Disk Cartridge

A disk cartridge, for example, a magnetic disk cartridge, mainly comprises a cartridge case having openings for inserting magnetic heads and openings for inserting a rotation driving shaft, a flexible magnetic disk rotatably encased in the cartridge case, and a cleaning sheet supported on the inside surfaces of the cartridge case.

The cleaning sheet for the conventional magnetic disk cartridge is composed of a non-woven fabric made of, for example, mixed-fibers of rayon and polypropylene, mixed fibers of rayon and polyethylene terephthalate, or single fibers of polyethylene terephthalate, and is fixed to the inside surfaces of a cartridge case by ultrasonic welding, heat seal, or by an adhesive.

However, the cleaning sheets composed of the fibers do not perform good cleanability of the magnetic disk, and further have such problems as the development of scratches on the magnetic disk surface by sliding contact with the cleaning sheet, falling-away of the fibers from the cleaning sheet by sliding contact with the magnetic disk, and attachment of the falling-away fibers to the magnetic disk or the magnetic head, thereby adversely affecting the recording-reproducing characteristics.

An object of the present invention is to provide a disk cartridge, such as a magnetic disk cartridge, which has markedly improved disk-handling characteristics and cartridge case-fixing characteristics, and a high welding strength of the cleaning sheets to the cartridge case.

The present invention is directed to a disk cartridge which comprises a cartridge case composed of a flexible sheet or a molding of rigid synthetic resin, a flexible disk rotatably encased in the cartridge case, and a cleaning sheet supported on the inside surface of the cartridge case by welding.

According to a first aspect of the present invention, the cartridge case is composed of a thermoplastic synthetic resin and the cleaning sheet is composed at least of a mixed fabric comprising acrylic fibers and rayon fibers.

According to a second aspect of the present invention, the cleaning sheet is composed of a sheet member of multi-layer structure comprising a disk-facing non-woven fabric layer composed of a non-woven fabric made mainly of acrylic fibers on the disk-facing side, a cartridge case-facing non-woven fabric layer composed of a non-woven fabric containing fibers at least a portion of which are embeddable into the inside surface of the cartridge case by welding of the cleaning sheet to the cartridge case while substantially retaining the fiber form, and an intermediate layer being provided between the disk-facing non-woven fabric layer and the cartridge-facing non-woven fabric layer and being composed of a mixed fabric comprising acrylic fibers and rayon fibers.

As described above, the desired disk-handling characteristics of the cleaning sheet are specifically am ability to clean a disk such as a magnetic disk, an ability to avoid scratching the disk, and a low lint characteristic of the cleaning sheet when in sliding contact with the disk. We have made extensive studies of non-woven fabrics for the cleaning sheet and have found that non-woven fabrics made of acrylic fibers alone have markedly improved disk-handling characteristics.

However, the non-woven fabrics composed of the acrylic fibers alone still have some problems. That is, when the non-woven fabrics composed of the acrylic fibers alone are subjected to heat sealing to the inside surfaces of a cartridge case, the acrylic fibers are liable to burn out while the fibers undergo shrinking and fusion owing to the characteristics of the acrylic fibers. Consequently, the cleaning sheet cannot have a satisfactory welding strength to the cartridge case, and the cleaning sheet may be peeled off from the cartridge case by repetitious of sliding contact with the disk, or hard materials may be formed on the surface of the cleaning sheet, lowering the cleanliness of the disk, of impart more severe scratches to the disk. Thus, the desirable characteristics of the acrylic fibers are lost.

In the present invention, all the foregoing problems have been solved by making the cleaning sheet from a mixed fabric of acrylic fibers and rayon fibers.

The thermoplastic synthetic resin for the cartridge case includes, for example, polyvinyl chloride, ABS resin, polyacetal resin, polystyrene resin, etc. and a desired cartridge case can be formed therefrom in a jacket shape or by injection molding.

The magnetic disk is prepared by forming a thin magnetic film on one side or both sides of a base film made of polyester, polyimide, or the like by an appropriate means such as coating, vapor deposition, or sputtering, so as to have an appropriate flexibility.

The structure of a cleaning sheet fixed to and supported on the inside surface of a cartridge case will be described in detail below, referring to embodiments by way of the accompanying drawings.

FIGS. 1 to 3 show a magnetic disk cartridge according to a first embodiment of the present invention, where FIG. 1 is a bottom plan view of the magnetic disk cartridge;

FIG. 2 is an unfolded view of the cartridge case and the cleaning sheet of the magnetic disk cartridge;

FIG. 3 is a plan view of the cleaning sheet before being fixed to the cartridge case;

FIG. 4 is a dismantled, schematic view of a magnetic disk cartridge according to a second embodiment of the present invention;

FIG. 5 is a bottom plan view of an upper case of the magnetic disk cartridge of FIG. 4 where the cleaning sheet is provided thereon;

FIG. 6 is a plan view of a lower case of the magnetic disk cartridge of FIG. 4 where the cleaning sheet is provided thereon;

FIG. 7 is an enlarged, cross-sectional view of the neighborhood of the openings for inserting the magnetic heads while the magnetic disk cartridge of FIG. 4 is put into operation;

FIG. 8 is an enlarged, cross-sectional view of the neighborhood of the elastic piece of the magnetic disk cartridge of FIG. 4;

FIG. 9 is an enlarged cross-sectional view of the cleaning sheet according to third embodiment of the present invention;

FIG. 10 is a schematic view of a process for preparing the cleaning sheet;

FIG. 11 is a partially enlarged, cross-sectional view of a linking state between the cartridge case and the fiber of the cleaning sheet;

FIG. 12 is an enlarged cross-sectional view of a cleaning sheet according to a fourth embodiment of the present invention.

In FIGS. 1 to 3, a disk cartridge comprises a cartridge case 1, a flexible, sheet-formed magnetic disk 2 rotatably encased in the cartridge case 1, and a cleaning sheet 3 fixed to the inside surface of the cartridge case 1. As shown in FIG. 2, the cartridge case 1 is composed of a rectangular case sheet member 4 made of, for example, polyvinyl chloride, and three extended edge parts 5a, 5b and 5c for welding are provided at a half section 4b of the case sheet member 4. A rectangular cleaning sheet member 6 having substantially the same area as that of the rectangular case sheet member 4 is fixed to one side of the case sheet member 4 by welding, as will be described later.

In the two square sections 4a and 4b, and 6a and 6b of the case sheet member 4 and the cleaning sheet member 6, respectively, divided by a center folding line X (imaginary line), openings 8 for inserting a rotation driving shaft, which are larger in diameter than the center hole 7 of the magnetic disk 2 (see FIG. 1) and are directed to expose the peripheral part around the center hole 7, openings 9 for inserting magnetic heads, detection openings 10 for detecting the index hole of the magnetic disk 2, thereby correctly tracking the magnetic disk 2, notches 11 for detecting the side A or B of the magnetic disk cartridge, etc. are provided at symmetrical positions along the center folding line X.

After the cleaning sheet member 6 has been placed on the case sheet member 4, the cleaning sheet member 6 is subjected to spotwise welding 12 substantially all over the cleaning sheet member 6, whereas the peripheral parts around the openings 8 for inserting a rotation driving shaft, the openings 9 for inserting magnetic heads, the detection openings 10 and the notches 11 are subjected to linear welding 13, as shown in FIG. 2, whereby the cleaning sheet members 6 can be fixed to the case sheet member 4 without impairing the softness and elasticity of the cleaning sheet member 6. In this case, it is not always necessary to make the spotwise welding 12 all over the cleaning sheet member 6, but to such a degree that the cleaning sheet member 6 is so fixed as not to be readily released from the case sheet member 4.

Then, the case sheet member 4 is folded along the center folding line X so that the cleaning sheet member 6 may be on the inside, and the extended edge parts 5a and 5c, which are counterposed to each other, among the three extended edge parts 5a, 5b and 5c for welding provided on the square section 4b, are folded over the outside of the other square section 4a, and subjected to partial welding 14 to prepare an envelope having an open end. A magnetic disk 2 stamped out of a magnetic sheet is inserted into the envelope, and then the remaining extended edge part 5b for welding is folded over the outside of the square section 4a and subjected to spotwise welding 14, whereby the magnetic disk cartridge as shown in FIG. 1 can be built up.

According to the first aspect of the present invention, the cleaning sheet 3 is composed of a mixed fabric of acrylic fibers and rayon fibers or a mixed fabric of acrylic fibers, rayon fibers and heat-meltable fibers.

The acrylic fibers are synthetic fibers containing more than about 85% of acrylonitrile, copolymerized with acrylate ester, vinyl acetate, styrenesulfonic acid, etc. to improve the frictional resistance or wear resistance, look like wool most among the synthetic fibers and have a distinguished soft-tough flexibility. The acrylic fibers (staples) have a tensile strength of about 2.5 to about 5.0 g/D, an elongation of about 25 to about 50%, an elastic elongation of about 90 to about 95% (at 3% elongation) and a specific gravity of about 1.14 to about 1.17. In the present invention, acrylic fibers having sizes of about 1 to about 6 denier are preferably used.

The rayon fibers for use in the present invention includes, for example, viscose rayon fibers, cuproammonium rayon fibers, acetate rayon fibers, etc. The rayon fibers (staples) have a tensile strength of about 2.5 to about 3.1 g/D, an elongation of about 16 to about 22%, an elastic elongation of about 55 to about 80% (at 3% elongation) and a specific gravity of about 1.50 to about 1.52.

The heat-meltable fibers for use in the present invention include, for example, polyethylene terephthalate fibers, polypropylene fibers, polyvinyl chloride fibers, vinyl chloride-vinyl acetate copolymer fibers, polyamide fibers, etc.

In case of a mixed fabric of acrylic fibers and rayon fibers, it is preferable that the mixed fabric is composed of 80 to 20% by weight of acrylic fibers and 20 to 80% by weight of rayon fibers. In case of more than 80% by weight of acrylic fibers, the welding strength of the cleaning sheet to the cartridge case is lowered, and hard materials are formed on the surface of the cleaning sheet, giving scratches to the disk, whereas in case of less than 20% by weight of acrylic fibers, much falling away of fibers takes place, lowering the cleanability, cuttability, etc.

When the cleaning sheet is composed of a mixed fabric of acrylic fibers, rayon fibers and heat-meltable fibers, it is preferable that the mixed fabric is composed of 80 to 20% by weight of acrylic fibers, 20 to 80% by weight of rayon fibers and 5 to 30% by weight of heat-meltable fibers, total being 100% by weight. In case of more than 80% by weight of the acrylic fibers, the welding strength is lowered, and hard materials are formed during the welding, whereas in case of less than 20% by weight of the acrylic fibers, the cleanability, cuttability, etc. are lowered. The heat-meltable fibers are added to the fabric to improve the adhesion between the fibers, and in case of more than 30% by weight of the heat-meltable fibers, the cleanability, cuttability, etc. are lowered.

Polyvinyl chloride sheet that makes the cartridge case 1 (case sheet member 4) softens at about 65.degree. to about 85.degree. C. and is plasticized at about 120.degree. to about 150.degree. C. and starts to melt at about 170.degree. C., while the rayon fibers in the cleaning sheet 3 (cleaning sheet member 6) has a property to decompose at about 260.degree. to about 300.degree. C. by heating without softening or melting. Thus, when the cleaning sheet 3 (cleaning sheet member 6) is subjected to welding to the cartridge case 1 (case sheet member 4) under some pressure, the rayon fibers 24 in the cleaning sheet 3 (cleaning sheet member 6) are embedded into the inside surface layer of the cartridge case 1 (case sheet member 4), while retaining the fiber form as shown in FIG. 11. Since the cross-sectional shapes of the rayon fibers 24 are non-circular, the cleaning sheet 3 can be firmly fixed to and held in the cartridge case 1, when the rayon fibers are embedded into the cartridge case 1 (case sheet member 4).

The remaining parts of the embedded rayon fibers 24 are in an entangled state with one another and with other fibers in the fabric, and ultimately the cleaning sheet 3 can be firmly fixed to and held in the cartridge case 1 thereby.

The heat-meltable fibers in the cleaning sheet 3 serve to reinforce the binding of acrylic fibers and rayon fibers, and the binding of cartridge case 1 and cleaning sheet 3.

The cleaning sheet member 6 is passed between rollers each provided with, for example, a knurling tool around the roller surface (embossing treatment), whereby an embossing pattern 23 can be formed on the cleaning sheet member 6, as shown in FIG. 3. In FIG. 2, the embossing pattern 23 are not shown for simplifying the drawing. Then, the thus embossed cleaning sheet member 6 is fixed to the case sheet member 4 by spotwise welding 12 and also by linear welding 13, as already described before.

Magnetic disk cartridges were prepared, using cartridge cases prepared in the following manner:

A cartridge case to which a cleaning sheet composed of mixed fabric of 50% by weight of acrylic fibers and 50% by weight of rayon fibers was fixed by heat sealing (Example 1); a cartridge case to which a cleaning sheet composed of a fabric of 60% by weight of acrylic fibers, 30% by weight of rayon fibers and 10% by weight of polyethylene terephthalate fibers was fixed by heat sealing (Example 2); a cartridge case to which a cleaning sheet composed of non-woven fabric of acrylic fibers alone was fixed by heat sealing (Comparative Example); a cartridge case to which a cleaning sheet composed of non-woven fabric of 80% by weight of rayon fibers and 20% by weight of polypropylene fibers was fixed by heat sealing (Comparative Example 1); and a cartridge case to which a cleaning sheet composed of non-woven fabric of polyethylene terephthalate fibers above was fixed by heat sealing (Comparative Example 2).

Cuttability, cleanability, magnetic disk scratchability, lint characteristics and weldability of the cleaning sheets of Example 1, Example 2, Comparative Example, and Conventional Examples 1 and 2 were determined according to the following procedures.

The respective cleaning sheet members 6 were fixed to the case sheet members 4 and then subjected to punching at a punching speed of 120 punchings per minute to provide openings 8 for inserting a rotation driving shaft and openings 9 for inserting magnetic heads together with the case sheet members 4. State of fluffy occurrence at cut parts of the openings 8 and 9 was observed.

The respective magnetic disk cartridges were placed in a recording reproducing apparatus, and the magnetic disk 2 was made to turn in the cartridge case 1, and a small amount of iron powders was added into the cartridge case 1 from the openings 9 for inserting the magnetic heads. Then, the disk was made to turn for 10 minutes. Then, the cartridge case 1 was unfolded to observe the state of adhesion of the iron powders to the cleaning sheet 3.

By turning a magnetic disk in the respective magnetic cartridge case continuously for one week (168 hours) at the ordinary temperature, occurrence of scratches on the magnetic disk by the respective cleaning sheets was observed.

A predetermined amount of the respective cleaning sheets were dipped in a Freon solvent and subjected to ultrasonic vibrations for 10 minutes to observe the state of falling away of the fibers from the respective cleaning sheets.

The respective cleaning sheet members 6 were spotwise welded to the case sheet members 4 at a spot distance of 7 mm by welding to once fix the cleaning sheet members 6 to the case sheet members 4. An edge part of the welded cleaning sheet members 6 were peeled off from the case sheet members 4 to a length of about 5 cm at a width of about 1 cm in a stripe form, while leaving the remaining body part as fixed on the case sheet member 4. By placing the case sheet member 4 on the upside and the cleaning sheet member 6 on the downside, the peeled part of the cleaning sheet member 6 was made to hang down from the case sheet member 4. A load was applied in the peeling direction of the cleaning sheet member 6 from the case sheet member 4 by fixing a weight to the tip end of the hanging-down part of the cleaning sheet member 6. A load weight (g) with which the fixed part (welded part) of the cleaning sheet member 6 started to peel off from the case sheet member 4 was measured by slowly increasing the weight.

The results of these tests are shown in the following Table 1.

As is obvious from the foregoing test results, the present magnetic disk cartridges according to Examples 1 and 2 have better cuttability, cleanability, magnetic disk scratchability, lint characteristics and weldability than those according to Comparative Example and Conventional Examples 1 and 2.

In FIGS. 4 to 8, a second embodiment of the present invention is shown.

As shown in FIG. 4, a magnetic disk cartridge comprises a cartridge case 26, a magnetic disk 27 rotatably encased in the cartridge case 26, and a shutter 28 slidably supported on the cartridge case 26.

The cartridge case 26 is composed of an upper case 26a and a lower case 26b, which are injection molded from a rigid resin, for example, ABS resin.

An opening 29 for inserting a rotation driving shaft is provided substantially at the center of the lower case 26b, and a rectangular opening 30 for inserting a magnetic head is provided near the opening 29. Similarly, an opening for inserting the magnetic head is provided on the upper case 26a. At the parts near the front side of the upper and lower cases 26a and 26b, there are provided recesses 31 in a slight depth to control the sliding range of the shutter 28. The said openings 30 for inserting the magnetic heads are provided at the intermediate position in the recesses 31.

As shown in FIG. 5, recesses 42 and 42 are provided on the inside surface of the upper case 26a and on both sides along the opening 30 for inserting the magnetic head. The longitudinal width W1 of the recesses 42 is controlled to be substantially equal to the width (longitudinal width) W2 in the longitudinal direction of the opening 30 for inserting the magnetic head, and the lateral width W3 of the recesses 42 is controlled to be at least 0.3 times, preferably 0.5 to 1.5 times the width (lateral width) W4 in the direction perpendicular to the longitudinal direction of the opening 30 for inserting the magnetic head. On the disk-coming side in the disk-turning direction with respect to the opening 30 for inserting the magnetic head on the upper case 26a there are provided projections 43 extended in a large number of rows, where the projections in both outermost rows are slightly higher than the rows 43 in the inner rows.

On the inside surface of the upper case 26a, there are provided arc-formed control ribs 44 that control the encasing position of the magnetic disk 27, and a part of the control rib 44 extends over the edge part of the recess 42 to serve as a reinforcing member for the peripheral edge of the recess 42.

As shown in FIG. 5, a substantially C-shaped cleaning sheet 45 having the same structure as that of the said first embodiment is placed within the control ribs 44. Lateral width W5 of an opening 46 of the cleaning sheet 45 provided at a position corresponding to the opening 30 for inserting the magnetic head is designed to be slightly larger than the lateral width W4 of the opening 30 for inserting the magnetic head. By placing the cleaning sheet 45 on the inside surface of the upper case 26a, the recess 42 and the projections 43 are covered by the cleaning sheet 45 and the cleaning sheet 45 is welded to the upper case 26a on the peripheral part by ultrasonic welding or heat sealing. Since the recess 42 of the upper case 26a has a sufficient area, as described above, the edge part of the opening 46 of the cleaning sheet 45 can be welded within the recess 42 as shown by 47 in FIG. 7.

As shown in FIG. 6, a support 48 for elastically supporting an elastic piece 50 and the projected rows 49 for preventing the magnetic sheet from protruding are provided on the inside surface of the lower case 26b at positions substantially counterposed to the projections 43 on the upper case 26a. As shown in FIG. 6 and FIG. 8, the base part 51 of an elastic piece 50 formed by folding a plastic sheet is fixed to the position near the support 48 on the inside surface of the lower case 26b by an appropriate means by bonding or heat sealing. The free end 52 of the elastic piece 50 is supported by the support 48 and retained in an inclined state.

Also on the inside surface of the lower case 26b, there are projected control ribs 44. The cleaning sheet 45 is placed within the control ribs 44. Lateral width W5 of the opening 46 of the cleaning sheet 45 provided at the position corresponding to the opening 30 for inserting the magnetic head is designed to be somewhat larger than the lateral width W4 of the opening 30 for inserting the magnetic head. As shown in FIG. 6, the elastic piece 50 is covered by the cleaning sheet 45 within the control ribs 44 on the lower case 26b, and the cleaning sheet 45 is welded to the lower case 26b at the peripheral part as shown by spots 47, but the welding is not carried out in the area near the elastic piece 50.

When a magnetic disk cartridge is built up with the upper case 26a and the lower case 26b, the cleaning sheet 45 on the lower case 26b is partially lifted by the elastic piece 50, as shown in FIG. 8, and also the lifting is somewhat lowered by the projections 43 provided on the upper case 26a to elastically pinch the magnetic disk 27 by the upper and lower cleaning sheets 45. The disk surfaces are cleaned by the cleaning sheets 45 as the magnetic disk 27 turns.

FIG. 7 shows the state of the disk cartridge in operation where numeral 53 is magnetic heads.

In this embodiment, it was found that the magnetic disk cartridge had better cuttability, cleanability, magnetic disk scratchability, lint characteristics and weldability than those of cleaning sheet members composed of other materials, as in the case of using the said case sheet member made of rigid polyvinyl chloride resin.

According to the first aspect of the present invention, the present cleaning sheet contains acrylic fibers, as described above, which are very soft and flexible among the synthetic fibers, and have a good effect without scratching the turning disk surface and without any fluffy occurrence. Owing to the good cuttability, a portion of fibers never protrude, for example, from the edges of the openings for inserting the magnetic head or a rotation driving shaft into the openings, where a disc cartridge is prepared by cutting. Particularly, when the fibers protrude into the openings for inserting the magnetic heads, errors may appear during the recording or reproducing owing to the protruded fibers, but in the present invention no such errors owing to the protruded fibers appear because of the improved cuttability of acrylic fibers are described above.

Furthermore, the rayon fibers in the cleaning sheet are strongly linked to the inside surface of a cartridge case, and thus the welding strength of the cleaning sheet is so high that there is no fear of release of the cleaning sheet from the cartridge case.

Thus, the present invention can provide a magnetic disk cartridge having a cleaning sheet of distinguished disk-handling characteristics and cartridge case-fixing characteristics.

According to the second aspect of the present invention, a cleaning sheet has the following structure as a third embodiment.

The cleaning sheet 3 is composed of three layers as shown in FIG. 9. The structure, etc. of the cleaning sheet 3 will be described in detail below, referring to FIGS. 9 to 12.

As shown in FIG. 9, the cleaning sheet 3 comprises a disk-facing non-woven fabric layer 15, which faces the magnetic disk 2, a cartridge case-facing non-woven fabric layer 16, which faces the cartridge case 1, and an intermediate layer 17 which links to disk-facing non-woven fabric layer fabric 15 and the cartridge case-facing non-woven fabric layer 16.

The disk-facing non-woven fabric layer 15 is made of acrylic fibers alone. The acrylic fibers having the properties and characteristics as described before can be also used in the second aspect of the present invention.

In the third embodiment, the disk-facing non-woven fabric layer 15 is made of acrylic fibers alone in order to fully exhibit the improved disk-handling characteristics of the acrylic fibers. However, the present invention is not limited thereto. For example, the acrylic fibers can contain not more than 50% by weight of other kind of fibers such as polyethylene terephthalate, polypropylene, polyamide, rayon, etc. in order to enhance the linking strength with the lower layer or improve the frictional resistance of the layer surface.

The cartridge case-facing non-woven fabric layer 16 is composed of a mixed fiber layer of rayon fibers and polyethylene terephthalate fibers, where the mixing ratio of the rayon fibers to the polyethylene terephthalate fibers by weight can be appropriately selected from a range of about 1/9 to about 9/1, preferably 3/7 to 7/3. The same rayon fibers as already described can be also used in the second aspect of the invention.

On the other hand, the polyethylene terephthalate fibers are polyester fibers obtained by polycondensation of terephthalic acid with ethylene glycol. The polyethylene terephthalate fibers (staples) have a tensile strength of about 4.7 to about 6.5, an elongation of about 20 to about 50%, and elastic elongation of about 90 to about 99% (at 3% elongation) and a specific gravity of about 1.38.

In the second aspect of the present invention, the disk-facing non-woven fabric layer 15 and the cartridge case-facing non-woven fabric 16 can be bonded together without impairing the distinguished softness of the acrylic fibers in the disk-facing non-woven fabric layer 15 by providing the intermediate layer 17 composed of a mixed fabric of acrylic fibers and rayon fibers therebetween, since the acrylic fibers are used in the disk-facing non-woven fabric layer 15 and the rayon fibers are used in the cartridge case-facing non-woven fabric layer 16, when the matching of the layer 15 to the layer 16 is taken into account. The mixing ratio of the acrylic fibers to the rayon fibers by weight can be appropriately selected from a range of 1/9 to 9/1, preferably 3/7 to 7/3.

Unit area weight of the cleaning sheet 3 composed of such layers as described above may be preferably limited, and is appropriately about 20 to about 40 g/m.sup.2. The unit area weight is an average of 5 samples, 50 cm.times.50 cm, obtained by measuring each weight.

In FIG. 10, one example of preparing the cleaning sheet 3 is shown, where a roll wound with a mixed fiber fabric 18, a roll wound with a mixed fiber fabric 19, a roll wound with a single fiber fabric 20 and a roll wound with a single fiber fabric 21 are arranged in this order.

The mixed fiber fabric 18 is a non-woven fabric made of rayon fibers and polyethylene terephthalate fibers at a mixing ratio of the rayon fibers to the polyethylene terephthalate fibers of 3:7 by weight and ultimately made into the cartridge case-facing non-woven fabric layer 16. The mixed fiber fabric 19 is a fabric made of rayon fibers and acrylic fibers at a mixing ratio of the rayon fibers to the acrylic fibers of 5:5 by weight and is ultimately made into the intermediate layer 17. The single fiber fabrics 20 and 21 are both non-woven fabrics made of acrylic fibers alone and are ultimately made in the disk-facing non-woven fabric layers 15a and 15b, respectively (see FIG. 9).

In FIG. 10, numeral 22 shows individual guide rollers for continuously letting out the fabrics 18, 19, 20 and 21, and 23 shows a wiremesh for conveying the overlaid non-woven fabrics. The fabrics 18, 19, 20 and 21 each have a thickness of 50 .mu.m, and the fabrics 18, 19, 20 and 21 successively laid one upon another on the wiremesh 23 are passed between heating rollers, whereby they are controlled to a predetermined thickness and the fibers mixed in the cartridge case-facing non-woven fabric layer 16 and the intermediate layer 17 are highly entangled with other fibers while shrunken by the heating. The disk-facing non-woven fabric layer 15, the cartridge case-facing non-woven fabric layer 16 and the intermediate layer 17 are integrally linked to one another thereby to form the cleaning sheet member 6.

In this embodiment, a first disk-facing non-woven fabric layer 15b is composed of the single fiber fabric 20 and a second disk-facing non-woven fabric layer 15a is composed of the single fiber fabrics 21, as shown in FIGS. 9 and 10. If the disk-facing non-woven fabric layer 15 is composed of a plurality of thin layers, as described above, there will be such an advantage that the unevenness in the total thickness can be reduced.

The thus obtained cleaning sheet member 6 is passed between rollers each provided with, for example, a knurling tool around the roller surface (embossing treatment), whereby an embossing pattern 23 can be formed on the cleaning sheet member 6, as shown in FIG. 3. In FIG. 2, the embossing pattern 23 is not shown for purposes of simplifying the drawing. Then, the thus embossed cleaning sheet member 6 is fixed to the case sheet member 4 by spotwise welding 12 and also by linear welding 13, as already described before.

Polyvinyl chloride sheet that makes the cartridge case 1 (case sheet member 4) softens at about 65.degree. to about 85.degree. C. and is plasticized at about 120.degree. to about 150.degree. C. and starts to melt at about 170.degree. C., as already described, while the rayon fibers in the cartridge case-facing non-woven fabric layer 16 decompose at about 260.degree. to about 300.degree. C. by heating without softening or melting. Thus, when the cleaning sheet 3 (cleaning sheet member 6) is subjected to welding to the cartridge case 1 (case sheet member 4) under some pressure, the rayon fibers 24 in the cartridge case-facing non-woven fabric layer 16 in the cleaning sheet 3 (cleaning sheet member 6) are embedded into the inside surface layer of the cartridge case 1 (case sheet member 4), while retaining the fiber form, as shown in FIG. 11. Since the cross-sectional shapes of the rayon fibers 24 are non-circular, the cleaning sheet 3 can be firmly fixed to and held in the cartridge case 1, when the rayon fibers are embedded into the cartridge case 1 (case sheet member 4).

The remaining parts of the embedded rayon fibers 24 are in an entangled state with one another and with the other fibers, or are heat sealed to one another, and ultimately the cleaning sheet 3 can be firmly fixed to and held in the cartridge case 1 thereby.

In this embodiment, the mixing ratio of the rayon fibers to the polyethylene terephthalate fibers of 3:7 by weight in the cartridge case-facing non-woven fabric layer 16 is used, but the mixing ratio can be increased, for example to about 7:3 by weight.

FIG. 12 is an enlarged cross-sectional view of the cleaning sheet 3 according to a fourth embodiment of the present invention, where the disk-facing non-woven fabric layer 15 is composed of a thick single layer made of acrylic fibers alone, differently from the third embodiment, and the intermediate layer 17 is composed of a mixed fabric of acrylic fibers and rayon fibers. In FIG. 12, the intermediate layer 17 is depicted as a layer of uniform thickness, but actually has no such a uniform layer as depicted in FIG. 12 owing to the welding of the intermediate layer 17. Other structural members are substantially the same as those of the third embodiment, and their description is omitted.

In this fourth embodiment, an embossing pattern can be formed on the surface of the cleaning sheet member 6 as shown in FIG. 5 by knurling tools to give the cleaning sheet member 6 a smooth sliding contact and a good cleanability to the magnetic disk. The present cleaning sheet member 6 can be given the function and effect similar to those of the embossing by injecting a water jet to the cleaning sheet, when prepared, to form a large number of fine perforations beside the embossing processing.

As shown in FIGS. 9 and 12, the softness, cleanability, etc. peculiar to the acrylic fibers can be fully obtained by making the thickness of the disk-facing non-woven fabric layer 15 made of acrylic fibers only at least twice the thickness of the cartridge case-facing non-woven fabric layer 16 and that of the intermediate layer 17. According to a fourth embodiment of the present invention, a magnetic disk cartridge as shown in FIG. 1 is prepared by fixing a cleaning sheet composed of a fabric of a single layer or a plurality of layers made of acrylic fibers alone to the inside surface of a cartridge case by welding, where the shape, etc. of the cartridge case and the cleaning sheet are the same as those of the third embodiment, and thus their description is omitted.

Magnetic disk cartridge was prepared, using a cartridge case to which the cleaning sheet of said third embodiment was fixed by heat sealing (Example 3).

Cuttability, cleanability, magnetic disk scratchability, lint characteristics and weldability of the cleaning sheets of Example 3 were measured in the same manner as described before and are shown in Table 2 together with those of Comparative Example, and Conventional Examples 1 and 2 as given, referring to Table 1.

As is obvious from the foregoing test results, the present magnetic disk cartridge according to Example 3 has better cuttability, cleanability, magnetic disk scratchability, lint characteristics and weldability than those according to Comparative Example and Conventional Examples 1 and 2.

According to the second aspect of the present invention, a highly integrated cleaning sheet without peeling off of the disk-facing non-woven fabric layer and the case-facing non-woven fabric layer can be prepared by the presence of an intermediate layer composed of a mixed fabric of acrylic fibers and rayon fibers, and thus the present invention can also provide a magnetic disk cartridge having a cleaning sheet remarkably improved disk-handling characteristics and cartridge case-fixing characteristics.