A tape cassette having tape guides made of polyethylene

Abstract: Tape cassette tape guides are moulded from a complex material of super macromolecular weight polyethylene-based resin having a molecular weight of from 500,000 to 1,000,000 mixed with polyphenyl sulfide resin or polybutylene terephthalate resin and carbon black of 1 to 15% by weight in order to reduce manufacturing costs.

Description: The present invention generally relates to tape cassettes and, more particularly, is directed to a tape cassette having stationary tape guides made of polyethylene-based resin. A tape cassette utilised in a video deck or the like is provided with stationary tape guides which come in contact with a magnetic tape so that the movement of the magnetic tape is stabilised. The stationary tape guides are positioned at opposite ends of a front wall of the cassette casing so that the magnetic tape is extended along the front wall of the tape cassette. Referring to figure 1 of the accompanying drawings which shows an example of a known tape cassette, there is shown a cassette casing 1 which is generally made of acrylonitrile butadiene styrene (ABS) resin. A pair of tape reels 2 are rotatably provided within this cassette casing 1. A magnetic tape 3 is supplied from one tape reel 2, contacted with and guided by a tape guide 4, withdrawn to the outside of the front wall of the cassette casing 1, contacted with, guided by the other tape guide 4 and is then taken up by the other tape reel 2. The tape guides 4 provided in the tape cassette are formed so as to come in contact with the rear surface of the magnetic tape (ie, tape base side) and the tape guides are unitarily formed with the cassette casing or the tape guides are made of a plastic material (see Japanese patent laid-open gazette number 61-110388) or made of metal and are inserted into and secured to the inside of the cassette casing. Further, Japanese patent laid-open gazette number 55-70976 describes such a tape cassette in which there are used as the tape guides rollers made of polybutylene terephthalate (PBT) resin. Most of the stationary type tape guides of the prior-art tape cassettes are made of metal because the metal tape guides are relatively low friction, long wearing, and have high durability compared to the magnetic tape. In that case, however, from the very nature of the metal material, the end face of the tape guide or the cylindrical face of the tape guide must be finished by a mechanical finishing-process. This brings about the following shortcomings and disadvantages: 1.The tape guides become very expensive; 2. A highly sophisticated technique is required to increase the accuracy in the surface-finishing process thereof. That is, if the surface of the tape guide is made too smooth, then build up of a static charge can occur, which causes the magnetic tape to be electrically attracted to the tape guide. Conversely, if the surface of the tape guide is too rough, the magnetic tape will be rapidly worn or damaged due to friction with the tape guide; and 3. If a convex shaped scratch occurs on the surface of the tape guide, the material of the tape guide is so hard that the magnetic tape is liable to be severely damaged. Thus, it becomes very important to inspect the tape guides during production for such flaws. Some of these disadvantages are reduced by the use of polyethylene having a molecular weight of from 500,000 to 1,000,000, as described in document EP-A-0,342,622,upon which the preamble of claim 1 is based. Other compositions which include polyethylene having a molecular weight of 500,000 are also known, such as from document JP-A-61-285,256. In that document the composition which is mostly polyphenylene sulphide has both self-lubricating properties and good abrasion resistance. Accordingly, it is an object of the present invention to provide an improved tape cassette having tape guides based on polyethylene in which the aforenoted shortcomings and disadvantages of the prior art can be reduced or substantially eliminated even further. More specifically, it is an object of the present invention to provide a tape cassette having tape guides which can be made at low cost. Another object of the present invention is to provide a tape cassette having tape guides in which it is unnecessary to employ a surface-finishing process involving a high degree of technical difficulty. A further object of the present invention is to provide a tape cassette having tape guides in which the inspection of products can be simplified. According to the present invention there is provided a tape cassette having tape guides comprised of a super macromolecular weight polyethylene-based resin whose molecular weight falls in a range of from 500,000 to 1,000,000, characterised in that the guides further comprise carbon black and one of polyphenyl sulphide resin and polybutylene terephthalate resin, wherein the mixing ratio of the polyphenyl sulphide resin or the polybutylene terephalate resin is in the range of from 5 to 40% by weight. The invention will be further described by way of non-limitative example with reference to the accompanying drawings, in which:- Figure 1 is a plan view of a conventional tape cassette, and to which reference will be made in explaining the function of tape guides thereof; Figure 2 is a graph of a molecular weight versus friction coefficient characteristic used to explain a first embodiment of the present invention; Figure 3 is a graph of the number of tape running versus friction coefficient characteristic used to explain the first embodiment of the present invention; Figure 4 is a table used to explain the present invention; and Figure 5 is a table used to explain the present invention. Referring to the drawings in detail, and initially to figures 2 and 3 thereof, a first embodiment of the present invention will be described hereinafter. The most effective way of removing the first disadvantage of the prior art is to change the material from metal to resin and to mould the resin tape guide. The applicants have experimented with sample, stationary tape guides moulded from various resins, and have found that the friction and abrasion relative to the magnetic tape are large. A suitable resin for tape guides was difficult to find. However, as a result of experiments repeatedly performed, it became clear that a friction characteristic and quality equivalent to those of the metal tape guide could be obtained by the combination of a polyethylene-based resin of super molecular weight and carbon black. Preferably, the molecular weight of super molecular weight polyethylene-based resin falls in a range of from 500,000 to 1,000,000. If the molecular weight is smaller than 500,000, the magnetic tape is damaged considerably, and the friction coefficient tends to increase as shown in Fig. 2. Further, if the molecular weight is larger than 1,000,000, then the molding-process thereof becomes difficult and a tape guide of such resin is too soft from a mechanical strength standpoint and the tape guide is easily deformed. The mixing ratio between the super macromolecular weight polyethylene-based resin and carbon black is in a range of from 1 to 15 percent by weight and the surface electrical resistance is 10² to 10¹²Ω. If the mixing ratio and the surface electrical resistance are selected as described above, the super macromolecular weight polyethylene-based resin presents stable characteristics. Polyacetals (polyoxymethylene-POM) are frequently utilized as a slidable resin material. Polyacetals bring about serious tape damage from friction relative to the tape and tend to increase drop-out, fluctuation of level and so on. Further, in the case of polyacetals, depending on the tape base material, the friction coefficient relative to the number of tape running is rapidly increased as shown in Fig. 3 with the result that the movement of the tape is stopped. However, the combination of super macromolecular weight polyethylene-based resin with the carbon black overcomes these problems. The friction coefficient relative to the number of tape running for this combination is presented as shown in Fig. 3. As a result of the applicant's investigations, it was noted that of the super macro molecular polyethylene-based resins, LUBMER (trade name) manufactured by Mitsui Petrochemical Industries, Ltd., achieved the most powerful effects. The tape guides molded by this resin can remove the second and third defects of the prior art mentioned above because the surface finishing thereof becomes satisfactory and the uneven surface condition can be removed. This allows the inspection process of products to be simplified. Even if a convex-shaped scratch exists on the surface of the tape guide, the tape guide is soft because of the nature of the resin so that damage to the magnetic tape is suppressed to a minimum. As described above, according to the first embodiment of the present invention, since the tape guide is made by the super macromolecular polyethylene-based resin having a molecular weight of 500,000 to 1,000,000, the manufacturing cost of the tape guide can be reduced and it is unnecessary to provide a surface finishing requiring a high degree of technical difficulty. In addition, the inspection-process of the product can be simplified. Further, according to the experimental results, it was concluded that a good friction characteristic and quality of the tape guide can be maintained by the combination of the super macromolecular weight polyethylene-based resin, polyphenyl sulfide (PPS) resin and carbon black. The mixing ratio of PPS resin is in a range of from 5 to 40 percent by weight, the mixing ratio of carbon black is in a range of from 1 to 15 percent by weight and the surface electrical resistance is in a range of from 10² to 10¹²Ω with stable characteristics being achieved. As a result of examination, it was again noted that as the super macro molecular polyethylene-based resin, LUBMER (trade name) manufactured by Mitsui Petrochemical Industries, Ltd., achieved the most powerful effects. As is clear from Fig. 4, the PPS resin can compensate for the disadvantage of the super macromolecular weight polyethylene-based resin in which it is too soft and it is inferior in form accuracy, and can form the tape guide without degrading the sliding characteristic thereof. In Figs. 4 and 5, an open circle having an open circular center represents an excellent result, an open circle represents a good result and an open triangle represents an ordinary result. As described above, according to the second embodiment of the present invention, since the tape guide is made by the combination of super macromolecular polyethylene-based resin having a molecular weight of 500,000 to 1,000,000 and polyphenyl sulfide resin, the manufacturing cost of the tape guide can be reduced and no surface finishing requiring a high degree of technical difficulty is necessary. In addition, the inspection-process of the product can be simplified. Furthermore, according to the experimental results of a third embodiment according to the present invention, it was concluded that a good friction characteristics and quality of the tape guide can be maintained by the combination of the super macromolecular weight polyethylene-based resin, polybutylene terephthalate (PBT) resin and carbon black. The mixing ratio of PBT resin is in a range of from 5 to 40% by weight, the mixing ratio of carbon black is in a range of from 1 to 15% by weight and the surface electrical resistance is in a range of from 10² to 10¹² Ω with stable characteristics being achieved. According to the combination of super macromolecular weight polyethylene-based resin, the PBT resin and the carbon black of the third embodiment, the friction coefficient relative to the number of tape running is presented as shown in figure 3, and thus the above mentioned shortcomings can be overcome. As described above, according to the third embodiment of the present invention, since the tape guide is made by the combination of super macromolecular polyethylene-based resin having a molecular weight of 500,000 to 1,000,000 and PBT resin, the manufacturing cost of the tape guide can be reduced and a surface finishing requiring a high degree of technical difficulty is unnecessary. In addition, the inspection-process of the product can be simplified. The applicants have found that suitable commercially available resins for practicing this invention are M2900 brand polyphenyl sulfide resin manufactured by Toray-Philips of Japan and PBT 1100P brand polybutylene terephthalate resin manufactured by Toray.

Claims: A tape cassette having tape guides comprised of a super macromolecular weight polyethylene-based resin whose molecular weight falls in a range of from 500,000 to 1,000,000, characterised in that the guides further comprise carbon black and one of polyphenyl sulphide resin and polybutylene terephthalate resin, wherein the mixing ratio of the polyphenyl sulphide resin or the polybutylene terephalate resin is in the range of from 5 to 40% by weight. A tape cassette according to claim 1, wherein the mixing ratio of the carbon black falls in a range of up to 15% by weight. A tape cassette according to claim 1 or 2, wherein the surface electrical resistance of the tape guide material mixture lies in a range of from 10² to 10¹² Ω. A tape cassette according to any one of the preceding claims, wherein the tape cassette further comprises a front wall and the tape guides are used as respective end guides by which a tape is extended along the front wall. A tape cassette according to claim 4, wherein the tape guides are stationary tape guides.

Inventors: HATAKAWA KAZUHIKO C O SONY COR, SATO SHINYA C O SONY CORPORATI, HATAKAWA, KAZUHIKO, C/O SONY CORPORATION, SATO, SHINYA, C/O SONY CORPORATION
Applicants: SONY CORP, SONY CORPORATION
Application year: 1990
Main classification: G11B23
IPC codes: C08L23, G11B23