JP2001184833A - Magnetic tape cassette - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic tape cassette capable of preventing the sticking of a magnetic tape without impairing the antistatic effect of a friction sheet even without using an antistatic agent, enhancing the rigidity of the friction sheet, prevents the chipping of the antistatic agent by rubbing with the tape edges of the magnetic tape and assuring the durability of the friction sheet. SOLUTION: The purposes described above the achieved by having a cassette body which consists of an upper half and a lower half, a pair of take-up hubs which are rotatably housed in this cassette body and are wound with the magnetic tape of <=7.7 μm in thickness, >=120 m in maximum winding length and >=2 m/sec in maximum winding speed to a cassette body, and the friction sheet made of a polyethylene resin of >=20% in carbon content in average area density which is interposed between a pair of the taken-up hubs and at least one of the upper half and lower half.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic tape cassette, and more particularly, to preventing a magnetic tape from being charged.
The present invention relates to a magnetic tape cassette provided with an improved friction sheet for ensuring the slidability of a magnetic tape.

[0002]

2. Description of the Related Art As is well known, a magnetic tape cassette is
After fixing each end of the long magnetic tape, a pair of take-up hubs around which the magnetic tape is wound are housed in a cassette body (upper half and lower half), and at least recording and reproduction of the magnetic tape is performed. When loaded into the apparatus, only a part of the magnetic tape stretched between the pair of winding hubs is exposed to the outside of the cassette body so that the magnetic tape can be brought into contact with the magnetic head. Has become. When the magnetic tape cassette is loaded into the recording / reproducing device, the magnetic tape cassette is stretched between the winding hubs, and a part of the magnetic tape exposed from the cassette body comes into contact with the magnetic head in the recording / reproducing device,
When the take-up hub is rotated and the magnetic tape runs and slides on the magnetic head in the apparatus, the magnetic head records information on the magnetic tape and reproduces information from the magnetic tape.

In an audio magnetic tape cassette or the like, when the magnetic tape cassette is loaded into a recording / reproducing apparatus, a part of the magnetic tape exposed from a cassette main body is stretched between winding hubs and is attached to a magnetic head in the apparatus. Abut,
When the take-up hub is rotated and the magnetic tape runs and slides on the magnetic head in the apparatus, the magnetic head records information on the magnetic tape and reproduces information from the magnetic tape. In a device such as a video magnetic tape cassette having a front cover for protecting the tape, when the magnetic tape cassette is loaded into the recording / reproducing device, the front cover is magnetically driven by a mechanism in the device in conjunction with the cassette. The tape is rotated to the position where the tape is released, and a part of the magnetic tape stretched between the winding hubs is exposed from the cassette body. Then, the take-up hub is rotated, the magnetic tape runs, and slides in contact with the magnetic head in the apparatus, so that the magnetic head records information on the magnetic tape and reproduces information from the magnetic tape. It has become.

If the magnetic tape moves up and down while the magnetic tape is running, the magnetic tape does not properly contact or slide with the magnetic head, so that proper recording / reproduction cannot be performed, and there is a possibility that other troubles may occur. is there. Therefore, it is necessary to suppress the vertical movement during the running of the magnetic tape, improve the regulation accuracy of the running position of the magnetic tape, and stabilize the running performance. For this reason, conventionally, in a magnetic tape cassette using a flangeless type winding hub, a friction sheet is interposed between the winding hub around which the magnetic tape is wound and the cassette body (upper and lower halves) to form a magnetic tape. The running position (height) of the magnetic tape is regulated to adjust the running position of the magnetic tape. Further, a shaping portion (squeezing) is provided on the friction sheet, and the running position (height) of the magnetic tape is defined by the height of the shaping portion.

On the other hand, when the thickness of the magnetic tape is 10 μm or less, the tape edge of the magnetic tape becomes sharp, depending on the type of the magnetic surface and the base material. Sex matters. The magnetic surface of the magnetic tape and the surface electrical resistance value (expressed by Rs) of the base material are 1 × 10
The resistance is ⁵ to 1 × 10 ¹² Ω, and there is a problem in that there is a fear that the charging due to the friction at the time of high-speed winding may affect the head of the recording / reproducing apparatus and may cause trouble such as sticking of the magnetic tape to the mechanical parts. In particular, the longer the length of the magnetic tape,
There is a problem that the influence is increased and the charging is easily performed.

[0006] The friction sheet (hereinafter, simply referred to as a sheet) is usually formed of a high-density polyethylene resin (high-density PE) or the like, and its electric resistance is very large, and is approximately 10 ^16. It is about Ω (ohm). For this reason, the sheet itself is easily charged, and the sheet is easily charged by the contact or sliding contact between the sheet and the inner wall surface of the cassette, the magnetic tape or the winding hub, and dust is easily attached. This is further problematic because the magnetic tape and the winding hub are in sliding contact with the sheet, and peeling charging occurs.

[0007]

Therefore, there is a need for improving the durability of the friction sheet and reducing the surface electric resistance Rs. Here, the durability of the friction sheet means scraping with the tape edge,
The scraping of the sheet by the tape edge can be prevented by adopting a porous sheet as the sheet, and the problem of durability can be solved.

By the way, in order to reduce the surface electric resistance Rs of the friction sheet, the sheet is immersed in an antistatic agent such as a mixture containing a quaternary ammonium salt by utilizing the fact that the sheet is porous. It is conceivable that the sheet is impregnated with an antistatic agent by coating or the like. In the case where the antistatic agent is used to reduce the surface electric resistance Rs of the sheet as described above, the surface electric resistance Rs generally decreases as the concentration of the antistatic agent increases. However, the cost increases due to the use of the antistatic agent, and the higher the concentration, the more the amount of the antistatic agent impregnated and adhered to the sheet, so if the sheet is scraped by the tape edge, The impregnated and adhered antistatic agent is peeled off and adheres to the magnetic tape, causing contamination of the tape and the inside of the cassette, impairing appearance and product performance, and deteriorating the quality of the magnetic tape itself and the magnetic tape cassette. There was a problem.

[0009] An object of the present invention is to solve the above-mentioned problems of the prior art, and to prevent the magnetic tape from sticking without impairing the antistatic effect of the friction sheet without using an antistatic agent. Another object of the present invention is to provide a magnetic tape cassette capable of increasing the rigidity of the friction sheet, preventing the antistatic agent from being scraped by rubbing with the tape edge of the magnetic tape, and ensuring the durability of the friction sheet.

[0010]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a cassette body formed by connecting an upper half and a lower half in a lid-like manner, and a rotatable housing inside the cassette body. The magnetic tape comprising: a pair of winding hubs that are housed and wound with a magnetic tape; a pair of winding hubs; and a friction sheet interposed between at least one of the upper half and the lower half. Has a thickness of 7.
7 μm or less, the maximum winding length is 120 m or more, the maximum winding speed in the recording / reproducing apparatus or the maximum winding speed in the cassette body is 2 m / sec or more, and the friction sheet contains carbon in an average area density of 20 m / s. %
It is another object of the present invention to provide a magnetic tape cassette comprising a polyethylene resin containing at least 30% by weight or more.

Here, the polyethylene resin is a high
Part or all of the hydrogen atoms in the molecules that constitute the child compound
Is preferably a fluororesin in which is replaced by a fluorine atom.
No. In addition, the carbon content of the friction sheet
The local area density is preferably 5% or more.
That is, in the friction sheet, carbon-containing
Even if the amount is unevenly distributed, its local area density is the lowest
However, it is preferably at least 5%. In addition, the flick
The surface electric resistance of the sheet is 1 × 10 ^Three~ 1 × 1
0^FiveIt is preferably Ω.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A magnetic tape cassette according to the present invention will be described in detail below based on preferred embodiments shown in the accompanying drawings.

FIG. 1 is a partially exploded perspective view showing a schematic configuration of an embodiment of the cassette body of the magnetic tape cassette according to the present invention, and FIG. 2 is housed in the cassette body of the magnetic tape cassette shown in FIG. FIG. 1 is an exploded perspective view showing a schematic configuration of an embodiment of a magnetic tape wound around a pair of winding hubs and a friction sheet sandwiching these from both sides. As shown in these drawings, a magnetic tape cassette (hereinafter, simply referred to as a cassette) 10 is formed as a housing by being combined with a lid, and a pair of upper and lower upper halves (upper cassette half) 12 constituting a cassette main body. And a lower half (lower cassette half) 14 (see FIG. 1), and a pair of winding hubs 16 and 16 housed in the cassette body.
And a magnetic tape 18 wound around the pair of winding hubs 16, 16, and between the winding hubs 16, 16, the magnetic tape 18 wound around them, and the upper half 12, and a pair. And the friction sheets (hereinafter, also simply referred to as sheets) 20, 20 (see FIG. 2) interposed between the lower half 14 and the magnetic tape 18 wound around the winding hubs 16, 16, respectively.

As shown in FIG. 1, a pair of upper halves 1
The second half 2 and the lower half 14 have substantially the same shape, and are provided with a partition wall 26 that divides the hollow interior of the cassette body formed by these into a recording / reproducing area 22 and a hub storage area 24 (in the upper half 12, it is illustrated). Is omitted). The center of the pair of upper and lower halves 12 and 14 at the center of both sides of the hub storage area 24 in the front-rear direction of the cassette (hereinafter, the recording / reproducing area 22 is referred to as the front with respect to the hub storage area 24). A pair of spindle shaft insertion holes 28, 28 into which a pair of spindle shafts of a recording / reproducing apparatus for rotationally driving the pair of take-up hubs 16, 16 are respectively inserted symmetrically with respect to the line; Insertion hole 2
A pair of hub supporting annular ribs 28a, 28a for rotatably regulating (or supporting) the pair of winding hubs 16, 16 along the inner peripheral edges of the pair of rotation guide rollers 30, 30 at both front ends. And so on. The pair of rotation guide rollers 30 is rotatably supported by a pair of pins 30a erected on the lower half 14, respectively.

In the recording / reproducing area 22 of the pair of upper and lower halves 12, 14, the pair of capstan insertion holes 32, 32 and the pair of cassette positioning holes 34, 34 are symmetrical with respect to the center line. Etc. are perforated. Inside the pair of cassette positioning holes 34, 34 in the recording / reproducing area 22 of the lower half 14, a pair of head pins 36, 36 and the like are erected symmetrically with respect to the above-mentioned center line. Further, in the recording / reproducing area 22, a leaf spring 40 which is a plate-like support member for supporting the pressure pad 38 is provided behind the pair of head pins 36, 36, and a shield plate 42 is provided behind the leaf spring 40. ing. A magnetic head (not shown) of a recording / reproducing apparatus is inserted into the recording / reproducing area 22 from the front of the cassette at the time of recording / reproducing, at the center of the front of the recording / reproducing area 22 of the pair of upper and lower halves 12, 14. A head insertion port 44 is formed.

Then, the magnetic head is inserted into the magnetic head insertion port 4.
When the magnetic tape 18 is inserted into the recording / reproducing area 22 from the position 4, the tip of the magnetic head is pushed into the cassette 10 together with the pressure pad 38. As a result, the magnetic tape 18 is formed at the tip of the magnetic head 18 by the tension of the magnetic tape 18 stretched between the pair of head pins 36 and 36 and the pressing force of the pressing pad 38 based on the urging force of the leaf spring 40. Head gap). When performing recording / reproducing, the take-up hubs 16 and 16 engaged with the pair of spindle shafts of the recording / reproducing apparatus are driven to rotate, and the magnetic tape 18 is attached to both head pins 36,
It is stretched around 36, runs while sliding against the magnetic head, and the audio information recorded on the magnetic tape is reproduced, and conversely, the audio information is recorded on the magnetic tape.

As shown in FIG. 2, the magnetic tape 18 is wound around a pair of winding hubs 16,16. Winding hub 1
Reference numeral 6 denotes a tape winding ring 16a provided on the outer periphery, and the side surface thereof is a magnetic tape winding surface. A small piece 17 for fixing an end of the magnetic tape 18 is attached to a part of the tape winding ring 16a. A small-diameter ring 16b is formed on the inner peripheral side of the winding hub 16, and engages with the hub supporting annular rib 28a of the spindle shaft insertion hole 28 of the pair of upper and lower halves 12 and 14,
The winding hub 16 is rotatably supported and the winding hub 1 is supported.
6 is restricted from coming off the position of the spindle shaft insertion hole 28.

Here, the magnetic tape 18 used in the present invention must have a thickness of 7.7 μm or less and a maximum winding length of 120 m or more. The magnetic tape 18 has a maximum winding speed of the cassette 10 into the cassette main body (the maximum winding speed in the magnetic tape cassette manufacturing apparatus or the recording / reproducing apparatus) of 2 m / sec or more. That is, the magnetic tape 18 used in the present invention
In the case of manufacturing the cassette 10 of the present invention, the winding speed when cut by a magnetic tape cassette manufacturing apparatus such as a slitter and wound into the cassette body may be 2 m / sec or more, and a recording / reproducing apparatus may be used. When loaded into the cassette, the speed of winding into the cassette body, such as the fast-forward speed and the rewind speed, may be 2 m / sec or more. In the following description, the maximum winding speed of the recording / reproducing apparatus or the magnetic tape cassette manufacturing apparatus into the cassette main body is simply referred to as the maximum winding speed of the cassette main body. In addition, the winding speed into the cassette main body when the recording / reproducing apparatus is normally loaded and recorded / reproduced, that is, the normal recording speed and the reproducing speed may be 2 m / sec or less. Usually, it is 2 m / sec or less.

In the present invention, the magnetic tape 1 used
8 is limited to 7.7 μm or less because the thickness of 7.7
This is because a magnetic tape of μm or less has a sharp tape edge, and the durability of a member that comes into contact with the tape edge, here, a friction sheet 20, which will be described later, becomes a problem. Further, the maximum winding length of the magnetic tape 18 is 12
The reason for limiting the maximum winding speed of the magnetic tape 18 to the cassette body to 2 m / sec or more is 0 m or more because the magnetic surface of the normal magnetic tape 18 and the surface electric resistance value (Rs ) Is from 1 × 10 ⁵ to
It is 1 × 10 ¹² Ω, and when a long tape is entangled or when it is entangled at a high speed, it is charged by friction, so that it may affect the head of the recording / reproducing device or stick to the mechanical parts of the magnetic tape. There is a problem of fear, especially,
This is because the longer the length of the magnetic tape is, the larger the effect is, and there is a problem that the magnetic tape is easily charged.

The magnetic tape 18 used in the present invention is not particularly limited as long as it has the above-mentioned thickness and length, and the winding speed into the cassette body may be the above-mentioned maximum winding speed. May be something.
That is, the material and use of the magnetic tape of the cassette of the present invention are not particularly limited. Accordingly, there is no particular limitation on the base material or magnetic material used, and any material may be used as the base material or magnetic material. Examples of the magnetic material of the magnetic tape used in the present invention include all conventionally known magnetic materials used for conventionally known magnetic tapes. Examples of the magnetic tape used in the present invention include general magnetic tapes in which such a magnetic material is closely adhered to a base material and slit to a certain width. In particular, it is preferable that a special coating is not applied to the edge of the magnetic tape after the magnetic tape is slit.

Examples of the base material of the magnetic tape used in the present invention include all conventionally known base materials used for conventionally known magnetic tapes. A preferred base material is PET (polyethylene terephthalate). ), Resins such as PEN (polyethylene naphthalate) and aramid. The thickness of the magnetic layer is preferably from 2 μm to 6 μm, and more preferably from 2 μm to 4 μm. The lower limit of the thickness of the magnetic tape is not particularly limited,
Preferably it is 3 μm or more. The magnetic tape used in the present invention has a Young's modulus of 500 kg.
/ Mm ² or more.

Further, as shown in FIG.
Are wound between the winding hubs 16 and 16 and the inner wall surface of the cassette 10 (between the winding hub 16 and the upper half 12 and between the winding hub 16 and the lower half 12, respectively). , 20. These sheets 2
0 and 20 are the four small holes 20a respectively drilled.
Are fitted to the four ribs 12 a and 14 a of the upper half 12 and the lower half 14 shown in FIG. 1 to be positioned and attached to the upper half 12 and the lower half 14. Also, the sheets 20 and 20 have upper and lower halves 1
A pair of insertion holes 20b, 20b are drilled corresponding to the two spindle shaft insertion holes 28, 28, respectively.

Further, the friction sheets 20, 20
Are two shaping portions 20c and 20d in the cassette left-right direction (the direction orthogonal to the front-rear direction of the cassette 10).
have. The sheets 20, 20 are taken up by the winding hubs 16, 1
6 reduces the sliding resistance when rotating, smoothes the rotation, and forms the magnetic tape 18 by the shaping portions 20c and 20d.
Supports the take-up hub 16 around which is wound, and also serves to regulate the height. In the above-described example, the friction sheet 20 made of the carbon-containing polyethylene resin includes the magnetic tape 18 and the pair of winding hubs 16, 16 and the upper half 1.
2 and between the lower half 14 and the lower half 14, but the present invention is not limited to this, and may be interposed only in either one.

The friction sheet 2 used in the present invention
0 needs to be made of a polyethylene resin containing 20% or more of carbon in average area density or 30% or more in weight density. Here, the friction sheet 2 of the present invention
If the polyethylene-based resin contains 30% or more by weight of carbon in the polyethylene-based resin in order to produce No. 0, a desired effect of reducing the surface electric resistance can be obtained. Further, the effect of reducing the surface electric resistance value depends on the amount of carbon distributed in the friction sheet when the polyethylene resin is molded as a friction sheet. Content is 20 in average area density
% Can be specified. The more preferable carbon content in the polyethylene resin in the friction sheet 20 is 30 to 90% in average area density, and the more preferable carbon content is 70 to 90% in average area density.
90% is good. Here, in the present invention, the polyethylene-based resin sheet is used as the sheet 20 because even if the magnetic tape 18 has a thickness of 7.7 μm or less and the tape edge is sharp, the sheet is not scraped due to contact with the tape edge. This is because the durability of the sheet can be secured. Since the durability of the sheet 20 can be further improved, the sheet 20 is more preferably a porous sheet.

In the sheet 20 used in the present invention,
The reason why carbon is contained at an average area density of 20% or more or a weight density of 30% or more is that the surface electric resistance can be reduced and the sticking of the magnetic tape can be eliminated. That is, even if the magnetic tape 18 has a maximum winding length of 120 m or more and a maximum winding speed of 2 m / sec or more into the cassette body, it is charged by friction when a long magnetic tape is wound or when it is wound at a high speed. This is because failures such as the influence on the head of the recording / reproducing apparatus and the sticking of the magnetic tape to the mechanical parts can be prevented. Here, the carbon content is 20% in average area density.
If it is less than 30% or less than 30% in weight density, not only is the antistatic effect of carbon lowered, but also rigidity is not increased, and the effect cannot be expected when scraping or abrasion at the tape edge is taken into consideration. . When the magnetic surface of a normal magnetic tape or the surface electric resistance of the base material is 1 × 10 ⁵
１1 × 10 ¹² Ω. When the surface electrical resistance of the mechanical component of the magnetic tape is high, it is easy to be charged.
By containing carbon in an amount of 30% or more by weight or 30% or more by weight, the surface electric resistance of the sheet 20 can be reduced without using an antistatic agent, and not only can the sticking of the magnetic tape 18 be prevented, but also the This is because the rigidity of a sheet made of polyethylene resin such as high-quality polyethylene is increased, and the sheet becomes extremely strong against scraping.

By containing 20% or more of carbon at an average area density or 30% or more at a weight density in this way, the longer the sheet or the higher the speed at which the sheet is rolled up, the more easily the sheet in contact with the magnetic tape 18 is charged. It is preferable that the surface electric resistance value of No. 20 is greatly reduced from approximately 10 ¹⁶ Ω of high-density PE, for example, to 1 × 10 ³ to 1 × 10 ⁵ Ω. By doing so, the sheet 20
It prevents or reduces the adhesion of dirt, dust, and dirt to itself, reduces the electrification of the magnetic tape 18, and prevents the influence on the head of the recording / reproducing apparatus and the sticking of the magnetic tape 18 to the mechanical parts. Because you can. Further, for example, the use of an antistatic agent such as a mixture containing a quaternary ammonium salt can be made unnecessary, and peeling of the antistatic agent and unnecessary harm caused by an unnecessary antistatic agent can be eliminated. For example, side effects of the antistatic agent 58 such as transfer of the antistatic agent 58 to a magnetic tape can be improved, the appearance can be maintained, and the product performance is not impaired. In the present invention, the method of measuring the surface electric resistance of the magnetic tape and the friction sheet is based on JIS.
A method based on X6130 can be employed.

In the friction sheet 20 used in the present invention, it is preferable that carbon is uniformly dispersed in the polyethylene resin and there is no local variation, but the dispersion is extremely uniform and the content does not vary. Since it is costly and time-consuming to produce a sheet by producing a carbon-added polyethylene resin, a sheet made of a polyethylene resin having a slight variation in carbon content may be used. However, in the friction sheet,
Even if the carbon content is locally uneven, the local area density is preferably at least 5% or more, that is, the local area density of the carbon content is preferably 5% or more.

Here, the friction sheet 20 of the present invention
Examples of the polyethylene-based resin used in the production of polyethylene include polyethylene (PE) resin, polyethylene terephthalate (PET) resin, and the like.

Further, the polyethylene resin used for the sheet 20 of the present invention is a fluorine-substituted polyethylene resin in which some or all of the hydrogen atoms in the molecules of the polyethylene resin composition are substituted with fluorine atoms. preferable. Examples of such a fluorine-substituted polyethylene resin include polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and polyvinylidene fluoride (PVDF). ) Etc. can be given. As described above, by using the fluorine-substituted polyethylene resin as the polyethylene resin for producing the sheet 20 used in the present invention, the coefficient of kinetic friction of the sheet 20 can be reduced, and the slidability of the magnetic tape can be improved. . For example, the value of the dynamic friction coefficient μ of the PE resin is about 0.22 to 0.35, while the value of the dynamic friction coefficient μ of the PTFE resin is about 0.2.
20 to 0.27. Therefore, instead of PE resin, P
By using TFE resin, the dynamic friction coefficient is reduced,
The slidability of the magnetic tape can be improved.

Examples of uses of the magnetic tape of the present invention include conventionally known uses such as a magnetic tape for audio, a magnetic tape for video, and a magnetic tape for computer backup. That is, the magnetic tape cassette of the present invention is not limited to the above-described audio magnetic tape cassette. For example, a magnetic tape cassette having a front cover and protecting a magnetic tape exposed forward, for example, a video (VHS) ) Magnetic tape cassette, an 8 mm cassette, a magnetic tape cassette having a front lid and a slider for protecting the magnetic tape exposed to the front, for example, a digital audio tape cassette (DA)
T) and digital data storage (DDS).

In the case where the state of use is determined, such as a video magnetic tape cassette or 8 mm cassette, a digital audio tape cassette, or a digital data storage, the take-up hub, the magnetic tape and the like are placed from below. The supporting side, that is, the lower friction sheet is preferably a carbon-containing sheet, and more preferably a carbon-containing fluorine-substituted polyethylene resin sheet. This is because the friction sheet on the lower side has a higher frictional force and a higher sliding force than the upper side, so that the antistatic effect by containing carbon greatly works. This is because the effect of improving the properties also greatly works.

The magnetic tape cassette according to the present invention has been described in detail with reference to various embodiments.
The present invention is not limited to the above embodiments, and various improvements and design changes may be made without departing from the spirit of the present invention.

[0033]

As described in detail above, according to the present invention,
The surface electric resistance of the friction sheet can be reduced, and the electrification of the magnetic tape that slides with it can be reduced, preventing the influence on the head of the recording / reproducing device and the sticking of the magnetic tape to the mechanical parts. In addition to preventing or reducing the adhesion of dust and dirt to the friction sheet, the rigidity of the friction sheet is increased, making it extremely resistant to scraping due to rubbing with the tape edge of the magnetic tape. Therefore, the durability of the friction sheet can be ensured.

Further, according to the present invention, an antistatic agent such as a mixture containing a quaternary ammonium salt can be made unnecessary, and the amount of the antistatic agent impregnated in the sheet can be reduced. It is possible to eliminate side-effects caused by peeling of the anti-static agent and unnecessary unnecessary anti-static agent, for example, it is possible to improve the side effect of the anti-static agent such as transfer of the anti-static agent to a magnetic tape, and to maintain the appearance. And does not impair product performance.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view of an embodiment of a cassette main body of a magnetic tape cassette according to the present invention.

FIG. 2 is an exploded perspective view of an embodiment of the magnetic tape wound around a pair of winding hubs and a friction sheet sandwiching these from both sides, which are housed in a cassette main body of the magnetic tape cassette shown in FIG. is there.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Magnetic tape cassette 12 Upper half 12a, 14a Rib 14 Lower half 16 Take-up hub 16a Tape take-up ring 16b Small diameter ring 17 Small piece 18 Magnetic tape 20 Friction sheet 20a Small hole 20b Insertion hole 20c, 20d Shaping part 22 Recording / reproducing area 24 Hub storage area 26 Partition wall 28 Spindle shaft insertion hole 28a Hub support annular rib 30 Rotation guide roller 30a Pin 32 Capstan insertion hole 34 Cassette positioning hole 36 Head pin 38 Pressure pad 40 Leaf spring 42 Shield plate 44 Magnetic head insertion hole

Claims (1)

[Claims] A cassette body formed by joining an upper half and a lower half in a lid-like manner; a pair of winding hubs rotatably housed in the cassette body and wound with a magnetic tape; The magnetic tape has a pair of winding hubs and a friction sheet interposed between at least one of the upper half and the lower half. The magnetic tape has a thickness of 7.7 μm or less and a maximum winding length of 120 m or more. A magnetic tape cassette, wherein the maximum winding speed in the cassette body is 2 m / sec or more, and the friction sheet is a polyethylene resin containing carbon in an average area density of 20% or more.