JPH087571Y2 - Magnetic tape cassette - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a magnetic tape cassette, and more particularly to a magnetic tape cassette in which a case body is composed of a pair of upper and lower cassette halves made of synthetic resin.

[Prior Art] In audio equipment such as a magnetic tape recorder and video equipment such as a VTR, a magnetic tape cassette is used as a recording / reproducing medium. A typical audio magnetic tape cassette will be described below. As shown in FIG. 3, the magnetic tape cassette 21 is composed of upper and lower cassette half 21.
It is a structure in which a pair of hubs 23a, 23b wound with a magnetic tape 22 is rotatably built in and held in a case body formed by a, 21b, and the upper and lower cassette halves 21a, 21b are fixed by screws 24 at important points. It is united and fixed, and integrated as a case body. Upper and lower cassette half like this
21a, 21 are injection molded from a synthetic resin such as an acrylonitrile-butadiene-styrene copolymer resin (hereinafter referred to as ABS resin).

However, when a signal is recorded / reproduced using the magnetic tape cassette 21 using the upper and lower cassette halves 21a and 21b injection-molded of a synthetic resin such as ABS resin, the magnetic tape cassette 21 drives on the tape recorder side. There is a problem that a modulation nozzle is generated under the influence of resonance due to external vibration of the device or the like, which may adversely affect sound quality.

Therefore, in the past, the actual developments of Sho 60-183986 and 60-1839
No. 87, No. 2-46984, No. 2-68382, and JP-A-59
-117768, 62-57182, 63-271785, and the like disclose a device for improving vibration characteristics.

In Japanese Utility Model Laid-Open Nos. 60-183986 and 60-183987, the case body is formed of a vibration-damping synthetic resin.

Japanese Utility Model Laid-Open No. 2-46984 discloses a case body in which the case outer layer is made of a hard resin and the inner layer is made of a soft resin. In Japanese Utility Model Laid-Open No. 2-68382, at least a part of the case body is made of a resin composition having a vibration loss coefficient of a certain value or more.

In the case of JP-A-59-117768, the specific gravity and rigidity of the cassette half are increased by mixing a filler such as a composite agent or metal powder into the synthetic resin material that is the raw material of the upper and lower cassette halves 21a and 21b. , Which has been proposed to make it less susceptible to vibrations.

The structure disclosed in Japanese Patent Laid-Open No. 63-271785 is configured such that a synthetic resin material, which is a raw material of the upper and lower cassette halves 21a and 21b, has a highly rigid material as an outer layer and an inner layer as a low resonance vibration damping material. However, it has been proposed to improve the cassette performance by making it less susceptible to external vibrations. This structure is intended to achieve both the vibration absorbing function and the strength at the same time.

JP-A-59-117768, JP-A-62-57182, and JP-A-60-18
Those disclosed in 3986 and 60-183987 gazettes are
The case body is a single layer and has a large loss elastic modulus (E ″), that is, a material that easily absorbs vibration by converting vibration energy from the outside into heat energy by internal friction of the material itself ( The loss factor δ is large).

[Problems to be solved by the device]

However, in the vibration absorption type structure in which the cassette body is composed of a single layer, if the elastic modulus of the case body is changed, there are restrictions from the viewpoint that the constituent materials become fragile, etc. There was a limit to increase (vibration absorption).

In addition, the two-layer type case body with different elastic modulus is a vibration damping principle called unconstrained damping method because of the energy absorption due to the elongation of its constituent materials, and its loss coefficient η
Is (Here, η ₂ is the loss coefficient of the damping material, E ₁ is the Young's modulus of the base material, E ₂ is the Young's modulus of the damping material h ₁ is the thickness of the base material, h ₂ is the thickness of the damping material) Given by.

Therefore, to obtain a sufficient vibration damping effect, E ₂
It is necessary to increase the value of / E ₁ or h ₂ / h ₁ .

However, in order to increase the value of E ₂ / E ₁ , the inner and outer layers form the outer surface of the case, and it is naturally impossible to use those whose hardness and softness are not suitable for the case, and there is a limit beyond the material selection. Also, if it is necessary to increase the thickness h _{2 of the} viscoelastic material that reduces the rigidity of the case body when increasing the value of h ₂ / h ₁ to improve the vibration damping performance, The thickness h ₂ is naturally limited, and the vibration damping effect is also limited in relation to other functions of the cassette.

Therefore, the problem of the present invention is that the vibration damping ability does not depend on the thickness of the material, and the vibration damping effect can be achieved without increasing the thickness of the cassette half and without increasing the weight. It is to provide a tape cassette.

[Means for solving the problem]

An object of the present invention is to provide a magnetic tape cassette in which a magnetic tape wound around a hub is housed in a case body composed of a pair of upper and lower cassette halves, wherein the upper and lower cassette halves are composed of three layers, and the Young's modulus of the inner layer is E. _1. A magnetic tape cassette characterized by being made of a material satisfying a relational expression of E ₁ ≧ E ₃ > E ₂ , where E ₂ is Young's modulus of the intermediate layer and E ₃ is Young's modulus of the outer layer. Can be solved by.

[Embodiment]

An embodiment of an audio magnetic tape cassette according to the present invention will be described in detail below.

FIG. 1 shows the essentials of the upper and lower cassette halves 21a and 21b (the lower cassette half 21b is shown in phantom for convenience) which constitutes the case body 20 of a cassette basically similar to the magnetic tape cassette shown in FIG. Sectional view (shown in FIG. 3
A cross section corresponding to the portion along the line AA) is shown.

The upper cassette half 21a includes an inner layer 25, an intermediate layer 26, and an outer layer 2.
It is composed of 7 layers. Then, the inner layer 25
The Young's modulus E ₁ is equal to or larger than the Young's modulus of the outer layer 27. The Young's modulus of the intermediate layer 26 is made of a material smaller than that of any other layer.

That is, the Young's modulus E _{1 of the} inner layer 25 and the intermediate layer 26
Young's modulus E ₂ of, between the Young's modulus E ₃ of the outer layer 27, E ₁
It is composed of materials that satisfy the functional formula of ≧ E ₃ > E ₂ .

To manufacture the above cassette half 21a,
For example, an injection molding machine as shown in FIG. 2 can be used.

Such an injection molding machine is composed of a cassette half molding die 1 and an injection device 2 as shown in FIG.

The cassette half molding die 1 is composed of a fixed die 3 and a movable die 4, and a die inner space 5 for molding the upper cassette half 21a shown in FIG. Are formed. A gate 6 for injecting and injecting the molten resin is communicated with the space 5 inside the mold, and the molten resin is injected and injected from outside the mold through the gate 6.

The injection device 2 is a so-called screw injection device,
A heating cylinder 8 for heating and melting a molding material, a screw 13 for kneading a molten resin and injecting it into a mold, a hydraulic cylinder 10 for giving a spray output to the screw 13, and a rotational force to the screw 13 via a speed reducer 11. It has a hydraulic motor 12 for supplying and a hopper 9 for supplying a molding material to the heating cylinder 8.

Although only one screw type injection device is illustrated, actually three screw type injection devices are provided on the fixed mold 3 side. The three injection devices 2 are connected to separate injection spaces formed in the fixed mold 3 at appropriate positions. On the other hand, the movable mold 4 is configured to be rotatable around a rotation axis (not shown). By moving the movable mold 4 back and forth and rotating, a three-layer structure as shown in FIG. 1 can be formed so as to be sequentially stacked from the inner layer side.

In the present embodiment, as the molding material for molding the upper cassette half 21a, high impact styrene,
Pellet of ABS resin, AS resin, polystyrene resin, etc. 15
For example, powder 16 such as barium sulfate, lead sulfate or zinc oxide
It is possible to change the Young's modulus of each of the layers as desired so as to meet the above-mentioned conditions by using the hoppers 9 mixed in different mixing ratios.

The upper cassette half 21a by the molding machine shown in FIG.
The molding step will be described.

The molding material in the hopper 9 falls into the heating cylinder 8 due to its own weight, is kneaded by the rotation of the screw 13, and is sent to the tip of the cylinder along the groove. At this time, the molding material is heated by the heater 14 arranged on the outer circumference of the heating cylinder 8, and the frictional heat generated by the kneading action is added to increase the temperature from the inside to the molten state.

Then, as the molten resin is stored in the tip portion of the heating cylinder 8, the screw 13 is pushed backward by the reaction force (back pressure) of the material. The amount of injection can be determined (measured) by restricting the backward movement amount by a limit switch and stopping the rotation of the screw 13 at a fixed position.

Next, when an injection pressure is applied to the screw 13 by the hydraulic cylinder 10, the screw 13 serves as an injection plunger, and the molten resin at the tip of the screw 13 is applied with high pressure to the cassette half molding die 1 It shoots in. The molten resin injected into the cassette half molding die 1 is injected and injected from the gate 6 into the die inner space 5.

When the molten resin filled in the mold space 5 is cooled and solidified, the movable mold 4 is opened, and the movable mold 4 is rotated a certain amount and then moved forward in the direction of the fixed mold 3. Thus, a new injection space is formed so that the other concave portion of the fixed mold 3 covers the portion corresponding to the inner layer 25 formed in the mold inner space 5. A resin corresponding to the intermediate layer 26 is injected into this injection space.

After that, the movable mold 4 is opened, the movable mold 4 is further rotated by a certain amount, and then the movable mold 4 is advanced toward the fixed mold 3 again. A new injection space is formed by covering the layers formed again. A resin corresponding to the outer layer 27 is injected into this injection space.

Through the above three-color molding process, the upper cassette half 21a having a three-layer structure is formed.

Finally, the molded product of the upper cassette half 21a is ejected from the molding die by being ejected by a protrusion pin (not shown). The lower cassette half 21b is similarly formed.

The action of vibration damping by the three-layer structure configured as described above will be described.

This structure absorbs vibration energy by shear deformation caused by displacement between the three layers in a so-called constrained type.

The loss factor η for three layers is E ₁ and E ₃ ; Young's modulus h ₁ and h _{3 of the} inner layer 25 and the outer layer 27; Thickness h ₃₁ of the inner layer 25 and the outer layer 27; Equivalent bending rigidity = {h ₂ +12 (h ₁ + h ₃ )} / 1
2 h ₂ ; thickness of the intermediate layer 26 η ₂ ; loss coefficient of the intermediate layer 26 g; Shore parameter = fs / f G ₂ is the shear modulus of the intermediate layer 26 h ₂ is the thickness of the intermediate layer 26 ρ ₁ is the density of the inner layer 25 η ₂ ² << 4, h ₂ h ₃ << h ₁ Thus, the loss coefficient can be expressed by the above equation (1).

The equation (1) does not include the item of the thickness h ₂ of the intermediate layer 26. That is, it is understood that the magnitude of the vibration damping action is almost irrelevant to the thickness of the viscoelastic material that is the intermediate layer 26.

Further, since the vibration characteristics of the three layers are different, resonance is effectively rejected, and further, the intermediate layer 26
Since it is not sandwiched by the inner and outer layers and is not on the surface of the cassette half, it is possible to select a material having high viscoelastic properties without considering mechanical strength and the like. Therefore, the vibration damping effect can be enhanced without making the intermediate layer 26 thick.

From this, for example, a sufficient effect can be expected if the intermediate layer 26 has a thickness of about 0.1 mm or more, and sufficient damping performance can be exhibited even if the total thickness of the cassette half is suppressed within the conventional range. . Further, since the intermediate layer 25 is generally made of a material having a large specific gravity, its thickness is extremely thin, such as about 0.1 mm or more, so that the total weight does not increase, and a vibration damping effect without increasing the weight can be achieved. .

In addition, in the outer layer 27 and the inner layer 25, an additive such as an antistatic agent, an antioxidant, an ultraviolet ray inhibitor, and a dispersant or a lubricant are contained in the molding material as long as the function is not impaired. But there is no problem.

Further, the present invention is not limited to the injection molding machine used in the above embodiment, and it goes without saying that various injection molding machines can be used. Further, the resin pellets and the metal powder used as the molding material are not limited to those in the above embodiment, and can be appropriately selected.

Further, in the above-described embodiment, the case body is manufactured by three-color molding, but the intermediate and outer layers may be formed by transfer molding, and further, the inner layer and the intermediate layer may be formed by two-color molding. Alternatively, the outer layer may be formed by transfer molding.

Furthermore, although the cassette half of the magnetic tape cassette for audio has been described in the above embodiment, the present invention is not limited to the magnetic tape cassette for audio, and can be applied to various injection molded products such as video cassettes and optical disk cartridges. Needless to say.

[Effect of device]

As described above, in the magnetic tape cassette according to the present invention, the upper and lower cassette halves are composed of three layers, and the Young's modulus of the constituent material of the inner layer is equal to or larger than the Young's modulus of the constituent material of the outer layer. In addition, the Young's modulus of the constituent material of the intermediate layer is smaller than the Young's modulus of any of the other layers, so that the elastic characteristics of the respective layers are different and vibration resonance is effectively exhibited, and Since the layer is not sandwiched by the inner and outer layers and is not on the cassette half surface,
Since it is possible to freely select materials with high viscoelasticity characteristics without considering mechanical strength, etc., it is possible to exert extremely high vibration damping action without thickening the viscoelastic layer, and to absorb vibration. In this respect, the influence of the thickness of the intermediate layer can be substantially eliminated, and sufficient vibration damping performance can be exhibited without increasing the total thickness of the cassette half.

Therefore, according to the present invention, it is possible to provide a magnetic tape cassette that does not increase the wall thickness of the cassette half and does not increase the overall weight of the case body, and achieves the vibration damping effect without increasing the weight. .

〔Example〕

Hereinafter, the effects of the present invention will be made more clear by examples.

The case body having the three-layer structure shown in FIG. 2 was provided with the intermediate layer and the outer layer on the base material layer (inner layer) by two-color molding and transfer molding.

Then, the top and bottom cassette halves have a three-layer structure with a top surface thickness (thickness H in FIG. 2) of 1.6 mm. The inner layer has a thickness of 0.8 mm, the middle layer has a thickness of 0.5 mm, and the outer layer has a thickness of 0.3 m.
It was m.

In addition, for each material, the material of the acrylic stylac 767 under the trade name was used for the outer layer that acts as the material of the damping layer. The Young's modulus E (kgf / cm ² ) of this outer layer is 3,600. For the intermediate layer that acts as a viscoelastic material, a trade name elastomer Tuftec H1041 material was used. The Young's modulus E (kgf / cm ² ) of this intermediate layer is 4,000. The material of trade name GP-polystyrene G-8259 was used for the inner layer. The Young's modulus E (kgf / cm ² ) of this inner layer is 26,000.

The inner layer and the intermediate layer were formed by the two-color molding method, but the outer layer was formed simultaneously on the intermediate layer by the transfer molding method when the intermediate layer was formed.

In the measurement of the vibration absorption effect of the thus-formed cassette half, forced vibration was applied to the half at a frequency of 100 Hz, and the damping of the vibration on the peripheral surface of the hub hole portion where the hub was mounted was obtained. The results are shown in FIG. 4 (B).

As a comparative example, FIG. 4 (A) shows a conventional type of cassette half whose material is GP polystyrene G825.
A single layer molded in 9 was used.

As is apparent from FIG. 4, the cassette half according to the present invention was able to improve the vibration resistance as compared with the comparative example.

[Brief description of drawings]

FIG. 1 is a sectional view of a main part of a cassette half of a magnetic tape cassette of the present invention, FIG. 2 is a schematic sectional view showing an injection molding machine for injection molding the cassette half shown in FIG. 1, and FIG.
FIG. 4 is a perspective view of the audio magnetic tape cassette, and FIG. 4 is a graph showing a vibration damping curve. (Symbols in the figure) 1 ... Mold for cassette half molding 2 ... Injection device, 3 ... Fixed mold 4 ... Movable mold, 5 ... Space inside mold 6 ... Gate, 8 ... Heating Cylinder 9 …… Hopper, 10 …… Hydraulic cylinder 11 …… Decelerator, 12 …… Hydraulic motor 13 …… Screw, 14 …… Heater 15 …… Resin pellet 16 …… Powder, 17 …… Nozzle 20 …… Case body 21 …… Magnetic tape cassette 21a …… Upper cassette half, 21b …… Lower cassette half 22 …… Magnetic tape, 23a, 23b …… Hub 24 …… Screw, 25 …… Inner layer 26 …… Intermediate layer, 27 …… Outer layer PL …… Parting line.

Claims (1)

[Scope of utility model registration request] 1. A magnetic tape cassette in which a magnetic tape wound around a hub is housed in a case body consisting of a pair of upper and lower cassette halves, wherein the upper and lower cassette halves are composed of three layers, and the Young's modulus of the inner layer is E ₁ The magnetic tape cassette is made of a material satisfying a relational expression of E ₁ ≧ E ₃ > E ₂ , where E ₂ is Young's modulus of the intermediate layer and E ₃ is Young's modulus of the outer layer.