JP2000021118A - Magnetic disk cartridge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an upper shell having no warp and an excellent flatness by forming the area near the internal side of the projected portion at the circumference of the upper shell almost in the same thickness as the external side of the projected portion of circumference. SOLUTION: An upper shell 1 as the projected portion of the circumference projected annually at the center area and the internal circumference area 9 near to the internal side 7 of the projected portion 3 of circumference is formed almost in the same thickness d1 as the external side of the recessed portion 3 of the circumference. Moreover, at the center of projected portion 3 of the circumference, a rectangular abutting part 11 which abbuts against the head portion of rotating shaft is formed thicker than the internal circumference 9 so that it is projected from the internal circumference 9. Thus, at least an area near the internal side of the projected portion of circumference of upper shell is formed in the same or almost same thickness as the external side of the projected portion of the circumference. Therefore, when the upper shell is formed by the injection molding, fluidity of fused resin does not hindered at the external and internal sides of the projected portion of the circumference and the fused resin is smoothly supplied up to the center area of the projected portion of the circumference.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a magnetic disk cartridge.

[0002]

2. Description of the Related Art Magnetic disk cartridges, for example,
The 3.5-inch micro floppy disk 41 is shown in FIG.
As shown in the figure, a disk-shaped magnetic recording medium 47 is rotatably housed inside a case body composed of an upper shell 43 and a lower shell 45. The upper shell 43 and the lower shell 45 house the magnetic recording medium 47 via liners 49a and 49b, respectively. In the center of the magnetic recording medium 47, a disk-shaped center core member 53 that is convex downward is fitted. The upper shell 43 and the lower shell 45 have a magnetic recording area 5 of a magnetic recording medium which is rotated at a high speed in the case body by a magnetic head.
To record the signal to 1, in order to read the signal recorded on the magnetic recording area 51, windows that open 57 ₂ and 57 ₃ are drilled by the shutter 55. The shutter 55 includes a spring 5 mounted on the lower shell 45.
By 9, and is biased so as to close the window 57 ₂ and 57 _3.

In this magnetic disk cartridge,
As shown in FIG. 5, a circumferential convex portion 63 projecting annularly from the center of the inner surface of the upper shell 43 is loosely fitted into the circular concave portion 61 on the upper portion of the center core member 53. The lower circular convex portion 65 of the center core member 53 is loosely fitted into an opening 67 formed in the center of the lower shell 45 shown in FIG. In the magnetic disk recording / reading apparatus, a drive mechanism (not shown) is inserted through an opening 67 of the lower shell 45 of the magnetic disk cartridge, the magnetic recording medium 47 is rotated at a high speed, and the shutter 55 is driven to open the window. 57 ₂ and 57 ₃
Is opened, a signal is recorded in the magnetic recording area of the magnetic recording medium 51 by the magnetic head, and the recorded signal is read.

The magnetic disk cartridge is inserted into a magnetic disk recording and reading device, and the magnetic recording medium is rotated at a high speed in the case body. Therefore, the upper shell and the lower shell have good flatness without warpage. What you have is required. In addition, a material that is less warped and deformed during use and storage is required. Further, the magnetic disk cartridge is desired to be flat and excellent in appearance without defects such as dents and glare on the surface in terms of product quality.

The upper shell and the lower shell of the magnetic disk cartridge are injection-molded using a synthetic resin, for example, a thermoplastic resin material such as a polycarbonate resin or an acrylonitrile-butadiene-styrene copolymer resin (ABS resin). It is molded by. In this injection molding, a step of preparing a molten resin by melting a thermoplastic resin material, an injection step of injecting the molten resin into a mold, and adjusting a shape of a molded product by maintaining a pressure in the mold for a predetermined time. It is performed by continuously repeating a series of steps of a pressure holding step and a cooling step of cooling and solidifying a molded article in a mold.

Conventionally, in the injection molding of the upper shell and lower shell of this magnetic disk cartridge, molding conditions in the pressure-holding step and the cooling step are adjusted in order to prevent warpage and obtain a flat surface. ing. For example, in order to compensate for deformation of a molded product, conditions such as a holding pressure and a holding time are adjusted to suppress the warpage of the upper shell or the lower shell. However, the molding conditions in these pressure holding steps have a narrow adjustable range,
In addition, since the upper shell and the lower shell of the magnetic disk cartridge are thin and have uneven thicknesses having different thicknesses, pressure is uniformly applied to each part of the molded article in the mold. It was difficult. In addition, since there are portions having different wall thicknesses, the cooling and solidifying speeds in the respective portions are different, and the thicker portions have low cooling speeds and do not sufficiently cool and solidify even after the holding pressure and cooling steps are completed.
After being taken out of the mold, heat shrinkage occurs to cause warpage, and it has been difficult to suppress the occurrence. In particular, for the upper shell, warpage could not be suppressed only by adjusting molding conditions such as pressure holding conditions, and it was difficult to obtain a flat surface. This is because in the conventional upper shell, the central part, that is, FIG.
As shown in the enlarged cross-sectional view of FIG.
When 1A is thicker than the outside 71B and the injection of the molten resin into the mold is started, the thin outside 71B is cooled and solidified first, and the flow of the resin to the inside 71A is hindered. Filling becomes insufficient, and the inside 71A
This causes slow cooling and distortion, which causes warpage due to thermal shrinkage after removal, or causes insufficient appearance of defects such as dents and glare due to insufficient resin filling. I was

Therefore, in order to prevent warpage and obtain an upper shell or a lower shell having excellent flatness, the cycle time of injection molding has conventionally been long, and in particular, the molded article has been cooled and solidified with a sufficient cooling time. The number of mold gates is reduced from 4 to 2
A method of adjusting the flow of resin in a mold to a point or a single point, and applying a compressive force to a predetermined portion of a molded product formed in the mold to reduce the flatness of the obtained shell of the cartridge. An apparatus or a method of providing flatness adjusting means for adjustment (JP-A-9-39057) has been adopted or proposed.

In recent years, as magnetic recording media housed in magnetic disk cartridges have a high density and a large recording capacity, the rotational speed of the magnetic recording medium housed therein has become higher. In view of the rotating operation of the medium and the magnetic disk recording / reading device, a higher degree of flatness is required for the shell of the cartridge. For example, as a conventional floppy disk with a recording capacity of about 2 MB becomes a larger capacity of 200 MB or more, the required flatness also becomes −
Instead of a level of about 0.3 mm, flatness with higher precision, for example, flatness on the order of 1/100 mm is required. However, a magnetic disk cartridge satisfying such a high level of demand could not be obtained by the above-described conventional apparatus or method.

In order to increase the capacity of a conventional disk cartridge having a shape compatible with that of the 3.5-inch micro floppy disk, the upper shell is required to have the same outer diameter as that of the 3.5-inch micro floppy disk. The total thickness of a pair of disk cartridges combining the lower shell and the lower shell is 3.3
mm ± 0.2 mm. For example, if the thickness is made large like a ZIP disk which is a large-capacity recording medium, the accuracy cannot be maintained.

In addition, a high-density disk cartridge is
As described above, the rotational speed of the magnetic disk is higher than that of a conventional 3.5-inch floppy disk having a recording capacity of about 2 MB, and therefore the driving torque is higher. Therefore, the internal space of the cartridge accommodating the disk is unnecessary. It must be as uniform as possible to prevent contact. This uniformity needs to be stable with little change depending on the environmental conditions in which the cartridge is handled and the use and storage conditions. Furthermore, high-density flexible disk cartridges are required to be more stable than conventional products.

On the other hand, it is advantageous to reduce the number of gates in order to reduce the cost of the mold in the injection molding process. However, when the number of gates is reduced, the molten resin can be uniformly and rapidly injected into the mold. Otherwise, it is difficult to sufficiently fill the mold with the molten resin. However, as described above, the upper shell and the lower shell of the conventional magnetic disk cartridge have a non-uniform thickness, so that it is difficult to uniformly fill the resin in the mold, and the number of gate points is reduced. When the number is smaller, not only a molding machine having higher speed performance and the like is required, but also it becomes more difficult to adjust the warpage. In addition, appearance defects such as dents and sink marks often occur, which is sufficient for not only magnetic disk cartridges satisfying recent high-level requirements, for example, large capacity, but also conventional magnetic disk cartridges. And it was difficult to reduce the number of gates and reduce the cost of the mold.

Regarding the material of the magnetic disk cartridge, JISX62 is used as the material of the conventional 3.5 inch micro floppy disk.
No. 23 describes an ABS resin. On the other hand, JP-A-5
Japanese Patent Publication No. -2850 discloses that as a disk cartridge having excellent heat resistance, an ABS resin or the like having a heat deformation temperature of 97 ° C. or more is used as a material. In the examples described in the publication, thermal deformation in a heat treatment at 90 ° C. for 72 hours was tested, and heat resistance was evaluated.

However, in general, conventional and high-density magnetic disk cartridges are rarely stored or handled in a temperature environment of 90 ° C. or higher, and the environmental temperature encountered during normal handling and storage is at most at most. It is about 60 ° C. On the other hand, if a resin with high heat resistance is used unnecessarily,
The flowability of the molten resin at the time of molding deteriorates, which causes deterioration of the moldability.In addition, if the mold temperature is increased to maintain the moldability at an appropriate level, the molding cycle becomes longer, the productivity deteriorates, and the cost decreases. Is raised. Furthermore, when a resin containing reinforcing fibers is used, the resulting molded article has a poor appearance and is not practical, so that the price of the resin increases and causes an increase in cost. As can be seen from the examples described in the above publication, when molding is performed at a high temperature such as a mold temperature of 70 ° C., deformation occurs when the molded product is taken out, and further, deformation due to shrinkage in the process of cooling the molded product to room temperature. A problem arises. In addition, the cooling time is prolonged, which causes an increase in cost.

On the other hand, JP-A-5-314710 discloses a disk cartridge having an upper shell and a lower shell made of a crystalline resin containing a filler such as glass fiber. However, when glass fiber is blended, rigidity and heat resistance can be improved, but the appearance of the obtained molded product is deteriorated, the gate is worn, the specific gravity of the resin is high, and the unit price is high. There are drawbacks such as cost.

[0015]

Therefore, the first aspect of the present invention
It is an object of the present invention to provide a magnetic disk cartridge, particularly a large-capacity magnetic disk cartridge, which is free from warpage of an upper shell, has excellent flatness, is excellent in appearance, and is effective in reducing the cost of a mold.

A second object of the present invention is to prevent the cartridge from deforming at a storage temperature of about 60 ° C. in a practical environment, not affecting the rotation of the magnetic disk and the stability of the driving torque, Provided is a magnetic disk cartridge which does not deform even when placed in a stacked state at the time of use or use, and which is excellent in moldability at the time of injection molding and can be manufactured at low cost by using inexpensive resin. It is in.

[0017]

In order to solve the above-mentioned problems, the present invention provides a disk-shaped magnetic recording medium in which a downwardly convex disk-shaped center core member is fitted at the center, and which is provided at the center of the inner surface of the upper shell. A circumferential convex portion projecting in an annular shape is loosely fitted in a circular concave portion formed in an upper portion of the center core member, and is formed in an opening portion formed in the center of the lower shell, and formed in a lower portion of the center core member. In the magnetic disk cartridge in which the circular convex portion is loosely fitted and rotatably housed between the upper shell and the lower shell, the thickness of at least the portion near the peripheral convex portion inside the peripheral convex portion of the upper shell is reduced to the outside of the peripheral convex portion. An object of the present invention is to provide a magnetic disk cartridge characterized in that it is formed to have substantially the same thickness.

A disk-shaped magnetic recording medium having a disc-shaped center core member projecting downward is fitted at the center, and a circumferentially projecting portion projecting annularly at the center of the inner surface of the upper shell is provided above the center core member. It is loosely fitted in the formed circular concave portion, and the circular convex portion formed in the lower portion of the center core member is loosely fitted in the opening formed in the center of the lower shell, so that it is between the upper shell and the lower shell. In the magnetic disk cartridge rotatably housed, the lower shell and the upper shell have a flexural modulus of 30000 kg / cm ² or more and a heat deformation temperature of 90 ° C.
An object of the present invention is to provide a magnetic disk cartridge obtained by injection molding the above resin.

Hereinafter, the magnetic disk cartridge of the present invention (hereinafter referred to as "the cartridge of the present invention") will be described in detail.

The cartridge of the present invention has a disk-shaped recording medium rotatably housed between an upper shell and a lower shell. At the center of the disc-shaped recording medium, a disc-shaped center core member projecting downward is fitted. A circumferential projection projecting annularly at the center of the upper shell is loosely fitted into the circular recess at the top of the center core member. Further, the lower circular convex portion of the center core member is loosely fitted to an opening formed in the center of the lower shell. A liner made of a nonwoven fabric or the like is interposed between the recording medium and the upper shell and the lower shell. The upper shell and the lower shell are provided with windows for recording signals in the magnetic recording area of the magnetic recording medium and for reading the recorded signals. This window is closed between the upper and lower shells and closed by a spring-biased shutter, except when inserted into a magnetic disk recording and reading device for recording or reading signals. Have been.

[0021] In the cartridge of the present invention, the thickness at least near the peripheral convex portion inside the peripheral convex portion of the upper shell is formed substantially the same as the thickness outside the peripheral convex portion. The thickness in the vicinity of the inner side of the circumferential protrusion is -0.1 mm to +
It is preferably in the range of 0.3 mm, particularly preferably in the range of -0.05 mm to +0.05 mm. Also,
The thickness of the inside of the peripheral convex portion may be the same, or the center portion may be formed to be thick, and only the thickness near the inside may be substantially the same as the outside thickness. Furthermore, a so-called center plate or the like may be adhered to the center of the circumferential protrusion, with which the pin head of the drive shaft of the magnetic disk cartridge of the magnetic recording and reading device abuts.

In the cartridge of the present invention, the constituent material of the upper shell and the lower shell is made of a resin or a resin composition which is excellent in scratch resistance when the cartridge is taken in and out of the magnetic recording / reading apparatus and which can be obtained at low cost. desirable. In addition, these resins or resin compositions, in order to ensure the rigidity required for the upper shell and the lower shell,
Preferable flexural modulus is 23000kgf / cm ² or more, further preferably not more 25000 kgf / cm ² or more, are preferred in particular 30000 kgf / cm ² or more.

Further, a resin or a resin composition used as a constituent material of a thin cartridge is desirably one having high fluidity at the time of melting because of excellent moldability.
A resin having an MI of 5 g / 10 min or more, preferably 10 g / 10 min or more, particularly 15 to 50 g / 10 min at 10 ° C. and a load of 10 kg is preferable. For example, as shown in Table 1 showing the results of Examples and Comparative Examples described below, Styrax A
The MI of BS301 is 3 g / 220 kg at 10 kg load.
Although it is 10 minutes, since the fluidity is low, it is necessary to make the temperature of the cylinder and the mold extremely high or perform molding using a high-speed and high-pressure injection molding machine, and to increase the number of gate points (for example, 4 Point). MI 220 ° C, 1
If it is 6 g / 10 minutes or more under a load of 0 kg, molding can be performed with a conventional molding temperature and molding machine, and MI is 15 g.
It was found that if the time was / 10 minutes or more, even if the number of gate points was reduced from 4 points to 2 points, it could be handled by slightly changing the conventional conditions.

Further, in the present invention, the resin or resin composition used as a constituent material has an Izod impact strength (hereinafter abbreviated as “IZ”) in that a cartridge that is strong against damage due to falling can be obtained. , 6kgf /
cm ² or more is preferable, and especially 10 to 30 kgf /
cm ² is preferred.

In the present invention, the above-mentioned flexural modulus, heat deformation temperature, MI and IZ are respectively JIS K720
3. Values measured in accordance with JIS K 7207-A method, JIS K 7210 and JIS K 7110.

The resin or resin composition used as the constituent material is preferably a resin composition containing an ABS resin as a main material and optionally containing other components. As a constituent material mainly composed of this ABS resin, for example, ABS resin alone, A
Resin composition containing BS resin and other resin, or AB
A resin composition having a structure in which the S resin component and other resin components are uniformly dispersed mutually, that is, a resin composition having a so-called polymer alloy structure (hereinafter, referred to as “alloy resin”) may be used. Examples of the other resin include a polycarbonate resin, a polyamide resin, and PBT.

Specific examples of alloy resins include those containing ABS resin, polycarbonate resin, polyamide resin, PBT and the like as components. Of these, AB
Since the alloy resin of S resin and polycarbonate has low hygroscopicity, it is possible to obtain a cartridge having a small dimensional change even when stored at high humidity, and it is inexpensive, and has relatively low mold temperature and molten resin temperature. It is more preferable than an alloy resin of an ABS resin and a polyamide resin or an alloy resin of ABS and a PBT in that it is moldable and effective in cost reduction.

In the present invention, specific examples of the ABS resin used as a constituent material of the upper shell and the lower shell, or an alloy resin of the ABS resin and another resin, are trade names TOYOLAC 325 and 250, TOYOLAC Parel TP40.
(Above, Toray); Diapet GL-4E (Mitsubishi Rayon); Classic KU-601, AN420, 45
1, MN, MHB (Sumika ABS latex); Taflex TFX-SKU (Mitsubishi Chemical); JSR-NC
NC-475, JSR-ABS 121G, 58, 3
8R (Nippon Synthetic Rubber); Stylax-ABS 02
6, 301, 191F, 100 (Asahi Kasei Corporation); Techno ABS 830 (Techno Polymer Co., Ltd.); and the like.

In the cartridge of the present invention, the upper shell and the lower shell have a flexural modulus of 30,000 kg, particularly in order to ensure high-temperature heat resistance required in a normal use and storage environment. / Cm ² or more, preferably 30,000 to 40,000 kg / cm ² , and a heat deformation temperature of 90 ° C. or more, preferably 90 to
A resin or resin composition at 105 ° C, particularly preferably 90 to 96 ° C, is desirable. This flexural modulus is 30,000
kg / cm ² or more, and as the main material of the thermal deformation temperature of the resin or the resin composition is 90 ° C. or higher, TOYOLAC (Toray) 560, Santakku GT-10 (manufactured by Mitsui Chemicals), DENKA ABS-ML ML-40X (electric Chemical Industry), Diamond Alloy PA / ABS N-804FS (Mitsubishi Rayon), Multilon PC / ABS N-3812BX (Teijin Chemical), and the like.

Further, other components may be added to these constituent materials as needed. For example, coloring agents such as pigments and dyes; surfactants, antistatic agents such as carbon, and inorganic or organic fillers such as carbon black, carbon fibers, and fillers may be added. When wear of the gate of the mold, the gate-facing surface, etc. becomes a problem, it is preferable not to mix reinforcing fibers such as glass fibers.

When the cartridge of the present invention is manufactured by injection molding, it is preferable to mold at a mold temperature of 50 ° C. or less. If the mold temperature is high, the temperature when the molded product is removed from the molding machine will be high, and it will be deformed in the process of cooling to room temperature.The removed cartridges will be stacked and stored in containers, etc. This leads to disadvantages in production, such as deformation due to a high molding temperature and a long molding cycle. This temperature condition can be achieved by using a known cooling means or the like.

In the manufacture of the cartridge of the present invention, when the resin has low fluidity during molding and it is necessary to increase the resin temperature or the mold cooling temperature, a high-speed high-pressure, for example, an injection speed Is 250mm / se
It is preferable to use an injection molding machine having a capacity of c to 1000 mm / sec. For example, an SG machine manufactured by Sumitomo Heavy Industries, Ltd., and a UH machine manufactured by Nissei Plastic Industry Co., Ltd. may be used. In particular, when an upper shell, a lower shell, or the like is injection-molded using an alloy resin of an ABS resin and a polycarbonate resin and an alloy resin of an ABS resin and a polyamide resin as a constituent material, these injection molding machines are suitable.

[0033]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described with reference to the upper shell shown in FIGS. 1 and 2 as a specific example of an upper shell of a magnetic disk cartridge of the present invention (hereinafter, referred to as "cartridge of the present invention"). I do.

FIG. 1A shows the structure inside the upper shell 1, and FIG. 1B is an enlarged sectional view thereof. The upper shell 1 has a peripheral convex portion 3 protruding in an annular shape at a central portion,
A window 5 opening from the center to one side piece is provided. In the upper shell 1, an inner peripheral portion 9 near the inner side 7 of the peripheral convex portion 3 is formed to have the same thickness d1 as the outer side of the peripheral concave portion 3, as shown in FIG. At the center of the circumferential projection 3, a head (not shown) of a rotating shaft for rotating a magnetic recording medium when a magnetic disk cartridge is inserted into a magnetic recording / reading apparatus for recording or reading a signal. Is formed thicker than the inner peripheral part 9 so as to protrude from the inner peripheral part 9. The thickness d2 of the contact portion 11 is appropriately determined according to the height of the rotating shaft of the magnetic recording / reading device, the thickness of the center plate to be attached, and the like.
It is.

FIGS. 2A and 2B are views showing another example of the upper shell of the cartridge of the present invention. FIG. 2A shows the structure inside the upper shell 21. FIG. FIG. 2B is an enlarged sectional view of the same. As shown in FIG. 2 (b), the upper shell 21 shown in FIG.
Is formed to have the same thickness d3 as that of the outer portion 27. The upper shell 21 shown in FIG. 2 has more excellent appearance than the upper shell shown in FIG. 1 with almost no depression or illumination on the surface serving as the outer surface. Since the wall thickness becomes more uniform, it has even better flatness.

In the cartridge of the present invention, FIG.
As shown in FIG. 2 and at least the vicinity of the inside of the peripheral convex portion of the upper shell, the same thickness or almost the same thickness as the outside of the peripheral convex portion is formed. Therefore, when the upper shell is formed by injection molding, the flow of the molten resin on the outside and inside of the peripheral convex portion is not hindered, and the molten resin is smoothly filled up to the central portion of the peripheral convex portion. Therefore, the present invention, conventionally, by controlling the molding conditions such as the pressure holding conditions, to sufficiently suppress the warp, excellent flatness, and has an upper shell that is free from defects such as dents and illuminated appearance. Can be a magnetic disk cartridge, -0.3m
m, as well as a conventional magnetic disk cartridge that requires a flatness of about m,
This is effective for obtaining a magnetic disk cartridge having a high density and a large recording capacity, which requires a flatness of the order of 100 mm or less. Further, even if a mold having a small number of gate points is used, it is possible to suppress the occurrence of warpage, or to obtain a magnetic disk cartridge having an upper shell free from appearance defects such as depressions and glare. The disk cartridge also has an advantage that the die cost can be reduced.

[0037]

Examples (Example 1, Comparative Example 1) As Example 1 of the present invention, an upper shell (improved type 1) having a structure shown in FIG. 1 and an upper shell (improved type 2) having a structure shown in FIG. Further, as Comparative Example 1, the upper shell (current type) of the current 3.5-inch micro floppy disk having the structure shown in FIG. 5 was used, and the holding pressure was 450 kg / cm ² and 580 kg / c.
The production was carried out under the following injection molding conditions except that m ² and 700 kg / cm ² were changed. Injection molding conditions Resin temperature: 250 ° C Mold cooling water temperature: 30 ° C Injection filling pressure: 1700 kg / cm ² Injection filling holding time: 1.45 seconds Cooling time: 1.5 seconds Mold opening / closing time: 1.5 seconds Cycle Time: 6.0 seconds

The amount of warpage of the obtained upper shell was measured by the following method. The results are shown in FIG. Measurement of Warpage Amount of Optical Displacement Sensor (PA-1800, manufactured by KEYENCE CORPORATION) shown in FIG. 7 is provided at the center of the upper shell 72 shown in FIG.
Series), and within the range indicated by the arrow W shown in FIG.
The upper shell was moved, and its displacement was measured. The warpage amount is (+) when the upper shell 72 is warped upward as shown in FIG. 8A, and (−) when the upper shell 72 is warped downward as shown in FIG. 8B. ).

From the results shown in FIG. 3, the upper shell (improved type 1) having the structure shown in FIG. 1 and the upper shell (improved type 2) having the structure shown in FIG. It can be seen that the amount of warpage is small and the flatness is excellent as compared with the upper shell (current type).

Examples 2 to 16 Using the resins shown in Table 1, upper shells and open shells of 3.5-inch floppy disks were manufactured under the following molding conditions. The obtained upper shell and lower shell were subjected to a thermal deformation test, a drop test and a stacking test according to the following methods. Table 1 shows the results. Molding machine: Sumitomo Heavy Industries SG150, hot runner type 4-cavity mold (Note) In Examples 9, 10 and 16, cylinder temperature 2
70 ° C. Cylinder temperature: 250 ° C. Injection speed: 250 mm / sec to 300 mm / sec Mold manifold temperature: 250 ° C. Mold cooling temperature: 30 to 50 ° C. (Note) In Examples 9, 10 and 16, the mold temperature is 70 ° C. cycle. : 6 seconds Holding time: about 1 second Cooling time: 2 seconds

Thermal Deformation Test (1) Thermal Deformation Test of Upper Shell and Lower Shell Immediately after Molding Immediately after molding, a pair of upper shells and lower shells that have not yet been completely cooled are temporarily assembled and stacked in units of 10 sets to form a container. Housed inside. At this time, the temperature of the temporarily assembled upper shell and lower shell was about 55 ° C. Two days later, the stacked upper shell and lower shell were taken out of the container, and the presence or absence of deformation was visually checked. In particular, one stacked
A liner, a magnetic disk, and the like were mounted on the bottom set and the top set (type) among the 0 sets of the upper shell and the lower shell, respectively, and the driving torque of both was examined.

(2) Thermal Deformation Test of Magnetic Disk Cartridge A magnetic disk cartridge was assembled by mounting a liner, a magnetic disk and the like on the obtained upper shell and lower shell. This magnetic disk cartridge was put into a hot air tester at 60 ° C. for 120 hours to perform a hot air test, and then the difference in drive torque between the one put in the hot air tester and the one not put in the hot air tester (type) was examined. Was.

Drop test A magnetic disk cartridge assembled in the same manner as in the above-mentioned thermal deformation test was applied for 1 m so that the four corners of the cartridge hit.
From the height of the cartridge and dropped on a concrete floor. The cartridge was examined for cracks, cracks, shutter detachment, etc., and evaluated according to the following criteria. ◎ No cracks, no shutter release ○ Shrinkage is very slight, but there is no practical problem, there is no shutter release △ Cracks, shutter release sporadic × Chipping, cracks, shutter release Also occur frequently

Stacking test Fifty magnetic disk cartridges assembled in the same manner as in the thermal deformation test were stacked and left at room temperature for 5 days. After that, among the stacked magnetic disk cartridges,
The difference in starting torque between the cartridge at the bottom and the cartridge (type) at the top was examined.

The results of each test were evaluated according to the following criteria based on the difference between the driving torques examined in the tests (1), (2) and (4). ◎ In comparison with the type, the starting torque of the cartridge at the bottom shows an increase within 20% ○ Shows an increase of 21 to 50% △ Shows an increase of 51 to 70% × Shows an increase of 71% or more

[0046]

[Table 1]

In the thermal deformation test of the upper shell and the lower shell immediately after molding shown in Table 1, the flexural modulus was 28500 k.
A resin having a heat distortion temperature of 90 ° C. at gf / cm ² , a resin having a flexural modulus of at least 30,000 kgf / cm ² and a heat deformation temperature of 87 ° C. shows good results, and has a flexural modulus of 300.
Resins having a heat deformation temperature of at least 90 ° C. at a pressure of at least 00 kgf / cm ² showed particularly good results. Therefore, it can be seen that the thermal deformation of the cartridge depends not only on the thermal deformation temperature of the resin used but also on the flexural modulus.

When the storage temperature of the cartridge is as high as 90 ° C., a resin having a heat distortion temperature of 100 ° C. or more is required, which is a temperature encountered in a practical storage environment.
Although the storage stability at about 0 ° C is certainly good for the resin with a high heat deformation temperature, the results of the heat deformation test of the magnetic disk cartridge show that the heat distortion temperature is lower than that of the resin with low flexural modulus and high heat deformation temperature. When a resin having a flexural modulus of 90 to 96 ° C. and a flexural modulus of 30000 to 40000 kgf / cm ² was used, it was found that there was no practical problem in a temperature environment of about 60 ° C.

Further, in the results of the drop test shown in Table 1,
The larger the IZ, which is an index of the impact strength of the resin used,
With less cracks or cracks, and IZ of 6 kgf /
cm ^TwoIt can be seen that the above resins are desirable. Also fall
In the test, when the shutter is released, it is dropped
In addition, one of the causes is that the cartridge is deformed.
Therefore, the higher the flexural modulus, the more the shutter comes off
It turned out to be bad. Therefore, the flexural modulus is 30,000-
40000kgf / cm^TwoIt turns out that resin is good
Was.

In the results of the stacking test shown in Table 1,
Deformation due to static load also depends on the flexural modulus.If a resin with a low flexural modulus is used even if the thermal deformation temperature is high, handling in the assembly process at room temperature, or when the cartridge is pressed under something heavy on the desk, It can be seen that when the shutter is deformed, the shutter is deformed, causing a problem in product quality.

[0051]

As described above, according to the magnetic disk cartridge of the present invention, by making the thickness of the central portion of the upper shell appropriate, the warp is small, the flatness is excellent, and the surface appearance is excellent. And an upper shell. for that reason,
INDUSTRIAL APPLICABILITY The present invention is effective for obtaining a magnetic disk cartridge having a high density and a large recording capacity that requires a high degree of flatness. Further, even with a mold having a small number of gate points, the occurrence of warpage can be suppressed, or a magnetic disk cartridge having an upper shell free from appearance defects such as depressions and glare can be obtained, thereby reducing mold costs. It is effective for

Although the cartridge of the present invention has a low thermal deformation temperature of about 90 ° C., the use of a resin having a high flexural modulus makes it possible to use the resin at 60 ° C. in a practical environment.
At about the storage temperature, there is no deformation of the cartridge, no deformation of the internal space of the disk rotating part, does not affect the rotation of the magnetic disk and the stability of the driving torque, and
The cartridge of the present invention does not deform even when stacked in normal use or during the manufacturing process. Furthermore, since the cartridge of the present invention has good fluidity and uses an inexpensive resin, it can be molded at a low mold temperature in a short molding cycle, and has an advantage that it can be manufactured at low cost.

[Brief description of the drawings]

FIGS. 1A and 1B are diagrams illustrating an example of an upper shell of a magnetic disk cartridge according to the present invention, wherein FIG. 1A shows a structure of an inner surface thereof, and FIG. 1B is an enlarged sectional view thereof.

FIGS. 2A and 2B are diagrams illustrating another example of the upper shell of the magnetic disk cartridge of the present invention, wherein FIG. 2A shows the structure of the inner surface thereof, and FIG. 2B is an enlarged sectional view thereof.

FIG. 3 is a diagram showing the results of measuring the flatness of an upper shell manufactured under different pressure-holding conditions in Examples and Comparative Examples of the present invention.

FIG. 4 is a diagram illustrating main components of a conventional magnetic disk cartridge.

5A and 5B are diagrams illustrating an example of an upper shell of a conventional magnetic disk cartridge, wherein FIG. 5A is an inner view thereof, and FIG. 5B is an enlarged sectional view thereof.

FIG. 6 is a diagram illustrating a method of measuring the amount of warpage of the upper shell.

FIG. 7 is a diagram showing an optical displacement sensor used for measuring the amount of warpage.

FIG. 8A is a diagram illustrating a (+) warpage of the upper shell, and FIG. 8B is a diagram illustrating a (−) warp state of the upper shell.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Upper shell 3 Peripheral convex part 5 Window 7 Inside of peripheral convex part 9 Inner peripheral part 11 Contact part 21 Upper shell 23 Peripheral convex part 25 Inner part of peripheral convex part 27 Outside part of peripheral convex part 41 3.5-inch micro floppy disk 43 Upper shell 45 Lower shell 47 Magnetic recording medium 49a, 49b liner 51 magnetic recording area 53 center core member 55 a shutter 57 _2, 57 ₃ window 59 outer 72 upper shell inner 71B circumferential projection part of the yen spring 61 recess 63 laps protrusions 65 Entotsu portion 67 opening 69 laps protrusions 71A circumferential protrusion

Claims (2)

[Claims] 1. A disk-shaped magnetic recording medium in which a disc-shaped center core member projecting downward is fitted at the center, and a circumferentially projecting portion projecting annularly at the center of the inner surface of an upper shell is provided. The upper shell and the lower shell are loosely fitted in the circular recess formed in the upper part, and loosely fitted in the opening formed in the center of the lower shell with the circular convex formed in the lower part of the center core member. A magnetic disk cartridge rotatably housed between the magnetic disk cartridges, wherein a thickness of at least a portion near the peripheral convex portion inside the peripheral convex portion of the upper shell is formed to be substantially the same as a thickness outside the peripheral convex portion. . 2. A disk-shaped magnetic recording medium having a disc-shaped center core member projecting downwardly fitted at the center thereof is provided with a circumferentially projecting portion projecting in an annular shape at the center of the inner surface of the upper shell. The upper shell and the lower shell are loosely fitted in the circular recess formed in the upper part, and loosely fitted in the opening formed in the center of the lower shell with the circular convex formed in the lower part of the center core member. In a magnetic disk cartridge rotatably housed between the lower shell and the upper shell, the bending elastic modulus is 30,000 kg.
A magnetic disk cartridge formed by injection molding a resin having a thermal deformation temperature of 90 ° C./cm ² or more.