JPH1076576A - Porous sheet and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable the high speed and stable running of a magnetic tape in a case adapted, for example, to a slide sheet for a magnetic tape cassette by improviding sliding properties. SOLUTION: A porous sheet 11 is composed of a thermoplastic resin like ultra-high mol.wt. polyethylene and has a large number of voids and emossed patterns 19 are formed on at least the single surface of the sheet 11. An antistatic agent may be contained in the porous sheet 11. This porous sheet 11 is obtained by sintering a thermoplastic resin powder to mold the same into a sheet having a large number of pores and forming enbossed patterns 19 to at least the single surface of this sheet.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a porous sheet and a method for producing the same, and can be used, for example, as a sliding sheet for a magnetic tape cassette.

[0002]

2. Description of the Related Art For example, in a magnetic tape cassette, a magnetic tape winding body is accommodated in a cassette case composed of two cassette halves. A sliding sheet is arranged between the cassette case and the side surface of the magnetic tape winding body. This sliding sheet is to reduce the frictional resistance during rotation of the magnetic tape winding body and to ensure stable running of the magnetic tape. As such a sliding sheet,
The use of porous sheets obtained by sintering ultra high molecular weight polyethylene (UHPE) powder has been proposed.

[0003]

In recent years, with the development and improvement of DATs (Digital Audio Tape Recorders), DCCs (Digital Compact Cassettes), etc., attempts have been made to increase the recording density and shorten the search time. Therefore, in magnetic tape cassettes, increasing the speed of tape running has become an issue. In general, it is known that the torque at the time of tape running is large at the start of running, and thereafter decreases and becomes in an equilibrium state. The large torque at the start of running causes a large turbulence of the tape.

Conventionally, various proposals have been made to improve such disadvantages. For example, a sliding sheet in which a porous sheet is impregnated with a silicone resin (JP-A-6-20436), a sliding sheet in which the average particle size of the UHPE powder is specified in a specific range and the content is specified (JP-A-6-20436) Showa 5-67
No. 385). Although some improvement can be achieved with these sliding sheets, further improvement in the sliding properties of the sliding sheet is required in order to cope with advances in DAT, DCC and the like.

[0005] Therefore, the present invention is to improve the slipperiness,
For example, an object of the present invention is to provide a porous sheet that enables high-speed and stable running of a magnetic tape when applied to a sliding sheet for a magnetic tape cassette, and a method for manufacturing the porous sheet.

[0006]

A porous sheet according to a first aspect of the present invention is made of a thermoplastic resin, has a large number of pores, and has an embossed pattern formed on at least one surface. .

The specific shape of the embossed pattern is arbitrary, for example, those in which concaves and convexes of irregularities are formed continuously in a ridge shape, those in which concaves and convexes of irregularities are formed discontinuously in a dot shape, Etc. The height difference of the unevenness may be arbitrarily set, but is, for example, 0.01 mm to 2.00 mm. If it is smaller than 0.01 mm, it is difficult to obtain the effect of the emboss pattern. On the other hand, if it is larger than 2.00 mm, the sintering state when sintering to form a sheet becomes non-uniform, or the required thickness of the sheet increases, which increases the cost.

When the sheet is produced by sintering a resin powder, for example, the pore is a pore having a size of a level formed between the powders of the resin powder. The ratio of the pores in the porous sheet varies depending on the production conditions, but is, for example, 10 to 50% (apparent density 0.46 to 0.87).
It is. If it is lower than 10%, the contact area with the object to be contacted increases, so that the slipperiness decreases, and if it is higher than 50%, the strength of the sheet deteriorates. The sheet includes a film having a relatively different thickness only. As the thermoplastic resin, high molecular weight polyethylene, ultra high molecular weight polyethylene,
Fluororesin, nylon, polypropylene, etc. can be used.

According to the porous sheet according to the present invention, good sliding properties can be obtained by a large number of fine pores appearing on the sheet surface, and the contact area can be increased by the large emboss pattern formed on the sheet surface. Is smaller, so that a greater effect of improving slipperiness can be obtained. The thermoplastic resin may contain an appropriate amount of an inorganic substance, an organic substance, a thermosetting resin, or the like in order to obtain necessary characteristics.

[0010] The porous sheet according to the second invention of the present invention comprises:
In the first invention, the pores form air holes communicating from the front surface to the back surface. According to the present invention, the pores are formed on both sides of the sheet and are formed continuously inside the sheet. As a result, the pores are ventilation holes communicating from the front surface to the back surface. . By forming an embossed pattern on both sides of such a sheet, a synergistic effect of improving slipperiness due to the large number of fine pores and the large embossed pattern can be obtained on any side.

[0011] The porous sheet according to the third invention of the present invention comprises:
In the first or second invention, the thermoplastic resin is ultrahigh molecular weight polyethylene (UHPE). As the UHPE, those having a molecular weight of, for example, 500,000 or more (measured by a viscosity method) can be used, but those having a molecular weight of 1,000,000 or more are preferable from the viewpoint of abrasion resistance, and more preferably 2 to 4,000,000. . The UHPE itself has an excellent sliding property. If this UHPE is powdered and sintered into a sheet, a large number of pores can be formed simultaneously.

[0012] The porous sheet according to the fourth invention of the present invention comprises:
In any one of the first to third inventions, an antistatic agent is contained. As the antistatic agent, cationic, anionic, nonionic, amphoteric and the like can be used. This antistatic agent can be contained by immersing the porous sheet in an antistatic agent-containing solution to impregnate the pores, or by compounding it in a thermoplastic resin material and molding.

In the method for producing a porous sheet according to a fifth aspect of the present invention, a thermoplastic resin powder is sintered into a sheet having a large number of pores, and an emboss pattern is formed on at least one surface of the sheet. It is characterized by the following.

The sintering is a method of manufacturing a porous body by heating a thermoplastic resin powder to a temperature equal to or lower than the melting point of the thermoplastic resin and bonding the powders together. The formation of the emboss pattern can be performed simultaneously with sheet molding.
It may be after sheet molding. The emboss pattern can be formed by pressing a mold for forming an emboss pattern against the surface of the porous sheet. The average particle size of the thermoplastic resin powder is arbitrary, but is, for example, 2 mm or less, preferably 1 mm or less. The particle size distribution is also arbitrary, but is preferably as narrow as possible. The particle shape of the thermoplastic resin powder is also arbitrary, and includes, for example, a round shape and a scale shape.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION

[First Embodiment] A porous sheet 11 and a method for manufacturing the same according to a first embodiment of the present invention will be described with reference to FIGS. First, an example of a manufacturing apparatus used in the manufacturing method of the present embodiment will be described.

As shown in FIG. 1, the manufacturing apparatus includes an endless belt 14 wound between two rolls 12,13.
And a press roll 15 arranged so as to be in contact with an endless belt 14 between the two rolls 12 and 13, and a feeder 17 for supplying a thermoplastic resin powder 16 on the endless belt 14. It is. 2 rolls 1
Among them, the first roll 12 is a heating roll incorporating a heating means, and the second roll 13 is a cooling roll incorporating a cooling means. At least one of these rolls 12, 13 is connected to a rotary drive.

The endless belt 14 is made of metal such as stainless steel, and has a mirror-finished surface on which a sheet is formed. The thickness is, for example, 0.1 to 1.5 mm. The press roll 15 is an endless belt 14 between the two rolls 12, 13.
The press roll 15 is arranged so as to press a part of the outer peripheral surface thereof. That is, this press roll 15
Are arranged such that a part of the outer peripheral surface is embraced by the endless belt 14.

As shown in FIG. 2, this press roll 15
A mold 18 for forming an embossed pattern is formed on the outer peripheral surface of the mold. The mold 18 has an inverted shape corresponding to the emboss pattern 19 to be formed on the porous sheet 11 (see FIG. 3). When the porous sheet 11 has an embossed pattern 19 in which, for example, a triangular concave portion 21 and a convex portion 22 are continuously formed in a ridge shape, the die 18 of the press roll 15 becomes a triangular concave portion 23 and a convex portion 24. Are continuously formed in a ridge shape. The feeder 17 is provided with the press roll 15
Is located upstream of the endless belt 14 and above the first roll 12.

Further, in this manufacturing apparatus, a doctor blade 25 for leveling the thermoplastic resin powder 16 on the endless belt 14, a heating means for heating the thermoplastic resin powder 16 such as an infrared heater 26, A pressure roll 27 for assisting the transfer of the mold to the sheet 11 and a peeling roll 28 for peeling the porous sheet 11 from the endless belt 14 are provided.

The doctor blade 25 is connected to the feeder 17
Is located slightly downstream of the endless belt 14. The infrared heater 26 is disposed between the doctor blade 25 and the press roll 15. The pressure roll 27
The endless belt 14 is disposed on the back side of the portion of the endless belt 14 that is in contact with the press roll 15 via the porous sheet 11 so as to press the endless belt 14 toward the press roll 15. The peeling roll 28 is located near the second roll 13 and at a position where the roll 13 can provide a sufficient cooling effect on the porous sheet 11.

Next, a method for manufacturing the porous sheet 11 using this manufacturing apparatus will be described. First, the endless belt 14 heated by the thermoplastic resin powder 16 from the feeder 17
The thermoplastic resin powder 16 supplied with the doctor blade 25
To a predetermined thickness. Subsequently, this thermoplastic resin powder
Immediately after the sheet 16 is heated and sintered by the infrared heater 26, the porous sheet 11 on the endless belt 14 is pressed against the press roll 15 with the endless belt 14 to form an emboss pattern 19 on one surface of the porous sheet 11. To form When the emboss pattern 19 is formed, the pressing roll 27 arranged on the back side of the endless belt 14
The transfer of the pattern to the porous sheet 11 by the mold 15 is assisted. Thereafter, the porous sheet 11 on which the pattern has been transferred is cooled by the second roll 13, and the endless belt 14 is separated by the peeling roll 28.
Then, the porous sheet 11 according to the present embodiment is obtained (see FIG. 3).

In this embodiment, the porous sheet
The specific shape of the 11 emboss patterns 19 is arbitrary. For example, as shown in FIG. 4, in the case of this porous sheet 11,
An embossed pattern 19 having hemispherical convex portions 31 regularly formed on one surface at appropriate intervals in front, rear, left and right and concave portions 32 which are flat portions between the plurality of convex portions 31 can be obtained. On the other hand, the press roll 15 has the die 18 having such a shape that the convex portion 31 and the concave portion 32 are inverted.

In the present embodiment, as shown in FIG. 5, the porous sheet 11 may have an embossed pattern 19 formed on both sides. In the apparatus for producing such a porous sheet 11, the emboss pattern forming die 18 is formed not only on the press roll 15, but also on the surface of the endless belt 14 on which the porous sheet 11 is formed.

[Second Embodiment] The porous sheet 11 manufactured in the same manner as in the first embodiment is immersed in an antistatic agent solution, pulled up, dried and the solvent is removed to remove the antistatic agent. It is fixed in the pores of the porous sheet 11.

[0025]

【Example】

[Example 1] In the first embodiment, the ultra-high molecular weight polyethylene (UHPE) was used as the thermoplastic resin powder 16.
Powder was used. This UHPE powder is manufactured by Mitsui Petrochemicals Co., Ltd., Hizex Million [trade name, average particle size: 80 μm (the ratio of 25 μm or less is 9% or less), molecular weight:
3 million].

The porous sheet 11 has triangular concave portions 21 and convex portions.
Reference numeral 22 denotes an embossed pattern 19 formed continuously in a ridge shape (see FIG. 3). The ratio of the pores in the porous sheet 11 is 35%. Concrete dimensions are adjacent recesses
The dimension a between 21 is 0.4 mm, and the dimension b from the back to the recess 21 is
0.1 mm, height c from the concave portion 21 to the upper end of the convex portion 22 is 0.2 mm
It is.

Example 2 In the first embodiment,
The embossed pattern 19 of the porous sheet 11 is
And a flat concave portion 32 (see FIG. 4). The specific dimensions are the adjacent protrusions
The dimension d between 31 is 0.5 mm, the height e of the projection 31 is 0.1 mm, and the projection is
The diameter f of the bottom surface of the base 31 is 0.2 mm, and the dimension g from the back surface to the recess 32 is 0.2 mm.

Example 3 In the second embodiment,
Eleknon (trade name) manufactured by Fine Chemical Co., Ltd. was used as the antistatic agent solution. The solvent was removed by drying after impregnating the porous sheet 11 with the antistatic agent solution at 80 ° C. for 2 minutes.

Comparative Example 1 A porous sheet having no emboss pattern was used as a porous sheet of this comparative example.

[Measurement of Characteristics] The friction coefficient and torque of the porous sheets of Examples 1 to 3 and Comparative Example 1 were measured. Table 1 shows the results. The friction coefficient was measured using a Baden-Leben friction tester [AFT-15-1 (trade name), manufactured by Tosoh Precision Industry Co., Ltd.]. During this measurement, the sample is fixed on a horizontal table, while the same sample is
It was adhesively fixed to the surface of a 10 mm steel ball. The steel ball was placed on the sample, and reciprocated (5 reciprocations) at a speed of 150 mm / min while applying a load of 200 g to the steel ball. In the case of the porous sheet of the example, the samples are arranged so that the embossed pattern surfaces of the samples face each other.

The torque is measured by assembling a porous sheet as a sliding sheet into a DAT cassette, and measuring the torque at which the other hub is driven when the tape is pulled out from one hub at a speed of 10 mm / sec. went. In the case of the porous sheet of the embodiment, the embossed pattern surface is arranged so as to face the tape.

[0032]

[Table 1]

According to Table 1, the porous sheets 11 of Examples 1 to 3 are made of UHPE and have an embossed pattern 19 in addition to a large number of pores. It turns out that all are small. Therefore,
When this porous sheet 11 is applied to a sliding sheet for a magnetic tape cassette, high-speed and stable running of the magnetic tape becomes possible.

On the other hand, since the porous sheet of Comparative Example 1 has no embossed pattern, it can be seen that both the coefficient of friction and the torque are large.

[0035]

According to the porous sheet and the method for producing the same according to the present invention, the porous sheet has good slipperiness. For example, when the porous sheet is applied to a slip sheet for a magnetic tape cassette, the magnetic tape runs. Can be fast and stable.

[Brief description of the drawings]

FIG. 1 is a schematic view of an example of a manufacturing apparatus used in a method for manufacturing a porous sheet according to an embodiment of the present invention.

FIG. 2 is a sectional view showing a mold of a press roll of the manufacturing apparatus.

FIG. 3 is a perspective view of a porous sheet according to the first embodiment.

FIG. 4 is a perspective view showing another emboss pattern of the porous sheet.

FIG. 5 is a perspective view of a porous sheet having an embossed pattern on both sides.

[Description of Signs] 11 Porous sheet 14 Endless belt 15 Press roll 16 Thermoplastic resin powder 18 Press roll mold 19 Emboss pattern

Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical display location G11B 23/087 509 G11B 23/087 509M // B29K 105: 04 B29L 7:00

Claims (5)

[Claims] 1. A porous sheet comprising a thermoplastic resin, having a large number of pores, and having an embossed pattern formed on at least one surface. 2. The porous sheet according to claim 1, wherein the pores form ventilation holes communicating from the front surface to the back surface. 3. The porous sheet according to claim 1, wherein the thermoplastic resin is ultra-high molecular weight polyethylene. 4. The porous sheet according to claim 1, further comprising an antistatic agent. 5. A method for producing a porous sheet, comprising sintering a thermoplastic resin powder to form a sheet having a large number of pores, and forming an embossed pattern on at least one surface of the sheet.