JP2856830B2 - Tape cassette - Google Patents

Description

The present invention relates to an improvement in a tape cassette case.

(Prior Art) A cassette case for accommodating a video tape is required to increase productivity while maintaining high accuracy and to mass-produce it in a short time.

As an example, a conventional video tape cassette accommodates a pair of tape reels 2a, 2a each having a tape wound inside a case composed of an upper case 1a and a lower case 1b as shown in an exploded view in FIG. And various guides and guide rollers, so that the tape is wound from one reel to the other reel via the front surface of the case.

Generally, such a cassette case is manufactured by injection molding of a resin. The gate system used in the conventional cassette case injection molding method is the spear gate system shown in FIG. 2 (a). A heater 5 is built in the gate, the tip 4 at the nozzle tip is an open gate, and the resin is melted or solidified by adjusting the heater power to open and close the gate, and the resin 6 is injected. At this time, a fluidized bed is formed on the resin along the heater, and a solidified layer is formed on the gate wall surface. In this gate method, the dimensional accuracy of the molded case is improved. However, in the spear gate method, the resin drips and solidifies at the tip of the gate each time injection molding is performed. Therefore, it is troublesome that the resin solidified portion must be removed at the beginning of molding, and the molding efficiency is reduced. In addition, it took time to process the solidified resin when changing the product type.

Therefore, an alternative molding method with high production efficiency is required. One of them is a valve gate method. In this gate system, as shown in FIG. 2 (b), a valve 14 is inserted into a gate 11 which is constantly heated externally, and is moved up and down to open and close the tip of a gate chip 12. This method uses chips
Since the 12 passages can be made sufficiently large, the injection pressure can be reduced, and not only can the injection work be streamlined, but also
It is possible to perform molding work much faster than the spear gate method, for example, the gate resin is good at the end of injection and the time for releasing residual pressure is not necessary, but the cooling speed is also increased due to the high molding speed There is a need. If the cooling rate is high,
Resin sink (formation of a recess due to local difference in shrinkage) occurs near the gate portion, resulting in poor appearance and reduced mechanical accuracy. For this reason, this method is hardly used for manufacturing a recording medium case.

(Object of the Invention) An object of the present invention is to provide a recording medium case with good dimensional accuracy, which avoids sink marks in a case for a recording medium formed by injection molding using a valve gate system.

(Summary of the Invention) The present invention is a tape cassette case composed of upper and lower cases which are attached to each other at a peripheral portion for accommodating a recording medium, wherein one or both of the upper and lower cases has a flat wall and the flat wall. The rib has a peripheral wall rib and an internal rib which stand upright, and a gate is set at a specific portion of the rib, and the thickness of the internal rib and the flat plate wall in the vicinity of the gate setting portion is smaller than the thickness of the ribs of the other portions. It is characterized by having done.

As described above, according to the present invention, the wall thickness of the upright rib and the flat plate wall in the vicinity of the gate is reduced as compared with the other portions, so that the problem of sink can be avoided and a highly accurate case can be provided.

(Specific Description of the Invention) Hereinafter, the present invention will be described in detail with reference to examples.

3 to 6 show an example in which the present invention is applied to the lower case 1b of the video cassette shown in FIG. FIG. 3 is a plan view of the lower case, FIG. 4 is a bottom view, FIG. 5 is a central longitudinal sectional view of FIG.
FIG. 6 is an enlarged plan view of a main part of FIG.

The lower case 1b has a configuration similar to that of the conventional lower case except for features of the present invention. The lower case has a generally rectangular flat wall 14 and has two openings 15, 16 therein for receiving the shaft of the tape reel hub. The flat plate wall 14 has a relatively thick peripheral wall rib 17 constituting an outer peripheral wall, and upright relatively thin internal ribs for reinforcing and forming a tape chamber, supporting other members, and the like, that is, front corner ribs 18 and 19. , Rear corner rib 20,
21, a front rib 22, and a central rear rib 23. In addition, there are various guide members, positioning pins, screw fixing means, and the like, but they are not directly related to the present invention, and thus description thereof is omitted.

The gate position in injection molding is usually set at a position where the flow of the molten resin is most uniform and the molding distortion is minimized. In this example, the gate position is set at a point G at the center bottom.

Injection molding using a mold with the same design as the conventional mold using the valve gate method produces a large sink near the gate because the cooling rate of the resin is higher than the conventional molding method I understood that. In the present invention, this problem is greatly improved by reducing the thickness near the gate. That is, in FIG. 6, the center rear rib 23 is formed thinner than the other internal ribs, ie, the ribs 18, 19, 20, 21, and 22. Further, a portion 24 at the center rear of the flat plate wall 14
(In this example it was part surrounded by a pair of ribs 23a for guiding the locking of the tape reels) formed thinner than the thickness d ₂ of the thick other parts of d ₁ the flat wall 14 of the.

With this configuration, an excellent lower case without sink marks can be manufactured by an injection molding method using a valve gate.

As an example, injection molding of the lower case was performed using a valve gate based on the above embodiment. The conventional example uses a VHS system video cassette using a normal mold. The case where the ribs 23 and 23a are too thin is taken as a comparative example.

 The thickness of each part was as follows.

Example Comparative example Conventional example Ribs 18-21 1.1mm 1.1mm 1.1mm Ribs 23, 23a 0.8mm 0.5mm 1.1mm Plate wall 14 2.0mm 2.0mm 2.0mm Plate wall 24 1.3mm 1.3mm 2.0mm The state of sink marks was observed. However, the examples are good,
In the conventional example, large sink marks were observed around the gate, and in the comparative example, a short shot (resin did not sufficiently flow) occurred.

(Summary of Effects) According to the present invention, in the case of a recording medium formed by injection molding using the valve gate method, it is possible to avoid a sink problem and to provide a case for a recording medium having high dimensional accuracy.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view schematically showing a magnetic tape cassette to which the present invention is applied, FIG. 2 is a sectional view showing two types of gate systems used in a conventional injection molding technique, and FIG. FIG. 4 is a bottom view, FIG. 5 is a central longitudinal sectional view of FIG. 3, and FIG. 6 is an enlarged plan view of a main part of FIG. 1a: Upper case 1b: Lower case 2: Tape reel 14: Flat wall 17: Peripheral rib 18, 19: Front corner rib 20, 21: Rear corner rib 22: Front rib 23: Center rear rib G: Gate setting position

──────────────────────────────────────────────────続 き Continuation of the front page (56) References Japanese Utility Model Showa 61-189476 (JP, U) Japanese Utility Model Showa 63-78386 (JP, U) (58) Field surveyed (Int. Cl. ⁶ , DB name) G11B 23/113 510 G11B 23/087 502

Claims (2)

(57) [Claims] In a tape cassette case for accommodating a recording medium having a flat plate wall, a peripheral wall rib standing upright from the flat plate wall, and an internal rib, a gate is set at a specific position of the rib, and a gate setting unit is provided. The thickness of the internal ribs in the vicinity is made smaller than the thickness of the ribs in the other portions, and the thickness of the flat wall in the vicinity of the gate setting portion is made smaller than the thickness of the flat walls in the other portions. Characterized tape cassette case. The case is an upper and lower case for a video tape cassette, the inner rib includes a central rib provided at a central portion of the lower case, and the gate setting portion is located at the center of the central portion at the peripheral wall rib. 2. The tape cassette case according to claim 1, wherein