GB2314087A

GB2314087A - Guide roller for tape cartridge

Info

Publication number: GB2314087A
Application number: GB9711437A
Authority: GB
Inventors: Hiroshi Kaneda; Masatoshi Okamura
Original assignee: TDK Corp
Current assignee: TDK Corp
Priority date: 1996-06-11
Filing date: 1997-06-04
Publication date: 1997-12-17
Also published as: JP3027121B2; DE19723619A1; GB9711437D0; KR980004605A; JPH09330581A; CN1170206A

Description

2314087 GUIDE ROLLER FOR TAPE CARTRIDGE

BACKGROUND OF THE INVENTION

This invention relates to a guide roller for tape cartridge made by molding from a polyolefinic resin.

For tape cartridges containing, e.g., a video, audio, digital, or cleaning tape, guide rollers located along the path in which the tape travels are essential. FIG. 1 shows, as exploded, a conventional video tape cartridge of the VHS format. The cartridge comprises an upper housing half 1 and a lower housing half 7 mated to form a housing, a front lid 2 pivotally connected to the front end of the housing, a pair of reels 3, 3 contained in the housing, a length of tape wound around the reels, and guide rollers 4 disposed in two or more locations along the path in which the tape moves from one reel to the other. Numeral 5 indicates a front lid locking mechanism and 6, a reel detent mechanism.

As for the material of the guide rollers 4, polyacetal (POM) has often been used. Based on formaldehyde, the material partly decomposes and evolves a gas upon exposure to high temperature during molding. The gas disturbs intimate contact between the plastic and the mold cavity surface, impairing the surface finish of the molded part or the transferability (exact transfer of the cavity surface finish to the molded part). The gas evolution thus deteriorates the dimensional accuracy and hence the performance of the resulting guide rollers, rendering it difficult to ensure smooth tape travel. The amount of gas produced is sometimes so large that in tape cartridges being stored in a high temperature environment the tapes using metallic powder tarnish or degenerate (by rusting, etc.). Polyolefinic material, on the other hand, causes no problem attributable to gas evolution. However, when an ordinary general-purpose polypropylene (PP) material is molded into guide rollers, the low melt index, e.g., of the order of 5 g/lomin, slows down the filling of a mold with the plastic. Thus, in an incompletely filled mold, solidification proceeds, yielding molded products with a defective configuration. In addition, the existing general-purpose PP exhibits a high enough tensile elongation at break, say 200%, to hamper exact gate cutting after molding. This leaves the remainder of the mold gate on the product, necessitating secondary treatment for gate removal. For these reasons, polyolefin guide rollers have had no practical use.

The present invention is aimed at manufacturing a guide roller for tape cartridges by molding without evolution of a gas, with good moldability and high dimensional accuracy. SUMMARY OF THE INVENTION

In order to solve the problems of the prior art, the invention provides a guide roller for tape cartridge made by molding from a polyolefinic resin having a melt index of from to 30 g/10min and a tensile elongation at break of 100% or less.

BRIEF EXPLANATION OF THE DRAWING FIG. 1 is an exploded view of an ordinary videotape cartridge.

DESCRIPTION OF A PREFERRED EMBODIMENT

As a resinous material for the present invention, a polyolefinic resin is used. A resin of this plastic family does not produce a gas. Choice of a resin having specific melt index and tensile elongation at break results in improved resin flow and good gate cutting. Polyolefins suited for the purposes of the invention are polyethylene and polypropylene resins, especially polypropylene resin.

The properties required of the polyolefin resin for use in the invention are a melt index of from 10 to 30 g/10min and a tensile elongation at break of 100% or less. It is advisable that testing of the material for these properties conf orm to the methods set forth in Japanese Industrial Standards K7210 for MI and JIS K7113 for tensile elongation at break.

With the product of the invention, speedup of the molding cycle (shortening of the molding time per cycle) will possibly come up as an issue to be considered. In view of the possibility, it is particularly desired that the material have a tensile elongation at break of 50% or less.

As regards MI, a value below about 10 g/10min shows a tendency to deteriorate the resin flow and instabilize the shape of the molded part. In excess of about 30 g/10min, the resin will flow so smoothly that burring frequently occur on the product. With tensile elongation at break, a value greater than about 100% tends to invite a problem of undesirable gate cutting.

Resin materials that satisfy the above property requirements were actually used in molding experiments. The results are compared with those of conventional resins in Table 1. To our knowledge, there is no resin among commercially available polyethylene and polypropylene resins that satisfies the requirements of the invention. The resins used in the following examples were prepared by varying the conditions for manufacture.

Examples and Comparative Examples Guide rollers indicated at 4 in FIG. 1 were made from a polypropylene resin (PP of the present invention) and a polyethylene (PE of the invention), both exhibiting. a melt index of about 10 g/10min and a tensile elongation at break of about 100%. For comparison purposes, guide rollers of the same dimensions were made from a POM and a general-purpose polypropylene resin (ordinary PP).

Various properties of the products were determined, and Table 1 shows the results. Criteria for evaluations were as follows:

1 Gas 0 = no evolution; x = evolution.

2. Moldability Moldability under ordinary molding conditions:

0 = good; A resin flow slightly poor.

3. Transferability Whether the mold cavity surface is exactly reproduced on the guide roller or not. Evolution of a gas would hamper the transfer, giving surface irregularities to the latter.

0 = good; A slightly poor.

4. Gate cutting Whether the remains of the gate on the product are long or not.

0 = short; x too long.

5. Dimensional accuracy 0 = good roundness; X inferior roundness.

6. High-temperature shelf stability A metal tape was tested as a magnetic tape at a temperature of 400C and at a relative humidity of 80% and was inspected for trace of rusting.

0 = no influence; x rusted.

7. Running torque Running load was determined on a VTR unit.

0 light; minimal.

- 1 T a b 1 e 1 POM ordinary pp of PE of pp inventiorinventio Gas X 0 0 0 2 Moldab'l'ty 0 0 0 3 Transfer- 0 0 ability 4. Gate cuttng 0 X 0 C) Dimensional 0 X 0 accuracy 6. High-temp X 0 (D shelf sta b' t-tc 7. Running 0 0 0 torque As Table 1 indicates, the PP material of the present invention has no offensive smell and exhibits favorable moldability and transferability, thus giving a product of good reliability. With regard to the running torque, it.is to be noted that in terms of the specific gravity the PP material is lighter than the POM material by 35%. When the cartridge using a test guide roller is inserted into a VTR, the load that is applied by the guide roller on the tape during playback or rewinding is less with the roller of the PP material than with the roller of the POM material, the former thus adding to the reliability of the VTR.

6 Although the test results with the PP material have been discussed, similar results were obtained with the PE resin. Ordinary PP materials that show poor fluidity, gate cutting, and other undesirable properties were excluded from the tests on the products incorporated into actual tape cartridges for evaluation.

According to this invention, a guide roller for tape cartridge is made by molding from a polyolefinic resin having a melt index of from 10 to 30 g/10min and a tensile elongation at break of 100% or less. The material does not evolve a gas on molding and, with fine gate cutting, gives a product of improved dimensional accuracy. The guide roller thus obtained neither reacts with a magnetic tape nor evolves a gas during storage at high temperatures. The material being lighter in specific gravity than polyacetal, the roller involves less load of rotation and smaller torque than a polyacetal roller.

The invention thus permits the provision of a guide roller which is excellently molded with great dimensional accuracy and is highly reliable for the travel of a tape.

Clabns:- 1. A guide roller for tape cartridge made by molding from a polyolefinic resin having a melt index of from 10 to 30 g/10min and a tensile elongation at break of 100% or less.

2. A guide roller according to claim 1, wherein the polyolefinic resin is selected from the group consisting of polyethylene and polypropylene.

3. A guide roller according to claim 1, substantially as hereinbefore described.

4. Any novel subject matter or combination including novel subject matter disclosed, whether or not within the scope of or relating to the same invention as any of the preceding claims.

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