RECORDING DISKETTE HAVING FLOCKED-FIBER WIPING FABRIC AND METHOD OF MAKING

Abstract: Magnetic recording diskette (32) has as the wiping fabric a flocked-fiber layer (22). While prior diskettes have required individual pieces of wiping fabric to be adhered to individual sheets of jacket material, the flocked-fiber layer (22) can be applied to a roll of the jacket material (10) continuously to provide roll stock (28) from which individual jacket blanks can be die-cut.

Description: RECORDING DISKETTE HAVING FLOCKED-FIBER WIPING FABRIC AND METHOD OF MAKING Technical Field This invention concerns recording media such as a diskette which comprises a flexible magnetic recording disk contained in a jacket to which is attached a wiping fabric in facing relationship to the disk. A typical diskette is disclosed in U. S. Patent No. 3,668,658. Background Art The wiping fabric of No. 3,668,658 comprises a porous, low-friction, anti-static material which may be a self-supporting dusting fabric. In most diskettes now on the market, the wiping fabric is fused to a sheet of the jacket material in point-contact patterns. Ultrasonic welding is sometimes employed instead of heat. Whether laminated by heat or by ultrasonic welding, there have been problems such as (1) delamination of self-supporting fabrics from the diskette jackets, (2) the fabric scratching the surface of the recording disk, especially by hard nodules created upon fusing the wiping fabric to the jacket sheet, and (3) torque variations, especially when the fiber distribution in the fabric has been nonuniform. A fourth problem stems from the tendency of fibers to protrude from the wiping fabric into the jacket openings, thus creating the hazard that the protruding fibers might be picked up by the drive mechanism and become trapped at the gap of the recording heads. It is believed that all commercial diskettes are fabricated by cutting the wiping fabric to size and adhering the cut pieces one at a time to individual sheets of the jacket material, leaving edges of each jacket sheet uncovered. Each sheet is then die-cut to provide a jacket blank; two edges which are not covered by the wiping fabric are folded and heat-sealed or otherwise adhered to the outer surface of the jacket blank to 0-_.PI - - provide an envelope; the recording disk is inserted; and a third uncovered edge is folded and then adhered to the outer surface to enclose the disk. There have been problems with adhesion of the folded edges to the 5 underlying jacket material. Disclosure of Invention The aforementioned problems may be eliminated in the present invention by substituting for the wiping fabric of prior diskettes a layer of short, closely-spaced upstanding fibers. One end of each fiber is bonded 10 directly to the inside surface of the jacket. The layer of fibers is economically produced by known flocking techniques and is generally here referred to as the flocked-fiber layer. The flocked-fiber layer does not produce noticeable scratching, does not cause any torque 15 variations, and has been found to resist delamination from the jacket material. The flocked-fiber layer can be applied to a roll of the jacket material continuously to provide roll stock from which individual jacket blanks can later be die-cut. 20 This should permit an economical' advantage compared to the individual-jacket-sheet assembly procedures of the prior art. The flocked-fiber layer of the diskette of the present invention comprises fibers which are predominantly 25 10 to 25 micrometers in diameter and 0.05 to 0.8 micrometers in length. In order to meet present diskette specifications, the flocked-fiber layer, including an adhesive added to bond it to the jacket, may increase the thickness of the jacke.t material about 0.15-0.3 mm to 30 provide an overall thickness of the jacket material with its flocked-fiber layer of 0.35-0.45 mm. It may be necessary to calender the flocked-fiber layer in order to reduce it to a desired thickness, thereby bending over free ends of the fibers which otherwise tend to be 35 upstanding. Preferably the fibers of the flocked-fiber Q..-FI layer are densely packed to about 17-102 g/m.2. if the fibers were too fine or too low in density, the recording surface might not be kept sufficiently clean, and the bonding agent might be exposed to scratch the recording surface. If the fibers were too coarse or too high in density, there might be undesirable variability in the torque required to rotate the disk. Especially useful fibers for the flocked-fiber layer are rayon, nylon, polyester, acrylic, cotton and mixtures thereof. The flocked-fiber layer may be created by conventional techniques. For example, a bonding agent may be applied to the jacket material to provide an adhesive layer which is viscous and tacky. Short, closely-spaced fibers are then embedded into the adhesive layer, each fiber being then bonded directly to the jacket material. The fibers may be attracted to the adhesive layer electrostatically or merely by gravity.. It is preferred that there be a beater-bar beneath the jacket material to assist in driving the fibers into the viscous, tacky adhesive layer. The bonding agent preferably is a water-based adhesive. A hot-melt adhesive may be used. The use of a solvent might be hazardous if the fibers are attracted to the adhesive layer electrostatically. However, the use of a solvent to activate the jacket material to an adhesive state provides certain known economies. If the jacket material comprises paper or otherwise has a fibrous nature, an adhesive coating can serve the dual functions of integrating those fibers and adhering the flocked-fiber layer. Preferably the fibers of the flocked-fiber layer are treated with an anti-static agent prior to flocking in order to provide a more uniform flocked-fiber layer, as is well known in the flocking art. That anti-static agent also enhances the bleeding off of charges from the magnetic recording disk of the diskette. Even so, it may be desirable to apply an additional anti-static coating t the fiber-flocked layer, preferably as an in-line process. Also as an in-line process and, if desired, simultaneousl with application of an anti-static coating, a lubricant 5 may be applied to the flocked-fiber layer as in British Patent specification No. 1,508,227. For economy of manufacture, the flocked-fiber layer may be applied to cover one face of the jacket material, the width of which may be a multiple of the 10 . width of an individual jacket. The fiber-flocked jacket material may then be wound up for convenient storage and shipment. The flocked jacket material may later be unwound and die-cut to provide individual jacket blanks, each of which is folded and adhesively bonded to itself t 5 enclose a magnetic recording disk. If desired, adhesive material may be applied only to selected areas of the jacket material, as by a gravure printing process, thus effecting a small raw material savings in both the adhesive material and the fibers. The need to maintain 0 registration in the die-cutting step would offset at least partially that cost saving. The diskette of the invention makes it more practical to use certain jacket materials that previously were believed to require uneconomical procedures, e.g., 5 paper, polycarbonate film, and biaxially-oriented polyester film. When using paper, the adhesive base for the flocked-fiber layer can serve the additional function of stabilizing the paper, a function which previously would have required a separate operation. Polycarbonate 0 and polyester films have not been adaptable to prior techniques for applying wiping fabric. Brief Description of Drawings Fig. 1 schematically illustrates the application of a flocked-fiber layer to jacket material; 5 Fig. 2 schematically shows a diskette of the invention; and Fig. 3 is an enlarged cross-section along lines 3-3 of Fig. 2. Referring to Fig. 1, jacket material 10 is unwound from a roll and coated with an adhesive composition at a hopper-fed-knife-coater 12. Fibers 14 falling from a brush hopper 16 are electrostatically attracted to the adhesive layer 18 with the aid of electrodes 19. A beater-bar mechanism 20 beneath the jacket material 10 assists in driving the fibers into the adhesive layer 18 to provide a flocked-fiber layer 22. An oven 24 drives off the water from the adhesive to bond the fibers to the jacket material. A cleaning station 26 removes loose fibers from both surfaces of the finished material which is then wound up into a roll 28. The finished material of the roll 28 is later unwound and die-cut to provide individual jacket blanks which are folded around a flexible magnetic recording.disk 30 to provide a diskette 32 as seen in Fig. 2. A series of adhesive dots 34 bond the folded edges to the surface of the jacket. Referring to Fig. 3, the jacket of the diskette 32 consists of the jacket material 10 and the flocked-fiber layer 22 (which includes the adhesive layer 18). The jacket material 10 at one side 35 of the ' diskette extends beyond and is folded around the other side 36 of the diskette and its overlapped fiber-flocked layer 22 is bonded by the adhesive 34 to the uncoated surface of the underlying jacket material 10. A better bond has been obtained than has been experienced in bonding folded edges in the prior art. Example 1 Opaque plasticized polyvinyl chloride film of 0.275 mm thickness of the type used for flexible diskette jackets was knife-coated on one face with a water-borne acrylic-vinyl latex adhesive to a wet thickness of about 0.125 mm which by itself would dry to a thickness of about 0.075 mm. Random-cut cotton flock (14-24 micrometers in diameter and 0.05-0.4 mm in length) was electrostatically attracted to the adhesive coating which was tacky and viscous, and the fibers were embedded into the adhesive with the aid of beater bars. After the flocked-fiber layer coat was dried in an air-circulating oven for 2 minutes at 50°C. , both surfaces were aggressively brushed and vacuumed to remove loose fibers, and the finished material was wound up into a stock roll. The stock roll was later slit to a useful width, further cleaned, and then calendered to reduce the overall thickness of the jacket material with its flocked-fiber layer to 0.45 mm. Sheets cut from the roll were stacked and placed in an oven at about 52°C. for two hours to remove the roll-induced curl. The sheets were die-cut to provide blanks which were folded and the two side flaps were sealed with a hot-melt adhesive. A magnetic recording disk was inserted, and the third flap was folded and sealed to provide finished diskettes. The openings in the jackets appeared to be free from any fibers protruding from the flocked-fiber layer which could not be delaminated. In these respects the diskettes of Example 1 appeared to be superior to any diskette now on the market. A number of diskettes of Example 1 were tested by rotating the jacket in the horizontal position while the disk was pinched between the two sides of the jacket as in ANSI Specification No. X3B8/78-145. Diskette users generally specify ten million rotations without any visible effect upon the magnetic recording disk. Not a single diskette of Example 1 has failed this test even though many specimens have been tested for ten million rotations and some have been tested for 20 million rotations. Initial tests suggest that the diskettes of this invention are at least equal in performance to all presently commercially available diskettes as to the O... -7- torque required and the variability in the torque required to rotate the disk. Examples 2-11 Various diskettes of the invention were made as in Example 1 except for changes indicated in the following table. Jacket hesive Thickness Thickness Example Material (mm) Material Wet (mm) Fibers 2 PET 0.15 A 0.15 nylon 3 PET 0.15 E 0.1 rayon I 4 PP 0.25 E 0.1 cotton 5 PP 0.25 E 0.1 rayon II 6 PC 0.25 B 0.125 rayon III 7 PVC 0.275 D 0.1 rayoή I 8 PVC 0.175 C 0.1 cotton 9 PC 0.25 B 0.125 polyester 10 P-I 0.175 C 0.125 cotton 11 P-II 0.25 C 0.1 cotton PET = opaque biaxially-oriented polyethylene terephthalate film PP = opaque biaxially-oriented low-density polypropylene film PC = opaque polycarbonate film PVC = opaque plasticized polyvinyl chloride film P-I = calendered manila paper made for tabulating card use P-II = latex-coated paper A = water-borne acrylic latex, 49% solids B = water-borne acrylic latex, 45% solids C = water-borne acrylic latex, 43% solids D = water-borne vinyl-acrylic latex of Example 1 E = water-borne ethyl acrylate/polyvinyl acetate latex, 50% solids nylon = randon-cut nylon, 11-19 micrometers in thickness and 0.25-0.625 mm in length rayon I = random-cut rayon, 9-17 micrometers in thickness and 0.25-0.625 mm in length rayon II = precision-cut rayon, 12 micrometers in thick¬ ness and 0.25 mm in length rayon III = precision-cut rayon, 12 micrometers in thick¬ ness and 0.375 mm in length cotton = random-cut cotton of Example 1 polyester = precision-cut, cold-drawn polyethylene terephthalate, 17 micrometers in thickness and 0.5 mm in length Of the fibers used in the diskettes of Examples 1-11, cotton provided the softest fabric and hence caused the least amount of wear of the facing magnetic recording layer. Rayon proyided nearly equal softness. Of the fibers, the free ends of the cotton had the greatest tendency to lie in the plane of the surface of the fabric. As a consequence, frictional drag was desirably low. Of the fabrics of Examples 1-11, those made with cotton had the least directionality and hence provided the least variability in the torque required to drive the disk. The random-cut rayon was nearly as good as cotton in this respect. Of the fabrics, those made with rayon best dissipated static charges, with cotton a close second. Of the jacket materials, polyvinyl chloride was the easiest to handle in folding and showed the least tendency for the fold to open upon exposure to elevated temperatures. However, polyvinyl chloride was the most susceptible to damage if exposed to unusually high temperatures which might carelessly be encountered.

Claims: CLAIMS 1. A diskette which comprises a thin jacket containing a flexible recording disk and a wiping fabric bonded to the jacket in facing relationship to the disk, characterized in that the wiping fabric comprises a layer of short, closely-spaced fibers, one end of each fiber being bonded directly to the jacket. 2. A diskette as defined in claim 1, further characterized in that said fibers predominantly are 10 to 25 micrometers in diameter and 0.05 to 0.8 mm in length. 3. A diskette as defined in claims 1 or 2, further characterized in that the fibers of said layer are present in the amount of 17 to 102 g/m 2 . 4. A diskette as defined in claims 1, 2 or 3, further characterized in that said fibers are selected from at least one of rayon, nylon, polyester, acrylic and cotton. 5. A diskette jacket for a flexible recording disk, which jacket has wiping fabric ' bonded to its inner-facing surfaces, characterized in that the wiping fabric comprises a layer of short, closely-spaced fibers, one end of each fiber being bonded directly to the jacket. 6. A method of making diskettes comprising the steps of bonding a wiping fabric to jacket material, cutting this into jacket blanks and forming each blank O...FI ' into a jacket to enclose a recording disk permanently, characterized in that the wiping fabric is bonded to, the jacket material by applying a bonding agent to the jacket material to provide an adhesive layer an embedding short, closely spaced fibers into the adhesive layer, one end of each fiber being thu bonded directly to the jacket material. 7. A method as defined in claim 6, further characterized in that the bonding agent is a water-borne adhesive and the fibers are embedded into the adhesive coating while it is tacky and viscous. 8. A method as defined in claim 6, further haracterized in that the fibers are treated with an anti-static agen prior to being embedded into the adhesive coating.

Inventors: LAMPHERE C, MIKLOS R
Applicants: MINNESOTA MINING & MFG, MINNESOTA MINING & MFG CO
Application year: 1980
Main classification: G11B23
IPC codes: D04H1, G11B23