JPS59225938A - Preparation of reel hub - Google Patents

Abstract

PURPOSE:To obtain a reel hub having good roundness and a good flatness degree and capable of stably winding up a magnetic tape, by forming a recessed part to the outer peripheral surface of an inner annular part along the peripheral direction thereof by utilizing the molding contraction of a molding material while using the outer peripheral surface of the inner annular part as the one constitutional surface of a cavity during the molding of an outer annular part. CONSTITUTION:An inner annular part 3 is formed into a thin wall at the inner peripheral part thereof surrounding a shaft hole 2 and a thick wall at the outer peripheral part thereof. The molding of this inner annular part 3 is performed under a molding condition easily generating a sink mark such that injection pressure is low or holding pressure is low. When molding is performed under this condition, a recessed part 5 due to the sink mark is formed to the outer peripheral surface of the inner annular part 3 along the peripheral surface thereof and, subsequently, an outer annular part 4 is molded by using the outer peripheral surface of the inner annular part 3 as one constitutional surface of a cavity. The depth of the recessed part 5 is pref. about 0.05-0.2mm. and, when 0.05mm. or less, the outer annular part 4 is easily pulled off from the inner annular part 3 and, when 0.2mm. or more, inferiority such as short is easily generated on the inner annular part 3.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a cartridge glue hub for a magnetic cartridge tape such as a cassette tape or a video tape by injection molding.

The reel nop of the magnetic cartridge tape is housed in a cassette half and rotates to wind up and feed the magnetic tape. This reel hub is mainly manufactured by injection molding, and since the reel hub rotates within the cassette half, polyacetal resin, which has excellent self-lubricity and wear resistance, is preferably used as the resin material. It is being

However, since this polyacetal resin is a material with a high molding shrinkage rate, there is a large difference in the shrinkage rate based on the flow direction, and the reel hub formed from this resin has poor roundness, so the magnetic tape winding @ 9 The tension fluctuated minutely, which had an adverse effect on the tape running of the magnetic cartridge tape.

In addition, materials with large mold shrinkage tend to cause sink marks, so when molding materials with large mold shrinkage rates such as polyacetal, it is necessary to mold to suppress sink marks by setting a high injection pressure or high holding pressure. Conditions are set. However, molded products molded under such severe molding conditions are prone to cracking because the resin is excessively filled. For this reason, the reel hub made of polyacetal resin has poor flatness, which also disturbs tape running.

Therefore, in order to solve these problems, various improvements have been made to the shape of the reel hub, molding conditions, etc. However, since polyacetal resin essentially has a large shrinkage during molding, sufficient effects have not been obtained.

This invention was made in view of the above circumstances, and the roundness,
An object of the present invention is to provide a method for manufacturing a hub with good flatness and capable of stably winding a magnetic tape.

A method of manufacturing a reel hub according to the present invention will be described below with reference to the drawings.

FIG. 1 shows an example of a reel hub manufactured by the method of the present invention, and its external shape and dimensions are the same as reel hubs commonly used for cassette tapes.

In this reel hub l, an inner ring part 3 that forms a shaft hole 2 into which the reel shaft of a tape recorder is inserted is first formed by injection molding, and then an outer ring part 4 that forms the outer peripheral surface of the reel hub l is injection molded on its outer periphery. It was formed and manufactured by.

To manufacture this reel hub 1, for example, a two-color molding machine equipped with two injection cylinders is used, and the inner ring part 3 is molded on the first injection cylinder side, and the outer ring part 4 is molded on the second injection cylinder side. ◎ First, on the first injection cylinder side, polyacecool,
The inner ring portion 3 is molded from a resin having excellent self-lubricating properties and wear resistance, such as polybutylene terephthalate. As shown in the second factor, the inner ring portion 3 has a thin inner peripheral portion surrounding the shaft hole 21, and a thick outer peripheral portion. This inner ring portion 3 is molded under molding conditions that tend to cause sink marks, such as low injection pressure or low holding pressure.

When molded under these conditions, the resin in the thick portion is stretched by the thin portion, so that a recess 5 due to sink marks is formed along the outer peripheral surface of the inner ring portion 3. This recess 5 is for locking the outer ring portion 4 so that it does not come off in the axial direction of the reel hub 1, as will be described later. The depth of this recess 5 is desirably set to a maximum depth of about 0.05 to 0.2B, and if this depth is 0.051111B or less, the outer ring part 4 can be easily removed from the inner ring part 3. , also 0, 2
If it is more than this, defects such as short circuits are likely to occur in the inner ring portion 3 during molding.

On the second injection cylinder side, the outer circumferential surface of the inner ring part 3 molded in this way is used as a constituent surface of the gavita to form the outer ring part 4.
is formed. The material resin that forms this outer ring portion 4 includes:
The same materials as those used for the inner ring portion 3, such as polyacetal and polybutylene terephthalate, are preferably used, but materials different from those used for the inner ring portion 3, such as ABS and PMMA, having a relatively small molding shrinkage rate may also be used.

The outer ring portion 4 forms the outer circumferential surface of the reel hub 1 on which the tape is wound, and makes the thickness of the reel hub 1 in the radial direction 0.
5~'1WLIL. This is because if the thickness of the outer ring part 4 is less than Q, 5 iut, the material resin will hardly flow during molding, and if it is more than 2B, sink marks will easily occur in the outer ring part 4. Since the outer ring part 4 is the part that determines the roundness of the reel knob 1, the conditions for molding the outer ring part 4 are such as high injection pressure or high holding pressure to ensure that the molding material is sufficiently filled and molded. It is set so that the contraction is small.

The inner peripheral surface of the outer ring part 4 formed in this way has the inner ring part 3
A protrusion 6 is formed which fits into a protrusion 9 in a recess 5 formed by a sink mark formed on the outer peripheral surface. This fitting between the convex part 6 and the concave part 5 prevents the outer ring part 4 from coming off from the inner ring part 3.

In the reel hub 1 molded by such a manufacturing method, after the inner ring part 3 is molded, the outer ring part 4 is formed on the outer periphery of the inner ring part 3.
The roundness of the reel knob 1 is determined by the outer ring portion 4.
It is determined by molding shrinkage within the thickness dimension.

The thickness dimension of the outer ring portion 4 is sufficiently smaller than the diameter of the reel hub l, and therefore the amount of material shrinkage itself is small, so that differences in shrinkage rate based on the flow direction of the material occur in each part of the outer ring portion 4. Since the change in the shrinkage dimension is minute, the reel hub 1 has good roundness.

In addition, since it was decided to form a recess 5 due to sink marks on the outer peripheral surface of the inner ring part 3, the molding conditions when molding the inner ring part 3 were changed to 1 sink mark 10, which was set when molding a conventional reel nope. The inner ring portion 3 can be molded with good flatness because the material resin is not filled unnecessarily, and the reel knob 1 has excellent flatness.

Furthermore, the four parts 5 provided on the outer circumferential surface of the inner ring part 3 are undercuts in the direction in which the beam 1 is drawn out in the mold, but since this is formed by the 1 sink mark 1, the mold There is no need to provide a structure for handling undercuts such as slides.

For this reason, the mold can be made of pure material, thereby reducing the cost of manufacturing the mold, and the molding cycle can be shortened due to fewer mold failures.

Furthermore, since the convex portion 6 of the outer ring portion 4 fits into the recess 5 of the inner ring portion 3, the outer ring portion 4 will not come off from the inner ring portion 3 even if the reel nozzle 1 is used for a long period of time. do not have.

Although it has been explained that the ring part 3 and the outer ring part 4 are continuously molded, when manufacturing with a general molding machine equipped with one injection cylinder, after the inner ring part 3 is continuously produced, the mold Replace it with a mold for molding the outer ring part 4 of the reel hub 1,
The inner ring part 3 is inserted into this, and the outer ring part 4 is molded.
It is also possible to form ``Rhap 1''. Continuous molding in the same color is also possible.

As explained above, in the method for manufacturing a reel hub of the present invention, after the inner ring portion forming the shaft hole is molded, the outer ring portion forming the outer peripheral surface of the reel hub is molded. A recess is formed along the circumferential direction by utilizing the molding shrinkage of the molding material, and the outer circumferential surface of the inner ring where the recess is formed is used as a part of the surface of the cavity when molding the outer ring. can be wound stably,
It is possible to manufacture reel knobs with excellent roundness and flatness, and the manufactured reel hubs do not have the outer ring part detached from the inner ring part even after long periods of use, and the molds used for manufacturing are also inexpensive. It has the advantage of being useful.

[Brief explanation of the drawing]

1 and 2 show an example of a reel nozzle manufactured by the method of the present invention. FIG. 1 is a cross-sectional view, FIG. 2 is a longitudinal sectional view, and FIG. 3 is an inner ring of the reel nozzle. FIG. 1...Reel knob, 2...Shaft hole, 3
...Inner ring part, 4...Outer ring part, 5...
...concavity. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] When manufacturing the reel hub of a magnetic tape cartridge by injection molding, which has a shaft hole in the center into which the reel shaft is inserted, first an inner ring portion having the shaft hole is molded, and then the outer circumferential surface of the reel hub and the outer circumferential surface of the inner ring portion are molded. A recess is formed along the circumferential direction of the outer circumferential surface of the inner ring using the molding shrinkage of the molding material, and the outer circumferential surface of the inner ring with the recess formed is A method for manufacturing a reel hub, characterized in that the reel hub is formed as one constituent surface of a cavity during contour molding.