JPH0521754Y2 - - Google Patents

Description

[Detailed explanation of the idea]

[Industrial Field of Application] The present invention relates to an improvement of a guide sheet for preventing the magnetic tape of cassette tapes such as audio cassettes and video cassettes from sagging. [Prior Art and its Problems] Cassette tapes such as audio cassettes and video cassettes are provided with guide sheets made of an elastic material to prevent the magnetic tape from sagging at openings and the like. Conventionally, such guide sheets have been used in the form of sheets made of resilient plastics such as polyethylene, polyethylene terephthalate, polyamide, and unstretched polycarbonate. Since this guide sheet is always used in a bent state, there is a problem in that its repulsion does not last for a long period of time and gradually weakens until it becomes unable to prevent the magnetic tape from sagging, especially in high-temperature environments. This tendency was noticeable. [Means for Solving the Problems] Therefore, the inventor of the present invention discovered that by using a specific polycarbonate, the rebound resilience can be maintained for a long period of time, leading to the present invention. That is, the present invention relates to a guide sheet that can maintain rebound resilience for a long period of time, and is a guide sheet for preventing the magnetic tape from sagging at the opening of a cassette case, etc. It is characterized by being made of polycarbonate whose bending load is 0.7 times or more the initial value. The polycarbonate guide sheet of this invention is
The thickness is usually 50 to 250μm, and the bending load after being held in a bent state for 100 hours at 100℃ is 0.7 of the initial value.
It is more than twice as large as the previous model, which is about 0.2 times or less. The bending load is approximately proportional to the rebound resilience, and a small decrease in the bending load over time means that the decrease in the rebound is small, that is, the rebound resilience continues for a long period of time. Therefore, in the guide sheet of the present invention, the force for pressing the magnetic tape is less reduced, and sagging of the magnetic tape can be prevented for a long period of time. For example, such a guide sheet can be made by heating a sheet of conventionally used polycarbonate to a temperature of 160°C.
It is obtained by uniaxial stretching at a temperature of ~230°C and a stretching ratio of 5 to 300%. In the present invention, conductive powder such as carbon or graphite may be mixed to prevent static electricity, and the amount of the mixed powder is usually 25 parts by weight or less, preferably 10 to 25 parts by weight, per 100 parts by weight of polycarbonate. Department. In addition, to reduce the coefficient of friction of the guide sheet, a low-friction material such as polytetrafluoroethylene, molybdenum disulfide, or polyethylene may be added, or a sheet of the low-friction material may be placed in the portion that contacts the magnetic tape. It is also possible to perform friction reduction treatment such as bonding them together. When the low-friction material is mixed, the amount thereof is usually 30 parts by weight or less, preferably 5 to 20 parts by weight, based on 100 parts by weight of polycarbonate. Hereinafter, examples of the present invention will be explained with reference to the drawings. In Figures 1 and 2, cassette case 1
A feed-out reel 2 and a take-up reel 7 are provided at predetermined intervals within the reel, and a magnetic tape T is wound around each reel 2, 7, and the magnetic tape T is guided by a plurality of guide pins 3, 4, 5, and 6. At this time, the bent guide sheet 8 is pressed against the magnetic tape T at the positions of the guide pins 3 and 6. By providing the guide sheet 8 in this way, it is possible to prevent the tape T from sagging in the vicinity of the cassette opening even when the reels 2 and 7 are in a free state. The bending load and bending state in the present invention are defined as follows. As shown in Figure 3, the temperature is 25℃
Depth (H) 5mm, width (W) in an atmosphere of
The guide sheet 8 is placed on a mold 20 having a 20 mm cavity so that the longitudinal direction of the guide sheet 8 coincides with the width direction of the cavity, and a load M is applied to the center of the guide sheet 8. The load M is gradually increased, and the load (minimum necessary load) when the bottom 21 of the cavity and the guide sheet 8 make contact for the first time is defined as the initial bending load M ₁
That's what it means. Further, the state of the guide sheet 8 at that time is referred to as a bent state. In this invention,
After applying a load M ₁ and storing it in an atmosphere at 100°C for 100 hours, the load M ₁ is removed and the bending load M ₂ is determined in an atmosphere at 25°C. In the guide sheet according to the present invention, M ₂ /M ₁ (hereinafter referred to as bending load ratio) is 0.7 times or more, preferably 0.8 to 1 times. The bent state here refers to the state of the guide sheet when measuring the bending load.
It does not necessarily indicate the state when actually applied to a cassette tape. [Example] Hereinafter, the present invention will be explained with reference to an example. Example 1 200 pieces of polycarbonate film with a thickness of 150 μm
It was uniaxially stretched to 100% at ℃ and cut out into a size of 15 x 30 mm to obtain a guide sheet of the present invention having a thickness of 105 μmm. Examples 2 to 5 Example 1 except that the stretching conditions are as shown in Table 1.
A guide sheet was obtained in the same manner. Comparative Example 1 A guide sheet was obtained in the same manner as in Example 1 except that the stretching temperature was 100°C. Comparative Example 2 An unstretched polycarbonate film with a thickness of 150 μm was used as a guide sheet. Comparative Example 3 A biaxially stretched polyethylene terephthalate film with a thickness of 125 μm was cut out into a size of 15×30 mm to be used as a guide sheet. Table 1 shows the results of measuring the characteristics of the guide sheets shown in the above Examples and Comparative Examples. Note that sustainability is the time it takes for the bending load ratio to increase to 0.7 times when the bending state is maintained at 100°C.

[Table] [Effects of the invention] The guide sheet of this invention can be heated at 100℃ as described above.
Since it is made of polycarbonate whose bending load after being held in a bent state for 100 hours is more than 0.7 times the initial value, there is little decline in its rebound elasticity and it is fully practical even when used for a long period of time.

[Brief explanation of drawings]

Fig. 1 is a sectional view showing the outline of the use of the guide sheet of the present invention, Fig. 2 is an enlarged sectional view of the main part of Fig. 1, and Fig. 3 is an outline of the method for measuring the bending load of the guide sheet. FIG. 8...Guide sheet, T...Magnetic tape.

Claims (1)

[Scope of Claim for Utility Model Registration] 1. A guide sheet for preventing the magnetic tape from sagging at the opening of a cassette case, etc., which has a bending load of the initial value after being kept in a bent state at 100°C for 100 hours. A guide sheet for cassette tape made of polycarbonate with a thickness of 0.7 times or more. 2. A guide sheet for a cassette tape according to claim 1 of the utility model registration, characterized in that it is subjected to a friction reduction treatment.