber sheet 20, and a

bottom surface 34, which is aligned with the floor surface 16. The nonwoven pad 30 is defined bv a pltirality of intermingled fiber segments 36 (FIG. 2) that are bonded together at fiber junctures to form a lofty matrix which is treated (e.g., coated) with an abrasive coating comprising adhesive and abrasive particles. One or more abrasive faced sheets 40 are disposed between the nonwoven pad 30 and the floor surface 16. FTG. 2 shows in more detail the interface between the nonwoven abrasive pad 30 with respect to the rubber sheet 20 and sheet of abrasive material 40.

As seen in FIG. 2, each abrasive sheet 40 is formed fi-om a generally planar substrate 42 having a back connecting side 44 and a front working side 46. On its front side 46, the sheet 40 has a layer or coating of abrasive material 48 thereon.

On its back side 44, the sheet 40 has means for mechanically engaging with the fibers 36 ofthe nonwoven pad 30 for fixing the sheet 40 relative to the nonwoven pad 30. Preferably, the engaging means is a plurality of engagement stems 50 projecting outwardly from the back side 44 of the sheet 40, kith each stem 50 having an enlarged head 52 adiaceiit its outermost end. The engagement between the nonwoven pad 30 and abrasive sheet 40 is in the nature of a hook and loop fastener, with certain fibers 36 on the bottom surface 34 of the nonwoven pad 30 being engaged by certain stems 50 on the back side 44 of the abrasive sheet 40 (as at 55 in FIG. 2).

Nonwoven pads suitable for surface treatment include those commercially available in various formats (circular disks. sheets or rolls) from Minnesota Mining and Manufacturing Company, St. Paul, Minnesota, and are referred to as SCOTCH- BRITETM pads. For floor treatlnelat applications, preferable pads include "SCOTCHBRITETNt Clean and Finish Discs," type A and type T. The lofty nonwoven pad 30 provides not only a cushioning layer between the abrasive sheet 40 and sander 10, btit also itself has abrasive characteristics so that any exposed portions thereof are usetill in treating the floor surface 16. Examples of lofty, nonwoven abrasive pads formed fi-om crimped staple fibers are taught in Hoover et al. U.S. Patent No. 2,958,593; Barnett et al. U.S. Patent No. 4,609,380; and Hayes U.S. Patent No. 5,082,720.

The abrasive sheet 40 may have a variety of shapes (as illustrated in FIGS.

3A-3F and 4A-4B), but in all respects it is smaller in size than the bottom surface 34 of the nonwoven pad 30. The abrasive material 48 on the front working side 46 of the sheet 40 may be any suitable, low profile abrasive, having different abrading characteristics from the nonwoven pad 30. The abrasive aggressiveness (or grade) of the abrasive material 48 can be as high or low as desired for a particular surface treatment application. Typically, the abrasive sheet is a coated abrasive article, also known as sandpaper. Coated abrasive articles can have a wide variety of properties, depending on what is desired. The backing of the article is generally a paper, film, or cloth, but can also be a reinforced thermoplastic backing such as taught by Stout et al U.S Patent 5,3 16,8 12. The abrasive particles can include any abrasive or polishing particle, for example, aluminum oxide (including fused and ceramic, i.e., "sol gel"), aliiiiinazirconia, silicon carbide, garnet, diamond, CBN, mullite, ceria, crushed glass, plastic particles, and other polishing materials. The abrasive particles are typically held onto the backing by a resinous adhesive, often by a phenolic or epoxy or bide glue. The adhesive can be thermal or radiation cured. Another abrasive material suitable for use on the working side 46 of the sheet 40 is a structured abrasive article, available under the trade designation "Trizact" 307EA and 407E.R structured abrasive article, from Minnesota Mining and Manufacturing Compan. St Paul, Minnesota. Further details regarding such structured abrasive articles are taught in Pieper et al. U.S. Patent 5, 152,917.

The engaging means on the back connecting side 44 of the sheet 40 is also relativel',' low profile, and preferably is formed from hook stem materials such as those disclosed in Melbye et al. U.S Patent No. 5,077,870; Chesley et al. U.S.

Patent No. 5,505,747; and in WlPO International Application Publication No.WO 95/19242. The hook stem material can be laminated to the abrasive article on the side opposite the working side, or tlie hook stems can be formed directly onto the side opposite the working side. Alternately, the abrasive coating (i.e., abrasive particles and adhesive) can be directly coated onto a substrate having the hook stems so that an integral sheet is formed.

As used herein, hool; stem means a stern having a tree end that is spaced from the surface to which the steni is attached and a structure (a head or J-shaped end) that enables the hook stem to releasably engage one or more fibers on an opposed engaging surface (the bottom surface 34 of the nonwoven pad 30). In FIG. 2, each stem 50 is illustrated as having a head 52 shaped in the form of a nail head. Alternative hook and stem head configurations will function to suitably engage the nonwoven pad 30. For instance, the head ofa hook stem may have any suitable three-dimensional shape, such as a hemisphere, sphere, mushroom cap, cube, pyramid, etc. Preferably, the head has at least one undercut portion that extends radially away fi-om tlie stem at a right angle, such as the heads 52 shown in FIG. 2, to hook the fibers oi- looped nonwoven filaments along the bottom surface 34 of the nonwoven pad 30. The hook stems and heads are sized and arranged to be sufficient to adhere the sheet 40 to the nonwoven pad 30, but allow for easy removal of the sheet 40 for replacement, or to allow use of the nonwoven pad 30 alone as a surface conditioning treatment material. Also, while the arrangement and formation of hook stems 50 are preferably generally uniform, alternative stem patterns, such as non-uniform stems and stem array arrangements will suffice.

Preferably, the stem height ranges from approximately .002 to 0. 102 inch (0.05 to 2.6 mm), and is more preferably about 0 020 inch (0.508 mm), and the stem density ranges from approximately 52 to 2000 stems per square inch (8 to 310 stems per square centimeter), and is more prefel-ably about 400 stems per square inch (62 stems per square centimeter). Depending on stem density, nonwoven pad density and desired engagement characteristics, in sonde applications engagement stems having no heads will suffice to secure the abrasive sheet to the nonwoven pad.

Low profile stems are important, so that the sheet 40 can lay with its abrasive material 48 nearly coplanar with the bottom surface 34 of tie nonwoven pad 30. The stems 52 need to be high enough to provide an engaging structure for the fibers of the nonwoven pad 30. but low enough so as not to add structural depth to the abrasive article assembly (and low enough not to extend through to the top surface 32 ofthe pad). it is intended that the back working side 46 ofthe sheet 40 lie as flush as possible with the bottom surface 34 of the nonwoven pad 30.

In use, one or more abrasive sheets 40 are engaged with the bottom surface 34 of the nonwoven pad 30 in a desired arrangement (see, e.g., FIGS. 3A-3F). The back connecting side 44 of the sheet 40 is urged against the bottom surface 34 of the nonwoven pad 30 to engage the hook stems 50 thereon with exposed fibers of the nonwoven pad 30. The abrasive article assembly thus defined is placed on a floor surface 16 to be treated, with the abrasive material 48 (on the front working side 46 ofthe sheet 40) and bottom surface 34 of tie abrasive nonwoven pad 30 facing the floor surface 16. The abrasive article assembly is then aligned with and attached to the floor sander I 0, or tlie floor sander 10 is simply aligned over the abrasive article assembly (as illustrated in FIG. 1), and then the motor ofthe sander 10 is activated. This rotates the drive platen 1 8 which in turn (via the rubber sheet 20) rotates the abrasive nonwoven pad 30 and abrasive sheet(s) 40 affixed thereto.

The inventive abrasive article assembly thus presents an abrasive treatment to the floor stirface I 6 which has two different abrasive characteristics: (I) that provided by the abrasive material 48 on the sheet or sheets 40, and (2) that provided by the exposed abrasive portions of tlic nonwoven pad 30 between adjacent sheets 40.

This simultaneous presentation of two materials having different abrasive characteristics has proved particularly useful in the surface treatment of water based floor coatings on wood flooring surfaces. When mounted on a rotary sander as described herein, the rotating abrasive nonwoven pad burnishes the coating on the floor stii-facc while the abrasive on the abrasive sheet or sheets engaged thereto sands down the wood gi-nilis (wood ends, fibers or nibs) that were raised by application of the coating. The nonwoven pad also removes or decreases any scratches that may have been left by the abrasive sheet. The partial covering ofthe nonwoven pad with one or more abrasive sheets enhances the ability of the resultant abrasive article assembly to conform to an uneven floor surface without cutting too deeply The present invention is useful for botli solvent-based and water-based coatings The abrasive assembly works well on any finish that may have dust or nibs caused by foreign contaminants or solid particles.

The use of the inventive abrasive article assembly allows for a wide range of abrasive presentation options using a single nonwoven pad.

For instance, an abrasive sheet having aggressive abrasive characteristics can be used in connection with a nonwoven pad, anci after use on a floor section, another abrasive sheet having a less aggressive abrasive grade can then be engaged with the nonwoven pad (instead of the original abrasive sheet) for further, finer floor surface conditioning. An endless variety of abrasive presentations can be configured, depending on the abrasive characteristics and abrasive grades of available abrasive nonwoven pads and abrasive sheets, and on the possible combinations thereof The abrasive characteristics of tic inventive abrasive assembly can also be manipulated by changing the number, size and layout of abrasive sheets on the nonwoven pad. FIGS. 3A-3F provide examples of alternative layouts for the abrasive sheets on an abrasive nonwoven pad. In FIG. 3A, a single abrasive sheet 40A is disposed and affixed across the bottom surface 34 of the abrasive nonwoven pad 30. In FIG. 3B, four circular abrasive sheets 40B are employed. In FIG. 3C, six generally rectangular abrasive strips 40C are employed. The generally rectangular strips 40C are aligned and elongated along radial lines extending out froiii the rotation axis of the iionwovcn pad 30. Alternatively. elongated abrasive strips may be laid out on chords of a circular pad, or mty be canted relative to radial lines to facilitate dust removal duiing pad rotation. In FIG. 3D, four triangular- shaped abrasive sheets 40D are employed. In FIG. 3E, four crescent-shaped abrasive sheets 40E are employed. In FIG. 3F, four generally rectangular strips 40F, similar to those of FIG. 3C, are arranged around the circumference.

In each of these illustrated configurations, the several abrasive sheets may have identical abrasive grades, or the abrasive grades may differ (even among several sheets mounted on the same nonwoven pad) to achieve a desired surface treatment combination. These abrasive sheets may be symmetrical in shape (as generally illustrated), or may be asymmetrically shaped, and any number of sheets may be employed. Further, shapes and sizes may be mixed t -0 attain desired surface treatment characteristics for the abrasive article assembly. One other example of an abrasive assembly is a circular nonwoven pad with an annular or "donut" shaped abrasive sheet. With a circular nonwoven pad, such as illustrated in

FIGS. 3A-3F, it is preferable that multiple abrasive sheets be aligned on the nonwoven pad in a symmetrical manner. For noncircular pads, such as shown in FIGS. 4A-B, the abrasive sheets 40G (FIG. 4A) and 40H (FIG. 4B) may be placed in a non-symmetrical manner. In addition, alternatively shaped sheets (such as L- shaped sheet 4011 in FIG. 4B) can be used.

While the disclosure herein is presented with respect to floor sanding and circular nonwoven pad configurations, the use of the present invention for other nonwoven pad configurations and other surface treatment applications is contemplated. Nonwoven pads of rectangular, square or other shapes can be used, along with other combinations of shapes, sizes and layouts (symmetrical or non- symmetrical) of abrasive sheets, so long as the abrasive on the abrasive sheet is accompanied by some exposed portion of the nonwoven pad to provide a second abrasive characteristic surface in combination with the abrasive characteristics of the abrasive e sheet hooked thereto. In addition, the use of the abrasive article assembly of the present invention is not limited to rotary floor sander niachines. The invention is useful for manual surface treatment techniques (e.g., a palm sander), as well as, foi- example, surface treatment operations using vibratory, orbital or industrial surface treatment appal-atus. Examples of workpicces that might be so treated include furniture, cabinets, wood trim, automobile bodies and drywall. As such, the workpiece may be horizontally orientated (such as a floor) or vertically oriented (such as a table ieg). Iqurtlner, the workpiece surface may be generally flat (i.e., planar) or may be curved or otherwise irregular.

Although the present invel1tion has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope ofthe invention.